A study of post-fire strengths of concrete strengthened with ultra high performance steel fiber reinforced concrete

This article aims to assess the post-fire mechanical properties of concrete strengthened with ultra high-performance fiber-reinforced concrete. Cylindrical concrete samples with a dimension of 150 x 300 mm. and having compressive strength of 51 MPa at 28 days were prepared and subjected to fire at a temperature of 500 oC for 30 minutes. Subsequently, the burnt concrete was strengthened with ultra high-performance fiber-reinfored concrete having thicknesses of 15, 30, and 45 mm. The length ratios of the strengthened concrete to burnt concrete varied at 1/3, 2/3, and 1. The mixture of ultra high-performance fiber reinforced concrete used in this study was prepared by using 50% of fly ash and ground bottom ash replacing hydraulic cement as a binder. The binder to fine aggregate ratio was 1:1 by weight and 3% by volume of steel fiber was used. The water to binder ratio was controlled at 0.19 with flowability of 230 mm. The compressive strength at 28 days was 150 MPa. The post-fire mechanical properties of concrete with and without strengthening by ultra high-performance fiber-reinforced concrete were evaluated such as compressive strength, modulus of elasticity, and failure behavior. The study revealed that the compressive strength of the strengthened concrete was increased with the increase of the thickness of the high-performance fiber-reinforced concrete. The elastic modulus of the strengthened concrete exhibited higher as compared to the concrete without strengthening. Additionally, the failure behavior occurred at the high-performance fiber-reinforced concrete followed by the burnt concrete.