干湿循环机制下碳化混凝土氯离子侵蚀试验研究

Experimental study on chloride penetration into concrete after carbonation under wet and dry cycle mechanism

海工混凝土结构的水上区部分,长期受到氯离子侵蚀和碳化的双重作用,较之一般大气环境下的混凝土结构,这一区域的混凝土结构更易发生钢筋锈蚀.本文开展了干湿循环机制下碳化混凝土的氯离子侵蚀试验,通过分析氯离子浓度分布规律,扩散系数以及微观结构,深入研究混凝土碳化对氯离子扩散的影响.研究结果表明,碳化反应增加了混凝土内部自由氯离子的含量,减缓了氯离子浓度的衰减,对混凝土的抗氯离子侵蚀性能造成了不利影响.碳化后,低水胶比混凝土的氯离子扩散系数有所下降,而高水胶比混凝土的氯离子扩散系数显著增大.碳化反应对混凝土的微观结构有一定的劣化作用,将会加速有害介质的侵入.降低水胶比可显著提高混凝土的密实度,增强混凝土自身的抗氯离子侵蚀性能,同时可以减轻碳化反应对氯离子侵蚀的加剧.

The part above the sea water of marine concrete structures will be subjected to chloride penetration and carbona- tion over a long period of time. Compared with the concrete structures in the general atmosphere, marine concrete struc- tures are more susceptible to reinforcement corrosion. In this paper, experiment of chloride penetration into concrete after carbonation under wet and dry cycle mechanism was carried out. Effect of concrete carbonization on chloride diffusion was deeply studied through analysis of the distribution of chloride ions, chloride diffusivity coefficient and microstruction of the concrete. The results showed that free chloride ion content in concrete was enhanced after carbonation, the decay of chloride ion concentration was slowed down. After carbonation, chloride diffusivity coefficient of concrete with low water- binder ratio was reduced, and chloride diffusivity coefficient of concrete with high water-binder ratio was increased appar- ently. And the microstruction of the concrete was deteriorated by carbonation. Both the density and chloride ion penetra- tion resistance of concrete could be increased by reducing the water-binder ratio.