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up with a poor result. Shotcrete is concrete—the Raccoon Dam and Spillway only difference being the method of placement. We began rehabilitation of Raccoon Dam and The mesh and reinforcing steel has to be securely Spillway at Raccoon State Park in Beaver County, anchored and tied in place, so there is no movement PA, in 1983 and completed the shotcrete repairs or flex when the shotcrete is gunned. Otherwise in the second phase of the work in 1984. Prior to it can pull from the surface, especially in overhead the shotcrete repairs, there had been problems applications. Good workmanship is necessary, as with a polymer­modified patching mortar. The are wetting down the receiving surface prior to gunning to get a saturated surface-dry (SSD) condition; using good gunning techniques; (a) ensuring a good, consistent shotcrete mixture; allowing the shotcrete to get its initial set before starting to cut­down and finish the surface; and making sure the shotcrete is properly cured. The 31st Street Bridge The oldest of our projects that I revisited was the 31st Street Bridge in Pittsburgh, PA. The bridge spans the Allegheny River and Herr’s Island, now referred to as Washington’s Crossing. (b) We were general contractor for the rehabilitation of the bridge and the work was done in 1973 and 1974. The project required steel repairs and exten- sive shotcrete repair work to the piers of the old bridge. The sand and cement was mixed on site with 3.5 ft3 (0.1 m3) of sand to one bag of cement. The mixture was measured in 1 ft3 (0.03 m3) wooden boxes as a quality-control measure. For the dry-process shotcrete placement, we used a Jetcreter, an early straight drop feed rotary gun. I remember the project well because I worked on Fig. 3(a) and (b): (Before) Rehabilitation work on Raccoon Dam and the concrete tear-out crew during the removal Spillway (Raccoon State Park, PA) included removal and replacement stage and on the gunning crew during shotcrete of deteriorated concrete on large sections of spillway and across top of placement. The most difficult part of the job dam. These photos show dry-process shotcrete placed on upper sections involved cutting and finishing the architectural of dam in autumn of 1984. Once placed, shotcrete was then cut down or details on bridge piers. The bridge has undergone rodded to grade before finishing additional rehabilitation work in recent years for steel repairs and to replace the bridge deck, but the shotcrete installed on bridge piers 42 years ago remains intact and in good condition. Bridgeville Arch Bridge The second job, in Bridgeville, PA, involved dry-process shotcrete repairs to a concrete arch bridge that we rehabilitated in 1977. On both sides of the bridge, the concrete arch was badly deterio- rated. We removed the concrete to a depth of 14 in. (350 mm) from the edge of the arch. Because of the depth of the repair, dowels were installed across the entire arch and reinforcing bars were installed. In addition to the arches, the concrete parapets were also badly deteriorated. So the deteriorated parapet concrete was removed, leaving the capstones in place. The shotcrete was then gunned in place and finished to grade. Considering the condition of the bridge when the repairs were done in 1977, it is Fig. 4: (After) Shotcrete repairs to Raccoon Dam remain in good remarkable that after 38 years, it has held up so condition across crest of dam 31 years after shotcrete work was well. When shotcrete is placed properly, it’s as performed. Water flowing over crest of dam and spillway shows a durable as any concrete repair. relatively even flow despite the passage of years Shotcrete • Spring 2015 19


2015SpringShotcreteEMag
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