Potentially Reactive Forms of Silica in Volcanic Rocks Using Different Analytical Approaches

World Multidisciplinary Earth Sciences Symposium 2017

Esteves, Hugo^1 ; Fernandes, Isabel^1,2 ; Janeiro, Ana^1,2 ; Silva, António Santos^3 ; Pereira, Manuel^4 ; Medeiros, Sara^5 ; Nunes, Joao Carlos^5

Department of Geology, Faculty of Sciences, University of Lisbon, Portugal^1

IDL, Institute Dom Luiz, Portugal^2

LNEC, Materials Department, National Laboratory for Civil Engineering, Lisbon, Portugal^3

CERENA, IST-University of Lisbon, Portugal^4

Department of Geosciences, Faculty of Sciences and Technology, University of Azores, Portugal^5

关键词: Alkali-silica reaction;    Analytical approach;    Analytical method;    Complementary methods;    Energy dispersive X-ray spectrometry;    Mineral phasis;    Silica phasis;    Volcanic glass;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/95/2/022040/pdf
DOI  :  10.1088/1755-1315/95/2/022040

来源: IOP

【 摘 要 】

Several concrete structures show signs of deterioration resulting from internal chemical reactions, such as the alkali-silica reaction (ASR). It is well known that these swelling reactions occur in the presence of moisture, between some silica mineral phases present in the aggregates and the alkalis of the concrete, leading to the degradation of concrete structures and consequently compromising their safety. In most of the cases, rehabilitation, demolition or even rebuilding of such structures is needed and the effective costs can be very high. Volcanic rocks are commonly used as aggregates in concrete, and they are sometimes the only option due to the unavailability of other rock types. These rocks may contain different forms of silica that are deleterious to concrete, such as opal, chalcedony, cristobalite, tridymite and micro- to cryptocrystalline quartz, as well as Si-rich volcanic glass. Volcanic rocks are typically very finegrained and their constituting minerals are usually not distinguished under optical microscopy, thus leading to using complementary methods. The objective of this research is to find the more adequate analytical methods to identify silica phases that might be present in volcanic aggregates and cause ASR. The complementary methods used include X-Ray Diffraction (XRD), mineral acid digestion and Scanning Electron Microscopy with Energy Dispersive X-Ray Spectrometry (SEM/EDS), as well as Electron Probe Micro-Analysis (EPMA).