Experimental Study On Residual Mechanical Properties Of Reactive Powder Concrete With Hybrid Fibers After Exposure To High Temperature

In this thesis, an experimental investigation was conducted to study residual mechanical properties of reactive powder concretes with hybrid fibers after exposure to high temperature.After exposure to different target temperatures (20℃,200℃,400℃,600℃), residual mechanical properties (residual compressive strength, residual tensile splitting strength, residual fracture energy) of reactive powder concretes under different conditions including 3 different water-binder ratios (0.16,0.18,0.20),2 different fibers (steel fibers and polypropylene fibers),3 different contents of steel fibers (1%,2%,3%) and 3 different contents of polypropylene fibers (0.10%,0.15%,0.20%) were all investigated. The effect of different water-binder ratios and hybrid fibers in different contents was studied on residual mechanical properties of reactive powder concretes after exposure to high temperature.The results of high temperature tests reveal that variations of surface features of reactive powder concretes with different water-binder ratios and different contents of hybrid fibers are basically the same after exposure to high temperatures. With the increase of temperature, the color of RPC range from slate gray to brown slightly, minor cracks of RPC range from never to many, hardness of steel fibers range from rigid to soft, knocking sound range from low to crisp.The results of residual strength tests reveal that residual strengths of reactive powder concretes with hybrid fibers are the highest when polypropylene fibers content is 0.15% and steel fibers content is 2% in volume. With the increase of temperature, residual strengths of reactive powder concretes with different water-binder ratios all increase at first, then decrease. However, the critical temperature (the temperature when the residual strength was maximum) of residual compressive strengths is 400℃, the critical temperature of residual tensile splitting strengths is 200℃. Variations of residual strengths of reactive powder concretes with different contents of hybrid fibers are basically the same. With the increase of temperature, residual compressive strengths increase apparently at first, then increase slowly or no increase, and finally decrease apparently. With the increase of temperature, residual tensile splitting strengths decrease slightly at first, then decrease apparently, and finally decrease significantly. The results of residual fracture energy tests reveal that the effect of polypropylene fibers in different contents is not obvious on residual fracture energy of reactive powder concretes. With the increase of steel fibers content (in a certain limit), residual fracture energy of reactive powder concretes increase. With the increase of temperature, residual fracture energy of reactive powder concretes with different water-binder ratios all increase at first, then decrease, and the critical temperature of residual fracture energy is 200℃. Variations of residual fracture energy of reactive powder concretes with different contents of hybrid fibers are basically the same. With the increase of temperature, residual fracture energy increase slightly at first, then decrease apparently, and finally decrease significantly.The above results reveal that if hybrid fibers content is reasonable in volume, hybrid effect of fibers will be the best, and residual mechanical properties of reactive powder concretes with hybrid fibers will be the best. High temperature can be divided into two ranges in terms of RPC's mechanical properties loss, namely 20-400℃and 400-600℃. In the range of 20-400℃, RPC maintained (even got an increase) in their original mechanical properties; in the range of 400-600℃, RPC lost their original mechanical properties considerably.