ASTM C918/C918M-20 PDF Download

ASTM C918/C918M-20 is a standard test method that provides a procedure for measuring the early-age compressive strength of concrete specimens and projecting their later-age strength. The test method allows for the estimation of the potential strength of a specimen based on its measured strength at an age as early as 24 hours. This information is valuable for process control in concrete production, as it provides insights into the variability of the production process.

The relationship between early-age strength and later-age strength depends on the materials used in the concrete. The test method assumes a linear relationship between strength and the logarithm of the maturity index, which is calculated using the measured temperature history of the specimen. This assumption has been found to be acceptable for test ages between 24 hours and 28 days under standard curing conditions. However, if the relationship is found to be non-linear, an appropriate equation should be used to represent it.

It is important to note that strength projections using this test method are limited to concretes made with the same materials and proportions as the ones used to establish the prediction equation. Confidence intervals, developed in accordance with section 10.2 of the standard, can be helpful in evaluating projected strengths. Additionally, it is stated that this test method is not intended for estimating the in-place strength of concrete, as there are other procedures (such as Practice C1074) available for that purpose.

The standard also includes general information, such as procedures for making and curing concrete specimens, as well as using the results of early-age compressive-strength tests to project later-age strength. The standard emphasizes that explanatory notes and footnotes should not be considered as requirements of the standard.