A new book published by the American Society of Concrete Contractors (ASCC) chronicles the current state of tolerances related to concrete construction. “Tolerances for Cast-In-Place Concrete Buildings” opens with a comprehensive but condensed, five-page tolerance specification that is followed by more than 130 pages of background and rationale organized by area of interest.
There's good reason for including such a volume of information.
“No document of this scope is likely to be adopted by standards developing organizations unless the rationale for the suggested tolerance provisions is thoroughly documented and justified,” says the authors. That is exactly what comprises the book's second part. Authors Ward Malisch and Bruce Suprenant have culled relevant information from more than a hundred sources including standards, books, committee reports, magazine articles, and research reports.
The authors' opening remarks set the stage and are well worth noting. They begin by reaffirming that tolerances simply are the permitted deviations from specified dimensions, locations, or quantities, and stress the importance of considering necessity and economic feasibility in setting useful tolerances.
The first of the 14 chapters in part 2 is an introduction to tolerances, including in the overview a clear statement of purpose. “This book was published to make tolerances more easily understood by the construction team and to minimize any misunderstanding of how tolerances are to be used in practice.”
It goes on to discuss the origin of many of the tolerances now in use, as well as the difficulties associated with using them, noting that many tolerances “have little relation to as-built data.” Although an umbrella approach has worked well in Europe where a single organization has developed a unified tolerance system, the authors note that such an approach is not likely to take hold in this country.
“Thus ASCC has chosen to study best practices from organizations representing the primary structural materials and use them in developing consistent and practical tolerances for cast-in-place concrete construction.”
One unique aspect of this volume is the historical reference it provides on the origin of many of the tolerances now in use. By researching ACI archives and other historical documents, the authors have provided both valuable perspective and interesting reading. A large chunk of this material is included in chapter 1, but another dozen historical highlights are included within the other chapters, making it easy for the reader to integrate current information with its historical origins. A list of the historic sidebars is at the end of the contents.
The main text is where the meaty issues are addressed. Again taking an example from the chapter on reinforcement placement, the authors tackle some tough questions. After a thorough discussion of how reinforcement location and concrete cover cannot be considered independently, they ask, does tighter inspection lead to fewer out-of-tolerance reinforcing bars? Field data show that it does not, they report. Is there an appropriate tolerance for bar placement? Research and analysis point to the need for a new way of specifying concrete cover, they argue, following up with two pages of tables and graphs. The chapter ends with an historical overview of tolerances for reinforcement placement and concrete cover.
Stepping back, it's impressive to see how much knowledge has been brought together in a single publication from so many disparate sources. Just keeping track of the information and where it was found must have been challenge enough for Suprenant and Malisch. By consolidating it all into one volume and including the benefit of their collective experience and expertise, they have put together a worthwhile reference work for the concrete industry. This volume will assist the ACI 117 Tolerances committee, and others, as they continue to resolve remaining issues.