Effect of low pressure on mechanical properties, microstructure, and durability of concrete: A Review

Examining the effects of low pressure (LP) on concrete is essential for construction in high-altitude regions. This study systematically reviews how LP environments influence the mechanical properties, microstructure and durability of concrete. Under LP, the compressive, flexural, and splitting tensile strengths of concrete tend to decrease. In high-altitude areas, air-entraining agents (AEAs) are added to improve the frost resistance of concrete. However, in LP environments, their use adversely affects the mechanical properties due to the reduced air-entraining efficiency caused by decreased bubble stability. Under LP, the stability of bubbles decreases, the merging and bursting intensify, and the pore deterioration of hardened concrete is relatively serious. Meanwhile, the LP environments lead to incomplete hydration reactions, and the hydration products do not fill the pores adequately. The incorporation of nanomaterials and mineral admixtures such as fly ash and silica fume can significantly improve the pore structure, thereby enhancing the mechanical properties of concrete. The pore deterioration caused by LP and the increase in crack width in the interface transition zone lead to the decrease in the durability of concrete. Finally, further research directions are proposed to address the challenges associated with concrete behavior under LP conditions.