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