Krüger, Miriam E.Miriam E.KrügerThome, VolkerVolkerThomeHilbig, HaraldHaraldHilbigKaliwoda, MelanieMelanieKaliwodaHeinz, DetlefDetlefHeinz2022-05-102022-05-102022-04-29https://publica.fraunhofer.de/handle/publica/41757110.3989/mc.2022.15621The alkali-silica reaction (ASR) remains a major challenge regarding the durability of concrete structures. The reaction mechanism is not sufficiently understood owing to the difficulty in characterizing the structure of the alkali-silica reaction gel (ASR gel) in concrete. Synthetic ASR gels with different compositions, i.e. Na/Si and Ca/Si molar ratios, were synthesized and analysed by Raman spectroscopy and, for comparison, 29Si NMR spectroscopy. The results show that higher Na/Si ratios increase the number of non-bridging oxygens in the gel structure, thus leading to a decrease in the degree of cross-linking. With increasing calcium content of the sodium-calcium silica gel, the structure tends towards that of C-S-H phases. Raman spectroscopy is a promising method to characterise synthetic ASR gels and provide new information on the effect of alkalis on the gel structure.enAlkali-silica reaction (ASR)Alkali-silica reaction gel (ASR gel)Raman spectroscopy29Si NMR spectroscopyconcretejournal article