The thermal expansion mismatch between cement mortar and aggregate at high temperature is one of the main reasons causing the deterioration of concrete at high temperature.In this study,the thermal damage of concrete ...The thermal expansion mismatch between cement mortar and aggregate at high temperature is one of the main reasons causing the deterioration of concrete at high temperature.In this study,the thermal damage of concrete caused by the thermal expansion mismatch between aggregate and cement mortar was investigated using a meso-scale concrete model.The meso-scale concrete model is composed of mortar,aggregate and the interfacial transition zone(ITZ).Laboratory tests on the mechanical properties of cement mortar at high temperature were conducted to provide the necessary mechanical parameter for the meso-scale concrete model.The simulation results show that the particle size,content,distribution and mechanical properties of the aggregate have an effect on the thermal damage of concrete at high temperature.The smaller the particle size of concrete aggregate and the higher the elastic modulus of aggregate,the greater the damage of concrete under high temperature.Due to the increasing thermal expansion difference between aggregate and cement mortar,and the deterioration of the cement mortar with the increasing temperature,the damage of concrete increased sharply after 500℃.展开更多
Oxidation behaviors of carbon fiber reinforced SiC matrix composites(C/SiC)are one of the most noteworthy properties.For C/SiC,the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coef...Oxidation behaviors of carbon fiber reinforced SiC matrix composites(C/SiC)are one of the most noteworthy properties.For C/SiC,the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coefficients of thermal expansion(CTEs)and elastic modulus between carbon fiber and SiC matrix.In order to improve the oxidation resistance,multilayer SiC–Si_(3)N_(4) matrices were fabricated by chemical vapor infiltration(CVI)to alleviate the above two kinds of mismatch and change the local stress distribution.For the oxidation of C/SiC with multilayer matrices,matrix microcracks would be deflected at the transition layer between different layers of multilayer SiC–Si_(3)N_(4) matrix to lengthen the oxygen diffusion channels,thereby improving the oxidation resistance of C/SiC,especially at 800 and 1000℃.The strength retention ratio was increased from 61.9%(C/SiC–SiC/SiC)to 75.7%(C/SiC–Si_(3)N_(4)/SiC/SiC)and 67.8%(C/SiC–SiC/Si_(3)N_(4)/SiC)after oxidation at 800℃for 10 h.展开更多
基金supported by the open Fund of State Key Laboratory of Disaster Reduction in Civil Engineering(Grant No.SLDRCE15-03)Beijing major science and technology projects(Grant No.Z191100008019002).
文摘The thermal expansion mismatch between cement mortar and aggregate at high temperature is one of the main reasons causing the deterioration of concrete at high temperature.In this study,the thermal damage of concrete caused by the thermal expansion mismatch between aggregate and cement mortar was investigated using a meso-scale concrete model.The meso-scale concrete model is composed of mortar,aggregate and the interfacial transition zone(ITZ).Laboratory tests on the mechanical properties of cement mortar at high temperature were conducted to provide the necessary mechanical parameter for the meso-scale concrete model.The simulation results show that the particle size,content,distribution and mechanical properties of the aggregate have an effect on the thermal damage of concrete at high temperature.The smaller the particle size of concrete aggregate and the higher the elastic modulus of aggregate,the greater the damage of concrete under high temperature.Due to the increasing thermal expansion difference between aggregate and cement mortar,and the deterioration of the cement mortar with the increasing temperature,the damage of concrete increased sharply after 500℃.
基金This work was supported by the National Natural Science Foundation of China(Nos.52072303 and 51821091)the National Science and Technology Major Project(No.J2019-VI-0014-0129)。
文摘Oxidation behaviors of carbon fiber reinforced SiC matrix composites(C/SiC)are one of the most noteworthy properties.For C/SiC,the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coefficients of thermal expansion(CTEs)and elastic modulus between carbon fiber and SiC matrix.In order to improve the oxidation resistance,multilayer SiC–Si_(3)N_(4) matrices were fabricated by chemical vapor infiltration(CVI)to alleviate the above two kinds of mismatch and change the local stress distribution.For the oxidation of C/SiC with multilayer matrices,matrix microcracks would be deflected at the transition layer between different layers of multilayer SiC–Si_(3)N_(4) matrix to lengthen the oxygen diffusion channels,thereby improving the oxidation resistance of C/SiC,especially at 800 and 1000℃.The strength retention ratio was increased from 61.9%(C/SiC–SiC/SiC)to 75.7%(C/SiC–Si_(3)N_(4)/SiC/SiC)and 67.8%(C/SiC–SiC/Si_(3)N_(4)/SiC)after oxidation at 800℃for 10 h.
