Preparation and characterization of a novel magnesium phosphate cement-based emulsified asphalt mortar

To improve the efficiency of repairing asphalt pavements, a rapid-hardening magnesium-based cement emulsified asphalt (MCEA) mortar was developed. The effect of mix parameters on the properties of MCEA sample was systematically discussed, including asphalt to cement (A/C) ratio, asphalt and cement (S/(A+C)) ratio, water to cement (W/C) ratio, and MgO to phosphate (M/P) ratio, as well as the fresh properties, mechanical behavior and microstructure of MCEA sample were investigated. The results show that the initial setting time of MCEA paste is within 30 min, and the fluidity is 60–180 mm, which can effectively improve the efficiency of pavement repair engineering. Meanwhile, by adjusting the mix proportion parameters, the setting time and fluidity can be adjusted according to engineering needs. The compressive and flexural strengths of plain magnesium phosphate cement mortar reach 46.45 and 7.7 MPa, respectively, and they decrease with the increase of A/C, W/C, and M/P ratios. With the increase of S/(A+C) ratio, the area of emulsified asphalt encapsulated particles decreases, which improves the mechanical properties of MCEA mortar. Increasing the A/C ratio results in an increase in the residual MgO content and a decrease in the struvite content in the MCEA paste. Meanwhile, the residual MgO content in the MCEA paste prepared by the S-type emulsified asphalt is significantly lower than that of the N-type MCEA paste, which is related to the water content of the emulsified asphalt. In addition, the incorporation of emulsified asphalt also increases the porosity of the MCEA sample, but the N-type emulsified asphalt can play a role in refining the pore structure of the sample.