Near-term pathways for decarbonizing global concrete production

Concrete, and specifically its hydraulic cement binder, is essential for global urban development and infrastructure, yet cement production accounts for roughly 8% of global anthropogenic CO2 emissions, largely due to high-temperature clinker production and limestone decarbonation. Achieving net-zero GHG emissions by 2050 requires mitigation in such hard-to-abate sectors. While strategies like alternative fuels, efficiency improvements, CCUS, and supplementary cementitious materials (SCMs) are discussed, the role of structural engineering decisions and material efficiency has been less quantified. This study aims to systematically quantify the mitigation potential from: (i) cement and concrete manufacturing changes, (ii) concrete mixture proportioning (e.g., reducing clinker via SCMs), (iii) structural member design choices (concrete strength, reinforcement ratios, and design code), and (iv) extending service life of structures. Focusing on reinforced concrete, the work integrates these methods to determine cumulative emissions reductions without relying on unproven technologies or wholesale material substitutions.

The paper situates its work within established pathways for decarbonizing cement and concrete, referencing industry roadmaps (e.g., GCCA) and prior academic work on manufacturing improvements, alternative binders and aggregates, and material efficiency. Previous studies have explored aspects such as low-carbon cements, geopolymers, carbonation, and life-cycle assessments of cement production technologies. Work by Habert, Reis, Eleftheriadis, and Marsh examined isolated mitigation strategies or design optimization, while research has highlighted the potential for early-stage design decisions to halve embodied CO2 in structural frames. Dynamic models of the global cement cycle (e.g., Cao et al.) inform stock and flow perspectives relevant to service life and demand. The present study extends this literature by quantifying, in an integrated framework, the combined effect of manufacturing, mixture design, structural design within existing codes, and service life extension on global emissions.

• Scope and baseline: Cradle-to-gate GHG emissions (CO2, CH4, N2O; 100-year GWPs) for cement-based materials (concrete and mortar) per m³ were modeled using established datasets reflecting global practice. Baseline years (1990–2015) draw on GCCA/GNR for kiln efficiency, thermal energy mix, electricity use, and SCM content; electricity mixes from IEA. Non-concrete cement uses were approximated as mortar due to data limitations.
• Future demand projection: Global cement demand (2015–2100) was projected for 10 world regions (North America, Latin America, Europe, CIS, China, India, Africa, Middle East, Developed Asia & Oceania, Developing Asia) using the stock-driven model of Cao et al. with Gompertz functions for per-capita stock saturation, UN medium-variant population projections, and application categories: residential, non-residential, and civil engineering. Service life distributions per region/application were incorporated; sensitivity analyses used UN low/high population variants.
• Concrete mixtures and emissions: A literature-derived dataset of mixtures spanning target strengths (±3 MPa around 20, 35, 50 MPa) with varying water-to-binder ratios, SCM levels, and aggregates informed binder/clinker content distributions and per-m³ emissions.
• Manufacturing interventions: Evaluated ready-to-implement measures: (i) higher kiln efficiency (best-in-class), (ii) switching higher-emitting kiln fuels to natural gas, (iii) meeting electricity needs with wind power, and (iv) combined implementation. CCUS and less-established technologies were excluded.
• SCM scenarios: Modeled increases in SCM content from 2015 average (20.3%) to 30% and 50%. SCMs considered include limestone filler, natural pozzolans (baseline proxy for additional SCM emissions), shale ash, calcined clay, silica fume, fly ash, and ground granulated blast furnace slag; recognizing evolving availability of FA/GGBS and regional NP/LC3 potential.
• Structural design optimization: Linked concrete compressive strength to mixture emissions using Fan’s relationships and linked strength and reinforcement ratio to member environmental impacts following Kourehpaz, adapting for three widely used codes: ACI 318 (US), Eurocode 2 (EU), and IS 456:2000 (India). Case studies included columns (3.5 m height) and slabs (7 m span) designed at crack control, yielding, and ultimate stages. Cross-sectional area and slab depth were allowed to vary with strength and reinforcement ratio within code constraints. Reinforcing steel assumed 80% recycled content with 1.03 kg CO2-eq/kg (sensitivity at 2.29 kg CO2-eq/kg). Other reinforcement (stirrups/mesh) and shear design were excluded for simplicity.
• Service life extension: Modeled the effect of increased durability via SCMs (e.g., FA, GGBS, calcined clays) on delaying chloride-induced corrosion in coastal regions, thereby extending in-use lifetimes. Scenarios included up to 50% SCM replacement in coastal applications, with threefold extension for buildings and fourfold for infrastructure, applied via stock dynamics to reduce future cement demand. While carbonation was discussed, chloride ingress was used as the illustrative durability mechanism; carbonation impacts were not included in the longevity model.
• Cumulative scaling: Member-level optimizations (for buildings) were scaled using simplified building models (average 3.5 m story height) relating volumes of vertical (columns) and horizontal (slabs at ultimate) members; civil infrastructure was not assumed to be reinforced like buildings. Global mitigation was computed by aggregating (i) manufacturing improvements, (ii) SCM substitution, (iii) design optimization (strength/rebar), and (iv) service life extension, with linear uptake of (i)–(iii) to 100% by 2100 and dynamic uptake for (iv). Assumed 20% of concrete-related GHG stems from applications outside slabs/columns. Figures were reproducible via provided code.

• Manufacturing interventions (per m³, cradle-to-gate): kiln efficiency improvement ~1% reduction; switching kiln fuels to natural gas ~15%; wind electricity ~6%; combined ~20% reduction. These are consistent with industry roadmaps and demonstrably deployable technologies.
• Strength–emissions relationship: Without manufacturing changes, median per-m³ emissions for a 50 MPa mix are ~75% higher than for a 20 MPa mix (≈+140 kg CO2-eq/m³); with manufacturing improvements, the median difference remains ≈130 kg CO2-eq/m³. Emissions correlate strongly with clinker content (R² = 0.98).
• Mixture selection within strength classes: Wide variability in emissions at fixed strength due to different binder/clinker contents: ~20% spread at 20 MPa, ~40% at 35 MPa, ~55% at 50 MPa. Selecting lower-emission mixtures within the same strength yields 25th-percentile values 4.5–9% below medians depending on strength class.
• Structural design optimization: For slabs designed at yielding/ultimate, highest reinforcement ratio with lowest concrete strength minimized emissions; for crack-control slabs, minimal reinforcement with low strength minimized impact. For columns, minimal reinforcement ratio with highest concrete strength minimized impact. Differences between highest/lowest-emission compliant members were large: columns showed 60–90% spreads depending on code; slabs at ultimate showed 58–93% spreads. Designing slabs per Eurocode 2 and columns per ACI-318 yielded the lowest impacts across codes.
• Member-to-system scaling: Using a simplified unit (1 slab + 4 columns), selecting optimal strength/rebar combinations can cut slab emissions by ~20–25%, column by ~18–22%, and unit by ~23% under baseline steel; with higher-impact steel, reductions were ~20% (slab), ~30% (column), and ~21% (unit).
• Global cumulative impacts (2015–2100): • All manufacturing improvements: ~21% reduction in GHG relative to business-as-usual. • SCM substitution: ~11% reduction at 30% SCM; ~34% at 50% SCM. • Design optimization of building members (strength/rebar): ~18.5% reduction. • Service life extension via improved durability (up to 3x/4x): reduces world cement demand by ~47.1% and avoids ~175.7 Gt CO2-eq. Even at 50% regional applicability, reductions ~25% (~90 Gt) are possible. • If all countries adopted lowest-impact code choices (Eurocode 2 slabs, ACI-318 columns), an estimated ~67 Gt CO2-eq reduction (2015–2100) could be achieved for the simplified building unit model.
• Overall potential: Combining strategies can reduce GHG emissions from cement and concrete production by over 76% by 2100 and cut cement demand by up to 65%, substantially curbing multiple environmental burdens.

The findings demonstrate that substantial GHG mitigation is achievable within existing materials, practices, and design codes by prioritizing material efficiency alongside mature manufacturing improvements. Emissions scale strongly with clinker content and member design choices; thus, performance-based mixture specifications and environmentally informed structural optimization can deliver significant reductions without capital-intensive technology shifts. Service life extension via durable binders provides the largest long-term benefit by curtailing future cement demand through better utilization of in-use stock. Incorporating environmental impact assessment into codes, specifications, and procurement can guide engineers and stakeholders toward designs that meet performance while minimizing embodied emissions. Given the immediacy and feasibility of these measures, rapid adoption can meaningfully contribute to net-zero trajectories in a sector where process emissions are otherwise hard to abate.

This study integrates manufacturing, mixture proportioning, structural design optimization, and service life extension to map near-term, high-impact pathways for decarbonizing global concrete. Readily deployable manufacturing changes can deliver ~20% per-m³ reductions; optimized mixture and member design can achieve sizable additional savings; and extending service life via SCM-enhanced durability yields the largest cumulative reductions by lowering future cement demand. Collectively, these strategies can reduce sectoral GHG emissions by over 76% by 2100, while improving resource efficiency and lowering other environmental impacts. Future research should: (i) operationalize environmental criteria in design codes and procurement; (ii) refine regional assessments of SCM availability and durability performance (including carbonation and multi-degradation mechanisms); (iii) expand structural system coverage (e.g., multi-span slabs, pre/post-tensioned systems, shear design, other member types); (iv) better characterize reinforcing steel pathways and their decarbonization; and (v) integrate construction, use-phase, and end-of-life stages to capture full life-cycle impacts and rebound effects.

• Scope limited to cradle-to-gate emissions; construction, use-phase, and end-of-life impacts were assumed equivalent across alternatives and excluded.
• CCUS and other emerging technologies were not modeled; only readily deployable manufacturing improvements were considered.
• Structural analysis simplified to columns and slabs (bending), omitting shear design and secondary reinforcement (stirrups/mesh), and using a simplified building representation when scaling to global impacts; civil infrastructure reinforcement optimization was not modeled.
• Reinforcing steel assumptions (80% recycled content, 1.03 kg CO2-eq/kg) may vary regionally; sensitivity considered a higher-impact case but uncertainty remains.
• Service life extension modeling emphasized chloride ingress in coastal environments; carbonation and other deterioration mechanisms were not fully integrated; actual retrofitting/maintenance needs and functional obsolescence may alter net benefits.
• SCM scenarios assume broad availability and adoption (30–50% replacement), with additional SCM emissions approximated by natural pozzolans; regional supply constraints and performance variability introduce uncertainty.
• Mixture dataset and code implementations represent typical practice but cannot capture all regional or project-specific designs; member optimization outcomes may differ for alternative systems (e.g., multi-span, pre/post-tensioned).
• Projections use UN medium-variant population and pre-COVID saturation assumptions; deviations in demographic/economic trends will affect demand and emissions trajectories.