An Experimental Study of Fiber Reinforced concrete ...

International Journal of Engineering Associates (ISSN: 2320-0804) # 59 / Volume 3 Issue 10

An Experimental Study of Fiber Reinforced concrete panels subjected to In-Plane and flexural forces Dr Mohammad Ahmad#1, Saiful Islam*2, Roohul Abad Khan#3 #

Department of Civil Engineering King Khalid University, Abha ,Kingdom of Saudi Arabia 1

3 *

[email protected] [email protected]

Department of Civil Engineering King Khalid University, Abha ,Kingdom of Saudi Arabia 2 [email protected]

Abstract— In this paper, an experimental study of fibre reinforced concrete wall and slab panels subjected to in-plane and flexure forces has been presented. The panels were casted of plain concrete as well as of concrete consisting of three different percentages of fibres. Steel fibres of diameter 0.426mm having aspect ratio of 72 were taken. Fibre content used were 0.4%, 0.5% and 0.6% by volume of concrete. These panels were tested in compression, one-way and two-way bending. Load- Deflection data were obtained and analysed. The crack patterns and failure mechanism were also examined. The fibre reinforced concrete panels were found to be stiffer at the serviceability loads and show ductile behaviour towards the failure stages of loading. Keywords— FRC panel, Bending, compression testing machine, Serviceability load

I. INTRODUCTION Fibre reinforced concrete is a relatively new construction material developed through extensive research and development work during the last two decades. It has been proved as a reliable construction material having superior performance characteristics compared to the conventional concrete. Incorporation of fibres in concrete has been found to improve several of its properties; cracking resistance, ductility and fatigue resistance, impact and wear resistance. Researchers have done great work on Fiber reinforced concrete. Nataraja, Dhang, Gupta [1] studied the effect of addition of crimped round steel fibres on the splitting tensile strength of concrete. Maria de Lurdes et al. [2] carried out experimental investigations on the compressive strength of steel fibre reinforced high strength concrete (SFHSC) subjected to high temperatures. Bindiganavalie. V and Banthia. N [3] studies on the Impact Response of Fibre Reinforced Concrete”. O.Kayali et al. [4] carried out experimental investigation on the effect of polypropylene and steel fibres on high strength light weight aggregate concrete. Kaushik S.K., et al. [5] carried out experimental investigation on the mechanical properties of reinforced concrete Peter H.Bischoff [6] studied the post cracking behaviour of reinforced tension members made with both plain and steel

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fibre - reinforced concrete. Song, Hwang and Shou [7]carried out experimental investigations to study the impact resistance of steel fibre reinforced concrete using drop weight test method. Kolhapure B.K. [8] investigated experimentally the mechanical properties of concrete using recron 3S fibres along with super plasticizer.F.B.A. Beshara, I.G. Shaaban and T.S. Mustafa [9] presented the development of simple semiempirical formulae for the analysis of nominal flexural strength of high strength steel fiber reinforced concrete (HSFRC) beams.The experimental investigation [10] was carried out on thealkali resistant (AR) glass fibers and studied the effect on compressive, tensile strength, split tensile and flexural strength on M20, M30, M40 and M50 grades of concrete. Osman Gencel et al. [11] studied the Workability and Mechanical Performance of Steel Fiber-Reinforced SelfCompacting Concrete with Fly Ash.. G.Murali et al.,[12] investigated the behaviour of fibre concrete by using the waste material such as lathe waste, soft drink bottle caps and beverage tin wastes and found that the strength of concrete for all the fibre has been increased significantly than ordinary concrete.[13] experimentally shows that Steel fibres reduce the permeability and water migration in concrete, which ensures protection of concrete due to the ill effects of moisture. [14] Studies Applications and Properties of Fibre Reinforced Concrete II. EXPERIMENTAL SET UP Panels tested in compression were subject to uni-axial compressive force uniformly distributed on the entire length of two sides facing each other. For producing one-way bending and two-way bending, the panels were supported on two and four sides respectively. Roller supports were placed over an iron plate, which is reinforced by stiffeners properly for preventing the plate from bending. All the panels were subjected to a point load transmitted on the panel over a surface area of 75mm x 75mm square, centrally with the panel. The applied load was measure accurately by 5t capacity proving ring, which was placed in between the panel and loading device of compression testing machine. Two dial

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International Journal of Engineering Associates (ISSN: 2320-0804) # 60 / Volume 3 Issue 10

gauges were fixed at an equal distance of 6cm from the central load position to note the transverse deflection corresponding to the load applied. It was not possible to place dial gauges in the centre of the panel due to the loading arrangement followed for caring out these tests. III. PREPARATION AND TESTING OF SLAB/WALL PANELS In order to study the compression and flexural behaviour of fibre reinforced concrete panels and to compare their behaviour with that of plain cement concrete panels, wall/slab panels of size 400 mm x400 mm x40mm thick of plain and fibre reinforced concrete were casted. The percentages of fibres mixed were 0.4%, 0.5% and 0.6% by volume of concrete. Steel fibres known for their better performance for most of the structural elements, relatively low cost and ease in mixing were used. Diameter of fibre used was 0.427mm. It has already been established 5 that at lower aspect ratios of fibres, there is a very little improvement in the strength of concrete and at higher aspect ratios, the balling or agglomeration of fibres will occurs which leads to reduction in strength. It is well known that aspect ratio lying between 70 and 100 gives better results, as the efficiency of transfer of stresses from matrix to the fibres is higher at these aspect ratios. Therefore, an aspect ratio of 72 has been selected for this work. Maximum size of coarse aggregate is an another important factor affecting the properties of fibre reinforced concrete. It gives better results if the maximum size of coarse aggregate is around 10mm. Therefore, concrete mix following the curve number 2, recommended by road research laboratory method10 was opted, as, the proportions recommended in this curve resulted in the maximum size of aggregate around 10mm. Testing of panels were carried after 28 days of curing on both the plain concrete panels as well as fibre reinforced concrete panels having the fibre content of 0.4%, 0.5% and 0.6% by volume of concrete. The dial gauges and the proving ring were first set to zero position. The load was then applied at a constant rate of 10kg/cm2/minute. Deflections were noted at a regular interval of 12.5kg transverse load. As the plain concrete panels forming a mechanism at the failure load under flexure loading were reduced into four pieces, their deflection could only be noted down up to the failure load. In case of fibre reinforced concrete panels subjected to axial compression, one-way and two-way pending, deflections were obtained event after the ultimate load and were continued till the rate of falling of the load had become very fast. During the progress of the tests, first crack load, ultimate load and deformations at various stages of loading were recorded. The tested panels are shown in Figs. 1 to 4.

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Fig .1 Crack patterns for plain concrete panels under compression (P1), one way bending (P2) and two way bending (P3)

Fig 2. Crack patterns for FRC panels under compression

Fig 3 Crack patterns for FRC panels under one way bending

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International Journal of Engineering Associates (ISSN: 2320-0804) # 61 / Volume 3 Issue 10

reinforced concrete panels having 0.4%, 0.5% and 0.6% fibres by volume of concrete respectively. The load-deflection relation for plain and fibre rei nforced concrete panels having volume percentages of fibre of 0.4%, 0.5% and 0.6% are shown in Fig. 5 through 7 for co mpression, one-way bending and two-way bending re spectively. The study of load-Deflection curves of fibre rei nforced concrete panels shows almost a linear relation in 40

30

Load (t)

Fig 4 Crack patterns for FRC panels under two way bending 20

IV. ANALYSIS OF DATA In all the test carried out, the load carrying capacity and deflections at serviceability loads and failure loads were determined. In order to see the response of fibre reinforced concrete panels to loads specially, failure load, the deformations at serviceability loads and failure loads, results of fibre reinforced concrete panels subjected to compression, one-way bending and two-way bending were compared with that of plain concrete panels subjected to similar loadings. The crack patterns and failure mechanism were also studied. The panels tested had failed in well-defined and known failure mode. Crack patterns developed under axial compression show the failure due to stresses developed perpendicular to the direction of the load applied. Difference in failure mode of plain and fibre reinforced concrete panels was visible in the splitting of aggregate pieces at the time of failure. Splitting of aggregate was more in plain concrete panels than in the fibre reinforced concrete panels. A distinct difference was observed in the pattern in which the plain and fibre reinforced concrete panels had failed in flexure. Whereas in the fibre reinforced concrete panels, there is a significant increase in the load after the development of mode and the crack gradually progressed from the point of development of first crack i.e. from the centre in the direction parallel to the supports to the end of the panels in one-way bending and from the centre in the direction parallel to the both supports perpendicular to each other to the corners of the panels in twoway bending converting into mechanism, the plain concrete panels had failed immediately after the development of first crack converting into mechanism instantaneously. The plain concrete panels were transformed into pieces at the failure load. The fibre reinforced concrete panels had remained intact even after converting into a mechanism. In both panels subjected to one-way bending and two-way bending, failure mechanism resembles a well-defined failure pattern, similar to the formation of yield lines of square slab subjected to similar loading. Failure patterns of plain concrete panels (P1, P2 and P3) tested under compression, one-way bending and two-way bending are shown in Fig. 1. Failure patterns of fibre reinforced concrete panels are shown in Fig. 2, 3and 4 for compression, one-way bending and two-way bending respectively. In these figures A, B and C denotes the fibre

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Plain Conc. 0.4% FRC 0.5% FRC 0.6% FRC

10

0 0

2

4

6

8

10

Deflection (mm)

Fig 5 Load-Deflection Curve of Plain and FRC Panels under Axial Compression

the initial stages of loading which become non-linear at the latter stages of loading. There is also remarkable difference in curves of plain and fibre reinforced concrete panels. Whereas the load-deflection curves of plain concrete panels is nonlinear since the beginning of loading, the curves of fibre reinforced concrete panels resemble an approximate linear relationship between load and deflection. From the point nearer to the first crack, there is a sudden change in the slope of the load-deflection curve of fibre reinforced concrete panels becoming non-linear beyond this point of loading. This indicates the transfer of stress from concrete matrix to the fibres at this stage of loading. Increase area under loaddeflection curve with the increase in fibre content indicate an improvement in the ductility of fibre reinforced concrete panels towards the failure stage of loading. This improvement in the ductility of fibre reinforced concrete panels is due to the addition of fibres. From the experimental observations, it is found that the loads at failure of fibre reinforced concrete panels are higher in fibre reinforced concrete panels as compared to these loads of plain concrete panels. The increase in failure loads subjected to compression, one-way bending and twoway bending are shown in Fig. 8. The percentage increase in the failure loads of fibre reinforced concrete panels subjected to compression with 0.4%, 0.5% and 0.6% fibres by volume of concrete are found as 1.49%, 4.47%, 10.45% respectively as compared to the failure loads of plain concrete panels. The increase in the failure loads of fibre reinforced concrete panels subjected to one-way bending and two-way bending are as (8.11%, 13.42%, 18.36%) and (10.74%, 15.02%, 23.96%) respectively as compared to the failure loads of corresponding plain concrete panels. This increase in the loads of fibre reinforced concrete panels at failure is a clear evidence of the fact that the fibres arrest the onset of crack and bond between concrete and fibres resist further load applied on the panels. The results also exhibit that the deflections in fibrous concrete panels as compared to plain concrete panels are

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International Journal of Engineering Associates (ISSN: 2320-0804) # 62 / Volume 3 Issue 10

30 25

Increase in Load (%)

found lesser at serviceability loads and found higher at failure loads. This is evident from the Figs.9-10. The deflections at serviceability loads decreases with the increase in fibre content. This shows that the addition of fibres increase the stiffness of concrete elements at the serviceability loads. The substantial increase of deflection in fibre reinforced concrete panels after the failure load is a clear evidence of the change in the property of concrete from brittle into ductile due to the addition of the fibres. For fibre reinforced concrete panels having fibres 0.4%, 0.5% and 0.6% by volume of concrete, percentage reduction at serviceability loads are found as (1.67%, 3.33%, 5.0%), (3.33%, 5.3%, 7.27%) and (2.78%, 5.55%. 8.33) for the panels subjected to compression, oneway bending and two-way bending respectively. Percentage increase in deflections at the failure of the fibre reinforced concrete panels having volume percentages of fibres of 0.4%, 0.5% and 0.6%, under one-way and two-way bending are (3.33%, 6.66%, 16.66%,), (7.57%, 10.61%, 18.18%) and (11.11%, 16.67%, 27.78) respectively over the deflections at the failure loads of plain concrete panels.

One-way bending Two-way bending Compression

20 15 10

5

0 0.30%

0.40%

0.50%

0.60%

0.70%

Percentage of Fibres

Fig 8. Percentage Increase in Failure Load of FRC Panels Under Compression, One-way and Two-way Bending

800

60 Increase in Def l. (%)

400

Plain Conc. 0.4% FRC 0.5% FRC

200

0 0

1

Deflection mm) 2

3

50 40 30 20

Compression One-way bending Two-way bending

10

4 0 0.30%

0.40%

0.50%

0.60%

0.70%

Percentage of Fibres

Fig 6. Load-Deflection Curve of Plain and

Fig 9. Percentage increase in Deflection at failure load of FRC

FRC Panels under One-way Bending

Panel under compression,one way and two way bending. 1200

1000

30 Red uction in Defl. (%

800

Load (Kg)

Load (kg)

600

Plain Conc. 0.4% FRC 400

0.5% FRC 0.6% FRC

200

0 0

1

2

3

4

5

Fig 7. Load-Deflection Curve of Plain and FRC Panels under Two-way Bending

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25

15 10

Compression One-way bending Two-way bending

5 0 0.30%

0.40%

0.50%

0.60%

Percentage of Fibres

62

0.70%

International Journal of Engineering Associates (ISSN: 2320-0804) # 63 / Volume 3 Issue 10

Fig 10 Percentage decrease in deflection at serviceability load of P.C under compression, one way and two way bending

V. CONCLUSION Based on the experimental study conducted on fibre reinforced concrete and plain concrete panels, the following conclusions were drawn. 1)

The study of load-Deflection curves of fibre reinforced concrete panels shows almost a linear relation in the initial stages of loading which become non-linear at the latter stages of loading.

2)

The failure load in plain concrete panels in bending reached immediately after the visibility of first crack, while in the case of fibre reinforced concrete panels, the failure load is found to be significantly higher than the first crack load.

3)

The load at failure in fibre reinforced concrete panels are higher than the plain concrete panels and the failure load of fibre reinforced concrete panels increase with the increase in fibre content in both compression and bending.

4)

In the panels subjected to compression and bending, the deflections at serviceability loads in fibre reinforced concrete panels are smaller than the deflections in plain concrete panels at their serviceability loads. These deflections decreased with the increase in fibre content.

5)

Deflections at failure loads are found to the more in fibre reinforced concrete panels, subjected to compression, one-way bending and two-way bending as compared to the deflections at failure load in plain concrete panels. Difference in the deflection increases with the increase in the fibre content.

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REFERENCES [1] Nataraja, M.C. “Splitting tensile strength of SFRC,” The Indian Concrete Journal, April 2001, pp. 287-290 [2] Maria de Lurdes et al., “High temperature compressive strength of steel fibre high-strength concrete”, Journal of Materials in Civil Engineering, May/June 2001, pp.230-234. [3] Bindiganavalie V., et al., “Some S tudies on the Impact Response of Fibre Reinforced Concrete”, Indian Concrete Institute Journal. , October-December, 2002 pp. 23-28. [4] O.Kayali, M.N. Haque, B.Zhu “Some characteristics of high strength fibre reinforced light weight aggregate concrete”, Cement & Concrete Composites25, 2003, PP – 207 – 213. [5] Yaghoub Mohammadi & kaushik, S.K., “Investigation on mechanical properties of steel fibre reinforced concrete with mixed aspect ratio of fibres”, Journal of Ferrocement, Vol. 33, No.1, January 2003, pp.1-14 [6] Peter H.Bischoff “Tension stiffening and cracking of steel fibre reinforced concrete”, Journal of Materials in Civil Engineering. ASCE, March / April, 2003. [7] Song, P.S., et al. “Statistical evaluation for Impact Resistance of Steel Fibre Reinforced Concretes”, magazine of Concrete Research, Vol. 56, No.8, October 2004, pp. 437-442. [8] Kolhapure. B.K., “Study of Recron 3S fibre –reinforced concrete with super plasticizer with reduction in cement”, Proceedings of the National Conference on Concrete Technology for the Future at Kongu Engineering College, Erode, 2006, pp-449-455 [9]F.B.A. Beshara, I.G. Shaaban and T.S. Mustafa “ Nominal Flexural Strength of High Strength Fiber Reinforced Concrete Beams” 11th Arab Structural Engineering Conference, 25-27 October 2009. [10]. Chandramouli K, Seshadri Sekhar T, Sravana P, Pannirselvam N and Srinivasa Rao P (2010), Strength properties of glass fiber concrete, ARPN journal of Engineering and Applied sciences, vol. 5, no. 4. [11]. Osman Gencel et al.. “ Workability and Mechanical Performance of Steel Fiber-Reinforced Self-Compacting Concrete with Fly Ash” Composite Interfaces 18 (2011) 169–184 [12] G.Murali, C.M.Vivek Vardhan, R.Prabu, Z.Mohammed Sadaquath Ali Khan, T.Aarif Mohamed And T.Suresh experimental investigation on fibre reinforced concrete using waste materials, international journal of engineering research and applications (ijera) issn: 22489622 www.ijera.com vol. 2, issue 2,mar-apr 2012, pp.278-283. [13]Rana A. “Some Studies on Steel Fiber Reinforced Concrete”, International Journal of Emerging Technology and Advanced Engineering, Volume 3, Issue 1, January 2013. [14] Amit Rai et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 5( Version 1), May 2014, pp.123-131

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