Fatigue and Rutting Performance of Porous Asphalt Mixtures in Comparison to Conventional Mixes

Abstract: Porous asphalt (PA) mixtures are characterized by their permeability due to high interconnected air void content, which contrasts with traditional dense-graded mixtures. Despite the well-established environmental benefits of the PA mixtures, only their hydrological design aspects have influenced most existing research efforts and implementations. The recent advancements in the structural design aspects of PA pavements have led to the expansion of this technology into high-traffic volume roadways. This requires the PA mixtures to meet the fatigue and rutting criteria. Even though fatigue failure was the primary concern compared to rutting in PA pavements, the binder and mixture modification developments made PA mixtures more resistant to fatigue failure. The goal of the study is to compare the performance of porous asphalt mixtures with dense-graded mixtures. The laboratory rutting and fatigue resistance were measured for six mixtures (three PA mixtures, two fiber-modified dense-graded mixtures, and one control mixture, which is an unmodified dense-graded mixture). Loose cellulose fiber at the same dosage was dry-mixed with three open-graded aggregates for the PA mixtures. The Nominal Maximum Aggregate Size (NMAS) was 9.5mm for one of the PA mixtures and 12.5 for the other two. One fiber-modified dense-graded mixture had Polyolefin/Aramid (PFA) fiber, and the other had Sasobit-Coated Aramid (SCA) fiber. The control mixture was a conventional dense-graded mixture without any fiber additives. All the dense-graded mixtures had the same aggregate gradation with 9.5mm NMAS. All six mixtures had polymer-modified PG76-22 binders.
Overlay Test (OT) and Indirect Tensile Asphalt Cracking Test (IDEAL-CT were conducted to evaluate the fatigue performance of PA and dense-graded mixtures. Test results demonstrated higher flexibility and better crack resistance of PA mixtures compared to the fiber-modified and conventional dense-graded mixture with significantly higher cycles to failure in the OT and higher CTindex in the IDEAL-CT. This behavior was attributed to the higher asphalt binder content and air voids. In addition, introducing PFA and SCA fibers in the dense-graded mixture reduced cycles to failure in the overlay test because fibers resist the deformation produced due to constant strain mode in the OT. However, aramid fiber-modified mixtures have demonstrated improved cracking performance compared to conventional dense-graded mixtures in the IDEAL-CT.
The Asphalt Pavement Analyzer (APA) was used to assess the rutting susceptibility of these mixtures. The rut depths of the PA mixtures were higher than the dense-graded control mixture, while the fiber-modified dense-graded mixtures had the lowest rut depths. The rut depths of PA mixtures were still within the New Jersey rut depth criteria of 5mm. The higher rut depth in the PA mixtures was influenced mainly by higher binder contents and higher air voids, which led to densification due to repeated loading. Although the loose cellulose fiber and polymer-modified binder helped stiffen the PA mixtures to reduce rut depths, the nominal maximum aggregate size showed little influence on the rutting potential.