Q.: We are bidding a concrete project on which slump doesn't seem to be specified. In the specifications there is reference to ACI 301, "Specifications for Structural Concrete for Buildings," and to ASTM C 143, Standard Test Method for Slump of Hydraulic Cement Concrete. The test method tells how to run the slump test but doesn't tell what slump is required for different types of construction. Is there any guideline for slump in this situation?
A.: Section 3.5 of ACI 301 deals with this situation. Unless otherwise permitted or specified, the concrete should be proportioned and produced to have a slump of 4 inches or less if it's to be consolidated by vibration. If it's consolidated any other way, the slump should be 5 inches or less. A tolerance of up to 1 inch above the maximum indicated is allowed for one batch in any five consecutive batches tested. Concrete of lower than usual slump may be used provided it is properly placed and consolidated. It's probably a good idea to confirm with the specifier that the lack of a slump specification isn't an oversight and that he'll permit the use of 4- or 5-inch-slump concrete.