Properties of low temperature belite cements made from aluminosilicate wastes by hydrothermal method

The aim of this study is the synthesis at low temperature (1000 °C) of reactive belite cement, rich in reactive C2S phases (α′L and/or β-C2S), starting from aluminosilicate wastes (oil well drilling mud and hydraulic dam sludge) and hydraulic lime dust recovered from bagging workshops. A hydrothermal treatment of the raw cement mixture was performed in an alkaline solution of KOH (0.6 M), with heating at 100 °C for 4 h under atmospheric pressure and continuous agitation. The burning of the hydrothermal mixture at 1000 °C produced reactive belite cements containing between 79% and 86% of C2S (α′L and/or β polymorphs), the rest being C12A7 (5–8%), C4AF (7–11%) and free lime (2%). The cements were characterized by X-ray Fluorescence (XRF), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), microprobe, and laser granulometry. The hardening evolution of belite cement pastes and mortars was followed by thermo-gravimetric analysis (TGA), setting time and compressive strength. The results showed a rapid production of hydrates (C–S–H/C–A–S–H, calcium aluminate hydrates and portlandite), with a fast setting time (reaction of C12A7) and compressive strength evolution that led to these cements being classified in the 32.5 category according to EN 197-1.