混凝土中氯离子侵蚀与碳化的相互影响

Interaction Effect of Chloride Attack and Carbonization in Concrete

设计了两组对比试验,结合扫描电镜分析方法,分别研究了碳化与氯离子侵蚀的相互影响.结果表明:碳化使氯离子扩散系数略有降低,在碳化区前沿形成了氯离子局部浓度峰值,而氯离子侵蚀细化了混凝土的孔隙结构,使混凝土抗碳化能力显著增强.进一步分析发现,碳化对氯离子侵蚀的影响存在着正负效应.阻碍方面,碳化产物填充了混凝土孔隙,阻止氯离子渗透;促进方面,碳化会释放结合氯离子导致氯离子浓度的局部峰值,加速氯离子渗透.因此,必须结合两方面的作用综合分析碳化对于氯离子渗透的影响.氯离子侵蚀会改变混凝土的孔隙结构,这可能是由于氯盐的结晶体填充了孔隙,也可能是由氯离子化学结合生成的Friede's在孔隙中的沉积作用,以及氯离子在C-S-H凝胶表面形成的化学吸附层造成的.

Two comparative tests have been designed to analyze combined effect of chloride attack and carbonization in concrete.The results show that chloride diffusion coefficient is reduced a little by carbonization, and local concentration peak at the front of carbonization zone is formed.Fine pore structure of concrete is formed by chloride attack,thus the ability of anti-carbonation of the concrete is significantly improved. Further analysis shows that there are positive and negative effects of carbonation on chloride penetration caused.As negative effect,carbonized product fills the pore in concrete,which prevents chloride penetration.However,the combined chloride ion can be released by carbonation to form a local concentration peak,which accelerates chloride penetration.SEM analysis shows that the pore structure of concrete is changed by chloride attack.This may be caused by chloride salt crystals filling the pores of concrete at drying time and Friede＇s deposition in pores and formation of chemical adsorption layer by chloride ion on the surface of C-H-S gel.