Slipform Paving
Concrete Barrier
Concrete safety barriers were originally developed in the USA and like most good American ideas travel well. Their use in the USA is commonplace and designers here have been quick to realise the safety and economic advantages a concrete barrier has over a conventional steel rope or beam.
Whilst both standard 800mm high Vertical Concrete Barrier and Wire Rope or Open Box Safety Barrier meet the minimum level of containment currently specified by the Highways Agency currently available statistics, provided by the Highways Agency, speak for themselves. Between 1992 and 1999 an average of 59 accidents per year including an average of 11 fatalities per year occurred on our motorway network. On our trunk roads there were 161 accidents per year including an average of 11 fatalities per year, where vehicles crossed the central reservation and travelled along the opposing carriageway.
Whilst the statistics do not reveal which type of safety barrier was breached, what is certain is that no concrete barrier installed on the United Kingdom's road network has ever been breached and this includes many miles constructed along the central reservation of the M25 London orbital motorway.
Although Vertical Concrete Barriers are on the whole more expensive to construct than Wire Rope or Double Open Box systems, information available to date strongly suggests that the whole life cost of concrete is significantly less. Although our car radios constantly inform us of temporary lane closures installed to repair or replace damaged steel safety barriers no replacement of any of the existing concrete barriers has been required.
A concrete barrier could reasonably be expected to provide a life of 30 to 40 years.
Concrete barrier types
The standard inverted "T" shaped 800mm high Vertical Concrete Barrier or VCB has been evolving rapidly of late as designers and contractors develop the shape to suit street lighting and uneven adjacent carriageway levels.
The Wide Vertical Concrete Barrier or WVCB adopts the same traffic face as the standard VCB but the width of the wall has been increased from 240mm to 600mm allowing street lighting columns to be fixed directly to the top. Ducts inside the wall allow services to be supplied to the lamp.
Where barrier is sited along the central reservation between two carriageways where the adjacent levels are different or even variable, a non-symmetrical barrier profile is required. A hydraulically variable barrier mould allows each carriageway to be provided simultaneously with the minimum height of barrier required.
Recent directives from the Highways Agency have dictated that bridge piers, potentially vulnerable to damage from vehicle impact, must be protected.
Conventional tensioned steel safety fence or open box beam cannot provide the level of protection required - a special Higher Vertical Concrete Barrier (HVCB) was therefore developed.
The barrier is slipformed at a total height of 1.650 metres although 0.250 metres is found below finished road level thus providing an effective height of 1.400 metres.
In order to achieve an aesthetically pleasing appearance to the motorist, short lengths of 0.800 metres high barrier are constructed at either ends of the main higher barrier.
Extrudakerb have developed a truncated version of the HVCB known as the Amended Vertical Concrete Barrier (AVCB) that enables all the slipform works to be carried out using a single variable height mould.
This specialist engineering allows a single length of wall to be constructed in as little as 3 shifts.
All barrier is slipformed insitu using a Gomaco GT6300 prime mover mounted on a unique X - Y paving frame designed and fabricated by Extrudakerb allowing the barrier mould to be mounted to either the right or left side of the paver. This permits the construction of barriers to progress in the same direction as adjacent traffic flow, avoiding the need to turn around the concrete delivery wagons.
Barrier construction is possible within restricted traffic management, providing a minimum width of xxx metres is maintained between the traffic face of the barrier and the limit of the closure.
Longitudinal reinforcement is placed, lapped and welded in advance of the paver. A specially designed pick up system is incorporated at the front of the paving mould to place the bars at the correct alignment within the barrier profile.
A pre-set guidance wire, supplied and erected by Extrudakerb is used to automatically control the alignment of the barrier.
Crack inducement cuts are placed transversely in the barrier when required and a curing compound applied by a team of experienced concrete finishers.
Tapers are formed by hand with termination and transition units cast between forms incorporating caged reinforcement and anchorage cradles.
Successfully completed projects include bridge pier protection schemes on the at numerous locations on almost all of the UK's major roads including the M1, M4, M5, M6, A2 & A3 together with many smaller roads.
References, Method Statements, Risk Assessments, group Safety Polices, COSHH information and insurance details are provided to all customers.
All works are carried our in accordance with our ISO 9002 Quality Procedures and ISO 14001 Environmental Policy.