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Rapid concrete construction practices have led to increasing pressure to assess the quality of concrete at a very early age. Therefore, a cooperative test program was conducted among nine laboratories to evaluate several existing test procedures involving the use of either hot water, boiling water, or the heat of hydration of portland cement to provide heat necessary to accelerate the compressive strength development of concrete. Depending upon which procedure was employed, the amount of acceleration ranged from 1.1 to 2.5 times the strength developed after the same period of moist curing. Statistical analyses of the data justified adoption of a standard method that can be used to judge the quality of concrete soon after mixing. This method involves three procedures of accelerated curing which are limited to concrete made with the same materials and tested by the same laboratory. It has been designated ASTM C 684-74 (Making, Accelerated Curing, and Testing of Concrete Compression Test Specimens). Use of it, under the conditions stated therein, results in as reliable an evaluation of the quality of the concrete at one or two days of age as compared to that measured at 28 days of age according to ASTM C 31-69 (Making and Curing Concrete Test Specimens in the Field).
Supervisor, Cement Technical Center, Martin Marietta Cement, Baltimore, Md.
Stock #: JTE10652J