Recycling concrete

Reduce and reuse are priorities for good circular economy practice.  When concrete does eventually reach the end of its life, it can be recycled.  

The majority of concrete’s volume/mass is aggregates, and when recycled, it becomes aggregate again. Some of this makes its way back into new concrete, but most is used “unbound” as sub-base materials, fill and hardcore, replacing primary aggregates. Concrete pieces from demolished structures can also be reused to protect shorelines, for example in gabion walls or as rip rap. The recycling process has the potential to be repeated again and again in perpetuity to provide a low carbon aggregate resource for a range of applications. 

The supply chain for recycling concrete is well established in the UK and feedback from demolition contractors, supported by data from other sources, is that practically all concrete demolition waste is recycled. The aggregates in concrete may be crushed on site for reuse in a new development on site, or transported to a local recycling centre for processing and distribution. 

Recycled and secondary aggregates account for around 29 per cent of the total aggregate use in the UK.  This plays an important role in the UK’s current circular economy, its use reducing the demand for primary aggregates. See Profile of the UK Mineral Products Industry on the MPA website.

Recycled aggregates 

Recycled concrete is a viable source of aggregate and has been satisfactorily used in granular subbases, soil-cement, and in new concrete. Recycled aggregates are classified in one of two ways, as: 

• Recycled Aggregate (RA) - aggregate resulting from the reprocessing of inorganic material previously used in construction.   
• Crushed Concrete Aggregate (CCA) – aggregate obtained from crushed concrete. 

 
A specific subset of recycled aggregates is crushed concrete aggregates (CCA) where the content of: concrete, concrete products, mortar, concrete masonry units, unbound aggregate, natural stone or hydraulically bound aggregate  must not be less than 90%. This high percentage inclusion of ‘good’ aggregate results in CCA having better performance characteristics than RA and consequently there are fewer restrictions on the use of CCA in concrete. Provision for the use of CCA in concrete is given in BS 8500:2023. 

For information on the use of recycled aggregates in concrete see below.   

Crushing concrete and carbonation 

Crushing concrete at the point of demolition substantially increases its surface area, allowing carbon dioxide to be more readily absorbed –  a process called carbonation. Exposure to rain has been shown to significantly increase the rate of carbonation during this stage. Carbonation occurs during demolition and while the aggregate is stored on site, but then continues during the concrete’s secondary life if used in groundworks, hardcore and landscaping. 

Recycled concrete fines and recycled concrete paste 

New uses for concrete demolition waste are in development. Recycled concrete fines are the residue of concrete waste after recycled aggregates are removed. It consists of cements pastes and sand. It accounts for ~15% of recycled concrete and currently has only low value uses.​ Research and development is taking place create new uses including carbon capture use and storage,  and the manufacture of recycled concrete fines and paste as a cement replacement and the manufacture of new cement.   

Recycling reinforcement  

Steel reinforcement can be recycled, used to create new reinforcing steel.