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2015SpringShotcreteEMag

Shotcrete Corner Layers in New York City Overhead Tunnels By Frank E. Townsend III TConstruction (MTACC) has several large- Superior Gunite prove our placement methods forof reinforcement, we chose to place the shotcretein layers. The NYCT MTACC requested that-he New York City Transit (NYCT) Metropolitan Transportation Authority Capital scale projects throughout New York, including these overhead placements in a mockup, where one major program: the East Side Access project. the structural performance could be verified by On many of these projects, Superior Gunite has bond testing. The pulloff test was conducted using been subcontracted to shotcrete the arch place- ASTM C1583/C1583M-13, “Standard Test ments in lieu of cast-in-place concrete due to Method for Tensile Strength of Concrete Surfaces construction form costs and time savings. These and the Bond Strength or Tensile Strength of arches range from 12 to 30 in. (300 to 760 mm) Concrete Repair and Overlay Materials by Direct thick, encasing two layers of No. 9 (No. 29M) Tension (Pull-off Method).” The criteria we had reinforcement at 6 in. (150 mm) on-center spacing. to meet in the bond test was 100 psi (0.69 MPa) The general contractor, MICHELS Corpora- or greater. tion, subcontracted Superior to shotcrete this We took this opportunity to test two different work, and due to the thickness and complexity surface preparations and configurations for lay- Fig. 1(a): Bond test panel, unreinforced Fig. 2(a): Nozzle-finished panel Fig. 1(b): Bond test panel after two layers Fig. 2(b): Scratch/etched finished panel, were shot unreinforced 34 Shotcrete • Spring 2015


2015SpringShotcreteEMag
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