Mechanical properties and water resistance study of basic magnesium sulfate cement-emulsified asphalt composite materials

Abstract

This study introduces a novel semi-flexible composite material (BMSC-EA), formed by merging the favorable properties of emulsified asphalt (EA), known for its high flexibility and crack resistance, with basic magnesium sulfate cement (BMSC), recognized for its high rigidity, early strength, and toughness. The research systematically explores the impact of varying EA dosages on BMSC properties. Furthermore, the study analyzes the phase composition, pore structure, and microstructure of BMSC-EA materials. Results indicate that an increase in EA dosage leads to a corresponding extension in the setting time of BMSC, accompanied by a gradual decrease in compressive and flexural properties. Interestingly, the flexural compression ratio of BMSC increases, suggesting that EA addition significantly enhances BMSC toughness. The principal hydration product of BMSC comprised crystals of 5Mg(OH)2∙MgSO4∙7 H2O (5∙1∙7 phase). However, the introduction of EA exerted an inhibitory influence on the generation of Mg(OH)2, leading to a scenario where more MgO remained uninvolved in the hydration reaction. The porosity of the BMSC matrix increases with higher EA content. After subjecting the BMSC-EA material to water immersion treatment, a noteworthy observation emerged: exceptional water resistance was evident when the EA dosage reached 10%. This phenomenon was primarily ascribed to the heightened densification (ultrasonic velocity) observed in the BMSC-EA samples under these conditions. Additionally, the study observes further growth of Mg(OH)2 in BMSC after water immersion treatment, but excessive Mg(OH)2 negatively impacts BMSC-EA. These findings serve as both experimental and theoretical foundations for advancing innovative semi-flexible composite pavement materials.