Significant efforts have been made in revealing the mechanism of thaumasite formation in concrete, which continues to be fraught with ambiguities and dissension. Chemical method was employed to synthesize pure C3S, C2...Significant efforts have been made in revealing the mechanism of thaumasite formation in concrete, which continues to be fraught with ambiguities and dissension. Chemical method was employed to synthesize pure C3S, C2S, C3A, ettringite, and thaumasite, and X-ray diffraction（XRD）, Raman spectroscopy and infrared spectroscopy（IR） were used to identify thaumasite from other hydrates. To investigate the direct route of thaumasite formation, C3S, C2S, gypsum, and calcium carbonate were used to prepare a cement paste so that the interference of ettringite formation can be avoided. The indirect route of thaumasite formation was also studied by considering the effect of C3A or ettringite content on thaumasite formation. Results show that thaumasite can be definitely generated in the absence of aluminium-bearing minerals or ettringite under appropriate conditions, while the ettringite presence promotes the thaumasite formation. No evidences support the heterogeneous nucleation route in this work. It is concluded that the method mentioned in this work can surely be used to investigate the mechanism of thaumasite formation, and thaumasite can form by both direct and woodfordite routes.展开更多
The effect of addition of Zn, Cu, Pb and Cr chlorides as admixtures on the hydration reaction of the system 3CaO·Al2O3-gypsum with molar ratio 1：3 was studied. Different ratios of each salt were used, namely 0.5...The effect of addition of Zn, Cu, Pb and Cr chlorides as admixtures on the hydration reaction of the system 3CaO·Al2O3-gypsum with molar ratio 1：3 was studied. Different ratios of each salt were used, namely 0.5%, 2% and 4% by weight of the solid mixture. Hydration reaction was carried out at 35℃ for various time intervals from 0.5 h to up to 7 d. Hydration rate of the system 3CaO·Al2O3-CaSO4·2H2O in absence and presence of different salts was studied via the determination of the combined water contents. X-ray diffraction analysis showed that the ettringite was the only hydration product formed in the different mixes. The hydration products were investigated by scanning electron microscopy （SEM） and thermal gravimetric analysis. The results indicated that the rate of formation of ettringite and its microstructure depend on the admixture and its dosage.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.51272222 and 51132010)
文摘Significant efforts have been made in revealing the mechanism of thaumasite formation in concrete, which continues to be fraught with ambiguities and dissension. Chemical method was employed to synthesize pure C3S, C2S, C3A, ettringite, and thaumasite, and X-ray diffraction（XRD）, Raman spectroscopy and infrared spectroscopy（IR） were used to identify thaumasite from other hydrates. To investigate the direct route of thaumasite formation, C3S, C2S, gypsum, and calcium carbonate were used to prepare a cement paste so that the interference of ettringite formation can be avoided. The indirect route of thaumasite formation was also studied by considering the effect of C3A or ettringite content on thaumasite formation. Results show that thaumasite can be definitely generated in the absence of aluminium-bearing minerals or ettringite under appropriate conditions, while the ettringite presence promotes the thaumasite formation. No evidences support the heterogeneous nucleation route in this work. It is concluded that the method mentioned in this work can surely be used to investigate the mechanism of thaumasite formation, and thaumasite can form by both direct and woodfordite routes.
文摘The effect of addition of Zn, Cu, Pb and Cr chlorides as admixtures on the hydration reaction of the system 3CaO·Al2O3-gypsum with molar ratio 1：3 was studied. Different ratios of each salt were used, namely 0.5%, 2% and 4% by weight of the solid mixture. Hydration reaction was carried out at 35℃ for various time intervals from 0.5 h to up to 7 d. Hydration rate of the system 3CaO·Al2O3-CaSO4·2H2O in absence and presence of different salts was studied via the determination of the combined water contents. X-ray diffraction analysis showed that the ettringite was the only hydration product formed in the different mixes. The hydration products were investigated by scanning electron microscopy （SEM） and thermal gravimetric analysis. The results indicated that the rate of formation of ettringite and its microstructure depend on the admixture and its dosage.
