High Reclaimed Asphalt Pavement (RAP) Asphalt Mixtures for Low Volume Roads

The inclusion of increased reclaimed asphalt pavement (RAP) quantities in the production of asphalt mixtures for low volume roads represents an environmental solution that manages to reduce waste and demand of fossil derivate products, and at the same time provides an opportunity for local agencies to optimize roadway construction and maintenance budgets. The objective of this research project was to develop guidance regarding the methodology for the performance assessment of asphalt mixtures with elevated contents of RAP (i.e. 60% to 100%) and define their suitability to perform as surface layers of pavements for low volume roads (i.e. less than 750 vehicles per day). Performance was evaluated for eight hot and ten cold recycled mixtures in relation to common pavement distresses including moisture susceptibility, rutting resistance, intermediate temperature cracking, durability and stiffness by modified Lottman, Hamburg Wheel Track Test (HWTT), Semicircular Bending Beam (SCB) test, Cantabro abrasion loss test and Resilient Modulus (Mvr), respectively. Compacted specimens were fabricated with RAP contents of 60, 80 and 100% employing two sources of RAP, limestone and granite virgin aggregates and two types of recycling agents per recycling methodology (hot and cold). One organic-based agent and one petroleum-based agent were selected for the hot recycling methodology and emulsified and foamed asphalt were selected for the cold recycling methodology. The performance results demonstrated that the evaluation of rutting and moisture susceptibility through HWTT and Modified Lottman, respectively, is likely too severe for high RAP mixtures. With few exceptions, all the recycled mixtures displayed accelerated rutting. However, hot recycled and cold recycled mixtures with emulsion exhibited capacity to perform as surface layers for low volume roads according to current standards based on requirements of tensile strength and moisture susceptibility. Cold recycled mixtures with foamed asphalt did not meet any distress threshold evaluated. Hot recycled mixtures including recycling agents exhibited improved cracking resistance in the SCB test, reduction in Mr and most of the cold recycled mixtures presented poor durability. Varied influence on the mixtures performance was observed for RAP content and recycling agent/additive type depending on factors such as virgin aggregate type, RAP source and recycling methodology. The inclusion of cracking resistance and durability thresholds in the design process of recycled mixtures was found effective at detecting better performing mixtures. In order to improve the assessment of rutting, it is recommended to investigate the use of dry tests such as asphalt pavement analyzer (APA). Likewise, further investigation is recommended with regard to the inclusion of active fillers (i.e., Portland cement or hydrated lime) to improve tensile strength and durability performance of cold recycled mixtures