Influence of steel fibres on strength and ductility of normal and lightweight high strength concrete

This paper presents the results of a series of experiments conducted to investigate the effectiveness of fibre inclusion in the improvement of mechanical performance of concrete with regard to concrete type and specimen size. Lightweight aggregate concrete and limestone aggregate concrete with and without steel fibres were used in the study. The compressive strength of the concrete mixes varied between 90 and 115 MPa and the fibre content was 1% by volume. Splitting tests on prisms and three-point bending test on notched beams were carried out on specimens of varying sizes to examine the size effect on splitting strength, flexural strength and toughness.

The experimental findings indicate that the low volume of fibre has little effect on compressive strength but improve remarkably splitting tensile strength, flexural strength and toughness. The increase in splitting tensile strength, flexural strength and toughness index for lightweight concrete seems much higher than that of normal aggregate concrete.

The size effect on prism splitting tensile strength is not significant beyond a critical (transition) size. There are apparent size effects on flexural strength and toughness index. As the specimen size increases, splitting and flexural strengths appear to decrease, and fracture behaviour tends to be more brittle.