Investigating the effects of salts on the coalescence process in bitumen emulsions

The breaking and coalescence process in bitumen emulsions during their application strongly influences the resulting long-term mechanical performance of the cold mix asphalt. This phase separation process is affected by physico-chemical changes at the bitumen/water interface. This paper describes the effects of addition of different salts on the destabilization of bitumen emulsions. This study is limited mainly to cationic rapid setting (CRS) bitumen emulsions and salts which are very commonly added to these emulsions as a stabilizer. However, a few samples with non-ionic emulsifiers were also prepared and analyzed comparatively to understand the electrostatic force balance with varying concentrations of selected salts. The experimental part includes a bitumen droplet relaxation test, droplet size distribution measurement, microscopy, and evaluation of physico-chemical properties of prepared soap solutions e.g. interfacial tension and density measurements. Some experiments on the effect of selected water-soluble organic solvents on the coalescence process were also carried out. The results showed that coalescence was delayed after the addition of salts, while the water soluble organic solvents proved not to affect the emulsion significantly.