RHEOLOGICAL PROPERTIES AND

SEGREGATION RESISTANCE OF SCC PREPARED

BY PORTLAND CEMENT AND FLY ASH

M.H. Ozkul and U.A. Dogan

Istanbul Technical University, Civil Engineering Faculty, Maslak, Istanbul

Abstract: Self-compacting concrete (SCC) provides high flowability, high filling capacity,

high passing ability through reinforcing bars, which are owned by using a powerful

superplasticizer as well as reducing both the coarse aggregate content and water/

powder ratio. It should also expose high segregation resistance, which can be

obtained by using high amount of fine material or by adding a viscosity modifying

admixture, or both. In this study, the rheological properties and segregation resis-

tance of SCC are examined. The effect of coarse aggregate concentration between

225-375 dm3/m

3 on both flow behavior and segregation resistance of SCCs are

investigated on concretes prepared with cement and fly ash as binder. The total

binder content (including both cement and fly ash) varies between 450 and 650 kg/

m3. The maximum aggregate sizes were chosen as 12, 16 and 20 mm. In the exper-

iments a specially designed apparatus, which was expired from the slump-flow and

L-shape box tests, has been used. This apparatus also allows the measurement of

segregation resistance. The other tests applied were slump-flow and penetration

resistance.

Key words: self-compacting concrete; segregation; rheology.

1. INTRODUCTION

Self-compactability is defined as a capability of concrete to be uniformly filled in

every corner of a formwork by the gravity force without any vibration during casting.

SCC is originally developed in Japan for underwater applications but it can also be uti-

lized in many cases such as repair of voids, production of tall walls and concrete mem-

bers with complex shape or heavily reinforced.

Self-compactability keeps on increasing with the increasing amount of superplasti-

cizer until it reaches a maximum value and then declines due to the segregation of the

concrete1. Slump-flow, V-funnel, U-box and L-box tests can be used to measure the flow-

463

M.S. Konsta-Gdoutos, (ed.), Measuring, Monitoring and Modeling Concrete Properties, 463–468. © 2006 Springer. Printed in the Netherlands.

M.H. Ozkul and U.A. Dogan 464

ing, filling and passing ability of SCC2. Not only high flowability, but also high resistance

to segregation are important properties for SCC. However, the most practical test, slump

flow test, to detect the deformability of SCC, is not sufficient for evaluating resistance to

segregation. Penetration test3, sieving fresh concrete through 5 mm mesh test

4, determin-

ing the coarse aggregate concentration in a L-box3 and J-ring with the Orimet

5 are some

of the proposed methods to measure the segregation resistance of SCC.

In this study, a previously developed apparatus6,7

by the authors is used to measure

rheological properties and segregation resistance of SCC prepared by Portland cement

and fly ash. Effects of total binder content, maximum aggregate size and coarse aggre-

gate concentration were chosen as testing parameters. The results obtained by the devel-

oped apparatus were compared with those obtained by slump flow and penetration tests.

2. EXPERIMENTAL

2.1 Materials

2.1.1 Aggregates

Natural and crushed stone sand were used as fine aggregates and their specific gravi-

ties were 2.62 kg/m3 and 2.71 kg/m

3, respectively. In order to investigate the effect of

maximum size of aggregate on SCC, crushed stone, with a specific gravity of 2.71 kg/m3

was separated into three different parts having maximum sizes of 12 mm, 16 mm and 20

mm. The grading of fine and coarse aggregate was calculated separately. The reference

grading was calculated by using Fuller parabola (1) where di is the mesh size of the sieve

and Pi is the percentage of the aggregate passed form the ith

sieve. In all the batches, fine

aggregate grading was same and coarse aggregate grading was changed according to

maximum size of aggregate.

Pi= (1)

2.1.2 Cement, additive and admixture

An ordinary Portland cement, PC 42.5 (CEM I, in accordance to TS EN 197-1 stan-

dard) and a fly ash, maintained from Cayirhan are used. The fly ash/cement ratio is kept

as 2.5/3 in all mixes. A polycarboxylate based HRWR admixture was employed in all the

mixtures to obtain a sufficient workability.

2.2 Mixing Proportions

The important criteria, fine particle content, coarse aggregate concentration and max-

imum size of aggregate to obtain a SCC are investigated in this study. Each of these three

variables had three levels to be examined. Total binder content was chosen as 450 kg/m3,

550 kg/m3 and 650 kg/m

3 with a fly ash/cement ratio of 2.5/3. The effect of coarse

aggregate concentration on both flow behavior and segregation resistance of SCC were

studied at 225, 300 and 375 dm3 of coarse aggregate contents. In all mixes, maximum

maxD

di

465

size of aggregate, affecting segregation and passing through the highly congested rein-

forcement, was changed between 12 mm 16 mm and 20 mm. Finally, 27 different

batches composed of 3 variable with 3 levels of each were produced. Water/binder ratio

was adjusted to have the best spread of itself at flow test.

2.3 Test Methods

In the experiments a specially designed apparatus (confined-slump flow), which was

expired from the slump-flow and L-shape box tests, has been used. It looks like the J-

ring apparatus, but was developed unaware of it, and consists of a cylinder with a 15 cm

diameter and 30 cm height, surrounded by 12 bars having 35 mm gap between adjacent

bars. This apparatus (Fig. 1) also allows the measurement of segregation resistance while

the concrete is flowing through the bars. For the latter purpose, the concrete left between

the bars is taken out after the flow is completed, wet-sieved through the 4 mm mesh, and

the change in the coarse aggregate concentration is determined with respect to the initial

state. Final diameter of concrete can be also recorded with this apparatus similar to

slump-flow test. The other tests applied were slump-flow and penetration3.

Figure 1. Confined-slump flow apparatus

3. TEST RESULTS AND DISCUSSION

A summary of the test results is presented in Table 1, together with the mix propor-

tions of the concretes. Slump flows of concretes were measured simultaneously by using

Abrams cone in inversed position and by the specially designed apparatus, and are

shown in Figure 2. Table 1 exhibits that, it is necessary to increase the superplasticizer

content over 2% to obtain slump-flow over 60 cm for the concretes with 450 kg/m3

binder content. However, in the confined-flow test, the spreads were remained under

those obtained from the free slump-flow, as shown in Figure 2, although the concrete in

the developed apparatus is 35 % larger than that of Abrams cone. This indicates that,

flow is prevented by the bars due to the insufficient passing ability of the concrete.

Rheological properties and segregation resistance of SCC

M.H. Ozkul and U.A. Dogan 466

On the other hand, for the concretes with 550 kg/m3 binder content, a superplasti-

cizer dosage of 1.2% was found sufficient to obtain slump-flows over 60 cm (Table 1).

Furthermore, the free and confined-slump values obtained on the latter concretes are

close to each other and there is no definite difference between the tendencies of results

for the two slump-flow methods (Figure 2). Table 1 and Figure 2 also show that, the

level of flows for both methods at 650 kg/m3 binder content, are higher than those of the

former two binder contents.

Table 1. Mix proportions and test results

Dmax: Max. aggregate size; W/B: Water/binder ratio; fd: final spread (in cm)

Moreover, for this higher binder content, the spread values obtained in the confined-

slump flow test are larger than those of the free one, indicating a high passing ability

through the obstacles in general, which can be due to the increased amount of powder

material (binder) in the mixtures.

Binder

(kg/m3)

Coarse

Agg.

(dm3)

Dmax

(mm)W/B

Admix

(%)

Slump Flow Penet.

(mm)

Seg.

RatioConfined Free

fd fd

450 375 20 0.31 2.2 46 58

450 300 20 0.31 2.5 49 61

450 225 20 0.32 2.5 58 63

450 375 16 0.31 2.5 41 55

450 300 16 0.32 2.5 58 62

450 225 16 0.33 2.0 54 62

450 375 12 0.30 2.5 47 55

450 300 12 0.31 2.0 44 58

450 225 12 0.33 2.5 54 61

550 375 20 0.26 1,2 60 65 8 1.07

550 300 20 0.26 1,2 64 62 8 1,15

550 225 20 0.27 1,2 62 61 8 1.23

550 375 16 0.26 1,2 63 68 6.5 1.02

550 300 16 0.27 1,2 64 63 5 1.10

550 225 16 0.27 1,2 66 63 3 1.33

550 375 12 0.26 1,2 62 60 5 1.08

550 300 12 0.27 1,2 65 62 8 1.00

550 225 12 0.27 1,2 66 66 2 1.15

650 375 20 0.23 1,2 72 69 4 1.11

650 300 20 0.23 1,2 70 65 9 1.12

650 225 20 0.23 1,2 68 65 15 1.34

650 375 16 0.22 1,2 68 63 10 1.14

650 300 16 0.23 1,2 74 68 17 1.23

650 225 16 0.23 1,2 74 68 15 1.04

650 375 12 0.22 1,2 66 67 6 1.02

650 300 12 0.23 1,2 74 68 20 1.21

650 225 12 0.24 1,2 78 73 17 1.05

Rheological properties and segregation resistance of SCC 467

Figure 3 illustrates the relation between segregation ratio and penetration. The segre-

gation resistance was calculated as the ratio of the coarse aggregate content over 4 mm

size measured on the sample taken from the concrete left between the bars, to the coarse

aggregate content of the original concrete. The results of 450 kg/m3

binder content were

not shown, because they exhibited high segregation. For the binder content of 550 kg/

m3, all the penetrations are equal or smaller than 8 mm, which was given as the pene-

tration limit for an unsegregated SCC3. Figure 3 also shows that the segregation ratio val-

ues measured in this study remain under 1.20 (which corresponds a 20% segregation)

except the mixtures with maximum aggregate sizes of 16 and 20 mm at a coarse aggregate

content of 225 dm3/m

3. Since a powder content of 550 kg/m

3 seems reasonable for

SCC,6,7

a segregation resistance of 20% can be taken as an upper limit.

Figure 3 exhibits the segregation ratio and penetration relations for the binder con-

tent of 650 kg/m3. All the penetration results except two (belonging to the coarse aggre-

gate content of 375 dm3/m

3) remain over the limit of 8. However, the segregation

resistance of 1.20 is exceeded by only three mixtures, and four mixtures exhibited pen-

etrations over 8. It seems that for a high binder content, when the coarse aggregate con-

tent is lower, than the penetration becomes higher. However, for these mixtures, higher

the penetration does not mean that lower the segregation tendency.

Figure 2. Comparison of confined and free spread methods

M.H. Ozkul and U.A. Dogan 468

4. CONCLUSION

The following conclusions can be drawn based on the results of this study:

1 For the low binder contents (450 kg/m3), the confined-slump flow values obtained

by the developed apparatus remained under those of the free slump-flows,

indicating the low passing ability and segregation resistance of these mixtures.

2 For the moderate binder contents (550 kg/m3), the confined and free slump values

were found close to each other and they did not exhibit a definite tendency over

each other. The penetrations remained under the limit of 8 for these mixtures,

however, two of them showed segregation over 20%.

3 For the high binder contents (650 kg/m3), some of the mixtures exhibited

penetrations over 8, although they showed segregations under 20%, which may

be due to the high binder content.

5. REFERENCES

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evaluation test methods, Journal of Advanced Concrete Technology, 1(1), 26-36 (2003).

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(2000).

3. V. K. Bui, D. Montgomery, I. Hinczak, and K. Turner, Rapid testing method for segregation

resistance of self-compacting concrete, Cem. Concr. Res., 32, 1489-1496 (2002).

4. H. Fujiwara, Fundemental study on self-compacting property of high-fluidity concrete, Proc.

Jpn. Concr. Inst., 14 (1), 27-32 (1992).

5. M. Sonebi, Application of statistical models in proportioning medium-strength self-consoli-

dating concrete, ACI Materials J., 101 (5), 339-346 (2004).

6. M. H. Ozkul, U. A. Dogan, Z. Cavdar, A. R. Saglam and N. Parlak, Properties of fresh and

hardened concretes prepared by new generation superplasticizers, Int. Conf. on Modern Con-

crete Materials: Binders, Additives and Admixtures, Ed. by R. K. Dhir, Dundee, Scotland,

467-474 (1999).

7. M. H. Ozkul, U. A. Dogan, Z. Cavdar, A. R. Saglam and N. Parlak, Effects of self compacting

concrete admixtures on fresh and hardened concrete properties, 2nd

Int. Symp. on Cement and

Concrete Technology in the 2000s, Ed. by A. Yeginobali, Istanbul, Turkey, 493-502 (2000).

Figure 3. Relation penetration and segregation ratio with respect to binder content and coarse aggregate ratio