Aggregates used in Concrete – Definitions 

Effectively this is aggregate resulting from a mining, quarrying or dredging process and used in its natural state. The aggregate would undergo processing such as crushing, washing and grading. Often these materials are grouped into crushed rock, sand and gravel. 

May also be known as primary or virgin aggregates. 

Manufactured aggregates are often a by-product of other industrial processes, for example blast furnace* and steel slags, incinerator bottom fly ash, furnace bottom ash, coal derived fly ash* aggregate product. As a by-product these aggregates could also fall under the definition of ‘secondary aggregates’. 

 *These can also be used as a cementitious addition 

The definition used within BS EN 12620 is the same as the definition for a recycled aggregate used in BS 8500. However, the term used in BS EN 12620 covers all recycled aggregates, whilst BS 8500 splits recycled aggregates into two categories: 

• Recycled Aggregates (RA), and 

• Crushed Concrete Aggregates (CCA) 

When specifying concrete in the UK, BS 8500 should be referred to for the composition requirements of both RA and CCA.  

Outside of BS 8500:2023 the term ‘recycled aggregate’ is often used as a catch all term for all recycled aggregates. However, within BS 8500:2023 recycled aggregates are split into two categories: 

• Recycled Aggregates (RA), and 

• Crushed Concrete Aggregates (CCA) 

In accordance with BS EN 12620, BS 8500-2:2023 table 5 provides criteria for quantity and type of constituent materials for coarse RA.  

BS 8500:2023 provides guidance on allowable use of coarse RA within concrete however does not provide guidance on the use of fine RA due to its variable nature.

The definition for a Crushed Concrete Aggregate (CCA) originates from BS 8500:2023. In accordance with BS EN 12620, the requirements for the constituent materials are set out in Table 4 in BS 8500-2:2023. 

BS 8500:2023 provides guidance on allowable use of coarse CCA within concrete however does not provide guidance on the use of fine CCA due to potential presence of deleterious materials.   

NOTE: This term should now be replaced with Crushed Concrete Aggregate (CCA) as per BS 8500:2023. 

This term has been replaced by Crushed Concrete Aggregate within BS 8500 since the 2015 revision. Therefore, other standards that have not been revised since this revision of BS 8500, for example BS EN 12620, may still use the term Recycled Concrete Aggregate. Also, the term is still often used across the construction sector in newer publications or guidance documents.   

The requirements of an RCA in older versions of BS 8500 vs current requirements of a CCA within the standard are broadly similar and therefore it can be assumed that when RCA is referred to that this is a CCA under BS 8500:2023. 

BS EN 206:2013+A2:2021 splits reclaimed aggregates into two categories: 

• Reclaimed washed aggregate – aggregate gained by washing fresh concrete 

• Reclaimed crushed aggregate – aggregate gained by crushing hardened concrete that has not been previously used in construction.  

Section 5.2.3.3 provides additional guidance on the use of reclaimed aggregates 

Reclaimed Washed Aggregate 

In the UK it is normal practice for ready-mixed concrete plants to wash their mixers using a small amount of water. The remaining aggregate within the mixer is therefore cleaned and can be put back onto their relevant aggregate stockpiles as reclaimed washed aggregate. 

BS EN 206 states that ‘Where the quantity of reclaimed washed aggregate is greater than 5% of the total mass of aggregate, they should be divided into separate coarse and fine aggregates and conform to EN 12620’. 

Reclaimed Crushed Aggregate 

Reclaimed crushed aggregate is produced from crushing hardened concrete that has not been previously used in construction. BS EN 206 states that ‘where the quantity of reclaimed crushed aggregates is greater than 5% by total mass of aggregate, they shall be treated as recycled aggregates’. In this scenario within the UK, this aggregate could generally be considered as a CCA based on the criteria set within BS 8500. 

Both make up a small percentage of the total aggregate used within the UK.  

These are aggregates derived from other industrial, production or extractive processes. This can include mineral extraction operations such as sand and crushed rock material from ball clay and China clay production or waste from slate production.  

Other sources, which could also be termed ‘Manufactured Aggregate’ include blast furnace and steel slags, incinerator bottom fly ash, furnace bottom ash and coal derived fly ash.