Low-carbon cementitious materials are a family of hydraulic binders and concrete constituents formulated to reduce the embodied carbon dioxide emissions associated with cement production, relative to ordinary Portland cement (OPC), while retaining the binding function required for structural concrete ^[1]. Emission reduction is achieved primarily by lowering the Portland-clinker fraction through partial replacement with supplementary cementitious materials such as fly ash, ground granulated blast-furnace slag, silica fume, metakaolin, and calcined clay, or by substituting alternative chemistries — alkali-activated binders, calcium sulfoaluminate cements, belite-rich cements, and magnesium-based cements — that require lower calcination temperatures or avoid limestone decarbonation ^[2]. Because OPC production emits CO2 both from the calcination of calcium carbonate and from fuel combustion in the kiln, the “low-carbon” designation is defined by a reduction in life-cycle greenhouse-gas emissions per unit of binder, rather than by a single fixed composition or strength class ^[3]. The category is distinguished from conventional blended cements by the magnitude of clinker substitution and by explicit targeting of embodied-carbon reduction.