The goal of the maturity calibration is to determine a relationship between concrete maturity and it’s strength for a specific mix. This calibration can be used to determine the in-place strength of the concrete and evidently replace the need for field-cured cylinders. To perform a maturity calibration, the ASTM C1074 standard must be followed.
- Make a minimum of 17 cylinders; 2 will be used for temperature monitoring while the other specimens will be used for compressive strength breaks. All cylinders must be cured together in a moist environment (ASTM C511).
- Select a minimum of 5 break times, for example, 1, 3, 7, 14, 28 days. For each day, obtain the compressive strength of two cylinders, break the third cylinder if the results vary more than 10% from the average. Note the time of the breaks.
- At the time of the break, obtain the maturity value from the two cylinders that were used for temperature monitoring and make an average of the maturity.
- You now have a set of at least 5 data points each with a strength associated to a maturity value. Plotting those data points allows you to obtain a curve with a logarithm equation.
- Validate your calibration curve by making a couple of additional cylinders on your next pour, compare the calculated strength obtained from the maturity value to the compressive strength obtained in the lab. Up to a 10% difference is acceptable.
Strength=a+b LOG (maturity) Eq.1: Formula for calculating the maturity value of concrete
Break Test vs. Maturity Test
Structural integrity is at risk when strength measurement data is inaccurate. This shortens the life cycle and decreases the strength of the mass concrete element. That is why receiving accurate and timely data that allow construction workers to move forward with form removal and
post-tensioning is crucial. Although the use of break tests has been common practice in the construction industry for decades, it does not mean that this is the most accurate and reliable method in obtaining strength data.
Lack of an accurate estimation of strength at early ages of construction is twofold:
- Contractors either wait too long for stripping formwork, which is mostly due to delays in completing the project, or
- They act prematurely which could cause the concrete structure to crack – this leads to future durability and performance issues – or even structural collapse.
In adopting the use of wireless sensors on-site, contractors can collect more accurate data and ensure the safety, efficiency, and reliability of their structure.
Read more about Concrete Maturity.