Cement & Concrete — 8% of Global CO₂, Process Emissions, Low-Carbon Alternatives & Decarbonisation Pathways
Cement is the binding agent in concrete, the world's most widely used construction material. Approximately 4.1 billion tonnes of cement are produced annually, generating ~4.1 Gt of CO₂ — roughly 7–8% of global emissions. Unlike most industries where emissions arise from burning fossil fuels for heat, approximately 60% of cement's CO₂ is "process emissions" — CO₂ chemically released from limestone (calcium carbonate) during calcination at 1,450°C, independent of the energy source. This makes cement uniquely hard to decarbonise: even switching to 100% renewable electricity for kilns would leave 60% of emissions untouched. Decarbonisation requires a portfolio approach: lower-clinker cements (LC3, fly ash blends), alternative binders (geopolymers, Roman-type pozzolanic cements), energy efficiency, and ultimately Carbon Capture, Utilisation and Storage (CCUS) on clinker kilns. China produces ~57% of global cement and will determine whether the sector can meet Paris targets.
~4.1 Gt CO₂/yr
Global cement industry CO₂ emissions (2022); ~7–8% of total global CO₂; sector on a "not-aligned" trajectory with Paris 1.5°C (IEA Cement Technology Roadmap 2023)
~0.6–0.8 t CO₂/t cement
Global average CO₂ intensity per tonne of cement produced; was ~0.9 t/t in 1990; efficiency improvements ongoing but offset by volume growth
~60%
Share of cement CO₂ from process emissions (calcination of limestone → lime + CO₂); unavoidable without CCS regardless of energy source
~57%
China's share of global cement production; ~2.4 Gt/yr; India second at ~8%; cement production dominated by the Global South where construction demand is highest
~35–40%
CO₂ reduction possible by switching from OPC (Ordinary Portland Cement) to LC3 (Limestone Calcined Clay Cement); deployable with existing kiln equipment; strong scaling in India
~$100–200/t CO₂
Estimated cost of CCS applied to cement kilns (post-combustion capture); high vs. $50–100 for power sector; but cement CO₂ concentration in flue gas is higher, aiding capture
Cement CO₂ by Source — Global Breakdown (% of ~4.1 Gt CO₂)
Source: IEA 2023 (Cement Technology Roadmap); Habert et al. 2020 (Nature Reviews — low-carbon strategies); GCCA (Global Cement and Concrete Association) 2023 Concrete Future Roadmap; Favier et al. 2019 (Frontiers in Materials — cement decarbonisation).
The Portland Cement Manufacturing Process
Ordinary Portland Cement (OPC) — the dominant binder worldwide — is made by heating limestone (CaCO₃) and clay minerals in a rotary kiln to ~1,450°C. This produces "clinker" (calcium silicate phases, primarily alite and belite), which is then ground with gypsum to produce cement powder. When mixed with water, cement undergoes hydration reactions that create the rigid calcium silicate hydrate (C-S-H) gel that gives concrete its strength.
Raw materials~80% limestone (CaCO₃), ~15–20% clay/shale, small amounts of iron ore and sand
Kiln temperature~1,450°C; one of the hottest industrial processes; requires high-grade thermal energy
Fuel usedCoal (dominant globally, especially Asia); petroleum coke; natural gas; alternative fuels (tyres, waste) ~15% of global thermal energy
Clinker-to-cement ratioGlobal average ~0.72 (72% clinker, 28% supplementary materials — gypsum, fly ash, slag, limestone); down from ~0.85 in 1990; IEA target ~0.60 by 2030
Thermal energy intensity~3.2–3.5 GJ/t clinker (best available); theoretically irreducible minimum ~1.7 GJ/t (calcination enthalpy alone)
Source: IEA 2023; Habert et al. 2020; Taylor 1997 (Cement Chemistry — Academic Press); Andrew 2019 (ESSD — global cement CO₂ emissions).
CO₂ Intensity Trajectory vs. Net Zero Pathway (kg CO₂ / tonne cement)
Source: Andrew 2019 (ESSD); IEA Cement Technology Roadmap 2018 & 2023 update; GCCA 2050 Concrete Future Roadmap 2021; Habert et al. 2020; Miller et al. 2021 (Nature Materials — concrete carbonation sink).
The Calcination Chemistry — Why Process Emissions Are Unavoidable
The core chemical reaction in cement manufacture is calcination:
CaCO₃ → CaO + CO₂ (ΔH = +178 kJ/mol)
Every tonne of pure limestone releases 0.44 t CO₂ by stoichiometry (44/100 molecular mass ratio). Since clinker is approximately 65–67% CaO, and cement is 70–75% clinker, approximately 0.5–0.6 tonnes of CO₂ is embedded as process emission in every tonne of ordinary cement produced — no matter how cleanly the kiln is heated.
Process CO₂ per tonne clinker (calcination)~0.54 t CO₂/t clinker (stoichiometric); actual ~0.52 t CO₂/t (GCCA 2022)
Thermal CO₂ per tonne clinker (fuel combustion)~0.25–0.35 t CO₂/t clinker; can be reduced by fuel switching or electric kilns (when powered by renewables)
Carbonation sink (concrete absorbs CO₂ over lifetime)~0.43 Gt CO₂/yr absorbed globally by concrete in use (Huang et al. 2018, Nature Geoscience); ~10–17% of calcination emissions re-absorbed over 50–100 year lifetime; often excluded from inventories
Source: GCCA 2022; Andrew 2019; Huang et al. 2018 (Nature Geoscience — concrete carbonation); Miller et al. 2021 (Nature Materials).
Global Cement Production by Country/Region (Mt/yr, 2022)
Source: USGS Mineral Commodity Summaries 2023 (global cement production); IEA 2023; Andrew 2019 (ESSD); GCCA 2023; Cements.org data 2022.
Demand Drivers — Why Cement Is Hard to Reduce
Global cement production (2022)~4.1 billion tonnes/year; 4× the 1990 level; primarily driven by China + India urbanisation
China peak cement debateChina may have peaked at ~2.4 Gt/yr (2014–2015 high point); property sector slowdown 2023–2024 causing real contraction; but India, Africa, SE Asia growing fast
Africa's construction boomAfrica cement demand expected to 3× by 2050; largest unmet infrastructure need globally; ~350M people without adequate housing; new cement plants being built with conventional technology
Concrete vs. steel in constructionReinforced concrete is 3–10× cheaper than structural steel in developing countries; no substitution is economically realistic at scale in the Global South
Mass timber / engineered woodCLT (Cross-Laminated Timber) can substitute for concrete in mid-rise buildings (5–20 floors); ~10× lower embodied carbon; but limited to high-value construction; <1% of global floor area
Source: USGS 2023; IEA 2023; UNEP 2022 (Global Status Report — buildings sector); Churkina et al. 2020 (Nature Sustainability — mass timber potential).
Low-Carbon Cement Technologies — CO₂ Reduction Potential vs. OPC (%)
Source: Habert et al. 2020 (Nature Reviews Materials — low-carbon strategies in cement); Lothenbach et al. 2011 (Cement Concrete Research — SCMs); Scrivener et al. 2018 (Cement Concrete Research — LC3); Mehta & Monteiro 2014 (Concrete — microstructure properties materials); Roman concrete studies: Masic et al. 2023 (Science Advances).
Alternative Binder Technologies
LC3 — Limestone Calcined Clay CementReplaces 45–50% of clinker with calcined clay + limestone; 35–40% CO₂ reduction; similar strength; clay is globally abundant; EPFL + IIT Delhi + ETH commercialising; 2020–2025: scale-up in India, Africa, Cuba
Fly ash blended cement (PFA)Replacing 20–35% of clinker with coal fly ash; well-established technology; CO₂ reduction 15–30%; limited by fly ash supply as coal plants close; quality variability an issue
Slag (GGBS) cementGround Granulated Blast Furnace Slag; up to 70% clinker substitution; very low CO₂; limited by global steel production volume; excellent durability; expensive to transport
Geopolymer cementAlkali-activated fly ash or slag; uses no Portland clinker; 40–80% CO₂ reduction; excellent durability; limited by alkali activator supply (NaOH) and specialist expertise; niche use
Novacem / Calix — magnesium oxide cementsMgO from magnesite can carbonate and reabsorb CO₂; potentially carbon-neutral or negative; pre-commercial; Calix (Australia) has LEILAC pilot with HeidelbergMaterials
Roman-style pozzolanic cementsVolcanic ash + seawater — Roman harbours lasted 2,000 years; research at UC Berkeley; tobermorite crystals strengthen over time; not scalable globally but instructive for low-CO₂ durability
Source: Habert et al. 2020; Scrivener et al. 2018; Masic et al. 2023; Lothenbach et al. 2011; Calix 2023 (LEILAC-2 project reports).
CCS Applied to Cement Kilns — Technology Cost Curve ($/t CO₂ captured)
Source: IEA 2023 (CCUS in cement — technology roadmap); Bosoaga et al. 2009 (Energy Procedia — post-combustion capture cement); Hills et al. 2016 (Energy Procedia — LEILAC process); Rootzén & Johnsson 2016 (Energy Policy — CCS costs in cement); Hegerland et al. 2006 (Norcem CCS pilot).
CCS Approaches for Cement
Post-combustion chemical absorption (amine)Solvent scrubbing of flue gas; mature technology from power sector; ~$120–180/t CO₂ for cement; energy penalty ~20–30% of kiln output; Norcem (Norway) pilot since 2013
Oxyfuel combustionBurning fuel in pure O₂ instead of air; exhaust is near-pure CO₂ (easy to capture); requires air separation unit; ~$90–140/t CO₂; CEMEX / LaFarge pilots; retrofitable challenge
LEILAC (Low Emissions Intensity Lime And Cement)Calix proprietary reactor separates process CO₂ (from calcination) from combustion gases; concentrates calcination CO₂ for capture without solvent; ~$50–90/t CO₂ potential; LEILAC-2 pilot 2022 at HeidelbergMaterials Hannover
Direct Separation Reactor (DSR)Electric calciner using resistance heating or microwave; eliminates combustion CO₂; captures pure process CO₂ stream; ~$80–120/t CO₂; requires renewable electricity
Norcem Brevik CCS (Norway)HeidelbergMaterials + Norwegian government; world's first full-scale cement CCS; 400,000 t CO₂/yr; ~$180/t CO₂ (including transport + storage); operational 2024–2025; used for North Sea Longship storage
Source: IEA CCUS 2023; Calix LEILAC-2 reports 2022; HeidelbergMaterials Brevik CCS project 2023; Bosoaga et al. 2009; Hills et al. 2016.
Brevik — the world's first full-scale cement CCS plant is live (2024): HeidelbergMaterials' Brevik cement plant in Norway is the world's first commercial-scale carbon capture project at a cement kiln. The €1.8B project (50% funded by the Norwegian government via Longship CCS programme) captures approximately 400,000 tonnes of CO₂ per year — roughly half the plant's total emissions — using post-combustion amine scrubbing. The captured CO₂ is liquefied and shipped to the Northern Lights offshore storage facility in the North Sea (Equinor-led). It proves the concept works at scale, but at ~€180/t CO₂ abatement cost, it requires substantial public subsidy at current carbon prices. The Norwegian government's willingness to fund it reflects both climate ambition and strategic importance as a reference project for the entire cement industry's decarbonisation roadmap.
Cement Sector CO₂ Reduction by Lever — 2030 Net Zero Scenario (Gt CO₂/yr)
Source: IEA Cement Technology Roadmap 2023 (Net Zero by 2050 scenario analysis); GCCA 2050 Concrete Future Roadmap 2021; Habert et al. 2020; Lehne & Preston 2018 (Chatham House — Making Concrete Change).
Policy Landscape & Industry Commitments
EU Carbon Border Adjustment Mechanism (CBAM)Cement included in CBAM (2023 transition, 2026 full); importers must pay carbon price on embedded emissions; protects EU producers who pay EU ETS; incentivises exporting countries to price carbon
EU ETS cement exposureEU cement within ETS but received ~100% free allocation until 2026; phase-out of free allocation will add €40–80/t CO₂ cost to European producers from 2026–2034
GCCA 2050 RoadmapGlobal Cement & Concrete Association; industry net-zero by 2050 commitment; clinker-to-cement ratio to 0.60 by 2030; CCS to provide 36% of emissions reduction by 2050
HeidelbergMaterials net zero 2050World's second-largest cement producer; Brevik CCS plant; targets net zero scope 1+2 by 2050; ~$2.5B decarbonisation capex commitment
Holcim (Switzerland)World's largest cement company; ECOPact low-carbon concrete; 20% lower embodied carbon on ~40% of sales by 2025; Solidia process (CO₂-cured concrete)
Green public procurementUSA Inflation Reduction Act §60112: Federal Buy Clean Initiative; mandatory low-carbon concrete in federally funded projects from 2024; estimated $2.5B/yr market for low-carbon concrete
Source: European Commission (CBAM regulation 2023); GCCA 2021; HeidelbergMaterials 2023 annual report; IEA 2023; US GSA Buy Clean 2024.