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2014SprShotcreteEMag

Goin’ Underground to allow low-pressure compressed air to escape from the rotor port prior to being charged with material as it rotates. Ensuring this port is clear and the air being discharged is contained as it is released is very important in controlling dust emissions. • Water ring inspection—Occasional inspection of the water ring will ensure that the holes are not plugged with cementitious material. Plugged holes will restrict the amount of water capable of wetting the material and may lead to increased dust levels at the nozzle. • Equipment settings—Keep wear pads, wear plates, and air settings properly adjusted to prevent “blow back” of dry shotcrete material from the hopper. • Wet/dry adjustments—Ensure sufficient water pressure and water volume to avoid excessive Fig. 2: When using bulk tote bags, a hopper hood manufactured to fit the wet/dry adjustments at the nozzle. Be aware hopper of the shotcrete machine will seal the hopper and prevent dust when drilling operations may draw water from from being released the same source as the shotcrete operation, causing inconsistencies in the water supply. • Pre-dampening equipment—When using prepackaged material or dry site-batched aggregates, use pre-dampening equipment to reduce the amount of airborne dust at the machine and at the nozzle (Fig. 3). • Hydro-nozzles or semi-wet nozzles—If pre- dampening equipment is not available, ensure that a hydromix-nozzle or semi-wet nozzle (one in which the water ring is moved back several feet from the nozzle) is used (Fig. 4). • Conveyance hoses—Ensure that the size of the material hose is adequate for the material aggregate gradation and mixture design. Fig. 3: Use pre-dampening equipment to reduce the amount of airborne The Shotcrete Crew dust at the machine and at the nozzle An experienced shotcrete crew that follows proper shotcrete practices will also contribute greatly to reduced dust levels, but even crews with years of experience sometimes require updated training to ensure that they are following proper shotcrete practices and are operating the equipment as per the manufacturer’s recommendations. A good shotcrete materials and equipment supplier should have technical personnel readily available to provide proper recommendations for equipment or materials required for specific projects. Intro- ductory and refresher training can also be a valuable tool when new personnel join the shotcrete crew. Even in cases where the new crew members have previous shotcrete experience, they may have Fig. 4: A hydromix-nozzle or semi-wet nozzle been trained on different equipment or crew (one in which the water ring is moved back operations and may require additional training on several feet from the nozzle) will also prevent the project’s specific operating procedures. the dust generation at the nozzle Shotcrete • Spring 2014 31


2014SprShotcreteEMag
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