Understanding the thermal deformations of cement-based materials is crucial to ensure the performance of building envelopes and infrastructures subjected to thermal loads. Thermal deformations are recognized as one of the major causes of cracking of cement-based materials. The prediction of thermal deformations relies on an accurate description of the thermal properties, namely the coefficient of thermal expansion (CTE), the heat capacity (a property related to the increase of temperature of a material upon heating) and the thermal conductivity. Sensitivity analysis shows that relatively small variations in the heat capacity and in CTE may significantly affect the thermal response of concrete structures. For cement-based materials, these properties are reported to be composition, time, temperature and relative humidity (RH) dependent. The goal of this project is to provide a model of the thermal properties of cement-based materials that are informed by the relevant physical phenomena in a multiscale framework and that can be used in the engineering practice. The target applications are concrete infrastructures and building envelopes made of cement-based materials that are subjected to thermal loads in an environment with a given RH. We will focus on the elucidation of the physical origins as well as the temperature and RH-dependency of the CTE and the heat capacity. We assume that accounting for the multiscale nature of cement-based materials is crucial to understand thermal deformations since key aspects of the thermo-mechanical behavior of cement-based materials are related to nanoscale processes. To tackle this problem, we propose a strategy combining molecular simulations, micromechanics and finite element analysis. Additionally, a major part of the project will be devoted to gathering data to create a database on the thermal properties of cement-based materials that will be used for validation of the model according to various environmental conditions and compositions of the materials. Molecular simulations are adapted to assess the behavior of water confined at nanopores because they allow quantifying the intermolecular forces associated with adsorption phenomena and confinement. Micromechanics will be used to bridge the scales from the molecular scale up to the scale of industrial application of cement-based materials. Finite elements simulations will be used to study the thermal deformation and cracking at the macroscopic scale. The expected outcomes of this project will contribute to reduce the empirism in thermo-hydro-mechanical modelling of concrete that can leads to the design more durable and resilient structures tailored to performance specifications, the extension of the service lives existing ageing infrastructures, and the reduction of the impact of using concrete.

Aging of Civil Engineering structures generally leads to important economical concerns, mainly linked to the choice between their replacements or their life extensions. Developing a more general understanding of cement-based materials behaviors and of the mechanisms associated to their long-term behaviors is thus of the greatest interest both on the environmental and financial points of view. To set up such a sustainable methodology associated to the field of cement-based materials industry requires a deep understanding of their behaviors under the numerous environmental conditions that may occur. Being at the crossroad of several scientific domains such as nonlinear continuum mechanics, chemistry, mass transfers or computational solid mechanics, this scientific issue is a highly interdisciplinary one. Dealing with concrete structures, it is now clearly established that most of the macroscopic scale observed behaviors (among which the pathological behaviors, such as drying or delayed ettringite formation, are our main cause for concern because they may strongly decrease the durability of the structure) find their roots within a set of specific physical and chemical phenomena. Though the latter take place at fine scale, their consequences at macroscale may be quite important, with a huge impact on the durability of concrete structures and their life expectation. This fact is the cornerstone of the MOSAIC project. Our aim is to improve the links between those fine scale mechanisms and their macroscopic consequences. To build such bridges shall consist of two main steps: - First to drive experiments within specific environmental conditions in order to trigger different pathologies and to measure their consequences at macroscale; - Second to find out, for each pathology, which minimum set of mechanisms is mandatory to be modeled, at fine scale, in order to get an accurate and predictive strategy. Hence, contrary to the usual macroscopic models, our aim here is to identify the simplest physical and chemical mechanisms, and to embed those within a multi-scale numerical strategy. Considering the potential numerical difficulties, the MOSAIC project aims at focusing on the mesoscopic scale, which amounts to explicitly representing heterogeneities larger than 1 mm as well as their interfaces. Chief among the degradation mechanisms for concrete, cracking is of the major importance and is strongly related to the present challenges dealing with the durability of concrete Civil Engineering structures. For the latter, some specific long-term environmental conditions are known to be quite prejudicial by causing cracking and thus involving an increase of mass transfers, and finally increasing the risk of corrosion of steel in reinforced concrete. The MOSAIC project deals with two of those conditions: delayed ettringite formation and drying. They are complementary in the sense that the former leads to cement paste swelling, while the latter corresponds to cement paste shrinkage. Those two phenomena are involving degradation mechanisms associated to the fine scale of concrete, and so are strongly influenced by the material heterogeneity. Hence the use of a fine scale analysis is also of the strongest interest in terms of durability of concrete structures. On a global point of view, the expected results of the MOSAIC project are: - First to be able to quantify mechanical and transfer properties at macroscale from the knowledge of the potential shrinkage and swelling of the cement paste on the one hand and, on the second hand from the morphology and volume fraction of the aggregates. - Second, concerning DEF, the ability to quantify the effect of drying-wetting cycles and the improvement of the ability to predict the swelling due to DEF. The latter shall be done considering mix-design parameters, chief among them the choice of the aggregates. Depending on the effect of drying-wetting cycles, an evolution of the control test on DEF will be propose

The project aims to define a new concept of modeling for RC structures reinforced by composite materials capable of taking into account all the elements independently strengthened and their interaction to assess the global response of the structure loaded under seismic conditions. The numerical approach is to use both conventional elements (type multi-fiber beam) in the less stressed areas and complex 3D numerical models in the most stressed areas. This new tool will be calibrated using experimental testing to define easily identifiable physical model parameters. This new method of modeling is intended to avoid the definition of boundary conditions typically required to calculate and highly dependent on the choice of the calculator.

The current craze for architectured materials results from 3 factors: 1. Expected exceptional properties: Studies (experimental, numerical, theoretical) show that in addition to mass gain, the presence of an internal architecture significantly improves certain properties (energy absorption), or even creates others (invisibility cap); 2. Shape optimization: Mesostructure design algorithms have emerged that allow a more automatic exploration of the links between architecture and resulting properties; 3. Additive manufacturing: Manufacturing techniques and their rapid development now make it possible to produce structures with complex internal architectures. However, the expected exceptional properties occur when the scale of mechanical loading is close to that of the mesostructure. Wave propagation and instabilities are situations where the lack of scale separation is necessary for producing non-standard effects. A streamlined approach to the design of such materials involves an intermediate step in which an equivalent effective medium is substituted to the mesostructure of the material. This effective continuum is first optimized, in order to satisfy a given set of specifications, then deshomogenized to reveal the desired mesostructure. However, the classical framework of homogenization assumes infinite scale separation and is therefore ill-suited to continuous modelling of expected phenomena. Taking into account the effects of the mesostructure within a continuous modeling is the scientific lock this project proposes to remove. The developed approach is based on generalized continuum mechanics supplemented by the use of group theory in order to clarify the role of material symmetries on effective behavior. The framework concerns periodic and pseudo-periodic materials and the considered applications are, on the one hand, control of wave propagation (Axis 1) and, on the other hand, prediction and control of instabilities (Axis 2). In both cases, the architecture of the elementary cell is decisive. Its determination from the target effective properties via an inverse problem of architecture is at the core of Axis 3 of the project. These axes are complemented by a transversal axis linked to the development of adapted experimental methods. In more details: 1. Elastodynamics of architectured materials: Dynamics adds distribution of inertia to the optimization problem that traditionally only deals with distribution of stiffness. Depending on the applications, the various networks may or may not be congruent. 2. Controlled instabilities, obtained by a succession of stable post-bifurcated configurations. This requires an optimization of the crystallographic symmetries of the architectured materials. The applications here concern the adjustment of the multifunctional properties of materials by a change in mesostructure due to instabilities generated by a mechanical loading. 3. The definition of an inverse problem of architecture allowing to determine associated mesostructures, for a set of invariants of the given effective material. This axis aims both at "deshomogenizing" the results obtained in Axes 1 and 2 in order to obtain a real architecture, but also at exploring and classifying mesostructures associated with exotic elastic anisotropies (2D and 3D). 4. Development of experimental methods adapted to architectured materials. Experimental homogenization implies a specific control of boundary conditions. Moreover, instabilities will generate large displacements at the edges requiring the development of appropriate experimental means. This axis will be limited to the static behavior of architectured materials.

Historical earthquake catalogues are one of the building blocks for the evaluation of seismic hazard. In spite of many years of research in archives, many earthquakes remain poorly known. New sources of information are hence required. Historical buildings are witnesses of natural catastrophes recorded in their walls as structural disorders or repairs. The ambition of this project is to study past earthquakes using buildings as “stone seismometers”, analysing the seismic ground motions necessary to explain building repairs/disorders, or their absence. To gain such a knowledge, it is necessary to define an interdisciplinary strategy based on: innovative techniques introduced in the building archaeology; seismic input signals consistent with the seismotectonic context; digital building models based on realistic geometry and construction materials. With this aim, a methodology connecting “ArChaeology, inventory of RecOnstruction, Seismology and Structural engineering” ACROSS is introduced. The project goal is to demonstrate that archaeological characterization of post-seismic repairs on buildings can be successfully used to infer key ground motion and earthquake source characteristics of historical earthquakes. The ACROSS method is declined in five steps, each of them challenging the concerned disciplines to use methods and technics at the state of the art and to strongly interact among them to obtain reliable outcomes, useful for all the involved communities. 1. Collecting the data produced by the archaeology of the buildings and the study of historical sources. 2. Identification of damage mechanisms 3. Definition of the digital building model used to perform seismic dynamic analysis. 4. Definition of ground motions to be used as input for the building dynamic analysis. 5. Comparison of the results of the numerical analysis, based on steps 3 and 4, with repairs and damage mechanisms, identified in steps 1 and 2. If the observed damages are successfully reproduced, then it is possible to retrieve quantitative information on the past ground motion features by analogy with the ones used in the dynamic analysis. The ambition of ACROSS is to move from catalogues of historical seismicity to the definition of the historical ground motion at a given site.