The Effect of Hollow Polymer Microspheres on the Pore Structure and Frost Resistance of Cement Mortar

This study elucidates the effects of total air content, pore size distribution, and bubble spacing coefficient on mortar frost resistance. It presents a systematic comparison between mortars obtained with different porous structures. Conventional porous mortars and mortars with controlled porosity were prepared using air-entraining agents (SJ2) and hollow polymer microspheres with a controllable particle size (WEA, 20-80 μm), respectively. The study shows that WEA can construct uniformly sized and regularly shaped pores in mortar and can introduce controllable and stable pore sizes compared with SJ2, which are almost independent of mixing, molding, hydration, and hardening factors. Under equivalent air content, WEA mortar exhibits superior mechanical properties and frost resistance compared to SJ2 mortar, showing a negative correlation with WEA particle size. The frost resistance of WEA (40 μm) mortar with 1% volume content is comparable to that of SJ2 air-entrained mortar with 4% air content; i.e., compared to an SJ2 air-entraining agent, to achieve the same frost resistance level, WEA mortar has lower air content and a larger bubble spacing coefficient.