Recycled Aggregates: What You Should Know

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What are the examples of recycled aggregates?

There are several types of recycled aggregates, including gravel, sand, crushed stone, asphalt, bricks and blocks, slags and recycled concrete. Recycled aggregate concrete (RAC) is also known as recycled concrete aggregate (RCA). Aggregate recycling describes the processing of ready-to-use building materials, from previously used crushed construction aggregates and demolition waste, which has been broken down into a specific size and mixed ready for reuse.

There’s also another category known as ‘secondary aggregates’. These are by-products from other areas which haven’t yet been used for construction - such as power station fuel ash, china clay and some types of slate. Both secondary and recycled aggregates are often used in modern methods of construction (MMC), which take advantage of reclaimed materials for a more eco-friendly alternative to natural concrete and newly mined materials.

Recycled aggregates in construction

Aggregates which have been repurposed, such as recycled aggregates in concrete, are popular in modern construction projects as they sometimes offer a money-saving alternative whilst being sustainable, high quality, readily available and more eco-conscious. Here are some of the benefits of using various types of recycled aggregates in construction, which are also commonly used for for laying patios and pathways:

It can be cost effective

Using some recycled building materials may help to save on construction costs. Although recycled aggregates aren’t always cheaper, other materials reclaimed and processed locally can help to cut down on transport costs. 

It’s high quality

Recycled aggregates are made to an exacting standard and size, designed for use in various construction projects. The materials conform to harmonised minimum European Standards for Aggregates and national specifications, to guarantee that they are fit for purpose. Recycled aggregate material has to meet specific legal requirements before they can be sold in the UK.

Environmental and sustainability

Concrete and other types of construction waste from demolished buildings can be reused, reducing the demand on landfill. By using recycled materials, there’s less of an impact on the environment overall. It also means that waste products from other industries can be used in a positive and sustainable way, such as using excess slag from the iron and steel industries. Like fossil fuels, the world only has a limited supply of aggregates, so in the future recycling aggregates may be the only option.

It helps with demand

Building materials are constantly needed throughout the world, and supply chain delays or delivery driver shortages mean prices can rise as demand increases. By recycling old materials, supplies can be maintained, so there’s more to go around and construction projects have fewer avoidable delays.

Recycled aggregates in concrete

Depending on the usage, desired finish and the structural durability needed, it’s worth considering the pros and cons of using recycled aggregates in concrete. Although it may be cheaper, better for the planet and versatile, there are some disadvantages - including the risk of contamination, strength to size ratio differences and non-uniform appearances. Whether this matters or not depends on individual projects.

Advantages

As well as potential cost-saving benefits, using recycled aggregates in concrete has other advantages:

• Reducing waste and energy consumption

• Increased protection from seepage in buildings

• Contributing towards the strength of concrete, without necessarily compromising on quality

• Less use of landfill

• Lower freight charges and costs

• Reducing the need for harmful gravel mining

• Sustainable aggregate sources for the future

• Preserves natural resources and protects the natural landscape

Disadvantages

Although using recycled materials has clear benefits, particularly for the environment, there are some possible downsides:

• The quality of the concrete may be lower, if using cheaper sources and materials

• It isn’t always cheaper, as aggregates have to be washed and sorted

• Some consider recycled aggregates less durable

• The compressive strength and elasticity may be reduced

• Recycled materials may vary in type, colour and availability

• Non-refined aggregates may contain other materials and chemicals

• Grading and structure may not be consistent, causing a non-uniform finish

• Not all types of aggregates are suitable for every use, requiring professional advice, evaluation and site preparation

Are there types of aggregates that should be avoided?

Although recycled aggregates make an ideal choice for many concrete mixes, there are certain types that you’ll want to avoid, including:

• Very soft, porous materials - offering low durability

• Types which are likely to split and/or break easily - such as shells

• Certain types of ‘chert’ rock - many are easily degraded

• Aggregates with a smooth texture - broken, rough surfaces bond better

• Materials with certain organic impurities - such as iron oxide or alkali-reactive ingredients, which can affect performance

• Aggregates smaller than 75-μm - may bond poorly

• Clay lumps and friable materials - may cause popouts

It’s worth remembering that different recycled aggregate types are usually designed for different uses. For example, load bearing sub bases will need an aggregate with the appropriate strength and drainage properties, plus a certain particle-size grading. Your local Travis Perkins branch can advise you on the best product for your project.

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Recycled Aggregates: FAQs

What are the examples of recycled aggregates?

There are several types of recycled aggregates, including gravel, sand, crushed stone, asphalt, bricks and blocks, slags and recycled concrete. Recycled aggregate concrete (RAC) is also known as recycled concrete aggregate (RCA). Aggregate recycling describes the processing of new granular building materials, from previously used crushed construction aggregates and demolition waste, which has been broken down into a specific size and mixed ready for reuse.

What types of aggregates should be avoided?

Although recycled aggregate makes an ideal choice for most concrete mixes, there are certain types that you’ll want to avoid, including very soft or porous materials, types which are likely to split and/or break easily, certain types of ‘chert’ rock which is easily degraded, aggregates with a smooth texture, materials with certain organic impurities, clay lumps and friable materials or aggregates smaller than 75-μm.

Is recycled aggregate cheaper?

Using recycled aggregates is an ideal way to help save on construction costs, as aggregate recycling means they won’t have the high costs associated with being dug fresh out of the quarry. Materials may even have been reclaimed and processed locally, cutting down on transport costs. 

Where could you use recycled aggregates?

Recycled aggregates can be used in home building as well as outdoor landscaping, such as patios and driveways. Crushed concrete is ideal for pathways, patios and driveways, whereas ballast mix is great for making concrete to use almost anywhere. Recycled shingle is a cheaper alternative to gravel, and recycled sharp sand can be used for floor screed, fence posts and more.

Is recycled concrete as strong as concrete?

Recycled concrete shows very little strength difference to traditional concrete, but it features the added bonus of being cost effective and better for the environment. Whilst some construction companies notice no difference in durability, others have noted that it can be 10–25% lower in strength than conventional concrete made with natural coarse aggregate. Its specific use depends on whether this poses a problem or not.

Disclaimer: The information contained on this page is intended as an overall introduction and is not intended as specific advice from a qualified professional.