Carbonation Depth
Definition
The depth to which CO2 has penetrated concrete and neutralised its alkalinity, destroying the protective environment around embedded steel and initiating corrosion. A standard indicator of long-term concrete durability.
- Cause
- CO2 penetration neutralising concrete alkalinity
- Consequence
- Loss of protective environment around embedded steel
- Use
- Indicator of long-term concrete durability
- Context
- Building collapse investigations
Common questions
How is carbonation depth measured in a forensic structural investigation?+
A core or fresh fracture surface is sprayed with a phenolphthalein indicator solution, which turns pink in the still-alkaline, uncarbonated zone and stays colourless in the neutralised carbonated zone, letting the examiner measure the depth directly.
Why does carbonation depth matter more in older structures?+
Carbonation advances gradually over decades, so a deeper carbonation front in an aged structure signals a longer period during which corrosion-initiating conditions have been present around the reinforcement, useful for estimating how long deterioration has been underway.
Does carbonation depth alone confirm that reinforcement corrosion caused a collapse?+
No, it establishes that the protective alkaline environment has been compromised, which is a necessary precondition for corrosion, but the investigator still needs direct evidence of section loss or corrosion product on the steel to link it to structural failure.
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