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2014FallShotcreteEMag

Nozzleman Knowledge Part II of a Two-Part Series on Wet-Mix Equipment Maintenance Maintenance Fundamentals for Nozzlemen: Often Overlooked Equipment and Maintenance Essentials Can Dramatically Influence In-Place Quality Do you know what they are? By Oscar Duckworth Atant factors that will determine in-place facturers offer pumps configured specifically for-Although traditional concrete pumps havebeen used in shotcrete operations, many manu-skilled nozzleman’s control of the nozzleduring placement is one of the most impor shotcrete quality. But like many things, there is wet-mix shotcrete use. These pumps offer robust much more to the task of proper nozzling than hopper, feed auger, and wear components, and simply controlling the nozzle. cooling configurations that are designed to Regardless of a nozzleman’s skill and experi- facilitate the placement of low-slump concrete ence, it is impossible to properly place wet-mix materials. Shotcrete pumps will provide lower shotcrete with poorly chosen or improperly func- placement volumes but have a much higher pres- tioning placement equipment. Because a nozzle- sure potential than traditional machines. man’s placement quality is reliant on the correct Pump choices affect all aspects of shotcrete functioning of many individual equipment compo- placement. Common concrete pumping equip- nents, it is vital that a nozzleman possess funda- ment used for shotcrete placement can lead to mental knowledge of the operation and main - costly placement and reliability problems. Noz- tenance of these components. zlemen often experience erratic material delivery, insufficient cylinder filling, low power, over- Wet-Mix Placement Starts at heating, or excessive plugging when using poorly chosen concrete pumping equipment for wet-mix the Pump shotcrete placement. Nozzlemen require an even Wet-mix shotcrete is commonly placed using flow of material from the nozzle to precisely specialty concrete pumping equipment. Pumps control material placement. Gunning with an are used to push concrete through a delivery irregular or “choppy” flow will not generate system. Nozzlemen should be familiar with how acceptable in-place material. Insufficient cylinder various pump functions influence in-place filling is the primary cause of uneven flow to the shotcrete quality. nozzle. A functioning auger is necessary to prop- Most concrete pumps are positive displacement erly fill the material cylinders during placement. type. They use pumping pistons in action with a Worn or nonfunctioning augers produce irregular valve to pressurize the delivery system. Typical flow rates that diminish in-place quality (Fig. 1 concrete pumps create moderate pressure to push and 2). materials within a normal slump range. Shotcrete Pumps must be kept full. Allowing a pump to placement requires considerable additional pres- run low on material creates strong airbursts sure to convey low-slump shotcrete materials known as slugging. Like other forms of uneven through the delivery system. flow, slugging will reduce accuracy; displace in- 48 Shotcrete • Fall 2014


2014FallShotcreteEMag
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