Why thermocouples for measuring concrete temperature?
When it comes to monitoring concrete temperature, using thermocouples can provide useful insight into concrete curing. By using it, you can reduce problems such as the overheating of concrete (often seen in large concrete structures, also called mass concrete) or avoid having large temperature gradients, which might lead to cracks in the finished concrete structure. These cracks break the concrete surface and serve as channels for chlorides and other fluids to get to the reinforcing steel (rebar) and damage it.
The other benefit of monitoring the concrete temperature is to follow the curing process/maturity of the concrete. If you have made a calibration for your concrete mix, you will be able to use the maturity method to estimate the concrete strength accurately.
So in other words too high temperatures can cause:
- Increased water use and thereby added costs
- Increased shrinkage leading to cracks in concrete
- Lower final concrete strength
- Potential corrosion attack on reinforcements due to chloride attack
To be able to control the heating in the concrete, you need to measure and monitor the process. This can be done by using thermocouples – an inexpensive solution and widely available.
A thermocouple is simply attached to the rebar/reinforcement before pouring the concrete and then connected to a data logger or a wireless sensor like the Orbit K.
In larger structures, you will often measure at several depths at each point to make sure the temperature gradient across the concrete does not exceed the safety limit.
Benefits of using thermocouples for concrete monitoring:
- Affordable method of measuring concrete (only losing the inexpensive cable)
- Acceptable and available worldwide
- An acceptable method for leading international standards for concrete curing (ex. ASTM1070)
- Can be installed and configured quickly
- Flexible in lengths
For monitoring the early age strength in concrete you might monitor the temperature with 10 minutes intervals because of the high-temperature changes/variations over a short period of time. While concrete cures over 7-10 days you might only need data every hour.
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Marc Cox
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