Influence of humidity on the mechanical properties of polymer-modified cement-based repair materials

Portland cement–aluminate cement–hemihydrate gypsum ternary binder repair mortars, as a type of road repair material, have the advantages of fast hardening and early strength, micro-expansion, stable strength, and good mechanical performance. However, problems on high brittleness, fast loss of fluidity, and poor toughness are also encountered. The effects of styrene butadiene copolymer and styrene acrylate on the construction performance of a ternary binder repair mortar composed of Portland cement, aluminate cement, and hemihydrate gypsum and the effects of different curing humidity conditions on the mechanical properties of the polymer-modified ternary repair mortar were investigated. Both polymers enhanced the fluidity and decreased the fluidity loss rate of the ternary binder cement paste and prolonged its setting time. Moreover, both polymers improved the toughness and reduced the water absorption of the ternary repair mortar in concordance with their filling effect and film-forming roles under different humidity curing conditions. Different curing humidity conditions affected the ettringite crystal morphology and polymer film formation of the polymer-modified ternary binder repair mortar. The polymer under natural curing conditions presented the best modification effect in terms of mechanical properties, and the inner structure was the densest of the repair mortar for the ternary binder. The toughness and flexural strength of the specimens were markedly improved.