掺石膏的低钙水泥水化过程及浆体结构研究

Low calcium cement (LCC) consisting of calcium sulphoaluminate (C4A3S) and dicalcium silicate can be made from high alumina fly ash.Gypsum (CSH2) plays an important role in hydration properties of C4A3S cementitious materials.In order to promote the application of LCC, the hydration properties of LCC with different CSH2 content were studied.The hydration process and paste structure of LCC were determined by isothermal conduction calorimetry, scanning electron microscopy and mercury intrusion porosimetry.The compressive strength of LCC pastes was also measured.The results show that the hydration of LCC is accelerated and the amount of ettringite (AFt) in the paste increases with the increase of CSH2 content.At the same time, AFt changes from needle-like morphology to columnar morphology and the porosity of pastes decreases gradually.A small amount of CSH2 (1%, mass fraction) can promote the formation of strätlingite at later stage and the 28 d compressive strength is increased by 22.6%.When CSH2 content is 5%, the compressive strength of LCC pastes increases significantly at each curing age.When CSH2 content is high (10%), the early performance develops rapidly and the later performance does not improve.Excessive CSH2 (20%) promotes the AFt to grow into tubular and columnar morphology, and the porosity of paste decreases to 8.4%.However, a large number of micron-scale pores is formed in the paste, which is not conducive to the improvement of later performance.The strength of LCC with different CSH2 content (1%-20%) develops steadily and its later strength does not shrink, showing the broad application prospects of LCC.