Reaserch About Uniaxial Compression Performance Of Concrete Under Freeze-thaw Cycles

During the lifetime of concrete structure under natural environment, material aging and mechanical performance deteriorating were unavoidable and irreversible. These changes which may cause damage or even catastrophic failure of the whole structure can not be attributed to mechanical factors solely. The durability of concrete can be defined as its ability of maintaining safe, serviceable and acceptable in appearance while subjected to various environmental effects in its lifetime. In China, where most areas were in severe cold region, concrete failure caused by freeze-thaw happened from time to time, as well as in some mild regions (e.g. east region north of the Yangtze River). Therefore, research about mechanical and deformation performance of concrete under freeze-thaw cycles was significant in understanding the concrete, improving the design method and reducing the cost.This paper, a part of"research about mechanical performance of reinforced concrete and pretsressed concrete structure under freeze-thaw cycles"(Natural Science Foundation of China)(Project approval 50978224), has done work as follows:(1)Concrete specimens of different compressive strength (C20, C30, C40 and C50) were made in to two shapes (cubic and prismatic)(2)C20 and C30 specimens were subjected to0,25, 50, 75 and 100 freeze-thaw cycles, while C40 and C50 specimens were subjected to 0,25, 50, 75, 100 and 125 cycles. Quality loss and Dynamic modulus were measured every 25 cycles.(3)Water absorption of specimens before and after freeze-thaw were measured. Water absorption of specimens in respond to freeze-thaw cycles were analyzed.(4)Compressive strength of cubic specimens before and after freeze-thaw were measured and their destructive pattern were analyzed. According to data collected in experiments, freeze-thaw effect on strength and deformation of four different strength grade concretes were analyzed. In addition, relation between relative strength of four different strength grade concretes and freeze-thaw cycles were set up, so were the relation between strength and relative dynamic modulus.(5) Uniaxial compression strength of concrete prismoids after freeze-thaw cycles were tested, and their destructive pattern were analyzed. Test results showed that with the increase of freeze-thaw cycle number, the concrete stress-strain curve became more flat, the peak stress decreased, but the peak strain and the limit strain increased. The relationships between peak strength, peak strain and limit strain and freeze-thaw cycle times, the relationship between the peak stress and relative peak dynamic elastic modulus, the equation with parameters of stress-strain curves for the concrete subjected to the action of freezing-thawing were established based on the test results.