MesOscopic Scale durAbility Investigations for Concrete – MOSAIC

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.

The main originalities of the MOSAIC project are:
- To investigate the effect of drying and DEF on macroscopic cracking (and thus on the durability of concrete structures) through the development of nonlinear mesoscale analysis.
- To consider drying and DEF but also their coupling.
- To set up an experimental methodology based on both morphologically controlled and real materials, both built from the same components.

On a global point of view, the expected results of the MOSAIC project are:
- Concerning DEF, the quantification of 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 proposed.
- 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.

The first period of the MOSAIC project corresponds to the the beginning of large and long-term experimental campaigns. Most of the results are expected during the next months.

None up to now.

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