Research On Preparation And Property Of Asphalt Emulsion For Cement And Asphalt Mortar

Cement asphalt mortar (hereinafter abbreviated to CA mortar) is the key component in the structure of slab track, which mainly consists of cement matrix, asphalt emulsion, fine aggregate, and a variety of admixtures. Asphalt emulsion is an important part of CA mortar, and its properties significantly influence CA mortar quality. When applied in CA mortar, asphalt emulsion should have good emulsify quality, excellent storage stability and nice cement compatibility except the properties of ordinary emulsion used in highway.The present study made a systemic study on the storage stability and cement compatibility of asphalt emulsion. The factors that influence the storage stability of emulsion are studied. The results showed that the instability of asphalt emulsion included both sedimentation caused by the particle gravitational force and flocculation and coalescence behaviours between droplets. Of which, the particle size is the key factor that related with sedimentation behaviours. The smaller particle size leads to a stable emulsion. The surface tension is an important factor that influences the emulsion stability, but not a key factor. The inorganic salt and thickeners play an effective influence on the stability, but when the dosage is over a certain dosage, the contra-ion is easy to destroy the double electrode layer structure; the thickeners will improve the volume stability of mortar as well as increase the water demand, a balance between workable time and volume stability should be obtained.A laser diffraction particle size analyzer was employed to measure the particle size variations of two asphalt emulsions under stress conditions to evaluate their storage stability, freeze-thaw stability, and mechanical stability. This new method may provide the desired information for fast and continuous evaluation on the dynamical changes of emulsion stability under stress conditions, compared to the traditional storage stability tests. Interfacial films between the emulsion droplets may play a significant role in emulsion stability. The strong film formed with main emulsifier and non-ionic emulsifier makes the particle more resistant to the freeze-thaw pressure and mechanical energy.The absorption behaviour between cement and asphalt emulsion in cement asphalt mortar under different temperatures were investigated to reveal the temperature sensitivity of their workable properties. A laser particle size analyzer was employed to characterize the particle size variation in the cement and asphalt emulsion (CAE) system. The results indicated that the particle size increased more prominently at elevated temperature; the viscosity of the CAE system was measured by a rotational viscometer, results indicated variation pattern of viscosity correlated well with that of particle size in the CAE system, the increase of particle size was partially accountable for the increase of viscosity and impairing the flowability of CA mortar. The addition of non-ionic emulsifier could retard the adsorption behaviour between cement and asphalt and prolong the workable time of CA mortar.The preparation technology is an important aspect to ensure the emulsion quality. The influences of different process temperatures, different colloid, and different mill gap on the particle size are studied. The results showed that the proper alleviated asphalt temperature is benefit for the preparation process; while the water temperature had little influence on the emulsion quality. The imported colloid had a better performance than the domestic colloid. With the decrease of colloid gap, the emulsion particle size is also decreased, but when the gap is less that 0.2mm, the effect on the size is minor. The emulsion temperature decided the mortar temperature during the construction of CRTS I mortar, so that the key point to control the emulsion quality during the construction is to control the emulsion temperature.