Cement Energy & Environment

9 in the concrete supply chain come from cement manufacturing[10][11]. Cement’s calcination reaction (heating limestone to make clinker) emits CO 2 (~40–50% of cement’s total emissions), and fossil fuels for heating contribute another ~40%[10]. Thus Portland cement production alone accounts for roughly 8% of total anthropogenic CO 2 [10]. Meanwhile, demand for concrete is rising: global population is projected to reach 10 billion by 2050 with 60% urbanized by 2030[12], driving a >30% increase in cement output by mid-century[13]. 1940 Africa Asia Europe North America South America World 0.00E+00 2.00E+08 4.00E+08 6.00E+08 8.00E+08 1.00E+09 1.20E+09 1.40E+09 1.60E+09 1.80E+09 1950 1960 1970 1980 1990 2000 2010 2020 2030 Co 2 Emissions from Cement (Kg/year) LITERATURE REVIEW / BACKGROUND This combination of high emissions and growing demand makes decarbonization urgent. However, cement production is notoriously hard to decarbonize: ~70% of its CO 2 arises from intrinsic processchemistry(limestonecalcinationandhigh- temperature heating) that cannot be eliminated by switching to green electricity[14]. Moreover, the industry is capital-intensive with slim margins and longproject lifetimes, deterring rapid change[15]. In short, meeting climate goals requires transforming cement technology, materials, and policies. Figure 1. CO 2 emissions from cement production by region over time. Global emissions rose sharply from ~0.5 Gt in 1970 to ~1.6 Gt in 2022[11], primarily driven by Asia. Current global cement-related CO 2 emissions are about 1.6 Gt/year[11]. As Figure 1 shows, emissions have grown especially in Asia, which accounts for the majority, followed by North America and Europe (smaller contributions). On the supply side, most cement plants burn coal, petcoke or natural gas for heat: around 80% of kiln fuel remains fossil- based[16]. Fuel switching (to biomass or waste) can reduce emissions, but the impact is modest when emissions from calcination remain. On the materials side, blendingclinkerwithsupplementary cementitious materials (SCMs) is common. Inert fillers like limestone and quartz, plus reactive SCMs such as blast furnace slag, fly ash, and calcined clays, can replace some clinker[17]. For instance, in many countries up to 30–50% of cement is now limestone or slag[17]. However, conventional SCMs are becoming scarcer: for example, a study notes a ~30% supply shortfall of fly ash in the U.S. as coal- fired power declines[18]. Environmental regulations also constrain new SCMs because industrial by- products may contain toxins[19]. Thus simple substitutionalonecannot fullydecarbonizecement. In practice, global cement carbon intensity has fallen only ~20% since 1990 by efficiencies, clinker reduction, and alternative fuels[20], indicating that existing methods are reaching limits. More radical “next-generation” materials are under study. Limestone–calcined clay cements (e.g. LC³) leverage abundant clays and modest limestone to cut clinker up to ~50%[5], yielding