By Achille Foncel, Amor Ben Fraj, Cerema

Introduction

In a context of resource depletion and global warming, the society is demanding of a more sustainable way of production. The building industry, with its significant CO₂ emissions and raw material consumption of concrete production, is prone to change and develop a circular economy model. For that reason, researches on the topic of recycling concrete are emerging, and projects like the Interreg SeRaMCo project are born.

The SeRaMCo project aims to promote the recycling of demolition by-products in new concrete. While the reuse of these aggregates is obviously beneficial to the environment, because it prevents the use of new resources, it is more difficult to compare the CO₂ emissions of the recycling process to the quarry extraction process. Hence our role in the SeRaMCo project: to evaluate the environmental impact of concrete recycling with Life Cycle Assessment (LCA).

What is life cycle assessment?

Life Cycle Assessment is a tool that uses the material and energy flows of each process to assess the environmental impacts of a product over its life cycle.

Figure 1: Product life cycle

In order to perform this analysis, we will follow these steps:

• Scope and process definition. It will define what we take into account for our study, and what we do not.
• Material and energy flows assessment. What each step of the process will consume/produce? It is the Life cycle Inventory (LCI).

Figure 2: Inputs/outputs example of a step in the recycling process [1]

• Impact assessment and interpretation. Thanks to the SimaPro software and the data acquired, we can simulate what impacts the products have on the environment.

Application to the SeRaMCo project

The environmental assessment of concrete recycling will be realised in three stages:

• LCA of recycled aggregates. In collaboration with Tradecowall, we will study the environmental impact of the production of recycled concrete aggregates. Thanks to exchanges we had with them, we established the list of all steps of the production and we began the LCI. When it will be complete, we will compare the environmental impacts of the production of 1 ton of recycled aggregates by two different processes.

Figure 3: SeRaMCo recycled aggregates production plant: sieving, St-Ghislain, Belgium

• LCA of recycled cement. The production of cement is the heaviest environmental impact of all the concrete production, thanks to the high amount of electricity required for the different heating stages. We want to reduce that impact by trying to replace some of the original components of cement with recycled concrete fines. We are currently working with Vicat on the process and on the LCI.
• LCA of concrete recycling. Finally, with all the data acquired in the two previous stages, we will conclude on the environmental benefits of concrete recycling.

Figure 4: Concrete production system boundaries [1]

During the simulation, we will study different concrete compositions: with more or less natural aggregates substituted by recycled ones, and with or without recycled cement.

 For this study to be comparable to others, we must set a Functional Unit (FU). This FU determines the products on which we realise the analysis. Per example, for stage 1, it was “the production of 1 ton of recycled aggregates”, and for stage 2, it was “production of 1 ton of cement”. For stage 3, we will test the FU: “production of 1m³ of concrete with required performance”.

References

[1] A. Ben Fraj and R. Idir. Concrete based on recycled aggregates - Recycling and Environmental analysis : a case of Paris' region. 2017