behavior of steel fiber-reinforced geopolymer …

United Arab Emirates University United Arab Emirates University

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BEHAVIOR OF STEEL FIBER-REINFORCED GEOPOLYMER BEHAVIOR OF STEEL FIBER-REINFORCED GEOPOLYMER

CONCRETE MADE WITH RECYCLED CONCRETE AGGREGATES CONCRETE MADE WITH RECYCLED CONCRETE AGGREGATES

Abdalla Ahmed Moallim Hussein

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ii

Declaration of Original Work

I, Abdalla Ahmed Moallim Hussein, the undersigned, a graduate student at the United

Arab Emirates University (UAEU), and the author of this thesis entitled “Behavior Of

Steel Fiber-Reinforced Geopolymer Concrete Made With Recycled Concrete

Aggregates”, hereby, solemnly declare that this thesis is my own original research

work that has been done and prepared by me under the supervision of Dr. Hilal El-

Hassan, in the College of Engineering at UAEU. This work has not previously been

presented or published, or formed the basis for the award of any academic degree,

diploma or a similar title at this or any other university. Any materials borrowed from

other sources (whether published or unpublished) and relied upon or included in my

thesis have been properly cited and acknowledged in accordance with appropriate

academic conventions. I further declare that there is no potential conflict of interest

with respect to the research, data collection, authorship, presentation and/or

publication of this thesis.

Student’s Signature: Date: __30/05/2021_________

iii

Copyright

Copyright © 2021 Abdalla Ahmed Moallim Hussein

All Rights Reserved

iv

Advisory Committee

1) Advisor: Dr. Hilal El-Hassan

Title: Associate Professor

Department of Civil & Environmental Engineering

College of Engineering

2) Co-advisor: Prof. Tamer El Maaddawy

Title: Professor

Department of Civil & Environmental Engineering


v

Approval of the Master Thesis

This Master Thesis is approved by the following Examining Committee Members:

1) Advisor (Committee Chair): Hilal El-Hassan


Department of Civil and Environmental Engineering


Signature Date

2) Member: Bilal El-Ariss


Department of Civil and Environmental Engineering


Signature Date

3) Member: Mahmoud Reda Taha

Title: Professor

Department of Civil Engineering

Institution: University of New Mexico, USA

Signature Date

May 31, 2021

May 31, 2021on behalf of external examiner

vi

This Master Thesis is accepted by:

Dean of the College of Engineering: Professor James Klausner

Signature Date

Dean of the College of Graduate Studies: Professor Ali Al-Marzouqi

Signature Date

Copy ____ of ____

24/6/2021

vii

Abstract

Industrial by-products and recycled concrete aggregates (RCA) have the potential to

fully replace cement and natural aggregates, respectively, in the production of concrete

rather than being discarded wastefully into landfills or stockpiles. Yet, their combined

use in the development of a novel RCA geopolymer concrete has been limited to non-

structural purposes, owing to the inferior mechanical and durability properties of said

concrete. To improve the properties of geopolymer concrete made with RCA, steel

fibers may be added to the mix. This research aims to study the feasibility of reutilizing

locally available industrial solid wastes and RCA in geopolymer concrete for structural

applications. A combination of ground granulated blast furnace slag and fly ash were

used to form a blended precursor binding material. The mechanical properties of steel

fiber-reinforced geopolymer concrete made with RCA were studied through testing

for compressive strength, splitting tensile strength, flexural properties, and modulus of

elasticity. In turn, the durability performance was assessed using water absorption,

sorptivity, bulk resistivity, and abrasion resistance. Experimental test results highlight

the ability to fully replace natural aggregates with RCA in blended geopolymer

concrete incorporating 2% steel fibers, by volume. Compared to the control mix made

with no RCA and steel fibers, such concrete provided superior mechanical and

comparable durability performance. Additionally, new tensile softening relationships

were established from the experimental test data and using inverse finite element

analysis. Three-dimensional finite element (FE) models were developed to simulate

and predict the shear behavior of steel fiber-reinforced RCA geopolymer concrete

beams. Based on regression analysis of FE results, a simplified empirical equation that

accounts for the compressive strength of concrete and steel fiber volume fraction was

established to predict the nominal shear resistance of steel fiber-reinforced geopolymer

concrete beams.

Keywords: Geopolymer, recycled concrete aggregate, steel fibers, performance

evaluation.

viii

Title and Abstract (in Arabic)

الركام من والمصنوعة الصلب بألياف المسلحة الجيوبوليمرية الخرسانة سلوك

تدويره المعاد الخرساني

ص الملخ

( تدويرها المعاد الخرسانة ومجموعات الصناعية الثانوية على RCAالمنتجات القدرة لديها )

استبدال الأسمنت والركام الطبيعي بالكامل ، على التوالي ، في إنتاج الخرسانة بدلا من التخلص

منها في مكبات النفايات أو المخزونات. ومع ذلك ، فإن استخدامها المشترك في تطوير الخرسانة

سبب الخصائص الميكانيكية الجديدة اقتصر على الأغراض غير الهيكلية ، ب RCAالجيوبوليمرية

والمتانة الرديئة للخرسانة المذكورة. لتحسين خصائص الخرسانة الجيوبوليمرية المصنوعة من

RCA يمكن إضافة ألياف فولاذية إلى المزيج. يهدف هذا البحث إلى دراسة جدوى إعادة استخدام ،

و محليا المتوفرة الصناعية الصلبة ال RCAالنفايات الخرسانة للتطبيقات في جيوبوليمرية

الإنشائية. تم استخدام مزيج من خبث الفرن العالي الحبيبي والرماد المتطاير لتشكيل مادة ربط

سلائف مخلوطة. تمت دراسة الخواص الميكانيكية للخرسانة الجيوبوليمرية المقواة بألياف الصلب

نشقاقي وخصائص الانحناء من خلال اختبار مقاومة الانضغاط وقوة الشد الا RCAالمصنوعة من

والامتصاصية الماء امتصاص باستخدام المتانة أداء تقييم تم ، المقابل في المرونة. ومعامل

على القدرة على الضوء التجريبية الاختبارات نتائج تسلط التآكل. ومقاومة السائبة والمقاومة

رية المخلوطة التي تحتوي على في الخرسانة الجيوبوليم RCAاستبدال الركام الطبيعي بالكامل بـ

٪ ، من حيث الحجم. بالمقارنة مع مزيج التحكم المصنوع من عدم وجود 2ألياف فولاذية بنسبة

مماثلة. RCAألياف ومتانة متفوقا ميكانيكيا أداء توفر الخرسانة هذه فإن ، فولاذية وألياف

القوانين التأسيسية للضغط والانفعال من بالإضافة إلى ذلك ، تم إنشاء علاقات تليين الشد الجديدة و

نماذج تطوير تم المعكوسة. المحدودة العناصر تحليل وباستخدام التجريبية الاختبار بيانات

ix

الجيوبوليمرية للخرسانة القص سلوك لمحاكاة الأبعاد ثلاثية المحدودة المقواة RCAالعناصر

، تم إنشاء معادلة تجريبية مبسطة تمثل قوة FEبناء على تحليل الانحدار لنتائج بألياف الصلب.

الضغط لكسر حجم ألياف الخرسانة والصلب للتنبؤ بمقاومة القص الاسمية لعوارض الخرسانة

الجيوسيلية المسلحة بألياف الصلب.

: الجيوبوليمر ، الركام الخرساني المعاد تدويره ، الألياف الفولاذية ، تقييم مفاهيم البحث الرئيسية

.الأداء

x

Acknowledgements

I would like to thank God for giving me the faith and strength to successfully complete

my research. I am so grateful to my advisor Dr. Hilal El-Hassan, as he is an outstanding

professor and excellent researcher. I thank him for all that he taught me and for the

support he has provided through my work. Also, I would like to express my sincere

gratitude to my co-advisor professor Tamer El-Maaddawy for his outstanding

guidance, constructive advice, and valuable assistance throughout the study. I would

like to thank all my family members and friends for their continuing support and

encouragement throughout the entire study. Special thanks to the examination

committee members for their time in reviewing this thesis.

My great thanks to my colleague Jamal Medljy for his outstanding help. The technical

assistance provided by the laboratory staff for the experimental works is appreciated.

My sincere appreciation to Eng. Abdelrahman Alsallamin, Eng. Tarek Salah and Mr.

Faisal Abdulwahab, and other staff for their help and technical assistance throughout

this research. In addition, special thanks are extended to ADEK and UAEU for

providing me with financial support to complete this research work under grant

number 21N209.

xi

Dedication

To my beloved parents and family

xii

Table of Contents

Title ............................................................................................................................... i

Declaration of Original Work ...................................................................................... ii

Copyright .................................................................................................................... iii

Advisory Committee ................................................................................................... iv

Approval of the Master Thesis ..................................................................................... v

Abstract ...................................................................................................................... vii

Title and Abstract (in Arabic) ................................................................................... viii

Acknowledgements ...................................................................................................... x

Dedication ................................................................................................................... xi

Table of Contents ....................................................................................................... xii

List of Tables ............................................................................................................. xv

List of Figures ........................................................................................................... xvi

List of Abbreviations ................................................................................................ xix

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

1.1 Overview .................................................................................................... 1

1.2 Scope and Objectives ................................................................................. 2

1.3 Outline and Organization of the Thesis ..................................................... 3

1.4 Research questions ..................................................................................... 4

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

2.1 Introduction ................................................................................................ 6

2.2 Concrete and the environment ................................................................... 6

2.3 Background on geopolymers ..................................................................... 8

2.4 GGBS-fly ash blended geopolymer composites ........................................ 9

2.5 Geopolymer concrete with recycled aggregate ........................................ 14

2.6 Geopolymer concrete reinforced with steel fiber ..................................... 16

2.7 Shear behavior of geopolymer concrete................................................... 19

2.8 Research Significance .............................................................................. 21

Chapter 3: Experimental Program.............................................................................. 23

3.1 Introduction .............................................................................................. 23

3.2 Test program ............................................................................................ 23

3.3 Material properties ................................................................................... 25

3.3.1 Precursor binding material ............................................................... 25

3.3.2 Coarse aggregates ............................................................................. 29

3.3.3 Fine aggregates ................................................................................. 31

3.3.4 Chemical activators .......................................................................... 33

xiii

3.3.5 Steel fibers ........................................................................................ 33

3.3.6 Superplasticizer ................................................................................ 33

3.4 Geopolymer concrete mixture proportions .............................................. 34

3.5 Sample preparation .................................................................................. 35

3.6 Performance evaluation............................................................................ 37

3.6.1 Compressive strength ....................................................................... 37

3.6.2 Modulus of elasticity ........................................................................ 38

3.6.3 Splitting tensile strength ................................................................... 38

3.6.4 Flexural strength ............................................................................... 39

3.6.5 Water absorption .............................................................................. 40

3.6.6 Sorptivity .......................................................................................... 40

3.6.7 Bulk electric resistivity .................................................................... 41

3.6.8 Abrasion resistance .......................................................................... 42

Chapter 4: Experimental Results and Discussions ..................................................... 43

4.1 Introduction .............................................................................................. 43

4.2 Mechanical Properties .............................................................................. 43

4.2.1 Compressive Strength ...................................................................... 43

4.2.2 Compressive stress-strain response .................................................. 52

4.2.3 Modulus of Elasticity ....................................................................... 55

4.2.4 Splitting tensile strength ................................................................... 59

4.2.5 Flexural performance ....................................................................... 63

4.3 Durability properties ................................................................................ 81

4.3.1 Water absorption .............................................................................. 81

4.3.2 Sorptivity .......................................................................................... 83

4.3.3 Bulk resistivity ................................................................................. 86

4.3.4 Abrasion resistance .......................................................................... 88

Chapter 5: Numerical Modelling ............................................................................... 94

5.1 Introduction .............................................................................................. 94

5.2 Geometry of the beam .............................................................................. 94

5.3 Finite Element Modeling ......................................................................... 96

5.4 Material Constitutive Laws ...................................................................... 98

5.4.1 Plain Geopolymer Concrete ............................................................. 98

5.4.2 Reinforcing steel ............................................................................ 100

5.4.3 Steel Plates ..................................................................................... 101

5.4.4 Steel Fiber-Reinforced Geopolymer Concrete ............................... 101

5.5 Results and discussion ........................................................................... 108

5.5.1 Load-deflection curves ................................................................... 108

5.5.2 Crack Patterns and Failure Modes ................................................. 112

5.5.3 Peak Load ....................................................................................... 123

Chapter 6: Conclusions ............................................................................................ 126

6.1 Introduction ............................................................................................ 126

6.2 Limitations ............................................................................................. 127

xiv

6.3 Conclusions ............................................................................................ 127

6.4 Recommendations for Future Studies .................................................... 130

References ................................................................................................................ 132

Appendix .................................................................................................................. 142

xv

List of Tables

Table 1: Experimental Test Matrix ............................................................................ 24

Table 2: Chemical composition of as-received materials .......................................... 26

Table 3: Physical properties of coarse aggregates ..................................................... 31

Table 4: Mixture proportions of geopolymer concrete (kg/m3) ................................. 35

Table 5: Percent increase in cube compressive strength with time. .......................... 46

Table 6: Cylinder and cube compressive strength of 28-day geopolymer

………...concrete ....................................................................................................... 51

Table 7: Equations relating the modulus of elasticity to the compressive

………...strength ........................................................................................................ 58

Table 8: Ratio of tensile splitting strength to compressive strength .......................... 60

Table 9: Equations relating splitting tensile strength and compressive

………...strength ........................................................................................................ 62

Table 10: Flexural performance test results ............................................................... 63

Table 11: Flexural and cylinder compressive strength of 28-day geopolymer

………….concrete ..................................................................................................... 71

Table 12: Equations relating flexural strength and cylinder compressive

………… strength ...................................................................................................... 72

Table 13: Water absorption and initial rate of absorption of geopolymer

………….concrete ..................................................................................................... 86

Table 14: Input parameters of monitoring points ...................................................... 97

Table 15: Mechanical properties of the geopolymer concrete mixes ........................ 99

xvi

List of Figures

Figure 1: SEM micrographs of (a) GGBS and (b) fly ash ......................................... 27

Figure 2: XRD spectrum of (a) GGBS and (b) fly ash .............................................. 28

Figure 3: Particle size distribution of (a) GGBS and (b) fly ash ............................... 29

Figure 4: Particle size distribution of different aggregate percentages ...................... 30

Figure 5: Particle size distribution of dune sand ........................................................ 32

Figure 6: Dune sand (a) SEM micrograph and (b) XRD spectrum ........................... 32

Figure 7: Materials used in casting geopolymer concrete.......................................... 36

Figure 8: Geopolymer specimens after demolding .................................................... 37

Figure 9: Development of cubic compressive strength of concrete mixes

…………made with SF (a) 0%, (b) 1%, and (c) 2% ................................................. 44

Figure 10: Cubic compressive strength for (a) 1-day, (b) 7-day and (c) 28-day

………….geopolymer concrete ................................................................................. 48

Figure 11: 28-day cylinder compressive strength of geopolymer concrete ............... 50

Figure 12: Relationship between cube and cylinder compressive strengths of

…………..geopolymer concrete ................................................................................ 51

Figure 13: Typical compression stress-strain curves of cylinder concrete

…………..specimens with RCA (a) 30%, (b) 70%, and (c) 100% ........................... 52

Figure 14: Typical compression stress-strain curves of cylinder concrete

…………..specimens with SF (a) 0%, (b) 1%, and (c) 2% ....................................... 54

Figure 15: Modulus of elasticity of concrete mixes with different RCA

…………..replacement percentages and SF volume fractions .................................. 56

Figure 16: Modulus of elasticity of concrete mixes as a function of

…………..compressive strength ................................................................................ 57

Figure 17: Experimental versus predicted modulus of elasticity ............................... 58

Figure 18: Splitting tensile strength of 28-day geopolymer concrete ........................ 59

Figure 19: Correlation between splitting tensile strength and compressive

…………..strength ..................................................................................................... 62

Figure 20: Experimental versus predicted splitting tensile strength .......................... 62

Figure 21: Typical load-deflection curves of geopolymer concrete mixes

…………..with SF (a) 0%, (b) 1%, and (c) 2% ......................................................... 65

Figure 22: Typical load-deflection curves of cylinder concrete specimens

…………..with RCA (a) 30%, (b) 70%, and (c) 100% ............................................. 68

Figure 23: Flexural strength of 28-day geopolymer concrete .................................... 71

Figure 24: Relationship between flexural and cylinder compressive strength

…………..of 28-day geopolymer concrete................................................................ 72

Figure 25: Experimental versus predicted flexural strength ...................................... 72

Figure 26: Deflection at peak load of concrete mixes with various …..…

…………..(a) RCA replacement percentage and SF volume fractions and (b)

…………..cylinder compressive strength .................................................................. 74

xvii

Figure 27: Residual strength of concrete mixes with various (a) RCA

…………..replacement percentage and SF volume fractions and (b) cylinder


Figure 28: Flexural toughness of concrete mixes with various (a) RCA

…………..replacement percentage and SF volume fractions and (b) cylinder


Figure 29: Equivalent flexural strength ratio of concrete mixes with various

…………..(a) RCA replacement percentage and SF volume fractions and (b)

…………..cylinder compressive strength .................................................................. 80

Figure 30: Effect of RCA and SF percentages on the water absorption of

…………..28-day geopolymer concrete .................................................................... 82

Figure 31: Absorption of concrete mixes over time: (a) SF 0%; (b) SF 1%;

………….(c) SF2% ................................................................................................... 84

Figure 32: Bulk resistivity of 28-day blended geopolymer concrete mixes .............. 87

Figure 33: Relationship between bulk resistivity and each of water absorption

…………..and compressive strength ......................................................................... 88

Figure 34: Abrasion resistance of geopolymer concrete made with SF (a) 0%,

………….(b) 1%, and (c) 2% .................................................................................... 89

Figure 35: Abrasion resistance of geopolymer concrete mixes made with

………….RCA (a) 30%, (b) 70%, and (c) 100% ...................................................... 91

Figure 36: Relationship between abrasion mass loss and cylinder compressive

…………..strength ..................................................................................................... 93

Figure 37: Modeled beam cross-section view (dimensions in mm) .......................... 95

Figure 38: Modeled beam elevation view (dimensions in mm)................................. 96

Figure 39: Typical FE model for geopolymer concrete beam ................................... 96

Figure 40: Constitutive laws of plain concrete: (a) compressive hardening

…………..law; (b) compressive softening law; (c) tensile softening law

…………..(Alkhalil and El-Maaddawy, 2017; Awani et al., 2016) .......................... 99

Figure 41: Steel reinforcing bars (a) Stress-strain relationship and ……

…………..(b) Arrangement of steel reinforcement in the FE models..................... 101

Figure 42: Typical compression stress-strain constitutive law of

…………..CC3DNonLinCementit2User ................................................................. 102

Figure 43: Concrete prism model used for inverse analysis .................................... 103

Figure 44: Inverse analysis results of R30SF1: (a) experimental and predicted

…………..load-deflection curves and (b) corresponding tension function ............. 103









xviii



Figure 50: Load-deflection response of concrete models with SF (a) 0%,

…………..(b) 1%, (c) SF 2% .................................................................................. 109

Figure 51: Load-deflection response of concrete models with RCA (a) 30%,

…………..(b) 70%, and (c) 100% ........................................................................... 111

Figure 52: R0SF0 FE models: (a) crack patterns, (b) maximum principal

…………..strains, and (c) minimum principal strains ............................................. 114



















Figure 62: Peak loads of geopolymer concrete beams ............................................. 124

Figure 63: Predicted versus experimental shear resistance ...................................... 125

xix

List of Abbreviations

AAS Alkaline Activator Solution

AR Abrasion Resistance

b Width of Specimen

BR Bulk Resistivity

d Depth of Specimen

DS Dune Sand

Ec Modulus of Elasticity of Concrete

f’c Cylinder Compressive Strength of Concrete

fcu Cube Compressive Strength of Concrete

FE Finite Element

FEM Finite Element Modelling

fr Flexural Strength

fsp Splitting Tensile Strength

f150 100

Residual Flexural Strength at L/150

f600 100

Residual Flexural Strength at L/600

GC Geopolymer Concrete

GGBS Ground Granulated Blast Slag

I Absorption

L Length of Specimen

NA Normal Aggregate

NC Normal Concrete

NMS Nominal Maximum Size

OPC Ordinary Portland Cement

xx

RT,150 100 Equivalent Flexural Strength Ratio

RCA Recycled Concrete Aggregate

SCM Supplementary Cementitious Material

SEM Scanning Electron Microscope

SF Steel Fiber

SH Sodium Hydroxide

SP Superplasticizer

SS Sodium Silicate

SSD Saturated Surface Dry

T150 100 Flexural Toughness

vf Steel Fiber Volume Fraction

Vn Nominal Shear Capacity

WA Water Absorption

XRD X-ray Diffraction

XRF X-ray Fluorescence

δp Peak Deflection

ν Poisson’s Ratio

1

Chapter 1: Introduction

1.1 Overview

Aging infrastructure and superstructures entail continuous renovation and

replacement, resulting in increases in demand for new concrete. The ability to recycle

concrete of construction and demolition waste and reutilize industrial solid by-

products as respective aggregates and binder in concrete provides a sustainable

solution to the pressing issues of depletion of natural resources and emissions of

carbon dioxide. Recycled concrete aggregate (RCA) has been proposed as a viable

alternative to natural coarse aggregates. However, its utilization in high-grade

applications as structural concrete is limited due to its inferior physical, mechanical,

and durability properties compared to those of natural aggregates (Akbarnezhad et al.,

2011; Hansen and Boegh, 1985). Nevertheless, numerous studies have been conducted

to improve the performance of RCA concrete by treating these aggregates or altering

the concrete mix design. These methods require excessive energy or cement, which

are not economic, environment-friendly, or feasible on construction sites.

Other efforts have been made to alleviate cement-induced CO2 emissions by

developing environment-friendly binders as inorganic alkali-activated geopolymer.

Upon incorporation into concrete, geopolymer promises to emit much less CO2 in its

production than conventional cement-based concrete (Jiang et al., 2014). Still, this

sustainable material provides a solution to one part of the problem, i.e. cement. To

further stimulate sustainable development, there is a pressing need to collectively

utilize RCA and geopolymer binder in producing concrete. The limited studies that

investigated RCA geopolymer concrete reported inferior mechanical and durability

2

performance compared to conventional concrete (Hu et al., 2019; Kathirvel and

Kaliyaperumal, 2016; Parthiban and Saravana Raja Mohan, 2017; Tang et al., 2019).

To promote its adoption by the construction industry, geopolymer concrete made with

100% RCA should present comparable results to its conventional cement-based

counterpart. One means is the novel incorporation of steel fiber reinforcement into the

geopolymer concrete mix. However, none of the available studies have evaluated the

mechanical and durability properties of geopolymer concrete made with RCA and steel

fibers.

1.2 Scope and Objectives

The main aim of this study is to evaluate the performance of GGBS-fly ash

blended geopolymer concrete made with different proportions of RCA and steel fibers.

Mechanical and durability properties are assessed using standardized test procedures.

Flexural strength test results are then be employed to develop tensile softening

relationships. Three-dimensional numerical models are subsequently developed to

examine the shear performance of beams made of the so-produced concrete. The

specific objectives of this work are as follows:

• Examine the effect of RCA replacement and steel fiber incorporation on the

mechanical properties of blended geopolymer concrete.

• Investigate the influence of different RCA and steel fiber proportions on the

durability performance of blended geopolymer concrete.

• Propose correlation equations among the properties of steel fiber-reinforced

RCA geopolymer concrete and compare them to codified equations.

• Develop tensile softening relations for steel fiber-reinforced RCA geopolymer

concrete.

3

• Examine the structural shear behavior of steel fiber-reinforced RCA

geopolymer concrete using numerical Finite Element Modeling (FEM).

1.3 Outline and Organization of the Thesis

The research work carried out in this thesis is organized into six chapters as

follows:

Chapter 1 provides a brief introduction and a summary of the research

objectives to be addressed throughout the thesis. It also includes an outline,

organization, and research significance of this work.

Chapter 2 presents a detailed and comprehensive literature review on the

available studies investigating geopolymer concrete. Topics will include fundamental

knowledge on geopolymers, the use of RCA in geopolymer concrete, and the use of

steel fiber in geopolymer concrete.

Chapter 3 presents details of the characteristics of the as-received materials,

mixture proportioning, sample preparation. It also comprises the testing methodologies

employed to evaluate the mechanical and durability performance of geopolymer

concrete.

Chapter 4 highlights the experimental test results. Compressive, splitting

tensile, and flexural strength, compressive stress-strain curves, modulus of elasticity,

flexural load-deflection curves, water absorption, sorptivity, and abrasion resistance

of various geopolymer concrete mixes are presented and discussed. Correlations

among these properties are also furnished.

4

Chapter 5 shows the details and results of the numerical FE modeling of the

shear behavior of blended geopolymer concrete beams made with different RCA and

steel fiber proportions.

Chapter 6 provides a summary of the research findings, general conclusions

and limitations of the completed work, and recommendations for future studies on steel

fiber-reinforced RCA geopolymer concrete.

1.4 Research questions

The replacement of natural aggregates by RCA has negatively impacted the

performance of geopolymer concrete. The addition of steel fibers is a promising

solution that may reverse this effect. However, there is a lack of knowledge about the

mechanical and durability performance of steel fiber-reinforced RCA blended

geopolymer concrete. Accordingly, this work aims to provide answers to the following

research questions:

• What is the feasibility of producing cement-free GGBS-fly ash blended

geopolymer concrete made with 100% RCA and steel fibers as a sustainable

alternative to conventional concrete?

• What is the effect of RCA replacement on the mechanical and durability

properties of blended geopolymer concrete?

• What is the influence of the addition of steel fibers on the mechanical and

durability properties of blended geopolymer concrete incorporating RCA?

• How are the mechanical and durability properties of blended geopolymer

concrete incorporating RCA and steel fibers correlated among each other?

5

• What are the tensile softening relations of geopolymer concrete made with

RCA and steel fibers?

• How do RCA replacement and steel fiber addition affect the structural shear

behavior of GGBS-fly ash blended geopolymer concrete beams?

6

Chapter 2: Literature Review

2.1 Introduction

A comprehensive literature review was conducted to summarize and discuss

the available experimental studies on geopolymer concrete. First, a short background

on the production of concrete is presented. Then, emphasis was placed on topics

including the geopolymerization process, use of GGBS and fly ash in producing

geopolymer concrete, RCA geopolymer concrete, and steel fiber-reinforced

geopolymer concrete. The research significance is also highlighted at the end of this

chapter.

2.2 Concrete and the environment

Concrete production is among the world’s fast-growing industries. It is

considered one of the most widely used materials globally with 15 billion tons and

around one cubic meter per capita being produced per year (US Geological Survey,

2016). According to current global statistics, Portland cement, the main binder in

concrete, is estimated to be produced in the range of 4.8 billion tons (Statistica, 2021).

Due to the high demand for concrete, one of its main resources, limestone, is expected

to reach an acute shortage within 25 to 50 years (Aleem and Arumairaj, 2012; Kline

and Kline, 2015). Indeed, Portland cement is manufactured by mixing specific

quantities of limestone and clay at elevated temperatures. The process consumes 1.6

kg of raw material, requires 3.7 MJ of energy, and emits 1 kg of CO2 per kg of cement

produced (Afkhami et al., 2015; Thakur and Wu, 2000). In fact, the cement industry

alone is accountable for 5-7% of the global CO2 emissions (Benhelal et al., 2013;

Davidovits, 1994), leading to an increase in the concentration of CO2 in the atmosphere

7

(Earth System Research Laboratory, 2013; Herzog et al., 2000). As a result, cement

production is becoming a critical global issue from an ecological, social, and

environmental standpoint.

To alleviate the consumption of natural resources and emission of CO2 from

cement manufacturing, scientists and environmentalists propose the incorporation of

supplementary cementitious material (SCMs) in concrete mixes. In most cases, these

SCMs are pozzolanic and non-pozzolanic industrial solid wastes. If integrated into

concrete mixes, they could have a dual benefit of reducing cement usage while also

usefully disposing of solid industrial by-products. Of these materials, fly ash and

ground granulated blast furnace slag (GGBS) are commonly used pozzolans. While

fly ash is an industrial waste from coal power plants, GGBS is a by-product of the

production of steel. Their incorporation in cement-based concrete has been reported to

improve the overall performance (Mehta, 2006).

Construction and demolition wastes management is another global pressing

issue. The massive amounts of debris generated in demolition, construction, and

renovation of structures are stretching the landfill capacity and inducing economic

leakages (Stoner and Wankel, 2008). In the United Kingdom, 20 million tons of debris

is deposited in landfills every year. Of this material, over 30% and 50% are masonry

and concrete respectively (Environmental Resources Limited, 1980). Recycling

construction and demolition wastes offers a sustainable solution to reduce the

consumption rate of landfill sites and natural resources (Kong et al., 2010; Poon and

Chan, 2007). For the past few decades, waste concrete has been reprocessed and reused

as aggregate. The so-produced recycled concrete aggregate (RCA) consists of 65-70%

original aggregate and 30-35% original cement paste by volume (Zhang et al., 2015).

8

A lifecycle inventory development study for the use of RCA in the UAE reported lower

global warming potential with RCA compared to NA (Alzard et al., 2021). However,

the use of RCA in structural concrete has been restricted due to its lower compressive

and tensile strength in comparison to those of normal concrete (Ikea et al., 1988). RCA

concrete also experiences more drying shrinkage and inferior durability properties

(Akbarnezhad et al., 2011; Hansen and Boegh, 1985).

2.3 Background on geopolymers

Davidovits (1991) introduced the word “geopolymer” as a form of inorganic

polymeric material. It is part of a larger family of materials known as alkali-activated

materials. They are typically formed through the activation of aluminosilicate-rich

precursor binding agents using alkaline solutions, including sodium silicate, sodium

hydroxide, potassium silicate, and/or potassium hydroxide. Typically, sodium or

potassium solutions were mixed to create the alkaline activator solution (AAS), but

single activators have also been used (Fernández-Jiménez and Puertas, 2003; Palomo

et al., 1999).

The chemical composition of the precursor dictates whether a certain

geopolymer was categorized with a Ca-Si or Al-Si system (Li et al., 2010). The first

system is a resultant of the alkali-activation of calcium-based binders such as GGBS.

It involves the hydration of calcium oxide in the presence of alumina to produce

calcium aluminosilicate hydrate (C-A-S-H) gel. The activation reaction generally

produces a material with limited workability, high strength, and drying shrinkage

(Aydın and Baradan, 2014; El-Hassan and Elkholy, 2019; El-Hassan and Ismail, 2018;

El-Hassan et al., 2018). Conversely, the second system develops due to the reaction of

fly ash, silica fume, metakaolin, and kaolinite clay. In the case of fly ash, the reaction

9

involves dissolving silica followed by coagulation, exothermic condensation, and

crystallization to produce sodium aluminosilicate hydrate (N-A-S-H) gel. Fernández-

Jiménez and Puertas (2003) concluded that the composition of fly ash had an impact

on the geopolymerization reaction, where class F fly ash was most suitable for its

optimization. However, this reaction was dependent on heat curing at 60-80°C and was

significantly retarded at ambient conditions. As such, its adoption for cast-in-situ

applications was limited. Nevertheless, several attempts have been made to combine

these two systems into a blended system made of GGBS and fly ash to reduce

shrinkage-induced cracks and eliminate the need for heat curing in the first and second

systems, respectively. The reaction products of this combined system highlight the

coexistence of C-A-S-H and N-A-S-H with a higher degree of cross-linking (Yip et

al., 2005).

2.4 GGBS-fly ash blended geopolymer composites

As noted in the previous section, several researchers mixed GGBS and fly ash

to form a blended geopolymer binder. Such a binding material has been utilized in

several past work. While several studies investigated the addition of slag to fly ash-

based geopolymers (slag-to-fly ash ratio < 1), limited investigations examined the

incorporation of fly ash to slag-based geopolymers (slag-to-fly ash ratio > 1).

Puertas et al. (2000) examined the mechanical performance behavior of fly

ash/GGBS geopolymer pastes. Results showed that alkaline activator concentration

and fly ash-to-GGBS ratio were the main contributors to strength development. The

curing temperature was found to have a less pronounced effect. The mixture made with

equal proportions of GGBS and fly ash and 10 M sodium hydroxide and cured at 25°C

could attain a compressive strength of about 50 MPa.

10

Nath and Sarker (2014) studied the effect of adding GGBS to fly ash-based

geopolymer concrete binder. The objective was to produce geopolymer concrete

mixtures suitable for curing at ambient temperature. GGBS and fly ash were activated

in an alkaline solution made of sodium silicate and sodium hydroxide. Results showed

that fly ash-based geopolymer concrete could be proportioned with GGBS for

desirable workability and setting time. In addition, 30% replacement of fly ash with

GGBS led to a compressive strength of 55 MPa.

Sofi et al. (2007) examined the mechanical properties of fly ash/slag-based

geopolymer concrete. Splitting tensile and flexural strengths were similar to the

models illustrated by the Australian standard AS3600 (2009) for conventional cement-

based concrete. While the difference between the splitting tensile and the flexural

strength of the GPC mixes was found to be about 2 MPa, the strength gains were

similar.

Deb et al. (2014) reported an increase in compressive and tensile strength and

a decrease in workability upon adding 10-20% GGBS into fly ash-based geopolymer

concrete. In fact, compressive strength could reach up to 51 MPa in geopolymer mixes

made with 20% GGBS and 80% fly ash and cured at 20°C. Codified equations of ACI

318 and AS3600 provided accurate predictions of the tensile strength but were slightly

more conservative for samples that were cured at elevated temperatures.

Prusty and Pradhan (2020a) investigated the use of GGBS on the strength and

corrosion resistance of fly ash-based geopolymer concrete. Results showed that the

slump decreased with GGBS addition due to the higher water demand of such particles.

The strength at 7 days was almost 80% higher upon replacing fly ash by GGBS with

lower potential values compared to fly ash-based geopolymer concrete.

11

Mehta et al. (2020) optimized the mixture proportions of fly ash-based

geopolymer concrete incorporating up to 20% GGBS. The optimum AAS-to-fly ash

ratio, sodium silicate to sodium hydroxide ratio, total aggregate content, and molarity

of sodium hydroxide were found to be 0.55, 2.5, 70%, and 10 M, respectively. The

addition of 20% GGBS increased the strength to approximately 65 MPa with 3-day

strength achieving 92-99% that at 28 days.

Bellum et al. (2020) studied the effect of GGBS addition on the modulus of

elasticity of fly ash-based geopolymer concrete. Results showed that 70% replacement

of fly ash by GGBS led to the highest compressive strength and modulus of elasticity.

Respective values could reach up to 38 MPa and 20 GPa.

Prusty and Pradhan (2020b) studied the effect of different mixture proportions

on the compressive, splitting tensile, and flexural strength of fly ash geopolymer

concrete. Optimization results noted that the replacement of 45% fly ash by GGBS

along with a sodium hydroxide molarity of 14 M and sodium silicate to sodium

hydroxide ratio of 1.5 were ideal to provide maximum strength.

Garanayak (2020) evaluated the mechanical performance of alkali-activated

fly ash GGBS paste cured in ambient conditions. Mixture proportions involved varying

the GGBS and fly ash proportions and sodium hydroxide molarity. The maximum

strength obtained was around 89 MPa with 30% fly ash and 12M sodium hydroxide

molarity.

Shang et al. (2018) reported that the incorporation of GGBS in fly ash-based

geopolymer enhanced the early performance. Yet, it was found critical to blend the

12

two precursors to balance setting time, fluidity, volume stability, strength, and chloride

permeability.

Rafeet et al. (2019) reported an increase in strength when GGBS was

incorporated into fly ash-based geopolymer pastes without the need for oven curing.

In turn, such mixes required lower activator content, which resulted in lower cost and

environmental footprint while maintaining high compressive strength.

Yazdi et al. (2018) studied the mechanical and transport properties of GGBS

fly ash blended concrete. The compressive and flexural strength of blended mixes

could reach up to 100 and 10 MPa, respectively. The porosity decreased as more

GGBS was incorporated into the mix. Nevertheless, increasing GGBS beyond 50%

did not seem to have any significant impact on the performance.

The resistance to weathering and chloride penetration of fly ash GGBS blended

geopolymer concrete was investigated (Lee et al., 2019). Samples cured in outdoor

conditions for 180 days could reach a compressive strength of 53 MPa with continuous

growth in strength. Conversely, indoor curing could attain a strength of 67 MPa.

Reddy et al. (2018) developed and validated a mix design procedure for fly

ash-GGBS blended geopolymer concrete. The ratio of fly ash to GGBS was set to 7:3,

while the solution to binder ratio varied between 0.4 and 0.8. Compressive strength

was found to decrease with higher solution content but the workability, characterized

by the slump, increased. Yet, the effect of the water-to-cement ratio on the compressive

strength of conventional concrete seemed to be more severe than the impact of the

solution-to-binder ratio on that of blended geopolymer concrete.

13

An amorphous mix design framework was developed for GGBS fly ash

blended geopolymer (Lau et al., 2019). Through the optimization technique, it was

found that the optimal Si/Al and (Na+2Ca)/Al ratios were 2.3 and 3.2, respectively.

The obtained compressive strength could reach up to 69 MPa.

Samantasinghar and Singh (2020) examined the impact of curing regime on fly

ash-GGBS blended geopolymer. Results showed that heat curing was essential for

mixes without GGBS, while those with GGBS experienced microcracks. Further,

autoclaving and microwave radiation presented the highest strength development

among the different regimes.

Other work investigated the influence of GGBS incorporation on the

performance of fly ash-based geopolymer mortar and lightweight concrete (El-Hassan

and Ismail, 2018; El-Hassan et al., 2017; Ismail et al., 2017). Experimental test results

highlighted an increase in mechanical properties, including compressive strength and

modulus of elasticity, as more fly ash was replaced by GGBS. Also, the performance

was less impacted by heat curing with higher GGBS incorporation.

The effect of the curing regime was also investigated by (El-Hassan et al.,

2018, 2021). The authors reported that a combination of air and water curing was ideal

for mixes made with GGBS and fly ash. However, the impact of curing was found to

be less apparent as more fly ash was incorporated into the mix. Nevertheless,

compressive strength of at least 40 MPa could be achieved regardless of curing regime.

Other work studied the effect of fly ash replacement on GGBS-based

geopolymer concrete (El-Hassan and Ismail, 2018; Ismail et al., 2014). Major findings

included the superior performance of blended geopolymers compared to counterparts

14

made with a single precursor. With fly ash contents exceeding 50%, the mixes tended

to have poor early performance and required heat curing, while mixes with no fly ash

were not workable and set quickly. Thus, a blend of the two was deemed ideal for

optimum performance.

2.5 Geopolymer concrete with recycled aggregate

To further enhance the sustainability of geopolymer concrete, several attempts

were made to replace natural aggregates (NA) with recycled concrete aggregate

(RCA). Most studies focused on the impact of such replacement on mechanical

properties, including compressive strength, flexural strength, splitting tensile strength,

and elastic modulus. In general, it was found that the geopolymer concrete

incorporating RCA had inferior performance compared to counterparts made with NA.

This was primarily due to the weak bond between the mortar and RCA and the porous

nature of RCA (Salesa et al., 2017). A more in-depth review of the studies is shown in

this section.

Shi, X.S. et al. (2012) studied the mechanical properties of fly ash geopolymer

concrete containing 50% and 100% recycled coarse aggregate as a replacement of

natural coarse aggregate. Based on the results, the geopolymer concrete comprising

RCA had a compressive strength and elastic modulus higher than counterpart OPC

concrete containing RCA with a better interfacial transition zone. Also, it was observed

that the mechanical properties decreased as the RCA content increases.

Nuaklong et al. (2016) examined the effect of recycled aggregate on the

strength and durability of high calcium fly ash-based geopolymer concrete. A

comparison was made with crushed limestone aggregates. Experimental findings

15

showed that geopolymer concrete made with RCA could reach a strength of up to 38

MPa, but were slightly lower than counterparts made with crushed limestone

aggregates. Further, the higher molarity of sodium hydroxide resulted in more durable

geopolymer concrete.

Kathirvel and Kaliyaperumal (2016) examined the effect of recycled concrete

aggregate (RCA) on the properties of GGBS geopolymer under ambient curing. The

compressive strength development of mixes made with up to 50% RCA replacement

is associated with the enhanced packaging and filling impact of RCA. However, higher

RCA replacement had a negative impact on strength, sorptivity, and chloride diffusion.

Shaikh (2016) investigated the mechanical and durability properties of fly ash

geopolymer concrete made with recycled coarse aggregate from local demolition and

waste. RCA replacement was set as 15, 30, and 50%, by weight. Results highlighted

decreases in compressive strength, splitting tensile strength, and modulus of elasticity

when 50% RCA was incorporated into the geopolymer concrete mix. Furthermore, the

durability, including sorptivity and chloride penetration, was negatively affected by

the replacement of NA by RCA.

Mesgari et al. (2020) investigated the properties of geopolymer concrete and

Portland cement concrete with varying contents of geopolymer RCA, namely 0, 20,

50, and 100% replacement. Respective reductions of 14, 1, and 3% in the compressive

strength, modulus of elasticity, and flexural strength are associated with the

replacement of natural aggregates with geopolymer RCA up to 20%. Higher RCA

content of 100% led to 33, 26, and 21% lower respective properties.

Xie et al. (2019a) examined the influence of RCA replacement on the

performance of GGBS-metakaolin blended geopolymer concrete. Results highlighted

16

decreases of up to 35% in compressive strength with a 75% increase in a slump when

100% NA was replaced by RCA. A lower compressive toughness was also reported

upon the incorporation of RCA in the mix.

Hu et al. (2019) studied the combined effect of GGBS and RCA on the

performance of fly ash geopolymer. The addition of GGBS to the mix reduced the

workability while the incorporation of RCA increased it. Further, the replacement of

100% RCA reduced the compressive strength, modulus of elasticity, splitting tensile

strength, and flexural strength of mixes made with 30% GGBS by 27, 22, 22, and 26%,

respectively. Yet, it should be noted that reductions were higher when geopolymer was

made only with fly ash.

Xie et al. (2019b) and Xie et al. (2019c) replaced 100% NA by RCA in GGBS-

fly ash geopolymer concrete. An increase in a slump was reported upon the addition

of RCA owing to the additional water required for absorption. Conversely, the

compressive strength and modulus of elasticity decreased by 16 and 21%, respectively.

2.6 Geopolymer concrete reinforced with steel fiber

Geopolymer concrete has been advocated as a sustainable alternative to

conventional cement-based concrete. Despite its impressive performance, geopolymer

concrete has very low tensile and flexural properties with brittle characteristics. For

conventional concrete, fiber reinforcement has been proposed to counter the weak

properties while enhancing ductility. Similarly, fibers, especially steel, have been

suggested to improve performance. The following section discusses the work that

utilized steel fibers in geopolymer concrete and mortar.

17

Guo and Pan (2018) added various fibers to geopolymer concrete consisting of

fly ash and GGBS as a binary geopolymer matrix. The effect of volume contents and

type of fibers including basalt fiber, polypropylene fiber, and steel fiber on the

mechanical properties of geopolymer was investigated. Among the various fibers, the

flexural and tensile strength of a geopolymer concrete improved significantly with

steel fiber.

Bernal et al. (2010) conducted a study on the effect of steel fibers on the

mechanical properties of GGBS-based geopolymer concrete. Results highlighted that

the use of steel fibers has reduced the compressive strength but significantly improved

the splitting tensile and flexural strengths. Water absorption and porosity were reduced

by approximately 20% in steel fiber-reinforced geopolymer mixes in comparison to

mixes without fibers.

Devika and Nath (2015) examined the impact of steel fibers on the mechanical

flexural behavior of geopolymer concrete beams. Results show that the addition of

steel fibers transformed brittle geopolymer concrete into a more ductile one, while also

significantly improving tensile strength, tensile strain, and toughness.

Al-Majidi et al. (2017) developed a steel fiber-reinforced, ambient-temperature

cured geopolymer concrete for in-situ applications. Fresh and mechanical properties

were measured. Experimental results showed that steel fiber addition reduced the

compressive strength of the geopolymer with 10 and 20% GGBS. However, it was

significantly improved at higher GGBS content compared to the respective mixes

without steel fibers.

Islam et al. (2017) focused on the development of sustainable concrete

geopolymer using palm oil fuel ash and GGBS as binders and oil palm shell as coarse

https://www.sciencedirect.com/topics/materials-science/polypropylene

18

aggregates. The hooked-end steel fiber was used in this study to investigate the impact

resistance of the concrete. The results indicated that the addition of 0.5% steel fibers,

by volume enhanced the splitting tensile and flexural strengths of fiber reinforced

geopolymer concrete by up to 38 and 44%, respectively, compared to the plain

counterparts. The addition of 0.5% steel fiber also increased the first crack load by

1.5–3.5 times.

The effect of adding steel fibers on the mechanical properties of GGBS-based

geopolymer concrete made with 0, 25, and 50% fly ash was investigated (El-Hassan

and Elkholy, 2019; Elkholy and El-Hassan, 2019). The compressive, splitting tensile,

and flexural strengths were reported to have increased by up to 30, 31, and 25%,

respectively, upon the incorporation of up to 2%, by volume. Codified equations could

be employed for such concrete after applying a modification factor for some mixes.

Liu et al. (2020) studied the influence of steel fiber and silica fume on the

mechanical and fracture performance of ultra-high performance geopolymer concrete.

Upon the addition of steel fibers, the workability of said concrete decreased while the

modulus of elasticity, compressive strength, splitting tensile strength, fracture energy,

flexural strength, and stress intensity factor increased.

Guo and Xiong (2021) studied the resistance of GGBS fly ash blended

geopolymer concrete reinforced with steel fibers to sulfate corrosion and drying-

wetting. The compressive strength of concrete made with 0.4%, by volume, steel fibers

was approximately 68 MPa after 15 durability cycles.

Gülşan et al. (2019) conducted a study on self-compacting fly ash geopolymer

concrete with up to 1% steel fiber, by volume. The addition of steel fibers reduced the

fresh concrete properties, including slump flow, flow time, V-funnel flow time, and L-

19

box passing ability. Yet, it enhanced the bond resistance, flexural strength, fracture

toughness, and stress intensity factor, owing to its bridging effect.

Their and Özakça (2018) incorporated nanosilica and steel fibers in fly ash

geopolymer concrete. The combined incorporation of these two additives increased

the compressive strength to up to 57 MPa with improved water penetration resistance.

While 1% steel fiber volume fraction seemed to generally have a positive impact,

higher percentages caused a decrease in durability properties, including sorptivity and

water penetration.

Shaikh and Hosan (2016) examined the performance of steel fiber-reinforced

geopolymer concrete after being exposed to elevated temperatures. Results showed

that steel fibers allowed for high residual compressive and splitting tensile strength

post-exposure with limited cracking and spalling. Models to predict the performance

were also developed.

Khan et al. (2018) examined the mechanical properties of high-strength

geopolymer concrete reinforced with spiral and hooked-end steel fibers. The inclusion

of steel fibers reduced the workability but provided higher compressive strength

compared to plain counterparts. Additionally, a multi-fold increase in the load-carrying

capacity, toughness, and post-peak residual strength.

2.7 Shear behavior of geopolymer concrete

The shear behavior of steel fiber-reinforced geopolymer concrete was

investigated in past work. Visintin et al. (2017) evaluated the shear capacity of eight

geopolymer concrete beams without stirrups. The beams were designed with a

variation in reinforcement ratio and span-to-depth ratio (a/d). The findings of the direct

shear tests illustrate that the shear-friction properties for the geopolymer concrete used

20

in the experimental investigation fall within the range of shear-friction properties of

conventional cement-based concrete.

Ng et al. (2013) investigated the shear behavior of steel fiber-reinforced

geopolymer concrete beams. Five series of 250 mm deep by 120 mm wide geopolymer

concrete beams spanning 2250 mm without stirrups were tested with varying quantities

and types of steel fibers. End-hooked and straight steel fibers varied from 0 to 1.5%,

by volume. The beams have a span-to-effective depth ratio of 3.7. Results showed that

the cracking load and shear strength increased significantly with the increase of steel

fiber volume fraction, while the rate of crack growth and crack widths decreased.

Chang (2009) studied nine fly ash-based geopolymer concrete beams with

2000 mm length. The crack patterns and modes of failure were found to be generally

similar to Portland cement concrete beams. The methods of calculations that were

typically used in the case of reinforced Portland cement concrete beams were

applicable in predicting the shear strength of reinforced geopolymer concrete beams.

The provisions of the code are generally conservative and safe to predict the shear

strength of geopolymer concrete beams.

Mo et al. (2017) evaluated the shear performance of steel fiber reinforced

cement-based and geopolymer oil palm shell lightweight aggregate concrete. Various

volume fractions of steel fibers were added for the cement-based and geopolymer

concrete. Experimental test results indicated that the shear resistance of geopolymer

concrete beams increased with the addition of steel fibers. The shear capacity existing

prediction equations for steel fiber-reinforced lightweight concrete was demonstrated

to be conservative for the steel fiber-reinforced cement-based and geopolymer

concrete.

21

Yacob et al. (2019) evaluated the shear behavior of fly ash geopolymer

concrete. The crack propagation and load-deflection response were similar in

geopolymer concrete as conventional cement-based concrete, while the crack patterns

were different. Response 2000 equations could conservatively predict the strength of

the investigated concrete beams with better predictions in the beams incorporating

shear reinforcement.

2.8 Research Significance

Aging infrastructure and superstructures entail continuous renovation and

replacement resulting in increases in demand for new concrete and supply of non-

renewable aggregates. The ability to recycle concrete of construction and demolition

waste and reutilize industrial solid by-products provides a sustainable solution to the

pressing issues of depletion of natural resources and emissions of carbon dioxide. RCA

has been proposed as a viable alternative to natural aggregates. However, it has only

been used in non-structural applications due to its inferior strength and durability

properties. Other efforts have been made to alleviate CO2 emissions by developing

sustainable construction materials as geopolymer concrete. Unlike normal concrete,

geopolymer is cement-free and emits much less CO2 in its production. As such, the

incorporation of these two sustainable solutions promises to further enhance the

sustainability of the construction industry.

Few studies have investigated the performance of geopolymer concrete made

with 100% RCA. Results generally showed a reduction in mechanical and durability

properties upon complete replacement of NA by RCA. Yet, it has been reported that

100% RCA replacement could not be attained without compromising the performance.

Additionally, limited studies have reported an improvement in the properties of

22

geopolymer concrete made with natural aggregates upon the addition of steel fibers.

As such, it seems that steel fibers may enhance the performance of geopolymer

concrete made with 100% RCA. However, such a study has yet to be investigated.

There is also a lack of studies on the shear performance of steel fiber-reinforced RCA


This research aims to fill this gap by assessing the feasibility of producing a

geopolymer concrete made with 100% RCA and steel fibers. Unlike past work, which

mainly focused on fly ash-based geopolymers, this work will utilize a blended binder

of GGBS and fly ash to eliminate the need for heat curing and reduce shrinkage cracks

associated with fly ash- and GGBS-based geopolymers, respectively. The mechanical

and durability properties of such innovative and sustainable concrete will be evaluated.

In addition, a finite element model will also be developed to evaluate the structural

shear performance of beams made of the so-produced concrete. Through experimental

investigation and in-depth analysis of results, this research will provide evidence on

the ability to fully replace natural coarse aggregates with RCA and cement with

industrial waste materials to produce an innovative and sustainable structural


23

Chapter 3: Experimental Program

3.1 Introduction

This chapter highlights the detailed experimental program carried out to

evaluate the effect of recycled concrete aggregate (RCA) and steel fibers (SF) on the

performance of geopolymer concrete made with a blend of GGBS and fly ash (1:1).

To attain the research objectives, this work was divided into three phases. In the first

phase, the characteristics of the as-received material were determined following

standardized test procedures. A description of sample preparation and mixture

proportioning was then provided. In the second phase, trial mixes were proportioned

to obtain a specific design compressive strength. Subsequently, natural aggregates

were replaced by different quantities of recycled concrete aggregates alongside steel

fibers. The mechanical and durability properties of such hardened geopolymer

concrete were assessed through extensive testing, including water absorption,

sorptivity, compressive strength, splitting tensile strength, flexural strength, modulus

of elasticity, bulk resistivity, and abrasion resistance. Furthermore, the third phase

encompassed the development of analytical finite element models to evaluate the shear

performance of various geopolymer concrete mixes incorporating different quantities

of RCA and SF.

3.2 Test program

At the early stages of this research, several trial mixes were designed to obtain

a desired cube compressive strength of 35 MPa, which is typically used for structural

applications in the United Arab Emirates. This step was critical, as unlike conventional

cement-based concrete, limited research on the mix design procedure of blended

24

geopolymer concrete was available. The trial mixes and associated cylinder

compressive strength are presented in Table A1 of Appendix A. The obtained 35-MPa

control mix served as a benchmark. Subsequently, the natural aggregates (NA) were

replaced by RCA with the incorporation of different volume fractions of steel fibers.

In fact, a total of 10 geopolymer concrete mixtures were proportioned, as shown in

Table 1. The mixes were divided into 4 main groups based on RCA replacement

percentage, by mass of total aggregate. Group [A] included the control mix made with

100% NA without steel fiber. Group [B], [C], and [D] comprised mixes consisting of

30, 70, and 100% RCA replacement, respectively, with the addition of 0-2% SF, by

volume.

Table 1: Experimental Test Matrix

Group

Mix

Number

Mix

Designation

RCA

Replacement

(%)

Fiber Reinforcement

0% 1% 2%

Group A Mix 1 R0SF0 0 x

Group B

Mix 2 R30SF0

30

x

Mix 3 R30SF1 x

Mix 4 R30SF2 x

Group C

Mix 5 R70SF0

70

x

Mix 6 R70SF1 x

Mix 7 R70SF2 x

Group D

Mix 8 R100SF0

100

x

Mix 9 R100SF1 x

Mix 10 R100SF2 x

25

3.3 Material properties

The main materials used in this study included GGBS, fly ash, natural

aggregates, recycled concrete aggregates, dune sand, chemical activators, and

superplasticizer. It is empirical to evaluate the properties of these materials prior to

incorporation in geopolymer concrete mixtures.

3.3.1 Precursor binding material

The geopolymer precursor binding materials were in the form of GGBS and

fly ash. The GGBS was provided by Emirates Cement Company, while the fly ash was

sourced from Ashtech Ltd. Table 2 presents the chemical composition using X-ray

fluorescence (XRF) of the binding materials. While the GGBS was predominantly

made of calcium oxide (CaO) and silica (SiO2), the fly ash mainly comprised silica

(SiO2) and alumina (Al2O3). Their respective Blaine fineness were 4250 and 3680

cm2/g, whereas their corresponding specific gravity were 2.70 and 2.32. Furthermore,

Figure 1 highlights the morphology of the as-received binding materials using

scanning electron microscopy. Spherical and irregular particles were noticed in fly ash

and GGBS micrographs, respectively. The X-ray diffraction (XRD) patterns of Figure

2 show that the binders comprised mainly of quartz and mullite with traces of gehlenite

and hematite in GGBS and fly ash, correspondingly. Additionally, their particle size

distribution is shown in Figure 3. The respective particle sizes of GGBS and fly ash

were in the ranges of 2-80 µm and 0.2-40 µm.

26

Table 2: Chemical composition of as-received materials

Oxide component Material (%)

GGBS Fly ash Dune sand

CaO 42.0 3.3 14.1

SiO2 34.7 48.0 64.9

Al2O3 14.4 23.1 3.0

MgO 6.9 1.5 1.3

Fe2O3 0.8 12.5 0.7

Loss in ignition 1.1 1.1 0.0

Others 1.1 10.5 16.0

Blaine Fineness (cm2/g) 4250 3680 5760

Specific gravity 2.70 2.32 2.77

27

(a)

(b)

Figure 1: SEM micrographs of (a) GGBS and (b) fly ash

28

(a)

(b)

Figure 2: XRD spectrum of (a) GGBS and (b) fly ash

29

(a)

(b)

Figure 3: Particle size distribution of (a) GGBS and (b) fly ash

3.3.2 Coarse aggregates

Coarse aggregates used in this research were natural aggregates (NA) and

recycled concrete aggregate (RCA). The NA was in the form of crushed dolomitic

limestone sourced from Ras Al Khaimah, UAE, and combined 30% of 10 mm and

70% of 20 mm aggregates. The combined aggregate, referred to as NA hereafter had

a nominal maximum size (NMS) of 20 mm. Conversely, the RCA was collected from

0

20

40

60

80

100

0.1 1 10 100

Cu

mu

lati

ve

pas

sin

g (

%)

Particle size (µm)

0

20

40

60

80

100

0.1 1 10 100

Cum

ula

tive

pas

sing (

%)

Particle size (µm)

30

Al Dhafra Recycling Industries (ADRI) that recycled construction and demolition

waste from old concrete structures with unknown compressive strength. The NMS of

the RCA was 25 mm. Figure 4 shows the grading curves for different mixes of NA

and RCA used in this study. It is worth noting that they all satisfy the requirements

and limits of ASTM C33 (ASTM, 2016). The physical properties of NA and RCA are

summarized in Table 3. The water absorption, Los Angeles (LA) abrasion mass loss,

soundness mass loss, and fineness modulus of the former were higher than the latter,

while its specific gravity and dry-rodded density were lower. This signifies that RCA

is indeed of weaker nature than NA. Also, it is worth noting that all measured

properties were within the typical limits given by the ASTM standards.

Figure 4: Particle size distribution of different aggregate percentages

0

10

20

30

40

50

60

70

80

90

100

1 10 100

Cum

ula

tive

Pas

sing (

%)

Particle Size (mm)

100%NA

30%RA 70%NA

70%RA 30%NA

100%RA

31

3.3.3 Fine aggregates

Locally abundant desert dune sand served as the fine aggregates in this work.

Its fineness modulus, dry-rodded density, specific gravity, and surface area were 1.45,

1663 kg/m3, 2.77, and 116.8 cm2/g respectively. The grading curve of dune sand,

shown in Figure 5, indicates that most of the particles are within the range of 100-600

µm. Figure 6 presents the SEM micrograph and XRD spectrum of dune sand. It is

mainly composed of irregular particles representing quartz with some traces of calcite,

ferric oxide, and aluminum oxide.

Table 3: Physical properties of coarse aggregates

Physical Property, Unit Standard Test NA RCA

Fineness modulus ASTM C136 6.82 7.44

Specific gravity ASTM C127 2.82 2.63

Water absorption, % ASTM C127 0.70 6.63

Dry-rodded density, kg/m3 ASTM C29 1635 1563

Los Angeles abrasion, % ASTM C131 16.0 32.6

Specific surface area, cm2/g ASTM C136 2.49 2.50

Soundness (MgSO4), % ASTM C136 1.20 2.78

32

Figure 5: Particle size distribution of dune sand

(a)

(b)

Figure 6: Dune sand (a) SEM micrograph and (b) XRD spectrum

0

20

40

60

80

100

10 100 1000

Per

cen

tage

pas

sin

g (

%)

Particle size (µm)

33

3.3.4 Chemical activators

To activate the precursor binding materials, an alkaline activator solution

(AAS) was formulated as a mixture of sodium silicate (SS) and sodium hydroxide

(SH). The SS solution was Grade N with a chemical composition of 26.3% SiO2,

10.3% Na2O, and 63.4% H2O. Conversely, the SH solution was prepared by dissolving

97%-pure SH flakes in a specific amount of water to obtain molarity of 14 M. This

molarity was chosen based on past research that optimized the reaction efficiency

(Kanesan et al., 2017; Patankar et al., 2014; Sani et al., 2016). Yet, it should be noted

that the SH solution was prepared 24 hours prior to casting to allow for the heat

associated with the exothermic reaction to dissipate.

3.3.5 Steel fibers

Double hooked-end steel fibers from Bekaert were employed in this study. The

fibers had a specific gravity, mean diameter, mean length, and aspect ratio of 7.9, 0.55

mm, 35 mm, and 65, respectively (Bekaert, 2012).

3.3.6 Superplasticizer

A polycarboxylic ether polymer-based superplasticizer (SP) was supplied by

BASF Chemicals Company under the brand name Masterglenium Sky 504. It was

employed in this work to maintain adequate fresh geopolymer concrete workability

without affecting the mechanical properties (Montes et al., 2012; Palacios and Puertas,

2005).

34

3.4 Geopolymer concrete mixture proportions

The mixture proportions of geopolymer concrete mixtures are shown in Table

4. The control mixture (R0SF0) has been designed using trial and error to attain a

cylinder compressive strength of 35 MPa concrete. Another nine mixes were prepared

with varying RCA replacement percentages and steel fiber volume fractions. Mixtures

were designated by RxSFy, where x and y represent the RCA replacement percentage

and steel fiber volume fraction, respectively. For all mixes, equal portions of GGBS

and fly ash were used, i.e. 125 kg/m3. The purpose of using both precursor binders was

to eliminate the need for heat curing associated with fly ash-based geopolymer and

reduce the drying shrinkage related to alkali-activated slag. Such a blended system also

enhanced the performance of geopolymer concrete due to the co-existence of calcium

aluminosilicate hydrate (C-A-S-H) and sodium aluminosilicate hydrate (N-A-S-H)

gels (El-Hassan and Elkholy, 2019; Ismail and El-Hassan, 2018; Yip et al., 2005).

Dune sand content was kept constant at 910 kg/m3. Due to the difference in specific

gravities between NA and RCA, slight changes in the mix design were made with each

coarse aggregate replacement percentage (30, 70, and 100%). The AAS-to-binder ratio

was fixed at 0.60 with an SS-to-SH ratio of 1.5. Superplasticizer was added as 2% of

the total binder mass, while steel fibers were incorporated between 0 and 2%, by

volume.

35

Table 4: Mixture proportions of geopolymer concrete (kg/m3)

Mix

No.

Mix

Designation

Binder Aggregates

Activator

Solution

SP SF GGBS

Fly

ash NA RCA

Dune

sand SS SH

1 R0SF0 125 125 1210 0 910 90 60 5 0

2 R30SF0 125 125 847 346 910 90 60 5 0

3 R30SF1 125 125 847 346 910 90 60 5 78

4 R30SF2 125 125 847 346 910 90 60 5 156

5 R70SF0 125 125 363 798 910 90 60 5 0

6 R70SF1 125 125 363 798 910 90 60 5 78

7 R70SF2 125 125 363 798 910 90 60 5 156

8 R100SF0 125 125 0 1137 910 90 60 5 0

9 R100SF1 125 125 0 1137 910 90 60 5 78

10 R100SF2 125 125 0 1137 910 90 60 5 156

3.5 Sample preparation

Blended geopolymer concrete was prepared and cast in the laboratory at

respective temperature and relative humidity of 24°C ± 2°C and 50% ± 5%. Figure 7

shows the materials prior to mixing. The SH solution was first was prepared by mixing

the SH flakes with a specific amount of water to obtain the 14 M molarity. Once the

heat dissipated, the SH solution was mixed with the SS solution to formulate the AAS.

The heat from the secondary reaction was also allowed to dissipate. This two-step

process was carried out 24 hours prior to incorporation into the concrete mix. The dry

components, including NA and/or RCA, dune sand, fly ash, and GGBS were mixed

for 3 minutes. It is worth noting that the coarse aggregates were used in saturated

surface dry condition. The prepared AAS was then gradually added followed by the

superplasticizer to the dry components and mixed for another 3 minutes to attain a

36

homogeneous and uniform mix. The obtained freshly-mixed geopolymer concrete was

cast in two to three layers into 100 mm diameter x 200 mm height cylinders, 150 mm

diameter x 300 mm height cylinders, 100 mm cubes, and 100 mm height x 100 mm

width x 500 mm length prisms. Samples were then compact-vibrated on a vibrating

table for a period of 10 seconds. Compacted geopolymer concrete samples were

covered with a plastic sheet for 24 hours at ambient conditions, then demolded and

kept in ambient conditions until testing age. The process served to simulate on-site

construction scenarios while excluding water curing. Figure 8 presents some of the

demolded samples for a geopolymer concrete mix.

Figure 7: Materials used in casting geopolymer concrete

37

Figure 8: Geopolymer specimens after demolding

3.6 Performance evaluation

The mechanical properties of blended geopolymer concrete made with RCA

and SF were evaluated through the compressive strength, splitting tensile strength,

flexural strength, and modulus of elasticity. Conversely, the durability performance

was assessed using water absorption, sorptivity, bulk resistivity, and Los Angeles

abrasion. These tests were employed to evaluate the geopolymer concrete’s ability to

withstand abrasive forces and penetration of aggressive ions as an indication of its

durability. For each test, three replicate samples per mix were tested to obtain an

average.

3.6.1 Compressive strength

The concrete compressive strength test was performed using a Wykeham

Farrance machine with a loading capacity of 2000 kN and at a loading rate of 7 kN/s.

Cubes (100 mm) were employed to evaluate the development of compressive strength

(fcu) at the ages of 1, 7, and 28 days according to BS EN 12390-3 (British Standard,

38

2009). Furthermore, the cylinder compressive strength (f’c) was evaluated using 28-

day cylinders (100 mm diameter x 200 mm height) in accordance with ASTM C39

(ASTM, 2015).

3.6.2 Modulus of elasticity

The modulus of elasticity (Ec) of 28-day geopolymer concrete was obtained

according to ASTM C469 (ASTM, 2014). A Wykeham Farrance machine with a

loading capacity of 2000 kN was used. Four 60-mm-long strain gauges were installed

at mid-height on diametrically opposite sides of the circumference of 100 mm diameter

x 200 mm height cylinder to record the compression strain. A 500-kN compression

load cell was also used to determine the compressive load which was applied at a

loading rate of 7 kN/s. The load and strain were recorded using a data acquisition

system. Then, the compressive stress-strain response was plotted. The modulus of

elasticity was obtained as the slope of the chord connecting the stress corresponding

to 40% of the ultimate stress (S2) and that corresponding to a strain of 0.00005 (S1).

Equation 1 was employed in the calculation of the modulus of elasticity.

Ec=S2 - S1

ε2 - 0.00005

(1)

3.6.3 Splitting tensile strength

The tensile strength of 28-day blended geopolymer concrete made with RCA

and SF was indirectly measured through the splitting tensile strength (fsp) test of ASTM

C496 (ASTM, 2011). Cylinders of 150 mm diameter and 300 mm height were used.

The load was applied at a loading rate of 1 kN/s across the entire length of the

specimen. The splitting tensile strength was calculated using Equation 2.

39

fsp

=2P

πDL

(2)

Whereas P is the compressive load at failure in N, L is the length of the cylinder in

mm, and D is the diameter of the cylinder in mm.

3.6.4 Flexural strength

The modulus of rupture or flexural strength of geopolymer concrete made with

different proportions of RCA and SF was measured following the four-point bending

test of ASTM C1609 (ASTM, 2019b). The test was conducted on 28-day 100 mm

height x 100 mm width x 500 mm length prisms by means of an electro-hydraulic

servo-controlled machine at a loading rate of 1 kN/s. A linear variable displacement

transducer (LVDT) measured the mid-span deflection, while the load was recorded via

a load cell. The load-deflection curve was utilized to determine the peak strength or

flexural strength (fp), peak load deflection (δp), and residual strengths f150

100and f

600

100

corresponding to the loads at 0.75 and 3mm deflections. For all strength variables, the

strength was calculated using Equation 3.

f =PL

bd2

(3)

Where P is either the peak load (Pp), P150 100and P600

100 in N; L is the span length of the

specimen in mm, b is the width of the specimen in mm; and d is the depth of the

specimen in mm.

The load-deflection curves were also employed in calculating the geopolymer

concrete capacity to absorb energy or flexural toughness, denoted as T150 100. The value

of T150 100 was determined as the area under the load-deflection curve to a deflection of

L/150 and then used in finding the equivalent flexural strength ratio, RT,150 100 , as per

Equation 4.

40

RT,150 100 =

150 x T150 100

fpbd

2 x 100% (4)

3.6.5 Water absorption

The water absorption of blended geopolymer concrete was evaluated as per the

standard procedure of ASTM C642 (ASTM, 2013a). The test was conducted on 28-

day concrete disc specimens of 100 mm diameter and 50 mm height. The specimens

were dried in an oven at 105°C for 24 hours until a mass change < 0.5% was attained.

The recorded mass was denoted as “oven-dried mass”. The specimens were then

immersed in water for 24 hours, and the mass of the SSD sample was recorded as “SSD

mass”. The water absorption was quantified as the change in mass as a function of the

oven-dried mass, as per Equation 5.

Water absorption (%) =SSD mass (g) - Oven-dried mass (g)

Oven-dried mass (g)×100%

(5)

3.6.6 Sorptivity

The sorptivity is an indirect measure of the material’s short-term durability, as

it relates to the tendency of a material to absorb and transmit water and other liquids

by capillarity action. The sorptivity test was performed on 28-day concrete disc

samples, similar to those used in the water absorption test, following the procedure of

ASTM C1585 (ASTM, 2013c). Prior to testing, specimens were vacuum-saturated and

preconditioned as per ASTM C1202 (ASTM, 2012). The circumferential and top sides

of the samples were then sealed with adhesive tape. This allowed water to penetrate

from the bottom side only while ensuring no evaporation takes place during the test.

Sealed samples were then weighed and placed on supports resting at the bottom of a

water-filled pan. The water only reached 1-3 mm above the supports. The rate of water

41

absorption was determined by measuring the increase in the mass of a specimen as a

function of time. In fact, the mass of the geopolymer concrete specimen was recorded

at 1, 5, 10, 15, 20, 30, and 60 minutes and then after every hour until 6 hours. The

absorption (I) was then calculated as the change in mass divided by the product of the

cross-sectional area of the test specimen and the density of water, as per Equation 6.

Subsequently, the initial rate of water absorption value (mm/s1/2) was determined as

the slope of the line of the best fit of absorption against the square root of time (s1/2).

As per ASTM C1585 (ASTM, 2013c), the test shall be repeated if the regression

coefficient, R2, was less than 0.98.

I (mm) =Change in mass at time t(g)

Exposed area (mm2) × Density of water ( g mm3)⁄

(6)

3.6.7 Bulk electric resistivity

The resistivity of the concrete to the diffusion of chloride ions due to electrical

current is represented by the bulk electric resistivity. In fact, a higher resistivity is

indicative of higher protection against steel corrosion, as noted by ACI 222R-01 (ACI

Committee 222R-01, 2001). A 28-day cylinder (100 mm diameter x 200 mm height)

was preconditioned according to ASTM C1202 (ASTM, 2012) and saturated in

preparation for testing as per ASTM C1760 (ASTM, 2019a). The bulk resistivity was

carried out by placing the sample between two conductive plates with pre-attached

soaked sponges and using a Giatec RCON. Equation 7 was employed to determine the

bulk resistivity in Ω.cm.

Bulk Resistivity (Ω.cm) =Applied voltage (V) × (Avg. sample diameter (mm))

2

1273.2 × Current at 1 minute (mA) × Avg. sample length (mm) (7)

42

3.6.8 Abrasion resistance

To evaluate the blended geopolymer concrete resistance to abrasive, friction,

and rubbing action, the abrasion resistance was determined. It is an indication of the

probable future durability of the geopolymer concrete incorporating different

quantities of RCA and SF (ACI Committee 201.2, 2016; Mehta, 2006). For this test, a

Los Angeles (LA) abrasion machine was utilized to measure the mass loss in 28-day

geopolymer concrete due to abrasive and impact forces in accordance with the

procedure of ASTM C1747 (ASTM, 2013b). The mass of disc specimens (50 mm

height x 100 mm diameter) was recorded before and after every 100 revolutions for a

total of 500 revolutions. The abrasion resistance was determined as the percent mass

loss of the sample as a function of the initial mass, as per Equation 8.

Mass Loss (%) =Final Mass - Initial Mass

Initial Massx 100%

(8)

43

Chapter 4: Experimental Results and Discussions

4.1 Introduction

After determining the properties of the as-received material, the feasibility of

replacing NA by 100% RCA with the incorporation of steel fibers is investigated

through mechanical and durability performance evaluation. This chapter provides

evidence of such feasibility by testing the blended geopolymer concrete for

compressive strength, splitting tensile strength, flexural performance, modulus of

elasticity, water absorption, sorptivity, bulk resistivity, and abrasion resistance.

4.2 Mechanical Properties

4.2.1 Compressive Strength

The strength development profile of blended geopolymer concrete made with

different proportions of steel fibers and RCA replacement is studied by testing cube

samples for compressive strength (fcu) at the ages of 1, 7, and 28 days. For each mix

and test age, three cube specimens were tested. The results are shown in Figure 9. The

compressive strength of the control mix (R0SF0) at 1, 7, and 28 days was 9.1, 28.6,

and 35.3 MPa, respectively, representing corresponding increases of 214 and 23%

from 1 to 7 days and 7 to 28 days, as shown in Table 5. This shows that the

geopolymerization reaction mainly occurred within the first 7 days, owing to an

accelerated reaction of GGBS and production of calcium aluminosilicate hydrate and

calcium-silicate-hydrate gels (Al-Majidi et al., 2016; Chi, 2012; Davidovits, 2008;

Palomo et al., 1999). Temuujin et al. (2009) also concluded that the high molarity of

the SH solution may improve the reaction efficiency at an early age. Nevertheless,

strength increase was also noted between 7 and 28 days, signifying a continuous

44

reaction of the fly ash and the development of sodium-aluminosilicate-hydrate gel. An

analogous finding was noted by Ismail et al. (2014). Similar strength increase trends

were noted for other mixes irrespective of RCA replacement percentage and SF

volume fraction. Yet, it is worth noting that the increase in strength over time generally

decreased as more steel fiber was added to the geopolymer concrete mix. In fact, the

cube compressive strength increased by 210, 157, and 151%, on average, from 1 to 7

days for mixes made with 0, 1, and 2% SF, by volume. Conversely, the same mixes

showed a 12, 14, and 13% increase in strength from 7 to 28 days. This indicates that

the addition of steel fiber to the geopolymer concrete was mostly impactful at an early

age of 1 day.

(a)

Figure 9: Development of cubic compressive strength of concrete mixes made with

SF (a) 0%, (b) 1%, and (c) 2%

0

10

20

30

40

50

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Com

pre

ssiv

e S

tren

gth

, ƒcu

(M

Pa)

Time (days)

R0SF0R30SF0R70SF0R100SF0

Control Strength = 35.3 MPa

45

(b)

(c)

Figure 9: Development of cubic compressive strength of concrete mixes made with SF

(a) 0%, (b) 1%, and (c) 2% (continued)

The effect of RCA replacement percentage and steel fiber on the 1-day

compressive strength of blended geopolymer concrete is shown in Figure 10(a).

Generally, the replacement of NA by RCA did not have a significant impact on the 1-

day strength, owing to a possibly sufficient interfacial bond between the geopolymeric

0

10

20

30

40

50

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Co

mp

ress

ive

Str

ength

, ƒ

cu (

MP

a)

Time (days)

R30SF1

R70SF1

R100SF1

Control Strength = 35.3 MPa

0

10

20

30

40

50

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Com

pre

ssiv

e S

tren

gth

, ƒcu

(M

Pa)

Time (days)

R30SF2

R70SF2

R100SF2

Control Strength

=35.3 MPa

46

mortar and coarse aggregates (NA and RCA). Furthermore, the addition of steel fibers

enhanced the 1-day compressive strength. Compared to that of the plain counterparts,

it increased by, on average, 36 and 67%, when 1 and 2% steel fibers, by volume, were

incorporated into the geopolymer concrete mixes.

Table 5: Percent increase in cube compressive strength with time.

Mix

No.

Mix

Designation

Increasea

(%)

Increaseb

(%)

1 R0SF0 215.8 23.1

2 R30SF0 191.3 8.5

3 R30SF1 203.0 9.1

4 R30SF2 198.5 12.5

5 R70SF0 342.7 12.1

6 R70SF1 163.7 15.4

7 R70SF2 134.6 2.8

8 R100SF0 95.2 15.3

9 R100SF1 104.4 18.3

10 R100SF2 120.6 24.3

aIncrease in fcu from 1 to 7 days

bIncrease in fcu from 7 to 28 days

Figure 10(b) presents the 7-day compressive strength of blended geopolymer

concrete with different RCA replacement percentages and SF volume fractions. While

the replacement of NA by 30% RCA did not have a substantial effect on the 7-day

strength, higher replacements of 70 and 100% reduced the strength by 12 and 15%,

respectively. This loss of mechanical performance could be attributed to the weak

47

aggregate to geopolymeric paste interfacial bond and rough, porous nature of the RCA

(Salesa et al., 2017). Nevertheless, the strength was improved by, on average, 12 and

28%, upon adding 1 and 2% steel fibers, by volume. In fact, the 7-day strengths of

mixes made with 100% RCA were comparable to that of the control with the addition

of at least 1% steel fiber volume fraction.

Figure 10(c) highlights the changes in the 28-day cube compressive strength of

GGBS-fly ash blended geopolymer concrete. Values ranged between 28.1 and 43.4

MPa. While the control mix with 100% NA had a 28-day strength of 35.3 MPa, those

of mixes that replaced NA by 30, 70, and 100% RCA were 31.0, 28.2, and 28.1 MPa,

respectively. Clearly, a loss in strength was noted with RCA replacement. Similar

findings were reported in geopolymer concrete made with a single precursor, i.e. class

C fly ash, class F fly ash, or GGBS (Kathirvel and Kaliyaperumal, 2016; Nuaklong et

al., 2016; Shi, X. S. et al., 2012). However, such loss could be countered by adding 1

and 2% SF, by volume. Indeed, the addition of these quantities of SF increased the 28-

day strength of the plain RCA geopolymer concrete mixes by, on average, 11 and 24%.

This is mainly due to the densification of the matrix and reduction of the pore space,

as evidenced by the water absorption and sorptivity results presented later in the thesis.

In addition, steel fibers may have enhanced the structural integrity of the geopolymer

concrete, owing to its bridging effect. Other studies on NA-based geopolymer concrete

reported similar enhancements in compressive strength upon the addition of steel

fibers (El-Hassan and Elkholy, 2019; Islam et al., 2017). As a result, it could be

concluded that the full replacement of NA by RCA (100%) is possible in steel fiber-

reinforced geopolymer concrete incorporating at least 1% steel fibers, by volume,

while sustaining a limited loss (< 6%) in the 28-day compressive strength.

48

(a)

(b)


geopolymer concrete

0

10

20

30

40

50

60

30 70 100

1-D

ay C

om

pre

ssiv

e S

tren

gth

(M

Pa)

RCA (%)

SF0SF1SF2

Control Strength

= 9.1 MPa

0

10

20

30

40

50

60

30 70 100

7-D

ay C

om

pre

ssiv

e S

tren

gth

(M

Pa)

RCA (%)

SF0SF1SF2

Control Strength

= 28.6 MPa

49

(c)


geopolymer concrete (continued)

The effect of different RCA percentages and SF volume fractions on the 28-

day cylinder compressive strength of geopolymer concrete is depicted in Figure 11.

Similar to the 28-day cube compressive strength results, increasing the RCA

replacement percentage led to a decrease in the 28-day cylinder compressive strength.

In fact, 30, 70, and 100% RCA replacement resulted in 26, 51, and 54% respective

reduction in strength. This is possibly owed to the old adhered mortar surrounding the

RCA that created a weak interfacial zone with the geopolymeric paste. It is also likely

due to the poor quality and abundancy of cracks and voids of the RCA (Kachouh et

al., 2019b). Yet, the RCA-associated loss in strength seemed to be more pronounced

in the cylinder samples rather than the cube counterparts. Furthermore, the addition of

1 and 2% steel fibers, by volume, enhanced the strength of the RCA plain concrete by

up to 79 and 174%, respectively. As such, it is clear that the adverse impact of RCA

could be reversed by the addition of steel fibers.

0

10

20

30

40

50

60

30 70 100

28-D

ay C

om

pre

ssiv

e S

tren

gth

(M

Pa)

RCA (%)

SF0SF1SF2

Control Strength =

35.3 MPa

50

Figure 11: 28-day cylinder compressive strength of geopolymer concrete

The f′c/fcu ratio is shown in Table 6. The ratio of the control mix made with

100% NA and no steel fiber was 0.67. It decreased as more NA was replaced by RCA

in plain concrete. This signifies that the difference between cube and cylinder

compressive strength increased as more RCA was incorporated into the geopolymer

concrete mix. Apparently, the confinement effect of cubes under compression became

more critical with RCA replacement. Nevertheless, this ratio increased as more steel

fiber was added to the mix. In fact, it increased, on average, to 0.69 and 0.80 with 1

and 2% steel fiber volume fractions. Based on these results, it is apparent that a

relationship exists between the cylinder and cube compressive strengths of blended

geopolymer concrete at the age of 28 days, as illustrated in Figure 12. The relationship,

shown in Equation 9, indicates the ability to predict f’c from fcu (or vice versa) with

reasonable accuracy (R2 = 0.90).

f'c = 1.70fcu – 35.09 (9)

0

10

20

30

40

50

60

30 70 100

Co

mp

ress

ive

Str

ength

, ƒ

'c (

MP

a)

RCA (%)

SF0SF1SF2

Control Strength =

27.7 MPa

51

Table 6: Cylinder and cube compressive strength of 28-day geopolymer concrete

Mix

No.

Mix

Designation

f’c

(MPa)

fcu

(MPa) f’c / fcu

1 R0SF0 27.7 35.3 0.78

2 R30SF0 17.4 31.0 0.56

3 R30SF1 31.1 37.7 0.82

4 R30SF2 34.1 43.4 0.79

5 R70SF0 11.6 28.2 0.41

6 R70SF1 19.5 31.7 0.68

7 R70SF2 31.9 36.8 0.87

8 R100SF0 10.9 28.1 0.39

9 R100SF1 18.9 33.3 0.57

10 R100SF2 25.3 34.7 0.73

Figure 12: Relationship between cube and cylinder compressive strengths of

geopolymer concrete

f'c = 1.703fcu - 35.092

R² = 0.90

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50

Cyli

nder

com

pre

ssiv

e st

ren

gth

(M

Pa)

Cube compressive strength (MPa)

52

4.2.2 Compressive stress-strain response

The effect of different SF volume fractions on the compressive stress-strain

behavior is examined by comparing mixes with the same RCA replacement, as shown

in Figure 13. The plots were obtained based on the procedure of section 3.6.2. The

peak stress increased by an average of 91, 73, and 72% for every 1% steel fiber volume

fraction added to the concrete mix incorporating 30, 70, and 100% RCA, respectively.

Furthermore, the strain at peak load increased, on average, 73 and 104% when 1 and

2% steel fibers were incorporated into the RCA mixes, by volume. Clearly, the

addition of steel fibers enhanced the compressive behavior and increased the

deformability of RCA blended geopolymer concrete, evidenced by the increase in peak

strain.

(a)

Figure 13: Typical compression stress-strain curves of cylinder concrete specimens

with RCA (a) 30%, (b) 70%, and (c) 100%

0

5

10

15

20

25

30

35

40

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Str

ess

(MP

a)

Strain (µε)

R30SF0

R30SF1

R30SF2

53

(b)

(c)


with RCA (a) 30%, (b) 70%, and (c) 100% (continued)

Figure 14 investigates the influence of RCA replacement percentage on the

compressive stress-strain behavior of blended geopolymer concrete. Regardless of the

SF volume fraction, the increase in RCA replacement led to a decrease in the peak

stress and slope of the stress-strain curve. This is primarily owed to the weaker

performance of RCA and lower modulus of elasticity of such mixes. Furthermore, the

0

5

10

15

20

25

30

35

40

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Str

ess

(MP

a)

Strain (µε)

R70SF0

R70SF1

R70SF2

0

5

10

15

20

25

30

35

40

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Str

ess

(MP

a)

Strain (µε)

R100SF0

R100SF1

R100SF2

54

peak strain generally increased as more RCA was incorporated into the mix. In

conclusion, it can be noted that steel fiber addition to RCA blended geopolymer

concrete promoted higher peak stress and strain compared to plain RCA counterparts.

(a)

(b)


with SF (a) 0%, (b) 1%, and (c) 2%

0

5

10

15

20

25

30

35

40

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Str

ess

(MP

a)

Strain (µε)


0

5

10

15

20

25

30

35

40

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Str

ess

(MP

a)

Strain (µε)

R30SF1R70SF1R100SF1

55

(c)


with SF (a) 0%, (b) 1%, and (c) 2% (continued)

4.2.3 Modulus of Elasticity

The modulus of elasticity, Ec (in GPa), refers to the ability of a material to

sustain a sustained stress as the strain increases within the elastic limit. It was

determined by analyzing the stress-strain curves in accordance with ASTM C469

(ASTM, 2014). Figure 15 illustrates the modulus of elasticity of 28-day blended

geopolymer concrete mixes with different RCA replacement and SF volume fractions.

An increase in RCA replacement percentage led to a decrease in the modulus of

elasticity. In fact, 30, 70, and 100% RCA replacement in plain concrete decreased Ec

by 17, 36, and 63%, respectively. This reduction could be attributed to the weak and

porous structure of RCA, porous old adhered mortars, microcracks in the RCA, and

weak interfacial bond between the old mortar and aggregate. Other work on fly ash-

based geopolymer reported similar results (Shaikh, 2016). On the other hand, as the

SF volume fraction increased, the modulus of elasticity increased. For 30, 70, and

0

5

10

15

20

25

30

35

40

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Str

ess

(MP

a)

Strain (µε)

R30SF2

R70SF2

R100SF2

56

100% RCA replacement, the addition of 1% SF to plain counterparts increased Ec by

12, 3, and 23%, respectively, while 2% SF led to respective increases of 17, 12, and

41%. Such an increase in modulus is owed to an increase in compressive strength and

stress, S2, of Equation 1. Based on these results, it can be concluded that the effect of

RCA replacement on the modulus of elasticity was more prominent than the addition

of SF.

Figure 15: Modulus of elasticity of concrete mixes with different RCA replacement

percentages and SF volume fractions

The modulus of elasticity results showed herein were correlated to the 28-day

cylinder compressive strength. The developed analytical relationship is in the form of

Equation 10 and is shown in Figure 16. It is clear that a low correlation (R2 = 0.45)

exists between the two mechanical properties. This is due to the significant impact of

RCA replacement on the modulus of elasticity. Accordingly, a regression model

involving the RCA replacement percentage and f’c was developed. Equation 11

presents this relationship, where f’c is the 28-day cylinder compressive strength in MPa

and RCA is the RCA replacement percentage. Yet, it is mainly valid for f’c values

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60 70 80 90 100

Modulu

s of

Ela

stic

ity (

GP

a)

RCA (%)

SF0SF1SF2

57

between 10 and 40 MPa. From the coefficients of Equation 11, it is clear that Ec and

f’c share a proportional relationship, signifying that an increase in f’c leads to higher Ec

values. In contrast, Ec and RCA replacement percentage are inversely proportional,

indicating that RCA has a negative impact on Ec.

Ec = 1.91√fc

'

(10)

Ec = 0.091f’c – 0.065RCA + 10.845 (11)

Figure 16: Modulus of elasticity of concrete mixes as a function of compressive

strength

The obtained relationship in Equation 11 is compared to those developed by

ACI Committee 318 (2014), CEB-FIP (Comité euro-international du béton and

Federation International de la Precontrainte, 1993), and AS3600 (2009). The codified

equations are presented in Table 7. Figure 17 depicts the predicted values of Ec versus

the experimental ones. With scatter plots converging around the 45°-line, it can be

noted that the model presented herein as Equation 11 was more accurate at predicting

the values of Ec. While the codified equations of ACI 318 and CEB-FIP significantly

Ec = 1.91√f'cR² = 0.45

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7

Modulu

s of

Ela

stic

ity (

GP

a)

Compressive Strength, √f'c (MPa)

58

overestimated Ec, the model proposed by AS3600 only slightly overestimated it. In

fact, the error between the experimental and predicted Ec from equation of AS3600

increased as more RCA and SF were incorporated into the geopolymer concrete.

Clearly, the codified equations are unsuitable for the geopolymer concrete produced

in this work.

Table 7: Equations relating the modulus of elasticity to the compressive strength

Reference Modulus of Elasticity (Ec)

ACI Committee 318 0.043w1.5 f’c0.5

AS3600 0.024w1.5 (f’c0.5+0.12)

CEB-FIP 9979.4f’c0.33

Note: w = density of concrete (kg/m3)

f’c = compressive strength (MPa)

Figure 17: Experimental versus predicted modulus of elasticity

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

Pre

dic

ted E

c(G

Pa)

Experimental Ec (GPa)

Equation 11

ACI 318

AS3600

CEB-FIP

59

4.2.4 Splitting tensile strength

The splitting tensile strength (fsp) was utilized as an indirect method to evaluate

the tensile performance of 28-day GGBS-fly ash blended geopolymer concrete made

with RCA and SF, as highlighted in Figure 18. The results show a similar trend to that

of the cylinder compressive strength, where an increase in RCA replacement

percentage in plain geopolymer concrete led to a decrease in splitting tensile strength.

In fact, the values of fsp were reduced by 17, 37, and 47%, when 30, 70, and 100%

RCA replaced NA, respectively. Shaikh (2016) and Hu et al. (2019) reported a similar

adverse effect of RCA on fsp of geopolymer concrete made with fly ash or a blend of

fly ash and GGBS. In comparison, f’c decreased by 26, 51, and 54 for the same RCA

replacement percentages. This indicates that RCA replacement was more influential

on the compressive strength rather than splitting tensile strength, as noted as an

increase in the fsp-to-f’c ratio of Table 8.

Figure 18: Splitting tensile strength of 28-day geopolymer concrete

0

1

2

3

4

5

6

30 70 100

Ten

sile

Sp

litt

ing S

tren

gth

, ƒ

sp(M

Pa)

RCA (%)

SF0

SF1

SF2

Control

Strength

= 2.185 MPa

60

The effect of adding SF was also investigated. Figure 18 shows that the

addition of 1 and 2% SF, by volume, increased the splitting tensile strength by, on

average, 134 and 230% respectively, compared to the plain concrete counterparts. In

fact, fsp could reach up to 4.4 and 4.9 MPa compared to 2.2 MPa for the control. Other

work on NA-based geopolymer concrete reported similar enhancements in fsp when SF

was added to the mix (Bernal et al., 2010; El-Hassan and Elkholy, 2019; Islam et al.,

2017). Furthermore, the ratio of fsp-to-f’c (Table 8) increased with steel fiber addition,

which indicates that the steel fibers were more influential on fsp rather than f’c. It is

clear that the adverse impact of NA replacement by RCA on the splitting tensile

strength could not only be reversed by SF addition but could also exceed that of the

control. This is primarily owed to the steel fibers’ ability to bridge the microcracks and

increase the energy requirements for crack propagation.

Table 8: Ratio of tensile splitting strength to compressive strength

Mix

No.

Mix

designation

f'c

(MPa)

fsp

(MPa)

fsp / f'c

(%)

1 R0SF0 27.7 2.2 7.6

2 R30SF0 17.3 1.8 10.3

3 R30SF1 31.1 4.3 14.1

4 R30SF2 34.0 4.9 14.5

5 R70SF0 11.6 1.3 11.7

6 R70SF1 19.4 2.9 15.1

7 R70SF2 31.8 4.8 15.2

8 R100SF0 10.9 1.1 10.6

9 R100SF1 18.9 2.7 14.6

10 R100SF2 25.2 4.1 16.5

61

The splitting tensile strength of geopolymer concrete is usually predicted

through codified equations that it to the 28-day cylinder compressive strength. Such

equations are presented in Table 9. Nevertheless, an equation was developed to relate

these two properties, as per Equation 12 and shown in Figure 19. Based on the

correlation coefficient, R2, it is possible to predict the splitting tensile strength from

the cylinder compressive strength with reasonable accuracy (R2 = 0.80). To improve

the accuracy of the relationship between these two properties, the SF volume fraction

was added, owing to its clear impact on fsp. Accordingly, Equation 13 was developed

with a higher regression coefficient, R2, of 0.98.

fsp = 1.40√fc

' - 3.53

(12)

fsp = 0.74√fc

' + 0.98SF - 1.30

(13)

The experimental splitting tensile strength was plotted against that predicted

from the codified equations as well as Equations 12 and 13. Figure 20 shows that

models developed by ACI 318, AS3600, and CEB-FIP (ACI Committee 318, 2014;

AS3600, 2009; Comité euro-international du béton and Federation International de la

Precontrainte, 1993) could predict fsp with reasonable accuracy until a value of 3 MPa

after which these codes underestimated it. With a non-conventional blended

geopolymer concrete made with RCA and steel fibers, it can be concluded that codified

equations cannot be employed for the prediction of the splitting tensile strength.

62

Table 9: Equations relating splitting tensile strength and compressive strength

Reference Tensile strength (fsp)

ACI Committee 318 0.56 f’c0.5

AS3600 0.36 f’c0.5

CEB-FIP 0.30 f’c0.67

Figure 19: Correlation between splitting tensile strength and compressive strength

Figure 20: Experimental versus predicted splitting tensile strength

fsp = 1.40√f'c - 3.54

R² = 0.80

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7

Spli

ttin

g t

ensi

le s

tren

gth

(M

Pa)

Compressive strength, √f'c (MPa)

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Pre

dic

ted f

sp(M

Pa)

Experimental fsp (MPa)

Equation 12Equation 13ACI 318AS3600CEB-FIP

63

4.2.5 Flexural performance

The flexural performance of GGBS-fly ash blended geopolymer concrete

having various RCA replacement percentages and SF volume fractions is characterized

by the peak strength, peak deflection, residual strength, toughness, and equivalent

flexural strength ratio. Results are summarized in Table 10 and are discussed in detail

in the following sections.

Table 10: Flexural performance test results

Mix

Designation fp δp f

600

100 f

150

100 T150

100 RT,150 100

Unit MPa mm MPa MPa J %

R0SF0 3.5 0.32 - - 1.8 0.8

R30SF0 2.6 0.35 - - 2.5 1.4

R30SF1 4.7 0.56 3.48 2.64 28.1 9.0

R30SF2 6.4 1.08 - 5.51 57.4 13.5

R70SF0 1.7 0.49 - - 2.7 2.4

R70SF1 3.0 0.79 - 2.03 25.7 12.8

R70SF2 5.0 1.20 - 4.41 45.0 13.5

R100SF0 1.5 0.55 - - 2.9 2.9

R100SF1 2.9 0.86 - 2.03 22.0 13.4

R100SF2 4.0 1.44 - 2.70 44.0 16.5

64

4.2.5.1 Load-deflection curves

The flexural performance is evaluated using the load-deflection curves. Figure

21 illustrates the effect of RCA replacement percentage on the flexural behavior of 28-

day blended geopolymer concrete mixes made with different steel fiber volume

fractions. While three samples were tested per mix, one representative curve was

presented. Plain geopolymer concrete mixes are shown in Figure 21(a). The load

increased in a pseudo-elastic mode until failure. The increase in RCA replacement

caused a decrease in the slope of the load-deflection curve. In fact, 30, 70, and 100%

RCA were associated with respective decreases of 2, 55, and 66%, owing to a reduction

in the modulus of elasticity with RCA replacement.

Figures 21(b-c) illustrate the load-deflection curves of steel fiber-reinforced

RCA blended geopolymer concrete. These curves consist of two main parts. The first

part represents the increase until a peak load is attained. Its slope is controlled by the

modulus of elasticity of the concrete specimen. Clearly, the increase in RCA

replacement did not significantly change the slope regardless of steel fiber volume

fraction. In the second part of the curve, the post-peak softening behavior was

observed. Such a phenomenon was not noted in plain concrete samples. A post-peak

tail was noted for steel fiber-reinforced concrete mixes, owing to the incorporation of

steel fiber reinforcement. In fact, these steel fibers improved the integrity of the

geopolymer concrete by reducing crack development and propagation through their

bridging effect. The RCA replacement percentage seemed to have a limited effect on

the rate at which the residual strength was attained, while the value of the residual

strength was relevant to the peak strength.

65

(a)

Figure 21: Typical load-deflection curves of geopolymer concrete mixes with SF (a)

0%, (b) 1%, and (c) 2%

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5

Lo

ad (

kN

)

Deflection (mm)

R0SF0

R30SF0

R70SF0

R100SF0

66

(b)

(c)

Figure 21: Typical load-deflection curves of geopolymer concrete mixes with SF (a)

0%, (b) 1%, and (c) 2% (continued)

The effect of adding steel fibers on the flexural load-deflection curves was

studied. For mixes made with 30% RCA [Figure 22(a)], the addition of 1 and 2% steel

fibers, by volume, increased the peak load by 43 and 158%, respectively, compared to

the plain counterpart. The deflection at peak load for these mixes also increased by

two and six times. However, the slope did not seem to be significantly impacted by the

addition of steel fibers.

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5

Lo

ad (

kN

)

Deflection (mm)

R30SF1R70SF1R100SF1

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5

Load

(kN

)

Deflection (mm)

R30SF2R70SF2R100SF2

67

Figure 22(b) shows the mixes with 70% RCA and different SF volume

fractions. The peak load, peak deflection, and slope of the first part of the curve

increased as more SF were incorporated into the mix. Such findings were associated

with the higher modulus of elasticity of SF-reinforced mixes. Additionally, past

research has reported that the bond between the matrix and steel fiber may have

delayed crack formation as the applied load was lower than the peak load (Bencardino

et al., 2013; Yoo et al., 2015). After the peak load was reached, cracks formed in the

geopolymeric matrix. Yet, these cracks were bridged by the steel fibers, thus, delaying

further crack propagation. Furthermore, the slope of the descending branch of the load-

deflection curve was nearly the same for 1 and 2% steel fiber volume fractions.

The effect of steel fiber addition on geopolymer concrete made with 100%

RCA is depicted in Figure 22(c). The load-deflection curves were similar to those of

mixes incorporating 70% RCA, except that the peak load was lower. Thus, it can be

concluded that the first part of the curve was mainly impacted by the RCA content,

while the second part was dependent on the SF volume fraction. Although RCA had a

negative impact on the flexural performance of blended geopolymer concrete, its effect

could be countered by SF addition. Not only that, but it could also enhance the flexural

performance beyond the control mix made with 100% NA.

68

(a)

(b)

Figure 22: Typical load-deflection curves of cylinder concrete specimens with RCA

(a) 30%, (b) 70%, and (c) 100%

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5

Lo

ad (

kN

)

Deflection (mm)

R30SF0

R30SF1

R30SF2

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5

Load

(kN

)

Deflection (mm)

R70SF0R70SF1R70SF2

69

(c)

Figure 22: Typical load-deflection curves of cylinder concrete specimens with RCA

(a) 30%, (b) 70%, and (c) 100% (continued)

4.2.5.2 Flexural strength

The flexural strength or modulus of rupture (fr) of 28-day GGBS-fly ash

blended geopolymer concrete made with different proportions of RCA and SF was

investigated. Table 11 presents the results. Similar to the splitting tensile strength, an

increase in RCA replacement percentage led to a loss in flexural strength. In fact,

replacing NA by 30, 70, and 100% RCA in plain geopolymer concrete reduced the

flexural strength by 25, 51, and 43%, respectively. Such decreases were analogous to

those reported in f’c. This indicates that RCA incorporation has a similar effect on fr

and f’c, as noted in the fr-to-f’c ratio of Table 11.

Figure 23 presents the flexural strength of steel fiber-reinforced blended

geopolymer concrete mixes made with different RCA replacement percentages. On

average, the addition of 1 and 2% steel fibers, by volume, increased the flexural

strength by 81 and 165%, respectively, compared to plain counterparts. Similar

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5

Lo

ad (

kN

)

Deflection (mm)

R100SF0R100SF1R100SF2

70

conclusions were reported in the case of reinforcing NA-based geopolymer concrete

made with GGBS or a blend of GGBS and fly ash with steel fibers (Bernal et al., 2010;

Devika and Nath, 2015; El-Hassan and Elkholy, 2019; Islam et al., 2017). Using the

ratio of fr-to-f’c (Table 11), it seems that the steel fiber addition was more influential

on fr than f’c. Additionally, the adverse effect of RCA on fr could be countered by SF

addition. In fact, it is possible to produce blended geopolymer concrete mixes made

with 100% RCA and 2% steel fiber, by volume, with slightly superior flexural

performance than the 100% NA control.

The flexural strength results were correlated to those of the 28-day cylinder

compressive strength, as shown in Figure 24. The resultant analytical model, in the

form of Equation 14, can be used to predict the fr from f’c with reasonable accuracy

(R2 = 0.90). Nevertheless, an attempt was made to utilize the codified equations of

ACI 318, AS3600, and CEB-FIP (ACI Committee 318, 2014; AS3600, 2009; Comité

euro-international du béton and Federation International de la Precontrainte, 1993),

shown in Table 12, to predict the flexural strength. Figure 25 displays the results. The

equations provided by ACI 318 and AS3600 provide relatively good predictions with

values below 4 MPa, whereas CEB-FIP was more accurate above 4 MPa. Still, the

developed equation seems to be most suitable with an average error of 8%, while those

of ACI 318, AS3600, and CEB-FIP were 21, 22, and 25%, respectively.

fr = 1.59√fc

' – 3.92

(14)

71

Figure 23: Flexural strength of 28-day geopolymer concrete

Table 11: Flexural and cylinder compressive strength of 28-day geopolymer concrete

Mix

No.

Mix

designation

f'c

(MPa)

fr

(MPa)

fr / f'c

(%)

1 R0SF0 27.7 3.5 12.6

2 R30SF0 17.3 2.6 15.2

3 R30SF1 31.1 4.7 15.1

4 R30SF2 34.0 6.4 18.8

5 R70SF0 11.6 1.7 15.0

6 R70SF1 19.4 3.0 15.4

7 R70SF2 31.8 5.0 15.7

8 R100SF0 10.9 1.5 13.8

9 R100SF1 18.9 2.9 15.3

10 R100SF2 25.2 4.0 15.8

0

1

2

3

4

5

6

7

30 70 100

Fle

xu

ral S

tren

gth

, ƒ

r(M

Pa)

RCA (%)

SF0SF1

SF2

Control Strength =

3.50 MPa

72

Figure 24: Relationship between flexural and cylinder compressive strength of 28-

day geopolymer concrete

Table 12: Equations relating flexural strength and cylinder compressive strength

Reference Flexural strength (fr)

ACI Committee 318 0.62f’c0.5

AS3600 0.60f’c0.5

CEB-FIP 0.81f’c0.5

Figure 25: Experimental versus predicted flexural strength

y = 1.59√f'c - 3.92

R² = 0.90

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7

Fle

xu

ral st

ren

gth

(M

Pa)

Compressive strength √f'c (MPa)

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Pre

dic

ted

fr(M

Pa)

Experimental fr (MPa)

Equation 14

ACI 318

AS3600

CEB-FIP

73

4.2.5.3 Deflection

The structural ductility of blended geopolymer concrete made with different

proportions of RCA and SF was evaluated using the mid-span deflection. Based on the

results of Table 10, the values of the peak deflection (δp) ranged from 0.32 to 1.44 mm

with the respective lowest and highest deflections associated with the 100% NA

control mix and that made with 100% RCA and 2% SF, by volume. Apparently, steel

fiber incorporation into geopolymer concrete increased its deflection capacity. Similar

findings in conventional cement-based concrete associated this increase to steel fibers’

bridging effect and ability to reduce crack propagation (Gao and Zhang, 2018).

However, while ASTM C1609 (ASTM, 2019b) reports that first and peak deflection

corresponding to first and peak load are typically reported, the first load and deflection

were not present in the load-deflection curves of Figures 21 and 22. Therefore, the

focus of the work presented herein was on the peak deflection, δp.

Figure 26(a) highlights the effect of RCA replacement and SF incorporation on

the peak deflection. It is clear that an increase in the replacement of NA by RCA led

to an increase in the value of δp. Indeed, for plain mixes, the replacement of NA by 30,

70, and 100% RCA increased the peak deflection by 9, 53, and 72%, respectively.

Similar trends were noticed for steel fiber-reinforced mixes. Furthermore, the addition

of SF on the deflection of GGBS-fly ash blended geopolymer concrete was

investigated. Steel fiber volume fraction of 1 and 2% resulted in, on average, 59 and

171% respective increases in δp.

Figure 26(b) presents the change in peak deflection (δp) as a function of 28-day

cylinder compressive strength (f’c). For plain geopolymer concrete, the peak deflection

values did not exceed 0.55 mm. Moreover, concrete having higher compressive

strength, i.e. lower RCA replacement percentage, was characterized by a lower peak

74

deflection. Conversely, δp of steel fiber-reinforced counterparts with 1 and 2% steel

fibers could reach up to 0.86 and 1.44 mm, respectively. Furthermore, for a specific

compressive strength value, the addition of steel fibers significantly increased the

value of δp. Thus, it is apparent that the peak deflection is proportional to the RCA

replacement percentage and SF volume fraction and inversely proportional to the

compressive strength. Similar relationships were developed for conventional cement-

based RCA concrete reinforced with steel fibers (Gao et al., 2019; Gao and Zhang,

2018; Kachouh et al., 2020a; Yoo et al., 2015).

(a)

Figure 26: Deflection at peak load of concrete mixes with various (a) RCA

replacement percentage and SF volume fractions and (b) cylinder compressive

strength

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 10 20 30 40 50 60 70 80 90 100

Def

lect

ion a

t pea

k (

mm

)

RCA Replacement (%)

SF0

SF1

SF2

75

(b)

Figure 26: Deflection at peak load of concrete mixes with various (a) RCA


strength (continued)

4.2.5.4 Residual strength

The concrete residual capacity at specific deflections after cracking is

characterized by the residual strength (ASTM, 2019b). In this work, the residual

strengths were determined at two deflection points, namely L/600 and L/150. As

shown in Table 10, no residual strength was reported for the plain concrete mixes, as

they did not experience any post-peak behavior. Also, the residual strengths of mixes

having the peak deflections larger than L/600 were left empty. As such, the main focus

of this work was on the residual strength at L/150, f150

100.

The effect of RCA replacement percentage and SF volume fraction on the

residual strength f150

100 was studied. Figure 27(a) shows that the replacement of NA by

RCA led to a decrease in the value of f150

100. Yet, such a decrease was more apparent

with a 2% steel fiber volume fraction with values dropping from 5.5 to 2.7 MPa when

RCA replacement increased from 30 to 100%. Furthermore, the incorporation of

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 10 20 30 40

Def

lect

ion

at

pea

k (

mm

)

Compressive strength, f'c (MPa)

SF0

SF1

SF2

76

higher steel fiber volume fractions in the geopolymer concrete mix resulted in higher

residual strength. At 30, 70, and 100% RCA replacement, the increase of SF from 1 to

2%, by volume, led to 109, 117, and 33% respective increases in f150

100. Clearly, the

residual strength was positively impacted by the addition of steel fiber but negatively

affected by RCA replacement. Similar conclusions were reported in conventional

cement-based RCA concrete incorporating steel fibers (Gao et al., 2019; Gao and

Zhang, 2018; Kachouh et al., 2020a).

Figure 27(b) presents the relationship between residual strength and 28-day

cylinder compressive strength. For each steel fiber volume fraction, an increase in f’c,

i.e. decrease in RCA replacement, resulted in an increase in f150

100. However, this

increase was more pronounced at 2% steel fiber, by volume. In fact, f150

100 for 1 and 2%

SF increased by an average of 0.05 and 0.32 MPa, respectively, for every 1 MPa

increase in f’c.

(a)

Figure 27: Residual strength of concrete mixes with various (a) RCA replacement

percentage and SF volume fractions and (b) cylinder compressive strength

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 10 20 30 40 50 60 70 80 90 100

Res

idu

al s

tren

gth

f1

50

(MP

a)

RCA Replacement (%)

SF1

SF2

77

(b)

Figure 27: Residual strength of concrete mixes with various (a) RCA replacement


(continued)

4.2.5.5 Flexural toughness

The flexural toughness is a measure of concrete’s energy absorption capacity.

Table 10 summarizes the toughness of blended geopolymer concrete incorporating

different quantities of RCA and SF. Values ranged between 1.8 and 57.4 J. It seems

that the addition of SF and replacement of NA by RCA increased the toughness.

Figure 28(a) presents the relationship between the flexural toughness and

varying mixture proportions, i.e. RCA replacement percentage and SF volume

fraction. For plain concrete, increasing the RCA content had an insignificant impact

on the toughness. Yet, it was more impactful as steel fiber was added to the mix. In

fact, the toughness decreased from 28 to 22 J and 57 to 44 J when RCA replacement

increased from 30 to 100% in mixes made with 1 and 2% steel fibers, by volume,

respectively. Additionally, the effect of steel fiber incorporation was investigated. The

toughness of plain blended geopolymer concrete mixes increased by, on average, 9

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 10 20 30 40

Res

idu

al s

tren

gth

f1

50

(MP

a)

Compressive strength, f'c (MPa)

SF1

SF2

78

and 18 times when 1 and 2% steel fiber volume fractions were added, respectively.

This is primarily owed to the bridging effect of steel fibers and their ability to reduce

crack propagation and increase flexural performance.

The flexural toughness is studied with respect to the cylinder compressive

strength in Figure 28(b). For plain geopolymer concrete, an increase in strength, i.e.

lower RCA replacement percentage, led to a slight increase in toughness. Yet, this

effect amplified upon incorporating 1 and 2% steel fibers, by volume, with respective

toughness increase by 0.5 and 1.5 J for every 1 MPa increase in strength. Furthermore,

it is worth noting that plain and steel fiber-reinforced mixes having the same

compressive strength had very different toughness values. For example, a 20-MPa

concrete had the toughness of 2.5 and 25 J with 0 and 1% steel fibers. Clearly,

toughness was significantly more influenced by the incorporation of steel fibers than

RCA replacement.

(a)

Figure 28: Flexural toughness of concrete mixes with various (a) RCA replacement


0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100

Fle

xura

l T

oughnes

s T

15

0(J

)

RCA Replacement (%)

SF0

SF1

SF2

79

(b)

Figure 28: Flexural toughness of concrete mixes with various (a) RCA replacement


(continued)

4.2.5.6 Equivalent flexural strength ratio

Table 10 presents the equivalent flexural strength ratio (RT,150 100 ). Values for

plain geopolymer concrete ranged between 0.8 and 1.9%, while those of steel fiber-

reinforced RCA counterparts reached up to 26.3%. This shows that steel fiber addition

and RCA replacement had a positive impact on the ratio.

Figure 29(a) illustrates the effect of SF addition and RCA replacement in more

detail. The replacement of NA by 30, 70, and 100% RCA increased the ratio by 100,

112, and 137%, respectively, compared to the NA-based control. This is attributed to

the increase in toughness and decrease in peak load in plain RCA concrete mixes. Yet,

such a positive impact on RT,150 100 was more pronounced in steel fiber-reinforced

concrete. In fact, mixes made with 1 and 2% steel fiber, by volume, noted average 12

and 16% increases in RT,150 100 for every 10% NA replaced by RCA. Furthermore, the

0

10

20

30

40

50

60

70

0 10 20 30 40

Fle

xu

ral T

ou

gh

nes

s T

15

0(J

)

Compressive Strength, f'c (MPa)

SF0

SF1

SF2

80

effect of steel fiber on the equivalent flexural strength ratio was evaluated. For 1 and

2% steel fiber volume fractions added to the geopolymer concrete mixes, the value of

RT,150 100 increased by, on average, 6 and 9 times, regardless of the amount of NA being

replaced by RCA. This highlights the much more significant impact of SF on the RT,150 100

compared to that of RCA replacement.

(a)

(b)

Figure 29: Equivalent flexural strength ratio of concrete mixes with various (a) RCA


strength

0

2

4

6

8

10

12

14

16

18

0 10 20 30 40 50 60 70 80 90 100

Equiv

alen

t R

atio

RT

,15

0(%

)

RCA Replacement (%)

SF0

SF1

SF2

0

2

4

6

8

10

12

14

16

18

0 10 20 30 40

Eq

uiv

alen

t R

atio

RT

,15

0(%

)

Compressive Strength, f'c (MPa)

SF0

SF1

SF2

81

The relationship between equivalent flexural strength ratio and cylinder

compressive strength is presented in Figure 29(b). It is clear that RT,150 100 tended to

decrease with higher strength and more RCA replacement. For plain concrete, RT,150 100

decreased by an average of 0.05% for every 1 MPa increase in compressive strength.

Yet, this trend was more prominent as more steel fiber was incorporated into the mix.

For steel fiber-reinforced geopolymer concrete, every 1 MPa increase in compressive

strength resulted in an average 0.4% decrease in RT,150 100 . Furthermore, plain and steel

fiber-reinforced mixes having equal compressive strength had different equivalent

flexural strength ratios. For instance, a 20-MPa concrete with 0 and 1% steel fiber, by

volume, had RT,150 100 values of 1.2 and 12%, respectively. Thus, it can be concluded that

the incorporation of steel fibers had a more significant effect on the equivalent flexural

strength ratio than RCA replacement.

4.3 Durability properties

4.3.1 Water absorption

The durability of concrete can be evaluated by the rate at which harmful agents

penetrate the concrete. In fact, concrete undergoes deterioration and damage due to the

ingress of moisture or other aggressive liquids through the interconnected pores. As

water is the primary carrier of aggressive ions, the ability of concrete to absorb water,

characterized by its water absorption, can give a good indication of its durability

(Mehta, 2006). Figure 30 illustrates the results of water absorption tests at the age of

28 days. It is observed that the water absorption increased with an increase in RCA

replacement. While the control specimen (R0SF0) had the lowest water absorption of

3.8%, mixes made with 30, 70, and 100% RCA had values of 5.0, 6.6, and 6.8%,

82

respectively. This represents 31, 73, and 76% respective increases in the water

absorption compared to the control mix. Such a finding correlates well with the

decrease in mechanical properties, including compressive, splitting tensile, and

flexural strength. It can therefore be noted that the water absorption increased by 7%,

on average, for every 10% NA replaced by RCA, owing to the porous structure of the

adhered mortar to the RCA and additional void sites in the RCA.

In addition, Figure 30 shows that the water absorption decreased as more SF

was incorporated into the mix. The addition of 1 and 2% SF volume fractions

compared to concretes without SF resulted in average reductions in water absorption

of 4 and 13%, respectively. Clearly, the incorporation of steel fibers into blended

geopolymer concrete made with RCA densified the matrix, leading to a decrease in the

water absorption and an increase in mechanical performance. Bernal et al. (2010)

reported similar findings for GGBS-based geopolymer concrete made with NA and

steel fibers.

Figure 30: Effect of RCA and SF percentages on the water absorption of 28-day

geopolymer concrete

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80 90 100

Wat

er A

bso

rpti

on (

%)

RCA (%)

SF0

SF1

SF2

83

4.3.2 Sorptivity

Sorptivity is a commonly used test to indirectly assess the durability of

concrete, as it relates to the tendency of concrete to absorb and transport water by

capillary action through its microstructure. In fact, the rate of absorption, i.e. sorptivity,

of water depends on the strength of capillary forces, the permeability of the concrete,

the porosity of the concrete, and structure and distribution of the pores (Mehta, 2006;

Neville, 1996). Sorptivity is categorized into two types: initial and secondary. The

initial and secondary sorptivity are governed by the sorption processes through the

large capillary and small gel pores, respectively (Martys and Ferraris, 1997). Because

water occupies the former pores faster than the latter ones, the initial sorptivity is

typically higher than the secondary sorptivity. Accordingly, this work only focused on

the initial sorptivity.

To find the rate of absorption or sorptivity, the change in weight of a concrete

sample over the square root of time is plotted as a scatter line graph, as shown in Figure

30. Within the first 60 minutes, the slope of the sorptivity curve was higher than the

remaining time of exposure. This is mainly a result of the corresponding early and late

filling of large and small pores. Figure 31(a) presents the sorptivity curves of plain

concrete mixes without SF. An increase in RCA replacement percentage led to an

increase in the slope and to higher water absorption, owing to the poor quality and

porous nature of the RCA and its adhered old mortar. It is also possible that RCA may

have cracks and fissures that had developed during the manufacturing process.

The effect of SF on the rate of water absorption is shown in Figure 31(b-c).

Higher steel fiber volume fractions led to lower slopes and water absorption.

Apparently, the steel fibers restricted the movement of water and occupied the larger

84

void space in the geopolymer concrete structure. Other work noted similar conclusions

in steel fiber-reinforced conventional concrete (Ramadoss and Nagamani, 2008; Şanal,

2018). As such, the sorptivity decreased.

(a)

(b)

Figure 31: Absorption of concrete mixes over time: (a) SF 0%; (b) SF 1%; (c) SF2%

0

1

2

3

4

5

6

7

8

9

10

0 15 30 45 60 75 90 105 120 135 150

I (m

m)

Time (√s)


0

1

2

3

4

5

6

7

8

9

10

0 15 30 45 60 75 90 105 120 135 150

I (m

m)

Time (√s)

R30SF1

R70SF1

R100SF1

85

(c)

Figure 31: Absorption of concrete mixes over time: (a) SF 0%; (b) SF 1%; (c) SF2%

(continued)

Table 13 summarizes the sorptivity results of 28-day GGBS-fly ash blended

geopolymer concrete mixes. The sorptivity values of plain concrete increased as more

NA was replaced by RCA. Compared to the NA-based control, the replacement of 30,

70, and 100% RCA increased the sorptivity by 40, 80, and 136%, respectively.

Conversely, steel fiber incorporation decreased the sorptivity of the RCA-based

mixtures, as they may have filled the geopolymer concrete voids. On average, the

addition of SF by 1 and 2%, by volume, resulted in a decrease in the sorptivity by 5.3%

and 13.9 %, respectively, compared to that of RCA-based plain concrete mixes. It is

possible that the steel fibers may have reduced the absorption and sorptivity, owing to

an improvement in the bond within the binding matrix (Tamrakar, 2012). Similar

findings were reported in conventional cement-based steel fiber-reinforced NA and

RCA concrete (Kachouh et al., 2019a; Ramadoss and Nagamani, 2008; Şanal, 2018).

0

1

2

3

4

5

6

7

8

9

10

0 15 30 45 60 75 90 105 120 135 150

I (m

m)

Time (√s)

R30SF2R70SF2R100SF2

86

Table 13: Water absorption and initial rate of absorption of geopolymer concrete

Mix

No.

Mix

Designation

RCA

(%)

SF

(%)

Water

Absorption

(%)

Initial Rate of

Absorption

(mm/√s)

1 R0SF0 0 0 3.80 0.025

2 R30SF0 30 0 4.96 0.035

3 R30SF1 30 1 4.52 0.034

4 R30SF2 30 2 4.28 0.033

5 R70SF0 70 0 6.57 0.045

6 R70SF1 70 1 6.24 0.043

7 R70SF2 70 2 5.41 0.038

8 R100SF0 100 0 6.7 0.059

9 R100SF1 100 1 6.77 0.054

10 R100SF2 100 2 6.12 0.047

4.3.3 Bulk resistivity

The concrete bulk resistivity is an indirect measure of the concrete durability.

Due to the conductive nature of steel fibers and the generation of unrepresentative

results, mixes incorporating 1 and 2% SF volume fractions were not considered in the

analysis. Accordingly, the results of the plain blended geopolymer mixes made with

different RCA replacement percentages were considered, as shown in Figure 32.

Generally, a decreasing resistivity trend was noticed as more RCA replaced NA with

values ranging between 2.0 and 4.6 kΩ.cm. In fact, the bulk resistivity was found to

decrease by 30, 52, and 57% compared to the control mix when RCA replacement was

30, 70, and 100%, respectively. Apparently, the most significant impact was noticed

87

up to a replacement of 70%; however, a higher replacement percentage of 100% had

limited effect. This is possibly due to the increase in the pore space of the geopolymeric

structure when 70% of NA was replaced by RCA to the extent that higher proportions

of RCA replacement did not cause a further reduction.

Based on these findings, it was believed that the bulk resistivity was related to

the 28-day water absorption and cylinder compressive strength. As such, correlations

between the former and latter two properties were developed, as shown in Figure 33.

Strong linear correlations exist between bulk resistivity and each of water absorption

and compressive strength with high correlation coefficients, R2, of 0.98. These

relationships are in the form of Equations 15 and 16, where BR and WA are the bulk

resistivity in kΩ.cm and water absorption in percent, respectively. They may be used

to predict the values of WA and f’c from bulk resistivity, which is a non-destructive

test.

f’c = 5.72BR (15)

WA = -1.15BR + 8.96 (16)

Figure 32: Bulk resistivity of 28-day blended geopolymer concrete mixes

0.0

1.0

2.0

3.0

4.0

5.0

6.0

R0SF0 R30SF0 R70SF0 R100SF0

Bu

lk R

esis

tivit

y (

kΩ

.cm

)

Mix Designation

88

Figure 33: Relationship between bulk resistivity and each of water absorption and

compressive strength

4.3.4 Abrasion resistance

The abrasion resistance of concrete is directly related to the mass loss after

exposing the samples to 500 revolutions in an LA abrasion machine. It is mainly

impacted by the mechanical properties of the concrete and the hardness of the

aggregates. In this work, the mass loss of blended geopolymer concrete mixtures with

different RCA and SF proportions was recorded every 100 revolutions until 500

revolutions to monitor the mass loss profile, as shown in Figure 34. In general, the

highest rate of mass loss was noted within the first 300 revolutions after which the rate

tended to decrease. Figure 34(a) presents the results of the plain concrete mixes. While

the control mix had a mass loss of 82% after 500 revolutions, those of mixes made

with 30, 70, and 100% RCA replacement were 82, 95, and 100%, respectively. This is

primarily owed to the higher porosity and inferior properties of RCA, the weak bond

between the old and new paste, and the porous structure of the adhered mortar. Other

f'c = 5.72BR

R² = 0.98

WA = -1.15BR + 8.96

R² = 0.98

0

1

2

3

4

5

6

7

8

0

5

10

15

20

25

30

0 1 2 3 4 5

Wat

er A

bso

rpti

on

(%

)

Com

pre

ssiv

e S

tren

gth

(M

Pa)

Bulk Resistivity (kΩ.cm)

89

work on conventional concrete made with RCA noted similar findings (Kachouh et al.,

2019a; Wu et al., 2011). Steel fiber-reinforced blended geopolymer concrete mixes

made with different RCA replacement percentages are shown in Figure 34(b-c). An

analogous trend to that of plain concrete was noted, whereby an increase in RCA

replacement led to an increase in the abrasion mass loss, i.e. less resistance to abrasive

loads. It can thus be concluded that replacing NA with RCA had a negative impact on

the abrasion resistance of GGBS-fly ash blended geopolymer concrete.

(a)

Figure 34: Abrasion resistance of geopolymer concrete made with SF (a) 0%, (b) 1%,

and (c) 2%

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500

Abra

sion M

ass

Loss

(%

)

Number of Revolutions


90

(b)

(c)

Figure 34: Abrasion resistance of geopolymer concrete made with SF (a) 0%, (b) 1%,

and (c) 2% (continued)

Figure 35 shows the effect of adding steel fiber reinforcement on the abrasion

resistance of blended geopolymer concrete made with 30, 70, and 100% RCA. For

mixes incorporating 30% RCA, the addition of 1 and 2% SF, by volume, reduced the

abrasion mass loss by 28 and 38%, respectively, compared to the plain counterpart.

Conversely, mixes made with 70 and 100% RCA showed respective reductions of up

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500

Ab

rasi

on

Mas

s L

oss

(%

)


R30SF1R70SF1R100SF1

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500

Abra

sion M

ass

Loss

(%

)


R30SF2

R70SF2

R100SF2

91

to 33 and 19% upon adding SF. This shows that the addition of steel fibers led to

improved geometric integrity and a more densified geopolymer concrete structure

capable of resisting abrasive and impact loading more effectively. In fact, the mix

made with 100% RCA and 2% steel fiber volume fraction showed comparable

abrasion resistance to that of the control mix.

(a)

(b)

Figure 35: Abrasion resistance of geopolymer concrete mixes made with RCA (a)

30%, (b) 70%, and (c) 100%

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500

Abra

sion M

ass

Lo

ss (

%)


R30SF0

R30SF1

R30SF2

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500

Ab

rasi

on M

ass

Loss

(%

)


R70SF0

R70SF1

R70SF2

92

(c)

Figure 35: Abrasion resistance of geopolymer concrete mixes made with RCA (a)

30%, (b) 70%, and (c) 100% (continued)

Based on the obtained results, it seems that the abrasion mass loss and

compressive strength are related. As such, these two properties were correlated using

a linear regression model. Figure 36 shows that an inversely proportional relationship

exists. It is shown in the form of Equation 17, where AR represents the abrasion

resistance mass loss in percent. Using this equation, it is possible to predict the

abrasion resistance of blended geopolymer concrete made with RCA and SF with

reasonable accuracy (R2 = 0.83).

AR = -1.70f'c + 116.35 (17)

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500

Ab

rasi

on

Mas

s L

oss

(%

)


R100SF0

R100SF1

R100SF2

93

Figure 36: Relationship between abrasion mass loss and cylinder compressive

strength

AR = -1.70f'c + 116.35

R² = 0.83

0

10

20

30

40

50

60

70

80

90

100

10 15 20 25 30 35 40

Ab

rasi

on

mas

s lo

ss (

%)

Compressive Strength (MPa)

94

Chapter 5: Numerical Modelling

5.1 Introduction

This chapter examines the effect of varying SF volume fraction and RCA

replacement percentages on the shear behavior of GGBS-fly ash blended geopolymer

concrete beams. The nonlinear analysis was conducted using the finite element (FE)

software ATENA. This software was used for the simulation and modeling of the

reinforced geopolymer concrete as a cost- and time-effective alternative to laboratory

testing. Flexural strength test results are employed to develop tensile softening

relationships using an inverse FE analysis. Ten three-dimensional (3D) FE beam

models were created to simulate and evaluate the shear behavior of concrete beams

made of the 10 mixes of the current study. The developed tensile softening

relationships and other concrete mechanical properties measured experimentally

served as input data in the FE analysis. The modeled reinforced geopolymer concrete

beams were designed to fail in shear. The results obtained from the FE analysis

included load-deflection curves, crack patterns, failure modes, and peak loads.

5.2 Geometry of the beam

The structural behavior of ten beams, representing the 10 geopolymer concrete

mixes, were investigated utilizing the suggested ATENA finite elements model. They

were designed in such a way to induce a shear mode of failure in the left segment.

Each beam had a span length of 2000 mm and a shear span-to-depth ratio (a/h) of 2.4.

All beams had a rectangular cross-section with a width and height of 150 and 250 mm,

respectively. The beams had no shear reinforcement within the shear span region,

while the remaining parts of the beams had 8 mm diameter stirrups spaced at 75 mm

95

distance except last stirrups at both edges with 50 mm spacing. The load was located

at one-third the length of the beam from the support. The longitudinal tensile and

compressive steel reinforcements consisted of 2 No. 20 (20 mm in diameter) and 4 No.

20 (20 mm in diameter) steel bars, respectively. The concrete cover to the center of the

steel reinforcement was 38 mm, rendering an effective depth of d = 198 mm. The steel

plates at the load and support points were 150 x 150 x 20 mm (length x width x

thickness). The dimensions and reinforcement details of geopolymer concrete beams

are illustrated in Figures 37 and 38.

Figure 37: Modeled beam cross-section view (dimensions in mm)

96

Figure 38: Modeled beam elevation view (dimensions in mm)

5.3 Finite Element Modeling

The mechanical properties of concrete were used as input data for defining the

behavior of the geopolymer material. Modeled beams had the same dimensions and

steel reinforcement but different mechanical properties based on the SF volume

fraction and RCA percentage. A typical 3D un-deformed shape of the developed model

is shown in Figure 39.

Figure 39: Typical FE model for geopolymer concrete beam

97

An iterative solution procedure based on the standard Newton-Raphson

method was implemented in the FE analysis in ATENA. The modeled beams were

loaded by a displacement-controlled incremental vertical loading method at the middle

of the top steel loading plate surface. Each step had a 0.1 mm change in the

displacement. The load at the middle of the top plate and the mid-span displacement

were monitored. The concrete beams were modeled using solid 3D brick macro-

elements with 8 nodes. The concrete element size was taken as 25 mm. The load and

support plates were modeled using solid 3D brick macro-elements. They were

connected to the beam through fixed contacts. The end support plates were restrained

from movement in the transverse and vertical directions (y and z directions,

respectively). These restrictions were applied by means of a support line placed at the

middle of the bottom surface of the plate. The end support plates were free to move in

the longitudinal direction (x-direction).

To obtain the numerical data, several monitoring points were added to the FE

models. The numerical values for the applied load, deflection, and steel strains were

attained utilizing these monitoring points. Table 14 shows the input parameters for all

types of monitoring points utilized in the FE models. The type and value specify the

required measurement which will be monitored nearest to the coordinates provided in

the location input. The component number indicates the direction of the monitored

value. Components 1, 2, and 3 represent the directions in X, Y, and Z, respectively.

Table 14: Input parameters of monitoring points

Title Type Value Item

Load Value at node Reaction Component 3

Deflection Value at node Displacement Component 3

98

5.4 Material Constitutive Laws

The software provides built-in material constitutive models that require

minimal user input. Furthermore, it provides alternative models where the user has

space to manually adjust constitutive models of the materials.

5.4.1 Plain Geopolymer Concrete

For concrete properties, the actual concrete strengths measured experimentally

were used for the geopolymer concrete beams. The CC3DNonLinCementitious2

concrete material model of the FE package was used to simulate the plain concrete

(NA and RCA). The properties entered in ATENA included modulus of elasticity (Ec),

cubic compressive strength (fcu), cylinder compressive strength (f’c), uniaxial tensile

strength (ft), assumed as 0.6fr, and a constant Poisson’s ratio (ν) of 0.2. Table 15 present

the mechanical properties of the mixes based on specimens tested in Chapter 4. Figure

40 shows the material constitutive laws of plain concrete in tension and compression.

Although the trend of the constitutive models of the plain geopolymer concrete was

assumed the same as that of a conventional concrete, key parameters such as

compressive strength, tensile strength, and Young’s modulus of the geopolymer

concrete that were measured experimentally were used as input data in the analysis.

99

Table 15: Mechanical properties of the geopolymer concrete mixes

Mix

No.

Mix

Designation

fcu

(MPa)

f’c

(MPa)

Ec

(GPa)

ft

(MPa)

1 R0SF0 35.3 27.7 12.6 2.1

2 R30SF0 31.0 17.4 10.4 1.6

3 R30SF1 37.7 31.1 11.6 2.8

4 R30SF2 43.4 34.1 12.2 3.8

5 R70SF0 28.2 11.6 8.1 1.0

6 R70SF1 31.7 19.5 8.3 1.8

7 R70SF2 36.8 31.9 9.1 3.0

8 R100SF0 28.1 10.9 4.7 0.9

9 R100SF1 33.3 18.9 5.8 1.7

10 R100SF2 34.7 25.3 6.7 2.4

(a)

Figure 40: Constitutive laws of plain concrete: (a) compressive hardening law; (b)

compressive softening law; (c) tensile softening law (Alkhalil and El-Maaddawy,

2017; Awani et al., 2016)

100

(b)

(c)

Figure 40: Constitutive laws of plain concrete: (a) compressive hardening law; (b)

compressive softening law; (c) tensile softening law (Alkhalil and El-Maaddawy,

2017; Awani et al., 2016) (continued)

5.4.2 Reinforcing steel

The finite element modeling of steel reinforcement is much simpler than

concrete modeling, where the steel reinforcing was connected between nodes. Steel

reinforcement was modeled as one-dimensional discrete reinforcement embedded into

the concrete beam. All reinforcing steel bars were assumed to have a bilinear stress-

strain relation modeled using the (CCReinforcement) material model, as shown in

Figure 41(a). The yield strength and modulus of elasticity were assumed to be 550

101

MPa and 200 GPa, respectively, for longitudinal and shear reinforcement. Figure 41(b)

presents a typical arrangement of steel reinforcement in the FE models.

5.4.3 Steel Plates

In the finite element models, steel plates have been added at the locations of

the support and load to prevent stress concentration problems. The steel plates were

modeled using the (CC3DElastIsotropic) material model with an elastic modulus

equal to 200 GPa and a Poisson ratio of 0.3.

(a)

(b)

Figure 41: Steel reinforcing bars (a) Stress-strain relationship and (b) Arrangement of

steel reinforcement in the FE models

5.4.4 Steel Fiber-Reinforced Geopolymer Concrete

To account for the presence of steel fibers on the material constitutive laws,

CC3DNonLinCementit2User has been used. Figure 42 shows a typical compressive

stress-strain of concrete adapted in this study. By testing concrete prisms under four-

point bending and applying an inverse FE analysis, the tensile function of SF

reinforced concretes was developed. The tension function (tensile softening) is needed

102

for modeling the response and post-cracking behavior of steel fiber-reinforced

geopolymer concrete beams. To establish a tension function by an inverse analysis, the

load-deflection responses of the tested four-point bending prisms, shown in Chapter 4,

were utilized. Then, ATENA software was used to perform numerical analysis on the

prism through the 3D FE model, as shown in Figure 43. In ATENA, the

CC3DNonLinCementit2User model allows users to define the tensile properties and

softening behavior of concrete with steel fibers. Specific tensile parameters were set

in the prism model as an initial procedure for inverse analysis. The numerically

predicted load-deflection response was then compared to the load-deflection response

obtained from the four-point bending test results of Chapter 4. The input tensile

function was adjusted with many iterations until the load-deflection attained from the

tension function was similar to that of the experimental test. Figures 44-49 show the

numerical and experimental load-deflection curves of the prisms having SF-reinforced

geopolymer concrete mixes with the corresponding tension function.

Figure 42: Typical compression stress-strain constitutive law of

CC3DNonLinCementit2User

0

0.2

0.4

0.6

0.8

1

1.2

0 0.002 0.004 0.006 0.008

Norm

aliz

ed S

tres

s, f

/f' c

Strain

103

Figure 43: Concrete prism model used for inverse analysis

(a)

(b)

Figure 44: Inverse analysis results of R30SF1: (a) experimental and predicted load-

deflection curves and (b) corresponding tension function

0

3

6

9

12

15

0 1 2 3 4 5

Load

(kN

)

Deflection (mm)

Exp. R30SF1

Pred. R30SF1

0

0.2

0.4

0.6

0.8

1

1.2

0 0.05 0.1 0.15

No

rmal

ized

Str

ess,

f/

f t

Strain

104

(a)

(b)



0

3

6

9

12

15

0 1 2 3 4 5

Load

(kN

)

Deflection (mm)

Exp. R30SF2Pred. R30SF2

0

0.2

0.4

0.6

0.8

1

1.2

0 0.1 0.2 0.3 0.4 0.5 0.6

Norm

aliz

ed S

tres

s,

f/f t

Strain

105

(a)

(b)



0

3

6

9

12

15

0 1 2 3 4 5

Load

(kN

)

Deflection (mm)


0

0.2

0.4

0.6

0.8

1

1.2

0 0.1 0.2 0.3 0.4 0.5 0.6

Norm

aliz

ed S

tres

s,

f/f t

Strain

106

(a)

(b)



0

3

6

9

12

15

0 1 2 3 4 5

Load

(kN

)

Deflection (mm)


0

0.2

0.4

0.6

0.8

1

1.2

0 0.1 0.2 0.3 0.4 0.5 0.6

Norm

aliz

ed S

tres

s, f/

f t

Strain

107

(a)

(b)



0

3

6

9

12

15

0 1 2 3 4 5

Load

(kN

)

Deflection (mm)


0

0.2

0.4

0.6

0.8

1

1.2

0 0.05 0.1 0.15

Norm

aliz

ed S

tres

s,

f/f t

Strain

108

(a)

(b)



5.5 Results and discussion

5.5.1 Load-deflection curves

The effect of RCA percentage on the the load-deflection relationships of the

25 mm mesh models is examined through comparing mixes with the same SF

percentages, as illustrated in Figure 50. Conversely, the impact of SF volume fraction

on the load-deflection relationships is evaluated by comparing mixes with the same

RCA replacement, as depicted in Figure 51. The numerical load-deflection curves

shown in these figures are stopped shortly after reaching the ultimate load.

0

3

6

9

12

15

0 1 2 3 4 5

Load

(kN

)

Deflection (mm)

Exp. R100SF2

Pred. R100SF2

0

0.2

0.4

0.6

0.8

1

1.2

0 0.05 0.1 0.15

Norm

aliz

ed S

tres

s,

f/f t

Strain

109

Figure 50(a) shows that concrete beam models made without SF exhibited a

load decay at the onset of crack initiation. After cracking, the deflection increased at a

higher rate. It is apparent that the increase in replacement percentage of RCA resulted

in a significant decrease in the slope. In fact, the replacement of 30, 70, and 100%

RCA resulted in a 9, 19, and 30% reduction in slope, owing to a lower modulus of

elasticity, as noted in the results of Chapter 4. Figures 50(b-c) present the load-

deflection curves of GGBS-fly ash geopolymer concrete made with SF and RCA.

Similar to plain concrete counterparts, higher RCA replacement led to a decrease in

slope. Yet, in these concrete mixes, a slight change in slope occurred at deflections

between 1-2 mm and 2-3 mm for 1 and 2% steel fiber volume fractions, respectively.

Such a phenomenon is associated with the improved integrity of the geopolymer

concrete due to steel fiber incorporation, leading to a reduction in crack development

and propagation.

(a)

Figure 50: Load-deflection response of concrete models with SF (a) 0%, (b) 1%, (c)

SF 2%

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7

Load

(kN

)

Deflection (mm)

R0SF0

R30SF0

R70SF0

R100SF0

110

(b)

(c)

Figure 50: Load-deflection response of concrete models with SF (a) 0%, (b) 1%, (c)

SF 2% (continued)

The impact of steel fiber addition on the load-deflection curves was

investigated in Figure 51. Regardless of the RCA replacement percentage, the

incorporation of steel fibers led to an increase in the slope. In addition, it resulted in

an increase in peak deflection. This is especially apparent in mixes made with 70 and

100% RCA. Such findings were associated with the higher modulus of elasticity of

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7

Load

(kN

)

Deflection (mm)

R30SF1

R70SF1

R100SF1

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7

Load

(kN

)

Deflection (mm)

R30SF2

R70SF2

R100SF2

111

SF-reinforced mixes while previous studies noted a delayed crack formation due to the

bond between the matrix and steel fiber (Bencardino et al., 2013; Yoo et al., 2015).

Even after these cracks formed, steel fibers bridged them and delayed their further

propagation. It could be thus concluded that although RCA had a negative effect on

the shear performance of GGBS-fly ash blended geopolymer concrete, its impact could

be countered by SF addition.

(a)

Figure 51: Load-deflection response of concrete models with RCA (a) 30%, (b) 70%,

and (c) 100%

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7

Load

(kN

)

Deflection (mm)

R30SF0

R30SF1

R30SF2

112

(b)

(c)

Figure 51: load-deflection response of concrete models with RCA (a) 30%, (b) 70%,

and (c) 100% (continued)

5.5.2 Crack Patterns and Failure Modes

At every applied load step, the ATENA program records a crack pattern. The

developed crack patterns, minimum and maximum principal strains recorded

numerically by ATENA at the peak load for the test models are illustrated in Figures

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7

Lo

ad (

kN

)

Deflection (mm)

R70SF0

R70SF1

R70SF2

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7

Load

(kN

)

Deflection (mm)

R100SF0R100SF1R100SF2

113

52-61. The minimum width of the displayed crack in FE models was set to be 0.1 mm.

Concrete beams without steel fibers experienced either one single diagonal shear crack

within the shear span connecting the support and load points or a diagonal shear crack

connected to a longitudinal crack along the tensile steel reinforcing bars. The concrete

beams without steel fibers eventually failed in a diagonal tension or shear tension mode

of failure. Apparently, the addition of steel fibers restricted the growth of shear cracks

and delayed the shear failure. Similar findings were reported in the modeling of

cement-based conventional concrete incorporating steel fibers and RCA (Kachouh et

al., 2020b). Furthermore, concrete beams with steel fibers exhibited a shear-tension

mode of failure, which included a shear crack in the vicinity of the load point with an

angle of inclination of 45 to 60o connected to a longitudinal crack running parallel to

the tensile steel reinforcing bars. This shear-tension mode of failure usually occurs in

concrete beams without stirrup, as the absence of stirrups’ confinement promotes

development of horizontal cracking along the tension reinforcement.

114

(a)

(b)

(c)

Figure 52: R0SF0 FE models: (a) crack patterns, (b) maximum principal strains, and

(c) minimum principal strains

115

(a)

(b)

(c)

Figure 53: R30SF0 FE models: (a) crack patterns, (b) maximum principal strains,

and (c) minimum principal strains

116

(a)

(b)

(c)



117

(a)

(b)

(c)



118

(a)

(b)

(c)



119

(a)

(b)

(c)



120

(a)

(b)

(c)



121

(a)

(b)

(c)



122

(a)

(b)

(c)



123

(a)

(b)

(c)



5.5.3 Peak Load

The numerical finite element model was applied to evaluate the shear behavior

of the SF-reinforced RCA geopolymer concrete beams. The peak loads of such beams

are compared in Figure 62. The replacement of NA by 30, 70, and 100% RCA led to

124

8, 32, and 33% respective decreases in the peak load. This is aligned with other

mechanical properties and owed to the generally weaker and more porous nature of

the RCA, as explained in Chapter 4. Nevertheless, this adverse impact could be

countered by the addition of steel fibers. Results showed that the peak load increased

with the incorporation of steel fibers. In fact, the addition of 1 and 2% steel fibers, by

volume, to RCA geopolymer mixes increased the peak load, on average, by 34 and

65%, respectively. Based on these findings, it can be concluded GGBS-fly ash blended

geopolymer concrete could be made with 100% RCA without compromising shear

behavior, subject that 2% steel fibers, by volume, be incorporated into the mix.

Figure 62: Peak loads of geopolymer concrete beams

The experimental shear resistance results were correlated to those of the 28-

day cylinder compressive strength (f’c in MPa) and steel fiber volume fraction (vf in

%) to introduce an empirical equation to predict the nominal shear resistance (Vn in N)

of GGBS-fly blended geopolymer concrete beams. As such, an analytical relationship

was developed using multivariable linear regression in the form of Equation 18, where

0

20

40

60

80

100

120

30 70 100

Pea

k L

oad

(kN

)

RCA Replacement (%)

SF0

SF1

SF2Control = 80.2 kN

125

b and d are the width and effective depth of the beam, respectively. The feasibility of

utilizing this newly-proposed equation in predicting the nominal shear resistance is

investigated through Figure 63. It can be seen that the scatter plot mainly converges

around the 45°-line, indicating a good accuracy of Equation 18. In fact, the error

between the experimental and predicted values did not exceed 8%.

Vn = 0.366bd√fc

' + 2.41vf

(18)

Figure 63: Predicted versus experimental shear resistance

0

20

40

60

80

0 20 40 60 80

Pre

dic

ted S

hea

r R

esis

tance

(kN

)

Experimental Shear Resistance (kN)

126

Chapter 6: Conclusions

6.1 Introduction

The main aim of this study is to investigate the feasibility of reutilizing locally

available industrial solid wastes and RCA in geopolymer concrete for structural

applications. A combination of ground granulated blast furnace slag (GGBS) and fly

ash were used to form a blended precursor binding material. To advance the use of

RCA in structural geopolymer concrete, steel fiber reinforcement was incorporated at

different volume fractions. This proposed geopolymer concrete promises to offer an

innovative and sustainable solution to ever-increasing global environmental issues,

including the consumption of non-renewable natural resources, emission of carbon

dioxide, and production of industrial waste materials.

The research work comprised experimental testing to study the effect of steel

fibers and RCA on the performance of GGBS-FA blended geopolymer concrete. The

experimental program involved the testing of ten geopolymer concrete mixes made

with different RCA replacement percentages (0, 30, 70, and 100%) and SF volume

fractions (0, 1, and 2%). The mechanical and durability properties under investigation

included compressive and splitting tensile strength, flexural performance, modulus of

elasticity, absorption, sorptivity, abrasion resistance, and bulk resistivity. Additionally,

numerical models that characterize the shear behavior of GGBS-FA blended

geopolymer concrete made with different proportions of RCA and steel fibers were

developed. The FE models accounted for the nonlinear behavior of concrete in tension

and compression adopting realistic materials laws. It analyzed the failure modes, crack

patterns, load-deflection response, and failure ultimate loads. The main findings of this

work and recommendations for future work are outlined in this chapter.

127

6.2 Limitations

The findings of this thesis are limited to the types of GGBS and fly ash

employed herein. The coarse and fine aggregates were dolomitic limestone and dune

sand. The alkaline activator solution was formulated from grade N sodium silicate and

14M sodium hydroxide. The steel fibers utilized were in the form of double hooked

end steel fibers with specific dimensions. Furthermore, the numerical results were

limited to the specific dimensions of the beams considered in the analysis. Variations

in the chemical compositions or physical properties of the mixture components or

beam dimensions may result in different outcomes than those presented in this work.

6.3 Conclusions

The following conclusions can be drawn based on the experimental testing and

numerical modeling result:

• The cube compressive strength at the ages of 1, 7, and 28 days were reduced

by up to 37, 14, and 20%, respectively, upon RCA replacement, compared to

the control mix. Yet, this loss of cube compressive strength could be countered

by adding steel fibers. In fact, the addition of up to 2% steel fibers, by volume,

increased the 1-, 7-, and 28-day cube compressive strength by as much as 67,

28, and 24% in comparison to the plain counterparts. This signifies the superior

impact of steel fibers at the age of 1 day. As such, it was possible to produce a

GGBS-FA blended geopolymer concrete made with 100% RCA and at least

1% steel fiber, by volume, while sustaining a limited loss (<6%) in cube

compressive strength.

• The 28-day cylinder compressive strength presented similar results as that of

the 28-day cube strength. A linear regression model correlating these two

128

properties was developed. With a correlation coefficient, R2, of 0.90, it was

deemed possible to predict one of these properties from the other with

reasonable accuracy.

• The compressive stress-strain curves noted a decrease in peak stress and an

increase in peak strain due to RCA replacement. Conversely, the addition of

steel fibers increased the peak stress and peak strain, leading to enhanced

deformability due to the bridging effect of steel fibers. The slope of the curves,

i.e. modulus of elasticity, decreased with RCA replacement and increased with

steel fiber incorporation. Yet, the adverse impact of the former was more

prominent than the positive effect of the latter.

• Experimental test results of the splitting tensile strength of GGBS-FA blended

geopolymer concrete followed a similar trend to the 28-day cylinder

compressive strength. Indeed, the replacement of NA by RCA resulted in up to

47% decrease in fsp. On the other hand, the addition of steel fibers increased

the value of fsp by up to 230% compared to the plain counterpart. Using the

ratio of fsp-to-f’c, it was noted that the RCA replacement was more influential

on f’c, while steel fiber incorporation was more impactful on fsp. Results

showed that it is possible to replace NA by 100% RCA while adding at least

1% steel fiber, by volume, without compromising the splitting tensile strength

of GGBS-FA blended geopolymer concrete.

• The flexural performance of GGBS-FA blended geopolymer concrete was

characterized by peak strength, peak deflection, residual strength, toughness,

and equivalent flexural strength ratio. The increase in RCA replacement caused

decreases in the slope of the load-deflection curve, fr, and f150

100, increases in δp

and RT,150 100 , and insignificant change in T150

100. On the other hand, the addition of

129

steel fibers increased all the flexural characteristics. Yet, it should be noted that

the positive impact of steel fiber incorporation surpassed the negative influence

of RCA replacement. As such, RCA could be used as the sole aggregate in

GGBS-FA blended geopolymer concrete subject that 2% steel fiber volume

fraction is used.

• The 28-day cylinder compressive strength (f’c) of GGBS-FA blended

geopolymer concrete was correlated to several mechanical and durability

properties, including the modulus of elasticity, splitting tensile strength, and

flexure strength. With R2 > 0.90, all regression models were noted to present

good correlations among the properties. As such, it is possible to predict these

properties from f’c with reasonable accuracy. Conversely, codified equations

were less accurate in predicting these properties.

• The abrasion mass loss continuously increased over the first 300 revolutions

after which the curve tended to plateau. The RCA replacement led to higher

mass loss due to abrasion, owing to the weaker RCA and more porous nature

compared to NA. In turn, the addition of steel fibers reduced the abrasion mass

loss to the point that the value of the mix made with 100% RCA and 2% steel

fiber volume fraction was comparable to that of the NA-based control mix.

Also, it was noted that abrasion mass loss was inversely proportional to f’c. The

correlation model (R2 = 0.87) could be used to predict the former from the latter

with reasonable accuracy.

• The bulk resistivity of GGBS-FA blended geopolymer concrete varied between

2 and 4.6 kΩ.cm with lower values being associated with mixes made with

higher RCA replacement percentages. The bulk resistivity was aligned with the

28-day cylinder compressive strength and water absorption. As such,

130

correlation models were developed to predict the 28-day compressive strength

and water absorption from this non-destructive test with reasonable accuracy

(R2 > 0.98).

• The water absorption and sorptivity were proportional to the RCA replacement

with values increasing by up to 76 and 136%, respectively, compared to the

NA-based control mix, owing to the porous nature of the aggregates. Yet, the

absorption decreased with steel fiber addition, providing evidence to the

densification of the matrix and enhancement of the mechanical properties.

• Tensile softening relations for GGBS-fly ash blended geopolymer concrete

made with RCA and steel fibers were established based on inverse analyses of

the experimental four-point bending/flexure data. Without these relations, it is

not possible to simulate the behavior of such geopolymer concrete beams using

finite element analysis.

• Three-dimensional finite element models were developed and used to simulate

the nonlinear shear behavior of geopolymer concrete beams with different

RCA percentages and steel fiber volume fractions. The use of steel fibers

improved the deflection response and the peak loads of the modeled beams.

• Based on a multivariable linear regression analysis of the numerical shear

resistance of the modeled beams, an analytical relationship was established to

predict the nominal shear resistance of geopolymer concrete beams having

different cylinder compressive strengths and steel fiber volume fractions.

6.4 Recommendations for Future Studies

This research work investigated the feasibility of utilizing geopolymer concrete

as an alternative to ordinary cement concrete and can be considered a promising step

131

towards implementing geopolymer concrete in structural applications. However,

further research is recommended for future studies as follows:

• Investigate the effect of different steel fibers with various geometry, lengths,

and aspect ratios.

• Examine the effect of different contents and types of superplasticizers on the

workability of GGBS-FA blended geopolymer concrete made with RCA and

steel fibers.

• Study the resistance of GGBS-FA blended geopolymer concrete to elevated

temperatures, seawater exposure, and acid and sulfate attack.

• Evaluate the performance of GGBS-FA blended geopolymer concrete

incorporating other waste materials in ternary and quaternary mixes.

• Conduct laboratory testing to verify the results of the numerical models of the

geopolymer concrete beams developed in the current study.

• Perform a lifecycle assessment analysis to verify the feasibility of utilizing

GGBS-FA blended geopolymer concrete in structural applications.

132

References

ACI Committee 201.2, 2016. Guide to Durable Concrete. American Concrete Institute,

Farmington Hills, MI, p. 87.

ACI Committee 222R-01, 2001. Protection of Metals in Concrete Against Corrosion,

Corrosion. American Concrete Institute, Farmington Hills, Michigan, p. 41.

ACI Committee 318, 2014. Building Code Requirements for Structural Concrete and

Commentary. American Concrete Institute, Farmington Hills, Michigan.

Afkhami, B., Akbarian, B., Beheshti A, N., Kakaee, A.H., Shabani, B., 2015. Energy

consumption assessment in a cement production plant. Sustainable Energy

Technol and Assess 10, 84-89.

Akbarnezhad, A., Ong, K.C.G., Zhang, M.H., Tam, C.T., Foo, T.W.J., 2011.

Microwaveassisted beneficiation of recycled concrete aggregates. Constr Build

Mater 25(8), 3469-3479.

Al-Majidi, M.H., Lampropoulos, A., Cundy, A., Meikle, S., 2016. Development of

geopolymer mortar under ambient temperature for in situ applications. Constr

Build Mater 120, 198-211.

Al-Majidi, M.H., Lampropoulos, A., Cundy, A.B., 2017. Steel fibre reinforced

geopolymer concrete (SFRGC) with improved microstructure and enhanced

fibre-matrix interfacial properties. Constr Build Mater 139, 286-307.

Aleem, A., Arumairaj, P., 2012. Geopolymer concrete - A review. International

Journal of Engineering Sciences & Emerging Technologies 1, 118-122.

Alzard, M., El-Hassan, H., El Maaddawy, T., 2021. Life Cycle Inventory for the

Production of Recycled Concrete Aggregates in the United Arab Emirates.

International Journal of Civil Infrastructure 4, 78-84.

AS3600, 2009. Concrete Structures. Standards Australia, Australia, p. 198.

ASTM, 2011. Standard Test Method for Splitting Tensile Strength of Cylindrical

Concrete Specimens, C496. ASTM, West Conshohocken, PA.

ASTM, 2012. Standard Test Method for Electrical Indication of Concrete's Ability to

Resist Chloride Ion Penetration, C1202. ASTM International, West

Conshohocken, PA.

ASTM, 2013a. Standard Test Method for Density, Absorption, and Voids in Hardened

Concrete, C642. ASTM International, West Conshohocken, PA.

133

ASTM, 2013b. Standard Test Method for Determining Potential Resistance to

Degradation of Pervious Concrete by Impact and Abrasion, C1747. ASTM

International, West Conshohocken, PA.

ASTM, 2013c. Standard Test Method for Measurement of Rate of Absorption of Water

by Hydraulic-Cement Concretes,, C1585. ASTM International, West

Conshohocken, PA.

ASTM, 2014. Standard Test Method for Static Modulus of Elasticity and Poisson’s

Ratio of Concrete in Compression, C469. ASTM International, West

Conshohocken, PA.

ASTM, 2015. Standard Test Method for Compressive Strength of Cylindrical

Concrete Specimens, C39. ASTM, West Conshohocken, PA.

ASTM, 2016. Standard Specification for Concrete Aggregates, C33. ASTM

International, West Conshohocken, PA.

ASTM, 2019a. Standard Test Method for Bulk Electrical Resistivity or Bulk

Conductivity of Concrete, C1876. ASTM International, West Conshohocken,

PA.

ASTM, 2019b. Standard Test Method for Flexural Performance of Fiber-Reinforced

Concrete, C1609. ASTM International, West Conshohocken, PA.

Aydın, S., Baradan, B., 2014. Effect of activator type and content on properties of

alkali-activated slag mortars. Compos B Eng 57, 166-172.

Bekaert, 2012. Dramix 3D 65/35 Report. Bekaert, Belgium, p. 1.

Bellum, R.R., Muniraj, K., Madduru, S.R.C., 2020. Investigation on modulus of

elasticity of fly ash-ground granulated blast furnace slag blended geopolymer

concrete. Materials Today: Proceedings 27, 718-723.

Bencardino, F., Rizzuti, L., Spadea, G., Swamy, R.N., 2013. Implications of test

methodology on post-cracking and fracture behaviour of Steel Fibre

Reinforced Concrete. Compos B Eng 46, 31-38.

Benhelal, E., Zahedi, G., Shamsaei, E., Bahadori, A., 2013. Global strategies and

potentials to curb CO2 emissions in cement industry. J Clean Prod 51, 142-

161.

Bernal, S., De Gutierrez, R., Delvasto, S., Rodriguez, E., 2010. Performance of an

alkali-activated slag concrete reinforced with steel fibers. Constr Build Mater

24(2), 208-214.

British Standard, 2009. Testing hardened concrete - Compressive strength of test

specimens, BS EN 12390-3. British Standard, London, UK.

134

Chang, E.H., 2009. Shear and Bond Behaviour of Reinforced Fly Ash-Based

Geopolymer Concrete Beams Department of Civil Engineering. Curtin

University of Technology, Australia, p. 409.

Chi, M., 2012. Effects of dosage of alkali-activated solution and curing conditions on

the properties and durability of alkali-activated slag concrete. Constr Build

Mater 35(Supplement C), 240-245.

Comité euro-international du béton, Federation International de la Precontrainte, 1993.

CEB-FIP Model Code 1990: Design Code. T. Telford.

Davidovits, J., 1991. Geopolymers: inorganic polymeric new materials. Journal of

Thermal Analysis 37, 1633-1656.

Davidovits, J., 1994. High-Alkali Cements for 21st Century Concretes. Special

Publication 144, 383-398

Davidovits, J., 2008. Geopolymer Chemistry and Applications. Institut Géopolymère,

France.

Deb, P.S., Nath, P., Sarker, P.K., 2014. The effects of ground granulated blast-furnace

slag blending with fly ash and activator content on the workability and strength

properties of geopolymer concrete cured at ambient temperature. Materials &

Design (1980-2015) 62, 32-39.

Devika, C.P., Nath, D.R., 2015. Study of Flexural Behavior of Hybrid Fibre

Reinforced Geopolymer Concrete Beam. International Journal of Science and

Research 4(8), 130-135.

Earth System Research Laboratory, 2013. Trends in Atmospheric Carbon Dioxide.

El-Hassan, H., Elkholy, S., 2019. Performance Evaluation and Microstructure

Characterization of Steel Fiber-Reinforced Alkali-Activated Slag Concrete

Incorporating Fly Ash. J Mater Civ Eng 31(10), 04019223.

El-Hassan, H., Ismail, N., 2018. Effect of process parameters on the performance of

fly ash/GGBS blended geopolymer composites. J Sustain Cem Mater 7(2),

122-140.

El-Hassan, H., Ismail, N., Al Hinaii, S., Alshehhi, A., Al Ashkar, N., 2017. Effect of

GGBS and curing temperature on microstructure characteristics of lightweight

geopolymer concrete. MATEC Web Conf. 120, 03004.

El-Hassan, H., Shehab, E., Al-Sallamin, A., 2018. Influence of Different Curing

Regimes on the Performance and Microstructure of Alkali-Activated Slag

Concrete. J Mater Civ Eng 30(9), 04018230.

135

El-Hassan, H., Shehab, E., Al-Sallamin, A., 2021. Effect of Curing Regime on the

Performance and Microstructure Characteristics of Alkali-Activated Slag-Fly

Ash Blended Concrete. Journal of Sustainable Cement-Based Materials, 1-29.

Elkholy, S., El-Hassan, H., 2019. Mechanical and micro-structure characterization of

steel fiber-reinforced geopolymer concrete, in: Ozevin, D., Ataei, H., Modares,

M., Gurgun, A., Yazdani, S., Singh, A. (Eds.), Interdependence between

Structural Engineering and Construction Management. ISEC Press, Chicago,

IL.

Environmental Resources Limited, 1980. Demolition Waste. Construction Press

Limited, Lancaster (England).

Fernández-Jiménez, A., Puertas, F., 2003. Effect of activator mix on the hydration and

strength behaviour of alkali-activated slag cements. Adv Cem Res 15(3), 129-

136.

Gao, D., Jing, J., Chen, G., Yang, L., 2019. Experimental investigation on flexural

behavior of hybrid fibers reinforced recycled brick aggregates concrete. Constr

Build Mater 227, 116652.

Gao, D., Zhang, L., 2018. Flexural performance and evaluation method of steel fiber

reinforced recycled coarse aggregate concrete. Constr Build Mater 159, 126-

136.

Garanayak, L., 2020. Behavior of alkali activated fly ash slag paste at room

temperature. Materials Today: Proceedings, 43, 1865-1873

Gülşan, M.E., Alzeebaree, R., Rasheed, A.A., Niş, A., Kurtoğlu, A.E., 2019.

Development of fly ash/slag based self-compacting geopolymer concrete using

nano-silica and steel fiber. Constr Build Mater 211, 271-283.

Guo, X., Pan, X., 2018. Mechanical properties and mechanisms of fiber reinforced fly

ash–steel slag based geopolymer mortar. Constr Build Mater 179, 633-641.

Guo, X., Xiong, G., 2021. Resistance of fiber-reinforced fly ash-steel slag based

geopolymer mortar to sulfate attack and drying-wetting cycles. Constr Build

Mater 269, 121326.

Hansen, T.C., Boegh, E., 1985. Elasticity and drying shrinkage concrete of recycled-

aggregate. ACI Journal 82(56), 648-652.

Herzog, H., Eliasson, B., Kaarstad, O., 2000. Capturing greenhouse gases. Scientific

American, 282(2), 72-79.

136

Hu, Y., Tang, Z., Li, W., Li, Y., Tam, V.W.Y., 2019. Physical-mechanical properties

of fly ash/GGBFS geopolymer composites with recycled aggregates. Constr


Ikea, T., Yamane, S., Sakamoto, A., 1988. Strength of concrete containing recycled

aggregate concrete, 2nd RILEM Symp. on Demolition and Reuse of Waste.

RILEM Publications, Bagneux, France.

Islam, A., Alengaram, U.J., Jumaat, M.Z., Ghazali, N.B., Yusoff, S., Bashar, I.I., 2017.

Influence of steel fibers on the mechanical properties and impact resistance of

lightweight geopolymer concrete. Constr Build Mater 152(Supplement C),

964-977.

Ismail, I., Bernal, S.A., Provis, J.L., San Nicolas, R., Hamdan, S., van Deventer, J.S.J.,

2014. Modification of phase evolution in alkali-activated blast furnace slag by

the incorporation of fly ash. Cem Concr Compos 45, 125-135.

Ismail, N., El-Hassan, H., 2018. Development and Characterization of Fly Ash/Slag-

Blended Geopolymer Mortar and Lightweight Concrete. J Mater Civ Eng

30(4), 04018029.

Ismail, N., Mansour, M., El-Hassan, H., 2017. Development of a low-cost cement free

polymer concrete using industrial by-products and dune sand. MATEC Web

Conf. 120, 03005.

Jiang, M., Chen, X., Rajabipour, F., Hendrickson, C.T., 2014. Comparative Life Cycle

Assessment of Conventional, Glass Powder, and Alkali-Activated Slag

Concrete and Mortar. J Infrastruct Syst 20(4), 04014020.

Kachouh, N., El-Hassan, H., El-Maaddawy, T., 2019a. Effect of steel fibers on the

performance of concrete made with recycled concrete aggregates and dune

sand. Constr Build Mater 213, 348-359.

Kachouh, N., El-Hassan, H., El-Maaddawy, T., 2020a. Influence of steel fibers on the

flexural performance of concrete incorporating recycled concrete aggregates

and dune sand. J Sustain Cem Mater, 1-28.

Kachouh, N., El-Hassan, H., El Maaddawy, T., 2019b. The Use of Steel Fibers to

Enhance the Performance of Concrete Made With Recycled Aggregate, in:

Claisse, P. (Ed.) Fifth International Conference on Sustainable Construction

Materials and Technologies (SCMT5). London, UK.

Kachouh, N., El Maaddawy, T., El-Hassan, H., 2020b. Numerical Modelling of Steel

Fiber Recycled Aggregate Concrete Deep Beams, 5th World Congress on

Civil, Structural, and Environmental Engineering (CSEE'20). Avestia, Virtual

Conference.

137

Kanesan, D., Ridha, S., Suppiah, R., Ravichandran, T., 2017. Mechanical properties

of different alkali activated slag content for oilwell cement under elevated

conditions. Contemporary Engineering Sciences 10(4), 165-177.

Kathirvel, P., Kaliyaperumal, S.R.M., 2016. Influence of recycled concrete aggregates

on the flexural properties of reinforced alkali activated slag concrete. Constr

Build Mater 102(Part 1), 51-58.

Khan, M.Z.N., Hao, Y., Hao, H., Shaikh, F.U.A., 2018. Mechanical properties of

ambient cured high strength hybrid steel and synthetic fibers reinforced

geopolymer composites. Cem Concr Compos 85, 133-152.

Kline, J., Kline, C., 2015. Cement and CO2: What is Happening. IEEE Transactions

on Industry Applications 51(2), 1289-1294.

Kong, D., Lei, T., Ma, C., Jiang, J., 2010. Effect and mechanism of surface-coating

pozzolanic materials around aggregate on properties and ITZ microstructure of

recycled aggregate concrete. Constr Build Mater 24(5), 701-708.

Lau, C.K., Rowles, M.R., Parnham, G.N., Htut, T., Ng, T.S., 2019. Investigation of

geopolymers containing fly ash and ground-granulated blast-furnace slag

blended by amorphous ratios. Constr Build Mater 222, 731-737.

Lee, W.-H., Wang, J.-H., Ding, Y.-C., Cheng, T.-W., 2019. A study on the

characteristics and microstructures of GGBS/FA based geopolymer paste and

concrete. Constr Build Mater 211, 807-813.

Li, C., Sun, H., Li, L., 2010. A review: The comparison between alkali-activated slag

(Si+Ca) and metakaolin (Si+Al) cements. Cem Concr Res 40(9), 1341-1349.

Liu, Y., Shi, C., Zhang, Z., Li, N., Shi, D., 2020. Mechanical and fracture properties

of ultra-high performance geopolymer concrete: Effects of steel fiber and silica

fume. Cem Concr Compos 112, 103665.

Martys, N.S., Ferraris, C.F., 1997. Capillary transport in mortars and concrete. Cem

Concr Res 27(5), 747-760.

Mehta, A., Siddique, R., Ozbakkaloglu, T., Uddin Ahmed Shaikh, F., Belarbi, R.,

2020. Fly ash and ground granulated blast furnace slag-based alkali-activated

concrete: Mechanical, transport and microstructural properties. Constr Build

Mater 257, 119548.

Mehta, P.K., and Monteiro, J. P., 2006. Concrete Microstructure, Properties and

Material. McGraw Hill, New York.

138

Mesgari, S., Akbarnezhad, A., Xiao, J.Z., 2020. Recycled geopolymer aggregates as

coarse aggregates for Portland cement concrete and geopolymer concrete:

Effects on mechanical properties. Constr Build Mater 236, 117571.

Mo, K.H., Yeoh, K.H., Bashar, I.I., Alengaram, U.J., Jumaat, M.Z., 2017. Shear

behaviour and mechanical properties of steel fibre-reinforced cement-based

and geopolymer oil palm shell lightweight aggregate concrete. Constr Build

Mater 148, 369-375.

Montes, C., Zang, D., Allouche, E.N., 2012. Rheological behavior of fly ash-based

geopolymers with the addition of superplasticizers. J Sustain Cem Mater 1(4),

179-185.

Nath, P., Sarker, P.K., 2014. Effect of GGBFS on setting, workability and early

strength properties of fly ash geopolymer concrete cured in ambient condition.

Constr Build Mater 66, 163-171.

Neville, A.M., 1996. Properties of Concrete. Wiley, New York.

Ng, T.S., Amin, A., Foster, S.J., 2013. The behaviour of steel-fibre-reinforced

geopolymer concrete beams in shear. Mag Concr Res 65(5), 308-318.

Nuaklong, P., Sata, V., Chindaprasirt, P., 2016. Influence of recycled aggregate on fly

ash geopolymer concrete properties. J Clean Prod 112(Part 4), 2300-2307.

Palacios, M., Puertas, F., 2005. Effect of superplasticizer and shrinkage-reducing

admixtures on alkali-activated slag pastes and mortars. Cem Concr Res 35(7),

1358-1367.

Palomo, A., Grutzeck, M.W., Blanco, M.T., 1999. Alkali-activated fly ashes: A

cement for the future. Cem Concr Res 29(8), 1323-1329.

Parthiban, K., Saravana Raja Mohan, K., 2017. Influence of recycled concrete

aggregates on the engineering and durability properties of alkali activated slag

concrete. Constr Build Mater 133(Supplement C), 65-72.

Patankar, S.V., Ghugal, Y.M., Jamkar, S.S., 2014. Effect of Concentration of Sodium

Hydroxide and Degree of Heat Curing on Fly Ash-Based Geopolymer Mortar.

Indian Journal of Materials Science 2014, 6.

Poon, C., Chan, D., 2007. The use of recycled aggregate in concrete in Hong Kong.

Resour Conserv Recycl 50(3), 293-305.

Prusty, J.K., Pradhan, B., 2020a. Effect of GGBS and chloride on compressive strength

and corrosion performance of steel in fly ash-GGBS based geopolymer

concrete. Materials Today: Proceedings 32, 850-855.

139

Prusty, J.K., Pradhan, B., 2020b. Multi-response optimization using Taguchi-Grey

relational analysis for composition of fly ash-ground granulated blast furnace

slag based geopolymer concrete. Constr Build Mater 241, 118049.

Puertas, F., Martiez-Ramirez, S., Alonso, S., Vazquez, T., 2000. Alkali-activated fly

ash/slag cement strength behaviour and hydration products. Cem Concr Res

30, 1625-1632.

Rafeet, A., Vinai, R., Soutsos, M., Sha, W., 2019. Effects of slag substitution on

physical and mechanical properties of fly ash-based alkali activated binders

(AABs). Cem Concr Res 122, 118-135.

Ramadoss, P., Nagamani, K., 2008. Tensile strength and durability characteristics of

high-performance fiber reinforced concrete. Arab J Sci Eng 41(17), 307-319.

Reddy, M.S., Dinakar, P., Rao, B.H., 2018. Mix design development of fly ash and

ground granulated blast furnace slag based geopolymer concrete. J Build Eng

20, 712-722.

Salesa, Á., Pérez-Benedicto, J.A., Colorado-Aranguren, D., López-Julián, P.L.,

Esteban, L.M., Sanz-Baldúz, L.J., Sáez-Hostaled, J.L., Ramis, J., Olivares, D.,

2017. Physico – mechanical properties of multi – recycled concrete from

precast concrete industry. J Clean Prod 141, 248-255.

Samantasinghar, S., Singh, S., 2020. Effects of curing environment on strength and

microstructure of alkali-activated fly ash-slag binder. Constr Build Mater 235,

117481.

Şanal, İ., 2018. Performance of Macrosynthetic and Steel Fiber–Reinforced Concretes

Emphasizing Mineral Admixture Addition. J Mater Civ Eng 30(6), 04018101.

Sani, N.A.M., Man, Z., Shamsuddin, R.M., Azizli, K.A., Shaari, K.Z.K., 2016.

Determination of Excess Sodium Hydroxide in Geopolymer by Volumetric

Analysis. Procedia Engineering 148, 298-301.

Shaikh, F.U.A., 2016. Mechanical and durability properties of fly ash geopolymer

concrete containing recycled coarse aggregates. International Journal of

Sustainable Built Environment 5(2), 277-287.

Shaikh, F.U.A., Hosan, A., 2016. Mechanical properties of steel fibre reinforced

geopolymer concretes at elevated temperatures. Constr Build Mater 114, 15-

28.

Shang, J., Dai, J.-G., Zhao, T.-J., Guo, S.-Y., Zhang, P., Mu, B., 2018. Alternation of

traditional cement mortars using fly ash-based geopolymer mortars modified

by slag. J Clean Prod 203, 746-756.

140

Shi, X.S., Collins, F.G., Zhao, X.L., Wang, Q.Y., 2012. Mechanical properties and

microstructure analysis of fly ash geopolymeric recycled concrete. J Hazard

Mater 237–238, 20-29.

Shi, X.S., Wang, Q.Y., Zhao, X.L., Collins, F., 2012. Discussion on Properties and

Microstructure of Geopolymer Concrete Containing Fly Ash and Recycled

Aggregate. Advanced Materials Research 450-451, 1577-1583.

Sofi, M., van Deventer, J.S.J., Mendis, P.A., Lukey, G.C., 2007. Engineering

properties of inorganic polymer concretes (IPCs). Cem Concr Res 37(2), 251-

257.

Statistica, 2021. Major countries in worldwide cement production from 2015 to 2019.

2021).

Stoner, J., Wankel, C., 2008. Global Sustainability Initiatives: New Models and New

Approaches. Information Age Publishing, USA.

Tamrakar, N., 2012. The Effect of Steel Fibers Type and Content on the Development

of Fresh and Hardened Properties and Durability of Self-consolidating

Concrete, Civil Engineering. Ryerson University, Toronto, ON, p. 144.

Tang, Z., Hu, Y., Tam, V.W.Y., Li, W., 2019. Uniaxial compressive behaviors of fly

ash/slag-based geopolymeric concrete with recycled aggregates. Cem Concr

Compos 104, 103375.

Temuujin, J., Williams, R.P., van Riessen, A., 2009. Effect of mechanical activation

of fly ash on the properties of geopolymer cured at ambient temperature. J

Mater Process Technol 209(12), 5276-5280.

Thakur, R.N., Wu, Z., 2000. Development of High-Performance Blended Cements,

College of Engineering and Applied Science. The University of Wisconsin,

USA.

Their, J.M., Özakça, M., 2018. Developing geopolymer concrete by using cold-bonded

fly ash aggregate, nano-silica, and steel fiber. Constr Build Mater 180, 12-22.

US Geological Survey, 2016. Minerals commodity summary - cement. (Accessed

October 6 2016).

Visintin, P., Mohamed Ali, M.S., Albitar, M., Lucas, W., 2017. Shear behaviour of

geopolymer concrete beams without stirrups. Constr Build Mater 148, 10-21.

Wu, H., Huang, B., Shu, X., Dong, Q., 2011. Laboratory Evaluation of Abrasion

Resistance of Portland Cement Pervious Concrete. J Mater Civ Eng 23(5), 697-

702.

141

Xie, J., Chen, W., Wang, J., Fang, C., Zhang, B., Liu, F., 2019a. Coupling effects of

recycled aggregate and GGBS/metakaolin on physicochemical properties of

geopolymer concrete. Constr Build Mater 226, 345-359.

Xie, J., Wang, J., Rao, R., Wang, C., Fang, C., 2019b. Effects of combined usage of

GGBS and fly ash on workability and mechanical properties of alkali activated

geopolymer concrete with recycled aggregate. Compos B Eng 164, 179-190.

Xie, J., Wang, J., Zhang, B., Fang, C., Li, L., 2019c. Physicochemical properties of

alkali activated GGBS and fly ash geopolymeric recycled concrete. Constr


Yacob, N.S., ElGawady, M.A., Sneed, L.H., Said, A., 2019. Shear strength of fly ash-

based geopolymer reinforced concrete beams. Engineering Structures 196,

109298.

Yazdi, M.A., Liebscher, M., Hempel, S., Yang, J., Mechtcherine, V., 2018. Correlation

of microstructural and mechanical properties of geopolymers produced from

fly ash and slag at room temperature. Constr Build Mater 191, 330-341.

Yip, C.K., Lukey, G.C., van Deventer, J.S.J., 2005. The coexistence of geopolymeric

gel and calcium silicate hydrate at the early stage of alkaline activation. Cem

Concr Res 35(9), 1688-1697.

Yoo, D.-Y., Yoon, Y.-S., Banthia, N., 2015. Flexural response of steel-fiber-reinforced

concrete beams: Effects of strength, fiber content, and strain-rate. Cem Concr

Compos 64, 84-92.

Zhang, J., Shi, C., Li, Y., Pan, X., Poon, C.S., Xie, Z., 2015. Performance

Enhancement of Recycled Concrete Aggregates through Carbonation. J Mater

Civ Eng 27(11).

142

Appendix

Table A1. Mixture proportions of trial mixes

Mix #

Component (kg/m3) Total

(kg/m3) GGBS FA SS SH RCA NA DS SP SF

1 250 250 179 71 0 1000 650 10 0 2410

2 250 250 179 71 0 1000 650 10 156 2566

3 250 250 179 71 1000 0 650 10 0 2410

4 250 250 179 71 1000 0 650 10 156 2566

5 225 225 161 64 0 1100 600 9 0 2384

6 225 225 161 64 0 1100 600 9 156 2540

7 225 225 161 64 1100 0 600 9 0 2384

8 225 225 161 64 1100 0 600 9 156 2540

9 200 200 132 88 0 1160 675 8 0 2463

10 200 200 132 88 1160 0 675 8 0 2463

11 200 200 132 88 1160 0 675 8 156 2619

12 180 180 119 80 0 1180 675 7 0 2422

13 180 180 119 80 1180 0 675 7 0 2422

14 180 180 119 80 1180 0 675 7 156 2577

15 180 180 130 86 0 1160 695 7 0 2438

16 180 180 130 86 1160 0 695 7 156 2594

17 160 160 115 77 0 1180 708 6 0 2406

18 160 160 115 77 1180 0 708 6 156 2562

19 150 150 108 72 0 1180 740 6 0 2406

20 150 150 108 72 1180 0 740 6 156 2562

21 125 125 90 60 0 1210 910 5 0 2405

22 125 125 90 60 1210 0 910 5 156 2561

143

Table A2. Mixture ratios of trial mixes

Mix #

Ratios

SF (%) FA/GGBS AAS/B SS/SH CA/DS RCA/DS Agg/B SP/B (%)

1 1.00 0.50 2.52 1.54 0.00 3.30 2.00 0.00

2 1.00 0.50 2.52 1.54 0.00 3.30 2.00 2.00

3 1.00 0.50 2.52 0.00 1.54 3.30 2.00 0.00

4 1.00 0.50 2.52 0.00 1.54 3.30 2.00 2.00

5 1.00 0.50 2.52 1.83 0.00 3.78 2.00 0.00

6 1.00 0.50 2.52 1.83 0.00 3.78 2.00 2.00

7 1.00 0.50 2.52 0.00 1.83 3.78 2.00 0.00

8 1.00 0.50 2.52 0.00 1.83 3.78 2.00 2.00

9 1.00 0.55 1.50 1.72 0.00 4.59 2.00 0.00

10 1.00 0.55 1.50 0.00 1.72 4.59 2.00 0.00

11 1.00 0.55 1.50 0.00 1.72 4.59 2.00 2.00

12 1.00 0.55 1.49 1.75 0.00 5.15 2.00 0.00

13 1.00 0.55 1.49 0.00 1.75 5.15 2.00 0.00

14 1.00 0.55 1.49 0.00 1.75 5.15 2.00 2.00

15 1.00 0.60 1.51 1.67 0.00 5.15 2.00 0.00

16 1.00 0.60 1.51 0.00 1.67 5.15 2.00 2.00

17 1.00 0.60 1.50 1.67 0.00 5.90 2.00 0.00

18 1.00 0.60 1.50 0.00 1.67 5.90 2.00 2.00

19 1.00 0.60 1.50 1.59 0.00 6.40 2.00 0.00

20 1.00 0.60 1.50 0.00 1.59 6.40 2.00 2.00

21 1.00 0.60 1.50 1.50 0.00 8.00 2.00 0.00

22 1.00 0.60 1.50 0.00 1.50 8.00 2.00 2.00

144

Table A3. Compressive strength development of trial mixes

Mix #

Compressive Strength (MPa) Development (%)

1-day 7-day 28-day 1 to 7 1 to 28

1 41.13 66.03 73.07 60.54 77.66

2 39.00 76.00 87.13 94.87 123.41

3 30.67 45.27 48.07 47.60 56.73

4 29.93 41.10 42.27 37.32 41.23

5 43.33 79.67 76.63 83.87 76.85

6 38.47 78.10 81.90 103.02 112.89

7 20.57 32.50 37.83 58.00 83.91

8 25.40 41.60 39.83 63.78 56.81

9 39.50 59.70 64.10 51.14 62.28

10 23.66 30.40 35.10 28.48 48.35

11 27.86 33.75 40.86 21.14 46.66

12 32.60 62.00 62.00 90.18 90.18

13 21.11 33.44 31.40 58.41 48.74

14 25.30 39.22 39.40 55.02 55.73

15 35.34 58.10 62.00 64.40 75.44

16 23.86 36.20 37.00 51.72 55.07

17 33.76 57.76 67.20 71.09 99.05

18 23.28 36.89 41.10 58.46 76.55

19 25.00 51.00 58.83 104.00 135.32

20 15.86 33.26 37.83 109.71 138.52

21 9.07 28.64 35.30 215.76 289.20

22 12.51 24.42 28.10 95.20 124.62

behavior of steel fiber-reinforced geopolymer …

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