Effect Of Freeze-thaw Cycle On Chloride Diffusion Behavior Of Concrete In Alternate Parts Of Dry And Wet

At present,the durability of concrete structures is becoming increasingly prominent in the world,especially in the cold areas of northeastern China,the damage of marine concrete structures is the most serious.The main factors affecting the durability of concrete are freeze-thaw damage and chloride ion erosion.Scholars at home and abroad have studied the durability of concrete structures under different environments,but the durability of concrete structures under single factors such as freeze-thaw cycles,chloride corrosion,wet-dry alternation and so on has been taken into account.The research objects are mainly concentrated on the concrete projects of highways or bridges,coastal and coastal engineering,in which the freeze-thaw mechanism of concrete and chloride erosion are thoroughly studied,and the study of freeze-thaw cycle-dry-wet alternation is rare.In this paper,25 kinds of test conditions are designed according to the number of wet-dry alternation and freeze-thaw cycles.Cylindrical specimens with the size of 100 mm x 50 mm are fabricated.The chloride ion concentration,electric flux and chloride ion diffusion coefficient of concrete specimens at different depths are taken as research indexes,which are single factor of wet-dry alternation,single factor of freeze-thaw cycle and dry-wet alternation-freeze-thaw cycle for concrete specimens.The diffusion behavior of chloride ion under the action of two factors provides a criterion for evaluation.The specific conclusions are as follows:After repeated immersion in NaCl solution,due to salt crystallization,white particles appear on the surface of concrete after drying.The more times the concrete undergoes wet-dry alternation,the more obvious the phenomenon of white particles appears.The surface chloride concentration of concrete specimens with dry-wet alternation-freeze-thaw cycle is 122.2% higher than that of concrete specimens only experiencing dry-wet alternation and 100% higher than that of concrete specimens only experiencing freeze-thaw cycle.The electric flux of concrete specimens with dry-wet alternation-freeze-thaw cycle is 59.85% higher than that of concrete specimens only experiencing freeze-thaw cycle.The chloride diffusivity of concrete specimens increased by 52.48%.The chloride diffusivity of concrete specimens with dry-wet alternation-freeze-thaw cycles increased by 608.6% compared with that of concrete specimens only experiencing dry-wet alternation,and increased by 381.1% compared with concrete specimens only experiencing freeze-thaw cycles.In addition,the loss of concrete specimens after dry-wet alternation-freeze-thaw cycles is much more serious than that only after dry-wet alternation and freeze-thaw cycles.