FIGURE 5 - uploaded by Isabel Fernandes
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SEM-EDS element maps revealing porosity and presence of two different carbonate minerals, namely calcite and dolomite (Ca and Mg) (b), and presence of very fine-grained silica (Si) as well as clay minerals (Si-Al) and possibly some detrital feldspar (Si-Al-K). Image on the top/left, in BSE, with scale bar.
Source publication
The reactive forms of silica present in an aggregate depend on the origin and geological history of the rocks. The detection of specific reactive silica must be focused on characteristics such as the identification of polymorphs, the quantification of microcrystalline to cryptocrystalline quartz, and/or on the deformation manifestations for each ag...
Context in source publication
Context 1
... quartz and other silicates, as well as neogenic clays in siliceous limestone, are micro-to cryptocrystalline and well beyond optical resolution of a petrographic microscope. Example of a siliceous limestone is shown in Figure 5. Element mapping by EDS reveals the presence of dolomite in characteristic rhombs, and of silica and clay minerals finely interspersed throughout the carbonate matrix. ...
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Citations
... For these reasons petrography is increasingly supported by complementary analytical techniques, especially X-ray powder diffraction (XRPD) analysis, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), FT-IR, and TGA-DTA. These complementary investigations can be performed on aggregates as received (Fernandes et al., 2020;Medeiros et al., 2022), as well as on mortar bars after expansion tests to detect ASR gel formation (Marinoni et al., 2012;Custódio et al., 2022;Doğruyol, 2024). ...
The study focused on natural aggregates used in concrete, sourced from six different production sites in Italy, and assessed their potential alkali-silica reactivity through two national standard methods. The first method, UNI 11530, involved a detailed petrographic examination, utilizing modal analysis for identifying and quantifying potentially alkali-reactive lithotypes. The second test method, UNI 11604, involved an accelerated expansion test at 38°C and high relative humidity on concrete including an established combination of size fractions of aggregates. This method allows the assessment of aggregate reactivity based on concrete expansion after 1 year of testing and an expansion limit value of 0.04%. A correlation analysis was done on the results from both test methods aimed to establish a relationship between the type and content of potentially reactive lithotypes of aggregates and concrete expansion. Chert and Chalcedony were identified as the primary contributors to concrete expansion. The sum of Chert and Chalcedony contents in the combined aggregates was found to vary between 1.8 vol% and 10.1 vol%. A critical content of approximately 5.5 % vol for the sum of Chert and Chalcedony was identified for deleterious expansion development in concrete subjected to UNI 11604 test method. This limit proves valuable in predicting the expansive behavior of aggregates where petrographic analysis has identified the presence of lithotypes potentially reactive to alkalis.
... Sedimentary rock are often used as coarse aggregates and ne aggregates in cement. Microcracks/highporosity seems to be the key factor [23] as for igneous rocks. ...
... Generally, experimental tests are performed to assess this reactivity. It consist in petrographic examination procedures, namely laboratory expansion tests with boosted alkali contents and storage of concrete prisms in conditions of elevated temperature and high relative humidity [23]. Reliable identi cation of very ne-grained rocks bene ts from supplementary methods, most notably SEM-EDS (Scanning Electron Microscopy -Energy Dispersive X-Ray Spectroscopy) in polished thin-sections, bulk whole-rock chemical analysis, or powder XRD (X-ray di raction). ...
This work were carried out in partnership with NTNU University (Norway), in the context of a M1 internship of 3 months. The subject was empirical modelling of lithium mitigation for Alkali-Silica Reactivity (ASR), a chemical reaction that damages concrete structures. It led to an article published in the Nordic Concrete Research journal. In this internship report, exhaustive matemathical demonstrations and explanations about statistical methods are developped with more precision.