PREDICTION OF COOLING CURVES FOR HOT-MIX PAVING MATERIALS BY A COMPUTER PROGRAM

Abstract

This report describes the development of a computer model designed to simulate the cooling behavior of hot paving material after laying. The accuracy of the model is examined by comparing experimentally determined cooling curves of hot materials laid under a variety of ambient conditions at five test sites, with cooling curves predicted by the model for these same sites. The comparison shows good agreement between experimental and predicted cooling curves. The rates of heat loss through the surfaces and bases of hot-mix layers are examined using the model and the effect on cooling rates of heated supporting layers, of increased layer thicknesses, and of variations in climatic conditions are studied. Simulation results show that initially the larger rate of heat loss from the hot layer is that through the bottom of the layer but that with increasing time after laying the surface rate of heat loss becomes dominant. Heating of the cold substrate reduces significantly the rate of heat loss through the bottom of the layer. Increasing the lift thickness marginally increases the overall rate of heat loss but because the thicker lifts lose a smaller proportion of their initial heat content they maintain a higher temperature for longer periods than the thinner lifts. Differences between mid-layer cooling rates for the extremes of climate considered are of the order of 1 C per minute for a 30 mm thick layer, reducing to 0.5 C per minute for 100 mm /thick layers. /Author/TRRL/