ASTM C918/C918M-07

This test method provides a procedure to estimate the potential strength of a particular test specimen based upon its measured strength at an age as early as 24 h.⁵ The early-age test results provide information on the variability of the concrete production process for use in process control.

The relationship between early-age strength of test specimens and strength achieved at some later age under standard curing depends upon the materials comprising the concrete. In this test method, it is assumed that there is a linear relationship between strength and the logarithm of the maturity index. Experience has shown that this is an acceptable approximation for test ages between 24 h and 28 days under standard curing conditions. The user of this test method shall verify that the test data used to develop the prediction equation are represented correctly by the linear relationship. If the underlying relationship between strength and the logarithm of the maturity index cannot be approximated by a straight line, the principle of this test method is applicable provided an appropriate equation is used to represent the non-linear relationship.

Strength projections are limited to concretes using the same materials and proportions as the concrete used to establish the prediction equation.

Note 1—Confidence intervals developed in accordance with 10.2 are helpful in evaluating projected strengths.

This test method is not intended for estimating the in-place strength of concrete. Practice C 1074 provides procedures for using the measured in-place maturity index to estimate in-place strength.

1.1 This test method covers a procedure for making and curing concrete specimens and for testing them at an early age. The specimens are stored under standard-curing conditions and the measured temperature history is used to compute a maturity index that is related to strength gain.

1.2 This test method also covers a procedure for using the results of early-age compressive-strength tests to project the potential strength of concrete at later ages.

1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

1.4 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.

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 and health practices and determine the applicability of regulatory limitations prior to use.