Sampling (per ASTM C 172) is the first step in determining if the concrete placed complies with specifications. The guidelines are to take composite samples of sufficient total volume (1 ft3 minimum) from the ready-mix truck after 10% and before 90% of the load has been discharged. These samples must be taken no more than 15 minutes apart and remixed to yield a composite sample. They are then covered to protect against rapid evaporation and to avoid contamination.

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