The Use of Zinc Oxide in Asphalts: Review

Zinc oxide (ZnO) is a wide-gap semiconducting material which is chemically stable at high temperatures and has been shown to be compatible with asphalt binders. Additionally, semiconducting nanoparticles such as ZnO could help to improve urban air quality. This has encouraged the use of this material as a binder and asphalt mix modifier. A review on the use of ZnO as an asphalt binder modifier was conducted in this study. Based on the review which we carried out, the following were mainly synthesized and described: the content of ZnO as a modifier, the mixing processes of the binder and the ZnO, the manufacturing process of the modified mix, the type of asphalt binder and/or modified mix, the tests carried out, general conclusions, and environmental effects. ZnO micro-particles increase the aging resistance of the asphalt binder (mainly to ultraviolet radiation (UV)). ZnO tends to increase rutting resistance and adhesion with aggregates, improving resistance to moisture damage. It also tends to improve binder fatigue resistance. At low service temperatures, the performance of ZnO as a modifier is unclear, and further studies should be performed. Few studies have evaluated the effect of ZnO on the environment when it is used as an asphalt binder modifier. Future studies should evaluate the effect of this technology on the environment, perform economic analyses, evaluate the physical–chemical interaction of the modified binder with the aggregate, and measure the long-term properties of asphalt mixtures. ZnO is viewed as an environmentally friendly material and as a promising modifier of asphalt binders for pavement construction.