Alkali-silica reaction - A case study in the Azores Archipelago throught the ReAVA project

Abstract

Concrete is one of the most widely used construction material in the world. However concrete structures can deteriorate during their lifetime due to material limitations, design and construction practices and severe exposure conditions. One of the causes of concrete deterioration is related to alkali-silica reactions (ASR) which are chemical reactions that occur between alkaline (Na+ and K+) and hydroxyl (OH-) ions in the cement paste and certain forms of silica in some aggregates. This deterioration phenomenon causes expansion and cracking that consequently reduces the life service of concrete structures. Basalts and other volcanic rocks have been found to be the cause of premature concrete structures deterioration in concrete in several countries, such as Japan, Iceland and Turkey, due to the occurrence of ASR. The characterization of the reactivity of volcanic aggregates in Azores has been implemented through the research project ReAVA (Characterization of Potential Reactivity of the Volcanic Aggregates from the Azores Archipelago: Implications on the Durability of Concrete Structures). Aggregates were selected and collected from a total of 13 places in 8 Islands. Corvo Island was the only exception due to the lack of local production. The program involved: (1) the petrographic characterization of the aggregates, (2) assessment of their performance in expansion tests and (3) site inspection of some existing large concrete structures in the Azores. The results of the lab tests show that one of the aggregates is potentially reactive. Also one of the concrete structures studied in this project evidenced some degradation, showing features that are very similar to ASR. This paper presents the results obtained on the characterization and performance of volcanic aggregates from Azores regarding the potential reactivity to alkalis using different methods and the concrete ASR diagnosis in a concrete structure.