condition assessment of existing structures using ndt ...

CONDITION ASSESSMENT OF EXISTING STRUCTURES USING NDT TECHNIQUES A Thesis submitted to Department of Civil Engineering , GITAM In partial fulfillment of the requirements for the Award of Degree of

MASTER OF TECHNOLOGY IN STRUCTURAL ENGINEERING AND NATURAL DISASTER MANAGEMENT Submitted By

Y.V.S.AJITESH (1221112128) Under The Guidance of

Dr. K. V. G. D. Balaji Ph.D. Professor of Civil Engineering, GITAM University

Dr. P. C. Kumar Ph.D. Assistant Professor of Civil Engineering, GITAM University

DEPATMENT OF CIVIL ENGINEERING GITAM INSTITUTE OF TECHNOLOGY GITAM UNIVERSITY (Est. U/s 3 of UGC act 1956)

VISAKHAPATNAM-530045

DEPARTMENT OF CIVIL ENGINEERING GITAM INSTITUTE OF TECHNOLOGY GITAM UNIVERSITY (Est. U/s 3 of UGC act 1956) VISAKHAPATNAM-530045

CERTIFICATE This is to certify that the thesis entitled “CONDITION ASSESSMENT OF EXISTING STRUCTURES USING NDT TECHNIQUES” submitted by Y.V.S.AJITESH, bearing Regd. No. 1221112128, in partial fulfilment of the requirements for the award of degree of Master of Technology in Civil Engineering with specialization in Structural Engineering and Natural Disaster Management. GANDHI INSTITUTE OF TECHNOLOGY is accorded to the student’s own work, carried out by his in department of Civil Engineering during the year 2012-2014 under our supervision and guidance. Neither his thesis nor any part of this thesis, has been submitted for any degree/diploma or any other academic award anywhere before.

Dr. K.V.G.D.Balaji

Dr. P.C. Kumar

Dr M. Ramesh

Professor

Assistant Professor

Professor & Head of Department

Dept. of Civil Engineering

Dept. of Civil Engineering

Dept. Of Civil Engineering

GITAM University

GITAM University

GITAM University

ACKNOWLEDGEMENT This thesis is completed with the help of many people who had given me their full support and encouragement all the time. However I would like to specially acknowledge and extend my heart- full gratitude to the few people who made this thesis completion possible. I would like to thank my project guide, Dr. P.C.KUMAR, who has given me his time and encouragement. I would also like to thank my project guide, Dr. K.V.G.D BALAJI, who has given me his valuable time, stimulated suggestions and encouragement in this thesis work. I would like to thank Dr. K.V.RAMESH, who has given me his support and suggestions from the beginning. I would like to thank Dr. M.POTHA RAJU, who has given me his length support in doing this thesis. I would like to thank Mr. T.SANTHOSH KUMAR, who has given me his experienced suggestions in doing the report. I would like to thank Mrs. K. REKHA, who has given me her advices from the beginning. I would like to thank specially Dr. M. Ramesh, Head of Department, Civil Engineering, who had given a special care and attention for me in submitting the report. I would like to show my special gratitude to my parents for their affection and love all the time. I would like to thank my friends who had given me support even at the critical times.

DEPARTMENT OF CIVIL ENGINEERING GITAM INSTITUTE OF TECHNOLOGY GITAM UNIVERSITY

M.Tech THESIS EVALUATION REPORT This thesis entitled “ CONDITION ASSESSMENT OF EXISTING STRUCTURES USING NDT TECHNIQUES ” submitted by Y.V.S.AJITESH

in partial fulfillment of the requirements for the award of the degree of Master of Technology in Civil Engineering with specialization in Structural Engineering and Natural Disaster Management of GITAM University, Visakhapatnam has been approved.

EXAMINERS 1. ………………………………

Thesis Supervisor

2. …………………………

External Examiner

3. …………………………

Head of the department Civil Engineering

Place : Visakhapatnam Date :

DECLARATION

I hereby declare that the work done in this thesis entitled “ CONDITION ASSESSMENT OF EXISTING STRUCTURES USING NDT TECHNIQUES ” has been carried out by me, in partial fulfillment of the

requirements for the award of degree of Master of Technology in Civil Engineering with a specialization in Structural engineering and Natural Disaster Management

in

GITAM Institute of Technology, GITAM

University and further declare that neither this thesis nor any part of this thesis has not been submitted for any degree/diploma

or any other

academic award anywhere before.

Place: Visakhapatnam Date:

Y.V.S.AJITESH

ABSTRACT Damage assessment of structures is one of the most important and emerging fields in Civil Engineering. Damage to structures may occur as a result of normal operations, accidents, deterioration or severe natural events such as earthquakes and storms. Most often the extent and location of damage may be determined through visual inspection. However, in some cases this may not be feasible. Non-destructive testing is conducted on the main structural and relatively more affected column and beam members in various buildings. In the present work, Condition Assessment of the Reinforced Concrete (RC) buildings is carried out with special reference for the further usage of the structures. Non-Destructive Tests (NDT) like Rebound Hammer and Ultrasonic Pulse Velocity Tests are used to carry out insitu evaluation and condition assessment. The report analyzes the deficiencies in the construction of a multi-storeyed reinforced concrete framed building and onshore cum offshore structure. NDT are conducted to assess the real strength gained by the RC elements like columns, beams and slabs. The test results show that there is a considerable effect of exposure to sea environment on durability of the RC buildings and the rebound number method is more efficient in predicting the strength of concrete under certain conditions. A combined method for the Rebound Hammer and UPV tests reveals an improvement in the concrete strength estimation. In addition, the structural analysis is

performed using STAAD PRO v8i software for evaluating the design of constructed components of the building and analysis results concluded that the structure requires immediate attention of strengthening the existing RC columns by adopting suitable rehabilitation techniques.

CONTENTS Abstract List of Tables List of figures Chapter Description

Pg. No.

No. 1.

Introduction

1

2.

Literature Review

5

2.1. Introduction

5

2.2. Condition Assessment of Structures

5

2.3. Role of Non-Destructive Techniques in 14 Condition Assessment 2.4. Case Studies

20

2.5. Rebound Hammer

23

2.6. Ultra Sonic Pulse Velocity test in 24 condition assessment

3.

4.

2.7. Corrosion

27

2.8. Carbonation

29

Methodology

30

3.1. Rebound Hammer

31

3.2. Ultrasonic Pulse Velocity

35

3.3. Carbonation

39

Case studies

41

4.1. Reinforced Concrete Building#1

41

I.

Visual Observations

41

II.

Results and Discussions

46

4.1.1 Rebound Hammer

46

4.1.2 Ultrasonic Pulse Velocity

59

4.1.3 STAAD Pro Analysis

67

4.2. Chinthapalli Structure I.

Visual Observations

80 80

5.

6.

II. Results and Discussions

85

4.2.1 Rebound Hammer

85

4.2.2 Carbonation

91

4.2.3 STAAD Pro Analysis

92

Summary and Conclusions

96

5.1. Summary

96

5.2. Discussions

99

5.3. Conclusions

100

References

102

List of Tables: Table

Page Description

No.

No.

3.1

Rebound Number v/s Quality of concrete surface

32

3.2

UPV velocity v/s concrete quality

38

3.3

Interpretation of results from Rebound numbers

38

and UPV 4.1.1

Rebound Hammer Column Results @ Stilt

47

4.1.2

Rebound Hammer Beam Results @ Stilt

48

4.1.3

Rebound Hammer Column Results @ Ground

50

Floor 4.1.4

Rebound Hammer Beam Results @ Ground

51

Floor 4.1.5

Rebound Hammer Column Results @ First Floor

53

4.1.6

Rebound Hammer Beam Results @ First Floor

54

4.1.7

Rebound Hammer Column Results @ Second

56

Floor

4.1.8

Rebound Hammer Beam Results @ Second Floor

57

4.2.1

UPV Test Column Results @ Stilt

59

4.2.2

UPV Test Beam Results @ Stilt

60

4.2.3

UPV Test Column Results @ Ground Floor

61

4.2.4

UPV Test Beam Results @ Ground Floor

62

4.2.5

UPV Test Column Results @ First Floor

63

4.2.6

UPV Test Beam Results @ First Floor

64

4.2.7

UPV Test Column Results @ Second Floor

65

4.2.8

UPV Test Beam Results @ Second Floor

66

4.1.9

Rebound Hammer Results for On Shore Structure

86

4.1.10 Rebound Hammer Beam Results for On Shore

87

Structure 4.1.11 Rebound Hammer Column Results for Off Shore

89

Structure 4.1.12 Rebound Hammer Beam Results for Off Shore Structure

90

5.1

ABSTRACT OF TEST RESULTS FOR RC

96

BUILDING#1

5.2

ABSTRACT OF TEST RESULTS FOR AQUA

97

STRUCTURE(on shore)

5.3

ABSTRACT OF TEST RESULTS FOR AQUA STRUCTURE(off shore)

98

List of Figures: Figure

Page Description

No.

No.

3.1

Rebound Hammer

31

3.2

Ultrasonic Pulse Velocity

37

3.3

Carbonation Effect on Concrete

41

4.1

Chajjas/ Fins damaged Condition

44

4.2

Chajjas/ Parapet and Columns Damaged Condition

44

4.3

Chajjas and Columns Damaged Condition

45

4.4

Columns Damaged Condition & Seepage Through

45

Basement 4.5

Kitchen-Wash Area Floor Condition (First Floor)

46

4.6

Walls Dampness & Chajja Condition (Ground Floor)

46

4.7

Typical view of RC Building

68

4.8

Plan view of RC Building

68

4.9

Side view of RC Building

69

4.10

Off shore cum on shore structure

82

4.11

On shore Structure

83

4.12

Off shore structure

83

4.13

Spalling of concrete in columns

84

4.14

Spalling of concrete in beams

84

4.15

Collapsed railings

85

4.16

Spalling in slab Portion

85

4.17

Typical view of Chinthapalli Structure

93

4.18

Plan view of Chinthapalli Structure

93

4.19

Side view of Chinthapalli Structure

94

4.20

Center line diagram of Chinthapalli Structure

94

CHAPTER - 1 INTRODUCTION Most of the Reinforced Concrete (RC) structures which are in service, around the world are aging and deteriorating due to harsh environmental exposure conditions and are damaged by natural earthquakes, hydrologic forces, etc. or man-made collisions, fire, road, etc. Consequently, the structural capacity of an existing structure is typically less than the structural capacity of just-built structure. Even if the deterioration does not lead to the direct failure of a structure, it may weaken the structure, making it more vulnerable to earthquakes and other hazards. The conventional design framework for concrete structures is primarily based on safety and currently focused on the aspects of durability. It is obvious that environment aspects should also be incorporated into the design of concrete structures. Most of the existing design codes do not provide tools with the exception of the environment impacts. The Non Destructive Test (NDT) of concrete in today’s scenario has received a great importance in terms of practical and engineering value. The subject has received a growing attention during recent years, especially the quality characterization of damaged structure made of concrete using NDT testing. Based on the rate of deterioration, the 1

structure is adapted to repair, rehabilitation and renovation. Non Destructive Evaluation (NDE) of concrete are well known and extensively used. It is important to select the appropriate NDE techniques. The main advantage of NDT method is to avoid the concrete damage or the performance of building structural components. Additionally, their usage is simple and quick. A single technique may not be sufficient, therefore combination of techniques are adopted to get a truly representative data of the condition of the structure. Commonly used NDE methods are Rebound Hammer Test, Ultra Sonic Pulse Velocity (UPV) Test, chloride test and carbonation test. The NDT adopted in this thesis for the assessment of strength of structure are Schmidt’s Hammer Test, Ultrasonic Pulse Velocity Test and Carbonation Test. The Schmidt Rebound Hammer (SRH) and the Ultrasonic Pulse

Velocity (UPV) tests are useful non-destructive tests,

which are so familiar Now-a-days and they are useful when a correlation can be developed between hammer/ ultrasonic pulse velocity readings and strength of the same concrete. Rebound hammer is useful to detect changes in concrete characteristics over time, such as hydration of cement, for the purpose of removing forms or shoring. This test is based on the principle that the rebound of an elastic mass depends on the hardness of the surface against which the mass impinges. The test procedure is described in IS: 13311 2

Part 2: 1992 and BS 1881 202 (1986). It is portable, easy-to-use, lowcost, and can quickly cover large areas but it is valuable only as a qualitative tool since it measures the relative surface hardness of the concrete. The energy absorbed by the concrete is related to its strength. There is no unique relation between hardness and strength of concrete but experimental data reveal relationships obtained from a given concrete. However, this relationship is dependent upon factors affecting the concrete surface such as degree of saturation, carbonation, temperature, surface preparation and location, and type of surface finish. A correlation between rebound number and strength of concrete structure is established, which can be used for strength estimation of concrete structures. The ultrasonic pulse velocity tester is the most commonly used ones in practice. Test is described in (IS: 13311 Part 1; 1992 and BS 1881-203; 1986). Longitudinal ultrasonic waves are attractive tool for investigating concrete. Such waves have the highest velocity so it is simple to separate them from the other wave modes. The equipment is portable, usable in the field for in situ testing, is truly non-destructive and has been successful for testing materials other than concrete. Corrosion of embedded reinforcing steel is the dominant cause of deterioration of reinforced concrete structures in marine environments. The corrosion of steel reinforcement is initiated by chloride ion attack upon the passive layer of steel. Corrosion can be caused by carbonation 3

or by chloride ions penetrating into concrete. Concrete provides physical and chemical protection to the reinforcing steel from penetrating chlorides which may cause steel depassivation leading to increased risk of steel corrosion. The corrosion damage in the concrete infrastructures is often observed by rust-staining of the surface, with cracking and spalling of the concrete cover from the formation of expansive corrosion products. The time for structural repair/ replacement due to corrosion is usually controlled by serviceability limit states. Often, the initiation of corrosion has been treated as a serviceability failure. It is based on the assumption that the initiation period i.e., the time from the initial exposure of a RC structure to an aggressive environment until corrosion initiation is much longer than the time from corrosion initiation to cracking. Timely maintenance and repairs have the potential to prolong the service life of corrosion affected RC structures. In the present work, the structures are analyzed in STAAD Pro V8i for knowing the critical column and beams, later NDT tests are conducted on the critical members. After incorporating NDT data in STAAD Pro we can observe whether members of the structure are critical or not. There by, providing necessary remedial measures for the members which are critical.

4

CHAPTER - 2 LITERATURE REVIEW 2.1 INTRODUCTION This chapter deals with the review of previous work in the area of Condition assessment and Non-Destructive testing of concrete buildings. Role of non-destructive testing in the field of condition assessment in the earlier studies are presented. Application of Rebound Hammer, Ultrasonic Pulse Velocity and Corrosion tests for condition monitoring is also discussed. 2.2 CONDITION ASSESSMENT OF STRUCTURES-GENERAL: In this part of literature review the previous works related to condition assessment in general are presented.  Taekeun Oh, P.E et al., (2013) [1] studied on Comparison of NDT Methods for Assessment of a Concrete Bridge Deck They studied on application of three different nondestructive tests (NDTs)—air-coupled impact echo (IE), infrared (IR) thermography and sounding (chain drag), where an actual inservice concrete bridge deck is tested. Two different contactless IE test equipment sets are deployed as part of an effort to develop new rapid measurement methods. For verification of the location of 5

near-surface delamination damage, eight drilled core samples were extracted from the test area. The results obtained from each of the individual NDT methods show reasonably good agreement with the drilled cores in terms of locating near-surface delamination. Finally, the NDT methods are compared across general performance criteria, considering accuracy, testing practicality, and costs. And they concluded the two types of air-coupled IE equipment that were deployed show good performance for bridge decks under active ambient traffic noise and vibration conditions. All of the evaluated NDT methods are comparable, and the chaindrag method is not more accurate and reliable for detection of shallow delamination in the deck.  S. Bhaskar et al., (2006) [2] carried out Condition Assessment of 30 Years Old Overhead RCC Reservoir. They discuss a case study, the assessment of 30 years old overhead Reinforced Cement Concrete (RCC) reservoir by NDT and PDT methods. A rational and systematic approach for the interpretation of test results based on NDT and PDT is presented for arriving at an economical repair procedure and rehabilitation measures. A detailed systematic methodology in conducting the condition assessment of overhead RCC reservoir is presented. This includes visual observation and documentation, ultrasonic testing 6

on columns and brace beams for assessing the integrity of concrete, core sampling and testing for estimating the compressive strength and water absorption. Half-cell potential measurements were also carried out for assessing the presence of corrosion activity. And they concluded by the test results which are been interpreted, and finally assessed the overall concrete quality and integrity. Based on the test results, it was found that the distressing of the supporting structure was mainly due to voids, honeycombing and carbonation of concrete. And necessary repair measures are suggested to improve the strength and performance of the structure in a qualitative manner.  Jochen H. Kurz et al., (2013)

[3]

studied on Condition Assessment

of Civil Infrastructure in Europe: Recent Developments and What Might Be Ahead. They discussed the combinations of non-destructive testing (NDT) methods and modular control and data acquisition approaches. a combination of various NDT methods is often required, which allow reliable results for material characterization, flaw detection, and the determination of component-specific geometry parameters. Two recently developed measurement devices (OSSCAR and BetoScan) will be described. Regarding steel constructions, an example from the field of pipeline inspection 7

is shown where the combination of NDT with fracture mechanical assessment is directly possible. He concludes with an outlook on future trends for degradation monitoring and If civil engineering structures have to last longer, then this can only happen economically when damage initiation is observed at a stage where restoration is still economically viable. This will require enhanced inspection.  Jochen H. KURZ et al., (2012) [4] carried out Condition assessment of reinforced concrete structures using automated multi-sensor systems They studied a combination of different non-destructive test methods is often a necessity to receive reliable results for material characterization, flaw detection and the determination of component specific geometry parameters. Therefore, a multi-sensor measurement approach is necessary with a high degree of automation. And they concluded the ndt technique for the capability of the BetoScan system is that all measurements can take place at the same time and with a persistent accuracy. Using ultrasound, radar, and eddy current for concrete coverage determination detailed information about the inner structure in different depth layers is gained. Multi-sensor NDT data is an important part for sustainable infrastructure assessments. A 8

sustainable maintenance can only be planned if a comprehensive data base is provided.  Waleed F. Tawhed et al., (2003)

[5]

presented work on Damage

Assessment of Concrete Bridge Decks using Impact-Echo Method. They both studied on concrete bridge decks using ImpactEcho Method by removing the bridge decks. While the concrete decks were in service, they were retrofitted with fiber-reinforced polymer composite materials to repair the extensive damage suffered during their service lives. In this study, two slabs were non-destructively evaluated in the laboratory using the impact-echo method after the removal of the reinforcement layer. Impact-echo tests were performed concurrently with fullscale static and dynamic load tests. Conclusions they drawn from the experiments conducted are the first slab was statically loaded to failure, and the second was tested dynamically with cyclic loading. Results from tests on the statically loaded slab detected a significant reduction in propagation wave velocity after failure, indicating a reduction in the slab stiffness. Impact-echo tests on the dynamically loaded slab quantified the degradation of the slab during dynamic testing. Significant damage, such as cracking, was detected earlier than visually observed and before the slab reached service failure.

9

 Ufuk Dilek et al., (2007)

[6]

studied on Comparison of Pulse

Velocity and Impact-Echo Findings to Properties of Thin Disks from a Fire Damaged Slab. They discusses and compares results of in situ pulse velocity and impact-echo testing with dynamic elastic modulus and air permeability index test results of 25 mm _1 in._ thick disks sawed from concrete cores removed from selected areas of the damaged slab. Both the NDE techniques and the laboratory testing of thin disks identified the presence of damage as a result of the fire and they observed that Compressive strength results were consistent with the results of other tests but largely inconclusive by themselves. Impact-echo testing was able to identify the presence of a severely deteriorated concrete layer but could not identify the extent or depth of damage or clearly identify less damaged areas. The findings highlighted a shortcoming of using conventional strength testing alone on investigations involving relatively thin layers of damage and pointed out several key limitations in the use and interpretation of non-destructive evaluation and associated analysis in a field assessment project. And they concluded as The presence of damage was detected in several areas of the slab with non-destructive evaluation techniques including pulse velocity and impact echo, however, significant limitations were exhibited which 10

can arise when damage is limited to layers of slight damage or layers which have not separated. Identification of slightly damaged areas using pulse velocity techniques was improved compared to impact echo but was also difficult and was complicated by uncertainty in the measurements associated with the degrees of freedom and statistical significance.  M. Uchida et al., (20011)

[7]

examined Damage of Reinforced

Concrete qualified by AE They experimentally examined the feasibility of the damage qualification is by using reinforced concrete beams which are damaged under incremental-cyclic loading.

It is found that the

damages qualified by the two ratios are in good agreement with actual damages of the beams. This suggests that the damages of such reinforced concrete structures in service as bridges, docks and buildings are quantitatively assessed, by simply applying cyclic loading and monitoring AE activity. And they concluded that the criterion proposed is applicable to assess the damage of reinforced concrete bridges and associated structures.  D. Breysse et al., (2008) [8] examined How to combine several nondestructive techniques for a better assessment of concrete structures They studied on combination of several techniques can offer precious help to assess the structural state of existing reinforced 11

concrete structures. They intend to show what kind of improvement can be expected from the combination of techniques. Examples are taken from series of on-site case studies and laboratory experiments. They focus on the assessment of water content and concrete quality.

 Sarah

L. Gassman et al., (2004)

[9]

studied on Nondestructive

Assessment of Damage in Concrete Bridge Decks. They performed impact-echo tests to non-destructively assess the initial condition and the distribution of damage throughout the slab by analyzing the variation in propagation wave velocity. They observed that after the in-service condition was assessed, the slab was subjected to a full-scale static load test in the laboratory and impact-echo tests were again performed, this time to evaluate the initiation and progression of damage (stiffness loss and crack development) within the slab. After structural failure of the slab, a reduction in propagation wave velocity up to 6% was observed correlating to a reduction in slab stiffness. Cracks were detected within the concrete slabs that were not visible from the surface. Areas with pre-Existing damage experienced more crack growth when subjected to the load test than those that were initially intact. Locations exhibiting stiffness loss, crack propagation, and localized damage can be differentiated such that the method can be 12

used to make decisions between rehabilitating and replacing concrete bridge decks depending upon the severity of damage.  Andy CC Tan et al., (2004)

[10]

presented Structural health

monitoring of bridges using acoustic emission technology They describes the current technologies used in bridge structures condition monitoring with its prime focus in the application of acoustic emission (AE) technology in the monitoring of bridge structures and its challenges. They concluded as Acoustic emission technology has proven to be a suitable method for this purpose and possess several distinct advantages over other monitoring methods. AE as a viable technique for testing steel, concrete and other materials commonly used in bridge structures. Although the use of AE as health monitoring tool for bridges is growing rapidly, limitations still exist. Presence of noises as one of the main problems, so denoising signals can be identified as a major challenge. Signal conditioning of AE data obtained from bridge structure monitoring, using methods such as Wavelets and Hilbert Huang, can be identified as the future direction of work.

13

2.3

ROLE

OF

NON-DESTRUCTIVE

TECHNIQUES

IN

CONDITION ASSESSMENT: The works, which focus on the role of non-destructive techniques in condition assessment done by various authors in recent and past, are listed in this part of literature review.  H. Wiggenhauser et al., (2009)[11] carried out Advanced NDT methods for the assessment of concrete structures He studied the development and application of NDT methods for concrete structures requires more than just using offthe-shelf testing equipment. Existing test methods must be improved for more reliable use. Using an array of methods and combining their results, preferably through data-fusion algorithms has a lot of potential. The focus of the research and developments efforts at the NDT-CE division at BAM has been on methods used to evaluate the geometrical properties of structure such as thickness, location of components as well as detection of the presence of voids, delaminations, ungrouted tendon ducts or cracks. Validation of his project by (GUM) (Guide to the Expression of Uncertainty in Measurement 1995) provides a good methodology that can be applied in the NDT-CE field. According to the GUM the uncertainty of thickness measurement of 70 to 120 cm thickness and having areas of different reinforcement ratio was 14

measured. The testing was performed with an automated testing device using dry point contact sensors. The measured data was first assessed as raw data and later assessed after improving it by creating the envelope of the transit time curve. The effect of improved data analysis for different reinforcements is shown in the below figure.

 Matteo Colombo et al., (2007) [12] examined New NDT techniques for the assessment of fire-damaged concrete structures They conducted a simplified interpretation technique for the indirect Ultrasonic Pulse Velocity (UPV) method, an affordable approach to concrete colorimetry and the real-time monitoring of the drilling resistance. In this paper, the pros and cons of the proposed techniques are pointed out, as revealed by laboratory 15

tests. The actual in situ viability of each method is then discussed, after the investigations conducted on two full-scale structures. And they concluded the proposed simplified approach to colorimetry proved to be a powerful tool for evaluating the well-known color changes of heated concrete without the need for an expert’s judgment. Compared to a common colorimeter, the considerable amount of data available in a single digital image (many thousands of pixels) allows to separately analyze the cement mortar and the aggregate and to outline some statistical trends ascribable to the inherent heterogeneity of the material.  Kevin L. Rens et al., (1997)

[13]

presented Review of Non-

destructive Evaluation Techniques of Civil Infrastructure They studied a detailed literature review to identify the most widely used NOE techniques applied to civil engineering structures. In addition, a short questionnaire was developed and sent to state highway organizations. The literature suggests that acoustic emission testing is widely used while the questionnaire revealed that ultrasonic testing is most popular among state highway agencies. And their investigation involved a survey of various transportation agencies of NDE applications in the civil engineering field and AE testing is the most widely used state-of-

16

the-art technique for monitoring conditions of bridges and other large or complicated structures.  Mahdi Shariati et al., (2011)[14] studied on Assessing the strength of reinforced concrete structures through Ultrasonic Pulse Velocity and Schmidt Rebound Hammer tests They conducted experimental studies on main members of an existing structure including column, beam and slab using Ultrasonic Pulse Velocity and Schmidt Rebound Hammer as Non Destructive Tests (NDT) to establish a correlation between the compressive strengths of compression tests and NDT values, which were used to determine the concrete quality by applying regression analysis models between compressive strength of in-situ concrete on existing building and tests values. The relationship between compression strength of concrete collected from crashing test records and estimated results from NDT’s records using regression analysis was compared together to evaluate their prediction for concrete strength. And they concluded that the rebound number method was more efficient in predicting the strength of concrete under certain conditions. A combined method for the above two tests, reveals an improvement in the concrete strength estimation and the latter shows better improvement. Applying combined

17

methods produces more reliable results that are closer to the true values.  Akash Jain et al., (2013)[15] examined Combined Use of NonDestructive Tests for Assessment of Strength of Concrete in Structure They conducted experimental investigation on the effects of concrete materials-, mix- and workmanship-related variables, on the Rebound Number and Ultrasonic Pulse Velocity of concrete, are presented and their investigations aimed at developing a method of combined use of both the non-destructive tests for assessment of strength of concrete with greater accuracy. They demonstrate the limitation of using ultrasonic pulse velocity tests for estimating compressive strength of concrete. IS: 13311 advocates combined use of Ultrasonic pulse velocity (UPV) and Rebound Hammer tests for assessment of concrete strength in structures with greater reliability. However, the approach is qualitative. Adopting such an approach in a quantitative manner, multiple regressions of both Rebound Numbers and Ultrasonic Pulse Velocity on compressive strength of concrete led to a series of graphs for better assessment of strength. From the experimental study they derives the readings of UPV increases with age but the change is very small, reason behind it is that the density of the 18

concrete remains same with the increase in age, so UPV alone cannot be used to find out the compressive strength, the readings of rebound number also increases with age, this is because hardness of concrete increases with age. There is a decrease in the UPV readings when the flaws are added in the same mix, this is because when flaws are present in the mix then the ultrasonic pulse takes more time to travel the cube length hence decreasing the pulse velocity.  Antoni (2006)

[16]

carried out Development of Non-Destructive

Monitoring System for Chloride Penetration into Reinforced Concrete Structures. He studied on embedded probe system to detect chloride penetration into concrete which was developed in Japan. This probe consists of a cementitious material body and some number of wires as sensors, which are set in the shallow ditches around the probe body. The system detect the chloride penetration by monitoring the initiation time of wire corrosion, it also has the advantages of continuous monitoring and early warning on the onset of corrosion in the reinforcement. However, the probe had not yet had high sensitivity for detecting critical chloride content in concrete. Therefore to increase its sensitivity, four types of improvements, namely partial coating of the wires, waterproofing 19

on the probe body, filling the ditches with porous material and supplying small current on the wires were evaluated in his study. From the experimental result, he observed that supplying small current and partial coating of the wires could improve the sensitivity of the probe significantly, while waterproofing treatment on the probe body and filling the ditches did not have significant contribution.  Nicholas J. Carino et al., (1999)[17] carried out Non Destructive Techniques To Investigate Corrosion Status in Concrete Structures. They provided an overview of the corrosion investigation and provide repair specialist with basic information to allow effective

communication

with

the

corrosion

engineer.

Electromagnetic principle methods such as Half-cell potential method, the concrete resistivity test, and the linear polarization method are implemented in corrosion of steel in concrete. They concluded the principles of operation and inherent limitations of these methods. 2.4 CASE STUDIES RELATED TO CONDITION ASSESSMENT: Case studies relevant to the area of condition assessment done by various authors are listed in this part of literature review.

20

 Dr.V.Karthikeyan et al., (2013)

[18]

carried out A Study on RC

Columns and Slabs and Restoration of RC Columns of an Existing Multi-storeyed Building. They analyses the deficiencies in the construction of a multistoreyed RC framed building and assessed the real strength gained by the RC elements like columns, beams and slabs. Nondestructive tests were conducted and representative cylindrical core samples were taken out from the RC elements and analyzed in the standard laboratory. The results compared with IS 456:2000 reveals that the major parts of slabs in ground, first and second floor from the RC elements in the structure are satisfying the minimum concrete grade M20. However, some of the columns in ground, first and second floor are not satisfying the minimum concrete grade M20 that required as per IS 456:2000. They recommended that the structure requires immediate attention of strengthening the existing RC columns by adopting suitable rehabilitation techniques.  Dr. Akil Ahmed et al., (2013)

[19]

carried out Investigation of

Structural Failure of a RC Hotel under Construction They conducted NDT experiment on distressed columns and available cubes, physo-chemical tests for concrete and water, geotechnical investigation for soil were carried out to find out the reasons. In addition, the structural analysis was performed with the 21

help of STAAD PRO software for checking the design of constructed components of the building. Based on the analysis, it can be concluded that the main causes of the crack/damage were varying lateral earth pressure around the retaining wall, ground water pressure beneath the mat, and poor grade of concrete for construction. They concluded the causes of the crack/damage were varying lateral earth pressure, ground water pressure, and poor grade of concrete. The lateral reinforcement was not adequate in the columns. The structural design needs to be revised for a high rise structure/building. The damaged components have to be repaired/retrofitted/re-casted depending upon the degree of damage.  N. Dawood et al., (2013) [20] examined Nondestructive Assessment of a Jetty Bridge Structure Using Impact-Echo and Shear-Wave Techniques They done nondestructive strategies included crack-opening measurements using the concrete crack microscope, impact-echo test to measure the depth of the different cracks, and shearwave testing to detect various defects inside the concrete girders and prestressed ducts. The combination of the two non-destructive techniques (impact-echo and shear wave) enabled inspectors to visualize the extension of the cracks in three dimensions and to 22

specify the location of various regions of deterioration within the structural members with a satisfactory level of efficiency. Repair recommendations for the damaged regions were made to maintain safe and economic operation of the Jetty’s facilities. And they concluded as NDT results played a crucial role in choosing more effective and economical repair strategies for the girders. Results from the NDT techniques enabled assessment of damage level, allowing formulation of recommendations for the repair of the defective structural elements. 2.5 REBOUND HAMMER: Applications of Rebound Hammer test in the area of condition assessment are discussed in this part of literature review.  Antonio Brencich et al., (2013)

[21]

examined Calibration and

Reliability of the Rebound (Schmidt) Hammer Test. They discussed an extensive research, and application, to identify the parameters affecting rebound hammer results and to estimate its reliability, the original Schmidt curve is still provided by the producers along with the hammer and is used in Structural Engineering Applications to a large number of cubes provided by the Laboratory for Building Materials of the University of Genoa, Italy, showing that several phenomena strongly affect the test: moisture content, maturity, stress state among the others. Strength 23

estimates may differ as much as 70% if these parameters are not taken into account. Besides, several in situ investigations on existing buildings were affected by a large dispersion of data, so that we should conclude that the Rebound Hammer is unable of giving a reliable estimate of the concrete strength. This is probably due to the very limited area of the material on which the test is performed that allows also small local in homogeneity to affect quite strongly the test. Therefore, the rebound hammer seems to be useless in the estimation of concrete compressive strength, being only a rough tool for estimating material homogeneity inside a specific concrete type. 2.6 ULTRASONIC PULSE VELOCITY: Applications of Ultrasonic Pulse Velocity test in the area of condition assessment are discussed in this part of literature review.  N. V. Mahure et al., (2011)

[22]

presented Correlation between

Pulse Velocity and Compressive Strength of Concrete. They monitor the post construction performance of concrete investigations were carried out for developing the relationship between the ultrasonic pulse velocity (UPV) and the compressive strength of concrete. The UPV measurement and compressive strength tests were carried out on concrete cubes at the age of 7 and 24

28 days. The relationship developed in the study is case specific as the UPV and the compressive strength of concrete depends on various factors such as cement-mortar paste content, water-cement ratio and coarse aggregate content and its quality, admixtures. Hardened concrete (at an age of 28 days) was selected as the subject for analysis in their study. They found a clear relationship curve can be drawn for different concrete mixes/grades to describe the UPV and compressive strength of hardened concrete used in concrete structures of Tehri Hydro Electric Project, Uttarakhand. The estimated correlation curves are verified to be suitable for prediction of hardened concrete strength with a measured UPV value in the health monitoring of structures under reference during its service period.  Lawson et al., (2011)

[23]

examined Non-Destructive Evaluation of

Concrete using Ultrasonic Pulse Velocity. They investigates the relationship between Ultrasonic Pulse Velocity (UPV) and the compressive strength of concrete. The specimens used in the studies were made of concrete with a paste content of 18% and the constituents of the specimens varied in different water-cement ratios (w/c). The UPV measurement and compressive strength tests were carried out at the concrete age of 2, 7, 15 and 28 days. They observed that the UPV and the 25

compressive strength of concrete increase with age, but the growth rate varies with mixture proportion. A relationship curve is drawn between UPV and compressive strength for concrete having different w/c from 0.35 to 0.7.  Ufuk Dilek, (2007)

[24]

conducted experiment on Ultrasonic Pulse

Velocity in Non-destructive Evaluation of Low Quality Damaged Concrete and Masonry Construction. He studied assessment of damage to concrete structures in service. The case study included in the paper involves exposure to elevated temperatures during a fire at a precast, double tee concrete parking structure. Nondestructive evaluation NDE testing findings were validated by subsequent laboratory testing or selective demolition to confirm NDE findings. He done some Case studies include detection of zones of high air content and low strength concrete in a cast-in-place, post tensioned structure and detection of voids and honeycombs in poorly consolidated cast-in-place beams. The third case study pertinent to construction involves detection of poorly consolidated collar joints in a masonry rehabilitation project. He concluded how quality of in-place concrete and masonry construction can be ascertained using pulse velocity technique. The specific applications discussed were detection of limits of low strength or high air content concrete, 26

detection of poorly consolidated sections of cast-in-place concrete members and detection of poorly consolidated collar joints in brick masonry. In addition to quality assessment during construction, the effects of exposure to extreme temperatures on concrete during service and the associated changes in pulse velocity were discussed. 2.7 CORROSION: Study of corrosion related problems in the area of condition assessment are discussed in this part of literature review.  Ha-Won Song et al., (2007)[25] carried out Corrosion Monitoring of Reinforced Concrete Structures - A Review They studied that failures in the structures do still occur as a result of premature reinforcement corrosion. The maintenance and repair of bridges and buildings for their safety requires effective inspection

and

monitoring

techniques

for

assessing

the

reinforcement corrosion. Better techniques for assessing the condition of the structure need to be able to identify any possible durability problems within structures before they become serious. They review all the electrochemical and nondestructive techniques from the point of view of corrosion assessment and their

27

applications to bridges, buildings and other civil engineering structures.  Jin-Keun Kim et al., (2009) [26] studied on Effect of carbonation on the rebound number and compressive strength of concrete. They conducted experimental research to clarify the influence of carbonation on the rebound number and the strength evolution of concrete for three strength levels. Their results reveal that the strength level dependent influence of carbonation is a source of errors in the existing equations for the strength reduction coefficient; these equations are used to compensate for the influence of surface carbonation in the rebound number method. A new equation for the strength reduction coefficient that can consider the influence of strength level was developed based on field test data extracted from technical reports of the Korea Research Institute of Standards and Science and of four universities. Over a wide range of strength levels, their equation shows good agreement with strength reduction coefficients established experimentally.  Nicholas J.Carino (1999)

[27]

carried out Non Destructive

Techniques to Investigate Corrosion Status in Concrete Structures. He studied on assessment of corrosion conditions and main objective is to provide the repair specialist with basic information 28

to allow effective communication with the corrosion engineer. He implemented some electrochemical principles like half-cell potential method, the concrete resistivity test, and the linear polarization method in the corrosion of steel in concrete, the principles of operation and the inherent imitations of these methods are emphasized. 2.8 CARBONATION: In this part of literature review Carbonation effect on the structure and their problems are discussed.  Mohammed Tarek Uddin (2011)

[28]

examined Carbonation

Coefficient of Concrete in Dhaka City. They investigated on seventy real structures (buildings) from Dhaka city for determination of carbonation rate of concrete structures. For evaluation of carbonation depth in structural elements of were selected for investigation and age of the structures was varied from 1 year to 79 years. Based on the relationship between carbonation depth and age of the structures, carbonation coefficient was determined for different structural elements. They observed more carbonation depth was found in outdoor exposure condition compared to the indoor exposure condition. More carbonation rate was also found for slab compared to beams and columns. 29

CHAPTER - 3 METHODOLOGY In the present study, two different structures are considered. Structure slightly away from the coastal environment and other structure exposed to aggressive marine environment respectively to study the deterioration effect. 1. Methodology includes identifying the building / structure exposed to aggressive marine environment. 2. Identifying various Non-Destructive Test Methods to be carried out on the structure/building. 3. Identification of the possible causes leading to the damage of the structure. 4. Assessing the amount of damage caused and to determine its suitability for future use. 5. Analysis and Design of structures are performed in STAAD Pro V8i. a. For Gravity Loads b. For Lateral Loads 6. Drawings and Detailing are done in AUTOCAD.

30

Following are various NDT Tests conducted to assess the structure 3.1 Rebound Hammer Test: This test is conducted using N type Schmidt hammers for concrete as per IS 13311 part II. The interpretation of rebound hammer results is carried out based on the guide lines given in BS: 188-6089 since IS 13311 part II remains silent in this aspect.

Fig 3.1: Rebound Hammer

Apparatus: Rebound Hammer- a spring loaded steel hammer which will release when strikes a steel plunger to concrete surface Test Anvil- a 6 inch diameter × 6 inch long high carbon steel cylinder hardened to Rockwell 65-67C Procedure: 31

1. Before commencement of the test, the rebound hammer has been tested against the test anvil, to get reliable results, for which the manufacturer of the rebound hammer indicates the range of readings on the anvil suitable for different types of rebound hammer. 2. Apply light pressure on the plunger. It will be released from the locked position and allow it to extend to the ready position to the test. 3. All the points of concrete structure selected for testing are to be in dry condition. 4. Press the plunger against the surface of the concrete keeping the instrument perpendicular to the test surface. 5. Apply a gradual increase in pressure until the hammer impacts. After impact, record the rebound number to the nearest whole number. 6. Average of about 6 readings is taken at each location. 7. The compressive strength is then determined by taking average of rebound reading. 8. Compressive strength of concrete can be determined from the relationship between the rebound number and the strength given by the compressive strength curves.

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Guidelines for Qualitative Interpretation of Rebound Hammer Test Table 3.1: Rebound Number v/s Quality of concrete surface Average Rebound Number

Quality Of Concrete Surface

> 40

Very good hard layer

30 to 40

Good layer

20 to 30

Fair

< 20

Poor concrete

0

Delaminated

Influence of Test Conditions The rebound numbers are influenced by a various factors like types of cement and aggregate, surface condition and moisture content, age of concrete and extent of carbonation of concrete. Influence of Type of Cement Concrete made with high alumina cement can give strengths 100 percent higher than that of ordinary Portland cement. Concrete made with super sulphated cement can give 50 percent lower strength than that of ordinary Portland cement. Influence of Type of Aggregate Different types of aggregate used in concrete give different correlations between compressive strength and rebound numbers. Normal aggregates

33

such as gravel and crushed rock aggregates give similar correlations, but concrete made with lightweight aggregates require special calibration. Influence of Surface Condition and Moisture Content of Concrete The rebound hammer method is suitable only for close texture concrete. Open texture concrete such as masonry blocks, honeycombed concrete or no-fines concrete is unsuitable for this test. All correlations assume full compaction, as the strength of partially compacted concrete bears no unique relationship to the rebound numbers. Toweled and floated surfaces are harder than moulded surfaces, and tend to overestimate the strength of concrete. A wet surface will give rise to underestimation of the strength of concrete calibrated under dry conditions. In structural concrete, this can be about 20 percent lower than in an equivalent dry concrete. Influence of Curing and Age of Concrete The relationship between hardness and strength varies as a function of time. Variations in initial rate of hardening, subsequent curing and conditions of exposure also influence the relationship. Separate calibration curves are required for different curing regimes but the effect of age can generally be ignored for concrete between 3 days and 3 months old. Influence of Carbonation of Concrete Surface The influence of carbonation of concrete surface on the rebound number is very significant. Carbonated concrete gives an overestimate of strength 34

which in extreme cases can be up to 50 percent. It is possible to establish correction factors by removing the carbonated layer and testing the concrete with the rebound hammer on the un-carbonated concrete. Interpretation of Results The rebound hammer method provides a convenient and rapid indication of the compressive strength of concrete by means of establishing a suitable correlation between the rebound index and the compressive strength of concrete. In general, the rebound number increases as the strength increases but, it is also affected by a number of parameters as already mentioned. It is also pointed out that rebound indices are indicative of compressive strength of concrete to a limited depth from the surface. If the concrete in a particular member has internal micro cracking, flaws or heterogeneity across the cross-section, rebound hammer indices will not indicate the same. As such, the estimation of strength of concrete by rebound hammer method cannot be held to be very accurate and probable accuracy of prediction of concrete strength in a structure is ± 25 percent. The accuracy of results can be increased by establishing relationship between rebound number and compressive strength through testing on structural core samples.

35

3.2 Ultra Sonic Pulse Velocity: UPV testing is a wave propagation test. It transmits electro acoustic pulses through the concrete medium from one side, receiving the signal from other side and measuring the transit time. The path length between the transmitting and receiving point is measured and the pulses velocity is calculated by dividing the path length by the transit time. Pulse velocity is influenced by the properties of concrete which determines its elastic stiffness and mechanical strength. There is a reduction in the pulse velocity if the concrete under the test has low compaction, voids or damaged material. The pulse velocity increases or decreases as the concrete matures or deteriorates or changes with time. This method is considered to be a valuable and reliable method of examining the interior of concrete in a non-destructive way. The pulse velocity measurements may be used to establish  The homogeneity of the concrete  The presence of cracks, voids and other imperfections  Changes in the structure of the concrete which occur with time  Quality of one element of concrete in relation to another  The values of elastic modulii of concrete.

36

Fig 3.2: Ultrasonic Pulse Velocity

Apparatus: 1. Electric pulse generator. 2. Transducer- one pair 3. Amplifier 4. Electronic timing device. Procedure: 1. Preparing for use: before switching on the ‘V’ meter the transducers should be connected to the sockets marked ‘TRAN’ and ‘REC’. 2. The ‘v’ meter may be operated with either a. The internal battery b. The external battery or c. The AC line 3. Set reference: A reference point is provided to check the instrument to zero such that the pulse time for the bar is engraved on it. Apply 37

a smear of grease to the transducers faces before placing it on the opposite ends of the bar. Adjust the ‘SET REF’ control until the reference bar transit time is obtained on the instrument read out. 4. Range selection: for maximum accuracy it is recommended that the 0.1 microsecond range be selected for path length up to 400mm 5. Pulse velocity is determined for the most suitable test points on concrete surface. Make careful measurements of the path length ‘L’. Apply couplant to the surfaces of the transducers while a reading is being taken, as this can generate noise signals and errors in measurement. Continue holding transducers onto the surface of the display readings should be taken when the unit digit hunts between two values. Pulse velocity = Path length/Travel time

38

General Guidelines for Concrete Quality Based On UPV Table 3.2: UPV velocity v/s concrete quality Velocity(km/sec)

Concrete Quality

>4.0

Very good to excellent Good to very good, slight porosity may

3.5-4.0 exist Satisfactory but loss of integrity is 3.0-3.5 suspected