Material Characteristics of Long Lasting Asphalt Pavements

Based on a catalogue of test roads in Denmark, four long lasting test sections constructed in the early 80's were selected for field sampling and extensive laboratory study. This paper focuses on characterizing the bituminous materials used in the test sections. First, asphalt cores were investigated in a non-destructive way using X-ray tomography and indirect tensile stiffness test. The field samples were further analyzed with respect to binder content, air void content, and aggregate gradation. To characterize recovered binders, both chemical and rheological tests were applied. It was found that the long lasting test sections consisted of thick asphalt layers of low air void contents. The wearing courses contained relatively high binder content except for one with a binder content of slightly below 6%. For all the test sections, no propagated cracks were observed. In achieving a long pavement lifetime, aging of bitumen was indicated as one of the key factors. Field aging of bitumen was strongly dependent on the air voids of asphalt mix. In the test sections of low air voids (< 3% at the time of field sampling), extremely slow bitumen aging was observed. The study also shows that field aged bitumens differ significantly in chemical compositions, and the aging- induced stiffing effect tends to correlate with carbonyl compounds and molecular weight, but not with sulfoxides.