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2016SummerShotcreteEMag

library were taken. Following the publication of a completely new version of our Specification in 2013, the Guide was revised both for content and format. The later was adapted to match the organizational structure of the specification document; although still a complete stand-alone document that merits reading on its own, it can also be considered to be a commentary to the Specification document. To illustrate this, Table 2 shows a simple example of the correlation between both documents about construction joints. In the left column, the specification tells us concisely how to do something, while in the right column, the guide provides further explanations. It is the intent of the committee to maintain the synchronization between these two documents in the future. One important change that was made in the 2013 Specification, and later supported by the Guide in 2016, is the removal of the Core Grading system. This is noteworthy because it leaves an apparent gap in our documents, as they offer little guidance to the engineer on the acceptance of shotcrete. In fact, the subject of shotcrete acceptance was (and still is!) an important part of the consideration in rewriting the 506.4R-94, Guide for the Evaluation of Shotcrete, document. It was also felt that that aging document (1994!) needed a complete rewriting to better address the changes in QA/QC seen in recent years. Evaluation of Shotcrete The document currently being revised by the committee will cover all the usual aspects of QA/ QC for shotcrete, from the tests to run on fresh material, all the way to durability-related tests, with emphasis on the frequency of testing, the interpretation of the results, and typical expected Table 2: Excerpt from the Specification (left) and Guide (right) documents on the topic of construction joints (underlined words to illustrate difference of language) 506.2-13, Specification for Shotcrete 506R-16, Guide to Shotcrete 3.2.1 - Construction joints_ Taper construction joints at approximately 45 degrees from receiving surface. Form joints by cutting plastic shotcrete. Roughen shotcrete in the joint face while shotcrete is still plastic. 3.2.1 - Construction joints_ Square construction joints are generally avoided in shotcrete construction because the corner is a trap for rebound and overspray. Construction joints are usually constructed at a 45-degree angle. Where the joint will be subjected to compressive stress, however, square joints are sometimes required, in which case, the crew should take the necessary steps to… values. For example, special care is being given to the “Compressive Strength” section and especially panel handling or core extraction, as experience has shown it is often the source of erroneous noncompliant results. A novel addition, however, is the inclusion of a special section on the “acceptance of shotcrete.” The openly stated objective of the acceptance of shotcrete section is to guide the engineer to evaluate what is and is not acceptable for the specific job at hand and realize that, similar to cast-in-place concrete, some limited defects may be present, especially as the complexity of the work increases. The task to define what “acceptable” shotcrete has turned out to be a complex one. It was decided by the committee to separate the exercise into two parts. The first part consisted of producing a methodology aimed at evaluating the quality of a set of shotcrete cores. These cores may come from pre- Shotcrete • Summer 2016 23


2016SummerShotcreteEMag
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