Alkali-Silica Reaction
Alkali-silica reaction is a chemical reaction between the alkalis contained in the cement paste and certain reactive forms of silica within aggregate. An aggregate may be most problematic if the silica within it is amorphous and porous. The reaction creates a gel that can swell and cause expansion and cracking of the concrete. Major factors that affect the amount of expansion include the nature and amount of the reactive silica, the particle size of the aggregate, the amount of available alkali, and the amount of available moisture.
In addition to the micrographs shown below, the Library also includes fluorescent optical micrographs that show ASR.