After only six years of service, a 6-foot long narrow piece of concrete spalled off an exposed slab edge of a 680-foot tall high-rise in Texas, and fell 160 feet to the podium below. The spall was attributed to premature corrosion at the drip edge. The building featured approximately 9,200 feet of exposed slab edge over its height. Given the potential risk to safety and property of additional concrete spalls, the Owner requested forensic investigations, which (1) identified other areas with signs of similar distress and (2) determined the underlying problem of low reinforcement cover at the drip edge was pervasive. In response, repair options were developed to address the problem and restore intended durability. Given the building height, difficult exterior-only access, downtown environment, and post-tensioning anchors along the slab edge, the repair design and construction both had unique challenges to consider and overcome.
A significant percentage of repairs are performed during the course of constructing new structures. Once a construction anomaly or error occurs the first concerns are for life safety and schedule impact. A review of the steps necessary to successfully perform repairs and minimize impacts to the ongoing construction. Examples of challenging problems and the traditional and non-traditional solutions to these problems will be discussed.