Roy Belton: The Rheological and Empirical Characteristics of Steel Fibre Reinforced Self-Compacting Concrete with GGBS and PFA

The Rheological Characteristics of Steel Fibre

Reinforced Self-Compacting Concrete with PFA and

GGBS

A thesis submitted to Trinity College Dublin

for the Degree of Master of Structural and Geotechnical Engineering

By

Roy Belton

Department of Civil, Structural and Environmental Engineering

Trinity College Dublin

August 2014

ii

DECLARATION

I hereby certify that this dissertation I submit for examination for the Degree of Master of

Structural and Geotechnical Engineering in Trinity College Dublin, is wholly my own

work. No work has been taken from others; any such work that has been used is correctly

cited and acknowledged throughout this text. It has not been submitted for any degree or

examination in any other University or Institution. TCD has my full permission to keep,

lend or copy my work presented here on the condition that any work used in this thesis be

accordingly acknowledged.

Signed: Date:

iii

ABSTRACT

When testing steel fibre reinforced self-compacting concrete (SFRSCC) on-site, it is not

practical to determine the fundamental properties (yield stress and plastic viscosity) of

SFRSCC by means of rheological testing. Therefore, various empirical tests have been

developed to overcome this rheological shortcoming. These tests attempt to evaluate the

workability of SFRSCC for its successful placement concerning the ability of SFRSCC to

fill and flow into all the areas within the formwork, under its own weight, while maintain

a uniform distribution of constituent materials throughout the composite.

Within this study, the focus is on evaluating both the rheological and empirical parameters

of SFRSCC with both pulverised fly ash (PFA) and ground granulated blast furnace slag

(GGBS) for the partial replacement of cement (CEM II/A-L). By considering both the

rheological and empirical aspects of SFRSCC with 30% PFA and 50% GGBS cement

replacements, a correlation between concrete rheology and concrete workability could be

determined.

The results show that the use of PFA and GGBS caused an overall reduction in g and an

increase in h. Intuitively, a reduction in the relative parameter g means a reduction in yield

stress, while an increase in the relative parameter h means an increase in plastic viscosity.

Therefore, the use of PFA and GGBS for the partial replacement of CEM II/A-L caused an

overall reduction in yield stress and an increase in plastic viscosity. In addition, the GGBS

degraded the passing ability of SFRSCC and the workability of SFRSCC is retained for

longer periods after the addition of water when incorporating 30% PFA and 50% GGBS

cement replacements.

Both the slump flow and slump flow t500 time showed a reasonably good correlation with,

respectively, g and h, 15 minutes after the addition of mixing water. Therefore, quick and

easy empirical tests (such as the inverted slump flow test) could be used onsite instead of

rheology to determine, once suitable calibration has been carried out, the fundamental

parameters of yield stress and plastic viscosity. In addition, the inverted slump flow test

could be used to determine the actual steel fibre content, when using the relationships of g

to slump flow, h to slump flow t500 time and the variation of g and h with an increase in

steel fibre content as proxy.

In addition, a good correlation was shown to exist between the L-box blocking ratio and

the J-ring step of blocking for all the mixtures.

iv

ACKNOWLEDGEMENTS

I would like to thank Dr Roger P West of Trinity College Dublin, for his outstanding

supervision, guidance, patience, and steadfast encouragement throughout the course of my

study.

Thanks are also extended to the staff of the Department of Civil, Structural and

Environmental Engineering, TCD for their expertise and assistance. In particular, Dr

Kevin Ryan, Michael Grimes, Mick, Dave and, Owen.

Thanks are also extended to Tom Holden of Roadstone for the constituent materials used

in this study.

Finally, my special thanks go to my family and friends for their never-ending love,

support and encouragement.

v

TABLE OF CONTENTS

DECLARATION ....................................................................................................................................... ii

ABSTRACT .............................................................................................................................................. iii

ACKNOWLEDGEMENTS ...................................................................................................................... iv

Table of contents .........................................................................................................................................v

Chapter 1 Introduction and motivation ..................................................................................................1

1.1. Self-compacting concrete...................................................................................................................1

1.2. Benefits of using self-compacting concrete ........................................................................................1

1.3. Concrete workability .........................................................................................................................2

1.4. Objectives and Scope .........................................................................................................................3

1.5. Limitations ........................................................................................................................................4

1.6. Methodology .....................................................................................................................................5

1.7. Layout of the Thesis ..........................................................................................................................6

Chapter 2 Review of the literature ..........................................................................................................7

2.1. Introduction .......................................................................................................................................7

2.2. Constituent Materials .........................................................................................................................8

2.2.1. Aggregates .................................................................................................................................8

2.2.2. Fine and Coarse Aggregates .......................................................................................................8

2.2.3. Cements and additions ...............................................................................................................9

2.2.4. Pozzolanic materials................................................................................................................. 10

2.2.5. Superplasticisers ...................................................................................................................... 13

2.2.6. Viscosity modifying admixtures ............................................................................................... 13

2.2.7. Steel fibres ............................................................................................................................... 14

2.3. Mechanism for achieving self-compactability .................................................................................. 15

2.3.1. Filling Ability .......................................................................................................................... 16

2.3.2. Passing Ability ......................................................................................................................... 16

2.3.3. Resistance to Segregation ......................................................................................................... 17

2.4. Rheology ......................................................................................................................................... 17

2.4.1. Principles and measurement of rheology .................................................................................. 17

2.4.2. Thixotropy ............................................................................................................................... 23

2.5. Constituent materials and effects on SCC workability and rheology................................................. 25

2.5.1. Influence of coarse and fine aggregates .................................................................................... 25

2.5.2. Cementitious materials ............................................................................................................. 27

2.5.3. Influence of PFA on rheology and workability ......................................................................... 28

2.5.4. Influence of GGBS on rheology and workability ...................................................................... 30

2.5.5. Blended cementitious materials ................................................................................................ 30

2.5.6. Steel fibres ............................................................................................................................... 31

2.5.7. Effect of delaying SP on rheology ............................................................................................ 32

vi

2.5.8. Influence of superplasticiser on rheology ................................................................................. 33

2.6. Concrete rheometers ........................................................................................................................ 33

2.7. Mixer and mix procedure ................................................................................................................. 37

Chapter 3 Empirical and Rheological tests ........................................................................................... 39

3.1. Rheological and workability tests .................................................................................................... 39

3.2. Passing ability tests .......................................................................................................................... 41

3.2.1. J-ring ....................................................................................................................................... 41

3.2.2. L-box test ................................................................................................................................. 43

3.2.3. U-test ....................................................................................................................................... 44

3.3. Filling ability tests ........................................................................................................................... 45

3.3.1. Slump Flow Test ...................................................................................................................... 45

3.3.2. V-funnel test ............................................................................................................................ 47

3.3.3. Orimet test ............................................................................................................................... 47

3.4. Segregation tests .............................................................................................................................. 48

3.4.1. Visual Inspection ..................................................................................................................... 48

3.4.2. Sieve Stability test .................................................................................................................... 48

3.4.3. Penetration Test ....................................................................................................................... 49

3.4.4. Review of empirical tests for SCC ............................................................................................ 50

3.4.5. Two point workability test........................................................................................................ 52

3.4.6. Summary.................................................................................................................................. 55

Chapter 4 Parametric study on constituent materials and tests........................................................... 56

4.1. Introduction ..................................................................................................................................... 56

4.2. Coarse and fine aggregates .............................................................................................................. 56

4.2.1. Particle size distribution of aggregates...................................................................................... 57

4.3. Powders ........................................................................................................................................... 57

4.3.1. Particle size distribution of powders ......................................................................................... 58

4.4. Water............................................................................................................................................... 59

4.5. Chemical admixtures ....................................................................................................................... 59

4.6. Fibres .............................................................................................................................................. 59

4.7. Rheological study of trial mixes ....................................................................................................... 60

4.8. Proposed mix design, mixes and testing procedure........................................................................... 68

4.8.1. Mixing sequence and mixer ...................................................................................................... 69

4.8.2. Testing methods ....................................................................................................................... 70

4.8.3. Trial SCC mixes ....................................................................................................................... 72

4.8.4. Summary.................................................................................................................................. 74

chapter 5 - Rheological study on SFRSCC with PFA and GGBS. .......................................................... 75

5.1. Introduction ..................................................................................................................................... 75

5.2. Testing sequence ............................................................................................................................. 75

5.3. Experimental program on SFRSCC with GGBS and PFA ................................................................ 76

5.3.1. Rheological analysis of SFRSCC with PFA and GGBS ............................................................ 77

vii

5.3.2. Empirical tests ......................................................................................................................... 82

5.3.3. Correlation of empirical tests with rheological parameters ........................................................ 86

5.3.4. Influence of time on the parameters .......................................................................................... 88

5.3.5. Summary.................................................................................................................................. 94

6. Conclusion and Recommendations ....................................................................................................... 96

6.1. Objective Number One: Conclusion................................................................................................. 96

6.2. Objective Number Two: Conclusion ................................................................................................ 96

6.3. Objective Number Three: Conclusion .............................................................................................. 97

6.4. Objective Number Four: Conclusion: ............................................................................................... 98

7. References............................................................................................................................................ 100

Appendix A Mix design ........................................................................................................................ 109

A.1 Mix Design for SCC-1 to SCC-7. ........................................................................................ 110

A.2 Mix design for SCC-8 to SCC-14. ....................................................................................... 111

A.3 Mix design for SCC-15 to SCC-21. ..................................................................................... 112

Appendix B Rheological data .............................................................................................................. 113

B.1 - Rheological data ................................................................................................................... 113

Appendix C Time evolution relationships ........................................................................................... 114

C.1 Time evolution relationship of torque versus speed for SCC-1 to SCC-7.............................. 115

C.2 Time evolution relationship of torque versus speed for SCC-8 to SCC-14. ........................... 116

C.3 Time evolution relationship of torque versus speed for SCC-15 to SCC-21. ......................... 117

C.4 - Hershel-Bulkley Rheological parameters for SCC-1 to SCC-21. ........................................... 118

Appendix D Compressive strengths .................................................................................................... 120

D.1 - Cube Strengths ..................................................................................................................... 120

Appendix E Correlation between empirical and rheological parameters .......................................... 121

E.1 - Correlations between empirical and rheological parameters for SCC-1 to SCC-7.................. 122

E.2 - Correlations between empirical and rheological parameters for SCC-8 to SCC-14. ............... 123

E.3 - Correlation between empirical and rheological parameters for SCC-15 to SCC21. ............... 124

E.4 - Correlation between empirical and rheological parameters ................................................... 125

E.5 - Time evolution of empirical tests.......................................................................................... 127

E.6 - Time evolution correlation between empirical and rheological parameters............................ 128

Appendix F Two-point theory and calibration ................................................................................... 131

F.1 - Theory of the Two-point method .......................................................................................... 132

F.2 - Calculation of results and Calibration ................................................................................... 136

Appendix G Technical data sheets ...................................................................................................... 139

G.1 Steel fibres........................................................................................................................... 139

G.2 Admixtures .......................................................................................................................... 139

CHAPTER 1 - INTRODUCTION

1

CHAPTER 1 INTRODUCTION AND MOTIVATION

1.1. Self-compacting concrete

In general, the construction of traditional concrete requires compaction to remove the

trapped air and densify the concrete. This type of concrete composite is known as

traditional vibrated concrete (TVC). On the other hand, self-compacting concrete (SCC)

possesses both superior flowability and a high segregation resistance, which consolidates

under its own weight without the need for conventional vibrating techniques (Goodier,

2003; Kuroiwa, et al, 1993).

1.2. Benefits of using self-compacting concrete

The use of SCC eliminates the need for conventional concrete vibrators, which improves

on-site health and safety by reducing serious health hazards, such as vibration white finger

and deafness. It can also be stated that the use of SCC reduces the potential for human

error in relation to compaction, as over-compacting and under-compacting the concrete

can lead to internal segregation and surface defects (such as honeycombing). Fewer

operatives are needed, but more time is required to test the concrete before placing. The

high binder content and the need for well-graded aggregates improves the concrete, which

produces a dense pore structure between the aggregate and the cement matrix and,

consequently improves concrete strength and durability.

The use of SCC leads to lower overall costs. However, it can lead to an increase and

decrease in direct costs, which are:

significant reductions in labour costs due to eliminating the need for operatives to

place and vibrate the concrete (See Fig 1.1 1.2);

reduced electrical energy requirements as concrete vibrators are not required,

which reduces the costs associated with SCC placement;

reduced placing times as conventional concrete vibrating techniques are not

required, which can increase productivity;

a more durable concrete due to its denser microstructure, particularly within the

concrete cover zone.


2

Fig 1. 1: A team of eight operatives placing and

finishing TVC (after De Schutter et al. 2008).

Fig 1. 2: A team of two operatives placing and

finishing SCC (after De Schutter et al. 2008).

According to Goodier (2003), the Lafarge Group investigated the overall cost savings

associated with using SCC. In this study, the Lafarge Group constructed two identical

concrete building; one from TVC and the other from SCC. The building constructed using

SCC materials was completed 2.5 months before the traditionally constructed building and

with an overall project saving of 21.4%.

1.3. Concrete workability

The term workability is described as that property of freshly mixed concrete or mortar

that determines the ease at which it can be mixed, placed, consolidated, and finished to a

homogenous condition (Koehler and Fowler, 2003). According to Tattersall (1991),

workability test methods can be placed into categories based on different classifications

(See Table 1.1).

Table 1. 1: Classes of workability measurement (after Tattersall 1991).

Concerning concrete workability test methods, most of the test methods fall into Class II

and Class III. Most test methods for concrete workability have been divided between

single-point tests (Class II) and multi-point tests (Class III). A single-point test measures

only one point on the flow curve relating shear stress to shear strain rate, whereas multi-

point tests measure multiple points on the flow curve and, therefore, provides a more


3

complete description of workability by the use of two parameters, namely, the yield stress

and plastic viscosity. For example, a single point test, such as the slump test only provides

one point on the flow curve, namely, the yield stress.

According to Tanner (2009), rheology plays a crucial role in understanding the material

behaviour of fresh concrete. Furthermore, rheology as a science allows one to determine

and evaluate the correct proportions of constituents within the mix. Therefore, the use of

this science, when applied to concrete in its fresh state, allows one to measure and

quantify the rheological properties of fresh concrete and thus provides a better

understanding of the rheological influence of various constituent materials on the fresh

state of concrete (Roussel, 2011).

Fresh concrete is considered a multiphase material, whereby complex interactions between

the paste and the aggregate control the flow of concrete and hence provide a certain level

of workability (De Schutter, et al., 2008). In general, the slump test is used to evaluate

concrete workability. However, different concrete mixtures possessing the same slump

may behave differently concerning flowability and workability (Ferraris, et al., 2001).

Consequently, evaluating concrete flow requires two parameters and not one, as in the

case of the slump test.

According to Ferraris et al. (2001), the slump flow test evaluates concrete yield stress and

shows reasonably good correlations with this parameter; however, the slump flow test

does not evaluate the plastic viscosity; that is, its continual flowability after flow has

initiated. It is important to recognise that evaluating the plastic viscosity allows one to

determine why different concrete mixtures possessing the same slump value differ in

terms of flowability and workability.

1.4. Objectives and Scope

This study presents a review of the constituent requirements for the successful placement

of SCC as well as the influence of these constituent materials on both the rheological and

workability aspects of SCC. In addition, both the importance and fundamental principles

of rheology are highlighted and discussed as well as the various empirical and rheological

test methods. In addition, the physical appearance and the particle size distributions of the

constituent materials used in this study are presented.

The research described in this dissertation had the broad objective of evaluating both the

rheological and empirical parameters of steel fibre reinforced self-compacting concrete


4

(SFRSCC) with both the use of pulverised fuel ash (PFA) and ground granulated blast

furnace slag (GGBS) for the partial replacement of cement (CEM II/A-L). Therefore, it is

possible that, by considering both the rheological and empirical aspects of SFRSCC with

PFA and GGBS cement replacements, a correlation between concrete rheology and

concrete workability could be determined. To achieve this objective, rheology was used to

determine the rheological parameters g and h, which are, respectively, related to the

fundamental parameters of yield stress and plastic viscosity. In addition, the workability

aspects were evaluated by using current empirical tests, such as the slump flow, L-box and

J-ring.

Various steel fibre reinforced self-compacting (SFRSCC) mixtures were used to determine

the effect of both pulverised fuel ash (PFA) and ground granulated blast furnace slag

(GGBS) on both the rheological and empirical parameters of these mixtures. In addition,

the influence of various steel fibre contents on both the rheological and empirical

parameters of SCC were investigated. The workability retention of the different

supplementary cementitious materials (PFA and GGBS) used in this study was also

investigated.

Evaluating the rheological properties of SCC is no easy task; these properties change as

concrete progresses through its various transitional stages of development. The reason for

this is due to progressive chemical changes/reactions occurring within the mix (De

Schutter, et al., 2008). Furthermore, according to De Schutter et al. (2008) the rheological

characteristics behave in a nonlinear manner. Therefore, the influence of time, after the

addition of mixing water, on both the rheological and empirical values was investigated in

this study.

1.5. Limitations

In this study, the main focus was on evaluating the rheological parameters g and h, which

are related and, consequently, used to obtain the fundamental parameters of yield stress

and plastic viscosity. Therefore, this study concentrated on the rheology and workability

of SFRSCC with PFA and GGBS cement replacements. Only one type of steel fibre was

used: Dramix R-65/35 hooked steel fibres. One sand was used in all the mixtures and the

fillers used in this study (i.e. limestone, pulverised fuel ash and ground granulated blast

furnace slag) were each restricted to a single source and, therefore, each one possessed the

same physical and chemical properties.


5

1.6. Methodology

A comprehensive review of the literature was undertaken to better understand the

development and production of SCC as well as the rheology and workability of concrete.

In this undertaking, information was compiled on SCC mix design and SCC testing as

well as various rheological models.

Initially, the laboratory technicians constructed the equipment for the empirical tests, i.e.,

slump flow, L-box and J-ring. Shortly after, the required constituents for all the mixtures

were quantified and ordered. To determine the influence of PFA and GGBS on the

rheological and workability parameters of SFRSCC, the constituent materials were each

acquired from a single source and hence each possessed the same physical and chemical

properties.

The Tattersall two-point apparatus was used to evaluate the rheological parameters g and h

for each mixture. Furthermore, these obtained parameters were not converted into their

fundamental units of shear stress and plastic viscosity by using both Newtonian and non-

Newtonian fluids of known flow properties. However, Appendix F gives the theory of the

Tattersall two-point method along with the calibration theory.

Since the author had not previously used the two-point apparatus, it was necessary to

perform tests on trial mixtures. This was done to assess the variability associated with

recording the resulting pressures and, therefore, the obtained torques as well as finding out

if the two-point apparatus was actually working. Also, various functional torque-speed

relationship were investigated and, therefore, their associated correlation coefficients were

investigated.

The workability of the mixtures was measured using the slump flow, L-box and J-ring

tests. The filling ability and segregation resistance were assessed with the slump flow test,

while the passing ability and segregation resistance were assessed with the L-box and J-

ring tests.

To verify the obtained rheological and empirical parameters, cubes were cast for each

mixture and tested at seven-day for their compressive strengths.


6

1.7. Layout of the Thesis

Chapter One presents the introduction and motivations, elaborating on the benefits of SCC

and the importance of concrete rheology and concrete workability.

Chapter Two presents the development of SCC, constituent materials and their influence

on concrete rheology and concrete workability, mechanisms for achieving self-

compactability, rheology, concrete rheometers and mix procedure.

All the empirical and rheological tests are described in Chapter Three. This chapter

involves describing the procedures for these tests, their limitations and the expression of

the obtained results. In addition, minimum and maximum criteria for the various empirical

tests are presented.

Chapter Four involves a parametric study on both the constituent material and tests used in

this study as well as a rheological study on trial mixes, the proposed mix design, mixes

and testing procedures.

The experimental program on SFRSCC with PFA and GGBS cement replacements is

presented in Chapter Five. This includes all the test results for all the mixtures that

underwent rheological and workability testing at different times after the addition of

mixing water.

Finally, the last chapter (Chapter Six) summarises the findings and conclusions of this

study. In addition, recommendations are given.

CHAPTER 2 REVIEW OF THE LITERATURE

7


2.1. Introduction

During the late 1980s, and due to the gradual decline of skilled operatives in Japans

construction industry, Professor Okamura of the University of Tokyo proposed and

developed various concepts for self-compacting concrete, and during 1988 the first

prototype was developed. The constituent materials used in SCC are the same as in

traditional concrete except that an increased amount of both fine materials (sand and

binders) and admixtures are needed combined with a reduction in coarse aggregates (See

Fig 2.1). These material requirements are essential in achieving self-compactability. Due

to its higher binder and chemical admixture content, the material costs associated with

SCC are usually 20 - 50% higher than traditional concrete (Nehdi, et al., 2004).

Fig 2. 1: Constituent requirements for TVC and SCC (after Okamura and Ouchi 2002).

In the mid to late 1990s, the development and use of SCC spread from Japan to Europe.

Some of the first research work to be published from Europe was at an International

RILEM (International Union of Laboratories and Experts in Construction Materials and

Structures) Conference held in Glasgow in 1996 (Bartos, et al., 1996; Goodier, 2003).

Domone and Chai (1996) produced some of the very first European scientific papers on

the design and testing of SCC, which involved an experimental programme in producing

and evaluating SCC with indigenous UK materials.

In 2000, the first European guidelines on SCC appeared in France and in the Nordic

countries. In 2001, the European Commission approved a SCC testing programme, known

as the Testing-SCC project, which was led by the ACM Centre, the University of Paisley,

W=Water

C = Cement

S = Sand

G = Gravel


8

Scotland. The project set out to evaluate existing testing methods in order to recommend

appropriate tests for international standardisation.

2.2. Constituent Materials

Concrete is considered a three-phase material, namely, cement, water and aggregates, with

the addition of admixtures. This section will briefly describe the constituents used to

produce SCC.

2.2.1. Aggregates

The choice of aggregates has a significant impact on the fresh and hardened properties of

concrete. In traditional concrete, the inherent characteristics of aggregates (such as shape,

surface morphology, size, grading and type) are known to significantly influence the

hardened properties of concrete (such as strength, robustness, durability, toughness,

shrinkage, creep, density and permeability) and the fresh properties of concrete (such as

workability, segregation, bleeding, finishability and pumpability (Dhir and Jackson, 1996;

Nanthagopalan and Santhanam, 2011). According to De Schutter et al. (2008), the use of

lightweight aggregates is feasible with special attention towards mix design.

According to the European specifications and guidelines for SCC, all constituent materials

shall conform and comply with the requirements set out in IS EN 206 (EFNARC, 2002).

2.2.2. Fine and Coarse Aggregates

In SCC, a sufficiently low coarse aggregate content is required to avoid aggregate bridging

and hence blocking of concrete in and around confined spaces (reinforcement) (De

Schutter, et al., 2008). However, reducing the coarse aggregate content can also cause a

decrease in particle packing, which if overdone can affect the overall performance of the

concrete (Fung and Kwan, 2014). Consequently, one should expect the coarse aggregate

content to affect both the fresh and hardened properties of concrete. Coarse aggregate

content normally ranges from 28 to 35 per cent per cubic meter of SCC (EFNARC, 2002).

Domone (2006) analysed 68 case studies on the use of SCC in many countries, published

during the period 1993 2003. The author stated that crushed rocks were used in over 75

per cent of these in relation to natural gravel deposits. In addition, maximum aggregate

sizes ranged from 16 20 mm, however in some cases larger aggregates of up to 40 mm

were used; it is possible that overall grading plays a more important role than aggregate

size (Domone, 2006). Furthermore, EFNARC (2002) states that consistency of grading is


9

critical for successfully placing SCC. Concerning aggregate conformity, EFNARC (2002)

recommends a limited aggregate size of 20 mm. According to EFNARC (2002), either

crushed or rounded sands are suitable for SCC. The quantity of fine aggregates provides

both lubrication between the coarse aggregates and overall concrete stability, while a

lower coarse aggregate content reduces interparticle friction. It is important to recognise

that fine aggregates below 0.125 mm should be considered as being part of the powder

fraction in SCC mix design (De Schutter, et al., 2008).

Fig 2. 2: Overall aggregate gradings for SCC mixes from testing SCC project partners (after Aarre and

Domone 2003).

In producing SCC, a well distributed overall grading is desirable. However, SCC has been

produced with aggregates of significantly different gradings. Fig 2.2 adapted from

Domone (2003) shows 11 aggregate gradings considered suitable for SCC, originally

compiled by a consortium of twelve partners, known as SCC project partners.

Furthermore, the need for a higher fine aggregate content in SCC is clear (Fig 2.2). In

addition, all aggregates in SCC shall conform to IS EN 12620 (EFNARC, 2002).

2.2.3. Cements and additions

In concrete, powders are the smallest solid particles with sizes less than 250 or 125 m

(Liu, 2009). The powder part of SCC consists of ordinary Portland Cement (OPC) and

fillers, which can be nearly inert or latent hydraulic (De Schutter, et al., 2008). SCC

requires a high powder content and a low water/cement ratio, which increases the

exothermic reaction during cement hydration and, therefore, increases the risk of cracking

from thermal effects. As mentioned previously, SCC requires a high cement content,

which results in high costs and thermal cracking (De Schutter, et al., 2008). It is therefore

necessary to reduce the cement content by additions such as limestone filler, fly ash or


10

GGBS. Additions are used in order to control, reduce, improve and/or extend certain

concrete properties. Additions of all types have been previously incorporated into

concrete, of which three types exist; which are: (i) nearly inert (Type I), such as limestone

filler (ii) pozzolanic (Type II), such as fly ash or microsilica, and (iii) latent hydraulic

(Type II), such as ground granulated blast furnace slag (De Schutter, et al., 2008; IS EN

206 1, 2000; EFNARC, 2002).

The performance of SCC in its fresh state is influence by cement composition. This

influence depends on the content of tricalcium aluminate (C3A) and tetracalcium

aluminoferrite (C4AF). Immediately after mixing, the superplasticisers are first absorbed

by the C3A and C4AF; therefore, the effect of a superplasticiser depends on the content of

C3A and C4AF (Liu, 2009). In addition, the C3A content influences the setting rate of

concrete; put simply, a large amount of C3A will cause an increase in concrete setting,

known as flash set. All cements that conform to IS EN 197-1 can be incorporated in SCC

(EFNARC, 2002).

2.2.4. Pozzolanic materials

A pozzolana is defined as a natural or artificial material containing silica in a reactive

form which by themselves possesses little or no cementitious value (Newman and Choo,

2003). However, in finely divided form and in the presence of water/moisture, SiO2

(silica) and Al2O3 (alumina) react with calcium hydroxide (Ca(OH)2) (lime) to form

compounds possessing cementitious properties, mainly calcium silica hydrates (C-S-H)

and calcium silica alumina hydrates (C-S-A-H) (Newman and Choo, 2003). These

cementitious compounds fill the voids in the concrete thus producing a dense impermeable

concrete, while also reducing the thickness of the transitional zone between coarse

aggregate and paste thus improving bond strength, long-term strength development and

durability. In addition, the use of pozzolanic materials for the partial replacement of

cement dilutes the overall C3A content, which reduces the rate of hydration, heat of

hydration and early strength development. It is important to acknowledge that reducing the

C3A content and hence the high heat rate of hydration will reduce the likelihood of

thermal cracking. In addition, the occurrence of shrinkage and creep is a notable factor as

SCC contains a much higher fraction of powder than traditional concrete mixes

(EFNARC, 2002).


11

The definition and effects of some frequently used additions in SCC are listed as follows:

Blast furnace slag is produced by rapid cooling of slag particles as obtained during

the smelting of iron ore (IS EN 197-1:2001). Once cooled, the slag particles are

ground into a fine cementitious powder, known as ground granulated blast furnace

slag (GGBS). As mentioned previously, GGBS possesses latent hydraulicity, i.e.,

the hydraulicity of the slag is locked within its glassy structure (Newman and

Choo, 2003). Details on the acceptable proportions of GGBS and cement clinker

are shown in Table 2.1 as given in IS EN 197-1:2011.

Table 2. 1: Composition for slag cements.

Constituents (%)

CEM II

CEM III

Portland-slag cement

Blast furnace cement

Type A Type B Type A Type B Type C

PC Clinker

80-94 65-79

35-64 20-34 5-19

GGBS

6-20 21-35

36-65 66-80 81-95

Minor constituents 0-5 0-5

0-5 0-5 0-5

It should be noted, that replacements of cement clinker are possible up to 95 per

cent. Typically speaking, however, replacement levels between 50-70 per cent are

suited for structural concrete purposes (Newman and Choo, 2003).

Kim et al. (2007) studied the effects of GGBS on concrete strength (tensile) and

fibre bonding; the authors reported that GGBS for the partial replacement of

cement increased the strength and improved fibre bonding.

Fly ash is produced when pulverised coal burns in a power station. It is a fine

powder of mostly spherical glassy particles of silica (SiO2), alumina (Al2O3), iron

oxide (Fe2O3) and other minor compounds, ranging from 1 to 150 m in diameter,

of which the most of it passes the 45 m sieve (IS EN 197-1:2011; Newman and

Choo, 2003; Tattersall, 2003).

It is well known that the use of fly ash for the partial replacement of cement

increases the workability and contributes towards long-term strength development.

According to Khatib (2008), the use of fly ash in SCC reduces the amount of

superplasticiser needed to achieve a similar flow spread value compared to SCC

containing only Portland cement and/or Portland cement + Limestone filler.


12

Siddique (2011) stated using fly ash reduces the need for stability admixtures such

as viscosity modifying agents. The authors (Khatib, 2008; Xie, et al., 2002;

Gesolu, et al., 2009) reported a reduction in drying shrinkage with increasing

amounts of fly ash, while Khatib (2008) stated that fly ash replacement levels of 80

per cent can reduce drying shrinkage by two thirds compared with binders

comprised of only Portland cement. Details on the acceptable proportions of PFA

and cement clinker are shown in Table 2.2 as given in IS EN 197-1:2011.

Table 2. 2: Composition of fly ash cements.

Constituents (%)

CEM II

CEM IV

Portland-fly ash cement

Pozzolanic cement

Type A Type B Type A Type B

PC Clinker

80-94 65-79

65-89 45-64

Fly ash

6-20 21-35

11-35 36-55

Minor constituents 0-5 0-5

0-5 0-5

Limestone powder is frequently used in SCC. IS EN 197-1:2011 states that

limestone can replace up to 35 per cent of the cement by mass. According to Pera

et al. (1999) and Ye et al. (2007), additions of limestone powder exceeding 30 per

cent replacement of cement increases the rate of hydration and contributes towards

strength development. This is because the calcium carbonate (CaCO3) increases

the acceleration rate of C3S (tricalcium silicate) and hence increases the rate of

cement hydration, which contributes towards early strength development. Zhu and

Gibbs (2005) stated that incorporating fine limestone powder in SCC could lead to

a reduction in superplasticiser dosage compared to SCC containing only Portland

cement because of improved particle packing, water retention and possible

chemical reactions.

The use of limestone as a filler in SCC is more effective than fly ash in terms of

early strength development. However, beyond 28 days, the use of fly ash achieves

higher strengths when compared to binders consisting of Portland cement and

limestone filler (Felekolu, et al., 2006).

Limestone filler is not a chemically active material; this means that the water

content is fully available for cement hydration (De Schutter, 2011). For example, if

using limestone filler for the partial replacement of CEM II to counteract the

negative effects of just using only CEM II (such as high heat of hydration) then the


13

overall water/cement ratio is available for the CEM II addition and not the

limestone filler. Therefore, it is important to recognise that increasing the

water/cement ratio will significantly influence workability and strength.

2.2.5. Superplasticisers

Superplasticisers improve the deformation capacity of concrete by keeping the

cementitious particles apart, which reduces interparticle friction forces between the

cement particles. However, increasing the dosage beyond the norm can give rise to

decreased stability and hence increased segregation (Tattersall, 2003). Furthermore, the

type and dosage of superplasticiser affects the deformation capacity of SCC. It is

important to recognise that certain types of superplasticisers can give rise to an excessive

air content within the paste; therefore, the volume of air should be added to the volume of

paste within the mix design.

In general, they work in two ways. First, they attach themselves to the individual

cementitious particles which temporarily neutralises the forces of attraction between the

cement particles (provides a negative charge on a once positive charged cement particle)

and this gives the concrete a much more liquid consistency (De Schutter, et al., 2008). In

addition, polycarboxylate ether based superplasticisers bind themselves around the cement

particles by the presence of long neutral molecules (chains and links) which allows the

free water to completely encapsulate the cement particles and hence improves fluidity, this

is known as steric repulsion (De Schutter, et al., 2008; aniewska-Piekarczyk, 2014). In

general, superplasticisers improve SCC fluidity by repelling the cement particles and

decreasing particle flocculation (Roussel, 2011).

aniewska-Piekarczyk (2014) reported that lignosulfonate, sulfonated naphthalene

formaldehyde and sulfonated melamine formaldehyde superplasticisers work by

neutralising the forces of attraction between the cement particles, thus improving concrete

fluidity. Broadly speaking, superplasticisers used in SCC are comprised of a

polycarboxylate ether or a modified acrylic polymer (West, 2009).

2.2.6. Viscosity modifying admixtures

SCC requires a high resistance against segregation while maintaining and/or improving a

uniform suspension of constituent materials. Viscosity modifying agents (VMA) are

water-soluble polymers or inorganic substances that increase the viscosity and cohesion of

the mixture, therefore enhancing concrete stability (Lachemi, et al., 2004). In addition,


14

providing adequate stability will allow the constituents to remain in suspension, which is

important for high segregation resistance. It should be noted, that the combined use of a

VMA with a high range water reducer (superplasticiser) would produce a highly flowable

yet cohesive cementitious material. According to Roussel (2011) the use of a VMA can

enhance the hardened properties of concrete; that is, enhance the bond strength between

reinforcing elements and the aggregates.

One should be cautious when selecting combinations of VMAs and SPs as certain types of

SPs can counteract the performance of the VMA; one of which is a methyl cellulose-based

VMA combined with a naphthalene-based SP (De Schutter, et al., 2008).

2.2.7. Steel fibres

IS EN 14889-1 (2006) defines steel fibres as straight or deformed pieces of cold-drawn

steel wire, straight or deformed cut sheet fibres, melt extracted fibres, shaved cold drawn

wire fibres and fibres milled from steel blocks which are suitable to be homogeneously

mixed into concrete or mortar. There are various types of steel fibres available, which

differ in shape and size. Furthermore, their pull out behaviour can be modified by

optimising the fibre anchorage properties and/or enhancing the chemical and physical

bond between the fibre surface and the cement paste (Cunha, et al., 2009). It was reported

that fibre strength, geometry and orientation have a direct influence on the load bearing

capacity of fibre-reinforced composites without traditional tensile reinforcement

(Holschemacher, et al., 2010). El-Dieb (2009) stated the inclusion of steel fibres improves

the compressive strength of concrete. However, Kayali et al. (2003) reported the opposite;

that is, the addition of steel fibres did not significantly affect the compressive strengths. In

both cases, different constituent (coarse aggregates) materials were used along with

varying amounts of constituents and steel fibres of different geometrical proportions.

Therefore, it is important to recognise that the compressive strength of fibre reinforced

concrete depends on the amount, type and quality of constituents in the mixture. Some

typical profiles of steel fibres used in concrete are presented in Table 2.3.


15

Table 2. 3: Steel fibre profiles (after Cunha et al. 2009).

As mentioned previously, SCC requires a high cement/paste content and a low

aggregate/cement ratio, which can affect the rate of shrinkage and can cause the formation

of cracks and crack development. The use of steel fibres improves cracking resistance thus

reducing the development of cracks. Furthermore, increasing amounts of fibres can be

added in SCC due to its high fine content and low aggregate/cement ratio (Grnewald and

Walraven, 2001). However, fibres all lead to a reduction in filling ability and an increase

in blocking. In 2002, researchers at the Polytechnical University in Italy (Corinaldesi and

Moriconi, 2004) reported that fibre addition in SCC proved very effective in counteracting

the effects of drying shrinkage. In this study, 50 kg/m3 of steel fibres were incorporated in

the mix design.

2.3. Mechanism for achieving self-compactability

SCC is not a new composite material. However, not many understands its complex

behaviour both in its fresh and hardened state (De Schutter, et al., 2008). De Schutter et al.

(2008) defines self-compacting concrete as its ability to flow under its own weight, fill

the required space or formwork completely and produce a dense and adequately

homogeneous material without the need for compaction. Therefore, it is widely

understood that SCC has three characteristics, which are required for the successful

casting of SCC. These three characteristics are:

filling ability;

passing ability;

resistance to segregation.


16

Broadly speaking and according to EFNARC (2002), there are numerous methods to

assess and characterise SCC workability.

2.3.1. Filling Ability

The filling ability of SCC is defined as its ability to flow into and fill all spaces within the

formwork, under its own weight, while passing through openings of heavily congested

reinforcement (Sonebi and Bartos, 2002). Broadly speaking, the main factor affecting

concrete workability is the water to cement ratio (w/c). Increasing the w/c will improve

concrete workability, which will reduce the yield stress. However, increasing the w/c will

reduce the plastic viscosity, which can give rise to segregation.

2.3.2. Passing Ability

During the placement of SCC, the concrete must pass freely through reinforcement

without blocking. As SCC passes through constricted spaces or narrow openings or

reinforcement, it causes an increase in internal stresses between the aggregates (RILEM

TC 7 SCC, 1999). When SCC flows through restricted openings, the energy required for

adequate flowability is consumed by increasing internal particle stresses, consequently

leading to an increased coarse aggregate content around the reinforced areas and,

therefore, blocking (See Fig 2.3).

Fig 2. 3: Blocking due to increased coarse aggregate content (after Von Selbstverdichtendem and Frais

2003).

Okamura and Ouchi (2003) states that a high deformation capacity can only be achieved

by the use of a superplasticiser, while ensuring a low water-cement ratio. West (2003)

stated it is difficult to achieve superior flowability by just altering the grading of

aggregates. Furthermore, the author suggests the need for a supplementary cementitious

material.


17

2.3.3. Resistance to Segregation

In SCC, good segregation resistance involves the uniform distribution of constituent

materials. Consequently, this means in all directions, both horizontal and vertical. De

Schutter et al. (2008) considered segregation of fresh concrete as a phenomenon related

to the plastic viscosity and density of the cement paste. In addition, the author stated that

when the density of the solid particles are greater than the cement paste, the solid particles

tend to sink or segregate. Furthermore, segregation can occur during the placement stage

(dynamic segregation) and after the placement stage (static segregation). Static

segregation occurs when the water separates from the mix and rises to the upper region of

formwork, also known as bleeding. Another form of dynamic segregation is pressure

segregation, which can occur during the pumping of concrete (De Schutter, et al., 2008).

When transporting and placing SCC, the fresh mix must maintain its original distribution

of constituent materials (aggregates). This is known as resistance to segregation.

Furthermore, De Schutter et al. (2008) suggest that segregation can occur in SCC, which

possesses adequate filling and passing abilities. It is important to recognise that inadequate

segregation resistance can cause poor deformability and blocking in and around

reinforcement areas, which will reduce the compressive strength of SCC (Bui, et al.,

2002).

2.4. Rheology

Tattersall and Banfill (1983) define rheology as the science of deformation and flow of

matter. Rheology is of Greek origin, referring to panta rei, everything flows. Rheology is

used to describe the behaviour of materials, which do not conform to the deformation of

simple elastic Newtonian gases, liquids and solids. In essence, rheology is concerned with

relationships between stress, strain, rate of strain and time. According to De Schutter et al.

(2008), rheology allows one to assess the properties of concrete in its fresh and transitional

states of development. Concrete possesses a certain resistance to flow, therefore the

application of a certain force is required for concrete to flow, and that force is known as a

shear stress.

2.4.1. Principles and measurement of rheology

In order to understand the rheology of cementitious materials, an understanding of the

simplest case is required; the simplest case is described by Hookes law. This law states

that the deformation of an ideal elastic material depends only on the applied force, which

means that the strain is proportional to the stress. For example, if a rectangular prism is


18

deformed by equal and opposite forces applied tangentially to opposite faces, then the area

A is deformed under shear stress, = F/A and the angle represents the deformation or

shear strain (See Fig 2.4). Therefore, shear stress is proportional to shear strain and,

therefore, expressed by the following equation:

= n (2. 1)

where n is the constant of proportionality, also known as the rigidity modulus or shear

modulus.

Fig 2. 4: Hookes law for a material in shear (F/A = n).

Fig 2. 5: Hookean solid in shear.

Fig 2.5 illustrates a straight-line relationship if is plotted as a function of whose slope

is equal to n. If a particular shear stress could be applied to a rectangular prism made of

simple fluid, the deformation of the fluid will not result in a definite deformation or shear

strain, but the fluid would deform and continue deforming once the initial shear stress is

applied. This constant deformation depends on the shear stress, and is measured by the

time differential of shear strain. Therefore, the time differential of is proportional to

and is represented by the following equation:

= nd

dt . (2. 2)

This equation is similar to Hookes law except that the shear strain rate replaces the shear

strain and in this case n represents the constant of proportionality and is known as the

coefficient of viscosity. According to Tattersall and Banfill (1983), a fluid can be

considered as moving in laminar motion relative to two parallel solid planes, which move

relative to each other along one of their directions (See Fig 2.6). Therefore, this represents

Newtons law of viscous flow, which states that shear stress is proportional to the velocity

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8

Shea

r st

ress

,

Shear strain,

Slope = n


19

v and inversely proportional to the distance L between the planes, and is expressed by the

following:

= ndv

dL (2. 3)

dv/dL is known as the velocity gradient, which can be shown to be the same as d/dt and,

therefore Newtons law of viscous flow can be expressed as:

= n (2. 4)

where is the rate of shear and n is the constant of proportionality.

Fig 2. 6: Newtons law of viscous flow.

For a Newtonian fluid at a constant temperature, which behaves according to laminar

flow, only one constant n is required to describe the flowing properties. In addition, the

relationship between rate of shear and shear stress passes through the origin (See Fig 2.7)

and the slope is equal to the coefficient of viscosity n.

Fig 2. 7: Newtonian fluid.

In the case of a Newtonian fluid, the relationship between the rate of shear and shear stress

is constant, which does not depend on the shear rate and the length of time for which the

Shea

r st

ress

,

Rate of shear,

Slope = n

= n


20

shear stress is applied. This is the simplest form to describe the behaviour of a fluid.

Actually the behaviour of most materials (such as concrete) do not conform to this model,

but depend on shearing resistance and, therefore, at least two different shear deformation

rates are required to describe its flow properties. Figure 2.8 illustrates this requirement,

while it can be seen that the straight-line relationship of shear stress to shear strain rate

does not pass through the origin and, therefore the relationship between shear and stress is

not constant, i.e., it intercepts the stress axis. Many authors (Tattersall and Banfill, 1983;

De Schutter, et al., 2008; Gram, 2009; Sheinn, et al., 2002) state that the strain-stress

relationship is described by the two parameters of the Bingham model, the yield stress and

plastic viscosity in the form of

= o + (2. 5)

where the term is the plastic viscosity, is the rate of shear and o is the distance from

the intercept to the origin, known as the yield value. It is clear that a material that follows

this equation needs two constants to characterise its rheological properties.

Fig 2. 8: Bingham model.

For non-Newtonian materials (such as concrete), their behaviour is slightly more

complicated than Newtonian materials. Their behaviour is more complex and may behave

in a non-linear manner (See Fig 2.9). If the flow curve is concave towards the shear rate

axis, it is described as shear thinning because the stress is increasing less rapidly than the

shear rate and at higher strain rates the material flows much easier compared to a shear

thickening material, i.e., the structure of a shear thinning material is broken down by an

Shea

r st

ress

,

Rate of shear,

Slope =

= o + A

B

o


21

increasing shear strain rate. The following equation represents this and is known as a

power law fluid in the form of

= kn. (2. 6)

Fig 2. 9: Linear and nonlinear flow curves.

On the other hand, if the flow curve is concave towards the stress axis, it is described as a

shear thickening material, where the shear stress is increasing more rapidly than the rate of

shear strain, which causes the material to become less workable at higher rates of shear

strain.

Feys et al. (2008) investigated the rheological properties of SCC and compared their

finding with the Bingham model. The authors reported that the rheological behaviour is

non-linear (due to negative values of yield stress) and shows shear thickening behaviour,

which can be described by the Herschel-Bulkley model. De Schutter et al. (2008) supports

this nonlinear behaviour. However, the authors do not suggest whether it shows shear

thickening or shear thinning behaviour. The Hershel-Bulkley model can be represented by

the following equation (Feys, et al., 2008):

= o + kn (2. 7)

where the term is the shear stress, k is a constant related to the consistence of the fluid

(consistency factor), is the imposed shear rate, n is the flow index which represents shear

thickening (n>1) or shear thinning (n


22

viscosity, where a high k means a greater viscosity. This model is similar to the power law

model but with the addition of a yield value.

The relationship between torque and the angular velocity in a rheometer is similar to the

Hershel-Bulkley model, which can be calculated by integrating the function relating the

velocity and torsional motion imposed by the geometry of the apparatus. This relationship

is in the following form:

T = To + ANb (2. 8)

where the term T is the torque, A and b are parameters that depend on both the geometry

of the apparatus and the concrete, N is the angular velocity and To is the amount of torque

needed to shear the concrete.

Zerbino et al. (2009) assessed the rheological properties of SCC; they stated that in most

cases the yield stress of SCC would be close to zero, while the plastic viscosity can vary.

It is important to recognise that non-Newtonian fluids, which exhibit a zero yield stress,

are generally called pseudoplastic materials. As previously stated, the yield stress and

plastic viscosity are important rheological parameters, which describe the behaviour of

fresh concrete. However, these parameters can vary depending on various factors, such as

the exposure conditions, the mixing and testing procedures, the constituents in the mix, the

equipment used in establishing the parameters and the idle time following the mixing

procedure.

As previously mentioned, the flow curve which describes shear thinning is concave

towards the shear rate axis; that is, the slope of the nonlinear relationship of strain to shear

increases as the shear rate increases, which means that the reciprocal of the slope

decreases, which means that the viscosity decreases (See Fig 2.10). The reason for this

decrease in viscosity is that the shearing forces are breaking down the structure that

existed in the material when it was at rest (up-curve). The longer the material is sheared

and until a maximum shear rate (1) is reached, then decreasing the rate of shear strain will

allow the structure to rebuild. In Fig 2.10, the down-curve illustrates this reduction in

shearing due to structural breakdown. Rheometers are normally used to measure this down

curve.


23

Fig 2. 10: Hysteresis loop for material suffering structural breakdown under shear.

2.4.2. Thixotropy

The area between the up-curve and the down-curve is known as the hysteresis loop or the

degree of thixotropy and, therefore, the greater the area the more thixotropic the material

is (See Fig 2.10). A material that exhibits a hysteresis loop is known as a thixotropic

material; that is, a material becomes thinner, which occurs in pseudoplastic systems under

increased shearing or when a material becomes thicker, which occurs in dilatant systems

under increased shearing. Thixotropy is reversible and time-dependent, which means that

when concrete is at rest, the viscosity increases, and when concrete is sheared, the

viscosity decreases. These changes in viscosities are time-dependent as it takes time to

build up or break down this thixotropic structure. Furthermore, thixotropy only occurs in

non-Newtonian fluids and not Newtonian fluids, as Newtonian fluids will revert to their

original shape, that is, they have identical upward and downward curves. This is because

their viscosity is constant. It is important to recognise that thixotropy is not the same as

shear thinning or shear thickening as these are not time dependent, but is mainly due to the

flocculation of cement particles when at rest, which results in an increase in viscosity,

while then breaking apart the flocs under shearing reduces the viscosity. Furthermore,

SCC is considered highly thixotropic in relation to traditional concrete (Loukili, 2013).

Shea

r ra

te,

Shear stress,

Down-curve

Up-curve

Hysteresis loop area

1

o(s) = Static yield stress

o = Dynamic yield stress

Shear thickening

Shear thinning

1


24

Fig 2. 11: Apparent viscosity napp as a function of shear rate.

Another important term is used to define thixotropy is the apparent viscosity napp, which

passes through the origin and is the shear stress divided by the shear rate (See Fig 2.11). In

addition, napp is the viscosity of a Newtonian fluid that would behave in a similar manner

as a non-Newtonian fluid at similar shear rates or similar speeds under identical testing

conditions.

Fig 2.11 illustrates shear thickening behaviour, which is represented by the Hershel-

Bulkley curve, it be clearly seen that the apparent decreases with an increase in shear

strain rate until a certain shear is reached 2, once this shear is exceeded, the apparent

viscosity increases. This increase in apparent viscosity (after a certain rate of shear)

suggests shear thickening behaviour because as the apparent viscosity increases, a larger

amount of energy is required to further increase the flow rate. The opposite holds true for

a Bingham material, in that, the apparent viscosity decreases with increasing shear rates

and for a shear thinning material the apparent viscosity decreases at larger increments

relative to a Bingham material at incremental shear rates.

In SCC, thixotropy is important as it creates a higher viscosity when concrete is at rest

than when it is flowing and that higher viscosity is critical for formwork pressure

reduction and segregation resistance. On the other hand, placing SCC, which has a high

degree of thixotropy or a high rate of flocculation, will result in distinct layer casting

which produces a weak interface between the concrete layers (See Figure 2.12).

Shea

r ra

te,

Shear stress,

Bingham Model = o +

napp1

1

o = dynamic yield stress

2

1

Hershel Bulkley Model = o + k

b


25

Fig 2. 12 Distinct layer casting caused by a high degree of SCC thixotropy.

2.5. Constituent materials and effects on SCC workability and rheology

In general, SCC can be produced with a wide variety of constituent materials. However,

these constituent materials influence the workability and rheology of fresh concrete.

Therefore, this section is aimed at evaluating the effect of constituent materials on both the

workability and rheological parameters of SCC.

2.5.1. Influence of coarse and fine aggregates

Incorporating coarse or fine aggregates into a concrete, mortar or cement mix, then

irrespective of their shape or surface texture, the workability of the mix will be reduced

because of the increase viscous drag provided by the particles (Bartos, 1993). Hu and

Wang (2011) stated that concrete rheology is influenced by various aggregate

characteristics such as gradation, size, shape, surface texture, volume fraction and

variability. Furthermore, as the aggregate volume fraction increases so will the

pseudoplastic parameters; that is, the yield stress and plastic viscosity. Fig 2.13 adapted

from Wallevik and Wallevik (2001) shows the influence of different aggregate shapes and

sand contents on the rheological parameters. Rheologically speaking, the use of rounded,

uncrushed aggregates would be preferable to crushed or flaky aggregates, while

incorporating different quantities of fine aggregates within the mix will influence its

rheological nature.


26

Fig 2. 13: Effect of aggregate shape and sand content (after Wallevik and Wallevik 2011).

The water requirements within SCC decrease as the aggregate particle size increases.

Therefore, fine aggregates require an increased water content for desired consistencies. It

is important to recognise that a high degree of particle packing will require less paste for a

given consistency, where a high degree of particle packing is achieved by sufficient

aggregate grading (Hu and Wang, 2011).

In SCC, achieving near optimum particle packing relative to low particle packing has

proven to increase the rheological performance of the mix, which provides an increased

filling capacity and better stability, when flowing (dynamic segregation). Ghoddousi et al.

(2014) reported that with a higher packing density, more free water is available to act as a

lubricant between the solid particles and, therefore, provides better fluidity; this statement

suggests that there is a connection between the rheological parameters and particle

packing. Figure 2.14 2.15 adapted from Fung et al. (2014) illustrates the importance of

particle packing. Providing a sufficient amount of fine materials reduces interlocking

between the coarse particles, which consequently improves the fundamental characteristics

(yield and viscosity) of SCC.

Fig 2. 14: Maximum packing density (after Fung

et al. 2014).

Fig 2. 15: Maximum mass flow rate (after Fung et

al. 2014).


27

Many authors (Zhao, et al., 2012; Mahaut, et al., 2008; Okamura and Ouchi, 2003;

Grunewald and Walraven, 2001) discuss the influence of coarse aggregate content and

grading on the properties of self-compacting concrete. Zhao et al. (2012) assessed four

SCC mixes comprised of different coarse aggregate ratios. In this study, the water-cement

ratio and fine aggregate content remained constant. They stated that the coarse aggregate

content, which ranged from 5 20 mm, had an influence on the workability of SCC.

Consequently, high volumes of 10 20 mm coarse aggregate content relative to high

volumes of 5 10 mm coarse aggregate caused a decrease in the passing ratio (See Table

2.4).

Table 2. 4: Properties of SCC with various A/B ratios (after Zhao et al. 2012).

A/B

ratio

Coarse aggregate (kg/m3)

Initial slump

flow (mm)

L Box test

5-10mm

(A)

10-20mm

(B)

Ratio

(%)

Time

(s)

4/6 434.4

651.6 826 0.96 18.2

5/5 544

544 802 0.95 18.3

6/4 651.6

434.4 786 0.92 18.5

7/3 760.2 325.8 775 0.9 18.7

2.5.2. Cementitious materials

SCC has a much higher paste volume relative to traditional concrete; this increase in paste

volume decreases the yield stress, while increasing the viscosity. Simply put, increasing

the paste will increase the flowability of the mix, while increasing its cohesion, a

characterisation known as rich or fatty (Newman and Choo, 2003). It is important to

recognise that binders incorporated in SCC comprised of just Portland cements will result

in inadequate cohesion, poor segregation resistance and an increase in hydration

temperatures, therefore supplementary cementitious materials (SCM) (fillers) and/or

admixtures are needed to counteract these effects (Domone and Chai, 1996; Yahia, et al.,

2005). In other words, selfcompacting concrete can be produced by simply increasing the

amount of fine materials, either pozzolanic or non-pozzolanic, without altering the water

content relative to traditional concrete. Another alternative is to incorporate a VMA into

the mix, which will provide sufficient stability (Lachemi, et al., 2004; Bosiljkov, 2003).

Domone and Chai (1996) stated that SCC binder contents are relatively high and typically

range between 450 550 kg per cubic meter.

Newman and Choo (2003) illustrated the rheological effects of replacing cement with

SCM, which causes a reduction in yield stress for both pulverised fuel ash (PFA) and


28

ground granulated blast furnace slag (GGBS) with an increase in viscosity for GGBS and

a decrease in viscosity for PFA. Fig 2.16 adapted from Newman and Choo (2003)

illustrates that an increase in paste volume will increase both the yield stress and plastic

viscosity. It is important to recognise that the appropriate usage of a superplasticisers will

decrease the yield stress, while not affecting the plastic viscosity or concrete stability.

Fig 2. 16: Illustration of the effects on the viscoplastic parameters by replacing cement with SCM (after

Newman and Choo 2003).

2.5.3. Influence of PFA on rheology and workability

It is well known that the inclusion of fly ash (FA) in concrete increases the workability

and enhances long-term strength development. Felekolu et al. (2006) reported that SCC

incorporated with SCMs, such as fly ash, will reduce the water content and enhance

concrete workability. Furthermore, the improvement is most likely due to the spherical

shape of the fly ash particles and possibly its surface texture; this improvement allows the

particles to pass easily around each other and, therefore, reduces the internal particle

stresses between the aggregate particles and the paste. It should be noted that the physical

properties of powders play an important role in rheology, i.e., the shape, surface texture,

fineness, particle size distribution and particle packing (Felekolu, et al., 2006). Indeed,

these physical properties are all equally important concerning rheology.

More recently, in 2014, researchers at the University of Petroleum and Minerals (Rahman,

et al., 2014) investigated the thixotropic behaviour of SCC with different mineral

admixtures; they concluded that the inclusion of fly ash, up to 15% cement replacement,

increased the flocculation rate considerably. In the field, flocculation rates are very


29

important, as SCC is required to flow into and fill all spaces within the formwork, under

its self-weight.

Over the last two decades, many researchers (Xie, et al., 2002; Monosi and Moriconi,

2007; Naik et al., 2012; Siddique, 2011; Bouzoubaa and Lachemi, 2001; Liu, 2010) have

studied the performance of SCC containing SCM, such as, Class C fly ash, Class F fly ash

and ultrafine pulverised fly ash (UPFA). Xie et al. (2002) studied the use of UPFA in

SCC. They stated that the appropriate viscosities could be achieved by replacing VMA

with UPFA. Siddique (2011) and Bouzoubaa and Lachemi (2001) studied the properties of

SCC with various levels of Class F fly ash. Siddique (2011) concluded that it is possible to

incorporate fly ash contents of up to 35% replacement of cement, whereas Bouzoubaa and

Lachemi (2001) stated fly ash contents ranging between 40 60% were achievable. In all

mixtures, both Siddique (2011) and Bouzoubaa and Lachemi (2001) used various

superplasticisers, while Bouzoubaa and Lachemi (2001) also used an air entraining

admixture (AEA). Furthermore, the differences in SCC Class F fly ash usage were most

likely due to a number of factors, mainly, the different chemical admixtures, and various

levels of constituent materials within the mixtures. Nevertheless, it is important to

recognise that fly ash, in general, will improve the rheological parameters, while reducing

the need for chemical admixtures and the level of fly ash usage depends on the types of

chemical admixtures and/or the quality, type, size, grading and quantities of constituent

materials within the mix.

According to Krishnapal et al. (2013), the inclusion of fly ash for cement replacement

levels of up to 30% improves the slump flow value, decreases the V-funnel time and

shows no significant variation in blocking ratio (L-box) when compared to SCC

comprised of only Portland Cement (PC). In this study Class F Fly ash replacements were

used, while various dosages of superplasticiser were used (Polycarboxylic ether based).

The authors reported that the addition of fly ash reduced the need for a superplasticiser in

achieving the same workability. It is important to recognise that reducing the V-funnel

time and increasing the spread capacity allows one to achieve a more workable mix.

However, its workability in terms of abilities must comply with known criteria set out by

EFNARC.

When using fly ash in SCC a reduction in superplasticiser dosage is needed along with an

increase in water/cement ratio in order to keep the slump flow and V-funnel time constant

when compared with zero replacement of fly ash (Liu, 2010).


30

2.5.4. Influence of GGBS on rheology and workability

As mentioned previously, the inclusion of GGBS within SCC mixes reduces the yield

stress and increases the viscosity. Indeed, GGBS can be used as a supplementary

cementitious cement replacement (SCCR) to improve SCC workability and provide long-

term strength development (Boukendakdji, et al., 2009). In 2009, Boukendakdji et al.

studied the effect of GGBS upon SCC rheology. A polyether-polycarboxylate based

superplasticiser and various levels of constituent materials were used in this study. In all

the mixtures, the authors concluded that the use of GGBS was found to improve the

workability, with an optimum slag content of 15%. (See Fig 2.17 2.18).

Fig 2. 17: Influence of slag content on filling

ability (after Boukendakdji et al. 2012).

Fig 2. 18: Influence of slag content on passing

ability (after Boukendakdji et al. 2012).

2.5.5. Blended cementitious materials

More recently, in 2009, researchers (Gesolu, et al., 2009) at the University of Gaziantep

studied the properties of SCC made with various blends of SCM. Table 2.5 summarises

the rheological effects of incorporating binary and ternary blends of SCM in SCC. The

authors reported that in all mixtures, relative to a reference mix (Control-PC), L-box

H2/H1 ratios increased, thus improving the passing and filling abilities of SCC. A

Polycarboxylic-ether type superplasticiser and various levels of constituent materials were

used in this study. In all mixtures, the authors reported that only the ternary use of

Portland cement (PC), fly ash (FA) and slag (GGBS) satisfied the acceptable criteria of

EFNARC.


31

Table 2. 5: Fresh properties of SCC with various level of SCM (after Gesolu et al. 2009).

Slump flow L-Box V-funnel

flow time (s)

Mix no Mix ID T50 D (cm) H2/H1

M1 Control-PC 1.0 67.0 0.706 3.2

M2 20FA 2.0 67.5 0.706 10.4

M3 40FA 2.0 73.0 0.800 6.0

M4 60FA 1.0 72.0 0.950 4.0

M5 20GGBS 3.0 67.0 0.704 10.0

M6 40GGBS 3.0 71.0 0.706 14.0

M7 60GGBS 3.0 70.5 0.732 12.0

M8 10FA10GGBS 3.0 70.5 0.854 9.9

M9 20FA20GGBS 2.2 69.0 0.859 6.6

M10 30FA30GGBS 3.0 73.0 0.904 6.2

Acceptable criteria of SCC suggested by EFNARC

Minimum 2.0 65.0 0.800 6.0

Maximum 5.0 80.0 1.000 12.0

2.5.6. Steel fibres

The benefits of using steel fibres in concrete are well known and established. In relation to

traditional concrete, the use of steel fibres enhances the structural performance of

concrete, mainly, improved structural rigidity and resistance to impact. (Holschemacher, et

al., 2010). Intuitively, these structural enhancements can be achieved in SCC, with

significant benefits due to its flowable nature. Cunha et al. (2009) stated that after the

occurrence of matrix cracking, the fibres bridge the crack, which providing a resistance

against increased cracking widths. In essence, the rheological characteristics of SFSCC

will ultimately dictate its performance in its fresh state.

Grnewald and Walraven (2001) investigated the influence of various fibre types and

volumetric proportions on the workability of SCC. In all the mixtures, the authors stated

that both the fibre type and fibre content affects the deformation of SCC. However, mixes

with fibre contents up to 120 kg per cubic meter produced satisfactory flow regimens, but

with some reduction in passing ability. It is important to recognise that incorporating

relatively high fibre content is dependent upon the geometrical proportions of the fibres in

question, i.e., aspect ratio and shape. Fig 2.19 adapted from Grnewald and Walraven

(2001) illustrates the maximum steel fibre content relative to fibre type.


32

Fig 2. 19: Maximum fibre content relative to fibre type for SCC (after Grnewald and Walraven 2001).

Similarly, Ponikiewski (2009) reported that increased fibre content and different aspect

ratios affected concrete workability. Furthermore, they showed that fibre type, volume

fraction, shape and length significantly influence the fresh pro

Roy Belton: The Rheological and Empirical Characteristics of Steel Fibre Reinforced Self-Compacting Concrete with GGBS and PFA

Documents

workability of sfrscc

plastic viscosity of

empirical parameters

empirical aspects of

slump flow t500 time

inverted slump flow

ggbs cement replacements

use of pfa