Investigation of Steel Fiber Reinforced Concrete on Compressive and Tensile Strength

Investigation of Steel Fiber Reinforced Concrete on Compressive and Tensile Strength

Vikrant S. Vairagade*, Kavita S. Kene*, Dr. N. V. Deshpande**

*Civil Engineering Department, Shri Ramdeobaba Engineering College, Nagpur, India

**Principal. Guru Nanak Institute of Engineering & Technology, Nagpur, Maharashtra, India

Abstract

Based on the laboratory experiment on steel fiber reinforced concrete (SFRC), cube and cylindrical specimens have been designed with steel fiber reinforced concrete (SFRC) containing fibers of 0% and 0.5% volume fraction of hook end and crimped round Steel fibers of 50 , 53.85, 62.50 (copper coated) aspect ratio were used without admixture. Comparing the result of SFRC with plain M25 grade concrete, this paper validated the positive effect of steel fiber with 0.5 percentage increases in compression and splitting improvement of specimen at 7 and 28 days, analyzed the sensitivity of steel fiber to concrete with different strength.

Keywords Co mpressive strength, Fiber Reinforced Concrete, Steel fiber, Split tensile strength, slump, volume fraction, workability

1. Introduction

   Concrete is characterized by brittle failure , the nearly complete loss of loading capacity, once failure is initiated. This characteristic, wh ich limits the application of the mate ria l, can be overcome by the inclusion of a s mall a mount of short rando mly distributed fibers (steel, glass, synthetic and natural) and can be practiced among others that remedy weaknesses of concrete, such as low growth resistance, high shrinkage cracking, low durability, etc. Stee l fiber reinforced concrete SFRC has the ability of e xcellent tensile strength, fle xu ral strength, shock resistance, fatigue resistance, ductility and crack arrest. Therefore, it has been applied abroad in various professional fie lds of construction, irrigation works and architecture.

   Steel fibers intended for reinforc ing concrete are defined as short, discrete lengths of steel having an aspect ratio in the range of 20-100, with any cross

   section and that are sufficiently s mall to be rando mly dispersed in an unhardened concrete mixture using usual mixing procedures. The most significant properties of steel fiber re inforced concrete (SFRC) are the improved fle xu ral toughness, impact resistance and fle xu ral fatigue performance. For this reason SFRC has found applications in flat slabs on grade where it is subject to high wheel loads and impact. There are currently 300,000 metric tons of fibers used for concrete reinforce ment. Steel fiber re ma ins the most used fiber of a ll (50% of total tonnage used) followed by polypropylene (20% ), glass (5%) and other fibers (25%) (Banthia ,2012). Stee l fiber re inforced concrete under compression and Stress-strain curve for steel fiber rein forced concrete in compression was done by Nataraja .C. Dhang, N. and Gupta, A.P. They have proposed an equation to quantify the effect of fiber on compressive strength of concrete in terms of fiber reinforc ing para mete r. Mechanical properties of high- strength steel fiber reinfo rced concrete were done by Song P.S. and Hwang S. They have marked brittleness with low tensile strength and strain capacities of high strength concrete can be overcome by addition of steel fibers. Tdyhey investigated an experimental study were steel fibers added at the volume of 0.5%, 1.0%, 1.5% and 2.0% . The observation indicate that compressive strength of fiber concrete reached a ma ximu m at 1.5% volume fract ion, being 15.3% improve ment over the HSC. The split tensile and Fle xura l Strength improved 98.3% and 126.6% at 2.0% volu me fraction. Fibers help to imp rove the compressive strength, tensile strength, fle xu ral strength, post peak ductility performance, pre-crac k tensile strength, fatigue strength, impact strength and eliminate temperature and shrinkage cracks. Essentially, fibers act as crack arrester restricting the development of crac ks and thus transforming an inherently brittle mat rix, i.e. ce ment concrete with its low tensile and impact resistances, into a strong composite with superior crack resistance, improved ductility and distinctive post-cracking

   behavior prior to fa ilure. Hence this study explores the feasibility of steel fiber re inforce ment; a im is to do parametric study on compressive strength, and tensile strength study etc. with M25 grade of concrete, aspect ratio and percentage of steel.

   1. Reinforcement Mechanisms in Fiber Reinforced (FR C):

      In the hardened state, when fibers are properly bonded, they interact with the matrix at the leve l of micro -cracks and effectively bridge these cracks thereby providing stress transfer med ia that delays their coalescence and unstable growth. If the fiber volu me fraction is suffic iently high, this may result in an increase in the tensile strength of the matrix [1]. Indeed, for some high vo lu me fraction fibe r co mposite, a notable increase in the tensile/fle xura l strength over and above the plain mat rix has been reported. Once the tensile capacity of the composite is reached, and coalescence and conversion of micro-c racks to mac ro- cracks has occurred, fibers, depending on their length and bonding characteristics continue to restrain crac k opening and crack growth by effectively bridging across mac ro-crac ks. This post peak macro-crac k bridging is the prima ry reinforce ment mechanis ms in ma jority of comme rcia l fiber reinforced concrete composites (Banthia N. 2012) [1].

2. EXPERIMENTAL PROGRAMME

   1. Material Use d

      In this experimental study, Ce ment, sand, coarse aggregate, water and steel fibers we re used.

      Ce ment: Ordinary Port land ce ment of 43 grade was used in this experimentation conforming to I.S-8112- 1989.

      Sand: Locally available sand zone II with specific gravity 2.45, water absorption 2% and fineness modulus 2.92, conforming to I.S. 383-1970.

      Water: Potable water was used for the e xperimentation.

      Steel Fibers: – In this e xperimentation, two d iffe rent Hook end Steel fibe rs were used.

      The Steel fibers with aspect ratios, its length and dia meter adopted were shown in table 1.

      Table 1: Dimensions of steel fibers used:

      Notation	Aspect Ratio	Length (mm)	Dia met er (mm)	Shape of fiber
      SF1	50.0	50	1.0	Hook end
      SF2	53.85	35	0.65	Hook end
      SF3	62.50	50	0.8	Crimped Round- Copper Coated

   2. Concrete mix proportions.

      Concrete for M25 grade were prepared as per I.S.- 10262:2009. A mix proportion of 1:1.508:2.465 with

      0.44 water ce ment ratio to get a characteristic strength of M25 was considered for this study. The exact quantity of materials for each mix was calculated. The constituent of materials used for making the concrete were tested and the results are furnished in Table2. The cement, fine aggregate, coarse aggregate were tested prior to the e xperiments and checked for conformity with re levant Indian standards. Concrete was mixed using a tilting type mixer and specimens were cast using steel moulds, co mpacted with table v ibrator.

      Mix proportion for M 25 grade concrete for tested materia l as follows:

      Table 2: Details of Quantity of Constituent Materials

      Material	Quantity
      Ce ment	435.45 Kg/ m3
      Sand	656.60 Kg/ m3
      Coarse aggregates	1073.34 Kg/ m3
      Water	192 Kg/ m3
      Steel Fibers	0.5% by volu me of concrete
      Slu mp	75-100 mm

      2.3 EFFECT ON WORKAB ILITY OF STEEL FIB ER:

      Slu mp tests were carried out to determine the workab ility and consistency of fresh concrete. The effic iency of a ll fiber re inforce ment is dependent upon achievement of a uniform d istribution of the fibers in the concrete, their interaction with the cement matrix, and the ability of the concrete to be successfully cast or

      sprayed (Brown J. & Atkinson T.2012) [05]. Essentially, each indiv idual fiber needs to be coated with ce ment paste to provide any benefit in the concrete. Regular users of fiber re inforce ment concrete will fully appreciate that adding more fibers into the concrete, particularly of a very sma ll dia mete r, results in a greater negative effect on workab ility and the necessity for mix design changes. The slump changed due to the different type of fiber content and form. The reason of lowe r slu mp is that adding steel fibe rs can form a network structure in concrete, which restrain mixtu re fro m segregation and flow. Due to the high content and large surface area of fibers, fibers are sure to absorb more ce ment paste to wrap around and the increase of the viscosity of mixture ma kes the slump loss (Chen and Liu, 2000)[06].

      The consistency and workability of a ll the concrete mixtu res was determined through slump tests. The slump tests were performed accord ing to IS 1199 – 1959 [23]. The vertica l d istance between the orig inal and displaced positions of the centre of the top surface of the concrete was measured and reported as the slu mp. In this work, 0.5% volu me fraction reduces workability of concrete to low workab le concrete.

      Table 3 shows the slump of p lain concrete and SFRC

      Concrete	0 %	SF1 (0.5% )	SF2 (0.5% )	SF3 (0.5% )
      Slu mp (mm)	104	80	85	68

3. EXPERIMENTAL METHODOLOGY

   1. Compre ssi ve Strength Test:

      For co mpressive strength test, both cube specimens of dimensions 150 x 150 x 150 mm and cylindrica l specimens of length 200 mm and dia meter 100 mm were cast for M25 grade of concrete. The moulds were filled with 0% and o.5% fibers. Vibration was given to the moulds using table vibrator. The top surface of the specimen was leveled and finished. After 24 hours the specimens were de moulded and were transferred to curing tank where in they were a llowed to cure for 7 days and 28 days. After 7 and 28 days curing, these cubes and cylinders were tested on digital comp ression testing machine as per I.S. 516-1959. The failure load was noted. In each category, three cubes and three cylinders were tested and their average value is reported.

      The compressive strength was calculated as follows:

      Co mpressive strength (MPa) = Failure load / cross sectional area.

   2. Tensile strength test:

      For tensile strength test, cylinder specimens of dimension 100 mm dia meter and 200 mm length were cast. The specimens were de moulded after 24 hours of casting and were transferred to curing tank where in they were allo wed to cure for 7 and 28 days. These specimens were tested under compression testing mach ine. In each category, three cylinders were tested and their average va lue is reported as per IS 5816-1999 [24].

      Tensile strength was calculated as follows as split

      tensile strength:

      Tensile strength (MPa) = 2P / DL,

      Where, P = failure load, D = dia meter of cy linde r, L = length of cylinder.

4. EXPERIMENTAL RESULTS

   1. Compressive Strength Test:

      1. Using cube S pecime n:

         The compressive strength test is consider the most suitable method of evaluating the behavior of steel fiber reinforced concrete for underground construction at an early age, because in many cases such as in tunnels, steel fiber re inforced concrete is ma inly subjected to compression [8]

         Results of Co mpressive strength for M-25 grade of concrete on cube and cylinder specimen with 0% and 0.5% steel fibers for SF1, SF2 and SF3 fibers are shown in table 4 and figure 1 belo w:

         Table 4: Results of Co mpressive strength using cubes specimen

         Days	Average Comp ressive Strength (Mpa)
         	0%	0.5%(SF1)	0.5%(SF2)	0.5%(SF3)
         7	27.88	28.79	29.58	32.12
         28	36.92	38.46	39.74	43.46

         Figure 1: Co mpressive strength using cube

         Figure.1 indicates the co mparison of result of compressive strength using cube specimen of M25 grade of concrete. It is observed that for addition of 0.5% Fiber SF3 gives slightly more co mpressive strength than other type of fiber at same volu me fraction.

      2. Using cylindrical S peci men:

         Results of Co mpressive strength for M-25 grade of concrete on cylinder specimen with 0% and 0.5% steel fibers for SF1, SF2 and SF3 fibers are shown in table and Figure below:

         Table 5: Results of Co mpressive strength using cylinder specimen

         Figure.1 indicates the comparison of result of compressive

         Days	Average Comp ressive Strength (Mpa)
         	0%	0.5%(SF1)	0.5%(SF2)	0.5%(SF3)
         7	16.04	15.93	17.36	19.86
         28	26.69	27.83	28.16	31.47

         strength using cylindrical specimen of M25 grade of concrete. It is observed that for addition of 0.5% Fiber SF3 gives maximum compressive strength than other fibers at same volume fraction

   2. Splitting Tensile Strength Test:

      Results of splitting tensile strength for M-25 grade of concrete with 0% and 0.5% steel fibers for SF1, SF2 and SF3 fibers are shown in table and Figure below:

      Table 6: Results of splitting tensile strength using cylinder

      Days	Average Splitting Tensile St rength (Mpa)
      	0%	0.5%(SF1)	0.5%(SF2)	0.5%(SF3)
      7	1.68	1.92	2.05	2.35
      28	2.81	3.14	3.42	3.73

      Figure 3: Sp litting Tensile strength of Concrete

      Figure 3 indicates the result for M 25 grade of concrete. It is observed that for addition of 0.5% SF3 fiber gives ma ximu m tensile strength at 28 days.

5. CONCLUSIONS:

The study on the effect of steel Fibers with d iffe rent aspect ratio (l/d) can still be a pro mising work as there is always a need to overcome the proble m o f brittleness of concrete.

The following conclusions could be drawn fro m the present investigation-

1. It is observed that the compressive strength for M25 grade of concrete fro m three d iffe rent cut length fibers at same volu me fract ion shows nearly same results with minor increase.

2. By addition of 0. 50% , SF3 Fibers shows ma ximu m compressive strength.

3. With sa m volu me fraction, change in length of fiber result nearly minor effect on co mpressive strength of Fiber Re inforced concrete.

4. It was observed that, the split tensile stren gth of fiber re inforced concrete was dependent on length of fiber used. By addit ion of longer length fiber, the split tensile strength increases.

5. By addition of 0. 50% , SF3 Fibers shows ma ximu m split tensile strength over fiber SF1 and SF2.

5. Addition of steel fiber in the concrete effect the workab ility of concrete. Addition of 0.50% steel Fibers reduces the slump value of fresh concrete. This problem of workab ility and flo w property of concrete can be overcome by using suitable ad mixtures such as Superplasicizers.

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International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 1 Issue 3, May – 2012