Mechanistic insights into interlayer-porous expanded vermiculite to enhance early-age frost resistance of cement mortar

Although air-entraining agents (AEA) are effective in mitigating frost damage in concrete, the air introduced by AEA induces defects within the matrix, which subsequently impairs the structural integrity of the microstructure. This study proposes expanded vermiculite (EV) as a viable alternative to AEAs, aimed at achieving enhanced freeze resistance in early-age mortar while improving matrix strength. The effects of two distinct particle sizes of EV on the mechanical properties, hydration process, porosity, electrical resistivity, ice content, and volumetric deformation of cement mortar were investigated. The results indicate that the incorporation of EV can improve the mechanical properties of mortar under negative temperature. After being cured at −10°C for 7 days, the compressive strength of mortar containing 4 % (by mass) of 150-mesh EV was increased by approximately 159 % compared to the reference group. As an inert filler, EV exhibits minimal influence on the cement hydration process. Mortar containing EV demonstrates low electrical resistivity and low ice content under sub-zero conditions, confirming that the addition of EV effectively reduces freezable water content in mortar. Furthermore, the abundant interlayer structure of EV effectively absorbs frost expansion in early-age mortar, thereby reducing microstructural damage from freezing. Finally, this study elucidates the mechanism through which EV enhances the performance of early-frozen mortar by reducing freezable water content and absorbing frost expansion. This study provides a novel approach to enhancing frost resistance in early-age mortar without sacrificing microstructure integrity and offers new insights into the development of durable cementitious materials for cold regions.