Impact of Asphalt Ageing on the Activity of Adhesion Promoters and the Moisture Susceptibility

Bitumen-aggregate adhesion is one of the crucial characteristics related to an asphalt mix. It affects the mix durability mainly in terms of its moisture susceptibility. Wide range of adhesion promoters is available to the market and can be used in regular practice, nevertheless usually only limited attention is paid to the long term activity (mainly the effective substances) and stability of the additives in the bitumen and the asphalt mix. Research done at the Czech Technical University in Prague is focused on studying the impact of differently aged asphalt mix using selected procedures defined in prEN 12697-52 as well as developing a self-defined procedure by applying the PAV equipment used since many years for long-term bitumen ageing. The results of aged mixtures were always compared to unaged control mixes. In parallel use of aged bitumen was assessed as well. The results were further compared to a simple adhesion test to get a more complex understanding of the activity of selected additives. In total more than 5 additives were selected and tested on one type of asphalt concrete with the application on a more hydrophilic aggregate type. Results gained during this experimental study are presented in the paper using as a criterion indirect tensile strength ratio determined either by EN 12697-12 or by modified procedure according to AASHTO T283.In parallel because of elevated temperatures used during ageing suitable covering of cylindrical test specimens was analyzed as well to avoid unnecessary deformations or even disintegration of the tested specimens. For this reason two types of protective collar were chosen – PVC and thin steel mash – in both cases fixed by plastic belts. It is assumed that steel mash can better simulate the effect of ageing keeping the envelope partly free for direct contact with hot air and pressure. Results of this comparison are presented in this paper as well.