Where Should You Measure Concrete Temperature?

The best recommendation is to measure the temperature in the spots where you expect the most extreme temperatures, both cold and warm:

Measuring Lowest Temperature in the Concrete

The spots with the lowest temperature development will have a slower hydration and thereby a slower strength development. This means that these spots are at increased risk of early frost and even if these will reach more or less equal strength in the end (studies do show small variations ), it would take a longer time. Therefore, it is a good idea to monitor the temperature and strength development at these spots. It is important to remember these spots both in your planning (simulation) and in your control (sensor readings), as you need to make sure that they reach the strength before removing the formwork.

You will often be able to find these spots in:

  • Corners or nearby surfaces and edges, where you have a large area exposed to the surroundings (heat conduction).
  • Areas with limited or no insulation
  • Areas casted against a cold surface (could be an existing concrete structure in the winter time)
  • Areas with potential thermal bridges that can easily transfer the internal heat energy to the surroundings.

Measuring Highest Temperature in the Concrete

The largest temperature stress occurs when you have a cold spot (described above) and a warm core temperature. You normally don’t want more than 10-20C differences in a cross section of your concrete. If you exceed these,  the risk of thermal cracks will increase. The cracks also are a result of much shorter exposure of sudden temperature variations, where stresses suddenly can occur. 

The temperature stresses are often highest in connection with:

  • Internal temperature development in large structures
  • Formwork removals
  • Casting against “old” existing concrete

In addition to monitoring to reduce risk of cracks, you might also take the following aspects into consideration, as you could benefit from additional monitoring to cover aspects like:

  • Differences in casting time; parts of the structure might be casted several hours before the other part. The curing of the concrete will therefore start much later
  • Control of heating; In winter concreting applications you might have heaters to make sure to avoid early frost and start the internal hydration process (temperature development). Financial and environmental cost of running these heaters under limited insulation will be significant. Managing these might be a good way to save costs.
  • In projects with post tensioning jobs, you might have specific spots inside the structure with a special interest in knowing exactly what the temperature and strength is, so you can do the job as fast as possible.