Experimental Study On Compressive Behavior Of Ordinary Concrete With Cooling Naturally After High Temperature

In modern society,the high-rise buildings formed by reinforced concrete make people highly dense.Fire accidents seriously threaten public safety and bring immeasurable losses to the lives and property of the general public.Studying and mastering the mechanical properties of building components after fire can reduce the loss and save the less damaged buildings.On the other hand,it provides the theoretical basis for fire resistance design of building,and provides the necessary data and theoretical guidance for the detection and reinforcement of buildings after the disaster.In this paper,the mechanical properties of ordinary concrete after high temperature are analyzed by means of experimental method and related theories.Taking different concrete strength grades(C25,C30,C35,C40),different heating temperatures(200??400??500??600??700??800?),and different constant temperature times(30min?60min)as changing factors,144 concrete standard prisms were designed for high temperature tests.Each strength is made of 3 standard prisms,a total of 12 specimens as room temperature contrast test blocks.By observing the surface color and cracks of the test block,the variation of concrete quality after high temperature is obtained,and the relationship between the burning rate of the test block and the strength,temperature and constant temperature time of the concrete after high temperature is analyzed.The pressure tests on the blocks cooled to room temperature were carried out.The destruction processes and patterns of each test block were observed.The stress-strain curve after high temperature is obtained.The relationship between the compressive strength and peak strain of concrete with temperature,intensity and constant temperature time after high temperature was studied.The results show that the burning rate of ordinary concrete increases with the increase of temperature,and the law of changing with the increase of constant temperature time is not obvious,but the higher the strength level of concrete,the lower the burning rate.With the increasing of temperature,both the rising and descending sections of the stress-strain curve change from steep to gentle,and the peak stress of the test block decreases gradually.On the basis of this experiment,it provides some reference value for the identification and evaluation of ordinary concrete structures after fire.