Measuring embodied carbon in concrete: what the numbers leave out
A lower kgCO₂e per cubic metre is a good start. It is not the same as a lower-carbon structure.
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- Ser Civil
Cement production is responsible for roughly 7 to 8 percent of global CO₂ emissions, and concrete is the main reason. It is no surprise that the industry's first response has been to lower the carbon intensity of the mix itself, through supplementary cementitious materials such as slag, fly ash and calcined clays.
The functional unit problem
Most comparisons are expressed per cubic metre of concrete. But nobody owns a cubic metre of concrete. Owners own a bridge deck that must carry traffic for decades. A mix with 30 percent less carbon that needs replacing 15 years earlier may emit more over the life of the structure.
The right functional unit is not a volume of material but a service delivered over time.
Three things to include
Quantity: a stronger mix can reduce member sizes and total volume.
Durability: the expected service life under the actual exposure class.
Maintenance: the carbon cost of repairs, overlays and traffic disruption.
A simple worked comparison
Option | Mix intensity (kgCO₂e/m³) | Expected life | Carbon per year of service |
|---|---|---|---|
Conventional deck | 360 | 35 years | Baseline |
Low-clinker deck | 245 | 35 years | 32% lower |
Low-clinker with membrane | 260 | 50 years | 50% lower |
The point is not that one option always wins. It is that a carbon comparison without a durability model is incomplete, and a durability model without carbon accounting misses half of the decision.
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