PSI - Issue 37

João Custódio et al. / Procedia Structural Integrity 37 (2022) 590–597 João Custódio et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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and serrated grain boundaries in quartz grains, the presence of subgrains, microcrystalline or cryptocrystalline quartz forms are also relevant features for this qualitative evaluation. All these varieties present quartz exsolutions, vermicular intergrowths considered as a potentially reactive form of silica nowadays. The type and extension of the alteration observed in feldspars is also considered for silica and alkalis release. Besides the qualitative evaluation for potential alkali-reactivity, the contribution of optical petrography for a better prediction of the behaviour under laboratory accelerated tests conditions (like AAR-3.1, AAR-4.1) must analyse the quantitative data of the relevant features previously indicated. Some open questions should be mentioned: the high value of expansion observed in BHS and CHS in comparison with DHS and the extreme low values registered in the FHS aggregate where at least one variety of rock used has characteristics that allow to consider it as “reactive”.

Grain size of quartz, shape of the of borders (BHS, XPL view)

Strained quartz, undulatory extinction, subgrains (VHS, XPL view)

Vermicular intergrowth of quartz, myrmekites (VHS, XPL view)

Feldspars decayed (BHS, PPL view) Feldspars decayed (EHS, PPL view on the left and XPL view, on the right) Fig. 3. Some examples of textural characteristics and mineral alterations relevant for ASR. Notation: Qz - quartz; Fk - potassium feldspar; P- plagioclase; B, Bcl - biotite, chloritized biotite; M - muscovite. Quartz intergrowths indicated by red arrows. 4. Conclusions It was found that, according to LNEC Specification E 415, all aggregates have in their composition forms of silica that are considered to be potentially alkali-reactive ( e.g. , mainly exsolutions of quartz in feldspars, deformed and microcrystalline quartz grains) and, therefore, had to be further assessed by the concrete prism test. In addition, the petrographic analysis revealed that the aggregates also contain minerals that may release alkalis into the concrete pore solution ( e.g. , feldspars, muscovite, sericite). The results obtained with the RILEM AAR-4.1 tests revealed that only the aggregates used in the AHS dam (two of the three batches assessed) and FHS dam (EHS dam has not been assessed with this method yet) is considered of having an ASR potential of Class II (potentially alkali-reactive or alkali-reactivity uncertain). The remaining aggregates had to be assessed by the CPT. In terms of the alkali-reactivity, the aggregates tested can be ordered, in terms of increasing alkali-reactivity, like follows: FHS < AHS < DHS < CHS < BHS.