Wheeltracking Fatigue Simulation of Bituminous Mixtures

In order to better simulate the dynamic effects of a rolling wheel travelling over an asphalt pavement, and to better understand the initiation and growth of cracks in bituminous pavement layers, a wheeltracking fatigue simulation facility was developed. This experimental facility permitted the testing of large slab specimens (305x305x50mm) using dynamic wheel loadings. The slab specimens were supported on a soft elastomeric foundation that simulated overlay behaviour on top of a weak pavement structure. Digital photography and image analysis techniques were utilised to monitor the initiation and propagation of fatigue cracks on the bottom of these slabs. Two standard Irish mixtures, a Dense Base Course Macadam (DBC) and Hot Rolled Asphalt (HRA), were evaluated with the fatigue simulation facility. Crack damage was seen to initiate on the bottom face of the slab specimen in a direction parallel to the direction of wheel travel. These cracks would interconnect to form a full width crack that propagated through the depth of the slab. Under similar loading conditions the DBC mix had significant lower fatigue strength (two orders of magnitude).