Experimental Study On Static And Dynamic Mechanical Properties Of Silica Fume Concrete After High Temperature

In all fire incidents,the number of building fires accounted for about 80%of the total number of fires,resulting in huge personnel and economic losses.Concrete is the most important and most used building material,Under high temperature conditions,although it is a thermally inert material,the hydration products of calcium hydroxide and ettringite have low decomposition temperature and poor resistance of high temperature.The deformation properties and strength of concrete will be degraded,and stress redistribution will occur inside.Which is undoubtedly fatal for concrete buildings.China can collect about 20 wt silicon powder every year.After the concrete is blended with silica fume,it can react with the poorly refractory cement hydration product Ca(OH)2 to form C-S-H(3Ca0·2SiO2·3H2O)which has relatively good fire resistance because of its better fire resistance.Therefore,research on the high temperature resistance of silica fume concrete,revealing the influence of high temperature on the mechanical properties and microstructure of silica fume concrete is of great significance for enriching and developing the theoretical study of silica fume concrete.And the main conclusions are as follows:(1)The test results of concrete compressive strength with different silica fume content under different ages show that the strength of concrete increases first and then decreases with the increase of silica fume content.The optimum dosage of silica fume is 8 wt%.In the early stage of the hydration reaction,the filling effect of the silica fume is attached to the C-S-H and filled between the AFt,so that the early compressive strength of the concrete is also increased;(2)The tension and compression strength test results of silica fume concrete at different temperatures show that the incorporation of silica fume into concrete increases the compressive strength,splitting tensile strength,elastic modulus and brittleness of concrete.After high temperature,the compressive strength of silica fume concrete is greater than that of plain concrete and the compressive strength loss rate is less than that of plain concrete,but the probability of high temperature bursting is greater than that of plain concrete,indicating that the fire resistance of silica fume concrete at medium and low temperatures has certain advantages over plain concrete.(3)SEM test of silica fume concrete shows that the C-S-H gel produced by the volcanic ash effect of silica fume effectively fills the internal pores of the concrete,and the filling effect of the silica fume also makes the particles better embedded in the C-S-H gel;(4)SHPB test of silica fume concrete after high temperature shows that silica fume concrete has higher dynamic strength,brittleness and broken particle size than plain concrete,and the energy absorption capacity of silica fume concrete under impact load is better than plain concrete.(5)When the static and dynamic concrete compressive strength with silica fume after high temperature is fitted by ultrasonic method,the order of the independent variables is:amplitude>wave velocity>wave amplitude+wave velocity,and the order of the independent variables when fitting the compressive strength loss rate is:amplitude>damage>wave velocity>damage+wave velocity>wave amplitude+wave velocity>wave amplitude+damage.Figure 43 table 16 references 90.