Validating the Maturity Calibration

In this article we will explain why it is important to validate your maturity calibration, when to do it and how to do it.

Why Is Important to Validate It

The maturity calibration is only valid for a specific concrete mix design as each mix design will have a different relationship between maturity and strength.

For example, some concrete mixes are designed to develop strength fast, while others have a much slower strength development curve. This is important because it means that if you try to apply a maturity calibration from a fast curing concrete mix to predict the strength development of a slow curing mix, then the strength estimations will be wrong. The strength will be perceived as much higher than the actual strength of the concrete.

The opposite will happen if you use a maturity calibration from a slow curing concrete mix to predict the strength development of a fast curing mix. In this case, the estimations will also be wrong, as these will be much lower than the actual concrete strength.

Another important factor is variances in the concrete mix. Minor variances will probably not have a big impact on the reliability of your maturity calibration. However, if you have high variances, e.g. significant changes in your water-cement ratio, then this will directly affect the concrete strength. The calculations using the maturity method will be wrong, since the concrete’s strength development may be faster or slower than normally (and according to the calibration).

As big changes or high variances can affect the accuracy when using the maturity method, then it is important to pay attention to these factors and perform validation on a regular basis and when considered necessary. This will guarantee that the strength estimation reflects the actual strength of your concrete mix.

If you change your mix design (w/c ratio, cement type, aggregate type, admixtures, etc.) then you must perform a recalibration to ensure that your strength estimation is precise.

When to Validate It

It is recommended that you verify your maturity calibrations periodically. However, there is not a consensus on the right interval for performing validations.

Things such as the criticality of your operations, the amount of variances in your concrete mix, and the regulations affecting your project will all influence how often a validation should take place. Therefore, the recommendation is that you weigh these factors and decide on a suitable period for your specific project. 

How to Validate It

1. Make samples

Cast three samples using the same procedure as used to develop the current maturity calibration. Remember to use moulds of the same size and dimensions.

Three samples for maturity calibration

2. Embed temperature sensors

Place a temperature sensor in one of the three samples and connect it to a data logger or transmitter. Cure all the samples under the same conditions.

Three cylinders with sensor for maturity calibration

3. Test the samples

Perform break tests of the samples as close as possible to the maturity value which represent the target strength. Calculate the average strength from the test results.

Two break tests for maturity calibration

4. Validate the strength estimation

Compare the compressive strength result from the break test with the strength estimated using the maturity method. If the difference is more than 10%, you should perform a recalibration.

Strength comparison for maturity calibration validation

Accuracy Testing

In the video below, we tested the accuracy of the maturity calibration at a precast factory that uses Maturix.

We made some samples, instrumented them with Maturix sensors, and left them to cure for six hours next to the structure. Then we compared the results from the break tests with the strength estimation from Maturix – and confirmed that their maturity calibration is accurate.

FAQ

Do I need a maturity calibration for every concrete mix design?
Yes. A calibration is only valid for each unique concrete mix, as the strength development changes depending on the mix design.

Do I need a new maturity calibration if I change one of my suppliers?
It depends. You should at least validate your maturity calibration as described above. If the difference is more than 10%, you should perform a recalibration.

Do I need a new maturity calibration if I add admixtures?
Most likely. Many admixtures change the properties and strength development of your concrete mix and you must ensure that your maturity calibration is accurate.

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