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.
![An ASR reaction of sand and chert, with accompanying cracking and gel. Concrete sample was taken from a Texas precast box beam originally thought to suffer from DEF. (Approx. 5 mm Full Width.) [Paul Stutzman, NIST]](http://publish.illinois.edu/concretemicroscopylibrary/files/2014/04/LAP06.jpg)
An ASR reaction of sand and chert, with accompanying cracking and gel. Concrete sample was taken from a Texas precast box beam originally thought to suffer from DEF. (Approx. 5 mm Full Width.) [Paul Stutzman, NIST]
![Concrete from parapet wall at the Green Mountain dam (Colorado-Big Thompson water project), incorporating the long-term test cements of PCA and assorted aggregates. [Paul Stutzman, NIST]](http://publish.illinois.edu/concretemicroscopylibrary/files/2014/04/ASR1.jpg)
Concrete from parapet wall at the Green Mountain dam (Colorado-Big Thompson water project), incorporating the long-term test cements of PCA and assorted aggregates. [Paul Stutzman, NIST]
![BEI of mortar with reactive opal aggregate at 3 days. [Ref: Aquino MS thesis, Material "CB"]. XRD spectra shown at 3 points. (Field width 660 microns, x 200) [Wilkins Aquino and David A. Lange, UIUC]](http://publish.illinois.edu/concretemicroscopylibrary/files/2014/04/cb_3d_ra4_200x.jpg)
BEI of mortar with reactive opal aggregate at 3 days. [Ref: Aquino MS thesis, Material “CB”]. XRD spectra shown at 3 points. (Field width 660 microns, x 200) [Wilkins Aquino and David A. Lange, UIUC]