Variations in the composition and relations between alkali-silica gels and calcium silicate hydrates in highway concrete

Alkali-aggregate reactions (AAR) are a form of severe concrete deterioration that can be found anywhere in the world. The rock type of aggregate is the crucial factor for AAR occurrence as well as for the chemical and morphological nature of their deleterious products - alkali-silica gels (ASG). The paper focuses on highway cement concrete pavement with aggregate composed of metamorphosed volcano-sedimentary complex rocks, such as proterozoic chert, black shale, spilite, and green schist, and alluvial sandy gravels. These petrographic types of aggregate were found to be potentially hazardous. The microchemical composition of ASG was analysed and compared to calcium silicate hydrates present in the vicinity of one another. The qualitative elemental composition of both is the same. Gradual variations of ASG within a single position and among different positions in cement concrete pavement slabs were monitored and compared.