The need for inducing shear instability to obtain relevant parameters for HMA rut-resistance
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Instability rutting is a major distress mode in hot mix asphalt (HMA) pavements, which occurs when the structural properties of the compacted mix cannot resist near surface critical stress conditions caused by traffic loads. Key mixture parameters relevant for HMA rut-resistance were identified. The Superpave gyratory compactor with shear measurements and the option of changing the compaction angle during compaction were used. Based on the testing of 31 mixtures with different void structure and aggregate characteristics, three distinctive responses were observed: i.e., brittle response; plastic response, under which once the mixtures loose strength due to rearrangement, they never regain another stable rearrangement; and optimal response, which is bracketed by the plastic and brittle types of responses. Using the new parameters identified, a framework for the evaluation of mixture rutting potential was developed. Based on a comparison of predicted rutting potential to Asphalt Pavement Analyzer rut depth measurements, as well as a statistical analysis of results, the validity of the proposed framework was established. The proposed framework evaluated for seven field mixtures with known rutting performance were classified correctly, including a mixture with a SBS modified binder. The proposed framework had the potential for becoming an index test for evaluating the rutting potential of mixtures. This is an abstract of a paper presented at the Association of Asphalt Paving Technologists 2004 Technology Sessions (Baton Rouge, LA 3/10-18/2004).