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The main objective of the study is to evaluate the impact of using polystyrene (PS) and polyethylene terephthalate (PET) plastics as an additive in asphalt mixtures. For this purpose, volumetric modification, moisture susceptibility along with performance variation at high, intermediate, and low temperature conditions were evaluated. Initially plastics were subjected to calorimeter analysis for assessing their melting characterization. Both PS and PET are included as dry mix additives individually at dosage levels of 3%, 6%, and 9% by weight of asphalt binder. Further, the changes in thermal properties of plastics occurring during mixture preparation were correlated to better understand the volumetric modification. PS, owing to its glass transition and partial amorphous nature, exhibited minimum deviation (<1%) from design air voids (4 ± 0.5%). PET was observed to increase the volumes of voids in mineral aggregate (VMA) and air void, owing to its crystalline nature. As regards performance, PS and PET modification enhanced the moisture resistance by 1.05 to 1.11 times the control mixture. The rutting tolerance index (RTindex) value increased for all plastic modified mixtures from the indirect tensile asphalt rutting test (IDEAL RT) performed at 58°C. However, the intermediate temperature cracking tolerance index (CTindex) at 19°C conveyed the high embrittled nature from plastic modification making the mixtures more susceptible to cracking. From the Gfversus l75/m75interaction diagram, it was conveyed that although addition of plastics improves the fracture toughness of asphalt mixtures, the ductile nature of mixtures is compromised. Also, PS and PET modification could not improve the ability of asphalt mixtures to resist thermal cracking, evaluated at −18°C.

In recent years, the asphalt paving industry has been strained by numerous factors including increased asphalt binder costs, funding that has not kept up with material costs, increased societal pressure to recycle, and deteriorating pavement networks. Mix design should account for the market in which it is used, which is very different now than when today’s volumetric mix design practices were developed (many of the aforementioned factors were less present). Given this reality, a statewide database of all 1,452 approved mix designs in Mississippi from 2005 to 2018 was compiled and analyzed, and the objective of this paper is to present findings, trends, and unintended consequences of exclusive reliance on volumetrics. With volumetrics-only mix design, asphalt content is primarily controlled by voids in mineral aggregate (VMA), which is influenced by aggregate bulk specific gravity (Gsb). Minor Gsbdeviations (i.e., within AASHTO d2slimits), can significantly affect VMA, so much so that 99% of Mississippi’s mixes could be failing VMA while reported VMA passes. This allows mix manipulation and economization, with 0.8% asphalt content reductions possible while still meeting volumetric requirements. Recycled materials can exacerbate this issue, and common approaches to increase asphalt content (decreasing design gyration level or using finer gradations) are ineffective with fixed VMA requirements. Overall, the mix design database analysis agrees with numerous smaller studies but does so with an entire state’s actual practice. This presents a compelling case that volumetrics-only mix design has limitations, and supports ongoing efforts to reintegrate mechanical tests.

The article offers information on the repair of potholes using cold-mix asphalt. Topics discussed include cold-mix asphalt (CMA) for pothole patching; subjected to extreme loading conditions of military aircraft including heavy cargo aircraft and fighter jets; and substitute steel particles for mineral aggregates for heating purposes without negatively impacting the stability.

Chip and scrub seal material selection is a long-standing challenge to favourable pavement performance and, historically, is based on empirical methods. This paper’s primary objective is to provide guidance for a seal treatment system (i.e. emulsion and aggregates) at high and low temperatures in the context of rejuvenation and aggregate retention. In contrast, commonly used methodologies are less comprehensive, focusing, for example, on only one performance aspect (e.g. aggregate retention) or one material (e.g. emulsion). Temperature is a major consideration of this paper since commonly used specifications call for test temperatures opposite of what may be optimal (e.g. viscosity testing at 135°C is commonly used to characterise rejuvenation, though rejuvenation seeks to address distresses typically associated with lower temperatures, such as cracking). Recommendations, which better align test temperatures, are to use bending beam rheometer mixture beam testing to evaluate rejuvenation and sweep testing to evaluate aggregate retention and traffic opening.