Carbonation-Induced Corrosion
Definition
Steel corrosion driven by CO2 absorption into concrete, which reduces the pore-water pH from about 13 to below 9, destroying the passive oxide layer on embedded reinforcement and initiating corrosion.
- Trigger
- CO2 absorption reducing pore-water pH
- pH shift
- About 13 down to below 9
- Mechanism
- Destruction of passive oxide layer on reinforcement
- Context
- Bridge collapse investigations
Common questions
How does carbonation-induced corrosion differ from chloride-induced corrosion?+
Carbonation lowers the overall pore-water pH across a broad carbonated zone, removing the passive layer generally, while chloride attack punctures the passive layer locally even at normal pH, producing more localized pitting corrosion rather than the broader corrosion pattern carbonation causes.
Why does the passive oxide layer matter for reinforcement durability?+
In normal high-pH concrete, this thin oxide film forms naturally on steel and effectively stops further corrosion. Once pH drops below roughly 9 through carbonation, the film breaks down and the steel begins actively corroding when moisture and oxygen are present.
What physical evidence at a collapse site points to carbonation-induced corrosion specifically?+
Investigators look for a measurable carbonation front reaching or exceeding the reinforcement's concrete cover depth, combined with generalized rather than localized corrosion and rust staining, distinguishing it from chloride-driven pitting or other failure mechanisms.
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