Tennessee DOT, FHWA
Alkali aggregate reactions, Cracking of concrete pavements, Hydraulic cement, Risk management
Alkali-silica reaction (ASR) is a chemical reaction in either concrete or mortar between hydroxyl ions of the alkalis (sodium and potassium) from hydraulic cement (or other sources), and certain siliceous rocks and minerals, such as opal, chert, microcrystalline quartz, and acidic volcanic glass, present in some aggregates. This reaction and the development of the alkalisilica gel reaction product can, under certain circumstances, lead to abnormal expansion and cracking of the concrete. This phenomenon affects the durability performance of concrete structures severely. ASR is known as the “cancer” within the concrete and recognized as a major cause of concrete deterioration in the USA. Identifying the reactivity of an aggregate to ASR is one of the most efficient ways for preventing damage in practice. Many aggregates, especially the surface aggregates, used in Tennessee have a relatively high siliceous content (e.g. gravels, siliceous limestones, granites, and quartzite). Thus, the aggregates with ASR potential have the possibility to be used already in the past projects, and will be probably used even more in the future high volume transportation concrete projects due to the new requirements on the aggregates for riding surfaces in 2015 TDOT Standard Specifications. A statewide aggregate ASR risk database is required to provide a solid foundation for guaranteeing a good long-term performance and a high-level safety of statewide transportation concrete structures.