Mixture-property-independent asphalt film thickness model

Abstract

The durability of asphalt mixtures and hence the service life of asphalt pavement surface layers depends to a large extent on the asphalt film thickness. The current Superpave Voids in Mineral Aggregate (VMA) criterion relates mixture durability with VMA. The need to modify the Superpave criterion was supported by a previous study [1]. As the Superpave VMA criterion is based on the minimum asphalt content in the asphalt mixture and not on the asphaltfilm thickness, this minimum requirement does not ensure mixture durability in many cases. Additionally, coarse asphalt mixtures that tend to have enough asphalt film thicknesses normally have difficulty fulfilling the Superpave minimum VMA criteria. From this contention, the need for simple and reasonably accurate models to estimate the asphalt binder film thicknesses in asphalt mixtures becomes essential.In this study, a model for estimating the asphalt film thickness (FTb) has been developed using only parameters/properties of the two mixture constituents (aggregate and asphalt binder) and without the inclusion of any mixture property. The derivation of the model is based on physics, and the determined model coefficients (constants) have been obtained through statistical regression analysis. Superpave aggregate gradations of three nominal maximum aggregate sizes (NMAS), 9.5, 12.5, and 19.0 mm with aggregate gradations passing above, below, crossover, hump through, and pass through restricted zone were used. Superpave Gyratory Compactor (SGC) test data of 100 compacted asphalt mixtures were used in developing the model, and SGC data of 31 mixtures were used for verification of the model. MS Excel program solver was used for regression analysis. The final outcome is a physics-based statistical regression model, with a high enough coefficient of determination (R2) value of 0.9 for FTb, which is easy to use and likely to predict the film thickness with a reasonable degree of accuracy.