Bruce A. Chadbourn 1 , James A. Luoma 1 , David E. Newcomb 1 , and Vaughan R. Voller 1 CONSIDERATION OF HOT-MIX ASPHALT THERMAL PROPERTIES DURING COMPACTION ________________________________________________________________________ REFERENCE: Chadbourn, B.A., Luoma, J.A., Newcomb, D.E., and Voller, V.R., “Consideration of Hot-Mix Asphalt Thermal Properties During Compaction,” Quality Management of Hot-Mix Asphalt , ASTM STP 1299 , Dale S. Decker, Ed., American Society for Testing and Materials, 1996. ABSTRACT: A computer program was developed at the University of Minnesota to predict asphalt concrete cooling times for road construction during adverse weather conditions. Cooling models require extensive experimental data on the thermal properties of hot-mix paving materials. A sensitivity analysis was performed to determine which thermal properties affect pavement cooling times significantly. The results indicated that more information on asphalt thermal conductivity and thermal diffusivity is required. Two suitable test methods for determining these properties at typical paving temperatures and densities were developed, and preliminary results for dense-graded and stone-matrix asphalt (SMA) mixes agreed well with values reported in the literature. KEYWORDS: cooling model, finite difference, hot-mix asphalt, late season paving, slab specimen, stone-matrix asphalt, thermal conductivity, thermal diffusivity, thermal probe _______________________ INTRODUCTION Background High demand for new asphalt pavements often requires that paving be done in unfavorable construction conditions. Low air temperatures, high winds, and night construction create adverse conditions for hot-mix asphalt paving. These conditions, though most common late in the paving season, may occur at any time. This presents a risk for owners and contractors. To achieve optimum load-bearing and weathering characteristics, an asphalt mix must be compacted to a specific range of density, and the time required for hot-mix asphalt to reach the proper compaction temperature to achieve this density decreases with an increased rate of cooling. Hot-mix asphalt compaction is generally begun as soon as the mix can support the roller weight. The roller operator determines the best time to begin compaction by means such as judging the depth of a heel imprint. This method works well when the ambient temperature is high enough. However, low ambient temperatures, high wind speeds, and night construction increase the rate of heat loss from the mix. During these conditions, the ability to predict mix temperature is more critical _____________________________________________________________________________________ 1 Research fellow, research assistant, associate professor, and associate professor, respectively, Department of Civil Engineering, University of Minnesota, 500 Pillsbury Dr. SE, Minneapolis, MN 55455.