Research On Measures To Improve Fire Resistant Performance And Estimate Methods Of High Strength Concrete

Research PurposesIt is known that High Strength Concrete (HSC in short) may spall when it is in a fire accident or under a high temperature. The reinforcing steel bars in the explosive spall concrete are exposed in the fire accident and attacked by the heat, which damages the residual strength and the permeability of concrete. The paper studies the performance of concrete bust-up and the treatment methods of resistance to concrete bust-up in a fire accident or under a high temperature. And the solutions were found in the research that the damaged residual strength and the permeability of spall concrete could be improved by the way of re-curing or addition of mineral admixtures. The evaluation method of concrete damage degree is also suggested in the paper. Research Contents and MethodsThe treatment methods of resistance to concrete bust-up in a fire accident or under a high temperature concludes the performance of HSC bust-up and the improvement measures of the residual strength and permeability of HSC after being attacked by heat. And based on the above investigations, the evaluation method of concrete damage degree is brought out. The research object is HSC of water-binder ratio 0.25 with the addition of silica fume and fly ash. The HSC specimens are heated in an oilstove according to a temperature ascent curve of ISO834. The spalling degree is used to value the concrete performance of explosive resistance. It studies the effect of organic fibers, polymer latex and fireproof coating on the HSC performance of resistance spalling. It also studies the effect of metakaolin, red mud, slag and other mineral admixtures on the residual strength of HSC after being heated. The concrete specimens were re-cured in solutions after being heated. So it studies the effect of the solutions on the residual strength reconversion. It studies the permeability of HSC after being heated through the test of water absorption coefficient and permeable coefficients of chlorine ion and air. It discusses the difference of the above three permeability tests and their relationship with the HSC performance of resistance to bust-up. The microstructures of HSC after being heated are studied by mercury intrusion porosimetry (MIP in short) and SEM. Conclusively, graded indexes of damage degree of HSC after fire are suggested through the research of safety tests and evaluation methods of damage degree of the performance of HSC after being heated. Research ConclusionsIt is found that polypropylene fibers (PP fibers in short) help HSC resist to bust-up under high temperature. At the same volume fraction of fibers, 19mm long PL fibers and 5mm long PS fibers are most significantly effective in improving the HSC performance of resistance to bust-up. The grainy vegetable fibers and polymer latex are considerably less evidently effective in improving the HSC performance of resistance to bust-up because with the addition of these fibers less continuous moisture accesses form in HSC. But fireproof coating helps HSC resist to bust-up in some manner. By the test of pore structure, it presents that with the addition of PP fibers continuous pores form in HSC after being attacked by heat, which improve the HSC performance of resistance to spalling. In the paper, it shows silica fume is more effective than fly ash in improving HSC performance of resistance to spalling under high temperature. The loss ratio of HSC strength increases with the rise of temperature. And the loss ratio of flexural strength is higher than the one of compressive strength. HSC strength before and after being attacked by the heat is less affected by organic fibers. The loss ratio of HSC compressive strength is enhanced by the addition of metakaolin. And the improving extent of metakaolin is large than the one of red mud. It is proved that the addition of CaF2 at a appropriate fraction improves the residual compressive strength of HSC after being attacked under the temperature of 800℃. The residual strength is recovered by the way of re-curing in various saline solu...