Matters arising

Efforts to demonstrate resource efficiency and minimise the environmental impact of demolition have traditionally focused on the amount or percentage of arisings – secondary or waste products – that have been recovered and recycled.

Indeed, increasingly sophisticated sorting and reprocessing technologies, combined with the need to demonstrate compliance with sustainability ratings such as BREEAM (the BRE Environmental Assessment Method) and Code for Sustainable Homes have enabled some demolition contractors to achieve recycling rates above 98%. Only hazardous waste, such as asbestos, has gone to landfill.

However, there is a category of management sitting above recycling in the hierarchy of waste which is often overlooked. Despite being – by definition – a more environmentally desirable option, the re-use of construction waste is rarely reported separately.

There is some confusion in the industry over the distinction between the two. While recycling involves some processing, such as shredding and melting, and reconstitution of the waste stream, re-use requires little or no treatment. A re-used waste material will often be employed in its original application, avoiding the sometimes considerable energy needed to reprocess it.

Most waste modelling software does not accommodate the recording of re-use but that may about to change with the announcement of a project to develop a BIM (Building Information Modelling) extension software tool, known as DRIM (Deconstruction and Recovery Information Modelling).

The project is being led by United Kingdom-based construction waste consultancy, Waste Plan Solutions Ltd (WPS), and is part-funded by an Innovate UK grant.

“DRIM will complete the ‘circular economy’ for buildings by identifying in advance the re-usable and recoverable materials at the end of a building’s life,” said Laura Ayris, managing director of WPS.

“It will introduce the concept of material recovery at the initial stages of the construction process. This will encourage designers to produce a deconstruction plan and simulate the deconstruction process to ‘build-in’ more efficient recovery of materials and the use of efficient waste collection and reuse or recycling schemes.”

The system is expected to be available within two years.

Barriers to re-use

To be fair, a number of barriers have discouraged or even prevented contractors from considering re-using demolition wastes. Apart from the obvious challenges of deconstructing the various items without damaging or contaminating them, there are issues regarding the quality of re-usable materials.

For example, structural components that have been subject to stress or fatigue loading while in-situ need to be tested to provide assurance of their future performance if they are to be suitable for re-use in subsequent construction.

Lack of standardisation of recovered materials may preclude them from use in a particular design specification, especially older items that may now be obsolete. There may not be adequate storage space for salvaged items and pressure to complete the demolition phase can rule out the more careful but time-consuming dismantling and deconstruction needed to salvage materials intact.

While data for demolition waste re-use tends to be anecdotal, there are a number of good examples where it has been re-used to make demolition projects more sustainable. Many of the best case studies involve reusing structural steelwork, which is robust enough to withstand deconstruction and intrinsically demountable. Demolition contractor R Collard’s winning entry at last year’s Sustainability of Resource Awards organised by the Chartered Institution of Wastes Management (CIWM) involved the re-use of 800 t of steelwork from a demolition project.

“During the planning phase, the size and length of some of the structural steelwork in the roof was identified as suitable for re-use in building our new materials recycling centre,” explained John Watson, the managing director of R Collard.

“More than 50 steel beams measuring 25 m each were carefully dismantled and sent to a local steelwork pre-fabrication supplier. There, they were cleaned, cut to the specification supplied by our installers, new baseplates fitted, re-painted and transported to our yard to provide structural steelwork for the roof of the new building.”

Representative samples were tested using mechanical and chemical analysis by an accredited laboratory to verify their suitability for re-use in structural applications.

Bricks are another good example of building materials that can be re-used. Good quality, undamaged items will typically be treated manually. Loose mortar or other items are carefully chipped away using brick hammers, and the brick cleaned with a wire brush, rinsed, stacked and left to dry.

Older bricks actually tend to be easier to salvage, according to Charlie Law of environmental consultancy Sustainable Construction Solutions.

“More modern bricks are normally laid on a cement mortar which binds to the brick and is very difficult to remove at end of life without damaging the brick,“ said Charlie.

“If we designed for deconstruction, we may go back to laying bricks in a lime mortar, which is easily removed, and explains why there is a good salvage market for bricks from older buildings. Laying bricks on lime mortar does take a bit longer, but due to changes in building methods, this brickwork is not normally load-bearing and is therefore rarely on the critical path of the construction programme.”

This is taken from the March-April issue of Demolition & Recycling International magazine. To read the article in full, or to receive the magazine on a regular basis, please visit www.khl.com/subscriptions