Effect of hybrid fibres on the mechanical properties of high performance concrete

Fibre reinforcement is a technique used to provide toughness and ductility to brittle cementitious matrices. Reinforcement of concrete using a single type of fibre could improve the properties to a limited level. A hybrid composite refers to two or more types of fibres that are rationally combined to produce a composite that stems benefits from each of the individual fibres and exhibits a synergetic response. This study intends to illustrate and quantify the mechanical properties of Hybrid Fibre Reinforced Concrete. For this purpose, a reference High Performance Concrete (HPC) of grade M65 with water-binder ratio of 0.34 was used. Specimens of plain concrete mix, HPC with silica fume, Steel Fibre Reinforced High Performance Concrete (SFRHPC) containing only steel fibres, and Hybrid Fibre Reinforced High Performance Concrete (HFRHPC) containing steel fibres and carbon fibres were prepared. Optimum amount of silica fume was taken as 12.5%. The crimped steel fibre was added initially at 0.25%, 0.5%, 0.75%, 1% and 1.25% by weight of concrete and its optimum percentage was found out. Once the optimum dosage of crimped steel fibre was obtained, carbon fibre was used to replace the optimum steel fibre dosage at 25%, 50%, 75% and 100% by volume fraction. Thus an optimum hybrid fibre dosage was obtained. The mechanical properties of the HFRHPC like compressive strength, flexural strength, splitting tensile strength, modulus of elasticity and impact resistance were studied and compared with HPC mix. The results revealed that the addition of steel fibre improved all the mechanical properties of concrete.