Limitations of the maturity method
The maturity method has proven to be a reliable and easy to use method to estimate the development of early concrete strength. Every test method has its limitations, so in this article, we will explain five of the limitations of the maturity method and what can you do to overcome them.
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A maturity calibration is required for every concrete mix
A maturity calibration is a process done in a laboratory that aims to find the relationship between the strength development and the concrete maturity. Finding this relationship is important, because without it, it would not be possible to estimate the concrete strength using the method.
A maturity calibration is exclusive for each specific concrete mix design. This is because every concrete mix has a unique relationship between the maturity and strength development.
Below you can see an example of two different maturity calibrations from two different concrete mixes:
If you compare them, you will realize that they have the same final strength after 28 days, but the relationship between the maturity and strength until then is different. That is why you must perform a maturity calibration for each concrete mix needed for your project, as the estimated strength for one will not be representative for the other.
Performing a maturity calibration sounds harder than it is. You essentially use the same testing equipment as when performing break tests, you just include the process of measuring the temperature history in some of the samples up to the compression tests to find the maturity.
Learn more about how to do a maturity calibration.
Limited concrete moisture affects strength development
The maturity method uses the strength-maturity relationship to estimate the in-place concrete strength. This relationship is established during a maturity calibration, where samples are cured either in a water bath or in a curing room, which assures that enough moisture is available.
Having enough moisture is important to allow the concrete hydration process to occur fully. If certain conditions such as water content and moisture are not available, the concrete will not be able to attain its strength potential which means that it will be weaker than expected.
The maturity method calculations assume that the concrete in your project has the moisture it needs to allow the hydration process to occur fully. If the needed moisture is not available, the concrete might not reach the estimated concrete strength at a given maturity index.
To overcome this limitation, it becomes extremely important to apply the necessary curing techniques to assure that the concrete reaches its strength potential. Depending on the type of project you have, the requirements for the concrete, and the conditions on-site, different methods will be more appropriate than others. Some of the techniques that can be used to maintain water content and prevent moisture loss are:
High temperatures can affect long term strength estimations
In cement hydration, there is a phenomenon called the crossover effect. This effect shows that if the concrete cures at high temperatures during the early stages, the final strength may be lower compared with curing at lower temperatures. For example, you can see in the figure below that the strength of two concrete samples cured under low temperatures and high temperatures have slightly different strength development curves.
You can see that in the concrete cured at high temperatures, the strength development goes faster at the beginning than the low curing one. However, this fast strength development does not last in the long term.
In contrast, if the same concrete is cured at low temperatures, the strength initially develops slower but the final strength ends up being higher than the high temperature curing concrete.
This crossover effect may affect the reliability of the maturity method to predict long-term strength. That is why the maturity method is better suited to estimate early-age strength development. If you need to validate the long-term strength, we recommend you use other test methods to verify that the strength estimates are correct. This becomes especially important if you are performing critical operations.
You can also consider doing your maturity calibrations at different temperatures (lower and higher than the standard at room temperature), or perform testing on the activation energy, to make your strength estimation as precise as possible.
Inaccurate parameters can affect the strength estimations
A reasonable assumption or experimental trial must be made to determine either the datum temperature or activation energy (depending on the chosen maturity method). If these do not reflect well the behaviour of your specific concrete mix, the strength estimations will be affected.
We recommend assessing the characteristics of your concrete carefully as well as the expected temperature and humidity conditions in the construction site. The ASTM C1074 provides standard values for datum temperature and activation energy. However, if your concrete mix has a lot of admixtures or other special components, you may consider determining these values experimentally by following the procedure in Appendix X1 of ASTM C1074. Using values found by doing experiments on the concrete mix will provide you with more accurate results.
Incorrect use or wrong procedures may affect strength estimations
The maturity method is a calculated estimation of the in-place concrete strength that is based on the measured temperature history of the structure held up against the maturity calibration. If the method is not followed correctly, the sensors placed incorrectly or not as specified, or if the parameters are not right, the strength estimations will be less accurate. Therefore, it is important to make sure that these steps are done correctly to minimize the risk of incorrect estimations.
Measures to assure the quality of the procedures are to follow the standard practices during the maturity calibration, read carefully the maturity system instructions to assure that the eqipment is used correctly, and become familiar with how the maturity method works. If you are performing critical operations, you may want to perform other additional tests to validate the strength estimations.
If all of these parameters are taken care of, the maturity method can estimate the strength very accurately. In this video, you can see an accuracy test done using the maturity method together with Maturix. You can also read about how to validate your maturity calibration.
If you are in doubt about how Maturix works, our resellers and support team is more than happy to help you.
Like any test method, the maturity method has some limitations. However, it is also a great way of estimating concrete strength. Read some of these articles to learn about the benefits: