Experimental evaluation of urban heat island mitigation potential of retro-reflective pavement in urban canyons

Retro-reflective (RR) materials have been studied as a potential mitigation technology for the Urban Heat Island (UHI) phenomenon, thanks to their ability to reflect the radiation towards the same incoming direction. In this paper, the positive effect of RR pavements on the energy kept inside the canyon was studied on a physical model that represents an urban canyon layout. The performance of RR materials was compared to that of white and beige traditional cool diffusive materials in the spectral range of the incoming radiation from 360 to 1100 nm. The objective was the evaluation of the albedo over the canyon’s lid, so that also the optic interaction between pavement and facades was taken into account.In addition, the RR cooling effect, defined as the ratio between RR and diffusive reflected energies which remain inside the canyon, was calculated for the small-scale canyon scenario and the related analytical model was experimentally verified. The results show a cooling potential of the RR material with respect to the white and the beige diffusive materials, with a maximum albedo increase of 4.6%. The cooling ratio, calculated comparing RR with the beige diffusive sample with similar global reflectance, is equal to 0.37, showing a significant decrease of the energy kept inside the urban canyon.