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Abstract:
The paper presents results of the microstructural analysis of the expressway pavements concrete exhibiting signs of potential alkali-silica reaction (ASR). The analysis was performed on cores drilled from pavements from the northern part of Germany. Specimens were selected from regions of the pavements representing the highest degree of distress. The results obtained during microstructural characterization performed in the laboratory are presented and discussed. The microstructure of concretes was investigated using microscopy in both transmitted and reflected light as well as in scanning electron microscope (SEM) operated in the backscattered (BSE). The chemical compositions of the phases of interest were determined using the Energy Dispersive X-ray analysis (EDS). The thin sections were analyzed using petrographic microscope (under plane, crosspolarized light and with gypsum plate). The petrographic analysis of aggregates was conducted to determine the presence of potentially reactive minerals. During the microstructural analysis particular emphasis was placed on establishing exactly the type of the reaction and the distribution and the composition of the resulting gel. In addition, the Damage Rating Index method has been used to ascertain the degree of concrete pavement damage caused by ASR. During the microstructural analysis particular emphasis was placed on establishing exactly the type of the reaction and the distribution and the composition of the resulting gel. The results of the analysis revealed the presence of the deleterious reactions in pavements. Concrete showed evidence of the ASR. The reactive components were identified as schist and sandstone in the coarse aggregate and reactive siliceous fine aggregate. The resulting gel was predominantly of Si-Ca-K-Na composition.

Keywords:
aggregate, alkali-silica reaction (ASR), gel, petrographic analysis, reactive minerals, SEM analysis