Designer's guide to cutting waste from construction projects
Five key principles to designing out waste from civil engineering projects
There are five key principles that you can use during the design process of a civil engineering project to help reduce construction waste and use materials more efficiently. These principles are design for:
- reuse and recovery
- off-site construction
- materials optimisation
- waste efficient procurement
- deconstruction and flexibility
Design for reuse and recovery
This is essential if you want to minimise the quantities of materials needed for the work. Reuse and recovery works well on civil engineering projects which generate large quantities of waste, eg earthworks, pavements and structures.
You should consider reuse and recycling of materials on site before importing materials with high recycled content, for example:
- reusing existing foundations, floor slabs, pavements, structures and drainage
- designing site layout to use existing topography and features
- balancing cut/fill quantities
- manufacturing soils on site using PAS 100 compost
- treating soils with cementitious agents and using hydraulically bound materials
- using geosystems to enable use of material on site
- in-situ remediation or encapsulation of contaminated land
- crushing and screening arisings for use as recycled aggregates
- cold recycling of pavements
You will not be able to eliminate the import of materials completely but you can use materials with high recycled content.
Design for off-site construction
This has the potential to considerably reduce waste on site by significantly changing on-site operations and the construction process overall, for example:
- reducing construction-related transport movements
- improving health and safety on site by avoiding accidents
- improving workmanship quality and reducing on-site errors and rework
- reducing construction timescales and improving programmes
Off-site construction is suitable for a number of civil engineering applications, including the use of:
- prefabricated units - such as manholes
- precast components for retaining walls, bridges and other structures
- precast piles rather than cast in situ
- precast tunnel segments rather than cast in situ tunnel linings
Design for materials optimisation
You can apply innovative ways to reduce overall material use, such as:
- voided slabs in bridges
- lightweight aggregate in concrete - especially when derived from a secondary material such as expanded pulverised fuel ash
- use of innovative lightweight materials - such as fibre reinforced composites
By reducing the weight of structures you reduce the loading, so the structural members and foundations will be thinner and require less cement and reinforcement.
You can also use geosystems to reduce the overall material use on a project. These will enable you to build steeper slopes without the need for concrete or steel retaining structures or thinner pavement layers.
Design for waste efficient procurement
Designers can work with contractors to identify areas where waste is likely to happen and contribute design decisions and initiatives to reduce waste through procurement, for example:
- preliminary design stage - investigate options that are simple to construct and minimise waste
- detailed design stage - develop work sequences and material logistics plans that will minimise waste
- programming - ensure work is efficient, avoiding unnecessary waste by excessive rework and taking the opportunity to reuse materials
Design choices during the detailed design stage will lead to the generation of waste on site - eg the selection of mesh size for reinforced concrete and the specification of geosynthetics. You can apply methods to reduce waste through the following:
- design - eg designing structural elements which can be constructed efficiently
- specification - eg writing tighter specifications of work procedures to avoid waste and allow the use of recycled materials
- contracts - eg encouraging early contractor involvement
You should encourage the inclusion of commitments to reducing waste in contracts throughout the supply chain.
Design for deconstruction and flexibility
This principle focuses on the requirement to ensure that the construction can be maintained, refurbished or extended as required.
During the preliminary design stages, it will be difficult to develop design for deconstruction and flexibility proposals to any great extent. However, it is important to agree as early as possible on the use of this principle as part of the overall strategy so that all parties are committed to considering it throughout the design process.
You should not include any materials or components that would make future extension or recycling difficult or impossible, eg using unbound post-tensioned steel in reinforced concrete structures or designing underground drainage services without considering future potential lateral connections. You should avoid the use of hazardous materials that might cause problems for future recycling.