O. Weichold, U. Antons
J. Infrastruct. Syst. 2017, 23, 04017010
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Assessing the Performance of Hydrophobing Agents on Concrete using Non-Destructive Single-Sided Nuclear Magnetic Resonance

ABSTRACT: Single-sided nuclear magnetic resonance is a nondestructive analytical technique by which the ingress behavior of hydrophobing agents as well as the properties and performance of the resulting hydrophobic layers can be assessed quantitatively. The method is used to compare the behavior of two low-molecular-weight hydrophobing agents, n-octyltriethoxysilane and i-butyltriethoxysilane, on concrete and to assess the properties of the resulting hydrophobic layers. For the octyl derivative, ingress appears to be a simple transport process without pronounced polycondensation in the liquid phase or reaction with the pore walls because the detectable amount stays rather constant during the first day of observation. In addition, the thickness of the resulting hydrophobic layer correlates well with the endpoint of the transport process. In contrast, the detectable amount of the butyl derivative is reduced to half during the first 18 h, indicating either substantial polycondensation or anchoring to the pore walls, and the hydrophobic layer is approximately 25% thicker than indicated by the ingress profiles. The different behavior could originate in differences in the molecular structure, particularly the steric demand of the alkyl substituents, although this requires a more detailed study. Both compounds proved to be excellent hydrophobing agents since the layers were found to be impermeable when kept in a shallow water bath (unidirectional transport through the layer) for more than 1 year. The results demonstrate that single-sided nuclear magnetic resonance is an excellent nondestructive tool for quality assurance when applying such protective layers.