季节冻土区盐渍土环境下混凝土抗冻耐久性机理

为了研究混凝土在冻融交替与盐类侵蚀双重因素作用下的抗冻耐久性能，根据季节冻土区大安境内盐渍土中主要易溶盐的类型与含量，配制了3种质量分数的复合盐侵蚀溶液，制备了普通混凝土、2种引气混凝土及2组粉煤灰混凝土试件，进行盐蚀CD*2]快速冻融循环试验，对盐冻破坏后混凝土的质量损失、动弹性模量衰减及其微观结构进行分析。试验结果表明:在冻融循环作用下，复合盐加剧了混凝土的冻融剥蚀破坏;混凝土的冻害程度与侵蚀盐溶液的质量分数、冻融循环次数、混凝土的含气量、粉煤灰掺量等因素有关;造成混凝土发生盐冻破坏的原因有水结成冰的膨胀压力，或冰与水的渗透压力以及复合盐与水泥水化产物发生的化学侵蚀和盐类的结晶膨胀，其中，盐类结晶压对混凝土内部结构的破坏更严重。

Frost Resistance and Durability Mechanism of Concrete Under Saline-Alkali Condition in Seasonal Frozen Soil Area

In order to study the frost resistance and durability of concrete structures under double factors of salts attack and freezing-thawing cycles in seasonal frozen soil area, multi-salt solution with three kinds of mass fraction and water were prepared according to the type and quantity of the main dissolved salts in the spring soil of Daan region. Specimens of ordinary concrete with different mixture ratios, two kinds of air-entraining concrete and two kinds of fly-ash concrete were prepared for the multiple salts and freezing-thawing cycle tests. The mass loss, dynamic elastic modulus reduction and microstructure of tested samples were analyzed. Results showed that concrete erosion was aggravated by multi-salt under the action of freezing-thawing cycles. The degree of frozen damage was related to the mass fraction of salt solution, times of freezing-thawing cycle, air content in concrete and fly-ash addition ratio. Reasons that lead salt-frozen damage occur were expansion pressure produced during the course of water turning into ice, the seepage pressure of ice and water and the chemical erosion and crystalline swelling of salt from the reaction between multi-salt and cement hydration production, among which salt crystallization played more important role in the damage of concrete internal structure.