Bibliometric Analysis of Nanomaterials in Asphalt Materials

Although there has been rapid growth in research on nanomaterials in asphalt engineering over the last decade, no study has attempted to provide a quantitative synthesis of the overall structure of this field of research, as well as its potential directions. This bibliometric review addresses that gap by analysing 863 English-language articles and reviews published between 2016 and 2025, retrieved from Scopus and Web of Science. A multi-tool methodology was adopted: VOSviewer for keyword co-occurrence and cluster visualisation, CiteSpace for temporal evolution and citation burst detection, and Bibliometrix (R package) for keyword growth and thematic evolution tracking. The total number of publications has been increasing steadily over the years, with a total of 53 articles published in 2016 and a peak of 122 articles published in 2020. A total of over 73% of the total articles were published within the period of 2020-2025. China leads research productivity (306 documents, 35.5%), followed by the United States (126) and Iran (122), though international collaboration remains limited. Seven thematic clusters were identified, covering petroleum chemistry, binder modification, photocatalytic applications, pavement durability, characterisation techniques, carbon-based nanomaterials, and geotechnical uses. Aging resistance, graphene oxide, and self-healing functionality emerged as the fastest-growing research frontiers. The review has identified seven critical gaps with the most prominent being the disconnect between nanomaterial research and recycled asphalt pavement technologies, the near-absence of cold mix asphalt studies, and incomplete laboratory-to-field translation. Other gaps include limited cost-effectiveness and life cycle assessment studies, unexplored waste-derived nanomaterials, restricted multi-functional system development, and a lack of standardised dispersion protocols. Also, the review concludes with targeted recommendations, prioritising nano-rejuvenator design for high-RAP blends, field validation, and cost-benefit assessment to accelerate the transition from laboratory findings to practical implementation.