How to recycle infrastructure

Lack of infrastructure capacity is a key issue facing modern cities all over the world, not least in the UK. London has a major housing crisis and a transport network that is the most congested in Europe, according to research conducted by the World Bank.

Addressing such challenges is not easy. However, innovative approaches that speed up construction on new-builds, refurbish existing assets and minimise impacts on existing users and surrounding neighbourhoods go a long way.

In London there are at least 40,000 publicly owned brownfield sites – previously used sites that may be contaminated. These sites could provide land for a minimum of 130,000 homes, almost two-thirds of the UK Government’s annual target.

Brownfield sites come with their own set of challenges, but Design for Manufacture and Assembly (DFMA) is an offsite manufacturing technique that can help tackle them. Gary Le Carpentier, Technical Director at Ramboll UK explains:

“Offsite manufacturing, where components are manufactured in a controlled offsite environment, has a number of advantages, including significantly reducing construction times by enabling construction and engineering challenges to be addressed before construction starts. It reduces the number of tradespeople on site by reducing the onsite activities. This helps to offset the increased costs associated with a brownfield site. For example, we have projects where we have saved 2.5 months on a 12-month construction programme.”

Other significant benefits realised include improved health and safety and less onsite noise, which in turn minimise the impact of construction on the local area.

Sustainable timber skyscrapers

Using materials like cross-laminated timber (CLT) can also reduce construction time and make it easier to build on difficult sites. At Dalston Lane in Hackney, London, Ramboll has designed what is set to be the world’s tallest and largest CLT building by volume.

The lighter construction weight of CLT enables smaller foundations, something critical to the Dalston Lane site, which has High Speed 1 and Crossrail passing underneath. The use of CLT at Dalston Lane has also saved 2,400 tonnes of carbon compared to an equivalent block with a concrete frame and so has great potential as a sustainable and quick-to-construct material.

CLT structures are the only sustainable solution to provide high-quality, high-density housing, and as such, this project – given its scale and ambition – is a seminal piece of architecture.

Refurbishing an existing flyover

London is investing heavily not only in buildings but also in road and rail, which includes upgrading existing infrastructure to make it fit for purpose. A critical part of Transport for London’s Structures and Tunnels Investment Programme was work on the Hammersmith Flyover, a vital link in West London carrying over 70,000 vehicles per day.

The post-tensioning system had suffered significant erosion that threatened to close the flyover unless the system was repaired. However, the innovative use of ultra-high performance fibre-reinforced concrete (UHPFRC) has enabled the structure to stay open and extended its life for many years to come.

This phenomenally complex EUR 130-million programme is believed to be the first time an all new pre-stressing system has been installed in a bridge where the original could not be removed. Such techniques and the intelligent use of 3D scanning technology are driving life extension and design efficiency, as well as eliminating programme and safety risks, speeding up repairs and thus minimising disruption to the public.

Managing Director Paul Bottomley from the post-tensioning sub-contractor Freyssinet calls the work unique:

“Replacing, fully, all the old post-tensioning without first removing it on such a significant structure is truly impressive,” he says. Mat McNab, Head of Buildings, Ramboll UK, adds:

“At a time when resource scarcity is at the forefront of our minds, innovations that make the best use of existing infrastructure and building plots will be vital to securing the increased capacity our growing cities need.”