高海拔地区低温成型磷酸镁水泥砂浆力学与抗冻性能

Mechanical Properties and Freeze-Thaw Cycling Resistance of Magnesium Phosphate Cement Mortar Prepared at Low Temperatures in Highland Regions

磷酸镁水泥(MPC)砂浆因其低温下卓越的强度发展潜力和免于蓄热保湿养护的特性,特别适用于高寒地区破损混凝土结构的修补工作。研究采用现场试验的办法,以成型温度、镁磷质量比、养护制度为变量,跟踪不同龄期下不同条件的磷酸镁水泥砂浆的抗折与抗压强度,厘清了高海拔地区低温成型磷酸镁水泥砂浆力学性能的发展规律。研究又以成型海拔、成型温度、镁磷质量比为变量,以气泡结构和水饱和度为中间指标,以单面盐冻中质量剥蚀和快速冻融循环中相对质量及相对动弹性模量的变化为直接指标,剖析了高海拔地区低温成型磷酸镁水泥砂浆抗冻性能的影响因素。研究结果表明,自然养护相较恒定低温养护对早期强度发展有利,但对后期强度发展有不良影响。低温环境下成型有利于自然养护的磷酸镁水泥砂浆的后期强度。成型海拔、成型温度和镁磷质量比与砂浆的含气量呈负相关,与砂浆的气泡间距系数和水饱和度呈正相关。试验条件下,这三个变量的值越小,砂浆的抗冻性越好。-10℃成型,镁磷质量比为4对砂浆强度最有利;而-10℃成型,镁磷质量比为3对砂浆抗冻性最有利。这些研究成果为高寒地区磷酸镁水泥砂浆的工程应用提供了技术建议与理论支持。

Magnesium phosphate cement mortar is particularly suitable for repairing damaged concrete structures in high-and-cold regions due to its outstanding strength development potential at low temperatures and its characteristic of not requiring heat retention and moisture preservation for curing.The study utilized on-site experimental methods,employing variables such as molding temperature,magnesium-phosphate mass ratio,and curing mode,to investigate the flexural and compressive strengths of magnesium phosphate cement mortar under various conditions at different ages,thereby clarifying the development patterns of its mechanical properties in high-altitude and low-temperature conditions.Further,the study identified the factors affecting the freeze-thaw cycling resistance of magnesium phosphate cement mortar formed at low temperatures in high-altitude regions,using molding altitude,temperature,and magnesium-phosphate mass ratio as variables,and air-void structure and water saturation as intermediate indicators.The scaled mass of the surface exposed to salt solution during unilateral freeze-thaw cycles and changes in relative mass and dynamic elastic modulus during freeze-thaw cycles were used as direct indicators.The findings reveal that natural curing,compared to constant low-temperature curing,is beneficial for early strength development but has a negative impact on later strength development.Low-temperature forming benefits the later strength of magnesium phosphate cement mortar under natural curing.Each of the molding altitude,temperature,and magnesium-phosphate mass ratio of mortar negatively correlates with the air content,but positively correlates with the air-void bubble spacing coefficient and water saturation.Under experimental conditions,lower values of these three variables enhance the mortar’s freeze-thaw cycling resistance.A molding temperature of-10℃with a magnesium-phosphate mass ratio of 4 is most beneficial for mortar strength,while a ratio of 3 is most advantageous for freeze-thaw cycling resistance.These research outcomes provide technical recommendations and theoretical support for the application of magnesium phosphate cement mortar in high-and-cold regions.