Study On Compressive Mechanical Properties Of Concrete At High Temperature Under The Combined Action Of Load And Carbonization

Research on the fire resistance performance of concrete is an important subject in the field of civil engineering.The performance of concrete when it is subjected to fire or high temperature is affected by many factors.First of all,concrete will inevitably bear the load transmitted by the superstructure during normal service.Moreover,concrete is in a state of natural carbonization all the year round.These factors will have an impact on the high-temperature mechanical properties and deformation properties of concrete.Therefore,studying the high-temperature performance of concrete under the combined action of load and carbonization is of great significance to the fire-resistant design and post-fire evaluation of the structure.In this papar,the carbonization test on the concrete specimen under sustained load was carried out.and when the carbonization age was reached,the high temperature test on the concrete specimen under sustained load was carried out.At the same time,the digital image correlation technology was used to test the deformation field data of the specimen surface in a high temperature environment.Study the effect of the joint action of load and carbonization on the free thermal expansion strain,high temperature transient creep strain,the axial compressive strength,elastic modulus,peak strain and stress-strain curve at high temperature,and establish the concrete damage constitutive model.The main results are as follows:(1)Under the action of carbonization,the free thermal expansion strain and high temperature peak strain of concrete are reduced,and the axial compressive strength and elastic modulus at high temperature are increased.Carbonization improves the high temperature compressive resistance performance of concrete and reduces the high temperature load-induced deformation of concrete.(2)The sustained load can reduce the high temperature damage of concrete,so that the compressive strength of the concrete is improved.Under the same load level,the slope of the stress-strain curve of concrete in the loading failure stage at each temperature is almost the same.The high temperature peak strain first decreases and then increases with the increase of the load level.The sustained load of 0.4fc reduces the high temperature peak strain of concrete,while the sustained load of 0.6fc increases the concrete peak strain at 200℃～400℃.(3)The high temperature transient creep strain of uncarbonized and carbonized concrete approximately increases linearly with time,and increases with the increase of load level and temperature,but the carbonization inhibited the development of the high temperature transient creep strain.The combined action of load and carbonization increases the compressive strength and reduces the peak strain of concrete at high temperature,and make the concrete brittleness more significant.(4)According to the principle of strain equivalence,Weibull probability distribution and the characteristics of the stress-strain curve of concrete under high temperature under load and carbonization,a concrete damage constitutive model is established,which can more accurately describe the evolution of concrete high temperature damage under load and carbonization.