This diploma thesis has three goals: 1. A comprehensive summary of the knowledge of the alkaline-silica reaction of aggregates in cement. 2. Clarification of the mechanism of reactive forms of SiO2 with alkali in aggregates of cement at the macroscopic and microscopic level. 3. Laboratory testing of reactive effects of silicites. To meet the goals of the thesis, literature focused on the understanding of the chemical principle of the formation of alkali-silica and its destructive manifestations in aggregates of cement, respectively when used in concrete. At the same time, a laboratory test was conducted on selected types of silicites, which form part of the petrographic composition of mined gravel in the area of Western Slovakia. The aim of the experiment was to test the valid technical standard in terms of its informative value in assessing the effects of the alkali-silica reaction of aggregates. The limiting factor of experiment time limitation over a period of 6 months caused that the test specimens tested were not significantly damaged by the net of macro- or micro-cracks, as in the case of long-term exposure in outdoor conditions. Nevertheless, the realized experiment can be considered a good theoretical preparation, which provides one only possibility of laboratory testing of aggregate reactivity in the context of possible dilatation changes.