Mechanical properties and abrasion resistance of polyurethane mortar subjected to freeze-thaw cycles and sulfate attack

The objective of this paper is to investigate the properties of polyurethane mortar subjected to freeze-thaw cycles in sulfate environment. Na2SO4 solutions with 5% and 10% sulfate concentrations were prepared. The mass loss, compressive strength, flexural strength and abrasion resistance of the polyurethane mortar were investigated. The interface transition zone and pore structure were then analysed. Results revealed that the damage degree of the mass, compressive strength and flexural strength of polyurethane mortar subjected to freeze-thaw cycles in sulfate solution are greater than that in water, and the high concentrations of sulfate solution can cause severe damage. The polyurethane mortar subjected to freeze-thaw cycles and sulfate attack will appear to have more severe surface damage after abrasion. The abrasion resistance of poly-urethane mortar decreases as the freeze-thaw cycles and abrasion time increase. The freeze-thaw cycles and sulfate attack can cause the crack width at the interface transition zone of poly-urethane mortar to expand, and the abrasion action accelerates this evolution. With the increase in freeze-thaw cycles, the gel and transition pores are gradually transformed into capillary and large polyurethane mortar pores. The volume fraction of capillary and large pores gradually increases, and the fractal dimension tends to decrease. Furthermore, the fractal dimension of the pore structure is positively correlated with mechanical properties and abrasion resistance. The mechanism analysis shows that abrasion can cause the detachment of loose mortar matrix of polyurethane mortar surface and form a weak area.