An Experimental Investigation Influence of Steel and Polypropylene Fibbers on Concrete under Elevate

IJSTE - International Journal of Science Technology & Engineering | Volume 2 | Issue 07 | January 2016 ISSN (online): 2349-784X

An Experimental Investigation Influence of Fibers on Concrete Under Elevated Temperature A. Narender Reddy Assistant Professor Department of Civil & Structural Engineering Guru Nanak Institutions Technical Campus Ibrahimpatnam, Hyderabad, R.R Dist, Telangana State, India

D. V. S. P. Rajesh Assistant Professor Department of Civil & Structural Engineering Guru Nanak Institutions Technical Campus Ibrahimpatnam, Hyderabad, R.R Dist, Telangana State, India

T. Ram Prasanna Reddy Assistant Professor Department of Civil & Structural Engineering Nalanda Institute of Engineering & Technology Sattenapalli, Guntur Dist, Andhra PradeshState, India

U.V. Tilak Assistant Professor Department of Civil & Structural Engineering Kallam Haranath Reddy Institute of Technology Chowdavaram, Guntur Dist, Andhra Pradesh State, India

N. Siva Rani PG Student Department of Civil & Structural Engineering Nova College of Engineering& Technology, Janga Reddy Gudem, West Godavari Dist, Andhra Pradesh State, India

Abstract Fire resistance of concrete structure is an important factor to be considered in the design of building. Fire may cause different degree of damage to the structure depending on the temperature and duration of its exposure. Adding of fibers in the concrete improves the residual strength and fracture energy. In this paper an experiment investigation has been carried out to study the impact strength of fiber reinforced concrete at elevated temperature. Specimens were heated from 27ยบC to 500ยบC and cooled by natural air and by water. Steel fiber (0.5% & 1%) and polypropylene fiber (0.5% & 1%) were added to enhance the fracture energy of concrete at elevated temperature. These specimens were heated by using Muffle furnace. After heating the specimens were allowed to cool naturally in the atmosphere for 24 hours in case of air cooling and sprayed water in case of water cooling. The Impact strength of specimens were compared with reference specimens (no fiber). The specimens with steel fiber showed higher toughness and impact strength after exposure to high temperature. The polypropylene could mitigate the spalling of specimens significantly.

Keywords: Concrete, Impact Strength, Steel and Polypropylene Fibers ________________________________________________________________________________________________________

I. INTRODUCTION Concrete is weak in tension and has a brittle character. The concept of using fibers to improve the characteristics of construction materials is very old. Early applications include addition of straw to mud bricks, horse hair to reinforce plaster and asbestos to reinforce pottery. Use of continuous reinforcement in concrete (reinforced concrete) increases strength and ductility, but requires careful placement and labour skill. Alternatively, introduction of fibers in discrete form in plain or reinforced concrete may provide a better solution. The modern development of fiber reinforced concrete (FRC) started in the early sixties. Addition of fibers to concrete makes it a homogeneous and isotropic material. When concrete cracks, the randomly oriented fibers start functioning, arrest crack formation and propagation, and thus improve strength and ductility. The failure modes of FRC are either bond failure between fiber and matrix or material failure. The addition of fibers significantly improves many of the engineering properties of mortar and concrete, notably impact strength and toughness. Flexural strength, fatigue strength, tensile strength and the ability to resist cracking and spalling are also enhanced. Fiber reinforced concrete (FRC) is a composite material consisting of cement, sand, coarse aggregate, water and fibers. In this composite material, short discrete fibers are randomly distributed throughout the concrete mass. The behavioral efficiency of this composite material is far superior to that of plain concrete and many other construction materials of equal cost. Due to this benefit, the use of FRC has steadily increased during the last two decades and its current field of application includes: airport and highway pavements, earthquake-resistant and explosive-resistant structures, mine and tunnel linings, bridge deck overlays, hydraulic structures, rock- slope stabilization, etc.

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An Experimental Investigation Influence of Fibers on Concrete Under Elevated Temperature (IJSTE/ Volume 2 / Issue 07 / 012)

II. MATERIALS AND MIX PROPORTION Fiber reinforced concrete made by different fibers like steel fiber, polypropylene fiber. These fibers reinforced concrete specimens were casted and curing done by 28 days. This specimen was placed in a furnace up to 500°c and cooled by air and water.

Material Specification 1) Cement: OPC 53 grade.

2) Fine aggregate: locally available river sand zone 2 having a specific gravity of 2.70.

3) Coarse aggregate: crushed granite coarse aggregate of maximum size 20 mm and having a specific gravity 2.70.

4) Water: water available in the college campus.

5) Steel fiber.

6) Polypropylene fiber.

Length (mm) Steel fiber Polypropylene fiber

Table - 1 Detail of Fibers Aspect ratio Elastic modulus (GPa)

Melting point (°C) 1425-1710 234-288

Tensile strength (MPa) 90-1250 270-650

Density (g/cm³)

Table - 2 Mix Proportion for M50 Grade of Concrete Length Aspect ratio Elastic modulus Melting (mm) (GPa) point (°C) 30 60 210 1425-1710 12 334 38 234-288

Tensile strength (MPa) 90-1250 270-650

Density (g/cm³)

30 12

60 334

210 38

0.9-1.6 0.91

Mix Proportion

Steel fiber Polypropylene fiber

0.9-1.6 0.91

III. EXPERIMENTAL INVESTIGATION In order to understand the effects of elevated temperature on the properties of concrete, an extensive laboratory investigation was carried out. Tests were carried out on impact cylinder. The specimens were heated and cooled by air and water to reach the room temperature. This type of test is known as unstressed residual strength test. Unstressed residual strength test was carried out to determine the different grades of concrete specimens subjected to elevated temperatures. Reference and heated specimens were cast these specimens were heated from 27°c to 500°c using muffle furnace. After the heating the specimens were cooled by air and water.

Test of Heated Specimens Experimental investigation was carried out to determine the effect of types of fibers on M50 of concrete. After 28 days of curing, all the specimens were air dried prior to high temperature exposure. The specimens were subjected to elevated temperatures and cooled by air and water. Then specimens were tested by impact behavior as impact strength of concrete and stress strain behavior of fiber reinforced concrete.

Impact Strength Behavior of Concrete Impact strength is the capability of the material to withstand a suddenly applied load and is expressed in terms of energy. The studies were extended to present the ductile characteristics of M50 grade concrete with different types of fibers under impact. For the studies on impact resistance of concrete, two hundred twenty-five specimens were casted. The drop weight impact testing apparatus was fabricated in the laboratory as per ACI 544 committee’s recommendations. Equations were developed to determine the first crack strength of concrete with elevated temperature.

Impact Energy The amount of energy required to fracture a material called impact strength.

The impact energy is calculated by the formula; E = W x h x n (N-m) Where; W = weight of hammer (N), h = height of fall (m) n = no. of blows required for complete failure.

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An Experimental Investigation Influence of Fibers on Concrete Under Elevated Temperature (IJSTE/ Volume 2 / Issue 07 / 012)

Impact Strength Effect of Temperature on Different Type of Fibers

Impact Energy (N-m)

Table - 3 Impact Energy for Different Types of Fiber (0.5% and Air Cooling) Temperature Type of Fibers Steel Polypropylene 27°C 2435.192 1452.9298 250°C 2189.627 1186.9004 500°C 245.5656 225.1018 3000 2500 2000 1500 1000 500 0

27°C 250°C 500°C Steel

Polypropylene

Types of Fibers Fig. 1: Impact Energy for Different Types of Fiber (0.5% and Air Cooling) Table - 4 Impact Energy for Different Types of Fiber (1% and Air Cooling) Temperature Type of Fibers Steel Polypropylene 27°C 2660.294 1698.4954 250°C

2476.12

1452.9298

500°C

286.4932

266.0294

Impact Energy (N-m)

3000 2500 2000 1500

27°C

1000

250°C

500

500°C

0 steel

poly propylene Types of Fibers

Fig. 2: Impact Energy for Different Types of Fiber (1% and Air Cooling) Table - 5 Impact Energy for Different Types of Fiber (0.5% and Water Cooling) Temperature Type of Fibers Steel Polypropylene 27°C 2435.192 1452.9298 250°C

1984.989

1064.1176

500°C

204.638

204.638

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An Experimental Investigation Influence of Fibers on Concrete Under Elevated Temperature (IJSTE/ Volume 2 / Issue 07 / 012)

Impact Energy (N-m)

3000 2500 2000 1500

27°C

1000

250°C 500°C

500 0 steel

poly propylene Types of Fibers

Fig. 3: Impact Energy for Different Types of Fiber (0.5% and Water Cooling) Table - 6 Impact Energy for Different Types of Fiber (1% and Water Cooling) Temperature Type of Fibers Steel Polypropylene 2660.294 1698.4954 27°C 250°C

2230.554

1166.4366

500°C

225.1018

245.5656

Impact Energy (N-m)

3000 2500 2000 1500

27°C

1000

250°C

500

500°C

0 steel

poly propylene Types of Fibers

Fig. 4: Impact Energy for Different Types of Fiber (1% and Water Cooling)

Effect of Percentage of Different Types of Fiber on Impact Energy Table - 7 Impact Energy for Different Percentage Fiber (250°C and Air Cooling) Types of Fiber Percentage of Fiber No fiber Steel Poly propylene

1166.437

0.5

1

2189.627

2476.12

1186.9

1452.93

Impact Energy (N-m)

3000 2500 2000 No Fiber

1500

Steel

1000

Polypropylene

500 0 0

0.5

1

Percentage of Fiber

Fig. 5: Impact Energy for Different Percentage of Fiber (250°C and Air Cooling)

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An Experimental Investigation Influence of Fibers on Concrete Under Elevated Temperature (IJSTE/ Volume 2 / Issue 07 / 012)

Table - 8 Impact Energy for Different Percentage Fiber (500°C and Air Cooling) Types of Fiber Percentage of Fiber No fiber Steel

Impact Strength (N-m)

Poly propylene

184.1742

0.5

1

245.5656

286.4932

195.1018

206.0294

350 300 250 200 150 100 50 0

No Fiber Steel Polypropylene

0

0.5 Percentage of Fiber

1

Fig. 6: Impact Energy for Different Percentage of Fiber (500°C and Air Cooling) Table - 9 Impact Energy for Different Percentage Fiber (250°C and Water Cooling) Types of Fiber Percentage of Fiber No fiber Steel Poly propylene

1043.654

0.5

1

1984.989

2230.554

1064.118

1166.437

Impact Energy (N-m)

2500 2000 1500 No fiber Steel

1000

Polypropylene 500 0 0

0.5

1

Percentage of Fiber

Fig. 7: Impact Energy for Different Percentage of Fiber (250°C and Water Cooling) Table - 10 Impact Energy for Different Percentage Fiber (500°C and Water Cooling) Percentage of Fiber Types of Fiber No fiber 0.5 1 Steel 204.638 225.1018 143.2466 Poly propylene 156.638 178.5656

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An Experimental Investigation Influence of Fibers on Concrete Under Elevated Temperature (IJSTE/ Volume 2 / Issue 07 / 012)

Impact Strength (N-m)

250 200 150 No fiber Steel

100

Polypropylene 50 0 0

0.5

1

Percentage of Fiber

Fig. 8: Impact Energy for Different Percentage of Fiber (500°C and Water Cooling)

IV. CONCLUSION During the present investigation steel fiber, polypropylene fibers were added in M50 concrete specimens to enhance the fire resistance. Different percentages of fiber (0.5%, 1%) were added in the concrete specimens. Impact strength of heated specimens with different fibers improves about 55% and 48% for the specimens with steel fiber and polypropylene fiber respectively compared to reference specimens in the case of air and water cooling. The impact strength of concrete decrease as the temperature increases in all the specimens with different fibers. Addition of steel improve the failure pattern and specimen’s integrity after high temperature, the fiber reinforcement concrete exhibits higher ultimate load and impact energy compare to the reference specimens.

During the high temperature polypropylene fiber can mitigate or prevent the explosive spalling, but does not increase the impact energy of the specimens. Fire resistance of aggregate is generally high. However, having non uniform high temperature effect of aggregate on cooling the aggregate using water may cause internal pressure in the aggregate. This pressure may make the aggregate to spall. Based on the experimental investigation the impact strength of heated specimens at 250°C increases in case of air and water cooling about 55%, 22% and 54%, 19% respectively for the specimens with steel fiber and polypropylene fiber compared to reference specimens (without fiber) in the case of air and water cooling respectively.The impact strength of heated specimens at 500°C increases in case of air and water cooling about 38%, 20% and 40%, 26% respectively for the specimens with steel fiber and polypropylene fiber compared to reference specimens (without fiber) in the case of air and water cooling respectively.

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