Concrete Specs Do NOT Specify a Maximum Slump…Now What?

The concrete code (ACI 318), IBC and ACI 301, Specifications for Structural Concrete” do a pretty good job of publishing concrete acceptance criteria for maximum w/c ratio, minimum compressive strength, cement factors and air content. What IBC and ACI 318 do NOT DO is present clear and simple acceptance criteria for concrete slump. Acceptance criteria for concrete slump is generally stipulated by the project specifications; however, what do you do when the project specifications FAIL to set forth slump acceptance criteria? You INVOKE ACI 301, section (See picture block information at the bottom of the page).

ACI 301, section mandates a concrete slump of 4 inches when acceptance slump criteria is not addressed or specified in the project specifications. This 4 inch slump is subject to the requirements of ACI 117, “Specifications for Tolerances for Concrete Construction and Materials” which would add a plus or minus 1” slump and this tolerance would amount to a slump tolerance range of from 3 inches to 5 inches. Section also addresses the addition of a high range water reducing admixture (HRWRA) if job site conditions require the use of a HRWRA when the project specifications do not address the issue. Section states that the concrete shall have been proportioned to a slump of 2 inches to 4 inches before the HRWRA is added and allows a maximum slump of 8 inches, at the point of delivery, after the admixture is added to the concrete mixture.

Please understand that ACI 301 is NOT code. IBC and ACI 318 are code but in our example, during this particular exercise, the code is lacking in that it has not stipulated a concrete slump acceptance criteria. We have invoked ACI 301 because section does set forth concrete slump acceptance criteria. Furthermore, ACI 301 is the foundation of ALL concrete specifications in the land and ACI 301 is listed as a reference document in project concrete specifications everywhere; therefore, the contents of ACI 301 are enforceable on the project. .

ACI 301, Section4.2.2.2 SLUMP. Unless otherwise specified or permitted, concrete shall have, at the point of delivery, a slump of 4 inches. Determine the slump by ASTM C 143. Slump tolerances shall meet the requirements of ACI 117.

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