Sensors in the slab: notes from a first season of structural health monitoring
What worked, what froze, and what we learned about data we did not plan to collect.
- Written by
- Ser Civil
Last autumn our team instrumented two bridge decks with temperature, relative humidity and corrosion-potential sensors. The goal was modest: collect one full winter of data at the depth of the top reinforcement, and test whether low-cost hardware could survive.
Installation
Sensors were installed in cored holes and grouted with a repair mortar of similar permeability to the parent concrete. Each deck has a data logger powered by a small solar panel and a battery sized for three weeks without sun.
What failed
Two connectors corroded within six weeks, both at points where the cable sheath had been nicked during installation.
One logger lost a week of data when its battery fell below the cut-off voltage during a cold spell at minus 31 °C.
Snow-clearing equipment damaged an exposed cable run at the deck edge.
What surprised us
The number of freeze-thaw cycles at the depth of the reinforcement was much lower than the number of air temperature cycles. Thermal mass damps short events. This matters, because many laboratory protocols use air temperature cycles as their reference.
The concrete experiences a calmer winter than the air above it, but a wetter one.
Next season we will add moisture sensors at two depths and compare the field record with our accelerated laboratory protocol.
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