Achieving sustainable cities requires materials that move beyond conventional carbon reduction, offering solutions to escalating urban heat and energy demands. This work examines two distinct pathways for developing carbon-negative infrastructure using waste-derived cementitious systems. One strategy centers on alkali-activated steel slag pressed blocks, leveraging ambient carbonation to create composites that efficiently capture CO2, exhibit enhanced solar reflectivity, and possess robust, durable microstructures—attributes enabled by synergistic carbonation and pozzolanic reactions. The second approach introduces carbonated aggregates sourced from food industry by-products, such as periwinkle shell powder, which are embedded into cementitious matrices to boost mineralization and radiative cooling in carbon-cured materials. Both approaches repurpose industrial waste to deliver sustainable, next-generation building materials while addressing both embodied and operational carbon challenges. Performance results demonstrate that these systems can achieve significant passive cooling in urban environments, with pavements and roofs registering up to 16 °C lower surface temperatures under peak solar loading compared to conventional solutions. Collectively, they offer scalable pathways to improved energy efficiency and public health within the evolving landscape of modern infrastructure.