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2015SpringShotcreteEMag

Shotcrete Corner ered, overhead shotcrete. Two boxes were made test by cleaning the surface and using an epoxy with a nozzle finish and the other two boxes were adhesive (J-B Weld, one-half tube of each per scratched, leaving an etched surface finish. No puck) to adhere a steel puck to the concrete. reinforcement was installed for any of the layers The test apparatus was calibrated prior to the test and all layers were prepared with a water hose and nine tests were performed at 11 days from the cleaning between layers. Each layer had a min- surface to the next layer down and three tests were imum cure time of 24 hours prior to the placement performed at the 28-day mark from the intermediate of the subsequent layer. Two layer configurations layer to third layer. The test involved pulling on were also tested on each of the finishes mentioned the steel plug (attached to the core face) using a previously: for one set, three layers were placed, hydraulic jack. The test equipment setup included: each with 4 in. (100 mm) lifts; and the second set a hydraulic jack (cylinder and piston with a center of boxes were placed in two layers, each with 6 in. hole); a manually operated hydraulic pump; (150 mm) lifts. hydraulic fluid pressure gauge; valve; threaded rods/ The boxes were 3 x 3 ft nuts; shackle; eyebolt; and steel U-frame. (0.9 x 0.9 m) plywood with Using the hand-operated hydraulic pump, the flared ends. All of the hydraulic jack was actuated and a tensile load panels were identified and applied on the test area. The load applied by the marked accordingly. Three jack on the specimen is related to the hydraulic fluid 4 in. (100 mm) cores in each pressure that is indicated by the pressure gauge box were taken 0.75 in. included in the setup. Calibration charts of the (19 mm) beyond the layer hydraulic pressure to load relationship for the com- interface into the second bination of jack and gauge were previously prepared layer from the four panels. by the testing lab during calibration of the jack. Surface preparation was The load applied on the test area was obtained done by the lab, Tectonic, Fig. 3(a): Epoxy by reading from the calibration chart corre- the day prior to the bond adhesive sponding to the pressure shown by the pressure gauge. The tensile load was gradually applied in four increments up to the required strength of 100 psi (0.69 MPa) and then load was gradually increased to failure. The maximum load applied and type of fracture was recorded. Test results (in psi) are shown in Table 1. The test data shows that the specimens where the surfaces between layers are scratched pass the bond test (Box 1 and 2). In fact, the failure stress was not at the interface but in the glue that adhered the steel puck to the concrete. In our testing, the nozzle finish alone did not pass an 11­day bond strength test. However, the testing lab also noted Fig. 3(b): Preparing each puck that the unevenness of the rough, nozzle­finished Fig. 3(c): Adhered pucks Fig. 4: Pressure being applied via hand jack Shotcrete • Spring 2015 35


2015SpringShotcreteEMag
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