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ACI 506 continued to develop an assortment of documents to provide the engineering and construction industry comprehensive technical information on shotcrete. Currently, the 506 committee’s catalog of documents includes: • ACI 506.1R-08, “Guide to Fiber-Reinforced Shotcrete”; • ACI 506.2-13, “Specification for Shotcrete”; • ACI 506.4R-04, “Guide for the Evaluation of Shotcrete”; and • ACI 506.5R-09, “Guide to Specifying Underground Shotcrete.” The latest version of the specification document, ACI 506.2, “Specification for Shotcrete,” was published in 2013. Because ACI’s format for specification documents requires concise, mandatory language without any explanatory commentary, it was decided to reorganize the next revision of the Guide to serve as a commentary for the new specification. ACI 506.2-13, “Specification for Shotcrete,” is organized in standard three-part format (1.0 General, 2.0 Materials, and 3.0 Execution). The new Guide follows the same format with the addition of extra sections on equipment and crew responsibilities, which were part of the old Guide. A new section on sustainability has also been added to the new Guide. The front end of the Guide was rearranged to accommodate sections on History, Application, New Developments, and Research. These sections form the Preface in the front to the Guide. Here are some of the key changes in the new Guide: Scope—ACI 506.2-13 directs the engineer to specify whether the shotcrete is structural or nonstructural. The new Guide defines structural shotcrete as shotcrete with a compressive strength of 4000 psi (28 MPa) or greater. After considerable discussion, it was decided to not address polymer shotcrete due to the numerous field problems and dwindling use. The Guide does not recommend use of polymer shotcrete. Submittals—This is a new section in the Guide. The purpose is to provide a handy crossreference for the contractor when preparing project submittals. It should also help the engineer when reviewing submittals. Preconstruction testing by contractor— Another new section. Increasingly, shotcrete is replacing “form-and-pour” concrete. Many engineers, however, are unfamiliar with shotcrete, so preconstruction testing by the contractor is recommended. This section gives guidance to both the engineer and contractor as to when preconstruction testing best serves the purpose and scope of the project. Preconstruction testing is typically needed to demonstrate that the contractor can properly encase complex reinforcing steel layouts on the project. In some cases, use of special concrete mixtures will necessitate preconstruction testing. Mockup panels are helpful for demonstrating a particular shotcrete surface finish early in the project. Agreement by the A/E on a mockup panel can prevent a lot of future conflict. On a side note, this section started out as a separate document but the committee eventually decided to include it in the Guide instead of referring to a separate document. Testing during construction—In the previous version of the Guide there was just a brief section on testing. Quality assurance and quality control (QA/QC) guidance has been expanded. However, implementing a QA/QC program requires a holistic approach so the size and character of the project should determine the amount of effort given to QA/QC. The Guide provides some guidance for making this determination. Shotcrete samples for compressive testing, unlike concrete cylinder samples, are cores taken from a shot panel. Compressive strength testing of samples of the concrete mixture taken from the back of a concrete truck only verifies concrete mixture capability. Because shotcrete placement uses high-velocity impact for consolidation and it has some change in mixture proportions as a Shotcrete • Summer 2016 17


2016SummerShotcreteEMag
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