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ASTM C 94 "Standard Specification for Ready Mixed Concrete" is the specification almost universally used in the United States for concrete manufactured and delivered to a purchaser in a freshly mixed and unhardened state. For almost any job, ASTM C 94 addresses the separate and joint responsibilities of various parties that include the contractor, concrete supplier, testing and inspection agency, specifier, and even the owner. C 94 clearly states that when the purchaser's requirements differ from those of C 94, the purchaser's requirements shall govern. This article answers commonly asked questions about ASTM C 94, such as: What ordering information is needed? Can a maximum water-cement ratio be specified? What are the allowable slump tolerances? Can water be added on the job? What are the tolerances on air content? Can the purchaser reject a load?