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A concrete step barrier is a
With effect from January 2005 and based primarily on safety grounds, the UK
Various types of
safety barrier
A safety barrier is a component which prevents passage into a dangerous area, commonly used to mitigate risk. Safety barriers may be hard barriers physically restricting passage or soft barriers that control circuits based on the presence of forei ...
used on the central reservation
The median strip, central reservation, roadway median, or traffic median is the reserved area that separates opposing lanes of traffic on divided roadways such as divided highways, dual carriageways, freeways, and motorways. The term also ...
of motorways
A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms ...
and dual carriageways
A dual carriageway ( BE) or divided highway ( AE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are ...
as an alternative to the standard steel crash barrier
Traffic barriers (sometimes called Armco barriers,AK Steel (formerly Armco) genericized trademark also known in North America as guardrails or guard rails and in Britain as crash barriers) keep vehicles within their roadway and prevent them fro ...
.
United Kingdom
With effect from January 2005 and based primarily on safety grounds, the UK National Highways
National Highways, formerly the Highways Agency and later Highways England, is a government-owned company charged with operating, maintaining and improving motorways and major A roads in England. It also sets highways standards used by all f ...
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. Government policy ensures that all future crash barriers in the UK will be made of concrete unless there are overriding circumstances.
Ireland
The usage of the concrete step barrier has become widespread inIreland
Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the s ...
. As of 2017, of motorways use this barrier. Some motorways such as parts of the M8 and M6 have had the crash barrier since their original construction. Other motorways had it installed as part of their upgrade (M50).
Hong Kong
Steel guard rails (since 2000s as thrie-beam barrier) and concrete profile barrier 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.Degradation processes
Various types of aggregate
Aggregate or aggregates may refer to:
Computing and mathematics
* collection of objects that are bound together by a root entity, otherwise known as an aggregate root. The aggregate root guarantees the consistency of changes being made within the ...
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
Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...
, chalcedony
Chalcedony ( , or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monocli ...
, flint
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and start ...
. Following the alkali-silica reaction (ASR), an expansive gel can form, that creates extensive cracks and damage on structural members.
See also
*Jersey barrier
A Jersey barrier, Jersey wall, or Jersey bump is a modular concrete or plastic barrier employed to separate lanes of traffic. It is designed to minimize vehicle damage in cases of incidental contact while still preventing vehicle crossovers resu ...
* Constant-slope barrier
* F-shape barrier
* Road-traffic safety
* Traffic barrier
Traffic barriers (sometimes called Armco barriers,AK Steel (formerly Armco) genericized trademark also known in North America as guardrails or guard rails and in Britain as crash barriers) keep vehicles within their roadway and prevent them from ...
References