Study On Temperature Response And Damage Of Bridge Structure Concrete Under Large Temperature Difference Environment

The concrete of bridge structures under strong radiation and wind environment suffers from strong sunlight radiation during the day,and the temperature gradually increases.At night,the temperature of concrete decreases with the decrease of ambient temperature and the influence of wind.The daily temperature difference of concrete can reach 40～50℃.This long-term large temperature difference environment is bound to damage and degrade the concrete,and then affects the service life of bridge structures.Therefore,taking the concrete commonly used in bridge structures as the research object,aiming at the temperature response and damage of concrete exposed to sunlight and wind,a three-dimensional sphere random aggregate model is established to simulate the temperature response,temperature stress and damage accumulation of the concrete under large temperature difference environment,and the temperature cycling test is designed to verify the simulation results.What’s more,the effects of mix proportion parameters and environmental factors on concrete temperature response and damage are simulated,and finally the measures to inhibit concrete damage in large temperature difference environment are put forward.Major work and conclusions are as follows:(1)The temperature response and damage accumulation of concrete under large temperature difference environment were studied by finite element simulation and experiment.Compared with the change of external environment temperature,the change of internal temperature of concrete lagged behind obviously.The thermal conductivity of concrete decreased and the heat transfer slowed down as the temperature cycle progresses.The interface between aggregate and mortar was almost all tensile stress,which produced damage first and accumulated during the process of heating up.The order from largest to smallest of loss rate on mechanical property of concrete was splitting tensile strength,compressive strength and static elastic modulus.The simulation results of concrete temperature response and static elastic modulus loss rate were generally close to the test results.(2)The effects of mix proportion parameters on the temperature response and damage of concrete were studied.The larger the water binder ratio(0.30～0.42),paste aggregate ratio(0.40～0.50)or sand ratio(35%～41%),the slower the temperature transfer.With increasing temperature cycling times,the larger the water binder ratio,the smaller the damage of concrete;The damage of concrete with paste aggregate ratio of 0.40 and0.45 was almost equivalent,while the paste aggregate ratio of 0.50 was obviously larger.The damage of concrete with sand ratio of 35% was significantly larger than that of sand ratio of 38% and 41% in the whole process.(3)The effects of environmental factors on the temperature response and damage of concrete were studied.The larger the temperature difference of temperature cycle,the larger the temperature change rate of concrete,and the larger the damage under the same cycle times.The damage of concrete after 120 temperature cycles was approximately twice that of the original as the temperature difference increases by 10 ℃.Wind speed had great influence on the temperature response of concrete,but had little influence on the loss of static elastic modulus.The damage and deterioration of concrete under the reference thermal condition was the worst.The damage of the upper half of concrete under beam thermal condition was larger than that under pier column thermal condition,and the damage of the lower half of concrete under beam thermal condition was the least.(4)The evolution mechanism of concrete performance under temperature cycle was analyzed,and the corresponding suppression measures were put forward.Due to the thermal stress caused by the uncoordinated deformation of concrete composition and temperature gradient,the concrete damage began from the interface between aggregate and cement mortar and continued to expand into cement mortar.The microstructure became loose and porous,and finally resulted in the degradation of mechanical properties.Adding active mineral admixtures such as fly ash and mineral powder,selecting aggregates with little difference from the thermal expansion coefficient of cement paste,and setting thermal insulation measures can reduce the deterioration of concrete performance.