VOL. 4, NO. 5, JULY 2009 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences © 2006-2009 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com METALLIC FIBER REINFORCED CONCRETE: EFFECT OF FIBER ASPECT RATIO ON THE FLEXURAL PROPERTIES Rashid Hameed, Anaclet Turatsinze, Frédéric Duprat and Alain Sellier Université de Toulouse, UPS-INSA, Laboratoire Matériaux et Durabilité des Constructions, Toulouse Cedex, France E-Mail: rhameed@insa-toulouse.fr ABSTRACT Since many decades efforts have been made to reduce the brittleness of cementitious materials by the use of micro and macro fibers of different mechanical, geometrical and physical properties. This contribution presents the results of an experimental investigation carried out to study the effect of fiber aspect ratio on the flexural properties of metallic fiber reinforced concrete (MFRC). The flexural properties, which have been studied, include maximum load bearing capacity (peak load), post-crack strength and flexural toughness. High performance metallic fibers of different aspect ratios were used. The dosage of fibers was kept 20 kg/m 3 (0.25% by volume fraction) for all the fibered concrete mixtures. Three point bending tests were performed on both control (without fibers) and fibered notched prismatic concrete specimens of cross section 100 x 100mm and clear span of 450mm. The results showed that the flexural properties of concrete matrix are significantly improved by the addition of high performance metallic fibers. Moreover, it was found that the level of improvement in flexural properties of MFRC varies with the aspect ratio of fibers. Out of the two different aspect ratios of metallic fibers used in this study, the fibers with larger aspect ratio showed better efficiency in improving the flexural response of MFRC. Keywords: fiber reinforced concrete, metallic fibers, aspect ratio, flexural properties. 1. INTRODUCTION Concrete being a brittle material has low tensile strength and low strain capacity, as a result, the mechanical behaviour of the concrete is critically influenced by crack propagation. Concrete in service may exhibit failure through cracks which are developed due to brittleness [1, 2, 3]. To improve properties of concrete like low tensile and low strain capacity, fiber reinforced concrete (FRC) has been developed which is defined as concrete containing dispersed randomly oriented fibers [4]. Fibers had been used to reinforce cementitious material since ancient times, sun-backed bricks were reinforced by using straw as fiber and masonry mortar and plaster were reinforced using horsehair. Experimental investigation involving the use of discontinuous fibers to improve the properties of concrete was started in 1910 [5]. During the early 1960, the first major investigation was made to evaluate the potential of steel fibers as reinforcement of the concrete [6]. The properties of concrete matrix and of the fibers greatly influence the character and performance of FRC. The properties of fibers which are of interest include fiber stiffness, bond between fiber and concrete matrix, fiber concentration, fiber geometry, fiber orientation, fiber distribution and fiber aspect ratio [7]. The mixture- stiffening or workability effect is a major factor limiting the type, aspect ratio and amount of fibers that can be uniformly distributed throughout a particular cementitious matrix, which in turn determine the degree of improvement in the mechanical properties of composites in hardened state. Ideally the amount of fibers and aspect ratio should be as large as possible to maximise the improvements in the mechanical properties. On the other hand, both should be as small as possible (but compatible with aggregate size) to minimise the mixture-stiffening effect of fibers and associated difficulties in fabricating components from FRC [8]. Metallic fiber reinforced concrete has been extensively studied in last five decades. Powerful characterisation method of FRC properties have to be used in order to get pertinent data required by the structural engineers to design structural elements [9]. Currently, several methods are available which are used to characterise the concrete. These methods are ASTM [10], JSCE standard SF-4 [11], RILEM recommendations [12] and post crack strength (PCS) method [13]. In the construction market, since same fibers are available with different dimensions and the price is paid as per kilogram of fibers, it is important to select fibers with such dimensions which give maximum degree of performance for a particular application. In this contribution, as a case study, high performance metallic fibers of different aspect ratios (ratio of length to equivalent diameter) have been studied. The objective of the present study was to investigate the effect of aspect ratio of commercially available metallic fibers on the flexural properties of FRC. For this purpose, concrete mixes containing metallic fibers of same mechanical and physical properties but different aspect ratio (125 and 105) at a constant dosage rate of 20 kg/m 3 (low dosage taking into account the high price of fibers) were tested in flexure. The results were analysed using post crack strength (PCS) method [13]. 2. MATERIALS AND METHODS 2.1. Materials The materials used for all concrete mixtures consisted of CEM I 52.5R cement, the coarse aggregates having size range of 4 to 10mm, and the locally available 67