Recycled Aggregate & Concrete

What is recycled aggregate?

Recycled aggregate (RA) is produced by crushing and screening demolition waste - primarily old concrete, masonry, and sometimes asphalt - to create granular material that can replace virgin quarried aggregate in new construction. Recycled concrete aggregate (RCA) specifically refers to aggregate derived from crushed concrete.

The UK demolishes and refurbishes enough buildings each year to generate approximately 60 million tonnes of construction and demolition waste. A significant proportion of this is concrete and masonry that can be processed into high-quality recycled aggregate, diverting it from landfill and reducing demand for primary extraction.

Modern recycled aggregate processing plants use jaw crushers, impact crushers, magnetic separators, and screening equipment to produce graded aggregate that meets the same BS EN standards as virgin material.

Types and quality grades

Not all recycled aggregate is the same. Quality varies depending on the source material, processing, and intended use.

Recycled concrete aggregate (RCA)

Crushed concrete - the highest quality, usable in new structural concrete when graded and tested to BS EN 12620.

Recycled aggregate (RA)

A blend of crushed concrete, masonry, and inert material. Suits sub-base, fill, and lower-grade applications.

Secondary aggregate

Industrial byproducts like slate waste or china clay sand - not strictly recycled but displaces primary aggregate.

Reclaimed aggregate

Material reused directly without crushing, such as reclaimed gravel from road reconstruction.

Note. BS 8500-2 permits up to 20% RCA in designated concretes (RC40-RC50) and up to 100% in lower-strength applications. Some specifiers are achieving higher replacement levels through project-specific testing and approval.

Performance and technical considerations

Recycled aggregate performs differently from virgin aggregate in some respects, and these differences must be accounted for in mix design and specification.

Topic	Detail
Water absorption	RCA typically absorbs more water than virgin aggregate (3-8% vs 1-2%) due to residual cement paste. This affects workability and requires adjusted water content in concrete mixes
Density	slightly lower than virgin aggregate (2,200-2,400 kg/m³ vs 2,500-2,700 kg/m³), affecting concrete density and structural calculations
Strength	concrete made with RCA can achieve equivalent compressive strength to virgin aggregate concrete at the same cement content, though mix design optimisation may be needed
Durability	chloride and sulphate content must be tested, particularly for aggregate sourced from marine or industrial environments. Carbonation resistance may differ
Shrinkage	slightly higher drying shrinkage is sometimes observed in RCA concrete - typically 10-20% higher than equivalent virgin aggregate mixes
Consistency	quality can vary between batches depending on the source demolition material. Regular testing is essential

Carbon and environmental benefits

Using recycled aggregate reduces environmental impact in multiple ways, though the magnitude depends on the specific comparison being made.

Topic	Detail
Avoided extraction	eliminates the energy and land disturbance associated with quarrying virgin rock
Reduced transport	recycled aggregate is often processed close to demolition sites in urban areas, reducing haulage distances compared to quarried aggregate from rural locations
Landfill diversion	redirects demolition waste from landfill, avoiding disposal costs and environmental impacts
Lower embodied carbon	recycled aggregate typically has 30-50% lower embodied carbon than equivalent virgin aggregate when transport savings are included
Resource conservation	extends the productive life of existing quarries and reduces pressure on finite mineral resources

Watch out. The carbon benefit of recycled aggregate is heavily dependent on transport distances. If the recycling plant is further from the project than the nearest quarry, the carbon advantage can be lost. Always compare on a project-specific basis.