【国外标准】 Standard Practice for Estimating Concrete Strength by the Maturity Method

5.1 This practice can be used to estimate the in-place strength of concrete to allow the start of critical construction activities such as: (1) removal of formwork and reshoring; (2) post-tensioning of tendons; (3) termination of cold weather protection; and (4) opening of roadways to traffic.5.2 This practice can be used to estimate strength of laboratory specimens cured under non-standard temperature conditions.5.3 The major limitations of the maturity method are: (1) the concrete must be maintained in a condition that permits cement hydration; (2) the method does not take into account the effects of early-age concrete temperature on the long-term strength (see Note 6) (3, 4); and (3) the method needs to be supplemented by other indications of the potential strength of the field concrete.5.4 The accuracy of the estimated strength depends, in part, on using the appropriate parameters (datum temperature or value of Q) for the maturity functions described in Section 6.NOTE 1: Approximate values of the datum temperature, To, and the Q-value for use in Eq 1 or Eq 2, respectively, are given in Appendix X2. If maximum accuracy of strength estimation is desired, the appropriate values of To or Q for a specific concrete mixture may be determined using the procedures given in Appendix X1.1.1 This practice provides a procedure for estimating concrete strength by means of the maturity method. The maturity index is expressed either in terms of the temperature-time factor or in terms of the equivalent age at a specified temperature.1.2 This practice requires establishing the strength-maturity relationship of the concrete mixture in the laboratory and recording the temperature history of the concrete for which strength is to be estimated.1.3 The values stated in SI units are to be regarded as standard for determining the maturity index. No other units of measurement are included for this purpose. There is, however, no restriction on the system of units for expressing strength in developing the strength-maturity relationship.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. (Warning—Fresh hydraulic cementitious mixtures are caustic and may cause chemical burns to skin and tissue upon prolonged exposure.2)1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.