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Aggregates are granular materials used in construction work. They include sand, gravel, crushed stone, recycled concrete, recycled asphalt, recycled brick and slags.

What are recycled aggregates?

Recycled aggregates come from reprocessing materials that have previously been used in construction. There are two methods of producing recycled aggregate:

• at the site of the source - the benefits of this include saving on transport costs and the environmental benefits of reducing lorry movements
• in a central plant

Examples of recycled aggregate include recycled concrete from construction and demolition waste material and railway ballast.

What are secondary aggregates?

Secondary aggregates are usually by-products of other industrial processes that have not previously been used in construction. Secondary aggregates can be further sub-divided into 'manufactured' and 'natural', depending on their source.

Examples of manufactured secondary aggregates are pulverised fuel ash and metallurgical slags.

Natural secondary aggregates include china clay stent and slate aggregate.

There are many opportunities for businesses to use recycled and secondary aggregates.

Recycled aggregates can be used in a variety of construction applications, such as:

• bituminous (asphalt) road construction
• ground improvements
• earthworks - cuttings and embankments
• utilities reinstatement
• shallow foundations
• shallow and deep foundations
• buildings - residential and industrial

Recycled and secondary aggregates (RSA) may also be used in a range of construction materials, such as:

• concrete - coarse and fine aggregates mixed with cement and water
• asphalt - coarse and fine aggregates mixed with bitumen
• hydraulically bound materials - coarse and fine aggregates which set and harden when a hydraulic binder is added
• unbound materials - materials ranging in size from fine grains to stony material

Geosystems

Geosystems are well-established techniques which involve using, or interfacing with, the ground - see geosystems and recycled and secondary aggregates.

Benefits of using recycled and secondary aggregates

Using sustainable aggregates that meet the same specifications as virgin aggregates should be no more expensive than your current supply and, depending on the location of the supplier, may be cheaper. Specific benefits include:

• avoidance of waste disposal charges and landfill tax
• avoidance of aggregates levy payments - as RSA are exempt
• reduced costs of transporting aggregates if recovered materials are available locally
• lower costs and shortened timescales associated with some construction techniques - for example 'crack and seat' in road maintenance

Using RSA also has potential environmental benefits, including:

• conserving natural resources by decreasing the demand for virgin materials
• protecting local ecosystems and maintaining biodiversity levels
• reducing energy consumption, transport emissions and disposal of waste to landfill

There can also be social benefits of using locally sourced RSA. For example:

• encouraging local employment
• reducing road haulage activities - and therefore reducing road congestion and increasing road safety
• creating educational opportunities

Geosystems are composite systems installed and working in the ground. They contain three elements:

• Engineering input - generally refers to professional, technical and design guidance.
• Soil - any type of unconsolidated fill material, either granular or cohesive. Types of fill that can be used in geosystems include excavated arisings, imported recycled or natural aggregates, weathered rock and soft clay sediments.
• Geo-components - an engineered product, sometimes geo-synthetically based, that is used in a geosystem. Engineered geo-components are manufactured elements such as steel meshes, strips, textiles, boxes and tubes, polymers, natural fibres, concrete and timber. They are used to provide a specific function within the geosystem, such as containment or reinforcement of the soil, or additional drainage.

Recycled and secondary aggregates can be used within geosystems for:

• steep slopes and retaining walls
• ground stability and retaining walls
• road pavements
• working platforms for crane or heavy plants
• erosion control of water courses or embankment slopes
• geotubes for erosion protection or filtration
• marine applications
• landfill applications

Benefits of using geosystems

Geosystems generally use resources much more efficiently than traditional ground improvement solutions in civil engineering, such as using concrete or steel.

Geosystems have the potential to deliver good cost and environmental benefits, including shorter construction times and reduced carbon emissions.

Geosystem standards and design

The British Standards Institution (BSI) has published , which covers the design and criteria of geosystems.

It is a good idea to get help from an independent design professional to check that the manufacturer's or supplier's suggestions for building solutions comply with any relevant design codes or environmental requirements.

Using recycled and secondary aggregates (RSAs) may cut your business' carbon emissions, lower costs and help demonstrate your environmental credentials to stakeholders, clients and investors.

To encourage your contractors to use RSA, you should:

• explicitly mention them in your sustainability and environmental policies
• set out your position on their use in your tender invitations
• use tender evaluation to give credit for using RSAs
• clearly state that RSAs can be used in any application as long as quality and material specifications are met
• spell out any targets and monitoring requirements
• specify clearly that any RSAs used must comply with quality protocols and should be ordered and delivered to a recognised specification, such as the Specification for Highway Works

Guidance for contractors

Contractors also have a role to play in promoting the use of RSAs. To encourage clients to allow you to use RSAs in their projects, you should:

• point out that RSAs meet their requirements and may also lead to cost savings and environmental benefits
• make sure that you always use established, reputable suppliers and show the client evidence of this - for example test certificates or quality procedures
• reassure them that the RSAs you order fully comply with specifications and quality protocols
• give examples of previous successful projects using RSAs
• go to the site with the first delivery of RSAs to discuss and resolve any concerns

RSAs and the procurement process

There are often opportunities to specify and obtain sustainable aggregates throughout the procurement process for both clients and contractors. The five main 'intervention points' are when you are:

• identifying your needs - begin to consider possible uses of RSAs at the very early stages in your project
• specifying requirements - make sure that targets are set for the use of RSAs, and that these are incorporated in your standard documents
• choosing suppliers - use sustainability and environmental criteria to pre-select potentially suitable tenderers
• evaluating tenders - incorporate sustainability and environmental criteria into the tender evaluation process
• managing the contract - monitor contractors' performance at regular intervals to ensure that targets will be achieved

Materials derived from construction waste include:

• bituminous bound waste
• bricks and masonry
• concrete waste
• mixed construction, demolition and excavation waste
• secondary materials
• trench arisings
• unbound granular material - including spent railway ballast

If you process, transport, store or use materials when they are still classed as waste, you may need to comply with legislation relating to:

• waste management licensing and exemptions
• duty of care for waste
• hazardous waste
• waste carriers

The quality protocol for the production of aggregates helps producers to demonstrate when their waste products have been fully recovered to produce aggregates, and should no longer be classified as waste. This means that the recycled aggregates, and those handling them, are exempted from the usual waste controls such as the duty of care.

The quality protocol for the production of aggregates from inert waste sets an industry benchmark for recycled aggregate production. It defines the point at which a product is no longer considered as waste. This is important because once a material is not classed as waste you do not have to follow waste controls such as using a registered waste carrier to transport your materials. However, you should continue to handle materials with care to ensure that you don't face enforcement action for causing pollution.

WRAP (Waste & Resources Action Programme) has also published checklists and guidance documents to help those producing and buying recycled aggregates to comply with the quality protocol. These provide:

• detailed guidance on the requirements for producers and specifiers of sustainable aggregates
• a roadmap that enables producers to prove that their material has been produced in a way that complies with the quality protocol
• guidance which allows end users to tell the difference between suppliers

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To ensure that your business has the right recycling infrastructure, you should consider carefully your choice of processes, equipment and equipment suppliers.

Aggregate reprocessing processes

To produce a quality aggregate product, you should first identify the appropriate production processes you will need. These will depend on the feedstock material you want to recycle and the type of product you want to produce.

Aggregate recycling equipment

There is a wide range of equipment types that may be used in an aggregate reprocessing facility, including different forms of:

• crushers
• screens
• conveyors
• magnets
• planers
• washing plant
• mobile bulk handling equipment

The equipment you choose will depend on the feedstock you are processing and the end product you are producing.

Each organisation within the construction supply chain can work together to make better use of recycled and secondary aggregates (RSAs), including:

• developers
• the design team
• building contractors
• demolition contractors
• reprocessors and suppliers

For example, including RSAs as a required component when designing new build projects will drive demand for recovered material, inspiring better practice from demolition contractors.

In turn, making cost-effective, quality recovered material readily available through better demolition practices will encourage developers to include it in their projects.

Demolition recovery of recycled and secondary aggregates

In order to recover as much reusable material as possible from demolition works, you should follow best practice. The three main steps are:

• pre-demolition audit - assessing the potential of the building to recover resources, the likely quantities and any potential problems, for example contamination of one material with another
• demolition site layout plan - designing the layout of the site to allow recovered materials to be collected, stored, processed and transported
• evidence of material recovery - demonstrating how much material has been recovered, for example by measuring quantities stored or moved

Procurement of recycled and secondary aggregates

There are also three stages to best practice when using RSAs recovered from demolition in new build projects:

• design - thinking about opportunities to use RSAs and how they could be supplied at the right quality, quantity and price
• supplier assessment - carefully assessing the potential of suppliers to provide and work with recovered materials
• evidence of recovered material procurement - demonstrating how much RSA material has been procured, for example by keeping purchase order notes