Hydration, fresh, mechanical, and freeze-thaw properties of cement mortar incorporated with polymeric microspheres

Air-entraining agent (AEA) has been used for decades to improve cementitious materials’ freezing–thawing resistance. However, the strength reduction and durability degradation concerns associated with using AEA make it a double-edged sword. Hollow polymeric microspheres have proved to be a promising solution to help concrete resist freezing–thawing attacks by means of encapsulated air without sacrificing mechanical performance or durability properties. In this study, the hydration, fresh properties, hardening performance, freezing–thawing resistance, and pore structure of cement mortar with the addition of AEA and thermo-expansible polymeric microspheres were studied. The properties of cement mortar with different dosages of AEA and microspheres were examined, and the mechanism behind the performance was also addressed. It was found that the used microspheres have an “internal curing” effect, improving cement mortar’s hydration, workability, and mechanical strength compared with plain mortar and AEA mixed mortar. The small size and compressible properties of the microspheres also contributed to cement mortar’s freezing–thawing resistance. For 1.5% and 2.0% of dosages (by the mass of cement), after 56 days of freezing–thawing cycles, the compressive strength improved 10.99% and 17.90%, respectively, and the tensile strength increased by 11.24% and 32.73%, respectively, and the flexural strength increased 6.58% and 5.79%, respectively. Adding microspheres and AEA in cement mortar significantly improved the content of permeable pores larger than 50 nm.