Study of Hungarian Rocks Regarding Potential Reactivity to Alkalis

The durability of concrete can be affected due to internal reactions between the alkalis of the cement paste and certain forms of silica present in the aggregates. Petrographic examination provides a useful tool to assess the alkali reactivity of aggregates. In the present work Hungarian stones that are used as aggregates were analyzed for alkali reactivity. Sandstone, two granitic rocks, one andesite and one diabase were studied using petrographic microscopy in order to identify the presence of potentially reactive forms of silica and to classify these rocks accordingly. Complementary methods such as scanning electron microscopy were also applied. Our results confirm that all studied rocks, except diabase, contain silica that has a potential of alkali reaction. Hence analyzed rocks are classified to Class II from the alkali reactivity point of view, while diabase is in Class I.