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

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. WestTrinity 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.

ComponentSeries 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

PE

RC

EN

TA

GE

PA

SS

ING

%

PARTICLE SIZE (MM)

GGBS

CEM II/A-L

Fly-ash

LS

Fig. 2. Particle size distribution of powders

To

rque

(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

PE

RC

EN

TA

GE

PA

SS

ING

%

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

To

rque

(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 SF5 kg/m3 SF

10 kg/m3 SF15 kg/m3 SF20 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

To

rque

(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)


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

To

rque

(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


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

Rheo

logic

al p

aram

eter

, g

Steel fibre content (kg/m3)

SFRSCC

SFRSCC with PFA

SFRSCC with GGBS0

1

2

3

4

5

6

7

0 5 10 15 20 25 30

Rheo

logic

al p

aram

eter

, 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-b

ox b

lock

ing r

atio

(H

2/H

1)

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-17SCC-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

Slu

mp

-flo

w s

pre

ad v

alue

(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-6SCC-7

SCC-8

SCC-9

SCC-10

SCC-12

SCC-11

SCC-13

SCC-15

SCC-16

SCC-17

SCC-18

SCC-19SCC-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

Rheo

logic

al p

aram

eter

, 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.


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

Rheo

logic

al p

aram

eter

, h


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 1.4R

heo

logic

al p

aram

eter

, h


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.



0 kg/m3 SF

5 kg/m3 SF

10 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

Rheo

logic

al p

aram

eter

, h


Series 3 (GGBS)



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