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

2. 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.

3. 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.

4. 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.

5. IntelliRock Embedded Concrete Temperature Sensor iBotton

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

7. 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).

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

9. 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.

10. strength-maturity relationship

11. 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

12. the equivalent age of concrete Eq. 2

13. 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, 8.314 J/mol-K, b T = average absolute temperature of the concrete during interval ∆t, Kelvin, and b Tr = absolute reference temperature, Kelvin.

14. 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).

15. 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.

16. 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.

17. ASTM Practice C 1074 Procedures

18. 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).