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2014WinShotcreteEMag

were often not available when required on our Shotcrete project, which resulted in downtime and quick As the accepted training and qualification changes in procedure. Available maintenance program was put into place, we began our journey crews had a variety of workers with vastly dif- along the learning curve. The crews and manage- ferent talents. While the range of expertise was ment settled on hand-nozzling with the aid of man ultimately an asset to the project, in the short- lifts. This was an important stance to take in term, it inhibited a uniform and productive deference to the qualifications of the workers. We shotcrete application. For example, if a large strongly believe that no matter how many class- robotic machine went down and was in dire need room sessions we had (2 full days for each noz- of service, its maintenance received no priority zleman, on average) or how many hours were but was added to the list on a “first-come, first- spent perfecting technique on the robotic served” basis. machines, the best way to learn quality shotcrete The final obstacle was that the areas to be shot- placement was to actually grab the nozzle and creted were also high-traffic sites, accessed by shoot by hand. workers in many trades. It was a bottleneck for all Under the observation of a qualified supervisor those involved and made implementation of the or previously qualified job foreman, we could shotcrete process and schedule very challenging. start with the nozzle in a low-risk wall or bench shooting to acquire hours of practice. Full quali- fication came after an accepted number of hand- nozzling hours were documented by the approved qualification trainer. It was of great benefit for the nozzleman to have a qualified trainer by his side, giving tips while shooting or discussing key issues with the foreman so he, in turn, could relay advice to the general crew. It should be pointed out that our qualification was geared toward the entire crew and full shotcrete process, not just the workers holding the nozzle. Both dry- and wet-mix shotcrete materials and equipment were used. With a 6 in. (150 mm) slick line, wet-mix concrete was sent from the street through a re-mixer down to the tunnels and into the Putzmeister Shotcrete Technology’s shotcrete pumps. Despite both the harsh physical environ- ment and the carelessness demonstrated by some tradesmen in moving equipment from one Fig. 3 shooting location to the next, the pumps withstood the abuse and operated successfully. According to the specifications, all the large- volume shooting was to be done with wet-mix (refer to Fig. 3). Some smoothing or short patching was handled with dry-mix. For the most part, the dry-mix placement on the project employed full skid-mounted guns with pre- dampeners from Putzmeister. The dry-mix mate- rial supplier used, after a thorough vetting process, was King Packaged Materials Company. King supplied MS-D1 Accelerated Shotcrete and MS-D1 Steel Fiber Shotcrete on both contracts. The 2205 lb (1000 kg) bulk bags were delivered by truck to a rail siding in the Bronx, where they were transferred underground to Grand Central Terminal’s Madison Yards by railcar. The crews had to understand more than just basic shotcrete (refer to Fig. 4). They used a sophisticated shotcrete mixture that included hydration control chemical dosing of concrete intended to sit for hours, yet remain plastic and Fig. 4 pumpable without separation; be pumped up to 34 Shotcrete • Winter 2014


2014WinShotcreteEMag
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