Can anyone explain why the concrete water-cementitious ratio requirements for ACI 318, Table 4.3.1, Exposure Class S3 of 0.45, is different than ACI 201.2R, Table 6.3, Class 3 exposure with a w-c ratio 0.40? I tend to take the more conservative approach of ACI 201.2R, but may need to explain to my client why the deviation from ACI 318.

Greg

When you consider both tables in ACI 318 (4.2.2 and 4.3.1), they are consistent with 201.2R, as you are to consider the lowest w/c ratio between the two tables. Class 3 exposure can be considered as including the "Very Severe" exposure of 4.3.1 and the considerations in Table 4.2.2.

4.2.2 was removed in the 2008 edition. I have not researched why this was done, but it was probably viewed as redundant.

The short explanation is that coordinating values between various codes and standards is difficult and may not always be appropriate. The committees at ACI are trying to eliminate overlap where they can. You will see changes to the next edition of 318 (that's an understatement), including where many such overlaps and redundancies are being removed and users are referred to another standard.

We may have allowed the complexity of these codes to become detrimental to designers and builders, which is why many of us in the industry are pushing for simplifying codes and standards. The International Code Council committees have a mantra "Minimum Code" when presented with the Next Big Thing. The goal of that is to only mandate minimum requirements, not best practices. ACI Committee 318 should be implementing code minimums in 318, and referring users to other standards for guidance toward best practices. However, this can create conflict - remember that 318 is the code, and the rest are just good information unless cited in 318 as mandatory. As a designer, you need to know about both and use your judgement about when to apply more than minimums.

I think there is a reference error in this thread. The reference stated as ACI 201 should be ACI 211, Table 6.3.4(b).