Performance Assessment of Hot-Asphalt Mixtures Produced with By-product Aggregates under Repetitive Heavy Traffic Loading

Typically, aggregates used for asphalt mixtures consist mainly of natural aggregates such as crushed rock and gravel. Sometimes the natural aggregates are substituted with limited amounts of industrial by-products, such as Reclaimed Asphalt (RA), slag, and waste foundry sand (WFS). Given the importance of overcoming the challenges associated with the management of nonrenewable resources, and to solve the industrial waste stream problems, this article presents the results of fundamental research conducted to assess the rutting and fatigue cracking performance of hot asphalt mixtures with high percentages of by-product aggregates. For this purpose, two full-scale flexible pavement test sections were constructed and tested at the accelerated loading facilities at VTI (Swedish National Road and Transport Research Institute). The accelerated test aimed at evaluating the performance of two developed asphalt mixtures, designated as mix 1 and mix 7, and made up of 98% of industrial by-products (namely, steel slag, WFS, and reclaimed asphalt pavement, in addition to biobased additives). The test sections were constructed in an indoor facility and loaded with a heavy vehicle simulator (HVS) equipped with a half-standard truck axle with dual wheels. The two road sections were constructed using the same construction materials obtained from the same source, as follows: asphalt surface layer of 50-mm thick, 70-mm thick granular base layer, and 160-mm thick subbase layer on top of a 2.6-m thick sandy subgrade soil. Horizontal asphalt strain sensors were embedded in the pavement test sections to assess the mixture’s resistance to fatigue and cracking and the laser surface profiler measurements were used to evaluate the rutting performance under controlled testing conditions. For comparison purposes, the long-term rutting developed in the sections paved with mix 1 and mix 7 was compared to the rutting observed in a previous similar HVS test carried out on a 70-mm thick asphalt surface layer section made only with natural virgin aggregates. The test results showed that mix 1 and mix 7 may suffer from higher rutting at the beginning when the road is open to traffic, as compared to asphalt mixtures of natural aggregate, but subsequently the alternative mixtures resisted the rutting development better with the increase of traffic loading as compared to the conventional asphalt mixtures. The horizontal strain measurements at the bottom of the asphalt layer during testing showed that failure began as cracks initiated at the bottom of the asphalt layer of mix 7 and started to propagate to the surface of the asphalt layer in the last stage of the HVS traffic loading of the test. No fatigue cracking was observed in the asphalt surface paved with mix 1 at the end of heavy vehicle simulation (HVS) testing. The study demonstrated that the adopted by-product hot mix asphalt (HMA) mixtures can substitute the conventional HMA material under the given heavy traffic loading and environmental conditions.