Ceramics-Silikáty 53 (1) 31-41 (2009)

ALKALI SILICA REACTION IN MORTARS MADE FROM AGGREGATES HAVING DIFFERENT DEGREES OF CRYSTALLINITY

A. Mladenovič, S. Šturm, B. Mirtič, J. Strupi Šuput

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.

Keywords: Alkali-silica reaction, Aggregates, Linear expansion, SEM, EDS