ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306198
MAINTENANCE, REPAIR, and REHABILITATION OF CONCRETE BRIDGES A drymix shotcrete process was used to repair the badly deteriorated piers on the Noblestown Road Bridge near Pittsburgh, Pa. The repair method allowed the bridge to remain open during construction and return to full operation quickly. ASPIRE, Winter 2010 | 41 The Noblestown Road Bridge had provided long service to citizens in Allegheny County, near Pittsburgh, Pa., but its piers had become badly deteriorated. In many places, the concrete appeared to have eroded away like a mud embankment. To repair the damage and restore the bridge, the contractors used shotcrete and a sequenced construction schedule to maintain traffic and return the bridge to full service in a short time. Sofis Company Inc. performed the work in conjunction with general contractor Thornbury Inc. of West Sunbury, Pa. As contractors could work on only one half of the bridge at a time, to allow traffic to be maintained, Thornbury set up a pattern diverting traffic to the two westbound lanes, with one lane in each direction. Towers were erected at Piers 1, 3, and 5, and the bridge was jacked up to support the structure during removal of concrete on the bridge piers. Due to structural concerns, removal of concrete from both sides of the piers' hammerheads at the same time was not permitted. The concrete on one side had to be removed, surfaces prepared, and shotcrete applied and allowed to cure, before working on the other side. After work was completed on the piers supporting the two eastbound lanes, traffic was diverted to those lanes so work could take place on the other piers supporting the westbound lanes. Drymix Shotcrete Process Used A drymix shotcrete process was chosen for several reasons. With the drymix process, both the overhead and vertical areas could be shot to the full depth of the repair without using accelerators. This approach eliminated the possibility of laminations that can occur when shooting in layers, which can create points of failure. The scattered repair areas also allowed work to stop and start more easily without concern about wet material in the hoses, as is the case with the wetmix shotcrete process. Utilizing the drymix process permits the nozzleman to make adjustments in water content at the nozzle and allows the material to be placed with less water content. The material being installed was essentially a zero-slump pneumatically placed concrete. The contractor saw-cut the perimeter of the repair areas, chipped out the deteriorated concrete, sandblasted the reinforcing bars, and added new reinforcing bars where needed. Welded wire reinforcement was installed, holes were drilled for epoxied anchor bars, and shotcrete gunned in place to restore the concrete piers to their original contours. Quikrete Shotcrete MS with an added Cortec migrating corrosion inhibitor was selected. This premixed material Noblestown Road Bridge: REHABILITATED WITH SHOTCRETE by Ted W. Sofis ASPIRE_Winter10.indb 41 12/18/09 2:06:37 PM