Beyene, M., R.J. Lee and M. Silsbee, “Floor Coating Failure: Gel found beneath a blistered coating may not always be NSAR”, Concrete Construction, 2012.
Topics: Failure Analysis, Materials Characterization
Near-surface alkali reaction (NSAR) gel has been reported as the cause of debonding and blistering of epoxy coatings. In this article, we describe blistering in a low-permeance floor coating system where lithium silicate was applied to a shot-blasted concrete surface. The initial analysis, based solely on optical studies, suggested that alkali-silica reaction (ASR) was the cause. Without additional, specialized analysis, such as scanning electron microscopy and electron dispersive spectroscopy (SEM/EDS), lithium silicate residue or its gel can mistakenly be identified as ASR gel. Although lithium cannot be detected by EDS, other alkalis found in ASR gel, such as sodium and potassium, can be identified. It is possible to inadvertently assume the residue or reaction product of lithium silicate applied on shot-blasted concrete surface is an ASR byproduct.