减缩剂对水泥基材料早期水化及收缩变形性能的影响

采用非接触式电阻率测定仪和半绝热实验方法分别研究了减缩剂对常温和半绝热条件下的水泥浆体早期水化的电阻率和温升的影响,对比研究了减缩剂对水泥砂浆在干燥条件和常温水中养护时的线性长度变化与强度发展情况的影响,应用五路裂缝测定仪研究了减缩剂在水泥砂浆中的抗裂效果.结果表明:在常温条件下减缩剂会延缓水泥早期水化,而在半绝热条件下则会加速水泥早期水化;减缩剂主要提高干燥环境下的水泥砂浆的抗裂性能,降低其线性收缩值与强度增长,推迟其约束收缩初始开裂时间,而对水中养护的砂浆无补偿收缩效应,因此不利于控制热裂缝.分析表明,减缩剂在水泥基材料中应用时不仅具有物理作用,而且具有化学作用.

Effect of shrinkage-reducing admixture on hydration and shrinkage deformation of cement-based materials at early ages

Electrical resistivity at normal temperature and semi-adiabatic temperature-rise of cement pastes with variant dosage of shrinkagereducing admixtures(SRA) were tested using a non contact resistivity meter and a semi-adiabatic apparatus respectively.Free linear change and strength development of the corresponding mortars under drying and water curing conditions were studied;and the initial cracking time of mortars cured at drying conditions was detected using a five-group crack apparatus.The results show that the SRA retards early hydration of cement pastes at normal temperature but accelerates early hydration at semi-adiabatic conditions.The SRA mortars cured in drying conditions show a lower linear shrinkage value,a lower strength development and a later initial cracking time.However,the SRA mortars cured in water show a higher shrinkage at earlier ages and consequently SRA may not be able to control thermal cracking.The results indicate the SRA has physical and chemical effects in cement-based materials.