The inadequate thermal insulation of the building envelope contributes significantly to the high power consumption of air conditioners in houses. A crucial factor in raising a building’s energy efficiency involves utilizing bricks with high thermal resistance. This issue is accompanied by another critical challenge: recycling and disposing of waste in a way that is both economically and environmentally beneficial, including using it to fuel industrial growth, in order to reduce the harmful effects of waste on the environment as waste generation in our societies grows. To this end, the current study sought to assess whether integrating a specific amount of eggshell waste as CaCO₃ filler within bricks consistently produces fired clay bricks with desirable thermal insulation capabilities. By systematically investigating the physicochemical and thermal characteristics of bricks doped with varying eggshell content, this work demonstrates how waste materials can be repurposed to produce sustainable construction materials with superior performance. The results highlight significant improvements in thermal conductivity, diffusivity, and effusivity, alongside favorable changes in porosity, bulk density, and mechanical strength. The XRD analysis revealed that once the firing temperature rises, a high insulation feature arises due to siliceous melt formation. EDX analysis gave important insights into the impact of eggshell dopants on the physicochemical parameters of burnt clay bricks. Compared to pristine brick, CEs7% brick constructed with clay and 7 wt% eggshell exhibited a 38.7% loss on dry shrinkage, an enhancement on average pore size of 78.8%, an apparent porosity of 52.7%, a bulk density of 8.3%, and a compressive strength of 57.5%. The reduced shrinkage enhances stability, while increased pore size and porosity improve thermal insulation, making the bricks more durable and energy-efficient. In this regard, the brick containing 10% eggshell that was fired at 1100°C possessed the greatest drop in heat conductivity (i.e., 50%), thermal diffusivity (30%), and thermal effusivity (30%) as compared to the pure one. Given the aforementioned findings, these additions hold the potential to reduce the energy required for both heating and cooling buildings. This brings us to the conclusion that combining eggshell waste to create calcium silicate makes it feasible to be utilized as a thermal insulation material, paving the way for improved construction materials’ performance and sustainability.

This work concerned the development of a unique reduced graphene oxide (rGO) nano-filler to provide innovative opportunities in enhancing the thermophysical performance of clay composite bricks. Whereas, a series of clay–rGO composite bricks were produced, doped with various levels of rGO nanosheets (i.e., 0, 1, 2, 4, and 6 wt% clay). Each clay–rGO composite’s microstructure, shrinkage, morphology, density, porosity, and thermophysical characteristics were carefully investigated, and the thermal conductivity performance was optimized. Incorporation of different levels of rGO NPs to the clay matrix allowed all the peaks intensity to rise relative to the untreated one in the XRD pattern. Meanwhile, the inclusion of these doping resulted in a grew in the crystallite sizes and apparent porosity within the compositions. In this vein, shrinkage fracture of fabricated brick composites varied depending on dopants type and levels during the drying and firing processes. Moreover, there are some changes in chemical compositions, as well as wave shifts, suggesting that functional groups of rGO may have contributed to partially introduce carbonyl groups in clay–rGO composites. Besides, the porous topography and bulk density improved rapidly with respect to the plane of the rGO nanosheets within the composites. The differ-dense microstructure displayed in the SEM micrographs supports these outcomes. Remarkably, clay–(4%)rGO compound not only has an optimum thermal conductivity value (0.43 W/mK), but it also has a high heat capacity (1.94 MJ/m³K). These results revealed the exceptional features of rGO sheets such as large surface area with high porosity within the modified clay composites.