Mechanical Properties Of Self-Compacting Concrete After Cooling Regimes From Elevated Temperatures

Compared with ordinary concrete,self-compacting concrete(SCC)in the pouring without strong pounding will be able to rely on its gravity flow and completely dense fill the formwork,which has been in some of the dense reinforcement,concrete pounding constraints,and urban construction noise restrictions and other engineering structures are widely used.In addition,building fire accidents occur in various places and the statistics of building fires in China are increasing year by year.Steel-reinforced SCC buildings will inevitably encounter different degrees of fire accidents during their service life.The mechanical properties of SCC will change after a fire,which will lead to the collapse of the whole structure and cause serious safety accidents and economic losses.Therefore,this paper intends to conduct an in-depth study on the damage characteristics,compressive bearing capacity,and deformation of SCC after a fire.The main research contents are as follows:(1)Experimental study on the mechanical properties of SCC after high-temperature cooling Obtain different target temperatures by heating and cooling,observe the surface color changes of SCC after natural cooling and water cooling,and count the crack formation and distribution.Summarize the influence of fire temperature and fire extinguishing methods on the apparent characteristics of SCC,and give the preliminary judgment criteria for the damage of SCC after fire;the damage detection of SCC from different high temperatures by natural cooling and water cooling was carried out by ultrasonic testing method,and the damage caused by fire temperature and fire extinguishing method on SCC was studied in combination with the mass loss of SCC after a fire.Finally,through the axial compression test of SCC cubes,the change law of compressive strength of SCC with the increase of fire temperature after the high temperature is studied.(2)Modeling the constitutive relationship of SCC after cooling from high temperatures Modification of the existing Jones-Nelson model of the constitutive relationship of SCC by introducing a fire temperature correction factor to give a nonlinear constitutive relationship model applicable to SCC after fire;Theoretical calculations are performed for the compression and deformation of SCC after cooling from different high temperatures,and the differences between the calculated results of the improved constitutive relationship model Jones-Nelson model,and the results of this test are compared and analyzed to verify the validity of the proposed model.(3)The temperature field and thermal coupling analysis of reinforced SCC column sections in high temperatureABAQUS,a finite element analysis software,is used to numerically analyze the reinforced SCC columns in high temperatures and calculate the cross-sectional temperature field of the reinforced SCC columns;the influence law of factors such as under the temperature rise curve,fire time,column cross-sectional size,fire surface and thickness of reinforcement protective layer on the cross-sectional temperature field of the reinforced SCC columns are studied.At the same time,the thermal coupling calculations are carried out to analyze the influence of different factors such as fire time,reinforcement rate,cross-sectional size,and fire surface on the fire resistance of reinforced SCC columns according to the temperature field of reinforced SCC columns.