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

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. © 2024 Cailiao Daobaoshe/ Materials Review. All rights reserved.