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CICE 2021, 10th International Conference on FRP Composites in Civil Engineering, Istanbul, TURQUIE, 08-/12/2021 - 10/12/2021; Flax fiber reinforced polymer (FFRP) composites are demonstrating promising outcomes which makes them potential candidates to replace synthetic composites in various industrial applications. However, there is limited information regarding their long-term performance, and it is usually acknowledged that natural fibers are less resistant than their synthetic counterparts. In this context, it is crucial to study their durability before considering their use for structural rehabilitation and strengthening in construction. This study aims to investigate and predict the performance of FFRP composites with a bio-based epoxy matrix.The test program consisted in exposing FFRP laminates and FFRP strengthened concrete slabs to different accelerated ageing conditions over a total period of 2 years, and with various combinations of temperature and relative humidity in the ranges 20-60 °C and 50-100% RH, respectively. Series of tensile, short beam and pull-off tests were periodically performed on ageing samples in order to evaluate their property evolutions over exposure time in the various environments. Finally, collected experimental data were analyzed using statistical tools, in view of developing a degradation model and evaluating the service lifetime performance of this new bio-based composite.

Hand lay-up Fibre Reinforced Polymers (FRP), made of either carbon or flax textiles, were considered in this study and were subjected to water immersion at 40 ℃ over 24 weeks. Tensile tests were carried out periodically to assess the mechanical properties of the composites and Acoustic Emission (AE) monitoring was simultaneously realized to characterize the different microstructural damage mechanisms during loading. Maximum force per unit width, stiffness and ultimate strain were determined based on tensile testing data whereas frequency features and number of events were extracted and cumulated from AE signals. The obtained results showed that the mechanical properties of composites were significantly reduced meanwhile a modification of failure mode over 24 weeks was observed. Moreover AE signals analysis allowed a quantification of the level of damage. It also provided a discrimination of the different damage mechanisms and clarified how each mechanism contributed to failure.

International audience; Flax fiber reinforced composites are demonstrating promising outcomes which make them potential candidates to replace synthetic composites in various industrial applications. However, there is limited information regarding their long-term performance, and it is usually acknowledged that natural fibers are less resistant than their synthetic counterparts. In this context, it is crucial to study their durability before considering their use for structural rehabilitation and strengthening in construction. This research aims to study and predict the performance of flax fiber reinforced polymer (FFRP) composites with a biobased epoxy matrix. The test program consists in exposing FFRP laminates and FFRP strengthened concrete slabs to different accelerated ageing conditions over a total period of two years. In the present study, not a single stress variable but various combinations and coupling of two environmental stress variables, temperature (T) and relative humidity (RH), are considered, thereby distinguishing this study from most of the works reported in the literature. Then, a series of mechanical destructive tests are performed periodically on aged samples to evaluate property evolutions over ageing time. The collected experimental data are analyzed to develop a performance evolution model and to evaluate the service lifetime performance of this new biobased FFRP composite. For that, the potential of the Tweedie exponential dispersion (TED) process model, which takes some famous stochastic processes (Wiener process, Gamma process, and inverse Gaussian process) as special cases, is investigated. The TED process modeling, particularly interesting in the cases of complicated degradation mechanisms, is written here for destructive tests and, finally, a reliability analysis based on the TED process model determined is carried out in order to update the FRP design equations provided by international codes in the specific case of FFRP.

This paper presents an experimental approach to study the durability of FRP composites used in the civil/structural engineering. Carbon epoxy (carbon/EP) and carbon vinylester (carbon/VE) composites were considered for accelerated ageing (thermal, hygrometric, chemical, thermochemical, hydrothermal, freezing–thawing cycles, etc.) over 18 months. The accelerated ageing tests were selected to reflect the real operating conditions on natural civil engineering environment. The same composites were also subjected to environmental ageing to assess the effectiveness and the relevance of the accelerated exposure. Changes in tensile strength and viscoelastic response were evaluated through mechanical testing and Kinemat analysis. The design factors prescribed by the existing principle guidelines were applied to experimental measurements. The results revealed the presence of drawbacks inherent in these regulations based on a determinist approach.

Various aspects related to the durability of Fibre Reinforced Polymer (FRP) composites used in the rehabilitation, repair and strengthening of existing concrete structures were studied as a function of cure behaviour. The performance of these FRP-composites containing thermoset matrix and implemented under civil engineering conditions, is unstable and their properties will change over time due to their partial cure. The present work attempts to raise awareness about the characteristic changes of FRP-composites materials immediately after their ambient cure, while emphasizing the implication of such phenomena on the durability. Both glass transition temperature Tg and mechanical characterization tests were performed to identify the effects of curing on thermorheological and mechanical stability of the composites immediately after the implementation. The experimental results indicate that overall composite performance was sensitive to the cure conditions. The implication of this sensitivity on the durability of FRP-composites was addressed and clearly identified through accelerated and natural exposure tests which reflected the civil engineering environment.

International audience; Environmentally friendly FRP composites, made of natural fibres and bio-based polymer matrices, may be used as externally bonded reinforcement for civil structures or buildings subjected to moderate outdoor conditions, in replacement of traditional carbon/epoxy systems. However, a major drawback of natural fibers is their sensitivity to moisture, which can affect both the mechanical properties of FRP composites and their adhesive bond with concrete. This research, funded by the French National Research Agency (ANR Project MICRO), aims at studying the influence of hygrothermal ageing on the performances of “green composites” manufactured by hand lay-up process using unidirectional flax fabrics and a bio-based epoxy matrix. The test program consists in subjecting FRP laminates and FRP strengthened concrete slabs to accelerated ageing conditions under various combinations of temperature and humidity. Aged laminates are then periodically characterized by tensile tests and interlaminar shear tests, while the bond properties of concrete/composite assemblies are assessed by pull-off tests. This paper presents the first results of this ongoing program which is scheduled over a period of 2 years. Results are discussed in the light of complementary investigations (water sorption behaviour, microscopic observations and evaluation of the glass transition temperature by differential scanning calorimetry – DSC) in order to relate observed performance evolutions to actual microstructural changes or damage processes taking place in the material.

The repair, the reinforcement as well as the setting in safety of buildings and existing reinforced and/or pre-stressed concrete structure is a real technological stake and a socio-economic problem for the near future. The introduction of composites in civil engineering is an interesting answer to these goals, but they brought an important amount of new problems that have to be solved for safe structural applications under combined mechanical and environmental loadings. In fact during the past five years, we have witnessed exponential growth in research or field demonstrations of fiber-reinforced composites in civil engineering. Manufacturers and designers have now access to a wide range of composite materials. However, they face great problems with forecasting the reliability of composite materials. Their introduction in civil engineering applications is a difficult operation due to working environment and weathering conditions. The objective of this paper is to study the effect of these conditions and their consequences on the mechanical properties of the final composite. An analysis of the rheological (viscoelastic) properties was carried out in order to observe the glass transition temperature evolution according to reactive mixture stoichiometry and weathering conditions.