碱硅酸反应作用下混凝土中氯离子扩散规律和结合能力

采用活性集料和非活性集料配成混凝土进行对比试验,研究了氯离子在同时受到碱硅酸反应(ASR)作用的混凝土中的扩散和结合特性.所用混凝土的碱含量分别为水泥质量的0.5%和1.5%,试验温度为60℃,并采用3.5%和7.5%两种不同质量分数的NaC l溶液浸泡混凝土,进行了氯离子渗透试验,测定了不同浸泡龄期下混凝土试件内部总氯离子含量和自由氯离子含量.用XRD和SEM以及压汞法对试件进行了微观结构分析.结果表明:在ASR同时作用时,混凝土的氯离子扩散速度减慢,混凝土对氯离子的结合表现为线性吸附关系,氯离子结合能力也明显降低;ASR所导致的开裂不会明显提高氯离子的侵入.由于氯离子扩散速度减慢,混凝土钢筋锈蚀时间延迟,但并不能得到抑制,并且由于氯离子结合能力的降低以及ASR的发生,孔溶液中C(C l-)/C(OH-)提高,反而会使锈蚀加快.

Chloride diffusion and binding capacity in concrete suffered from ASR

Experiments were conducted to investigate the chloride diffusion and binding capacity of concrete suffered from both ASR(alkali-silica reaction) and chloride ingression.Two levels of ASR were set by adding different amount of alkali in concrete,and the ASR was accelerated by heating.Two sodium chloride solutions of various concentrations were used to ingress the concrete simultaneously.The contents of free and total chloride ion in the concrete specimens of various depths were measured after different exposure periods.The structures of some specimens were analyzed by XRD(X-ray diffraction),SEM(scanning electron microscopy) and MIP(mercury intrusion porosimetry).The results show that the diffusion rate of chloride ion is alleviated in the existence of ASR.The binding capacity of chloride in the concrete with ASR is much lower than that in the concrete without ASR.The crack induced by ASR does not promote the ingression of chloride significantly.The results suggest that in the concrete structure susceptible to ASR,the inclusion of chloride can speed up the chloride erosion because of the low capacity of chloride binding.And the chloride in surroundings,although diffuse slowly into concrete,can corrode the reinforcement in concrete in the long run.