Page 72

2017WinterShotcreteEMag

| TECHNICAL TIP HIDDEN TROUBLE WITH COUPLERS All air delivery systems rely on couplers as a means to connect various individual components, but coupler designs vary between manufacturer and country of origin. Most major coupler manufacturers have produced full flow couplers for decades. Fig. 5: Beware of prefabricated air hoses supplied with restrictive couplers 70 This type of coupler has an interior diameter that is nearly the same as the interior diameter of the delivery line to diminish internal restriction. Unfortunately, many currently available imported couplers do not incorporate a full-flow design (refer to Fig. 4). Because a low-price, non-full-flow coupler may be identical in exterior appearance and primary function to a full-flow design, these couplers are currently in use on countless applications such as inexpensive prefabricated air  supply lines, jackhammers, valves, or air-operated tools (refer to Fig. 5). Unfortunately, if used in even one location within a 0.75 in. (19 mm) wet-mix shotcrete air delivery system, the coupler will act as an air restricting device, limiting air flow to levels well below the minimum requirement for nearly every common nozzle in current production. Because restrictive coupler designs do not create obvious differences in the sound or feel of the wet-mix equipment operation, workers may not realize that a serious problem is occurring. It is important to inspect each 0.75 in. (19 mm) air coupler within the system and replace any coupler or other delivery component that does not incorporate a full-flow design. High-velocity placement is a key element for producing the full compaction and consolidation required for quality concrete. It is essential that the correct amount of air energy be delivered to the nozzle to achieve the needed velocity. Insufficient air delivery to the nozzle, whether caused by air delivery line choices, restrictive couplers, or the use of an air compressor with less than the required output present major obstacles to attaining acceptable compaction and consolidation. If low air energy is suspected, check by inspecting for poor air compressor function, restrictive couplers, or an air delivery system that may be too small for the project. Simple steps are useful to help assure that your air delivery system is functioning properly. Can you be sure yours is? ACI Certified Nozzleman Oscar Duckworth is an ASA and American Concrete Institute (ACI) member with over 15,000 hours of nozzle time. He has worked as a nozzle- man on over 2000 projects. Duckworth is currently an ACI Examiner for the wet- and dry-mix processes. He currently serves on the ASA Board of Direction and as Chair of ASA’s Education Committee. He continues to work as a shotcrete consultant and certified nozzleman. Shotcrete | Winter 2017 www.shotcrete.org


2017WinterShotcreteEMag
To see the actual publication please follow the link above