To estimate the concrete strength using the maturity method, you need to make a calibration.
The aim of performing a calibration is to find the relationship between time, temperature, and strength for each concrete mix design that you intend to use.
This relationship is called the strength-maturity relationship and is established in a controlled environment such as a laboratory.
Once you have found the strength-maturity relationship for your specific concrete mix, you can use this to estimate the in-place strength of the concrete at your job site.
Calibration procedure
The procedure for making a proper maturity calibration is well described in the ASTM C1074 standard practice. We recommend to become familiar with all the details on how to make a successful calibration.
Required equipments
- Temperature sensors to measure temperature.
- Instruments (nodes) to connect to the sensors and record the data.
- Equipment for preparing and curing test samples.
- Universal testing machine.
How to perform a maturity calibration
Prepare the samples
Prepare samples (as per standard) so that you are able to perform tests at different test ages. Two to three samples are needed for each test age, two for the actual tests and the third in case the difference between the two first test results is higher than 10% from their average.
The samples must be prepared according to standard procedures for making and curing concrete test samples in the laboratory or in the field.
Embed temperature sensors
Embed temperature sensors in at least two of the samples. The sensors must be placed within ±15 mm of the center or as the used standard outlines.
Connect data loggers or transmitters
Connect an instrument to the sensors as soon as possible. These will record the data, which will be used to chart maturity, calculate and predict strength.
Cure the samples
Once the samples have been prepared, cure all of them according to standard procedures and under the same conditions, e.g. in a water bath or moist room.
It is important to have the same curing conditions for all the samples in order to obtain a correct correlation between the strength and maturity.
Perform compression tests
For the first test age, break two samples and note down the compressive strength for each of them. Also note down the date and time. Finally, calculate the average strength for the samples.
- If the difference between the two tests is higher than 10% from their average, break the third sample and use the average of the three.
- The samples with the temperature sensors embedded should be tested last to remain for maturity monitoring.
When using thermocouples, the consensus is that you can break test all three samples. When using digital sensors, test the two samples that are not wired.
Determine the maturity
Find the related maturity value at the time of the compression tests. When you have determined the maturity for each of the instrumented samples, calculate the average maturity of these.
- You are not using instruments? You will need to manually calculate the maturity using one of the maturity functions.
- You use concrete.fit or Hilti? The maturity will be calculated automatically and you can read it directly from the graph.
Determine the strength-maturity relationship
You have now determined the strength-maturity relationship for your first test age. This consists of:
- The average compressive strength found through the break testing.
- The average maturity found by calculating the maturity from the temperature history up until the time of the test
Now find the strength-maturity relationship for the remaining test ages by repeating the last three steps above.
Once you are finished with all the test ages, gather the results in the application. Each test age shows the correlation between the average compressive strength and the average maturity.
Create a maturity curve
Plot the maturity / strength for each test age and create the best fitting curve.
Enter the maturity and strength into the calibration format in your application, and it will automatically create the maturity curve.a
You can now use the maturity calibration to estimate the in-place strength of the concrete at your job site.