On Bio-Deterioration of Solar Reflective Materials: An Innovative Experimental Procedure to Accelerate the Ageing Process of Surfaces

Abstract

Solar reflective materials are one of the most efficient solution to the urban heat island effect, according to which temperatures, in urban areas are significantly higher than those in the surrounding rural areas. Solar reflective materials (SRM) are characterized by the ability to reflect solar radiation in the whole wavelength spectrum remaining cooler under the sun. The importance of radiative properties focused the attention more on SRM subjected to aging processes instead of the new products. According to this, several standards are, nowadays, available to investigate natural (ASTM G7, ANSI CRRC/S100) and accelerated (ASTM D7897) aging. Unfortunately, these standards do not take into account the presence and the growth of microorganisms such as algae and cyanobacteria, which can be responsible not only for the decrease of radiative properties against time, but also for the decay of physical and chemical properties of SRM themselves. This study outlines an experimental procedure to accelerate natural bio-deterioration of building materials through a laboratory test. Two types of SRM have been involved, studying their thermal properties before and after the bio-deterioration accelerated treatment. The methodology involves the use of a Temporary Immersion System (TIS bioreactor), which is based on the temporized soaking of materials samples with a liquid growth medium inoculated by selected species of algae or cyanobacteria. The system promotes a homogeneous contact between the materials surfaces and these microorganisms blowing sterilized air into the medium inside the bioreactor chamber. Within three weeks into TIS bioreactor, materials samples have shown large areas of biofilm deposition on themselves. The experimental procedure, hence, confirms the capability of the system to optimize environment conditions where the growth of microorganism and their interactions with materials results accelerated. Very high attention is given to the aim to make the procedure repeatable. For this proposal, all the variable factors are minimized, maintaining constant the environmental condition and working on sterility in order to do not contaminate or alter the growth inside the bioreactor.