Innovative pavement surfaces as urban heat islands mitigation strategy: chromatic, thermal and mechanical characterisation of clear/coloured mixtures

Abstract

The issues related to the global warming are increasingly becoming of crucial importance for governments and scientific communities, which are trying to develop policies and solutions to slow down this problem in order to limit the related negative effects on environment, human health and economy. The Urban Heat Island (UHI) phenomenon, i.e. the increasing of temperatures within cities with respect to the neighbouring rural spaces, is one of the main aspects related to such a global warming. In this regard, cool road pavements can be really considered as a valuable technological solution to mitigate such a phenomenon. Given this background, the present paper illustrates a comprehensive experimental investigation principally aimed at providing a specific overview of the main thermal behaviour of selected clear and coloured mixtures for pavement surface courses as mitigation strategy for the UHI phenomenon. To this aim, specific indoor (laboratory) and outdoor monitoring were carried out on samples subjected to artificial radiations and sun exposure, respectively. Basic chromatic characteristics and mechanical properties of such materials were also investigated to evaluate prospective correlations with the thermal response as well as real field applicability. Clear mixtures were prepared using “traditional” limestone or “unusual” white marble aggregates bound with a synthetic transparent resin whereas the coloured mixtures were obtained by adding oxide pigments (red or yellow) to a plain bituminous blend. A traditional reference “black” bituminous mixture was also studied for comparison purposes. The experimental findings mainly showed that an optimisation of the thermal response of pavement surface can be achieved leading to remarkable temperature reductions also interesting the surrounding environment, in particular when a transparent binder is used. However, some issues related to the mechanical properties of clear mixes should be addressed since they could limit the real applicability of such materials.