Roy Belton: M.Sc. Dissertation - 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

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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:

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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.

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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.

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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

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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

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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
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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.

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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

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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

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(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.

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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.

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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
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2.1. Introduction
During the late 1980s, and due to the gradual decline of skilled operatives in Japan’s 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

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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

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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 μm (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

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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).

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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 μm in diameter, of which the most of it passes the 45 μm 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.

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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; Gesoğlu, 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 (Felekoğlu, 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; Łaźniewska-Piekarczyk, 2014). In general, superplasticisers improve SCC fluidity by repelling the cement particles and decreasing particle flocculation (Roussel, 2011). Łaźniewska-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 (Grünewald 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 Hooke’s 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, τ = F/A and the angle γ 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: τ = nγ (2. 1) where n is the constant of proportionality, also known as the rigidity modulus or shear modulus.
Fig 2. 4: Hooke’s law for a material in shear (F/A = nγ).
Fig 2. 5: Hookean solid in shear.
Fig 2.5 illustrates a straight-line relationship if τ is plotted as a function of γ 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, τ and is measured by the time differential of shear strain. Therefore, the time differential of γ is proportional to τ and is represented by the following equation: τ=ndϒdt . (2. 2)
This equation is similar to Hooke’s 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 Newton’s 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
Shear stress, τ
Shear strain, γ
Slope = n

19
v and inversely proportional to the distance L between the planes, and is expressed by the following: τ=ndvdL (2. 3)
dv/dL is known as the velocity gradient, which can be shown to be the same as dγ/dt and, therefore Newton’s law of viscous flow can be expressed as: τ = nγ (2. 4) where γ is the rate of shear and n is the constant of proportionality.
Fig 2. 6: Newton’s 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
Shear stress, τ
Rate of shear, γ
Slope =n
τ= nγ

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 τ = τo + μγ (2. 5) where the term μ is the plastic viscosity, γ is the rate of shear and τo 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
Shear stress, τ
Rate of shear, γ
Slope =μ
τ= τo+ μγ
A
B
τo

21
increasing shear strain rate. The following equation represents this and is known as a power law fluid in the form of τ = kγn. (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): τ = τo + kγn (2. 7) where the term τ is the shear stress, k is a constant related to the consistence of the fluid (consistency factor), γ is the imposed shear rate, n is the flow index which represents shear thickening (n>1) or shear thinning (n<1) and τo is the yield stress. When n is equal to 1, the model takes the form of a Bingham model. In addition, the term k is related to plastic
γ

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 (γ1) 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).
Shear rate, γ
Shear stress, τ
Down-curve
Up-curve
Hysteresis loop area
γ1
τo(s)= Static yield stress
τo = Dynamic yield stress
Shear thickening
Shearthinning
1
μ

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 γ2, 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).
Shear rate, γ
Shear stress, τ
Bingham Model
τ = τo+ μγ
napp
1
μ
1
τo = dynamic yield stress
γ2
γ1
HershelBulkleyModel
τ = τo+ kγb

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).

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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, self–compacting 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. Felekoğlu 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 (Felekoğlu, 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).

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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 (Gesoğlu, 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.

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Table 2. 5: Fresh properties of SCC with various level of SCM (after Gesoğlu 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. Grünewald 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 Grünewald 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 Grünewald 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 properties of SCC. Rheologically speaking, they recommended a fibre volume fraction of 2.0%, approximately 45kg per cubic meter, while recommending the feasible use of high fibre contents with short fibre lengths. Hossain et al. (2012) discussed the influence of steel fibres on the fresh and rheological properties of SCC. They concluded that increasing fibre content increases the plastic viscosity and yield stress, while the use of short fibres relative to long fibres enhances flowability. Grünewald and Walraven (2001) stated that for a required fibre content a lower aspect ratio would achieve a more workable mix relative to the same fibre content with a higher aspect ratio. However, its performance in its hardened state would be slightly compromised as a higher aspect ratio performs somewhat better in its elastic state. The authors also reported that increasing the amount of fibres decreases the slump flow and hence decreases the deformation capacity of SCC. Furthermore, increasing the fibre content while also increasing their aspect ratio increases V-funnel times. Therefore, both higher fibre contents and aspect ratios will reduce workability in terms of abilities.
2.5.7. Effect of delaying SP on rheology Aiad et al. (2002) assessed whether the addition of certain admixtures would affect the rheological properties of cement pastes. More importantly, the authors suggested that

33
delaying certain admixtures, after the addition of water, could significantly reduce the shear stress, while not greatly altering the relative viscosity.
2.5.8. Influence of superplasticiser on rheology
The use of a superplasticiser improves the ability of concrete to deform under its own weight therefore improving its deformation capacity and reducing the yield value. However, superplasticisers should be used with caution as increasing its dosage above the norm can result in an unstable mix, which can compromise its segregation resistance.
2.6. Concrete rheometers
As previously mentioned, a single parameter such as yield stress does not adequately describe the behaviour of fresh concrete. Therefore, concrete rheometers can be used to evaluate the workability of SCC in terms of two parameters. Furthermore, they apply physical measurements to rheology to measure the flow of concrete. i.e., measure the resistance of concrete (shear stress) to flow at varying shear rates (Ferraris, et al., 2001). According to Feraris et al. (2001), various rotational rheometers for concrete are available and are as follows:
 BML (coaxial cylinder)
 BTRHEOM (parallel plate)
 CEMAGREF-IMG (coaxial cylinder)
 IBB (impeller/mixing action)
 Two-point (impeller/mixing action)
Two point and IBB based rheometers operate in a similar manner by rotating an impeller or vane in fresh concrete contained within a container. However, the IBB is fully automated and uses a data input system, which automatically generates the rheological parameters, yield stress and plastic viscosity (Feraris, et al., 20011). In addition, the IBB rheometer requires 21 litres of concrete (Fig 2.20 – 2.21) and is suitable in testing concrete with slumps ranging from 20 mm to 300 mm and does not require calibration and, therefore, the results are not expressed in fundamental units.

34
Fig 2. 20: IBB Rheometer (after Feraris et al. 20011).
Fig 2. 21: H impellers for IBB rheometers for concrete (after Feraris et al. 20011).
The opposite applies to the Two-point apparatus, in that, it is not fully automated and requires two stage calibration: (i) torque calibration and (ii) calibrating the two constants. Furthermore, the two-point apparatus possessing a helical vane arrangement, which is suitable for slumps higher than 100 mm (See Fig 2.22 – 2.23). In both cases (Two- point/IBB), the rotational speed of the vane or impeller is increased and then decreased while the resulting pressure is measured at appropriate speed settings or intervals (Feraris, et al., 2001; Tattersall and Banfill, 1983; Tattersall, 2003).
Fig 2. 22: Two-point workability rheometer (after Feraris et al. 20011).
Fig 2. 23: Impeller arrangement and dimensions (after Feraris et al. 20011).

35
CEMAGREF-IMG and BML are coaxial rheometers. The CEMAGREF-IMF rheometer (Fig 2.24 – 2.25) is a large coaxial rheometer, which requires approximately 500 litres of concrete. Due to its large concrete requirement, it not considered practical. The BML rheometer (Fig 2.26 – 2.27) requires approximately 17 litres of concrete with slumps greater than 120 mm (Roussel. N, 2011). In both cases, a cylinder is rotated at increasing and decreasing speeds and hence the resulting torque is measured.
Fig 2. 24: CEMAGREF-IMG Rheometer (after Feraris et al. 20011).
Fig 2. 25: Inside view of CEMAGREF-IMG Rheometer with grid and blades (after Feraris et al. 20011).
Fig 2. 26: BML Rheometer-version 3 (after Feraris et al. 20011).
Fig 2. 27: BML Rheometer-version 4 (after Feraris et al. 20011).
According to Feraris et al. (2001) evaluating and modelling the flow of concrete in the IBB and Two-point rheometer is no easy task. In addition, the flow of concrete can be mathematically modelled for coaxial rheometers (such as BML, CEMAGREF-IMG) and for the parallel plate rheometer (BTRHEOM), while for the BML, CEMAGREF-IMG and BTRHEOM rheometers it is possible to express their rheological properties in fundamental units of plastic viscosity and yield stress by suitable calibration.

36
The BTRHEOM is a parallel plate rheometer (Fig 2.28 – 2.29) which consists of two parallel disks, one of which is fixed at the bottom while the other is free to shear the material and hence its rotational speed and resistance to shear are measured (Feraris, et al., 2001; Roussel, 2011). According to Roussel (2011), the rotational speed range is between 0.1 rev/s to 1.0 rev/s while its maximum measurable torque is around 14 N/m. Furthermore, its principal requirements are seven litres of concrete, which must possess a slump greater than 100 mm.
Fig 2. 28: BTRHEOM Rheometer (after Feraris et al. 20011).
Fig 2. 29: BTRHEOM Rheometer showing arrangement of blades at top and bottom (after Feraris et al. 20011).
During the period 2000 – 2001, a study was carried out in France (Feraris, et al., 2001), which involved comparing five different rheometers to assess the appropriate method in evaluating concrete workability in terms of yield stress and plastic viscosity. It is important to recognise that no self-compacting mixtures were used in this study. Nevertheless, their study is a good indication of whether any differences exist in the rheological properties between different rheometers. Consequently, the authors concluded that the degree of correlation of both yield stress and plastic viscosity between any two rheometers possessed considerable differences. Furthermore, they stated that these differences were most likely due to calibration, wall slippage and volumetric confinement. Fig 2.30 – 2.31 adapted from Feraris et al. (2001) illustrates these differences in both yield stress and plastic viscosity measurement between five different rheometers.

37
Fig 2. 30: Comparison of yield value (after Feraris et al. 2001).
Fig 2. 31: Comparison of plastic viscosity (after Feraris et al. 2001).
2.7. Mixer and mix procedure
In SCC, the mixer is a key element in producing a well-mixed concrete. SCC can be produced with any concrete mixer, such as paddle mixers (free-fall mixers), truck mixers and force-action mixers. However, force action mixers are preferred if available. The mixing time is doubled when using a paddle mixer to mix SCC when compared with traditional concrete (De Schutter, et al., 2008). The reason for this is due to the higher addition of fine material, which may stick to certain parts of the mixer. According to De Schutter et al. (2008), adding some of the water with some of the superplasticiser and all of the coarse aggregates before adding the finer materials may reduce the adhesion of the fine material to the mixer.
EFNARC (2005) suggests adding two thirds of the water and superplasticiser followed by the aggregates and cementitious materials. However, previous studies have suggested that delaying the addition of superplasticiser could significantly reduce the shear stresses between the cementitious particles, which will improve concrete workability when compared with stage one addition. Therefore, adding more superplasticiser towards the second stage could be a very useful means of achieving the required deformation capacity (650-800 mm) without having to alter the constituents and dosage of superplasticiser in the mix. Wallevik and Wallevik (2011) stated that when using a free-fall mixer the dosage of superplasticiser has to double to maintain the SCC properties (yield value and plastic viscosity) when compared with using a force action mixer. The reason for this may be due

38
to the high shearing of materials in the force action mixer. Furthermore, the VMA should be added after the superplasticiser and just before adjusting the water content for consistency. Grünewald (2004) and Grünewald and Walraven (2001) suggest the following mixing procedure for steel fibre reinforced self-compacting concrete:
Fig 2. 32: Mixing procedure for SFSCC in a force action mixer (after Grunewald and Walraven 2001).
It is important to recognise that the above mixing method is used in combination with a force action mixer. Therefore, adopting this mixing method for a free-fall mixer may cause the paste to adhere to the drum and it does not allow for the adjustment of water content and superplasticiser dosage for consistency.
Testing-SCC reported that a change in mixing temperature from 14ᵒC to 22ᵒC reduced the slump flow value by approximately 50-100 mm. In addition, they stated that the temperature should be maintained at 20ᵒC ± 2ᵒC.

CHAPTER 3 – EMPIRICAL AND RHEOLOGICAL TESTS
39
3.1. Rheological and workability tests
During 1983, it was found that the use of superplasticisers to produce very high workable concrete led to workability assessment problems because none of the existing British Standard tests could be used. These tests include the Vebe test, the Compacting Factor test and the Slump test. For example, the slump test could not be used because concretes possessing a high degree of workability all give collapsed slumps (See Fig 3.1).
Fig 3. 1: Four types of slump (after Koehler and Fowler 2003).
The solution to this assessment problem was to introduce a new testing procedure, known as the flow-table test (See Fig 3.2). The apparatus usually consists of an upper wooden square board with 700 mm sides, which is connected to a baseboard by hinges. In principle, the cone is filled in two layers while each layer is tamped ten times with a wooden rod. Once full, and after the resting and cleaning period, the top board is lifted to the stopping position and allowed to drop, and after 15 consecutive drops the mean of the largest diameter and the diameter perpendicular to it are recorded. According to Tattersall (1991), the flow-table test was reasonably good for assessing segregation by visual inspection, which would suggest that the flow-table method could be used to assess the consistency of concrete. However, the flow-table test was severely criticised by Dimond and Bloomer well before its inclusion in British Standards.

40
Fig 3. 2: Slump flow table test (after Koehler and Fowler 2003).
Due to these criticisms, a modified slump test was developed for evaluating high workable TVC, known as the slump flow test. As SCC possesses a high deformation capacity, the slump flow test is now one of the primary methods for evaluating SCC workability.
Many tests have been developed in an attempt to characterise the fresh properties of SCC. The European federation for SCC, EFNARC, sets out specifications and guidelines for evaluating the fresh properties of SCC. Table 3.1 adapted from EFNARC (2002) illustrates the various test methods for SCC.
Table 3. 1: Various SCC testing methods (after EFNARC 2002). Method Property
1
Slump-flow by Abram’s cone
Filling ability 2 T500 slump flow Filling ability
3
J-ring
Passing ability 4 V-funnel Filling ability
5
V-funnel at T 5 minutes
Segregation resistance 6 L-box Passing ability
7
U-box
Passing ability 8 Fill-box Passing ability
9
GTM screen stability test
Segregation resistance 10 Orimet Filling ability
In order for SCC to fulfil its workability requirements, that is its passing and filling abilities, EFNARC (2002) provides minimum and maximum acceptable criteria for each

41
test method (See Table 3.2). In addition, there is no reliable test for segregation; therefore, it is important to pay close` attention to the risk of segregation.
Table 3. 2: Minimum and maximum criteria for various testing methods (after EFNARC 2002). Method Unit Typical range of values
Minimum
Maximum 1 Slump-flow by Abram’s cone mm 650 800
2
T500 slump flow
sec
2
5 3 J-ring mm 0 10
4
V-funnel
sec
6
12 5 V-funnel at T 5 minutes sec 0 3
6
L-box
(h2/h1)
0.8
1 7 U-box (h2-h1) mm 0 30
8
Fill-box
%
90
100 9 GTM screen stability test % 0 15
10
Orimet
sec
0
5
3.2. Passing ability tests
SCC is required to achieve self-compactability and possesses a relatively high resistance against segregation, while also being able to flow in and around heavily congested reinforcing areas. Amongst the various empirical test methods listed in Table 3.1, the J- ring and L-box are the most common methods for assessing the passing ability of SCC.
3.2.1. J-ring
The J-ring test simulates concrete flow through reinforcement by the use of numerous vertical blocking mechanisms. More specifically, the apparatus is composed of a ring with 12 or 16 vertical steel bars; the latter simulates a more congested reinforcement system (See Fig 3.3).

42
Fig 3. 3: Dimensions of J-ring and measurement positions.
IS EN 12350-12:2010 sets out the basic procedure, in which the conical mould is lifted at a steady rate in an upward direction, which allows the concrete to flow through the bars, and across the base plate. Consequently, the J-ring measures three parameters: flow spread (SFj), flow time (t500j) and blocking step (Bj). The flow spread and flow time simulates SCC deformability within confined reinforcement and defines the rate of deformation (De Schutter, 2005; Testing-SCC, 2005). Once the concrete has ceased flowing and/or reached a spread diameter of 500 mm, the largest spread diameter, dmax, and the one perpendicular to it, dperp, are measured and the t500j time is recorded; that is, the time taken for the concrete to reach a 500 mm spread diameter. The flow spread, SFj, is expressed as the average of dmax and dperp. In an attempt to quantify the blocking mechanism, the average relative flow heights outside the J-ring minus the flow height at a central position inside the J-ring are measured and quantified, called the blocking step value (De Schutter, 2005; Testing-SCC, 2005; IS EN 12350-12:2010).

43
Drawbacks and limitations (De Schutter, et al., 2008):
(i) The base plate must be placed on stable level ground to record the appropriate deformation. An oval shape spread rather than a circular spread indicates uneven ground. It is important to measure the largest spread diameter and the spread diameter perpendicular to it.
(ii) Appropriate results depend on the surface moisture of the base plate therefore the base plate should be wet, but not too wet.
3.2.2. L-box test
In a similar manner to the J-ring, the L-box simulates concrete flow through reinforcement, which evaluates the passing ability of SCC. The L-box is composed of a chimney section and a channel section with different arrangements of vertical bars. The concrete flows from the chimney section, through the vertical bars and into the horizontal channel section (See Fig 3.4).
Fig 3. 4: L-box test on a stable SCC and L-box dimensions (after Nguyen et al. 2006).

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Expression of results
The mean depths of concrete within both the chimney section H1, and channel section H2 are measured and expressed as a ratio, known as the passing ratio PL:
PL = 퐻2 퐻1 . (3. 1)
If the concrete flows freely through the vertical bars, then the passing ratio is equal to 1.0. Likewise, if the ratio is equal to 0.8, then the concrete is too stiff and hence is deemed unacceptable (De Schutter, 2005). ERNARC (2002) recommends acceptable passing ratios ranging from 0.8 – 1.0. Nguyen et al. (2006) stated that yield stress is the most important parameter in deciding on whether the concrete will flow and fill all the spaces within the formwork.
Drawbacks and limitations (De Schutter, et al., 2008):
(i) If a concrete has an extremely high passing and filling ability, the passing ratio maybe greater than 1.0, which can result in the concrete pilling up and splashing out of horizontal channel. This pilling up and spilling effect will significantly affect the test results.
3.2.3. U-test
In a similar manner to the L-box test, the U-test is used to evaluate the passing ability of SCC. The U-test consists of a channel that is divided by a middle wall and hence splits the channel into two compartments. An opening at the bottom of the apparatus is fitted with a sliding door and the sliding door consists of an arrangement of vertical bars with centre to centre spacing of 50 mm (See Fig 3.5).
Fig 3. 5: Schematic of U-box test.

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

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

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