Concrete & Cement Embodied Emissions

What Counts as Embodied Carbon in Concrete and Cement

Embodied carbon is the greenhouse-gas emissions associated with producing, transporting, installing, maintaining, and disposing of a material — everything except the operational energy the finished building consumes in use. For concrete, the dominant share sits at the very start of that chain, in the manufacture of the cement binder. The methodology that follows resolves a single question into a defensible number: how much CO₂e is attributable to a given volume of concrete, and over which life-cycle stages.

1.1 Cradle-to-gate (A1–A3)

The cradle-to-gate boundary covers raw-material supply (A1), transport to the manufacturing plant (A2), and manufacturing (A3). For ready-mix concrete this captures cement production, aggregate extraction, admixtures, water, batching, and the energy of the plant. The A1–A3 figure is the headline embodied-carbon value cited on a product Environmental Product Declaration (EPD) and is the number most corporate inventories and whole-building assessments start from. Under the ISO 14040/14044 LCA framework, cradle-to-gate is one declared boundary among several — the calculation is only meaningful once the boundary is stated.

1.2 Beyond the gate (A4–A5, B, C, D)

A complete material assessment extends past the factory gate: transport to site (A4), installation including wastage and formwork (A5), in-use stages such as repair and replacement (B1–B5), end-of-life demolition and processing (C1–C4), and benefits or loads beyond the system boundary — reuse, recovery, and recycling potential (module D). Concrete has unusual behaviour in two of these: it slowly reabsorbs CO₂ over its service life through carbonation (a B/C-stage credit under EN 16757), and crushed concrete carries a module D reuse credit as secondary aggregate. Both are addressed in §8.

1.3 The Scope 3 mapping

Where embodied carbon lands in a corporate GHG inventory depends on what the concrete is for. Concrete purchased as an input to a product the organisation sells is Scope 3 Category 1 (purchased goods and services). Concrete embodied in the organisation’s own buildings and infrastructure — capital assets — is Scope 3 Category 2 (capital goods). The GHG Protocol Scope 3 Standard draws this line on the use of the asset, not on the material. The MasterBrain tags ÖKOBAUDAT embodied rows scope3_cat2 by default precisely because most building-material embodied carbon is capital-goods carbon.

Why Cement Carries the Footprint

Concrete is roughly 10–15% cement by mass, yet cement is responsible for the overwhelming majority of its embodied carbon. The reason is chemical, not merely energetic. Producing Portland cement clinker releases CO₂ from two distinct sources, and one of them cannot be removed by switching fuels.

2.1 Calcination chemistry

The core reaction is the thermal decomposition of limestone (calcium carbonate) into lime and carbon dioxide:

2.2 Process CO₂ versus thermal CO₂

The second source is the fuel burned to reach the ~1,450 °C clinkering temperature — thermal CO₂. For conventional clinker the split is approximately 60% process, 40% thermal. Decarbonising the kiln fuel (biomass, hydrogen, electrification) addresses only the thermal portion; the process portion can be cut only by making less clinker per tonne of cement — which is exactly what supplementary cementitious materials (SCMs) do.

The clinker process emission factor is itself a live, regulated value. Under the EU Carbon Border Adjustment Mechanism, default grey-clinker factors are published per producing country — for example, India-origin grey clinker carries a direct emission factor of 1.39 tCO₂e per tonne, against Korea-origin at 0.88 tCO₂e per tonne. The spread between origins reflects kiln efficiency and grid carbon intensity, and it matters for any importer (see §12).

Governing Standards Stack

These element-level factors roll up into the building-scale whole-building LCA methodology and the RICS whole life carbon methodology; for design-option comparisons, see the material-substitution methodology.

Concrete embodied-carbon methodology nests several standards. They do not compete — each supplies a different input to the same audit-grade output: the scientific and LCA rules at the bottom, the product-declaration rules in the middle, and the building- and portfolio-level assessment rules on top.

Two adjacent frameworks are worth naming even though they are not the primary basis here. The GHG Protocol Product Standard governs corporate product-footprint reporting and reconciles to the same boundary logic, and the WBCSD Pathfinder Framework standardises primary-data exchange between supply-chain tiers — increasingly the route by which a concrete supplier’s EPD reaches a buyer’s inventory.

The Calculation Model and Unit Discipline

4.1 The core equation

At its base the calculation is deliberately simple. The complexity lives in sourcing the factor and matching its unit, not in the arithmetic.

4.2 Unit discipline — the most common failure

Concrete factors are quoted on three incompatible bases, and mixing them is the single most frequent error in embodied-carbon work. The MasterBrain stores each row with its own unit, and that unit must be read before the factor is used — never assumed.

Concrete Emission Factors by Grade

Cradle-to-gate (A1–A3) factors for ready-mix concrete rise with compressive-strength grade, because higher-strength mixes carry more cement per cubic metre. The values below render live from the MasterBrain ÖKOBAUDAT 2024 dataset — each is the module A1–A3 factor in kg CO₂e per m³. The grade ladder is the dataset’s actual ladder: note it steps from C35/45 directly to C45/55, with no C40/50 row.

The same grades in cubic yards, with worked examples, are in the carbon footprint of concrete.

Cement, Binders and SCM Substitution

Because clinker is the carbon, the binder choice dominates the result. The methodology treats cement type as the primary design lever and renders each binder family’s factor live. Replacing a portion of Portland clinker with a supplementary cementitious material lowers the embodied carbon roughly in proportion to the clinker displaced — the dominant effect being the avoided process CO₂ from §2.

6.1 Cement types (live factors)

The MasterBrain stores cement-binder factors under the materials.concrete.cement.* prefix (note: a materials.cement.* family does not exist). Each value is the module A1–A3 cradle-to-gate factor; read the row’s unit before use.

6.2 GGBS and fly ash — keyed, live substitution

Slag and fly ash are by-products of steelmaking and coal power, and how much of that upstream burden they carry is an allocation choice. The MPA’s Fact Sheet 18 publishes economic allocation as its default (GGBS 0.155, fly ash 0.022 kg CO₂e/kg) alongside by-product values that carry almost none of it (GGBS 0.075, fly ash 0.001). The choice moves a 50% GGBS mix from 179 to 165 kg CO₂e/m³, so state which one you used (see §11.1).

The cement rows above are not a like-for-like ranking. In ÖKOBAUDAT the CEM I and CEM III/A rows are representative German industry datasets, while the CEM II/A and CEM IV rows are generic datasets from a different family, which is why CEM II reads higher than CEM I. To size the binder lever, compare mixes on one consistent set of factors. On the MPA’s UK factors (CEM I 0.84, GGBS 0.155, fly ash 0.022, calcined clay 0.274 and limestone 0.044 kg CO₂e/kg), a C30/37 mix with 340 kg of binder per m³ gives:

Aggregates (1,050 kg coarse, 760 kg fine at 0.0052) and 170 kg of water add 9.6 kg CO₂e/m³ to every row. The same figures come out of the concrete embodied carbon calculator. High-GGBS mixes trade embodied carbon against slower early strength gain — a buildability constraint, not an accounting one.

6.3 LC3 and calcined clay

Limestone calcined clay cement (LC3) replaces a large fraction of clinker with calcined clay and limestone, and is one of the most promising routes to lower-clinker binders at scale. The calcined-clay constituent itself appears in the CBAM dataset — for example a catch-all-origin calcined clay carries a direct factor of 0.21 tCO₂e per tonne, well below grey clinker. LC3 is modelled from its constituents rather than as a single binder factor:

Life-Cycle Modules A1–D

A whole-life view assigns emissions to standardised modules under EN 15978. Embodied carbon is the sum of the production, construction, use (excluding operational energy/water B6/B7), and end-of-life modules, with module D reported separately as a benefit beyond the system boundary.

Biogenic Carbon and Carbonation

Concrete has no biogenic carbon of its own, but two related effects must be handled correctly because they are routinely mis-stated.

8.1 Carbonation (recarbonation)

Over its service life, and accelerated once crushed at end of life, hardened concrete reabsorbs atmospheric CO₂ as the calcium hydroxide in the cement paste reverts toward carbonate — chemically the partial reverse of calcination. EN 16757 provides the method to quantify this uptake as a credit in modules B and C. The credit is real but bounded: it recovers only a fraction of the original process CO₂, depends on exposure conditions and surface area, and must be modelled, not assumed. The uptake stoichiometry uses the same molecular ratio as biogenic CO₂ accounting — 3.667 kg CO₂ per kg of carbon — though applied to mineral carbonation rather than biomass.

8.2 Why it is not an offset

Carbonation uptake is an inventory adjustment within a declared boundary, not a tradable offset and not a substitute for reducing clinker. Counting a speculative future carbonation credit against present-day production emissions — particularly before the concrete exists — is a misuse of the method. Under the ISO 14040/14044 permanence logic mirrored in the LCA keyspace, biogenic and uptake credits are only creditable where storage is demonstrable over the relevant horizon.

Data Quality Hierarchy

The factor sourced for any concrete element should follow a strict preference order. Each step down trades specificity for availability, and the step taken must be documented per material in the assessment.

Worked Example: RC Frame, CEM I versus 50% GGBS

A complete worked example with all arithmetic shown. Values are fixed at the publication snapshot date — this is an audit record, not a live calculation. It compares the cradle-to-gate (A1–A3) embodied carbon of a reinforced-concrete frame element specified in CEM I versus the same element in a CEM III (50% GGBS) mix, illustrating the binder lever from §6.

Inputs, formula, and result reconcile: 120 × 295.18 = 35,421.6; 120 × 178.73 = 21,447.6; the difference is 13,974.0 kg CO₂e, a 39.45% cradle-to-gate reduction from the binder swap alone, before any A4–C or module D consideration. The reinforcement steel embodied carbon is a separate line (see §11.3) and is not included in these concrete figures.

Allocation and Edge Cases

11.1 By-product allocation (GGBS, fly ash)

GGBS and fly ash are by-products of steelmaking and coal power. How much upstream burden they carry into the concrete system is an allocation decision. The cut-off convention common to EN 15804 EPDs assigns them only their own processing and transport — the position that underpins the large reductions in §6. An economic or mass allocation that loaded part of the steel or power burden onto the SCM would raise the result substantially. The chosen convention must be declared; results computed under different conventions are not comparable.

11.2 Recycled aggregate

Concrete made with recycled aggregate (crushed from demolition) carries the processing burden of crushing and grading but avoids virgin extraction. The corresponding module D reuse credit accrues to the donor building’s assessment, not the recipient’s — claiming it in both is double-counting. Trace which assessment owns the credit.

11.3 Reinforcement boundary

Reinforcing steel (rebar) is embodied carbon, but it is not concrete and must not be folded into the concrete factor. Rebar is assessed separately — typically via steel EFs reflecting primary versus electric-arc-furnace recycled routes — and reported as its own line in the element total. Conflating the two is a frequent source of both under- and over-counting depending on which generic factor is misapplied. A reinforced element’s embodied carbon is concrete (per m³) plus steel (per kg/tonne), computed independently and summed.

11.4 Multi-output kilns and declared units

Cement plants co-produce clinker, blended cements, and sometimes captured heat. EPD factors already resolve this allocation at the product level, which is why a product EPD is preferred over reconstructing the figure from clinker EFs. Equally, an EPD’s declared unit (often 1 m³ or 1 tonne of a specified mix) must match the quantity basis used — a declared-unit/functional-unit mismatch is a silent error.

CBAM Intersection

For organisations importing clinker or cement into the EU, the same embodied-carbon question carries a regulatory obligation. The EU Carbon Border Adjustment Mechanism requires importers to declare the embedded direct emissions of cement-sector goods (CN heading 2523, plus calcined clay under 2507) and, in the definitive period, to surrender certificates against them.

Where verified producer-specific data is unavailable, the importer uses the published default factor for the producing country — or the catch-all oth origin where the country is not separately listed. These are live MasterBrain values:

Error Traps with Magnitudes

Each trap below produces a specific, quantifiable distortion. Magnitudes are illustrated against the §10 worked example (120 m³ C30/37) where applicable.

Implementation Workflow

A defensible concrete embodied-carbon assessment follows the same sequence every time. Treat the steps below as a pre-publication checklist.

1. Declare boundary and unit. State A1–A3, A1–C4, or A1–D, and whether figures are per m³, per kg, or per tonne. Everything downstream depends on this.
2. Take off quantities. Concrete volume per element (m³) from drawings or BIM; binder content (kg/m³) from the mix design; reinforcement mass (kg) separately.
3. Source factors by tier. Product-specific EPD first; regional generic (§5 ladder) next; ICE; CBAM default only for declarations. Record the tier per element.
4. Match units. Reconcile each factor’s factor.unit against its quantity unit before multiplying. This is the step that catches the order-of-magnitude error.
5. Apply the binder lever. Where design allows, evaluate CEM III (GGBS) or CEM IV (fly ash) against the CEM I baseline using the live deltas (§6).
6. Compute per element, then sum. Concrete line plus separate reinforcement line per element; aggregate to the building under EN 15978.
7. Report module D separately. Reuse/recovery credits as their own line — never netted into A1–C.
8. Handle CBAM in parallel if importing. Run the regulatory declaration on the CBAM basis independently of the inventory assessment.
9. Document assumptions. Allocation convention, EPD vintages, carbonation treatment, and any fixed value (e.g. LC3) with its source.

Methodology Metadata — for LCA Documentation

Copy into the methodology statement of an embodied-carbon or whole-building assessment for transparency. Adjust the data-tier line to reflect the actual sourcing used.

Frequently Asked Questions