| The degradation of concrete is varied,and the mechanism and process of most durability deterioration(such as freezing thawing,carbonation,drying shrinkage,etc.)are closely related to the existence,penetration or diffusion of moisture.Also,the moisture that is a carrier will transport chloride ion and other aggressive agents in the pore structure of concrete,causing the corrosion of the steel bar and other deterioration.Currently,most of the studies are moisture movement or chloride ion transportation in cement based materials,while the study on the mechanism of moisture and chloride transport is relatively rare.Therefore,based on the above problem,this thesis will focus on the transport law of moisture and chloride ions in mortar.The detailed content of this thesis are present as following:(1)The pictures of moisture and chloride penetration in mortar under capillary absorption of salt water were obtained by photograph.And then,digital image process was used to calculate the penetration depth of moisture and chloride,and ultimately,the curves of penetration depth of moisture and chloride ion with time were achieved.The results show that the penetration depth of moisture and chloride of mortar with high watercement ratio is larger than that of mortar with low water-cement ratio and the penetration depth of water in mortar with the same water-cement ratio was significantly larger than that of chloride,that is to say the chloride transport lags behand the transport of moisture.The penetration depth of moisture in mortar exposed to pure water is not much difference from that exposed to salt solution.(2)Mortar specimens with two kinds of water-cement ratio were left for capillary suction test under 3%?6%?10% sodium chloride solution.Results show that the penetration depth of chloride increases with the increase of sodium chloride concentration.However,when the salt solution reaches 10% and the contact time of 0.6 water-cement ratio specimens reaches 7d,the penetration depth of moisture and chloride in mortar is less than that exposed to 6% sodium chloride solution.The near surface pore of 0.6 water-cement ratio mortars exposed to 10% sodium chloride solution generated sodium chloride crystals by SEM and corresponding spectra when the contact time reaches 7d and 28 d.And the formation of sodium chloride crystals in capillary pores decreased the pore diameter which hinders the transport of moisture and chloride ion.(3)With the extension of the contact time,the penetration depth and content of chloride ion in mortar increase gradually.At the same depth,chloride content in mortar increases with the increase of sodium chloride concentration and the penetration depth of chloride also increases.The distribution of chloride in mortar was determined by electron microprobe which indicates that chloride penetrated into mortar is unevenly distributed.The chloride content penetrated into mortar with water-cement ratio of 0.6 is larger than that with water-cement ratio of 0.4.(4)The porosity of mortar exposed to water decreases as the increase of the contact time and the porosity of mortar exposed to salt water also decreases as the increase of the contact time.Then the pore size distribution of mortar under 28 days of capillary absorption with salt water is better than that of mortar under 7 days of capillary absorption with salt water.(5)Saturated mortars were exposed to varied concentration of sodium chloride solution to conduct pure diffusion.Under a gradient of chemical potential,the chloride ions move along the gradient in mortar.Results indicate that the penetration depth of chloride and chloride content increases with the increase of salt water concentration.The chloride diffusion coefficient of mortar decreases gradually as the increase of erosion time,for example,when the pure diffusion is from 3d to 7d,the chloride diffusion coefficient declined by 70%.And the chloride diffusion coefficient increases as the increase of sodium chloride concentration on the whole. |
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