Delayed Ettringite Formation (DEF) Within Pre-Cast Concrete Cladding Panels on a Mid-Rise Commercial Office Building: A Case Study

摘要

This paper will present the findings of multiple forensic Investigations on a fourteen-story office building located in Houston, Texas. During our Initial survey, widespread cracking was observed within the concrete cladding panels that warranted a more extensive investigation. Construction of the building was completed in 1985; 17 years prior to our initial investigation. Exterior cladding components are comprised of pre-cast concrete panels over each of the floor lines, with a continuous, structurally glazed, horizontal window system at each floor level. The cladding panels are nonload bearing, pre-cast concrete panels, installed at the time of the building's construction. The concrete panels are attached to the structure via steel plates that are welded and bolted to the building's frame. It is intended that this paper will present the results of observations made at the site over a period of several years, as well as the results of testing conducted to assist in the evaluation. A system was developed to locate and catalog the visible anomalies on the panels; including cracks, exposed steel, spalls, pop-outs, and efflorescence on the panels. Full-depth cores were removed from select panels to perform a petrographic analysis and scanning electron microscopy/energy dispersive x-ray microanalysis (SEM/EDXA). The results revealed the presence of delayed ettringite formation (DEF) and alkali-silica reactivity (ASR), with varying degrees of severity. Specific conclusions will be derived related to the conditions at this project and how these anomalies have affected the cladding system performance. Current repair and maintenance provisions will be discussed, in addition to the necessary recladding that will be required in the future. Recommendations will be developed regarding construction practices so that the cladding panel failure observed may be avoided in the future.