To choose a lower-carbon concrete mix, first define the project’s strength, durability, placement and schedule requirements. Then ask local ready-mixed concrete producers for proposals that meet them, with mix-specific Environmental Product Declarations (EPDs) where available. Compare the proposals’ global warming potential (GWP) on a consistent basis against an appropriate regional or industry benchmark. The best choice is the lowest documented-GWP mix that can be reliably supplied, placed and accepted under the project’s requirements—not simply the mix with the highest supplementary cementitious material (SCM) percentage.
How to choose a lower-carbon concrete mix for a construction project
Treat this as a performance-and-procurement decision, not an ingredient-shopping exercise. A mix must meet the design and service requirements, work with the construction sequence, and have evidence supporting its carbon comparison. For projects with several concrete classes, evaluate the portfolio as well as individual mixes: the best opportunity to reduce total GWP may differ by application.
- Set the performance envelope. Document required strength and acceptance age, exposure conditions, specified durability properties, placement and finishing needs, curing assumptions, construction sequence, and any high-early-strength or cold-weather requirements. Confirm applicable code and specification constraints with the project engineer.
- Consult local producers early. Ask which cements, blended cements, fly ash, slag cement, silica fume, natural pozzolans and other qualified materials are available and familiar to the producer. A specification that calls for a material the local supplier cannot source or routinely use may narrow options or complicate production.
- Request comparable proposals. For each mix that meets the performance envelope, request its GWP and supporting EPD when available. Ask for the declaration’s declared unit, product category rules, geographic and production applicability, and validity period.
- Compare on a consistent basis. Use the same units and compatible EPD scope and rules for proposals and benchmarks. Prefer product-specific evidence when available; use an industry-wide EPD or regional benchmark as context where it is not.
- Assess the concrete portfolio. Match proposals to the relevant strength class and application, then consider quantity-weighted GWP across the project. A whole-building life-cycle assessment (LCA) can help establish a carbon budget instead of imposing an identical limit on every class.
- Resolve field and schedule questions. Review strength development, set, finishability, curing, formwork release and opening dates against the actual construction plan. Confirm trial batches, acceptance testing, submittals, EPD version and change-control expectations before procurement.
- Check applicable rules. Identify any owner criteria, building-code provisions, public procurement requirements or rating-system rules that govern the project. Use the baseline and calculation method for the project’s jurisdiction and program.
What to compare in concrete proposals
| Comparison | What to request or verify | Why it matters |
|---|---|---|
| GWP and EPD basis | Mix-specific GWP, declared unit, product category rules, geography, validity and applicable EPD version. | Different units, scopes or declaration rules can make a simple number-to-number comparison misleading. |
| Strength and durability | Required strength, acceptance age, exposure-related durability and any specified permeability or other properties. | A carbon improvement is not suitable if the mix fails design or service requirements. |
| Schedule | Early-age and later-age strength development, curing needs, set, formwork release and dates when the concrete must carry loads or be opened to service. | Strength timing and construction milestones affect which mix designs are practical. |
| Supply and production | Locally available cementitious materials, producer experience, batching capability, consistency and transport considerations. | Local availability and familiarity affect whether a proposal can be supplied dependably. |
| Placement and finish | Pumpability, slump retention, finishability, set behavior and the weather plan. | A mix must perform in the intended placement conditions, not just satisfy a paper specification. |
| Project impact | Concrete quantities by class and quantity-weighted GWP compared with a suitable project benchmark or budget. | Portfolio analysis can reveal reductions that a rigid per-class cap may overlook. |
| Compliance | Applicable owner, code, procurement or rating-system criteria and required EPD documentation. | Targets and calculation methods depend on the location and governing program. |
How to compare concrete EPDs and benchmarks
An EPD is a third-party-verified environmental report prepared under a product category rule. It is evidence for evaluating a product’s reported impacts, but it is not by itself a guarantee that one mix is preferable for a particular project. NRMCA’s EPD resources distinguish product-specific declarations from industry-wide EPDs and benchmarks; a product-specific EPD can better reflect a producer’s facility and mix when one is available.
- Confirm what product the declaration represents. Check whether it covers the proposed mix, a producer’s product group, or an industry average. Do not treat a broad industry declaration as if it were a measurement of a particular batch or project mix.
- Check the declared unit and rules. Verify the unit, product category rules and geographic applicability before comparing GWP values. If those bases differ, request clarification or use a benchmark that supports a fair comparison.
- Check dates and validity. EPDs and benchmarks have editions and validity periods. NRMCA’s resource page links to distinct dated editions; the Lower-Carbon Concrete Task Force resource directory identifies the U.S. industry-average EPD v3.2 from 2023. Confirm which edition is applicable to the proposal and project.
- Use tools as support, not as a substitute for review. The Carbon Leadership Forum describes EC3 as a free cloud-based tool for benchmarking and assessment using digital third-party-verified EPDs and project material quantities. Its comparisons can support design and procurement, but EPD interpretation still requires attention to material-specific life-cycle and performance issues.
For a project with multiple concrete classes, NRMCA recommends using LCA to assess benchmark and proposed mixes and to set a building-level carbon budget. That lets the team target reductions across the concrete portfolio while retaining mixes that meet each application’s requirements.
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How SCMs affect mix choices
Fly ash, slag cement, silica fume, natural pozzolans and blended cements may be part of a lower-carbon strategy. Their suitability depends on the mix’s performance, local supply, producer experience, exposure conditions and schedule. NRMCA’s November 2021 specification guide advises against unnecessarily restricting SCM types or setting inflexible minimum and maximum amounts: such limits can restrict supplier options and innovation.
Strength development is one important trade-off. NRMCA’s 2022 carbon-footprint guide gives examples of around 30% fly ash or slag replacement for applications with high early-strength needs, and up to 70% for some applications without those needs; it also describes testing at 56 or 90 days rather than 28 days in some cases. These are illustrations in that guide, not universal design limits or automatic permissions. The project team must establish allowable materials, proportions and acceptance ages for the actual materials, exposure class, structural design, code and construction schedule.
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Where exposure-related provisions restrict materials or proportions, confirm the governing requirements rather than assuming a general SCM allowance applies. NRMCA’s specification guidance specifically discusses restrictions for certain continuously moist, freezing and deicing exposures.
Why the project’s total concrete impact matters
A single carbon ceiling for every concrete class can be a poor fit if classes have different strength, exposure or schedule requirements. NRMCA’s The Top 10 Ways to Reduce Concrete’s Carbon Footprint advises: “Resist the temptation to set carbon footprint limits for individual classes of concrete.” The guide recommends using whole-building LCA to set a carbon budget for the building’s concrete. In practice, compare the quantities and GWP of proposed mixes across their intended uses, while keeping each class within its performance requirements.
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Jurisdiction-specific targets: the NSW example
Carbon targets, baselines and calculation rules are not universal. New South Wales’ 2025 Low Carbon Concrete Specifications guidance sets the following minimum embodied-carbon reduction targets for the structural concrete types it covers. It allows adjustment based on project and regional supply capability; these are NSW guidance values, not general benchmarks for other locations.
| Structural concrete in NSW guidance | Minimum reduction target |
|---|---|
| Cast-in-situ concrete | 45% |
| Precast and prestressed concrete | 35% |
The same NSW guidance prefers EPDs and provides fallback greenhouse-gas intensity factors when EPDs are unavailable. It gives the following factors, sourced there to AusLCI; use them only within the guidance’s specified calculation context.
| Material | NSW fallback intensity factor |
|---|---|
| Fly ash | 19.8 kg CO2e/tonne |
| Slag | 192 kg CO2e/tonne |
| Portland cement | 967 kg CO2e/tonne |
For a project elsewhere, use its governing jurisdiction’s benchmark, policy method and procurement rules rather than importing NSW targets or factors.
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Common mistakes to avoid
- Choosing by SCM percentage alone instead of comparing documented GWP and required performance.
- Comparing EPD values without checking units, scope, category rules, geography and validity.
- Setting the same carbon cap for every concrete class without considering the project’s total impact and distinct performance needs.
- Specifying a cementitious material that local producers cannot source or are unfamiliar with.
- Assuming a digital comparison tool replaces technical review of EPDs and project requirements.
- Applying a regional policy target or emissions factor as though it were a universal standard.
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