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2015FallShotcreteEMag

Over the last 40 years I have used a checklist from my article “What You Need to Know before Checklist for Choosing the Right Manufacturer Selecting a Wet-Mix Shotcrete Pump”7 to help (reproduced from Shotcrete, Summer 20097) choose the right manufacturer or dealer of wet • Check the years of shotcrete knowledge and experience of the pumps, dry machines, and systems needed for manufacturer’s or dealer’s sales staff. either shotcrete process. Although originally • Research the equipment’s field track record from a production formulated for wet-mix equipment, the same standpoint. format of the checklist can be used for selecting • Evaluate the manufacturer’s or dealer’s customer service. This is dry-mix equipment as well. helpful for troubleshooting pump- or gun-related problems or other Once you have selected the right manufacturer shotcrete-related issues. or distributor, the next step is to choose the right • Check on the availability of repair parts and the sales staff’s know- pump/gun to meet your job requirements. The ledge of the inner workings of the concrete pump/gun (for trouble- price of the equipment will likely play a key role shooting problems). The manufacturer or dealer should offer on-site in your selection. It is important to research the setup and testing prior to startup (to make sure there is no gunning performance and maintenance history of the wet- or pumping problems with the mixture proportions selected for or dry-mix equipment under consideration. More the job). time and money may be spent on repair and • The manufacturer or dealer should be able to offer hands-on shot- maintenance for a less expensive model than for crete training as an option (check to see how many years of hands- one that is more rugged with a good track record. on training experience the trainers have). The checklist can be used for any civil or mining • Identify accessories the seller offers (hoses, clamps, reducers, con- projects. Following, you will see a comparison crete pipe, shotcrete nozzles, or fittings and accessories needed to between both processes. Advancement in mate- equip the pump/gun for a robotic arm or robotic unit or accelerator rial, admixtures, and equipment has made both dosing systems if the job requires it). processes almost equal. (Figures 4 through 10 are of dry-shotcrete equipment; Fig. 11 through 15 are wet-shotcrete equipment.) There are three (Fig. 8) with outputs of up to 15 yd3/h (11.5 m3/h). areas you need to look at: 1) which process do The rotary barrel has over 50 years of field expe- you want to get into; 2) the right high-velocity rience. It is very simple to run, has direct feed, nozzle setup; and 3) the correct material hose for and can handle any type of synthetic fibers (micro safety and nozzlemen efficiency. Auxiliary/acces- and macro) to steel fibers with the correct barrel sory equipment may be needed depending on size. It has an external exhaust chamber that project requirements. An article found on the ASA allows any excess air to bypass without bubbling website called: “The Value of Shotcrete Acces- up through the hopper. Dust collectors have been sories”8 explains the accessory equipment. designed to eliminate the exhaust dust. Distances for materials up to 1000 ft (300 m) horizontally Dry Machines and with inline material booster distances of over The dry equipment shown ranges from the 2500 ft (762 m) have been achieved. Vertical high-velocity dry nozzle setup to all three types material heights of 400 ft (120 m) have been of dry guns (ACI lists two classes of guns: pres- achieved without an inline material booster. sure vessel and rotary guns). Figure 7 is the newer These rotary guns were constructed for the civil version of the N-gun (pressure vessel), which was and mining projects where the equipment wear introduced back in 1909 by Carl Akeley. The and tear is at its highest. This type of machine Cement Gun Company commercialized the N-gun was designed for a less skilled worker, who just in 1910 and the word “gunite” was coined in 1912. has to feed the hopper of the machine (gun) The N-gun has 105 years of field use and is still during operation. commonly used up and down the East Coast and The bowl-type gun in (Fig. 6) has over 50 years many other countries globally. With the sealed of field experience. It is a production-type gun for pressure vessel, the N-gun has shot long distances sand and cement. The U-shape bowl design makes over 1000 ft (300 m) and heights of over 500 ft it tough to push macro-synthetic and steel fibers (150 m) without the aid of an inline booster. They up through the bowl pockets into the material hose have very few wear parts and older version N-gun proficiently. Due to its low cost, most contractors parts can be replaced with the new present-day choose this type of gun. In most setups, a 2 in. parts. It was built to last for at least 100 years. It (50 mm) inline air is reduced to a 1 in. (25 mm) takes a well-trained gun runner to run the machine. pipe attached to the top of the clamping plate and Often the nozzlemen and gun runner switch posi- rubber pad seal. From there, the 1 in. (25 mm) air tions daily. volume pushes the material through the U-shape The rotary barrel-type gun (Fig. 5) comes in bowl backup to 1-1/2 in. (38 mm) or 2 in. (50 mm) two sizes depending on the output (low production material hose. This alone reduces the volume of of up to 6 yd3/h (4.5 m3/h) and the larger gun air flow and material velocity to distances of Shotcrete • Fall 2015 11


2015FallShotcreteEMag
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