In roads building, classical asphalt mix manufacturing commonly requires the heating (at 160°C) and the complete drying of aggregates. The induced energy cost has opened the way to develop alternatives processes and materials with low energy/carbon materials such as Warm Mix Asphalt (WMA). In warm mixes processes, aggregates manufacturing temperatures are different and lower than the Hot Mix ones. However, manufacturing temperature reduction can locally lead to poor bonding between bitumen and aggregate during the mixing step, due to the bitumen viscosity increasing, although bonding quality measurement remained a challenge. The aim of our study was to presents two thermal inverse methods for bonding quality assessment. These methods are based on Thermal Contact Resistance (TCR) assessment between bitumen and aggregate, during asphalt mix manufacturing. The experimental test principle consisted of heating both bitumen and cylindrical aggregate to their manufacturing temperatures (over 100°C) and to put them into contact thanks to a special experimental device. According to initial samples temperatures, heat transfer occurs from the bitumen to the aggregate. Two variants of the sequential Beck’s method were used to solve the inverse heat conduction problem. The first one consisted of determining the TCR from heat flux and temperatures and the second one consisted of identifying directly the TCR. The TCR values were interpreted as bonding quality criteria.

Results showed low sensitivity to temperature measurement noise in the second variant of the inverse method. Moreover our study showed that bonding quality depends on bitumen and aggregate temperatures. The higher the component’s temperatures, the lower the TCR values and better is the bonding quality.

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