Contents lists available at JFIPS Science and …measured by Slump test Compaction factor test and Vee-bee consistometer. Figure.1 shows measuring workability.Table.2 shows measurement

Science and Engineering Applications 1(3) (2016) 15-21 ISSN-2456-2793(Online)

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Study on Strength Characteristics of Hybrid Fibre

Reinforced Concrete with Mineral Admixtures

G. Nandini Devi

Department of Civil Engineering, Adhiyamaan College of Engineering, Hosur, Tamilnadu,

Email: [email protected]

ABSTRACT

Concrete is a brittle material with a low tensile strength. Fibres when added to concrete increases strength,

toughness and ductility. The addition of fibres improves the post-cracking behaviour of concrete. In this project,

the strength characteristics of hybrid fibre reinforced concrete is studied experimentally by testing cubes, cylinders

and prisms under compression, tension and flexure. Fibres used are glass and steel fibres. The combinations of

different types of fibres potentially will improve the overall performance of concrete. Admixtures silica fume and

fly ash improves workability of concrete. M25 grade concrete was investigated with addition of steel fibres and

glass fibres with admixtures silica fume and fly ash. The test results shows that use of hybrid fibre reinforced

concrete with admixtures improves compression, split tensile and flexural performance.

Keywords: Fibre Reinforced Concrete, Glass Fiber, Steel Fiber, Fly Ash, Silica Fume.

Received on: 31/8/2016 Published online on: 5/9/2016

1. INTRODUCTION

Concrete is strong in compression but weak in tension. This

weakness makes the concrete to crack at the tensile end thus

leading to failure. Tensile strength of concrete is found to

increase with the addition of fibres and also helps to convert the

brittle characteristics of concrete to ductile. Fibres are metallic

or non-metallic like steel, glass, synthetic and carbon.These short

discrete fibres when uniformly distributed and randomly

arranged act as crack arrestors and and provide crack resistance

and crack control. Hybrid Fibre Reinforced Concrete (HyFRC)

consists of two or more types of fibres of different sizes and

shapes. Different types of fibres have different effects on the

properties of fresh and hardened concrete. Addition of fibres to

concrete improves the post cracking performance of concrete by

improving strength, toughness, energy absorption capacity and

ductility. The most used fiberis steel i.e. 50% of total tonnage

used, then polypropylene (20%), glass (5%) and other fibers

(25%).

Eswari et.al has investigated the influence of fiber content on

the ductility performance of 100 X 100 X 500 mm hybrid fiber

reinforced concrete specimens. A total of 27 specimens were

tested to study modulus of rupture, ultimate load, service load,

ultimate and service load deflection, crack width, energy

ductility and deflection ductility. Fang Yuan et.al has studied

high-performance fiber reinforced cementitious composite with

strain hardening and multiple cracking properties. Manu

Santhanam et.al has carried out an experimental study on high

strength concrete reinforced with hybrid fibres (combination of

hooked steel and a non-metallic fiber) up to a volume fraction of

0.5% using different hybrid fiber combinations – steel–

polypropylene, steel–polyester and steel–glass.Nandini Devi

have investigated the workability and mechanical properties of

plain SCC and GFRSCC.For a given length of S-glass fibre, the

compressive strength of GFRSCC increases when the content of

the S-glass fibres in the mix increases. Singh et.al has

investigated the strength and flexure toughness of HyFRC

containing different combinations of steel and polypropylene

fibres. The results indicate that compressive strength, flexural

strength and flexural toughness of concrete containing a fibre

combination of 75% steel fibres + 25% polypropylene fibres can

be adjudged as the most appropriate combination. Vikranth

et.al has concluded that concrete containing a fiber combination

of 75% steel fibers + 25% polypropylene fibers can be the most

appropriate combination to be employed in HFRC for

compressive strength, flexural strength and flexural toughness.

Yamin Patel et.al has investigated beam-column joint by using

special hybrid fiber combination of steel and polypropylene

fiber. The hybrid combination of 0.50% steel fiber and 0.50%

polypropylene fiber has best performance considering the

strength, energy dissipation capacity.

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G. Nandini Devi, Science and Engineering Applications 1(3) (2016) 15-21


16

Extensive research work on HyFRC has established that the

behaviour of HyFRC depends on aspect ratios, distributions,

orientations, geometrical shapes and mechanical properties of

fibres. By adding two different types of fibre one being non-

metallic, it is observed that fresh concrete properties like

workability and hardened concrete properties like strength,

toghness can be improved as each type of fibre function

individually to yield optimum performance. The hybrid

combination of low and high modulus fibres i.e. metallic and

non-metallic fibres offers potential benefits to arrest the micro

and macro cracks and improves overall properties of concrete

with reduced cost of concrete. Most researchers limit volume of

fibres to 4.0% and aspect ratio to 100 to avoid unworkable

mixes.This paper investigates the influence of admixtures like

silica fume and fly ash and various volume fraction of fibre

content on fresh and hardened properties of concrete. Steel fibres

(metallic fibre) and glass fibres (nonmetallic fibre) are used.

2 MATERIALS AND METHODOLOGY

2.1 Materials Used

Materials used are cement, fine aggregate, coarse aggregate,

silica fume, fly ash, steel frber, glass fiber and water. For

conventional concrete, proportional mix of cement: fine

aggregate: coarse aggrgateas recommended by IS 456:2000 for

M25 Grade is used i.e. 1:1:2 with water-binder ratio of 0.45.

Coromandal king OPC 53 Grade cement having

specific gravity 3.12 and standard consistency 32% was used.

Fine aggregate used is river sand conforming to Zone III and

specific gravity of 2.62. Coarse aggregate of 20mm size, crushed

angular in shape with specific gravity of 2.69 was used. The

aggregates are free from dust before used in the concrete. Fibres

selected were steel fibres (crimpled) and glass Fibres (straight).

From investigations, it can be found out that good results are

obtained at an aspect ratio around 80 for glass fibers. Keeping

that in view we have considered fibres with aspect ratio of 80

(Length 12 mm and Diameter 0.4 mm). Steel fibres have length

60 mm, width of 3 mm and thickness of 1mm have been used.

Fly ash for the study is taken from Tuticorin Thermal Power

Plant(TTPP) at Tuticorin. The physical properties of silica fume

used is its diameter is about 0.1 micron to 0.2 micron, surface

area about 30,000m2/kg and density is about 550kg/m3. The

chemical composition are it contains more than 90 percent

silicon dioxide with other constituents like carbon, sulphur and

oxides of aluminium, iron, calcium, magnesium, sodium and

potassium. Potable tap water available in laboratory with pH

value of 7.0±1 and conforming to the requirement of IS 456:2000

was used for mixing, casting the concrete and curing the

specimen as well. Cubes, cylinders and prisms were casted,

cured using water and tested.

2.2 Mix Proportioning

From literatures it is found that optimum replacement of silica

fume and fly ash is 10% and 20% by weight of cement

repectively. Fiber combination adopted was 50% steel fiber and

50% glass fiber for fiber volume content variation from 0.5,

1.0,1.5, 2, 2.5%.Table.1 gives the mix proportion.

The total dosage of fibres was maintained at 1.5% primarily

from the point of view of providing good workability.

Mix 1: Conventional concrete with 0% fibre and no admixtures

– CC

Mix 2: Concrete with 0% fibre and with admixtures - CA

(70% cement, 20% fly ash and 10% silica fume by weight)

Mix 3: Concrete with fibre and with no admixtures – CF-1.5

(concrete with 0.75% Steel fiber and 0.75% glass fiberby weight

of cement)

Mix 4: Concrete with fibre and with admixtures – CFA-0.5

(70% cement, 20% fly ash, 10% silica fume, 0.25% steel fiber

and 0.25% glass fiber)


(70% cement, 20% fly ash, 10% silica fume, 0.5% steel fiber and

0.5% glass fiber)





(70% cement, 20% fly ash, 10% silica fume, 1% steel fiber and

1% glass fiber)




2.3 Casting of Specimens

For casting the specimens, standard cast iron moulds of size

150mm x150mm x150mm cubes, cylinders of 150mm diameter

and 300mm height, prisms 100mm x100mm x 500mm are used.

The moulds have been cleaned of dust particles and applied with

mineral oil on all sides, before the concrete is poured into the

moulds. Thoroughly mixed concrete is filled into the mould in

three layers of equal heights followed by tamping. Then the

mould is placed on the table vibrator for compaction. The

specimens are removed from the moulds after 24 hours and cured

in clean and fresh water.

2.4 Test on Concrete

2.4.1 Tests on Fresh Concrete

Tests on fresh concrete was to study its workability which is

measured by Slump test Compaction factor test and Vee-bee

consistometer. Figure.1 shows measuring workability.Table.2

shows measurement of workability.




17

Table. 1 Quantities of Materials Used

Mix CC CA CF CFA-0.5 CFA-1.0 CFA-1.5 CFA-2.0 CFA-2.5

Design Grade of concrete

M 25(1:1:2) M 25 M 25 M 25 M 25 M 25 M 25 M 25

Cement (kg) 24.66 17.262 24.66 17.262 17.262 17.262 17.262 17.262

Fine Aggregate(kg) 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66

Coarse Aggregate (kg)

49.32 49.32 49.32 49.32 49.32 49.32 49.32 49.32

Fly Ash (kg) - 4.932 - 4.932 4.932 4.932 4.932 4.932

Silica Fume (kg) - 2.466 - 2.466 2.466 2.466 2.466 2.466

Steel Fibre (kg) - - 0.185 0.061 0.123 0.185 0.246 0.308

Glass Fibre (kg) - - 0.185 0.061 0.123 0.185 0.246 0.308

w/b ratio 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45

Vee Bee Test

Compaction Factor Test

Figure. 1 Measurement of Workabilty

2.4.2 Tests on Hardened Concrete

a). Cube Compression Test

This test was conducted as per IS 516-1959. The cubes of

standard size 150 mm x150 mm x 150 mm were casted to find

the compressive strength of concrete. Specimens were placed on

Compression Testing Machine (CTM) of capacity 1000kN

without eccentricity and a uniform rate of loading of 140kg/cm2

per minute was applied till the failure of the cube. The maximum

load was noted. Cube compressive strength (fck) in MPa= P/A,

where, P= cube compression maximum load, A= area of the cube

on which load is applied.

b). Split Tensile Test




18

a. Cube Compression test b. Split Tensile Test c. Flexural Test

Figure.2 Testing of Specimens

Concrete cylinders of size 150mm diameter x 300mm height

were casted. The test was carried out by placing a cylindrical

specimen horizontally between the loading surface of a

compression testing machine and the load is applied until the

failure of the cylinder, along the vertical diameter. Apply the

load continuously without shock at a rate of approximately 14-

21kg/cm2/minute which corresponds to a total load of

9900kg/minute to 14850kg/minute. Note down the breaking

load(P). When the load is applied along the generatrix, an

element on the vertical diameter of the cylinder is subjected to a

stress of = 2P/πld, where, P is the compressive load on the

cylinder, l is the length of the cylinder, d is diameter of the

cylinder.

c). Flexural Test

Prisms of size 500x100x100mm are tested using a flexure testing

machine. The specimen is simply supported on the two rollers of

the machine which are 600mm apart, with a bearing of 50mm

from each support. The load shall be applied on the beam from

two rollers which are placed above the prism with a spacing of

200mm. The load is applied at a uniform rate such that the

extreme fibres stress increases at 0.7N/mm2/min i.e. the rate of

loading shall be 4 kN/min. The load is increased till the specimen

fails. The maximum value of the load applied is noted down. The

modulus of rupture is calculated,σs=Pl/bd²where, P = load in N

applied to the specimen, l = length in mm of the span on which

the specimen is supported, b = measured width in mm of the

specimen, d = measured depth in mm of the specimen at point of

failure.

3. RESULTS AND DISCUSSIONS

3.1 Measurement of Workability

Workability of concrete is measured in terms of slump,

compaction factor and vee bee time and the results are tabulated

in Table. 2.

As volume fraction of fibres are increased, the workability of

concrete decreases. For volume fraction of 1.5%, it is seen that

with addition of admixtures, the workability of concrete is

improved.

3.2 Compressive Strength

Cubes were tested for compressive strength at 7th, 14thand

28thday. The compressive strength results of 7th, 14th and 28th

day are tabulated in Table.3, 4 and 5 respectively. It is found that

compressive strength increases to 51.48%with addition of 2.5%

fiber to conventional concrete. For 1.5% addition of fiber,

concrete with admixture is 3.7% higher than concrete without

admixtures. Figure.3 shows cube compressive strength of

different mix.

a). Comparison of Compressive Strength at 7th day

3.3 Comparison on Split Tensile Strength at 28th day

Cylinders were tested for split tensile strength at 28thday. The

results are tabulated in Table.6. It is found that split tensile

strength increases to 45.6%with addition of 2.5% fiber. As

observed earlier, for 1.5% addition of fiber, concrete with

admixture is 19.1% higher than concrete without admixtures.

Figure.4 shows split tensile strength of different mix.

3.4 Comparison on Flexural Strength at 28th day

Prismswere tested for flexuralstrength at 28thday. The results are

tabulated in Table.7. It is observed that flexural strength




19

Table.2 Measurement of Workability

Mix Slump in mm Compaction Factor Vee Bee Time in Seconds Degree of Workability

CC 39 0.87 13 Good

CA 34 0.85 12 Good

CF-1.5 25 0.80 33 Low

CFA-0.5 37 0.85 12 Good

CFA-1.0 32 0.81 12 Good

CFA-1.5 29 0.83 18 Good

CFA-2.0 27 0.80 20 Low

CFA-2.5 26 0.79 22 Low

Table.3 Compression Test on Cube at 7th day

Mix Initial crack load, kN

Average failure load, kN

Compressive strength, N/mm2

% Increase in strength with CC

CC 215 355 15.77 -

CA 187 386 17.26 9.45

CF-1.5 272.5 368.5 16.54 4.88

CFA-0.5 190 357.5 15.90 0.82

CFA-1.0 248 396 17.60 11.60

CFA-1.5 316 408.5 18.16 15.16

CFA-2.0 314 427 19.02 20.61

CFA-2.5 321 497 22.10 40.14

Table.4 Compression Test on Cube at 14th day





CC 368 474 21.00 -

CA 392.5 498.5 22.60 7.62

CF-1.5 329 546 24.27 15.57

CFA-0.5 306 478.5 21.26 1.24

CFA-1.0 335 528 23.47 11.76

CFA-1.5 341 567.5 25.22 20.10

CFA-2.0 367.5 590 26.22 24.86

CFA-2.5 378 612 27.20 29.52




20

Table.5 Comparison on Compressive Strength of Cube at 28th Day





CC 416 615 27.33 -

CA 460.5 682 30.31 10.90

CF-1.5 512 783 34.80 27.33

CFA-0.5 437 660 29.33 7.32

CFA-1.0 520 738 32.80 20.01

CFA-1.5 567 812 36.10 32.09

CFA-2.0 658 865 38.44 40.65

CFA-2.5 705 931 41.4 51.48

Figure.3 Cube Compressive Strength of Different Mix

Table. 6 Comparison of Split Tensile Strength of Cylinder at

28th Day

Mix

Average

failure load,

kN

Split Tensile

Strength, N/mm2

% Increase in

strength with CC

CC 175 2.5 -

CA 183.5 2.65 6.00

CF-1.5 193 2.77 10.80

CFA-0.5 229 3.23

29.20

CFA-1.0 231 3.27

30.80

CFA-1.5 233 3.30

32.00

CFA-2.0 248 3.51

40.40

CFA-2.5 257 3.64

45.60

Figure.4 Split Tensile Strength on Cylinder at 28th day

Table.7 Comparison of Flexural Strength of Prism at 28th Day

Mix

Average

failure

load, kN

Flexural

Strength, N/mm2

% Increase in

strength with CC

CC 10.35 4.31 -

CA 12.125 4.97 15.31

CF-1.5 13.8 5.51 27.84

CFA-0.5 12.1 4.83 12.06

CFA-1.0 12.7 5.09 18.10

CFA-1.5 14.6 5.99 38.98

CFA-2.0 15.4 6.19 43.62

CFA-2.5 16.0 6.41 48.72




21

Figure.5 Flexural Strength on Prism at 28thday

increases to 48.72% with addition of 2.5% fiber. For 1.5%

addition of fiber, concrete with admixture is 8.7% higher than

concrete without admixtures. Figure.5 shows flexural strength of

different mix.

4. CONCLUSIONS

From experimental investigations, it is found that compressive

strength increases to 51.48%, split tensile strength increases to

45.6%, flexural strength increases to 48.72%with addition of

2.5% fiber to conventional concrete. For 1.5% addition of fiber,

concrete with admixture has compressive strength 3.7% higher,

split tensile strength19.1% higher and flexural strength8.7%

higher than concrete without admixtures. Workability and

mechanical properties of concrete is found to improve with

addition of silica fume and fly ash.

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Glass-Polyester Composites Formed by Resin Transfer Moulding and Hand Lay-

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[3] Fang Yuan, Jinlong Pan, ZhunXu and C. K. Y. Leung, ‘A comparison of

engineered cementitious composites versus normal concrete in beam-column joints under reversed cyclic loading’, Materials and Structures, January

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[4] Manu SanthanamandA. Sivakumar, ‘Mechanical properties of high strength

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[7] S. Eswari, P.N. Raghunath and K. Suguna, ‘Ductility Performance of Hybrid Fibre Reinforced Concrete’, American Journal of Applied Sciences, 2008, vol. 5

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[8] Sivakumar.A, (2011), ‘Influence Of Hybrid Fibres On The Post Crack Performance Of High Strength Concrete: Part I Experimental Investigations’,

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Documents

Contents lists available at JFIPS Science and …measured by Slump test Compaction factor test and Vee-bee consistometer. Figure.1 shows measuring workability.Table.2 shows measurement