Effect of emulsifier type on the properties of cement asphalt mortar for non-ballast slab tracks

This study examines the impact of asphalt emulsions produced from ionic (cationic and anionic) and non-ionic emulsifiers on the properties of cement asphalt mortar (CAM) concerning to high-speed rail slab track applications. Fresh and hardened mortar properties, such as flow time, material separation, and compressive strength are critical CAM properties considering specific application requirements in Shinkansen slab track systems. CAM were produced with asphalt emulsions of different polarity. Rheological, surface, and thermal properties were studied to understand the behavior of the mortar at different scales. Results reveal that CAM with anionic emulsions offers better stability and workability in cement environments compared to non-ionic and cationic emulsions. The evaluation of the thixotropic behavior of cement asphalt pastes revealed that cationic emulsion-based pastes exhibited higher flocculation over time. Material separation tests of hardened mortar properties show that CAM with cationic emulsion leads to the highest homogeneity, followed by non-ionic emulsions, while anionic emulsions result in poor homogeneity and the highest material separation. This behavior is attributed to the adaptability of asphalt emulsion to fine aggregates. Compressive strength study indicates that using cationic emulsions in CAM production enhances early strength (1 day), whereas CAM with anionic emulsions show delayed setting with relatively low early strength but higher later strength (28 days) due to the selective adsorption of asphalt droplets over cement phases. Considering flow time, material separation, and compressive strength, CAM with non-ionic emulsions exhibits balanced performance and is suitable for producing CAM with the desired characteristics.