March 2009

Glossary

Alkali-Silicate Reactivity: The reaction between the alkalies (sodium and potassium) in Portland cement with certain siliceous rocks and minerals, such as opaline chert, strained quartz, and acidic volcanic glass, present in some aggregates; the products of the reaction can cause abnormal expansion and cracking of concrete in service. Class F fly ash is used in concrete to reduce the occurrence of alkali-silica reactivity.