Concrete step barrier
Encyclopedia
A concrete step barrier is a safety barrier used on the central reservation
of motorways and dual carriageways as an alternative to the standard steel crash barrier.
The barrier has contained all vehicles up to 13.5 tonnes.
With effect from January 2005 and based primarily on safety grounds, the UK Highways Agency
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.
. As of November 2008, 405 kilometres (251.7 mi) of new motorway under construction at present will use the new barrier. Existing motorways such as parts of the M8
and M6
already have the crash barrier. Other motorways are now installing them as part of upgrades (M50).
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 the alkali-silica reaction
(ASR), an expansive gel forms, that creates extensive cracks and damage on structural members.
Central reservation
On divided roads, such as divided highways or freeways/motorways, the central reservation , median, parkway , median strip or central nature strip is the area which separates opposing lanes of traffic...
of motorways and dual carriageways as an alternative to the standard steel crash barrier.
United Kingdom
Highways Agency
The Highways Agency is an executive agency, part of the Department for Transport in England. It has responsibility for managing the core road network in England...
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 now become widespread in IrelandIreland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
. As of November 2008, 405 kilometres (251.7 mi) of new motorway under construction at present will use the new barrier. Existing motorways such as parts of the M8
M8 motorway (Ireland)
The M8 motorway is an inter-urban motorway in Ireland, which forms part of the road from the capital - Dublin - to Cork city. The 149 km motorway commences in the townland of Aghaboe, County Laois and runs through the counties of Kilkenny, North Tipperary, South Tipperary and Limerick,...
and M6
M6 motorway (Ireland)
The M6 motorway is a motorway in Ireland, which runs from Dublin to Galway. The M6 extends from its junction with the M4 at Kinnegad all the way west to the outskirts of Galway City, but the Athlone bypass and the approach to Galway city - while of dual carriageway standard - have not been...
already have the crash barrier. Other motorways are now installing them as part of upgrades (M50).
Degradation processes
Various types of aggregateConstruction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...
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
Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most...
, chalcedony
Chalcedony
Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the minerals quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic...
, flint
Flint
Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. Inside the nodule, flint is usually dark grey, black, green, white, or brown in colour, and...
. Following the alkali-silica reaction
Alkali Silica Reaction
The alkali–silica reaction is a reaction which occurs over time in concrete between the highly alkaline cement paste and reactive non-crystalline silica, which is found in many common aggregates....
(ASR), an expansive gel forms, that creates extensive cracks and damage on structural members.
See also
- Jersey barrierJersey barrierA Jersey barrier or Jersey wall is a modular concrete barrier employed to separate lanes of traffic. It is designed to both minimize vehicle damage in cases of incidental contact while still preventing crossover in the case of head-on accidents....
- Constant slope barrierConstant Slope BarrierA constant slope barrier is a traffic barrier made of reinforced concrete and designed with a single slope that is used to separate lanes of vehicular traffic...
- F-shape barrierF-Shape BarrierThe F-shape barrier is a concrete crash barrier, originally designed to divide lanes of traffic on a highway. It is a modification of the widely-used Jersey barrier design, and is generally considered safer....
- Road-traffic safetyRoad-traffic safetyThe term road traffic safety is about the risk of a person being killed or seriously injured while using the road network as a pedestrian, cyclist, motorist or user of on road public transport...