Concrete Maturity Method Reliable Nondestructive Method to Determine in-Place Concrete Strength

Concrete Maturity Method b The maturity method is a technique to account for the combined effects of time and temperature on the strength development of concrete. b This method relies on the measured temperature history of the concrete during the curing period to estimate its strength.

Concrete Maturity Method b The method provides a relatively simple approach for making reliable estimates of in-place strength during construction. b This method can be used to speed construction and reduce construction cost by removing form and loading the concrete early.

Concrete Maturity Method b Since the cost of temperature sensors embedded in concrete has been reduced, this makes the method attractive to construction industries b These sensors may not constitute real nanotechnology, but illustrate what can be accomplished by the nanotechnology as the dimension is reduced.

IntelliRock Embedded Concrete Temperature Sensor iBotton

Maturity or temperature-time factor (ASTM C 1074) ( option 1: Nurse-Saul function ) Eq. (1)

Maturity or temperature-time factor ( option 1: Nurse-Saul function ) b M = maturity index, °C-hours (or °C-days), b T = average concrete temperature, °C, during the time interval ∆t, b To = datum temperature, usually taken to be -10 °C. b t = elapsed time (hours or days), and b ∆t = time interval (hours or days).

Schematic of temperature history and temperature-time factor computed according to Eq. (1).

the maturity rule: b Concrete of the same mix at the same maturity (reckoned in temperature-time) has approximately the same strength whatever combination of temperature and time go to make up that maturity.

strength-maturity relationship

Option2: alternatives to the Nurse-Saul function b Eq. (1) is based on the assumption that the initial rate of strength gain is a linear function of temperature. b this linear approximation might not be valid when curing temperatures vary over a wide range. b the equivalent age of concrete was proposed as alternatives to the Nurse-Saul function

the equivalent age of concrete Eq. 2

the equivalent age of concrete b te = the equivalent age at the reference temperature, b E = apparent activation energy, J/mol, b R = universal gas constant, J/mol-K, b T = average absolute temperature of the concrete during interval ∆t, Kelvin, and b Tr = absolute reference temperature, Kelvin.

ASTM Practice C 1074 b ASTM adopted a standard practice on the use of the maturity method to estimate in- place strength b ASTM C 1074 permits the user to express the maturity index using either the temperature-time factor based on Eq. (1) or equivalent age based on Eq. (2).

ASTM Practice C 1074 b For Eq.1, it is recommended that the datum temperature be taken as 0 °C if ASTM Type I cement is used without admixtures and the expected curing temperature is within 0 °C and 40 °C. b For Eq.2, an activation energy of 41.5 kJ/mol is recommended.

ASTM Practice C 1074 Procedures b Determination of the appropriate maturity function for the specific concrete that will be used in construction. b Determination of the relationship between compressive strength and the maturity index. b Measurement of the in-place maturity index and estimation of the in-place strength.

ASTM Practice C 1074 Procedures

Develop Strength-maturity Relationship b Cylindrical concrete specimens are prepared using the same as the concrete to be used in construction. b Temperature sensors are embedded at the centers of at least two cylinders. b The sensors are connected to recording devices. b The specimens are cured in in a moist curing room. b Compression tests are performed on at least two specimens at ages of 1, 3, 7, 14, and 28 days. b At the time of testing, the average maturity value for the instrumented specimens is recorded. b If maturity instruments are used, the average of the displayed values is recorded. b If temperature recorders are used, the maturity is evaluated according to Eq. (1) or Eq. (2).