Utilization of Recycled Aggregates and Waste in Sustainable Road Materials

Dear Colleagues,

Granular layers, comprising unbound aggregates, are placed on top of the subgrade to provide stability, drainage, and support to the pavement system. Given the range of aggregate types available for the pavement’s granular layer construction, the most appropriate choice depends on various factors, such as availability, intended use, material properties, short- and long-term performance requirements, environmental issues, sustainability, and cost-effectiveness. Much research in the past has focused on gaining a better understanding of the mentioned factors, particularly concerning virgin aggregate (VA). This approach has allowed transportation agencies to establish regionally variable standards and guidelines for pavement construction and facilitates further studies for a refined insight.

Recycled concrete aggregate (RCA) is a type of aggregate produced after the dismantling of concrete pavements and structures. Though recent studies have demonstrated that RCA is stronger than VA when used in pavements’ granular layers, further investigations are needed to address the hydrophilic nature and slow hydration process of cementitious materials. These investigations assess the ultimate strength gain and feasibility of a project depending on the laboratory and/or field testing methods used to evaluate it. In contrast, reclaimed asphalt pavement (RAP) aggregates display hydrophobic characteristics; however, the aggregate’s asphalt coating may cause softening in warm climates and may, thus, prove counterproductive for use in pavement construction.

More recently using steel slag in the unbound layers has also been a popular research topic. However,  it ability to improve strength and durability, as well as potential environmental concerns, including the leachate of heavy metal contamination, need to be addressed further. Crushed brick is another type of recycled material that can replace VA in sub-base layers. It may stabilize the pavement system in some cases, but such materials must undergo further durability analysis to ensure their effectiveness.

Mechanical methods used to support unbound material in granular layers have recently gained increased attention from the scientific community. Past studies have demonstrated the benefits of using geosynthetics in pavement construction. In this context, future research may propose different designs and installation techniques to reduce costs and enhance performance. Studies may also compare the available types of materials and consider incorporating newer technologies.

Future research may emphasize testing protocol development, suggest construction procedures, create optimum gradation tools, propose different material blends, and assess the long-term performances of alternate aggregate types. It may also incorporate techniques to stabilize granular layers, e.g., lime-related additives, salts, plastic fines, etc. However, studies of chemical stabilization techniques must consider environmental aspects and requisite solutions, as the possible leaching of harmful elements can pollute the surrounding environment.

Dr. Syed Waqar Haider
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Buildings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• resilient modulus
• dynamic modulus
• FWD testing
• drainage and fatigue
• rutting performance