Electrical and thermal characterisation of cement-based mortars containing recycled metallic waste

The management and disposal of solid waste from industrial sources is a problem around the world. In recent years, several studies have been carried out to develop advanced construction materials based on the waste valorisation. As a result, building materials with self-healing and self-monitoring properties have been developed using electrically conductive metallic waste. Nevertheless, the addition of metallic waste may influence the electrical and thermal performance of the new building materials. This paper aims to evaluate the effect of the type and content of metallic waste (steel fibres and steel shavings) on the volumetric, electrical, and thermal properties of cement-based mortars designed with self-monitoring purposes. Physical, electrical, and thermal properties of cement-based mortars with four different contents of metallic waste were evaluated by measuring their bulk density, porosity, electrical resistivity, and thermal conductivity. In addition, metallic waste distribution inside the mortar specimens was measured by ultrasonic tests. All the properties were measured on specimens at two curing ages, 7 and 28 days. The main results showed that the addition of metallic waste produced a reduction of the bulk density and an increase of the porosity of cement-based mortars. Furthermore, it was proven that it is possible to evaluate the metallic waste distribution inside the mortars by ultrasound, and that this evaluation is more effective in specimens with fibres than in those with shavings. Likewise, it was proven that metallic waste can modify the electrical resistivity and the thermal conductivity of mortars, regardless of the type and amount of metallic waste. Finally, it was concluded that both the type and amount of metallic waste, and the curing time used in this research did not present a significant influence on the variation of the electrical resistivity and thermal conductivity of the evaluated cement-based mortars.