Alkali-silica reaction (ASR) is a deleterious chemical process that may occur in cement-based materials such as mortars and concretes, where the hydroxyl ions in the alkaline solution attack the siloxane groups (Si-O-Si) of the siliceous mineral components in the aggregates. Aggregates containing siliceous minerals are known to be particularly susceptible to this reaction[1-3]. Hydroxyl ions together with alkali metal cations (sodium or potassium) bind with siliceous species derived from the reactive minerals to form a cross-linked alkali-silica gel, see Fig. 1.1. The alkali-silica gel swells in the presence of water from the surrounding material[4, 5]. Expansion of the gel results in cracking when the swelling stress exceeds the tensile strength of the paste or aggregates, see Fig. 1.1. As expansion increases, cracks grow and eventually coalesce; the strength and modulus of the material are decreased and the permeability is increased. The cracking produced by ASR can significantly undermine the durability of concrete structures and may result in reduced service life.
The chemical constituents in the cement and aggregates play a key role in the durability of concrete structures. High alkali contents in cement, espec...
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