ASR is caused by chemical reaction between alkalis and certain reactive silica minerals which form a gel. The gel absorbs water, causing expansion which may damage the concrete and adjacent structures. Alkalis are introduced by the Portland cement or possibly chemical pavement deicers (or both). Symptoms of ASR include: cracking of the concrete, often in a map pattern, aggregate popouts, and increase in concrete volume that may result in distortion of adjacent or integral structures or physical elements. Examples include shoving of asphalt pavements, light can tilting, slab faulting, joint misalignment, and extrusion of joint seals or expansion joint fillers. ASR is generally present throughout the section; coring and concrete petrographic analysis is a definitive method to confirm presence of ASR. Some of the indicators ASR is present are:
Age of concrete when distress developed, generally ASR distresses are observed in a few to many years after construction, in contrast to plastic shrinkage cracking which occurs the day of construction and is apparent within the first year. ASR is differentiated from “D” Cracking in that ASR has cracks perpendicular at the joint faces.
White, brown, gray or other colored gel or staining may be present at the crack surface.