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2013SumShotcreteEMag

Technical Tip Proper Selection of Equipment and Nozzle for ACI Shotcrete Nozzleman Certification By Raymond C. Schallom III and Marc Jolin Sa number of Examiners have encountered 365 ft3/min 5.25 to 10.5 m3/min if using awet material around the reinforcement and intothe receiving surface (a minimum of 185 toince the beginning of the ACI ShotcreteNozzleman Certification program in 2001, owners or nozzlemen requesting use of equipment blowpipe for wet-mix and 600 to 750 ft3/min and nozzle setups meant for low-volume/low- 17 to 21 m3/min for dry-mix). The high velocity velocity applications such as fireproofing, plaster, provided by an adequate flow rate of compressed stucco work, or even spin casting of sewer pipes air is an essential element needed to provide the (generally vertical layers of 1 in. 25 mm or less). excellent material properties found in shotcrete. Unfortunately, none of these setups meet the true In contrast, plaster and stucco nozzles do not definition of shotcrete, which is “mortar or con- supply enough air volume or ft3/min (m3/min) crete pneumatically projected at high velocity onto (typically only using a 1/4 to 1/2 in. 6.5 to 13 mm a surface”; thehigh velocity component of this supply air hose up to the nozzle) to accelerate the definition is critical and essential in providing material adequately enough to provide high com- superior bond characteristics and increased den- paction or force it around the reinforcement. sity, strength, durability, and toughness typical of These nozzles were designed to apply a fine high-quality structural concrete. All these qualities mortar material only (not concrete materials with are highly desirable in the wide variety of shotcrete 3/8 in. 10 mm aggregate or fiber-reinforced applications, including ground support, concrete concrete mixtures) at 6 in. (150 mm) or less from repair, swimming pools, soil nail walls, structural the surface in a splatter pattern when adjusting walls, and lining applications. In North America, the 0.25 in. 6.5 mm air nozzle. Shotcrete refer- shotcrete is sometimes referred to as “pneumati- ence document CP-60(09), “Craftsman Workbook cally applied concrete,” whereas in Europe it is for ACI Certification of Shotcrete Nozzleman,” more commonly referred to as “sprayed concrete.” clearly states that the nozzle with adequate material In terms of equipment, the capacity of the air velocity should be between 2 and 4 ft (0.6 and compressor controls the acceleration of shotcrete 1.2 m) using a 3/4 in. (20 mm) delivery air hose material to a high velocity as it exits the nozzle. for wet-mix shotcrete and 2 in. (50 mm) delivery The high velocity is essential to drive the fresh, air hose for dry-mix shotcrete. The nozzle setups shown here are not recognized as shotcrete nozzles by ACI. They all have a 1/4 to 1/2 in. (6.5 to 13 mm) air lines into the nozzle. These low-velocity spray nozzles were designed for the type of applications noted previously that need low ft3/min to splatter the material for thin applications that do not have reinforcement to shoot around. The spin casting head is designed to fling the grout-type material onto the pipe surface, again, with no reinforcement. None of these nozzles can handle a 3/8 in. (10 mm) coarse aggregate concrete mixture with or without fibers of any type 18 Shotcrete • Summer 2013


2013SumShotcreteEMag
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