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The 3 rd ACF International Conference-ACF/VCA 2008

347

A.33

INFLUENCE OF TYPES OF STEEL FIBER ONPROPERTIES OF ULTRA HIGH PERFORMANCE CONCRETE

Kim Huy Hoang- MSc, Huynh Ba Phat Student, Le Viet Duc Hien - StudentNguyen Van Chanh - Assoc. Professor, PhD

University of Technology, Faculty of Civil Engineering, Department of Building Materials, HCMC, VietNam

ABSTRACT: Ultra high performance concrete (UHPC) with high compressive strength, ductility, flowability and long term stability have been researched in many country. This paper dealswith the influence of types of steel fiber on properties of UHPC. In this experiment, self-compacting ultra high strength concrete has been manufactured, short steel fiber (straight fiber)with L

f1 /d

f1= 17/0.2 and long steel fiber (hooked ends) with L

f2 /d

f2= 35/0.5 have been added, in

order to improved ductility. A reasonable combination of two steel fiber types guarantee for high flowability, flexural strength of over 20 MPa and compressive strength of over 150 MPa .

KEYWORD: Ultra high performance concrete, high compressive strength, ductility, steel fiber

1. INTRODUCTION

Ultra High Strength Concrete (UHSC) with a ultra high compressive strength and excellentdurability is characterized with high density of cement, silica fume, fine filler, quartz sand.UHSC shows very brittle fracture behaviour, the addition of steel fibers improves the ductilebehaviour (flexural strength and toughness). Specific characteristic and content of steel fibers andfresh UHSC characteristic effect not only dispersion and orientation of steel fibers but alsoproperties of steel fibers concrete (workability, mechanical strength).In this experiment, short steel fiber with L f1 /d f1 = 17/0.2 and long steel fiber with L f2 /d f2 = 35/0.5have been used. Extra experiments were carried out on composition of UHSC and combination of short steel fiber and long steel fiber, in order to create a self - compacting UHPC and find a shortsteel fiber / long steel fiber combination in conection with an optimal mechanical performance. Inthe experiment, not only specimens stored under normal conditions (submerged in water) wereconsidered, but also specimens subjected to steam treatment for 10 hour at 90 oC at an early age.

2. EXPERIMENT

2.1. MaterialsOrdinary portland cement (C) and silica fume (SF) as supplementary cementing material wereused in the experiment, their physical and chemical properties are show in Table 1 & 2.Filling powder (FP) has everage grain size of 1.5 m, density of 2.7 g/cm 3 Quarzt sand (S) has grain size of 0.16 ~ 5 mm, density of 2.63 g/cm 3.Polycarboxylate - type superplasticizer (SP) with density of 1.1 g/ml (liquid) was used.


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Two types of steel fiber, which have density of 7.8 g/cm 3, were used to increase the ductilebehaviour; short steel fiber (straight fiber) has L f1 /d f1 = 17 / 0.2 and long steel fiber (hooked ends)has L f2 /d f2 = 35 / 0.5

Table 1: Physical properties of cement

Density(g/cm 3)

Specific area(cm 2 /g)

Comp. Strength 7days(MPa)

Comp. Strength 28days(MPa)

3.1 3430 44.1 53.3

Table 2: Physical and chemical properties of silica fume

Density(g/cm 3)

Specific area(cm 2 /g)

Everage Grain Size(m)

SiO 2 (%)

2.2 180000 1.0 95

2.2. Test Method

2.2.1. Fresh ConcreteThe initial flow of fresh concrete was tested with the flow table spread (Haegermann) accordingto EN 459-2; without compacting, lifting and dropping the base-plate. Test result give anindication of the flowability.

2.2.2. Hardened ConcreteAll specimens were demolded at 24 hour.The compressive strength was measured according to ASTM C39. Specimens which weresubjected to steam treatment at 90 oC and 100% relative humidity steam bath for 10 hours

(including ramp up and ramp down times) were used to compression test at an early age.Specimens which were stored under normal conditions (submerged in water) were used tocompression test at the age of 28 days.The flexural toughness and first crack strength were measured according to ASTM C1018.(four point bending test)

Table 3. The form, the curing regimes and the quantities of specimensfor each mix proportion of concrete.

Mixproportion

Mechanical testing Form Curing regime Quantities(piece)

Age of testing

(days)Submerged inwater 6 28Compressivestrength

Cylinder75x150

Steam treated 6 3Withoutfibers Flexural toughness

and first crack strength

Prism75x75x300

Submerged inwater 3 28

Withfibers

Compressivestrength

Cylinder75x150



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Flexural toughnessand first crack

strength

Prism75x75x300


2.3. Mix proportion

Table 4 shows mix proportion of concrete without fiber, relative ratio of materials base onthe quantity of cement.

Table 4. Mix proportion of concrete without fiber

BinderCement Silica fume

Water/Binder Filling powder Quarzt sand Superplasticizers

1 0.15 ~ 0.2 0.2 ~ 0.22 0.2 ~ 0.25 1.4 0.022

Steel fibers were added in concrete mix without fiber which have high flowability and highmechanical performance, in order to improve the flexural strength and toughness. Influence of

steel fiber type and content on properties of concrete was interested in study. Steel fiber type andvolumetric ratio are show in Table 5.

Table 5 . Steel fiber type and volumetric ratio

Steel fiber(L f / d f )

Content 1(%)

Content 2(%)

Content 3(%)

Content 4(%)

Content 5(%)

Content 6(%)

17 / 0.2 1.0 Vol 1.0 Vol 1.5 Vol 1.5 Vol 2.0 Vol 0.0 Vol35 / 0.5 0.5 Vol 1.0 Vol 0.0 Vol 0.5 Vol 0.0 Vol 2.0 Vol

3. EXPERIMENTAL RESULT

3.1. Concrete without steel fiberFigure 1 shows flowability testing with the flow table spread (Haegermann). Figure 2 shows flowtest result. The result showed that an increase in amount of ultrafine silica fume or microfillerlead to good fluidity when concrete was made using a very low water-binder ratio, the ratio of silica fume wasnt lower 0.15 and the ratio of microfiller wasnt lower 0.2. Effect of ultrafinesilica fume on increase in the flowability is better than microfiller because the silica fumeparticle is smaller, but microfiller is much more cheap.Figure 3 shows compression test result of concrete without fiber in various curing regimes. Theresult showed that the compressive strength was highest when the ratio of silica fume reached 0.2

and the ratio of microfiller was 0.2. The amount of cement decreased when the ratio of silicafume and microfiller exceeded the limit, therefore it would cause the decrease of compressivestrength. The result shows that the compressive strength of concrete in steam curing was lowerthan concrete in water curing (lower 4~10%) because the hydration of cement and pozzolanicreaction had occured very quickly but not complete when concrete with very low water binderratio was steam treated at 90 oC and 100% relative humidity steam bath for 10 hours (includingramp up and ramp down times).


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Figure 1. Flowability testing with the flow table spread (Haegermann)

15

17

19

21

23

25

MIX PROPORTION (C:SF:W:FP:S:SP - by w eight)

F L O W ( H a e g e r m a n n

) ( c m

)

Figure 2. Flow test result of concrete without fiber


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1 : 0 . 2

: 0 . 2

: 0 . 2

: 1 . 4

: 0 . 0

2 2

1 : 0 . 1

5 : 0 . 2

: 0 . 2

5 : 1 . 4

: 0 . 0

2 2

1 : 0 . 2

: 0 . 2

2 : 0 . 2

: 1 . 4

: 0 . 0

2 2

1 : 0

. 1 5 : 0 . 2

2 : 0 . 2

5 : 1 . 4

: 0 . 0

2 2

100

110

120

130

140

150

160

MIX PROPORTION (C:SF:W:FP:S:SP - by weight)

C O M P R E S S I V E S T R E N G T H ( M P a

)

STEAM CURING - 90oC 10 hours - Comp. Test 3 days

WATER CURING - Comp. Test 28 days

Figure 3. Compression test result of concrete without fiber in various curing regimes

The concrete mix with C :SF :W :FP :S:SP = 1 :0.2 :0.2 :0.2 :1.4 :0.022 had high flowability and ultrahigh compressive strength, it called SC-UHSC (self-compacting ultra high strength concrete).The addition of steel fibers in SC-UHSC would be suitable to create self-compacting UHPC withhigh ductility.

3.2. Concrete with steel fiberAccording to Table 5, short steel fiber with L f1 /d f1 = 17/0.2 and long steel fiber with L f2 /d f2 =35/0.5 were added in SC-UHSC mix.Table 6 shows test result, Figure 4 shows the dispersion of steel fibers in SC-UHSC and Figure 5shows mechanical strength test result . The quantity of short steel fiber is thirteen times muchthan long steel fiber with the same volume, besides short steel fiber is lighter, it didnt sink deepat the bottom mould and it was high dispersion in SC-UHSC, therefore volume of short steelfiber was used not less than 1%. However dispersion of short steel fiber reduced workability of fresh concrete when it was used more than 1.5% volume in SC-UHSC. Long steel fiber with lowdispersion sunk deep in SC-UHSC mix and decreased effect on mechanical properties. Thecombination of short steel fiber and long steel fiber is necessary for creating self-compacting

UHPC with high ductility; in this case, the short steel fiber with high dispersion preventedsinking deep of long steel fiber and total volume steel fibers can be reached 2%.


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Table 6. Influence of Steel Fiber Types on Properties of Ultra High Performance Concrete

Concrete with steel fibers Flexural Strength (MPa)ConcreteMatrix

ShortSteel Fiber

(%Vol.)

LongSteel Fiber

(%Vol.)

Flow(Haegermann)(cm)

Comp.Strength28 days(MPa)

First-Cracking

UltimateState

0 0 22.5 154.0 9.61 0.5 22.5 159.7 17.7 19.21 1 21 161.5 16.2 19.8

1.5 0 20 162.7 19.1 23.41.5 0.5 19.5 167.0 21.4 26.42 0 < 15 S

C - U

H S C

0 2 22.5 fiber

sunk deep

(a) (b)

Figure 4. The dispersion of steel fibers in SC-UHSC(a) short steel fiber; (b) Two steel fiber types combined


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Figure 5 . Compressive and flexural strength of concrete with steel fibers.

When short steel fiber with no less than 1% volume combined with long steel fiber to reach 2%volume of steel fibers in concrete, the flowability of fresh concrete didnt depend on the increaseof long steel fiber. Short steel fiber content was high influence on properties of concrete. Theincrease of short steel fiber reduced flowability but improved flexural strength. Optimum volumesteel fibers in SC-UHSC included 1.5% volume of short steel fiber and 0.5% volume of long steelfiber.

Figure 6 shows the load delection relationship and Table 7 shows values of toughness indices inbending test.

Figure 6. The load delection relationship in bending test.


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Table 7 . Values of toughness indices of SC-UHSC with steel fibers

Concrete with steel fibers Toughness indicesConcreteMatrix

ShortSteel Fiber

(%Vol.)

LongSteel Fiber

(%Vol.)

I5 (3)

I10 (5.5 )

I20 (10.5 )

0 0 1 - -1 0.5 4.99 7.56 -1 1 5.18 6.63 -

1.5 0 5.36 7.38 S C - U

H S C

1.5 0.5 5.31 8.20 10.38( is first crack deflection)

Test result showed that the toughness strength of concrete depend on the increase of short steelfiber, optimum volume short steel fiber isnt less than 1% in SC-UHSC.

4. CONCLUSION

The test results can be summarised as follows:o The optimum ratio of silica fume is suggested to be 0.2 and ratio of filling powder is

suggested to be 0.2 ~ 0.25 for manufacturing self-compacting ultra high strength concretewith water-binder ratio of 0.2.

o Flexural strength and toughness of SC-UHSC is improved by the addition of steel fibers.The combination of short and long steel fiber in which short steel fiber isnt less than 1%volume is necessary to manufacturing self compacting ultra high performance concretewith an optimal mechanical performance. The properties of SC-UHSC depend on theshort steel fiber content (micro steel fiber).

ACKNOWLEDGEMENT

The experiment was supported by Construction Materials Laboratory and Full-Scale StructuralLaboratory, University of Technology HCMC. The authors thank the Holcim VietNam, Mapei VietNam Ltd., Bekaert Singapore Pte. Ltd fortheir support of materials.

REFERENCES

[1] P. Richard and M. Cheyrezy, Composition of Reactive Powder Concrete, Cement andConcrete Research, Vol. 25, No.7, pp. 1501 1511, 1995.

[2] Abouzar Sadrekarimi, Development of Light Weight Reactive Powder Concrete, Journal of Advanced Concrete Technology, Vol.2, No.3, pp. 409 417, 2004.[3] J. Ma, M. Orgass, F. Dehn, Detlef Schmidt and N.V. Tue, Comparative Investigations on

Ultra-High Performance Concrete with and without Coarse Aggregates, Proceeding of TheInternational Symposium on Ultra-High Performance Concrete, Kassel, Gemany, 2004.

[4] Patrick Rougeau and Batrice Borys, Ultra-High Performance Concrete with ultrafineparticles other than silica fume, Proceeding of The International Symposium on Ultra-HighPerformance Concrete, Kassel, Gemany, 2004.


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[5] Marko Orgass and Yvette Klug, Fibre Reinforced Ultra-High Strength Concretes,Proceeding of The International Symposium on Ultra-High Performance Concrete, Kassel,Gemany, 2004.

[6] Benjamin A. Graybeal, Material Propety Characterization of Ultra-High PerformanceConcrete, FHWA HRT 06 103, Federal Highway Administration, 2006.

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