Frit-Free solar reflective porcelain stoneware ceramic tiles using recycled granite Waste: An investigation on its engobe and glaze formulations

The design of tiles can accelerate the transition of urban environments towards sustainability when building materials are prepared with sustainable, indigenous, renewable or recycled resources and additionally, present solar reflective properties for mitigating the Urban Heat Island (UHI) phenomenon. Here, an innovative approach to develop frit-free ceramics having solar reflectance property using locally sourced recycled granite waste was explored. The investigation unfolds in three parts: (i), the formulations were tailored for the engobe or glaze by varying raw material proportions; (ii), the solar reflectance was improved using whitening agents; and (iii), the selected formulations were subjected to an industrial trial casting of porcelain stoneware tiles. The full replacement of nepheline and feldspar with recycled granite powder offered properties suitable for the engobe such as a matte surface with high roughness and low gloss, while the same was identified to be less suitable in the glaze. The glaze formulation without any industrial frits was achieved by altering the proportions of nepheline and feldspar in the matrix. The solar reflectance of the engobe was enhanced by adding 10% of fine-grained zircon. The industrial trial showed that the developed formulation retained its conventional characteristics and superior functional performance in stain and chemical resistance.