Short answer
Concrete carbonation is a chemical reaction where CO2 penetrates concrete, lowers pH, and destroys the alkaline passivity layer protecting embedded rebar. Once pH drops below roughly 9.0, moisture triggers rapid corrosion, steel expansion, and spalling that compromises the structural load path in parking garages, warehouses, and multi-family complexes.
Dive deep
Fresh concrete is alkaline, which keeps embedded steel from rusting. Over decades—accelerated in urban Seattle with higher ambient CO2—carbon dioxide migrates through the porous matrix and neutralizes that protection. Any moisture reaching the rebar then drives rapid oxidation.
Rusting steel expands significantly, creating tensile stress inside the member. Spalling follows: chunks of concrete break away, exposing corroded rebar. In parking decks and foundations, this is structural erosion, not a patch-and-paint problem.
On site we assess spalling depth, rebar condition, and carbonation front progression. Our protocol may include electrochemical re-alkalization or migrating corrosion inhibitors (MCIs) to stop the reaction, followed by polymer-modified mortar repairs to restore monolithic strength. Ignoring spalling or sealing over it without addressing corrosion and moisture ingress is the repair that fails within seasons.
When it applies
- Commercial parking structures, warehouses, or foundations with visible spalling
- Exposed rebar, delamination, or rust staining on structural concrete
- Older urban buildings with decades of CO2 exposure
- Post-flood concrete where carbonation and moisture combine to accelerate corrosion
When it does not
- Surface efflorescence on non-structural walls with intact rebar cover
- Minor cosmetic chips in non-load-bearing elements
- New construction with verified cover depth and no carbonation indicators
What we do next
We evaluate corrosion activity, repair spalled zones, and address the moisture path feeding oxidation. For commercial concrete deterioration, work with our commercial restoration team.
