Variation Mechanism in Water Resistance of Red Mud–Modified Magnesium Phosphate Repair Mortar with Water-Binder Ratio

Abstract

This study explored the influence mechanism on the water resistance of magnesium phosphate repair mortars. The fluidity, setting time, mechanical properties, water resistance, and interfacial bonding strength of red mud–modified magnesium phosphate repair mortars (RMPMs) were systematically investigated. Through capillary absorption tests, the effect of the water-binder ratio (W/B) on the water transfer characteristics was explored, and then the actuating mechanism of capillary porosity and capillary absorption coefficients on water resistance was clarified. The results show that the fluidity and setting time of RMPM increase with the increase of W/B. When W/B increased from 0.18 to 0.20, the compressive strength, flexural strength, strength retention, and interfacial bonding strength of RMPM changed little and decreased linearly. And the interfacial bonding strength of RMPM was significantly reduced after 7 days of water curing. The capillary water absorption of RMPM was linear with the square root of time. The capillary absorption coefficient and capillary porosity of the RMPM increased greatly with increasing W/B when the W/B is between 0.20 and 0.28, while the water resistance, mechanical properties, and interfacial bonding property decreased linearly. Variations in W/B changed the capillary pore characteristics of the RMPM, which in turn affected the mechanical properties, capillary water absorption characteristics, and water resistance.