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2013SumShotcreteEMag

Nozzleman Knowledge Can You Pass the Strength Panel Test? By Oscar Duckworth Often Overlooked Requirements That All Nozzlemen Need to Know Author’s note: The purpose of this article is to provide insight on the proper placement and care of test panels required for strength development testing only. Test panels are used in a number of varying situations, and it is important to note that this article does not address the particular concerns for all panels shot for other purposes. Although practices presented within this text should not be overlooked, test panels shot for core grading purposes, such as for the ACI Nozzleman Performance Evaluation, require far more discussion of nozzle techniques than could be responsibly covered in this article. This topic will be covered in a future Nozzleman Knowledge article. Nprofessional, it is simply a compulsory ritual strength potential. When test results come up low,handling, improper storage, or insufficient curingcan result in test panels with less than half theirearly everyone in the shotcrete industry isfamiliar with test panels. To the shotcrete of our daily routine. We shoot the panels, cores are it can be difficult to determine if low core extracted from panels, and the cores are tested for strengths are caused by poor test-panel shotcrete strength compliance. Numbers are always good. But placement, handling practices, or other factors. what if something goes wrong? Do the nozzleman Test panel placement, early-age handling, and and crew share responsibility for strength values? protection techniques are crucial to allow the Many shotcrete workers possess little knowl- maximum strength development of shotcrete test edge about the proper handling and storage of a specimens. But many shotcrete workers lack typical test panel. Casual research seems to indi- specific knowledge about these important prac- cate that most workers know that, once shot, tices. Currently, various ACI and ASTM docu- panels should not be moved…or dropped. ments provide guidance on the proper care, How much do you actually know about the handling, and storage of shotcrete test panels. proper care of a typical test panel? Are you con- fident that you are currently creating and handling The First Step: Correctly Shoot test panels in an approved manner? If not, don’t worry. A few low-strength test panels are sure to the Panel draw plenty of attention to your company’s test Any test panel used to determine a shotcrete panel protocol. mixture’s compliance with job specifications should closely match the actual placement condi- “Produce a material test panel for each mixture and each work day or tion. This is one of the reasons we derive strength every 50 yd3 (38 m3) placed, whichever is less.” (Typical specification) data from cores extracted from test panels rather than cast concrete cylinders. If a mixture is to be Studying for the Test Panel Test pneumatically applied, the mixture’s properties Experienced shotcrete craftsmen know that the should be tested following placement by the same ultimate quality of in-place shotcrete is largely procedure. Unfortunately, the act of shooting a test dependent on the skill and knowledge of the panel may introduce unexpected variables that can placement crew. Shotcrete must be carefully dramatically affect test results. A nozzleman who placed, consolidated, and cured to gain its full is responsible for shooting a test panel must be design strength. When we shoot the test panel, able to correctly place material in a manner that placement techniques and materials should mirror will not significantly alter its hardened properties. the in-place work. Many times after a test panel Poorly shot panels are susceptible to various is shot, however, it is generally forgotten. Mis- internal flaws that will negatively affect strength. Similar to other difficult-to-shoot areas, place- “Using techniques that assure a repeatable standard of care for each ment of the test panel requires precise nozzle test panel should be a component of every shotcrete worker’s educa- techniques to attain satisfactory results. Skilled tion program.” nozzlemen are aware that the size of the test panel 48 Shotcrete • Summer 2013


2013SumShotcreteEMag
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