• Energy Research

Abstract Solar reflective materials, so called cool roofs, can be identified as one of the most promising solutions to counteract urban heat island. Cool roof market is nowadays dominated by polymeric product, which can ensure good optical properties but poor durability against weathering and ageing. Ceramic-based products can be an excellent solution combining both good solar properties and higher durability against time, in particular if glazed. Embedded colored pigments, moreover, can help the introduction of these materials in Mediterranean building policies. These cool colored ceramic-based products, in fact, match naturally high thermal emissivity ( e =0.90) with higher mechanical, chemical and physical durability. A traditionally engobed porcelain stoneware tile was used as a substrate for a new generation of colored glazes characterized by different surfaces reaching promising values in solar reflectance.

The 2030 Agenda for Sustainable Development charts the course for transforming the world socially, economically, and environmentally by 2030. Cities represent a critical issue in this transformation: the population growth and the intense anthropogenic activity make them centers of strong environmental impact. For instance, cities have become Urban Heat Islands (UHIs) due to the significant increase in temperatures caused by pollution and heat produced by human activities. The urgency to make cities sustainable from an environmental point of view urges the search for innovative solutions to counter this phenomenon. One of those solutions is reflective tiles, as they absorb less heat and stay cooler than traditional materials and are considered an effective mitigation technique against the UHI phenomenon. This study investigated the obtaining of solar reflective ceramic tiles through the modification of the engobe's formulation. To achieve this goal, a glass-ceramic frit with high solar reflectance (SR) property (0.95) was incorporated into the formulation of a commercially available ceramic engobe. To verify whether the modified engobe can be used to prepare solar reflective cool color ceramic tiles, the tiles were decorated in quadrichromy by ink-jet printing according to the four-color CMYK color model. The Gray Scale (GS) printing system was used to investigate five different printing intensities. The results suggest that when a glass-ceramic frit with a high intrinsic SR value is incorporated into the formulation of an industrial engobe, it can raise its SR value, passing from 0.69 to 0.75. However, the productive process used to obtain ceramic tiles limits the SR values due to crystallization. It was also found that ink-jet decoration negatively affects the solar reflective property of the tiles prepared with the new engobe due to its coverage by the inks and their mineralogical composition. Thus, the results presented in this work evidence that changing the engobe's formulation is not enough to obtain ceramic tiles with high solar reflective properties.

In this study RHA was used as silica source in the obtainment of clay bricks. Different compositions were prepared, substituting the clays with diverse percentages of RHA (0–20 wt%) and requested water contents. The pastes obtained were extruded in laboratory, dried and then fired in an industrial camera kiln. Technological tests were performed after drying (linear shrinkage and naphtha absorption) and firing [(24-h immersion) water absorption, linear shrinkage, weight loss, average flexural strength] steps. Besides, to analyze the effect on the microstructure and mineralogy, SEM/EDS and XRD analysis of the fired bricks were performed. From the tests conducted it is possible to note that RHA content contributes to reduce the linear shrinkage during drying while an opposite effect is observed for the water absorption. Regarding mechanical test, the products containing up to 5 wt% of RHA are in according to the recommended values for roof. Bricks containing higher amounts of RHA could be used in building manufacturing (light weighted faced load bearing walls) where moderate strengths and penetration protection (porosity/permeability) are required. The carbon unburned present in the RHA contributes to increase the final porosity and the weight loss of the bricks.