Abstract:

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.

Key words: saline-alkali soil, salt corrosion, freezing-thawing cycle, concrete, frost resistance