Impact Mechanical Properties Of Steel Fiber Self-compacting Concrete After High Temperature

With the more mature engineering technology in our country,the number of buildings for all kinds of uses is increasing rapidly,and the application of Steel fiber self compacting concrete(Steel fiber self compacting concrete for short)is more widely,and the gas pipeline leakage and electrical fire in the building often occur,It will cause extremely serious damage to engineering structures,and in extreme cases,it will cause building collapse accidents.At the beginning of the design of our building structure,the main consideration is that it is under the normal state of the impact of various loads on the safety performance,few scruples of some extreme circumstances.Therefore,it is of great significance to study the mechanical properties of steel fiber self-compacting concrete after high temperature in practical engineering safety evaluation application.In this paper,a series of experimental studies have been carried out on the mechanical properties of steel fiber self-compacting concrete after high temperature heat treatment.The key research contents and conclusions include:(1)Dynamic tests of self-compacted concrete with different steel fiber content under different strain rates were carried out by SHPB at room temperature,and stress-strain curves and damage states were obtained.The test shows that the impact resistance of self compacting concrete is improved by the addition of fiber when compared with that of plain concrete,and the impact performance is optimal when the fiber volume fraction is 2%.This result is to provide a basis for subsequent research,so this paper takes steel fiber self-compacting concrete with fiber volume fraction of 2%as the research object to explore its static and dynamic mechanical properties after heat treatment.(2)The steel fiber self-compacting concrete was prepared for heat treatment at different temperatures by Muffle furnace,and the mechanical properties of the treated specimens were tested by RMT-150 C mechanical system.The experimental results show that there are a large number of cracks in the SFRC with great differences in development degree and distribution form,resulting in its nonlinear morphology under temperature load.Specifically,at 100℃ and 200℃,the compressive strength slightly increases,mainly due to the compactness of cracks caused by the expansion of aggregate.The decrease pattern shown at 400℃,600℃,800℃,and 1000℃ is mainly due to the excessive expansion of aggregate,which leads to the spread of crack depth.After 800℃,the decrease range of peak strength is greatly increased,which is mainly due to the thermal decomposition of aggregate.(3)The dynamic mechanical properties of steel fiber reinforced self compacting concrete after heat treatment at 100℃,200℃,400℃,600℃,800℃ and 1000℃ were tested by SHPB,and the impact compression mechanical properties of steel fiber reinforced concrete after high temperature were obtained.The results show that steel fiber reinforced concrete still has a significant rate effect after high temperature heat treatment,and the dynamic compressive strength shows a nonlinear shape with the increase of heat treatment temperature.Specifically,at 100℃ and 200℃,the dynamic compressive strength of the test piece shows a gradual increase,and after 600℃,the damage form of the test piece is expressed as powder.This result reflects that temperature load has different effects at different temperatures.When the ambient temperature is not high and does not exceed the threshold temperature of the physical and mechanical properties of steel fiber reinforced self compacting concrete,it indicates the strengthening effect.If it does,it will cause the material to weaken.A constitutive equation of dynamic stress-strain relationship of SFRC after high temperature heat treatment was established by putting forward a coefficient of temperature attenuation effect more suitable for SFRC after high temperature heat treatment and further simplifying the Z-W-T model,and the required parameters were obtained by fitting method.(4)According to the characteristics of concrete materials,the damage factor is established,through which the Z-W-T constitutive model is improved,and the damage viscoelastic constitutive model for concrete materials is established.According to the characteristics of high temperature,the temperature effect coefficient is introduced,and the viscoelastic constitutive model of rate dependent steel fiber reinforced self compacting concrete considering temperature is established.Through the test data,the corresponding parameters of the established constitutive model are obtained when the contract is drawn up,which can provide a certain reference for the subsequent research.(5)Through ABAQUS finite element software,the meso model of steel fiber reinforced concrete is established,and the CDP model is corrected with the static and dynamic test data to ensure the correctness.By adding temperature load,the change morphology of aggregate and fiber in the specimen under different temperatures is explored.The simulation results are more consistent with the test damage morphology results,revealing the action mechanism of temperature load strengthening effect and weakening effect.The numerical simulation of different temperature damage process is consistent with the temperature effect theory,which is mutually verified with the theory.