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

1. TEMPLATE DESIGN © 2008
www.PosterPresentations.com
The Rheological Characteristics of Steel Fibre Reinforced Self-Compacting
Concrete with GGBS and PFA
Roy P. Belton and Dr. Roger P. West
Trinity College, Dublin, Centre of Civil, Structural and Environmental Engineering
Abstract
Materials and Test Methods
C. Mix procedure
A free-fall mixer was used throughout this study. The following mix procedure was adopted: (i)
Coarse aggregates and 40% water for 10s (ii) Fine aggregates and powders for 60s (iii)
Superplasticiser and 50% water for 20s (iv) Stabiliser and 10% water for 20s (v) Resting period of
600s (vi) Mixing period of 60s and (vii) Steel fibres for 60s.
D. Test methods
The quantitative empirical tests used in this experiment were the slump flow, L-box and J-ring. The
inverted slump flow cone method was used in this experimental program. After lifting the slump flow
cone, the slump flow is the mean horizontal flow spread and the t500 time is the time taken to reach a
flow spread of 500 mm. Both the L-box and J-ring were used to assess the passing ability. The
concrete in the L-box is placed in the vertical channel. Opening the gate allows the concrete to flow
through the vertical bar spacings and into the horizontal channel, the height of concrete in both the
vertical and horizontal channel are then expressed as a ratio, known as the passing ratio, where an
acceptable passing ratio ranges from 0.8 – 1.0. In the J-ring, the inverted cone is lifted, the t500 time
recorded, that is, the time for the concrete to reach a 500 mm spread distance and its passing ability is
assessed by the average height of concrete at four points around the ring minus the height at the
central position and expressed in mm, where an acceptable passing value ranges from 0 – 10 mm.
When testing steel fibre reinforced self-compacting concrete (SFRSCC) on-site, it is not practical to
determine the fundamental properties 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. Within this paper, 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). Three self-compacting mixtures with different PFA and GGBS contents were used as
reference. Each of the concretes were tested with one type of steel fibre at different contents. This was
done to evaluate the influence of PFA and GGBS on both the rheological and empirical parameters of
SFRSCC. In doing so, therefore, a correlation between concrete rheology and concrete workability
could be determined. The results show that the use of PFA and GGBS in SFRSCC caused an overall
reduction in g and an increase in h. 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 using
30% PFA and 50% GGBS. 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 on-site 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.
A Glenium 27 superplasticiser based on chains of a modified Polycarboxylic ether complex was used
to achieve an adequate workability. RheoMatrix 100, an aqueous solution of a high-molecular weight
synthetic copolymer was used to modify the viscosity and cohesion of the mixtures. Ordinary tap
water was used as mixing water in all the mixtures. One steel fibre (SF) type with hooked ends (R
65/35) were used in all the SFRSCC mixtures. The 65 is the aspect ratio and the 35 in the fibre length
in mm. Both locally available sand and gravel were used. Crushed stone aggregates of nominal
maximum size 10 mm were used as coarse aggregates. Fig. 3 shows the particle size distributions of
all the aggregates.
Introduction
Self-Compacting Concrete (SCC) is defined as a concrete that possesses both superior flowability and
a high resistance to segregation, which must flow and fill into all the areas in the formwork, under its
own weight, and without the need for conventional vibrating techniques. It is well known that the use
of steel fibres enhances the structural performance of concrete, mainly improved rigidity, resistance to
impact and improved resistance to cracking. Intuitively, these structural enhancements can be achieved
in SCC. However, fibres are known to significantly affect the workability of concrete.
Various empirical tests have been developed to evaluate the workability of SCC (such as Slump
flow, L-box and J-ring) concerning its ability to flow and fill into all the areas in the formwork, while
producing an adequate uniform distribution of constituent materials. It is well known that the slump
flow test is the most widely used test for evaluating the flowability of SCC. It is a modified version of
the slump test, which measures two parameters: horizontal flow spread and flow time. The flow spread
evaluates unconfined deformability and the flow time evaluates the rate of deformation within a
confined flow distance.
Grunewald and Walraven (2001) investigated the influence of both different types of fibres and
aspect ratios with various volumetric proportions on the workability of SCC. In all the mixtures, the
authors report stated that the fibre type and fibre content affects the workability of SCC. Furthermore,
a higher fibre aspect ratio caused a reduction in workability. The aspect ratio describes the fibre length
divided its diameter.
Tattersall and Banfill (1983) define rheology as the “science of deformation and flow of matter”. In
essence, rheology is concerned with relationships between stress, strain, rate of strain and time.
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. Feys et al. (2008) investigated the
rheological properties of SCC and compared their finding with the Bingham model. The authors
reported that the stress-strain relationship of SCC is nonlinear and, therefore, shows shear thickening
behaviour, which can be described by the Hershel-Bulkley model. The Hershel-Bulkley model can be
represented by the following equation:
τ = τo + kγn (1)
where the term τ is the shear stress, τ0 is the yield stress, k is a constant related to the consistency, γ is
the imposed shear strain rate and n is the flow index which represents shear thickening (n>1) or shear
thinning (n<1) and when n equals 1, the model takes the form of the Bingham model.
The torque-speed relationship in a rheometer is similar to the Hershel-Bulkley model, which can be
evaluated by integrating the function speed and torsional motion by the geometry of the rheometer.
This relationship is in the following form:
T = T0 + ANb (2)
where the term T is the torque, A and b are parameters that depend on the geometry of the rheometer
and the concrete, N (rev/s) is the speed and T0 (N/m) is the amount of torque required to shear the
concrete. By using equation (2) the nonlinear relationship of torque to speed can be determined.
OPTIONAL
LOGO HERE
OPTIONAL
LOGO HERE
Fig. 1. Hershel-Bulkley torque-speed relationship.
A. Experimental program on SFRSCC with PFA and GGBS
Three self-compacting reference mixtures were developed with different compositions. Table 1
summarises these different compositions.
Component
Series 1
(kg/m3)
Series 2
(kg/m3)
Series 3
(kg/m3)
CEM II/A-L 580 406 290
Limestone filler 20 20 20
GGBS - - 290
PFA - 174 -
Fine aggregate 1020 1020 1020
Coarse aggregate 630 630 630
Superplasticiser (Glenium 27) 12.5 12.5 12.5
Stabiliser (RheoMatrix 100) 7.8 7.8 7.8
Water 215.5 215.5 215.5
Table 1: Mixture composition for all reference mixtures
Steel fibre type
Steel fibre
content
SCC-Series
1 (R 65/35)
SCC-Series 2
(R 65/35)
SCC-Series 3
(R 65/35)
0 (kg/m3) (REF) o o o
5 (kg/m3) o o o
10 (kg/m3) o o o
15 (kg/m3) o o o
20 (kg/m3) o o o
25 (kg/m3) o o o
30 (kg/m3) o o o
Table 2: Experimental program
0
10
20
30
40
50
60
70
80
90
100
0.0001 0.001 0.01 0.1 1
PERCENTAGEPASSING%
PARTICLE SIZE (MM)
GGBS
CEM II/A-L
Fly-ash
LS
Fig. 2. Particle size distribution of powders
Torque(N/m)
Speed (rev/s)
Slope = h
T = To + ANb
g
Linear approximation
of Hershel-Bulkley
model
0
10
20
30
40
50
60
70
80
90
100
0.01 0.1 1 10 100
PERCENTAGEPASSING%
PARTICLE SIZE MM
Sand B & Coarse
aggregates
Sand B
Series 1
Series 2
Series 3
Fig. 3. Particle size distribution of the aggregates
To verify the obtained empirical and rheological parameters, cubes were cast for each mixture and
tested at seven-day compressive strengths. The compressive strengths for series 1 and series 2 ranged
from, respectively, 64.7 – 68.1 Mpa and 33.9 – 36.8 Mpa, while series 3 ranged from 52.1 – 56.3 Mpa.
B. Materials
The cement used throughout this experiment was CEM II/A-L, while also using PFA, GGBS and
limestone filler (LS). The volume ratio of both the PFA and GGBS was kept constant at, respectively,
70:30 and 50:50, and 95:05 for the LS. Fig. 2 shows the particle size distributions of all the powders
used in this experiment.
concrete sample to be raised and supported both during testing and following the testing regime. The
effective height between the top of the bowl and the shearing surface is 75 mm. Before initiating the
testing regime, the apparatus must run for 30 minutes to allow the oils (both hydraulic and gear) to
reach their operating temperatures, and during the warmup period, the recommended speed is 0.7
rev/s. However, Tattersall (2003) recommended speeds of 3.0 rev/s because at a warmup speed of 0.7
rev/s the idling pressure can change even after 80 minutes. In essence, the torque-speed relationship
for the concrete undergoing testing is determined by reducing the speed (rev/s) from 0.7 to 0.3 rev/s
at various speed intervals, while recording the resulting pressure (lb/in2) at these intervals of speed.
In doing so, the torque intercept and slope and, therefore, the rheological parameters g and h are
determined.
Fig. 4. Empirical test methods: (i) L-box (ii) Slump flow and
(iii) inverted J-ring.
Fig. 5. Schematic diagram of TWT.
A. Effect of SF, PFA and GGBS on rheology
Rheological testing was performed on all the mixtures, 15 min after the addition of mixing water. In
considering all the possible functional relationships for all the mixtures, the polynomial function
seems to produce the best fit correlation between torque and speed. The slopes of these relationships
and, therefore, the h parameters were determined by a linear approximation of the fitted Hershel-
Bulkley model. Fig. 6 – Fig. 8 illustrates these fitted Hershel-Bulkley relationships for all the
mixtures corresponding to a TWT carried out 15 min after the addition of water. In Fig. 6 – Fig. 8,
SCC-1 to SCC-7 represents series-1 with 0kg/m3 – 30kg/m3 of SF, SCC-8 to SCC-14 represents
series-2 with 0kg/m3 – 30kg/m3 of SF and SCC-15 to SCC-21 represents series-3 with 0kg/m3 –
30kg/m3, respectively.
0
1
2
3
4
5
6
7
8
9
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3
Torque(N/m)
Speed (rev/s)
SCC-1, 15 min
SCC-2, 15 min
SCC-3, 15 min
SCC-4, 15 min
SCC-5, 15 min
SCC-6, 15 min
SCC-7, 15 min
Series 1 (CEM II/A-L)
0 kg/m3 SF
5 kg/m3 SF
10 kg/m3 SF
15 kg/m3 SF
20 kg/m3 SF
25 kg/m3 SF
30 kg/m3 SF
0
1
2
3
4
5
6
7
8
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3
Torque(N/m)
Speed (rev/s)
SCC-8, 15 min
SCC-9, 15 min
SCC-10, 15 min
SCC-11, 15 min
SCC-12, 15 min
SCC-13, 15 min
SCC-14, 15 min
Series 2 (PFA)
0 kg/m3 SF
5 kg/m3 SF
10 kg/m3 SF
15 kg/m3 SF
20 kg/m3 SF
25 kg/m3 SF
30 kg/m3 SF
Results and Discussion
0
2
4
6
8
10
12
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3
Torque(N/m)
Speed (rev/s)
SCC-15, 15 min
SCC-16, 15 min
SCC-17, 15 min
SCC-18, 15 min
SCC-19, 15 min
SCC-20, 15 min
SCC-21, 15 min
Series 3 (GGBS)
0 kg/m3 SF
5 kg/m3 SF
10 kg/m3 SF
15 kg/m3 SF
20 kg/m3 SF
25 kg/m3 SF
30 kg/m3 SF
Fig. 6. Fitted Hershel-Bulkley models for SCC-1 to SCC-7, 15 min
after the addition of water.
Fig. 7. Fitted Hershel-Bulkley models for SCC-8 to SCC-14,
15 min after the addition of water.
Fig. 8. Fitted Hershel-Bulkley models for SCC-15 to SCC-21, 15 min
after the addition of water.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 5 10 15 20 25 30
Rheologicalparameter,g
Steel fibre content (kg/m3)
SFRSCC
SFRSCC with PFA
SFRSCC with GGBS
0
1
2
3
4
5
6
7
0 5 10 15 20 25 30
Rheologicalparameter,h
Steel fibre content (kg/m3)
SFRSCC
SFRSCC with PFA
SFRSCC with GGBS
Fig. 1 illustrates the Hershel-Bulkley
relationship of torque to speed. The Hershel–
Bulkley parameters (A and b) are determined by
plotting ln (T – T0) versus ln N. The constant A
is determined by the intercept on the y-axis (ln T
–T0 axis) and b is the slope of the straight-line
relationship. The rheological parameter g is the
intercept of this relationship on the torque axis
and is related to the fundamental parameter of
yield stress. The dashed black line in Fig. 1 is a
linear approximation of the fitted Hershel-
Bulkley model, in which the slope of this line h
is related to the fundamental parameter of
plastic viscosity. In this paper, the rheological
properties of all the mixtures were evaluated by
the rheological parameters g and h.
Fig. 9. Effect of PFA and GGBS on the rheological parameter g, 15
min after the addition of mixing water.
Fig. 10. Effect of PFA and GGBS on the rheological parameter
h, 15 min after the addition of mixing water.
B. Empirical and rheological parameters for SFRSCC
The relationship between the J-ring step of blocking and L-box blocking ratio for all the mixtures
(i.e. 15 to 95 min after the addition of water) is presented in Fig. 14. From Fig. 14, it may be
observed that a linear relationship exists between these empirical values with a correlation
coefficient (R2) of 0.83 and a coefficient of variation of -2.13, which suggests that the J-ring step of
blocking is inversely related to the L-box blocking ratio. Therefore, as the J-ring step of blocking
(mm) decreases, L-box ratio increases. The following empirical relation may be obtained by least
square regression:
LB = 1.09-0.029(JR) (3)
where JR is the J-ring step of blocking in mm and LB is the L-box blocking ratio.
LB = -0.029JR + 1.09
R² = 0.83
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60 80
L-boxblockingratio(H2/H1)
J-ring, step of blocking (mm)
SCC-1 to SCC-21, 15 min
SCC-1 to SCC-21, 30 - 65 min
SCC-1 to SCC-21, 60 - 95 min
SCC-7, 95 min
CV = -2.13
Initially, it was assumed that the steel
fibres would reduce the workability.
Therefore, it was necessary to design a
self-compacting reference mixture with a
high degree of flowability. For this
reason, both the paste and mortar content
were varied by increasing the ratio of
sand to aggregate and increasing the
cement content, while the contents of
water, superplasticiser and stabilizer
were adjusted by trial and error to obtain
both a high slump (700 mm) and high
passing ability (J-ring: 7.25 mm). Table 1
summarises the final mix design. Next,
to evaluate both the empirical and
rheological parameters of SFRSCC
various steel volumetric proportions of
steel fibres were incorporated into each
reference mix. Table 2 lists all the
SFRSCC mixtures as part of this
experimental program. Three SCC and
18 steel fibre reinforced mixtures were
tested.
SCC-1
SCC-2
SCC-3
SCC-4
SCC-5
SCC-6
SCC-7
SCC-8
SCC-10
SCC-9
SCC-11
SCC-12
SCC-13
SCC-15
SCC-16
SCC-17
SCC-18
SCC-20
SCC-19
SCC-14
SCC-21
SF = -43g + 730.9
R² = 0.8
640
650
660
670
680
690
700
710
720
730
0.00 0.50 1.00 1.50 2.00 2.50
Slump-flowspreadvalue(mm)
Rheological parameter, g
CV = -4.57
Fig. 14. Variation of J-ring step of blocking with L-box blocking
ratio for SCC-1 to SCC-21, 15 to 95 min after the addition of water.
Fig. 15. Variation of Slump flow with rheological parameter
g for SCC-1 to SCC-21, 15 min after the addition of water.
The variation of slump flow and slump t500 time with, respectively, g and h is presented in Fig. 15
and Fig. 16. It may also be observed from Fig. 15 that there exists a linear relationship between
slump flow and g with an obtained correlation coefficient (R2) of 0.8 and a coefficient of variation
(CV) of -4.57, which suggests that g is inversely related to slump flow. As the rheological parameter
g decreases, slump flow increases. In addition, the obtained parameters g and h for SCC-7 and SCC-
21 were not included in this analysis, as a significant amount of coarse aggregates and steel fibres
had settled to the bottom of the TWT bowl. The following empirical relation may be obtained by
least square regression:
SF = 730.9-43(g) (4)
where SF is the slump flow in mm and g is the rheological parameter in N/mm, which is related to
yield stress.
SCC-1 SCC-2
SCC-3
SCC-4
SCC-5
SCC-6
SCC-7
SCC-8
SCC-9
SCC-10
SCC-12
SCC-11
SCC-13
SCC-15
SCC-16
SCC-17
SCC-18
SCC-19
SCC-20
SCC-14
SCC-21
h = 1.63t500 - 0.68
R² = 0.835
0
1
2
3
4
5
6
7
8
9
0 2 4 6
Rheologicalparameter,h
Slump-flow, t500 time (sec)
CV = 0.72
It may be observed from Fig. 16 that there also
exists a relationship between slump flow t500
time and h with a correlation coefficient (R2) of
0.835 and a coefficient of variation of 0.72,
which suggests that the slump flow t500 time is
positively related to the rheological parameter
h. Therefore, the following empirical
relationship may be obtained by least square
regression:
h = 1.63(t500)-0.68 (5)
where h is the slope of the torque-speed
relationship (i.e., the slope of the linear
approximation of the Hershel-Bulkley model,
which is related to plastic viscosity and t500 is
the slump flow t500 time in seconds.
Fig. 16. Variation of Slump flow t500 time with h for SCC-1 to
SCC-21, 15 min after the addition of water.
Conclusion
(i) There is a good correlation between the J-ring step of blocking and L-box blocking ratio for all the
mixtures at testing times corresponding to 15 to 95 min after the addition of both mixing water and
cementitious materials. J-ring step of blocking decreases linearly as L-box blocking increases.
(ii) A good correlation between inverted slump flow and g for all the mixtures, 15 min after the
addition of both mixing water and cementitious materials.
(iii) A good correlation between inverted slump flow t500 time and h, 15 min after the addition of
water and cementitious materials.
(iv) The rheological parameters g and h increased with an increase in steel fibres content. In addition,
there is a good correlation between the relative parameters g and h with increasing steel fibre
contents. Using 30% PFA and 50% GGBS CEM II/A-L cement replacements reduced the parameter
g, while causing an increase in h.
(v) The workability of SFRSCC is retained for longer periods when using 30% PFA and 50% GGBS
CEM II/A-L cement replacements.
(vi) 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.
It may be observed that, in both cases (Fig. 9 – 10), the rheological parameters g and h increase with
an increase in steel fibre content. In addition, the parameter g decreases when using PFA and GGBS
CEM II/A-L cement replacements in SFRSCC. However, the parameter g is somewhat constant for
both the SFRSCC and the SFRSCC with 50% GGBS CEM II/A-L replacement at SF contents ranging
from 0 – 15kg/m3. In Fig. 13, it may be observed that the parameter h increases when using 30% PFA
and 50% GGBS CEM II/A-L replacements in SFRSCC.
20 kg/m3 SF
0 kg/m3 SF
5 kg/m3 SF
10 kg/m3 SF
15 kg/m3 SF
25 kg/m3 SF
30 kg/m3 SF
h = 1.939g2 - 2.764g+ 3.601
R² = 0.855
0
1
2
3
4
5
6
7
8
0 0.4 0.8 1.2 1.6 2 2.4
Rheologicalparameter,h
Rheological parameter, g
Series 1 (CEM II/A-L)
0 kg/m3 SF
5 kg/m3 SF
10 kg/m3 SF
15 kg/m3 SF
20 kg/m3 SF
25 kg/m3 SF
30 kg/m3 SF
h = 2.923e0.386g
R² = 0.841
3
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
0.4 0.6 0.8 1 1.2 1.4Rheologicalparameter,h
Rheological parameter, g
Series 2 (PFA)
Fig. 11. Variation of g and h with increasing steel fibre (SF)
contents for SCC-1 to SCC-7, 15 min after the addition of water.
Fig. 12. Variation of g and h with increasing steel fibre (SF)
contents for SCC-8 to SCC-14, 15 min after the addition of water.
0 kg/m3 SF
5 kg/m3 SF
10 kg/m3 SF
15 kg/m3 SF
20 kg/m3 SF
25 kg/m3 SF
30 kg/m3 SF
h = 4.362e0.272g
R² = 0.708
4
4.5
5
5.5
6
6.5
7
0.6 0.8 1 1.2 1.4
Rheologicalparameter,h
Rheological parameter, g
Series 3 (GGBS)
Fig. 13. Variation of g and h with increasing steel fibre (SF)
contents for SCC-15 to SCC-21, 15 min after the addition of water.
Fig. 11 – Fig. 13 illustrates the variation of g and h with increasing steel fibre contents for SCC-1 to
SCC-21. In addition, the obtained correlation coefficients for SCC-1 to SCC-21, 15 min after the
addition of water are illustrated. As shown in Fig. 11, a second order polynomial function seems to
yield the best-fit correlation between the rheological parameters g and h, with a best-fit correlation,
R2, of 0.855. It is the author’s opinion that the obtained rheological parameters (g and h) associated
with SCC-7 are most likely underestimated, because during testing a significant degree of
segregation was encountered. Nevertheless, the results for SCC-7 were included in this analysis.
The rheological tests were performed with the Tattersall Two-point workability apparatus (TWT), in
particular, the MK II model, which involves an axial impeller with four angled blades positioned in a
helical arrangement around a central drive shaft. The schematic diagram is shown in Fig. 5. A
cylindrical bowl containing the concrete is supported by means of an adjustable arm. This allows the
From Fig. 12 – Fig. 13, it may be observed
that an exponential function seems to yield
the best fit correlation between g and h for
SCC-8 to SCC-13, and SCC-15 to SCC-20
with best fit correlations of, respectively,
0.841 and 0.708. Also, the torque-speed
relationships and, hence, the obtained
parameters g and h for SCC-14 and SCC-21
were not included in this analysis, as the
obtained torque-speed relationship for these
data points possessed a significant degree of
nonlinearity, which is an indication of
segregation. Furthermore, during rheological
testing a high degree of segregation was
encountered in SCC-14 and SCC-21.
The 33rd Irish Concrete Society Awards