Bryn Mawr College Thomas Library Stairs, Bryn Mawr, Pennsylvania

GeoStructures retrieved concrete cores from various locations within two sets of the library’s exterior stairs. Petrographic examination revealed that the concrete was generally of good quality, showing no evidence of carbonation, cement paste degradation, or alkali-silica reaction (ASR) between the cement paste and the coarse aggregate. Petrographic analysis did reveal, however, a lack of air-entrainment in the core. Without properly entrained air voids, the concrete’s resistance to freeze-thaw cycles is diminished, as was manifested in the macrostructural scaling and near-surface cracking observed in localized areas of the stairs.

Since the library stairs have a thickness of 8 in., and since the maximum frost penetration in Bryn Mawr is about 3 ft. (even for very mild years), GeoStructures concluded that such deteriorations will likely continue over time. Temporary remedial measures included the use of sealants that might help to reduce the infiltration of water, thereby lessening the impact of freeze-thaw cycles. The only conclusive or permanent solution, however, is replacement of the non-air-entrained concrete with air-entrained concrete, thereby providing sufficient space to accommodate the expansion stresses of freezing water.