石膏对石灰石粉水泥基材料水化及硬化性能的影响

针对我国目前非荷载作用下混凝土严重开裂的问题,以"比表面积较低的水泥熟料-比表面积较高的掺合料-足够掺量的石膏"构成的胶凝材料体系为研究对象,通过水化热速率、X射线衍射(XRD)、扫描电子显微镜(SEM)、压汞法(MIP)及热重-差示扫描量热法(TG-DSC)等手段,研究石膏对石灰石粉水泥基材料水化及硬化体微结构的影响。结果表明,石灰石粉能够加速C3A与石膏作用生成钙矾石相,在足量石膏存在的条件下,能够阻碍钙矾石向低硫型硫铝酸钙转变;石灰石粉的掺入与石膏一起延缓了C3A的水化;在石灰石粉和足够石膏同时存在的情况下,C3A水化生成具有膨胀性的水化碳铝酸钙和高硫型硫铝酸钙,补偿了收缩,提高了水泥基材料的抗裂性能;熟料粗磨、掺合料细磨及较高石膏掺量的胶凝材料体系配制的C30和C50等级混凝土,强度能持续增大,从28d到180d,强度分别提高了36.7%和33.3%,混凝土结构紧密、孔隙率低、有害孔含量少。

Influence of Gypsum on Hydration and Hardening Performance of Limestone Powder in Cement Based Material

Focusing on the problem of serious cracking of concrete under non-load, this paper presents a cementitious material system which composed by cement clinker with low specific surface area, mineral admixtures with high specific surface area and gypsum with high dosage. The influence of limestone powder and gypsum on hydration and hardening micro-structure of cement based cementitious material was studied by hydration rate test, X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and thermal gravimetric-differential scanning calorimetry (TG-DSC). The results showed that limestone powder accelerated the react of C₃A and gypsum to generate ettringite. In the presence of a sufficient amount of gypsum, limestone powder could hinder the transformation of ettringite to low-sulfur type hydrated calcium sulphoaluminate. The incorporation of limestone powder and gypsum further delayed the hydration of C₃A. In the case of coexistance of enough limestone powder and gypsum, C₃A hydrated to generate hydrated carbon calcium aluminum with expansion property and high-sulfur type hydrated calcium sulphoaluminate, which compensated the shrinkage and improved crack resistance of cement based materials. C30 and C50 concrete prepared with the cementitious material composed by coarse grinding clinker, fine grinding mineral admixtures and gypsum with high dosage had momentum of increasing compressive strength continuously. The strength increased by 36.7% and 33.3% respectively from 28 days to 180 days. The concrete had close structure, low porosity and less content of harmful hole.