IDENTIFICATION OF AGGREGATES FOR TENNESSEE BITUMINOUS SURFACE COURSES. PHASE II. FINAL REPORT

Current methods of pre-evaluation of aggregates for bituminous surface courses such as the British Pendulum/British Polishing Wheel and chemical or mineralogical methods are used to identify aggregates with a high probability of performing well. There is no general agreement between researchers as to what engineering properties will provide adequate skid performance at various daily traffic (ADT) levels. The lack of agreement has led to conservative polish resistance specifications and subsequently higher pavement costs. The Tennessee Textural Retention Method (TTRM) uses single size aggregate (6.35-9.52 mm), the Los Angeles Abrasion device, and a modified version of the National Aggregate Association's Particle Shape Tester (ASTM C 1252, AASHTO TP33) to characterize particle shape and texture throughout simulated aging. In this evaluation, using 25 Tennessee aggregates, the TTRM was used to characterize aggregate polish-resistance performance at various ADT levels by comparing the results obtained on other aggregates to the results from field proven performers. The TTRM ranked all Tennessee proven performing siliceous limestones and gravels in the appropriate ADT category for which they are currently approved. In addition, new promising aggregate sources were revealed. The test method had a coefficient of variation for aggregate ratings of less than 3% for a 9 sample repeatability test. In addition, the maximum coefficient of variation of voids tests at any given aging revolution for an individual aggregate never exceeded 2%. The TTRM may be helpful in pairing aggregate polish resistance performance with pavement need based on ADT. The research team recommends that the TTRM be used as a pre-evaluation procedure for aggregate sources. In addition, the TTRM should be used as an acceptance test for individual aggregate lots.