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International audience; In this work, wood–cement composites (WCC) based on poplar sawdust were developed and fabricated by the extrusion process. The volume fraction of wood particles in the mixes was varied from 23% to 46%. The mechanical properties of these WCC were characterized in compression to determine the maximum compressive strength and the Young’s modulus. In the second part, these Young’s modulus values were estimated in compression using a 3D numerical homogenization which takes into account the variability in wood particle lengths and the random distribution in the mixes. The obtained results show a good agreement between the experimental data and numerical calculations up to a 35% volume fraction. The model’s poor estimation for large volume fractions (over 35%) could be attributed to the experimental sample size, which is not representative for large volume fractions, the percolation of the wood particles into the mixes and the inhibition of the cement setting.

L’utilisation des huiles recyclées pour le décoffrage du béton est une voie de valorisation intéressante pour les industriels. En effet, une entreprise spécialiste de la récupération et du traitement des huiles usagées a mis au point différents procédés permettant de générer des huiles industrielles ayant déjà été utilisées. Un marché pour cette entreprise concerne les huiles de décoffrage. Afin d’étudier les propriétés de ces huiles, deux formulations ont été testées, une base et une base avec solvant. Les propriétés physico-chimiques ont été déterminées par le calcul des énergies d’adhésion puis une étude portant sur la qualité des parements est réalisée à vue et par analyse d’images à 1 jour et 7 jours après décoffrage. Les résultats obtenus ont été comparés à une huile à base végétale commercialisée., Academic Journal of Civil Engineering, Vol 40 No 1 (2022): Special Issue - RUGC 2022

The addition of 10 wt% aluminum hydroxide to two crude kaolinitic clays, a commercial and a natural freshly mined one, has enhanced their pozzolanic activity, more substantially in the natural sample containing gibbsite. The obtained blends were used as replacement of 20 wt% of Portland cement in the formulations of pastes and mortars which exhibited significant decrease of setting time and increase of compressive strength from early age to 28 days. Also, SEM/EDX analyses showed very heterogeneous structures with hydrated phases identified from XRD. Specific interpretation of the role played by aluminum hydroxide revealed its aptitude to promote the formation of metastable hydrated phases (CAH10/C2AH8) at early age, which temporally inhibited the hydration of cement. This progressive transformation led to the formation of more stable hydrated phases such as C–A–S–H which favored the increase of mechanical strength of the specimens. The sequence of transformation reactions is fully obtained with limited aluminum hydroxide content in clays. Either added as synthetic or naturally occurring in clays, aluminum hydroxide has close role in the strengthening process of cement. Hence, kaolinitic clays that naturally contain gibbsite are suggested as suitable supplementary cementitious material for partial replacement of cement.

Formwork removal by means of polarization offers an alternative solution to compensate for some of the disadvantages and risks of using mineral-based oil due to its petrochemical origin. This technique consists of applying an electrical current between the steel reinforcing bars and the metal formwork wall in order to obtain a thin water film at the concrete/formwork interface and allow for formwork removal. This paper focuses on the facing quality of the reinforced concrete and formwork surface at various temperatures for both conventional and self-compacting concretes. A series of experimental tests have been conducted in the laboratory to determine the optimal polarization parameters (voltage value, time and duration of its application). On-site tests were then performed to observe the scaling effect. Results indicate that the proposed polarization technique can indeed provide an effective means to separate the concrete from its formwork without requiring demoulding oil. Concrete mixtures implemented both in the laboratory and on-site display high-quality facing without the presence of any attachment points. A chromatographic analysis of the concrete pore solution and water transported by electro-osmosis shows that ion concentrations remain unaffected. This polarization approach can thus be used as an alternative to avoid the use of oils of a chemical or petrochemical origin.

In recent years, many studies have focused on the mix-design and characterization of cementitious composites reinforced with plant fibres. It appears that in the fresh state, the morphology and the hydrophilic nature of these fibres significantly affect the rheology of the material. In the hardened state, the mechanical performances of the composites are lower than that of composites reinforced with standard fibres (glass, synthetic, etc.). These poor mechanical performances are mainly due to weak neo-formed fibre/matrix interface. Indeed, the high-water absorption capacity causes swelling/shrinkage of the fibre within the matrix, which subsequently generates an unbounded interface. In order to address these issues, numerous studies have been carried out over the past few years on compatibilisation treatments applied to plant fibres. In most cases, these are chemical treatments to leach the fibre, which often have a significant environmental impact. This work examines the influence of a coating treatment with linseed oil applied to flax fibres on the properties of cementitious composites. The first part of this study deals with the optimisation of this treatment. The second part focuses on the effect of this treatment on the properties of the composite in the fresh and hardened states. The results showed a noticeable improvement in the workability of the treated fibre composites. The linseed oil coating treatment can also significantly improve the flexural strength of the composite, depending on the mix-design. Flax fibres and linseed oil can also slightly enhance the thermal insulation properties of the material.

International audience; The friction of concrete on the interior skin of formworks takes place during the pouring of concrete into the molds. The present work investigates the friction of a granular material (i.e. fresh concrete) against metallic and polymeric surfaces. Interfacial behavior between different formulated concretes and formwork skins is characterized using a plane-plane tribometer dedicated to concrete tribometer. The formwork surface is measured before and after testing to quantify the wear issue. A Coulomb friction law is observed within the range of tested normal pressures. Tribological tests reveal that friction mechanisms depend on the interface properties. Two underlying mechanisms are hypothesized to explain the wearing of the formwork skin: a granulate-formwork solid-solid friction and a capillary-dominated friction.

Alfa plants are endemic to the Maghreb, where they cover great areas and are of prime socio-economic interest. This study investigated use of the alfa plant in a fibre-reinforced cement composite for facade panels. Alfa fibres were ground in a knife mill, sieved through a 2 mm sieve and added to the mixture in different addition ratios (1, 2 and 3 vol%). The results showed that the incorporation of ground alfa fibres did not significantly influence the fresh properties of the mortar. Compared with a control mortar, there was a decrease of 4% in the workability of the mortar reinforced with 2 vol% of alfa fibres. An enhancement in flexural strength was observed for all three addition ratios, with the evolution of flexural strength linearly related to the increase of the fibre addition ratio. However, the compressive strength of the composites decreased with the addition of fibres, mainly due to the high porosity inside the matrix. This was confirmed by a capillary test, which showed that a high addition ratio led to high water absorption by capillary motion.

In the aim of enhancing the reuse potential of poplar sawdust stemming from the transformation of wood into particleboard for woodworking purposes, wood-reinforced concrete mix designs are optimised to obtain composites in compliance with French standard NF EN 771-3/CN. Two criteria are assessed herein for structural elements, namely dimensional tolerance and mechanical strength (7-day levels above 6 MPa). Wood aggregates are introduced by means of a volumetric substitution for sand. Easily demoldable concrete blocks have been produced by means of vibrocompaction. A high vibration frequency is coupled with a compaction process in order to generate semi-dry cylindrical concrete blocks (100 mm in diameter, 200 mm high). The addition of wood into the cementitious composite exerts a noticeable influence on its workability, as well as on its thermophysical and mechanical behaviour. Wood alters how the cementitious composite is hydrated and has an impact on its mechanical strength in compression, which drops considerably with an increase in sawdust content. A 50% rate of substituting poplar sawdust for sand was chosen for testing purposes. This concrete composition actually yields mechanical strength values similar to that of the reference concrete used to manufacture masonry blocks.

An experimental investigation was undertaken to evaluate the potential use of poplar by-products in cement mortars. Two by-products from poplar processing were studied: sawdust (from sawing wood) and milled fibres (from wood waste obtained during cutting). Poplar fibres and sawdust were incorporated into mortars as sand volume substitution with rates ranging from 0 to 100%. Before introduction into the mortar, poplar aggregates were characterized (morphology and water absorption). It appeared that these wood aggregates absorb very quickly a large amount of water (up to 200%). The introduction of these poplar by-products has significant effects on the composite properties in both fresh and hardened states. It was noted that the workability of the mixtures with the poplar wood varies with the substitution rate. The inhibition of cement setting with poplar sawdust is characterized by maturity tests and affects the mechanical properties of mortars. In addition, increasing the poplar aggregates content causes a continuous increase of the material porosity, which leads to a decrease in density. Besides, it appears that the incorporation of poplar aggregates into mortars also decrease their thermal conductivities, which would help to reduce building heat losses. A significant decrease in the mechanical properties of poplar-based mortars was also noted, related to the rate of fibres or sawdust introduced into mixtures. The hydration disturbances, the high internal porosity of the wood particles and their low density can explain these lower mechanical strengths. However, despite these disturbances, the valorisation of poplar wood by-products remains possible in cementitious materials for the manufacture of concrete masonry blocks.

ACL; The wood industry generates some 12 million tons of waste in France, 60% of which basically stems from sawmills. The reuse of this waste in the most common construction materials (e.g., concrete) may offer a sustainable solution. In the literature, the optimization of composites formulations generally focuses on aggregates plant pretreatment regardless of classical optimization parameters and the implementation process that can afford to get a high strength composite. The work presented herein is intended to optimize the mix design of a mortar made from poplar wood by-products, without involving any pretreatment. The conventional mix design parameters (i.e., paste volume, W/C ratio) have been varied. An optimal implementation technique (i.e., extrusion) was used. The wood mortar mix designs have been optimized in order to obtain composites compliant with French standard NF EN 771-3/CN, with respect to criteria regarding both dimensional tolerance and mechanical strength for structural elements (i.e., above 8 MPa at 7 days).A mortar mix design, optimized by means of extrusion, has been used as a reference. Poplar wood particles have been introduced through substitution for the sand volume. Test results indicate that the blocks produced from two wood mortar mixes with 60 and 70% wood aggregate-for-sand substitution rates are in line with the normative requirements relative to dimensional tolerances and mechanical strength. This material compliance underscores the potential use of such blocks as load-bearing masonry elements, thus facilitating the building of structures with a limited environmental impact.

In this study, a nonlinear numerical analysis is carried out to predict the creep response of reinforced concrete (RC) beams externally strengthened using carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) laminates. The beams are tested under static four-point bending; the level of sustained service load is equal to 59% of the ultimate capacities of the un-strengthened beams. The Burger rheological model is used to evaluate the flexural creep response (compressive and tensile creep) and then to validate the findings with experimental results. It is shown that the Burger model effectively predicts the creep of CFRP-bonded RC. Furthermore, parametric studies are performed to investigate the effects of: three fiber orientations of CFRP composites (0°, 45° and 90°), the CFRP thickness, and the type of FRP (CFRP and GFRP) on the flexural creep of FRP-externally retrofitted RC beams based on the Burger rheological model. According to the numerical results, a major reduction in creep strain is obtained with the 45° orientation of CFRP. An increase in CFRP-thickness significantly lowers the creep strain. Moreover, the CFRP laminates prove to be more effective than GFRP in improving the creep response.

This study deals with an experimental and numerical investigation focused on the total shrinkage of concrete made with recycled coarse aggregates (RCA) and subjected to various isothermal temperatures. The objective of the experimental work is to assess the influence of the external temperatures (20, 35 and 50 °C) and the percentage of RCA replacements on the total shrinkage of recycled aggregates concrete. Natural coarse aggregates (NCA) are substituted by RCA at different weight levels (0%, 25%, 50%, 75% and 100%). The obtained results relate that the mechanical properties are adversely affected by the RCA replacement ratio. In addition, the total shrinkage strain rises with increase in the replacement ratio and the curing temperature. On the other hand, finite element analysis (FEA) using ANSYSⒸ software is used to predict the shrinkage of concrete regarding the thermal and mechanical properties. The shrinkage is estimated by means of the maturity approach and the two-phase serial model. The results founded from the FEA illustrate a good accuracy with the experimental ones.

This study deals with experimental investigations of beam performances in a marine environment. Two kinds of concrete beams, unreinforced and reinforced with carbon plates and carbon rods, are being tested. The first one is stored in a laboratory, the other is exposed to a marine environment located in the north of France. After 12 months, all beams are tested via a four-point bending test in a laboratory. Results obtained have shown that beams stored in marine environment have a better behaviour than those stored in laboratory. It should be noted that no damage has occurred on these beams. However, we observe a significant increase of load of about 32% to 48% causing the first crack observed on the beams stored in marine environment compared to those stored in the laboratory. This means that beams in situ offer increased stiffness and a slight gain of failure loads. This may be due to the development of living organisms (in a marine environment) which acted as additional adhesive and sealing, providing a protection of concrete structures against damage.

This article presents an experimental study aiming to provide reliable experimental data for the prediction of the shear strength of reinforced concrete beams without stirrups. The shear strength results obtained from the proposed model as well as those from the design codes (ACI 318, Eurocode 2 and BS 8110) are compared with the database containing 700 beams made of both high strength concrete and normal strength concrete. Furthermore, the experimental results were used to assess the contribution of each shear mechanism obtained from Chen’s, Cavagnis’s and Fernández Ruiz’s models. The contribution of these various shear-transfer actions is also quantified experimentally, using a digital image correlation. As a result, the measured contributions of dowel action, aggregate interlock and compression zone to the total shear resistance were estimated as 45% to 50%, 20% to 35% and 17% to 31%, respectively, for high strength concrete beams. On the contrary, the average test-to-predicted contribution of the shear-transfer action ratio determined by the Chen formula is 1.15 for short beams, whereas the Fernández Ruiz and the Cavagnis models yielded average ratios of 1.04 and 1.52, respectively, for slender beams. The proposed formulae give a rational prediction for either both short and slender beams, and yield accurate and consistent results compared to the other models used in this study, with a lowest average value of the test-to-predicted at 1.08 and that of the coefficient of variation at 23.06%, particularly for short beams. However, ACI 318 is the only code that does not take into account the size effect, leading to a severe underestimation of the shear strength for short beams.

Diaphragm walls are used either to support excavation walls on site or prevent water move through the ground. The observations recorded following excavation and planning of diaphragm walls demonstr...

In recent years, numerous studies focused on the development of sustainable cement-based binders through the use of supplementary cementitious materials such slag, fly ash, metakaolin, silica fume, pozzolan, etc. The use of wood biomass for power generation is increasingly common which lead to an important amount of waste produced in the combustion process such as fly ash, which must be transported to landfills for deposition, or used as sludge in farming. Depending on their chemical and physical characteristics, wood biomass fly ashes could be reuse in blended cements as supplementary cementitious material. Different sources of biomass fly ashes have been selected to evaluate their potential for use as a cement replacement. Their chemical and mineralogical compositions, as well as their morphology were first evaluated via X-ray and laser diffraction (XRD), inductively coupled plasma (ICP) and scanning electron microscopy (SEM coupled with energy-dispersive X-ray spectroscopy (EDX). Fly ashes showed variable physicochemical characteristics but some present interesting compositions for the intended use. One fly ash present a high content of CaO and minors of SiO2 and Al2O3. The chemical composition does not allow to categorize this fly ash as a pozzolan material but it may have a latent hydraulic behaviour, which could be interesting as cement substitution. This fly ash has been incorporated into a cement paste by progressive replacement of Portland cement (from 0 to 70%). It has been observed that biomass fly ash has a higher water demand compared to Portland cement. This additional water demand was evaluated by the Vicat consistency test and by an evaporometry method. The setting time and kinetic hydration of the biomass fly ash pastes were also assessed with the standardized Vicat test and by isothermal calorimetry.

An experimental investigation was undertaken to evaluate the potential use of poplar by-products in cement mortars. Two by-products from poplar processing were studied: sawdust (from sawing wood) and milled fiber (from wood waste obtained during cutting). The fibers and sawdust were incorporated into the mortars as a sand substitution with rates from 10 to 100%. The introduction of these poplar by-products has a significant on the composite properties in both fresh and hardened state. It was noted that the workability of the mixtures with the poplar wood varies with the substitution rate. Moreover, the increase in the amount of fibers or sawdust causes a continuous increase in the porosity of the material, which leads to a decrease in density. A significant decrease in the mechanical properties of bio-sourced mortars was noted, again related to the rate of fibers or sawdust introduced in mixtures. The high internal porosity of the wood particles and their low density can explain these lower mechanical strengths.

The Alfa plant is indigenous and spans a large zone throughout North Africa. Recently, Alfa plant has been used in building materials, notably as a reinforcement. This study aims to valorize the Alfa plant into fiber-reinforced mortar based on a cement-glass composite mix design. Two Alfa fiber morphologies are considered herein: different cutting lengths (10, 20 and 30 mm), and ground using a knife mill (shorter than 2 mm). These fibers were added to mortars at various volume ratios: 1, 2 and 3%. The workability and density of these distinct formulations were then measured in their fresh state. In comparison with the control mortar (CM), the introduction of Alfa fibers (either cut or ground), with ratios below 2% vol., leads to a slight decrease in mixture workability. However, Alfa fibers do not significantly alter the fresh material density. It was recorded a delay in setting time of the composites as a function of fiber addition rate. In the hardened state, an improvement in flexural strength is noticed for mortars reinforced with 1% vol. of fibers compared to the CM. However, results show that the increase in either type of fiber (cut or ground) generates a decrease in compressive strength compared to the CM. This outcome can be confirmed by both the decrease in heat released during the hydration reaction and water-accessible porosity inside the matrix.

This paper presents a DEM study of a confined granular material sheared between two parallel bumpy walls. The granular material consists of packed dry spherical particles. The bumpiness is modeled by spheres of a given diameter glued on horizontal planes. Different bumpy surfaces are modeled by varying diameter or concentration of glued spheres. The material is sheared by moving the two bumpy walls at fixed velocity. During shear, the confining pressure applied on each bumpy wall is controlled. The effect of wall bumpiness on the effective friction coefficient and on the granular material behavior at the bumpy walls is reported for various shearing conditions. For given bumpiness and confining pressure that we have studied, it is found that the shear velocity does not affect the shear stress. However, the effective friction coefficient and the behavior of the granular material depend on the bumpiness. When the diameter of the glued spheres is larger than about the average grains diameter of the medium, the latter is uniformly sheared and the effective friction coefficient remains constant. For smaller diameters of the glued spheres, the effective friction coefficient increases with the diameter of glued spheres. The influence of glued spheres concentration is significant only for small glued spheres diameters, typically half of average particle diameter of the granular material. In this case, increasing the concentration of glued spheres leads to a decrease in effective friction coefficient and to shear localization at the interface. For different diameters and concentrations of glued spheres, we show that the effect of bumpiness on the effective friction coefficient can be characterized by the depth of interlocking.

To ensure a performing demoulding, a release agent must resist the friction of concrete on the formwork. Emulsions are interesting alternatives that leads to a reduced consumption of oil on construction sites. The behaviours of two commercial emulsions are compared with two conventional demoulding oils. The adhesion energy calculated were favourable to the emulsions. The water evaporation kinetics leads to the measurements of film thickness. Tests with the tribometer have shown that the films produced from the emulsions generate a friction reduction of 30% and 40% at the concrete/formwork interface. Such performance can be explained by Wenzel's state of wettability, which facilitates the film fit into the formwork roughness.

This paper experimentally investigates the potential use of poplar sawdust as replacement material to sand in semi-dry concrete, manufactured by vibrocompaction and used in concrete masonry blocks. The substitution of sand by wood waste can relieve the scarcity of raw materials and lighten concrete masonry block weight. The introduction of a varying proportion (30, 40, 50 and 60 %) of poplar sawdust in the concrete has a significant influence on its thermophysical and mechanical behavior. The inhibition of hydration of cement with this poplar sawdust has a main influence. It affects the hydrates formed in the concrete and has an impact on the compressive strength at 7 days. This strength decreases significantly with increasing poplar sawdust proportion. But the method of concrete manufacturing by vibrocompaction increases the strength and could decrease the inhibitory effect of wood on the hydration reaction of the concrete. Substitution of 50 % of sand by poplar sawdust in the masonry concrete block manufactured by vibrocompaction is proposed. Indeed, this concrete composition gives similar mechanical strength to that of the conventional manufacture of masonry concrete block.

A reduction in rehabilitation costs by about 20% is the main objective of this project while reducing response times in situ and maintaining an equivalent efficiency of the reinforcement. The first part recounts the history of the various stages of the Parisian sewer system construction. It subsequently takes stock of the pathologies, the repair techniques and the investigation methods of these structures. The second part deals with the design of test pieces through numerical calculation while taking into consideration the various parameters applied to each material. The selected model is a vault representing the upper part of an ovoid. The third part is an experimental approach to characterizing materials and in particular the coating/glue/composite interface.

In this study, a numerical investigation is conducted to simulate the total shrinkage strain of High-Strength Concrete (HSC) and Steel Fiber Reinforced High-Strength concrete (SFRHSC) by means of the transient thermal-stress analysis. The ANSYS finite element software has been used in order to evaluate the shrinkage by taking into account both the thermal and mechanical properties of the concrete. These properties are calculated using the maturity concept and the two-phase serial model. The experimental work was carried out to assess the influence of the external temperatures, steel fibers (SF) and their volume fraction on the total shrinkage strain of the SFRHSC which has been exposed to isothermal temperature of 20, 35 and 50 °C. Two dosages of 0.5% and 1% for the SF with aspect ratio of 55 have been considered. The main results obtained from the FE analysis show a good agreement with the founded experimental results under different thermal conditions. According to the obtained numerical results, an increase of the dosage of fibers will reduce the total shrinkage strain. Additionally, the curing temperature raises significantly the evolution of the total shrinkage strain.

The present study is focused on experimental investigations and numerical analyses of compressive and tensile total creep at long-term of high-strength concrete (HSC) beams. Reinforced concrete (RC) beams with and without steel fibres were investigated for their long-term creep behaviour. These beams are under sustained uniformly distributed load (SUDL) in bending containing steel fibres (SF) with two aspect ratios (55 and 80) and two steel fibre dosages (0.5% and 1%). The objective of this work is to evaluate the influence of steel fibres, their dosage and their aspect ratio on compressive and tensile total creep. Experimental results show that the long-term total creep is influenced by the volume fractions of steel fibres. Moreover, steel fibres decrease the tensile total creep more than the compressive one. A non-linear finite element method (FEM) is performed to simulate the long-term total creep strain rate included thanks to the time hardening model called generalized Garofalo creep which is based on Bailey-Norton law called power law creep. It was found a good agreement between the experimental and numerical results.

Wall roughness plays a crucial role in granular medium - rough wall interface friction. In this study, an experimental device has been designed to study the influence of boundary conditions, more specifically wall roughness, on the behavior of sheared granular medium. The study is based on use of an analog model, and consists of simulating roughness by means of notches and grains in the medium by monodisperse beads and on use of a numerical model based on the discrete element method. The test protocol entails displacing at fixed speed notched rods under confined granular medium. Movement of the beads layer near the rods as well as friction of the beads against the rods are both studied herein. Results indicate that the parameter controlling friction at the granular medium - rough wall interface is primarily the depth of beads embedment in surface asperities. The objective of the associated numerical modeling is to supplement the experimental results.

International audience; The quality of the concrete facings results from the implementation of release agents and the casing surface quality. It is interesting to characterize the behaviour of release agents over the lifetime of the formwork. This study is based on the many ones test physicochemical and esthetics realized on two types of surface of formwork like on three types of applications. In complement, the ageing of the casing formwork was characterized by electrochemical spectroscopy of impedance and thanks to the correlation with the aesthetic tests will allow to find from new mechanisms to the interfaces related to the studied oil's formulations. (C) 2014 Elsevier Ltd. All rights reserved.

A recent study proposed a new process for demoulding concrete elements based on the principle of electro-osmosis, consisting of applying an electric potential between the reinforcement and formwork which causes the water displacement towards the concrete/formwork interface where a film of water is formed avoiding the adhesion of the concrete on the formwork. The quality of facing and demoulding has been shown to be dependent on the polarization parameters (voltage value, time and duration of its application) and therefore optimal parameters were assessed. However these parameters were found in a very limited condition of temperature, only at 20 ± 2 °C. In this new study we consider the parameters optimization scheme in other room temperature conditions. In this respect an experimental device was developed in order to quantify the amount of displaced water at (20 ± 2 °C) and (8 ± 2 °C) according to the voltage value and duration of its application. We showed that, under the same polarization conditions, the quantity of water transported decreases with decreasing room temperature. This decreasing of water quantity caused the alteration of demoulding and facing quality. To overcome this issue, the optimal polarization conditions have been revisited in order to take into account the temperature. When transposed in situ, our method performed successfully at 20 ± 2 °C and at 8 ± 2 °C as well and it could be a better choice than the previous demoulding methods like those using vegetable oils, developed recently to replace mineral oils, they cannot be used at low temperatures.

Sewerage systems are subject to many types of degradation. In France, an estimated 10% of the total systems length requires work due to structural degradation. At present, there is no method to localised rehabilitation of man-entry sewers. Laboratory tests have validated localised methods that involve bonding composite plates to the sewer. Those tests were performed on pre-damaged (multi-cracked) ovoid test pieces. The degradation observed was a longitudinal crack opened at the crown. The tests were performed under vertical loading. Our Study concerns the application of partial lining of sewer with composites plates. The composite strengtheners used were 1.2 mm thick pultruded carbon plates. A series of experiments were carried out on reinforced-concrete ovoids (T180) strengthened and unstrengthened by carbon plates in the keystone. After this test, a vertically-loaded ovoid was subjected to three-dimensional modelling in order to determinate its structural behavior and collapse mechanism. Knowledge of the latter make it possible to limit the areas in need of strengthening. An ovoid strengthened by composite plates adhered to the damaged areas was also modelled. Using real case data, modelling was carried out using a finite-element computational software program. This program allows cracking to be monitored until the structure collapses. Many conventional approaches using intensity factors k and contour integrals J have already been reported in the literature. We used methods for restituting energy G. Because nonlinear elasticity was being calculated, the constitutive laws of the various materials had to be taken into account. These constitutive laws describe the evolution of the materials. Moreover, those laws are subject to deformation limits. The simulated models were homogeneously meshed with physically nonlinear, triangular elements. The test results were then compared to those of the digital models. Partial lining of a sewer with composite plates, compared to a traditional reinforced-concrete lining, achieves a cost reduction of about 55%.

The parameters likely to influence the appearance of the concrete facings are in particular the casting process of the concrete in the formwork, characteristics of the wall and the nature of the release agent. This study looks at the influence of the thickness of vegetable or mineral-based oils on the aesthetic quality of facings. The thickness of the oil films has been measured with a variant of the PIXE method specially developed for this study. Moreover, to create the conditions of a concrete poured into a formwork, a tribometer for fluid material developed in our laboratory was used. With the help of these devices, the thickness of the oil film before and after the pouring of a concrete in a metallic mould was studied. The vegetable oil film has a good resistance with the concrete friction and a film from 1 to 2 μm is enough to obtain a high quality facing.

The friction of fresh concrete and granular materials against a metallic plate was investigated using ultrasonic wave reflection. Two complementary experimental devices, one a global device using a tribometer, the other a device based on an ultrasonic reflectometer giving a local approach at the formwork/fresh concrete interface. This approach is based on the evaluation of the density variation of the interface between the metallic wall and the material during the casting process. The authors propose a method to maintain a high impedance contrast by using a water layer interleaved between the transducer and the studied material. Good agreement between the ultrasonic parameter and the friction parameter was observed.

Architects nowadays demand impeccable aesthetic qualities of demoulded rough concretes. New mix designs are increasingly complex, and a concrete mix characterization often limits the workability attributes, in the aim of providing an assessment of concrete behavior at the time of its placement. The aesthetics of concrete facings however also depend on the actual mix design, location and release agents used. This study focuses on analyzing the influence of self compacting concrete (SCC) and the choice of release agent on the evolution of frictional stresses at the concrete/formwork interface. A follow-up study has been conducted on the aesthetic quality of facings between an SCC and a concrete with additives, including mix designs with both mineral and vegetable oil. An analysis of shading color was also carried out over three periods, namely: 1 day, 2 days, and 7 days.

The level of pressure exerted by fluid concrete is not yet well understood. Tests conducted on instrumented formwork (total system of support for freshly placed concrete including the mould) show that, once a critical pressure has been reached, the real pressure exerted by concrete is less than the hydrostatic pressure recommended by the standard governing formwork sizing. The difference is due to the friction between the concrete and the wall. Janssen's theory concerning ensiled granular material is applied to fresh concrete. A comparative study based on model and experimental results (tribometer, instrumented wall) reveals good agreement between predicted results and on site measurements.

Release agents are a significant source of pollution in the construction and prefabrication industries. Conventional products are known to be toxic for humans and the environment. New formulations based on vegetable esters have appeared on the market to mitigate against this drawback. However, more knowledge is required about the properties and behaviour of these products to make them more attractive for industry. Understanding the phenomena that occur over the formwork–oil–concrete interface is a real challenge. The present paper begins with a physicochemical survey of release agents by defining the formwork–oil and oil–concrete interfaces. It then characterises the formwork–oil–concrete interfaces by dynamic studies (tribometer). Physicochemical mechanisms are proposed.

International audience; Les travaux présentés ici rentrent dans le cadre du projet de bétons de fondations profondes financé par la FNTP. Ils s'intéressent aux problèmes de mise en œuvre rencontrés sur les chantiers de pieux forés à la tarière creuse, parmi lesquels la difficulté d'introduction de la cage d'armatures après le bétonnage du pieu. Ils se proposent de valider un protocole d'essai de laboratoire permettant de caractériser l'enfoncement d'une cage d'armatures en fonction de la charge qui lui est appliquée et du temps de repos du béton. Pour ce faire, des essais expérimentaux ont été réalisés sur une formulation courante de béton de pieu pour étudier l'effet du temps de repos sur les propriétés rhéologiques du béton et la capacité des armatures à y pénétrer. Les résultats obtenus ont permis de déterminer, pour le dispositif proposé, les paramètres d'essai à prendre en compte.

Sewerage systems undergo a wide variety of structural damage. It is estimated that 10% of French sewer length is in need of renovation. This paper is concerned with restructuring by carbon-fibre plates. The finite-element method is necessary to obtain the failure mechanism and thus locate the areas in need of strengthening. Experimental tests were conducted to characterise the materials (concrete, adhesive and carbon-fibre plates) and then obtain their constitutive laws. A control ovoid and a carbon plate-strengthened ovoid were compared.

France's sewerage systems are extensive and ageing. Ten per cent in length of the urban network requires rehabilitation work. In order to restore to the degraded structure their primary functions, many rehabilitation techniques exist but are expensive and applied to the full section of the sewer. The construction industry is now expert in methods of reinforcement using composite plates. The companies SIKA France SA, Structure & Rehabilitation and VALENTIN Environment et Travaux Publics, in collaboration with Laboratoire d'Artois Mecanique Thermiques et Instrumentations, applied this technique to reinforced-concrete man-entry drainage sewers, with and without multiple cracks. A large series of full-scale tests was carried out in the laboratory and then in situ.

Les reseaux d'assainissement subissent de nombreuses degradations d'ordres structurelles. Les maitres d'ouvrages estiment a 10 % du lineaire au moins, la longueur des collecteurs dont l'etat de degradation structurelle exige des travaux. Cet article concerne la restructuration d'ouvrages d'assainissement par lamelles composites. Afin d'appliquer cette technique de renforcement, une analyse par elements finis est necessaire pour connaitre le mecanisme de ruine et donc les zones a renforcer. Une campagne experimentale a permis de caracteriser les differents materiaux (beton, colle et lamelles de carbone) et d'obtenir leurs lois de comportement. Une comparaison entre ovoide temoin et ovoide renforce par lamelle de carbone pourra etre effectuee.

This article concerns the repair and reinforcement of sewage structures using composite plates. Tests were performed to characterise the interface, using prisms reinforced with pultruded carbon fibre-based plates in different environments (normal, water-saturated, submerged). The prisms were then subjected to four-point bending to study the behaviour of the concrete/adhesive/composite interface and to obtain the intrinsic properties of the materials. A finite-element analysis was performed to reproduce the behaviour of the reinforced prisms. The results of these numerical calculations were then compared with the experimental tests.