CO₂‑mineralised and biochar materials discussed

Carbon can be locked into roads, walls, and insulation instead of sold only as a stand-alone credit, and that idea is drawing fresh attention in low-carbon construction. (pnas.org) The basic chemistry is simple: carbon dioxide can react with calcium-rich materials and turn into stone-like carbonates inside concrete. A 2024 Proceedings of the National Academy of Sciences paper found all 10 concrete-related mineralisation pathways it studied cut life-cycle emissions versus conventional materials. (pnas.org) That same paper estimated economically competitive concrete mineralisation technologies could cut 0.39 gigatonnes of carbon-dioxide-equivalent emissions globally, about 15% of cement production emissions, with supply of recoverable end-of-life cement paste as the main limit. (pnas.org) Commercial products already use that approach. CarbonCure said its system injects captured carbon dioxide into fresh concrete, where the gas mineralises immediately, stays permanently embedded, and can let producers reduce cement while maintaining performance. (carboncure.com) A second route uses biochar, a charcoal-like solid made by heating biomass with little oxygen, and mixes it into construction products so the carbon stays inside a long-lived material. A 2022 review in the journal Biochar said biochar is compatible with cement, asphalt, and polymer materials and can add functions including thermal insulation and humidity regulation. (springer.com) That is moving from papers to pilot projects. The American Society of Civil Engineers reported in July 2025 that Verde installed a 110-ton bio-asphalt section at Auburn University’s National Center for Asphalt Technology Test Track in December 2024, and the project received 8 tons of carbon removal credits in April 2025 from Puro.earth. (asce.org) Biochar developers are also pushing building products beyond roads. Carbon Cell said its biochar-based expandable foam is meant to replace polymer foams in insulation and “locks in carbon for centuries,” while Wakefield BioChar lists insulation and concrete additives among its construction uses. (carboncell.co) (wakefieldbiochar.com) Researchers are testing a third category: living materials that keep pulling carbon from the air after installation. ETH Zurich said on June 20, 2025 that its team built a printable hydrogel filled with cyanobacteria that uses sunlight and nutrients to form both biomass and carbonate minerals, storing carbon in two ways. (ethz.ch) ETH Zurich said the material is still experimental, but it has already been shown in architecture exhibits at the Venice Biennale and the Triennale in Milan as a possible future building component. The researchers described it as a “photosynthetic living material” in a Nature Communications study cited by the university. (ethz.ch) The market argument behind all three approaches is that builders buy concrete, asphalt, and insulation every year whether carbon credit prices are high or low. BloombergNEF said in a 2025 outlook that an over-the-counter carbon removal market has grown alongside a broader carbon market reset, with bespoke bilateral transactions rising 27-fold since 2022. (about.bnef.com) Standards groups are still working through the accounting. Puro.earth says its biochar methodology measures net carbon removal from producing biochar for non-energy uses, and Carbon Sink Cities says construction pathways still face baseline, traceability, and contamination questions. (puro.earth) (carbonsinkcities.com) The thread running through these materials is straightforward: if carbon can become part of a product that contractors already specify, removal demand can come from procurement budgets as well as climate budgets. Concrete, asphalt, and insulation are ordinary purchases; the carbon claim is attached to the invoice. (carboncure.com) (springer.com)