Volcanic Aggregates from Azores and Madeira Archipelagos (Portugal): An Overview Regarding the Alkali Silica Reactions

World Multidisciplinary Earth Sciences Symposium 2017

Medeiros, Sara^1,2 ; Ramos, Violeta^3 ; Fernandes, Isabel^2,4 ; Nunes, Joao Carlos^1 ; Fournier, Benoit^5 ; Silva, António Santos^6 ; Soares, Dora^6

Department of Geosciences, Faculty of Sciences and Technology, University of Azores, Ponta Delgada

9500-321, Portugal^1

IDL-Institute Dom Luiz, Lisboa, Portugal^2

ICT, Institute of Earth Sciences, University of Porto, Porto

4169-007, Portugal^3

Department of Geology, Faculty of Sciences, University of Lisbon, Lisboa

1749-016, Portugal^4

Department of Geology and Geological Engineering, Laval University, Quebec

G1V 0A6, Canada^5

LNEC, Materials Department, National Laboratory for Civil Engineering, Lisboa

1700-066, Portugal^6

关键词: Alkali reactivity of aggregate;    Alkali-aggregate reactions;    Alkali-silica reaction;    Concrete expansion;    Durability of concrete structure;    Energy dispersive X ray spectroscopy;    Geochemical analysis;    Reactive aggregate;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/95/2/022034/pdf
DOI  :  10.1088/1755-1315/95/2/022034

来源: IOP

【 摘 要 】

Alkali-silica reaction (ASR) is a type of deterioration that has been causing serious expansion, cracking and durability/operational issues in concrete structures worldwide. The presence of sufficient moisture, high alkali content in the cement paste and reactive forms of silica in the aggregates are the required conditions for this reaction to occur. Reactive aggregates of volcanic nature have been reported in different countries such as Japan, Iceland and Turkey, among others. The presence of silica minerals and SiO2-rich volcanic glass is regarded as the main cause for the reactivity of volcanic rocks. In Portugal, volcanic aggregates are mainly present in Azores and Madeira Archipelagos and, for several years, there was no information regarding the potential alkali-reactivity of these rocks. Since the beginning of this decade some data was obtained by the work of Medeiros (2011) and Ramos (2013) and by the national research projects ReAVA, (Characterization of potential reactivity of the volcanic aggregates from the Azores Archipelago: implications on the durability of concrete structures) and IMPROVE (Improvement of performance of aggregates in the inhibition of alkali-aggregate reactions in concrete), respectively. In order to investigate the potential alkali-reactivity of aggregates from both archipelagos, a total of sixteen aggregates were examined under the optical microscope and, some of them, also under the Scanning Electron Microscope with Energy Dispersive X-ray Spectroscopy. A set of geochemical analyses and laboratory expansion tests were also performed on those volcanic aggregates. The main results showed that the presence of volcanic glass is rare in both archipelagos and that the samples of Madeira Archipelago contain clay minerals (mainly from scoria/tuff formations inter-layered with the lava flows), which can play a role in concrete expansion. The results of the laboratory tests showed that one of the samples performed as potentially reactive in the accelerated mortar-bar test (ASTM C 1260) and that the majority of the Azores samples started to show some expansion just after one year of testing in the concrete prism test (CPT) at 38°C.