Investigation of Deteriorated Concrete Arch Dam

Investigation of a 40-yr old concrete arch dam is described. Apparent normal weathering processes had caused deterioration to a point where repairs were necessary. Repairs were started but suspicions arose that other destructive processes were at work. A concrete coring program led to inconclusive results. Sonic testing of the dam along with supplementary coring, and a petrographic examination led to the conclusion the concrete was subjected to: alkali-silica reactions, sulfate attack, and leaching of soluble substances from the cement paste matrix. A concurrent stress analysis indicated a factor of safety less than desirable. This led to the immediate replacement of the dam with a similar structure just downstream. Demolition of the old dam verified that the concrete had indeed deteriorated. This dam illustrated that those agents of deterioration are not always easily recognized even though their affects may have reached and advanced stage during service. It also demonstrated the values of petrographic examination and of the sonicscope as a tool for evaluation of concrete, provided it is used in its proper context and with ample supplemental data.