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emanc (Civil/Environmental) (OP)
20 Dec 09 21:05
I am reviewing a proposed concrete design mix, 'would like to inquire if there is any mention of minimum water cement ratio of 0.40 in ACI code, and what is the difference between w/c ratio per ACI and the adjusted w/c ratio in the design mix?

'appreciate any clarification on this.
ishvaaag (Structural)
21 Dec 09 5:33
R4.1.1 — Maximum water-cementitious material ratios
(w/cm) of 0.40 to 0.50 that may be required for concretes exposed to freezing and thawing, sulfate soils or waters, or for corrosion protection of reinforcement will typically be equivalent to requiring an fc′ of 5000 to 4000 psi, respectively.

4.3 — Requirements for concrete mixtures
4.3.1 — Based on the exposure classes assigned from Table 4.2.1, concrete mixtures shall comply with the most restrictive requirements according to Table 4.3.1.


R4.3 — Requirements for concrete mixtures
R4.3.1 — Table 4.3.1 gives the requirements for concrete on
the basis of the assigned exposure classes. When a structural concrete member is assigned more than one exposure class, the most restrictive requirements are applicable. For example, a prestressed concrete member assigned to Exposure Class C2 and Exposure Class F3 would require concrete to comply with a maximum w/cm of 0.40 and minimum fc′ of 5000 psi, respectively.

TABLE 4.3.1 — REQUIREMENTS FOR CONCRETE BY EXPOSURE CLASS

For seawater exposure, other types of portland cements with tricalcium aluminate (C3A) contents up to 10 percent are permitted if the w/cm does not exceed 0.40.

Table 4.3.1 lists seawater under Exposure Class S1 (moderate
exposure), even though it generally contains more than 1500 ppm SO4. Portland cement with higher C3A content improves binding of chlorides present in seawater and the Code permits other types of portland cement with C3A up to 10 percent if the maximum w/cm is reduced to 0.40.



These are the occurrences found in a pdf search of the code.

Respect cementitious materials...

4.1.1 —The value of fc′ shall be the greatest of the values required by 1.1.1, for durability in Chapter 4, and for structural strength requirements and shall apply for mixture proportioning in 5.3 and for evaluation and acceptance of concrete in 5.6. Concrete mixtures shall be proportioned to comply with the maximum water-cementitious material ratio (w/cm) and other requirements based on the exposure class assigned to the concrete structural member. All cementitious materials specified in 3.2.1 and the combinations of these materials shall be included in calculating the w/cm of the concrete mixture.

Structural members
assigned to Exposure Class F3 are additionally required to
comply with the limitations on the quantity of pozzolans and slag in the composition of the cementitious materials as
given in 4.4.2.

In addition to the proper selection of cementitious materials, other requirements for durable concrete exposed to watersoluble sulfate are essential, such as low w/cm, strength, adequate air entrainment, adequate consolidation, uniformity, adequate cover of reinforcement, and sufficient moist curing to develop the potential properties of the concrete.

The primary means to obtain low permeability is to use a low w/cm. Low permeability can be also achieved by optimizing the cementitious materials used in the concrete mixture.

TABLE 4.4.2 — REQUIREMENTS FOR CONCRETE SUBJECT TO EXPOSURE CLASS F3

The total cementitious material also includes ASTM C150, C595, C845, and C1157 cement.

R5.2.1 — The selected water-cementitious material ratio should be low enough, or in the case of lightweight concrete
the compressive strength, high enough to satisfy both the strength criteria (see 5.3 or 5.4) and the requirements for applicable exposure categories of Chapter 4.




So for ACI 318 a limit is established for the total amount in weight of cementitious materials for the mix. This that I remember was not the case in the spanish EHE code, where each class of cementitious material was given a cement equivalent, and so a higher total amount of cementitious materials was allowed for the cases where cementing addons were used, for the same w/cm ratio. I don't know if the clause is standing in the current EHE 2008, would have to look.  

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