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2015SummerShotcreteEMag

Fig. 1: The tent to help trap heat a low around 20°F (–7°C) on a daily basis. Finally, winter ever began burying the jobsite in roughly we had to produce warm concrete that would set 3 ft (0.9 m) of snow in the first storm and then in cooler temperatures. Our mobile concrete batch receiving another 3 ft (0.9 m) of snow 2 weeks truck has a water tank that used water circulated later, putting a complete halt to construction through a jobsite water heater so all of our mix and completely negating the use of the rigid water ended up being approximately 100 to 120°F foam insulation forms. Boston, roughly 10 (38 to 49°C). All concrete sand and crushed 3/8 minutes from the jobsite, would go on to receive in. (10 mm) stone was stored overnight indoors roughly 10 ft (3 m) of snow in the first 4 months at our warehouse at 50°F (10°C) to keep the mate- of 2015. rial from freezing or even being too cold. Addi- The job wouldn’t resume again until late April, tionally, we used a water reducer that contained when the snow finally started to melt and we a mild accelerator additive. shoveled off the work area. This delay left our Once the shotcreting began, we made good floor exposed for over 3 months to the severe progress installing the floor. We chose to shoot weather, a surface that would then be shot against the floor because of the many different sloping to maintain a monolithic pool shell. Unfortunately, angles in the floor along with the need for the jobsite sat in a low, tree-covered area which monolithic construction. Some of the areas substantially hindered the melting of the snow. would be very difficult to cast monolithically Shotcrete resumed once normal spring conditions with traditional slab construction. SSG shot the started, and made the working conditions much floor in 10 ft (3 m) wide strips, taking meticu- more comfortable and easier to work with. How- lous care at the joints to maintain a steel trowel- ever, there was still the task of creating a steel paintable finish upon completion. The edges of trowel-finish pool construction. the slab were left 3 in. (45 mm) low for the The wall thickness ranged from 8 to 24 in. (200 outside 6 ft (1.8 m) to accept the wall shotcrete to 600 mm). With the varying wall thicknesses, when the time came. The floor was installed in we knew that set times and final finish times would the week between Christmas and New Year’s. vary significantly. To counter this, SSG decided The compressive strength test results for the to go with the layering technique. SSG started by floor were approximately 8000 psi (55 MPa). completely cleaning the surface to be shot against Once the floor was complete, the crew moved to continue the wall of the monolithic pool struc- into constructing the wall forms. The wall forms ture (refer to Fig. 2). consisted of 1 x 3 in. (25 x 75 mm) rough-cut When shot, the floor area immediately under lumber construction using 1 in. (25 mm) thick the wall was intentionally left very rough. This rigid foam insulation to help the concrete trap area was heavily power washed to remove any- in as much heat as it could while working under thing that could hinder a bond. A bonding agent a tent. Once the forms were complete and ready does not need to be used as properly applied for shotcrete, the snow hit. Boston’s snowiest shotcrete will adhere to old concrete as if it were Shotcrete • Summer 2015 15


2015SummerShotcreteEMag
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