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What is an eco-material?

Ecological concrete? Two examples, with concrete produced using lime and hemp (left) and another using lime and rice husk (right).

Reducing the environmental footprint of human constructions is one of the major issues facing the ecological transition. Achieving this goal requires the use of eco-materials. Gwenn Le Saout, a researcher in materials at IMT Mines Alès, explains what these materials are, their advantages and the remaining constraints that prevent their large-scale use.

 

How would you define an eco-material?

Gwenn Le Saout: An eco-material is an alternative to a traditional material for a specific use. It has a lower environmental impact than the traditional material it replaces, yet it maintains similar properties, particularly in terms of durability. Eco-materials are used within a general eco-construction approach aimed at reducing the structures’ environmental footprint.

Can you give us an example of an eco-material?

GLS: Cement has a significant COfootprint. Cement eco-materials are therefore being developed in which part of the cement is replaced by foundry slags. Slags are byproduct materials from steel processes that are generated when metal is melted. So, interestingly, we now call slags “byproducts”, whereas they used to be seen as waste! This proves that there is a growing interest in recovering them, partly for the cement industry.

Since concrete is one of the primary construction materials, are there any forms of eco-concrete?

GLS: Eco-concrete is a major issue in eco-construction, and a lot of scientific work has been carried out to support its development. Producing concrete requires aggregates—often sand from mining operations. These natural aggregates can be replaced by aggregates from demolition concrete which can thus be reused. Another way of producing eco-concrete is by using mud. Nothing revolutionary here, but this process is gaining in popularity due to a greater awareness of materials’ environmental footprint.

Are all materials destined to be replaced by eco-materials?

GLS: No, the goal of eco-materials is not to replace all existing materials. Rather, the aim is to target uses for which materials with a low environmental impact can be used. For example, it is completely possible to build a house using concrete containing demolition aggregates. However, this would not be a wise choice for building a bridge, since the materials do not have exactly the same properties and different expertise is required.

What are the limitations of eco-materials?

GLS: The key point is their durability. For traditional concrete and materials, manufacturers have several decades of feedback. For eco-materials, and particularly eco-concrete, there is less knowledge about their durability. Many question marks remain concerning their behavior over time. This is such an important aspect of the research: finding formulations that can ensure good long-term behavior and characterizing the existing eco-materials to predict their durability.  At The Civil Engineering Institute (IGC), we worked on the national RECYBETON from 2014 to 2016 with Lafarge-Holcim, and were able to provide demonstrators for testing the use of recycled aggregates.

How can industrial stakeholders be convinced to switch to these eco-materials?

GLS: The main advantage is economic. Transporting and storing demolition materials is expensive. In the city, reusing demolition materials in the construction of new buildings therefore represents an interesting opportunity because it would reduce the transport and storage costs. We also participated in the ANR project ECOREB with IGC on this topic to find solutions for recycling concrete. We must also keep in mind that Europe has imposed an obligation to reuse materials: 70% of demolition waste must be recycled. Switching to eco-materials using demolition products therefore offers a way for companies to comply with this directive.

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