Evaluation of the effect of aggregate mineralogy on the durability of asphalt pavements

Abstract

Shape, gradation, hardness and texture are among the aggregate characteristics necessary to consider during the asphalt mixture design process. However these characteristics do not provide direct information on the compatibility between the aggregate and the bitumen, nor do they give any indication on how this compatibility evolves when other factors as water, additives and other chemicals interact with the mixture. Other aspects, such as aggregate chemistry, can also significantly affect the asphalt durability influencing the affinity between aggregate and bitumen and thus also the service life of the mixture. This study aims to investigate how the mineralogy of the aggregates affects the bitumen-aggregate system in different conditions. After selecting four different aggregate types and one neat binder, laboratory tests on both uncompacted and compacted mixtures were carried out in order to identify one or more minerals affecting the pavement service life. Abrasion and moisture sensitivity tests were used to evaluate how the environment affects the bitumenaggregate interaction and to establish a basis for comparison. De-icing agents and anti-stripping additives were later added to the system to investigate how the mixture performance would evolve. Quartz, alibite and microcline content were observed to negatively affect the mixture performance in all conditions affecting both the bitumen-aggregate system in terms of adhesion resistance and the binder in terms of cohesion and rheological properties. The mixtures containing aggregates with high alibite and quartz content were also the most readily affected by de-icing solutions although the samples performance was largely dependent on the concentration of the de-icer. When antistripping additives are incorporated in the mixture, their efficiency is largely dependent on the mixing technique and the test method rather than the mixture components.