Study On Mechanical Properties Of Basalt Fiber Concrete After High Temperature Loads

In the fire,the concrete was effected by high temperature,and its mechanical properties after fire was also influenced by the load.Therefore,in recent years,the attenuation rule of the basic mechanical properties concrete after both high temperature and load is widely attention.The basalt fiber with good resistance to high temperature mixed in the concrete will slow down the damage of the concrete after high temperature,and improve its mechanical properties.In this paper,the apparent morphology,mass loss,compressive strength,flexural strength and the stress-strain curve relation ship of the basalt fiber reinforced concrete after high temperature are studied.At the same time,the strain change rule of the specimen surface was analyzed by using digital image correlation(DIC)technology.The main conclusions are as follows:(1)With the increase of temperature the compressive strength and folding strength of basalt fiber concrete decreased.After different temperature,the compressive strength attenuation speed is also not the same.It can generally be divided into two stages: 200℃ ~ 400℃,the strength decreased within 15%,and the overall attenuation is slow.400℃~800℃,the strength decreased fast and by about 70% after 800℃.Under the conditions of this test,when the temperature was between 20℃ ~ 400℃,the concrete with 0.2%fiber contenthad the greatest compressive strength.(2)With the temperature increased,the peak stress basalt of the fiber concrete gradually reduced,the peak strain increased,the elastic modulus decreased linearly.After the same temperature,with the increase of fiber content,the peak stress of the concrete increased,the peak strain decreased,and thus,the fiber plays the role in constraining concrete deformation and enhancing strength.(3)According to the experimental data,the stress-strain relation curve of basalt fiber concrete is fitted under different temperatures.And the concrete stress-strain curve at the rise stage under different temperature is given.Compared with the test curve and theoretical curve,the model can effectively describe the compression process of the basalt fiber reinforced concrete under different temperature before the peak stress.(4)Through the analysis of the damage evolution curve,it shows that within 400 ℃,the damage evolution curve is roughly experienced smooth,transition,the rapid growth stage.As the temperature increased,the smooth phase accounts for the proportion of the whole damage process is reduced,but the transition stage increased.The fiber incorporation can delay the damage,improve the brittleness of concrete,and make the bending damage more obviously.The effect of fiber inhibition is mainly reflected in the transition stage of injury.After 400℃,the damage the phase character was no longer obvious,the curve became approximately linear.(5)Combined with the strain equivalence principle and the damage evolution factor d,the concrete bending damage constitutive model and damage evolution equation under different temperature gradient and different fiber content was established by using DIC to get the full vertical strain on the surface of the specimen.Compared with the experiment and theoretical curve,it shows that the model can effectively describe the failure process of the basalt fiber reinforced concrete under bending load after high temperature before the peak stress.