PSI - Issue 37

João Custódio et al. / Procedia Structural Integrity 37 (2022) 590–597

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João Custódio et al. / Structural Integrity Procedia 00 (2019) 000 – 000

1. Introduction Deterioration of concrete structures by Alkali-Silica Reaction (ASR) has increased dramatically over the past couple of decades in Portugal. ASR has important economic implications, since it is normally observed in very large structures ( e.g. , dams and bridges) and the work necessary to remediate the problem involves large areas of reconstruction and complex and expensive repairing techniques and materials. Moreover, ASR diminishes the affected structure service life, may involve the interruption of its function and, ultimately, can lead to its decommissioning and demolishing. In Portugal, ASR has been detected in more than fifty bridges and dams, a dam was partially demolished and replaced by a new one in 2014 due to ASR induced expansion and distress, and a bridge had to be decommissioned and replaced by a new one in 2015 due to deleterious development of ASR and DEF (delayed ettringite formation), and several bridges had to suffer expensive rehabilitation works to keep them operational. Due to the rhythm at which ASR is being identified in existing structures and the large number of structures recently built or under construction in Portugal, which may also develop ASR, it is predicted that concrete structures deterioration due to ASR will continue to increase in the next years. Presently, at an European level, only two standards mention ASR, namely EN 206 (IPQ, 2017) and EN 12620 (IPQ, 2010), and they just state that actions shall be taken to prevent ASR in new structures using procedures of established suitability. Due to the complexity and multiplicity of factors involved in ASR together with the variability of the materials used, no such established procedures exist, and each country must rely on national specifications. Because of that, in Portugal, LNEC Specification E 415 was created in 1993 (LNEC, 1993a) and LNEC Specification E 461 was created in 2004 (LNEC, 2004) and revised in 2007 (LNEC, 2007a). However, due to the scientific developments occurred since then, new versions were prepared and will soon be published (LNEC, 2021a, LNEC, 2021b). Although, LNEC Specifications provide guidance on the identification of potentially alkali-silica reactive aggregates, i.e. , aggregates that contain forms of silica that can be potentially reactive with alkalis, there are still some knowledge gaps on how to reliably assess the potential reactivity of some minerals present in granites and similar rocks, which are the type of aggregate most used in large structures in Portugal. Therefore, to contribute to the current ongoing discussion on the role of the main components of these rocks on ASR development, this paper presents the methodology that was applied in the evaluation of granitic aggregates used in recently built hydroelectric projects as well as in a dam constructed abroad several decades ago, and in which the deleterious development of ASR was detected 15 years after construction. In this latter case, the rock varieties used as aggregates have a local origin and the most frequent one is not similar to any type of variety used in Portugal. However, its inclusion in this study is considered very relevant due to the singular characteristics of texture/ mineralogical composition. 2. Hydroelectric schemes The study summarised in this paper concerns the aggregates used in eight recently built Portuguese dams, corresponding to four hydroelectric schemes (AHS, BHS, CHS, DHS, EHS), and a dam constructed several decades ago (FHS). The structural type of the dams and the volume of concrete used are presented in Table 1.

Table 1. Da ms’ type and volume of concrete used. Hydroelectric scheme Structural type

Volume of concrete (m 3 )

AHS

Double-curvature arch Double-curvature arch

18,500 786,100 191,100 414,600 322,000 89,500 222,000 240,000

BHS

Gravity

CHS

Double-curvature arch

Arch-Gravity

DHS

Gravity

Double-curvature arch

EHS

Arch-Gravity

FHS

Double-curvature arch

n/a

NOTATION: n/a – information not available.