Water enclosed within the droplets of bitumen emulsions and its relation to viscosity changes during storage

The viscosity of bitumen emulsions is influenced by the presence of bitumen droplets which also contain an internal aqueous phase, effectively increas ing the disperse phase volume. In this study the concentrations of this int ernal water in a range of commercial emulsion formulas are determined by a differential scanning calorimetry (DSC) technique. The choice of emulsifier and the salt content of the bitumen influence the amount of internal water , which ranges up to 10% and strongly affects viscosity. Changes in emulsio n viscosity during storage more closely parallel changes in the level of in ternal water rather than changes in particle size. Typically the internal w ater phase increases during storage, followed by a decrease and these chang es generally occur over a few days or weeks depending on the temperature. S alt in the bitumen causes an osmotic swelling of the internal water phase w hich starts to occur inside the colloid mill and can be followed quantitati vely by the DSC technique. (C) 1999 Elsevier Science B.V. All rights reserv ed.