Experimental studies and sustainability assessments of use of reclaimed asphalt pavement (RAP) in pavement layers

Abstract

This study examines the feasibility and sustainability benefits of incorporating reclaimed asphalt pavement (RAP) into subgrade and subbase layers, aiming to reduce cement consumption in soil stabilization practices. The rising volume of RAP waste, driven by road maintenance activities, presents environmental and economic challenges. While previous research has demonstrated the effectiveness of RAP in base and subbase layers when blended with aggregate materials, studies focusing on RAP for soil stabilization in subgrade and subbase layers are limited. This study presents experimental results on various mix designs, including Unconfined Compressive Strength (UCS) tests to evaluate their strength with and without exposure to Wetting-Drying (W-D) cycles. The findings indicate that RAP-cement mixes with reduced cement content- 15 % RAP with 4 % cement (S-4C-15RAP) and 20 % RAP with 6 % cement (S-6C-20RAP)- meet the 7-day strength requirements for subgrade and subbase layers, similar to the conventional 8 % cement mix (S-8C). Durability tests demonstrated that these RAP-cement mixes retained more than 70 % of their strength after 14 W-D cycles, outperforming mixes with higher cement content. Microstructure analysis using Scanning Electron Microscopy (SEM) revealed strong bonds between RAP particles and cement hydration products, contributing to improved strength and durability. A multi-criteria sustainability assessment revealed that incorporating RAP with lower cement dosages significantly reduced both environmental and economic impacts. The sustainability index (I_SUS) for S-4C-15RAP was 49 % lower than the traditional 8 % cement mix (S-8C), highlighting RAP’s potential as a sustainable alternative. These findings suggest that RAP can effectively reduce cement content in soil stabilization, offering a sustainable and cost-effective alternative to traditional cement-based methods.