FIGURE 3 - uploaded by Isabel Fernandes
Content may be subject to copyright.
Image obtained by SEM (backscatter electron image mode -BSE) of a particle of amphibolite crossed by a crack. EDS spectra confirm the presence of alkali-silica gel (Z1), the existence of chlorite (Z2) and that a silicate mineral (alkali feldspar) (Z3) occurs in the interstitial "cloudy" areas observed under optical microscope. No pure silica was identified in this field of view.

Image obtained by SEM (backscatter electron image mode -BSE) of a particle of amphibolite crossed by a crack. EDS spectra confirm the presence of alkali-silica gel (Z1), the existence of chlorite (Z2) and that a silicate mineral (alkali feldspar) (Z3) occurs in the interstitial "cloudy" areas observed under optical microscope. No pure silica was identified in this field of view.

Source publication
Conference Paper
Full-text available
The mechanisms involved in alkali-aggregate reaction and the characteristics of reactivity of some aggregates are not completely understood, although tens of thousands of mortar and concrete prisms have been tested in the laboratory and field exposure sites have been installed in a number of countries. Aggregates are the least well understood compo...

Context in source publication

Context 1
... was confirmed that cracks are lined by alkali-silica gel. However, no pure silica is present close to the crack (Figure 3). EDS spot analyses from different areas within the aggregate particles confirm that quartz is scarce and limited to inclusions dispersed within in the amphibole grains, as verified by element mapping (Figure 4). ...

Similar publications

Article
Full-text available
Transfer of tyre rubber suit a tremendous difficulty in India step by step. Analysts are attempting to utilize waste rubber in structural building venture from numerous days back. When coarse aggregate was replaced with 20% chipped rubber it was found that the optimum replacement is5% but still there is a deficit in some strength from conventional...

Citations

... In the group of quarries, the aggregates are divided in large sets concerning mainly the mineral composition and texture, such as e.g. in granite s.l. and in basalt s.l., including a range of compositions. The sample of amphibolite was included as it showed to be a challenging aggregate [21]. Samples of crushed rock were collected in the quarries from batches ready to be sold as aggregate for concrete. ...
Article
Full-text available
IMPROVE Project (2012-2015) is aimed at studying the alkali-reactivity of Portuguese aggregates, including innocuous, slowly-reactive and normally-reactive aggregates collected all over the country. The granitic samples were the most numerous, considering the fact that several important concrete structures have been constructed with these aggregates for decades and an increasing number is showing manifestations of alkali-silica reaction (ASR) since the 1990s. The aggregates were characterized by petrographic methods before being submitted to concrete prism tests (CPT) under 38 ºC for 1 year and 60 ºC for 20 weeks. After the conclusion of the expansion tests, thin sections were produced for identification of the minerals and/or textures in the aggregates which might have caused ASR and to recognise the main microscopic features originated in concrete when submitted to such aggressive environmental conditions. In the present work, several samples were selected from each of the classes of potential reactivity according with the petrographic characterization of the aggregates. The petrographic classification is compared with the results of expansion obtained in the CPT and a rating is made regarding the features observed in the concrete thin sections, namely the cracks developed and the distribution of ASR gel, aiming to find a possible correlation with the expansion values observed for the two test conditions used.
Article
Determination of the potential reactivity of slow-reacting aggregates has been an openly debated subject worldwide for decades, and it remains ongoing. The province of Buenos Aires is the main producer of concrete aggregates in Argentina, and many quarries exploit migmatites and granites affected by deformation processes. Therefore, it is important to determine their potential behavior in concrete as they can cause alkali–silica reactions. The objective of this study is to determine the potential reactivity of aggregate samples from seven quarries of this sector by different methods and evaluate their performance. Petrographic studies were carried out according to the Instituto Argentino de Racionalización de Materiales (Argentine Normalization and Certification Institute; IRAM) 1649 standard, and different microstructural characteristics of quartz were quantified. The potential reactivity of the aggregates was evaluated by three expansion test methods, namely, the accelerated mortar-bar test (AMBT), the concrete prism test at 38 °C (CPT), and the accelerated concrete prism test at 60 °C (ACPT). The content of microcrystalline quartz (grain size < 60 μm) was found to correlate very well with the expansion measured in the AMBT and CPT when the limits and testing time of the IRAM standards were adopted. However, no correlation was found with the ACPT, and the results of this test were contradictory to those of the AMBT and CPT. Based on these results, a limit of 5 vol% of microcrystalline quartz appears to be adequate to differentiate reactive from non-reactive behaviors in the rocks studied.