In the road paving industry, bitumen emulsions are increasingly used for safety and environmental reasons. A bitumen emulsion can be described as a dispersion of bitumen droplets in an aqueous continuous phase, stabilized by the addition of a surfactant. The objective of the work was to produce bitumen in the submicron range, with a particle size distribution as narrow as possible, using a technique known as high internal phase ratio (HIPR) emulsions. Experiments were carried out in a 10L coaxial mixer, following a 4-step protocol namely: bitumen addition, mixing of the concentrated emulsion, water dilution and final homogenization. The surfactant was introduced in the emulsification tank prior to the bitumen feeding step. The droplet size and the particle size distribution of the resulting emulsions were characterized using a laser granulometer. It was shown that the surfactant concentration significantly affects the droplet size, in agreement with the literature. The investigation on the dispersed phase content illustrated the existence of an optimum bitumen concentration at which the measured droplet size is minimum, also in good agreement with other work on the HIPR process. When working at constant formulation, it was found that the lower is the bitumen feeding rate, the smaller is the droplet size.

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