The aim of this study is the synthesis at low temperature (1000 degrees C) of reactive belite cement, rich in reactive C2S phases (alpha'(L) and/or beta-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 degrees C for 4 h under atmospheric pressure and continuous agitation. The burning of the hydrothermal mixture at 1000 degrees C produced reactive belite cements containing between 79% and 86% of C2S (alpha'L and/or beta polymorphs), the rest being C(12)A(7) (5-8%), C(4)AF (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 C(12)A(7)) and compressive strength evolution that led to these cements being classified in the 32.5 category according to EN 197-1. (c) 2014 Elsevier Ltd. All rights reserved.