Bangladesh Steel Re-Rolling Mills Limited … · BNBC, and AASHTO permit ... CHAPTER 2 Literature Review ... 3.6.2 Flexure Test

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 BSRM and BUET, 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.

i

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 Specimens .......................................................................................................................... 23

3.3.1 Pull Out Test Specimens .................................................................................................... 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 specimens...................................................................................................... 31

3.5.1 Pull out specimens ............................................................................................................. 31

3.5.2 Flexure Specimens ............................................................................................................. 31

3.6 Instrumentation .......................................................................................................................... 32

3.6.1 Pull out Test ....................................................................................................................... 32

3.6.2 Flexure Test ....................................................................................................................... 33

3.7 Testing Procedure ...................................................................................................................... 33

3.7.1 Pull out Test ....................................................................................................................... 33

3.7.2 Flexure Test ....................................................................................................................... 34

ii

CHAPTER 4 Results of Experiments ...................................................................................................... 35

4.1 Results of Pull-out Test .............................................................................................................. 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

iii

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. – 4.3: 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)




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)




Fig. – 4.11: Failure Modes of ES2R1 and US2R1 (3.5 Ksi, 12mm 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)


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)


Fig. – 4.18: Comparison of loads-slip response of pull-out specimen (2.5 ksi, Brick chips, 16 mm bar)




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)


Fig. – 4.27: Comparison of deflection time response of beams (3 ksi, stone chips, 3-12 mm bars)


Fig. – 4.28: Comparison of load-crack width response of beams (3 ksi, stone chips, 3-12 mm bars)


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

iv

Fig. – 4.30: Comparison of loads-deflection response of beams (3 ksi, brick chips, 3-12 mm bars)


Fig. – 4.31: Comparison of deflection time response of beams (3 ksi, brick chips, 3-12 mm bars)


Fig. – 4.32: Comparison of load-crack width response of beams (3 ksi, brick chips, 3-12 mm bars)


Fig. – 4.33: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, brick chips, 3-12 mm


Fig. – 4.34: Comparison of loads-deflection response of beams (3.5 ksi, stone chips, 3-12 mm bars)


Fig. – 4.35: Comparison of deflection time response of beams (3.5 ksi, stone chips, 3-12 mm bars)


Fig. – 4.36: Comparison of load-crack width response of beams (3.5 ksi, stone chips, 3-12 mm bars)


Fig. – 4.37: Comparison of Crack Pattern and Deflected Shape for Beams (3.5 ksi, stone chips, 3-12 mm


Fig. – 4.38: Comparison of loads-deflection response of beam (3 ksi, stone chips, 2-16 mm Spliced bars)


Fig. – 4.39: Comparison of deflection time response of beams (3 ksi, stone chips, 2-16 mm Spliced bars)


Fig. – 4.40: Comparison of load-crack width response of beams (3 ksi, stone chips 2-16 mm Spliced bars)


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)


Fig. – 4.43: Comparison of deflection time response of beams (3 ksi, brick chips, 2-16 mm Spliced bars)


Fig. – 4.44: Comparison of load-crack width response of beams (3 ksi, brick chips, 2-16 mm Spliced


Fig. – 4.45: Comparison of Crack Pattern and Deflected Shape for Beams (3 ksi, brick chips, , 2-16 mm














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



v







Fig. – 4.57: Comparison of loads-deflection response of beam (3.5 ksi, stone chips, 2-16 mm Spliced


Fig. – 4.58: Comparison of deflection time response of beams (3.5 ksi, stone chips, 2-16 mm Spliced


Fig. – 4.59: Comparison of load-crack width response of beams (3.5 ksi, stone chips 2-16 mm Spliced




Fig. – 4.61: Comparison of loads-deflection response of beams (2.5 ksi, brick chips, 3-12 mm bars)


Fig. – 4.62: Comparison of deflection time response of beams (2.5 ksi, brick chips, 3-12 mm bars)


Fig. – 4.63: Comparison of load-crack width response of beams (2.5 ksi, brick chips, 3-12 mm bars)


Fig.– 4.64: Comparison of Crack Pattern and Deflected Shape for Beams (2.5 ksi, brick chips, 3-12 mm


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 Pull-

out…………………………………………………………………………………………………………38


out…………………………………………………………………………………………………………41


out .............................................................................................................................................................. 44


out…………………………………………………………………………………………………………46


out…………………………………………………………………………………………………………47


out…………………………………………………………………………………………………………50

vi


out…………………………………………………………………………………………………………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)


Table – 4.10: Comparison of Crack Width at Design Load for Beams (3 ksi, stone chips, 3-12 mm bars)


Table – 4.11: Comparison of Number of Total Cracks for Beams (3 ksi, stone chips, 3-12 mm bars)


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)


Table – 4.14: Comparison of Crack Width at Design Load for Beams (3 ksi, brick chips, 3-12 mm bars)


Table – 4.15: Comparison of Number of Total Cracks for Beams (3 ksi, brick chips, 3-12 mm bars)



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)


Table – 4.18: Comparison of Crack Width at Design Load for Beams (3.5 ksi, stone chips, 3-12 mm bars)


Table – 4.19: Comparison of Number of Total Cracks for Beams (3.5 ksi, stone chips, 3-12 mm bars)


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


stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB ............................................................ 68


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)


Table – 4.24: Comparison of Crack Width at Design Load for Beams (3 ksi, stone chips, 2-16 mm bars)


Table – 4.25: Comparison of Number of Total Cracks for Beams (3 ksi, stone chips, 2-16 mm bars)



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)


Table – 4.28: Comparison of Crack Width at Design Load for Beams (3 ksi, brick chips, 2-16 mm bars)


Table – 4.29: Comparison of Number of Total Cracks for Beams (3 ksi, brick chips, 2-16 mm bars)



brick chips, 2-16 mm bars) reinforced with ECR and BB ......................................................................... 75

vii

Table – 4.31: Comparison of Deflections at Design Load for Beams (3.5 ksi, stone chips, 2-16 mm bars)


Table – 4.32: Comparison of Crack Width at Design Load for Beams (3.5 ksi, stone chips, 2-16 mm bars)


Table – 4.33: Comparison of Number of Total Cracks for Beams (3.5 ksi, stone chips, 2-16 mm bars)



ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB .................................................................. 78


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)


Table – 4.37: Comparison of Crack Width at Design Load for Beams (2.5 ksi, brick chips, 3-12 mm bars)


Table – 4.38: Comparison of Number of Total Cracks for Beams (2.5 ksi, brick chips, 3-12 mm bars)



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

1

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 life-

cycle 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 epoxy-

coated 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.

2

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.

3

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

e or e n or hydroxides e e 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.

4

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:

e e e

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:

e

The ferrous ion moving through concrete pore water would reach out to these cathodes to be electrically

neutral. Thus hydroxides are formed as follows:

e e (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.

5

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, de-

icing 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:

e Cl eCl

eCl e C

2.1.3 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 p value of more than 1 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.

6

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

7

enhanced by cracks because the ions penetrate the concrete cover from the walls of the crack as

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.

8

Stage 7: Buckling of bars and bulging of concrete

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.

9

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;

10

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]

11

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

($/yd2)

Life Cycle Cost

($/yd2)

Uncoated 189 444

Epoxy Coated 196 237

Stainless – Steel 319 319

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 corrosion-

resistant 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]

12

Once started, the corrosion rate of rebars in concrete is dependent on the following [35]

(i) The pH level of the surrounding concrete

(ii) The availability of oxygen and water,

(iii) Concentration of Fe2+

near rebar

(iv) 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

13

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 non-

metallic 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

14

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

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.

Testing of Performance

of rebar

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:

15

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.

16

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 two-

part 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 non-

conductive 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.

17

A pictorial description of extra care practiced for fabrication and placement is provided in Fig.-2.11.

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.

(a) (b)

(c) (d)

18

Table 2.2: Chronology of Changes Made to ASTM A775 [49]

Year 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 120

o

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

bars. 7-16 mil (Nos. 6-18)

7-12 for all bar sizes

2004 Clarified individual thickness measurements no

single measurement <80% of minimum or >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 powder-

coating 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

19

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].

20

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.

21

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.

22

b. Construct a “Bond Stress vs. Slip” diagram to better understand the slip behavior of epoxy-

coated 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.

23

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 bond-

slip 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 1 ”X1 ”X1 ” 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.

24

Table – 3.1: Test matrix for pull out test of ECR and black bar.

Specimen Name No. of Specimen (psi) Aggregate type Bar Type, Bar Dia, mm

ES1R1 3 3000 Stone Chips Epoxy coated 12


US1R1 3 3000 Stone Chips Uncoated 12


EB1R1 3 3000 Brick Chips Epoxy coated 12


UB1R1 3 3000 Brick Chips Uncoated 12














ES1R1_FLd 6 3000 Stone Chips Epoxy coated 12

US1R1_FLd 6 3000 Stone Chips Uncoated 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

25

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. Flexural cracking load

b. Crack pattern and crack width

c. Deflection under load

d. Ultimate flexural strength

e. 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 X section

(in*in)

(ksi)

Aggreg

ate type

Rebar Type Rebar

Size

(mm)

No. of

Sample

U_2.5_BC_12 6*9.5 2.5 BC Black Bar 12 3

U_3_BC_12 6*9.5 3 BC Black Bar 12 3

U_3_BC_16 6*9.5 3 BC Black Bar 16 2

U_3_SC_12 6*9.5 3 SC Black Bar 12 3

U_3_SC_16 6*9.5 3 SC Black Bar 16 2

U_3.5_SC_12 6*9.5 3.5 SC Black Bar 12 3

U_3.5_SC_16 6*9.5 3.5 SC Black Bar 16 2

U_3_BC-S_16 (splice) 6*9.5 3 BC Black Bar 16 1

U_3_SC-S_16 (splice) 6*9.5 3 SC Black Bar 16 1

U_3.5_SC-S_16 (splice) 6*9.5 3.5 SC Black Bar 16 1

E_2.5_BC_12 6*9.5 2.5 BC Epoxy Coated 12 3

E_3_BC_12 6*9.5 3 BC Epoxy Coated 12 3

E_3_BC_16 6*9.5 3 BC Epoxy Coated 16 2

26

Specimen Name X section

(in*in)

(ksi)

Aggreg

ate type

Rebar Type Rebar

Size

(mm)

No. of

Sample

E_3_SC_12 6*9.5 3 SC Epoxy Coated 12 3

E_3_SC_16 6*9.5 3 SC Epoxy Coated 16 2

E_3.5_SC_12 6*9.5 3.5 SC Epoxy Coated 12 3

E_3.5_SC_16 6*9.5 3.5 SC Epoxy Coated 16 2

E_3_BC-S_16 (splice) 6*9.5 3 BC Epoxy Coated 16 1

E_3_SC-S_16 (splice) 6*9.5 3 SC Epoxy Coated 16 1

E_3.5_SC_S_16 (splice) 6*9.5 3.5 SC Epoxy Coated 16 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.

27

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 Testing day Cylinder

Compressive Strength (psi)

Average Strength

(psi) Standard Deviation

I-SC

3847

4162 228.19 4381

4257

I-BC

3939

3933 22.81 3903

3958

II-SC

5644

5992 249.05 6213

6119

III-SC

6817

7053 221.83 7350

6992

IV-BC

3441

3655 161.97 3833

3690

I-SC-FLd

4330

4311 216.89 4294

4310

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 load-

deflection 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 Original Bar

diameter (mm)

Yield Load

(kN)

Ultimate Load

(kN)

Percent Elongation

(%)

12 mm Epoxy Coated 12.07 66.2 78.74 12

12 mm Uncoated 11.87 67.87 77.61 13.67

16 mm Epoxy Coated 16.11 117.6 138.78 13.67

16 mm Uncoated 15.9 113.99 135.61 16

28

Fig. – 3.7(a): Load-Deflection curve for 12mm Epoxy Coated bars

Fig. – 3.7(b): Load-Deflection curve for 12mm Uncoated bars

29

Fig. – 3.7(c): Load-Deflection curve for 16mm Epoxy Coated bars

Fig. – 3.7(d): Load-Deflection curve for 16mm Uncoated bars

30

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.

Table 3.5 : Compressive Strength of Concrete

Beam Type

Testing day Cylinder

Compressive Strength

(psi)

Average Strength

(psi) Standard Deviation

I-SC

3690

3727 29.81 3763

3728

I-BC

3555

3445 89.81 3335

3445

II-SC

5770

5720 40.82 5670

5720

III-SC-S

3650

3716 60.58 3700

3796

III-BC-S

3555

3445 89.81 3335

3445

IV-SC

3794

3864 64.60 3950

3849

IV-BC

5220

4767 350.79 4361

4809

V-SC

4633

4573 122.39 4402

4683

V-SC-S

5770

5730 43.2 5670

5750

VI-BC

3882

4001 261.70 3757

4364

3.4.2.2 Steel

The steel properties are discussed at section 3.4.1.2.

31

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.

32

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

33

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 Location Function

Deflectometer 1 At the unloaded end of specimen To observe unloaded slip

Deflectometer 2 At the loaded end of the bottom plate Measure total slip + strain

Deflectometer 3 At the loaded end of the main

reinforcement

Measure strain of the

reinforcement.

Two HD video cameras To focus and take accurate

readings from deflectometer.

3.6.2 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 At the middle of the beam Measure deflection

3.7 Testing Procedure

3.7.1 Pull out test

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.

34

Fig. – 3.14: Pull-out test frame with

specimen in the UTM

Fig. – 3.15: Two HD video cameras to record the data at

both loaded and unloaded end of the bars.

3.7.2 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.

35

Fig. – 3.16: Experimental test setup for flexure.

Fig. – 3.17: Crack Comparator.

36

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 Type of Rebar

I-SC 3 12 & 16 mm Stone Chips

3 Specimen of 12 mm BB

3 Specimen of 12 mm ECR



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 6 Specimen of 12 mm BB


Total = 72 Specimen

4.1.1 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.

37


reinforced with ECR and BB



0

10

20

30

40

50

60

70

80

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 8.5 9 9.5 10

Load

(kN

)

Slip (mm)

ES1R1 sample 1

US1R1 sample 1

ES1R1 sample 2

US1R1 sample 2

ES1R1sample 3

US1R1 sample 3

0 10 20 30 40 50 60 70 80 90

100 110 120 130 140 150

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Load

(kN

)

Slip (mm)

ES1R2 sample 1

US1R2 sample 1

ES1R2 sample 2

US1R2 sample 2

ES1R2 sample 3

US1R2 sample 3

38

Table – 4.2: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under

Direct Pull-out

Specimen

Name

Developmen

t length

provided,

mm

Ba

r D

ia, m

m

Bar Type

**Developme

nt length

calculated as

per ACI Eqn

25.4.2.3b,

mm

Yie

ld L

oa

d,

kN

Fa

ilu

re M

od

e

Ult

imate

Fa

ilu

re L

oa

d,

KN

Ra

tio

of

ult

imate

to

yie

ld l

oad

ES1R1

sample 1 300 12

Epoxy

coated 600 65

Tensile

Failure of Bar 78 1.200

ES1R1

sample 2 300 12

Epoxy

coated 600 65

Tensile


ES1R1

sample 3 300 12

Epoxy

coated 600 65

Tensile


US1R1

sample 1 300 12 Uncoated 400 65

Tensile


US1R1

sample 2 300 12 Uncoated

400 65

Tensile


US1R1


400 65

Tensile


ES1R2

sample 1 300 16

Epoxy

coated 750 100 Bond Failure 126 1.260

ES1R2

sample 2 300 16

Epoxy

coated

750 100 Bond Failure 128 1.280

ES1R2

sample 3 300 16

Epoxy

coated

750 100 Bond Failure 139 1.390

US1R2


Tensile


US1R2


500 100

Tensile


US1R2


500 100

Tensile


**Confinement effect was considered for calculating the development lengths.

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

39

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

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.

40





0

10

20

30

40

50

60

70

80

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Load

KN

Slip (mm)

Uncoated Sample 1

Epoxy Coated sample 1

Uncoated Sample 2


Uncoated sample 3

Epoxy coated sample 3

0

20

40

60

80

100

120

140

160

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Load

KN

Slip (mm)

Uncoated sample 1

Epoxy sample 1

Epoxy sample 2

Uncoated sample 2

Epoxy sample 3

Uncoated sample 3

41


Direct Pull-out

Specimen

Name

Developmen

t length

provided,

mm

Ba

r D

ia, m

m

Bar Type

**Developme

nt length

calculated as

per ACI Eqn

25.4.2.3b,

mm

Yie

ld L

oa

d,

kN

Fa

ilu

re M

od

e

Ult

imate

Fa

ilu

re L

oa

d,

KN

Ra

tio

of

ult

imate

to

yie

ld l

oad

EB1R1

sample 1 300 12

Epoxy

coated 600

64 Tensile


EB1R1

sample 2 300 12

Epoxy

coated 600

66 Tensile


EB1R1

sample 3 300 12

Epoxy

coated 600

66 Tensile


UB1R1

sample 1 300 12 Uncoated 400

64 Tensile


UB1R1


400 65 Tensile


UB1R1


400 65 Tensile


EB1R2

sample 1 300 16

Epoxy

coated 750

124 Bond Failure

147 1.185

EB1R2

sample 2 300 16

Epoxy

coated

750 116 Bond Failure

140 1.207

EB1R2

sample 3 300 16

Epoxy

coated

750 122 Bond Failure

142 1.164

UB1R2


112 Tensile


UB1R2


500 108 Tensile


UB1R2


500 114 Tensile



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

42

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.

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

0

10

20

30

40

50

60

70

80

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 8.5

Load

KN

Slip (mm)

Epoxy sample 1

Uncoated sample 1

Epoxy sample 2

Uncoated sample 2

Epoxy sample 3

Uncoated sample 3

0

20

40

60

80

100

120

140

160

0 1 2 3 4 5 6 7 8 9 10 11 12

Load

KN

Slip (mm)

Uncoated sample 1

Epoxy sample 1

Epoxy sample 2

Uncoated sample 2

Epoxy sample 3

Uncoated sample 3

44

Table – 4.4: Comparison of Failure Mode and Ultimate Failure Load of ECR and BB under Direct

Pull-out

Specimen

Name

Development

length

provided,

mm

Ba

r D

ia, m

m

Bar Type

**Developme

nt length

calculated as

per ACI Eqn

25.4.2.3b,

mm

Yie

ld L

oa

d,

kN

Fa

ilu

re M

od

e

Ult

imate

Fa

ilu

re L

oa

d,

KN

Ra

tio

of

ult

imate

to

yie

ld l

oad

ES2R1

sample 1 300 12

Epoxy

coated 550

62 Tensile Failure

of Bar 78 1.258

ES2R1

sample 2 300 12

Epoxy

coated 550

64 Tensile Failure

of Bar 78 1.219

ES2R1

sample 3 300 12

Epoxy

coated 550

65 Tensile Failure

of Bar 80 1.231

US2R1


66 Tensile Failure

of Bar 77 1.167

US2R1


375 66 Tensile Failure

of Bar 76 1.152

US2R1



of Bar 78 1.147

ES2R2

sample 1 300 16

Epoxy

coated 700 114

Tensile Failure

of Bar 136 1.193

ES2R2

sample 2 300 16

Epoxy

coated

700

120

Tensile Failure

of Bar 142 1.183

ES2R2

sample 3 300 16

Epoxy

coated

700

120

Tensile Failure

of Bar 144 1.200

US2R2


112 Tensile Failure

of Bar 134 1.196

US2R2



of Bar 134 1.207

US2R2



of Bar 135 1.205


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.


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.

45



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


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.

46





0

10

20

30

40

50

60

70

80

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

Load

KN

Slip mm

Epoxy sample 1

Uncoated sample 1

Series3

Uncoated sample 2

Series5

Uncoated sample 3

0

20

40

60

80

100

120

140

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Load

KN

Slip mm

Uncoated sample 1

Epoxy sample 1

Uncoated sample 2

Epoxy sample 2

Uncoated sample 3

Epoxy sample 3

47


Direct Pull-out

Specimen

Name

Developmen

t length

provided,

mm

Ba

r D

ia, m

m

Bar Type

**Developme

nt length

calculated as

per ACI Eqn

25.4.2.3b,

mm

Yie

ld L

oa

d,

kN

Fa

ilu

re M

od

e

Ult

imate

Fa

ilu

re L

oa

d,

KN

Ra

tio

of

ult

imate

to

yie

ld l

oad

ES3R1

sample 1 300 12

Epoxy

coated 525

64 Tensile Failure

of Bar 78 1.219

ES3R1

sample 2 300 12

Epoxy

coated 525 66 Tensile Failure

of Bar 80 1.212

ES3R1

sample 3 300 12

Epoxy


of Bar 76 1.226

US3R1


65 Tensile Failure

of Bar 76 1.169

US3R1



of Bar 76 1.169

US3R1



of Bar 76 1.169

ES3R2

sample 1 300 16

Epoxy

coated 650 120

Tensile Failure

of Bar 147 1.225

ES3R2

sample 2 300 16

Epoxy

coated 650 118

Tensile Failure

of Bar 134 1.136

ES3R2

sample 3 300 16

Epoxy

coated 650 118

Tensile Failure

of Bar 142 1.203

US3R2


Tensile Failure

of Bar 140 1.250

US3R2



of Bar 134 1.196

US3R2



of Bar 132 1.211


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.


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.



length provided for 16mm epoxy coated bars was 46% of code specified development length, yet it

showed tensile failure.

48

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.

49

Fig. – 4.17: Comparison of loads-slip response of pull-out specimen (2.5 ksi, Brick chips, 12 mm


Fig. – 4.18: Comparison of loads-slip response of pull-out specimen (2.5 ksi, Brick chips, 16 mm


0

10

20

30

40

50

60

70

80

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

KN

Slip mm

Uncoated Sample 1


Uncoated Sample 2


Uncoated sample 3

Epoxy coated sample 3

0

20

40

60

80

100

120

140

160

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Load

KN

Slip mm

Uncoated sample 1


Uncoated sample 2


Uncoated sample 3

Epoxy sample 3

50


Direct Pull-out

Specimen

Name

Developmen

t length

provided,

mm

Ba

r D

ia, m

m

Bar Type

**Developme

nt length

calculated as

per ACI Eqn

25.4.2.3b,

mm

Yie

ld L

oa

d,

kN

Fa

ilu

re M

od

e

Ult

imate

Fa

ilu

re L

oa

d,

KN

Ra

tio

of

ult

imate

to

yie

ld l

oad

ES3R1

sample 1 300 12

Epoxy

coated 675

64 Tensile Failure

of Bar 78 1.219

ES3R1

sample 2 300 12

Epoxy

coated


of Bar 76 1.169

ES3R1

sample 3 300 12

Epoxy

coated


of Bar 78 1.200

US3R1


65 Tensile Failure

of Bar 76 1.169

US3R1



of Bar 76 1.152

US3R1



of Bar 77 1.167

ES3R2

sample 1 300 16

Epoxy

coated 825

120 Bond Failure 142 1.183

ES3R2

sample 2 300 16

Epoxy

coated

825 122 Bond Failure 145 1.189

ES3R2

sample 3 300 16

Epoxy

coated

825 116 Bond Failure 138 1.190

US3R2


110 Tensile Failure

of Bar 134 1.218

US3R2



of Bar 134 1.229

US3R2



of Bar 133 1.220


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.


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


51

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.


samples


samples

52

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.


Direct Pull-out

Specimen

Name

Development

length

provided,

mm

Ba

r D

ia, m

m

Bar Type

**Developme

nt length

calculated as

per ACI Eqn

25.4.2.3b,

mm

Yie

ld L

oa

d,

kN

Fa

ilu

re M

od

e

Ult

imate

Fa

ilu

re L

oa

d,

KN

Ra

tio

of

ult

imate

to

yie

ld l

oad

ES1R1_FLd

sample 1 600 12

Epoxy

coated 600

63 Tensile Failure

of Bar 78 1.238

ES1R1_FLd

sample 2

600 12

Epoxy


of Bar 76 1.169

ES1R1_FLd

sample 3

600 12

Epoxy


of Bar 78 1.200

ES1R1_FLd

sample 4 600 12

Epoxy

coated 600 64

Tensile Failure

of Bar 78 1.219

ES1R1_FLd

sample 5 600 12

Epoxy

coated 600 63

Tensile Failure

of Bar 76 1.206

ES1R1_FLd

sample 6 600 12

Epoxy

coated 600 64

Tensile Failure

of Bar 77 1.203

US1R1_FLd


Tensile Failure

of Bar 76 1.152

US1R1_FLd


Tensile Failure

of Bar 78 1.200

US1R1_FLd


Tensile Failure

of Bar 78 1.200

US1R1_FLd


Tensile Failure

of Bar 77 1.167

US1R1_FLd


Tensile Failure

of Bar 76 1.169

US1R1_FLd


Tensile Failure

of Bar 78 1.182


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

53

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

54

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

55

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 Specimens

Beam Type Concrete

Strength (ksi)

Size of Main Bar Aggregate Type Type of Rebar

I-SC 3 3-12 mm Stone Chips 3 Specimen of BB

3 Specimen of ECR

I-BC 3 3-12 mm Brick Chips 3 Specimen of BB

3 Specimen of ECR

II-SC 3.5 3-12 mm Stone Chips 3 Specimen of BB

3 Specimen of ECR

III-SC-S 3 2-16 mm (spliced) Stone Chips 1 Specimen of BB

1 Specimen of ECR

III-BC-S 3 2-16 mm (spliced) Brick Chips 1 Specimen of BB

1 Specimen of ECR

IV-SC 3 2-16 mm Stone Chips 2 Specimen of BB

2 Specimen of ECR

IV-BC 3 2-16 mm Brick Chips 2 Specimen of BB

2 Specimen of ECR

V-SC 3.5 2-16 mm Stone Chips 2 Specimen of BB

2 Specimen of ECR

V-SC-S 3.5 2-16 mm (spliced) Stone Chips 1 Specimen of BB

1 Specimen of ECR

VI-BC 2.5 3-12 mm Brick Chips 3 Specimen of BB

3 Specimen of ECR

Total = 42 Specimen

56

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.



0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45

Load

(kN

)

Deflection (mm)

Uncoated 1

Uncoated 2

Uncoated 3

Epoxy Coated 1

Epoxy Coated 2

Epoxy Coated 3

Design Strength 69KN

57

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





0

5

10

15

20

25

30

0 50 100 150 200 250 300 350 400

Def

lect

ion

(m

m)

Time (s)

Uncoated 1

Uncoated 2

Uncoated 3

Epoxy Coated 1

Epoxy Coated 2

Epoxy Coated 3

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5

Load

(kN

)

Crack width mm

Uncoated 2

Uncoated 1

Uncoated 3

Epoxy Coated 1

Epoxy Coated 2

Epoxy Coated 3


58

Table – 4.10: Comparison of Crack Width at Design Load for Beams (3 ksi, stone chips, 3-12 mm


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


Beam name Number of total cracks

U_3_SC_12 sample 1 17



E_3_SC_12 sample 1 18



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

59

Sample name Deflected Shape after failure Mid zone crack distribution and crack

width

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



0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40

Load

(kN

)

Deflection (mm)

Uncoated 1 Uncoated 2 Uncoated 3 Epoxy Coated 1 Epoxy Coated 2 Epoxy Coated 3 Design strength 69 KN

60

Table – 4.13: Comparison of Deflections at Design Load for Beams (3 ksi, brick chips, 3-12 mm


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





0

5

10

15

20

25

30

35

40

0 50 100 150 200 250 300 350 400 450 500

De

fle

ctio

n (

mm

)

Time (s)

Uncoated 1

Uncoated 2

Uncoated 3

Epoxy Coated 1

Epoxy Coated 2

Epoxy Coated 3

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3 3.5

Load

(K

N)

Crack width mm

Uncoated 2

Uncoated 1

Uncoated 3

Epoxy Coated 1

Epoxy coated 2

Epoxy coated 3

Design Strength 69 KN

61

Table – 4.14: Comparison of Crack Width at Design Load for Beams (3 ksi, brick chips, 3-12 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



U_3_BC_12 sample 1 20



E_3_BC_12 sample 1 22




(3 ksi, brick chips, 3-12 mm bars) reinforced with ECR and BB

U_3_BC_12 E_3_BC_12




62

Sample

name Deflected Shape after failure

Mid zone crack distribution and crack

width

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, 3-

12 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.

63

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.



Table – 4.17: Comparison of Deflections at Design Load for Beams (3.5 ksi, stone chips, 3-12 mm



U_3.5_SC_12 sample 1 72 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

0

10

20

30

40

50

60

70

80

90

100

110

0 5 10 15 20 25 30 35 40

Load

(kN

)

Deflection (mm)

Uncoated 1

Uncoated 2

Uncoated 3

Epoxy Coated 1

Epoxy Coated 2

Epoxy Coated 3


64





0

5

10

15

20

25

30

0 50 100 150 200 250 300 350

De

fle

ctio

n (

mm

)

Time (s)

Uncoated 1

Uncoated 2

Uncoated 3

Epoxy Coated 1

Epoxy Coated 2

Epoxy Coated 3

0

10

20

30

40

50

60

70

80

90

100

110

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

(kN

)

Crack Width

Uncoated 2

Uncoated 1

Uncoated 3

Epoxy Coated 1

Epoxy Coated 2

Epoxy Coated 3

Design Strength 72 KN

65

Table – 4.18: Comparison of Crack Width at Design Load for Beams (3.5 ksi, stone chips, 3-12


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



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


(3.5 ksi, stone chips, 3-12 mm bars) reinforced with ECR and BB

U_3.5_SC_12 E_3.5_SC_12

Average 1st cracking load (kN) 20 12.4


Average Ultimate failure load (kN) 88.4 92

66


width

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


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.

67

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.

Fig. – 4.38: Comparison of loads-deflection response of beam (3 ksi, stone chips, 2-16 mm Spliced


Fig. – 4.39: Comparison of deflection time response of beams (3 ksi, stone chips, 2-16 mm Spliced


0

10

20

30

40

50

60

70

80

90

100

110

120

0 5 10 15 20 25 30 35 40

Load

(kN

)

Deflection (mm)

Uncoated 16 mm Spilce

Epoxy Coated 16 mm Spilce

Design Strength of 68 KN with Fy = 60 ksi

0

5

10

15

20

25

30

0 50 100 150 200 250 300 350 400

De

fle

ctio

n (

mm

)

Time (s)



68

Fig. – 4.40: Comparison of load-crack width response of beams (3 ksi, stone chips 2-16 mm Spliced



(3 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB

U_3_SC-S_16 (splice) E_3_SC-S_16 (splice)

1st cracking load (kN) 20.33 21.57

Spalling load (kN) 98 96

Ultimate failure load (kN) 106 103

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

0

10

20

30

40

50

60

70

80

90

100

110

120

0 0.5 1 1.5 2 2.5 3 3.5 4

Load

(kN

)

Crack width (mm)


Epoxy Coated 16 mm Spilce Design Strength of 68 KN with Fy = 60 ksi

69

Fig. – 4.42: Comparison of loads-deflection response of beams (3 ksi, brick chips, 2-16 mm Spliced


Fig. – 4.43: Comparison of deflection time response of beams (3 ksi, brick chips, 2-16 mm Spliced


0

10

20

30

40

50

60

70

80

90

100

110

0 5 10 15 20 25 30 35 40

Load

(kN

)

Deflection (mm)




0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350 400 450

De

fle

ctio

n (

mm

)

Time (s)



70

Fig. – 4.44: Comparison of load-crack width response of beams (3 ksi, brick chips, 2-16 mm Spliced



(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)

1st cracking load (kN) 20.46 14.09

Spalling load (kN) 97.46 80

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

0

10

20

30

40

50

60

70

80

90

100

110

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Lo

ad (

kN)

Crack width (mm)




71

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.



0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40

Load

(K

N)

Deflection (mm)

Uncoated 1

Uncoated 2

Epoxy Coated 1

Epoxy Coated 2

Design Strength of '79 KN'

72

Table – 4.23: Comparison of Deflections at Design Load for Beams (3 ksi, stone chips, 2-16 mm


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





0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350 400 450 500

De

fle

ctio

n (

mm

)

Time (s)

Uncoated 1

Uncoated 2

Epoxy Coated 1

Epoxy Coated 2

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5

Load

(kN

)

Crack width mm

Uncoated 2

Uncoated 1

Epoxy Coated 1

Epoxy Coated 2

Design Strength of '79 KN'

73

Table – 4.24: Comparison of Crack Width at Design Load for Beams (3 ksi, stone chips, 2-16 mm



U_3_SC_16 sample 1 79 0.45

U_3_SC_16 sample 2 79 0.4

E_3_SC_16 sample 1 79 0.5

E_3_SC_16 sample 2 79 0.48

Table – 4.25: Comparison of Number of Total Cracks for Beams (3 ksi, stone chips, 2-16 mm








(3 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB

U_3_SC_16 E_3_SC_16



Average Ultimate failure load (kN) 105 98.95



0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40

Load

(K

n)

Deflection (mm)

Uncoated 1

Uncoated 2

Epoxy Coated 1

Epoxy Coated 2

Design Strength of '79KN'

74

Table – 4.27: Comparison of Deflections at Design Load for Beams (3 ksi, brick chips, 2-16 mm



U_3_BC_16 sample 1 79 13.15

U_3_BC_16 sample 2 79 12.6

E_3_BC_16 sample 1 79 13.5

E_3_BC_16 sample 2 79 15.05





0

2

4

6

8

10

12

14

16

18

0 50 100 150 200 250

De

fle

ctio

n (

mm

)

Time (s)

Uncoated 1

Uncoated 2

Epoxy Coated 1

Epoxy Coated 2

0

20

40

60

80

100

120

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Load

(kN

)

Crack width mm

Uncoated 2

Uncoated 1

Epoxy Coated 1

Epoxy Coated 2


75

Table – 4.28: Comparison of Crack Width at Design Load for Beams (3 ksi, brick chips, 2-16 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








(3 ksi, brick chips, 2-16 mm bars) reinforced with ECR and BB

U_3_BC_16 E_3_BC_16




76

Sample

name Deflected Shape after failure

Mid zone crack distribution and crack

width

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.

77



Table – 4.31: Comparison of Deflections at Design Load for Beams (3.5 ksi, stone chips, 2-16 mm



U_3.5_SC_16 sample 1 81 12

U_3.5_SC_16 sample 2 81 13

E_3.5_SC_16 sample 1 81 13.45

E_3.5_SC_16 sample 2 81 12.8



0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40

Load

(K

n)

Deflection (mm)

Uncoated 1

Uncoated 2

Epoxy Coated 1

Epoxy Coated 2


0

5

10

15

20

25

0 50 100 150 200 250 300 350 400

De

fle

ctio

n (

mm

)

Time (s)

Uncoated 1

Uncoated 2

Epoxy Coated 1

Epoxy Coated 2

78



Table – 4.32: Comparison of Crack Width at Design Load for Beams (3.5 ksi, stone chips, 2-16



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



(3.5 ksi, stone chips, 2-16 mm bars) reinforced with ECR and BB

U_3.5_SC_12 E_3.5_SC_12


Average Spalling load (kN) 97 92.2

Average Ultimate failure load (kN) 104 97.35

0

20

40

60

80

100

120

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Load

(kN

)

Crack width mm

Uncoated 2

Uncoated 1

Epoxy Coated 1

Epoxy Coated 2



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

79


width

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


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.

Fig. – 4.57: Comparison of loads-deflection response of beam (3.5 ksi, stone chips, 2-16 mm Spliced


0

20

40

60

80

100

120

0 5 10 15 20 25 30 35

Load

(K

n)

Deflection (mm)

Uncoated 1

Epoxy Coated


80

Fig. – 4.58: Comparison of deflection time response of beams (3.5 ksi, stone chips, 2-16 mm Spliced


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


(3.5 ksi, stone chips, 2-16 mm Spliced bars) reinforced with ECR and BB

U_3.5_SC-S_16 (splice) E_3.5_SC-S_16 (splice)

1st cracking load (kN) 32 17.46

Spalling load (kN) 93.2 90.5

Ultimate failure load (kN) 100 96.5

0

5

10

15

20

25

30

0 50 100 150 200 250 300 350

De

fle

ctio

n (

mm

)

Time (s)

Uncoated 1

Epoxy Coated 1

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Load

KN

Crack Width

Uncoated 1

Epoxy Coated 1


81

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.

82

Fig. – 4.61: Comparison of loads-deflection response of beams (2.5 ksi, brick chips, 3-12 mm bars)


Table – 4.36: Comparison of Deflections at Design Load for Beams (2.5 ksi, brick chips, 3-12 mm



U_2.5_BC_12 sample 1 66 12.6

U_2.5_BC_12 sample 2 66 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

Fig. – 4.62: Comparison of deflection time response of beams (2.5 ksi, brick chips, 3-12 mm bars)


0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45

Load

(K

n)

Deflection (mm)

Uncoated 1

Uncoated 2

Uncoated 3

Epoxy Coated 1

Epoxy Coated 2

Epoxy Coated 3

Design Strength of 66 KN

0

5

10

15

20

25

30

35

40

45

0 100 200 300 400 500 600

De

fle

ctio

n (

mm

)

Time (s)

Uncoated 1

Uncoated 2

Uncoated 3

Epoxy Coated 1

83

Fig. – 4.63: Comparison of load-crack width response of beams (2.5 ksi, brick chips, 3-12 mm bars)


Table – 4.37: Comparison of Crack Width at Design Load for Beams (2.5 ksi, brick chips, 3-12



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



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


(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 Spalling load (kN) 80.2 83


0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1 1.2

Load

KN

Crack width mm

Uncoated 1

Uncoated 2

Uncoated 3

Epoxy Coated 1

Epoxy Coated 2

Epoxy Coated 3

Design Strength of 66 KN

84


width

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


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

85

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.

86

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) With exposure to extreme saline environment, the epoxy coated rebar demonstrates superior

performance against corrosion led deterioration of concrete structures.

(ii) 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.

(iii) 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.

(iv) 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.

(v) 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,

87

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.

88

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