Whether below ground, on the surface or above ground, the benefits of using precast during construction and maintenance are many, says Martin Clarke, chief executive, British Precast
In recent years the focus on transport infrastructure has shifted firmly away from new road construction and towards making the most of what we have. Conventional rail and light rail systems have taken the limelight.
Now the emphasis has switched again to value for money – Infrastructure UK, a department within HM Treasury, is rightly insisting on a greater degree of civil engineering output per unit of finance from the scarce funds that are available. A good time therefore to look at the role of precast concrete in the era of road transport management.
Broadly speaking precast has three roles in road building – below ground, on the surface and above ground – although classification of bridges challenges this definition.
Below ground precast concrete pipeline systems and rectangular box culverts are a key component to deal efficiently with surface water from rainfall and flood and with the routeing of culverts and sewers across roads and motorways. Both pipes and box culverts can be pushed under existing roads and embankments by jacking techniques thereby minimising disruption to live traffic.
Precast systems can be dynamically active in cleaning run-off water and in the provision of holding capacity to deal with storm surges. The increasing move to hard shoulder running emphasises the need for strong and rigid drainage systems that will not buckle under heavier loads.
Increasingly intelligent traffic management and communication needs are producing renewed interest in durable and vermin proof precast cable conduit systems with easy inspection access. Cables can also be clipped inside lengths of concrete pipelines, one solution to the massive programme of information highway installation around the UK. A range of design and estimating tools are available from www.concretepipes.co.uk
On the surface
On the surface precast paving and linear drainage systems can be designed to deal effectively with rainfall. Permeable jointed systems readily comply with SUDS – sustainable urban drainage system – criteria.
The role of concrete paving in drainage systems is likely to grow as more urban areas reduce traffic speed limits to 20mph and slower, a move that opens up the design options to use modular paving. It is expected that a considerable programme of block paved urban and estate roads will result.
Well designed paving can play a major part in embedding low-speed driving as a habit. Transport operators can also yield major benefits in engineering and aesthetics by plumping for concrete block paving for car parks, park and ride facilities, picnic and rest areas.
Above ground precast concrete is used extensively for over and under bridges.
Conventional prestressed beam bridges have been supplanted as options by arched precast structures such as the Matiere system. Precast gantries now straddle several motorways.
Precast reinforced earth systems and both panellised and modular retaining wall systems feature strongly in modern road systems. Growing resistance to traffic noise and the legal requirements for local councils to deal with it should see also a growth in the use of noise barriers.
Safety for everyone
Motorway drivers will be aware of the long-overdue adoption of concrete median barriers, a move that will ultimately save over 30 lives each year by minimising lethal cross-over accidents. In 2010 precast barriers were approved by the Highways Agency and the Welsh Office for permanent median use for the first time and have proven easier to install and less disruptive than the in-situ concrete alternative – another example of the benefits of offsite fabrication.
A range of portable precast barriers are also now available to protect the lives of road workers. These can now be laid down safely and quickly by machine as evidenced in Kent on the Channel Tunnel approaches of the M20 for Operation Stack.
Durability and performance
Perhaps the major contribution of concrete to sustainable transport infrastructure is its durability and strong whole-life performance – whole life in terms both of cost and its life-cycle environmental impact. Design for 120 years life is standard and of course all concrete can be recycled into productive use at the end of a structures life. Design for deconstruction can also ensure that individual precast components can be reused in new structures, subject to technical checks of course.
The maintenance period of a precast concrete structure can be enhanced by building intelligence into the concrete itself. There are a variety of active and passive systems using tagging technology to store technical information and to report actively on performance such as loading levels.
Urban heat island effects
Transport and parking facilities cover a significant 15 per cent of a typical urban area and therefore can play a significant role in cutting down the urban heat island effect, which can add four degrees to average summer temperatures.
International studies have shown that the use of lighter colour materials such as concrete can dramatically reduce temperatures adding comfort to citizens and reducing the air conditioning load of city buildings. Lighter coloured paving can also reduce the power consumed by street lighting. Good news for carbon footprints.
Leading the way on sustainability
The precast industry has led the way in construction products by having an agreed sector sustainability strategy in place since our 2006 white paper. In late 2007 we launched our sustainability charter with the help of Paul King of the UK Green Building Council.
This year the industry is making the sustainability charter mandatory – a major step forward. Together with the other key parts of the concrete industry namely reinforcement, cement, aggregates, readymix and admixtures, we participate in the Sustainable Concrete Forum or SCF. In 2008 the SCF issued a collective signed sustainability pledge and has published three annual reports on progress made, focusing on targets and KPI facts – downloadable from www.sustainableconcrete.org.uk British Precast has already published its 2010 KPI data downloadable from www.britishprecast.org
Many transport engineers will be familiar with the CEEQUAL scheme, which is managed jointly by CIRIA and Crane Environmental (see www.ceequal.com for full deatils).
CEEQUAL is the assessment and awards scheme for improving sustainability in civil engineering and the public realm. It aims to deliver improved project specification, design and construction and to demonstrate the commitment of the civil engineering industry to environmental quality and social performance. The precast industry fully supports CEEQUAL and encourages its members to get involved to the point of employing its own assessors.
The Scheme rigorously assesses performance across 12 areas of environmental and social concern. It rewards project and contract teams in which clients, designers and constructors go beyond the legal and environmental minima to achieve distinctive environmental and social standards.
Road clients, engineers and contractors can now climb well up the CEEQUAL scorechart by sourcing from British Precast member companies. In 2011we launched our Raising the Bar initiative to improve standards in every area of operation. At the hub is the British Precast Charter scheme (see www.bpcfcharter.com). The Charter scheme is built on two existing schemes run by British Precast – the Concrete Targets health & safety scheme, now compulsory to all members, and the Sustainability Charter, which becomes mandatory in 2011.
All members are audited against the charters once they have signed up and on passing audit become Charter members. The website records other achievements including accreditation to ISO 9001, ISO 14001, OSHAS 18001, Achilles and the responsible sourcing standard BES6001.
MPA Cycle Safe campaign
Safety for British Precast and its members does not stop at the factory gate or the building site. We also care passionately about load safety and road safety.
As members of the Mineral Products Association we fully support the Cycle Safe Campaign aimed at preventing fatalities and injuries resulting from collisions between cyclists and LGVs. Left hand turns are a particular problem area for drivers and cyclists. Further information is at www.safequarry.com and www.mineralproducts.org
For more information
Readers can obtain free copies of the 100 advantages of precast and the little green book of concrete by e-mailing email@example.com