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Scripture's paper on Setting Time , published in 1955, summarized the problems involved and the progress made, as of that time, in developing methods for measuring the setting time of concrete. He pointed out that the setting time of cement does not adequately define the setting time of concrete and warned that very misleading conclusions may result from assuming such to be the case. Many criteria for defining setting time of concrete had been suggested, including loss of workability before placing, impairment of bond of freshly placed concrete to concrète in place, time of finishing for floors, ability to strip forms, and early strength gain. Scripture was of the opinion that none of these criteria represents the setting time of concrete, stating that as soon as concrete has any appreciable strength it has certainly set, and conversely, as long as concrete maintains any significant degree of workability, it is not set. He concluded that one or more points between these two extremes represent the setting time of concrete and, like the setting time of cement, will necessarily have to be defined by a particular test method and apparatus. Subsequent investigations of the rate of hardening of concrete have tended to substantiate these conclusions.
Kelly, T. M.
Vice president for operations, Master Builders, Division of Martin Marietta Corp., Cleveland, Ohio