Abstract Concrete construction is responsible for around 8% of global greenhouse gas emissions. Reducing the carbon footprint of concrete is becoming crucial as its global production is expected to increase sharply in the coming years. One way to achieve this goal is to use the ability of concrete to fix CO2 by carbonation. Controlled by the diffusion of gaseous CO2 gas, carbonation is a reactive transfer which turn calcium oxides into calcium carbonates. At the end of their service-life, concrete structures are reduced by crushing into recycled concrete aggregates (RCA). Commonly used in road construction, recycled aggregates are also more and more reused in concrete mixtures as a substitute for natural aggregates. The CO2NCRETE project is focused on the sequestration of CO2 by accelerated carbonation of aggregates recycled with industrial gases. Recent literature reviews showed that this approach is the most promising among the strategies envisaged to reduce the carbon footprint of concrete construction. Most studies also show that carbonation improves the properties of RCA and thus their recyclability. The carbonation of crushed concrete aggregates is therefore a step towards a circular and carbon neutral economy, called the wishes of Europe. Among CO2 mineralization methods for capture, utilization and carbon sequestration (CCUS), carbonation of RCA can be envisaged as an attractive one, since the raw material, i.e. demolition concrete, is available in large quantity. The most obvious source of CO2 for this process is gas from cement kiln, since cement manufacturing is the main cause of the high CO2 emissions from concrete construction. However, there are other potential sources of gas with high concentrations of CO2. These includes petrochemical plants or more local sources such as household waste incinerators. Optimizing the carbonation process is the main scientific obstacle raised by the accelerated carbonation of RCA. If the atmospheric carbonation of concrete is an inevitable phenomenon, the degree of carbonation under natural conditions can remain quite low. Consequently, the ambition of the CO2NCRETE project is a fundamental understanding of the sequestration of CO2 by RCA for gases rich in CO2 at high temperatures and / or pressures. The expected result is the identification of the levers of acceleration and maximization of carbonation by means of the process conditions. These are in particular the CO2 concentration, the pressure and the temperature of the gas, the contact time between the gas and the material and the initial state of RCA. To that end, the CO2NCRETE project is organized into five tasks offering original approaches, from experiments on carbonation of RCA under severe conditions to advanced modelling with coupling of discrete models and reactive transfer models. A task is also devoted to assessing the effectiveness of the processes with respect to environmental and economic impacts. The project brings together laboratories recognized for their work in the fields of carbonation, recovery of deconstruction waste, multi-scale modelling and thermochemistry of complexes, namely: LaSIE, GeM, IFSTTAR, IRC and LGM. CERIB completes this team to make the link with the industrial sector of concrete.

In most cases, the deterioration of reinforced concrete structures is due to corrosion caused by aggressive agents from the external environment such as carbon dioxide and chloride ions. In order to control the lifetime of structures, efforts have to be made to manage the risk of corrosion from the structure design. This is of course an economic challenge since the maintenance of ageing concrete structures is nowadays more and more costly for owners. It is also an environmental challenge because, like other materials, the use of concrete has impacts at global scale (8% of the worldwide greenhouse gas emissions) or at local scale (natural aggregates consumption). In the current design standards, the control of structures lifetime is done through an obligation of means. For instance, the European standards require a minimum cover of reinforcement or a minimum binder content in the concrete composition. In the coming years, the performance-based approach will be introduced as a second way to design the concrete formulation. Concrete performances can be assessed through accelerated ageing tests or durability indicators. In France, application methods of the performance-based approach are available. A national project under construction (PERFDUB) shall gather most of construction actors to optimize these methods and use it in a global approach. To determine the threshold values of durability properties measured by tests, the performance-based approach need modeling tools which are able to predict the long-term behavior of reinforced concrete structures. The models will be used to quantify the durability indicators and to verify the reliability of the values. The objective of the project MODEVIE is to provide such models applicable by end-users in the frame of the performance-based approach. In recent years, many progresses have been done in the modeling of physical, chemical and mechanical phenomena acting on the durability of reinforced concrete. However, the existing models are often focused on only one of the stages of corrosion process, for instance on the stage of aggressive agents transfers or on the phase of corrosion propagation. The aims of MODEVIE is first to take into account all the different periods of the structure life in chaining behavior models, from transfers to corrosion and mechanical damage, and secondly to define a model adapted to the use of the performance-based approach in the normative context. MODEVIE will also provide a better understanding of parameters favorable to steel reinforcement depassivation and corrosion propagation. Limit states associated with reinforcement corrosion will be also rationally defined. Organized into six tasks, the project will involve modeling and experiments. The latter will take into account parameters such as concrete casting, aggregates nature and binder type. We will study concretes potentially qualified by the performance-based approach, i.e. concretes with high content of mineral addition or recycled aggregates. Finally, MODEVIE will lead to the definition of an “engineer” type model usable by end-users for the calculation of the structure lifetime for a given limit state (corresponding to an acceptable corrosion state). The entry parameters will be the concrete mix parameters, environmental conditions and materials data available from standard tests. MODEVIE gathers specialists partners in the fields of mass transfer, corrosion and normative context for the durability of concrete structures, which are all involved in the development of the performance-based approach for concrete structures: university laboratories (LaSIE, GeM, LMDC ), public laboratories (IFSTTAR, CEREMA) or private (LAFARGE, Eurovia, VINCI Construction France, CERIB).