Alkali-silica reaction products: Comparison between samples from concrete structures and laboratory test specimens

Alkali-silica gels (ASG) were investigated in concrete from bridge structures (constructed from the 1920s to 2000), as well as in experimental specimens; employing optical microscopy, petrographic image analysis, and scanning electron microscopy combined with energy dispersive spectroscopy (SEM/EDS). The main differences were found in the chemical composition and morphology of the ASGs. ASGs which had formed in older concrete samples (50–80 years old) show a partly crystalline structure and higher Ca2+ content, indicating their aging and maturation. Younger concrete samples and experimental test specimens exhibit the presence of amorphous ASG. The chemistry of ASG from experimental specimens reflects the chemical composition of accelerating solutions.