混凝土劈拉开裂和裂缝自愈合机理

Self-healing mechanism of concrete cracks induced by splitting tensile loading

采用混凝土圆盘试件,研究了劈拉加载下混凝土的开裂过程和裂缝形态,分析了试件劈拉应力-裂缝口张开位移曲线的特征,探讨了不同卸载位移下曲线的变化规律;对劈拉开裂后混凝土在不同环境中(海水、淡水和标准养护)的性能恢复规律和自愈合机理开展了试验研究。结果表明:混凝土劈拉开裂导致自身刚度降低,并且裂缝口张开位移越大,刚度降低越明显;自愈合产物与混凝土基体黏结强度较低,再次劈拉加载下试件刚度虽有恢复,但恢复值相对于初始刚度较小;裂缝自愈合是各种物理和化学过程综合作用的结果,愈合机理主要包括水泥的再水化作用、结晶作用、水泥水化产物的分解作用和颗粒杂质等的堵塞作用。

By using the disc specimens,the cracking process under splitting tensile loading and morphological characteristics of cracks were investigated.The tensile stress-COD(Crack Opening Displacement)curves during loading and unloading were obtained and analyzed in terms of different unloading displacements.And then,the performance recovery and healing mechanisms of the cracked specimens within different conditions,i.e.,sea water,fresh water and standard curing condition,were experimentally studied.The results indicate that cracking of concrete leads to the decrease of its own stiffness,and the greater the COD,the more the stiffness decreases.By reloading the healed disk specimens,the bond strength between self-healing products and concrete matrix is relatively low,and although the stiffness has been to some extent restored,the recovered degree is relatively low compared with its initial stiffness.Self-healing of cracks can be regarded as an integrated result of physical and chemical reactions,and the mechanism consists of further hydration of cement,crystallization,resolution of hydrated products and blockage of loose particles or impurities.