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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.

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.

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...

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.

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.

International audience; To ensure an easy demoulding of the concrete, the release agent must form a homogeneous film on the formwork to resist the casting concrete. The adherence of oil with the support was studied via the solid/liquid energy adhesion. This energy was calculated using the Zisman equation involving the angle of drop and the surface tension. Various formulations were studied, in order to establish correlations between their composition and the interfacial properties. Formwork release tests were performed to assess cladding aesthetics; it was possible to define a minimal level of adhesion energy to meet the facings quality after concrete demoulding.

International audience; The release agents protect the internal surfaces of formwork against corrosion and also ensure easy removal of the concrete elements. On the other hand, the superplasticizers are used to enhance the fluidity of the fresh concrete without adding water, thanks to their surfactant properties. Their contact with release agents can cause interactions near the formwork surfaces during the concrete pouring. The aim of this study is to identify the effect of a polycarboxylic ether superplasticizer on the tribological behavior of fresh concrete at the concrete/oil/formwork interface. Friction tests were performed using a plane/plane tribometer on three concretes with 30% of paste at different dosages of superplasticizer. Moreover, the purpose of the physicochemical study was to clarify the nature of the interactions between concrete pore solutions and release agents. Results showed that the superplasticizer dosage did not have the same effect on the friction according to the oil nature involved at interface. Thus, a description of the processes occurring at the concrete/oil/formwork interface is proposed. When the superplasticizer generates a deflocculating action of the cement particles, it also acts on the stabilization of the soap-oil micellae present at the interface.

International audience; Improving the knowledge of rheological and tribological characteristics of fresh concrete is important to contribute to the progress of construction sites and the final quality of the work. The objective of this study is to identify the effect of a superplasticizer based on polycarboxylic ether on the tribological behavior of fresh concrete at the concrete/formwork and concrete/oil/formwork interfaces. Friction tests on fresh concrete were carried out using a plan/plan tribometer. In order to study the behavior of the superplasticizer close to the formwork, three concretes with 30% of paste and different dosage of superplasticizer were formulated. The results show that the increase of the dosage of superplasticizer reduces the friction stress. The properties of the superplasticizer generate a deflocculating action of concrete grains and lead to a stabilisation of the soap-oil micellae present in the vicinity of the formwork. Thus, the efficiency of superplasticizer depends on the quantity of fines, on the quantity of soap formed and so, on the release agent formulation.

This study concerns the prediction of lateral pressure exerted by self-compacting concrete (SCC) on formwork during the casting process. This estimation is obtained using Janssen's model as used in the statics of ensiled granular material. The model has been adapted to SCC. The friction coefficient between the concrete and the wall occurring in the model is measured with a new type of tribometer. The case of SCC placed in 12 m high formwork by three companies using two different techniques is presented. Comparison of the predicted results with on site measurements shows good agreement.