Laboratory evaluation of asphalt concrete mixtures to permanent deformation

Several laboratory tests have been developed in order to detect the resistance of asphalt concrete mixtures to permanent deformation. Among them, the most commonly used are the wheel-tracking and the cyclic compression test. The purpose of this study was to compare the permanent deformation behaviour of asphalt concrete, under different testing procedures, when gradation and binder content was varied but within the tolerance limits. The asphalt concrete used was an AC 20 with 50/70 penetration grade bitumen. For the wheel-tracking test, three different procedures at two testing temperatures (45 and 60°C), were used: procedure A and B, in air, in accordance with EN 12697-22, and the procedure specified in BS 598-110. For the triaxial cyclic compression test, method B per EN 12697-25, was used at a testing temperature of 45°C. The results of the study showed that the aggregate gradation and the binder content even when both varied within the tolerance limits affect the performance in terms of permanent deformation. The ranking of the mixtures was found to be the same regardless of the testing procedure employed. As far as the acceptability of the mixtures was concerned it was found that by applying the limiting values set by PD 6691:2010, the BS 598-110 procedure and the small device, procedure B per EN 12697-22 gave different outcomes.