Less than six years after construction of the 59-story building, a large piece of concrete from a slab edge fell more than 200-feet onto the podium. After the incident, a visual survey of the exposed slab edges in the building identified 31 locations with signs of severe cracking and distress. The repair design team performed a forensic investigation to determine the cause of the premature damage and identify repair solutions. Using a suite of non-destructive and destructive testing techniques, the investigation determined that the cause of the observed concrete damage was carbonation-induced corrosion due to improper placement of slab reinforcement during original construction. The investigation also revealed that the issue was systemic and widespread.

Based on the investigation findings, the adopted repair plan included full-depth removal and replacement of all exposed slab edges in the building (approximately 9,200-linear-feet). The repair design addressed numerous dimensional constraints, including steel congestion in the slab edges and the presence of unbonded post-tensioning (PT) anchors along the slab edge. The repair dimensions and the risk of incidental galvanic corrosion cell formation necessitated the use of electrochemically-inert glass fiber reinforced polymer (GFRP) reinforcement. To ensure adequate long-term performance, the repairs incorporated installation of a waterproofing membrane on all exposed concrete in the building. The repair design complied with ACI Committee 562-16 requirements.

The contractor used 12 swing stages to access the exposed slab edges, sometimes at elevations exceeding 600-ft. The demolition and surface preparation equipment used were specifically selected to mitigate damage to existing PT assemblies. The prepackaged concrete repair material was mixed at balconies near the placement locations to avoid transportation delays. The repairs also included a four-step quality control program for each of the repaired slab edges. The repair engineer and contractor coordinated the construction details and methods, including both off-site and on-site mockups.