Low-carbon cementitious materials: Scale-up potential, environmental impact and barriers

The construction industry's heavy reliance on ordinary Portland cement (OPC) significantly contributes to global carbon emissions, accounting for 7–9 % of CO₂ emissions. This paper reviews low-carbon cementitious materials (LCCMs) as sustainable alternatives to OPC. Key LCCMs examined include supplementary cementitious materials (SCMs), limestone calcined clay cements (LC3), alkali-activated materials (AAMs), belite-rich Portland cements (BRPCs), ye'elimite-rich cements (YRCs), and non-hydraulic carbonatable binders (CBs). The paper examines the reaction mechanisms, hydration products, and properties of these materials, whereas scalability potential, cost, environmental impact, barriers, and research gaps are also highlighted. LC3 demonstrates high scalability potential due to its similarities with OPC, cost-effectiveness, and the abundant availability of raw materials. Environmentally, AAMs offer the most significant impact reduction, achieving a 40–75 % decrease compared to OPC, followed by LC3 (∼40 %), CBs (∼37 %), YRC (∼20–25 %), and BRPC (∼10 %). However, the costs of AAMs, YRC, and CBs may be higher than OPC and other LCCMs. Technical challenges and research gaps for LCCMs include low reactivity of SCMs, low early-age strength, prolonged setting times, availability of suitable activators, finding compatible superplasticizers, and a lack of long-term performance studies, which shall be further explored in the future. Existing infrastructure may not be adaptable for the new LCCMs, which may require a significant initial investment. Policy barriers are also significant, as updating standards is linked with the satisfactory long-term performance of LCCMs and is hindered by the dominance of OPC market. There is a need of enhanced collaboration efforts among researchers, industry, and policymakers to overcome these technical, economic, and policy barriers, paving the way for sustainable construction practices.