低温盐侵蚀环境下砂浆孔隙水相变特性研究北大核心CSCD

砂浆孔隙溶液水盐相变特性是研究其水-热-盐耦合模型以及水泥基材料损伤机理的关键理论基础。为探究河西走廊盐渍土地区砂浆孔隙溶液水、盐相变规律,首先利用差示扫描量热法测定水盐相变过程中热流、相变温度等热参数;其次基于热量守恒和水分质量平衡方程,初步实现水盐分离;然后分别计算不同温度下的冰、盐晶和未冻水含量,揭示了低温下砂浆孔隙溶液水盐相变机理;最后结合微观扫描和物质能谱图,明晰了砂浆内部劣化机制。研究结果表明:随着盐浓度增大,砂浆孔隙溶液冻结温度降低、相变时间延后、水盐相变顺序调换及未冻水含量向低温方向移动;相同盐浓度下,氯化钠对砂浆孔隙溶液冻结温度的降幅最大,混合盐次之,硫酸钠最小;砂浆在低温盐侵蚀下遭受物理化学耦合作用,其中氯化钠对砂浆破坏性最大,混合盐次之,硫酸钠劣化相对较轻。

Phase transformation characteristic of pore solution in mortar at low temperature salt erosion environment

The water-salt phase transformation characteristic of pore solution in mortar is the key theoretical basis for studying the water-thermal-salt coupling model and the damage mechanism of cementitious materials. In order to study the variation of the pore solution in saline soil area of Hexi Corridor， the thermal parameters such as heat flow and phase transition temperature were measured by Differential Scanning Calorimetry. According to the conservation principle of mass and heat， the separation of water and salt was preliminarily realized. Ice， salt crystal， and unfrozen water contents at different temperatures were calculated to reveal the mechanism of water and salt phase transformation of the pore solution at low temperature. Moreover， the internal degradation mechanism of mortar was clarified by Scanning Electron Microscopy and Energy Dispersive Spectroscopy. The results show that the freezing point of the pore solution decreases and phase transition time delays， as salt concentration increases. Meanwhile， the sequence of water-salt phase transformation reverses and the content of unfrozen water moves towards low temperature as the concentration increases. At the same salt concentration， the effect of sodium chloride， mixed salt and sodium sulfate on the freezing temperature of the pore solution decreases in turn. Mortar suffers physical-chemical coupling action under low temperature and salt erosion environment. Sodium chloride is the most destructive to mortar， and the effects of mixed salt and sodium sulfate on failure of mortar are in decreasing order.