Synthesis of β-C2S-based binder from limestone and calcium silicate wastes

Abstract

The present paper deals with the preparation of eco-friendly and low-energy cementitious binders using industrial by-products or materials based on waste sludge from mining and washing of limestone. Supplementary raw material containing mainly tobermorite and xonotlite is the waste of calcium silicate materials used as porous filling material of acetylene gas cylinders. Mixtures of raw materials were calcined at temperature 1150\xa0°C for 120\xa0min. Hydration products were characterized by thermogravimetric analysis (TG/DTA) and by X-ray diffraction. The heat of hydration of binder was investigated by means of isothermal calorimeter. Other techniques, such as scanning electron microscopy, were also used to characterize the microstructure. The compressive strength of pastes cured standard conditions was lower than 5\xa0MPa even during 90\xa0days. After pre-curing during 2, 5 and 7\xa0days, samples were submitted to the hydrothermal curing at 170\xa0°C for 24\xa0h. Samples developed much higher compressive strengths (30\xa0MPa). The formation of α-C2SH and γ-C2S was observed in samples after autoclaving. Pre-curing duration and hydrothermal curing conditions significantly influence the performances of cementitious materials.