The influence of environment and carbonation of fiber cement tiles on the reflectance of a cool surface exposed in four Brazilian cities

Abstract

Cool materials are a suitable way to mitigate urban heat islands and help dimmish CO2 emissions and thermal discomfort in cities. However, the deposition of particulate matter and microbial growth reduces the reflectance of cool materials over time. There is little literature on this, especially in tropical climates. This research aimed to investigate the effects of biofilm formation over a white cool paint exposed in different Brazilian environments with Köppen’s climate classifications Cfb, Cfa, Am and Af. The paint was applied over fiber cement panels, without or after accelerated carbonation, to mimic new and aged tiles, respectively. Pre-carbonation of the fiber cement favored intense colonization by Scytonema that influenced the loss of reflectance in the panels aged in Belém, northern Brazil. The panels exposed in Pirassununga in South-East Brazil, on the other hand, presented an intense growth of phototrophs and fungi, that, together with deposition of particulate soil rich in iron oxide, caused a reduction of over 0.35 reflectance for the carbonated tiles. The loss of reflectance varied from 19% in the samples exposed in São Paulo to 36% in the samples exposed in Belém. This study has shown that the reduction in reflectance caused by biofilm development is not uniform in different Brazilian environments even when the substrate and coating are the same.