Citation: Abouelsaad, A.; White, G. The Combined Effect of Ultraviolet Irradiation and Temperature on Hot Mix Asphalt Mixture Aging. Sustainability 2022, 14, 5942. https:// doi.org/10.3390/su14105942 Academic Editor: Don Cameron Received: 11 April 2022 Accepted: 11 May 2022 Published: 13 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article The Combined Effect of Ultraviolet Irradiation and Temperature on Hot Mix Asphalt Mixture Aging Ahmed Abouelsaad and Greg White * School of Science, Technology and Engineering, University of the Sunshine Coast, Sippy Downs, QLD 4556, Australia; ahmed.abouelsaad@research.usc.edu.au * Correspondence: gwhite2@usc.edu.au; Tel.: +61-(400)-218-048 Abstract: Reliable accelerated simulation of asphalt aging is of significant interest to asphalt re- searchers and pavement practitioners alike. However, current laboratory aging protocols are either based on binder aging rather than mixture aging or use dry ovens to heat asphalt mixtures, omitting the important effects of UV radiation. Binder aging cannot take into account the interactions between the binder and aggregate phases during aging, while the omission of UV radiation ignores an impor- tant catalyst in the aging process. In this study, a comparison of the effect of conventional thermal oven aging to the combined effect of heat and ultraviolet irradiation on the resilient modulus and surface texture of dense-graded asphalt field cores and gyratory-compacted samples was undertaken. Significantly higher rates of modulus increase with aging time were measured for the samples aged by both heat and ultraviolet irradiation. The gyratory-compacted samples showed more realistic results in terms of surface texture compared to the field cores, likely due to the extraction of field cores from a small area of pavement that was subjected to concentrated pneumatic tyre rolling, which was not representative of typical asphalt construction. It was concluded that using aging indices, calculated as the ratio of the aged value to the initial value, is recommended for asphalt aging investigations. The findings of this study highlight the significance and importance of developing aging protocols that combine heat, ultraviolet irradiation, and any other environmental factors that may affect the aging behaviour of asphalt mixtures. Keywords: asphalt; accelerated; laboratory; aging; ultraviolet irradiation 1. Introduction Flexible pavements with asphalt surfaces dominate highway and airport pavement construction. Each year, billions of dollars are spent by the asphalt pavement industry; hence, providing durable asphalt surfaces is critical to providing cost-effective and sustain- able flexible pavement structures. The properties of asphalt mixtures are greatly affected by any changes in the rheological properties or chemical composition of the bituminous binder with time, a phenomenon known as bitumen aging [1]. In recognition of the increased inter- est in sustainable asphalt mixtures and asphalt preservation treatments for longer-lasting surfaces, developing reliable procedures to simulate the aging of bituminous binders and asphalt mixtures in the laboratory has become increasingly important. The oven-based mixture aging process detailed in AASHTO R30 is the only accelerated laboratory aging protocol for compacted asphalt mixture specimens. It requires samples to be stored at 85 ◦ C for five days, which is intended to reflect ten years of field aging [2]. However, this process is relatively simple and was developed based on only limited field aging data [3]. Conse- quently, it has been questioned by researchers for two primary reasons. First, the single time-temperature combination may not be applicable to different climatic conditions [3,4]. Second, applying only heat is not representative of other environmental factors, including ultraviolet (UV) irradiation, which is a catalyst for the oxidation process that causes the aging of asphalt mixtures [5]. Sustainability 2022, 14, 5942. https://doi.org/10.3390/su14105942 https://www.mdpi.com/journal/sustainability