Maturity Index is the latest method to find out concrete maturity & in-place strength during curing

The Maturity Index offers a simple process to estimate the in-place strength of concrete throughout curing. It is developed on the basis of the principle that the strength is can be obtained depending on the temperature-time history throughout the curing process.

By applying a thermocouple data logger with simple thermocouple temperature sensors implanted in the concrete, the data can be recorded easily. This data can then be instantly evaluated with excel spreadsheet to work out the maturity index.

Concrete maturity belongs to a measuring system of how much a batch of freshly poured concrete has cured. It is a quick indicator of the in-place strength at that point in time corresponding to the ultimate strength when the concrete is completely cured. Usually, the concrete strength is calculated on the basis of compression tests. The maturity method works out an index on the basis of time-temperature data that offer a relative indicator of strength.

This method is very useful since it can be performed instantly on-site with a temperature data logger and thermocouple sensors implanted in the pour. Besides, the method can save significant time and enhance safety by facilitating form removal, post-tensioning, joint sawing or putting structures in service ensuring that necessary strength has been achieved.

What is the Maturity Index?

The maturity is created on the perception that strength of concrete is dependent on the hydration of cement in the mix. This hydration stands for an exothermic reaction that emits heat. By recording the temperature profile at regular time gaps throughout the curing process, the strength of concrete can be computed on-site in real-time.

The American Society for Testing Methods (ASTM) developed a standard method for measuring the concrete strength with the maturing method, ASTM standard C 1074. This method is based on initial calibration process that needs assessment of the maturity index in line with more traditional compressive strength test to create the maturity index vs. strength curve. Once this curve is set it is supposed to be applicable for any pours which employ the identical mix recipe.

The maturity index is computed from the raw time temperature data with the following 2 expressions:

The temperature-time factor:
M(t)= ∑▒〖(Ta-To)∆t〗

Where:

M(t)= Maturity temperature-time factor
Ta = Average temperature during time interval ∆t
To = Datum temperature below which no hydration occurs
Δt = time interval between measurements

Equivalent age using an Arrhenius function:
t_e= ∑▒e^(-Q(1/Ta- 1/Ts)) ∆t

Where:
te = Equivalent age
Q = Activation energy divided by gas constant K
Ta = Average temperature during time interval ∆t
Ts = Datum temperature below which no hydration occurs

Δt = time interval between measurements

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Maturity Index is the latest method to find out concrete maturity & in-place strength during curing