Recent Advances in Asphalt Materials and Their Applications

Dear Colleagues,

Granular layers, comprising unbound aggregates, are placed on top of the subgrade to provide stability, drainage, and support to a pavement system. Given the range of aggregate types available for a pavement’s granular layer construction, an 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, with a particular view to virgin aggregate (VA). It has enabled transportation agencies to establish standards and guidelines for pavement construction in different regions and facilitates further studies for refined insights.

Recycled concrete aggregate (RCA) is a type of aggregate produced after the dismantling of concrete pavement and structures. Though recent studies have demonstrated that RCA exhibits superior strength to VA when used in granular layers of pavements, further investigation is needed to address the hydrophilic nature and slow hydration process of cementitious materials. In contrast, reclaimed asphalt pavement (RAP) aggregates display hydrophobic characteristics; however, the asphalt coating of the aggregate may cause softening in warm climates and resultantly prove counterproductive for use in pavements.

The use of steel slag in the unbound layers has also been a research topic in the recent past. Where it offers improved strength and durability, potential environmental concerns, including the leachate of heavy metal contamination, need to be addressed further. Crushed brick is another recycled material that can replace VA in sub-base layers. It may stabilize a pavement system in some cases, but further durability analyses are needed to ensure its effectiveness.

The research community has recently devoted much attention to mechanical methods with which to support unbound material in granular layers. Studies are presenting the benefits of using geosynthetics in pavement construction. In this context, future research may propose different designs and installation techniques with which to reduce financial costs and enhance performance. Studies may also focus on comparing the available types of materials and consider incorporating newer technologies.

Future research may emphasize developing testing protocols, suggesting construction procedures, creating optimum gradation tools, proposing blends of different materials, and assessing long-term performance regarding alternate aggregate types. It can also incorporate techniques to stabilize granular layers, e.g., lime-related additives, salts, and plastic fines; however, studies regarding chemical stabilization techniques must always consider environmental aspects and requisite solutions, as the possible leaching of harmful elements can pollute the surrounding environment.

Dr. Syed Waqar Haider
Guest Editor

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• unbound materials
• asphalt
• recycled concrete aggregates
• aggregate base
• sub-base
• stabilization
• durability
• moduli