To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste,several measuring methods including X-ray diffraction(XRD),atomic absorption spectroscopy(ASS),ion chroma...To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste,several measuring methods including X-ray diffraction(XRD),atomic absorption spectroscopy(ASS),ion chromatography,conductivity meter,alternating-current impedance spectroscopy and nuclear magnetic resonance(NMR)are employed to investigate the hydration characteristics,pore solution composition and conductivity,resistivity and pore structure during the steam curing process.Experimental results show that steam curing promotes the hydration process,greatly raises the resistivity,and decreases the porosity of specimen at early age.Compared with being treated at 45℃,higher temperature leads to a fast decomposition of ettringite at initial stage of the constant temperature treatment period,which improves the relative content and ionic activity of the conductive ions in pore solution.Furthermore,the number of pores larger than 200 nm increases significantly,which reduces the resistivity of the hardened cement paste.Cement paste treated at 45℃ has a more stable and denser microstructure with less damages.展开更多
The aim of this research was to examine the influence of vanadium on the structure, hardness and tensile strength of X I60CrMo 12-1 self-hardened steels. It is known that vanadium affects the process of solidification...The aim of this research was to examine the influence of vanadium on the structure, hardness and tensile strength of X I60CrMo 12-1 self-hardened steels. It is known that vanadium affects the process of solidification of this alloy in a way that narrows temperature interval of crystallization. Vanadium, as an alloying element, moves liquidus and solidus lines toward higher temperatures, approximately for 25 to 30 ~C. In addition, vanadium forms V6C5 carbides, which, are partly distributed between present phases in the steel; carbide （Cr,Fe）7C3 and austenite. The presence of vanadium enables the formation of （Cr, Fe）23C6 carbide and its precipitation into austenite during the cooling process. In local areas around fine carbide particles, austenite is transformed into martensite, i.e., vanadium reduces remained austenite and improves steel air-hardening. Vanadium concentration over 2.5% significantly improves the impact toughness. The basic problem in the application of high alloyed Cr-Mo steels is to increase their impact toughness and thereby sustain a relatively high value of hardness. Recent studies, concerning to the chemical composition and heat treatment regime, show that it is possible to get a martensitic structure with a very small amount of retained austenite. Investigations are directed toward the testing of the influence of alloying elements such as molybdenum, manganese and especially vanadium. Vanadium has great influence to the crystallization process. With increasing of its content, the eutectic point moves toward lower carbon concentrations and the temperature interval of solidification is narrowing.展开更多
基金Projects(U1534207,11790283,51878583)supported by the National Natural Science Foundation of China。
文摘To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste,several measuring methods including X-ray diffraction(XRD),atomic absorption spectroscopy(ASS),ion chromatography,conductivity meter,alternating-current impedance spectroscopy and nuclear magnetic resonance(NMR)are employed to investigate the hydration characteristics,pore solution composition and conductivity,resistivity and pore structure during the steam curing process.Experimental results show that steam curing promotes the hydration process,greatly raises the resistivity,and decreases the porosity of specimen at early age.Compared with being treated at 45℃,higher temperature leads to a fast decomposition of ettringite at initial stage of the constant temperature treatment period,which improves the relative content and ionic activity of the conductive ions in pore solution.Furthermore,the number of pores larger than 200 nm increases significantly,which reduces the resistivity of the hardened cement paste.Cement paste treated at 45℃ has a more stable and denser microstructure with less damages.
文摘The aim of this research was to examine the influence of vanadium on the structure, hardness and tensile strength of X I60CrMo 12-1 self-hardened steels. It is known that vanadium affects the process of solidification of this alloy in a way that narrows temperature interval of crystallization. Vanadium, as an alloying element, moves liquidus and solidus lines toward higher temperatures, approximately for 25 to 30 ~C. In addition, vanadium forms V6C5 carbides, which, are partly distributed between present phases in the steel; carbide （Cr,Fe）7C3 and austenite. The presence of vanadium enables the formation of （Cr, Fe）23C6 carbide and its precipitation into austenite during the cooling process. In local areas around fine carbide particles, austenite is transformed into martensite, i.e., vanadium reduces remained austenite and improves steel air-hardening. Vanadium concentration over 2.5% significantly improves the impact toughness. The basic problem in the application of high alloyed Cr-Mo steels is to increase their impact toughness and thereby sustain a relatively high value of hardness. Recent studies, concerning to the chemical composition and heat treatment regime, show that it is possible to get a martensitic structure with a very small amount of retained austenite. Investigations are directed toward the testing of the influence of alloying elements such as molybdenum, manganese and especially vanadium. Vanadium has great influence to the crystallization process. With increasing of its content, the eutectic point moves toward lower carbon concentrations and the temperature interval of solidification is narrowing.
