Ceramics-Silikáty 53, (1) 31 - 41 (2009) |
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ALKALI SILICA REACTION IN MORTARS MADE FROM AGGREGATES HAVING DIFFERENT DEGREES OF CRYSTALLINITY
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Mladenovič Ana 1, Šturm Sašo 2, Mirtič Breda 3,
Strupi Šuput Jerneja 1
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1 Slovenian National Building and Civil Engineering Institute,
Dimičeva 12, 1000 Ljubljana, Slovenia
2 Jožef Stefan Institute, Department for Nanostructured Materials,
Jamova 39, 1000 Ljubljana, Slovenia
3 Faculty of Natural Sciences and Engineering, Department of Geology,
University of Ljubljana, Aškerčeva 12, 1000 Ljubljana, Slovenia
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Keywords: Alkali-silica reaction, Aggregates, Linear expansion, SEM, EDS
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In the study, mortar bars containing three different types of silica aggregate and aged according to ASTM C 1260 were
examined in order to investigate the characteristics of the reaction rims which occur between individual grains of these
aggregates and the cement paste due to alkali-silica reaction (ASR). Three silica aggregates were used: well-crystalline
quartz crystal, intermediate-crystalline flint, and poorly-crystalline diatomite. SEM was used to determine the morphology
of the reaction rims, and EDS to determine their chemical composition. The quantity of Si ions diffusing towards the cement
paste was determined, as well as the quantity of Ca ions and alkalis diffusing towards the silica aggregate. It was found that,
in the case of the flint aggregate, the CaO–SiO₂ rich gel caused, after 18 days of ageing, a linear expansion of approximately
0.24 %, whereas in the case of the diatomite aggregate, an expansion of approximately 0.56 % was observed (no significant
expansion occurred in the case of the quartz aggregate). It was found that alkali silica reaction correlates inversely with
crystallinity, although a strong effect was observed in the case of the intermediate- and poorly-crystalline aggregates, which,
at certain volume proportions in concrete and mortar, could predominate over the effect of crystallinity |
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