Bonded Prestressed Concrete Structure Freeze-thaw Durability Study

Freezing injury is the second important reasons next to the corrosion of reinforcement,which cause durable damage of concrete structure.Anti freeze-thaw injury has become an important direction in the field of the durable study of concrete structure.At present,the study on concrete resisting to freeze-thaw damage focuses mostly on material level,and the research of structual level especially for prestressed concrete structure is seldom.Combined with the research for fatigue and durability of unbonded prestressed concrete structure supported by the national natural science foundation of china,the paper mainly studies the effect of different stress level on freeze-thaw durability of concrete.The main works are presented as follows:1,Studying the effect of different stress level on freeze-thaw durability of concrete.Through antifreeze-thaw experiment of concrete specimen added five different stress ratios(that is 0.0f_c,0.10f_c,0.25f_c,0.5 f_c and 0.75f_c),the paper studies the influence law of different stress level on relative dynamic modulus of elasticity and mass loss rate of concrete,then summarizes the relationship between stress level and freeze-thaw life of concrete.The results show that there is asignificant effect of stress level on freeze-thaw life of concrete.2,According to the influence law of stress level on the freeze-thaw life of concrete measured in experiment,and introducing compressive stress coefficient,the paper modified the forecasting model under non-stress provided by Jinyu Li.The modified forecasting model can better reflect frost resistance of actual structure under different load level.3,Studying on the corrosion resistance of non-cohesive prestress steel strand in freeze-thaw environment.Through setting different test conditions,this paper comparativly studies the effect of freeze-thaw and prestress on the corrosion resistance of steel strand.Analysis and experimental results show that concrete deterioration in freezing-thawing environment provides much passage for corrosive media into the surface of steel strand.Under combined freeze-thaw and prestress,the corrosion rate of non-cohesive steel strand is more than simple addition of independent action of freeze-thaw and prestress.4,Initially explorating the effect of freezing-thawing cycle on the prestress loss of non-cohesive prestress steel strand.Through freeze-thaw experiment of unbonded prestressed concrete specimen,the paper studies the change law of prestress of UPS following freeze-thaw cycle times.The results show that the prestress level of UPS presents difficult change law following frost-thaw continuing while precompressed stress level of concret is difficult during freeze-thaw.