Experimental Research On Mechanical Properties Of Concrete And Reinforced Concrete After High Temperature

Temperature mechanical properties are important theoretical basis of concrete buildings, underground structure fire concrete material degradation process and mechanism. In this paper, C30, C40, C50strength grade plain concrete, steel fiber reinforced concrete, polypropylene fiber reinforced concrete and steel-polypropylene fiber reinforced concrete under high temperature of the compressive strength splitting tensile strength, flexural strength and stress-strain curve and other mechanical properties of the two cooling methods was tested. Observing the specimen of after cooling in the heating process, the macroscopic phenomena; Concrete mechanical properties change with temperature, with the changes in intensity level off and cooling method analysis of the impact of the mechanical properties of concrete; The principle of the application of mathematical statistics the temperature dependence of the relationship between the high temperature mechanical properties of concrete regression analysis, get the mathematical relationship.As the temperature increases, the internal structure of the plain concrete gradual and the deterioration of the mechanical properties of the gradual decay. In the natural cooling conditions, the rate of decline of plain concrete compressive strength were10%～75%when the target temperature to200℃～800℃,and Splitting tensile strength decreased rates with similar compressive strength of the order of15%～75%; flexural strength decrease rate of5%～80%.SF, PF, SPF mechanical performance index gradually decreased as the temperature increased. But have a different degree of improvement in its mechanical performance compared with reference concrete, SF and SPF is in larger improve.400℃to800℃, SF residual compressive strength than JF mean compressive strength of the remaining rate of about7.3%residual rate of the splitting tensile strength increased by about21.2%. The remaining rate of the flexural strength is the same to the JF remaining rate. The mechanical property of PF is better than JF in low temperature; SPF mechanical performance is slightly less than the SF, while representing JF has greatly improved.When temperature is lower, with the higher the level of plain concrete strength, the compressive strength and splitting tensile bending the smaller the residual rate. But while above a certain temperature, the strength of the remaining rate and intensity level is not obvious. Cooling is an important factor to affect the characteristics of the concrete high temperature strength. when temperature is low, the mechanical properties of the natural cooling conditions is higher than the water spray to cool; formation of a great thermal stress, water spray to cool the concrete cooling water at the same time to repair the internal structure of the concrete role, when the temperature higher than500℃, the two roles conflict with each other, resulting in high temperature mechanical properties under the two cooling methods vary.Concrete stress-strain curve of peak stress decreased with increasing temperature, and a significant increase in the peak strain; The shape of the curve transition to the flat tip towering and the peak point to the right, when the temperature above400℃this shape change is more obvious, The same temperature, the higher the concrete strength, the greater the peak strain; spray cooling conditions to be greater than the peak strain under natural cooling conditions, As the temperature increases, the peak stress of the fiber concrete is gradually decreased with the peak strain becomes larger, especially above600℃such a change in shape is more obvious. Room temperature, strain SF、SPF peak is slightly larger than the JF, as the temperature increases, the peak strain of the SF and the SPF less than JF; When800℃, the peak strain of several concrete tends to close.Based on the principle of mathematical statistics, obtained regression relationship of mechanical properties of various concrete; Apply S-curve fitting each concrete standardized stress-strain curve; Based on existing experimental data fitting the relationship of each temperature mechanical properties tied with concrete strength, high temperature.