STRUCTURAL CHARACTERISTICS OF DEHYDRATED PHASE OF HARDENED CEMENT PASTE AND ITS REHYDRATING ABILITY

Hardened cement paste was calcined at different low temperatures, and various dehydrated phases were acquired. Ther-mogravimetric–differential scanning calorimeter (TG–DSC), X-ray diffraction, infrared and 29Si nuclear magnetic resonance were used to investigate the structural characteristics, rehydration ability and rehydrating products structure of dehydrated phases prepared at 400, 650 ℃ and 900 ℃. The results show that, at 400 ℃, amorphous phase was generated in the dehydrating process of calcium silicate hydrate (C–S–H) gel. At 650 ℃, incompletely crystallized β-dicalcium silicate (C2S) was produced, and at 900 ℃, well-crystallized β-C2S was acquired. In the rehydration process, the dehydrated phases prepared at 400 ℃ and 650 ℃ reacted with water and produced C–S–H gel; the hydration activity of the latter, and the polymerization level of its hydration product were higher. However, the dehydrated phase prepared at 900 ℃ showes little rehydration ability; there is almost no change in the structural charac-teristic before and after the hydration process.