掺石膏的低钙水泥水化过程及浆体结构研究

Study on the hydration process and paste structure of low calcium cement with gypsum

利用高铝粉煤灰可烧制主要矿物组成为硫铝酸钙(C_(4)A_(3)S)和硅酸二钙的低钙水泥(LCC),石膏(CSH_(2))对C4A3S系列胶凝材料的水化性能起重要作用。为推广LCC的应用,研究了不同CSH_(2)掺量的LCC水化性能。通过等温量热仪、扫描电子显微镜、压汞仪等分析了LCC水化过程及浆体结构,并对LCC抗压强度进行检测。结果表明,随着CSH_(2)掺量增加,LCC水化反应加速,产物钙矾石(AFt)增多且由针状向柱状演变,浆体孔隙率呈现下降趋势;少量CSH_(2)(1%(质量分数))有利于浆体中水化钙铝黄长石的形成,28 d强度增长22.6%;CSH_(2)掺量为5%时,各龄期强度均显著提升;CSH_(2)掺量较高时(10%),浆体早期性能发展迅速而后期性能未见改善;过量CSH_(2)(20%)促使AFt发育成管、柱状,尽管浆体孔隙率降至8.4%,但形成了较多微米级粗孔,不利于后期性能提升;不同CSH_(2)掺量(1%~20%)的LCC强度均稳定发展且后期强度不倒缩,展现了LCC的广阔应用前景。

Low calcium cement(LCC)consisting of calcium sulphoaluminate(C_(4)A_(3)S)and dicalcium silicate can be made from high alumina fly ash.Gypsum(CSH_(2))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 CSH_(2) 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 CSH_(2) 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 CSH_(2)(1%,mass fraction)can promote the formation of strätlingite at later stage and the 28 d compressive strength is increased by 22.6%.When CSH_(2) content is 5%,the compressive strength of LCC pastes increases significantly at each curing age.When CSH_(2) content is high(10%),the early performance develops rapidly and the later performance does not improve.Excessive CSH_(2)(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 CSH_(2) content(1%-20%)develops steadily and its later strength does not shrink,showing the broad application prospects of LCC.