prof. yahia qawasmi- 3rd ims

8/8/2019 Prof. Yahia Qawasmi- 3rd IMS

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THE EFFECT OF FIBER CHARACTERISTICS ON WORKABILITY OF STEEL

FIBER-REINFORCED SELF-COMPACTING CONCRETE

Yahia Abdel-Jawad (Qawasmi) 1 Naela Khaled Al-Daoud2

1- Professor of Civil Engineering , Jordan University of Science and Technology, Irbid-Jordan

2- Materials Engineer, Royal Jordanian Scientific Society, Amman-Jordan

ABSTRACT: An experimental investigation has been conducted to evaluate the effect of steel fiber characteristics on the workability of self-compacting concrete. Two w/c ratios

(0.42 and 0.52) plain mixtures were cast as control mixes. Three aspect ratios of hooked

and one of crimped steel fibers were added for separate mixtures of 0.42 and 0.52 w/cratios. The addition of steel fibers was in three volumetric fractions (0.5, 1.0, and 1.5%)

for each aspect ratio done by making replacement with the same fraction of coarseaggregate.

The workability of self-compacting concrete (SCC) were evaluated using slump flow

diameter, slump flow time (T50), V-funnel, L-box, and sieve segregation resistance withthe dimensions suggested by the European Guidelines.

The results showed that increasing steel fibers content more than 1% will increase the

risk of material clustering, movement restriction, and blocking. It was also noticed thatfiber length and shape have more effect than aspect ratio on the workability and passing

ability of fresh SCC.

INTRODUCTION: Usually, reinforced concrete requires a high degree of compaction

to get a dense material. Vibration of concrete during and after casting in the forms is the

procedure to get a fully compacted concrete, this practice increase the labor cost and thenoise at the construction site. The situation becomes more difficult when the concrete cast

in thin sections or sections congested with steel reinforcement, where the filling capacity

of concrete can be reduced due to the interaction between reinforcement and the concrete.

Realizing this situation, research has been conducting in developed countries, especiallyin Japan, resulting in producing "vibration-free" concrete, known as Self-Compacting

Concrete (SCC)1. The main characteristics of the produced concrete were:

1. The ability to fill and flow into all the cavities within the formwork, under its own

weight.2. The ability to pass between steel reinforcing bars during placement, under its own

weight.3. The ability to remain cohesive and homogeneous (no segregation) during the entire

concreting process, from plant to form.



The basic components for the mix composition of SCC are the same as used inconventional concrete2. The properties of self-compatibility are achieved by reducing

coarse aggregate content and increasing ultra fines which, together with the water and

superplasticizer form the suspension (paste), in which all the coarse aggregate floatwithout segregation3. A comparison of a typical mix design of SCC and conventional

concrete is shown in Fig. 1.

Figure 1: Mix composition of SCC in comparison with normal vibrated concrete2.

It has been considered that SCC represents one of the most outstanding advances inconcrete technology during the last decade, and due to its specific properties it may

contribute to a significant improvement of the quality of concrete structures 4, 5.

Inherently concrete is brittle under tensile loading, the mechanical properties of concrete

may be improved by randomly oriented discrete fibers. The improvements of concrete

properties include resistance to crack propagation, increased ductility, and increasedtensile and flexural strength.

It has been shown that using short fibers as reinforcement for concrete mixes in one handimproves concrete mechanical properties, but in the other hand reduces concrete

workability to an extant that the mixes become hardly compacted6. It seems that same

problem or may be worse obtained in the case of using fibers to enhance the mechanical

properties of SCC.

The main objective of this study is to experimentally investigate the effect of steel fiber

characteristics on the flowability and compactability of self-compacting concrete.



EXPERIMENTAL EVALUATION:

i- Materials: Two plain SCC mixes having w/c ratio of 0.42 and 0.52, and a total of 24steel fiber reinforced mixes were prepared using Type II Pozzolanic Portland Cement and

coarse lime stone aggregates, natural silica sand and limestone powder as a filler. Super

plasticizer and viscosity modifier were used to enhance concrete workability. Hookedends and crimped steel fibers were used to reinforce the 24 mixes, 12 for each w/c. The

steel fibers were used in three volumetric fractions (0.5, 1.0, and 1.5%) by making

replacement with coarse aggregate. The Mechanical and geometrical properties of steelfibers are presented in Table 1.

Table 1: Mechanical and geometrical properties of steel fibers.Fiber type Geometrical

configuration

Tensile

strengt

h

(MPa)

Specific

gravity

(gm/cm3 )

Fiber diameter, d

(mm)

Fiber

length,

l (mm)

Fiber aspect

ratio, l/d

Crimped ,C 1192 7.8 1.0 50 50

Hooked,H 1 1192 7.8 0.8 60 75

Hooked,H 2 1192 7.8 1.0 50 50

Hooked,H 3 1192 7.8 0.8 40 50

ii- Mix Proportions: SCC mixtures were designed according to volumetric proportionsranges suggested by EFNARC8. Many trial mixtures were carried out to obtain the best

proportions depending on the properties of the available materials. At the beginning, two

plain SCC mixtures were prepared with 0.42 and 0.52 w/c ratios to be considered ascontrol ones. Then, steel fibers with different aspect ratios were added at different

percentages. The used dosage of viscosity enhancer was kept constant in all mixtures (0.8

L/m

3

), while superplasticizer dosage was adjusted in each mix to obtain slump flow valuewithin self-compatibility limits suggested by the European Guidelines7 and EFNARC6.

The mix proportions of the 0.42 and 0.52 w/c fiber reinforced concrete mixes are

presented in Table 2 and Table 3, respectively.

Table 2: Mix Proportions of 0.42 w/c ratio concrete mixesConcrete Mixtures F vf (0.0%)

(kg/ m3 )

F vf (0.5%)

(kg/ m3 )

F vf (1.0%)

(kg/ m3 )

F vf (1.5%)

(kg/ m3 )

Cement 400 400 400 400

Coarse Aggregate, C1 375 375 375 375


Silica Sand, S 832 832 832 832

Limestone Powder, F1 110 110 110 110 Kumkha* , F2 110 110 110 110

Water (Free) 168 168 168 168

Steel Fibers 0 39 78 117

(W/C) mass 0.42 0.42 0.42 0.42

(W/P) mass 0.27 0.27 0.27 0.27



Table 3: Mix Proportions of 0.52 w/c ratio concrete mixesSFR Mixtures F vf (0.0%)

(kg/ m3 ) F vf (0.5%)(kg/ m3 )

F vf (1.0%)(kg/ m3 )

F vf (1.5%)(kg/ m3 )

Cement 323 323 323 323



Silica Sand, S 832 832 832 832

Limestone Powder, F1 142 142 142 142

Kumkha* , F2 142 142 142 142

Water (Free) 168 168 168 168

Steel Fibers 0 39 78 117

(W/C) mass 0.52 0.52 0.52 0.52

(W/P) mass 0.28 0.28 0.28 0.28

* byproduct of tile production process.

f vf = fiber volume fraction (%)

iii- Workability Testing

1- Slump Flow Test: The slump-flow and T50 time is a test used to assess the flowability

and the flow rate of self-compacting concrete in the absence of obstructions9. It is based

on the slump test described in EN 12350-2. The result is an indication of the fillingability of self-compacting concrete. The T50 time is also a measure of the speed of flow

and hence the viscosity of the self-compacting concrete. The test apparatus and test

procedures are according to the European Guidelines7 and shown in Fig.1.

Fig.1- Slump-flow and T50 time test

2- V-Funnel Test: It is used to asses the viscosity and filing ability of self-

compacting concrete. The test apparatus and test procedures are according to theEuropean Guidelines and illustrated in Fig.2.



Fig. 2- V-Funnel Test

3- L-Box Test: The European Guidelines defined the L-Box as an apparatus used to

assess the passing ability of self-compacting concrete to flow through tight openings

including spaces between reinforcing bars and other obstructions without segregation or

blocking. There are two variations; the two bar test and the three bar test. The three bar test simulates more congested reinforcement; this is illustrated in Fig. 3.

Fig. 3- L-Box Test, three bars and two bars apparatus

4- Sieve Segregation Resistance Test: a test is used to asses the resistance of self-compacting concrete to segregate. The test is shown in Fig.4.

Fig. 4- Sieve Segregation Resistance Test



RESULTS AND DISCUSSIONS: The results of the experimental study conducted to

investigate the effect of steel fibers addition on the workability of SCC are presented anddiscussed. The results were evaluated according to European Guidelines and EFNARC.

According to these guidelines, a concrete will be considered as a self-compacting

concrete if it satisfies the following limits shown in Table 4.

Table 4: Acceptable practical ranges of workability tests for SCC

The workability test results of all 0.42 w/c ratio concrete mixes are shown in Table 5,

while the results for all the 0.52 w/c ratio concrete mixes are presented in Table 6. It isclear from these tests that in spite of fiber inclusion, all mixes had enough deformability

and moderate viscosity after adjusting the superplasticizer dosage.

The results show that with some modifications in the proportion of the control mixes a

fiber-reinforced self-compacting concrete can be produced and used in constructions, and

that all produced mixes had enough deformability and moderate viscosity after adjusting

the superplasticizer dosage.

It has been noticed that increasing steel fibers content more than 1% will increase the risk of material clustering, movement restriction, and blocking, and that fiber length andshape have more effect than aspect ratio on the workability and passing ability of fresh

SCC.

During preparing the concrete mixes containing the different ratios of steel fibers, there

was a need to increasing the superplasticizer dosage to keep the mix within the self-

compactability limits, but it should be well controlled as it was notices that increasing the

superplasticizer dose will reduce the segregation resistance of the concrete mix.

Test Unit Acceptable Range

Slump flow mm 640 - 800

T50 sec 2 - 5

V-Funnel sec 6 -12

L-Box h2/h1 0.8 -1.0

Sieving analysis % 0 - 15



Table 5: Workability tests results for the 0.42 w/c concrete mixes

Mix*

Slump Flow T50 TFunnel L-Box SievingP 670 2.5 7.5 0.98 6.5

H1(0.5) 690 2.5 7.0 0.93* 8.4

H2(0.5) 700 3.0 8.5 0.95* 7.8

H3(0.5) 680 3.0 7.0 0.95* 8.1

C(0.5) 730 2.5 10.0 0.93* 10.5

H1(1.0) 710 4.5 7.0 ** 12.6

H2(1.0) 740 3.0 11.0 0.90* 13.2

H3(1.0) 740 2.5 9.0 0.90* 13.7

C(1.0) 670 3.0 11.5 ** 11.9

H1(1.5) 690 4.5 10.0 ** 13.6

H2(1.5) 670 5.0 10.5 ** 14.4H3(1.5) 690 4.3 12.5 ** 11.5

C(1.5) 680 4.0 8.5 ** 12.8

* P = plain concrete, H1,H2,H3 and C designate the fiber type as shown in Table 1, the

value between ( ) shows the fiber volume fraction.

Table 6: Workability tests results for the 0.52 w/c concrete mixes

Mix Slump Flow T50 TFunnel L-Box Sieving

P 710 3.0 7.0 0.98 7.7

H1(0.5) 760 3.5 10.0 0.93* 10.3

H2(0.5) 700 4.0 9.5 0.95* 7.3

H3(0.5) 720 4.0 12.0 0.93* 9.6

C(0.5) 750 4.0 13.0 0.90* 9.9

H1(1.0) 740 3.5 15.0 ** 11.4

H2(1.0) 700 4.0 13.5 0.90* 12.5

H3(1.0) 700 3.5 14 0.90* 10.1

C(1.0) 710 5.0 17.0 ** 12.3

H1(1.5) 670 4.0 ** ** 13.3

H2(1.5) 720 5.0 ** ** 11.9

H3(1.5) 700 4.5 ** ** 12.5C(1.5) 690 4.5 ** ** 12.8

* P = plain concrete, H1,H2,H3 and C designate the fiber type as shown in Table 1, thevalue between ( ) shows the fiber volume fraction.



CONCLUSIONS: The factors and parameters affecting the workability of self-

compacting concrete (SCC) have been analyzed and tested, it had been shown that fiber-

reinforced self-compacting concrete is achievable with certain restrains regarding thevolume fraction of fibers, fiber-aspect ratio and fiber geometry. For example, Mixtures

with steel fiber volume fraction equals 1% show uniform slump flow and slight material

clustering at the flow center, while mixes with 1.5% volume fraction show a non-uniformflow with a noticeable clustering.

The philosophy of self-compacting concrete mix design is based on improving thecement paste flowability while improving the paste viscosity to decrease the potential of

concrete segregation.

REFERENCES:

1- Okamura, H., and Ozawa, K., “Mix Design for Self-Compacting Concrete”,

Concrete library of JSCE, Vol.25, pp. 107-120, 1995.

2- Holschemacher K. and Klug Y. "A Database for the Evaluation of Hardened

Properties of SCC", LACER 2002; 7. Available from URL http: //www.aspdin.wifa.uni-leipzig.de/ institut/lacer/lacer07/l07_13.pdf

3- Dehn F., Holschemacher K., Weibe D. "Self-Compacting Concrete TimeDevelopment of the Material Properties and the Bond Behaviour", LANCER

2000; 5. Available from URL http://www.spdin.wifa.uni-leipzig.de/institut/

lacer/lacer05/l05_15.pdf 4- Abdel-Jawad, Y. “Balancing Flowability and Stability of Self-Compacting

Concrete” Proceedings of the 10th Arab Structural Conference, pp 177-184.

Kuwait 13-15 November 2006.

5- Abdel-Jawad, Y.A., and Dehn, F., “Self-healing of Self-Compacting Concrete”Proceedings of SCC2005 , pp 1023-1029, Chicago USA, 2005.

6- Sahmaran M., Yurtseven A., Yaman O. "Workability of Hybrid Fiber ReinforcedSelf-Compacting Concrete". Building and Environment 40, pp. 1672- 1677, 2005.

7- The European Guidelines for Self-Compacting Concrete. May 2005 Available

from URL http://www.efnarc.org/pdf/SCCGuidelinesMay2005.pdf .

8- 8- EFNARC.Specifications and Guidelines for Self-Compacting Concrete.February 2002. Available from URL

http://www.efnarc.org/pdf/SandGforSCC.PDF.

9- Khayat, K.H., “Workability Testing and Performance of Self-Consolidating Concrete,” ACI Materials Journal, Vol.96, No.3,pp.346-353, 1999.

http://www.aspdin.wifa.uni-leipzig.de/


http://www.spdin.wifa.uni-leipzig.de/institut/

http://www.efnarc.org/pdf/SCCGuidelinesMay2005.pdf1


http://www.efnarc.org/pdf/SandGforSCC.PDF.%0D%20


http://www.spdin.wifa.uni-leipzig.de/institut/


http://www.efnarc.org/pdf/SandGforSCC.PDF.%0D%20

prof. yahia qawasmi- 3rd ims

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