CONCRETE KNOWLEDGE

Concrete Maturity

For a given mixture, concrete strength is a function of the time and thermal history. The concept of maturity is introduced to account for the effect of temperature and time on cement hydration and also the development of concrete mechanical properties.
As the concrete cures at different speeds at different temperatures, the concrete maturity gives you the opportunity to compare concrete cured under different circumstances. It is a method to monitor directly inside the structure compared to traditional lab-testing of external test specimen (see Break Test VS. Maturity Method).
Concrete maturity can therefore be used as a non-destructive method to estimate early-age strength development of concrete.
The maturity method has proven to be a method with high reliability and precision in estimating concrete strength.
The underlying principle of the maturity method is that concrete cured with different temperatures, but with the same maturity index will have an equal concrete strength.

Maturity is often measured in degree-hours (°C-hr) or degree-days (°C-day) or at an equivalent age at a specified temperature: hours at 20 °C or days at 20 °C

Concrete maturity is the concept of calculating the concrete age
based on the continuous temperature and time history.

ASTM C1074 
Standard Practice for Estimating Concrete Strength by the Maturity Method describes the maturity concept.

Maturity hot cold curing

As an example, then a concrete mix design might obtain the same maturity and thereby concrete strength if cured under 20 °C for 10 days (M1) as cured at 35 °C for 5 days (M2). The higher the concrete temperature is, the faster is the concrete strength development, because a higher temperature speeds up the hydration process (the reaction between cement and water).

As a result of new innovations within wireless embedded sensors to monitor concrete temperature, the use of concrete maturity has been widely adopted over the past 10 years. The Maturix solution is one of the leading solutions to enable easy and efficient monitoring of the in-place temperature and automatic strength calculations.

DIFFERENT WAYS TO CALCULATE MATURITY

Concrete Maturity Methods

The maturity method is used for estimating the in-place strength of concrete from the in-place maturity index and already determined laboratory data about the strength-maturity relationship of the specific concrete mix.

The maturity method assumes that samples of a given concrete mix will have equal strength values if they have equal values of the maturity index. To compute the maturity index, a maturity function is used.

In order to make the concrete calibration curve, these methods are the most used maturity methods:

  • Temperature-Time factor (Nurse Saul)
  • Equivalent Age (Arrheninheus or Freiesleben-Hansen and Pedersen)
  • Dutch Weighted Maturity
  • Weaver and Sadgrove
UNDERSTANDING CONCRETE MATURITY

Concrete Temperature and Clock hours

Measuring the concrete temperature enables you to calculate concrete maturity to any given point in time. But the maturity index doesn’t say anything about the concrete strength without a related calibration curve. The concrete calibration tells you what the related concrete strength should be for each level of concrete maturity. Each calibration curve is unique for each concrete mix design.

The concrete maturity for each concrete mix is calculated using different maturity functions. All maturity functions are based on a temperature. A scheme is available to read examples using the Freiesleben-Hansen maturity function, which you can use to account for the elevating temperature and curing speed.

Maturity overview
SIMPLE EXAMPLE

Maturity Calculation

Example with 1 hour curing time

1 hour at 20 °C = 1 x 1,0 = 1 hour at 20 °C
1 hour at 30 °C = 1 x 1,6 = 1,6 hour at 20 °C
1 hour at 35 °C = 1 x 2,0 = 2 hour at 20 °C
1 hour at 52 °C = 1 x 3,9 = 3,9 hour at 20 °C

Example with 12 hours curing time

12 hours at 20 °C = 12 x 1,0  = 12 hour at 20 °C
12 hours at 30 °C = 12 x 1,6  = 19,2 hour at 20 °C

WHY MONITORING IS IMPORTANT

Control your in-field concrete with concrete maturity

When concrete is mixed an exothermic chemical reaction happens between water and cement, which causes a sudden increase in temperature. As the temperature increases, the speed of the curing increases as well. The concrete follows a common shape of curing, but the speed on would differentiate from concrete to concrete. Concrete maturity is a way to accommodate these temperature variances, as it calculates everything back to a temperature on either 20 °C (widely used in Europe and Africa) and 23 °C (commonly used in North America). You in this way establish an equivalent age for your concrete when counting back the temperature-dependent time.

Concrete Part
When making your concrete simulation and planning you have taken a lot of choices like an expected weather forecast, expecting casting time and temperature. All this enables you only to give an approximation of an expected curing curve for temperature and strength. What happens in real life will for sure always be different, but it is just important to monitor how different it is. Therefore it is recommended to embed wireless sensors inside the concrete to validate data against your expectations. Monitoring in-field curing enables you to take actions and reschedule your plan based on data, rather than expectations. Examples could be that you for some reason doesn’t reach the expected temperature inside the concrete, and the curing will, therefore, be slower than expected. This would mean your concrete wouldn’t reach the desired strength at the time you need. If you know this in advance with sensors and simulation in combination, you would have the chance, for example, to cover your concrete with an insulation layer and thereby increase your concrete temperatures.

Why not just use Break Tests?

Pouring concrete in any type of application (precast, high-rise, tilt-up, mass concreting etc.) you always wants to know when you have the needed maturity (age) and related strength to continue the construction process. If you want to process fast, then you always need to make sure you don’t risk anything. You can do this by measuring the on-site concrete strength with a traditional break test or using a non-destructive test like calculation of concrete maturity from sensor data.

 

COMPARISON

To estimate in-field concrete strength the following method is often used:

  • Field Cured Cubes (ASTM C31 & C 39)
  • Rebound Hammer* (ASTM C805)
  • Penetration Resistance* (ASTM C 803)
  • Pullout Strength* (ASTM C 900)
  • Maturity Testing* (ASTM C 1074)
    * require correlation
WHY BREAK TESTS ARE NOT OPTIMAL

Problems with Break Tests

The infield cured specimens (cubes or cylinders) is a preferred method in many regions across the globe. It has been selected due to its simplicity and limited cost to perform. But it also comes with a set of drawbacks:

  • No visible curing curve with continues information (only points when you do the compression test
  • Time wasted between when concrete reach concrete strength and when you do your compression test
  • Often conservative in its estimate of the in-place strength of your concrete structure

The reason why the specimen if often underestimating the in-place concrete strength is, that the volume of the specimen is much smaller compared to your concrete structure. This means the energy released inside the specimen escape much faster and you thereby won’t be able to follow the same high concrete temperature curve, as in your concrete structure.

Read more about Break Tests VS. Maturity

WHY BREAK TESTS ARE NOT THE OPTIMAL SOLUTION

Test specimen
=
Smaller mass
=
Lower temperature & slower curing

In-place concrete
=
Larger mass
=
Higher temperature & faster curing

When casting concreting it generally makes sense to use concrete sensors to validate your curing against your simulations

  • Validate the pouring temperature
  • Check concrete temperature development continuously (not just a few sample test with a break test)
  • Get a visualization of the realtime curing profile

And then use break tests to

  • Validate the concrete quality is as ordered
  • Validate concrete strength
  • Validate 28-day strength
Connect transmitter - white

Have a question about using Maturix® for calculating the concrete maturity?

Send us a message and we will get back to you.