In May 2024, researchers at the University of Cambridge published a paper in Nature describing a process that uses recovered cement paste from demolished concrete as a fluxing agent in electric-arc steelmaking. The combined process produces steel and material that can be converted into new Portland cement clinker. If implementable at scale, this could connect two high-emitting material industries—steel and cement—in a way that recovers value from demolition waste rather than landfilling it. The University of Cambridge described the process as producing "zero-emissions cement," a characterisation that requires careful unpacking. The "zero-emissions" label assumes specific system boundaries: the emissions credit from displacing conventional fluxes, the emissions from the electric-arc furnace (which depend entirely on the electricity supply), transport of demolition waste, and the emissions associated with converting the recovered material into clinker all affect the lifecycle result. The peer-reviewed paper in Nature confirms the technical feasibility of the combined process; it does not independently establish that the full production chain is emissions-free. For residential buildings, the pathway to relevance runs through demolition-waste separation quality, the availability of electric-arc steel capacity near where concrete is demolished, and eventual standards recognition for cement produced by this route. The International Energy Agency's cement analysis and the Global Cement and Concrete Association's roadmap provide the broader decarbonisation context. Editorial caution: Keep "zero-emissions cement" in quotation marks or attribute it directly to Cambridge. Explain which assumptions make the zero-emissions claim conditional.