Insights into the Diagnosis and Prognosis of the Alkali–Silica Reaction (ASR) in Concrete Dams, Highlighting the Case of the Demolished Alto Ceira Dam in Portugal

Abstract

Over the past few decades, a significant number of large concrete structures with deterioration problems related to the alkali–silica reaction (ASR) have been identified in Portugal and worldwide. Assessing the condition of ASR-affected concrete dams involves both diagnosis and prognosis. Diagnosis evaluates the structure’s current state, while prognosis predicts deterioration and safety implications. This is key to estimate the period during which the structure will effectively perform its function, and essential for the timely and cost-effective planning of the necessary mitigation, rehabilitation, and/or reconstruction works. This article aims to contribute to the ongoing discussion of this topic by the scientific and technical community and, therefore, presents the methodology adopted to assess the condition of a severely ASR-affected concrete dam in Portugal, the Alto Ceira dam, in which the concrete was produced with susceptible to ASR quartzitic aggregates and that was decommissioned and replaced by a new one in 2014. The article provides a brief review of the diagnosis and prognosis of the ASR in concrete dams, presents and analyses the results from laboratory testing (including chemical, microstructural, physical, mechanical, and expansion tests), in-situ testing, structural monitoring systems, visual inspections, and numerical modelling, aiming at assessing ASR impacts and evidencing the utility of the reported methodology on the appraisal of ASR-affected structures.