Experimental Study On Mechanical Properties And Frost Resistance In Different Concrete Ratio After High Temperature Process

The concrete material which applied high temperature process under different influence factors,their mechanical and frost resistance properties will be vary.In this paper,the degradation rules of mechanical property of concrete materials(disposed by high temperature)will be discussed under the following influence factors: water binder ratio(0.34,0.4 and 0.5),fly ash content(30%,50%),curing time(3D,7D,14 D,28Dand56D),cooling mode(natural cooling,spray cooling),standing time(1D,3D,7D,14 D,28D)and the specimens size.Besides,the degradation of frost resistance of concrete under the target temperature(20℃,200℃,400℃ and 600℃),the water binder ratio(0.34,0.4 and 0.5),fly ash content(30%,50%)and the freeze-thaw condition(water-frost cycles,salt-frost cycles)influence factors will also be investigated.The study shows that the ability of high temperature resisting of concrete under a low water binder ratio is optimal after processed by 200℃ high temperature,while the high temperature resistance of concrete in high water binder ratio acting better when the temperature reach to 400℃.Furthermore,after disposed by different temperatures(200℃,400℃,600℃),the concrete mixed with fly ash shows a better high temperature resistance ability.Meanwhile,the high temperature resistant performance of concrete with a fly ash content of 30% acting better than concrete with 50% fly ash.The high temperature resistance of concrete at early age is significantly lower than it within the standard curing age.By the influences such as cooling mode and standing time,With the standing time lapse,the compressive strength of concrete will decreasing at the firsttime and then bounce back to the normal level.The study indicate that the larger size of concrete can performance a better high temperature resistance.In addition,the higher target temperature has been reached,the more evidently of the size effect.The frost resistance of low water binder ratio and low fly ash content concrete are better functional after the same times of freeze-thaw cycles;The water-frost resistance of concrete is better than that of salt-frost resistance.The frost resistance of concrete at room temperature is better than that of concrete after high temperature and when it with high temperature processed can be greatly degraded.The degeneration of concrete which has a poor anti-freeze condition will be more exaggerated.The test results can provide references and experiences for the design of anti-fire buildings in some practical engineering.And it can also support a theoretical basis for the maintenance and strengthen of the building structures who involved with fire in the freezing area of north China.This research has important theoretical significance and application value.