高碱度水泥基材料早期开裂敏感性研究

选用粉煤灰、减缩剂和减水剂，采用五路裂缝测定仪和非接触式电阻率测定仪，分别测试了相同水灰比、不同碱类型的水泥砂浆在干燥条件下约束收缩开裂的初始时间与水泥浆体早期水化24h内的电阻率变化，并测定了水泥砂浆在干燥环境下的抗压、抗折强度．结果表明：碱度增加会加速水泥的早期水化硬化以及微结构的形成与发展；Na^ 提高水泥砂浆早期强度、增加约束收缩开裂敏感性的作用要比K^ 的明显，尤其在低水灰比、掺减水剂时其影响更为明显；粉煤灰和减缩荆可延缓水泥(尤其是高碱度的水泥基材料)的早期水化硬化，降低水泥砂浆强度的发展，推迟初始开裂时间．

Investigation on Early-age Cracking Sensitivity of Cement-based Materials with Excessive Alkali

Initial time of cracking ocurring in restrained shrinkage under dry condition of mortar and electrical resistivity of cement pastes with different alkali and admixtures were tested using a multicenter ellipse ring apparatus with an automatic monitoring system and a non-contact resistivity meter, respectively. Besides, compressive and flexural strength of mortar under dry curing condition were also determined. Experimental results show that alkali(R_2SO_4) accelerates hydration process of cement with or without fly ash or shrinkage-reducing admixtures(SRA) or water-reducing admixtures, and enhances the strength development of corresponding mortar but also shortens greatly the initial cracking time, especially under lower water-cement ratio and with water-reducing admixtures. However, fly ash or SRA is capable of resisting drying shrinkage crack and reducing strength development of mortar at early ages, because fly ash or SRA may retard the hydration and hardening process of cement, especially for cement-based materials with high alkalinity.