The ACI 211.1 Method, Step by Step
ACI 211.1 proportions normal-weight concrete by a weight / absolute-volume method. The eight steps below take a design strength and materials data through to a preliminary mix, ready for trial batching.
The 8 steps
- Choose the slump and the nominal maximum aggregate size for the work.
- Read the approximate mixing water and air content from ACI 211.1 Table 6.3.3, based on slump and maximum aggregate size.
- Select the water-cement ratio from the required strength (ACI 211.1 Table 6.3.4a), then cap it at the ACI 318 durability limit for the project’s exposure classes, adopting whichever w/c is lower.
- Calculate cement content: cement = water ÷ w/c.
- Estimate coarse aggregate content from ACI 211.1 Table 6.3.6 — a dry-rodded volume fraction that depends on the nominal maximum aggregate size and the fineness modulus of the sand — multiplied by the aggregate’s dry-rodded unit weight.
- Find the fine aggregate content by the absolute-volume method: fill the remaining volume of the cubic yard after cement, water, coarse aggregate and air are accounted for.
- Correct all aggregate weights for moisture and absorption so the batch matches the as-batched (not SSD) condition.
- Confirm the design with trial batches before use on a project.
Strength-based water-cement ratio (Table 6.3.4a, non-air-entrained)
Values interpolate between the strengths shown. Air-entrained mixes use slightly lower w/c ratios than the values below. This table is the strength-based starting point; the ACI 318 durability limit for the project’s exposure can require a lower w/c still, in which case the lower value governs.
| Specified strength f′c | Water-cement ratio (w/c) |
|---|---|
| 6000 psi | 0.41 |
| 5000 psi | 0.48 |
| 4000 psi | 0.57 |
| 3000 psi | 0.68 |
| 2000 psi | 0.82 |
Frequently asked questions
What is the difference between ACI 211.1 and ACI 318?
ACI 211.1 is the practice for how to proportion a mix — water, cement, and aggregate quantities for a target slump, strength, and aggregate size. ACI 318 is the structural building code; it sets the durability and exposure limits (maximum w/c, minimum f′c) that a mix must also satisfy, and which can govern instead of the strength-based w/c.
Do I still need trial batches?
Yes. ACI 211.1 proportions are a starting point. Trial batches with the actual project materials confirm strength, workability, and durability before the mix is used.