Research On Frost Resistance Durability Of Concrete Under The Coupling Of Load And Freeze-Thaw

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.C25 concrete is commonly used in water conservancy constructions and C50 concrete is commonly used in large bridges,in order to study their frost resistance durability under loads,specimens under axial tension,axial compression,eccentric compression and bending moment were designed.The main research contents are as follows:(1)Two kinds of strength,many kinds of loads and stress levels concrete specimens were designed and made.The loads and stress levels of C25 and C50 specimens are roughly the same.They are 0.3(C50 only),0.4,0.5 and 0.6(C25 only)times design value of compressive strength,0.1,0.15,0.2 times design value of tensile strength,eccentric pressure that make the pressure edge achieve 0.5 times the design value of the compressive strength and the bending moment that make the tension edge achieve 0.15 times design value of tensile strength.Standard rapid freeze-thaw tests were carried out on all the specimens and the mass loss rate,relative dynamic elastic modulus and compressive strength change of concrete under stress were studied.The results show that the existence of stress has a great influence on the frost resistance durability of concrete and different types of loads have different effects on the frost resistance durability of concrete.The frost resistance durability of the axial tensile specimens is the worst in all kinds of specimens and do not reach 100 freeze-thaw cycles.Concrete under 0.3,0.4 and 0.5 compressive stress levels can improve its frost resistance durability.(2)Experimental analysis on the prestress loss of short concrete specimens during tensioning and freeze-thaw process shows the proportion of prestress loss to the added prestressing is about 20% and the prestress loss can be counteracted by 1.25 times over tensioning.The prestress loss increases with the number of freeze-thaw cycles and reaches about 10% after 75 cycles.(3)According to the influence law of stress level on the freeze-thaw life of concrete measured in experiment,and introducing correction coefficient under compression,the paper modified freeze-thaw life forecasting model provided by Li Jin-yu.The modified forecasting model can better reflect freeze-thaw life of concrete structure under different stress level.