With global warming and climate change, resource recovery of waste through energy-saving and carbon-reduction methods has become a critical issue. The water purification process in water treatment plants generates a large amount of sludge. If this sludge can be recycled and reused, it will not only address environmental issues but also enhance its added value. This study adopts an experimental approach, mixing 60% ground granulated blast furnace slag (GGBS) with 40% sludge (G60S40). Alkaline activation technology is used to activate the GGBS, followed by high-temperature sintering at 300 ℃ (compared to the traditional brick firing temperature of 1000–1200 ℃). The experimental results were compared with the mix ratios of pure GGBS (G100) and pure sludge (S100). The specimens were subjected to tests for compressive strength, thermal resistance, thermal conductivity, and durability. The experimental results show that the G60S40 mixture achieves a compressive strength that meets structural standards (34.14 MPa), exhibits the best thermal resistance, and has the lowest energy consumption. In terms of thermal conductivity, the G60S40 brick can effectively reduce the heat retention effect, significantly improving indoor temperature, while also demonstrating better durability. The method proposed in this study can effectively address environmental issues and the recycling of sludge. This technology can be applied to the development of various building materials. The method proposed in this study can effectively address environmental issues and the recycling of sludge. This technology can be applied to the development of various building materials.