The Islamic University of Gaza - library.iugaza.edu.pslibrary.iugaza.edu.ps/thesis/114040.pdf · The Islamic University of Gaza ةزغ – يهلاسلإا ... Post-installed rebars

The Islamic University of Gaza غزة –الجاهعة اإلسالهية

Higher Studies Deanery عوادة الدراسات العليا

Faculty of Engineering كلية الهندسة

Civil Engineering Department قسن الهندسة الودنية

Design And Rehabilitation of Structures تأهيل هنشآت تصوين و

Efficiency of Post Installed Rebar

Connections

كفاءة وصالث حديد التسليح المغروست في

الخرسانت المصبوبت سابقا

By

Zeyad M. EL dada

Supervised By

Prof. Samir Shihada

In partial fulfillment of the requirement for degree of Master of Science

in Civil Engineering/ Design and Rehabilitation of Structures

م 4153 -هـ 5341

Dedication

I would like to dedicate this work to memory of my father.

I would like to dedicate this work to my mother, to my

brothers and sisters, to my loving wife, sons and daughters,

for their support in preparing this research.

Also, I would like to dedicate this work to all of Palestinian

people specially in Gaza Strip who suffer from the Israeli

siege.

Abstract Efficiency of Post Installed

Rebar Connections

I

Abstract:

Post-installed rebars using adhesives has a great spread in Gaza Strip, because of the

need of post-installed rebars in construction works for rehabilitation and strengthening

of reinforced concrete structure, some workers use chemical adhesives while the other

use mortar and other materials.

This research investigates the effectiveness of several types of adhesives used in

post-install rebar connections to use as bonding agent between steel reinforcement

bars and old concrete. And this research is concerned with the comparison between

the pull-out load of steel reinforcement bars embedded in concrete in cast in place

concrete and the pull-out load of steel reinforcement bars inserted in old concrete

using several types of adhesives.

On the other side, this research determine the best adhesive to use in post-installed

rebar connection in rehabilitation and strengthening of reinforced concrete structure

according to the pull-out load of the reinforced steel bars resulting from using each

adhesive, and according to the cost of each adhesive. Also we will discuss the

efficiency of the length and diameter of the used rebars in the post installed rebars

connections.

The research samples are divided into five groups. Group I consists of 24 samples of

concrete cylinders 15 cm in diameter and 30 cm in height which are cast in place

using pre-installed steel anchors. The used steel reinforcement is 8 mm, 10mm and 12

mm. While the embedment lengths are 10 db, 15db and 20 db for bars 8mm and 10

mm, and the embedment lengths are 10 db and 15db for 12 mm bars.

Group II consists also of 24 samples having the same dimensions but the steel

reinforcement bars are post-installed into concrete using EPICHOR 1768 adhesive.

Group III, IV and V are the same as group II but the adhesives used are Sikadure-

31CF , UHPSCC and mortar.

The analysis of the results obtained from the experimental program showed that, the

pull-out load of anchors in post-installed rebars using chemical adhesives is equal to

or more than that of cast in place samples and the pull-out load of the anchor using

chemical adhesives is relatively very close to their manufactures' data sheets.

The results also showed that, the pull-out load of anchors in post-installed rebars

samples using UHPSCC is approximately equal to the pull-out load of cast in place

samples, but the problem with this adhesive is that it hardens rapidly, so it is preferred

to be used only in non construction works.

Moreover, when the diameter size of the bar increases, the pull-out load of the anchor

increases, and when the embedment length of the anchor increases the, the pull-out

load increases.

Abstract Efficiency of Post Installed

Rebar Connections

II

انخالصت :نقذ اخششث طشقت غشص حذذ انخغهح ف انؼاصش اإلشائت باعخخذاو اناد انشابطت كثشا ف قطاع

غضة رنك نضو أػال انخصهح انخقت نهشآث انخشعات ,فبؼض انؼايه غخخذي اناد

أخش. انشابطت انكائت آخش غخخذي خهظ انشيم األعج ياد

زا انبحث ذسط حؤثش ز اناد انشابطت ف ػهت غشط حذذ انخغهح ف انبااط انقاذى كؼايام سباظ

ب حذذ انخغهح انباط انقذى , قو بؼم يقاست ب قاة عاحس عاد حذاذ انخغاهح انثباج أثاا

اخى غشعا بؼاذ فخاشة يا ػهات صس انخشعات فا انؼصاش با قاة عاحس عاد حذاذ انخغاهح اناز

انصس باعخخذاو اناد انشابطت.

ذسط انبحث أضا أفضم يادة سبظ نخى اعخخذايا فا ػهااث انخاشيى انخقات نهشاآث انخشعاات

ي خالل دساعت انادة انخ خج ػ اعخخذايا قة عحس كبشة نغد حذذ انخغهح, ي خاالل يؼشفات

. كا ذسط انبحث حؤثش كم ي قطش انغد انغخخذو ػا انغاد وفش اقخصادا ف االعخخذاانادة األ

داخم انباط ف انخؤثش ػه قة عحس انغد.

ػات يا اعاطااث 42حى حقغى ػااث انبحاث ىنا خغات ياػااث , اناػات األنا حخكا يا

حى صبا حثبج قطغ حذاذ انخغاهد خاالل انصاس, عى انخ 03عى اسحفاع 51انباط راث قطش

ضؼف انقطش( , كا حى اعخخذاو قطاغ 43 51 53يهى بؼ ) 53يهى 8قذ حى اعخخذاو أقطاس حذذ

ضؼف انقطش( 51 53يهى بؼ ) 54حذذ حغهح بقطش

خى حثبج حذذ انخغهح بؼاذ ػت ي فظ ػاث انباط نك 42أيا اناػت انثات ف حخك ي

. 5678 انصس بفخشة رنك باعخخذاو ياد سابطت اإلبكس

اناػت انثانثات انشابؼات انخايغات فاظ اناػات انثاات نكا باعاخخذاو يااد سابطات ا انغاكا

م. انشي األخش باعخخذاو خهظ األعج باط فائ األدا راح انذيك ع أف 05 -دس

بخحهم انخائج احضح أ قة عحس انغد انثبج ؼذ انصس بفخاشاث طهات باعاخخذاو انااد انشابطات انكائات

ب انباط حذذ انخغهح حؼادل أ حضذ ػ قة عحس انغد انثباج أثاا صاس انبااط, كاا احضاح أ قاة

فظ انقة انخ حى حذا ف يشساث انششكاث انصؼت.عحس انغد انغخخذو ف حثبخ ياد كائت

فائ األدا راح انذيك فا حثباج حذاذ انخغاهح ؼطا قاة عاحس باط كا احضح ي انخائج أ اعخخذاو

حغا حقشبا قاة عاحس انغاد انثباج أثاا صاس انبااط , نكا ال صاح باعاخخذاو از اناادة فا

.ئت ظشا نغشػت حصهبا, نز صح باعخخذايا ف انؼاصش انغش ىشائتاألػال اإلشا

كا احضح ي انخائج أ صاادة قطاش عاد حذاذ انخغاهح صاادة ػا عاد حذاذ انخغاهح فا انبااط

حضذ ي قة عحس انغد.

III

ACKNOWLEDGEMENT

I would like to express my sincerest thanks to my supervisor,

Prof. Samir Shihada for the great help and guidance during the

period of working and preparing this research.

Furthermore, I would like to thank the staff of the Consulting

Center for Quality and Calibration particularly Eng Mohammed

Ghanem, Eng Ahmed Ghanem and Ahmed al Sdoody for their

help during the testing of the samples.

Finally, I would like to thank my partners and friends who

helped me in preparing the samples.

IV

TABLE OF CONTENTS

Abstract …………………………………………………………....……I

ACKNOWLEDGMENT………………...……………………………………….III

TABLE OF CONTENTS……………………………………………………...…IV

LIST OF FIGURES…………………………………………………………,..…VII

LIST OF TABLES…………………………………………………………..….VIII

LIST OF ABBREVIATIONS………………………………………………...…IX

CHAPTER 1. Introduction

1.1 Introduction………………………………………………………………………..1

1.2 Problem statement:………………………………………………………….…….2

1.3 Research objectives: ……………………………………………………….……..2

1.4 Methodology………………….…………………………………………………..2

1.5 Needed equipment………………………………………………………..………..2

1.6 Materials to be used……………………………………………………………….3

1.7 Thesis organization………………………………………………………………..3

CHAPTER 2 . Literature Review

2.1 Introduction……………………………………………….………………………4

2.2 Application of post-installed reinforcement ……………….……………………..5

2.2.1 When adding new parts of an emerging structure ……….…………………….5

2.2.2 Post-installed rebars for strengthening existing members …..…………………..5

2.3 Bond behavior ……………………………………………………………………6

2.4 Behavior of anchors ………………………………………………………………8

2.5 Factors affecting anchor performance ……………………………………………9

2.5.1 Concrete strength ……………………………………………………………...9

2.5.2 Steel strength ……………………………………………………………….…10

2.5.3 Edge distance ……………………………………………………………….…11

2.5.4 Embedment depth ………………………………………………………….….11

2.5.5 Thickness of the structural member …………………………………………..12

V

2.6 What are adhesive anchors ………………………………………………………12

2.7 Selection of adhesive anchors …………………………………………………..13

2.8 Previous studies and tests………………………………………………………..13

2.9 Pullout strength ……………………………………………………………….…18

2.10 Development of deformed bars in tension …………………………...……….19

……………………...……………….…21 2.11 Failure Modes under tensile loading

Failure of anchor bars...……………………………………………………….21 2.11.1

2.11.2 Pull-out of the anchor ………………………………………………….…….22

2.11.3 Splitting of concrete failure ……………………………………………...…..24

Chapter 3 Experimental Program

3.1 Introduction………………………………………………………………..……25

3.2 Description of the samples………………………………………………………25

3.3 Materials…………………………………………………………………………27

3.3.1 Concrete ……………………………………………………………………….27

3.3.2 Cement ………………………………………………………………………..27

3.3.3 Water……………………………………………………………………….….27

3.3.4 Reinforcing steel bars : ………………………………………………………...27

3.3.5 Adhesives …………………………………………………………………….28

3.3.5.1 EPICHOR 1768 …………………………………………………………….28

3.3.5.2 Sikadure - 31 CF ……………………………………………………………28

3.3.5.3 UHPSCC…………………………………………………………………….29

3.3.5.4 Mortar………………………………………………………….........……….29

3.4 Mixing, casting and curing procedures …………………………………………29

3.4.1 Mixing procedures …………………………………..…………………………29

3.4.2 Casting procedures ……………………………………………………………29

3.4.3Curing procedures …………………..………………….………………………30

3.4.4 Drilling of the holes …………………………………………………………..30

3.4.5 Cleaning of the holes …………………………………………………………31

3.4.6 Preparing the adhesives…………………………………………………….…31

3.4.7 Injecting the adhesives into the holes………………………………………...32

3.4.8 Inserting of the anchors ……………………………………………………….33

3.4.9 Pull-out Tests …………………………………………………………………33

VI

Chapter 4 Results & Discussion

4.1 Introduction ……………………………………………………………………...35

4.2 Pull-out loads and failure modes ………………………………………………..35

4.2.1 –14 mm diameter bars………………………………………………………....35

4.2.1.1 - Pull-out loads of Ø12 bars…………………………………………………37

4.2.1.2 - Failure mode under pull-out load of Ø12 bars…………………………….37

4.2.2 – 13 mm diameter bars……………………………………………………...….38

4.2.2.1 - Pull-out loads of Ø10 bars…………………………………………………40

4.2.2.2 - Failure mode under pull-out load of Ø10 bars…………………………….41

4.2.0 – 8 mm diameter bars……………………………………………………..…...41

4.2.3.1 - Pull-out loads of Ø8 bars…………………………………..………………43

4.2.3.2 - Failure mode under pull-out load of Ø8 bars………………..…………….44

4.3 Failure modes under pull-out load…………………………………...…………45

4.3.1 Failure of Anchor Steel………………………………………………………..45

4.3.2 Pull-out of the Anchor…………………………………………………………45

4.3.3 Splitting of Concrete Failure…………………………………………………..46

Chapter 5 Conclusion and recommendation

5.1 Conclusion and recommendation………………………………………………..48

5.2 Recommendation for the future studies…………………………………………50

References………………………………………………………………………..…52

Appendix : Manufactures' data sheets………………………………………………..A

VII

LIST OF FIGURES

Figure (2.1): Post installed reinforcement bar in a bridge abutment …….……………5

Figure (2.2): Bond force transfer mechanism……………………..…………………..6

Figure (2.3): Cracking and damage mechanisms in bond……………………………….…8

Figure (2.4): Possible loading types of anchors……………………..………………...9

Figure (2.5): Influence of concrete compressive strength……….…………………...10

Figure (2.6): Injection of epoxy ………………………..……………………...…….14

Figure (2.7): Samples of the Waterloo study………………………...………………14

Fig (2.8): Creep testing instrumentation……………………………..………………15

Figure (2.9): On site verification test……………………………………………..….16

Figure (2.10): Variation of capacity ratio…………………………………………....18

Figure (2.11 ): Failure of anchor steel……………………...……………..………….20

Fig (2.12 ) : Combined cone failure mode ……………………….………………….23

Figure (2.13 ): Bond failure without concrete cone……………………….…………23

Fig (2.14): Splitting of concrete failure ………………………………..….…………24

Figure (3.1 ): Concrete cylindrical samples………………………………………….25

Figure (3.2) : Experimental program flowchart……………………………………...26

Figure (3.3 ): Sikadure – 31CF and EPICHOR 1768 adhesives…………..…………29

Figure(3.4): Casting of cylindrical specimens………………………………...…......30

Figure (3.5 ): Drilling of the holes………………………………………………...…30

Figure (3.6): Cleaning of the drilled holes…………………………………………...31

Figure (3.7): EPICHOR 1768 mixing procedure…………………………………….31

Figure (3.8 ): Sikadure – 31CF mixing procedure…………………………………..32

Figure (3.9): Injection of the adhesives into the holes………………………………32

Figure (3.10 ): Pull-out testing machine……………………………………………..34

Figure(4.1):Capacity of bonded 12 mm anchors using several types of adhesives.....36

Figure(4.2):Capacity of bonded 10 mm anchors using several types of adhesives.....40

Figure(4.3):Capacity of bonded 8 mm anchors using several types of adhesives…...43

Figure (4.4 ): Yielding of steel bar …………...………………………………..…....45

Figure (4.5 ): Cone failure mode………...……………………………………..……46

Figure (4.6 ): Splitting of Concrete Failure ……………………………………….....47

VIII

LIST OF TABLES

Table (3.1) : Properties of cement …………………………………............………..27

Table (3.2) : Properties of steel reinforcement ……………………………............…27

Table (3.3) : Prosperities of EPICHOR 1768 ………………………………………..28

Table (3.4) : Prosperities of Sikadure - 31CF…………………………………….....28

Table (3.5): One cubic meter components of UHPSCC mixture……………….........29

Table ( 4.1.a) : Control samples …………………………………….....…………….35

Table ( 4.1.b): Sikadure – 31CF samples……………………………………...……..35

Table ( 4.1.c) : EPICHOR 1768 samples ……………………………………………35

Table ( 4.1.d) :UHPSCC samples……………………………………………………36

Table ( 4.1.e) : Mortar samples……………………………………………………....36

Table ( 4.2.a) : Control samples ……………………………………………………..38

Table ( 4.2.b): Sikadure – 31CF samples……………………………………...……..38

Table ( 4.2.c) : EPICHOR 1768 samples…………………………………………….39

Table ( 4.2.d) :UHPSCC samples………………………………………………….....39

Table ( 4.2.e) : Mortar samples………………………………………………………39

Table ( 4.3.a) : Control samples………………………………………………..…….41

Table ( 4.3.b): Sikadure – 31CF samples………………………………………….…42

Table ( 4.3.c) : EPICHOR 1768 samples……………………...……………….…….42

Table ( 4.3.d) :UHPSCC samples…………………………………………………….42

Table ( 4.3.e) : Mortar samples………………………………………………………43

IX

LIST OF ABBREVIATIONS

RC Reinforced concrete

fc /

Compressive Strength of concrete cylinders at 28 days

fy Specified yield strength of reinforcement, kg/cm2

ASTM American Society for Testing and Materials

ACI American Concrete Institute

w/c Water cement ratio

Ld Development length , cm

db Nominal diameter of bar , cm

√fc Square root of specified compressive strength of concrete, kg/cm2

Ψs Factor used to modify development length based on reinforcement size.

Ψt Factor used to modify development length based on reinforcement location.

Ψe Factor used to modify development length based on reinforcement coating.

ƛ Lightweight aggregate concrete factor

Cd The smaller of either the distance from the center of the bar to the nearest

concrete surface on one half the center-to-center spacing of bars being

developed.

°C Degree Celsius

Ktr A transverse reinforcement factor that represent the contribution of confining

reinforcement.

Atr Total cross sectional area of transverse reinforcement

Fu The ultimate strength of the anchor

A Tensile stress area, cross sectional area of the anchor steel

σult Ultimate tensile strength of the anchor.

Ø Diameter of the steel bar

NA Not approved

UHPSCC Ultra Height Performance Self Compacted Concrete

Introduction

CH.1 Introduction Efficiency of Post Installed

Rebar Connections

5

1.1-Introduction

Post installed reinforcement is a reinforcement that is installed into a hardened

concrete member by drilling holes and inserting the bar with or without adhesives.

Post installed reinforcement bars are used for different purposes such as

attaching new concrete to existing RC members, thus enabling the flow of forces via

joints or strengthening existing structures by means of additional straight

reinforcement bars. Such bars are typically inserted into a pre-drilled hole and glued

in with special appropriate mortars [1].

The main principle of using post installed rebar connections is how the load or stress

is transferred in reinforced concrete. We know that transfer of load or stress in

reinforced concrete is based on bond between the reinforcing steel and the

surrounding concrete. This transfer is provided by the resistance to relative motion or

slippage between the concrete and the rib faces of the embedded steel bar. The

resistance to slippage is defined as bond or bond stress. Bond between deformed steel

bar and the surrounding concrete depends on three actions: (1) chemical adhesion; (2)

friction; (3) mechanical interaction between the ribs of the bar and the surrounding

concrete [2].

In order to achieve the best installation of reinforced steel bars in old concrete

members we use adhesives. But materials available at the local markets have never

been tested, so the efficiency of these materials is thus questioned.

This research work is to investigate the effectiveness of using these materials and to

determine the most efficient material for use. In addition, the required post-installed

development lengths are to be evaluated and compared with those of the pre-installed

reinforcement bars.


Rebar Connections

4

1.2 - Problem Statement:

The terrorism of the Israeli occupation has been damaging a large number of

buildings in Gaza Strip, either completely or partially. So we need to repair these

buildings by adding new concrete members to carry the loads. The problem discussed

in this research is how to bond new concrete to old concrete using materials available

at the local Gaza markets. The efficiency of such materials have never been tested.

Thus, laboratory tests are to be carried out on these materials to decide on the best

available adhesive to use.

1.3- Research Objectives:

The objectives of this research are:

(1) Study the performance of the adhesives to be used for post-installing

reinforcement bars in concrete. The adhesives to be used are those available at Gaza

local markets.

(2) Decide on an efficient and more economical adhesive material that can do the job.

(3) Determine the required embedment lengths associated with each of the used

adhesive.

1.4 - Methodology:

To achieve the objectives of this research, the following tasks will be executed:

1. Review previous research related to the subject of post-installed rebar

connections and the used techniques .

2. Carry out an experimental program that includes the following :

- Cast several samples of concrete cylinders without reinforced steel .

- Cast control samples of concrete cylinders with reinforcing steel bars.

- Apply all of the available adhesives in installing the new reinforcing bars.

- Subject each sample to a pullout test.

3. Compare the post installed rebar samples with the control ones.

4. Decide on the most efficient adhesive that is available in Gaza Strip, based on

the test results .

1.5 -Needed equipment :

The following equipment are to be used in order to achieve the objectives of the

testing program:


Rebar Connections

0

1- A drill with different diamond sizes.

2- Air compressor " to clean out the drilled holes".

3- Pull-out testing machine.

1.6 -Materials to be used:

1- Normal strength concrete .

2- Reinforcement bars 8 mm, 10 mm and 12 mm in diameter.

3- EPICHOR 1768 adhesive.

4- Sikadure – 31CF adhesive.

5- Ultra High Performance Self Compacting Concrete.

6- Mortar.

1.7- Thesis Organization

The thesis contains 5 chapters as follows:

Chapter 1 (Introduction): This chapter gives background about post-installed

rebar connections and the adhesives that are used to install post-installed steel bars. It

also gives a description of the research importance, scope, objectives, methodology

and the thesis organization.

Chapter 2 (Literature Review): This chapter reviews past scientific research

related to post installed rebar connections.

Chapter 3 (Experimental Program): Outlines the steps followed in order to achieve

the objectives of the research in the laboratory.

Chapter 4 (Results & Discussion): This chapter discusses the results of the tests which

are carried out on the prepared samples.

Chapter 5 (Conclusions and Recommendations): This chapter states the main

conclusions and recommendations drawn from the research work.

References : It references all of past research used in this research.

Literature Review

CH. 2 Literature Review Efficiency of Post Installed

Rebar Connections

2

Literature Review

2.1- Introduction:

This chapter shows the difference between post-installed rebar connections and cast-

in place anchors and it shows the factors that affect post-installed rebar connection,

Also it shows a number of previous studies and tests about post-installed rebar

connection.

Post-installed reinforcement bars are used for different purposes such as attaching

new concrete to existing reinforced concrete members, enabling the flow of forces

via joints or strengthening existing structures by means of additional straight

reinforcement bars. Such bars are typically inserted into a pre-drilled holes and glued

in with special appropriate mortars, developed in a way that they lead to more or less

the same bond strength as if the bars were cast-in [1].

In other words, we can say that, anchors in reinforced concrete structures are often

used either in rehabilitation of existing structures or attaching new parts. In addition,

the pull-out strength of an existing or a newly cast concrete can also be determined

by the use of mechanical anchoring devices.

Anchors to concrete can be divided into two general categories as cast-in-place

anchors and post-installed anchors.

Cast-in place anchor is an anchor that is installed prior to the placement of concrete

and derives its holding strength from plates, lugs, or other protrusions that are cast

into the concrete . Cast-in place anchors provide less flexibility to the designer than

post-installed anchors.

On the other hand, post-installed anchors are installed in a hole drilled in the hardened

concrete [3].

Anchors are steel elements either cast into concrete or post-installed into hardened

concrete member and used to transmit applied loads to the concrete. Cast-in place

anchors include headed bolts, hooked bolts (J- or L-bolt), and headed studs. Post-

installed anchors include expansion anchors, undercut anchors, and adhesive anchors.

Steel elements for adhesive anchors include threaded rods, deformed reinforcing bars,

or internally threaded steel sleeves with external deformations.

Post-installed anchor is an anchor installed in hardened concrete. Expansion,

undercut, and adhesive anchors are examples of post-installed anchors.


Rebar Connections

1

Undercut anchor — A post-installed anchor that develops its tensile strength from the

mechanical interlock provided by undercutting of the concrete at the embedded end of

the anchor. The undercutting is achieved with a special drill before installing the

anchor or alternatively by the anchor itself during its installation [4].

2.2- Application of post-installed reinforcement

Post-installed rebars are commonly used in two main places; the first is when adding

new parts of an emerging structure and the second is for strengthening existing

members.

2.2.1- When adding new parts of an emerging structure

During the erection process, newer parts of an emerging structure are cast against

already existing sections and loads have to be transferred via the joints, see Figure

(2.1). Above that the completion and extension of existing structures as well as

strengthening of members in the sense of adding more reinforcement are of main

interest. Some times post-installed rebars are preferred to pre-installed reinforcement

for the sake of more flexibility, e.g. when anchoring footings of columns.

Figure (2.1): Post installed reinforcement bar in a bridge abutment

2.2.2- Post-installed rebars for strengthening existing members

Post-installed rebars themselves may serve as additional reinforcement for

strengthening existing concrete members. Recent research projects have proved the

applicability for strengthening slabs against punching for increasing their shear

resistance. In both cases the method is the same: post-installed rebars are inserted into

pre-drilled mortar-injected holes from the bottom side of the concrete member and

anchored with metal plates at the accessible bar end on the bottom side. The

effectiveness depends on the available anchorage length which requires an inclined

installation (preferably 45°). Moreover, the position of the rebars with respect to the


Rebar Connections

7

decisive shear load transfer zones and the mortar properties determine the increase of

the load bearing capacity of the whole member [1].

2.3-Bond behavior

In reinforced concrete construction, efficient and reliable force transfer between

reinforcement and concrete is required for optimal design. The transfer of forces from

the reinforcement to the surrounding concrete occurs for a deformed bar as shown in

Figure (2.2) by:

• Chemical adhesion between the bar and the concrete;

• Frictional forces arising from the roughness of the interface, forces transverse to the

bar surface, and relative slip between the bar and the surrounding concrete; and

• Mechanical anchorage or bearing of the ribs against the concrete surface.

Figure (2.2): Bond force transfer mechanism [2]

After initial slip of the bar, most of the force is transferred by bearing. Friction,

however, especially between the concrete and the bar deformations (ribs) plays a

significant role in force transfer, as demonstrated by epoxy coatings, which lower the

coefficient of friction and result in lower bond capacities. Friction also plays an

important role for plain bars, with slip-induced friction resulting from transverse

stresses at the bar surface caused by small variations in bar shape and minor, though

significant surface roughness.

When a deformed bar moves with respect to the surrounding concrete, surface

adhesion is lost, while bearing forces on the ribs and friction forces on the ribs and

barrel of the bar are mobilized. The compressive bearing forces on the ribs increase

the value of the friction forces. As slip increases, friction on the barrel of the


Rebar Connections

6

reinforcing bar is reduced, leaving the forces at the contact faces between the ribs and

the surrounding concrete as the principal mechanism of force transfer. The forces on

the bar surface are balanced by compressive and shear stresses on the concrete contact

surfaces, which are resolved into tensile stresses that can result in cracking in planes

that are both perpendicular and parallel to the reinforcement as shown in Figure ( 2.3).

The cracks shown in Figure ( 2.3.a) can result in the formation of a conical failure

surface for bars that project from concrete and are placed in tension. They otherwise

play only a minor role in the anchorage and development of reinforcement. The

transverse cracks shown in Figure ( 2.3.b) form if the concrete cover or the spacing

between bars is sufficiently small, leading to splitting cracks, as shown in Figure (

2.3.c). If the concrete cover, bar spacing, or transverse reinforcement is sufficient to

prevent or delay a splitting failure, the system will fail by shearing along a surface at

the top of the ribs around the bars, resulting in a ―pullout‖ failure, as shown in Fig(

2.3.d). It is common, for both splitting and pullout failures, to observe crushed

concrete in a region adjacent to the bearing surfaces of some of the deformations. If

anchorage to the concrete is adequate, the stress in the reinforcement may become

high enough to yield and even strain harden the bar. Tests have demonstrated that

bond failures can occur at bar stresses up to the tensile strength of the steel.

From these simple qualitative descriptions, it is possible to say that bond resistance is

governed by:

• The mechanical properties of the concrete (associated with tensile and bearing

strength);

• The volume of the concrete around the bars (related to concrete cover and bar

spacing parameters);

• The presence of confinement in the form of transverse reinforcement, which can

delay and control crack propagation;

• The surface condition of the bar; and

• The geometry of the bar (deformation height, spacing, width, and face angle) [2].


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Figure (2.3): Cracking and damage mechanisms in bond: (a) side view of a deformed bar

with deformation face angle showing formation of cracks; (b) end view showing formation

of splitting cracks parallel to the bar; (c) end view of a member showing splitting cracks

between bars and through the concrete cover; and (d) side view of member showing shear

crack and/or local concrete crushing due to bar pullout [2].

2.4-Behavior of anchors

Understanding anchor behavior is necessary in specifying the appropriate anchorage

for a given application. This includes an understanding of failure modes and strengths

as well as load displacement and relaxation characteristics of various anchor types [5].

Also, it requires an in-depth understanding of the physical phenomena involved in the

complete process of setting and loading in building material, mainly in concrete [6].

Anchors are loaded through attachments to the embedded anchor in tension and shear

or combinations of both Figure (2.4). Anchors may also be subjected to bending

depending on the shear transfer through attachments. Dynamic loading may occur in

pipelines, bridges, railway barriers and machine foundations. Fatigue loads and

seismic loads may also act on anchorage systems [7].


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9

Figure (2.4): Possible loading types of anchors

2.5-Factors affecting anchor performance

Factors that influence the bond strength of adhesive anchors can be classified as

either internal or external. Internal factors (such as chemical formulation,

manufacturing processes, and packaging) are generally beyond the control of the

designer and installer. Internal factors are not to be investigated in this study. External

factors are generally beyond the direct control of the manufacturer, but usually can be

accommodated by the designer and controlled by the installer [8].

2.5.1- Concrete strength

When the capacity of the anchor is controlled by concrete properties, it is the tensile

properties of the concrete which controls the failure modes of anchors. Tensile

properties of concrete are related to compressive properties, but the tensile-

compressive strength relationship can be complicated by the influence of grain size,

type and distribution of aggregate particles [9]. For this reason, construction practices

which permit segregation of aggregate will increase the variability of tensile strength

more than the compressive strength [10]. Segregation of the concrete is influenced by

the slump, the height of drop of the concrete and the amount of vibration during

placement [11]. That is probably why the capacity of anchors may vary depending on

their location on the structural member.

The capacity of an anchor usually increases with increasing tensile strength of the

concrete until the capacity reaches to steel failure capacity of the anchor for shallow

embedment depths.

Eligehausen and Spieth [12] presented the bond strength of cast-in-place and post-

installed rebars as a function of concrete compressive strength Figure (2.5) and

showed that while the bond strength of cast-in-place rebars increases with increasing


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53

concrete compressive strength, the bond strength of post-installed bars increases only

up to a concrete strength fc/ = 40 MPa .

Figure (2.5): Influence of concrete compressive strength [12].

Gesoğlu et al. [13] studied the load-deflection behavior of adhesive and grouted

anchors embedded in both plain and steel fiber reinforced normal (30 MPa) and high

(60 MPa) strength concrete and concluded that the anchor capacity generally

increased with the concrete strength even though the increment was not uniform for

different types of anchors having various embedment depths. At small embedment

depths, the concrete strength appeared to be more effective mainly because shallow

anchors failed generally via concrete cone breakout. As the anchor embedment depth

was increased, however, this beneficial effect was reduced due to shifting of failure

mode of the anchors from concrete cone failure to pullout or steel failure.

2.5.2- Steel strength

The type of steel used in anchorage is largely dependent on the type of the anchorage.

For chemically bonded post-installed anchors, the most widely used steel type is

threaded rebars. Steel failure is likely to occur only with sufficiently long embedment

depths [13, 14]. To achieve this failure mode, the tensile strength of the anchor steel

must be less than the strength associated with the embedded portion of the steel.

When the steel failure is the accepted failure mode, it is obvious that the bond strength

will increase with increasing tensile strength of the steel. Threaded rebars will have

greater bond strengths than the unthreaded ones, especially when the bond failure is

the accepted failure type. Çolak [14] stated that the threaded rebars (or ribbed bars)

significantly improve bond performance under seismic conditions.


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55

Klingner and Mendonca [15] claimed that nominal tensile capacity can reasonably be

calculated as the product of the appropriate cross sectional area of the anchor times

the specified minimum yield strength of the anchor steel.

Gesoğlu et al. [13] performed pull-out tests on steel fiber reinforced concretes and

showed that the pull-out capacities of the anchors were not significantly affected by

the addition of steel fibers into the concrete. The ultimate deflection and toughness,

however, were greatly improved provided that the anchor failed through concrete

breakout.

2.5.3- Edge distance

If the anchor is placed too close to an edge of the concrete, the failure cone of the

anchor will overlap with the edge and the failure load will be reduced. Then, the

failure type will be the edge cone failure. Therefore, the edge distance of the anchor

should be enough to prevent edge cone failure.

2.5.4- Embedment depth

Effective embedment depth is the overall depth through which the anchor transfers

force to or from the surrounding concrete. The effective embedment depth will

normally be the depth of the concrete failure surface in tension applications. For cast-

in place headed anchor bolts and headed studs, the effective embedment depth is

measured from the bearing contact surface of the head [3].

The testing of embedments deeper than 230mm for individual anchors unaffected by

the proximity of edges has largely been limited to steel failures . The bond strength of

the anchor increases with increasing embedment depth until the steel failure becomes

the governing failure mode.

Gesoğlu et al. [13] showed that the embedment depth was the most important

parameter affecting the pullout capacity of the anchors. As the properties of the

anchor and concrete were kept unchanged, the pullout capacity of the anchor

increased almost linearly with the depth of the embedment into concretes.

Unterweger and Bergmeister [16] claimed that the effective embedment depth is

about 10 times larger than the diameter of the threaded rod or reinforcing bar for

chemically bonded anchors.

Çolak [14] showed that the ultimate tension capacity of steel rods increases as the

embedment length of steel rods increases. However, this increase is not linear. There

is little increase in strength once a certain embedment length is reached. The other


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54

notable feature is that the ultimate tension capacity starts to deviate from linearity at

bonded lengths above about 75 mm. This indicates that linear bond stress distribution

is not correct for longer bonded lengths.

2.5.5-Thickness of the structural member

Anchors installed in thin, unreinforced slabs and beams may result in a split structural

member where the concrete slab or beam fails in bending [17]. Minimum distance

from the bar to the surface of concrete or the next bar tend to small splitting load.

Splitting failure surface tend to develop a long the shortest distance between the bar

and the concrete surface or between two adjacent bars [18].

2.6-What are adhesive anchors

Adhesive anchor :- A post-installed anchor, inserted into hardened concrete with an

anchor hole diameter not greater than 1.5 times the anchor diameter, that transfers

loads to the concrete by bond between the anchor and the adhesive, and bond between

the adhesive and the concrete [3].

Adhesive anchors are anchors in concrete or masonry that derive their resistance to

applied tension load by adhesion or bond. The adhesive for attaching bolts, rods, etc.

to the concrete is available in both cartridge and capsule configurations. Each type

consists of two essential parts, a resin and a hardener.

In the cartridge format, the two components are contained in separate parallel tubes

connected on the end by a manifold that allows the materials to be proportioned in the

proper ratio and mixed together. The cartridge tool forces the materials out of the

tubes, through the manifold, into and through a mixing nozzle and into the drilled

hole. The mixing nozzle assures that the components are well mixed and the adhesive

resin is activated by the hardener.

With a capsule anchor, the resin and hardener are kept separate, but are contained

within a single glass or foil capsule. The entire capsule is inserted into the drilled

hole. The anchor element, usually a threaded rod, is then inserted into the pre-drilled

hole with a rotational motion using a rotary drill. The rotary motion of the anchor

breaks the capsule causing the resin and hardener to mix, initiating the chemical

reaction that hardens the adhesive.

Adhesive anchors are available in a variety of chemistries, each with its own specific

characteristics and capacities. The adhesive materials include epoxies (many different

formulations), acrylates, vinyl esters, polyesters, hybrid mortars, and others. The


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50

specifier, installer, and end user should become familiar with the requirements of the

specific application to ensure the selected adhesive anchor and adhesive material is

appropriate for the given application [19].

2.7- Selection of adhesive anchors

The selection of the appropriate adhesive anchor system requires an understanding of

the loads required to be resisted (for example: tensile loads, shear loads, or a

combination of tension and shear, sustained (long-term) loads, short term loads like

wind or seismic, as examples). Proper selection also requires the matching of the

adhesive material to the environment of the application (for example: expected

ambient environments, elevated temperatures, protected from adverse weather, etc.)

Assuming that a correct adhesive anchor system has been selected, installation is the

next critical aspect to be considered for a successful application [19].

2.8- Previous studies and tests :

A study was carried out by students at the University of Engineering and Technology

Peshawar, Pakistan [20] to evaluate the ability of single adhesive anchors to resist

sustained tensile load when installed in concrete and to develop a rationale guideline

for their design and selection, as shown in Figure (2.6). To evaluate the tensile

strength of the epoxies used for reinforcing anchors, pull out tests were performed on

the steel bars anchored at two different development lengths of 75 and 150 mm using

the materials of two manufacturers. This helped in recommending the minimum depth

for the installation of anchors using epoxies.

For the purpose of comparison pullout test were also performed on steel bars

anchored, at two different development lengths 150 and 230 mm, using ready mixed

grouts. The results shown by the epoxies for 75 mm anchorage depth did not agree

with the claims made by the manufacturers, however, the epoxies showed good

results for 150 mm anchorage depth. For 230 mm or more anchorage depths for the

ready mixed grout showed better results than epoxies.


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52

Figure (2.6): Injection of epoxy [20].

Another experimental study was carried out at the University of Waterloo in Canada

[21] on the long-term creep behavior of adhesive anchors under sustained tensile

loads in combination with different environmental exposures. The experimental

program comprised of 82 test specimens. The specimens consisted of a cylindrical

shaped concrete blocks of 300 mm in diameter and 200mm depth, with 15 mm

deformed steel bars post-installed to an embedment depth of six times the bar

diameter or 125mm. Three types of adhesives were used for anchor installation:

Type-A fast setting two component methyl methacrylate adhesive, Type-B a fast

setting two part epoxy adhesives and Type-C a standard set two part epoxy adhesive,

as shown in Figure (2.7).

(a) Hole drilling (b)Brush cleaning (c) Blasting of compressed air

Figure (2.7): Samples of the waterloo study[21]

The results of the static pullout testing showed that specimens with epoxy based

adhesive exhibited stronger bond strength, forcing the anchor to fail by rupture prior

to bond failure. Under sustained load testing, specimens with standard set epoxy,


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51

based adhesive showed insignificant creep displacement under room conditions.

However, when exposed to moisture noticeable creep displacements were recorded.

Specimens with both fast setting epoxy and methyl methacrylate based adhesives

showed higher creep displacements under environmental exposure (moisture,

freeze/thaw) versus those kept at room temperature.

Another study was done by Jinshan et al. [22] on Post-installed anchors by adhesive

anchorage pullout test method to estimate the in-place compressive strength of

concrete. In this method, the threaded metal probe is anchored into the concrete by

means of a high strength epoxy resin adhesive. To get the best calibration graph, the

linear regression models, nonlinear regression models, interpolation, or splines are

employed.

In that research, 76 batches of specimen with different concrete mixes were cast

including 152 concrete beams with dimensions of 240mm×750mm×2100mm and

2600 concrete cubes with dimensions of 150mm×150mm×150mm cured under

conditions identical to the concrete beam specimens, Figure( 2.8).

Figure (2.8): Specimen and test laboratory

For each concrete mix to be tested, four types of correlation are established between

the compressive strength of the standard concrete cube and the pullout force index of

concrete beam specimens using the adhesive post installed method. It was decided

that determination of best fit relationships using both linear and geometric regressions

should be considered.


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57

From this information it was apparent that, due to the high correlation coefficient (r)

values which range from 0.926 to 0.950, almost all forms of the calibration graphs

would be suitable. However, with regard to the highest correlation coefficient which

belongs to the cubic form, this calibration graph appears to be most suitable. A closer

inspection of the best fit lines, however, reveals that, in view of the obvious

advantages of having simple calibration factors, the linear calibration graph will be

the best fit curve for our purpose. It can be deduced that the effect of cubic curve is

very much similar to the linear form, and noting the insignificant difference between

the r (i.e., 0.982-0.979=0.003), it seems reasonable to choose the linear relationship

for its simplicity.

In order to examine the applicability, accuracy, and reliability of this new method,

post-installed by adhesive anchorage pullout method and the drilled core method were

conducted for three in-place selected concrete members, refer to Figure (2.9).

The result shows that concrete strength estimated using the post-installed by adhesive

anchorage pullout method is lower than that obtained using drilled core by 5.12

percent.

Figure (2.9): On site verification test

In laboratory and theory of the failure of the concrete frustum, the following

conclusions have been reached:

1) It is shown that the pullout force of the frustum anchorage method is proportional

to the concrete compressive strength.

2) The linear relationship between the pullout force and the concrete compressive

strength is reasonable and accurate in estimating the in-place concrete strength.

The post-installed by adhesive anchorage pullout method can provide accurate and

reliable estimates of in-place concrete strength using very simple and cheap apparatus.


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56

Chi-Ping et al. [23] describes a preliminary experimental study on the bond effect

between post-installed rebar and concrete after exposure to elevated temperature.

Three levels of high temperature, 400oC, 500

oC and 800

oC, in addition to 25

oC (room

temperature) are considered. The bond effect is investigated by comparing the

ultimate shear stresses between rebar and concrete as rebars are pulling-off in the

pull-out tests. Adhesive material tests are also carried out to determine the variations

of compressive strength and flexural strength due to different temperatures.

Ten cylindrical adhesive specimens, and ten flat adhesive specimens were prepared

for compressive tests, and bending test, respectively. Five temperatures ranging

between 25oC and 300

oC are chosen. Sixteen sets of pull-out tests in three series were

conducted. Most pull-out test sets contain five identical specimens. Three elevated

temperatures, 400oC, 500

oC, and 800

oC in addition to room temperature (25

oC) are

chosen. All the holes in concrete were prepared by utilizing a heavy-duty electric

drill with a 12 mm drill bit

Based on the limitation of the testing equipment, Ø10 mm steel deformed

reinforcing bars were used. Ready-mix concrete with design compressive strength of

27.6 MPa were cast in-situ as the base material. Any drilling or heating process was

carried out after the concrete reaches its 28-day strength. Two brands of adhesives

(so called Adhesive I and Adhesive II herein) were selected as the bonding material.

These adhesives are both two-component injection type with epoxy resin and

hardening agent.

The sizes of adhesive specimens for material tests are 15 cm in diameter and 15 cm in

height .

The specimens for pull-out tests were divided into three series. The first series, Series

N, is the reference test set with specimens not heated. These specimens were

prepared by the standard process as follows.

a. Drill a 5cm deep hole in the center of the prepared concrete specimen, and

completely clean the hole.

b. Install a rebar into the cleaned hole with proper amount of adhesive, and make no

movement of the entire system for 24 hours.

The second series, Series A, contains the install-then-heat specimens. These

specimens were first made by the above mentioned standard process. 24 hours after

rebar installation, the chosen fire resistive material was spray-applied on the surface


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58

of the part of rebar outside of the concrete. Then the specimens were heated to the

target temperature, 400oC, 500

oC or 800

0C.

C. After a heating duration of 30 minutes at the target temperature, the specimens

were air-cooled in lab and the fire resistive material was removed.

Although it is indicated in previous study that adhesive may not perform well under

temperature above 120oC, adhesive specimens in this study were exposed to

temperatures up to 400 o to examine the material strength change due to different

temperature. Since the adhesive is not a ductile material, bending test is chosen to

replace the tensile test. The variations of capacity ratio (ultimate strength of heated

specimen divided by the ultimate strength of unheated specimen) are illustrated in

Figure(2.10).

Figure (2.10): Variation of capacity ratio

2.9-Pullout strength

Anchor pullout strength is the strength corresponding to the anchoring device or a

major component of the device sliding out from the concrete without breaking out a

substantial portion of the surrounding concrete [3].

Concrete breakout strength is the strength corresponding to a volume of concrete

surrounding the anchor or group of anchors separating from the member.

Undercut anchor is a post-installed anchor that develops its tensile strength from the

mechanical interlock provided by undercutting of the concrete at the embedded end of

the anchor. The undercutting is achieved with a special drill before installing the

anchor or alternatively by the anchor itself during its installation.

Post-installed anchors shall be qualified for earthquake loading in accordance with

ACI 355.2R-10. The pullout strength and steel strength in shear of expansion and


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59

undercut anchors shall be based on the results of the ACI 355.2R-10 Simulated

Seismic Tests. For adhesive anchors, the steel strength in shear and the characteristic

bond stresses shall be based on results of the ACI 355.4M Simulated Seismic Tests.

Post-installed anchors do not have predictable pullout strengths, and therefore

qualification tests to establish the pullout strengths per ACI 355.2R-10 are required.

For a post-installed anchor to be used in conjunction with the requirements of this

appendix, the results of the ACI 355.2 tests have to indicate that pullout failures

exhibit an acceptable load-displacement characteristic or that pullout failures are

precluded by another failure mode. For adhesive anchors, the characteristic bond

stress and suitability for structural applications are established by testing in

accordance with ACI 355.4M. [3].

2.10- Development of deformed bar in tension

According to ACI 318M-11[3] the development length to bar diameter ratio Ld / dp is

given by :

sψ eψ tψ yf = dL

dp 3.5 ƛ √fc ((Cb + Ktr ) /dp)

in which the term (Cd + Ktr ) /dp is not to be greater than 2.5

where

Ld = development length , cm

dp = nominal diameter of bar , cm

fy = specified yield strength of reinforcement, kg/cm2

√fc = square root of specified compressive strength of concrete, kg/cm2

Cd = spacing or cover dimension, cm

Ψs =factor used to modify development length based on reinforcement size.

Ψt =factor used to modify development length based on reinforcement location.

Ψe =factor used to modify development length based on reinforcement coating.

ƛ = lightweight aggregate concrete factor

Cd is the smaller of either the distance from the center of the bar to the nearest

concrete surface on one half the center-to-center spacing of bars being developed.

ACI Code 12.2.3 provides the factors for use in the expression for development of

deformed bars in tension as follow:


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Ψt is a reinforcement location factor to reflect the adverse effects of the top

reinforcement casting position, such as bleeding and segregation, this factor is given

for two cases:

- horizontal reinforcement so placed that more than 30 cm of fresh concrete is cast in

the member below the development length or splice……………………………….1.3

Other reinforcement ………………………………………………………………..1.0

Ψe is coating factor that reflects the adverse effects of epoxy coating. It is given of

three cases:

- Epoxy coated bars with cover less than 3dp , or clear spacing less than 6dp ………1.5

- all other epoxy coated bar ……………………………………………………,,,,…1.2

Uncoated reinforcement …………………………………………………………….1.0

However the product Ψt Ψe is not to be grater than 1.7

Ψs is a reinforcement size factor that reflects better performance of the smaller

diameter reinforcement. This factor is given in two cases:

- Φ20mm and smaller bars………………………………………………………..…0.8

- Φ22mm and larger bars…………………………………………………………….1.0

ƛ is the lightweight concrete factor that reflects the reduction in splitting resistance of

lightweight concrete. It takes on one of the following values:

- when lightweight aggregate concrete is used …………………………………….1.3

- when normal weight concrete is used ……………………………….…………….1.0

Ktr is a transverse reinforcement factor that represent the contribution of confining

reinforcement, given by

Ktr = 40 Atr

s n

where Atr = total cross sectional area of transverse reinforcement within the spacing

s, cm2

fyt = specified yield strength of transverse reinforcement, kg/cm2

s = maximum center-to- center spacing of transverse reinforcement within

development length Ld, cm.

n = number of bars being developed along the splitting.

A limit on the term (C + Ktr) / dp of 2.5 is included to safeguard against pullout type

of failure.


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It is permitted to use Ktr = 0 as design simplification even if transverse reinforcement

is present [24].

2.11 - Failure Modes under Tensile Loading Loading type may be an important factor which influences the failure mode, but only

the failure modes under tensile loading are examined throughout this study. There are

five primary failure modes of anchors under tensile loading which are examined

below.

Failure of Anchor Steel 2.11.1

Anchor steel failure is characterized by yielding and fracture of steel rod and is likely

to occur only with sufficiently long embedment depths with strong adhesives as

shown in Figure (2.11). To achieve this failure mode, the tensile strength of the

anchor steel must be less than the strength associated with the embedded portion of

the steel [26].

Fu = A * σult

where Fu = the ultimate strength of the anchor

A = tensile stress area, cross sectional area of the anchor steel

σult = ultimate tensile strength of the anchor.

This failure mode defines the upper limit for the tensile load carrying capacity since

the anchor steel reaches to its maximum tensile capacity under the applied tension

load. Failure of the anchor under a tensile load is often not possible in retrofit works,

as the embedment depth is usually kept minimal and the strength of the concrete is

often low.


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44

Figure (2.11 ): Failure of anchor steel [26]

2.11.2- Pull-out of the Anchor

Pull out of the anchor failure is also called bond failure, or some times combined cone

and bond failure which are provided in Figure (2.12). For embedment lengths greater

than 50-100 mm, the most commonly observed failure is characterized by the

combined cone-bond failure mode with a shallow cone (usually less than 50 mm

deep) attached to the top of the anchor. In some installations, bond failure without a

concrete cone as shown in Figure (2.13) may occur if the bonded surface lacks

adequate strength due to the adhesive itself, improper curing, or inadequate hole

preparation [26].


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40

Figure (2.12 ): Combined cone failure mode [26]

Figure (2.13 ): Bond failure without concrete cone [26]


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42

Cook et al. [27] showed that bond failure without a concrete cone (Fig.2.13) can occur

when the top portion of the embedment length is debonded about 50 mm.

The pull-out capacity of the anchors increases with increasing embedment depth;

however after a depth that is approximately equal to nine anchor diameters, the

increase is not proportional to embedment depth [28]. This is due to high bonding

effect resulting in high load transfer to the concrete at the top of the anchor. The bond

stress is no longer uniform, and if the tensile load is sufficiently high, the failure

initiates with a concrete failure in the upper portion of the concrete and then the bond

fails in the remaining embedment depth.

2.11.3 - Splitting of concrete failure

Anchors installed in thin, unreinforced slabs and beams may result in a split in the

structural member where the concrete slab or beam fails in bending. Splitting failure

is characterized by the propagation of a crack in a plane containing the anchor.

Splitting may lead either to complete split of the structural element, or to cracks

between adjacent anchors or between the anchors or the edge shown in Figure (2.14).

The failure load is usually smaller than that of a concrete cone failure.

Figure (2.14 ): Splitting of concrete failure [26]

Experimental Program

CH. 3 Experimental Program Efficiency of Post Installed

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41

Experimental Program

3.1- Introduction

This chapter shows the experimental program of the research, Also it describes the

material that will be used in the research as concrete and other adhesives.

The executed experimental program consists of pull-out tests. These tests will

examine the strength of the adhesives that bond the steel reinforcement to the concrete

in post- installed rebar connections. The program consists of casting a number of

concrete cylinders, 15 cm in diameter and 30 cm in height as shown in Figure (3.1).

These samples will be drilled after 28 days of casting date, and a number of steel

reinforcement bars 8 mm, 10 mm and 12 mm in diameter will be inserted in the

concrete using several types of adhesives.

Figure (3.1 ): Concrete cylindrical samples

The aim of this study is to provide useful data for retrofitting works, where the

common adhesive types which are available at Gaza strip will be evaluated. The

samples are prepared in a way similar to site conditions and the drilling starts 28 days

after casting date. The drilling of the holes is performed using mechanical drills.

The site conditions and the experimental study performed are to be explained in detail

in this chapter.

3.2- Description of the samples

Concrete samples are cast in place using pre-installed steel anchors and used as

control samples in pull-out tests. The development lengths are taken as 10d, 15 d and

20 d , where d is the diameter of the reinforcement bar. These control samples include

nine samples cast in place with embedded steel reinforcement 8 mm diameter but the

embedded lengths are 10 db, 15 db and 20 db. Moreover, nine more samples are cast

in place with embedded reinforcement bar 10 mm in diameter but the embedded

lengths are 10 db, 15 db and 20 db. The third group consists of six samples cast in


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47

place with embedded steel reinforcement 12 mm in diameter but the embedded

lengths are 10 db and 15 db.

I haven’t used Embedded length 20 db for 12 mm diameter bars because it is very

difficult to penetrate 24 cm in the sample.

A number of 96 concrete cylinders, 15 cm in diameter and 30 cm in height are cast in

place without embedded steel reinforcement. These samples are prepared and cured

for a period of 28 days. After that, these samples are drilled and steel reinforcement

bars are inserted using four different types of adhesives. These adhesives are

EPICHOR 1768 , Sikadur – 31CF , UHPSCC and mortar. Each group of samples has

the same distribution as those of the control samples, as shown in Figure ( 3.2).

Cast in place samples

Post- installed using EPICHOR 1768 10 db anchors

Ø 8 mm bar 15 db anchors Post- installed using Sikadure – 31CF

20 db anchors Post- installed using UHPSCC

Post- installed using mortar



Ø 10 mm bar 15 db anchors Post- installed using Sikadure – 31CF





Ø 12 mm bar Post- installed using Sikadure – 31CF



Figure (3.2): Experimental program flowchart.


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46

3.3 – Materials

In our research, it is important to know the properties of all the materials used

including concrete, cement, steel reinforcement and adhesives.

3.3.1- Concrete

The target compressive strength of the concrete use in this research at 28 days is 250

kg/cm3. The required amounts of all constituent materials are weighed properly

according to the contents " minimum concrete content 325 kg/m3 , maximum w/c

53% , Max Aggregate Size 3/4" (20mm) crushed limestone aggregate, Coarse

aggregate 1100 kg/m3 , Fine aggregate sand 730 kg/cm3.

The actually compressive strength of the tested concrete samples is 265 kg/cm2

3.3.2- Cement

The cement used in this research is Portland cement "EN 197-1-cem 1 ( 42.5 N) type

1. Table (3.1 ) summarizes the cement properties.

Table (3.1): Properties of cement

Description Sample Results EN-197

spec.

Normal consistency 26.5%

Setting time

1- Initial sitting (min)

2- Final sitting (min)

95

185

Compressive strength (Mpa)

1- 2 days

2- 3 days

3- 28 days

18.4

37.0

48.6

Min 10

Min 42.5 , max 62.5

3.3.3- Water

Drinking water is used in mixing and curing all of the samples.

3.3.4-Reinforcing steel bars :

The reinforcement bars which are used in this research are 8 mm, 10 mm and 12 mm

in diameter. The properties of these bars as shown in Table (3.2).

Table (3.2): Properties of steel reinforcement

Diameter mm Yield strength

(kg/cm2)

Ultimate strength

(kg/cm2)

Ø 12 mm 4669 6210

Ø 10 mm 4210 4930

Ø 8 mm 4928 6915


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48

3.3.5 - Adhesives

Four types of adhesives are used for post–installed reinforcement bars.

3.3.5.1- EPICHOR 1768

This adhesive consists of two components, one component is the resin and the other is

the hardener. In order to prepare the mix, fine sand is added to the resin where the

ratio of the ( resin + hardener) to fine sand is 1 : 4 .

The resin, the hardener and the fine sand are mixed according to the manufacturer’s

recommendations. Properties of the adhesive is shown in Table ( 3.3).

Table (3.3): Prosperities of EPICHOR 1768 (according to the manufacture )

Description Sample Results

Compressive strength

After 6 days

After 22 days

42 N/mm2

67 N/mm2

Tensile strength (after 7 days) 2.9 N/mm2

Flexural strength (after 7 days) 54 N/mm2

Time after mixing 20 min in 240C

3.3.5.2- Sikadure - 31 CF

Sikadure - 31CF is a solvent free thixotropic consists of two components, based on a

combination of epoxy resins and specially selected high strength fillers. Table (3.4)

shows the properties of Sikadure - 31CF and Figure (3.3) shows photos of EPICHOR

1768 and Sikadure – 31CF containers.

Table (3.4): Prosperities of Sikadure - 31CF (according to the manufacture )

Description Sample Results

(After 10 days)

Compressive strength

After 24 hrs at 200 C



60 - 70 N/mm2

40 – 45 N/mm2

35 – 40 N/mm2

Tensile strength 15 – 20 N/mm2

Flexural strength 30 – 40 N/mm2

Bond strength to concrete

Bond strength to steel

3.5 N/mm2

15 N/mm2

Time after mixing 40 min in 200C

20 min in 30 0C


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49

Figure (3.3 ): Sikadure – 31CF and EPICHOR 1768 adhesives

3.3.5.3 -UHPSCC

UHPSCC is mixed according to the quality listed in Table (3.5 ), with w/c ratio equals

0.24.

The compressive strength of the tested UHPSCC samples is 1270 kg/cm2. The test of

compressive strength was done in the Islamic university laboratory.

Table (3.5): One cubic meter components of UHPSCC mixture [ 29]

3.3.5.4 Mortar

The mortar is prepared using cement and sand in the same amounts 1cement : 1 sand,

where water to cement ratio is 0.5.

3.4- Mixing, casting and curing procedures

3.4.1- Mixing procedures

The concrete mixtures are proportioned where the constituent materials are weighed

properly and then mixed in a rotary mixer.

3.4.2-Casting procedures

The fresh concrete is cast in cylindrical forms 15 cm in diameter and 30 cm in

height. as shown in Figure (3.4). Casting is done in three equal layers.

Materials Proportion (kg/m3)

Cement CEM I 42.5R 900

Water 216

Silica fume 135

Quartz sand 1125

Superplastisizer 27


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03

Figure (3.4): Casting of cylindrical specimens.

3.4.3-Curing procedures:

After 24 hours from casting time, all of the samples are submerged in a curing water

basin for a week period. After that, the specimens are left in open air for three more

weeks. The curing process is done according to ASTM C192 [30].

3.4.4 - Drilling of the holes

Holes are all drilled using a rotary hammer drill ( drill and vibrator). The hole

diameter for Ø8 anchors are drilled with a 12 mm diamond diameter, the hole

diameters for Ø10 anchors are drilled with a 15 mm diamond diameter, and the hole

diameters for Ø12 anchors are drilled with a 18 mm diamond diameter. All of the

drilled holes are made at the longitudinal axes of the specimens shown in Figure (3.5).

Figure (3.5 ): Drilling of the holes


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05

3.4.5 - Cleaning of the holes

In order to remove all of the loose concrete particles inside the holes, and in order to

improve the potential bond surface, compressed air and pumped water are used to

clean the holes, see Figure (3.6 ).

Figure (3.6): Cleaning of the drilled holes

3.4.6 - Preparing the adhesives

All types of adhesives are mixed according to the manufacturer’s recommendations.

Individual groups of concrete samples are prepared as described in the testing

program flowchart.

The EPICHOR 1768 adhesive is mixed according to the ratio 1( resin + hardener) : 4

fine sand, while Sikadure - 31 CF adhesive is mixed according to the ratio 2 resin : 1

hardener by weight , as shown in Figures (3.7) and (3.8).

Fig(3.7) : EPICHOR 1768 mixing procedure


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04

Figure(3.8):Sikadure–31CF mixing procedure

UHPSCC is mixed in the quantities specified earlier while the mortar is mixed in 1

cement : 1 sand ratio.

3.4.7 - Injecting the adhesives into the holes

Injection of all the adhesives is done using empty silicon containers, by filling all

amounts of the adhesives in the empty cans then using the silicon gun in filling the

holes, as shown in Figure (3.9).

Figure (3.9): Injection of the adhesives into the holes


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00

3.4.8- Inserting of the anchors

According to ACI Code 318-11 the development length to bar diameter ratio Ld / db is

given by :

24.29 cm =4200(1)(1)(0.8) = sψ eψ tψ yf = dL

db 3.5 ƛ √fc ((Cb + Ktr ) /db) 3.5(2.5) √250

where Ld = development length,

db = bar diameter.

fy = 4200 kg/cm2 for steel bar Φ10mm and Φ12mm,

fc = 250 kg/cm2 for cylindrical sample,

Ψt = 1.0 for Other reinforcement (see section 2.10),

Ψe = 1.0 for Uncoated reinforcement,

Ψs = 0.8 for Φ20mm and smaller bars,

ƛ = 1.0 for normal weight concrete,

(C + Ktr) / dp = 2.5

For Φ8mm , Ld = 24.29 * ( 0.8) ≈ 20 cm

For Φ10mm , Ld = 24.29 * ( 1.0) ≈ 25 cm

For Φ12mm , Ld = 24.29 * ( 1.2) ≈ 30 cm

After filling two - thirds of the hole length by the adhesive using the silicon gun, the

anchors are also brushed with the adhesive. Then the anchors are inserted into the

holes by twisting them slowly and cleaning the excess adhesive around the holes. By

this procedure, it can be guaranteed that the whole volume between the anchor and the

surfaces of the holes is filled with the adhesive.

The anchors are also marked for embedment depths before installation. The

embedment depths are 10, 15 and 20 times the anchor diameter.

3.4.9- Pull-out Tests

All of the samples are labelled and recorded for identification purposes. The

embedded lengths, the type of adhesive and date of casting are also recorded on the

concrete samples.


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02

Some modifications are made to the pull-out testing machine, where a steel cylinder

15 cm in diameter and 3 cm height is drilled from the middle (1,5 cm diameter) to let

the steel reinforcement bars pass through it.

Pull-out tests are started at least 36 hours after the installation of the anchors using

EPICHOR 1768 and Sikadure - 31CF adhesives according to the manufactures

recommendation, and after 14 days after installation of the anchors where UHPSCC

and mortar are used. The load is applied to the loading shoe through a high strength

steel rod by using a hydraulic ram which is manually operated. A load cell was

attached to the system and the failure loads are recorded from the load cell. Load is

applied to the anchors until the maximum load is reached. The pull–out testing

machine is shown in Figure (3.10).

Figure (3.10 ): Pull-out testing machine

Results and Discussion

CH. 4 Results and Discussion Efficiency of Post Installed

Rebar Connections

01

Results & Discussion

4.1- Introduction

This chapter shows the results of the carried out pull- out tests. Moreover, the

obtained results and the modes of failures are also discussed.

4.2- Pull-out loads and failure modes

We will record the value of pull-out load for each diameter of the steel

reinforcement and the types of adhesives and the embedded lengths.

4.2.1 – 12 mm diameter bars

The average values of pull-out loads are shown in Table (4.1).

Table ( 4.1.a): Control samples

Failure mode Average pull –out load( KN)

Pull-out load

(KN)

Embedment length

Concrete Failure 46.6

42.7

10 db

Concrete Failure NA


Concrete Failure

58.2

58.4

10 db Concrete Failure 58

Table ( 4.1.b): Sikadure – 31CF samples


Pull-out load

(KN)

Embedment length


39

10 db



Concrete Failure

57.9

58.3

15db Concrete Failure 60.4

Concrete Failure 55

Table ( 4.1.c): EPICHOR 1768 samples


Pull-out load

(KN)

Embedment length


42.1

10 db



Concrete Failure

55.2

51.4


Concrete Failure 54


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07

0

10

20

30

40

50

60

70

10 db 15 db

Embedment length (cm)

Avera

ge p

ull-

ou

t lo

ad

(K

N)

mortar

UHPSCC

EPICHOR 1768

sikadure - 31CF

control

Table ( 4.1.d): UHPSCC samples


Pull-out load

(KN)

Embedment length


30.9

10 db Concrete Failure 34.3

Concrete Failure

55.8

57.4

15db Concrete Failure 55


Table ( 4.1.e): Mortar samples


Pull-out load

(KN)

Embedment length

Pull out of the anchor + concrete

Failure

34.6

36

10 db


Failure

41.9

Concrete Failure 26

Concrete Failure

43.4

37.5


Concrete Failure 49

Figure (4.1) shows a comparison between pull-out strength of the anchors in the

control samples and pull out strength of the anchors using several types of adhesives.

Figure ( 4.1): Capacity of bonded 12 mm anchors using several types of adhesives


Rebar Connections

06

4.2.1.1 - Pull-out loads of Ø12 bars

The results listed in Table (4.1) and Figure (4.1) show that the average pull-out load

of Ø12 bars in post-installed rebar samples using sikadure – 31CF adhesive for

embedment length of 10db is about 82% of cast in place pull-out load, and for

embedment length of 15db is about 100% 0f cast in place pull-out load.

In post-installed rebar samples using EPICHOR 1768 adhesive with embedment

length of 10db the pull-out load is about 100% of cast in place pull-out load, and for

embedment length of 15 db is about 96% of cast in place pull-out load.

In post- installed rebars using UHPSCC adhesive with embedment length of 10db the

pull-out load is about 69 % of cast in place pull-out load, and for embedment length

of 15db is about 96% of cast in place pull-out load. It means that using of UHPSCC is

good for long embedment length.

In post-installed rebars using mortar with embedment length of 10db the pull-out load

is about 73 % of cast in place pull-out load, and for embedment length of 15db is

about 74 % of cast in place pull-out load.

So it appears from the shown results for installing the bars in post-install rebar

samples using adhesives is equivalent to installing that bars in cast in place samples.

Also, the results show that EPICHOR 1768 adhesive is the most effective in both the

embedment lengths 10db and 15db, since it gives average pull-out load approximately

equal to the average pull-out load of cast in place samples.

4.2.1.2 - Failure mode under pull-out load of Ø12 bars

The results show that, the mode of failure of using Ø12 bars either by cast in place or

by post-installed rebars using chemical adhesives and UHPSCC adhesive for

embedment length 10db and 15db is concrete failure mode.

The results also show that, the failure mode results from using mortar in post-installed

rebars with embedment length 10db is pull-out of the anchors, but the mode of failure


Rebar Connections

08

of using mortar in post-installed rebars with embedment length 15db is concrete

failure mode.

The results from using mortar in post-installed rebars with embedment length 10db is

pull-out of the anchors, but the mode of failure of using mortar in post-installed

rebars with embedment length 15db is concrete failure mode. These results show the

effect of friction of mortar, since the effect of friction increases when increasing the

embedded length of the bars.

The Ø12 bars didn’t show any yielding failure mode in installing the bars with

embedment lengths of 10db and 15db neither in cast in place nor in post-installed

rebars using adhesives.



Table ( 4.2.a): Control samples


Pull-out load

(KN)

Embedment length


37.5



44.5



49.6




Pull-out load

(KN)

Embedment length


33.5



35.7

15db Concrete Failure 33

Yielding of the anchor followed

by elongation in the bar

46.7

44.5

20 db



50.3



45.3


Rebar Connections

09



Pull-out load

(KN)

Embedment length


42.2

10 db


Concrete Failure 37


45.8

15db

Concrete Failure 40



by anchor rupture

13.1

51.4

20 db




Pull-out load

(KN)

Embedment length


37



39.2

15 db

Concrete Failure 45


by anchor rupture

50.7

51.1

20 db Yielding of the anchor followed


52.4




Pull-out load

(KN)

Embedment length

Pull-out of the Anchor 25.3

25.6

10 db Pull-out of the Anchor 24.9


40.7


Pull-out of the Anchor +

concrete failure

49.1

47.4

20 db Pull-out of the Anchor +

concrete failure

48.8

Pull-out of the Anchor 51


Rebar Connections

23

0

10

20

30

40

50

60

10 db 15 db 20 db


Ave

rag

e p

ull-

ou

t lo

ad (

KN

)

mortar

UHPSCC

EPICHOR 1768

sikadure - 31CF

control






of Ø10 bars in post-installed rebar samples using Sikadure – 31CF adhesive with



embedment length of 20db is about 94% of cast in place pull-out load, and these

values are less than the pull-out load of cast in place samples.

The average pull-out load of Ø10 bars in post- installed rebar samples using

EPICHOR 1768 adhesive with embedment length of 10db is about 101% of cast in

place pull-out load, and for embedment length of 15 db is about 101% of cast in

place pull-out load, and for embedment length of 20 db is about 101% of cast in place

pull-out load, and these values are more than the pull-out load of cast in place

samples, so the use of EPICHOR 1768 is preferred.

The average pull-out load for the same bars in post- installed rebars using UHPSCC

adhesive is approximately same as that for EPICHOR 1768 adhesive.


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25

So it appears from the shown results that installing the bars in post-install rebar

samples using adhesives is equivalent to installing the bars in cast in place samples,

especially when using EPICHOR 1768.


The mode of failure of using Ø10 bars either in cast in place samples or in post-

installed rebar samples using adhesives with embedment lengths 10 db and 15 db is

concrete failure mode. While the mode of failure of post-installing rebar samples

using mortar with embedment lengths 10 db, 15 db and 20 db is the pull-out of the

anchors. So, the use of mortar in post-installed rebars is not preferred.

The mode of failure of Ø10 bars in cast in place samples with embedment length

20db is concrete failure mode, while the mode of failure for Ø10 bars in post-installed

bar samples using chemical adhesives and UHPSCC adhesive with embedment length

20 db is yielding of the anchor followed by rupture or elongation in the bar.

The yielding failure mode of Ø10 bars did occur in post-installed rebar samples using

adhesives when installing the bars with embedment length of 20 db (20 cm ) means

that, Ld is less than calculated by the ACI code.



Table ( 4.3.a) : Control samples


Pull-out load

(KN)

Embedment length


22.5



30.9



by bond failure

32

32.5

20 db Yielding of the anchor followed

by bond failure

31.5


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Pull-out load

(KN)

Embedment length

Concrete failure 23.8

23

10 db Concrete failure 23.7


Pull out , combined cone failure 32.2

30.8

15 db Pull out , combined cone failure 31.5

Pull out , combined cone failure 32


33





Pull-out load

(KN)

Embedment length


failure

27.9

26.9

10 db


by anchor rupture

29


31



Pull out of the anchor 33.5

32.5

20 db Pull out of the anchor 33.1

Pull out of the anchor 35



Pull-out load

(KN)

Embedment length


21.1

10 db Pull out of the anchor 22.8


31.8

15 db Pull out of the anchor 33



by anchor rupture

32.4

32.4

20 db

Steel yielding of the anchor

followed by elongation of the

bar.

25.5 NA


by anchor rupture

32.4


Rebar Connections

20

0

5

10

15

20

25

30

35

40

10 db 15 db 20 db


Ave

rag

e p

ull-

ou

t lo

ad (

KN

)

mortar

UHPSCC

EPICHOR 1768

sikadure - 31CF

control



Pull-out load

(KN)

Embedment length


18



19.2




26.7







of Ø8 bars in post-installed rebar samples using Sikadure – 31CF, EPICHOR 1768

and UHPSCC adhesives with embedment lengths of 10db, 15db and 20db is

approximately equal to the average pull-out load of Ø8 mm bars which are inserted in

concrete in cast in place samples.

The average pull-out load for Ø8 bars which are embedded in concrete in post-

installed rebar samples using mortar with embedment length of 10db is about 73% of

cast in place samples pull-out load, for embedment length of 15 db is about 67% of


Rebar Connections

22

cast in place samples pull-out load and for embedment length of 20 db is about 90%

of cast in place samples pull-out load.


The mode of failure of Ø8 rebars in cast in place samples with embedment length of

10db and 15db is concrete failure, while the mode of failure of Ø8 bars in cast of

place samples with embedment length of 20 db is yielding of the anchor followed by

bond failure.

The mode of failure of using Ø8 rebars in post-installed bar samples using chemical

adhesives with embedment length of 10db is concrete failure, while the mode of

failure of using Ø8 mm bars in post-installed rebar samples using chemical adhesives

with embedment length of 15db and 20db is pull-out of the anchors and combined

cone failure.

The mode of failure of using Ø8 bars in post-installed rebar samples using mortar

with embedment length of 10 db, 15 db and 20db is pull-out of the anchor, so the use of

mortar is not preferred.

The yielding failure mode of Ø8 bars did occur in post-installed rebar samples using

adhesives when installing the bars with embedment length of 20 db (16 cm ) which

means that, Ld is less than calculated by the ACI code.


Rebar Connections

21

4.3 - Failure mode under pull-out loads

4.3.1- Failure of anchor steel

This failure is characterized by yielding and fracture of steel rod and is likely to

occur only with sufficiently long embedment depths with strong adhesives, and in our

research this failure appears in the next locations :

- Yielding in steel Ø10 mm embedded with length of 20db in concrete using

Sikadure – 31CF , EPICHOR 1768 and UHPSCC adhesives.

- Fracture of steel rod in steel Ø8mm embedded with length of 20db in concrete in

cast in place concrete and when the bars are installed using UHPSCC.

Figure (4.4) shows a photo of steel yielding.

Figure (4.4 ): Yielding of steel bar

4.3.2- Pull-out of the anchor

Pull-out of the anchor failure is also called bond failure. In our research this failure

appears on the following cases:

- Pull- out of Ø10 mm steel bars installed in concrete using mortar because of the

weak bond.

- Combined cone failure mode occurs in Ø8 mm steel bars imbedded in concrete

using Sikadure-31CF , EPICHOR 1768, UHOSCC adhesives, or cast in place with

embedded lengths of 10db and 15db.


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27

- Pull- out failure in Ø8 mm steel bars embedded in concrete using mortar because of

the weak bond .

Figure (4.5) shows pull out failure with cone.

Figure (4.5 ): Cone failure mode

4.3.3- Splitting of concrete failure :

Anchors installed in thin, unreinforced slabs and beams may result in a split in the

structural member where the concrete slab or beam fails in bending. In our research

this failure appears in the following cases:

- All concrete samples with steel bars Ø12 mm that are anchored in concrete with

embedment lengths of 10db and 15db by all kinds of adhesives and the concrete

samples that are cast in place with steel anchors.


embedment lengths of 15 db and 20 db using " Sikadure – 31CF , EPICHOR 1768 ,

UHRSCC " adhesives, and the concrete sample that are cast in place with steel

anchors.


embedment lengths of 10db by all kinds of adhesives and the concrete samples that are

cast in place with steel anchors. Figure (4.6) shows splitting of concrete failure.


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26

Figure ( 4.6 ): Splitting of concrete failure

Conclusion and Recommendations

CH. 5 Conclusion and Recommendation Efficiency of Post Installed

Rebar Connections

28

Conclusion and Recommendation

After recording the test results of all samples, the following conclusions and

recommendations are outlined from this study.

5.1- Conclusion and recommendation

The results show that, post-installed rebar connection is suitable for works of repair,

rehabilitation and strength of old constructions and the results shows that the post-

installed rebar connection using adhesives gives equal pull-out strength compared to

cast in place concrete with similar embedment length.

The following conclusions have been reached:

Post-installed bars using adhesives can provide accurate and reliable estimates

of in-place concrete strength using very simple and cheap apparatus. The most

important thing in this process is doing all steps of fixing the bar according to

the steps shown before as cleaning the holes and filling the hole around the bar

by sufficient amount of adhesive.

Reinforcing bar diameter in either cast in place concrete or post-installed

rebar using adhesives has very important effect on the bond strength, since the

bond strength increases with increasing the diameter of the steel

reinforcement.

Using of the mortar as bonding materials in post-installed rebar is not

preferred because of the week bond between the steel bar and concrete

compared to the other adhesives.

The results shown using mortar in Ø 10 mm bars with anchorage depth 10

db, 15 db and 20 db is not recommended in fixing new bars, since the mode of

failure is pull out of the bars since it depends on friction only.

The pull-out strength of the two chemical adhesives " EPICHOR 1768 and

Sikadure – 31CF" used in this research are relatively very close, although the


Rebar Connections

29

results of EPICHOR 1768 adhesives give relatively higher pull-out strength in

several samples.

The use of EPICHOR 1768 is more economical because of the amount of

filler that mixed with the resin and hardener, since the amount of the filler is

four times the amount of the resin and hardener, and since the price of the

containers of the two chemical adhesives " EPICHOR 1768 and Sikadure –

31CF" is the same in the local market.

For all the diameters used in this study and with embedment length of 15 db or

more anchorage depths, the use of UHPSCC adhesive is recommended.

For Ø 8 reinforced steel bars and for all types of adhesives, the recommended

depth of anchorage is between anchorage length of 10 db and 15 db because

the mode of failure in these samples is between concrete failure " in anchorage

length 10 db to steel yielding failure" in anchorage length 15 db. And in this

case the pull-out strength is about 28 KN , and this is useful for repair of

constructions especially in jacketing of columns.

For Ø 10 reinforced steel bars and for all types of adhesives except mortar,

the recommended depth of anchorage should not be more than 15 db because

of the yielding of the anchor is followed by anchor rupture or bar elongation.

According to the failure mode specially concrete failure in post-installed rebar

Ø10, Ø12 mm, the confinement gives a high pull-out strength if used, since

the confinement and stirrups give more strength to concrete cylinders.

Using UHPSCC is the most cheep adhesive " of the non chemical adhesives"

for post installed rebar connection, since it gives good results in pull- out load.

The pull-out strength of the two chemical adhesives " EPICHOR 1768 and

Sikadure – 31CF" used in this research are relatively very close to their

manufactures' data sheets.


Rebar Connections

13

The anchorage length in post-installed rebar connections by chemical

adhesives are often much shorter than the values required according to ACI

318-11 code equation of Ld. We show this conclusion on reinforced steel 10

mm, since the best anchorage length is 15 cm in post installed but in the code

equations 25 cm is needed. Also for steel bars 8mm the best anchorage length

is between 8 cm to 12 cm while the length in the code equation is 20 cm.

Using EPICHOR 1768 is the most economical in construction works.

The bonding of the anchorage reinforced steel bars to concrete in post-

installed rebar must be more than the tensile strength of the reinforced steel

bar. And we can achieve this by increasing the length of the anchors and by

choosing the best adhesives.

We should determine the amount of adhesives that are needed for any work to

deal with the allowed workability time after mixing the adhesives according

to the manufacturer’s recommendations, and according to the ability of the

worker to do the work in time.

In order to achieve the best pull-out strength of post-installed rebar

connections by adhesives we must follow the steps of work in chapter 3 like

cleaning and drying the holes, and injecting a sufficient amount of adhesives .

5.2 - Recommendation for the future studies

Some recommendations for future studies are stated:

Post- installed rebar samples without any adhesives, only driving by hammer

down the bars into concrete need to be studied.

Using concrete samples more than 20 cm in diameter.


Rebar Connections

15

Testing the effects of confinement for post installed rebar samples compared

to the same samples of post installed rebar without confinement.

Since the pull-out strength of post installed rebar connection using chemical

adhesives is equal or larger than the pull-out strength of cast in place, so a

research should be conducted about the durability of those adhesives and the

behavior of the adhesives when exposed to fire and other durability

conditions.

Using concrete samples of compressive strength more than 250 kg/cm

2.

References

References Efficiency of Post Installed

Rebar Connections

14

References

[1] Norbert Randl, " Behavior , design and application of post installed

reinforcement" fib symposium Prague 2011 pp. 1189 – 1192.

[2] ACI Committee 408 "Bond and Development of Straight Reinforcing Bars in

Tension" (ACI 408R-03 ) American Concrete Institute, 2003 ,pp 3 – 4.

[3] Levent Mazillguney., ― Tensile behavior of chemically bonded post installed

anchors in low strength reinforced concrete" MS. Thesis, Middle East Technical

University, Ankara, 2007, pp. 4 – 4.

[4] ACI Committee 318"Building Code Requirements for Structural Concrete"(ACI

318M-11) American Concrete Institute, Farmington Hills, MI, 2011, pp 421-446.

[5] ACI Committee 355, ―State-of-Art Report on Anchorage to Concrete‖, ACI

Structural Journal, July 1991, pp. 1-71.

[6] Li, Y., Winkler, B., and Eckstein, A., ―Failure Analysis of Anchoring Systems in

Concrete‖, VIII International Conference on Computational Plasticity, CIMNE,

Barcelona, 2005, pp. 1-4.



University, Ankara, 2007, pp. 28-33,

[8] Cook, R.A., Konz, R.C., ―Factors Influencing Bond Strength of Adhesive

Anchors‖, ACI Structural Journal, Vol. 98, No.1, January-February 2001, pp.76-86.

[9] Erdoğan, T.Y., ―Beton‖, ODTÜ Geliştirme Vakfı, Ankara, 2003, pp. 450-452

[10] Gesoğlu, M., ―Load Deflection Behavior of High Strength Concrete Anchors

Under Static and Cyclic Tension, and Shear Loading‖, MS. Thesis, Boğaziçi

University, İstanbul, 1995, pp. 26-41.

[11] Erdoğan, T.Y., Erdoğan, S.T., ―Sorular ve Yanıtlarıyla Beton‖, Türkiye Hazır

Beton Birliği, Ankara, 2006, pp. 89-97.

[12] R. Eligehausen, H. Spieth,., ―Post-Installed Rebar Connections‖, International

Symposium on Connections Between Steel and Concrete, Rilem, 2001 pp. 29-41.

[13] M. Gesoğlu, T. Özturan, M. Özel,., and E. Güneyisi,., ―Tensile Behavior of Post-

Installed Anchors in Plain and Steel Fiber-Reinforced Normal and High- Strength

Concretes‖, ACI Structural Journal, Vol. 102, No.2, March-April 2005 pp. 224-231


Rebar Connections

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[14] A. Çolak, ―Parametric Study of Factors Affecting the Pull-out Strength of Steel

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University, Ankara, 2007, pp. 15 – 20.

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Appendix A

YASMO MISR Chemicals For Construction

EPICHOR 1768 Patch Repairing Quick Setting Epoxy

For more information please contact our technical department Head Office : 21 Takseem El Awkaf – EL Sawah Sq. Cairo – Egypt Tel : 002 / 02 24535678 ‐ 24535679 Fax : 002 / 02 24538986 Web site : www.yasmomisr.com E‐mail: [email protected]

YASMO MISR Quality between your hands

Epoxy

General Properties: EPICHOR 1768 is two component solvent free, clear epoxy product. Can be mixed with graded sand to be used as a fixing dowels in concrete and repairing mortar. Is relatively insensitive to moisture. Has quick initial setting time. Has thyrotrophic effect, thus suitable for fixing steel dowels to concrete especially to soffits and vertical surfaces. Has high compressive, tensile & bond strength which ensures monolithic behavior with concrete.

Uses: As an adhesive mortar for fixing dowels in concrete. As patch repair mortar for concrete. In machinery & rail grouts. For repairing & coatings of potable water tanks.

Application: 1. Clean the holes and remove oil and grease or foreign materials. 2. Wear gloves & eye goggles before working & be sure of good ventilation. 3. Add resin EPICHOR 1768 to hardener and mix well. Apply EPICHOR 1768 as a primer inside the hole

(the hole should be 6mm wider than the steel bar). 4. To make the mortar add resin EPICHOR 1768 to hardener and mix well, then add the filling to the

previous mixture & mix well till reaching a mortar with homogenous consistency. 5. Apply EPICHOR 1768 mortar with the suitable tool according to usage purpose. 6. Fill 2/3 of the hole with mixed mortar, insert the steel bar in. Be sure that the bar is imbedded with enough

suitable depth in the hole, 7. Failure should happen to steel before its separation from hole. 8. Clean tools using solvent ex: Thinner.

Technical Data: ASTM (C - 580 Method A) : Flexural test

Flexural strength (After 7 days) 42 N/mm2 Flexural strength (After 24 days) 67 N/mm2

Modulus of Elasticity 2320 N/mm2

Bs-En 1881-2006 : PULLOUT test 1. For pure epoxy (Resin + Hardener)

Bond strength 6.7 N / mm2 Failure happened to steel bar For rod Ø = 8mm, Imbedded length = 51mm Failure load = 0.88 ton The steel bar used is mild steel test done after 15 days from casting date.

2. For Mortar epoxy (Resin + Hardener + filling) Bond strength 9.70 N / mm2 Failure happened by yield of steel bar before pullout

• For rod Ø =11mm, Imbedded length = 94 mm Failure load = 3.0 ton • Tests were carried after 7 days from casting date. • Concrete compressive strength 31.4 N /mm2.• Bond between steel and concrete is achieved by Epichor 1768 mixed with graded special sand

by thickness about 3 mm around steel bar (R+H) : filling 1 : 4Tensile strength : 2.90 N/mm2 (After 7 days) ASTM (C 301) Compressive strength : 54.0 N/mm2 (After 7 days) ASTM (C 579 Method B) Initial Curing Time : After 24 hours of mixing Final Curing Time : After 7 days at ambient temperature Pot Life : 20 min. at 24oC Density : 2.1 gm / cm3 for mortar epoxy Chemical Resistance : Excellent resistance against water, alkalis, and detergents, moderate against acids; poor against organic solvents. Shelf Life : 18 months in closed container and away from sun light, heat and humidity.

Environment: - Boots, rubber gloves, dust masks, and safety goggles.

- Refer to MATERIAL SAFETY DATA SHEETS (MSDS) END OF TECHNICAL DATA

Documents

The Islamic University of Gaza - library.iugaza.edu.pslibrary.iugaza.edu.ps/thesis/114040.pdf · The Islamic University of Gaza ةزغ – يهلاسلإا ... Post-installed rebars