Whether the concrete is protected or unprotected from environment ...... Rambøll, Pier in Progresso â Mexico Inspection Report â Evaluation of the Stainless ...
Bangladesh Steel Re-rolling Mills Limited EXPERIMENTAL STUDY ON BOND PERFORMANCE OF EPOXY COATED BARS AND UNCOATED DEFORMED BARS IN CONCRETE
DR. ISHTIAQUE AHMED DR. TANVIR MANZUR IKRAM HASAN EFAZ TOUSIF MAHMOOD MARCH 2017
Department of Civil Engineering Bangladesh University of Engineering & Technology (BUET), Dhaka-1000, Bangladesh
Disclaimer This report was prepared based on the experimental study conducted at the laboratory of Bangladesh University of Engineering and Technology, Dhaka under sponsorship from Bangladesh Steel Re-rolling Mills Limited (BSRM). The contents of this publication do not necessarily reflect the views and policies of the university or BSRM. This report was prepared under the supervision of faculty members whose name appears in the cover page. While endeavoring to provide practical and accurate information, BSRM, BUET and the authors, assume no liability for, nor express or imply any warranty with regard to the information contained herein. Information contained in this report shall be used in compliance with the established engineering practice under guidance of the relevant code.
Acknowledgement The authors express sincere appreciation to Bangladesh Steel Re-rolling Mills Limited (BSRM) for arranging publication of this paper. Under a MoU between BUET and BSRM, BSRM has also provided funds for conducting experimental program for flexural behavior of beams reinforced with FBECR as well as direct pull out tests. Cooperation received from Mr. M. Firoze, Head of Product Development and Marketing, BSRM is particularly acknowledged for his enthusiastic efforts in collecting the recent research publications from across the globe.
Abstract Fusion bonded epoxy coated rebar (FBECR) has been in use in USA and other countries for over forty years to protect corrosion led damage of RC structures. Structures that are exposed to extreme weathers, particularly coastal structures exposed to salinity, are in immense risk of rebar corrosion. Durability of these structure can be improved with a consequent reduction in life-cycle cost if FBECR is used instead of conventional steel rebars with minimal additional cost. This report reviews the salient features of using FBECR including its past performances and construction challenges. Laboratory tests have been conducted at BUET to compare bond performance in flexural members as well as bond performance under direct pull out of locally produced epoxy coated rebar (ECR) used with local construction materials. ECR reinforced beams, constructed with stone-chips and brick-chips aggregates, demonstrated identical response and behavior with those reinforced with black bars. The bond strength of ECR in concrete is less than that of black bars. However, with higher strength concrete (3500 psi or higher), the direct pull out tests of embedded ECR demonstrated bar yielding type failure. Code provisions in ACI, BNBC, and AASHTO permit use of ECR with minimal change in design process. Improper handling and uncontrolled field fabrication may cause damage to coating and may lead to counterproductive results. With special care, and adequate provision for handling, transporting and fabrication in-place, the use of FBECR will be beneficial for structures that are particularly vulnerable to early deterioration due to corrosion of rebars.
Key Words: Epoxy coated rebar, corrosion protection, durability, flexural performance.
TABLE OF CONTENTS CHAPTER 1 Introduction ........................................................................................................................ 1 1.1 General ....................................................................................................................................... 1 1.2 Objectives .................................................................................................................................. 1 1.3 Report Outline ............................................................................................................................ 1 1.3.1 Chapter 1 ............................................................................................................................ 1 1.3.2 Chapter 2 ............................................................................................................................ 2 1.3.3 Chapter 3 ............................................................................................................................ 2 1.3.4 Chapter 4 ............................................................................................................................ 2 1.3.5 Chapter 5 ............................................................................................................................ 2 CHAPTER 2 Literature Review ............................................................................................................... 3 2.1 Deterioration of Concrete Due to Rebar Corrosion .................................................................... 3 2.1.1 Corrosion Process............................................................................................................... 3 2.1.2 Effect of Chlorides ............................................................................................................. 5 2.1.3 Carbonation of Embedded Steel ......................................................................................... 5 2.1.4 The Influence of Cracks in the Concrete on the Corrosion of Embedded Steel .................. 6 2.1.5 Damages to Concrete Due to Corrosion of Steel Reinforcement ........................................ 7 2.2 Methods of Improving Concrete Durability by Protecting Rebars ............................................. 8 2.2.1 Galvanized Steel Reinforcing Bars ..................................................................................... 8 2.2.2 Stainless Steel Reinforcing Bars......................................................................................... 9 2.2.3 Non-metallic Reinforcement .............................................................................................. 9 2.2.4 Epoxy Coated Bars ............................................................................................................. 9 2.3 Design and Construction Related Challenges of using Epoxy Coated Bars ..............................12 2.3.1 Bond Related Problem of ECR..........................................................................................14 2.3.2 Care During Manufacturing, Handling, Fabrication and Construction ..............................14 2.3.3 Quality Control Issues .......................................................................................................17 2.3.4 Historic Performance of ECR ............................................................................................18 2.4 Possible Use of Epoxy Coated Bar in Bangladesh Context .......................................................20 CHAPTER 3 Experimental Program .......................................................................................................21 3.1 Background ...............................................................................................................................21 3.2 Objectives .................................................................................................................................21 3.3 Test Specimen ...........................................................................................................................23 3.3.1 Pull Out Test Specimen .....................................................................................................23 3.3.2 Flexure Test Specimens.....................................................................................................25 3.4 Material Properties ....................................................................................................................26 3.4.1 Pull out test .......................................................................................................................27 3.4.2 Flexure Test.......................................................................................................................30 3.5 Fabrication of the specimen ......................................................................................................31 3.5.1 Pull out specimen ..............................................................................................................31 3.5.2 Flexure Specimen ..............................................................................................................31 3.6 Instrumentation .........................................................................................................................32 3.6.1 Pull out Tests .....................................................................................................................32 3.6.2 Flexure Tests .....................................................................................................................33 3.7 Testing Procedure .....................................................................................................................33 3.7.1 Pull out test .......................................................................................................................33 3.7.2 Flexure test ........................................................................................................................34
i
CHAPTER 4 Results of Experiments ......................................................................................................35 4.1 Results of Pull-out tests .............................................................................................................36 4.1.1 Comparison of Bond performance of ECR and BB of Type I-SC .....................................36 4.1.2 Comparison of Bond performance of ECR and BB of Type I-BC.....................................39 4.1.3 Comparison of Bond performance of ECR and BB of Type II-SC ....................................42 4.1.4 Comparison of Bond performance of ECR and BB of Type III-SC ..................................45 4.1.5 Comparison of Bond performance of ECR and BB of Type IV-BC ..................................48 4.1.6 Comparison of Bond performance of ECR and BB of Type I-SC-FLd .............................52 4.2 Results of Flexural Test ............................................................................................................55 4.2.1 Comparison of Flexural Test Response of ECR and BB Reinforced Beam .......................56 4.2.2 Comparison of Flexural Bond Strength of ECR and BB reinforced beams .......................84 CHAPTER 5 Conclusions and Recommendations ..................................................................................86 Recommendations .....................................................................................................................................87 References 88
LIST OF FIGURES Fig. – 2.1: Corrosion of rebar in concrete. ................................................................................................. 4 Fig. – 2.2: Rebar corrosion leads to cracking and spalling. ........................................................................ 4 Fig. – 2.3: Carbonation leads to the general corrosion along the full length of the bar. ............................. 5 Fig. – 2.4: Schematic illustration of chloride diffusion in cracked concrete............................................... 6 Fig. – 2.5: Galvanized Steel Rebars ........................................................................................................... 9 Fig. – 2.6: Fusion Bonded Epoxy Coated bars ..........................................................................................10 Fig. – 2.7: Reduced rate Half-cell redox reaction in epoxy coated reinforcements [32] ............................10 Fig. – 2.8: Comparison of various rebar option for corrosion protection [34] ...........................................11 Fig. – 2.9: Tuuti Model for Predicting Service Life of Concrete Structure [2] ..........................................12 Fig. – 2.10: (a) Storage (b) Bending of bars (c) Patching of damaged area (d) Fabrication ......................13 Fig. – 2.11:Extra Care for Fabrication and Placement: (a) placement at casting yard (b) coating applied to bar ends (c) & (d) repair of bar damage using special epoxy. ...................................................................17 Fig. – 2.12: Three ECR bars after exposure in Cl contaminated concrete, first with coating holidays identified (upper photograph of each bar pair) and, second, showing bar appearance upon removal of disbanded coating (lower photograph of each pair).[61] ...........................................................................19 Fig. – 3.1: Bond-ship behavior of rebar in concrete under different state of confinement [81] .................21 Fig. – 3.2: Pull-out test experimental set-up and dial gauge ......................................................................22 Fig. – 3.3: Experimental setup for flexural study with two point loading. ................................................23 Fig. – 3.4: Arrangement of Reinforcements at the centre of the specimen ................................................24 Fig. – 3.5: Arrangement of Reinforcement ...............................................................................................26 Fig. – 3.6: Arrangement of Reinforcement ...............................................................................................26 Fig. – 3.7(a): Load-Deflection curve for 12mm Epoxy Coated bars .........................................................28 Fig. – 3.7(b): Load-Deflection curve for 12mm Uncoated bars ................................................................28 Fig. – 3.7(c): Load-Deflection curve for 16mm Epoxy Coated bars .........................................................29 Fig. – 3.7(d): Load-Deflection curve for 16mm Uncoated bars ................................................................29 Fig. – 3.9: Pull out specimens during casting ............................................................................................31 Fig. – 3.10: Casting Procedure of beam specimen ....................................................................................32 Fig. – 3.11: FE model of the pull-out test frame .......................................................................................32 Fig. – 3.12: Pull-out test frame in UTM ....................................................................................................32 Fig. – 3.13: Pull-out test specimen and instrumentation............................................................................32 ii
Fig. – 3.14: Pull-out test frame with specimen in the UTM .....................................................................34 Fig. – 3.15: Two HD video cameras to record the data at both loaded and unloaded end of the bars. ......34 Fig. – 3.16: Experimental test setup for flexure. .......................................................................................35 Fig. – 3.17: Crack Comparator. .................................................................................................................35 Fig. – 4.1: Comparison of loads-slip response of pull-out specimen (3 ksi, stone chips, 12 mm bar) reinforced with ECR and BB ....................................................................................................................37 Fig. – 4.2: Comparison of loads-slip response of pull-out specimen (3 ksi, stone chips, 16 mm bar) reinforced with ECR and BB ....................................................................................................................37 Fig. – 4.3: Failure Modes of ES1R1 and US1R1 (3Ksi, 12mm Epoxy and Uncoated bars ) samples .......39 Fig. – 4.4: Failure Modes of ES1R2 and US1R2 (3Ksi, 16mm Epoxy and Uncoated bars ) samples .......39 Fig. – 4.5: Comparison of loads-slip response of pull-out specimen (3 ksi, brick chips, 12 mm bar) reinforced with ECR and BB ....................................................................................................................40 Fig. – 4.6: Comparison of loads-slip response of pull-out specimen (3 ksi, brick chips, 16 mm bar) reinforced with ECR and BB ....................................................................................................................40 Fig. – 4.7: Failure Modes of EB1R1 and UB1R1 (3Ksi, 12mm Epoxy and Uncoated bars ) sample ........42 Fig. – 4.8: Failure Modes of EB1R2 and UB1R2 (3Ksi, 16mm Epoxy and Uncoated bars ) samples ......42 Fig. – 4.9: Comparison of loads-slip response of pull-out specimen (3.5 ksi, Stone chips, 12 mm bar) reinforced with ECR and BB ....................................................................................................................43 Fig. – 4.10: Comparison of loads-slip response of pull-out specimen (3.5 ksi, Stone chips, 16 mm bar) reinforced with ECR and BB ....................................................................................................................43 Fig. – 4.11: Failure Modes of ES2R1 and US2R1 (3.5 Ksi, 12mm Epoxy and Uncoated bars ) samples .45 Fig. – 4.12: Failure Modes of ES2R2 and US2R2 (3.5 Ksi, 16mm Epoxy and Uncoated bars ) samples .45 Fig. – 4.13: Comparison of loads-slip response of pull-out specimen (4 ksi, Stone chips, 12 mm bar) reinforced with ECR and BB ....................................................................................................................46 Fig. – 4.15: Failure Modes of ES3R1 and US3R1 (4 Ksi, 12mm Epoxy and Uncoated bars ) samples ....48 Fig. – 4.16: Failure Modes of ES3R2 and US3R2 (4 Ksi, 16mm Epoxy and Uncoated bars ) samples ....48 Fig. – 4.17: Comparison of loads-slip response of pull-out specimen (2.5 ksi, Brick chips, 12 mm bar) reinforced with ECR and BB ....................................................................................................................49 Fig. – 4.18: Comparison of loads-slip response of pull-out specimen (2.5 ksi, Brick chips, 16 mm bar) reinforced with ECR and BB ....................................................................................................................49 Fig. – 4.19: Failure Modes of ES3R1 and US3R1 (2.5 Ksi, 16mm Epoxy and Uncoated bars ) samples .51 Fig. – 4.20: Failure Modes of ES3R1 and US3R1 (2.5 Ksi, 16mm Epoxy and Uncoated bars ) samples .51 Fig. – 4.21: Testing of ES1R1_FLd and US1R1_FLd (3 Ksi, 12 mm Epoxy and Uncoated bars ) samples ..................................................................................................................................................................53 Fig. – 4.22: Failure Modes of ES1R1_FLd and US1R1_FLd (3 Ksi, 12 mm Epoxy and Uncoated bars ) samples .....................................................................................................................................................53 Fig. – 4.23: Failure Modes of ES1R1_FLd and US1R1_FLd (3 Ksi, 12 mm Epoxy and Uncoated bars ) samples .....................................................................................................................................................54 Fig. – 4.24: Failure Modes of ES1R1_FLd (3 Ksi, 12 mm Epoxy Coated bars ) samples .........................54 Fig. – 4.25: Failure Modes of US1R1_FLd (3 Ksi, 12 mm Uncoated bars ) samples ...............................55 Fig. – 4.26: Comparison of loads-deflection response of beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................56 Fig. – 4.27: Comparison of deflection time response of beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................57 Fig. – 4.28: Comparison of load-crack width response of beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................57 Fig. – 4.29: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ...........................................................................................................59 iii
Fig. – 4.30: Comparison of loads-deflection response of beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................59 Fig. – 4.31: Comparison of deflection time response of beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................60 Fig. – 4.32: Comparison of load-crack width response of beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................60 Fig. – 4.33: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ...........................................................................................................62 Fig. – 4.34: Comparison of loads-deflection response of beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................63 Fig. – 4.35: Comparison of deflection time response of beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................64 Fig. – 4.36: Comparison of load-crack width response of beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................64 Fig. – 4.37: Comparison of Crack Pattern and Deflected Shape for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ...........................................................................................................66 Fig. – 4.38: Comparison of loads-deflection response of beam (3 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB ....................................................................................................................67 Fig. – 4.39: Comparison of deflection time response of beams (3 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB ....................................................................................................................67 Fig. – 4.40: Comparison of load-crack width response of beams (3 ksi, stone chips 2-16 mm Spliced bars) reinforced with ECR and BB ....................................................................................................................68 Fig. – 4.41: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB ...............................................................................................68 Fig. – 4.42: Comparison of loads-deflection response of beams (3 ksi, brick chips, 2-16 mm Spliced bars) reinforced with ECR and BB ....................................................................................................................69 Fig. – 4.43: Comparison of deflection time response of beams (3 ksi, brick chips, 2-16 mm Spliced bars) reinforced with ECR and BB ....................................................................................................................69 Fig. – 4.44: Comparison of load-crack width response of beams (3 ksi, brick chips, 2-16 mm Spliced bars) reinforced with ECR and BB ...........................................................................................................70 Fig. – 4.45: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, brick chips, , 2-16 mm Spliced bars) reinforced with ECR and BB...............................................................................................70 Fig. – 4.46: Comparison of loads-deflection response of beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................71 Fig. – 4.47: Comparison of deflection time response of beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................72 Fig. – 4.48: Comparison of load-crack width response of beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................72 Fig. – 4.49: Comparison of loads-deflection response of beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................73 Fig. – 4.50: Comparison of deflection time response of beams (3 ksi, brick chips, 2-12 mm bars) reinforced with ECR and BB ....................................................................................................................74 Fig. – 4.51: Comparison of load-crack width response of beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................74 Fig. – 4.52: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, stone chips and brick chips, -16 mm bars) reinforced with ECR and BB ....................................................................................76 Fig. – 4.53: Comparison of loads-deflection response of beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................77 iv
Fig. – 4.54: Comparison of deflection time response of beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................77 Fig. – 4.55: Comparison of load-crack width response of beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................78 Fig. – 4.56: Comparison of Crack Pattern and Deflected Shape for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ...........................................................................................................79 Fig. – 4.57: Comparison of loads-deflection response of beam (3.5 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB ...........................................................................................................79 Fig. – 4.58: Comparison of deflection time response of beams (3.5 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB ...........................................................................................................80 Fig. – 4.59: Comparison of load-crack width response of beams (3.5 ksi, stone chips 2-16 mm Spliced bars) reinforced with ECR and BB ...........................................................................................................80 Fig. – 4.60: Comparison of Crack Pattern and Deflected Shape for Beams (3.5 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB ...............................................................................................81 Fig. – 4.61: Comparison of loads-deflection response of beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................82 Fig. – 4.62: Comparison of deflection time response of beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................82 Fig. – 4.63: Comparison of load-crack width response of beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................83 Fig.– 4.64: Comparison of Crack Pattern and Deflected Shape for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ...........................................................................................................84
LIST OF TABLES Table-2.1: Cost Comparison of Different Reinforcement Types [33] .......................................................11 Table 2.2: Chronology of Changes Made to ASTM A775 [49] ................................................................18 Table – 3.1: Test matrix for pull out test of ECR and black bar. ...............................................................24 Table – 3.2: Details of Beam Specimens Prepared for Flexural Testing ...................................................25 Table 3.3 : Compressive Strength of Concrete ..........................................................................................27 Table 3.4: Steel properties of tested Epoxy Coated and Black Bars ..........................................................27 Table 3.5 : Compressive Strength of Concrete ..........................................................................................30 Table – 3.6: Summary of Location, and Function of External Devices .....................................................33 Table – 3.7: Summary of Location, and Function of External Device ......................................................33 Table – 4.1: Pull out test specimens ..........................................................................................................36 Table – 4.2: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pullout…………………………………………………………………………………………………………38 Table – 4.3: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pullout…………………………………………………………………………………………………………41 Table – 4.4: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pullout .............................................................................................................................................................44 Table – 4.5: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pullout…………………………………………………………………………………………………………46 Table – 4.5: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pullout…………………………………………………………………………………………………………47 Table – 4.6: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pullout…………………………………………………………………………………………………………50 v
Table – 4.7: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pullout…………………………………………………………………………………………………………52 Table – 4.8: Beam Specimens ...................................................................................................................55 Table – 4.9: Comparison of Deflections at Design Load for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................57 Table – 4.10: Comparison of Crack Width at Design Load for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................58 Table – 4.11: Comparison of Number of Total Cracks for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................58 Table – 4.12: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB.........................................................................58 Table – 4.13: Comparison of Deflections at Design Load for Beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................60 Table – 4.14: Comparison of Crack Width at Design Load for Beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................61 Table – 4.15: Comparison of Number of Total Cracks for Beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................61 Table – 4.16: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB .........................................................................61 Table – 4.17: Comparison of Deflections at Design Load for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................63 Table – 4.18: Comparison of Crack Width at Design Load for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................65 Table – 4.19: Comparison of Number of Total Cracks for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................65 Table – 4.20: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB ..................................................................65 Table – 4.21: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB ............................................................68 Table – 4.22: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, brick chips, 2-16 mm Spliced bars) reinforced with ECR and BB ............................................................70 Table – 4.23: Comparison of Deflections at Design Load for Beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................72 Table – 4.24: Comparison of Crack Width at Design Load for Beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................73 Table – 4.25: Comparison of Number of Total Cracks for Beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................73 Table – 4.26: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB.........................................................................73 Table – 4.27: Comparison of Deflections at Design Load for Beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................74 Table – 4.28: Comparison of Crack Width at Design Load for Beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................75 Table – 4.29: Comparison of Number of Total Cracks for Beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................75 Table – 4.30: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB .........................................................................75 vi
Table – 4.31: Comparison of Deflections at Design Load for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................77 Table – 4.32: Comparison of Crack Width at Design Load for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................78 Table – 4.33: Comparison of Number of Total Cracks for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ....................................................................................................................78 Table – 4.34: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB ..................................................................78 Table – 4.35: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3.5 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB .....................................................80 Table – 4.36: Comparison of Deflections at Design Load for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................82 Table – 4.37: Comparison of Crack Width at Design Load for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................83 Table – 4.38: Comparison of Number of Total Cracks for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ....................................................................................................................83 Table – 4.39: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB ..................................................................83 Table – 4.40: Comparison of Design and Failure bond strength for black bars and Epoxy coated bars. …………………………………………………………………………………………………………….84
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CHAPTER 1 Introduction 1.1
General
The corrosion of steel rebar embedded in concrete is one of the major causes of premature deterioration of concrete structures. The corrosion process is aggravated under aggressive exposure conditions particularly with moist condition and presence of salinity. Early deterioration of concrete structures could lead to serviceability, durability concerns. The associated repair and maintenance would bring the lifecycle cost issue of the structure in fore front. Various methods of controlling the corrosion problem have been practiced as industry standard. These include cathodic protection, use of admixtures, slilica fume, fly ash, slag, and latex in concrete, various surface treatment options of the rebars and use of surface coating on the concrete. Details of these options are available elsewhere [1]. The particular surface treatment by application of fusion bonded epoxy coating on rebars will be the fours of this paper. The effectiveness and durability of fusion bonded epoxy coatings on steel reinforcement (FBECR) in corrosion prevention has undergone major research in past few decades. The corrosion of steel reinforcements in concrete by intrusion of chlorides, sulphates H2S and CO2 severely deteriorates structures‟ serviceability, durability and safety. In contrast, epoxy coating acts as a physical and electrochemical barrier inhibiting the corrosion reaction on steel surface. Recent studies have shown corrosion rates of epoxy coated steel rebars to be 40-50 times less than that of uncoated bars [2]. Bangladesh construction industry faces the durability concern of concrete infrastructures particularly in coastal regions due to adverse environmental conditions where reinforcement corrosion is one of prime reasons for degradation of concrete structures. Epoxy coated steel reinforcement, used since 1973 in US, may become a viable solution for combating corrosion related durability problem. In order to facilitate use of FBECR in structures, the design and construction issues should be thoroughly understood by engineers, constructors and other stakeholders. The quality control issues and improvement of life expectancy due to its use needs to be identified from industry experience and research findings. This paper aims to review historical and technical aspects of using epoxy coated steel reinforcements in concrete structures and its potential application in Bangladesh as a means of effective corrosion protection of embedded steel rebar. 1.2
Objectives
The main objectives of the study were set as follows: a. Compare the bond strength of epoxy-coated reinforcing steel bars and uncoated deformed bars. b. Construct a “Bond Stress vs. Slip” diagram to better understand the slip behavior of epoxycoated bars as compared to conventional deformed bars. c. Assess the flexural performance of the beams and the effect of concrete strength, aggregate type and bar diameter on beams reinforced with epoxy and uncoated bars in standard two point beam flexural test. 1.3
Report Outline
This report includes 6 chapters. A brief description of the chapters follows. 1.3.1
Chapter 1
This chapter provides a general introduction and the objectives of the project. 1
1.3.2
Chapter 2
This chapter provides a brief literature review on the use of epoxy coated rebars in RCC members. The literature review covers the history of epoxy coated rebars, a summary of the provisions on the use of epoxy coated reinforcement reported in code documents. 1.3.3
Chapter 3
Chapter 3 provides details on the experimental program and the particular specimens tested. In addition, this chapter contains details of the instrumentation of the specimens. This chapter also includes specifics of the test set-up and testing procedures. 1.3.4
Chapter 4
This chapter presents the experimental data and corresponding analysis. The objective of this chapter is to examine the bond performance of epoxy coating reinforcements in flexure and direct pull out tests, effect of concrete compressive strength, aggregate types, reinforcement diameter and development length. Comparisons are made among the specimens to describe the function of different parameters. 1.3.5
Chapter 5
This chapter provides a summary of the research program and states the pertinent conclusions obtained from the experiments. It also provides recommendations for future study.
2
CHAPTER 2 Literature Review 2.1
Deterioration of Concrete Due to Rebar Corrosion
Reinforced Concrete (RC) is the main construction material used in buildings, bridges, power plants, and other infrastructure throughout the world. Performance of reinforcement in concrete is vital to provide desired strength ensuring safety, serviceability, and durability, which are all affected by deterioration of reinforcement over time. Corrosion of reinforcement is one of the major concerns regarding durability of RC structures particularly in marine environment. Moreover, corrosion can also be induced through carbonation, intrusion of chloride, aggregates and admixtures containing corrosive elements, poor workmanship, exposure to aggressive weather condition etc. Due to its inherent alkaline property, concrete itself is inert to corrosive chemical reactions. However, presence and intrusion of deleterious materials in concrete can adversely affect its corrosion resistance. A poor, porous concrete will also be vulnerable to early deterioration due to rebar corrosion. Concrete has become the single most widely used construction material of the modern civilization. The reasons behind the widespread use of concrete in construction industry are low cost of construction as well as maintenance, ease of construction, excellent fire resistance, high compressive strength and excellent durability. However, its rather weak tensile property requires steel rebars to be used almost invariably to counter the shrinkage and tensile force. The embedded steel rebar, mostly made of mild steel, is susceptible to corrosion if not protected from aggressive environmental agents. This corrosion of reinforcing steel could lead to early deterioration of concrete structures. To pave the way to a meaningful discussion towards control of corrosion of steel rebar for construction of durable infrastructures, the subsequent sections would be devoted to explaining corrosion process and corrosion agents. 2.1.1
Corrosion Process
As naturally occurring iron ore is processed through refinement to produce steel, energy is added to the metal. Steel has a tendency to release energy to revert back to its natural state, iron oxide (Fe2 O3 or Fe2 O3 nH2 O) or hydroxides (FeO(OH) Fe(OH)3 ) by combining with oxygen in presence of water. This leads to the fact that the following, four elements must be present for corrosion to take place:
Presence of at least two metals or two locations of a single metal at different energy levels. Presence of an electrolyte (concrete acts as the electrolyte) A metallic connection (ties, chair supports or rebar itself acts as metallic connection) between the two metals.
The electro chemical process of corrosion involves flow of charges as shown in Fig. 2.1.
3
Fig. – 2.1: Corrosion of rebar in concrete. For steel embedded in concrete iron atoms loose electrons and resulting ferrous ions move through the concrete (Fig. 2.1). This process is called half-cell oxidation reaction or anodic reaction as represented below: 2Fe
2Fe2
4e
The electrons that remain in the steel bar and flow through the steel bar to cathodes to combine with water and oxygen available within concrete. This reaction at cathode is called a reduction reaction and is represented as follows: 2H2 O O2 4e 4OH The ferrous ion moving through concrete pore water would reach out to these cathodes to be electrically neutral. Thus hydroxides are formed as follows: 2Fe2
4OH
2Fe(OH)2 (a form of rust)
The precipitated hydroxide reacts with oxygen and produce higher form of oxides (rust). These corrosion products cause an increase in volume leading to development of internal stress at the rebar-concrete interface. This stress develops internal cracks in concrete cover, leading to localized disintegration and spalling of concrete cover (Fig. 2.2). The corrosion process of embedded steel can be greatly reduced by eliminating the agents of corrosion which include the crack free concrete with low permeability and adequate cover to reinforcement. This will ensure embedded steel not to come in contact with water and oxygen. Moreover, concrete being alkaline in nature with pH higher than 12 provides an inherent protection to embedded steel by forming a thin oxide layer. This passive layer, for majority of good quality concrete, protects steel to a great extent and structures remain durable for its entire life span.
Fig. – 2.2: Rebar corrosion leads to cracking and spalling. 4
2.1.2
Effect of Chlorides
Presence of chloride in concrete adversely affects durability of concrete. Chloride ion is known to be the most active chemical responsible for accelerated corrosion damage of rebars in concrete. The chloride ion breaks the protective oxide layer around the rebar making it vulnerable to corrosion. Chlorides are generally acidic in nature and can come from a number of different sources, the most common being, deicing salts, use of unwashed marine aggregates, sea water spray, and certain accelerating admixtures. Chlorides induced corrosion is potentially more harmful than that resulting from carbonation. Like most of the aspects of concrete durability, deterioration due to corrosion of the reinforcement can take place as early as five years of construction [2-6]. In the absence of chloride ions in the solution, the protective film on steel is reported to be stable if the pH of the solution stays above 11.5. Normally there is sufficient alkalinity in concrete to maintain the pH above 12. In exceptional conditions (e.g., when concrete has high permeability and alkalies and most of the calcium hydroxide are either carbonated or neutralized by an acidic solution), the pH of concrete near rebar steel reduces to less than 11.5, which destroys the passivity of steel making it vulnerable to the corrosion process. In the presence of chloride ions, depending on the Cl – / OH– ratio, it is reported that the protective film may be destroyed even at pH values considerably above 11.5 [2-6]. For corrosion to be initiated, the passivity layer must be penetrated. Chloride ions activate the surface of the steel to form an anode, the passivated surface being the cathode. The reactions involved are as follows: Fe 2Cl FeCl2 FeCl2 2.1.3
2H2 O
Fe(OH)2
2HCL
Carbonation of Embedded Steel
It is well known that the concrete, in which steel is embedded, is an alkaline medium with pH values from 9 upwards inherently protects steel. During the setting of concrete, cement begins to hydrate, this chemical reaction between cement and water in the concrete causes calcium hydroxide to be formed from the cement clinker. This ensures the concrete‟s alkalinity, producing a pH value of more than 12 which renders the steel surface passive, giving an anticorrosive coating on rebar. Protection of the reinforcement from corrosion is thus provided by the alkalinity of the concrete, which leads to passivation of the steel. The content of calcium hydroxide is very high to ensure protection against corrosion of steel even when water penetrates to the embedded rebar. This is why minor cracks of width up to 0.1 mm does not pose any concern for corrosion led damage.
Fig. – 2.3: Carbonation leads to the general corrosion along the full length of the bar. 5
The Fig. 2.3 above shows that with the propagation of carbonation, signs of corrosion taking place showing surface cracking of the concrete along the plane of embedded steel. As the corrosion proceeds, the concrete will spall away completely to expose the steel. With exposure to adverse environment, carbon dioxide in particular, concrete‟s pH value is reduced. This process is known as carbonation and would remove the passive layer around the rebar making it prone to corrosion damage. In the process of carbonation, CO2 from the atmosphere reacts with alkaline component in concrete, Ca(OH)2, in the presence of moisture. Calcium hydroxide thus is converted to CaCO3. The calcium carbonate is slightly soluble in water. Ca(OH)2 + CO2 + H2O = CaCO3 + 2H2O Due to carbonation of concrete, the pH is reduced to less than 9. The passive protection layer of rebar is no longer effective in this range of pH. As a result corrosion is started and gets accelerated in presence of moisture and oxygen. The extent of carbonation in a particular concrete would depend on:
Depth of cover available Permeability of concrete Grade of concrete Age of concrete Whether the concrete is protected or unprotected from environment The aggressiveness of environment.
The corrosion cycle of steel begins with the rust expanding on the surface of the bar and causing cracking near the steel-concrete interface. As time progresses, the corrosion products build up and cause more extensive cracking until the concrete breaks away from the bar, eventually causing spalling. 2.1.4
The Influence of Cracks in the Concrete on the Corrosion of Embedded Steel
Cracks in concrete are caused by a wide variety of reasons, which include shrinkage [7], chemical reactions (e.g. alkali aggregate reaction [8], weathering processes (e.g. freezing and thawing) [9], reinforcement corrosion [10] and loading.
Fig. – 2.4: Schematic illustration of chloride diffusion in cracked concrete Concrete always contains cracks and codes on structural concrete design such as ACI 318 [11] take this into account and permissible crack widths are specified for various exposure conditions. However, an understanding of the effects of cracks on corrosion may be found in literature [12-14]. For concrete with multiple cracks, corrosion at one crack appears to protect the steel at the other cracks by forming a galvanic cell or there is a low corrosion rate at all the cracks [15]. Chloride ingress is significantly enhanced by cracks because the ions penetrate the concrete cover from the walls of the crack as 6
well as from the outer surface of the concrete [16], as illustrated schematically in Fig. 2.4. Thus, while the chlorides reach the steel directly through the crack, they also reach adjacent areas of steel more rapidly than in uncracked concrete. The overall low pH of the adjoining concrete coupled with ingress of moisture and oxygen make it conducive for rebar corrosion and early deterioration of concrete. 2.1.5
Damages to Concrete Due to Corrosion of Steel Reinforcement
The process of corrosion eventually results in deterioration and distress of the RC members. The various stages of destruction are as follows:
Stage 1: Signs of Carbonation
The porous concrete allows rather easy passage of water and carbon dioxide from surface to interior and carbonation advances towards the layer of rebar. Carbon dioxide reacts with calcium hydroxide in the cement paste to form calcium carbonate. The free movement of water carries the unstable calcium carbonates towards the surface and forms white patches. The white patches at the concrete surface indicates the occurrence of carbonation.
Stage 2: Brown patches along reinforcement
With corrosion of rebar in the RC structures, a layer of ferric oxide is formed on the reinforcement surface. This brown product resulting from corrosion may permeate along with moisture to the concrete surface without cracking of the concrete giving patches of brown color on surfaces – an indication of the on set of corrosion of embedded rebar.
Stage 3: Occurrence of cracks
The products of corrosion normally occupy a much greater volume about 6 to 10 times than the parent metal. The increase in volume exerts considerable bursting pressure on the surrounding concrete and results in cracking. The hair line crack in the concrete surface lying directly above the reinforcement and running parallel to it is the positive visible indication that reinforcement is corroding.
Stage 4: Formation of multiple cracks
With further corrosion, there will be formation of multiple layers of ferric oxide on the reinforcement which in turn increase pressure on the surrounding concrete resulting in widening of hair cracks. At this stage multiple new hair cracks are formed. The bond between concrete and the reinforcement is considerably reduced. There will be a hollow sound when the concrete is tapped at the surface with a light hammer.
Stage 5: Spalling of cover concrete
Due to loss in bond between steel and concrete and formation of multiple layers of scales, the cover concrete starts falling off from the rebar layer. Considerable reduction of the rebar area has also taken by place by this time.
Stage 6: Snapping of bars
With uninhabited corrosion, the affected rebars are snapped off. Usually snapping occurs in ties/stirrups first. Stage 7: Buckling of bars and bulging of concrete 7
The spalling of the cover concrete and snapping of ties causes the main bars to buckle in compression member. This will result in bulging of the surrounding concrete. 2.2
Methods of Improving Concrete Durability by Protecting Rebars
In reinforced concrete structures, corrosion of steel rebars almost invariably leads to the deterioration of concrete leading to durability problem. While in the case of good quality concrete within controlled environment steel generally remains protected, the problem of accelerated corrosion takes place in aggressive environment. Structures exposed to weathering action are prone to carbonation. Marine structures or structures that are subjected to alternate drying and wetting suffer early deterioration due to rebar corrosion. Structures built in the coastal area are particularly susceptible to rebar corrosion led premature deterioration due to chloride attack or presence of chloride in concrete ingredients during casting. Various techniques of protection against rebar corrosion have become industry standard practice. These are discussed in this section. 2.2.1
Galvanized Steel Reinforcing Bars
Galvanized steel reinforcement (Fig.- 2.5) has been used in reinforced concrete structures since 1930s [17]. This has two advantages compared to most other forms of coatings. The metallurgical bond formed between the steel and the zinc ensures that the coating is not susceptible to flaking or other forms of separation from the substrate. Secondly, zinc not only forms a barrier coating but acts as a sacrificial anode. Thus, any scratches or other flaws in the coating are not critical and do not lead to active corrosion of the underlying steel. Morevoer, zinc has the advantage over black steel that it is more resistant to chlorides (approx 2.5 times) [18-20] and lower pH levels [pH~8] before significant active corrosion takes place. Galvanizing, therefore, would provide better protection than black steel to both chloride induced and carbonation-induced corrosion. The galvanized bar has the disadvantage that the galvanization corrodes very rapidly in the wet cement but the corrosion reaction rate ceases once the concrete hardens [21-22]. Because of its passivation in neutral solutions and its sacrificial anode role when in contact with steel, galvanized steel is ideally suited for parts which are to be partially embedded in concrete and partially exposed to the atmosphere. Advantages of Galvanizing:
The layer of zinc is able to protect the metal in two main ways. First, through fighting of rust, and then by providing an extra layer the rust must go through if it becomes contaminated. With zinc coating, it is harder for oxygen and water to cause reaction.
If however, it does manage to become corroded, the zinc layer will be damaged first, providing a longer life. Disadvantages of Galvanizing:
Marine studies and accelerated filed studies have shown that galvanizing will delay the onset of delimitations and spalls but will not prevent them. It appears that only a slight increase in life will be obtained in severe chloride environment. If done incorrectly, for example if cooled too quickly, the zinc has the possibility of peeling or chipping off.
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Fig. – 2.5: Galvanized Steel Rebars 2.2.2
Stainless Steel Reinforcing Bars
The demand for increasing service life of structures, stainless steel is being regarded as a viable alternative reinforcement despite its higher cost. The most common grades of stainless steel for reinforcement are 316LN and 2205, both of which have excellent corrosion resistance [23-24] and are commercially available. Service lives well in excess of 100 years can be expected when these are used as rebars. Research shows that grade 304 is less corrosion resistant than the other two grades [25] but, the most reliable field record of corrosion resistance has been observed in concrete using stainless steel [26]. The cost of the stainless steels is more than five times that of black steel [27], as such its use is not common. 2.2.3
Non-metallic Reinforcement
The carbon-fiber reinforcements currently being marketed [28] do not suffer from corrosion. Although the long term performance of these materials in concrete has not yet been evaluated, its use as replacement of steel has been made [29]. However, it did not get wide acceptance due to high cost, low ductility and poor bond with concrete. 2.2.4
Epoxy Coated Bars
First introduced in early 1960s as a protective coating, fusion bonded epoxy (FBE) is an epoxy-based powder coating used to protect rebars from corrosion. In epoxy coated bar an epoxy layer (with resin, hardener, fillers, extenders and color pigments) is applied at high temperature on the rebar. Epoxy coated rebars has been used in North America since 1973. Ever since more than 65,000 bridges and numerous other structures have been built in US. The history of its use, specifications, manufacturing and corrosion protection mechanisms, field performance are reviewed by McDonald [30]. The use of ECR is reported to be the second most common strategy to prevent reinforcement corrosion after increasing concrete cover [31]. Use of other techniques such as application of galvanized or stainless steel bars is less than three percent of the total North American reinforcement market. The epoxy coated bars provide distinct advantages which are discussed below:
since the coating is done on the coating lines, better quality control is achieved. The process gives uniform coating thickness; bonding of coating with the steel is very strong as FBE has very good adhesive properties; because of flexibility, the coating does not get damaged when the straight bar is bent during fabrication on a special mandrill; FBE coating acts as insulator for electro chemical cells and offer barrier protection to steel which prevents chloride ions to pass through it; 9
well established criteria are available for acceptance for FBE coating in different standards; FBE coated reinforcement bars provide the most effective corrosion protection to the reinforcement bars;
However, the disadvantages of ECR are:
epoxy coated bars have less slip resistance than uncoated bars. major concern is preventing damage to the coating during transportation and handling. cracking of coating during fabrication may take place due to inadequate cleaning of bars at plant. even a small damage in the coating can initiate corrosion in severe environment, since the coating has no cathodic protection.
Fig. – 2.6: Fusion Bonded Epoxy Coated bars The resin used in fusion bonded epoxy-coating, is an “epoxy” type resin (Fig. – 2.6). Permeability, hardness, color, thickness, gouge resistance etc. and other characteristics are controlled by these components. The application of epoxy coating in rebars involves spray of fluidized powders of resin onto the hot blast cleaned rebars using suitable spray guns at a typical temperature of 225°C to 245°C. By incorporating an ionizer electrode, the electrostatic spray gun gives the powder particles a positive electric charge. The charged powder particles uniformly enclose around the rebars and melt into a liquid form. Standard coating thickness range of FBE coatings is between 250 and 500 micrometers which can be varied depending on service condition. The molten powder becomes a solid coating within few seconds after coating application (ASTM A775). 2.2.4.1 Corrosion Resistance Mechanism of Epoxy Coated Bars Epoxy-coating provides a physical barrier and thus prevents the reinforcement from the contact of moisture, oxygen and chloride ion. Furthermore being a dielectric coating, epoxy resists electron and ion flow between the metal and the electrolyte, hence impeding the charge transfer between anode and cathode [30-32].
Fig. – 2.7: Reduced rate Half-cell redox reaction in epoxy coated reinforcements [32] 10
By using epoxy-coated bars in both top and bottom layers, anode may occur at the holes or holidays only. Thus locations for both anode and cathode becomes limited as shown in Fig. 2.7. Laboratory tests [32], showed about 98 percent reduction of corrosion rates when epoxy coated bars are used in place of black bars. 2.2.4.2 Life Cycle Cost Comparison Extensive laboratory and field research have already been conducted evaluating the economic aspects particularly addressing the life cycle cost of infrastructures. The University of Kansas Center for Research [33] conducted an in depth research on corrosion protection system for bridge decks which included a life cycle cost analysis for a period of 75 years for Uncoated, Epoxy Coated and Type 2205 stainless-steel reinforcements. Initial cost and life cycle cost [33] for uncoated, epoxy coated and Stainless-steel reinforcement are given below in Table 2.1: Table-2.1: Cost Comparison of Different Reinforcement Types [33] Reinforcement Type Initial Cost Life Cycle Cost 2 ($/yd ) ($/yd2) 189 444 Uncoated 196 237 Epoxy Coated 319 319 Stainless – Steel From Table 2.1 it is evident that, though epoxy coated reinforcements yield about 3.7% increase in initial cost, but eventually the life cycle cost decrease by 46.6 % in comparison to uncoated bars. Whereas, stainless steel show an increase of 70% in initial cost and decrease of 28.2 % in life cycle cost compared to uncoated bars. Performance vs cost shown in Fig. 6 presents the relative cost and durability on various corrosionresistant bars. It is expected that design lives will be well over 50 years for structures using high quality epoxy-coated bars in both mats in good concrete.
Fig. – 2.8: Comparison of various rebar option for corrosion protection [34] 11
Once started, the corrosion rate of rebars in concrete is dependent on the following [35] (i) (ii) (iii) (iv)
The pH level of the surrounding concrete The availability of oxygen and water, Concentration of Fe2+ near rebar The concentration of free chloride ions (cl -)
With good quality concrete having pH of 12 or more, the required chloride threshold to start corrosion is about 7000 to 8000 ppm. With carbonation, as the pH is lowered to 10 to 11, the chloride threshold is significantly lower, close to 100 ppm [36]. Carbonation destroys the passive film of the reinforcement, but does not affect the rate of corrosion as does the chloride ion. There are several service life prediction models available for concrete structures. The most common model is based on corrosion deterioration rate [2]. Fig. 2.8 shows the simplified model of predicting service life of concrete. Ti = Time for corrosion initiation Te = Time for crack propagation Ts = Time to repair where surface cracks evolves into spalls.
Fig. – 2.9: Tuuti Model for Predicting Service Life of Concrete Structure [2] The predicted life by Tuuti model is subject to considerable variation depending on the input variability as shown schematically by dotted line in Fig. 2.9. The predicted life span of a concrete structure require detailed knowledge of the following: Amount of applied chloride Permeability of concrete Effects of cracks on permeability Amount of cracking Corrosion threshold for a particular reinforcing Rate of corrosion Acceptable level of deterioration Repair options Repair durability 2.3
Design and Construction Related Challenges of using Epoxy Coated Bars
Epoxy coating on reinforcement reduces bond capacity in comparison with uncoated bars. Consequently, epoxy coated bars requires increased development and splice lengths when used in concrete [37]. ACI 318-14 provision for use of epoxy coated bar in concrete specify only an increased lap and development lengths by 50% for clear cover less than or clear spacing less than . For other cases (clear cover of or clear spacing and more) 20% extra development lengths are specified for epoxy coated bar. No other modification in the usual design procedure is required. In this sense use of epoxy coated bar 12
does not pose any design challenge. However, quality control of the coating could be a critical issue in specifying ECR. Some studies have found that bond strength decreases with increasing coating thickness [38]. Manufacturing deficiencies during the coating process may also result in inadequate adhesion of epoxy coating to steel. The quality of epoxy coating has also been shown to be a key factor affecting the corrosion performance and bond strength of fusion-bonded epoxy-coated rebars [39]. Extensive research on bond performance of epoxy coated reinforcements has been conducted to assess the long-term performances of structures built with epoxy coated bars. The use of FBECR in concrete provides protection against corrosion and long lasting durability of structures are expected even in adverse environment. However, for ensuring proper corrosion protection with FBECR the strict quality control at manufacturing plant to every stages of transportation, handling and placement at job site will all have to be done with utmost care. There has been few cases of early deterioration of structures with FBECR reportedly due to improper manufacturing and poor handling at field (see section 4.2). Therefore, it is extremely important that apart from strict quality compliance at manufacturing plant, the transportation, stacking, handling and fabrication, job site placement and concreting operation are to be done under a series of standard guideline. ASTM A775 has been continually upgraded with stringent provisions since its first version issued in 1981 (see chronology of changes in section 4.3). Concrete Reinforcing Steel Institute (CRSI) has published guidelines for inspection and acceptance of epoxy coated rebar at job site [40]. To ensure minimal damage on coating special careful measures should be taken during job site placement, handling and fabrication of epoxy coated bars. The ASTM D3963 specifies that bars with more than 2% of its coated area damaged in 1ft section, should be discarded. The reason behind such protective actions is that, the holiday/ holes in epoxy coating might initiate local electric cells thus causing aggressive localized corrosion. A few measures include, use of nylon slings instead of bare chains or cables during unloading, opaque sheets to cover the coated bars while storing, using nonmetallic dielectric tying wires, power shears or chop saw cut should be done instead of flame cut, Teflon or nylon coated mandrel should be used while fabricating the coated bars. During concreting, plastic headed vibrator nozzles should be used to reduce abrasion effect on coatings (ASTM D3963). Any kind of damage during unloading, bending and placement should be treated with patching material (Appendix, ASTM 775). A pictorial description of practicing extra care for FBECR are presented in Fig.-2.10.
Fig. – 2.10: (a) Storage (b) Bending of bars (c) Patching of damaged area (d) Fabrication 13
2.3.1
Bond Related Problem of ECR
The change of surface properties caused by epoxy coatings leads to a loss of adhesion and friction and alters the mechanical interaction between the steel and the concrete; all of which lead to a substantial change in a mechanisms of bond. The roughness of the bar surface influences both the adhesion and the friction between the bar and the concrete; the geometric properties of the deformed bar cause the mechanical interaction [41]. In view of the substantial change in bond mechanism, several researchers have been concerned with the bond of epoxy coated reinforcement to concrete. The first study of the bond of epoxy coated bars was conducted by Mathey and Clifton [42-44] using pull out specimens. From the initial study, they concluded that bars with epoxy coatings of approximately 10 mils or less in thickness, have a bond strength that is quite similar as that of uncoated bars. Moreover, six slab specimens and forty beam end specimens were tested [45] using #6 and #11 bars. Based on these tests, recommendations were delivered that development length should be increased by 15% for epoxy coated bars and conclusion was drawn that effect of epoxy coating is independent of bar size. Further evidence of adhesion loss was provided in a series of tests [46] conducted to compare frictional properties of mill scale steel surfaces and fusion bonded epoxy surfaces. The coating caused a significant loss of adhesion. The difference between surfaces, as expressed by the ratio of shear strength for coated to mill scale surfaces reduced with increasing normal stress. Bond stiffness (i.e bond stress at a defined value of slip) is also generally reduced by coating, particularly at low slips [46-48]. The experiments report that bond stiffness ratio increased approximately from 0.5 to 1.1 as slip increased from 0.01 mm to 1 mm. It is also reported that conclusions based upon difference between loaded and free end slips of beam end specimens and pull out test [47-48] points to a lesser bond stiffness for the coated bars. 2.3.2
Care During Manufacturing, Handling, Fabrication and Construction
The manufacturing of FBECR bar has to go through a strict, in-plant quality control system. Manufacturing defects in epoxy coating have led to poor performance and rebar corrosion started at early stages posing question as to the reliability of ECR. In US, the Concrete Reinforcing Steel Institute (CRSI) has introduced plant certification program since 1991 where quality of coating goes through a series of routine checks and tests. In North America there are 38 certified plants for FBECR. To ensure quality fabrication at job site without damage to the coatings, the fabricators certification has also been introduced. The range of checking, quality control tests commonly conducted at manufacturing are described below: Checking of continuity of coating Testing of Performance of rebar
Online and offline holiday checks, thickness checks are carried out. The adhesion of the coated bars is also tested frequently by bending of the bar. At manufacturing plant various quality tests are performed like chemical resistance, short spray, resistance in boiling water, abrasion resistance and impact resistance etc. These are conducted on every batch of production.
For protection against damages to the coating of ECR, special care at every stages of transporting, handling, fabrication and concreting are needed. Handling requirements are covered in ASTM D 3963. A summary of care and protection during transporting to concreting is provided below:
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Transporting, handling & stacking
Fusion Bonded Epoxy Coated Bars require padded contacts during transportation, stacking, handling and till the concreting is done. Following precautions are to be taken: Bars should be lifted using a spreader bar or strong-back with multiple pick-up points to minimize sag. During sagging, steel may rub on each other, causing coating damage. At no time should coated steel be dragged. Nylon or padded slings should be used and at no times should bare chains or cables be permitted. Steel should be unloaded as close as possible to the point of concrete placement to minimize rehandling. Bundles of steel should be stored on suitable material, such as timber cribbing. At no time should steel be stored directly on the ground. If the steel are to be exposed outdoors for more than 30 days, they should be covered with a suitable opaque material that minimizes condensation. Coated and uncoated steel should be stored separately.
Cutting, bending & welding
During bar fabrication at site, the cut ends, welded spots and handling damages are required to be repaired with special liquid epoxy compatible with the coating material as per specification of the coating agency. Bars should not be dragged or placed directly on the forms as this may result in oil contamination of the surface. Bars should be placed on supports coated with non-conductive material, such as epoxy or plastic bar supports, and these should meet class 1A, as defined in the CRSI Manual of Standard Practice. Bars should be tied using coated tie wire. Coated bars may be cut using power shears or chop saws and cut ends should be repaired using a two-part epoxy. Bars must not be flame cut. Bars may only be bent at the jobsite with the permission of the engineer responsible for the particular project and this should be documented. If bending is to be conducted it must be conducted at ambient temperatures.
Concreting
Special care are needed during pouring and compacting of concrete. After placement, movement over the epoxy-coated steel should be kept at minimum. Concrete hoses on placed steel should be avoided as they may damage the coating on movement. Care should also be taken to ensure that items such as unprotected couplers for concrete delivery hoses are not dragged across the steel as these may result in coating damage.
15
A site meeting may be beneficial with the concrete contractor. At no time should stands or rails used for concrete placement machines be welded to the epoxy-coated steel. Care should be used to ensure that activities during the concrete placement do not result in damage to the epoxy-coated steel. Concrete pumps should be fitted with an “S” bend to prevent free fall of concrete directly onto the coating. Plastic headed vibrations should be used to consolidate concrete. Steel vibrators may cause coating damage. Bars that are partially cast in concrete, and then remain exposed for extended periods, should be protected against exposure to UV, salts and condensation. It has been found that wrapping with plastic or individual tubing is suitable for providing long-term protection. Care during bar fabrication
Bends: The coating at bends should not exhibit any cracking or fractures. Particular care should be taken to inspect the condition of the coating in these regions as damage may occur during fabrication. Repair of all damage: Repairs to any visible damage should be made allowing sufficient time for coatings to dry. Such repairs should be conducted using a twopart epoxy. Spray can repair materials are not recommended. If the bar has more than 2% of its area damaged in any given 1ft. section of coated reinforcement it should be replaced. ASTM D3963 states that if the total bar surface area covered by patching material exceeds 5% in any given 1ft. section of coated reinforcement, the bar may be rejected. This limit does not include sheared or cut ends. Bar supports: Reinforcement should be placed on supports coated with nonconductive material, such as epoxy or plastic bar supports. Tie wire: Reinforcement should be tied using a coated tie wire. Bar samples: Some agencies require inspectors to collect coated steel samples from the jobsite and these should be clearly identified prior to submittal to the appropriate laboratory for testing. Welding: Welding should only occur with the permission of the engineer. Any welds should be cleaned and patched with repair materials.
16
A pictorial description of extra care practiced for fabrication and placement is provided in Fig.-2.11. (a)
(b)
(c)
(d)
Fig. – 2.11: Extra Care for Fabrication and Placement: (a) placement at casting yard (b) coating applied to bar ends (c) & (d) repair of bar damage using special epoxy.
2.3.3
Quality Control Issues
The quality of ECR has become an issue from manufacturing to field level handling and fabrication. The ASTM standard that deals with ECR are described below. The specification for epoxy-coated bars to be used as reinforcement is ASTM A775: Standard Specification for Epoxy-Coated Steel Reinforcing Bars. The first version of this standard was introduced in 1981 and ever since subsequent changes have been made meeting the field and laboratory based research works. The chronology of changes in the ASTM A775 are presented in Table 2.2 [49]. With these changes the compliant FBECR are more likely to give a durable reinforced concrete structure.
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Year
Table 2.2: Chronology of Changes Made to ASTM A775 [49] Changed Status Provision of Prior Version
1981
First version approved
-
1989
Permissible damage reduced to 1%
2%
1989
Introduction of anchor profile of 1.5-4 mil
-
1990
Repair of all damage
Repair of damage >0.1 in2
1993
Coating thickness 7-12 mil
90 percent between 5 and 12 mil
1994
Increase bend test to 180o
120o
1995
Reduce allowable holidays to less than 1 per foot
2 per foot
1995
No coating deficiency allowed
0.5 percent
1995
Coat within 3-hours
8 hours
1997
Coating adhesion CD test
-
1997
Cover bars stored outside if longer than 2 months
-
2004
Coating thickness increased for larger diameter 7-12 for all bar sizes bars. 7-16 mil (Nos. 6-18)
2004
Clarified individual thickness measurements no single measurement 120% of maximum
2006
Clarification on thickness measurements added
-
2007
Added patching material requirements
-
ASTM A934: Standard Specification for Epoxy-Coated Prefabricated Steel Reinforcing Bars deals with fusion-bonded epoxy-coated bar that is cut and bend into specific required sizes, shapes and lengths. This is applicable, for example for stirrups and hooks. In this case the bar cleaning and application of powdercoating is done after giving due shape and size to the rebar. ASTM D3963: Standard Specification for Fabrication and Jobsite Handling of Epoxy-Coated Steel Reinforcing Bars deals with the handling and fabrication related issues of epoxy-coated bars. 2.3.4
Historic Performance of ECR
The most wide application of ECR is traced in North America with majority use in bridges and marine structures to cater for the corrosion problem due to salinity. The use of ECR dates back to 1973. In US the performance of ECR in corrosion protection has been subject to question when just after seven years of construction, corrosion induced cracking and spalling of marine sub-structures in Florida Keys have been noticed. This time span matches with the time projected for structures built with black bar to show signs of deterioration. This has raised serious concern regarding the claim of corrosion protection of ECR in concrete. As a result a number research studies [50-66] for projecting the long term performance of structures built with ECR have been initiated. The Florida Department of Transport (FDOT), based on laboratory and field studies, had to discontinue the use of ECR [52-53, 59, 67-69]. The findings of the above mentioned studies include ECR experienced corrosion damage at coating defects along with cathodic disbondment of adjacent coating, underfilm corrosion. Fig. 2.12 [61] shows result of the damage that occurred to the three of epoxy coated rebars, when these were all subjected to chloride admixed test yard slabs that had undergone cyclic tap water ponding. The upper bar of each pair shows black marker dots on the bars that identify presence of coating defect at indicated locations, as determined using 18
holiday detector. The lower bar of each pair shows the bar appearance subsequent to peeling away disbonded coating using a knife. This clearly establishes a one-to-one correlation between presence of defect and coating disbonding and underfilm corrosion.
Fig. – 2.12: Three ECR bars after exposure in Cl contaminated concrete, first with coating holidays identified (upper photograph of each bar pair) and, second, showing bar appearance upon removal of disbanded coating (lower photograph of each pair).[61] Laboratory and field studies by Weyers et. al. [70-72] reported ECR coating disbonment and underfilm corrosion on bridges in Virginia which has led the Virginia Department of Transportation (VDOT) to discontinue use of ECR in 2010. Pianca et. al. [72] conducted study on the field performance of ECR in concrete barrier walls and unprotected portion of bridge decks and found that corrosion damage did occur in ECR. This has led the Ontario Ministry of Transportation (OMOT) to change its specification to use stainless steel for structure barrier walls and for decks of high traffic volume bridges for which repair/rehabilitation could cause traffic disruption due to lane closure. Moreover, Canadian Standards Association [73] clause 6.1.3 provides a cautionary note as follows: “Such reinforcement should be selected with caution, based on the severity of the concrete exposure and the desired service life of the concrete component or structure. There is a growing body of knowledge suggesting that the benefits of epoxy coatings for long-term corrosion protection are not what was originally anticipated. Potential users should review recent literature on the subject for further information.” Another study by A.A. Sohanghpurwala et. al. [74] by field survey and laboratory analysis of 240 extracted bar segments from 80 bridges decks with ECR in Pennsylvania and New York of age 4-18 years has demonstrated generally good performance but also identified some locations where corrosion had commenced. Although a service life of 75 years of low maintenance had been extrapolated through linear extrapolation, the validity of such extrapolation had been doubted by others [51]. All the above mentioned studies are related to extreme harsh environmental condition where almost invariably high concentration of chloride ion was present due to application of de-icing salt on bridge decks. However, following general conclusions can be drawn from the various North American studies on ECR performance: a) Thickness of concrete cover provides the best protection to rebar corrosion by preventing penetration of chloride or carbonation to the rebar. Once the corrosion is started, the rate of corrosion is independent of cover thickness [75].
19
b) Uncertainties exit regarding the long-term performance of ECR and the prediction of service life of concrete with ECR in chloride exposed concrete. Despite this, where a side-by-side comparisons had been possible, ECR has outperformed black bars [54-55, 76]. c) Some researches have projected an ECR service life of less than fifty years [58] while other projected seventy five years [74] in chloride contaminated concrete. However, these claims did not receive wide acceptance by the experts. d) Most of the reported poor performances of epoxy coated bars within 6~10 years of construction (e.g. Florida Keys and water-line in the $45 million seven-mile Bridge) are due to poor coating, lower coating thickness than present day requirement of ASTM A775, poor handling, transporting, stacking methods employed than the present day recommended practice. Out of the 65000 structures built with ECR, most of the structures serving for more than 37 years have demonstrated low maintenance service life. Problems have been encountered only in few of them due to poor or damaged coating [76]. e) With the more stringent requirements of present day standards for manufacturing of ECR (ASTM A 775) and standard for fabrication and job site handling of ECR (ASTM D 3963), it is believed that structures built with ECR should provide a maintenance free service life many fold than ordinary black bar, particularly in adverse environmental exposure. The various performance evaluations have made experts to believe that ECR is performing well in high quality concrete with good cover but not in situations where either of these two conditions (good quality concrete and cover) is not met [77]. 2.4
Possible Use of Epoxy Coated Bar in Bangladesh Context
Due to salt water intrusion in the coastal region of Bangladesh, the nearby coastal structures such as bridge piers and abutments, cyclone shelters, dams and other concrete structures exposed to saline water are in immense threat of corrosion. Apart from coastal regions, other structural members such as top floor slabs exposed to dampness, shallow and deep foundations, bridge piers subjected to intermittent drying and wetting, water treatment plants are also threatened with rapid deterioration of design life span due to corrosion. Currently, widespread corrosion resistant system adopted in Bangladesh is limited only to increase in concrete cover. In adverse weather cover alone is not sufficient and additional protection is warranted. Epoxy coated reinforcement can be a cost effective and feasible solution to cater the durability issues in the structures of Bangladesh. Though epoxy coated bars are globally accepted as an effective corrosion resistant system, local engineering community needs to be conversant about its design and construction related challenges. Before large scale application in Bangladesh, due training of the engineers, fabricators and contractors are essential. This will help the professionals to gain confidence in using epoxy-coated bars in RC structures which appears to have a significant impact on durability and overall economy of concrete structures.
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CHAPTER 3 Experimental Program 3.1
Background
Steel to concrete bond is the many-faceted phenomena which allow longitudinal forces to be transferred from the reinforcement to the surrounding concrete in a reinforced concrete structure. Due to this force transfer, the force in a reinforcing bar changes along its length, as does the force in the concrete embedment. Whenever steel strains differ from concrete strains, a relative displacement between the steel and concrete (slip) does occur. Many factors can affect the bond of deformed bars to concrete. Experimental and theoretical work makes it possible to recognize the basic three mechanisms of bond [41]. These are adhesion, friction and mechanical interaction, mainly between the bar rib and the surrounding mortar. The roughness of the bar surface influences both the adhesion and the friction between the bar and the concrete. The geometric properties of the deformed bar cause the mechanical interaction [41]. At increasing value of bond stress adhesion is destroyed as a consequence of slip and wedging of the ribs. After the loss of adhesion, the next mechanisms, friction and mechanical interaction between the ribs and the concrete, occur together. In the case of ECR, the change of surface properties altered by epoxy coating leads to a loss of adhesion and friction and alters the mechanical interaction between the steel and concrete: all of which lead to a substantial change to the mechanism of bond. Figure 3.1 presents the bond stress vs slip relationship as published by for various confining condition [81].
Fig. – 3.1: Bond-ship behavior of rebar in concrete under different state of confinement [81] 3.2
Objectives
The primary focus of this study is to compare the bond performance of commercially produced epoxy coated rebars and conventional uncoated deformed rebars under direct pull-out and also the flexural performance of the coated and uncoated bars. With this end in view following objectives are set: a. Compare the bond strength of epoxy-coated reinforcing steel bars and uncoated deformed bars.
21
b. Construct a “Bond Stress vs. Slip” diagram to better understand the slip behavior of epoxycoated bars as compared to conventional deformed bars. c. Assess the flexural performance of the beams and the effect of concrete strength, aggregate type and bar diameter on beams reinforced with epoxy and uncoated bars in standard two point beam flexural test. In order to attain the stated objectives, the considerations and details of the testing program are described below: a. For purpose of comparing the bond performance, total testing of 24 variations with 3 samples in each category making a total of 72 samples were performed in pull-out test. The testing have been designed with epoxy-coated as well as uncoated steel reinforcements. Two different types of coarse aggregate i.e. stone chips and brick chips were be used. Three concrete mixes for each aggregate type have been prepared. Concrete with stone chips with design strengths of 3000, 3500 and 4000 psi have been considered. For brick chips, design strengths of 2000, 2500 and 3000 psi have been selected. Two different rebar size (12mm, 16mm) for both epoxy-coated bars and uncoated deformed bars were used for the experiments. b. The pull-out tests were carried out using the UTM machine available in the Strength of Materials laboratory of Civil Engineering Department of BUET. A steel frame was prepared [Fig. 3.2] for the pull-out test in which the BB and ECR specimen were tested for bond performance. Dial gauges were used to measure the deformation of steel bars and the concrete sample. In addition to manual measurement, two HD video cameras with tripod arrangements were placed to continuously monitor the dial gauge reading for precise results.
Fig. – 3.2: Pull-out test experimental set-up and dial gauge c. For purpose of evaluating the flexural response of epoxy coated rebars, a total of 42 tests beams were constructed using both coated and uncoated conventional rebars. The beam sections were designed to ensure tension controlled sections. The beams are to be tested in a two point loading scheme, with pure flexure in the central zone as shown in Fig. 3.3.
22
Fig. – 3.3: Experimental setup for flexural study with two point loading. 3.3
Test Specimen
In this section, the two types of specimen, their design and other salient features are discussed. The specimen include – 3.3.1
Pull Out Test Specimen
3.3.1.1 General The main objective of this experimental program is to investigate the bond behaviors of Epoxy Coated bar as reinforcement for concrete structures. A total of Seventy two concrete cube specimens were tested. Thirty six of them were reinforced with uncoated steel and thirty six of them were reinforced with Epoxy Coated bars.. A total of six batches of concrete were used for both type of samples. All specimens were loaded up to either bond failure or tensile failure using a direct Pull out test. The main variables are the compressive strength of concrete, aggregate type, diameter of bars, length of embedment and coating of steel bars. The overall performance of the tested specimens was evaluated based on the overall bondslip behavior. The parameters used to evaluate bond performance were: a. Failure mode (Tensile failure or bond failure) b. Slip with respect to load c. Ultimate bond strength 3.3.1.2 Design of Specimens The selected dimensions for Sixty specimens were 12”X12”X12” inches. The development length of 12mm uncoated bars is considered according to ACI 318-14 and was used as the standard specimens (assuming ). In addition to the basic lengths, bars with longer development lengths – 16mm bars were tested to help evaluate the bond-stress relationship for bars with epoxy coating. Another Twelve cube specimen were casted varying the embedment length for 12mm bars according to the ACI 318-14 specified development length of 16 inches (400 mm) for uncoated and 24 inches (600mm) for epoxy coated bars (assuming . Table 3.1 summarizes the test matrix. 23
Table – 3.1: Test matrix for pull out test of ECR and black bar. Specimen Name ES1R1 ES1R2 US1R1 US1R2 EB1R1 EB1R2 UB1R1 UB1R2 ES2R1 ES2R2 US2R1 US2R2 ES3R1 ES3R2 US3R1 US3R2 EB2R1 EB2R1 UB2R1 UB2R2 ES1R1_FLd US1R1_FLd
No. of Specimen 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 6 6
(psi) 3000 3000 3000 3000 3000 3000 3000 3000 3500 3500 3500 3500 4000 4000 4000 4000 2500 2500 2500 2500 3000 3000
Aggregate type Stone Chips Stone Chips Stone Chips Stone Chips Brick Chips Brick Chips Brick Chips Brick Chips Stone Chips Stone Chips Stone Chips Stone Chips Stone Chips Stone Chips Stone Chips Stone Chips Brick Chips Brick Chips Brick Chips Brick Chips Stone Chips Stone Chips
Bar Type, Epoxy coated Epoxy coated Uncoated Uncoated Epoxy coated Epoxy coated Uncoated Uncoated Epoxy coated Epoxy coated Uncoated Uncoated Epoxy coated Epoxy coated Uncoated Uncoated Epoxy coated Epoxy coated Uncoated Uncoated Epoxy coated Uncoated
Bar Dia, mm 12 16 12 16 12 16 12 16 12 16 12 16 12 16 12 16 12 16 12 16 12 12
3.3.1.3 Pull out Reinforcement All specimens were reinforced with 36 inches centre main reinforcement subjected to direct tension pull out. All reinforcements are BS 4449 Grade 500 as well as BDS ISO 6935-2 Grade 500W. Figure 3.4 illustrates the typical reinforcement for the pull out reinforcements.
Fig. – 3.4: Arrangement of Reinforcements at the centre of the specimen 24
3.3.1.4 Shear Reinforcement To prevent an undesired bursting failure of the concrete specimen, ample shear reinforcement was provided. A total of 4 closed types 10 mm diameter stirrups were used at 2.75 inch (70 mm) c/c spacing within the entire specimen. An arrangement of shear reinforcement along the specimen is shown in Figure 3.4. 3.3.2
Flexure Test Specimens
3.3.2.1 General The main objective of this experimental program is to investigate the flexural behaviors of Epoxy Coated bar as reinforcement for concrete structures. A total of forty two half-scale rectangular concrete beams were tested. Twenty one of them were reinforced with uncoated steel and twenty one of them were reinforced with Epoxy Coated bars. A total of six batches of concrete were used for both type of samples. All specimens were loaded up to failure using a two point flexural test under monotonic loading condition. The main variables are the compressive strength of concrete, diameter of bars and coating of steel bars. The overall performance of the tested specimens was evaluated based on the overall flexural behavior. The parameters used to evaluate flexural performance were: a. b. c. d. e.
Flexural cracking load Crack pattern and crack width Deflection under load Ultimate flexural strength Failure mode
3.3.2.2 Design of Specimens All specimens were designed to have a half-scale dimension to simulate typical field behavior of concrete beam applications. The selected dimensions were 6 inches (150 mm) wide, 9.5 inches (241 mm) deep and 8.5 feet (2590 mm) long. All beams were designed to achieve the minimum strain in the steel of 0.005 in/in at nominal load capacity. The reinforcement ratios for all beams satisfied the minimum and maximum value recommended by ACI 318-14 [1].All beams were designed to comply with ACI-318-14 code requirement for under reinforced beams (ϵs= 0.005 in/in). Table 3.2 summarizes the test matrix. Table – 3.2: Details of Beam Specimens Prepared for Flexural Testing Specimen Name
U_2.5_BC_12 U_3_BC_12 U_3_BC_16 U_3_SC_12 U_3_SC_16 U_3.5_SC_12 U_3.5_SC_16 U_3_BC-S_16 (splice) U_3_SC-S_16 (splice) U_3.5_SC-S_16 (splice) E_2.5_BC_12 E_3_BC_12 E_3_BC_16
X section (in*in) 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5
Rebar Type
(ksi)
Aggreg ate type
2.5 3 3 3 3 3.5 3.5 3 3 3.5 2.5 3 3
BC BC BC SC SC SC SC BC SC SC BC BC BC
Black Bar Black Bar Black Bar Black Bar Black Bar Black Bar Black Bar Black Bar Black Bar Black Bar Epoxy Coated Epoxy Coated Epoxy Coated
25
Rebar Size (mm) 12 12 16 12 16 12 16 16 16 16 12 12 16
No. of Sample 3 3 2 3 2 3 2 1 1 1 3 3 2
Specimen Name
X section (in*in)
Aggreg ate type
Rebar Type
(ksi)
6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5 6*9.5
3 3 3.5 3.5 3 3 3.5
SC SC SC SC BC SC SC
Epoxy Coated Epoxy Coated Epoxy Coated Epoxy Coated Epoxy Coated Epoxy Coated Epoxy Coated
E_3_SC_12 E_3_SC_16 E_3.5_SC_12 E_3.5_SC_16 E_3_BC-S_16 (splice) E_3_SC-S_16 (splice) E_3.5_SC_S_16 (splice)
Rebar Size (mm) 12 16 12 16 16 16 16
No. of Sample 3 2 3 2 1 1 1
3.3.2.3 Flexural Reinforcement All beams were reinforced as singly reinforced beam. All flexure reinforcements are BS 4449 Grade 500 as well as BDS ISO 6935-2 Grade 500W. For 12 mm bottom bars, 3 longitudinal bars were used. For 16 mm bottom bars 2 longitudinal bars were used. Two # 3 longitudinal rebars were used as compression reinforcement for all beams to simplify the construction of the steel cage. Figure 3.5 illustrates the typical reinforcement for beams.
Fig. – 3.5: Arrangement of Reinforcement 3.3.2.4 Shear Reinforcement To prevent an undesired shear failure in the beams, ample shear reinforcement was provided. A total of 24 closed types 10 mm diameter stirrups were used at 4 inch (100 mm) c/c spacing within the entire beam. A typical epoxy coated shear reinforcement along the beam is shown in Figure 3.6.
Fig. – 3.6: Arrangement of Reinforcement 3.4
Material Properties
In this section, mechanical properties of concrete and steel are reported based on test results conducted in accordance with ASTM standards. 26
3.4.1
Pull out test
3.4.1.1 Concrete Six batches of cement concrete were used in this program. The concrete was produced at Concrete laboratory of the Civil Engineering Department of BUET. The mix proportion for all batches of concrete were 1:1.5:3 (cement: sand: aggregate), nine 4x8 inch (100X200 mm) concrete cylinders were prepared for each batch and cured at room temperature. For each batch three concrete cylinders were tested at 7 days, 14 days and other three cylinders were tested at the time of testing beam specimens as per ASTM C39-01. All cylinders were loaded to failure. The compressive strengths of each set of pull out specimen at testing day are presented in Table 3.3. Table 3.3 : Compressive Strength of Concrete Beam Type I-SC
I-BC
II-SC III-SC
IV-BC
I-SC-FLd
Testing day Cylinder Compressive Strength (psi) 3847 4381 4257 3939 3903 3958 5644 6213 6119 6817 7350 6992 3441 3833 3690 4330 4294 4310
Average Strength (psi)
Standard Deviation
4162
228.19
3933
22.81
5992
249.05
7053
221.83
3655
161.97
4311
216.89
3.4.1.2 Steel Tension tests were performed according to ASTM A615/A615M to determine the stress strain characteristic of the steel reinforcements of both epoxy coated and uncoated variations. The actual loaddeflection curves for all reinforcements can be found in the Figure 3.7. All tensile properties are reported in terms of average value. The failure mode of the reinforcements was found by subjecting them to a tension test until rupture. Tests on rebars were done at the Strength of Materials Laboratory, Department of Civil engineering, BUET and results are shown in Figure 3.8. Table 3.4 shows the bar original diameter, average yield load, average ultimate load and percent elongation of the steel bars. Table 3.4: Steel properties of tested Epoxy Coated and Black Bars Bar Type 12 mm Epoxy Coated 12 mm Uncoated 16 mm Epoxy Coated 16 mm Uncoated
Original Bar diameter (mm) 12.07 11.87 16.11 15.9
Yield Load (kN) 66.2 67.87 117.6 113.99
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Ultimate Load (kN) 78.74 77.61 138.78 135.61
Percent Elongation (%) 12 13.67 13.67 16
Fig. – 3.7(a): Load-Deflection curve for 12mm Epoxy Coated bars
Fig. – 3.7(b): Load-Deflection curve for 12mm Uncoated bars
28
Fig. – 3.7(c): Load-Deflection curve for 16mm Epoxy Coated bars
Fig. – 3.7(d): Load-Deflection curve for 16mm Uncoated bars
29
3.4.2
Flexure Test
3.4.2.1 Concrete Six batches of cement concrete were used in this program. The concrete was produced at Concrete laboratory of the Civil Engineering Department of BUET. The mix proportion for all batches of concrete were 1:1.55:2.3 (cement: sand: aggregate) , nine 4x8 inch (100X200 mm) concrete cylinders were prepared for each batch and cured at room temperature. For each batch three concrete cylinders were tested at 7 days, 14 days and other three cylinders were tested at the time of testing beam specimens as per ASTM C39-01. All cylinders were loaded to failure. The compressive strengths of each set of concrete beam at testing day are presented in Table 3.5.
Beam Type
I-SC
I-BC
II-SC
III-SC-S
III-BC-S
IV-SC
IV-BC
V-SC
V-SC-S
VI-BC
Table 3.5 : Compressive Strength of Concrete Testing day Cylinder Average Strength Compressive Strength Standard Deviation (psi) (psi) 3690 3763 3727 29.81 3728 3555 3445 89.81 3335 3445 5770 5670 5720 40.82 5720 3650 3700 3716 60.58 3796 3555 3335 3445 89.81 3445 3794 3950 3864 64.60 3849 5220 4361 4767 350.79 4809 4633 4402 4573 122.39 4683 5770 5670 5730 43.2 5750 3882 3757 4001 261.70 4364
3.4.2.2 Steel The steel properties are discussed at section 3.4.1.2.
30
3.5
Fabrication of the specimen
3.5.1
Pull out specimen
All specimens were fabricated at the BUET Concrete laboratory. Majority of the formworks were constructed from 0.0625 inch (1.5875 mm) thick steel sheets with stiffeners of steel angle and flat bar. Others were constructed using wood boards. Each reinforcing steel cage was carefully assembled to the specifications required ¾ inch (19 mm) concrete blocks were installed at the bottom of the steel cages to ensure a target of ¾ inch concrete cover. The form was then sprayed with an oil-based material to simplify removal efforts. The steel cages were then placed in the form. The form was moved to the pouring site. Concrete was prepared using mixing machine at BUET concrete laboratory. Slump tests were performed within 2.5 minutes after obtaining the sample as stated in ASTM C143-00. This process was crucial for determining the workability of the concrete. The casting of the specimens began soon after the slump test. The finishing process followed shortly. At the same time, nine 4 × 8 inch (100 × 200 mm) cylinders were prepared to obtain the strength parameters for each of concrete. Figure 3.9 illustrates the casting process of the concrete specimen.
Fig. – 3.9: Pull out specimens during casting 3.5.2
Flexure Specimen
All specimens were fabricated at the BUET Concrete laboratory. All formworks were constructed from 0.0625 inch (1.5875 mm) thick steel sheets with stiffeners of steel angle and flat bar. Each reinforcing steel cage was carefully assembled to the specifications required ¾ inch (19 mm) concrete blocks were installed at the bottom of the steel cages to ensure a target of ¾ inch concrete cover. The form was then sprayed with an oil-based material to simplify removal efforts. The steel cages were then placed in the form. A series of bracing was installed at the top of the form. The bracings were located at 34 inches (863.6 mm) spacing to ensure proper dimensions of the beam. The form was moved to the pouring site. Concrete was prepared using mixing machine at BUET concrete laboratory. Slump tests were performed within 2.5 minutes after obtaining the sample as stated in ASTM C143-00. This process was crucial for determining the workability of the concrete. The casting of the specimens began soon after the slump test. The finishing process followed shortly. At the same time, six 4 × 8 inch (100 × 200 mm) cylinders were prepared to obtain the strength parameters for each batch of concrete. Figure 3.10 illustrates the casting process of the concrete specimen. The beams and cylinders were left to cure in the same condition by wrapping with moist hessian cloth. The beams were stripped at the time of testing. 31
Fig. – 3.10: Casting Procedure of beam specimen 3.6
Instrumentation
3.6.1
Pull out Tests
A metal frame was constructed to conduct the direct pull out test and to obtain a load vs slip diagram. Metal plates of 1.5 inch thickness were used as base and top plates, 4-25mm shafts were used as corner supports and a center 40 mm shaft was used at the top plate to support the entire frame and the concrete block. The stress analysis of the metal frame was done using ABAQUS FEA as shown in Fig. 3.11. The final fabricated test setup is shown in Fig. 3.12 and Fig. 3.13.
Fig. – 3.11: FE model of the pull-out test frame
Fig. – 3.12: Pull-out test frame in UTM
Fig. – 3.13: Pull-out test specimen and instrumentation 32
All pull out specimens were fully instrumented to measure the applied loads on the specimen, deflections associated with loading, and the corresponding slips, as illustrated in Fig. 3.13. Loading data associated with time was recorded in the loading machine. Three mechanical deflectometers were installed at the positions as shown in the Fig. 3.13, to measure the loading and unloading slip. The whole procedure was recorded in two HD video cameras. Table 3.6 gives the precise location and function of each device. Table – 3.6: Summary of Location, and Function of External Devices Device Deflectometer 1 Deflectometer 2 Deflectometer 3
Location At the unloaded end of specimen At the loaded end of the bottom plate At the loaded end of the main reinforcement
Two HD video cameras
3.6.2
Function To observe unloaded slip Measure total slip + strain Measure strain of the reinforcement. To focus and take accurate readings from deflectometer.
Flexure Tests
All beams were fully instrumented to measure the applied loads on the beams, deflections associated with loading as illustrated in Figure 11. Loading data associated with time was recorded in the loading machine. A mechanical deflectometer was placed just below the midpoint of the beam. The whole procedure was recorded in a video camera. Table 3.7 gives the precise location and function of each device. Table – 3.7: Summary of Location, and Function of External Device Device Location Function Deflectometer 3.7
Testing Procedure
3.7.1
Pull out test
At the middle of the beam
Measure deflection
3.7.1.1 Test Setup After curing period, all specimen were moved to perform the pull out test. Each specimen was tested to failure by bond or by tension using the Universal Testing Machine (UTM). A tested specimen was placed on the bottom steel plate of the frame as shown in Figure 3.14. The bottom end of the reinforcement was fixed at the grip of the UTM. The frame was fixed at the top shaft. The setup was carefully leveled and aligned to prevent any source of errors due to the lateral eccentricity. 3.7.1.2 Preparation for testing After the specimen was properly positioned deflectometers were manually checked to verify the operational condition. The data acquisition system was thoroughly checked. Figure 3.15 illustrates pull out specimen prior to loading. 3.7.1.3 Testing All specimen were monotonically tested to failure by the Universal Testing Machine (UTM). The specimens were subjected to a direct tension pull out loading at a constant rate. Loading rates were selected to meet the requirements of ASTM C 234. Failure mode, pull out force, slip and strain were recorded via HD video cameras during the tests as shown in Figure 3.15. 33
Fig. – 3.14: Pull-out test frame with specimen in the UTM 3.7.2
Fig. – 3.15: Two HD video cameras to record the data at both loaded and unloaded end of the bars.
Flexure test
3.7.2.1 Test Setup After curing period, all beams were moved to perform of a two point flexural test. Each beam was tested to failure by a Universal Testing Machine (UTM). A tested specimen was placed on two steel members placed on the hydraulic platform of the machine. A steel pin support was carefully set between the specimen and the steel member at a distance of 3 inches (75 mm) from the right end of the beam, while a steel roller support was positioned at the same distance but at the left end of the beam. The details of the support are presented in Figure 3.16.The hydraulic platform was raised during testing. The setup was carefully leveled and aligned to prevent any source of errors due to the lateral eccentricity. The loading rollers were installed on the top of the concrete beam at 32 inches (812.8 mm) from each support. Geotextile sheets were provided below each roller to ensure an even distribution of the concentrated load. 3.7.2.2 Preparation for testing After the specimen was properly positioned deflectometer was manually checked to verify the operational condition. The data acquisition system was thoroughly checked. Figure 3.16 illustrates beam prior to loading. 3.7.2.3 Testing All beams were monotonically tested to failure by the Universal Testing Machine (UTM). The specimens were subjected to a two-point static loading at a constant rate. Loading rates were selected to meet the requirements of ASTM C 293-02. At the time of testing, load and strain information was displayed on the screen of the data acquisition system and was carefully monitored. Crack propagation and crack width were visually observed and measured manually via crack comparator during the tests as shown in Figure 3.17.
34
Fig. – 3.16: Experimental test setup for flexure.
Fig. – 3.17: Crack Comparator.
35
CHAPTER 4 Results of Experiments 4.1
Results of Pull-out tests
The experimental results of 72 pull out specimen are available. Properties of concrete and steel reinforcing bars are also reported here. Details of the test scheme and test matrix have been presented earlier in section 3. Material properties included the measure of concrete strength, and the mechanical properties of BDS ISO 6935-2 Grade 500W steel. Characteristics of the concrete are the compressive strength of the cylinder specimens determined at the time of testing of the specimen. Experimental results of the 72 specimen included this presentation of load vs slip diagram, ultimate bond failure load, and failure modes. Table 4.1 gives pull out test specimens and material properties. Table – 4.1: Pull out test specimens Pull out Specimen Type
Concrete Strength (ksi)
Main Pull out Bar
Aggregate Type
I-SC
3
12 & 16 mm
Stone Chips
I-BC
3
12 & 16 mm
Brick Chips
II-SC
3.5
12 & 16 mm
Stone Chips
III-SC
4
12 & 16 mm
Stone Chips
IV-BC
2.5
12 & 16 mm
Brick Chips
I-SC-FLd
3
12 mm
Stone Chips
Total = 4.1.1
Type of Rebar 3 Specimen of 12 mm BB 3 Specimen of 12 mm ECR 3 Specimen of 16 mm BB 3 Specimen of 16 mm ECR 3 Specimen of 12 mm BB 3 Specimen of 12 mm ECR 3 Specimen of 16 mm BB 3 Specimen of 16 mm ECR 3 Specimen of 12 mm BB 3 Specimen of 12 mm ECR 3 Specimen of 16 mm BB 3 Specimen of 16 mm ECR 3 Specimen of 12 mm BB 3 Specimen of 12 mm ECR 3 Specimen of 16 mm BB 3 Specimen of 16 mm ECR 3 Specimen of 12 mm BB 3 Specimen of 12 mm ECR 3 Specimen of 16 mm BB 3 Specimen of 16 mm ECR 6 Specimen of 12 mm BB 6 Specimen of 12 mm ECR 72 Specimen
Comparison of Bond performance of ECR and BB of Type I-SC
The principal objective of the pull-out test was to observe the bar slip of the embedded steel rebar under direct tensile load. Tests were conducted on 12mm and 16mm specimens with epoxy coating and black bar. The 12in (300mm) cubical concrete block of with stone chips was cast to hold the bars . The results of bar slip against applied direct pull are presented in Figures 4.1 and 4.2 for 12mm and 16mm bars, respectively. Each of these Figures compare the performances of 3 specimen of ECR and 3 specimen of BB all tested under identical situation.
36
80 70
Load (kN)
60 50
ES1R1 sample 1 US1R1 sample 1
40
ES1R1 sample 2 30
US1R1 sample 2 ES1R1sample 3
20
US1R1 sample 3
10 0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5 5 5.5 Slip (mm)
6
6.5
7
7.5
8
8.5
9
9.5 10
Fig. – 4.1: Comparison of loads-slip response of pull-out specimen (3 ksi, stone chips, 12 mm bar) reinforced with ECR and BB
150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0
Load (kN)
ES1R2 sample 1 US1R2 sample 1 ES1R2 sample 2 US1R2 sample 2 ES1R2 sample 3 US1R2 sample 3
0
1
2
3
4
5
6
7
8
9 10 11 Slip (mm)
12
13
14
15
16
17
18
19
Fig. – 4.2: Comparison of loads-slip response of pull-out specimen (3 ksi, stone chips, 16 mm bar) reinforced with ECR and BB
37
Ratio of ultimate to yield load
Epoxy Tensile ES1R1 300 12 600 65 coated Failure of Bar sample 1 Epoxy Tensile ES1R1 300 12 600 65 coated Failure of Bar sample 2 Epoxy Tensile ES1R1 300 12 600 65 coated Failure of Bar sample 3 Tensile US1R1 300 12 Uncoated 400 65 Failure of Bar sample 1 400 Tensile US1R1 300 12 Uncoated 65 Failure of Bar sample 2 400 Tensile US1R1 300 12 Uncoated 65 Failure of Bar sample 3 Epoxy ES1R2 300 16 750 100 Bond Failure coated sample 1 Epoxy 750 ES1R2 300 16 100 Bond Failure coated sample 2 Epoxy 750 ES1R2 300 16 100 Bond Failure coated sample 3 Tensile US1R2 300 16 Uncoated 500 100 Failure of Bar sample 1 500 Tensile US1R2 300 16 Uncoated 100 Failure of Bar sample 2 500 Tensile US1R2 300 16 Uncoated 100 Failure of Bar sample 3 **Confinement effect was considered for calculating the development lengths.
Ultimate Failure Load, KN
Bar Type
**Developme nt length calculated as per ACI Eqn 25.4.2.3b, mm
Failure Mode
Developmen t length provided, mm
Yield Load, kN
Specimen Name
Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pull-out Bar Dia, mm
Table – 4.2:
78
1.200
78
1.200
78
1.200
75
1.154
76
1.169
76
1.169
126
1.260
128
1.280
139
1.390
132
1.320
131
1.310
134
1.340
Discussion: The ultimate failure loads for all 12 bar specimens are compared in Table 4.2. A close examination of the results plotted in Figures 4.1 and 4.2 reveals that: Bar slip of the ECR at yield is nearly double when compared to corresponding black bar with value of slip at yield in the range of 1.5~2mm for 12mm bar while it is 1.0~1.5mm for 16mm bar. The bond stress at yield is higher for lower diameter bars. All bars coated or black, sustained load in excess to the corresponding yield load. The 12 mm epoxy coated bars sustained around 120% of the corresponding yield load, while the 16 mm epoxy coated bars sustained more than 130% of the corresponding yield load. Though the 12 mm epoxy coated bars showed larger slip values at yield, the bars failed at tension. However the 16 mm epoxy coated bars showed lesser slip values at yield than 12mm epoxy coated bars, but showed bond failure at larger slip values after yielding. The embedded length provided for 12mm epoxy coated bars was 50% of that of code specified development length. Despite such inadequacy, the 38
bars failed at tension. Nonetheless, the embedded length provided for 16mm epoxy coated bars was 40% of code specified development length, it showed bond failure. Since, bond stress is predominantly governed by , effect of larger is discussed in Type II and Type III specimens. The pictorial views of the failed specimens are shown in Figures 4.3 and 4.4.
Fig. – 4.3: Failure Modes of ES1R1 and US1R1 (3Ksi, 12mm Epoxy and Uncoated bars ) samples
Fig. – 4.4: Failure Modes of ES1R2 and US1R2 (3Ksi, 16mm Epoxy and Uncoated bars ) samples
4.1.2
Comparison of Bond performance of ECR and BB of Type I-BC
Tests were conducted on 12mm and 16mm specimen with epoxy coating and black bar and the concrete block of 12in (300mm) cube of with brick chips was cast to hold the bars. The results of bar slip against applied direct pull are presented in Figures 4.5 and 4.6 for 12mm and 16mm bars respectively.
39
80 70 60
Load KN
50
Uncoated Sample 1 Epoxy Coated sample 1 Uncoated Sample 2 Epoxy Coated sample 2 Uncoated sample 3 Epoxy coated sample 3
40 30
20 10 0 0
0.5
1
1.5
2
2.5 Slip (mm)
3
3.5
4
4.5
Fig. – 4.5: Comparison of loads-slip response of pull-out specimen (3 ksi, brick chips, 12 mm bar) reinforced with ECR and BB
160 140 120
Load KN
100 Uncoated sample 1
80
Epoxy sample 1 60
Epoxy sample 2 Uncoated sample 2
40
Epoxy sample 3
20
Uncoated sample 3
0 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Slip (mm)
Fig. – 4.6: Comparison of loads-slip response of pull-out specimen (3 ksi, brick chips, 16 mm bar) reinforced with ECR and BB
40
Table – 4.3:
Ultimate Failure Load, KN Ratio of ultimate to yield load
Failure Mode
Yield Load, kN
Bar Dia, mm
Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pull-out **Developme Developmen nt length Specimen t length calculated as Bar Type Name provided, per ACI Eqn mm 25.4.2.3b, mm Epoxy Tensile EB1R1 64 78 1.219 300 12 600 coated Failure of Bar sample 1 Epoxy Tensile EB1R1 66 80 1.212 300 12 600 coated Failure of Bar sample 2 Epoxy Tensile EB1R1 66 80 1.212 300 12 600 coated Failure of Bar sample 3 Tensile UB1R1 64 74 1.156 300 12 Uncoated 400 Failure of Bar sample 1 400 Tensile UB1R1 65 78 1.200 300 12 Uncoated Failure of Bar sample 2 400 Tensile UB1R1 65 76 1.169 300 12 Uncoated Failure of Bar sample 3 Epoxy EB1R2 124 147 1.185 300 16 750 Bond Failure coated sample 1 Epoxy 750 EB1R2 116 140 1.207 300 16 Bond Failure coated sample 2 Epoxy 750 EB1R2 122 142 1.164 300 16 Bond Failure coated sample 3 Tensile UB1R2 112 126 1.125 300 16 Uncoated 500 Failure of Bar sample 1 500 Tensile UB1R2 108 132 1.222 300 16 Uncoated Failure of Bar sample 2 500 Tensile UB1R2 114 136 1.193 300 16 Uncoated Failure of Bar sample 3 **Confinement effect was considered for calculating the development lengths. Discussion: The ultimate failure loads for all 12 bar specimens are compared in Table 4.3. A close examination of the results plotted in Figures 4.5 and 4.6 reveals that: Bar slip of the ECR at yield is nearly double when compared to corresponding black bar with value of slip at yield in the range of 0.75~1.75mm for 12mm bar while it is 0.75~2.5 mm for 16mm bar. All bars coated or black, sustained load in excess corresponding yield load. The 12 mm epoxy coated bars sustained around 120% of the corresponding yield load, while the 16 mm epoxy coated bars sustained around 118% of the corresponding yield load. For brick chips, 16mm epoxy coated bars showed lesser value for ratio of ultimate to yield compared to stone chips. Moreover, the 16 mm epoxy coated bars showed bond failure while uncoated bars failed at tension at an average slip value of 9mm. For stone chips, 16mm epoxy coated bars showed bond failure at an average slip of 13.5mm. From this, it can be concluded that, epoxy coated bars in brick chips specimen fail by bond failure at lesser slip values than stone chips. Moreover, both the types of epoxy coated bars showed
41
initial higher slip values compared to black bars and also when compared to epoxy coated bars in stone chips specimens. This observation of higher initial slip is found mainly in case of brick chips. The embedded length provided for 12mm epoxy coated bars was 50% of that of code specified development length. Despite such inadequacy, the bars failed at tension. Nonetheless, the embedded length provided for 16mm epoxy coated bars was 40% of code specified development length, it showed bond failure. Since, bond stress is predominantly governed by , effect of smaller is discussed in Type IV specimens. The pictorial views of the failed specimens are shown in Figures 4.7 and 4.8.
Fig. – 4.7: Failure Modes of EB1R1 and UB1R1 (3Ksi, 12mm Epoxy and Uncoated bars ) sample
Fig. – 4.8: Failure Modes of EB1R2 and UB1R2 (3Ksi, 16mm Epoxy and Uncoated bars ) samples 4.1.3
Comparison of Bond performance of ECR and BB of Type II-SC
Tests were conducted on 12mm and 16mm specimen with epoxy coating and black bar. The concrete block of 12in (300mm) cube of with Stone chips was cast to hold the bars. The results of bar slip against applied direct pull are presented in Figures 4.9 and 4.10 for 12mm and 16mm bars respectively.
42
80 70 60
Load KN
50
Epoxy sample 1 Uncoated sample 1 Epoxy sample 2 Uncoated sample 2 Epoxy sample 3 Uncoated sample 3
40 30 20 10 0 0
0.5
1
1.5
2
2.5
3
3.5
4 4.5 Slip (mm)
5
5.5
6
6.5
7
7.5
8
8.5
Fig. – 4.9: Comparison of loads-slip response of pull-out specimen (3.5 ksi, Stone chips, 12 mm bar) reinforced with ECR and BB
160 140 120
Load KN
100 Uncoated sample 1 80
Epoxy sample 1 Epoxy sample 2
60
Uncoated sample 2 Epoxy sample 3
40
Uncoated sample 3 20 0 0
1
2
3
4
5
6
7
8
9
10
11
12
Slip (mm)
Fig. – 4.10: Comparison of loads-slip response of pull-out specimen (3.5 ksi, Stone chips, 16 mm bar) reinforced with ECR and BB
43
300
16
Epoxy coated
ES2R2 sample 3
300
16
Epoxy coated
120
Tensile Failure of Bar
142
1.183
120
Tensile Failure of Bar
144
1.200
134
1.196
134
1.207
135
1.205
700
700
Ultimate Failure Load, KN Ratio of ultimate to yield load
Failure Mode
ES2R2 sample 2
Yield Load, kN
Bar Dia, mm
Table – 4.4: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pull-out **Developme Development nt length Specimen length calculated as Bar Type Name provided, per ACI Eqn mm 25.4.2.3b, mm Epoxy Tensile Failure ES2R1 62 78 1.258 300 12 550 coated of Bar sample 1 Epoxy Tensile Failure ES2R1 64 78 1.219 300 12 550 coated of Bar sample 2 Epoxy Tensile Failure ES2R1 65 80 1.231 300 12 550 coated of Bar sample 3 Tensile Failure US2R1 66 77 1.167 300 12 Uncoated 375 of Bar sample 1 375 Tensile Failure US2R1 66 76 1.152 300 12 Uncoated of Bar sample 2 375 Tensile Failure US2R1 68 78 1.147 300 12 Uncoated of Bar sample 3 Tensile Failure Epoxy ES2R2 300 16 700 114 of Bar 136 1.193 coated sample 1
US2R2 112 Tensile Failure 300 16 Uncoated 475 of Bar sample 1 475 Tensile Failure US2R2 111 300 16 Uncoated of Bar sample 2 475 Tensile Failure US2R2 112 300 16 Uncoated of Bar sample 3 **Confinement effect was considered for calculating the development lengths. Discussion: A close examination of the results plotted in Figures 4.9 and 4.10 and Table 4.4 reveals that:
Bar slip of the ECR at yield when compared to corresponding black bar with value of slip at yield is in the range of 0.8~1.5mm for 12mm bar while it is 0.75~2.5 mm for 16mm bar. The bond stress at yield is higher for lower diameter bars. All bars coated or black, sustained load in excess to the corresponding yield load. The 12 mm epoxy coated bars sustained more than 120% of the corresponding yield load, while the 16 mm epoxy coated bars sustained more than 118% of the corresponding yield load. Though the 12 mm epoxy coated bars showed larger slip values at yield, the bars failed at tension. However the 16 mm epoxy coated bars showed lesser slip values at yield than 12mm epoxy coated bars, and also showed tensile failure.
44
The embedded length provided for 12mm epoxy coated bars was 54% of that of code specified development length. Despite such inadequacy, the bars failed at tension. Nonetheless, the embedded length provided for 16mm epoxy coated bars was 43% of code specified development length, yet it showed tensile failure. Since, bond stress is predominantly governed by , the calculated development length according to code decreases with higher . The slip values for both the 12mm and 16mm epoxy coated bars are found to be less compare to that of = 3ksi. This can be accounted due to larger percentage of embedded length provided. The pictorial views of the failed specimens are shown in Figures 4.11 and 4.12.
Fig. – 4.11: Failure Modes of ES2R1 and US2R1 (3.5 Ksi, 12mm Epoxy and Uncoated bars ) samples
Fig. – 4.12: Failure Modes of ES2R2 and US2R2 (3.5 Ksi, 16mm Epoxy and Uncoated bars ) samples 4.1.4
Comparison of Bond performance of ECR and BB of Type III-SC
Tests were conducted on 12mm and 16mm specimens with epoxy coating and black bar in 12in (300mm) cubical concrete block of with Stone chips was cast to hold the bars. The results of bar slip against applied direct pull are presented in Figures 4.13 and 4.14 for 12mm and 16mm bars respectively. 45
80 70 60
Load KN
50
Epoxy sample 1 Uncoated sample 1 Series3 Uncoated sample 2 Series5 Uncoated sample 3
40 30 20 10 0 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
Slip mm
Fig. – 4.13: Comparison of loads-slip response of pull-out specimen (4 ksi, Stone chips, 12 mm bar) reinforced with ECR and BB
140 120
Load KN
100 Uncoated sample 1
80
Epoxy sample 1 Uncoated sample 2
60
Epoxy sample 2 Uncoated sample 3
40
Epoxy sample 3 20 0 0
1
2
3
4
5
6
7
8
9
10
11
12
13
Slip mm
Fig. – 4.14: Comparison of loads-slip response of pull-out specimen (4 ksi, Stone chips, 16 mm bar) reinforced with ECR and BB
46
Table – 4.5:
Ultimate Failure Load, KN Ratio of ultimate to yield load
Failure Mode
Yield Load, kN
Bar Dia, mm
Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pull-out **Developme Developmen nt length Specimen t length calculated as Bar Type Name provided, per ACI Eqn mm 25.4.2.3b, mm Epoxy Tensile Failure ES3R1 64 78 1.219 300 12 525 coated of Bar sample 1 Epoxy Tensile Failure ES3R1 525 66 80 1.212 300 12 coated of Bar sample 2 Epoxy Tensile Failure ES3R1 525 62 76 1.226 300 12 coated of Bar sample 3 Tensile Failure US3R1 65 76 1.169 300 12 Uncoated 350 of Bar sample 1 Tensile Failure US3R1 350 65 76 1.169 300 12 Uncoated of Bar sample 2 Tensile Failure US3R1 350 65 76 1.169 300 12 Uncoated of Bar sample 3 Epoxy Tensile Failure ES3R2 300 16 650 120 147 1.225 coated of Bar sample 1 Epoxy Tensile Failure ES3R2 300 16 650 118 134 1.136 coated of Bar sample 2 Epoxy Tensile Failure ES3R2 300 16 650 118 142 1.203 coated of Bar sample 3 Tensile Failure US3R2 300 16 Uncoated 450 112 140 1.250 of Bar sample 1 US3R2 450 112 Tensile Failure 134 1.196 300 16 Uncoated of Bar sample 2 US3R2 450 109 Tensile Failure 132 1.211 300 16 Uncoated of Bar sample 3 **Confinement effect was considered for calculating the development lengths. Discussion: The ultimate failure loads for all 12 bar specimens are compared in Table 4.5 and the results plotted in Figures 4.13 and 4.14. Bar slip of the ECR at yield when compared to corresponding black bar with value of slip at yield is slightly higher. The 12mm epoxy coated bars show slip in the range of 0.6~0.9mm at yield, while it is 1.4~2.0 mm for 16mm bar. All bars coated or black, sustained load in excess to the corresponding yield load. The 12 mm epoxy coated bars sustained more than 120% of the corresponding yield load, while the 16 mm epoxy coated bars sustained on an average of 118% of the corresponding yield load. Both the 12mm and 16mm epoxy coated bars failed at tension. The embedded length provided for 12mm epoxy coated bars was 57% of that of code specified development length. Despite such inadequacy, the bars failed at tension. Nonetheless, the embedded length provided for 16mm epoxy coated bars was 46% of code specified development length, yet it showed tensile failure. 47
Since, bond stress is predominantly governed by , the calculated development length according to code decreases with higher . The slip values for both the 12mm and 16mm epoxy coated bars are found to be less compared to that of = 3 ksi and = 3.5 ksi. This can be accounted due to larger percentage of embedded length provided. The pictorial views of the failed specimens are shown in Figures 4.15 and 4.16.
Fig. – 4.15: Failure Modes of ES3R1 and US3R1 (4 Ksi, 12mm Epoxy and Uncoated bars ) samples
Fig. – 4.16: Failure Modes of ES3R2 and US3R2 (4 Ksi, 16mm Epoxy and Uncoated bars ) samples 4.1.5
Comparison of Bond performance of ECR and BB of Type IV-BC
Tests were conducted on 12mm and 16mm specimens with epoxy coating and black bar. The cubical concrete block of 12in (300mm) o with brick chips was cast to hold the bars. The results of bar slip against applied direct pull are presented in Figures 4.17 and 4.18 for 12mm and 16mm bars respectively, and the ultimate failure loads for all 12 bar specimens are compared in Table 4.6.
48
80 70 60
Load KN
50
Uncoated Sample 1 Epoxy Coated sample 1
40
Uncoated Sample 2
Epoxy Coated sample 2
30
Uncoated sample 3 20
Epoxy coated sample 3
10 0 0
0.5
1
1.5
2
2.5
3
3.5
4
Slip mm
Fig. – 4.17: Comparison of loads-slip response of pull-out specimen (2.5 ksi, Brick chips, 12 mm bar) reinforced with ECR and BB
160 140 120
Load KN
100 80 Uncoated sample 1 60
Epoxy Coated sample 1 Uncoated sample 2
40
Epoxy Coated sample 2 Uncoated sample 3
20
Epoxy sample 3 0 0
1
2
3
4
5
6
7 8 Slip mm
9
10
11
12
13
14
15
Fig. – 4.18: Comparison of loads-slip response of pull-out specimen (2.5 ksi, Brick chips, 16 mm bar) reinforced with ECR and BB
49
Table – 4.6:
Ultimate Failure Load, KN Ratio of ultimate to yield load
Failure Mode
Yield Load, kN
Bar Dia, mm
Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pull-out **Developme Developmen nt length Specimen t length calculated as Bar Type Name provided, per ACI Eqn mm 25.4.2.3b, mm Epoxy Tensile Failure ES3R1 64 78 1.219 300 12 675 coated of Bar sample 1 Epoxy 675 Tensile Failure ES3R1 65 76 1.169 300 12 coated of Bar sample 2 Epoxy 675 Tensile Failure ES3R1 65 78 1.200 300 12 coated of Bar sample 3 Tensile Failure US3R1 65 76 1.169 300 12 Uncoated 450 of Bar sample 1 450 Tensile Failure US3R1 66 76 1.152 300 12 Uncoated of Bar sample 2 450 Tensile Failure US3R1 66 77 1.167 300 12 Uncoated of Bar sample 3 Epoxy Bond Failure ES3R2 120 142 1.183 300 16 825 coated sample 1 Epoxy 825 Bond Failure ES3R2 122 145 1.189 300 16 coated sample 2 Epoxy 825 Bond Failure ES3R2 116 138 1.190 300 16 coated sample 3 US3R2 110 Tensile Failure 134 1.218 300 16 Uncoated 550 of Bar sample 1 550 US3R2 109 Tensile Failure 134 1.229 300 16 Uncoated of Bar sample 2 550 US3R2 109 Tensile Failure 133 1.220 300 16 Uncoated of Bar sample 3 **Confinement effect was considered for calculating the development lengths. Discussion: Bar slip of the ECR at yield when compared to corresponding black bar with value of slip at yield is over a wide range of 0.4~2.8mm for 12mm bar while it is 0.75~2.2 mm for 16mm bar. All bars coated or black, sustained load in excess to the corresponding yield load. The 12 mm epoxy coated bars sustained around 118% of the corresponding yield load, while the 16 mm epoxy coated bars sustained around 118% of the corresponding yield load. Moreover, the 16 mm epoxy coated bars showed bond failure while uncoated bars failed at tension at an average slip value of 8 mm. For brick chips, 16mm epoxy coated bars showed bond failure at an average slip of 9 mm. Moreover, both the types of epoxy coated bars showed initial higher slip values compared to black bars and also when compared to epoxy coated bars for brick chips specimens. The embedded length provided for 12mm epoxy coated bars was only 44% of that of code specified development length. Despite such inadequacy, the bars failed at tension. Nonetheless, the embedded 50
length provided for 16mm epoxy coated bars was only 36% of code specified development length. Thus it showed bond failure. The pictorial views of the failed specimens are shown in Figures 4.19 and 4.20.
Fig. – 4.19: Failure Modes of ES3R1 and US3R1 (2.5 Ksi, 16mm Epoxy and Uncoated bars ) samples
Fig. – 4.20: Failure Modes of ES3R1 and US3R1 (2.5 Ksi, 16mm Epoxy and Uncoated bars ) samples
51
4.1.6
Comparison of Bond performance of ECR and BB of Type I-SC-FLd
In order to observe the effect of full development length on bond performance of Epoxy Coated bar, 12 Pull out specimens of 12 mm bars were prepared using both Uncoated and Epoxy Coated bars according to ACI 318R-14 (equation 25.4.2.3a). 6 specimens were casted using black bars and other 6 were casted using Epoxy Coated bars. The Specimens were tested under direct Pull out and corresponding failure mode and slips are observed. Table 4.7 presents the comparison of failure mode for ECR and BB under full development length. Table – 4.7:
ES1R1_FLd sample 1 ES1R1_FLd sample 2 ES1R1_FLd sample 3 ES1R1_FLd sample 4 ES1R1_FLd sample 5 ES1R1_FLd sample 6 US1R1_FLd sample 1 US1R1_FLd sample 2 US1R1_FLd sample 3 US1R1_FLd sample 4 US1R1_FLd sample 5 US1R1_FLd sample 6
Ultimate Failure Load, KN Ratio of ultimate to yield load
Failure Mode
Yield Load, kN
Bar Dia, mm
Specimen Name
Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct Pull-out **Developme Development nt length length calculated as Bar Type provided, per ACI Eqn mm 25.4.2.3b, mm Epoxy 63 Tensile Failure 78 1.238 600 12 600 coated of Bar Epoxy 600 600 65 Tensile Failure 76 1.169 12 coated of Bar Epoxy 600 600 65 Tensile Failure 78 1.200 12 coated of Bar Epoxy Tensile Failure 600 12 600 64 78 1.219 coated of Bar Epoxy Tensile Failure 600 12 600 63 76 1.206 coated of Bar Epoxy Tensile Failure 600 12 600 64 77 1.203 coated of Bar Tensile Failure 400 12 Uncoated 400 66 76 1.152 of Bar Tensile Failure 400 12 Uncoated 400 65 78 1.200 of Bar Tensile Failure 400 12 Uncoated 400 65 78 1.200 of Bar Tensile Failure 400 12 Uncoated 400 66 77 1.167 of Bar Tensile Failure 400 12 Uncoated 400 65 76 1.169 of Bar Tensile Failure 400 12 Uncoated 400 66 78 1.182 of Bar **Confinement effect was considered for calculating the development lengths.
Discussion: Tests were conducted on 12mm specimen with epoxy coating and black bar samples. 12in x 16in rectangular block for black bars and 12in x 24in rectangular block for Epoxy coated bars of with Stone chips was cast respectively to hold the bars. Each of these Figure compare the performances of 6 specimen of ECR and 6 specimen of BB all tested under identical situation. The ultimate failure loads for all 12 bar specimen are compared in Table 16. After providing full development length, it was observed that for both type of specimens no considerable slip occurred. The bars in the specimens failed before occurring any measurable slip. So, there was no 52
comparable difference in the bond performance of Epoxy Coated bars and Black bars when ACI specified development length was provided in direct Pull out test. The tested specimen on the pull out frame is shown in Figure 46. The failure modes are shown in Figures 4.21 to Figure 4.25.
Fig. – 4.21: Testing of ES1R1_FLd and US1R1_FLd (3 Ksi, 12 mm Epoxy and Uncoated bars ) samples
Fig. – 4.22: Failure Modes of ES1R1_FLd and US1R1_FLd (3 Ksi, 12 mm Epoxy and Uncoated bars ) samples
53
Fig. – 4.23: Failure Modes of ES1R1_FLd and US1R1_FLd (3 Ksi, 12 mm Epoxy and Uncoated bars ) samples
Fig. – 4.24: Failure Modes of ES1R1_FLd (3 Ksi, 12 mm Epoxy Coated bars ) samples
54
Fig. – 4.25: Failure Modes of US1R1_FLd (3 Ksi, 12 mm Uncoated bars ) samples 4.2
Results of Flexural Test
As described in section 6.3, a total of forty two half scale concrete beams were tested to study the flexural behavior of concrete beams reinforced with Epoxy Coated bars and uncoated bars. Details of the test scheme and test matrix have been presented earlier. Experimental results of the following beams are presented in terms of cracking load, crack pattern, crack width, deflection, ultimate flexural strength, and failure modes. Table 4.8 gives the tested beam specimen material properties. Table – 4.8: Beam Type
Beam Specimens
Size of Main Bar
Aggregate Type
I-SC
Concrete Strength (ksi) 3
3-12 mm
Stone Chips
I-BC
3
3-12 mm
II-SC
3.5
3-12 mm
III-SC-S
3
2-16 mm (spliced)
III-BC-S
3
2-16 mm (spliced)
IV-SC
3
2-16 mm
IV-BC
3
2-16 mm
V-SC
3.5
2-16 mm
V-SC-S
3.5
2-16 mm (spliced)
VI-BC
2.5
3-12 mm
55
Type of Rebar
3 Specimen of BB 3 Specimen of ECR Brick Chips 3 Specimen of BB 3 Specimen of ECR Stone Chips 3 Specimen of BB 3 Specimen of ECR Stone Chips 1 Specimen of BB 1 Specimen of ECR Brick Chips 1 Specimen of BB 1 Specimen of ECR Stone Chips 2 Specimen of BB 2 Specimen of ECR Brick Chips 2 Specimen of BB 2 Specimen of ECR Stone Chips 2 Specimen of BB 2 Specimen of ECR Stone Chips 1 Specimen of BB 1 Specimen of ECR Brick Chips 3 Specimen of BB 3 Specimen of ECR Total = 42 Specimen
4.2.1
Comparison of Flexural Test Response of ECR and BB Reinforced Beam
4.2.1.1 Comparison of Response of ECR and BB Reinforced Beam Type I-SC and I-BC The results of the flexural tests are presented in this section. The response of beam for various combination of concrete (3 ksi stone chips and brick chips aggregate) used with ECR and BB of different sizes will be presented separately. Figures 4.26 to 4.29 and Tables 4.9 to 4.12 present the response of beams with 3-12 mm longitudinal bars, embedded in concrete strength of 3 ksi and aggregate type is stone chips. Similarly response relationships for beams with identical features (3 ksi strength and 3-12 mm rebar) but constructed using brick chips are presented in Figures 4.30 to 4.33 and Tables 4.13 to 4.16. For stone chips concrete, the load-deflection responses (Fig. 4.26) of uncoated bar and epoxy coated bar do not show any difference (within the limit of expected variability of experimental results). The ultimate loads sustained by the beams with both types of rebar are also practically same. The crack width (Table 4.10 ) observed is slightly higher for ECR when compared to BB, although at design load level the crack width is within the allowable limit as per ACI 318-14. For concrete made with brick chips and strength of 3 ksi the load-deflection response for both bypes of bars (ECR and BB) are also practically same. The ultimate loads sustained by beams with both ECR and BB are also identical. For brick chips aggregate the spread of various response parameters are slightly higher when compared with the same parameters as obtained for stone chips concrete. Despite the above similarities in the responses and behavior of beams with ECR and BB at failure the beam with epoxy coated bar showed higher number cracks with higher width of cracks. This observation is applicable for both stone aggregate concrete as well brick chips aggregate concrete as shown in Figures 4.29 and 4.33. 100 90 80
Load (kN)
70 60 50 Uncoated 1 40
Uncoated 2
30
Uncoated 3 Epoxy Coated 1
20
Epoxy Coated 2 Epoxy Coated 3
10
Design Strength 69KN
0 0
5
10
15
20
25
30
35
40
45
Deflection (mm)
Fig. – 4.26: Comparison of loads-deflection response of beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB 56
Table – 4.9:
Comparison of Deflections at Design Load for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB Beam name Design Load, KN Deflection at Design load, mm U_3_SC_12 sample 1 69 10.4 U_3_SC_12 sample 2 69 10.9 U_3_SC_12 sample 3 69 10.35 E_3_SC_12 sample 1 69 10.38 E_3_SC_12 sample 2 69 10.4 E_3_SC_12 sample 3 69 11.3 30
Deflection (mm)
25 20 Uncoated 1
15
Uncoated 2 Uncoated 3
10
Epoxy Coated 1 Epoxy Coated 2
5
Epoxy Coated 3 0 0
50
100
150
200 Time (s)
250
300
350
400
Fig. – 4.27: Comparison of deflection time response of beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB 100 90 80
Load (kN)
70
Uncoated 2
60
Uncoated 1
50
Uncoated 3
40
Epoxy Coated 1
30
Epoxy Coated 2
20
Epoxy Coated 3
10
Design Strength 69KN
0 0
0.5
1
1.5 Crack width mm
2
2.5
Fig. – 4.28: Comparison of load-crack width response of beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB
57
Table – 4.10: Comparison of Crack Width at Design Load for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB Beam name
Design Load, kN
Crack width, mm
U_3_SC_12 sample 1
69
0.39
U_3_SC_12 sample 2
69
0.29
U_3_SC_12 sample 3
69
0.29
E_3_SC_12 sample 1
69
0.38
E_3_SC_12 sample 2
69
0.38
E_3_SC_12 sample 3
69
0.41
Table – 4.11: Comparison of Number of Total Cracks for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB Beam name
Number of total cracks
U_3_SC_12 sample 1
17
U_3_SC_12 sample 2
20
U_3_SC_12 sample 3
20
E_3_SC_12 sample 1
18
E_3_SC_12 sample 2
21
E_3_SC_12 sample 3
20
Table – 4.12: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB U_3_SC_12
E_3_SC_12
Average 1st cracking load (kN)
17.45
14.92
Average Spalling load (kN)
83.82
83.12
Average Ultimate failure load (kN)
87.2
85.6
58
Sample name
Mid zone crack distribution and crack width
Deflected Shape after failure
Top sample: E_3_SC_12 sample 1 Bottom sample : U_3_SC_12 sample 1 Top sample: U_3_SC_12 sample 2 Bottom sample : E_3_SC_12 sample 2
Top sample: E_3_SC_12 sample 3 Bottom sample : U_3_SC_12 sample 3 Fig. – 4.29: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB 100 90 80
Load (kN)
70 60
Uncoated 1 Uncoated 2 Uncoated 3 Epoxy Coated 1 Epoxy Coated 2 Epoxy Coated 3 Design strength 69 KN
50 40 30 20
10 0 0
5
10
15
20 25 Deflection (mm)
30
35
40
Fig. – 4.30: Comparison of loads-deflection response of beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB
59
Table – 4.13: Comparison of Deflections at Design Load for Beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB Beam name
Design Load, kN
Deflection at Design load, mm
U_3_BC_12 sample 1
69
12.7
U_3_BC_12 sample 2
69
12.3
U_3_BC_12 sample 3
69
11.05
E_3_BC_12 sample 1
69
11.98
E_3_BC_12 sample 2
69
11.9
E_3_BC_12 sample 3
69
10.7
40 35 Deflection (mm)
30 25 20
Uncoated 1 Uncoated 2 Uncoated 3 Epoxy Coated 1 Epoxy Coated 2 Epoxy Coated 3
15 10 5 0 0
50
100
150
200
250 Time (s)
300
350
400
450
500
Fig. – 4.31: Comparison of deflection time response of beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB 100 90 80
Load (KN)
70
60 50
Uncoated 2 Uncoated 1 Uncoated 3 Epoxy Coated 1 Epoxy coated 2 Epoxy coated 3 Design Strength 69 KN
40 30 20 10 0 0
0.5
1
1.5 2 Crack width mm
2.5
3
3.5
Fig. – 4.32: Comparison of load-crack width response of beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB
60
Table – 4.14: Comparison of Crack Width at Design Load for Beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB Beam name
Design Load, kN
Crack width, mm
U_3_BC_12 sample 1
69
0.48
U_3_BC_12 sample 2
69
0.3
U_3_BC_12 sample 3
69
0.4
E_3_BC_12 sample 1
69
0.48
E_3_BC_12 sample 2
69
0.48
E_3_BC_12 sample 3
69
0.57
Table – 4.15: Comparison of Number of Total Cracks for Beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB Beam name
Number of total cracks
U_3_BC_12 sample 1
20
U_3_BC_12 sample 2
21
U_3_BC_12 sample 3
23
E_3_BC_12 sample 1
22
E_3_BC_12 sample 2
19
E_3_BC_12 sample 3
24
Table – 4.16: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB U_3_BC_12
E_3_BC_12
Average 1st cracking load (kN)
20.70
14.63
Average Spalling load (kN)
83.8
79.45
Average Ultimate failure load (kN)
85.24
85.9
61
Sample name
Mid zone crack distribution and crack width
Deflected Shape after failure
Top sample: E_3_BC_12 sample 1
Bottom sample : U_3_BC_12 sample 1
Top sample: E_3_BC_12 sample 2 Bottom sample : U_3_BC_12 sample 2 Top sample: E_3_BC_12 sample 3
Bottom sample : U_3_BC_12 sample 3
Fig. – 4.33:
Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, brick chips, 312 mm bars) reinforced with ECR and BB
4.2.1.2 Comparison of Response for ECR and BB Reinforced Beam Type II SC Figures 4.34 to 4.37and Table 4.17 to 4.20 present the response of beam with 3-12 mm longitudinal bars, embedded in concrete strength of 3.5 ksi constructed with stone chips aggregate. The load deflection responses (Fig. 4.34) of uncoated bar and epoxy coated bar do not show any difference considering the expected variation of experimental observations. The ultimate loads sustained by the beams with both types of rebars are also practically same against design load level of 72 kN, the recorded failure is above 88 kN. 62
The crack width observed (Table 4.18) is slightly higher for ECR when compared to BB. Though the allowable limit of 0.41 mm is specified by ACI 224R-01, the maximum crack width for ECR Table 16 exceeds the code allowable value. However, the code also states that a portion of the structure may exceed this value. And in the experiment, the maximum crack width was reported, while the width of other cracks was within the code limit. Nonetheless, the behavior of the beams with epoxy coated bar showed higher number of cracks with greater crack widths as shown in Figure 4.37. 110 100 90 80
Load (kN)
70
60 Uncoated 1
50
Uncoated 2
40
Uncoated 3 Epoxy Coated 1
30
Epoxy Coated 2
20
Epoxy Coated 3
10
Design Strength 72KN
0 0
5
10
15
20 Deflection (mm)
25
30
35
40
Fig. – 4.34: Comparison of loads-deflection response of beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB Table – 4.17: Comparison of Deflections at Design Load for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB Beam name U_3.5_SC_12 sample 1
Design Load, kN 72
Deflection at Design load, mm 10.5
U_3.5_SC_12 sample 2
72
9.8
U_3.5_SC_12 sample 3
72
10.33
E_3.5_SC_12 sample 1
72
9.75
E_3.5_SC_12 sample 2
72
10.26
E_3.5_SC_12 sample 3
72
10.55
63
30
Deflection (mm)
25
20
15
Uncoated 1 Uncoated 2
10
Uncoated 3 Epoxy Coated 1
5
Epoxy Coated 2 Epoxy Coated 3
0 0
50
100
150
200
250
300
350
Time (s)
Fig. – 4.35: Comparison of deflection time response of beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB
110 100 90 80 70 Load (kN)
Uncoated 2
60
Uncoated 1
50
Uncoated 3
40
Epoxy Coated 1
30
Epoxy Coated 2
20
Epoxy Coated 3
10
Design Strength 72 KN
0 0
0.5
1
1.5
2
2.5
3
3.5
4
Crack Width
Fig. – 4.36: Comparison of load-crack width response of beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB
64
Table – 4.18: Comparison of Crack Width at Design Load for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB Beam name
Design Load, kN
Crack width, mm
U_3.5_SC_12 sample 1
72
0.3
U_3.5_SC_12 sample 2
72
0.32
U_3.5_SC_12 sample 3
72
0.38
E_3.5_SC_12 sample 1
72
0.4
E_3.5_SC_12 sample 2
72
0.5
E_3.5_SC_12 sample 3
72
0.43
Table – 4.19: Comparison of Number of Total Cracks for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB Beam name
Number of total cracks
U_3.5_SC_12 sample 1
18
U_3.5_SC_12 sample 2
17
U_3.5_SC_12 sample 3
20
E_3.5_SC_12 sample 1
15
E_3.5_SC_12 sample 2
20
E_3.5_SC_12 sample 3
19
Table – 4.20: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB U_3.5_SC_12
E_3.5_SC_12
20
12.4
Average Spalling load (kN)
85.38
82.7
Average Ultimate failure load (kN)
88.4
92
Average 1st cracking load (kN)
65
Sample name
Mid zone crack distribution and crack width
Deflected Shape after failure
Top sample: E_3.5_SC_ 12 sample 1
Bottom sample : U_3.5_SC_ 12 sample 1
Top sample: E_3.5_SC_ 12 sample 2 Bottom sample : U_3.5_SC_ 12 sample 2 Top sample: E_3.5_SC_12 sample 3
Bottom sample : U_3.5_SC_ 12 sample 3 Fig. – 4.37: Comparison of Crack Pattern and Deflected Shape for Beams (3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB 4.2.1.3 Comparison of Response for ECR and BB Reinforced Beam Type III-SC-S and III-BC-S Figures 4.38 to 4.41 and Table 4.21 represent the response of beam with 2-16 mm longitudinal bars with both bar spliced at location of maximum stress. The calculated splice length of 53 inch for ECR and 37 inch BB were used. These lengths were calculated based on for both types of bars. The concrete strength is 3 ksi and aggregate type is stone chips. The response relationships for beams with identical features (3 ksi strength and 2-16 mm splice rebars ) but constructed using brick chips are presented in Figures 4.42 to 4.45 and Table 4.22. For stone chips concrete the load deflection responses (Fig. 4.38) of uncoated bar and epoxy coated bar do not show any difference (within the limit of expected variability of experimental result). The ultimate loads sustained by the beams with both types of rebars are also practically same. At design load level of 68 kN with fy= 60 ksi , both the beams showed no failure, even with 100% splice at maximum stress – a situation normally not encountered in practice. 66
The crack width observed (Fig. 4.41) is slightly higher for ECR when compared to BB, although at design load level the crack width is within the allowable limit as per ACI 318-14. For concrete made with brick chips and strength of 3 ksi, the load deflection response for both types of bars (ECR and BB) is practically same. The ultimate loads sustained by the beams are also quite identical. For brick chips aggregate, the spread of various response parameters are slightly higher when compared with the same parameters as obtained for stone chips concrete. Despite the above similarities in the responses and behavior of beams with ECR and BB at failure, the beam with epoxy coated bar showed higher number of crack with greater crack widths. This observation applies for both stone aggregate concrete as well as brick chips aggregate concrete as in figures 4.41 and 4.45. 120 110 100 90 80 Load (kN)
70 60 Uncoated 16 mm Spilce
50 40
Epoxy Coated 16 mm Spilce
30 20
Design Strength of 68 KN with Fy = 60 ksi
10 0 0
5
10
15
20 Deflection (mm)
25
30
35
40
Fig. – 4.38: Comparison of loads-deflection response of beam (3 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB 30
Deflection (mm)
25 20 15 10
Uncoated 16 mm Spilce Epoxy Coated 16 mm Spilce
5 0 0
50
100
150
200
250
300
350
400
Time (s)
Fig. – 4.39: Comparison of deflection time response of beams (3 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB 67
Load (kN)
120 110 100 90 80 70 60 50 40 30 20 10 0
Uncoated 16 mm Spilce Epoxy Coated 16 mm Spilce Design Strength of 68 KN with Fy = 60 ksi 0
0.5
1
1.5
2
2.5
3
3.5
4
Crack width (mm) Fig. – 4.40: Comparison of load-crack width response of beams (3 ksi, stone chips 2-16 mm Spliced bars) reinforced with ECR and BB Table – 4.21: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB st
1 cracking load (kN) Spalling load (kN) Ultimate failure load (kN)
U_3_SC-S_16 (splice)
E_3_SC-S_16 (splice)
20.33 98 106
21.57 96 103
Fig. – 4.41: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB 68
110 100 90 80 Load (kN)
70 60 50 40
Uncoated 16 mm Spilce
30 Epoxy Coated 16 mm Spilce Design Strength of 68 KN with Fy = 60 ksi
20 10 0 0
5
10
15
20
25
30
35
40
Deflection (mm)
Fig. – 4.42: Comparison of loads-deflection response of beams (3 ksi, brick chips, 2-16 mm Spliced bars) reinforced with ECR and BB 35 30
Deflection (mm)
25 20 15
Uncoated 16 mm Spilce Epoxy Coated 16 mm Spilce
10 5 0 0
50
100
150
200 250 Time (s)
300
350
400
450
Fig. – 4.43: Comparison of deflection time response of beams (3 ksi, brick chips, 2-16 mm Spliced bars) reinforced with ECR and BB
69
110 100 90
Load (kN)
80 70 60 50
Uncoated 16 mm Spilce
40
Epoxy Coated 16 mm Spilce
30
Design Strength of 68 KN with Fy = 60 ksi
20 10 0
0
0.5
1
1.5
2 2.5 Crack width (mm)
3
3.5
4
4.5
Fig. – 4.44: Comparison of load-crack width response of beams (3 ksi, brick chips, 2-16 mm Spliced bars) reinforced with ECR and BB Table – 4.22: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, brick chips, 2-16 mm Spliced bars) reinforced with ECR and BB U_3_BC-S_16 (splice) E_3_BC-S_16 (splice) 20.46 14.09 1st cracking load (kN) 97.46 80 Spalling load (kN) Ultimate failure load (kN)
105
83
Fig. – 4.45: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, brick chips, , 2-16 mm Spliced bars) reinforced with ECR and BB 70
4.2.1.4 Comparison of Response of ECR and BB Reinforced Beam Type IV-SC and IV-BC Figures 4.46 to 4.48 and Tables 4.23 to 4.26 present the response of beams with 2-16 mm longitudinal bars, embedded in concrete strength of 3 ksi and aggregate type is stone chips. Similarly response relationships for beams with identical features (3 ksi strength and 3-16 mm rebar) but constructed using brick chips are presented in Figures 4.49 to 4.51 and Tables 4.27 to 4.30. For stone chips concrete, the load-deflection responses (Fig. 4.46) of uncoated bar and epoxy coated bar do not show any difference (within the limit of expected variability of experimental results). The ultimate loads sustained by the beams with both types of rebar are also practically same. The crack width (Table 4.24) observed is slightly higher for ECR when compared to BB, although at design load level the crack width is within the allowable limit as per ACI 318-14. For concrete made with brick chips and strength of 3 ksi the load-deflection response for both bypes of bars (ECR and BB) are also practically same. The ultimate loads sustained by beams with both ECR and BB are almost same. For brick chips aggregate the spread of various response parameters are slightly higher when compared with the same parameters as obtained for stone chips concrete. Despite the above similarities in the responses and behavior of beams with ECR and BB at failure the beam with epoxy coated bar showed higher number cracks with higher width of cracks. This observation is applicable for both stone aggregate concrete as well brick chips aggregate concrete as shown in figure 4.52. 120
100
Load (KN)
80 Uncoated 1 60
Uncoated 2 Epoxy Coated 1
40
Epoxy Coated 2 Design Strength of '79 KN'
20
0 0
5
10
15
20
25
30
35
40
Deflection (mm)
Fig. – 4.46: Comparison of loads-deflection response of beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB
71
Table – 4.23: Comparison of Deflections at Design Load for Beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB Beam name Design Load, KN Deflection at Design load, mm U_3_SC_16 sample 1 79 11 U_3_SC_16 sample 2 79 12.4 E_3_SC_16 sample 1 79 12.25 E_3_SC_16 sample 2 79 14.1 35 30
Deflection (mm)
25 20 Uncoated 1
15
Uncoated 2 10
Epoxy Coated 1
5
Epoxy Coated 2
0 0
50
100
150
200
250 Time (s)
300
350
400
450
500
Fig. – 4.47: Comparison of deflection time response of beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB 120 100
Load (kN)
80 Uncoated 2
60
Uncoated 1 Epoxy Coated 1
40
Epoxy Coated 2 20
Design Strength of '79 KN'
0 0
0.5
1 Crack width mm 1.5
2
2.5
Fig. – 4.48: Comparison of load-crack width response of beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB
72
Table – 4.24: Comparison of Crack Width at Design Load for Beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB Beam name
Design Load, kN
Crack width, mm
U_3_SC_16 sample 1
0.45
U_3_SC_16 sample 2
79 79
E_3_SC_16 sample 1
79
0.5
E_3_SC_16 sample 2
79
0.48
0.4
Table – 4.25: Comparison of Number of Total Cracks for Beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB Beam name
Number of total cracks
U_3_SC_16 sample 1
22
U_3_SC_16 sample 2
20
E_3_SC_16 sample 1
24
E_3_SC_16 sample 2
25
Table – 4.26: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB U_3_SC_16
E_3_SC_16
Average 1st cracking load (kN)
25.04
19.95
Average Spalling load (kN)
90.5
89.2
Average Ultimate failure load (kN)
105
98.95
120 100
Load (Kn)
80 Uncoated 1
60
Uncoated 2
40
Epoxy Coated 1 Epoxy Coated 2
20
Design Strength of '79KN' 0 0
5
10
15
20 Deflection (mm)
25
30
35
40
Fig. – 4.49: Comparison of loads-deflection response of beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB
73
Table – 4.27: Comparison of Deflections at Design Load for Beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB Beam name
Design Load, kN
Deflection at Design load, mm 13.15
U_3_BC_16 sample 2
79 79
E_3_BC_16 sample 1
79
13.5
E_3_BC_16 sample 2
79
15.05
U_3_BC_16 sample 1
12.6
18 16
Deflection (mm)
14 12 10 Uncoated 1
8
Uncoated 2
6
Epoxy Coated 1
4
Epoxy Coated 2
2 0 0
50
100
Time (s)
150
200
250
Fig. – 4.50: Comparison of deflection time response of beams (3 ksi, brick chips, 2-12 mm bars) reinforced with ECR and BB 120 100
Load (kN)
80 60
Uncoated 2 Uncoated 1
40
Epoxy Coated 1 20
Epoxy Coated 2 Design Strength of '79KN'
0 0
0.2
0.4
0.6 0.8 Crack width mm
1
1.2
1.4
Fig. – 4.51: Comparison of load-crack width response of beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB
74
Table – 4.28: Comparison of Crack Width at Design Load for Beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB Beam name
Design Load, kN
Crack width, mm
U_3_BC_16 sample 1
79
0.3
U_3_BC_16 sample 2
79
0.3
E_3_BC_16 sample 1
79
0.3
E_3_BC_16 sample 2
79
0.3
Table – 4.29: Comparison of Number of Total Cracks for Beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB Beam name
Number of total cracks
U_3_BC_16 sample 1
20
U_3_BC_16 sample 2
19
E_3_BC_16 sample 1
26
E_3_BC_16 sample 2
28
Table – 4.30: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB U_3_BC_16
E_3_BC_16
Average 1st cracking load (kN)
21.79
14.87
Average Spalling load (kN)
97.5
99.2
105.75
111.35
Average Ultimate failure load (kN)
75
Sample name
Mid zone crack distribution and crack width
Deflected Shape after failure
Top sample: U_3_SC_16
Bottom sample : E_3_SC_16
Top sample: U_3_BC_12
Bottom sample : E_3_BC_12 Fig. – 4.52:
Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, stone chips and brick chips, -16 mm bars) reinforced with ECR and BB
4.2.1.5 Comparison of Response for ECR and BB Reinforced Beam Type V SC Figures 4.53 to 4.55 and Table 4.31 to 4.34 present the response of beam with 2-16 mm longitudinal bars, embedded in concrete strength of 3.5 ksi constructed with stone chips aggregate. The load deflection responses (Fig. 78) of uncoated bar and epoxy coated bar do not show any difference considering the expected variation of experimental observations. The ultimate loads sustained by the beams with both types of rebars are also very close against design load level of 81 kN, the recorded failure is above 97 kN. The crack width observed (Table 4.32) is higher for ECR when compared to BB. Though the allowable limit of 0.41 mm is specified by ACI 224R-01, the maximum crack width for ECR Table 16 exceeds the code allowable value. However, the code also states that a portion of the structure may exceed this value. And in the experiment, the maximum crack width was reported, while the width of other cracks was within the code limit. Nonetheless, the behavior of the beams with epoxy coated bar showed higher number of cracks with greater crack widths as shown in figure 4.56.
76
120
100
Load (Kn)
80
Uncoated 1
60
Uncoated 2 Epoxy Coated 1
40
Epoxy Coated 2 Design Strength of '81KN'
20
0 0
5
10
15
20 Deflection (mm)
25
30
35
40
Fig. – 4.53: Comparison of loads-deflection response of beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB Table – 4.31: Comparison of Deflections at Design Load for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB Beam name Design Load, kN Deflection at Design load, mm U_3.5_SC_16 sample 1 81 12 81 U_3.5_SC_16 sample 2 13 E_3.5_SC_16 sample 1
81
13.45
E_3.5_SC_16 sample 2
81
12.8
25
Deflection (mm)
20
15 Uncoated 1 10
Uncoated 2 Epoxy Coated 1
5
Epoxy Coated 2
0 0
50
100
150
200 Time (s)
250
300
350
400
Fig. – 4.54: Comparison of deflection time response of beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB 77
120
Load (kN)
100 80 Uncoated 2
60
Uncoated 1 40
Epoxy Coated 1 Epoxy Coated 2
20
Design Strength of '81KN' 0 0
0.2
0.4
0.6 0.8 Crack width mm
1
1.2
1.4
Fig. – 4.55: Comparison of load-crack width response of beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB Table – 4.32: Comparison of Crack Width at Design Load for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB Beam name
Design Load, kN
Crack width, mm
U_3.5_SC_16 sample 1
81
0.3
U_3.5_SC_16 sample 2
81
0.3
E_3.5_SC_16 sample 1
81
0.5
E_3.5_SC_16 sample 2
81
0.38
Table – 4.33: Comparison of Number of Total Cracks for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB Beam name
Number of total cracks
U_3.5_SC_16 sample 1
20
U_3.5_SC_16 sample 2
22
E_3.5_SC_16 sample 1
23
E_3.5_SC_16 sample 2
24
Table – 4.34: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB U_3.5_SC_12
E_3.5_SC_12
19.48
20.315
Average Spalling load (kN)
97
92.2
Average Ultimate failure load (kN)
104
97.35
st
Average 1 cracking load (kN)
78
Sample name
Mid zone crack distribution and crack width
Deflected Shape after failure
Top sample: E_3.5_SC_ 16
Bottom sample : U_3.5_SC_ 16 Fig. – 4.56: Comparison of Crack Pattern and Deflected Shape for Beams (3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB 4.2.1.6 Comparison of Response for ECR and BB Reinforced Beam Type V-SC-S Figures 4.57 to 4.59 and Table 4.35 represent the response of beam with 2-16 mm longitudinal bars with both bar spliced at location of maximum stress. The calculated splice length of 53 inch for ECR and 37 inch BB were used. These lengths were calculated based on for both types of bars. The concrete strength is 3.5 ksi and aggregate type is stone chips. For stone chips concrete the load deflection responses (Fig. 4.57) of uncoated bar and epoxy coated bar do not show any difference (within the limit of expected variability of experimental result). The ultimate loads sustained by the beams with both types of rebars are also practically same. At design load level of 70 kN with fy= 60 ksi , both the beams showed no failure, even with 100% splice at maximum stress – a situation normally not encountered in practice. The crack width observed (Fig. 4.60) is slightly higher for ECR when compared to BB, although at design load level the crack width is within the allowable limit as per ACI 318-14. Despite the above similarities in the responses and behavior of beams with ECR and BB at failure, the beam with epoxy coated bar showed higher number of crack with greater crack widths as shown in figure 85. 120
100
Load (Kn)
80 60 Uncoated 1
40
Epoxy Coated Design Strength of '70KN'
20 0 0
5
10
15 20 Deflection (mm)
25
30
35
Fig. – 4.57: Comparison of loads-deflection response of beam (3.5 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB 79
30 25
Deflection (mm)
20 15 Uncoated 1 Epoxy Coated 1
10 5 0 0
50
100
150 Time (s) 200
250
300
350
Fig. – 4.58: Comparison of deflection time response of beams (3.5 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB
120 100
Load KN
80 60 Uncoated 1 40
Epoxy Coated 1
20
Design Strength of 70 KN with Fy = 60 ksi
0 0
0.5
1
1.5
2
2.5 Crack Width
3
3.5
4
4.5
5
Fig. – 4.59: Comparison of load-crack width response of beams (3.5 ksi, stone chips 2-16 mm Spliced bars) reinforced with ECR and BB Table – 4.35: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (3.5 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB
st
1 cracking load (kN) Spalling load (kN) Ultimate failure load (kN)
U_3.5_SC-S_16 (splice)
E_3.5_SC-S_16 (splice)
32 93.2 100
17.46 90.5 96.5
80
Fig. – 4.60: Comparison of Crack Pattern and Deflected Shape for Beams (3.5 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB 4.2.1.7 Comparison of Response for ECR and BB Reinforced Beam Type VI BC Figures 4.61 to 4.63 and Table 4.36 to 4.39 present the response of beam with 3-12 mm longitudinal bars, embedded in concrete strength of 2.5 ksi constructed with brick chips aggregate. The load deflection responses (Fig. 4.61) of uncoated bar and epoxy coated bar do not show any difference considering the expected variation of experimental observations. The ultimate loads sustained by the beams with both types of rebars are also practically same against design load level of 66 kN, the recorded failure is above 85 kN. The crack width (Table 4.38) observed is slightly higher for ECR when compared to BB, although at design load level the crack width is within the allowable limit as per ACI 318-14. Nonetheless, the behavior of the beams with epoxy coated bar showed slight higher number of cracks with greater crack widths as shown in figure 4.64. 81
100 90 80
Load (Kn)
70 60 50
Uncoated 1
40
Uncoated 2 Uncoated 3
30
Epoxy Coated 1
20
Epoxy Coated 2
10
Epoxy Coated 3 Design Strength of 66 KN
0 0
5
10
15
20 25 Deflection (mm)
30
35
40
45
Fig. – 4.61: Comparison of loads-deflection response of beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB Table – 4.36: Comparison of Deflections at Design Load for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB Beam name Design Load, kN Deflection at Design load, mm U_2.5_BC_12 sample 1 66 12.6 66 U_2.5_BC_12 sample 2 13.2 U_2.5_BC_12 sample 3
66
12
E_2.5_BC_12 sample 1
66
12.9
E_2.5_BC_12 sample 2
66
13.5
E_2.5_BC_12 sample 3
66
13.6
45 40 Deflection (mm)
35 Uncoated 1
30 25
Uncoated 2
20 15
Uncoated 3
10
Epoxy Coated 1
5 0 0
100
200
300 Time (s)
400
500
600
Fig. – 4.62: Comparison of deflection time response of beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB 82
100 90 80 Load KN
70 60
Uncoated 1 Uncoated 2 Uncoated 3 Epoxy Coated 1 Epoxy Coated 2 Epoxy Coated 3 Design Strength of 66 KN
50 40 30 20 10 0 0
0.2
0.4
0.6 Crack width mm
0.8
1
1.2
Fig. – 4.63: Comparison of load-crack width response of beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB Table – 4.37: Comparison of Crack Width at Design Load for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB Beam name Design Load, kN Crack width, mm U_2.5_BC_12 sample 1
66
0.27
U_2.5_BC_12 sample 2
66
0.35
U_2.5_BC_12 sample 3
66
0.2
E_2.5_BC_12 sample 1
66
0.25
E_2.5_BC_12 sample 2
66
0.25
E_2.5_BC_12 sample 3
66
0.35
Table – 4.38: Comparison of Number of Total Cracks for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB Beam name Number of total cracks U_2.5_SC_12 sample 1
25
U_2.5_SC_12 sample 2
20
U_2.5_SC_12 sample 3
27
E_2.5_SC_12 sample 1
27
E_2.5_SC_12 sample 2
21
E_2.5_SC_12 sample 3
32
Table – 4.39: Comparison of Cracking Load, Spalling Load and Ultimate Load Values for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB U_2.5_BC_12 E_2.5_BC_12 Average 1st cracking load (kN)
19.67
14.37
Average Spalling load (kN)
80.2
83
Average Ultimate failure load (kN)
85.6
89.1
83
Sample name
Mid zone crack distribution and crack width
Deflected Shape after failure
Top sample: E_2.5_SC_ 12
Bottom sample : U_2.5_SC_ 12 Fig.– 4.64: Comparison of Crack Pattern and Deflected Shape for Beams (2.5 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB 4.2.2
Comparison of Flexural Bond Strength of ECR and BB reinforced beams
The bond stress developed along the surface of the reinforcing bar in beams is due to shear stresses and shear interlock [88]. The average bond stress is a function of shear stress and sum of perimeters of bars in the section at the tension side. The design bond stress and the ultimate bond stress at failure is found by the following equation –
(1)
∑
Where „u‟ is the average bond stress, „d‟ is the effective depth of the reinforcement and ∑ is the sum of perimeters of bars in the section at the tension side and „V‟ is the shear force. Table 4.40 summarizes the design and ultimate flexure bond comparisons. Table – 4.40: Comparison of Design and Failure bond strength for black bars and Epoxy coated bars. Beam types Black Bars Epoxy Coated Bars Design Flexure Bond stress (MPa)
Flexure Bond strength at Failure MPa)
Design Flexure Bond stress(MPa)
Flexure Bond strength at Failure (MPa)
3 ksi, Stone Chips, 12mm
19.31
24.4
19.31
23.95
3 ksi, Brick Chips, 12mm
19.31
23.85
19.31
24.03
3.5 ksi, Stone Chips, 12mm
20.15
24.74
20.15
25.74
3 ksi, Stone Chips, Splice, 16mm
19.03
29.6
19.03
28.82
3 ksi, Brick Chips, Splice, 16mm
19.03
29.38
19.03
23.23
3 ksi, Stone Chips, 16mm
22.10
29.38
22.10
27.69
3 ksi, Brick chips, 16mm
22.10
29.59
22.10
31.16
3.5 ksi, Stone Chips, 16mm
22.67
29.1
22.67
27.24
3.5 ksi, Stone Chips, Splice 16mm
19.59
27.98
19.59
27
2.5 ksi, Brick Chips, 12mm
18.47
23.95
18.47
24.93
84
Design flexure bond stress for both ECR and BB are theoretical bond stresses calculated using equation 1 where „V‟ is calculated from theoretical two point loading condition. The analytical equation for the beam does not include any coating factor. Thus, the design flexural bond is same for both ECR and BB. But, the flexure bond strength is calculated using equation 1 at failure load. It is found that, the flexure bond strength at failure is higher for both ECR and BB when compared to design bond stress.
85
CHAPTER 5 Conclusions and Recommendations Based on the review of worldwide research and results of experiments conducted at BUET on epoxy coated reinforcements (ECR) and conventional black bars (BB), the following conclusions are drawn: A. A review of research findings on corrosion led deterioration of concrete structures has been made. As a protection against early deterioration of concrete in aggressive environment, epoxy coated rebars have been in use for more than forty years in North America. Its use has gained popularity in constructions of infrastructures that are exposed to adverse weathering conditions. Based on the review, the following conclusions are made: (i) (ii)
(iii)
(iv)
(v)
With exposure to extreme saline environment, the epoxy coated rebar demonstrates superior performance against corrosion led deterioration of concrete structures. During initial years of its production and use quality of coating as well as less stringent requirements of care and protection during handling and fabrication have led to concerns about the effectiveness of ECR in corrosion protection. However, the ASTM A775 has had several revisions with stringent quality control requirements. With higher quality requirements coupled with introduction of ASTM D3963 (Standard Specification for Fabrication and Jobsite Handling of Epoxy-Coated Steel Reinforcing Bars) for minimizing coating damage during handling, transporting and fabrication, it is expected that ECR will have maintenance free service life many-fold than the ordinary black bars, particularly in extreme weather condition. Over the life-cycle of a structure exposed to extreme weather condition, epoxy coated reinforcement proved to be much economic. The ECR involves only an increase in initial cost of 3.7% but the life-cycle cost is decreased by more than 46% when compared with the uncoated bars. The design of structures with epoxy-coated rebar does not require any change from the conventional un-coated bars. The only change that is required to be addressed is in the development and splice length of ECR to be 20 to 50% higher than the black bars. The transportation, handling, storage and jobsite fabrication of ECR require a detail and careful procedure not to damage the coatings for a sustained and durable performance. This may become a crucial issue in construction practice. Special trained transporters and fabricators would be necessary to cater for this.
B. A series of laboratory tests on two-types of concrete specimens have been conducted to evaluate performance of locally produced FBECR over the conventional black bars. Results on specimens of (a) direct pull-out and (b) flexural beams revealed the following: (i)
The ECR expectedly demonstrated slightly higher slip than the BB. A few samples behaved otherwise which can be discarded as sample variations. With code specified embedment, the ECR can sustain higher stress than the corresponding yield load of the bar. (ii) The 12 mm epoxy coated bars sustained around 118-120% of the corresponding yield load, while the 16 mm epoxy coated bars sustained around 118-130% of the corresponding yield load. (iii) The flexural load-deflection behavior of beams tested under two-point loading shows identical response for both ECR and BB type reinforcements. (iv) The beams reinforced with ECR showed higher crack width than conventional deformed bars, 86
although at design load the observed crack-width was within code specified limit. (v) Though the average number of total cracks and crack widths are higher in case of ECR, some individual beams with ECR showed equal or lesser crack number and crack width compared to BB. Thus, it cannot be solely concluded based upon crack number and crack widths that, ECR perform poorly under flexure compared to BB. (vi) The concrete made with brick-chips aggregate demonstrated satisfactory performance in bond behavior under direct pull-out as well as load-deflection response of beams. The observed slip, deflection, crack widths are higher when ECR is used with brick chips concrete. Despite this fact, the pull-out force and crack width satisfied the code specified limits. (vii) The slip values for Epoxy Coated bars for both 12 mm and 16 mm decrease as concrete strength increases. This is true for both brick chips and stone chips specimens. (viii) Bond failure occurred for 16 mm Epoxy coated bars with for both stone chips and brick chips specimens. This is because the embedded length of the bars was only 40% of the code specified development length. Bond failure also occurred for 16 mm Epoxy Coated bars with for brick chips specimens for the same reason. For the same cases with 12 mm Epoxy Coated bars, no bond failure occurs due to increased percentages of embedded lengths provided compared to 16 mm Epoxy Coated bars. (ix) For higher strength concretes (e.g. and ) no bond failure occurs for both 12mm and 16mm Epoxy Coated bars. So higher strength concrete would ensure better performance of ECR. (x) For the specimens with full development length, no difference in bond performance was noticed for ECR and BB (see figure 4.22 and figure 4.23).With the use of code specified development length the use of epoxy coated bar does not cause any poor performance. C. Based on research conducted on performance of ECR in concrete, it may be concluded that with proper quality assurance and care of handling and fabrication against coating damage, use of ECR in concrete members will maintain comparable performance as expected with the use of BB reinforcements. This is particularly the case when stone chips aggregate is used. With brick chips aggregate, the poor bond performance leads to higher flexural crack width and deflection when ECR is used.
Recommendations In case of both flexure tests and pull out tests, some specimens showed spurious results. This discrepancy can be avoided with larger sample size so that the results obtained can be concluded as more statistically significant one. Further research should be done with larger sample size.
87
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