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2013WinShotcreteEMag

The Overall Application with the desired quality. Cores of the test panel Procedures encapsulated in dense shotcrete without excessiveshowed that all the reinforcing steel was thoroughly Daesang E&C Company undertook the plan- voids, shadows, or entrapped rebound or overspray, ning, project management, and design of the as shown in Fig. 5. Grading of the cores was based project. Careful consideration was given to the on visual examination and measurements of defects, construction material specifications and the resulting in “ Core grade 1” according to ACI CP-60. importance of proper curing. These were both The mockup was kept on site and formed the stan- extremely important factors considering the hot dard for acceptance/rejection of future shotcrete temperatures expected during the project. work on site. Cores with a diameter of 4 in. The field procedures for the project were as (100 mm) were extracted for a series of test programs. follows: 1) remove the damaged curved-concrete The tests for hardened concrete included compres- surface of the spillway by hydrodemolition; 2) sive strength using a core cylinder of 4 x 8 in. (100 x set wire guide lines for controlling the overlay 200 mm) and a beam of 4 x 4 x 18 in. (100 x 100 x thickness and maintain the surface with a satu- 450 mm) according to ASTM C42 to monitor strength rated surface-dry condition; 3) mock up panel development at 1 day, 7 days, and 28 days. The test; 4) analyze test results; 5) mix with a mobile compressive strengths were measured to be 3100 psi mixer; 6) shoot shotcrete; 7) finish the surface; (21.4 MPa), 3480 psi (24.0 MPa), and 5800 psi 8) spray curing compound for immediate and (40.0 MPa) at 1 day, 7 days, and 28 days, respectively. temporal cure to resist early-age plastic shrinkage It satisfied the specified requirements and achieved cracking; 9) cover exposed surfaces with wet the EFNARC C55 Grade. The flexural strengths were burlap and sprinkle water for long-term curing; 780 psi (5.1 MPa) and 885 psi (6.1 MPa) at 7 days and 10) perform the final inspection and and 28 days, respectively. The result of pulloff bond acceptance of the structure. Figure 4 illustrates strength showed 290 psi (2.0 MPa), which was above the detail of field application procedures. the criteria of 200 psi (1.4 MPa). Durability of the reservoir spillway is very mockup test and test results important because it is naturally subjected to The mockup was constructed to demonstrate continuous cycles of freezing and thawing, as that the contractor, equipment, nozzleman, and well as wetting and drying. The results of the finishing crew were capable of constructing the work ASTM C1202 rapid chloride permeability test, Fig. 4: Field procedures 50 Shotcrete • Winter 2013


2013WinShotcreteEMag
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