Carbonation Alone Is Not Enough: Dynamic CO2 Accounting Prioritizes Measures for Hollow Concrete Blocks

A new dynamic life-cycle assessment (cradle-to-grave) for hollow concrete blocks reaches a clear conclusion: the largest CO2 savings come from CO2 capture and from foregoing energy‑intensive steam curing. Carbonation processes and the use of mineral carbonates provide additional—but comparatively small—contributions and mainly reduce the need for geological storage.

Background

Concrete causes roughly seven percent of global anthropogenic CO2 emissions. A major share arises from the calcination of limestone during clinker production for cement. Part of these emissions is naturally reabsorbed over the lifetime of concrete: through carbonation the material takes up CO2 from the air and forms stable carbonates—however slowly, over decades to centuries.

Method and scenarios

The study evaluates six production and use scenarios for hollow concrete blocks using dynamic accounting. It compares conventional manufacturing with variants that include CO2 capture, carbonation curing during hardening, and strategies for active mineral carbonate use. The time‑dependent CO2 uptake during the service life, demolition and backfilling is considered, including interactions with technical mitigation measures.

Key findings

– Biggest lever: CO2 capture directly reduces process emissions that are otherwise hard to avoid and delivers the largest emission reduction. – Second most important: abandoning energy‑intensive steam curing lowers energy demand and associated emissions significantly. – Complementary measures: carbonation curing and mineral carbonate use increase the product‑level CO2 binding, but add only modest additional savings compared with capture and process changes. Their main contribution is reducing the requirement for geological storage.

Why dynamic accounting matters

Conventional, static CO2 balances often treat natural carbonation as an instantaneous offset. Dynamic analysis shows instead that uptake is spread over long periods and depends on mix design, exposure and end‑of‑life pathway. Ignoring these temporal dimensions overestimates short‑term climate benefits. While carbonation curing increases long‑term binding, its incremental benefit is limited in a dynamic comparison with CO2 capture and process changes.

Temporal aspects and storage needs

Scenarios relying on capture alone create a need for permanent geological storage. If part of the captured CO2 is converted to carbonates or bound already during curing, this storage demand declines—but does not disappear. This is particularly relevant in regions with limited storage acceptance or lacking infrastructure.

Implications for industry and policy

– Priority should be investments in CO2 capture and in process changes that replace steam curing. – Carbonation techniques and mineral carbonate use are sensible supplements, especially where geological storage is limited. – Accounting rules should reflect time‑differentiated CO2 uptake, avoid double counting and ensure that credits represent real, timely climate benefits. – Life‑cycle assessments should use dynamic models to underpin regulatory and market decisions.

Research needs

– More precise measurements and models on the rate and magnitude of natural carbonation across different concrete compositions and exposure scenarios. – Field‑oriented studies on integrating CO2 capture and carbonation processes into existing production chains to assess scalability and economic viability.

Outlook

The results move away from the idea of a single silver‑bullet solution. Technical CO2 capture and process changes make the largest contribution to decarbonizing concrete products; carbonation and mineral carbonates complement these pathways and primarily reduce the need for geological storage. In practice, combined, regionally adapted strategies are likely to be the most effective.