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2015SummerShotcreteEMag

Project Profile: Underwood Pool Belmont, MA By Mason Guarino Tin the United States. It was originally built in and the overall job made this approach feasible.our preferred method. We chose to go with theon-site batching method as the space was availablehe Underwood pool in Belmont, MA, is knownas the first outdoor public swimming pool built 1912. Our recent project to renovate the pool was Anything under 100 yd3 (76 m3) is typically a specified shotcrete as the knowledgeable pool design ready mixed job. engineer wanted the capabilities of shotcrete. This With a late November construction start and a job used all the best characteristics that shotcrete can complicated excavation, which included dewa- offer from light formwork to bonding capabilities. tering issues along with a complex form job, SSG We ended up using all of our shotcrete and pool was not able to start shotcrete placement until late construction knowledge to create a successful project December. Our original plan was to start on the for the Town of Belmont, MA. larger pool and then move to the smaller pool When the bids came in, all the bidders but one whenever we could. This meant that some severe were high. Then the lowest bidder decided to drop winter conditions protection would likely be out when he saw how low he ended up being. The needed. We hoped the snow would hold off. next low bid was about $400,000 over what was The first step in the construction process was budgeted. However, being a relatively wealthy to form the floor as quickly as possible, as floor Boston suburb, the Underwood Pool Committee forms would go much faster than trying to build turned to the town for help to raise that last the entire form system Also, the wall forms could $400,000 required to get the job going. A local be attached to the concrete floor rather than bank stepped up early, saying it would match attempting to drive stakes into frozen earth. every donation, so the town only needed to raise The second step was to install ground thaw about $200,000 to fund the project. The town hose in the 0.75 in. (20 mm) crushed stone layer ended up raising the money in about a month and under the pool. The ground thaw hose was a half so the project could then proceed. The bad installed in loops at 12 in. (300 mm) on center news was the delay in funding pushed the con- runs. This process ended up using roughly 5000 ft struction start time back over 2 months. This (1500 m) of ground thaw hose that would be moved the start date for South Shore Gunite Pools drained and buried at the completion of the & Spas, Inc. (SSG), and the swimming pool con- project. The ground thaw hose was connected to struction to late November. a glycol heating unit that gave us a constant As a swimming pool project, shotcrete was the ground temperature of roughly 50°F (10°C) on obvious method for construction. It helped that the coldest days. the engineer agreed and had specified the project The final step to protect the area to receive the as a shotcrete structure. Fortunately, they did not material was building a temporary tent that would specify wet- or dry-process shotcrete. This is a trap some heat and keep out some of the cold air and good practice because the shotcrete method elements. Ropes, braces, and 100 x 60 ft (30 x 18 m) should always be up to the applicator. SSG chose woven tarps were hung over the entire area and six to go with the wet-mix method as this is a large to eight heaters were placed under the tent to help project and the high production capability of wet- keep temperatures up (refer to Fig. 1). mix was needed. The project consists of two On typical cold weather projects, we would swimming pools: one was a 6000 ft2 (560 m2) keep the ground and reinforcing steel warm by water surface area competition pool with racing laying down thermal blankets until we got to the lanes with a 11 ft (3.4 m) deep diving well and area, placing the shotcrete, and then covering the the other was a 5000 ft2 (465 m2) water surface fresh shotcrete as soon as it was finished to trap area wading/play pool. The project ended up using in the heat. This project would require a steel about 500 yd3 (380 m3) of shotcrete total. The final trowel finish so laying anything directly on the decision was whether or not to use ready mixed fresh shotcrete was not an option. concrete. SSG has the capability of batching Jobsite temperatures ended up averaging concrete material for shotcrete on-site and it is between a high somewhat below 40°F (4°C) and 14 Shotcrete • Summer 2015


2015SummerShotcreteEMag
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