Petrographic analyses of the foundation concrete (walls and slabs) examined the extent of deleterious phases and the extent of cracking throughout the structural members. The analyses showed expansive, damaging chemical reactions known as alkali silica reaction (ASR) and delayed ettringite formation (DEF) to be ongoing. These water driven reactions caused cracking, expansion and deterioration of the concrete. Large cracks, observed by optical microscopy, were primarily associated with ASR reactive aggregate. The most deteriorated sections of the foundation were in areas of maximum debris impact and fire damage. Unfilled cracks, observed by scanning electron microscopy (SEM), are indicative of cracking induced by the collapse impact and/or the ongoing chemical reactions. An investigation of physical properties of the foundation concrete confirmed the conclusions from petrography. Results indicated that the impact of debris, the exposure to fire and the deleterious reactions have severely reduced the engineering properties of the concrete. Very high porosities, ionic diffusion coefficients and moisture transport values were measured for samples extracted from the fire damage and the impact damaged areas.

As deterioration of concrete occurs on large concrete structures, repair and future preventative action depends on a thorough understanding of the cause of the failure. RJ Lee Group (RJLG) has leveraged extensive petrography experience to analyze concrete failures and identify their causes. This skillset enabled RJLG to assist a parking garage manager protect the facility.  Visual observations, optical microscopy, and scanning electron microscopy with energy dispersive X-ray microanalyses have all contributed to the forensic investigation. Through source determination of the failure, RJLG provided the facility manager with the information necessary to effectively repair or replace the damaged cement.