The SO4^（2-）concentration distributions in surface region of cement mortar immersed in sulfate solution at early stage were measured by layered sampling method combined with chemical analysis, and the diffusion coef...The SO4^（2-）concentration distributions in surface region of cement mortar immersed in sulfate solution at early stage were measured by layered sampling method combined with chemical analysis, and the diffusion coefficients of SO4^（2-）anions in surface region of mortar into internal area were calculated by means of instantaneous plane diffusion theory. The experimental results showed that the SO4^（2-）concentration gradually reduced when the diffusion depth increased in the surface region of mortar. Diffusion coefficient（D） was relevant with the concentration and kind of environmental sulfate solution, which reduced with immersion time at the beginning, and then rose slowly after a period of time. The calculation of initial diffusion coefficient（D0） and starting time of deterioration（t∞） caused by sulfate attack was further attempted based on the data of diffusion coefficient, and it was found that D0 and t∞ were all relevant with concentrations of sulfate and different kind of sulfate as well.展开更多
Mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, the mortars were submerg...Mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, the mortars were submerged in 2% magnesium sulfate solution at different temperatures (5 ℃, 20 ℃ and alternate temperature between 5 ℃ and 20 ℃) for a year. The appearance and strength development were measured on these immersed prisms at intervals, and samples selected from the surface of prisms were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that the influence of temperature on the resistance to sulfate attack of mortar is related to the binder compositions. A higher temperature leads to a quicker strength loss and appearance deterioration of the mortar without mineral admixture. For blended cements, a higher temperature is favorable for the pozzolanic reaction of mineral admixture and the overall deterioration of mortar is reduced with the increasing temperature. When the mineral admixture has a lower reactivity, such influence of temperature on the resistance to sulfate attack of mortar containing admixtures becomes greater. At the three different solution temperatures, two blended cements show significantly improved resistances to sulfate attack. After 1 year of exposure to magnesium sulfate solutions, the formation of thaumasite was checked in the OPC mortars at both 5 ℃ and 20 ℃. It is concluded that the thaumasite formation is not limited to structures at low temperature (less than 15 ℃).展开更多
The deterioration mechanism of thaumasite towards cement or concrete structure and the deterioration pattern of in-situ construction caused by the formation of thaumasite were studied in this paper. To improve the TSA...The deterioration mechanism of thaumasite towards cement or concrete structure and the deterioration pattern of in-situ construction caused by the formation of thaumasite were studied in this paper. To improve the TSA (the thaumasite form of sulfate attack) resistance, the cement type, water to cement ratios, the mineral admixture and the circumstance factors should be taken into consideration.展开更多
Effect of uniaxial compression on the nucleation of micro-damage in cement mortar under sulfate attack is investigated. Shape and size of micro-voids in cement mortar is detected using Micro Computed Tomography techni...Effect of uniaxial compression on the nucleation of micro-damage in cement mortar under sulfate attack is investigated. Shape and size of micro-voids in cement mortar is detected using Micro Computed Tomography techniques. The formation of delayed ettringite crystal is analyzed using scanning electron microscope and energy disperse spectrum methods. Deformation of micro-voids and the distribution of stress at the surface of a micro-void are calculated. It is found that the nucleation of micro-cracks is caused by the tensile stress at the voids＇ surface, and such damage nucleation will be speeded up by the remote uniaxial compressive load.展开更多
基金Funded by the Major State Basic Research Development Program of China(No.2011CB013800)
文摘The SO4^（2-）concentration distributions in surface region of cement mortar immersed in sulfate solution at early stage were measured by layered sampling method combined with chemical analysis, and the diffusion coefficients of SO4^（2-）anions in surface region of mortar into internal area were calculated by means of instantaneous plane diffusion theory. The experimental results showed that the SO4^（2-）concentration gradually reduced when the diffusion depth increased in the surface region of mortar. Diffusion coefficient（D） was relevant with the concentration and kind of environmental sulfate solution, which reduced with immersion time at the beginning, and then rose slowly after a period of time. The calculation of initial diffusion coefficient（D0） and starting time of deterioration（t∞） caused by sulfate attack was further attempted based on the data of diffusion coefficient, and it was found that D0 and t∞ were all relevant with concentrations of sulfate and different kind of sulfate as well.
基金Funded by the National Natural Science Foundation of China (No. 50408016) the "863" High-Tech Research and Development Program of China (No. 2005AA332010)
文摘Mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, the mortars were submerged in 2% magnesium sulfate solution at different temperatures (5 ℃, 20 ℃ and alternate temperature between 5 ℃ and 20 ℃) for a year. The appearance and strength development were measured on these immersed prisms at intervals, and samples selected from the surface of prisms were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that the influence of temperature on the resistance to sulfate attack of mortar is related to the binder compositions. A higher temperature leads to a quicker strength loss and appearance deterioration of the mortar without mineral admixture. For blended cements, a higher temperature is favorable for the pozzolanic reaction of mineral admixture and the overall deterioration of mortar is reduced with the increasing temperature. When the mineral admixture has a lower reactivity, such influence of temperature on the resistance to sulfate attack of mortar containing admixtures becomes greater. At the three different solution temperatures, two blended cements show significantly improved resistances to sulfate attack. After 1 year of exposure to magnesium sulfate solutions, the formation of thaumasite was checked in the OPC mortars at both 5 ℃ and 20 ℃. It is concluded that the thaumasite formation is not limited to structures at low temperature (less than 15 ℃).
文摘The deterioration mechanism of thaumasite towards cement or concrete structure and the deterioration pattern of in-situ construction caused by the formation of thaumasite were studied in this paper. To improve the TSA (the thaumasite form of sulfate attack) resistance, the cement type, water to cement ratios, the mineral admixture and the circumstance factors should be taken into consideration.
基金Project supported by the National Natural Science Foundation of China (Nos. 10932001,51079069,10972109,and 10802039)the National Basic Research Program of China (973 Program,No. 2009CB623203)+1 种基金the Ministry of Education of the People’s Republic of China (No. 20103305110001)K.C.Wong Magna Fund in Ningbo University
文摘Effect of uniaxial compression on the nucleation of micro-damage in cement mortar under sulfate attack is investigated. Shape and size of micro-voids in cement mortar is detected using Micro Computed Tomography techniques. The formation of delayed ettringite crystal is analyzed using scanning electron microscope and energy disperse spectrum methods. Deformation of micro-voids and the distribution of stress at the surface of a micro-void are calculated. It is found that the nucleation of micro-cracks is caused by the tensile stress at the voids＇ surface, and such damage nucleation will be speeded up by the remote uniaxial compressive load.
