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The Tennessee Dept. of Transportation (TDOT), as part of an overall plan to achieve minimum HMA resurfacing cycle goals of 8 yr on inter-states and 12 yr on state routes, initiated a project to pair aggregate polish resistance with pavement functional needs. A new pre-evaluation procedure for aggregate polish resistance was developed and named the Tennessee Terminal Textural Condition Method (T3CM). Thirty-two bituminous surface projects were selected for the T3CM evaluation. The projects selected included both test strips and in-service bituminous surfaces. Further, several projects contained coarse aggregates from the same source. When possible, the coarse aggregates used in the projects were sampled at the HMA cold-feed stockpile rather than the aggregate source to ensure that the exact aggregates placed in the bituminous surface course were tested. The aggregates were subjected to two physical tests: T3CM and British polishing wheel/British pendulum, as well as three chemical/mineralogical tests: Percent silica ASTM C25, percent silica by x-ray diffraction, and loss-on-ignition (LOI). In addition, the bituminous surface courses containing these aggregates were monitored for skid resistance (i.e., polish resistance) by TDOT personnel using the locked-wheel trailer. A plot of project skid data versus time was considered to have a terminal skid number if the later skid results were stable or increasing. No project was considered to have had a terminal skid number unless more than three skid data points were available. Correlation coefficients between laboratory test methods and terminal skid numbers of bituminous surface aggregates were 0.705, 0.065, 0.076, 0.366, and 0.116 for the T3CM, the British Pendulum and British Wheel Method, ASTM C25 percent silica, LOI, and x-ray diffraction percent silica, respectively. Information is also presented on aggregate variability characterized by the T3CM, the British Pendulum, and British Wheel Method, and ASTM C25 percent silica.
aggregate, loss-on-ignition, bituminous, silica, polish resistance
Crouch, L. K.
Dept. of Civil and Environmental Engineering, Tennessee Technological Univ., Cookeville, TN
Brown, Heather J.
Concrete Industry Management Program, Middle Tennessee State Univ., Murfreesboro, TN