Study On Degradation Law And Mechanism Of Partially Immersed Mortar Under Coupling Effect Of Temperature And Humidity And Mixed Salt Solution

Salt weathering is serious threaten for structure in sulfate laden environment.At present,few literature is found about salt weathering of Na₂SO₄-NaCl mixed solution,which is widespread in field environment,such as the salt lake,the ocean environment and the underground railway structures.The main characteristics of marine areas in South China Sea are high temperature and high humidity.Therefore,according to the environment of the South China Sea and the salt lakes in Western China,a mixed solution of Na₂SO₄-NaCl with a certain concentration gradient is set up.The temperature and humidity which change from 20?and 80%RH to 35?and 30%RH every other day is set up to explore the characteristics of structure partial immersion erosion in mixed solution when NaCl concentration is higher than or lower than Na₂SO₄ concentration.Several factors affecting partial immersion erosion are explored.What's more,preliminary protective measures for partial immersion erosion are also proposed.The main conclusions are as follows:In this paper,the mechanism of partial immersion erosion of mortar is explored by setting the experimental conditions as temperature and humidity change and partial immersion in mixed solution.The mechanism of partial immersion erosion of mortar is explored by comparing the deterioration of ordinary mortar and surface treated mortar specimens.The experimental results show that:the failure of the immersed part of mortar is mainly caused by physical sulfate attack when the mortar is partially immersed in salt solution.High concentration of NaCl can inhibit partial immersion erosion in Na₂SO₄-NaCl mixed solution.The main mechanism is that NaCl crystallization occurs on the surface of specimens with high concentration of chloride salt and gradually forms a protective layer.In this paper,the effects of chloride salt on the deterioration of mortar with different water-binder ratios and mineral admixtures were investigated by setting different water-binder ratios and adding mineral mortars specimens partially immersed in salt solution.The results show that NaCl can reduce the damage of partial immersion erosion of mortar in low water-binder ratio mortar.In high water-binder ratio mortar,the existence of NaCl changes the damage mechanism of mortar,and the upper part of mortar is subjected to chemical sulfate attack.What's more,the immersion part of mortar with mineral admixtures is mainly subjected to chemical sulfate attack.The bottom exfoliation of mineral admixtures mortars in partial immersion is more serious than that of ordinary Portland cement mortars.In this paper,four kinds of protective materials like silane?polyurethane?epoxy resin and sodium silicate were used to protect the drying part of mortar specimens.The protective effect of four kinds of surface treatment materials was studied and evaluated.The results show under the partial immersion state of Na₂SO₄ solution,the comprehensive protective effects of various materials are compared:silane treatment>polyurethane treatment>epoxy resin treatment>sodium silicate treatment>standard specimens.