Monitoring of Sulfate Attack in Concrete by Al27 and Si29 MAS NMR Spectroscopy

Si29 and Al27 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy techniques were employed towards evaluation of hydrated cement paste and concrete subjected to accelerated sulfate attack. Quantitative analyses of the Si29 NMR spectra of specimens subjected to different periods of sulfate attack indicated that the chain length CL of SiO4/AlO4 tetrahedra was lowered by sulfate attack. Al27 NMR spectra indicated that sulfate attack produced a significant rise in the intensity of ettringite and a sharp drop in the concentration of monosulfate hydrate, which are some primary indications of sulfate attack on concrete. Fourier-transform infrared (FTIR) spectroscopy method was employed in order to verify the result of NMR spectroscopy.