Indian Journal of Engineering & Materials Sciences Vol. 21, April 2014, pp. 219-226 Flexural behaviour of latex modified steel fiber reinforced concrete Tarannum Meraj, A K Pandey* & B K Rao CSIR-Central Building Research Institute, Roorkee 247 667, India Received 12 October 2012; accepted 1 November 2013 The flexural behaviour of plain concrete (PC), latex modified concrete (LMC) and latex modified steel fiber reinforced concrete (LMSFC) beams are studied under monotonic third point loading till ultimate stages. All the three types of concretes are designed for M-30 grade concrete. In LMC styrene butadiene latex 10% of cement weight is used. LMSFC concrete crimped steel fiber of aspect ratio of 16.67 at 1% of volume of concrete and SBR latex equal to 10% weight of cement are incorporated. An experimental program consisting of tests on latex modified concrete, latex modified steel fiber reinforced concrete and plain reinforced concrete are conducted under flexural loading. Beams are reinforced with bottom longitudinal steel bars and transverse steel stirrups. Tests on PC, LMC and LMSFC beam specimens have been conducted to establish load-deflection curves. The various parameters, such as stress-strain variation, first crack load, ultimate load, deflection ductility and strain variation along the depth of the beams have been carried out and a quantitative comparison are made at various stages of loading. It is found from this study that the neglect of fiber and latex contribution may considerably underestimate the flexural capacity of latex modified fiber-reinforced concrete beams. The present study also indicates that the ductility in LMC and LMSFC is increased by 45.94% and 50.27% respectively as compared to PC beams. Keywords: Polymer, Plain concrete, Latex modified concrete, Latex modified steel fiber reinforced concrete Concrete is a widely used construction material and regarded for its high strength and insulating capability, among other characteristics. Nevertheless, it has several limitations, including low tensile strength and poor environmental durability. In recent years, considerable interest has developed to solve these problems; various approaches have been tried, for example mechanical method by adding fibers, chemical method by adding latexes, special cements, admixtures and combination of both fibers and latexes. Among various methods, use of fiber especially steel has been recognized as a finer reinforcement which can reduce brittleness and increase the load carrying capacity of concrete members. The influence of steel fibers on the flexural strength of concrete is much greater than the direct tensile and compressive strengths 1,2 . The use of fibers, in a correct percentage for structural purposes, and in combination with traditional steel reinforcement, allows the achievement of better performances compared to those of conventionally reinforced beams, even when shear-moment interaction occurs 3 . From the various studies it is observed that the ultimate resistance of fiber-reinforced concrete beams is increased with an increase of fiber content, also the ductility and energy absorption capacity are considerably enhanced with the addition of steel fibers 4 . SFRC beams showed significant increase in first crack load, average increase in service load and better stiffness characteristics compared with RC beams 5 . Conventional concrete materials combined with polymers could yield composites with excellent mechanical and physical properties. Polymer materials with wide variations in properties could provide complex properties to polymer modified concrete, and thus, present an opportunity to design structural materials with tailored properties. Polymer modified concrete has a longer maintenance-free service life than PC and possesses also other advantages compared to PC such as: increased bond strength (bonding to previously existing concrete); increased flexural, compressive and tensile strengths 6 . Investigations have been made to determine the behaviour of latex modified concrete. It is concluded that compressive strength is slightly increased when the polymer-cement ratio used up to 7%. About 40% flexural strength increased for concrete modified with 7% of polymer admixture in relation to the control specimen 7 . The polymer modified concrete beams have a stiffer response in terms of structural behaviour, and —————— *Corresponding author (E-mail: akp_sed@rediffmail.com)