Quantitative characterization of frost resistance effect of air pores in early-age concrete based on volumetric deformation

Early-age concrete is more prone to frost damage than mature concrete due to its higher water content. Air pores provide storage space for water squeezed by phase change expansion and alleviate the frost heave stress and damage. This paper quantifies the frost-resistant effect of air pores from the perspective of volumetric deformation. Firstly, a theoretical model is proposed to quantify the compositions of apparent frost deformation. The apparent deformation of freezing concrete consists of frozen water expansion, absorbed deformation by air pores, and thermal deformation. Then, the evolutions and compositions of apparent deformation in freezing concrete and mortar with different air pore systems are analyzed. An air pore absorption efficiency coefficient (denoted as γ) is introduced to further understand the processes of air-volume utilization and water migration. Finally, the volume ratio of capillary water-to-air pores and the degree of saturation in concrete at a critical frost-resistant state are determined, and a design method for optimizing air-entraining agent (AEA) dosage and pre-curing time is proposed. This research offers theoretical guidance for the frost-resistant design of concrete in winter construction.