Alkali-silica reaction (ASR)

ASR means that substances contained in the aggregates sensitive to alkali react with the alkaline pore solution (free water in concrete that is not chemically bound during the hydration) to form a swellable alkali-silica gel. Water absorption increases the gel volume and causes damages to the concrete/concrete element as e.g. cracks, spalling, bulging (autobahn) etc. As reactions do not occur only in the surface area but also in deeper areas, towards which the water needed for the swelling action seeps through only slowly, ASR may remain undetected over a long period of time as the subsequent damages develop slowly and become obvious only after months or years. The gel is not always visible in the damaged area so that the cause of the damage ASR may be confused with other causes (cycle, extreme temperatures, false/no after treatment of the fresh concrete, etc.).