Effect Of Addition Of Hybrid Fibres On Strength Biology Essay

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Silica Fume Concrete (SFC) produced with hybrid Fibres is a relatively new and advanced material of construction. A typical SFC with Hybrid Fibres mixture consist of absence of coarse aggregate replaced by fine sand in conventional concrete. The Portland cement plays the role of fine aggregate and the silica fume that of the cement. SFC has no large aggregate and contains small steel Fibres that provides additional strength and in some cases can replace traditional reinforcement.

The strength and ductility characteristics of SFC may be improved by using hybrid Fibres. The different combinations of hybrid Fibres like (Steel + galvanized iron) (Steel + polypropylene) (Steel + Waste coiled steel Fibres) (Steel + HDPEF) can improve the characteristics properties of SFC.

In this paper, the experimental investigation has been made to evaluate strength properties of SFC using Hybrid Fibres like Compressive Strength, Tensile Strength, Flexural Strength and Impact Strength. Results are compared with strength properties of SFC without Fibres and SFC with Mono Fibres.

Keywords - SFC, Steel Fibres (SF), Galvanized Iron Fibres (GIF), Waste Coiled Steel Fibres (WCSF) High Density Polyethelene Fibres (HDPEF), Polypropylene Fibres(PPF), Mono Fibres, Hybrid Fibres, Compressive Strength, Tensile Strength, Flexural Strength, Impact Strength.

INTRODUCTION

Concrete is a critical material for the construction of infrastructure facilities throughout the world. One can not imagine any construction without the use of concrete. The production and usage of concrete has almost become an index of development. Traditional concrete has some of the limitations like low tensile strength, low flexural strength and low impact strength. Basically concrete is brittle material. It has been shown that the introduction of steel reinforcement can substantially improve the tensile strength and this composite material, popularly known as reinforced cement concrete is used in almost all structural applications. Several researchers have also shown that the addition of Fibres improve the tensile strength, flexural strength and impact resistance of plain concrete. The upper limit of compressive strength for material that can be used in commercial applications continues to be pushed higher and higher. The modern sky scrappers and the recent earthquakes demand high strength and high ductility in the concrete structure. This high strength and high ductility can be achieved by the recent innovation called silica fume concrete (SFC) using Hybrid Fibres.

SFC with Hybrid Fibres is an ultra high strength and high ductility composite material with advanced mechanical properties, developed in the 1990s by Bouygues laboratory in France. It consists of special concrete where its microstructure is optimized by precise gradation of all particles in the mix to yield maximum density. It uses extensively the pozzolnic properties of highly refined silica fume and optimization of the Portland cement chemistry to produce the highest strength hydrates.

SFC with Hybrid Fibres represents a new class of Portland cement based material with compressive strength in excess of 200 MPa range by introducing fine steel Fibres. SFC can achieve remarkable flexural strength upto 50 MPa. The material exhibits high ductility with typical values for energy absorption approaching those reserved for metals. SFC with Hybrid Fibres can create materials that extend from those with traditional heterogeneous characteristics normally associated with concrete to more homogeneous material that have isotropic and energy absorption capabilities that approach the characteristics of metals.

In a typical SFC with Hybrid Fibres mixture design the least costly components of conventional concrete have been basically eliminated by more expensive materials. The fine sand used in SFC becomes equivalent to the coarse aggregate of conventional concrete, the Portland cement plays the role of fine aggregate the silica fume that of the cement. SFC has no large aggregates and contains small steel Fibres that provides additional strength and in some cases, can replace traditional steel reinforcement.

SFC with Hybrid Fibres is a better alternative to high performance concrete and has the potential to structurally compete with steel. SFC provides improved seismic performance by reducing inertia loads with lighter member, allowing large deflections with reduced cross sections and providing higher energy absorption.

RESEARCH PROBLEM

SFC with Hybrid Fibres is an ultra high strength and high ductility composite material with advanced mechanical properties. SFC uses Fibres in its production. Also it utilizes an industrial waste viz. silica fume in its production. The use of hybrid Fibres may improve the strength and ductility characteristics of SFC. The different combinations of hybrid Fibres like (Steel + Polypropylene), (Steel + GI) etc. can improve upon the characteristic properties of SFC. The available literature is silent about the properties of SFC produced with Fibres. Thus there is a need to investigate in detail about the addition of hybrid Fibres into SFC.

SIGNIFICANCE OF RESEARCH WORK

Silica fume concrete may become the most wanted construction material of tomorrow. The recent earthquakes in India and elsewhere in other parts of the world are forcing the researchers to innovate high ductile construction materials. Since SFC is more ductile, the study of the same becomes important. These research works propose the effective use of hybrid in the production of SFC for the enhancement of the strength and ductility characteristics.

1.0 Experimental Programme

Main aim of this experimentation is to study the strength characteristic of reactive powder concrete produced from hybrid Fibres. The results are compared with SFC produced from monoFibres. Different monoFibres used are steel Fibres (SF) Galvanized iron Fibres (GIF) Waste Coiled Steel Fibres(WCSF) High density polythelene fiber (HDPEF) and polypropelyne Fibres (PPF) The hybrid Fibres used in experimentation are (SF + GIF), (SF + WCSF), (SF + HDPEF), and (SF + PPF). The different strength characteristics studied are compressive strength, tensile strength Flexural strength and impact Strength

2.0 Materials Used

In the experimentation 53 grade ordinary Portland cement used. Locally available sand was used, whose specific gravity was found to be 2.66. The sand belongs to zone-II. The silica fume used in the experimentation was obtained from Elekem Laboratory, Navi Mumbai. The chemical composition of silica fume is shown in table.

Chemical composition of silica fume

Chemical Composition

Percentage

Silica (SiO2)

89%

Alumina( Al2O3)

0.5%

Iron Oxide (Fe2O3)

2.5%

Alkalies as (Na20+K2O)

1.2%

Calcium oxide (CaO)

0.5%

Magnesium oxide

0.6%

The Steel Fibres used in the experimentation were obtained from Stelwols Company, 5, Industrial estate, Kamptea Road, Uppalwadi, Nagpur. These Steel Fibres were of corrugated shape having a length of 50 mm and an average thickness of 1mm leading to a aspect ratio of 50. The Young's modulus of Steel Fibres was found to be 2 x 105 MPa. The density of steel fiber was found to be 78500 N/m3.

Polypropylene Fibres were obtained from Nina Industries, Mani Bhutan 54, Hughes road, Mumbai and obtained by Choourariiia's chamber, B.V.K. lyenger road, Banglore, The polypropylene Fibres were having a length of 12 mm and their average thickness was found to be 7.5 Micron leading to an aspect ratio of 1600. The Young's modulus of PP Fibres was found to be 5 x 103 MPa. The density of PP Fibres was found to be 9100N/m3.

The GI Fibres having a length of 50 mm and diameter of 1 mm, which leads to an aspect ratio of 50 were used in the experimentation. The GI Fibres were cut from GI wires. The density of GI fiber was found to be 64000 N / m3 .

The waste HDPE Fibres were obtained by cutting the waste HDPE pipes. The thickness of the fiber was 1.5mm, its breadth 5mm and its length 50mm leading to an aspect ratio of 35. The density of waste HDPE fiber was found to be 9870 N / m3.

The individual Fibres were used at the rate of 1% by volume fraction and the hybrid Fibres were used at the rate of (0.5% + 0.5%) by volume of fraction.

To affect the workability a super plasticizer by trade name Conplast -430 was used. It was added at rate of 1.8% (by weight of cement). It is manufactured by Fosroc chemical India Ltd. Banglore, Conplast -430 is based on sulphonated naphthalene polmer. It has specific gravity of 1.22 to 1.225 at 300C. its chloride content is nil. It is non-toxic and non-flammable. It has minimum shelf-life of 12 months when stored under normal temperature.

3.0 Casting and Testing Procedure

Cement, sand and silica fume were weighed according to proportion 1:1:0.25 and dry mixed. To this dry mix the required quantity of Fibres were added and thoroughly mixed. The MonoFibres were used at the rate of 1 %. (by volume fraction) Hybrid Fibres were used at the rate of (0.5% + 0.5% ) (by volume fraction ). To this dry mix required quantity of water (W/C = 0.28) was added. Now super plasticizer was added at the rate of 1.8 %( by weight of cement). The entire mass is homogenously mixed. This homogenous mix was poured in to the mould, which were kept on the vibrating table. Compaction was given to concrete by table vibration and hand compaction. Compacted specimen was finished smooth and was kept under wet gunny bags. After 12 hours they were demoulded and water cured for 28 days.

For the compression strength test, specimens of size 150x150x150 mm were cast. They were tested on 2000 KN capacity CTM as per IS 516- 1959. For split tensile strength, cylindrical specimens of diameter 150mm and length 30mm were cast. Split tension test was carried out to find tensile strength of concrete on 2000 kN capacity CTM as per IS 5816-1999. For flexural strength, beam specimens of dimension 100x100x500mm were cast. Two point loading was adopted on an effective span of 400mm as per IS 516-1959. For impact strength cylindrical specimens of dimension 150mm diameter and 60mm height were cast. For testing these specimens Schruders impact machine was used. Schruders impact machine is based on drop weight test. The specimen was kept in the Schrudrs impact testing machine and a hammer weighing 4.54 kg was dropped from a height of 457mm, Number of blows required to cause first crack and final failure were noted down. The final failure is defined as the opening of cracks in the specimen sufficiently so that pieces of concrete are touching at least out of the four positioned lugs on the base plate. The impact energy is calculated as follows;

Impact energy = m.g.h.n.

= (w/g) g.h.n.

= w.h. n.

Where,

w= weight of the ball= 4.54 kgs = 45.4 N

h= height of fall = 457 mm=0.457m

n= number of blows required to cause first crack or final failure as the case may be.

Table No. 1 : OVERALL RESULTS OF COMPRESSIVE STRENGTH

Description of SFC

Average Compressive Strength (MPa)

Percentage increase of compressive strength w.r.t. reference mix

SFC with no fibre (Ref Mix)

24.44

SFC with SF

48.00

96.36%

SFC with GIF

45.63

86.67%

SFC with WCSF

45.04

84.24%

SFC with HDPEF

40.89

67.27%

SFC with PPF

25.78

5.45%

SFC with (SF+GIF)

49.19

101.21%

SFC with (SF+WCSF)

48.89

100.00%

SFC with (SF+HDPEF)

48.44

98.18%

SFC with (SF+PPF)

48.00

96.36%

The variation in compressive strength of SFC can be depicted in the form of graph as shown in Fig.No.1

Fig No. 1. The variation in compressive strength of SFC

Table No. 2 : OVERALL RESULTS OF TENSILE STRENGTH

Description of SFC

Average Tensile Strength (MPa)

Percentage increase of tensile strength w.r.t. reference mix

SFC with no fibre

(Ref Mix)

1.79

SFC with SF

4.34

142.11%

SFC with GIF

4.01

123.68%

SFC with WCSF

3.11

73.68%

SFC with HDPEF

2.36

31.58%

SFC with PPF

2.36

31.58%

SFC with (SF+GIF)

4.81

168.42%

SFC with (SF+WCSF)

4.62

157.89%

SFC with (SF+HDPEF)

4.43

147.37%

SFC with (SF+PPF)

4.39

144.74%

The variation in tensile strength of SFC can be depicted in the form of graph as shown in Fig. No. 2

Fig No. 2. Variation of Tensile Strength of SFC

Table No. 3 : OVERALL RESULTS OF FLEXURAL STRENGTH OF SFC

Description of SFC

Average Flexural Strength (MPa)

Percentage increase of flexural strength w.r.t. reference

mix

SFC with no fibre

(Ref Mix)

1.73

SFC with SF

3.68

112.31%

SFC with GIF

2.99

72.31%

SFC with WCSF

2.53

46.15%

SFC with HDPEF

2.21

27.69%

SFC with PPF

1.97

13.85%

SFC with (SF+GIF)

4.31

148.46%

SFC with (SF+WCSF)

4.16

140.00%

SFC with (SF+HDPEF)

3.79

118.46%

SFC with (SF+PPF)

3.76

116.92%

The variation in flexural strength of SFC can be depicted in the form of graph as shown in Fig. No. 3

Fig No. 3. Variation of Flexural Strength of SFC

Table No. 4 : OVERALL RESULTS OF IMPACT STRENGTH OF SFC

Description of SFC

Impact strength of concrete to cause (N-m)

Percentage increase of impact strength w.r.t. reference mix

First crack

Final failure

First crack

Final failure

SFC with no fibre (Ref Mix)

456.45

650.10

SFC with SF

1161.88

1514.59

154.55

132.98

SFC with GIF

1127.30

1459.26

146.97

124.47

SFC with WCSF

995.89

1293.28

118.18

98.94

SFC with HDPEF

816.08

1037.39

78.79

59.57

SFC with PPF

608.60

933.65

33.33

43.62

SFC with (SF+GIF)

1327.86

1625.24

190.91

150.00

SFC with (SF+WCSF)

1258.70

1569.92

175.76

141.49

SFC with (SF+HDPEF)

1217.20

1542.25

166.67

137.23

SFC with (SF+PPF)

1217.20

1514.59

166.67

132.98

The variation in flexural strength of SFC can be depicted in the form of graph as shown in Fig. No. 3

Fig No. 4. Variation of Impact Strength of SFC

OBSERVATIONS AND DISCUSSIONS

Following observations were made with reference to the experimentation conducted on SFC produced from different monofiber and hybrid fiber.

It is observed that the Compressive strength, Tensile strength, Flexural strength and Impact strength of SFC produced with different monofiber such as SF, GIF, WCSF, HDPEF, and PPF is higher as compared to SFC produced without any Fibres. Among the Mono Fibres the performance of SF, GIF, WCSF and HDPEF is better with respect to Compressive strength, Tensile strength, Flexural strength and Impact strength.

This may be due to fact that addition of Fibres will act like aggregates which interlock themselves in the powder matrics thus resulting in higher strength properties. Thus it can be concluded that the use of mono Fibres will enhance the strength characteristics of SFC

It is observed that the compressive strength of SFC produced with different hybrid Fibres such as (SF+GIF), (SF+WCSF),(SF+HDPEF), and (SF+ PPF) is higher as compared to SFC produced with respective mono Fibres and without any Fibres.

This may be due to fact of synergistic response of different hybrid fibres in SFC. The hybrid fibre added will come into play at different stages of loading by bridging the different cracks.

Thus it can be concluded that the strength properties of SFC produced with different hybrid fibres such as (SF+GIF), (SF+WCSF), (SF+HDPEF) and (SF + PPF) are higher as compared to SFC produced with respective monofibres and without any fibre.

It is observed that strength characteristic of SFC with (SF+GIF) and (SF+WCSF) have yielded higher strength characteristics as compared to (SF+HDPEF), and (SF+PPF).

This may be due to fact of higher modules of elasticity for both the fibres.

It can be concluded that SFC produced with hybrid fibres such as (SF+GIF) and (SF+WCSF) will yield higher strength characteristics.

It is observed that SFC produced with hybrid fibres absorbed more energy as seen in flexural strength and impact strength results.

This may be due to the fact that hybrid fibre used induces sufficient ductility by which it can absorb more energy.

Thus is can be concluded that SFC produced with hybrid fibre can be used in earthquake resistant structure, which is characterized by more energy absorption.

CONCLUSION

Based on the experimentation conducted, following conclusions can be drawn

Use of mono Fibres will enhance the strength characteristics of SFC.

The Strength properties of SFC produced with different hybrid Fibres such as (SF+GIF), (SF+WCSF), (SF+HDPEF) and (SF+PPF) are higher as compared to SFC produced with respective mono Fibres and without any fiber.

Strength characteristics of SFC with (SF+GIF) and (SF+WCSF) have yielded higher strength characteristics as compare to (SF+HDPEF) and (SF+PPF).

SFC produced with hybrid Fibres can be used in earthquake resistant structure, which is characterized by more energy absorption.

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