The World Trade Center destruction on September 11, 2001, physically destroyed significant portions of the interior and exterior of the building located at 130 Liberty Street, New York, NY. The collapse of the south tower crushed into the North side of the 130 Liberty building creating a gash from the 5th to 23rd floors and collapsed the plaza area in front, exposing the basement area. Over 1,500 additional windows were broken. A 20,000-gallon diesel fuel tank in the northwest corner of the upper basement area (Level A) ruptured during the collapse of the south tower. Fuel spilled onto Level A and then through the collapsed floor, settling in the lower basement area (Level B). Some of the fuel ignited in Level B and burned along with other debris and materials damaging steel beams and concrete elements. Water from various sources was also introduced into Level B. Thus, a fuel and water mixture soaked into and saturated the concrete foundation in Level B for approximately 2 and a half months.
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.
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