The Influence Of High Temperature On Explosive Spalling Behavior And Mechanical Properties Of Reactive Powder Concrete

In this thesis, an experimental investigation was conducted to study explosive spalling behavior, permeability and residual mechanical properties of reactive powder concrete subjected to high temperature.The effect of moisture content and water-binder ratio on explosive spalling was investigated firstly. Seven kinds of moisture contents and three kinds of water-binder ratios were designed. Explosive spalling test was conducted on steel-fiber reactive powder concrete. After explosive spalling test, all specimens that didn't encounter spalling were sawn into two pieces. Internal permeability test was conducted on the sawn surfaces of the specimens.The effect of high temperature and water-binder ratio on the residual mechanical properties of reactive powder concrete was also investigated. Residual mechanical property test (compressive strength, splitting tensile strength and fracture energy) was conducted on the hybrid fiber reactive powder concrete (polypropylene fiber and steel fiber) after exposure to 200℃,400℃,600℃and 800℃high temperature.The results of the explosive spalling test indicate that moisture content and water-binder ratio have a significant influence on the explosive spalling occurrence of reactive powder concrete. While the moisture content was less than 63%, for specimens with 0.18 and 0.20 water-binder ratio, the frequency of spalling increases with increasing moisture content. While the moisture content was less than 63%, the frequency of spalling increased with reducing water-binder ratio.The results of the internal permeability test indicate that moisture content and water-binder ratio also have a significant influence on the permeability of reactive powder concrete after exposure to high temperature. For concrete at a given water-binder ratio, internal permeability increases with increasing moisture content. With the same moisture content, the internal permeability of concrete at a low water-binder ratio is higher than that at a high water-binder ratio.The results of the residual mechanical properties test indicate that the variation of residual mechanical properties of reactive powder concrete with different water-binder ratio is the same (all the properties increase with critical temperature increasing at first and then decrease) after high temperature. However, the critical temperatures (the temperature:when the residual mechanical properties were maximum) of residual mechanical properties are different. Compared to the critical temperature of residual compressive strength is 400℃, the critical temperatures of both residual splitting tensile strength and residual fracture energy are 200℃. The residual mechanical properties decreased to minimum after exposure to high temperature of 800℃.The results above indicate that reactive powder concrete occurs explosive spalling during heating (heating rate of 10℃-20℃/min) to 700℃, and the initial explosive spalling occurs between 420℃and 583℃. The residual mechanical properties decrease after exposure to high temperature of 800℃.