Sustainable concrete – the remix

Guidelines for making concrete from recycled ingredients could help the construction industry reduce its environmental impact. An EU-funded project developed the guidelines based on tests of recycled concrete, recycled steel from old tires and natural fibres from sisal.

As the most widely used construction material in the world, concrete has a significant impact on the environment. Producing it consumes large amounts of raw materials and is responsible for around 10 % of all human-sourced emissions of greenhouse gases, according to the team behind the ENCORE project. Concrete from demolished buildings and structures also generates a large amount of waste each year.

Standard concrete used for houses, office buildings and other structures is a mix of water, cement, and aggregates, such as sand, gravel, or crushed stone. Industrial steel fibres are sometimes added in a class of materials generally referred to as ‘fibre-reinforced concrete’.

Could recycled substitutes be used to replace some of these ingredients to make concrete production more sustainable? Yes, say researchers for the EU-funded project ENCORE, which demonstrated that sustainable substitutes could be used in the place of aggregates and fibres.

The project has produced three model guidelines on the technical standards for using recycled concrete, steel from waste tyres and natural fibres obtained from plants, such as sisal.

These model guidelines are recommendations or ‘instructions’ for the construction industry on how to produce, process and mix concrete with recycled ingredients, says project coordinator Enzo Martinelli of the University of Salerno, Italy.

“Before ENCORE, the level of knowledge on the mechanical performance of concrete made from waste was mainly empirical and consisted of various proposals merely based on experimental observations,” Martinelli says. “Our project has formulated a fundamental approach for predicting the relevant mechanical properties of the materials under consideration.”

The project’s research and the three guidelines have been disseminated to European and international industry organisations. The project conceived the guidelines as a possible annex to the International Federation for Concrete’s ‘Model Code for Concrete Structures’ for field applications, Martinelli says.

“They are ready to be considered for adoption in future revisions of that document,” he adds. “Inclusion would be a key step towards a more rational and wider use of recycled constituents in structural concrete.”