Evaluation of damage in concrete from structures affected by internal swelling reactions. A case study

Abstract

Currently, a significant number of concrete infrastructures (e.g. dams and bridges), in Portugal and throughout the world, are affected by internal swelling reactions (ISR). Among the various reactions that can cause concrete swelling, the most common in Portugal are the alkali-silica reaction (ASR) and the internal sulfate reaction (DEF). From the 60 large concrete dams that are currently being monitored in Portugal, there are 19 dams in which the concrete swelling phenomena has already been identified. It is expected that the number of ISR affected bridges will soon surpass that of dams. In Portugal, a dam was demolished and replaced by a new one in 2014 due to ASR induced expansion and distress, a bridge was decommissioned and replaced by a new one in 2015 due to deleterious development of both ASR and DEF, and several bridges had to suffer expensive rehabilitation works the keep them operational. Moreover, there are still new structures being built that will ultimately suffer from ISR deterioration either because existing guidance was not followed or simply due to limitations of available recommendations. As such, ISR-affected structures will continue to wave our infrastructure for years to come. Existing knowledge on ISR does not allow for a complete assessment of the actual condition of an affected structure and an accurate prediction of the mechanical properties deterioration and, consequently, of the period during which the structure will effectively perform its function, essential for the timely and cost-effective planning of the necessary mitigation, rehabilitation or reconstruction works. Therefore, to help surpassing this situation, a research project is being conducted at LNEC to contribute to the establishment of a method for the accurate determination of the current level of ISR progression and of the deterioration of the concrete mechanical properties. These are essential to the adequate overall appraisal of an affected structure, and the development of structural models that predict risks to structural integrity, potential for further deterioration due to other mechanisms, need for mitigation or remediation actions, and the remaining service life of the affected structure. This communication aims to contribute to the ongoing discussion of this topic by the scientific community and, therefore, presents the methodology followed to assess the condition of the concrete from an ISR-affected bridge in Portugal. It includes an extensive experimental campaign, performed to concrete cores extracted from the structure, comprising the latest advances in the field, to allow for an adequate diagnosis and prognosis of the expansive reactions development in the concrete. The results obtained in the study evidenced the utility of such a methodology on the appraisal of the actual expansion level attained to date in the concrete from ISR-affected structures.