Nowadays, there is increasing concern in transportation engineering about the use of techniques less harmful to the environment and also about road safety. Heterogeneous photocatalysis based on the application of semiconductor materials onto asphalt mixtures is a promising technology because it can mitigate air pollution and road accidents. The functionalized asphalt mixtures with photocatalytic capability can degrade pollutants, such as damaging gases and oil/grease adsorbed on their surface, from specific reactions triggered by sunlight photons, providing significant environmental and social benefits. In this article, a review of photocatalysis applied in asphalt mixtures is presented. The most important characteristics related to the functionalization of asphalt mixtures for photocatalytic applications and their corresponding characterization are presented, and the achieved main results are also discussed.

A cost-effective solution to provide asphalt pavements with the photocatalytic property was addressed for the first time, based on the combination of low percentages of two semiconductors, TiO₂ and ZnO. Two photocatalytic techniques – spray deposition and bitumen modification – were used. With the former, the chemical properties were evaluated by FTIR after spraying the bitumen samples with two aqueous solutions, one with acid PH and another alkaline, of nano-TiO₂. The solution with less chemical impact was the alkaline one. With the latter, Penetration, Softening Point, Mass Loss, Dynamic Viscosity, Complex moduli and Performance Grade, after the modification by TiO₂ nano/microparticles and ZnO microparticles, were analysed with two levels of ageing produced by the RTFOT. TiO₂ nano/microparticles and ZnO microparticles conducted to softer bitumens and better results of short-term ageing resistance and did not cause any deterioration to the bitumen before or after either short- or long-term ageing.

This research presents a dual-pronged bibliometric and systematic review of the integration of phase change materials (PCM) in asphalt pavements to counteract the urban heat island (UHI) effect. The bibliometric approach discerns the evolution of PCM-inclusion asphalt research, highlighting a marked rise in the number of publications between 2019 and 2022. Notably, Chang’an University in China has emerged as a leading contributor. The systematic review addresses key questions like optimal PCM types for UHI effect mitigation, strategies for PCM leakage prevention in asphalt, and effects on mechanical properties. The findings identify polyethylene glycols (PEGs), especially PEG2000 and PEG4000, as prevailing PCM due to their wide phase-change temperature range and significant enthalpy during phase transitions. While including PCM can modify asphalt’s mechanical attributes, such mixtures typically stay within performance norms. This review emphasises the potential of PCM in urban heat management and the need for further research to achieve optimal thermal and mechanical balance.

Transparent binder is used to substitute conventional black asphalt binder and to provide light-colored pavements, whereas nano-TiO₂ has the potential to promote photocatalytic and self-cleaning properties. Together, these materials provide multifunction effects and benefits when the pavement is submitted to high solar irradiation. This paper analyzes the physicochemical and rheological properties of a transparent binder modified with 0.5%, 3.0%, 6.0%, and 10.0% nano-TiO₂ and compares it to the transparent base binder and conventional and polymer modified binders (PMB) without nano-TiO₂. Their penetration, softening point, dynamic viscosity, master curve, black diagram, Linear Amplitude Sweep (LAS), Multiple Stress Creep Recovery (MSCR), and Fourier Transform Infrared Spectroscopy (FTIR) were obtained. The transparent binders (base and modified) seem to be workable considering their viscosity, and exhibited values between the conventional binder and PMB with respect to rutting resistance, penetration, and softening point. They showed similar behavior to the PMB, demonstrating signs of polymer modification. The addition of TiO₂ seemed to reduce fatigue life, except for the 0.5% content. Nevertheless, its addition in high contents increased the rutting resistance. The TiO₂ modification seems to have little effect on the chemical functional indices. The best percentage of TiO₂ was 0.5%, with respect to fatigue, and 10.0% with respect to permanent deformation.