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2013WinShotcreteEMag

Preconstruction testing Each nozzleman had to shoot a set of four preconstruction test panels that demonstrated the most challenging reinforcing steel configurations in the project. A mean grade of 2.0 was required to pass, with no single core having a core grade exceeding 3.0. Seven of the eight nozzlemen suc- cessfully passed the test. The engineer selected the following test panel conditions: • Type 1: A historic wall shotcrete overlay intersected with a shear wall, with three curtains of No. 10 (No. 32M) and No. 9 (No. 29M) reinforcing steel with additional boundary reinforcing bar elements each 24 in. (610 mm) thick. Refer to Fig. 1 through 3. Fig. 5: Application of 40 ft (12.2 m) tall shotcrete layer 36 in. (914 mm) • Type 2: A historic wall shotcrete overlay thick over the existing historic perimeter wall intersected with a shear wall with an existing pilaster obstruction and three curtains of No. 10 (No. 32M) and No. 9 (No. 29M) reinforcing steel with additional boundary reinforcing bar elements each 18 in. (457 mm) thick. • Type 3: A historic wall shotcrete overlay with an embedded existing pilaster with reinforcing steel cages 20 in. (508 mm) thick. • Type 4: A miscellaneous interior wall with an embedded column 12 in. (305 mm) thick. Work Production Shotcrete work occurred from May 2011 to February 2012 with a 6-day work week. As many as two to three shotcrete crews were on the job site each work day. The average pumping distance on the project was about 300 to 400 ft (91 to 122 m) from the shotcrete pump to the work location. The dense steel configuration motivated the JWG Fig. 6: Existing historic wall after shotcrete overlay application crew to take an unconventional approach to shot- crete application. At some locations, the actual field measurements for the historic wall overlays were over 36 in. (914 mm) thick and required full height installation of up to 40 ft (12.2 m; refer to Fig. 4 through 6). To address this problem, shotcrete was applied in 12 ft (305 mm) tall lifts. Once the concrete material set up, the next shotcrete lift was installed. Consequently, there were no major voids as a result of poor consolidation reported on the project. The walls were applied in one layer of scratch coat from the bottom to the top, and then the final finish coat from the top down was later applied (refer to Fig. 7). By taking this approach, JWG was able to ensure a uniform steel trowel finish. A unique experience at this project was that JWG found that the use of additional water-reducing admixture was actually detrimental to work pro- duction. As a result, JWG used a low dosage when applying a scratch finish so more concrete mate- rial could be stacked on the wall. The dosage was Fig. 7: Shotcrete shear wall after the forms were stripped. The right side increased when applying the final coat finish, of the wall is the stripped form side. The left side is the shotcrete steel which accommodated extra time for the finishers trowel finish side to complete their work before the concrete set. 22 Shotcrete • Winter 2013


2013WinShotcreteEMag
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