Bond strength and interface characteristics between magnesium phosphate cement mortar and ordinary Portland cement concrete in a frigid environment

The rapid repair of airport runways and concrete pavements using magnesium phosphate cement mortar (MPCM) in frigid environments requires the MPCM to have high bond strength with ordinary Portland cement (OPC). In this study, the effects of the pouring temperature of MPCM, surface roughness, water content, and strength grade of concrete on the interfacial bond strength and characteristics between MPCM and OPC were investigated in a frigid environment (-20 degrees C +/- 2 degrees C). The results indicated that the 3-h compressive strength of MPCM reached 30 MPa, whereas the 3-h flexural bond strength between MPCM and OPC (BSMPCM-OPC) exceeded 2.5 MPa when the pouring temperature for the MPCM mixture is 0-5 degrees C in a frigid environment. The moisture content of concrete before freezing had a more significant impact on BSMPCM-OPC than the influence of concrete roughness in a frigid environment; however, the influence of the concrete strength grade can be disregarded. The hydration heat of MPCM can quickly release with an increase in the pouring temperature, which accelerates phosphate dissolution and promotes the generation of struvite and the development of the BSMPCM-OPC. Furthermore, the interface bonding between MPCM and OPC involves physical bonding, mechanical anchoring, and weak chemical bonding in a frigid environment.