ABSTRACT
As noted in Chapter 1, the Alkali-Silica Reaction (ASR) is a result of the reaction between the alkaline pore solution in concrete and reactive silica in the aggregate. The reaction leads to the formation of a secondary reaction product, a so-called alkali-silica gel, which can absorb water and exert an expansive force on the concrete. In certain conditions, and as a function of the extent of internal/external restraints applying on the affected structure/element, the reaction can lead to damaging expansion and cracking in the concrete. For such damaging expansion to occur, all of the following conditions must be present simultaneously:
A sufficiently alkaline pore solution
A critical amount of reactive silica
A sufficient supply of water
Effective specifications to avoid damage from the reaction are based on ensuring that at least one of these conditions is absent. Additionally, there are interactions with other environmental actions, such as freezing and thawing, application of de-icing salts and exposure to a marine atmosphere, for which allowance must be made.