Research On Mechanical Properties Of Steel-basalt Hybrid Fiber Concrete After High Temperatur

Fiber concrete as a new composite material has been widely used in special engineering fields such as tunnel engineering,underground energy reserve engineering,subway engineering and military defense engineering.From the analysis of spatial force dimension,most of the special engineering structures are in complex stress state,when the building is subjected to accidental fire,military strike or explosive shock load caused by terrorist attack,the dynamic damage law of fiber concrete members caused by the coupling of initial stress,high temperature and dynamic load is very complex.Therefore,the study of the mechanical properties of fiber concrete materials should not be limited to the mechanical properties under a single factor of static or dynamic loading,but should pay more attention to its dynamic mechanical properties under multi-factor coupling conditions.In this paper,the study of static mechanical properties and dynamic mechanical properties under different initial stresses of fiber concrete with different combinations of fiber doping after high temperature is carried out,and the microscopic fracture morphological characteristics and high temperature deterioration mechanism of fiber concrete are analyzed by microscopic means.The numerical simulation study of impact under different working conditions was carried out.The main research contents and conclusions are as follows:(1)The specimens with different fiber doping combinations were heated in KRX-17 B box-type resistance furnace to study the changes of basic physical and mechanical properties of the specimens with temperature.The results showed that the steel fibers can significantly improve the compressive and tensile strength of concrete,basalt fibers can improve the effect of high temperature on the degree of deterioration of concrete,and the experimental group HFRC0.2((1 vol% steel fiber + 0.2 vol% basalt fiber)has the best static mechanical properties at each temperature among the studied fiber doping combinations.(2)The dynamic mechanical properties of fiber concrete specimens under high temperature and load were investigated by using SHPB device.The results showed that the dynamic splitting strength and the total absorbed energy of the specimens showed a trend of increasing and then decreasing with the increase of temperature in the dynamic splitting experiments.the DSF level of HFRC0.2 was significantly higher under different working conditions.In the one-dimensional impact loading experiments,the DCF of the specimens in different experimental groups showed a trend of increasing with the increase of impact rate,and the larger the impact rate,the larger the increase of DCF,and the DCF of the specimens in the high temperature condition decreased.In the three-dimensional combined dynamic and static loading experiments,the larger the enclosing pressure ratio,the greater the dynamic peak stress and peak strain showed an increasing trend.The larger the enclosing pressure ratio,the more significant the temperature effect of the specimen,and the higher the temperature,the less obvious the enhancement effect of the enclosing pressure on the specimen.(3)The dynamic compressive and tensile properties of HFRC after high temperature were simulated in LS-DYNA software using the modified HJC model and RHT model,and a three-dimensional fine-view concrete model considering aggregate,mortar and ITZ(interface layer)was established to study the dynamic mechanical properties of non-homogeneous concrete specimens under the load.The results show that the higher the temperature in the impact compression simulation,the more severe the damage of the specimen;the higher the temperature in the splitting tensile simulation,the larger the damage area of the specimen.In the one-dimensional impact compression simulation,the specimens exhibited significant strain rate enhancement effect.At the same impact rate,the peak internal energy absorbed by the mortar is the largest,followed by ITZ,and the aggregate is the smallest.In the three-dimensional combined dynamic and static loading simulation,the initial static load affects the internal stress distribution state of the specimen,and the larger the enclosing compression load,the lower the damage degree of the specimen.(4)The physical phase analysis and microstructure analysis of the fiber concrete at different temperatures were carried out by means of XRD and SEM.The results showed that the secondary hydration reaction occurring under the influence of lower temperature could result in a small enhancement of the mechanical properties of the fiber concrete.Under the influence of higher temperatures,the crystal structures of hydrated calcium silicate and calcium hydroxide are thermally damaged,and calcium carbonate also decarbonates and decomposes,and the mechanical properties of concrete deteriorate.The mechanical properties of the specimen are seriously degraded.HFRC has a small number of tough nests only at 400°C.The mixing of steel-basalt hybrid fibers can increase the high temperature mechanical properties of concrete.mechanical properties.