Modeling of the durability of concrete constructions – MODEVIE
Modeling to guarantee good health for constructions - Sea water and CO2, recurring causes of the pathology of reinforced concrete
The primary cause of deterioration of reinforced concrete structures is reinforcement corrosion. Mastering the lifespan of structures therefore means control at conception the risk of corrosion. This requires use predictive modeling. The challenge is of course for economic reason because maintenance of an older heritage buildings is expensive but it is also environmental because it is well to validate the use of new materials with less impact environmentally.<br />
Prediction of the performance and life of structures in the context of the risk of corrosion of reinforcement in concrete
«The feedback shows that better management of aging structures, in a context of sustainable development, requires appropriate tools for predicting the performance and life of the structures. Furthermore, the development of such tools is also today an important issue that emerged during the conception of new constructions for which the project's economic sustainability also depends on maintenance costs. Many examples show that for the heritage built in the 20th century, predictable repair costs may encumber the value of certain buildings significantly.<br />On the other hand, it is now technically possible to significantly reduce the environmental impact of concrete (reduction of 30% to 50% of CO2 emission factor for example) through optimal use of local materials (aggregates, cements, additions) and modern additives (which can reduce the water content of concrete and thus ensure high compactness conducive to good sustainability). Moreover, the ways to reduce the environmental impact of concrete also contributes to cost reduction through the use of recycled materials and / or to reduce transport distances which are a significant part of the economy of concrete structures. The ability to optimize both the environmental impact and the cost of construction due to the performance-based approach is a particularly important topic for the building, civil engineering, nuclear ....<br />These various findings show that it is now necessary for the various players in the construction of reinforced concrete to address the lifecycle of the works and their life more effectively, efficient and relevant. Such action is a must for today ultimately optimize their maintenance agreement with a strategy of sustainable development.«<br />
«To achieve the objectives described above, it is necessary to identify different scientific obstacles:
• Model the initiation phase of corrosion under stress coupled carbonation - medium chloride ions partially saturated using sustainability indicators as input data used in the performance-based approach;
• Changing models to account parameters related to aggregates and implementation;
• Model the corrosion limit states in the presence of chloride ions and carbonation
• To ensure the grouping of different stages of life of a concrete structure by chaining models starting from the transfer of ions and through the depassivation of reinforcement, the spread of corrosion and mechanical damage associated.
To meet the needs of stakeholders in construction in general and engineers in particular, it is also important to take into account some technical obstacles:
• Set from model ««useful to researchers,«« a simple model available to engineers for the implementation of performance-based approach initially to structural elements of undergoing degradation by laboratory tests (coupling carbonation and salt spray)
• Apply the ««engineer«« model to quantify the level of degradation vis-à-vis structural reinforcement corrosion in a state framework limits as shown below:
• LIVE ««A«« problem purely in appearance;
• LIVE ««F««: malfunction (excessive deformation);
• AN ««I««: the problem of mechanical integrity of the structure.
• Provide for each EL increasing target indexes based on the severity of the consequences of the corrosion of steel
• Apply performance-based approach to real cases.
The results of this work will also be useful to building owners who run an aging fleet of reinforced concrete structures.«
«The MODEVIE project aims to lay the foundations of the performance-based approach, with regard to reinforcement corrosion to validate such a methodology and make available to players in the construction tools developed.
Therefore, to ensure the widest possible dissemination of project results, a final presentation of the project will be prepared collectively by all the partners then returned within 5 regional presentations (Ile de France, Nantes, Toulouse, Lyon, Lille) to swarm our approach and (or) models developed (s) with all the actors of the civil engineering sector. These days restitution will address among others the owners, businesses, teachers, students, engineers, etc.«
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).
Madame Myriam CARCASSES (Laboratoire Matériaux et Durabilité des Constructions)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
GeM Institut de recherche en Génie Civil et Mécanique
Cerema Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement
LaSIE Laboratoire des Sciences de l'Ingénieur pour l'Environnement
LAFARGE CENTRE DE RECHERCHE
LMDC Laboratoire Matériaux et Durabilité des Constructions
VINCI CONSTRUCTION FRANCE
IFSTTAR Institut Français des Sciences et Technologies, des Transports, de l'Aménagement et des Réseaux
Help of the ANR 697,777 euros
Beginning and duration of the scientific project: September 2014 - 42 Months