LAUSR

Abstract Several researchers have considered waste marble sludge (WMS) as an admixture to cementitious composites. However, the scientific community is divided into two groups—one advocating WMS as a suitable microfiller, while the other claiming that WMS inhibits hydration of clinker minerals. Here, the role played by WMS during Portland cement (PC) hydration was placed under scrutiny. SEM-BSE microscopy, EDX analysis, porosimetry, and nanoindentation were employed for investigating the microstructure of cement pastes, and calorimetry for studying the rate of hydration. The impacts of hydration and microstructure development in the presence of WMS on mechanical properties of blended pastes were assessed using the resonance method and destructive tests. It was found that replacing PC with WMS by up to 15 wt% can lead to an increase of compressive and flexural strength because WMS lowers the porosity of pastes, contributing to a more homogeneous distribution of phases, and reinforces the brittle cementitious matrix. A weak transition zone around marble grains was observed, but this was not significant for WMS replacement at 15 wt% or less. Given the amount of WMS produced annually, its utilization for the production of building materials, even in relatively low concentrations, could potentially have a considerable impact on the sustainable reuse of WMS.