Concrete Structure Durability In Freezing-thawing Circumstance Based On Multi-factor Effects

Concrete durability has become the hot research field of civil engineering. The concrete structure suffered freezing-thawing damage in different degree in north China and south parts, so, freezing-thawing cycle is one of the important factors affecting the durability of concrete construction. In order to fully realize the interaction between various environmental factors, this paper will research concrete durability in freezing-thawing environment under the coupled action, study of concrete durability damage law degradation under coupling, according to the theoretical analysis and the laboratory test data. It is of great theoretical and practical value, and to lay the foundation of concrete durability research in freezing-thawing environment.Papers selected freezing-thawing environmental impact factors of concrete structure durability (freeze-thaw cycles) and concrete neutral environmental factors (CO2 and acid), design many factors durability test scheme and implementation methods. Through a single and double experiments under the influence factors of concrete anti-freeze regularity and neuter performance, reveal the mechanism and the coupling effect, and freezeing-thawing environment concrete reliability analysis and prediction capacity, establish the freeze-thaw environment concrete structure neuter depth prediction model. Major to study the contents of the following:Firstly,in the fast freezing-thawing test of concrete, study of various factors (water-binder ratio, fly ash, air content) affect anti-freeze regularity. Analysis of the different factors affecting the quality of concrete under the environment of freezing-thawing loss, the dynamic elastic modulus and compressive strength of variation. The testing results were discussed and considering the water- cement ratio, fly ash contents and the air-entraining agents, the prediction model of number cycles of freezing and thawing of concrete is built, which choose the compressive strength as the evaluation index. Secondly,design the freezing-thawing cycles and carbonization of concrete durability test under the joint action,study the freeze-thaw cycles and carbonization of concrete quality,dynamic elastic modulus,compressive strength variation and neuter rule,analysis freeze-thaw cycle and carbonization mechanism and the coupling effect between them.The conclusion through the analysis:in freezing-thawing cycles and carbonization function test mode,the strength of concrete quality loss is more than a single loss of freeze-thaw cycle test mode,relative dynamic elastic modulus is less than a single freeze-thaw cycles test results of the model.Thirdly,design the freezing-thawing cycles and acid rain of concrete durability test under the joint action,study of the freeze-thaw cycles and carbonization of concrete quality,dynamic elastic modulus,compressive strength variation and neuter rule.Results show that:in freezing-thawing cycles and acid rain function test mode,concrete surface spalling and present mechanical performance degradation,the concrete quality loss,dynamic elastic modulus,and strength loss is more than single loss of freeze-thaw cycle test mode.Fourthly,from the macroscopic damage mechanics theory,the damage can be divided into two phases:damage caused by freezing-thawing cycle and freeze-thaw cycles and uniaxial compressive,a damage evolution equation of two stages established,derived from natural freeze-thaw cycle times related with the concrete uniaxial damage constitutive relationship.Established the damage evolution equation of concrete in freezing-thawing cycle,freezing-thawing cycle and carbonization, freezing-thawing cycle under the action of acid rain.Fifthly,a predicting model of carbonation depth in freezing-thawing envirment was established on the basis of analysis of main influencing factors of concrete's porosity and carbonation mechanism. The calculation of important parameter De , that is the effective diffusion coefficient,was proposed on the basis of the mechanism gas diffusion in concrete through the experiment data regression.Finally,based on the concrete neuter depth,the damage evolution process and reliability analysis,put forward concrete structure prediction research under the environment of freezing-thawing. Reliability analysis and prediction capacity under the environment of freezing-thawing reinforced concrete structural,for concrete structure durability in freezing-thawing environment under the action of the prediction provided the basis and reference。...