Cementitious Content
Once mixing water and the water-cementitious ratio are set, cementitious content follows directly. ACI 318 and ACI 302 each add their own minimum requirements on top of that calculation.
The calculation: water ÷ w/cm
Cementitious content — the combined mass of portland cement and any SCM per unit volume of concrete — is calculated directly from the two quantities already fixed earlier in the ACI 211.1 method: cementitious content = mixing water ÷ w/cm. The mixing water comes from ACI 211.1 Table 6.3.3 (see Mixing Water Content), and the w/cm is whichever of the strength-based or durability-based values is lower (see Water-Cementitious Ratio). A lower w/cm for the same water demand means a higher required cementitious content.
ACI 318's F3 minimum
Beyond the w/cm ceiling, ACI 318 sets a specific minimum cementitious content requirement for concrete assigned to F3 exposure — the most severe freeze-thaw category, combined with exposure to deicing chemicals. This exists because concrete exposed to repeated freezing, thawing, and deicing salts benefits from a minimum paste quantity independent of what the w/cm-driven calculation alone would produce. The exact minimum value is set in the current ACI 318 edition and should be checked there rather than assumed.
No single ACI table of minimums by exposure
Unlike some other national concrete codes that publish one comprehensive table of minimum cement content indexed by exposure category, ACI 318's primary durability control is the maximum w/cm requirement, with the F3-specific minimum cementitious content as a targeted addition rather than part of a broader table. Separately, ACI 302, which covers concrete floor and slab construction, sets its own recommended minimum cementitious content and other requirements specifically for flatwork — a different document, driven by different concerns (finishability, durability of exposed floor surfaces) than the structural durability provisions in ACI 318. Do not expect to find one unified ACI table of minimum cement by exposure the way some other codes provide.
Frequently asked questions
Is there a single ACI table of minimum cement content by exposure?
No. Unlike some other national codes, ACI 318 does not publish one comprehensive table of minimum cementitious content indexed by exposure category. Its main durability control is the maximum w/cm requirement; a specific minimum cementitious content applies for F3 exposure, and separate minimums come from ACI 302 for flatwork rather than one unified ACI 318 table.
Does higher cementitious content always mean better concrete?
Not necessarily. Cementitious content is a consequence of hitting the target w/cm at the water demand for the chosen slump and aggregate size, not an independent quality target on its own — very high cementitious content can increase shrinkage and heat of hydration.
What is ACI 302?
ACI 302 covers guidance for concrete floor and slab construction, including its own recommended minimum cementitious content and other requirements for flatwork, separate from the structural durability provisions in ACI 318.