DOI: 10.5593/SGEM2014/B12/S2.062


S.Medeiros, I. Fernandes, J. Nunes
Wednesday 1 October 2014 by Libadmin2014

References: 14th International Multidisciplinary Scientific GeoConference SGEM 2014, www.sgem.org, SGEM2014 Conference Proceedings, ISBN 978-619-7105-08-7 / ISSN 1314-2704, June 19-25, 2014, Book 1, Vol. 2, 487-494 pp

Volcanic rocks have been found to be the cause of concrete deterioration in several countries (Argentina, Iceland, Japan, New Zealand and Turkey), due to the occurrence of alkali-silica reactions. Alkali-silica reaction (ASR) is a deterioration phenomenon that occurs between alkaline (Na+ and K+) and hydroxyl (OH-) ions in the cement and certain reactive forms of silica in the aggregates. The reactivity of volcanic rocks is usually associated with the presence of dacitic or rhyolitic volcanic glass (SiO2>62- 65%), altered minerals and the occurrence of free silica forms such as opal, tridymite and cristobalite. The characterization of the reactivity of Azores volcanic aggregates 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) that comprises mainly the petrographic assessment of the aggregates. The petrographic study of the aggregates is complemented by petrographic examination of samples from large structures in order to confirm the potential reactivity of the aggregates. In Santa Maria Island a program was carried out to produce thin sections from: (1) rock samples of two quarries of the island and (2) concrete core samples from the local airport pavement. The petrographic examination and the geochemical analyses of the two rock samples showed a significant alteration of both rocks. The examination of the concrete thin sections showed that the sand fraction is mainly composed by volcanic glass and that the cement paste has almost completely been replaced by an alkali-silica gel, as confirmed by scanning electron microscopy.

Keywords: volcanic aggregates, alkali-silica reaction, petrography, Azores