MICRO

The built heritage in France is wide and aging. For this reason, structural strengthening by externally bonded Fiber Reinforced polymers (FRP) composites is an attractive solution to upgrade/repair existing infrastructures and to increase their life-span. As it makes it possible to reduce maintenance costs and to streamline infrastructure management, FRP strengthening is a technique of interest for infrastructure owners and for Society. The MICRO Project aims at removing barriers to the large scale development of FRP strengthening systems, by addressing the following issues: - on the one hand, both the durability and the reliability of this innovative building process will be assessed through a statistical approach and a multi-scale analysis. - besides, in order to anticipate upcoming changes in the European environmental regulations, innovative composite materials showing a reduced environmental footprint will be developed, based on natural/bio-sourced components that do not contain CMR substances. The development of a probabilistic approach is justified by the fact that composites materials have been introduced only recently in the field of construction, compared to other and well known traditional building materials. Their performances are dependent upon complex mechanisms which cannot be well understood by classical deterministic approaches, due to a high level of variability. To address properly the issues related to the rehabilitation of civil infrastructures, it is thus necessary to predict the lifespan of the repaired structures and to evaluate the risk of failure, expressed in probabilistic terms. The reliability study proposed in the MICRO Project will take into account indicators and parameters determined from a statistical analysis, relying on a rigorous Design of Experiments. This latter involves an optimized set of accelerated ageing tests representing actual service conditions. Besides, the multi-scale approach will make it possible to choose relevant durability indicators, and to identify the various mechanisms involved in the degradation of the bonded assembly (at the level of the polymer matrix, the fiber/matrix interface or the FRP/concrete adhesive bond). The following strengthening materials will be investigated: - the traditional carbon fibers-epoxy resin system, commonly applied by wet layup on the field, which will be considered as the reference process, - innovative and more eco-friendly composite materials: fabrics based on vegetal fibers or basalt fibers, and green polymer matrices (such as bio-based epoxy thermosetting resins). An emphasis will be put on the fiber surface treatment (sizing) that will ensure a good compatibility with the selected polymer matrix, and on the composite forming process. These materials and the upgraded structures will be studied in order to predict their lifetime. A major objective of the MICRO Project is to provide a comprehensive scientific and technical background to help infrastructure owners in the design of bonded composite repairs, while respecting the semi-probabilistic approach of Eurocodes and meeting requirements imposed by the latest European regulations in terms of safety, reliability and durability. In this line, it is proposed to conduct a 48 months research program, well-structured and coordinated, which will rely on 7 renowned teams from academic laboratories. These latter bring together complementary competences (material development, durability studies, structural design and reliability analysis) that will be crucial for the success of the project. MICRO addresses practical issue and will be useful to the Economy. Its ambitious goals justify the proposed structure and the estimated cost of the project.