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2016SummerShotcreteEMag

Shotcrete Corner velocity or spray-up method. A rotor stator pump can generate up to 600 psi (4.1 MPa) of pumping pressure. These pumps are commonly used for pumping highly flowable materials, but they can tolerate small aggregate. Too sharp of aggregate may result in premature wear of the stator. Advantages of rotor stator pump: • No pulsation; • Low cost to purchase; and • Good mid-range pumping pressure. Disadvantages of rotor stator pump: • Aggregate will affect rotor stator wear; and • Rotor stator costs. Rotary Gunite Machine A rotary gunite machine (refer to Fig. 5) is recommended for the dry-mix shotcrete process. In the rotary barrel-type gun, a rotor, available with rotor openings of various shapes and sizes, is sandwiched between a top plate and a bottom plate that has been machined flat. Rubber wear pads are mounted to the underside of the top plate and the top of the bottom plate. Case-hardened metal wear plates are mounted to the top and bottom of the rotor. A single, self-leveling bolt tightens the top plate to the bottom plate and seals the rotor between the two rubber wear pads to guarantee a seal. A high volume of compressed air is connected to an inlet on the top plate and this compressed air is used to convey the material from the pockets of the rotor that are full of material through a 90-degree fitting attached to the underside of the bottom plate and into the delivery line. Additional compressed air is connected to the delivery line. The speed the rotor turns is directly related to the amount of material that will pass through the rotor section. A nozzle with a water ring is attached to the end of the delivery line to hydrate the material. A water valve adjusted by the nozzleman provides control of the level of water injected into the dry-mix materials flowing through the nozzle. Standard delivery lines vary from 2.5 in. (62 mm) down to 1.25 in. (30 mm) in diameter. Acceptable hydration has occurred when the material has been hydrated to 10 to 12% by weight of the concrete materials. The power supply is available with an electric motor, air motor, gas or diesel engine, and hydraulics. The rotary gun is also available as a skidsteer work tool. The dry-mix shotcrete process means that the material remains “dry” until it is properly hydrated at the nozzle. Best results occur if the material has 3 to 5% moisture when loaded into the hopper of the gunite machine. To accomplish this, preparation should be made to pre-dampen the material, if needed. Fig. 4: The benefit of a rotor stator pump, such as this one, is there is no pulsation when material is continuously fed Fig. 5: A concrete pump and a gunite machine, such as the one pictured, are work tools that can help a contractor turn a nickel’s worth of concrete material into a dime, a quarter, or even a dollar using the wet- or dry-shotcrete process Advantages of rotary gun for dry-mix shotcrete process: • Precise control of material flow for low or high output; • Easy stop and start with no cleanup; and • More forgiving to variations in aggregate size. Disadvantage of rotary gun for dry shotcrete: • Generates more dust and waste, particularly if not properly hydrated; and • Requires more compressed air to convey material. Jim Farrell, CEO of Blastcrete Equipment Company, has nearly 40 years of experience in specialty refractory products, including shotcrete and gunite equipment. He heads the family-owned company based in Anniston, AL, and serves customers around the world. Shotcrete • Summer 2016 59


2016SummerShotcreteEMag
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