IDENTIFICATION OF AGGREGATES FOR TENNESSEE BITUMINOUS SURFACE COURSES, PHASE III

Current methods of pre-evaluation of aggregates for bituminous surface courses are only able to clearly identify aggregates with a very high probability of performing well. There is no general agreement between researchers as to what engineering properties will provide adequate skid performance at various average daily traffic (ADT) levels. The lack of agreement has led to very conservative polish resistance specifications by many state departments of transportation and subsequently higher pavement costs. In 1992, the Tennessee Department of Transportation (TDOT) initiated a project to pair aggregate performance with the functional needs of the pavements (based on ADT) so that all Tennessee aggregate sources can be used most efficiently. The principal result of the project was a new aggregate polish resistance pre-evaluation procedure called the Tennessee Terminal Textural condition Method (T3CM). In this evaluation, using twenty Tennessee and Kentucky aggregates, the T3CM was used to characterize aggregate polish-resistance performance by comparing the results obtained on other aggregates to the results from proven field performers. The T3CM ranked five of six Tennessee proven performing siliceous limestones in the upper two performance categories. The test method had a coefficient of variation for aggregate ratings of less than one percent for a nine sample repeatability test. The results of this study have shown the T3CM to be a logistical success. Ease of performance, repeatability, substantially reduced costs (compared to British Wheel and British Pendulum) and increased productivity are advantages indicating that this test may be an ideal addition to normal aggregate prequalification tests. The research team recommends that the T3CM be used as a pre-evaluation procedure for aggregate sources. In addition, the T3CM should be used as a verification test for random aggregate lots.