Surfside (Florida), 2021. Moisture is almost always the primary driver. But the structural consequences in reinforced concrete often manifest through the next mechanism: rebar corrosion. In a coastal environment (salt aerosol, high humidity) and with waterproofing problems, corrosion stops being a “slow background” process and becomes a persistent degradation mode.
This post is not about “predicting a collapse.” It’s about a practical question that operations teams and engineers can answer with instrumentation:
Is corrosion active here – and how fast is it progressing?
Why corrosion monitoring matters
Visual signs (rust staining, delamination, exposed rebar) typically appear late. By the time you can see them, the process has often been ongoing for years.
Monitoring provides what’s missing between inspections:
- activity/likelihood indicator (is corrosion likely active or not);
- rate indicator (is it slow, or accelerating);
- trend and persistence (did it improve after remediation, or is it still worsening).
1) Two sensor layers that work best together
A) Half-Cell Potential (HCP)
What it tells you: Half-cell is primarily an indicator of corrosion likelihood/activity. It helps identify where corrosion is more likely already active (or becoming active) and where monitoring should be intensified.
Best use cases:
- baseline zone-based risk map;
- identifying hotspots for deeper monitoring;
- tracking whether a zone is deteriorating over time.
What it does not do: It does not measure “metal loss per year.” It answers: where corrosion is most likely active.
B) LPR/ER (corrosion rate / metal loss trend)
This is where corrosion stops being an opinion and becomes a rate.
- LPR (Linear Polarization Resistance) estimates corrosion current and is often used as a proxy for corrosion rate.
- ER (Electrical Resistance) tracks changes associated with metal loss over time (implementation depends on the system).
Best use cases:
- determining whether corrosion is “low/medium/high” based on trend;
- catching acceleration after repeated wet exposure;
- validating remediation effectiveness (waterproofing, coatings, cathodic protection, etc.).
2) Where to place corrosion sensors
Place sensors where three factors overlap: moisture/water + chlorides + structural criticality.
A practical placement strategy:
- Under the deck / along the garage ceiling where moisture data shows chronic dampness (from Post 1/3).
- At joints, interfaces, penetrations, and drains where water concentrates and persists longer.
- Near critical connections where load transfer is sensitive to rebar condition and concrete–steel bond.
- Use paired locations: a “suspect zone” plus a “control zone” for comparison.
If you only have a few points, don’t spread them across the building. Put them where the moisture data clearly shows a wet persistence regime.
3) What the dashboard must show
1) Corrosion risk map (Half-Cell)
Zone-based visualization answering:
- where corrosion is most likely active;
- whether hotspots are expanding;
- whether risk is intensifying over time.
2) Corrosion rate trend (LPR/ER)
Time-series trends answering:
- is the rate stable, decreasing (post-fix), or increasing;
- is there acceleration;
- is there correlation with season/weather/moisture regime.
3) “Moisture → Corrosion” correlation
The most valuable “engineering story” in one view:
- wet persistence increases,
- then corrosion activity/rate increases,
- alerts trigger on persistence, not a single spike.
