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Recycling materials

Scarcity of resources and the need to reduce the environmental impacts of winning and processing construction materials and products is placing a greater emphasis on resource efficiency within the construction industry. It is estimated that the UK construction industry consumes some 400Mt of materials annually and generates some 120Mt of (construction, demolition and excavation) waste, of which 5Mt ends up in landfill. Therefore, there is significant scope for improving resource efficiency within the industry, particularly at the end-of-life of buildings.

Importantly, the majority of the construction and demolition arisings are heavy bulk wastes such as concrete, masonry and asphalt which are generally crushed and downcycled into lower grade applications such as general fill. Although landfill is avoided, downcycling is low-grade recycling and low down on the UK waste hierarchy. More has to be done to encourage reuse and higher grade recycling of these problem materials.

The developing Circular economy agenda, particularly the Action plan launched by the EU in 2016, is also focussing greater attention on waste, resource efficiency and recycling and reuse in construction.

An estimated 600 million tonnes of steel are recovered and recycled annually worldwide

Major improvements in materials resource efficiency are possible without increasing cost by:

• Reducing the quantity of materials being sent to landfill during the construction process by ‘designing out waste’ and effective site waste management
• Reusing, recycling and recovering waste material as appropriate
• Utilising materials and products with a high recycling and reuse potential.

The focus of this article is the second and third of these; reuse and recycling. These are also fundamental to achieving the goal of the circular economy.

What is recycling and reuse?

Reuse and recycling are key stages of the UK Waste Hierarchy and are the preferred options after all has been done to prevent waste in the first place through design and manufacture.

UK waste hierarchy

Reusing and recycling construction products avoids or reduces waste and saves primary resources. By using materials that have a greater potential for reuse and recycling, it is more likely that the value of these products at their end-of-life will be realised and extended in future applications.

Some materials are more recyclable than others, for example the process of recycling may be easier or the recycled product may have the same or a higher economic value than the original product. It is therefore more likely that such products will be efficiently recycled in the future and designers should be encouraged to use such products.

Recycling

By recycling, we contribute to more sustainable development by eliminating or reducing waste and by saving primary resources. Also, recycling some materials, like metals, saves energy (and reduces carbon emissions) since it requires less energy to re-melt scrap than it does to produce new metal from primary resources, i.e. iron ore.

The benefits of recycling are well understood and include:

• Reducing waste, i.e. diverting waste from landfill
• Saving primary resources, i.e. substituting primary production
• Saving energy and associated greenhouse gas emissions through less energy intensive reprocessing.

Although these benefits apply to many commonly recycled materials, there are some important differences in the properties of materials that influence the environmental benefit of recycling and particularly how these benefits are quantified.

Metals, for example, are infinitely recyclable, i.e. they can be recycled again and again into functionally equivalent products – this is the most environmentally beneficial form of recycling.

Other products are ‘down-cycled’ into new products that are only suitable for lower grade applications because the recycled product has different, usually lower, material properties. Although waste is diverted from landfill by down-cycling, only lower grade primary resources are saved. For example crushing bricks and concrete for hardcore, sub-base or general fill saves aggregates but doesn’t save the resources required to make new bricks or new concrete.

For recycling to be sustainable in the long term, it is important that the recycling process is financially viable. This is frequently the biggest hurdle to recycling, particularly for products and materials that are down-cycled into lower grade, low value applications.

Current end-of-life scenarios for three of the most common construction materials; concrete, timber and steel are shown. The table describes the end-of-life outcomes of these materials against the established UK Waste Hierarchy.End-of-life scenarios for concrete, timber and steel from buildings

Current end-of-life outcomes for concrete, timber and steel

The challenge in assessing the embodied environmental impacts of products therefore is how the benefits of highly recyclable materials and reusable products should be quantified and assessed relative to products that are downcycled or landfilled. This is a new discipline for designers who are used to thinking about how buildings are constructed, i.e. put together, but have generally not been concerned about how they are deconstructed (taken apart) so that their constituent parts can either be easily recovered for reuse or recycling.

If the recyclability and reusability of construction products at the end-of-life of buildings are not considered in assessing building designs, this effectively equates products that are downcycled or landfilled with products that are truly recycled or reused. This is why all recent guidance and standards for the environmental assessment of buildings advocate a robust whole life assessment that includes assessment of these aspects of the building.

A case study on recycling of steel at the Teesside Meltshop at Lackenby can be accessed by 

How to account for the benefits of recycling?

Life cycle assessment (LCA) is widely recognised as the best and most rigorous tool for assessing the environmental impacts of products and services.

In LCA the benefit of recycling may be considered as an ‘environmental credit’ or benefit. Recycling avoids the higher burdens of primary material production but this environmental saving lies in between two adjoining product systems, i.e. the upstream system which produced the scrap materials, e.g. demolition of a building; and the downstream system which will consume the recycled material, e.g. steel production. How this ‘benefit’ is shared (or allocated) between the two adjoining systems is an important and controversial issue in LCA and, to a large extent, depends on the goal and scope of the study being conducted.

Steel and recycling

Steel is 100% recyclable and is highly recycled. In the UK, the overall average end-of-life recovery rate for steel from buildings has been estimated from surveys to be 96% It is important to remember that this is true or closed-loop recycling; every tonne of scrap recovered substitutes one tonne of primary steelmaking and this can happen again and again, with existing technology and without any degradation in terms of properties or performance of the steel.