PETROGRAPHIC EVALUATION OF REACTIVE MINERALS IN SELECTED CRUSHED AGGREGATES IN POLAND

The long term performance of concrete pavements can be reduced due to improper selection of aggregates, thus prevention of damage due to alkali-silica reaction (ASR) requires a detailed examination of minerals in aggregates. The amount of reactive silica in the aggregate is an important factor governing the severity of ASR, which depends critically on the nature of the reactive aggregate. In the present study the potential for ASR in selected rocks in Poland was evaluated using petrographic methods. The tests were performed on crushed aggregates from different regions, covering a variety of rock origin and their geological structure. The optical microscopy in transparent light on thin sections was used as a principal tool to assess the mineral composition of aggregates. The content of reactive siliceous minerals was assessed. The petrographic examination concerned different forms of silica. Quartz grains were classified according to their mean diameter so as to identify the reactive range. The application of the petrographic method allowed for classification of aggregate for ASR potential using RILEM recommendation. The results of the study allow to make a quick and responsible decision to direct the aggregates to further detailed tests, reject or accept them as concrete components for concrete pavements.