If you have not looked at American Concrete Institute's (ACI) new tolerance standard, you could be missing a good opportunity to begin simplifying how you look at and resolve design and construction issues related to tolerances. As described in recent issues of Concrete Construction (see Changing the Way We Look at Tolerances), the committee continues to formulate an even better, statistics-based approach to tolerances. But the result of their recently completed major effort to update the 1990 standard likely will be in service for the next few years.
The new version replaces ACI 117-90 “Standard Specifications for Tolerances for Concrete Construction and Materials,” which consisted of a 12-page specification and an 11-page commentary. ACI 117-06 became effective in August 2006 and consists of 70 pages, including new guidelines and additional explanation.
The 2006 document is presented in a new format—the commentary now appears alongside the text to which it refers. Numerous graphics have been added, mostly in the commentary, to better illustrate the intent of the specifications. For example, Section 4, Cast-in-place concrete for buildings, has been expanded in both the standard and the commentary. More illustrations now clearly show the intent behind the terminology of the specific tolerances provided. (See illustration) The dimensions being measured also have been regrouped. Although this section of the earlier standard had six subsections, the new standard has eight. The subsection on floor finish surface tolerances, which used to be covered in subsection 4.5, is now in subsection 4.8. But more significantly, it has been expanded to provide detailed information to accompany the various elements of the standard. It also specifically permits a statistical approach to evaluation of slab thickness for slabs on ground.
Just as notable as the expanded areas of this standard are two areas where it has been cut back. Section 5, Precast concrete, has been removed. The commentary defers instead to the Precast/Prestressed Concrete Institute's "Tolerance Manual for Precast and Prestressed Concrete Construction," MNL 135. Similarly, Section 6, Masonry, has been removed in deference to the "most recent edition of Specification for Masonry Structures (ACI 530.1)."
One additional element has been added to the end of the commentary, after Section 14, namely a "Mandatory Requirements Checklist." Although not a part of the standard, the checklist has been put together to assist specifiers in understanding the effect of tolerances in various aspects of concrete construction. It calls out the areas in which the specifier must provide guidance in the way of expectations through either tolerances or specific values. For example, the checklist notes that for projects with concrete floors, the specifier must choose an overall FF and an overall FL, if applicable.
For those choosing to refer to the document electronically, ACI offers a PDF version. The PDF features a table of contents with hyperlinks to the corresponding pages within the document. Another new feature for this version is that each section reference in the text appears in red and is hyperlinked to the appropriate point in the document, making it very easy to navigate the sometimes awkward cross-references.
Many aspects of concrete construction have made significant advances since the 1990 version of this standard was prepared, not the least of which include measurement and data processing capabilities. The 2006 version provides a valuable update, allowing all parties to take advantage of these improvements and providing a beginning basis through which to anticipate and deal with potential incompatibilities.