Experimental Study On The Mechanical Properties And Damage Evolution Of Basalt Fiber Reinforced Concrete After High Temperature

Fire resistant performance of the concrete structure is an important subject in the study of civil engineering.High temperature produced by fire will result in changes of concrete material microstructure,bearing capacity drops,using performance deterioration.Basalt fiber has good mechanical properties,resistance to high temperature,corrosion resistance and so on,it has good prospects to improve the high temperature performance of concrete.The basic mechanics and deformation properties which include the mass loss,compressive strength,flexural strength and compressive failure strain of basalt fiber reinforced concrete after high temperature were studied.At the same time,based on the horizontal displacement and strain of basalt fiber reinforced concrete bending specimens after high temperature measured by the digital image correlation,a damage factor and a localization factor were proposed to characterize the bending failure process and the crack extended morphology were observed,the main results were as follows:(1)The concrete mass loss increased due to high temperature,and the mass loss rate of compressive specimens slightly higher than that of bending specimens;the basalt fiber effect on concrete mass loss is not obvious.At room temperature to 400? range,the compressive strength increases,the peak compressive strain slower growth and the flexural strength decline accelerated relative.Temperature range from 400 ? to 800 ?,with the temperature increasing,the compressive strength and flexural strength fell rapidly,the compressive peak strain increase rapidly.Under this experimental condition,the fiber content is 2.0 kg/m~3,reached the maximum compressive and flexural strength,the compressive peak strain is the smallest.(2)In terms of two factors about the high temperature and dosage of basalt fiber,the effect of high temperature on concrete strength and deformation is bigger,a major role.Basalt fiber can improve the high temperature performance of concrete to a certain extent,but not completely inhibit heat damage,and high temperature damage to a certain extent,weaken the fiber reinforced effect.(3)The basalt fiber reinforced concrete flexural failure process can be divided into three stages: micro-fracture dispersion phase,macroscopic crack choice stage and the main crack extension stage.The damage degree factor and the damage localization factor can reflect the damage process of basalt fiber reinforced concrete bending specimen very well.Both basalt fiber and high temperature can make the bending damage process of specimens change from the abrupt failure to the gradient failure.,but the mechanism is different.Basalt fiber reinforced will extend the plastic deformation process of concrete specimens,and improve the strength of concrete.But high temperature will shorten the elastic deformation process and reduce the flexural strength due to the specimen internal damage.(4)For specimen bending failure process,basalt fiber will accelerate the expansion of the crack width at the beginning of the load,but can effectively control the expansion of the crack width and improve the flexural bearing capacity of the specimens in the late loading.High temperatures gradually accelerated the expansion of the crack width,but flexural bearing capacity gradually reduced.Both basalt fiber and high temperature can make the critical crack widths increase,namely the damage deformation of concrete bending specimens increase,and basalt fiber can improve the flexural bearing capacity of the specimens,but the high temperature is just the opposite.