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.
CHAPTER 1 - INTRODUCTION
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
CHAPTER 1 - INTRODUCTION
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
CHAPTER 1 - INTRODUCTION
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.
CHAPTER 1 - INTRODUCTION
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.
CHAPTER 1 - INTRODUCTION
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
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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).
CHAPTER 2 REVIEW OF THE LITERATURE
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.
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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,
CHAPTER 2 REVIEW OF THE LITERATURE
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.
CHAPTER 2 REVIEW OF THE LITERATURE
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.
CHAPTER 2 REVIEW OF THE LITERATURE
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.
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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.
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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.
CHAPTER 2 REVIEW OF THE LITERATURE
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).
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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
CHAPTER 2 REVIEW OF THE LITERATURE
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).
CHAPTER 2 REVIEW OF THE LITERATURE
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.
CHAPTER 2 REVIEW OF THE LITERATURE
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.
CHAPTER 2 REVIEW OF THE LITERATURE
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