Study On Dynamic Mechanical Properties Of Sfrc After Freeze-thaw Cycles

As a new type of engineering composite material,steel fiber reinforced concrete(SFRC)has been widely used in water conservancy and electric power,pavement engineering and structural engineering because of its excellent physical and mechanical properties.At present,most of the researches on the mechanical properties of SFRC are focused on the static load with low strain rate and the impact load with high strain rate.However,the research under the earthquake load still needs to be further improved.In addition,there are few studies on the dynamic mechanical properties of SFRC after freeze-thaw cycles,so it is necessary to further study.This paper conducted uniaxial and triaxial compression tests on SFRC specimens which have undergone freeze-thaw cycles by using a uniaxial testing machine and a microcomputer hydraulic servo large-scale dynamic and static triaxial apparatus.The main researches are focused on the influence of steel fiber content,freeze-thaw cycles,strain rate and confining pressure level on the dynamic mechanical properties of SFRC.At the same time,in order to study the effect of freeze-thaw cycles on the microstructure of SFRC,the microstructure of SFRC was observed by Scanning Electron Microscope(SEM).The main research results are as follows:(1)At the same strain rate and confining pressure level,as the number of freeze-thaw cycles increases,the axial compressive strength of SFRC gradually decreases,while the peak strain increases gradually,and the area surrounded by the stress-strain curve decreases gradually.(2)Under the same confining pressure,with the addition of strain rate,the axial compressive strength of SFRC after 100 freeze-thaw cycles increases little by little and the peak strain decreases slowly.The stress-strain curve has an obvious stage of pore compaction under quasi-static strain rate.The decline of the curve becomes more steep as the strain rate increases,and the failure speed increases.(3)Under the same strain rate,the axial compressive strength and peak strain of SFRC after 100 cycles of freeze-thaw increased with the addition of confining pressure,and the stress-strain curve reached the peak value first under 0 MPa confining pressure.(4)With the raise of freeze-thaw cycles,the number of micro-cracks in the internal structure of plain concrete increases.The addition of steel fiber slows down the expansion speed of micro cracks in the concrete,reduces the width of cracks in the aggregate-matrix interface transition zone,and enhances the frost resistance.However,the addition of steel fiber also increases the number of initial micro-cracks and holes,and the interface between steel fiber and matrix is weak.In this paper,the dynamic mechanical properties of SFRC after freeze-thaw cycles are studied by means of experiments.The research results will be of great significance to the prediction of the dynamic response of SFRC structures,and provide reference for the seismic design and analysis of SFRC structures.