Lake Akiba Dam Rehabilitation Evaluation, Monroe County, Pennsylvania

Overview: Built in 1926, the Lake Akiba Dam was constructed to provide recreational activities to Monroe County, Pennsylvania. Over time, however, dam deterioration became evident. To compliment a field condition survey, test borings, and laboratory compressive strength tests, GeoStructures performed petrographic laboratory analyses on existing concrete core, thus helping to evaluate dam conditions and provide recommendations for dam rehabilitation.

A visual assessment of the dam core, spillway, and spillway walls revealed wide cracks and deterioration, along with a buildup of calcite and vegetation along cracked surfaces. Further observations revealed that the spillway walls had newer concrete placed over original concrete, separated by a bond that was generally delaminated and degraded.

Laboratory petrographic analyses were conducted to validate field observations and to confirm the extent of the concrete degradation. By using a Leica DM750 P petrographic microscope, GeoStructures’ petrographers characterized the air void system, the composition and quality of aggregates and cement paste, and the chloride ion content of the concrete.

Although macroscopic field observations suggested significant deterioration and degradation of the concrete, petrographic analyses revealed that the concrete integrity of the dam core was generally intact except for surface disintegration and spalling in some localized areas. Concrete aggregates were petrographically observed to be of good hardness, uniform distribution, and of strong bonding with the surrounding cement paste. No evidence of large cracking distress was observed, and a low chloride ion percentage suggested there was no detrimental chloride ion within the concrete. It was petrographically confirmed, however, that the concrete was not air-entrained (1.5%), thus leaving it more vulnerable to damage from freeze/thaw cycles.