Water-Cementitious Ratio and Exposure Cap (ACI 318)
The single strongest lever on concrete strength and durability: w/cm = mixing water / total cementitious (cement + fly ash + slag + pozzolans). 282 lb water over 470 lb cement + 94 lb fly ash (564 cementitious) is 0.50 -- which EXCEEDS the ACI 318 Table 19.3.2.1 cap of 0.45 for severe freeze-thaw or sulfate exposure. Lower w/cm means lower permeability, so ACI caps it by exposure class (0.55 F1 down to 0.40 F3/C2). Count the aggregate free-moisture and admixture water, not just plant batch water, or the real ratio is higher than the ticket. Checks the durability cap only; strength, minimum cementitious, and air are separate. A durability screen; the spec and mix design govern.
Formula and source
w/cm = water_lb / (cement_lb + scm_lb); checked against the ACI 318 Table 19.3.2.1 exposure-class maximum (F1 0.55, W/S1 0.50, F2/S2-S3 0.45, F3/C2 0.40).
Water-cementitious ratio and exposure caps (ACI 318 Table 19.3.2.1; ACI 211.1), by name; the project specification and the mix design govern.
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