Thermodynamics Between RAP/RAS and Virgin Aggregates During Asphalt Concrete Production—A Literature Review.

摘要

In hot-mix asphalt (HMA) plants, virgin aggregates are heated and dried separately before being mixed with RAP/RAS and virgin asphalt binder. RAP/RAS materials are not heated or dried directly by a burner to avoid burning of aged binder coating on the materials so they are heated and dried indirectly by the hot virgin aggregates. A literature review shows that virgin aggregate temperature has been predicted for drying and heating RAP at batch plants only. In this study, thermodynamics and heat transfer principles are used to predict virgin aggregate temperature for drying and heating RAP/RAS at a drum plant. Among many results, it was shown that virgin aggregates become superheated (more than 1000°F) when both virgin aggregate and RAP moisture content were in the range of 3% to 5% and the material proportions were in the range of 30% to 50%. The size of virgin aggregates and RAP/RAS, the moisture content of virgin aggregates and RAP/RAS, and the mix proportion of virgin aggregates and RAP/RAS were the major contributing parameters in predicting virgin aggregate temperature in the drum plant. The plant’s moisture content data indicate that virgin coarse aggregates hold a lower amount of moisture compared with virgin fine aggregates. However, in comparing samesize virgin aggregates and RAP, RAP contained a higher amount of moisture. The reason might be that the aged binder coating of RAP holds moisture better than virgin aggregates do. Also, RAS contains a higher amount of moisture compared with RAP of the same size.