Influence of hybrid fibres on strength and stress-strain behaviour of concrete under uni-axial stresses

Abstract

Abstract Combination of different kinds of fibre to achieve synergic response in concrete is termed hybrid fibre reinforced concrete (HFRC). Earlier research demonstrates that short and fine fibres enhance the fresh property of concrete by controlling the growth of micro-cracks. Long and coarse fibres enhance the hardening property of concrete by arresting the propagation of macro-cracks. Thus a combination of short-fine fibres and long-coarse fibres improves the overall performance of concrete. In this study an attempt has been made to investigate the effect of fibre hybridization on mechanical behaviour of concrete reinforced with metallic (Steel) and non-metallic (Polyester and Polypropylene) fibres on 30 MPa concrete. Hybridization was done in two stages; the first stage of investigation was to study the effect of polyester (PO)-polypropylene (PP) HFRC, where three hybrid combinations were considered i.e. 75% PO + 25% PP, 50% PO + 50% PP and 25% PO + 75% PP at a total fibre volume of 0.15%. The optimum hybrid combination was achieved at 75% PO + 25% PP. Further, the investigation was carried out to develop a HFRC made with metallic and non-metallic fibres at a total fibre dosage of 1%. Mechanical properties, namely compressive strength, direct tensile strength, flexural strength and stress-stain behaviour of concrete under uni-axial stresses were investigated. The results obtained were compared with mono-fibre reinforced concrete and conventional concrete. Significant improvement in tensile strength and toughness was observed with the fibre hybridization. This may be due to synergic response of different fibres at different scales of cracking at different stress levels in concrete. Superior results were observed at metallic – non-metallic hybridization.