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This paper describes repairs on two prestressed concrete pipelines (inverted siphons) that were found to have distressed areas. The distressed areas included disbonded mortar coating, and corroded and broken prestressing wires. The siphons were dewatered, during January and part of February 1991, for repairs and inside inspection. Repairs in areas of major corrosion and broken prestressed wires consisted of removing the earth cover, excavating a limited-length trench under a pipe unit, and completely removing the mortar coating and prestressing wire around the pipe for 360 deg. High-strength steel tendons were placed around the pipe and stressed to the initial prestressing force. Shotcrete was placed over the tendons and anchors, followed by backfilling. The two siphons were returned to service on Feb. 15, 1991. The repairs appear to be successful in restoring the concrete pipe to its initial design strength.

Injection methods for repairing concrete to maintain the integrity of structural members were studied. As a general rule, the lower is the viscosity of epoxy, the longer the setting time and the deeper the grout goes. Further, the deeper the placing, the better the result will be. In the actual case, splitting tension test of core cylinders from repaired sections show that the repair method that adopts a specially designed injector will do better work than that using a conventional one.

The Story Bridge is a densely trafficked, important corridor over the Brisbane River. Built in the 1940s, the bridge (particularly the southern approaches) are showing signs of distress. The main span of the bridge consists of two steel cantilever trusses with a drop-in steel span. The overall length of the main span is 446 m. The southern approach spans consists of steel trusses, concrete girders, and a grillage of beams with a concrete deck, for a combined length of 515 m. There have been longstanding concerns with respect to some elements of the bridge. These are expressed most visibly by extensive cracking and spalling of the concrete. In some locations primary reinforcement is completely rusted through, leaving doubts about the safety of local areas of the bridge. Some rocker bearings appear to be partially or totally seized. The investigation involved an historical review of the design and construction details used in the bridge. Design loads were compared with modern standards. The concrete quality was investigated and the level of corrosion determined. These are reported in the context of the original specifications and details, and repair procedures recommended.

An intense fire in the antioxidant plant of a chemical factory near Bombay caused extensive damage to the reinforced concrete frame of the building as well as to the flooring, equipment, fixtures, and fittings. Consultants were appointed to investigate the damaged structure and later to design and supervise the rehabilitation work. After the preliminary investigation, the consultants decided that it was not necessary to demolish the structure, as long as it was possible to restore the structural members at a reasonable cost and within a short time span. In addition to visual inspection and sounding, extensive nondestructive tests were conducted to determine the extent of damage and the residual strength of the important load-carrying members of the structures. The findings of the investigations were analyzed and the restoration system was designed by the consultants. The paper outlines the considerations that led to restoration of the structure in preference to demolition, the details of investigations, the analysis of the findings, and the successful rehabilitation techniques that followed.

The crest of Kakabeka Falls, a major tourist attraction near Thunder Bay, Ontario, had changed rapidly within 15 years. Geotechnical evaluation had concluded that, due to the geometry of the rock formation, there was little continuous cap-rock beyond the crest of the falls. Undercutting by water and subsequent ice jacking and freeze-thaw action was eroding the remaining cap-rock. Without prompt remedial work, the falls would degenerate to rapids over 50 years. Rapid recession of the falls also threatened the foundations of two bridges. In 1988 and 1989, remedial works were undertaken to stabilize the erosion process and improve the appearance of the falls. Concrete mixes were designed using powdered color dyes to duplicate the color and appearance of the reddish brown cap-rock and black hales. The crest of the falls was reconstructed incorporating a weir which spread the water flow evenly across the width of the falls. Special formwork and hand-finishing techniques were used to texture the concrete surface to match the existing rock. Two years in planning and eight weeks in construction, the project successfully restored the falls to its former beauty.