Investigation of a series of synthetic alkali silicate gels and gels produced by the alkali silica reaction (ASR) in field concrete using 29Si NMR spectroscopy, X-ray diffraction, & bulk chemical analysis shows that local structures of the synthetic & field gels are quite similar. The most abundant Si sites for the field & synthetic gels with similar compositions have Q3 polymerisation, & the number of non-bridging oxygens per Si is similar for these samples. These samples also field a basal X-ray diffraction peak near 8-12A, suggesting that the structure is dominated by sheet-like units, consistent with the dominant Q3 polymerisation. The results provide strong support for the basic structural concepts of the so-called kanemite model for ASR gel proposed by Wieker and co-workers, although the overall gel structure is likely to be more complex.
