Development of new film thickness models for hot mix asphalt

The current standard model for calculating film thickness is not sufficiently detailed to adequately reflect differences in hot mix asphalt mixtures; and therefore, has limited value as a tool to evaluate research or mix designs. Modifications to the model (or replacement of the model) would give practitioners a better tool to assess the durability potential of a hot mix asphalt mixture.; Durability is an important characteristics of hot mix asphalt that must get adequate attention to insure long-term performance of hot mix asphalt. Film thickness is one mixture parameter used to characterize a mixture's potential durability. The standard film thickness model is only a nominal approximation that applies 1940's technology.; This study develops two film thickness models that more accurately reflect the relationship of the asphalt binder coating to other mixture parameters. The INDEX Model uses basic weight and volume relationships on each aggregate source in the mixture to improve the surface area value used in the standard model. The VIRTUAL Model uses three-dimensional concepts to redefine film thickness as the spatial relationship between aggregate particles and air voids. The VIRTUAL Model allows the practitioner to compute the film thickness at any level of field compacted density.; The study examines the historical development and application of the standard film thickness model. The proposed film thickness models account for the individual aggregate source gradations, specific gravities, and particle shape that comprise the hot mix asphalt blend. The study provides a practical approach to the significant contribution of the mineral filler as both an aggregate and asphalt binder extender. These parameters were not adequately accounted for prior to this study.; These new film thickness models provide the asphalt community with improved approaches to calculating film thickness that better reflect the unique properties of each hot mix asphalt mixture. Based on the analysis in this study, future studies of hot mix asphalt durability will have a more accurate perception of film thickness to compare differences in hot mix asphalt durability.