Alkali Aggregate Reaction Essay -- essays research papers

ASR is one example of a more general problem known as Alkali Aggregate Reaction [AAR]. ASR is a chemical process in which alkalis, usually predominantly from the cement, combine with certain types of silica in the aggregate when moisture is present. This reaction produces an alkali-silica gel that can absorb water and expand to cause cracking and disruption of the concrete. For damaging reaction to take place the following need to be present in sufficient quantities. High alkali cement Reactive aggregate [e.g. crushed greywacke type sandstone] Moisture Structures most at risk are bridges, hydraulic structures, exposed frames [e.g. open multistorey car parks] and foundations. In relation to total construction volume, the incidence of significant damage due to ASR in the UK is small. ASR was discovered in the USA in the 1940s; no case was found in the UK until 1971 [in a concrete dam in Jersey]. The problem is known to exist in at least 35 countries. Affected concrete often exhibits map cracking of the surface, known colloquially as Isle of Man cracking after that island`s three legged emblem. In heavily loaded sections the cracking will probably follow the line of the main reinforcement. An excellent overview of the phenomenon can be found in BRE Digest 330. Since the early 1980s recommendations have been produced and refined to the stage where ASR is unlikely if these are adopted. Principal methods include.  ·Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Controlling the level of available ...