Cet article presente une theorie previsionnelle de la rupture des assemblages colles. Le modele e... more Cet article presente une theorie previsionnelle de la rupture des assemblages colles. Le modele est fonde sur le principe des puissances virtuelles applique a l'endommagement (Fremond, 1987). Il couple les endommagements volumique et surfacique. La presentation est scindee en deux parties. Dans la premiere, la signification physique des differents parametres du modele est discutee et des intervalles de variation sont definis pour chacun des parametres. Dans un second temps, le modele est mis en oeuvre pour decrire le comportement a la rupture d'assemblages colles soumis a des sollicitations de traction homogene ou de cisaillement. Les simulations sont confrontees aux resultats experimentaux obtenus dans le cadre de campagnes d'essais. (A). (Voir fiche generale F101003 et fiches specifiques F101004 a F101084).
European Journal of Environmental and Civil Engineering, 2018
The determination of the energy consumption of a building requires the computation of the coupled... more The determination of the energy consumption of a building requires the computation of the coupled heat and mass transfers inside the wall. The existing models require the determination of the hygrothermal properties of the materials, and of the boundary and initial conditions, prior to computing numerically the temperature and vapour fluxes and the energy and mass balance of the building. However, the experimental measurements do not give accurate values, yielding a wrong estimation of the energy consumption. In order to determine the influence of the uncertainties on the values of the input parameters of the Kunzel model, we carried out a local sensitivity analysis (LSA) by varying by 5% the hygrothermal properties of the materials, the surface transfer coefficients and the initial conditions. The results of the LSA are treated by means of quartile boxes in order to identifiy the most influent parameters. The LSA is applied to two walls made of highly porous and hygroscopic materials: limestone and hemp concrete. The results show that the surface transfer coefficients and the adsorption isotherm are the most influential parameters. However, the conclusions are slightly different between the two materials, because of differences in the relative importance of transfer phenomena.
The effects of thermal oxidation on the molecular and macromolecular structures of additive free ... more The effects of thermal oxidation on the molecular and macromolecular structures of additive free PE were investigated between 100 8C and 140 8C in air in order to tentatively establish non-empirical structure/property relationships. In the first part, the changes in POOH concentration were assessed by three different analytical methods: iodometry, modulated differential scanning calorimetry, and Fourier transform infrared (FTIR) spectrophotometry after SO 2 treatment. All these methods provided very similar results until the end of the induction period, after which iodometry overestimated strongly POOH concentration because it titrates also other chemical species formed at high conversion ratios, namely double bonds. In parallel, the changes in carbonyl group concentration were determined by FTIR spectrophotometry after NH 3 treatment. As the accumulation kinetics of ketones, aldehydes, and carboxylic acids were closely interrelated, the question of their actual formation mechanisms in the current thermal oxidation mechanistic scheme was raised. An alternative reaction pathway was proposed for the bimolecular decomposition of POOH. In the second part, the corresponding changes in weight and number average molecular masses were monitored by high temperature gel permeation chromatography equipped with a triple detection technology. As both quantities decreased dramatically from the beginning of exposure and their ratio M w /M n tends toward the asymptotic value of 2 and it was concluded that a "pure" chain scission process operated. Finally, as the number of chain scissions perfectly correlates, the concentration sum of aldehydes and their oxidation products (i.e., carboxylic acids), it was also concluded that these carbonyl groups result exclusively from the b scission of alkoxy radicals.
In this paper, two kinds of tests were designed to investigate and study the bond behavior betwee... more In this paper, two kinds of tests were designed to investigate and study the bond behavior between fiber-reinforced-plastic (FRP) and concrete. By newly designed double-shear test setup, the strain development and distribution in FRP plate was acquired. At the same time, the direct shear bond distribution was given and the effective bond length was suggested. Through a bending test on simply supported beam with an extended end, the strain and stress distribution of FRP plate in the negative moment zone were studied. Based on the test results, conclusions including the maximum effective bond length, the mean bond stress and the development length for flexural bond in the negative moment zone were presented. The effective bond length is about 100 mm and the mean bond stress is about 1.287 MPa. The development length for flexural bond in the negative moment zone is about 300 mm.
LABORATOIRE CENTRAL DES PONTS ET CHAUSSEES (LCPC), Apr 10, 2010
Cette methode d'essai decrit un test de cisaillement par traction directe permettant de carac... more Cette methode d'essai decrit un test de cisaillement par traction directe permettant de caracteriser le joint adhesif entre un renfort externe en materiau composite et un element de structure en beton. Ce test conduit a la determination d'indicateurs d'efficacite du procede, tels que la capacite maximale du joint colle en termes d'effort repris, et la longueur d'ancrage effective. Plusieurs methodes d'exploitation des resultats sont ensuite proposees afin de repondre a la fois aux problematiques de dimensionnement des ingenieurs de genie civil et aux besoins des chercheurs. (A).
One of the goals of sustainable development applied to bridge infrastructure is to provide bridge... more One of the goals of sustainable development applied to bridge infrastructure is to provide bridge owners with strengthening solutions that may lead to an increase of existing structures service life. In the case of steel bridges, the assessment of the remaining service life is most often linked to the determination of the structural deterioration caused by corrosion and fatigue. Damage caused by fatigue is very difficult to assess before crack initiation, and is more bound to occur in old structures, for which the phenomenon was not taken into account in design before 1970. In addition, old steel materials present a more brittle behavior. In answer to these challenges, the FASSTbridge project, financed through European Infravation call, aimed at developing a pre- cracking fatigue assessment and strengthening methodology for steel bridges based on the technology of adhesively bonded composite. The proposed article presents some of the results of this project.
Environmentally friendly FRP composites, made of natural fibers and bio-based polymer matrices, m... more Environmentally friendly FRP composites, made of natural fibers 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 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, and to natural ageing in outdoor environment as well. Aged laminates are then periodically characterized by tensile tests and interlaminar shear ...
The present study investigates the environmental durability of a distributed optical fiber sensin... more The present study investigates the environmental durability of a distributed optical fiber sensing (DOFS) cable on the market, commonly used for distributed strain measurements in reinforced concrete structures. An extensive experimental program was conducted on different types of specimens (including samples of bare DOFS cable and plain concrete specimens instrumented with this DOFS cable) that were exposed to accelerated and natural ageing (NA) conditions for different periods of up to 18 months. The instrumentation of both concrete specimens consisted of DOFS cables embedded at the center of the specimens and bonded at the concrete surface, as these two configurations are commonly deployed in the field. In these configurations, the alkalinity of the surrounding cement medium and the outdoor conditions are the main factors potentially affecting the characteristics of the DOFS component materials and the integrity of the various interfaces, and hence impacting the strain transfer p...
This paper presents an experimental study on the durability of two commercially available optical... more This paper presents an experimental study on the durability of two commercially available optical fiber cables intended for distributed strain measurements and crack monitoring of reinforced concrete structures. The experimental program is based on accelerated aging tests performed on small concrete specimens instrumented with these two embedded optical fiber cables. Pull-out tests are carried out after three months of accelerated aging, in order to evaluate the effect of aging on the mechanical response of the cable/concrete interfaces, as this response is directly related to the strain transfer from the host material (concrete) to the optical fiber core. After three months, the cable/concrete interface of one of the two cables was found severely damaged.
Distributed Fiber Optic Systems (DOFS) are an emerging and innovative technology that allows long... more Distributed Fiber Optic Systems (DOFS) are an emerging and innovative technology that allows long-range and continuous strain/temperature monitoring with a high resolution. However, strain profiles measured in the optical fiber may differ from actual strain in the structure, due to the shear transfer through the intermediate material layers between the optical fiber and the host material (i.e., in the protective coating of the sensing cable and in the adhesive). Therefore, fiber optic sensors need to be qualified in order to provide accurate quantitative strain measurements. This study presents a methodology for the qualification of a DOFS. It is proposed to establish a numerical modeling of the system, in which the mechanical parameters are calibrated from experiments. A specific surface-mounted sensing cable connected to an Optical Frequency Reflectometry Domain (OFDR) interrogator is considered as case study. We found that (i) tensile and pull-out tests are able to provide full i...
Afin de pouvoir developper l'assemblage par collage dans le domaine du Genie Civil, il est ne... more Afin de pouvoir developper l'assemblage par collage dans le domaine du Genie Civil, il est necessaire de pouvoir predire de facon fiable la durabilite des joints colles. La plupart des modeles existants sont des modeles purement mecaniques qui ne prennent pas en compte la physico-chimie des adhesifs, et se limitent generalement a l'etude de la rupture. Une nouvelle approche est donc mise en place a partir de la theorie du premier gradient de l'endommagement, afin de pouvoir introduire des parametres physicochimiques dans les equations mecaniques. Des experiences sont ensuite mises au point pour identifier les coefficients theoriques correspondant a la resine epoxy commerciale etudiee. (Voir fiche generale F100684).
Flax fiber reinforced polymer (FFRP) composites are demonstrating promising outcomes which makes ... more 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.
Creep behavior of cold-curing epoxy adhesives: analysis and predictive approach This study invest... more Creep behavior of cold-curing epoxy adhesives: analysis and predictive approach This study investigates the creep behavior of two commercially available cold-curing epoxy adhesives, intended for the bonding of external composite reinforcements on concrete structures. In a preliminary stage, the characteristics of the mineral fillers (nature, content and size) contained in the two systems were determined, and the viscoelastic properties of the unfilled epoxy matrices extracted from these systems were analyzed. Short-term tensile creep experiments were then carried-out on cured samples of the two adhesives and their unfilled matrices, in order to evaluate the influence of the fillers and the polymer network characteristics on the instantaneous and delayed mechanical responses. Finally, two predictive approaches based on either the Time-Temperature Superposition Principle (TTSP) or the Time-Stress Superposition Principle (TSSP) were applied to evaluate the long-term creep behavior, and...
This study investigates the durability of glass fiber-reinforced polymer (GFRP) reinforcing bars ... more This study investigates the durability of glass fiber-reinforced polymer (GFRP) reinforcing bars (rebars) and their bond in concrete. Accelerated aging tests were first conducted on bare rebars that were either subjected to direct immersion in an alkaline solution or previously embedded in concrete before immersion in the solution (indirect immersion). Accelerated aging was conducted at different temperatures of the solution (20 °C, 40 °C and 60 °C) and for various periods up to 240 days. Residual tensile properties were determined for rebars subjected to direct immersion and served as input data of a predictive Arrhenius model. A large decrease in the residual tensile strength assigned to the alkali-attack of glass fibers was extrapolated in the long term, suggesting that direct immersion is very severe compared to actual service conditions. Short-beam tests were also performed on rebars conditioned under direct/indirect immersion conditions, but did not reveal any significant evol...
The present study investigated the strain response of a distributed optical fiber sensor (DOFS) s... more The present study investigated the strain response of a distributed optical fiber sensor (DOFS) sealed in a groove at the surface of a concrete structure using a polymer adhesive and aimed to identify optimal conditions for crack monitoring. A finite element model (FEM) was first proposed to describe the strain transfer process between the host structure and the DOFS core, highlighting the influence of the adhesive stiffness. In a second part, mechanical tests were conducted on concrete specimens instrumented with DOFS bonded/sealed using several adhesives exhibiting a broad stiffness range. Distributed strain profiles were then collected with an interrogation unit based on Rayleigh backscattering. These experiments showed that strain measurements provided by DOFS were consistent with those from conventional sensors and confirmed that bonding DOFS to the concrete structure using soft adhesives allowed to mitigate the amplitude of local strain peaks induced by crack openings, which m...
h i g h l i g h t s Characterization of the properties of epoxy adhesive at high temperature. Pul... more h i g h l i g h t s Characterization of the properties of epoxy adhesive at high temperature. Pull-out tests at high temperature, parallel and perpendicular to the wood grain. Two different pull-out test methods at stabilized temperature and at constant load. Analysis of the failure modes of the tests specimens.
In the present work, the hygrothermal behavior of a wall structure made of a novel biobased mater... more In the present work, the hygrothermal behavior of a wall structure made of a novel biobased material, i.e. date palm fiber reinforced concrete was investigated. In this context, a specific setup was developed which allows simulating a bi-climatic environment with separate outdoor and indoor environments. This device made it possible to apply various scenarios of static / dynamic hygrothermal loading to the outer side of wall, involving variation/cycling of temperature (T) and /or relative humidity (RH). During these experiments, resulting variations of T and RH across the wall thickness were monitored with in-situ sensors. Outstanding thermo-hygric phenomena were highlighted, such as high coupling effect between heat and moisture transfers, resulting from evaporation-condensation and sorption-desorption processes. Besides, significant thermal and hygric inertia was observed through the Date Palme Concrete (DPC) wall. The response time of this DPC wall to temperature variations remains shorter than in the case of humidity variations. Even so, large damping effect is obtained compared to outdoor boundary conditions, which make this DPC wall a good candidate for mitigating overheating during summertime and reducing interstitial condensation as well.
Two mathematical models describing heat and moisture transfer in porous media were used to predic... more Two mathematical models describing heat and moisture transfer in porous media were used to predict the hygrothermal behavior of a new type of bio-based materials made of date palm concrete (DPC). The finite element method was used for the resolution of partial differential equations and numerical results were compared to experimental data considering similar conditions of temperature and relative humidity through the DPC wall. At first, a mesh sensitivity analysis was carried out and the optimum mesh configuration was determined. Afterwards, the hysteresis effect was implemented in the models and its influence on the variation of the relative humidity through the wall was discussed. The results revealed that the proposed models globally provided satisfactory results for the DPC wall, with an improved accuracy when considering the hysteresis effect. Finally, a comparison in terms of thermal insulation and moisture buffering capacity between DPC and a classical building material was performed numerically. Results showed that the new bio-based wall is very promising and can contribute to mitigate temperature variation and ensure hydrothermal comfort in buildings.
Hygrothermal behavior of a new building material, composed of cement, sand and date palm fibers w... more Hygrothermal behavior of a new building material, composed of cement, sand and date palm fibers was investigated in the present work. In a first part, the sorption-desorption isotherm behavior and the hysteresis effect was characterized under static conditions, revealing the high hydric capacity of this Date Palm Cement (DPC) mortar. In addition, the application of GAB model (Guggenheim-Anderson-de Boer) successfully described the experimental sorption isotherm curve. In a second step, the moisture buffer value and the effect of temperature on successive adsorption/desorption cycles were assessed under dynamical conditions. It was found that the sorption process is highly affected by temperature. Finally, this bio-based mortar was classified as hygroscopic and breathable material with excellent moisture buffering capacity.
Cet article presente une theorie previsionnelle de la rupture des assemblages colles. Le modele e... more Cet article presente une theorie previsionnelle de la rupture des assemblages colles. Le modele est fonde sur le principe des puissances virtuelles applique a l'endommagement (Fremond, 1987). Il couple les endommagements volumique et surfacique. La presentation est scindee en deux parties. Dans la premiere, la signification physique des differents parametres du modele est discutee et des intervalles de variation sont definis pour chacun des parametres. Dans un second temps, le modele est mis en oeuvre pour decrire le comportement a la rupture d'assemblages colles soumis a des sollicitations de traction homogene ou de cisaillement. Les simulations sont confrontees aux resultats experimentaux obtenus dans le cadre de campagnes d'essais. (A). (Voir fiche generale F101003 et fiches specifiques F101004 a F101084).
European Journal of Environmental and Civil Engineering, 2018
The determination of the energy consumption of a building requires the computation of the coupled... more The determination of the energy consumption of a building requires the computation of the coupled heat and mass transfers inside the wall. The existing models require the determination of the hygrothermal properties of the materials, and of the boundary and initial conditions, prior to computing numerically the temperature and vapour fluxes and the energy and mass balance of the building. However, the experimental measurements do not give accurate values, yielding a wrong estimation of the energy consumption. In order to determine the influence of the uncertainties on the values of the input parameters of the Kunzel model, we carried out a local sensitivity analysis (LSA) by varying by 5% the hygrothermal properties of the materials, the surface transfer coefficients and the initial conditions. The results of the LSA are treated by means of quartile boxes in order to identifiy the most influent parameters. The LSA is applied to two walls made of highly porous and hygroscopic materials: limestone and hemp concrete. The results show that the surface transfer coefficients and the adsorption isotherm are the most influential parameters. However, the conclusions are slightly different between the two materials, because of differences in the relative importance of transfer phenomena.
The effects of thermal oxidation on the molecular and macromolecular structures of additive free ... more The effects of thermal oxidation on the molecular and macromolecular structures of additive free PE were investigated between 100 8C and 140 8C in air in order to tentatively establish non-empirical structure/property relationships. In the first part, the changes in POOH concentration were assessed by three different analytical methods: iodometry, modulated differential scanning calorimetry, and Fourier transform infrared (FTIR) spectrophotometry after SO 2 treatment. All these methods provided very similar results until the end of the induction period, after which iodometry overestimated strongly POOH concentration because it titrates also other chemical species formed at high conversion ratios, namely double bonds. In parallel, the changes in carbonyl group concentration were determined by FTIR spectrophotometry after NH 3 treatment. As the accumulation kinetics of ketones, aldehydes, and carboxylic acids were closely interrelated, the question of their actual formation mechanisms in the current thermal oxidation mechanistic scheme was raised. An alternative reaction pathway was proposed for the bimolecular decomposition of POOH. In the second part, the corresponding changes in weight and number average molecular masses were monitored by high temperature gel permeation chromatography equipped with a triple detection technology. As both quantities decreased dramatically from the beginning of exposure and their ratio M w /M n tends toward the asymptotic value of 2 and it was concluded that a "pure" chain scission process operated. Finally, as the number of chain scissions perfectly correlates, the concentration sum of aldehydes and their oxidation products (i.e., carboxylic acids), it was also concluded that these carbonyl groups result exclusively from the b scission of alkoxy radicals.
In this paper, two kinds of tests were designed to investigate and study the bond behavior betwee... more In this paper, two kinds of tests were designed to investigate and study the bond behavior between fiber-reinforced-plastic (FRP) and concrete. By newly designed double-shear test setup, the strain development and distribution in FRP plate was acquired. At the same time, the direct shear bond distribution was given and the effective bond length was suggested. Through a bending test on simply supported beam with an extended end, the strain and stress distribution of FRP plate in the negative moment zone were studied. Based on the test results, conclusions including the maximum effective bond length, the mean bond stress and the development length for flexural bond in the negative moment zone were presented. The effective bond length is about 100 mm and the mean bond stress is about 1.287 MPa. The development length for flexural bond in the negative moment zone is about 300 mm.
LABORATOIRE CENTRAL DES PONTS ET CHAUSSEES (LCPC), Apr 10, 2010
Cette methode d'essai decrit un test de cisaillement par traction directe permettant de carac... more Cette methode d'essai decrit un test de cisaillement par traction directe permettant de caracteriser le joint adhesif entre un renfort externe en materiau composite et un element de structure en beton. Ce test conduit a la determination d'indicateurs d'efficacite du procede, tels que la capacite maximale du joint colle en termes d'effort repris, et la longueur d'ancrage effective. Plusieurs methodes d'exploitation des resultats sont ensuite proposees afin de repondre a la fois aux problematiques de dimensionnement des ingenieurs de genie civil et aux besoins des chercheurs. (A).
One of the goals of sustainable development applied to bridge infrastructure is to provide bridge... more One of the goals of sustainable development applied to bridge infrastructure is to provide bridge owners with strengthening solutions that may lead to an increase of existing structures service life. In the case of steel bridges, the assessment of the remaining service life is most often linked to the determination of the structural deterioration caused by corrosion and fatigue. Damage caused by fatigue is very difficult to assess before crack initiation, and is more bound to occur in old structures, for which the phenomenon was not taken into account in design before 1970. In addition, old steel materials present a more brittle behavior. In answer to these challenges, the FASSTbridge project, financed through European Infravation call, aimed at developing a pre- cracking fatigue assessment and strengthening methodology for steel bridges based on the technology of adhesively bonded composite. The proposed article presents some of the results of this project.
Environmentally friendly FRP composites, made of natural fibers and bio-based polymer matrices, m... more Environmentally friendly FRP composites, made of natural fibers 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 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, and to natural ageing in outdoor environment as well. Aged laminates are then periodically characterized by tensile tests and interlaminar shear ...
The present study investigates the environmental durability of a distributed optical fiber sensin... more The present study investigates the environmental durability of a distributed optical fiber sensing (DOFS) cable on the market, commonly used for distributed strain measurements in reinforced concrete structures. An extensive experimental program was conducted on different types of specimens (including samples of bare DOFS cable and plain concrete specimens instrumented with this DOFS cable) that were exposed to accelerated and natural ageing (NA) conditions for different periods of up to 18 months. The instrumentation of both concrete specimens consisted of DOFS cables embedded at the center of the specimens and bonded at the concrete surface, as these two configurations are commonly deployed in the field. In these configurations, the alkalinity of the surrounding cement medium and the outdoor conditions are the main factors potentially affecting the characteristics of the DOFS component materials and the integrity of the various interfaces, and hence impacting the strain transfer p...
This paper presents an experimental study on the durability of two commercially available optical... more This paper presents an experimental study on the durability of two commercially available optical fiber cables intended for distributed strain measurements and crack monitoring of reinforced concrete structures. The experimental program is based on accelerated aging tests performed on small concrete specimens instrumented with these two embedded optical fiber cables. Pull-out tests are carried out after three months of accelerated aging, in order to evaluate the effect of aging on the mechanical response of the cable/concrete interfaces, as this response is directly related to the strain transfer from the host material (concrete) to the optical fiber core. After three months, the cable/concrete interface of one of the two cables was found severely damaged.
Distributed Fiber Optic Systems (DOFS) are an emerging and innovative technology that allows long... more Distributed Fiber Optic Systems (DOFS) are an emerging and innovative technology that allows long-range and continuous strain/temperature monitoring with a high resolution. However, strain profiles measured in the optical fiber may differ from actual strain in the structure, due to the shear transfer through the intermediate material layers between the optical fiber and the host material (i.e., in the protective coating of the sensing cable and in the adhesive). Therefore, fiber optic sensors need to be qualified in order to provide accurate quantitative strain measurements. This study presents a methodology for the qualification of a DOFS. It is proposed to establish a numerical modeling of the system, in which the mechanical parameters are calibrated from experiments. A specific surface-mounted sensing cable connected to an Optical Frequency Reflectometry Domain (OFDR) interrogator is considered as case study. We found that (i) tensile and pull-out tests are able to provide full i...
Afin de pouvoir developper l'assemblage par collage dans le domaine du Genie Civil, il est ne... more Afin de pouvoir developper l'assemblage par collage dans le domaine du Genie Civil, il est necessaire de pouvoir predire de facon fiable la durabilite des joints colles. La plupart des modeles existants sont des modeles purement mecaniques qui ne prennent pas en compte la physico-chimie des adhesifs, et se limitent generalement a l'etude de la rupture. Une nouvelle approche est donc mise en place a partir de la theorie du premier gradient de l'endommagement, afin de pouvoir introduire des parametres physicochimiques dans les equations mecaniques. Des experiences sont ensuite mises au point pour identifier les coefficients theoriques correspondant a la resine epoxy commerciale etudiee. (Voir fiche generale F100684).
Flax fiber reinforced polymer (FFRP) composites are demonstrating promising outcomes which makes ... more 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.
Creep behavior of cold-curing epoxy adhesives: analysis and predictive approach This study invest... more Creep behavior of cold-curing epoxy adhesives: analysis and predictive approach This study investigates the creep behavior of two commercially available cold-curing epoxy adhesives, intended for the bonding of external composite reinforcements on concrete structures. In a preliminary stage, the characteristics of the mineral fillers (nature, content and size) contained in the two systems were determined, and the viscoelastic properties of the unfilled epoxy matrices extracted from these systems were analyzed. Short-term tensile creep experiments were then carried-out on cured samples of the two adhesives and their unfilled matrices, in order to evaluate the influence of the fillers and the polymer network characteristics on the instantaneous and delayed mechanical responses. Finally, two predictive approaches based on either the Time-Temperature Superposition Principle (TTSP) or the Time-Stress Superposition Principle (TSSP) were applied to evaluate the long-term creep behavior, and...
This study investigates the durability of glass fiber-reinforced polymer (GFRP) reinforcing bars ... more This study investigates the durability of glass fiber-reinforced polymer (GFRP) reinforcing bars (rebars) and their bond in concrete. Accelerated aging tests were first conducted on bare rebars that were either subjected to direct immersion in an alkaline solution or previously embedded in concrete before immersion in the solution (indirect immersion). Accelerated aging was conducted at different temperatures of the solution (20 °C, 40 °C and 60 °C) and for various periods up to 240 days. Residual tensile properties were determined for rebars subjected to direct immersion and served as input data of a predictive Arrhenius model. A large decrease in the residual tensile strength assigned to the alkali-attack of glass fibers was extrapolated in the long term, suggesting that direct immersion is very severe compared to actual service conditions. Short-beam tests were also performed on rebars conditioned under direct/indirect immersion conditions, but did not reveal any significant evol...
The present study investigated the strain response of a distributed optical fiber sensor (DOFS) s... more The present study investigated the strain response of a distributed optical fiber sensor (DOFS) sealed in a groove at the surface of a concrete structure using a polymer adhesive and aimed to identify optimal conditions for crack monitoring. A finite element model (FEM) was first proposed to describe the strain transfer process between the host structure and the DOFS core, highlighting the influence of the adhesive stiffness. In a second part, mechanical tests were conducted on concrete specimens instrumented with DOFS bonded/sealed using several adhesives exhibiting a broad stiffness range. Distributed strain profiles were then collected with an interrogation unit based on Rayleigh backscattering. These experiments showed that strain measurements provided by DOFS were consistent with those from conventional sensors and confirmed that bonding DOFS to the concrete structure using soft adhesives allowed to mitigate the amplitude of local strain peaks induced by crack openings, which m...
h i g h l i g h t s Characterization of the properties of epoxy adhesive at high temperature. Pul... more h i g h l i g h t s Characterization of the properties of epoxy adhesive at high temperature. Pull-out tests at high temperature, parallel and perpendicular to the wood grain. Two different pull-out test methods at stabilized temperature and at constant load. Analysis of the failure modes of the tests specimens.
In the present work, the hygrothermal behavior of a wall structure made of a novel biobased mater... more In the present work, the hygrothermal behavior of a wall structure made of a novel biobased material, i.e. date palm fiber reinforced concrete was investigated. In this context, a specific setup was developed which allows simulating a bi-climatic environment with separate outdoor and indoor environments. This device made it possible to apply various scenarios of static / dynamic hygrothermal loading to the outer side of wall, involving variation/cycling of temperature (T) and /or relative humidity (RH). During these experiments, resulting variations of T and RH across the wall thickness were monitored with in-situ sensors. Outstanding thermo-hygric phenomena were highlighted, such as high coupling effect between heat and moisture transfers, resulting from evaporation-condensation and sorption-desorption processes. Besides, significant thermal and hygric inertia was observed through the Date Palme Concrete (DPC) wall. The response time of this DPC wall to temperature variations remains shorter than in the case of humidity variations. Even so, large damping effect is obtained compared to outdoor boundary conditions, which make this DPC wall a good candidate for mitigating overheating during summertime and reducing interstitial condensation as well.
Two mathematical models describing heat and moisture transfer in porous media were used to predic... more Two mathematical models describing heat and moisture transfer in porous media were used to predict the hygrothermal behavior of a new type of bio-based materials made of date palm concrete (DPC). The finite element method was used for the resolution of partial differential equations and numerical results were compared to experimental data considering similar conditions of temperature and relative humidity through the DPC wall. At first, a mesh sensitivity analysis was carried out and the optimum mesh configuration was determined. Afterwards, the hysteresis effect was implemented in the models and its influence on the variation of the relative humidity through the wall was discussed. The results revealed that the proposed models globally provided satisfactory results for the DPC wall, with an improved accuracy when considering the hysteresis effect. Finally, a comparison in terms of thermal insulation and moisture buffering capacity between DPC and a classical building material was performed numerically. Results showed that the new bio-based wall is very promising and can contribute to mitigate temperature variation and ensure hydrothermal comfort in buildings.
Hygrothermal behavior of a new building material, composed of cement, sand and date palm fibers w... more Hygrothermal behavior of a new building material, composed of cement, sand and date palm fibers was investigated in the present work. In a first part, the sorption-desorption isotherm behavior and the hysteresis effect was characterized under static conditions, revealing the high hydric capacity of this Date Palm Cement (DPC) mortar. In addition, the application of GAB model (Guggenheim-Anderson-de Boer) successfully described the experimental sorption isotherm curve. In a second step, the moisture buffer value and the effect of temperature on successive adsorption/desorption cycles were assessed under dynamical conditions. It was found that the sorption process is highly affected by temperature. Finally, this bio-based mortar was classified as hygroscopic and breathable material with excellent moisture buffering capacity.
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Papers by Karim BENZARTI