When performed by a skilled petrographer knowledgeable about concrete, this method can be very reliable in
identifying the mineralogical phases that are susceptible to ASR. The examination can’t predict if potentially reactive materials will produce harmful expansions. particularly for fine aggregates that have shown deleterious reactions in the field.

Considered by many to be the most trustworthy test for reactivity, this test unfortunately requires one year to
yield meaningful results. It may give false negatives, particularly for fine aggregates that have shown deleterious reactions in the field.

This method can fail to show a material to be reactive, even though the material has proven to be reactive in field use.

ASR appears most often as “Y-shaped” cracks that join to create a map-cracking pattern (Fig. 3). The crack
pattern, however, is also related to stress distribution as affected by restraint. Cracks caused by ASR expansion tend to align parallel to the direction of maximum restraint. In a pavement, for instance, the prominent
This method will correctly identify most aggregates that have a potential for reaction, if low enough expansion
limits are used. This test method has indicated potential reactivity for some aggregates in the laboratory although the aggregates have no history of deleterious reaction in the field. This may simply indicate that the
aggregates were not used in a situation that would lead to deleterious reaction.

A: Alkali-silica reactivity is the process in which certain minerals (mostly glass type silica) in the presence of moisture are broken down by the highly alkaline environment of concrete producing a gel that expands creating tensile forces in the concrete matrix which cause cracking of the concrete. The cracking then allows more water to infiltrate into the concrete creating more gel, more expansion etc. Ultimately the concrete fails or disintegrates.