The damage process of concrete exposed to sodium sulfate attack and drying-wetting cycles was investigated. The water to binder(W/B) ratio and the concentration of sulfate solution were taken as variable parameters. T...The damage process of concrete exposed to sodium sulfate attack and drying-wetting cycles was investigated. The water to binder(W/B) ratio and the concentration of sulfate solution were taken as variable parameters. Through the experiment, visual change, relative dynamic modulus of elasticity(RDME) and the surface damage layer thickness of concrete were measured.Furthermore, SEM and thermal analysis were used to investigate the changing of microstructure and corrosion products of concrete.The test results show that the ultrasonic velocity is related to the damage layer of concrete. It approves that an increase in damage layer thickness reduces the compactness and the ultrasonic velocity. The deterioration degree of concrete could be estimated effectively by measuring the surface damage layer and the RDME of concrete. It is also found that the content of gypsum in concrete is less than that of ettringite in test, and some gypsum is checked only after a certain corrosion extent. When the concrete is with high W/B ratio or exposed to high concentration of sulfate solution, the content of ettringite first increases and then decreases with corrosion time. However, the content of gypsum increases at a steady rate. The content of corrosion products does not correspond well with the observations of RDME change, and extensive amount of corrosion products can be formed before obvious damage occurs.展开更多
Liquid nitriding of Cll0 steel was conducted in a wide range of temperatures （400-670 ℃） using a kind of chemical heat-treatments, and the hardness, mechanical and corrosion properties of the nitrided surface were ...Liquid nitriding of Cll0 steel was conducted in a wide range of temperatures （400-670 ℃） using a kind of chemical heat-treatments, and the hardness, mechanical and corrosion properties of the nitrided surface were evaluated. Experimental results revealed that the microstructure and phase constituents of the nitrided surface alloy are highly depended on the processing condition. When C 110 steel was subjected to liquid nitriding at 430 ℃, the nitrided layer was almost composed of a thin e-Fe2-3N layer. When C 110 steel was subjected to liquid nitriding at 640 ℃, the phase composition of the nitrided layer was greatly changed. The nitrided layer depth increased significantly with increasing the treating temperature. The liquid nitriding effectively improved the surface hardness. After liquid nitriding, the absorption energy of the treated sample decreased and the tensile strength increased by Charpy V-notch （CVN） test. But the elongation of treated sample decreased. The reason is that the nitrided layer of sample is hardened and there is brittlement by diffusion of nitrogen atom. Despite of treatment temperature, the liquid nitriding can improve the corrosion. After being nitrided at 430 ℃, the nitrided layer of the C110 steel was mainly composed by e-Fe2 3N, which has excellent corrosion resistance and high microhardness, the nitrided sample has the best corrosion resistance. After nitriding temperature over 580 ℃, especially at 680 ℃, the sample＇s surface was covered by the thick oxide layer, which has very low hardness and corrosion resistance. So, the corrosion resistance of samples is severely compromised.展开更多
基金Project(51278403)supported by the National Natural Science Foundation of China
文摘The damage process of concrete exposed to sodium sulfate attack and drying-wetting cycles was investigated. The water to binder(W/B) ratio and the concentration of sulfate solution were taken as variable parameters. Through the experiment, visual change, relative dynamic modulus of elasticity(RDME) and the surface damage layer thickness of concrete were measured.Furthermore, SEM and thermal analysis were used to investigate the changing of microstructure and corrosion products of concrete.The test results show that the ultrasonic velocity is related to the damage layer of concrete. It approves that an increase in damage layer thickness reduces the compactness and the ultrasonic velocity. The deterioration degree of concrete could be estimated effectively by measuring the surface damage layer and the RDME of concrete. It is also found that the content of gypsum in concrete is less than that of ettringite in test, and some gypsum is checked only after a certain corrosion extent. When the concrete is with high W/B ratio or exposed to high concentration of sulfate solution, the content of ettringite first increases and then decreases with corrosion time. However, the content of gypsum increases at a steady rate. The content of corrosion products does not correspond well with the observations of RDME change, and extensive amount of corrosion products can be formed before obvious damage occurs.
基金Projects(51471112,51611130204)supported by the National Natural Science Foundation of China
文摘Liquid nitriding of Cll0 steel was conducted in a wide range of temperatures （400-670 ℃） using a kind of chemical heat-treatments, and the hardness, mechanical and corrosion properties of the nitrided surface were evaluated. Experimental results revealed that the microstructure and phase constituents of the nitrided surface alloy are highly depended on the processing condition. When C 110 steel was subjected to liquid nitriding at 430 ℃, the nitrided layer was almost composed of a thin e-Fe2-3N layer. When C 110 steel was subjected to liquid nitriding at 640 ℃, the phase composition of the nitrided layer was greatly changed. The nitrided layer depth increased significantly with increasing the treating temperature. The liquid nitriding effectively improved the surface hardness. After liquid nitriding, the absorption energy of the treated sample decreased and the tensile strength increased by Charpy V-notch （CVN） test. But the elongation of treated sample decreased. The reason is that the nitrided layer of sample is hardened and there is brittlement by diffusion of nitrogen atom. Despite of treatment temperature, the liquid nitriding can improve the corrosion. After being nitrided at 430 ℃, the nitrided layer of the C110 steel was mainly composed by e-Fe2 3N, which has excellent corrosion resistance and high microhardness, the nitrided sample has the best corrosion resistance. After nitriding temperature over 580 ℃, especially at 680 ℃, the sample＇s surface was covered by the thick oxide layer, which has very low hardness and corrosion resistance. So, the corrosion resistance of samples is severely compromised.
