Experimental investigation of optimum adhesion properties for anionic emulsions in road maintenance applications

Anionic emulsions are widely used in North America for road maintenance applications but are less popular in Europe. Due to their distinctive characteristics, the use of anionic emulsions is advantageous when local aggregate is excessively dusty and the cost to wash them to meet requirements would be too expensive. However, anionic emulsions’ compatibility, in terms of adhesion, with certain types of aggregate is reported to be limited. This paper presents the results of an experimental study that was conducted firstly to investigate the effect of aggregate mineralogy on the degree of adhesion (i.e. the bond) between the aggregate and the bitumen using anionic and cationic bitumen emulsions, and secondly to evaluate the potential development and use of new adhesion agents/anti-strips for anionic rapid-set emulsions used in chip seal applications. For this purpose, the degree of adhesion that was achieved between the emulsions used and a range of selected aggregates was measured by means of a series of internationally recognised laboratory adhesion tests. The experimental laboratory work confirmed that the degree of adhesion between the aggregate and emulsion is governed to a large extent by aggregate mineralogical composition and, in particular, its associated electrostatic interaction with a given emulsion. The results obtained indicated that a higher degree of adhesion was achieved when an aggregate was combined with an emulsion possessing the opposite surface charge. Further laboratory test results suggest that the addition of amine-based adhesion agents to an anionic emulsion can significantly improve its degree of adhesion with aggregates possessing an electro-negative surface charge.