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Project specifications, including those that cite ACI 301, "Specifications for Structural Concrete," and ASTM C94, "Specification for Ready-Mixed Concrete," state time limits for the discharge of concrete. ASTM C94 states that discharge of the concrete shall be completed within 1-1/2 h after the introduction of the mixing water to the cement and aggregates or the introduction of the cement to the aggregates. This time limitation is permitted to be waived by the purchaser if the concrete is of such slump or slump flow after the 1-1/2 h time limit has been reached that it can be placed, without the addition of water, to the batch. This waiver is seldom used because the reasons for allowing the waiver are not well understood.
ASTM...