Assessment of Hot Mix Asphalt Performance Using Reclaimed Asphalt Pavement as a Sustainable Partial Replacement

Introduction

Road transport is the dominant mode of mobility in Ethiopia, accounting for more than 95% of freight and passenger movement (JICA, 2019). When the Road Sector Development Program (RSDP) began in 1997, the sector faced major challenges. Since then, Ethiopia’s road network has expanded dramatically—from 26,550 km in 1997 to 165,863 km in 2023, reflecting an average annual growth rate of 7.5%. Consequently, road density increased from 24.1 km to 144.5 km per 1,000 km² over the same period, and the paved network rose from 3,708 km to 18,238 km (ERA, 2024). Despite these significant improvements, road conditions have shown only marginal progress. The proportion of federal asphalt roads rated as “good” increased modestly from 17% at the start of RSDP to just 22% in 2023. Notably, only 4.4% of total RSDP expenditure over the past 26 years was allocated to the maintenance of federal roads (ERA, 2024), indicating a substantial maintenance gap. This gap highlights the need for technically sound and environmentally responsible approaches to rehabilitating deteriorated pavements.

Sustainable road maintenance and rehabilitation have become essential components of modern infrastructure management (Hernan et al., 2019). Asphalt recycling and reclaiming, practiced in various forms since the early 1900s, has emerged as one such solution, offering technical, economic, and environmental benefits (Sadie, 2013). Advances in recycling technologies during the 1970s improved feasibility, particularly in regions with long, straight roadway segments (ARRA, 2015; Imran, 2007). The Federal Highway Administration (FHWA) further strengthened this trend by issuing policies that promote recycling nationwide (FHWA, 2002).

Asphalt recycling supports the construction of safe, durable, and cost-effective pavements while significantly reducing energy consumption and environmental impact. Around the world, the pavement industry has evolved considerably, yet challenges related to sustainability persist. Recycling with stabilizing agents aligns well with sustainability goals by allowing the reuse of existing pavement materials while delivering technical and economic advantages (Hernan et al., 2019). In Ethiopia, many asphalt pavements deteriorate prematurely, failing to reach their intended design life and creating an urgent need for efficient rehabilitation strategies (Adefris et al., 2022).

Given Ethiopia’s dependence on road transport, the performance and reliability of its road network are crucial for socio-economic development (ERA, 2021). The rising cost of virgin asphalt and energy has also encouraged greater interest in reclaimed asphalt pavement (RAP) (Elie Y. Hajj et al., 2007). A systematic review by Endale et al. (2022) identified full-depth reclamation (FDR) as one of three potential methods for sustainable rehabilitation, noting that recycling may achieve cost savings of up to 80% while preserving material quality. However, limited pilot applications and a narrow focus on specific regions and additives point to the need for broader trials and supportive policies. Adefris et al. (2022) further reported that RAP can improve pavement moisture susceptibility, rutting resistance, and tensile strength, while findings by Sadie (2013) confirmed the durability and moisture resistance of FDR-treated mixtures. Overall, the literature demonstrates that asphalt recycling offers multiple benefits across performance, cost, and sustainability dimensions.

The ERA Flexible Pavement Design Manual (ERA, 2013) states that unbound materials containing RAP may be used as base course materials provided, they meet grading, density, and CBR specifications. RAP’s advantages include reduced energy consumption, lower emissions, minimized landfill use, conservation of natural resources, and reduced disposal costs (Siddharth et al., 2020; Adefris et al., 2022). With maintenance and rehabilitation receiving renewed priority within the Ethiopian Roads Authority, increasing quantities of RAP will become available for reuse. The overall objective of this study is to evaluate the laboratory-based performance of hot mix asphalt mixtures incorporating different percentages of (RAP).

Method

Study Area

This study focuses on the laboratory evaluation of hot mix asphalt (HMA) mixtures incorporating reclaimed asphalt pavement (RAP) for use in asphalt binder course construction. The RAP material used in the research was sourced from Addis Ababa City, specifically from the Total–Ayertena road section, which had served traffic for more than eight years. The material consisted of milled RAP that had been stockpiled by the Addis Ababa City Roads Authority (AACRA). Milled RAP was selected because it is the form most used in practical HMA production and is generally preferred over core RAP for partial replacement in asphalt mixtures.

Source of Data and Sampling Techniques

RAP samples were obtained from the AACRA stockpile located near the Winget area in Addis Ababa. Since sampling accuracy directly influences the validity of laboratory test results, the material was collected with careful attention to established sampling protocols. As emphasized by Adefris et al. (2022), proper sampling is as critical as the testing process itself. The collected RAP material was then transported to the laboratory for preparation and subsequent evaluation.

Figure 1 Source of RAP material from AACRA road project (photo taken during sampling)