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Aconcrete step barrier is asafety barrier used on thecentral reservation ofmotorways anddual carriageways as an alternative to the standard steelcrash barrier.[1]
With effect from January 2005 and based primarily on safety grounds, the UKNational Highways policy is that all new motorway schemes are to use high-containment concrete barriers in the central reserve. All existing motorways will introduce concrete barriers into the central reserve as part of ongoing upgrades and through replacement when these systems have reached the end of their useful life. This change of policy applies only to barriers in the central reserve of high-speed roads and not to verge-side barriers. Other routes will continue to use steel barriers.[1] Government policy ensures that all future crash barriers in the UK will be made of concrete unless there are overriding circumstances.[2]
The usage of the concrete step barrier has become widespread inIreland. As of 2017, 530 kilometres (330 mi) of motorways use this barrier. Some motorways such as parts of theM8 andM6 have had the crash barrier since their original construction. Other motorways had it installed as part of their upgrade (M50).
Steel guard rails (since 2000s as thrie-beam barrier)[3] and concrete profile barrier[4] are the barrier systems used in expressways in the territory. The designs of their beam barrier are based in American and Australian designs and concrete based in European standards.
Various types ofaggregate may undergo chemical reactions in concrete, leading to damaging expansive phenomena. The most common are those containing reactive silica, that can react with the alkalis in concrete. Amorphous silica is one of the most reactive mineral components in some aggregates containing e.g.,opal,chalcedony,flint. Following thealkali–silica reaction (ASR) an expansive gel can form, creating extensive cracks and damaging structural members.[citation needed]
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