Coupling effects of silica fume and steel-fiber on the compressive behaviour of recycled aggregate concrete after exposure to elevated temperature

The use of recycled concrete aggregates in structural concrete is a sustainable solution to deal with the construction and demolition waste. This technology reduces serious impact on the ecological environment caused by the shortage of natural mineral resources. The aim of present study is to assess the coupling effects of silica fume and steel-fiber on the compressive performance of recycled aggregate concrete (RAC) under elevated temperatures. A total number of 90 cylindrical concrete specimens are prepared and tested under axial compression, after heating by elevated temperatures. Comprehensive studies are conducted on the temperature dependence of compressive strength, elastic modulus, and toughness. The degradation mechanisms of recycled concrete are also examined by scanning electronic microscopy (SEM) study. It has been found that the evaporation of water and the decomposition of hydro chemicals in concrete are the main reasons for the reduction of RAC compressive performance from 25 °C to 400 °C and from 400 °C to 800 °C, respectively. The compressive performance of RAC decreases with increasing temperatures, but the addition of steel fibers significantly counteracts this negative impact. Thanks to the superior coupling effect of silica fume and steel fibers, the steel-fiber RAC (SRAC) with silica fume shows excellent compressive behaviour under high temperature environment. This study provides important engineering insights into the use recycled concrete in high temperature environment.