Recycling concrete

Crushed concrete can replace stones and sand in new concrete. In many European countries the regulation allows for crushed concrete to replace 20% of the stone fraction and 10% of the sand fraction. In 2020, Denmark approved the special standard DS/EN 206 DK NA:2020, which allows for up to 100% of the stone and sand to be replaced with crushed concrete. The CityLoops demonstration actions in Høje-Taastrup and Roskilde helped push this development in Denmark.

This Replication Package describes how to replace up to 100% of the stones/coarse aggregate and up to 50% of the sand in new concrete with recycled concrete. It contains a guide describing the process, legal framework, barriers, and opportunities when recycling concrete; interviews with key actors; as well as business cases and descriptions of the activities in two demonstration projects demolishing buildings and crushing concrete for use in new constructions.

Lessons learnt
  • If it is not possible to procure recycled concrete, the first step is to establish the value chain including the donor of concrete, the demolisher, the transformation actors and the new construction receiving the recycled concrete.
  • Reflect on incoming flows as well as outgoing flows regarding concrete: for instance, where do you get the aggregates and for what should the concrete be used? Which recipes do you need?
  • Recycling concrete the first time is labour intensive as it demands active management, but this will become less when it becomes a standard procedure.
  • Close dialogue and coordination across the value chain: a key factor ensuring the success of both demonstration cases was the willingness of all value-chain actors to engage in close dialogue and coordination throughout the projects, looking to help each other solve the problems rather than placing costs and risk somewhere else.
  • Early risk management: This was ensured by up-front dialogue concerning potential risks and how to manage them as well as efforts to clarify the type of documentation each partner required. Roskilde’s demonstration action holds a particularly good example of this dialogue and risk management.
  • The right expertise: The process behind the production of recycled concrete – including demolition, crushing, sieving and pile building – requires knowledge and attention. The demonstration projects included actors with prior experience of recycling concrete in these steps of the process, but if this is not possible, it is important to build such experience by following the guidelines.
  • Procurement as driver: To create strong business cases and mainstream the use of recycled concrete, it is necessary to increase the amount of recycled concrete procured. Both demonstration cases highlight the considerable opportunity public procurers have in driving this demand. In case that the National or European Standards are not covering the recycling wanted, additional risk may apply.
  • Pay attention to meet the demands for End of Waste criteria.
  • Support the development of a functioning recycled concrete flow, so you do not have to establish the value chain with donor concrete every time.
  • Make sure you properly lay down the info about the concrete in the construction project for future reuse.
  • CO2-savings are much lower when recycling instead of reusing concrete, but the natural resource savings are important. However, you should not transport concrete waste for recycling more than 25 km – then there is no CO2e gain.

CityLoops instruments

CityLoops demonstration experiences