Effect of Glass Fiber Reinforced Polymer on Mechanical

Behavior of High Strength Concrete

للخرسانة عالية القوةالسلوك الميكانيكي تأثير االلياف الزجاجية على

Mahmoud Mazen Hilles

Supervised by:

Prof. Mohammed Ziara

Professor of Civil Engineering

A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of

Science in Civil Engineering - Design and Rehabilitation of Structures

November/ 2016

زةــغ –ةــالميــــــة اإلســـــــــامعـالج

ن البحث العلمي والدراسات العلياشئو

الهندســـــــــــــــــةة ــــــــــــــــليــــك

-الهندســــــة المدنيـــــــــة ر ــــماجستي

تصميم و تأهيل المنشات

The Islamic University–Gaza

Research and Postgraduate Affairs

Faculty of Engineering

Master of Civil Engineering- Design

and Rehabilitation of Structures

إقــــــــــــــرار

ان:أنا الموقع أدناه مقدم الرسالة التي تحمل العنو

Effect of Glass Fiber Reinforced Polymer on Strength

Properties of High Strength Concrete

تأثير االلياف الزجاجية على خصائص القوة للخرسانة عالية القوة

ن هذه أقر بأن ما اشتملت عليه هذه الرسالة إنما هو نتاج جهدي الخاص، باستثناء ما تمت اإلشارة إليه حيثما ورد، وأ

لنيل درجة أو لقب علمي أو بحثي لدى أي مؤسسة تعليمية أو بحثية االخرين الرسالة ككل أو أي جزء منها لم يقدم من قبل

أخرى.

Declaration

I understand the nature of plagiarism, and I am aware of the University’s policy on this.

The work provided in this thesis, unless otherwise referenced, is the researcher's own work, and

has not been submitted by others elsewhere for any other degree or qualification.

:Student's name محمود مازن حلس اسم الطالب:

:Signature التوقيع:

14/11/2016 التاريخ:Date:

I

Abstract

The usage of high strength glass fiber reinforced concrete (HSGFRC) in the construction

applications has been increasing worldwide and will make an impact in Gaza Strip. Due to the

limited land area available for construction, the fast growing population, bad and unstable

political conditions, and the continuing wars in Gaza Strip, strong, relatively cheap, and locally

available repairing and strengthening material should be produced.

The main objective of this investigation is to study the effect of addition of alkali resistant glass

fiber reinforced polymer (AR-GFRP) with various proportions typically 0.3, 0.6, 0.9, and 1.2

by weight of cement on the mechanical behavior of plain HSC (without fiber) with 28 days

cube compressive strength up to 60 MPa using available materials in the Gaza local market.

Results show that it is possible to produce HSGFRC in Gaza strip using materials that are

available at the local markets if they are carefully selected. Based on the experimental results,

the compressive strength, splitting tensile strength, flexural strength and density of HSC is

found to be increases as fiber percentage increases for both ages 7 and 28 days. The compressive

strength of HSC is found to be 57.85, 61.05, 66.01, 66.34 and 66.60 MPa at fiber percentage of

0.0, 0.3, 0.6, 0.9, and 1.2 respectively for 28 days. The 28 days percentage of increasing over

the reference mix is found to be maximum equal to 13.14 percent at 1.2 fiber percentage. The

density of HSC is found to be increases very slightly as fiber percentage increases from 0.0 to

1.2, typically from 2417 to 2441 kg/m3. The splitting tensile strength of HSC is found to be

4.12, 4.77, 5.53, 5.84 and 6.73 MPa at fiber percentage of 0.0, 0.3, 0.6, 0.9, and 1.2 respectively

for 28 days. The 28 days’ percentage of increasing over the reference mix is found to be

maximum equal to 63.22 percent at 1.2 fiber percentage. The flexural strength of HSC is found

to be 6.35, 7.53, 8.28, 8.79 and 9.68 MPa at fiber percentage of 0.0, 0.3, 0.6, 0.9, and 1.2

respectively for 28 days. The 28 days’ percentage of increasing over the reference mix is found

to be maximum equal to 52.36 percent at 1.2 fiber percentage. The mode of failure is found to

be taken place gradually with the formation of cracks as fiber percentage increase, compared

with plain HSC specimens, the failure was sudden and completely destruction. Hence it is

established that the presence of fibers in the matrix has contributed towards prevent sudden

crack formation.

II

الملخص

ان استخدام الخرسانة عالية القوة المسلحة بااللياف الزجاجية في التطبيقات االنشائية يتزايد و بشكل كبير

. بسبب ضيق مساحات الراضي المتاحة على مستوى العالم, و من المؤكد ان يكون له اثره في قطاع غزة

ضاع االمنية الغير مستقرة و تكرار حدوث للبناء, و التزايد الكبير في اعداد السكان, باالضافة الى االو

الحروب, االمر الذي يستدعي استخدام مثل هذه المواد الرخيصة نسبيا و موادها المتوفرة محليا كمواد تقوية

تاثير اضافة االلياف الزجاجية دراسة هو البحث ان الهدف االساسي لهذا و ترميم للمنشات المتضررة.

على خصائص القوة من وزن االسمنت 1.2, و 0.9, 0.6, 0.30مختلفة و هي المقاومة للقلويات بعدة نسب

ميجا باسكال 60يوم تساوي 28عند تحمل ضغط للمكعببقوة البحتة ) بدون الياف( للخرسانة عالية القوة

. في قطاع غزة باستخدام المواد المتوفرة بالسوق المحلي

القوة المسلحة بااللياف الزجاجية في قطاع غزة باستخدام ائج انه يمكن انتاج الخرسانة عاليةاظهرت النت

االنحناء, بناءا على النتائج المخبرية, قوة الضغط, الشد, المواد المتوفرة محليا في حال تم اختيارها بعناية.

قوة الضغط وجدت انها تساوي للخرسانة عالية القوة وجدت بانها تزيد مع زيادة نسبة االلياف. و الكثافة

1.2, و 0.9, 0.6, 0.3, 0.0عند نسبة الياف تساوي ميجا باسكال 66.60, و 66.34, 61.05, 57.85

يوم وجدت لتكون القيمة القصوى 28. نسبة الزيادة عن الخلطة المرجعية بعد يوم 28 بعدعلى التوالي

كل طفيف جدا مع يوم وجد بانها تزيد بش 28بعد . اما الكثافة1.2عند نسبة الياف تساوي 13.14تساوي

. قوة الشد وجدت انها تساوي 3كجم/م 2441الى 2417 بالضبط من, 1.2الى 0.0زيادة نسبة االلياف من

1.2, و 0.9, 0.6, 0.3, 0.0عند نسبة الياف تساوي ميجا باسكال 6.73, و 5.84, 5.53, 4.77, 4.12

يوم وجدت لتكون القيمة القصوى 28. نسبة الزيادة عن الخلطة المرجعية بعد يوم 28على التوالي بعد

,و 8.79, 8.28, 7.53, 6.35. قوة االنحناء وجدت انها تساوي 1.2عند نسبة الياف تساوي 63.22تساوي

. نسبة يوم 28على التوالي بعد 1.2, و 0.9, 0.6, 0.3, 0.0عند نسبة الياف تساوي ميجا باسكال 9.68

عند نسبة الياف 52.36وجدت لتكون القيمة القصوى تساوي يوم 28الزيادة عن الخلطة المرجعية بعد

شكل االنهيار وجد بانه يحدث تدريجيا اثناء تشكل الشقوق كلما زادت نسبة االلياف, مقارنة .1.2تساوي

مع عينات الخرسانة عالية القوة البحتة حيث ان شكل االنهيار كان مفاجئا و هش. لذا فانه تم استنتاج ان

تشكل الشقوق المفاجئ. منعف في الخلطة الخرسانية يساهم في وجود االليا

III

Dedication

To my father’s soul, my mother, and my fiancee

IV

Acknowledgment

I would like to express my sincere appreciation to Prof. Mohammed Ziara, Department of Civil

Engineering, Faculty of Engineering, The Islamic University of Gaza, for their help and

guidance in the preparation and development of this work. The constant encouragement,

support and inspiration they offered were fundamental to the completion of this research.

Special thanks go to the material and soil lab of the Islamic University of Gaza, for their logistic

facilitations and their continuous support. Finally, I would like to thank everyone who gave

advice or assistance that contributed to complete this research.

V

Table of contents

Abstract ..................................................................................................................................... I

II ......................................................................................................................................... الملخص

Dedication ............................................................................................................................... III

Acknowledgment ................................................................................................................... IV

Table of contents ...................................................................................................................... V

List of Tables ....................................................................................................................... VIII

List of Figures ........................................................................................................................ IX

List of Abbreviations ............................................................................................................ XII

Chapter 1: Introduction ........................................................................................................... 2

1.1 General Background ......................................................................................................... 2

1.2 Research Significant ......................................................................................................... 2

1.3 Research Aim and Objectives ........................................................................................... 3

1.4 Methodology ..................................................................................................................... 3

1.5 Thesis Organization .......................................................................................................... 4

Chapter 2: Literature Review ................................................................................................. 6

2.1 High Strength Concrete (HSC) ......................................................................................... 6

2.1.1 Definition ................................................................................................................... 6

2.1.2 Benefits and Limitations of Using HSC in Practice .................................................. 6

2.1.3 Application of HSC ................................................................................................... 7

2.1.4 Materials Selection of HSC ....................................................................................... 8

2.1.4.1 Cement ................................................................................................................ 8

2.1.4.2 Supplementary Cementitious Materials (SCMs) ................................................ 9

2.1.4.3 Water Reducing Admixtures ............................................................................ 10

2.1.4.4 Aggregates ........................................................................................................ 12

2.1.4.5 Mixing Water .................................................................................................... 13

VI

2.1.5 Microstructure of HSC ............................................................................................ 13

2.1.6 Mix Proportion ........................................................................................................ 14

2.2 Fiber Reinforced Concrete (FRC) .................................................................................. 17

2.2.1 General Background ................................................................................................ 17

2.2.2 Glass Fiber Reinforced Concrete (GFRC)............................................................... 21

2.2.3 Applications of GFRC ............................................................................................. 23

2.3 High Strength Fiber Reinforced Concrete (HSFRC) ...................................................... 24

2.4 Concluding Remarks ...................................................................................................... 26

Chapter 3: Test Program and Laboratory Works .............................................................. 28

3.1 General Description ........................................................................................................ 28

3.2 Test Program................................................................................................................... 28

3.3 Materials Selection and Properties ................................................................................. 29

3.3.1 Cement ..................................................................................................................... 29

3.3.2 Coarse Aggregates ................................................................................................... 30

3.3.3 Fine Aggregate ........................................................................................................ 32

3.3.4 Normal Range Water Reducing Admixture (NRWR) ............................................. 33

3.3.5 Glass Fiber Reinforced Polymer (GFRP) ................................................................ 34

3.3.6 Water ....................................................................................................................... 34

3.4 Mix Proportioning of HSGFRC ..................................................................................... 34

3.5 Preparation of HSGFRC and Mixing Procedure ............................................................ 37

3.6 Testing Procedure ........................................................................................................... 38

3.6.1 Compressive Strength Test ...................................................................................... 38

3.6.2 Splitting Tensile Strength Test ................................................................................ 39

3.6.3 Flexural Strength Test ............................................................................................. 42

3.6.4 Unit Weight ................................................................................................................. 45

3.7 Curing Procedure ............................................................................................................ 46

VII

Chapter 4: Test Results and Discussion ............................................................................... 48

4.1 Compressive Strength and Density Test Results ............................................................ 48

4.1.1 Effect of AR-GFRP on the Compressive Strength of HSC ..................................... 50

4.1.2 Effect of AR-GFRP on the Strength Gain with Age of HSC .................................. 52

4.1.3 Effect of AR-GFRP on the Density of HSC ............................................................ 53

4.1.4 Crack Pattern and Mode of Failure .......................................................................... 54

4.2 Splitting Tensile Strength Test Results .......................................................................... 57

4.2.1 Effect of AR-GFRP on the Splitting Tensile Strength of HSC ............................... 58

4.2.2 Crack Pattern and Mode of Failure .......................................................................... 60

4.3 Flexural Strength (Modulus of Rapture) Test Results .................................................... 63

4.4 Result Summary ............................................................................................................. 66

Chapter 5: Conclusions and Recommendations .................................................................. 68

5.1 Conclusions .................................................................................................................... 68

5.2 Recommendations .......................................................................................................... 69

The Reference List .................................................................................................................. 70

VIII

List of Tables

Table (2.1): Chemical Analysis for Normal Portland Cement and Supplementary

Cementitious Materials (Nawy, 2008). ..................................................................................... 10

Table (2.2): Mixture Proportions and Properties of Commercially Available HSC (Steven et

al. 2003). ................................................................................................................................... 15

Table (2.3): Requirements of Ingredient Materials for HSC (Rashid and Mansur, 2009). ..... 16

Table (2.4): Properties of Different Types of Fibers (Steven et al. 2003). .............................. 19

Table (2.5): Chemical Composition of Selected Glasses, (Percent) (ACI Committee 544.1,

2002). ........................................................................................................................................ 22

Table (2.6): Properties of Selected Glasses (ACI Committee 544.1, 2002). ........................... 22

Table (3.1): Test Program. ....................................................................................................... 29

Table (3.2): Physical Properties of Cement According to Manufacturer Data Sheet. ............. 30

Table (3.3): Sieve Analysis and Physical Properties of Coarse Aggregate Types. ................. 30

Table (3.4): Sieve Analysis of Combined Coarse Aggregate According to ASTM C33 (2003)

and Physical Properties. ............................................................................................................ 31

Table (3.5): Grain Distribution of Fine Aggregate and Physical Properties. .......................... 32

Table (3.6): Properties of Normal Range Water Reducer. ...................................................... 33

Table (3.7): Properties of AR-GFRP. ...................................................................................... 34

Table (3.8): Mix Proportioning for 1 m3 of Concrete for The Reference Mixture. ................. 35

Table (3.9): 28 Day Cylinder Compressive Strength Test Result. .......................................... 36

Table (3.10): HSGFRC Mixtures for 1 m3 of Concrete........................................................... 37

Table (4.1): Cube Compressive Strength and Density Test Results. ....................................... 49

Table (4.2): Average Cube Compressive Strength and Density Test Results. ........................ 49

Table (4.3): Splitting Tensile Strength Test Results. ............................................................... 57

Table (4.4): Average Splitting Tensile Strength Test Results. ................................................ 58

Table (4.5): Flexural Strength (Modulus of Rapture) Test Results. ........................................ 63

Table (4.6): Average Flexural Strength (Modulus of Rapture) Test Results. ......................... 64

IX

List of Figures

Figure (1.1): Summary of Methodology Flow Chart. ............................................................... 3

Figure (2.1): Effect of Superplasticizers on Slump Loss (Mindess, 1988). ............................ 11

Figure (2.2): Microstructure of NSC (Buyukozturk and Lau, 2007). ..................................... 13

Figure (2.3): Microstructure of HSC (Buyukozturk and Lau, 2007). ..................................... 14

Figure (2.4): Steel, Glass, Synthetic and Natural Fibers (Steven et al. 2003). ........................ 17

Figure (2.5): Load–Displacement Curves ............................................................................... 21

Figure (2.6): Chopped Strands AR-GFRP (Nippon Electric Glass Co. Ltd. 2007). ............... 23

Figure (2.7): Alkali Resistivity of Glass Fiber and ZrO2 Content (Nippon Electric Glass Co.

Ltd. 2007). ................................................................................................................................ 23

Figure (2.8): Mechanical Behavior of FRC Compared with Plain Matrix (Buyukozturk and

Lau, 2007). ................................................................................................................................ 25

Figure (3.1): Coarse Aggregate Sieve Analysis According to ASTM C33 (2003). ................ 31

Figure (3.2): Grain Distribution of Fine Aggregate. ............................................................... 33

Figure (3.3): 150 x 300 mm Cylindrical Specimens. .............................................................. 36

Figure (3.4): MATEST C104 Servo Plus 2000 KN Capacity Compression Test Machine. ... 36

Figure (3.5): The Power-Driven Revolving Drum Mixer Used on This Research. ................ 37

Figure (3.6): (a) and (b) Cube Specimens. .............................................................................. 38

Figure (3.7): MATEST C104 Servo Plus 2000 KN Capacity Compression Test Machine. ... 39

Figure (3.8): Cylindrical Specimens. ....................................................................................... 40

Figure (3.9): Split Cylinder Test Setup. .................................................................................. 40

Figure (3.10): (a), (b), and (c) Failure on Cylindrical Specimen after Split Cylinder Test. .... 41

Figure (3.11): (a) and (b) Prism Specimens. ........................................................................... 43

Figure (3.12): Schematic View for Flexure Test Setup of Concrete by Center-Point Loading.

.................................................................................................................................................. 44

Figure (3.13): Center Point Loading Flexural Test Machine. ................................................. 44

Figure (3.14): Fracture on Prism Specimen after Flexural Prism Test. ................................... 45

X

Figure (3.15): Specimens at Curing Basin. ............................................................................. 46

Figure (4.1): Effect of AR-GFRP on 28 Days Compressive Strength of HSC. ...................... 50

Figure (4.2): The Percentage of Increase in Compressive Strength Over the Reference Mix

Due to Addition of AR-GFRP on HSC……………………………………………………….50

Figure (4.3): Comparisons of compressive strength test results with other related researches.

.................................................................................................................................................. 52

Figure (4.4): Effect of AR-GFRP on the Strength Gain with Age of HSC………………….53

Figure (4.5): Effect of AR-GFRP on %7days / 28days Compressive Strength. ..................... 53

Figure (4.6): Effect of AR-GFRP on Density of HSC. ........................................................... 54

Figure (4.7): Mode of Failure and Crack Pattern of Plain HSC Specimens (Without Fiber). 55

Figure (4.8): (a) and (b): Mode of Failure and Crack Pattern of HSC Specimens with 0.3

Fiber Percentage. ...................................................................................................................... 55

Figure (4.9): Mode of Failure and Crack Pattern of HSC Specimens with 0.6 Fiber

Percentage. ................................................................................................................................ 56

Figure (4.10): Mode of Failure and Crack Pattern of HSC Specimens with 0.9 Fiber

Percentage. ................................................................................................................................ 56

Figure (4.11): Mode of Failure and Crack Pattern of HSC Specimens with 1.2 Fiber

Percentage. ................................................................................................................................ 56

Figure (4.12): Effect of AR-GFRP on Splitting Tensile Strength of HSC. ............................. 59

Figure (4.13): The Percentage of Increase Over the Reference Mix Due to Addition of AR-

GFRP on HSC: Comparison between Compressive Strength and Splitting Tensile

Strength……………………………………………………………………………………….59

Figure (4.14): Comparisons of splitting tensile strength test results with other related

researches. ................................................................................................................................. 60

Figure (4.15): Mode of Failure of Plain HSC Specimens (Without Fiber). ............................ 61

Figure (4.16): Mode of Failure of HSC Specimens with 0.3 Fiber Percentage. ..................... 61

Figure (4.17): Mode of Failure and Crack Pattern of HSC Specimens with 0.6 Fiber

Percentage. ................................................................................................................................ 61

XI

Figure (4.18): Mode of Failure and Crack Pattern of HSC Specimens with 0.9 Fiber

Percentage. ................................................................................................................................ 62

Figure (4.19): Mode of Failure and Crack Pattern of HSC Specimens with 1.2 Fiber

Percentage. ................................................................................................................................ 62

Figure (4.20): Effect of AR-GFRP on Flexural Strength (Modulus of Rapture) of HSC. ...... 65

Figure (4.21): The Percentage of Increase Over the Reference Mix Due to Addition of AR-

GFRP on HSC: Comparison Between Compressive, Splitting Tensile and Flexural Strength.

.................................................................................................................................................. 65

Figure (4.22): Comparisons of flexural strength test results with other related researches. ... 66

XII

List of Abbreviations

ACI American Concrete Institute

ASTM American Society for Testing and Materials

AR-GFRC Alkali Resistant-Glass Fibers Reinforced Concrete

AR-GFRP Alkali Resistant-Glass Fibers Reinforced Polymer

CV Coefficient of Variation (%)

Fst Concrete Splitting Tensile Strength

Fr Concrete Flexural Strength or Modulus of Rapture

FRC Fiber Reinforced Concrete

GFRC Glass Fibers Reinforced Concrete

GFRP Glass Fibers Reinforced Polymer

HRWRA High-Range Water-Reducing Admixture

NRWRA Normal-Range Water-Reducing Admixture

HSC High Strength Concrete

HSFRC High Strength Fiber Reinforced Concrete

HSGFRC High Strength Glass Fiber Reinforced Concrete

ITZ Interfacial Transition Zone

NSC Normal Strength Concrete

S Stander Deviation

SFRC Steel Fibers Reinforced Concrete

UHSC Ultra High Strength Concrete

VHSC Very High Strength Concrete

W/C Water / Cement Ratio

Chapter 1

Introduction

2

Chapter 1: Introduction

1.1 General Background

A High Strength Glass Fiber Reinforced Concrete (HSGFRC) it is an advanced form for

concrete technology, which have all advantages of high strength concrete (HSC) and glass fiber

reinforced concrete (GFRC). By using this form of concrete technology, the problems and

disadvantages of each type of concrete alone can be overcome.

Unfortunately, HSC has a brittle behavior at ultimate limit state of loading, so, fibers can be

added to improve the structural properties of concrete. It has been recognized that the addition

of small, closely spaced and uniformly dispersed fibers to concrete would act as crack arrester

and would substantially improve its mechanical behavior. The addition of fibers results in a

product which has higher flexural and tensile strengths as compared with normal concrete

(Gustavo and Parra, 2005).

HSFRC shows an improved performance in the hardened state due to the addition of fibers.

Many types of fibers are available; glass fiber reinforced polymer (GFRP) are preferred than

other type due to high ratio of surface area to weight and high strength properties to unit cost

ratio. However, glass fiber which is originally used in conjunction with cement was found to

be affected by alkaline condition of cement. The alkali resistant glass fiber reinforced polymer

(AR-GFRP), which is used, recently has overcome this defect and can be effectively used in

concrete. (ACI Committee 544.1, 2002).

The use of new form of material such as HSGFRC in practice must be based on actual behavior.

Therefore, the effect of addition of AR-GFRP with various percentages on mechanical behavior

of HSC in compression, split tension and flexure is studied on this research.

1.2 Research Significant

Due to bad and unstable political conditions and the continuing wars in Gaza Strip, strong,

relatively cheap, easy to use and locally available repairing and strengthening material should

be produced for that purposes. For new materials like HSGFRC, studies on mechanical

properties are of paramount important for initializing confidence in engineers and builders.

Most of researches related about the study of strength properties of FRC, were made so far with

steel, carbon, and natural fibers. However, insufficient attempts were made with glass fibers. In

addition, the literature indicates that most of studies are available with normal strength concrete

3

(NSC) reinforced with insufficient proportions of glass fibers. However, this study was

conducted to investigate the mechanical behavior of HSC reinforced with various percentages

of glass fibers. Also, several types of glass fibers are available, the initial studies showed

deterioration of glass fibers due to corrosive alkali environment of the cement paste. The AR-

GFRP, which is used, recently has overcome this defect and can be effectively used in concrete.

1.3 Research Aim and Objectives

The aim of this research is to study the effect of the addition of AR-GFRP with various

proportions on the mechanical behavior of HSC using available materials in the Gaza local

market and to help for use the composite of HSGFRC in practice.

In the present experimental investigation, the following are the objectives:

i. To study the strength characteristics of HSGFRC with various percentages of AR-GFRP

and compare it with plain HSC (without fibers), by performing laboratory tests that are

related to compressive strength, splitting tensile strength, flexural strength, and density.

ii. To compare the mode of failure and cracks pattern between HSGFRC and plain HSC.

iii. To evaluate the strength gain with age of HSGFRC.

1.4 Methodology

In general terms, the following methodology shown in Figure 1.1 has followed

Figure (1.1): Summary of Methodology Flow Chart.

Leterature Review

To conduct comprehensive literature review related to the study.

Materials Selection and Tests

Carfull selection and test of suitable ingredient materials required for the experimental study.

Mix Proportoning

Determine the relative quantities of materials to obtain the mix design proportions that achieved the adopted design strength.

Experimental Program

Performing mechanical laboratory tests to achieve the research objectves.

Results and Discussion

Analyzing the experimental output test results to draw conclusions.

4

1.5 Thesis Organization

Chapter 1 (Introduction) This chapter gives general background about HSGFRC, statement

of problem, aim and objectives of the research, and the adopted methodology.

Chapter 2 (Literature Review) This chapter gives general comprehensive literature review

related to HSC and GFRC, in addition of the man constituent materials.

Chapter 3 (Test Program and Laboratory Works) This chapter discusses the materials

properties, adopted mix design, type of laboratory tests and procedures, samples and

specimens that required for tests, and curing condition.

Chapter 4 (Test Results and Discussion)

This chapter includes presentation of the results obtained from testing. Detailed discussion of

results and mechanical properties of each mix also included.

Chapter 5 (Conclusion and Recommendations)

This chapter includes main conclusions and recommendations drawn from this research.

Chapter 2

Literature Review

6

Chapter 2: Literature Review

2.1 High Strength Concrete (HSC)

2.1.1 Definition

ACI committee 363 (1997) defined the high strength concrete (HSC) as a concrete with

specified compressive strength for design of 41MPa or greater. Freedman (1970) defined the

HSC as a concrete with the strength of at least 41MPa at 28 days. Iravani and MacGregor (1998)

stated that HSC is typically recognized as concrete with a 28-day cylinder compressive strength

greater than 42MPa. More generally, concrete with a uniaxial compressive strength greater than

that typically obtained in a given geographical region is considered HSC, although the

preceding values are widely recognized. According to Li (2011), Strengths of up to 140MPa

have been used in different applications, laboratories have produced strengths approaching

480MPa.

2.1.2 Benefits and Limitations of Using HSC in Practice

HSC resists loads that cannot be resisted by normal strength concrete (NSC). In addition, it also

increases the strength per unit cost, per unit weight, and per unit volume as well. These concrete

mixes typically have an increased modulus of elasticity, which increases stability and reduces

deflections.

HSC is specified where reduced weight is important or where architectural considerations

require smaller load carrying elements. In high rise buildings, HSC helps to achieve more

efficient floor plans through smaller vertical members and has also often proven to be the most

economical alternative by reducing both the total volume of concrete and the amount of steel

required for a load bearing member. Also, formwork is a large portion of the cost of constructing

a column; smaller column sizes reduce the amount of formwork needed and result in further

cost savings (PCA, 1994).

In general terms, the main benefits of using HSC in practice can be summarized as follow:

1. High compressive and early strength which make HSC resists loads that cannot be

resisted by NSC.

2. High modulus of elasticity, which increases stability and reduces deflections.

3. Enhanced durability characteristics due to extremely low porous volume.

4. Toughness and impact resistance.

7

5. Increases the strength per unit cost, per unit weight, and per unit volume.

6. Reduction in member size, resulting in increase in useable area and direct savings in the

concrete volume saved.

7. Construction of high rise buildings with the accompanying savings in real estate costs

in congested areas.

8. Longer spans and fewer beams for the same magnitude of loading.

9. Reduction in the number of supports and the supporting foundations due to the increase

in spans.

Along with the inherent benefits of HSC, several less clearly defined limitations can

materialize. Most of these limitations are due to a lack of adequate research under field

conditions, although many of the issues are currently being alleviated though the use of

improved admixtures.

In general, the main limitations of using HSC in practice can be summarized as follow:

1. Increased quality control is needed in order to maintain the special properties desired.

2. Careful materials selection is necessary. High quality materials must be used. These

materials may cost more than materials of lower quality.

3. Low water to cementitious materials ratios require special curing requirements.

4. Since serviceability conditions such as deflection can control design, increased capacity

may not be fully utilized.

5. In concrete plant and at delivery site, additional tests are required. This increases the

cost.

2.1.3 Application of HSC

Accordance to ACI committee 363 (2010), the largest application of HSC in buildings has been

for columns of high rise structures. Since 1972, more than 30 buildings in the Chicago area

have been constructed with columns having a design compressive strength of 62MPa. Also

there have been many applications of HSC in pre-cast pre-stressed bridge girders. In tall

building structures, the load plays a very severe effect on structural members, especially the

columns near the ground level which are required to resist a tremendous axial load which is

mainly due to the accumulated load from all the floors above.

It can be imagined that there will be no space in the ground level if NSC is used for a very tall

building (i.e. more than 60 story). Hence, it is a normal trend to adopt HSC in tall building

8

construction due to its advantages (ACI Committee 363, 2010). According to PCA (1994)

concrete compressive strength of 131 MPa have already been batched by a few ready mix

producers, and placed by contractors in some major structures.

2.1.4 Materials Selection of HSC

The selection of suitable cementitious materials for concrete structures depend on the type of

structure, the characteristics of the aggregates, material availability, and method of

construction. The varieties of HSC do not require exotic materials or special manufacturing

processes, but will require materials with more specific properties than conventional concretes.

As the target strength of concrete increases, it becomes increasingly less forgiving to variability,

both material and testing related. Compared with conventional concrete, variations in material

characteristics, production, handling, and testing will have a more pronounced effect with HSC.

Therefore, as target strengths increase, the significance of control practices intensifies

(Caldarone, 2008).

Evaluating cement and other cementitious materials, chemical admixtures, and aggregates from

various potential sources in varying proportions will indicate the optimum combination of

materials. Variations in the chemical composition and physical properties of any of these

materials will affect the concrete compressive strength (ACI Committee 211.4, 2008).

The supplier of HSC should implement a program to ensure uniformity and acceptance tests for

all materials used in the production of HSC. In general term, the composition of HSC usually

consists of cement, water, fine sand, water reducing admixtures, and supplementary

cementitious materials.

However, the key elements of HSC can be summarized as follows:

1. Low water-to-cement ratio.

2. High dosage of water reducing admixtures (superplasticizers).

3. Large quantity of supplementary cementitous material, i.e. silica fume, fly ash (and/or

other fine mineral powders).

4. Smaller aggregates.

2.1.4.1 Cement

Almost any portland cement type meeting the compositional requirements of ASTM C 150 can

be used to obtain concrete with satisfactory workability having compressive strength up to

about 60 MPa.

9

However, within a given cement type, different brands will have different strength development

characteristics because of the variations in compound composition and fineness that are

permitted by ASTM C 150 (ACI Committee 363, 2010).

2.1.4.2 Supplementary Cementitious Materials (SCMs)

Supplementary cementitious materials (SCMs) or mineral admixtures have undeniably played

a significant role in the evolution of HSC. SCMs are important materials that contribute to the

properties of concrete when used in conjunction with portland cement by reacting either

hydraulically or pozzolanically. Pozzolans are siliceous or alumino-siliceous materials that, by

themselves, possess no hydraulic (cementing) value, but will, in finely divided form and in the

presence of water, chemically react with calcium hydroxide to form compounds having

cementitious properties. Examples are fly ashes, silica fumes, and slag cement (Caldarone,

2008).

The major difference between conventional concrete and HSC is essentially the use of mineral

admixtures in the latter. Fly ash, silica fume, and slag, have been the most commonly used

SCMs in HSC (Steven, 2003).

Mineral admixtures like fly ash and silica fume act as puzzolonic materials as well as fine fillers,

thereby the microstructure of the hardened cement matrix becomes denser and stronger.

The use of silica fume fills the space between cement particles and between aggregate and

cement particles. When combined with cement, these materials have been used for

economically producing binary concretes with specified compressive strengths of at least 70

MPa. For higher strengths, particularly above 80MPa, ternary mixtures containing very fine,

paste densifying pozzolans such as silica fume, metakaolin, or ultra-fine fly ash can be quite

advantageous (Caldarone, 2008). Table 2.1 present the chemical analysis for normal portland

cement and supplementary cementitious materials.

10

Table (2.1): Chemical Analysis for Normal Portland Cement and Supplementary

Cementitious Materials (Nawy, 2008).

Normal Portland

Cement (%)

Microsilica

(%)

Fly Ash,

Class F

(%)

Fly Ash,

Class C

(%)

Slag,

Grade

100 (%)

Silica (SiO2) 20.13 94–98 49.00 40.40 27–38

Calcium oxide (CaO) 63.44 0.08–0.30 5.00 25.40 34–43

Magnesium oxide

(MgO) 2.86 0.30–0.90 1.50 4.70 7–15

Ferric oxide (Fe2O3) 2.96 0.02–0.15 6.00 5.90 .2–1.6

Aluminum oxide (Al2O3) 5.10 0.10–0.40 26.00 17.00 7–12

Sulfur trioxide (SO3) 3.00 — 0.50–0.60 2.75 .15–.23

Potassium oxide (K2O) 1.12 0.20–0.70 0.80–0.90 0.27 —

Sodium oxide (Na2O) 0.30 0.10–0.40 0.25 1.60 .6–.9

Loss on ignition 0.80 0.80–1.50 3.50 0.43 —

Silicon carbide (SiC) — 0.20–0.10 — — —

Carbon (C) — 0.20–1.30 — — .78

C4AF 9.00 — — — 8.89

C3S 57.40 — — — 54.00

C2S 14.40 — — — 19

C3A 8.50 — — — 8

Blaine (cm2g) 3782 100,000+ — — 5360

2.1.4.3 Water Reducing Admixtures

Water reducing admixtures are used to reduce the quantity of mixing water required to produce

concrete of a certain slump, reduce water/cement ratio, reduce cement content, or increase

slump. Water reducers are classified broadly into two categories: normal and high range water

reducers. The normal range water reducers (NRWR) are called plasticizers, while the high range

water reducers (HRWR) are called superplasticizers (Steven et al. 2003).

NRWR meeting the specifications of ASTM C 494 Type A, will provide strength increases

without altering rates of hardening and reduce the water demand by 5–10%. Lignosulfonate

salts of sodium and calcium are an example of NRWR. Their selection should be based on

strength performance (ACI Committee 363, 2010).

11

Increases in dosage above the normal amounts will generally result in significant side effects,

such as decreasing on strength and retardation with some binder blends especially at lower

temperatures (ACI Committee 363, 2010).

HRWR meeting the specifications for superplasticizers which are detailed in ASTM C 494 as

Type F for HRWR with normal set times or Type G for HRWR with retarded setting times.

HRWR are most effective in concrete mixtures that are rich in cement and other cementitious

materials. HRWR help in dispersing cement particles, and they can reduce mixing water

requirements by more than 30%, thereby increasing concrete compressive strengths (ACI

Committee 211.4, 2008).

Reduction in water/cement ratio is against the different water reducers admixtures (See Figure

2.1). While NRWR allow 5-12% reduction of water, HRWR melamine/naphthalene based

admixtures reduces water 16-25 %, and HRWR polycarboxylate ether polymer based admixture

reduces water 20 to 35% (Nawy, 2008).

Figure (2.1): Effect of Superplasticizers on Slump Loss (Mindess, 1988).

In general, according to Collepardi (1984) and Nawy (2008), the main objectives for using

water reducing admixtures are the following:

1. Reduce the water/cement ratio for higher strengths and improved durability while

maintaining the same workability and cement content.

2. Reduce the paste portion of the matrix, water, and cement, for the purpose of reducing

shrinkage and heat development in massive placements; workability, strength, and

durability are maintained at a comparative level.

12

3. Keep water and cement the same and maintain the same strength and durability but

improve flow and workability.

2.1.4.4 Aggregates

In HSC, careful attention must be given to aggregate size, shape, surface texture, mineralogy,

and cleanness. Cubically shaped crushed stone with a rough surface texture appears to produce

the highest strength. For each source of aggregate and concrete strength level there is an

optimum size aggregate that will yield the most compressive strength per unit of cement.

The quantity of coarse aggregate (CA) in HSC should be the maximum consistent with required

workability. Because of the high percentage of cementitious material in HSC, an increase in

CA content beyond values recommended in standards for normal strength mixtures is necessary

and allowable (Steven et al. 2003).

For optimum compressive strength with high cement content and low water-cement ratios the

maximum size of CA should be kept to a minimum, at 12.5 mm or 9.5 mm. The strength

increases were caused by the reduction in average bond stress due to the increased surface area

of the individual aggregate. Smaller aggregate sizes are also considered to produce higher

concrete strengths because of less severe concentrations of stress around the particles, which

are caused by differences between the elastic moduli of the paste and the aggregate. Gradation

of CA within ASTM limits makes very little difference in strength of HSC. Optimum strength

and workability of HSC are attained with a ratio of CA to FA above that usually recommended

for NSC. Also, due to the already high fines content of HSC mixes, use of ordinary amounts of

CA results in a sticky mix (Rashid and Mansur, 2009).

In high strength concretes, the strength of the aggregate itself and the bond or adhesion between

the paste and aggregate become important factors. Tests have shown that crushed stone

aggregates produce higher compressive strength and modulus of elasticity in concrete than

gravel aggregate using the same size aggregate and the same cementing materials content, this

is probably due to a superior aggregate to paste bond when using rough, angular, crushed

material. Smoother faced, uncrushed gravel may be used to produce strengths of up to about 70

MPa but it does not have the bond strength necessary to produce higher strengths (Nawy, 2008).

According to ACI 363R (2010), Rashid and Mansur (2009), Steven et al. (2002), and Peterman

and Carrasquillo (1986), fine aggregates (FA) with a rounded particle shape and smooth texture

have been found to require less mixing water in concrete and for this reason are preferable in

13

HSC. The grading of the FA used in HSC -typically contain such high contents of cementitious

materials- is relatively unimportant. However, it is sometimes helpful to increase the fineness

modulus (FM) as the lower FM of FA can give the concrete a sticky consistency (i.e. making

concrete difficult to compact) and less workable fresh concrete with a greater water demand.

Therefore, sand with a FM of about 3.0 is usually preferred for HSC.

2.1.4.5 Mixing Water

The requirements for water quality for HSC are no more stringent than those for conventional

concrete. Usually, water for concrete is specified to be of potable quality. This is certainly

conservative but usually does not constitute a problem since most concrete is produced near a

municipal water supply. The single most important variable in achieving HSC is the water-

cement ratio. HSC produced by conventional mixing technologies are usually prepared with

water-cement ratios in the range of 0.22 to 0.40, and their 28 days compressive strength is about

60 to 130 MPa when normal density aggregates are used (Rashid and Mansur, 2009).

2.1.5 Microstructure of HSC

The microstructure of concrete can be described in three aspects, namely composition of

hydrated cement paste, pore structure and interfacial transition zone. The hydrated cement paste

is in fact the hydration products when cement is reacted with water which is referred to as

cementitious calcium silicate hydrate (C-S-H) gel. The pore structure refers to the gel pores,

capillary pores and voids, as well as their connections within the hardened concrete. The

interfacial transition zone refers to the boundaries between the cement paste, and aggregates or

particles of admixtures. The composition of NSC is relatively simple, which consists of cement,

aggregate and water (See Figure 2.2) (Buyukozturk and Lau, 2007).

Figure (2.2): Microstructure of NSC (Buyukozturk and Lau, 2007).

14

In order to improve the concrete performance, the following three aspects are considered:

1. The hydrated cement paste should be strengthened. This can be achieved by reducing

the gel porosity inside the paste. By adding suitable admixture (e.g. silica fume)

2. The porosity in concrete should be lowered. This can be achieved by adding suitable

fine admixture which can fill up the empty space inside concrete.

3. The interfacial transition zone should be toughened. This can be achieved by lowering

the locally high water-to-cement ratio and by improving the particle packing in this

zone. Fine admixtures, like silica fume or fly ash, is added as well to improve the particle

packing in the interfacial transition zone.

It is noticed that in order to improve the concrete performance, admixture is a necessary

component which must be added into the design mix in order to generate HSC. Hence, its

microstructure is quite different from that of NSC. Figure 2.3 shows the microstructure of HSC.

Figure (2.3): Microstructure of HSC (Buyukozturk and Lau, 2007).

2.1.6 Mix Proportion

Concrete mix proportions for HSC have varied widely depending upon many factors. The

strength level required, test age, material characteristics, and type of application have

influenced mix proportions.

The main requirements for successful and practical HSC are a low water/cement ratio combined

with good workability characteristics. In the absence of a standard mix design method, the

importance of trial mixes in achieving the desired concrete performance is increased (Newman

and Choo, 2003).

Thus, the trial mixture approach is best for selecting proportions for HSC. Table.2.2 shows

some mixture proportions and properties of commercially available HSC.

15

To obtain high strength, it is necessary to use a low water to cementing materials ratio and a

high cement content. The water requirement of concrete increases as the fine aggregate content

is increased for any given size of coarse aggregate. Because of the high cementing materials

content of these concretes, the fine aggregate content can be kept low. However, even with

well-graded aggregates, a low water-cementing materials ratio may result in concrete that is not

sufficiently workable for the job (Steven et al. 2003).

Table (2.2): Mixture Proportions and Properties of Commercially Available HSC (Steven et

al. 2003).

Units per m3 Mix number

1 2 3 4 5 6

Cement, Type I, kg 564 475 487 564 475 327

Silica fume, kg — 24 47 89 74 27

Fly ash, kg — 59 — — 104 87

Coarse aggregate SSD

(12.5 mm crushed

limestone), kg

1068 1068 1068 1068 1068 1121

Fine aggregate SSD, kg 647 659 676 593 593 742

HRWR Type F, liters 11.6 11.6 11.22 20.11 16.44 6.3

Retarder, Type D, liters 1.12 1.05 0.97 1.46 1.5 —

Water to cementing

materials ratio 0.28 0.29 0.29 0.22 0.23 0.32

Fresh concrete properties

Slump, mm 197 248 216 254 235 203

Density, kg/ m3 2451 2453 2433 2486 2459 2454

Air content, % 1.6 0.7 1.3 1.1 1.4 1.2

Compressive strength, 100 x 200-mm moist-cured cylinders

7 days, MPa 67 71 71 92 77 63

28 days, MPa 79 92 90 117 100 85

56 days, MPa 84 94 95 122 116 —

91 days, MPa 88 105 96 124 120 92

Modulus of elasticity in compression, 100 x 200-mm moist-cured cylinders

91 days, GPa 50.6 49.9 50.1 56.5 53.4 47.9

Drying shrinkage, 75 by 75 x 285-mm prisms

7 days, millionths 193 123 100 87 137 —

28 days, millionths 400 287 240 203 233 —

90 days, millionths 573 447 383 320 340 —

16

The materials proportion of HSC is different from NSC. As described before, for the aggregate

to be used in making HSC, it is better to choose one with a high crushing strength, if possible.

The maximum size of aggregate is usually kept to be minimum. The limitation on maximum

aggregate size is to reduce the influence of the transition zone and to get a more homogeneous

material. The moisture content in aggregates has to be carefully calculated to make sure the

right water/cement ratio is secured. The cement content is usually high, in a range of 400–600

kg/m3 leads to a more homogenous concrete structure. Moreover, water-reducing admixtures

and mineral admixtures such as fly ash, slag, and silica fume are incorporated in the mix for

HSC (Li, 2011).

Requirement of different ingredient materials required for producing HSC can be summarized

as stated in Table 2.3 adapted from Rashid and Mansur (2009).

Table (2.3): Requirements of Ingredient Materials for HSC (Rashid and Mansur, 2009).

Material Requirements

Cement - Portland cement.

- Higher content.

Water - w/b ratio 0.22 to 0.40.

Fine

aggregate

- Higher FM (around 3.0).

- Smaller sand content or coarser sand.

- Grading is not critical for concrete strength.

Coarse

aggregate

- Smaller maximum size (10 – 12 mm) is preferred.

- Angular and crushed with a minimum flat and elongated particle.

- Type of aggregate depending on the concrete strength targeted.

- Gradation within ASTM limits has little effect on concrete strength.

- Higher CA/FA ratio than that for normal strength concrete.

Admixtures

(chemical and

mineral)

- Type of admixture depends on the property of the concrete to be improved.

- Reliable performance on previous work can be considered during selection.

- Optimum dosage.

Overall basic

considerations

- Quality materials

- Improved quality of cement paste as well as aggregates.

- Denser packing of aggregates and cement paste.

- Improved bond between aggregate surface and cement paste.

- Minimum numbers as well as smaller sizes of voids in the paste.

17

2.2 Fiber Reinforced Concrete (FRC)

2.2.1 General Background

The application of cement concrete is limited due to the characteristics of brittle failure; this

can be overcome by the inclusion of a small amount of short and randomly distributed fibers

such as steel, glass, synthetic and natural. Such concrete can be practiced where there is a

weakness of concrete such as less durability, high shrinkage cracking, etc. (Li, 2011).

Concrete has some deficiencies such as low tensile strength, low post cracking capacity, and

brittleness, highly porous, susceptible to chemical and environmental attack. The above

deficiencies of plain concrete are overcome in the new materials which have unique

characteristics, which make them highly susceptible to any environment. Fiber Reinforced

concrete (FRC) is one of them and relatively a new composite material in which concrete is

reinforced with short discrete uniformly distributed fibers so that it will improve many

engineering properties such as flexural strength, shear strength and resistance to fatigue, impact

and eliminate temperature and shrinkage cracks (Harle, 2014).

Fibers made from steel, glass, and natural materials (such as wood cellulose) are available in a

variety of shapes, sizes, and thicknesses; they may be round, flat, crimped, and deformed with

typical lengths of 6 mm to 150 mm and thicknesses ranging from 0.005 mm to 0.75 mm (see

Figure 2.4) (Steven et al. 2003).

Figure (2.4): Steel, Glass, Synthetic and Natural Fibers (Steven et al. 2003).

18

The main objectives of the modern engineer in attempting to modify the properties of concrete

by the inclusion of fibers are as follows:

1. To improve the rheology or plastic cracking characteristics of the material in the fresh

state or up to about 6 hours after casting.

2. To improve the tensile or flexural strength.

3. To improve the impact strength and toughness.

4. To control cracking and the mode of failure by means of post cracking ductility.

5. To improve durability.

It is generally accepted that the inclusion of any type of short fiber in a three-dimensional

random fiber distribution at practical fiber volumes will not significantly alter the load at which

cracking occurs in hardened concrete. Therefore, the main benefits of the inclusion of fibers in

hardened concrete relate to the post cracking state. In this context, it is worth considering an

understanding of the word ‘reinforcement’. If it is assumed that any loadbearing capacity

greater than zero is described as reinforcement, then all types of fibers at any volume addition

will reinforce hardened concrete. However, if we consider ‘reinforcement’ to mean carrying a

force in excess of the force required to crack the concrete, then less than about 0.4 percent by

volume of short three dimensional random fibers will not generally provide load capacity in

excess of the cracking load in beams and slabs, and two or three times this fiber volume is

required to increase the load capacity in uniaxial tension (Newman and Choo, 2003).

According to Li (2011), the properties of FRC can be influenced by many parameters, such as

fiber type, fiber amount, and matrix variation. In this section, these parameters are discussed as

follow:

(a) Fiber type: The fiber type can be viewed with different criteria. From the size point of view,

fibers can be classified into macro and microfibers. The diameter of macrofibers is in the range

of 0. 2 to 1 mm and for microfibers is in a range of a few to tens of micrometers. Basically,

microfibers are efficient in restraining micro cracks and macrofibers in restraining macroscopic

cracks. From the materials point of view, the fibers that are commonly used in FRC are carbon,

glass, polymeric (acrylic, aramid, nylon, polyester, polyethylene, polypropylene, and poly vinyl

alcohol), natural (wood cellulose, sisal, coir or coconut, bamboo, jute, akwara, and elephant

grass), and steel (high tensile and stainless). Different types of fibers have different values of

Young’s modulus, different tensile strength, different surface texture, and different elongation

ability, as can be seen in Table 2.4 adapted from Steven et al. (2003).

19

Table (2.4): Properties of Different Types of Fibers (Steven et al. 2003).

Fiber type Relative density

(specific gravity)

Diameter,

µm

Tensile

strength, MP

Modulus of

elasticity, MPa

Strain at

failure, %

Steel 7.80 100-1000 500-2600 210,000 0.5-3.5

Glass

E 2.54 8-15 2000-4000 72,000 3.0-4.8

AR 2.70 12-20 1500-3700 80,000 2.5-3.6

Synthetic

Acrylic 1.18 5-17 200-1000 17,000-19,000 28-50

Aramid 1.44 10-12 2000-3100 62,000-120,000 2-3.5

Carbon 1.90 8-0 1800-2600 230,000-

380,000 0.5-1.5

Nylon 1.14 23 1000 5,200 20

Polyester 1.38 10-80 280-1200 10,000-18,000 10-50

Polyethylene 0.96 25-1000 80-600 5,000 12-100

Polypropylene 0.90 20-200 450-700 3,500-5,200 6-15

Natural

Wood cellulose 1.50 25-125 350-2000 10,000-40,000

Sisal 280-600 13,000-25,000 3.5

Coconut 1.12-1.15 100-400 120-200 19,000-25,000 10-25

Bamboo 1.50 50-400 350-500 33,000-40,000

Jute 1.02-1.04 100-200 250-350 25,000-32,000 1.5-1.9

Elephant grass 425 180 4,900 3.6

20

(b) Fiber volume ratio: Another important factor that greatly influences FRC properties is the

fiber volume fraction ratio, which is defined as the ratio of the fiber volume to the total volume

of FRC. At low fiber volume ratio, the addition of fibers mainly contributes to the energy-

consuming property. At a higher fiber volume fraction ratio, the tensile strength of the matrix

can be enhanced and the failure mode can be changed.

(c) Matrix variation: The properties of the matrix influence the bond with the fibers and the

mechanical properties of FRC, such as ultimate tensile strength. The FRC matrix can be

modified using mineral admixtures, such as fly ash, slag, silica fume, and metakaolin. It can

also be modified by adding some water soluble polymers. Changing the matrix composition

can increase the bond properties with the fibers, improve the matrix toughness, and enhance the

matrix tensile strength and, hence, the mechanical properties of FRC.

According to Li (2011), the functions of the fibers in cement based composites can be classified

into two categories: shrinkage crack control and mechanical property enhancement. For

shrinkage crack control, usually small amounts of low modulus and low strength fibers are

added to restrain the early age shrinkage and to suppress shrinkage cracking. For mechanical

property enhancement, fiber reinforcement has been employed in various concrete structures to

improve flexural performance, to increase impact resistance, and to change the failure mode.

The amount of fiber added has a significant influence on the mechanical properties and failure

mode of FRC. In conventional applications of FRC, usually with a low volume fraction of

fibers, the function of the fibers is apparent only after a major crack has formed in the

composite. Although there is still only one major crack and the overall behavior of the

composites is still characterized by strain softening after the peak load is reached, the

incorporation of fibers leads to a significant increase in the total energy consumption and overall

toughness of the composites, represented by the area under a stress–strain or load–displacement

curve, as shown in Figure 2.5. In such cases, as long as there is no fiber fracture, the fiber

de-bonding and pullout process can consume a great amount of energy. On the other hand, with

an increase in fiber volume fraction, it is possible that microcracks formed in the matrix will be

stabilized due to the interaction between the matrix and fibers through bonding, hence

postponing the formation of the first major crack in the matrix. Thus, the apparent tensile

strength of matrix can be increased.

21

Figure (2.5): Load–Displacement Curves (Li, 2011).

Moreover, when a sufficient volume fraction of small diameter steel, glass, or synthetic fibers

is incorporated into the cement based matrix, the fiber-matrix interaction can lead to strain

hardening and multiple cracking behavior, changing the failure mode from quasi brittle to

ductile. As a result, not only the composites toughness, but also the matrix tensile strength can

be significantly improved. One of the mechanisms in slowing down growth of a transverse

crack in unidirectional fiber composites can be attributed to development of longitudinal

cylindrical shear micro cracks located at the boundary between the fiber and the bulk matrix,

allowing the fibers to de-bond while transferring the force across the faces of the main crack.

In addition to enhancing the toughness and tensile strength, the addition of fibers can also

improve the bending resistance of cement based composites (Li, 2011).

2.2.2 Glass Fiber Reinforced Concrete (GFRC)

Much of the original research performed on glass fiber reinforced concrete (GFRC) took place

in the early l960s. This work used conventional borosilicate glass fibers (E-Glass) and soda-

lime-silica glass fibers (A-Glass). However, Glass compositions of E-glass and A-glass, used

as reinforcement, were found to lose strength quickly due to the very high alkalinity (PH of

12.5) of the cement based matrix. Consequently, early A-glass and E-glass composites were

unsuitable for long term use. Continued research resulted in the development a new alkali

resistant-glass fiber reinforced polymer (AR-GFRP) that provided improved long term

durability. The chemical compositions and properties of selected glasses are listed in Tables 2.5

and 2.6, respectively (ACI Committee 544.1, 2002).

22

Table (2.5): Chemical Composition of Selected Glasses, (Percent) (ACI Committee 544.1,

2002).

Component A-glass E-glass AR-glass

SiO2 73.0 54.0 61.0

Na2O 13.0 — 15.0

CaO 8.0 22.0 —

MgO 4.0 0.5 —

K2O 0.5 0.8 2.0

Al2O3 1.0 15.0 —

Fe2O3 0.1 0.3 —

B2O3 — 7.0 —

ZrO2 — — 20.0

TiO2 — — —

Li2O — — 1.0

Table (2.6): Properties of Selected Glasses (ACI Committee 544.1, 2002).

Property A-Glass E-Glass AR-Glass

Specific gravity 2.46 2.54 2.74

Tensile strength, ksi 450 500 355

Modulus of elasticity, ksi 9400 10,400 11,400

Strain at break, percent 4.7 4.8 2.5

Metric equivalent: 1 ksi = 1000 psi = 6.895 MPa

AR-GFRP shown in Figure 2.6 containing 16% - 20% zirconia (ZrO2), which protects the fibers

from high alkali attack was successfully formulated (see Figure 2.7). Glass fiber is available in

continuous or chopped lengths. Fiber lengths of up to 35 mm are used in spray applications and

25 mm lengths are used in premix applications.

Compressive strength, flexural strength and split tensile strength for these AR-GFRP are more

as compared to other glass fibers (ACI Committee 544.1, 2002).

Glass fiber has high tensile strength (2 – 4 GPa) and elastic modulus (70 – 80 GPa) but has

brittle stress-strain characteristics (2.5 – 4.8% elongation at break) and low creep at room

temperature. Claims have been made that up to 5% glass fiber by volume has been used

successfully in sand-cement mortar without balling (Concrete institute, 2013).

23

Figure (2.6): Chopped Strands AR-GFRP (Nippon Electric Glass Co. Ltd. 2007).

Figure (2.7): Alkali Resistivity of Glass Fiber and ZrO2 Content (Nippon Electric Glass Co.

Ltd. 2007).

2.2.3 Applications of GFRC

By far, the single largest application of GFRC has been the manufacture of exterior building

facade panels. Since the introduction of AR-GFRP in the 1970s, growth in applications has

been appreciable. Over 60 million square feet of GFRC architectural cladding panels have been

erected from 1977 to 1993 (ACI Committee 544.1, 2002).

It is suitable for use in direct spray techniques and premix processes and has been used as a

replacement for asbestos fiber in flat sheet, pipes and a variety of precast products. GFRC

products are used extensively in agriculture; for architectural cladding and components; and for

small containers (Concrete institute, 2013).

24

In Gaza strip, the GFRC is recently used in large scale as an architectural material for building

faces. However, because of the lack of data on long term durability, GFRC has been confined

to non-structural uses where it has wide architectural applications in Gaza strip.

2.3 High Strength Fiber Reinforced Concrete (HSFRC)

HSC is brittle and has very steep descending branch of the stress-strain curve. These causes

explosive failure after peak and make it difficult to get descending part because the strain

change is small. To overcome brittle characteristic of HSC, fiber has been used. Fiber has been

used to reinforce the brittle materials since ancient times, such as straw in sunbaked bricks and

horsehair in reinforced plaster. Nowadays, fibers have been produced from steel, plastic, and

glass in various shapes and sizes. The capacity of a structure to absorb energy, with acceptable

deformation and without failure is essential in seismic design. So sufficient ductility is needed

and can be achieved using HSFRC. Currently, steel fiber is used widely in HSC, including

highway, airport pavement, and hydraulic structures. However, sufficient literature is

unavailable on the structural behavior of HSC reinforced with glass fiber (Lee, 2002).

According to Buyukozturk and Lau (2007), it is known that the ductility can be improved by

applying a confining pressure on HSC. Besides confinement, the ductility of HSC can be

improved by altering its composition through the addition of fibers in the design mix. The

conventional FRC made by adding fibers in NSC only exhibits an increase in ductility compared

with the plain matrix, whereas HSFRC made by adding fibers in HSC exhibits substantial strain

hardening type of response which leads to a large improvement in both strength and toughness

compared with the plain matrix as shown in Figure 2.8. Because of this increased improvement

in terms of ductility, HSFRC is referred to as ultra-ductile concrete as well. In order to examine

the scope of HSFRC, it is useful to identify two performance related parameters: elastic limit,

and strain hardening response. The elastic limit refers to the point of first cracking. The strain

hardening response refers to the plastic region. Traditionally, it was assumed that the elastic

limit of FRC is influenced by the tensile strength of the matrix itself and that the fibers primarily

control deformation after cracking. Recently, it was reported that fibers can enhance the elastic

limit provided that they effectively bridge the matrix microcracks. The effectiveness of the

fiber-bridging action will depend on volume fraction, length, diameter, and distribution of

fibers, as well as the properties of the fiber matrix.

25

It was found that the inherent tensile strength and strain capacity of the matrix itself was

enhanced when small fibers were used. When 4% (by volume) of fibers were added, the first

cracking, indicating the elastic limit, was observed at about 30% of the maximum tensile load

(Buyukozturk and Lau, 2007).

Figure (2.8): Mechanical Behavior of FRC Compared with Plain Matrix (Buyukozturk and

Lau, 2007).

Strain hardening is caused by the process of multiple cracking which occurs after the start of

the first crack. In the post-peak region, the number of cracks remains constant while crack

widths increase. Failure is obtained by fiber pullout and fiber rupture. Uniform distribution of

the fibers affects the stress distribution in the matrix and hence, higher stress is required to

propagate the crack. After the first crack starts, distributed multiple matrix cracking follows.

The width of the cracks is usually between 1-3 mm. The multiple cracking process exhibits a

ductile behavior which causes strain hardening phenomenon of the HSFRC. To increase the

elastic limit of HSFRC and achieve strain hardening response, the volume content of the fibers

should be increased as well. Meanwhile, the fibers should be closely spaced and well

distributed. It was found that the decreasing fiber length significantly enhances the tension and

flexure response of HSFRC. In general, short fibers are advantageous because they are easier

to handle during mixing and result in less broken fibers and better dispersion. It was also found

that the distribution of the smaller fibers was more homogeneous than that of larger fibers

(Buyukozturk and Lau, 2007).

26

2.4 Concluding Remarks

Through surveying the literature, concluding remarks that are related and could help on this

research work can be drawn as follow:

i. In HSC, materials selection and mix proportioning can consider the most significant

stage to get higher strength.

ii. In the absence of a standard mix design method for HSC, the importance of trial and

error basis in achieving the desired concrete performance is increased.

iii. Several types of fiber are existed; glass fiber can prefer than other type due to high ratio

of surface area to weight and high strength properties to unit cost ratio.

iv. Glass fiber which is originally used in conjunction with cement was found to be affected

by alkaline condition of cement. The alkali resistant glass fiber reinforced polymer (AR-

GFRP), which is used, recently has overcome this defect and can be effectively used in

concrete.

v. To understand how can fiber work and enhance the mechanical behavior of HSC; two

level of cracks should be defined, micro and macro level. The micro level starts when

the first micro crack occurs (at elastic limit), and then in the plastic region multiple

cracking occur. In the macro level, the number of cracks remain constant while crack

width increased and propagate until formation of the first major crack in the matrix that

cause the failure.

vi. Fiber can enhance the mechanical behavior by control and stabilized of micro cracks

and postponing the crack transformation from micro to macro, hence, increase the

energy absorption capacity result in enhancing the mode of failure. At macro level fiber

can make a bridge action to control and stabilized macro cracks propagation and

postponing the formation of the first major crack in the matrix that cause the failure.

Hence increase the tensile strength and enhance the mode of failure from brittle to quasi-

ductile.

vii. While plain HSC have a very brittle behavior at failure, HSGFRC could have all

advantages of HSC and GFRC. By using this form of concrete technology, the problems

and disadvantages of each type of concrete alone can be overcome.

Chapter 3

Test Program and

Laboratory Works

28

Chapter 3: Test Program and Laboratory Works

3.1 General Description

This chapter presents the experimental program and the materials selection and its properties

used to produce HSGFRC associated with this research work. The laboratory investigation

consisted of testing strength properties which included compressive strength tests, splitting

tensile strength tests, flexural strength tests, and unit weight tests was carried out to achieve the

aim of this research. The test procedures, details and equipment used to assess concrete

properties are illustrated in the following sections.

3.2 Test Program

In order to achieve the research objectives, the test program illustrated in Table 3.1 was carried

out. Tests which include compressive strength test, splitting tensile strength test, flexural

strength test, and density were carried out to evaluate the strength properties of HSGFRC. Five

fiber percentages were chosen, typically, 0.0, 0.3, 0.6, 0.9, and 1.2 by weight of cement led to

five mixtures including the reference mixtures (without fibers) made to evaluate the effect of

AR-GFRP on the mechanical behavior of plain HSC. These percentages were chosen in a range

that can give better observation and evaluation on the mechanical behavior of HSGFRC when

contain a small amount of fiber and when contain a large amount of fiber. Each test is

determined at ages 7 and 28 days, except for the density which determined at 28 days. 150 x150

x150 mm cube specimens were prepared for compressive strength test and density. The test of

compressive strength was made according to BS 1881, Part 108 (1993) standard test method.

150 x 300 mm cylinder specimens were prepared for splitting tensile strength test in accordance

to ASTM C496 (2004) standard test method. 100 x 100 x 500 mm prism specimens were

prepared for flexural strength test in accordance to ASTM C293 (2002). For each mix, three

specimens were made for testing for each test for period of 28 days and two specimens were

made for testing for each test for period of 7 days, the mean value of the specimens was

considered as the test result of the experiment. A detailed description of test procedures,

equipment, and curing conditions will be discussed in the following sections.

29

Table (3.1): Test Program.

Test

Mixture

Designation M50 F0 M50 F1 M50 F2 M50 F3 M50 F4

% GFRP by

Weight of Cement 0.0 0.3 0.6 0.9 1.2

Co

mp

ress

ion

Tes

t a

nd

Den

sity

Ages (day) 7 28 7 28 7 28 7 28 7 28

NO. of Specimens 2 3 2 3 2 3 2 3 2 3

Specimen Type and

Dimension (mm)

Cube

150 x150

x150

Cube

150 x150

x150

Cube

150 x150

x150

Cube

150 x150

x150

Cube

150 x150

x150

Sp

litt

ing T

ensi

le

Str

ength

Tes

t

Ages (day) 7 28 7 28 7 28 7 28 7 28

NO. of Specimens 2 3 2 3 2 3 2 3 2 3

Specimen Type and

Dimension (mm)

Cylinder

150 x 300

Cylinder

150 x 300

Cylinder

150 x 300

Cylinder

150 x 300

Cylinder

150 x 300

Fle

xu

ral

Str

ength

Tes

t

Ages (day) 7 28 7 28 7 28 7 28 7 28

NO. of Specimens 2 3 2 3 2 3 2 3 2 3

Specimen Type and

Dimension (mm)

Prism

100 x 100

x 500

Prism

100 x 100

x 500

Prism

100 x 100

x 500

Prism

100 x 100 x

500

Prism

100 x 100 x

500

3.3 Materials Selection and Properties

HSGFRC constituent materials used in this research include ordinary portland cement, course

aggregate, fine aggregate, normal range water reducer (NRWR), in addition to GFRP.

Proportions of these constituent materials have been chosen carefully in order to optimize the

packing density of the mixture.

3.3.1 Cement

On this research, ordinary portland cement CEM II 42.5R produced from local market was used

for the production of HSGFRC.

30

The cement met the requirements of ASTM C150 (2007) specifications. Table 3.2 shows the

physical properties of cement according to manufacturer data sheet.

Table (3.2): Physical Properties of Cement According to Manufacturer Data Sheet.

Properties Cement ASTM C150-07

Requirements

Fineness (cm2/gm.) 3500 Min. 2800

Setting Time, Vicat Test (hr:min) Initial 2 hr 5 min ≥ 45 min

Final 5 hr ≤ 375 min

Mortar Compressive Strength (MPa) 3 days 25 > 10

28 days 58 > 42.5

3.3.2 Coarse Aggregates

According to the local market surveying, two types of coarse aggregate are used on this

research, natural crushed lime stone of 12.5 mm nominal maximum size was used as coarse

aggregate in the mix proportions. Table 3.3 illustrate the sieve analysis and the physical

properties of these types.

Table (3.3): Sieve Analysis and Physical Properties of Coarse Aggregate Types.

Sample Description Type (1) Type (2)

Sieve Size (mm) % Passing % Passing

25 100 100

19 100 100

12.5 91.11 100

9.5 32.28 96.12

4.75 3.018 31.33

2.36 0.40 6.46

1.18 0.12 2.11

Dry unit weight (Kg/m3) 1504 1488

Dry specific gravity 2.63 2.61

Saturated specific gravity 2.67 2.64

Absorption % 2.4% 3.1%

31

To achieve the ASTM C33 (2003) standard requirements for coarse aggregate, a mix design of

these two types by 70% of type 1 and 30% of type 2 was prepared as shown in Table 3.4 and

Figure 3.1

Table (3.4): Sieve Analysis of Combined Coarse Aggregate According to ASTM C33 (2003) and

Physical Properties.

Sieve Size (mm) %Passing %Passing (Min.) %Passing (Max.)

19.00 100.00 100 100

12.50 94.67 90 100

9.50 57.82 40 70

4.75 14.35 0 15

2.36 2.83 0 5

Unit Weight (KG/m3) 1499.2

Dry Specific Gravity 2.624

Saturated Specific Gravity 2.661

Moisture Content % 0.14

Absorption % 2.60

Figure (3.1): Coarse Aggregate Sieve Analysis According to ASTM C33 (2003).

-5.00

15.00

35.00

55.00

75.00

95.00

115.00

1.00 5.00 25.00

% P

ass

ing

Sieve Size (mm)

Combined Coarse Aggregate ASTM min. Limits ASTM max. Limits

32

3.3.3 Fine Aggregate

According to the local market surveying, the available fine aggregate is dune sand type which

is finer than required by standard specifications of ASTM C33 (2003) and its gradation does

not fall within the limits. However, as mentioned before in chapter two, many researchers

mentioned that the role of FM and gradation of the fine aggregate in HSC is not as crucial as in

conventional strength mixtures.

In spite of the FM does not necessary to comply with the requirements of ASTM C33 (2003),

higher FM or coarser fine aggregate may be highly desirable in HSC, since HSC typically

contain high volumes of cementitious material. However, this problem is largely related with

workability of concrete, to overcome this problem, many researchers recommend to use higher

CA/FA ratio and water reducing admixtures, and the fine aggregate content can be kept low.

Figure 3.2 and Table 3.5 illustrate the grain distribution of fine aggregate used on this research

and its properties.

Table (3.5): Grain Distribution of Fine Aggregate and Physical Properties.

Sieve Size (mm) % Passing

4.75 100

2.36 100

1.18 95.99

0.6 87.33

0.425 73.14

0.3 39.33

0.15 1.50

0.075 0

Fineness Modulus FM 1.75

Dry Unit Weight (Kg/m3) 1635.14

Dry Specific Gravity 2.61

Saturated Specific Gravity 2.632

Absorption (%) 0.71

33

Figure (3.2): Grain Distribution of Fine Aggregate.

3.3.4 Normal Range Water Reducing Admixture (NRWR)

According to the local market surveying the available water reducers type is NRWR confirming

ASTM C494(2004) Type “A” specification which is used on this research with dosage of

2Lit./m3 based on manufacturer’s suggestion. Table 3.6 illustrate the properties of used NRWR

according to manufacturer data sheet.

It should be noted that NRWR, when used with upper the dosage range suggested by the

manufacturer’s, often result in very significant secondary effects, such as decreasing on strength

and retardation with some binder blends especially at lower temperatures. As a result of this

low dosage of NRWR, the amount of water reduction and workability performance is limited

and less good than for HRWR.

Table (3.6): Properties of Normal Range Water Reducer.

Type Property

Appearance Dark brown liquid

Specific Gravity Approx. 1.2

Basis Lignosulfonate salts of calcium

Dose 0.2 to 0.6 lit./100 kg of cement

Toxicity Non-Toxic under relevant health and safety codes

-5

15

35

55

75

95

115

0.05 0.5 5

% P

assi

ng

Sieve Size (mm)

34

3.3.5 Glass Fiber Reinforced Polymer (GFRP)

On this research, alkali resistant glass fiber reinforced Polymer (AR-GFRP) is used, the

available AR-GFRP in the Gaza local market has a hybrid length, typically ranged from 8 mm

to 30 mm. According to manufacturing data sheet, the properties of AR-GFRP used on this

research are shown in Table 3.7.

Table (3.7): Properties of AR-GFRP.

3.3.6 Water

Potable tap water without any salts or chemical was used in the study for the experimentation

and for the curing process. The water source was the laboratory of the Islamic University of

Gaza.

3.4 Mix Proportioning of HSGFRC

The reference concrete mixture (without GFRP) was developed on a trial and error basis to

obtain 28-day cylinder compressive strength for design of 50 MPa. The first trail mixture was

based on Steven et al. (2003), then modifications were applied to obtain the best determinable

mix design proportions that achieved the target design strength which illustrated in Table 3.8.

The following factors were considered when designing a HSC mixture.

i. Usually, for the aggregate to be used in making HSC, it is better to choose one with a

high crushing strength, if possible. The maximum size of aggregate is usually limited to

Fiber Properties Quantity

Fiber Length Hybrid 8 to 30 mm

Diameter 14µ

Specific Gravity 2.68 g/cm3

Density 2.7 t/m3

Modulus of Elasticity 72 GPa

Tensile Strength 1,700 MPa

Chemical Resistance Very high

Electrical Conductivity Very low

Softening Point 860 °C

Zro2 Content 15-20 %

Material Alkali Resistant Alkali Resistant Glass

35

12.5 mm. The limitation on maximum aggregate size is to reduce the influence of the

transition zone and to get a more homogeneous material.

ii. The quantity of coarse aggregate in HSC should be the maximum consistent with

required workability.

iii. The water requirement of concrete increases as the fine aggregate content is increased

for any given size of coarse aggregate. Because of the high cementing materials content

of these concretes, the fine aggregate content can be kept low.

iv. The cement content is usually high, in a range up to 600 kg/m3. The higher cement

content is the result of limiting the maximum aggregate size and the need for workability

under the smaller water/cement ratio condition. Moreover, the higher cement content

also leads to a more homogenous concrete structure.

v. The appropriate free water/cement ratio should be selected as minimum as possible

either from reference to published data or on a trial and error basis.

vi. The workability of concrete mix should be enough to obtain good compaction using

suitable chemical admixtures such as water reducer.

Table (3.8): Mix Proportioning for 1 m3 of Concrete for The Reference Mixture.

Material Type Units / m3

Cement (kg) 600

Fine Aggregate (kg) 484

Coarse aggregate (kg) 1068

NRWR (Lit.) 2

W/C 0.37

The compressive test carried out in the trial mix stage was according to ASTM C39 (2003)

standard test method. The average 28-day cylinder compressive strength of three 150 x 300 mm

cylinder specimens (See Figure 3.3) was 51.149 MPa as shown in Table 3.9. The rate of loading

was constant for the specimens equal 0.34 MPa/sec. confirming the standard requirements.

Before testing, cylinders are capped from the faces of specimens that will be in contact with the

bearing plate of the testing machine. The testing machine used on this research for compressive

strength is MATEST C104 Servo Plus 2000 KN capacity showed in Figure 3.4.

36

Figure (3.3): 150 x 300 mm Cylindrical Specimens.

Table (3.9): 28 Day Cylinder Compressive Strength Test Result.

NO.

Failure

Load

(KN)

Compressive

Strength

(Mpa)

Rate of

Loading

(Mpa/sec)

Average

Compressive

Strength (Mpa)

S CV

1 976.36 55.251

0.34 51.149 3.67 7.17 2 884.45 50.05

3 850.84 48.148

Figure (3.4): MATEST C104 Servo Plus 2000 KN Capacity Compression Test Machine.

To achieve the objectives of this research, varying percentages of AR-GFRP are added to the

reference mixture to produce HSGFRC mixtures, typically 0.0, 0.3 0.6 0.9, 1.2 by weight of

cement as shown in Table 3.10.

37

Table (3.10): HSGFRC Mixtures for 1 m3 of Concrete.

Designation

% AR-GFRP

by Weight of

Cement

Cement

(kg)

Fine

Aggregate

(kg)

Coarse

Aggregate

(kg)

NRWR

(Lit.) W/C

M50 F0 0 600 484 1068 2 0.37

M50 F1 0.3 600 484 1068 2 0.37

M50 F2 0.6 600 484 1068 2 0.37

M50 F3 0.9 600 484 1068 2 0.37

M50 F4 1.2 600 484 1068 2 0.37

3.5 Preparation of HSGFRC and Mixing Procedure

After selection of all needed constituent materials and amounts to be used (mix proportioning);

all materials are weighed properly. Then mixing with a power-driven revolving drum mixer

showed in Figure 3.5 started to ensure that all particles are surrounded with each other.

Figure (3.5): The Power-Driven Revolving Drum Mixer Used on This Research.

For the reference mixture M50 F0 (without fibers), mixing procedures was applied in

accordance with ASTM C192 (2002). However, for addition of the glass fibers; careful

attention must be given when mixing the glass fibers. The glass fibers are always added last

and mixed for the minimum time required to achieve uniform dispersion. It is important to

ensure that minimum time is spent mixing the fibers because they can be damaged by excessive

mixing. In addition, mixing the glass fibers at the higher speed would also damage the fibers.

38

3.6 Testing Procedure

In this section, testing procedures to evaluate the strength properties of HSGFRC are

presented.

3.6.1 Compressive Strength Test

A significant portion of this research focused on the behaviors of HSGFRC cube specimens

under compressive loading. The compressive tests discussed on this section were all completed

nominally according to BS 1881, Part 108 (1993) standard test method. Total of 25 cubes were

manufactured. For each batch of HSGFRC made, 150x150x150 mm cube specimens were

prepared, (See Figure 3.6). The cubes were filled with fresh concrete and then compacted by

rod method in accordance to the standard, after preparing the specimens, cubes were covered

with plastic sheets for about 24 hours to prevent moisture loss prior to the curing stage.

(a)

(b)

Figure (3.6): (a) and (b) Cube Specimens.

39

After 24 hours; Cubes extracted from forms and stored in water (curing phase) up to the time

of test. Before testing, any loose sand grains or incrustations from the faces of specimens that

will be in contact with the bearing plate of the testing machine are removed. The testing

machine used on this research for compressive strength is MATEST C104 Servo Plus 2000 KN

capacity shown in Figure 3.7.

Figure (3.7): MATEST C104 Servo Plus 2000 KN Capacity Compression Test Machine.

The cubes then placed in the testing machine so that the load is applied through flat and parallel

sides. The rate of loading was constant for the tests of compression strength equal 0.34 MPa/sec.

confirming the standard requirements. The compressive strength of the specimen, (in MPa), is

calculated by dividing the maximum load carried by the cube specimen during the test by the

cross-sectional area of the specimen.

The compressive strength was determined at different ages 7, and 28 days. Three cubes were

tested for each mix for period of 28 days and two cubes were tested for each mix for period of

7 days, the mean value of the specimens was considered as the compressive strength of the

experiment.

3.6.2 Splitting Tensile Strength Test

The splitting tensile strength of HSGFRC was measured based on ASTM C496 (2004) standard

test method. This test often referred to as the split cylinder test, indirectly measures the tensile

strength of concrete in which a cylindrical specimen (See Figure 3.8) is placed on its side and

loaded in diametrical compression as shown in Figure 3.9, so to induce transverse tension.

40

Figure (3.8): Cylindrical Specimens.

Figure (3.9): Split Cylinder Test Setup.

The load applied (compressive force) on the cylindrical concrete specimen induces tensile and

shear stresses on the aggregate particles inside the specimen, generating the bond failure

between the aggregate particles and the cement paste (See Figure 3.10). The failure of concrete

in tension is governed by micro-cracking, associated particularly with the interfacial region

between the aggregate particles and the cement, also called interfacial transition zone (ITZ).

However, the most important advantage is that, when applying the splitting procedure, the

tensile strengths are practically independent of either the test specimen or of the test machine

sizes, being only a function of the concrete quality alone. Thus, much inconvenience is

eliminated.

41

(a)

(b)

(c)

Figure (3.10): (a), (b), and (c) Failure on Cylindrical Specimen after Split Cylinder Test.

42

Total number of 25 cylinder of 300 x 150 mm were manufactured. The cylinders were filled

with fresh concrete and then compacted by rod method in accordance to the standard, after

preparing the specimens, cylinders were covered with plastic sheets for about 24 hours to

prevent moisture loss prior to the curing stage. All cylinder specimens were tested after 28 days

from casting. The rate of loading was constant for the tests equal 1.4 MPa/min. The testing

machine used on this research for split tensile strength is MATEST C104 Servo Plus 2000 KN

capacity, the same that used for compression test.

The split tensile strength was determined at different ages 7, and 28 days. Three cylinders were

tested for each mix for period of 28 days and two cylinders were tested for each mix for period

of 7 days, the mean value of the specimens was considered as the split tensile strength of the

experiment.

The maximum fracture strength can be calculated based on Eq. 3.1 according to ASTM C496

(2004).

Fsp = 𝟐𝑷

𝝅𝑫𝑳 (3.1)

Where:

Fsp = Splitting tensile strength in MPa

P is the fracture compression force acting along the cylinder in N;

D is the cylinder diameter in mm;

π = 3.14;

L is the cylinder length in mm.

3.6.3 Flexural Strength Test

Total number of 25 prisms were manufactured. The specimens are prisms 100 x 100 x 500 mm

(See Figure 3.11). The flexural strengths or the modulus of rapture of concrete specimens are

determined by the use of simple beam with center point loading in accordance to ASTM C293

(2002) as shown in Figure 3.12. The mold is filled with fresh concrete and then compacted by

rod method in accordance to the standard. After preparing the specimens, they are covered with

plastic sheets for about 24 hours to prevent moisture loss. After 24 hours, the specimens are

extracted from the molds and placed in water for curing up to time of test. At the time of testing,

and because the flexural strengths of the prisms are quickly affected by drying which produces

skin tension, they are tested immediately after they are removed from the curing basin.

43

The flexural strength was determined at different ages 7, and 28 days. Three prisms were tested

for each mix for period of 28 days and two prisms were tested for each mix for period of 7 days,

the mean value of the specimens was considered as the flexural strength or the modulus of

rapture of the experiment.

(a)

(b)

Figure (3.11): (a) and (b) Prism Specimens.

44

Figure (3.12): Schematic View for Flexure Test Setup of Concrete by Center-Point Loading.

The casted beam specimens to be tested, turned on their sides with respect to their position as

molded. This should provide smooth, plane and parallel faces for loading. The pedestal on the

base plate of the test machine shown in Figure 3.13 is centered directly below the center of the

upper spherical head, and the bearing plate and support edge assembly are placed on the

pedestal. The center loading device is attached to the spherical head. The test specimen is turned

on its side with respect to its position as molded and it is placed on the supports of the testing

device.

Figure (3.13): Center Point Loading Flexural Test Machine.

The longitudinal center line of the specimen is set directly above the midpoint of both supports.

The center point loading device is adjusted so that its bearing edge is at exactly right angles to

the length of the beam and parallel to its top face as placed, with the center of the bearing edge

directly above the center line of the beam and at the center of the span length. The load contacts

with the surface of the specimen at the center.

45

The specimen is loaded continuously and without shock at until rupture occurs (See Figure

3.14). Finally, the maximum load indicated by the testing machine is recorded.

Figure (3.14): Fracture on Prism Specimen after Flexural Prism Test.

The flexural strength of the beam, Fr (in MPa), can be calculated by using Eq. 3.2 according to

ASTM C293 (2002):

Fr = 𝟑𝑷𝑳

𝟐𝒃𝒅𝟐 (3.2)

Where:

Fr = Flexural strength or modulus of rapture in MPa:

P = maximum applied load indicated by the testing machine in N;

L = span length in mm;

b = average width of specimen in mm, at the point of fracture;

d = average depth of specimen in mm, at the point of fracture.

3.6.4 Unit Weight

On this research, the unit weight of the concrete cube specimen is the theoretical density. The

density is calculated by dividing the weight of each cube by the volume. The same cube

specimens which are used to determine the compressive strength was used to determine the

density.

46

3.7 Curing Procedure

Curing is an important process to prevent the concrete specimens from losing of moisture while

it is gaining its required strength. Lack of curing will tend to lead the concrete specimens to

perform less well in its strength required. All concrete samples were placed in curing basin after

24 hours from casing (See Figure 3.15). All samples remained in the curing basin up to time of

testing at the specified age. Curing water temperature is around 25oC. The curing condition of

lab basin followed the ASTM C192 (2004).

Figure (3.15): Specimens at Curing Basin.

Chapter 4

Test Results and Discussion

48

Chapter 4: Test Results and Discussion

4.1 Compressive Strength and Density Test Results

The results of 7 and 28 days compressive strength and 28 days density are shown in Table 4.1

and Table 4.2. As mentioned before in chapter three, the 28 days cylinder compressive strength

of plain HSC specimens (without fiber) obtained from adopted mix proportion that achieve the

target design strength used on this research was equals to 51.149 MPa, however, the 28 days

cube compressive strength of plain HSC specimens as shown in Table 4.2 equal to 57.85, make

the ratio of cylinder to cube compressive strength equal to 0.88 which is obviously higher than

for normal strength grade. However, according to Mindess (2002) it has been recognized that

as concrete strength increases, the ratio of cylinder to cube compressive strength also increases.

The compression test assumes a state of pure, uniaxial compression. Which is not true because

of the friction between the ends of the specimen and the bearing plates of the test machine.

Through friction, the bearing plates act to restrain the lateral expansion of the ends of the

specimen and to introduce a lateral confining pressure near the specimen ends. This confining

pressure is greatest right at the specimen end and gradually dies out forward the middle of the

specimen.

According to Neville (2011), the restraining effect of the bearing plates of the testing machine

may extends over the entire height of a cube specimen, however, it leaves unaffected part of

cylinder specimen. It is, therefore, to be expected that the strength of cubes specimen is greater

than for cylinder specimen made from the same concrete. For NSC, the ratio of cylinder to cube

compressive strength is around 0.8, but, in reality, there is no simple relation between the

strength of the specimens of two shapes. However, for HSC, the effect of specimen’s size and

shape on the compressive strength is insignificant as for NSC. The ratio of cylinder to cube

compressive strength increases strongly with an increase in strength and is nearly 1 at strength

of more than 100 MPa. This increasing in the ratio can be explained that, as concrete strength

increased, the tensile strength also increased, and as concrete strength increased, the Poisson

ratio decreased result in less effect of the lateral expansion of specimen against the induced

lateral confining pressure near the ends make whole specimen approximately in uniaxial

compression.

49

Table (4.1): Cube Compressive Strength and Density Test Results.

Designation

%

GFRP

by

Cement

Wt.

Specimens Density

(t/m3) Failure Load (KN)

Cube Compressive

Strength (MPa)

28 Days 7 Days 28 Days 7 Days 28 Days

M50 F0 0

1 2.434 1048.72 1309.19 46.60 57.80

2 2.431 1023.73 1151.23 45.49 59.37

3 2.386 1035.07 56.3

M50 F1 0.3

1 2.427 1073.26 1368.23 47.70 60.81

2 2.426 1085 1441.58 48.22 63.64

3 2.411 1329.59 58.70

M50 F2 0.6

1 2.448 1174.48 1506.86 51.85 66.97

2 2.396 1123.84 1412.98 49.61 62.79

3 2.444 1536.08 68.27

M50 F3 0.9

1 2.452 1080.47 1542.27 47.70 68.54

2 2.431 1169.1 1477.45 51.61 65.66

3 2.425 1468.32 64.82

M50 F4 1.2

1 2.448 1089.96 1576.1 48.12 69.58

2 2.452 1156.08 1482.42 51.04 65.44

3 2.424 1457.69 64.78

Table (4.2): Average Cube Compressive Strength and Density Test Results.

Designation

%

GFRP

by

Cement

Wt.

Density

(t/m3)

Average Compressive Strength

(MPa) % 7

Days /

28 Days

%

Increase

Over the

Reference

Mix 28

Days 28 Days 7 Days

28

Days

S

28

Days

CV

28

Days

M50 F0 0 2.4172 46.055 57.854 1.49 2.58 79.605 0

M50 F1 0.3 2.421 47.96 61.052 2.48 4.06 78.556 5.238

M50 F2 0.6 2.429 50.735 66.013 2.86 4.33 76.856 12.36

M50 F3 0.9 2.436 49.659 66.345 1.95 2.94 74.85 12.798

M50 F4 1.2 2.441 49.581 66.606 2.60 3.90 74.439 13.14

50

4.1.1 Effect of AR-GFRP on the Compressive Strength of HSC

From Table 4.2, it is observed that with increase in fiber percentage, the compressive strength

also increases. As shown in Figure 4.1, the 28 days’ compressive strength increases sharply

from 57.85 to 66.01 MPa with increase in fiber percentage from 0.0 to 0.6 respectively. Then,

a very slight increase is observed in the compressive strength from 66.01 to 66.6 MPa when

fiber percentage increases from 0.6 to 1.2 respectively. In general, as shown in Figure 4.2, the

percentage of increase over the reference mix at fiber percentage of 0.6 and 1.2 is 12.36 and

13.14 percent respectively, hence it is established that fiber percentage of 0.6 can be consider

the optimum value of fiber addition for compressive strength enhancement since the difference

between those values of fiber percentage is insignificant.

Figure (4.1): Effect of AR-GFRP on 28 Days Compressive Strength of HSC.

Figure (4.2): The Percentage of Increase in Compressive Strength Over the Reference Mix

Due to Addition of AR-GFRP on HSC.

57.854

61.052

66.013 66.345 66.606

55

57

59

61

63

65

67

69

0 0.3 0.6 0.9 1.2 1.5

28 D

ays

Com

pre

ssiv

e

Str

ength

(Mpa)

% AR-GFRP

0

5.238

12.36 12.798 13.14

0

2

4

6

8

10

12

14

0 0.3 0 .6 0 .9 1 .2% I

ncr

ease

Over

Ref

eren

ce M

ix 2

8

Day

% AR-GFRP

51

The behavior of curve shown in Figure 4.1, can be explained that according to Li (2011), the

reinforcement provided by fibers can work at both a micro and macro level. At a micro level

fibers arrest the development of micro cracks. The ability of the fiber to control micro cracking

growth depends mainly on the number of fibers. Whereas at a macro level, fibers control crack

opening and increasing the energy absorption capacity of the composite.

Hence, a higher number of fibers in the matrix leads to a higher probability of a microcrack

being intercepted by a fiber leading to higher compressive strengths as can be seen in Figure

4.1 where a sharp increase in the compressive strength is observed as fiber percentage increase

from 0.0 to 0.6. Whereas at a macro level, the mode of failure will be enhanced -as will be seen

later- due to the great amount of energy that consumed by fibers and due to postponing the

formation of the first major crack in the matrix.

On the other hand, fiber addition causes some perturbation of the matrix and appear strongly at

high percentage of fibers, which can result in higher voids during the micro level due to fiber

de-bonding and pullout process as long as there is no fiber fracture. When the macro level starts,

voids can be seen as defects where macro cracking starts. In addition, as the amount of fiber

exceeded the optimal value, larger surface area of coarse aggregate particles will be surrounded

be fibers which is soft polymeric material could weaken the aggregate interlock thereby

reducing the compressive strength of the concrete. It is safe then to say that the influence of

fibers on the compressive strength at higher percentages could not enhance or increase the

compressive strength as discussed and as can be seen in Figure 4.1 where a very slight increase

is observed at fiber percentage from 0.6 to 1.2.

Test result show good agreement with other research studied the effect of addition of GFRP on

structural concrete, Swami et. al. (2010) and Ghorpade (2010) show that the concrete

compressive strength can increased obviously when small amount of fiber used, however, there

was no additional significant enhancement in compressive strength when fiber percentage

increased upper the optimum value as shown in Figure 4.3. Ghorpade (2010) -whose use VHSC

to study the effect of addition of GFRP- show that the optimum amount of fiber addition can

be achieved at 1 percent, while when using HSC -such this research- the optimum amount of

fiber addition can be achieved at 0.6 percent, frequently, using lower strength -such Swami et.

al. (2010)- the optimum amount of fiber addition could decrease to 0.3 percent. Hence, it was

established that as concrete strength increase, the optimum amount of fiber addition for

compressive strength enhancement also increase as shown in Figure 4.3.

52

Figure (4.3): Comparisons of compressive strength test results with other related researches.

4.1.2 Effect of AR-GFRP on the Strength Gain with Age of HSC

Figure 4.4 illustrate the strength gain with age for each mix. From Table 4.2, it is obvious that

the ratio of 7 days to 28 days compressive strength for the reference mix (M50 F0) is higher

than for normal strength grade, typically 79.6 percent. However, according to ACI committee

363 (2010), it has been recognized that HSC shows a higher rate of strength gain at early ages

compared to lower strength concrete. The higher rate of strength development of HSC at early

ages is caused by an increase in the internal curing temperature in the concrete mixtures due to

a higher heat of hydration and shorter distance between hydrated particles due to low water-

cement ratio. However, as shown in Figure 4.5, the ratio of 7 days to 28 days’ compressive

strength decrease from 79.6 to 74.43 as fiber percentage increase from 0.0 to 1.2 respectively.

This can be explained simply that fiber can absorb a part of increased temperature and can make

the distance between hydrated particles longer result in less internal curing temperature in the

concrete mixtures.

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.628

Day

s C

ub

e C

om

pre

ssiv

e St

ren

gth

(M

Pa)

% GFRP

Test Results Swami et. al. (2010) Ghorpade (2010)

53

Figure (4.4): Effect of AR-GFRP on the Strength Gain with Age of HSC.

Figure (4.5): Effect of AR-GFRP on %7days / 28days Compressive Strength.

4.1.3 Effect of AR-GFRP on the Density of HSC

From Figure 4.6, it is observed that with increase in fiber percentage, the density increases

very slightly, this can be explain due to the extremely light weight and high ratio of surface

area to weight of AR-GFRP.

0

10

20

30

40

50

60

70

0 7 2 8

Co

mp

ress

ive

S

tren

gth

-M

pa

Age-Days

M50 F0

M50 F1

M50 F2

M50 F3

M50 F4

79.60578.556

76.85674.85 74.439

55

60

65

70

75

80

85

0 0.3 0.6 0.9 1.2 1.5

% 7

day

/ 2

8day

Com

pre

ssiv

e

Str

ength

% AR-GFRP

54

Figure (4.6): Effect of AR-GFRP on Density of HSC.

4.1.4 Crack Pattern and Mode of Failure

It was not possible to measure the strain during the test because the strain measurement devices

(Transducers) of the test machine of the Islamic University of Gaza laboratory was broken.

Several attempts were made to fix it but unfortunately the attempts were failed and there wasn’t

any help presented to solve this problem. However, observation of specimens during

compressive strength test shows, in the case of plain HSC specimens (without fibers), the failure

is sudden, brittle and completely destruction with sound (Loudly) as shown in Figure 4.7.

However, the results observe that with addition of fiber by 0.3 percent on HSC specimens, the

appearance of failure becoming more normal and less dispersion as shown in Figure 4.8.

Frequently, from Figure 4.9 and Figure 4.10, it is observed that HSC specimens with 0.6 and

0.9 fiber percentage show finer cracks and less dispersion compared with HSC specimens with

0.3 fiber percentage. At highest fiber percentage of 1.2 on HSC specimens, the appearance of

specimens after failure still standing and the cracks are extremely fine and not clear as shown

in Figure 4.11.

It is observed that failure has taken place gradually with the formation of cracks as fiber

percentage increase, this can indicate that glass fiber contributes to crack resistance. Hence it is

established that the presence of fibers in the matrix has contributed towards arresting sudden

crack formation. Moreover, although the higher percentage could not enhance the compressive

strength as explained before, at a macro level fibers at higher percentages can control crack

opening, consume a great amount of energy, and postponing the formation of the first major

crack in the matrix, hence changing the failure mode from brittle to quasi-ductile.

2.4172 2.421 2.429 2.436 2.441

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

0 0.3 0.6 0.9 1.2 1.5

DE

NS

ITY

(t/

m3)

% AR-GFRP

55

Figure (4.7): Mode of Failure and Crack Pattern of Plain HSC Specimens (Without Fiber).

(a) (b)

Figure (4.8): (a) and (b): Mode of Failure and Crack Pattern of HSC Specimens with 0.3

Fiber Percentage.

56

Figure (4.9): Mode of Failure and Crack Pattern of HSC Specimens with 0.6 Fiber

Percentage.

Figure (4.10): Mode of Failure and Crack Pattern of HSC Specimens with 0.9 Fiber

Percentage.

Figure (4.11): Mode of Failure and Crack Pattern of HSC Specimens with 1.2 Fiber

Percentage.

57

4.2 Splitting Tensile Strength Test Results

The results of 7 and 28 days splitting tensile strength are shown in Table 4.3 and Table 4.4.

According to ACI Committee 363 (2010), Eq. 4.1 was recommended for the prediction of the

splitting tensile strength of HSC with 28 days cylinder compressive strength within 21 to 83

MPa.

Fsp = 0.59√𝒇𝒄′ (4.1)

As mentioned before, the 28 days cylinder compressive strength of plain HSC (without fiber)

was equals to 51.149 MPa. Which make the predicted splitting tensile strength Fsp using

Equation 4.1 equals to 4.21 MPa which seems very close with the average experimental value

of plain HSC specimens (M50 F0) equal to 4.12 MPa shown in Table 4.4 with percent error

equal to 2.1 percent.

Table (4.3): Splitting Tensile Strength Test Results.

Designation

% GFRP

by Cement

Wt.

Specimens

Failure Load (KN) Split Tensile

Strength (MPa)

7 Days 28 Days 7 Days 28 Days

M50 F0 0

1 233.54 302.98 3.31 4.35

2 198.38 271.61 2.81 3.90

3 286.30 4.11

M50 F1 0.3

1 261.42 297.26 3.71 4.25

2 242.48 373.33 3.44 5.36

3 328.35 4.71

M50 F2 0.6

1 289.91 418.25 4.12 5.92

2 261.44 382.42 3.71 5.41

3 372.05 5.28

M50 F3 0.9

1 300.67 392.52 4.27 5.55

2 287.36 451.84 4.07 6.37

3 395.96 5.61

M50 F4 1.2

1 359.25 504.92 5.10 7.17

2 334.0 462.58 4.74 6.56

3 452.05 6.44

58

Table (4.4): Average Splitting Tensile Strength Test Results.

Designation

% GFRP

by

Cement

Wt.

Average Split Tensile Strength (MPa) % Increase Over

the Reference Mix

(28 Day) 7

Days

28

Days S CV

M50F0 0 3.066 4.124 0.22 5.5 0

M50F1 0.3 3.579 4.777 0.55 11.6 15.83

M50F2 0.6 3.917 5.538 0.33 6.1 34.28

M50F3 0.9 4.177 5.845 0.45 7.8 41.73

M50F4 1.2 4.924 6.731 0.39 5.8 63.22

4.2.1 Effect of AR-GFRP on the Splitting Tensile Strength of HSC

From Table 4.4, it is observed that with increase in fiber percentage, the splitting tensile strength

also increases significantly. As shown in Figure 4.12, the splitting tensile strength increases

continuously from 3.06 to 4.92 MPa with increase in fiber percentage from 0.0 to 1.2

respectively for 7 days, and 4.12 to 6.7 MPa when fiber percentage increase from 0.0 to 1.2

respectively for 28 days. From the test results shown in Table 4.4, it is observed that the

percentage of increase in the splitting tensile strength over the reference mix due to addition of

fibers is much higher than for the compressive strength as shown in Figure 4.13.

In addition, the mode of increasing in splitting tensile strength due to addition of fibers is

keeping continuous ascending until the highest value of 6.73 MPa (28 Days) at the highest fiber

percentage of 1.2 as shown in Figure 4.12, comparing with the increasing in compressive

strength where Figure 4.1 shows continuous ascending just until 0.6 fiber percentage and then

at fiber percentage from 0.6 to 1.2, the increasing turned to very slight. This difference between

the increasing mode of compressive strength and splitting tensile strength curves shown in

Figure 4.1 and Figure 4.12 can be explained simply that the defects that caused by higher fiber

percentages during the micro level, which are as discussed before, the voids due to fiber de-

bonding and pullout process, and the weakness of the aggregate interlock due to softening and

polymeric characteristic of fibers, appear strongly when the concrete fail due to compressive

stress. However, in splitting tensile test, although the cylinder specimen subjected to

compressive load, the specimen fail due to the induced tensile stresses before reach its ultimate

compressive strength capacity.

59

It is safe then to say that with higher percentage of fibers, it is possible that micro cracks formed

in the matrix at micro level will be stabilized due to the interaction between the matrix and

fibers through bonding, hence postponing the formation of the first major crack in the matrix.

Thus, the apparent tensile strength of matrix can be increased. Hence it is established that AR-

GFRP inclusion in HSC mixtures is more powerful for enhancing the tensile strength than

compressive strength.

Figure (4.12): Effect of AR-GFRP on Splitting Tensile Strength of HSC.

Figure (4.13): The Percentage of Increase Over the Reference Mix Due to Addition of AR-GFRP on

HSC: Comparison between Compressive Strength and Splitting Tensile Strength.

Test result show good agreement with Swami et. al. (2010) and Ghorpade (2010). The authors

show that the concrete splitting tensile strength can increased significantly with addition of

4.124

4.777

5.5385.845

6.731

3.0663.579

3.9174.177

4.924

0

1

2

3

4

5

6

7

8

0 0.3 0.6 0.9 1.2Spli

ttin

g T

ensi

le S

tren

gth

(M

pa)

% AR- GFRP

28 Days

7 Days

05.238

12.36 12.798 13.14

0

15.834

34.28

41.731

63.223

0

10

20

30

40

50

60

70

0 0.3 0.6 0.9 1.2

% I

ncr

ease

Over

The

Ref

eren

ce

Mix

(28 D

ays)

% AR- GFRP

Compressive Strength

Splitting Tensile Strength

60

glass fiber even when large amount was used as shown in Figure 4.14. However, Ghorpade

(2010) -whose use VHSC to study the effect of addition of GFRP- show that splitting tensile

strength could decrease when use fiber percentage larger than 1 percent.

Figure (4.14): Comparisons of splitting tensile strength test results with other related

researches.

4.2.2 Crack Pattern and Mode of Failure

Observation of specimens during splitting tensile strength test shows, in the case of plain HSC

specimens (without fibers), the failure is sudden, brittle and completely splitting with sound

(Loudly) as shown in Figure 4.15. Moreover, the results observe that with addition of fiber by

0.3 percent on HSC specimens, the mode of failure still sudden and completely splitting as plain

HSC specimens (without fibers) as shown in Figure 4.16.

However, from Figure 4.17 and Figure 4.18, it is observed that HSC specimens with 0.6 and

0.9 fiber percentage, show normal failure without splitting compared with plain HSC specimens

and HSC specimens with 0.3 fiber percentage. At highest fiber percentage of 1.2 on HSC

specimens, the appearance of specimens after failure still standing and the cracks are single,

extremely smooth and not clear as shown in Figure 4.19. It is observed that failure has taken

place gradually with the formation of cracks as fiber percentage increase, this can indicate that

glass fiber contributes to crack resistance. Hence it is established that the presence of fibers in

the matrix has contributed towards arresting sudden crack formation.

2

3

4

5

6

7

8

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.628

Day

s Sp

litti

ng

Ten

sile

Str

engt

h (

MP

a)

% GFRP

Test Results Swami et. al. (2010) Ghorpade (2010)

61

Figure (4.15): Mode of Failure of Plain HSC Specimens (Without Fiber).

Figure (4.16): Mode of Failure of HSC Specimens with 0.3 Fiber Percentage.

Figure (4.17): Mode of Failure and Crack Pattern of HSC Specimens with 0.6 Fiber

Percentage.

62

Figure (4.18): Mode of Failure and Crack Pattern of HSC Specimens with 0.9 Fiber

Percentage.

Figure (4.19): Mode of Failure and Crack Pattern of HSC Specimens with 1.2 Fiber

Percentage.

63

4.3 Flexural Strength (Modulus of Rapture) Test Results

The results of 7 and 28 days’ flexural strength or modulus of rapture are shown in Table 4.5

and Table 4.6. According to ACI Committee 363 (2010), Eq. 4.2 was recommended for the

prediction of the flexural strength or modulus of rapture of HSC with 28 days’ cylinder

compressive strength within 21 to 83 MPa.

Fr = 0.94√𝒇𝒄′ (4.2)

As mentioned before, the 28 days’ cylinder compressive strength of plain HSC (without fiber)

was equals to 51.149 MPa. Which make the predicted flexural strength or modulus of rapture

Fr using Equation 4.2 equals to 6.72 MPa which seems close with the average experimental

value of plain HSC specimens (M50 F0) equal to 6.35 MPa shown in Table 4.6 with percent

error equal to 5.5 percent.

Table (4.5): Flexural Strength (Modulus of Rapture) Test Results.

Designation

% GFRP

by Cement

Wt.

Specimens

Failure Load (KN) Flexural Strength

(MPa)

7 Days 28 Days 7 Days 28 Days

M50 F0 0

1.00 6.87 10.02 4.68 6.76

2.00 7.32 8.60 4.99 5.80

3.00 9.61 6.49

M50 F1 0.3

1.00 7.66 10.87 5.17 7.34

2.00 7.90 11.34 5.39 7.73

3.00 11.12 7.51

M50 F2 0.6

1.00 9.59 12.58 6.41 8.58

2.00 9.14 12.19 6.11 8.31

3.00 11.79 7.96

M50 F3 0.9

1.00 10.16 12.53 6.86 8.54

2.00 9.72 13.52 6.50 9.22

3.00 12.87 8.60

M50 F4 1.2

1.00 10.50 14.49 7.09 9.88

2.00 11.03 14.83 7.45 10.01

3.00 13.54 9.14

64

Table (4.6): Average Flexural Strength (Modulus of Rapture) Test Results.

Designation

% GFRP

by Cement

Wt.

Average Flexural Strength (MPa) % Increase

Over the

Reference Mix

(28 Day) 7 Days 28

Days S CV

M50F0 0 4.84 6.35 0.49 7.79

M50F1 0.3 5.28 7.53 0.20 2.63 18.50

M50F2 0.6 6.26 8.28 0.31 3.75 30.41

M50F3 0.9 6.68 8.79 0.37 4.24 38.35

M50F4 1.2 7.27 9.68 0.47 4.85 52.36

From Table 4.6, it is observed that with increase in fiber percentage, the flexural strength or

modulus of rapture also increases significantly. As shown in Figure 4.20, the flexural strength

increases continuously from 4.84 to 7.27 MPa with increase in fiber percentage from 0.0 to 1.2

respectively for 7 days, and 6.35 to 9.68 MPa when fiber percentage increase from 0.0 to 1.2

respectively for 28 days. From the test results shown in Table 4.6, it is observed that the

percentage of increase in the flexural strength over the reference mix due to addition of fibers

is much higher than for the compressive strength but little less than for splitting tensile strength,

except at 0.3 fiber percentage where flexural strength shows the highest percentage of increase

as shown in Figure 4.21.

In addition, the mode of increasing in flexural strength due to addition of fibers is the same as

for splitting tensile strength, which also keeping continuous ascending until the highest value

of 9.68 MPa (28 Days) at the highest fiber percentage of 1.2 as shown in Figure 4.20. comparing

with the increasing in compressive strength as discussed before where Figure 4.1 shows

continuous ascending just until 0.6 fiber percentage and then at fiber percentage from 0.6 to

1.2, the increasing turned to very slight. This difference between the increasing mode of

compressive strength and Flexural strength curves shown in Figure 4.1 and Figure 4.20 can be

explained simply as the same as discussed for splitting tensile strength before, where the defects

that caused by higher fiber percentages during the micro level appear strongly when the

concrete fail due to compressive stresses rather than due to the induced tensile stresses. Hence

it is established that AR-GFRP inclusion in HSC mixtures is more powerful in enhancing the

tensile strength than compression strength.

65

Figure (4.20): Effect of AR-GFRP on Flexural Strength (Modulus of Rapture) of HSC.

Figure (4.21): The Percentage of Increase Over the Reference Mix Due to Addition of AR-

GFRP on HSC: Comparison Between Compressive, Splitting Tensile and Flexural Strength.

Test result show good agreement with Swami et. al. (2010) and Ghorpade (2010). The authors

show that the concrete flexural strength can increased significantly with addition of glass fiber

even when large amount was used as shown in Figure 4.22. However, Ghorpade (2010) -

whose use VHSC to study the effect of addition of GFRP- show that flexural strength could

decrease when use fiber percentage larger than 1 percent.

6.35

7.538.28

8.799.68

4.845.28

6.266.68

7.27

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0 0.3 0.6 0.9 1.2

Fle

xu

ral S

tren

gth

(M

pa)

% AR- GFRP

28 Days

7 Days

5.238

12.36 12.798 13.14

18.50

30.41

38.35

52.36

15.834

34.28

41.731

63.223

0

10

20

30

40

50

60

70

0 0.3 0.6 0.9 1.2

% I

ncr

ease

Over

The

Ref

eren

ce M

ix (

28

Day

s)

% AR- GFRP

Compressive Strength Flexural Strength Splitting Tensile Strength

66

Figure (4.22): Comparisons of flexural strength test results with other related researches.

4.4 Result Summary

Based on the experimental results, the compressive strength, splitting tensile strength, and

flexural strength of HSC is found to be increases as fiber percentage increases. However, it is

observed that the percentage of increase in the splitting tensile strength and flexural strength

over the reference mix due to addition of fibers is much higher than for the compressive

strength. Hence it is established that AR-GFRP inclusion in HSC mixtures is more powerful

for enhancing the tensile strength than compression strength of HSC. In addition, the mode of

failure is found to be taken place gradually with the formation of cracks as fiber percentage

increase, compared with plain HSC specimens (without fibers), the failure was sudden, brittle

and completely destruction with sound (Loudly). Hence it is established that the presence of

fibers in the matrix has contributed towards arresting sudden crack formation.

4

5

6

7

8

9

10

11

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

28

Day

s Fl

exu

ral S

tren

gth

(M

Pa)

% GFRP

Test Results Swami et. al. (2010) Ghorpade (2010)

Chapter 5

Conclusions and

Recommendations

68

Chapter 5: Conclusions and Recommendations

5.1 Conclusions

The effect of the addition of alkali resistant glass fibers reinforced polymer (AR-GFRP) with

various proportions on the mechanical behavior of high strength concrete (HSC) with up to 60

MPa 28 days’ cube compressevie strength using available materials in the local market was

studied on this research. The main objective of this investigation was to compare the strength

characteristics and the mode of failure of the HSGFRC composition with various percentages

of AR-GFRP with plain HSC (without fiber), by performing laboratory tests at different ages 7

and 28 days that are related to compressive strength, splitting tensile strength, flexural strength,

and density. Based on the experimental investigation carried out on this research, the following

conclusions are drawn:

i. The compressive strength of HSC is found to be maximum at 1.2 percentage of fiber

with 13.14 percentage of increasing over the reference mix. However, it considered that

the optimum percentage of fiber was 0.6 with 12.36 percentage of increasing over the

reference mix since the difference between those values of fiber percentage is

insignificant.

ii. The ratio of 7 days to 28 days’ compressive strength is found to be decrease as fiber

percentage increase, typically, from 79.6 to 74.43 as fiber percentage increase from 0.0

to 1.2 respectively.

iii. The density of HSC is found to be increases very slightly as fiber percentage increases

from 0.0 to 1.2, typically from 2417 to 2441 kg/m3. this can be explained due to the

extremely light weight and high ratio of surface area to weight of AR-GFRP.

iv. The splitting tensile strength of HSC is found to be increases continuously until the

highest value of 1.2 fiber percentage with 63.22 percentage of increasing over the

reference mix at 28 days.

v. The flexural strength or modulus of rapture of HSC is also found to be increases

continuously until the highest value of 1.2 fiber percentage with 52.36 percentage of

increasing over the reference mix at 28 days.

vi. It is observed that the percentage of increase in the splitting tensile strength and flexural

strength over the reference mix due to addition of fibers is much higher than for the

compressive strength. Hence it is established that AR-GFRP inclusion in HSC mixtures

is more powerful for enhancing the tensile strength than compression strength of HSC.

69

vii. The mode of failure during compressive strength and splitting tensile strength tests is

found to be taken place gradually with the formation of cracks as fiber percentage

increase, compared with plain HSC specimens, the failure was sudden, brittle and

completely destruction with sound (Loudly). Hence it is established that the presence of

fibers in the matrix has contributed towards prevent sudden crack formation.

5.2 Recommendations

The following recommendations are proposed for further research.

i. Study the effect of AR-GFRP on the mechanical properties of HSC with more research

variable such as various strength grade, various fiber percentages and various fiber

length.

ii. Study the stress-strain behavior in compression and tension and develop a generalized

stress-strain curve for HSGFRC.

iii. Develop a flexural model based on generalized stress-strain curve for HSGFRC to use

it in practice.

iv. Study the performance of HSGFRC under impact load.

v. Study the effect of AR-GFRP on the fresh properties of HSC such as workability.

vi. Investigate the durability aspects of HSGFRC such as performance under high

temperatures and chemical resistance.

vii. Further testing and studies needed to be carry out, to test the behavior of HSGFRC when

used as a repair and strengthening material to rehabilitate the different deteriorated

structural elements.

70

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