Alkali-silica reaction, ASR is a type of concrete degradation. Three conditions are necessary for ASR to occur such as a reactive form of silica or silicates, available alkali and moisture. ASR gel formation is possible when these conditions are present.
Though, the existence of ASR gel does not necessarily mean concrete damage will occur. Impairment can be caused as the ASR gel absorbs moisture and swells. This leads to extreme pressure from expansion. It typically takes years to develop and results in cracked aggregates.
Near-surface alkali reaction gel is another cause responsible for debonding and blistering of epoxy coatings. It occurs closer to the surface, involves smaller aggregates. It takes less time to develop, and is associated with a low-permeance floor coating. This also requires the presence of reactive silica or silicates, available alkali, and moisture to form the gel. The failure leads to blistering in the low permeability surface coating applied to the concrete.
The occurrence of excess alkali from NSAR at the concrete surface creates disproportion of solute. This generates an osmotic cell leading to attraction of more water. The water is pulled through the concrete. This acts as a semi-permeable membrane and collects on the concrete surface. The existence of the relatively impermeable coating covering traps the excess moisture. This results in blistering of the coating.
Lithium compounds have been used in concrete to inhibit ASR from causing degradation. Also, to protect the surface by aiding in the concrete densification.
When performing investigations of blistering and other failures of Epoxy Flooring systems, it is important to observe and take into account a number of factors, such as, Lithium silicate was applied to the concrete surface and the cracks present in the field core samples were parallel or sub-parallel to the surface.
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