盐冻环境下混凝土的微结构和氯离子渗透性

Microstructures and Chloride Permeability of Concretes under Salt Frost

研究了水灰比、含气量等因素对混凝土在冻融和盐冻环境下劣化的影响,进行了混凝土微观形貌分析和冻融条件下氯离子在混凝土中的传输性试验,分析了盐冻条件下混凝土孔结构变化及氯离子传输规律.结果表明:当冻融循环25次时,盐冻条件下混凝土的质量损失率约是水冻条件下混凝土质量损失率的10倍;在冻融早期,盐冻条件下的混凝土动弹性模量损失比水冻条件下的混凝土动弹性模量损失缓慢;引气混凝土中50"m以上孔径的气泡较多,未引气混凝土的平均气泡间距为引气混凝土的2.5倍;引气能够降低冻融下混凝土的氯离子渗透性,但盐冻后引气混凝土表层有氯离子富集现象,考虑到钢筋混凝土构件的保护层厚度范围,这有可能不利于钢筋的保护.

Performance degradation of concretes with varied water-cement ratio and air content under freeze-thaw cycles or salt frost cycles were investigated. After suffering from salt frost, microstructures of hardened cement pastes were analyzed by mercury intrusion method and scanning electron microscope, and chloride transport performance was measured experimentally. The results show that, mass loss of concrete after 25 times of salt frost cycles is 10 times of that after pure water frost. At early stage of freeze-thaw cycles, there is a small descent of dynamic elastic modulus of concrete after salt frost compared with the one after water frost. There is a large amount of air voids with size of more than 50 μm in air-entrained concrete. Mean space of air void in non air-entrained concrete is 2.5 times of that in air-entrained concrete. Chloride penetration of concrete is weakened by increasing air content. However, chloride ions concentrate in surface layer of concrete, which may be unfavorable for reinforcement protect against corrosion consid- ering the depth of cover to reinforcement.