use can also be reduced by consumers choosing to purchase and use buildings, vehicles and other products that are smaller but provide the same functionality.

End-of-life stage

Alternatives to disposal at the end of a product’s life can also help to use materials more efficiently. Reusing a product or material prevents the need for new production. Reuse can occur in various forms, including:

relocating – the component is used in another product of the same type for the same purpose with little refurbishment

refurbishing – the component is used in another product of the same type for the same purpose after undergoing significant repair and reconditioning

cascading – the component is used in a different type of product with little reconditioning

re-forming – the component is used in a different type of product after significant repair and reconditioning (Cooper and Allwood, 2012).

In most cases, reuse would reduce energy use compared to recycling or new production, although energy use for transportation and re-manufacturing processes would need to be considered. Furthermore, in some cases where reuse and refurbishment would extend the lifespan of old and inefficient energy-using components, replacement may be a better option from a life-cycle energy use perspective.

Reuse rates for most metal components are currently low. While technical factors such as incompatibility or degradation may limit reuse, economic, regulatory and behavioural barriers may also play a key role. For example, it may not be economical to pursue reuse in the absence of financial incentives; regulations tend to favour using new rather than used materials and some constructors may be sceptical about reused materials. Better tracking of materials, development of economical testing procedures, integration of supply chains and adaptation of regulations could help overcome these barriers. A starting point may be easier to achieve opportunities for steel reuse, which include relocation of steel buildings components and re-forming of ship plates and line pipes (Cooper and Allwood, 2012).

Reuse opportunities may be more limited for other materials. In the case of cement, most of the cement particles are reacted with water during the concrete curing process, and the resulting change in chemical properties prevents cement from being used again to form new concrete. Estimates suggest that approximately 30-40% of cement in concrete may be unreacted, leaving potential for recovery of this unhydrated cement for reuse (Bakker et al., 2015). While several technologies are under development to recover unhydrated cement, they have not yet been commercialised and thus their technical and economic potential remains uncertain. Research has shown that recycling concrete fines as an input to cement kilns can reduce process emissions by a factor of three compared to the limestone inputs it would replace (Lotfi and Rem, 2016). A limited number of cements are now available that make use of recycled fines, such as Susteno cement in Switzerland (Holcim, 2018). Some opportunities may also exist to reuse whole concrete components for other purposes, thus reducing the need for new cement. However, difficulties in cutting, transporting and re-forming concrete blocks may limit this potential.

When reuse is not possible, recycling is another option to reduce the need for new materials. Although recycling consumes energy, the consumption is generally substantially less than that from producing primary materials. For example, producing crude steel from scrap consumes

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