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2014WinShotcreteEMag

(1 MPa) shotcrete-to-steel, but no data were avail- able showing this was achievable. The specifica- tion required hydrodemolition of the existing shotcrete followed by an abrasive blast of the surface. This created some degree of ambiguity. Thus, it was decided that a surface preparation mockup test should be conducted. The initial surface preparation test section was divided into three areas: one with a walnut shell blast, the second with a light sand blast, and the final area with just an air and water blast. The initial process was the belief that minimizing the removal of the existing material (steel surface and attached mesh) would be a good approach, and to then build the sections back up from there. The surface preparation tests had almost identical results from each of the three methods, with values ranging from 0 to 120 psi (0 to 0.83 MPa) with the majority being 0. After this initial test, it Fig. 5: Positioning the equipment for the next shoot was obvious that more extensive testing would be required. Steel road plates were used to repre- sent the bridge surface during the next test, which included a variety of differing parameters, including more extensive sandblasting, bonding agents, accelerators, hydration stabilizers, and different curing methods. In the end, a complete white blast of the steel surfaces proved to be the most effective with a multi-course sandblast mate- rial. But even then, the results were still not very consistent. Some sections would bond well and meet the specification and others would have no bond at all. Other attributes that seemed to be creating variability were the shrinkage and the flexural properties of the shotcrete material. The specification called for minimum levels of silica fume and cement, but we decided we needed to rethink this. This is typically where I’ve seen a great number of projects become dysfunctional. The focus changes from getting the job done correctly to minimizing the damage and protecting one’s best interest. The parties become more adversarial than trying to work together to solve the problems and move forward. Fortunately, with this project, the Oregon Department of Transportation (ODOT) and its team stepped up not only finan- Fig. 6 and 7: Ever-changing shooting positions Fig. 8: Overhead finishing 28 Shotcrete • Winter 2014


2014WinShotcreteEMag
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