Characterization of ASR in Concrete by Si29 MAS NMR Spectroscopy

Abstract

Si29 MAS NMR spectroscopy was employed for the evaluation of the alkali-silica reaction (ASR) in laboratory and field concrete specimens. A series of NMR data was collected on the individual constituents of cement as well as on samples subjected to accelerated aging in a carefully controlled laboratory setting. Peaks associated with ASR were assigned and quantified. In spite of the spectral complexity due to the diverse constituents and the heterogeneous nature of concrete, changes due to ASR, including increased polymerization of C-S-H and A-S-H formation, could be identified and quantified. The trends established through Si29 NMR spectroscopy of the laboratory specimens were used to identify the presence and extent of the alkali-silica reaction in samples from operational bridges. Both bridge samples exhibited spectral evidence of ASR. Fourier transform infrared spectroscopy was used to verify the Si29 NMR spectroscopy observations.