Investigation of Foamed Warm Mix Asphalt Performance Using the MEPDG

Abstract

In recent years, warm mix asphalt (WMA) produced using foamed asphalt binder has gained popularity in the United States due to its ability to improve workability and compactability of asphalt mixtures produced at lower temperatures. As compared to other WMA technologies, foamed warm mix asphalt does not require the use of costly additives, making it less expensive to produce. In spite of the advantages, several concerns have been raised regarding the performance of this material due to use of lower production temperatures and its impact on aggregate drying and asphalt binder aging. This study aims at evaluating the performance of foamed WMA mixtures in comparison to that of Hot Mix Asphalt (HMA). Two types of aggregates (crushed limestone and natural gravel) and two asphalt binders (neat PG 64-22 and polymer modified PG 70-22M) were used in this study. Dynamic modulus (E*) tests were conducted to evaluate the mechanical properties of the considered mixtures. The new Mechanistic Empirical Pavement Design Guide (MEPDG) software was used to compare the performance of pavement sections construction using foamed WMA and traditional HMA. In addition, it was used to investigate the effect of using foamed WMA on the design thickness of the asphalt layer. The results of this study indicated that the effect of the foamed WMA technology on pavement performance was primarily controlled by the combination of the aggregate and binder types used in the mixture. Such that, for mixtures that had natural gravel the influence of the WMA was dependant on the type of asphalt binder used. For the PG 70-22M binder, the WMA resulted in slightly better performance than HMA. On the other hand, for the neat asphalt binder (PG 64-22), the use of the WMA significantly increased the rutting and International Roughness Index (IRI) of the pavement structure. In addition, for the limestone mixtures, the use of WMA resulted in similar pavement performance to that of HMA. Meanwhile, the use of the WMA yielded much higher design thickness for the gravel mixture with 64-22 binder, while it did not have a significant effect for all other mixtures.