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Q. One of our young engineers has raised a question about the strength of the concrete required in a footing. She's pointed out that, although our standard contract documents call for 3000 psi concrete in foundation elements, Table 4.2.1 of ACI 318-08 defines Exposure Class F1 as "Concrete exposed to freezing-and-thawing cycles and occasional exposure to moisture."1 Table 4.3.1 effectively states that normalweight concrete in Exposure Class F1 must be produced with a minimum water-cementitious material ratio (w/cm) of 0.45 and a minimum strength of 4500 psi. This requirement appears to be new. We're in a cold climate. Does this provision apply to footings and foundation walls?
A. Although the 2008 edition of ACI 318 is the first to present durability requirements in terms of exposure categories, limits on w/cm or strength of concrete that will be exposed to cycles of freezing and thawing have a long history in the Code. A recommended limit of 0.45 on water-cement ratios (w/c) was instituted, by reference, in ACI 318-56,2 Section 301(b): "Concrete without air entrainment which will be exposed to the action of freezing weather shall...