Red mud-modified magnesium potassium phosphate cement used as rapid repair materials: Durability, bonding property, volume stability and environment performance optimization

The mechanical properties and microstructure of magnesium potassium phosphate cement (MKPC) modified with red mud have been studied. However, the durability and environmental risks of red mud-modified MKPC have not been reported. This paper focuses on the water resistance, frost resistance, bonding properties, drying shrinkage and environmental performance of red mud-modified MKPC repair materials. The experimental results proved that the addition of red mud is beneficial for improving the durability, bonding properties, and volume stability of MKPC. The MKPC matrix with a 10% red mud content has the best water and frost resistance, which can reduce the loss rate of immersion and freeze-thaw compressive strength of MKPC by 20.28% and 31.6%, respectively. Additionally, the bonding strength of MKPC at 1 d and 28 d increased by 15.2% and 21.9%, respectively, when the content of red mud was 10%similar to 20%. The early mechanical interlocking effect and the subsequent interfacial chemical action also contributed to the formation of strong interfacial bonds between the OPC matrix and the MKPC repair materials. The ion leaching results also showed that the MKPC matrix can effectively solidify and stabilize harmful components (Na, Cr, As, and Pb ions) in red mud. This study will further guide the application of red mud-modified MKPC in practical cement and concrete structure repair engineering.