Concrete Deterioration in Spillway Warm-Water Chute, Raystown Dam, Pennsylvania

摘要

The concrete in the walls and floor of the warm-water chute of the spillway of Raystown Dam, a relatively new structure (less than 10 years old), was showing an excessively rapid deterioration in quality. Surface concrete appeared extremely sandy and rough, resulting from an apparent dissolving away of cement paste and coarse aggregates. In addition to the surface problems, the walls separating the warm-water chute from the main spillway chutes contained interconnected voids, allowing water to flow under and through the walls. Several of these voids were large enough to reach inside. A limited sampling program provided concrete cores, aggregate, water, and efflorescence samples for chemical and petrographic analysis. A review of the pH history of the water in the reservoir was also conducted. The petrographic examination revealed that the surface concrete had been attacked by an aggressive liquid. Calculation of the Langlier Index for the reservoir water showed it to be aggressive to concrete. The pH history and the lack of evidence of introduction of acid into the reservoir, coupled with the chemical and petrographic evidence, led to the conclusion that the water itself was causing the surface damage. The voids in the walls were attributed jointly to poor consolidation of the concrete and design details which allowed the agressive water access to the interior of the walls. This is believed to be the first reported case of aggressive water attack on a concrete structure in the United States. (Author)