Manufacturing and characterization of eco-friendly reflective ceramic cool roof tiles using waste glass to mitigate the urban heat island (UHI) effect

Abstract

The consequences of global temperature rise due to climate change continue to manifest, leading to elevated temperatures in urban areas at a local scale and contributing to the creation of urban heat island (UHI) effect. In the other hand, the implementation of heat absorbing materials contributes as well to the exacerbation of this phenomenon and increases the cooling energy consumption in buildings. In this context, cool surfaces present one of the strategies approached to reduce this effect, in which the scientific community is constantly working through the development of adaptable reflective materials. This strategy consists of the implementation of solar radiation reflective materials for roofs, walls and pavements, which are designed to reflect solar radiations and exhibit effective emissivity to release the absorbed heat, allowing to reduce the heat transferred into the buildings and subsequently reduce the cooling energy consumption. Moreover, the environmental impact and sustainability aspects related to the development and implementation of these materials have been gaining interest in the research field, which help to avoid entering in a feedback loop with the global warming by reducing raw materials depletion, energy consumption, and greenhouse gas emissions. In this context, the use of reflective pigments in the fabrication of cool materials has been widely discussed in the research field, particularly for cool roofs that are gaining significant attention compared to other applications of cool surfaces. These pigments could achieve solar reflectance up to 95% in comparison with TiO2, that represents the most widely used standard cool pigment. However, it's worth noting that the manufacturing process for these materials may require intensive energy. On the other hand, the integration of secondary materials into the production of sustainable reflective materials has been encouraged. This approach aims to reduce the use of natural raw materials and lower energy consumption during the processing and production phases. On the other hand, as a secondary resource, using recycled materials is considered as a positive strategy for saving natural resources and mitigating potential environmental risks. In this regard, waste glass (WG) being recycled globally is deemed insufficient compared to the discarded quantity intended for landfill disposal. As the generation of WG increases and landfill-related environmental issues persist, recycling WG has become an appealing alternative used for the substitution of raw materials in the ceramic industry. Although studies on using WG in the fabrication of construction materials have been approached, the use of WG particles as coatings for roof tiles in particular, has not been investigated yet for the solar reflectance performance assessment. Consequently, the main objective of this research is the characterisation and the evaluation of the performance of ceramic roof tiles using WG as reflective coatings to mitigate UHI effect. This first proof of concept was evaluated following a methodological approach including four main steps: (i) the evaluation of the scientific evolution of the cool surfaces field; (ii) the introduction to the practical experimentation of this work through the preliminary characterization in terms of visual appearance, lightness and solar reflectance performance of clay specimens covered with WG; (iii) the real scale approach including the fabrication and the physical, mechanical and optical characterization of roof tiles with WG coatings; (iv) finally, the evaluation of the environmental impact of using roof tiles with WG coatings performing a life cycle analysis. The results obtained in this work showed a research field in constant evolution and highlighted the feasibility of the sustainable potential use of recycled WG as roof tiles coatings for cool roof applications, which provides a solution based on the use of a secondary resource contributing to the development of mitigation strategies of the UHI effect. The application of WG coatings for tiles increased the solar reflectance for up to 90%. As a result of the environmental impact assessment, the studied solution proved to decrease the cooling energy consumption in buildings, particularly in zones with severe summer conditions. The climate zones B4, C3, and A4 represent the optimal cases for this application with flat roofs, that allows savings percentages of 13%, 12% and 9% respectively. Moreover, this specific use of WG contributes to the decrease of natural resources depletion, by presenting an alternative for raw materials in the fabrication of reflective coatings and saving as much as possible the energy required for the fabrication process. In conclusion, the results obtained represent interesting contributions to the scientific field as it provides future researchers with a reference for the scientific evolution of cool surfaces field and a first proof of concept of using WG coatings to enhance the solar reflectance performance for tiles.