Alkali-Silica Reactivity (ASR) – Concrete Cancer in the Southeast

Abstract Only - Alkali-silica reactivity (ASR) is the process in which certain minerals with high silica content are exposed to sodium and potassium hydroxide alkalies in Portland cement. In a moist environment, a gel is formed around the reactive aggregate, creating tension cracks around the aggregate and ultimately leading to extensive expansion and fracturing of the concrete. ASR has resulted in cracking of concrete in numerous dams in the United States. Many of these dams were constructed prior to the discovery of ASR in the 1930’s. Since that time, ASR has been identified in all types of concrete structures, particularly water retaining structures such as dams.
Much of the early research on ASR was based on the rapidly reacting rock and mineral aggregates used in the western United States. In contrast, the Atlantic seaboard and Appalachian area had slowly reacting rock types that were used indiscriminately. Only with passage of time did it become apparent that ASR distress could result from their use with high alkali cements.
This paper will present the mechanism of ASR, outline the investigative steps to determine the cause and extent of ASR in concrete, discuss possible means to repair or mitigate with ASR infected dams, the extent of ASR infected dams in the southeast United States and discuss the remediation approaches used for these dams.