Warm mix asphalt: mechanical performanceassessment and coating quality evaluation

Asphalt mix manufacturing requires heating and the drying of aggregates. The induced energy cost has opened the way to develop alternatives processes with low energy/ carbon materials such as Warm Mix (WMA). Their manufacturing requires specifics techniques to achieve similar performances to those of Hot Mix (HMA). However, the manufacturing temperature reduction can locally lead to imperfect bonding between bitumen and aggregates, although bonding quality measurement remains a challenge. This paper deals with mechanical performance of some mixes manufactured according to WMA processes in comparison to HMA. In addition, bitumen was extracted from the mixes and its rheological properties were studied. In a second step, the bonding quality was assessed by studying the heat fluxes exchanged between hot bitumen and warm aggregate in asphalt mix manufacturing conditions. This approach is based on the Thermal Contact Resistance (TCR) assessment at the binder / aggregate interface. The TCR reflects the contact imperfection at the microscopic scale when two materials are put into contact. This TCR was proposed as bonding quality indicator. Our studies showed that bonding quality depends on bitumen and aggregate temperatures during the contact. The higher the component?s temperatures, the lower the TCR values and better the bonding quality.