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The objective of this work was to study fresh concrete flow in the L-box test, predict the final deposit shape after flow stoppage and estimate the yield stress. This is very useful for controlling concrete casting in real structures, detecting problems and developing solutions on time. Concrete rheometers used for measuring the rheological parameters of concrete are expensive, not always available and can lead to measurement disparity. To overcome these issues, an effective method is to analyse concrete flow phenomena physically and solve the problem analytically based on L-box measurements. In the first part of this work, fresh concrete was considered as a homogeneous yield stress fluid moving under the effect of its self-weight. By developing momentum equations for an incompressible fluid, a theoretical approach was used to study three probable final shapes depending on the concrete rheology. Expressions were established for predicting the final shape and the yield stress. In the second part, the results obtained were compared with those of previous models and good agreement was found, thus validating the proposed approach. This study provides a consolidation of rheometer results, allowing evaluation and perhaps a calibration to reinforce their validity.

In the context of the development of green building materials using plant fibers, this research has focused on the characterization of natural fibers extracted from Juncus plant, commonly called Juncus. A well-known chemical extraction method was applied here for the first time at our knowledge to the Juncus plant, in order to obtain better mechanical characteristics (tensile strength and elastic modulus) and better surface morphology. Therefore, a chemical treatment with alkalization through various factors such as temperature, NaOH concentration (alkalizing agent), presence or not of sodium dithionite Na2S2O4 (for reducing lignin) and sodium hypochlorite NaOCl (chlorine bleach delignification agent) was performed. This study aims to determine the effects of different chemical treatments applied to the fiber extraction of Juncus stem, on the change in fiber diameter, surface state morphology, density, tensile strength and elastic modulus. As one of the Juncus fiber treatments considered in this work, the cold alkali-treatment did not give good results in terms of delignification of the Juncus fibers (There is always non-cellulosic products on the treated fiber) and low values of tensile stress and modulus of elasticity. The treatment with a solution of 8% NaOH, sodium hypochlorite and sodium dithionite at hot temperature present the best result due to the effective delignification of the fibers which has allowed reaching highest tensile strength and highest elastic modulus.

International audience; In this work we focus on the study of the acoustic and mechanical behavior of compressed earth blocks (CEBs). The aim was to study the influence of compaction pressure on the compressive strength and intrinsic acoustic parameters influencing sound absorption of these materials (porosity, tortuosity, airflow resistivity, viscous characteristic length). Specimens made by varying the applied compaction pressure and therefore having various bulk densities were studied. Low bulk density CEBs where stabilized by adding 15% cement. The acoustic absorption coefficients of the different specimens were determined experimentally employing data obtained using the Kundt tube. The intrinsic acoustic parameters were identified by minimizing the discrepancies between the experimentally measured absorption coefficient (α) and the theoretical one modeling the CEBs using the equivalent fluid model. The results showed that the acoustic and mechanical behavior of CEBs were strongly influenced by the applied compaction pressure including, inter alia, the bulk density of the specimen and the added cement used as stabilizer.

One of the modern techniques of earth construction is the Interlocking Stabilized Earth Block (ISEB), which realizes the requirement of a certain type of construction in an economic and technical way compared to conventional materials. The use of this technique fits suitably within the framework of high environmental quality since the process uses an abundant material not requiring a lot of transformation energy. The aim of this study is to perform compressive tests on superposed ISEB that are laid dry without grout mortar. Testing results show that the ​​contact area and the clearance between the blocks have an effect on the masonry's compressive strength, causing it to decrease. For that, particular attention is given to analyzing the contact area effect on the mechanical behavior of superposed ISEB. A finite element method (FEM) analysis is also performed in order to highlight the effect of the local stress around the clearance on the macroscopic compressive behavior of the masonry. Finally, a simplified spring model is considered in order to estimate the vertical apparent Young's modulus of ISEB walls.

Compressed earth blocks (CEB) were used for the construction, always and until now systematically with a bulk density of about 1800 and 2100 kg m −3 . These earth construction materials have a relatively high thermal conductivity of about 1.1 W m −1 K −1 . This study aims to obtain lightweight CEB by varying their bulk density in order to modify their porosity and consequently to act on their thermal conductivity. The approach adopted here involves an experimental study of the influence of compaction pressure on the bulk density of the compressed earth block (CEB) and its effects on their thermal performance (thermal conductivity and thermal effusivity) and mechanical properties (compressive strength and modulus of elasticity). Results show that bulk density has a strong influence on thermal and mechanical behavior of CEB. The decrease in the bulk density of CEB was accompanied by a significant reduction in their thermal conductivity and their thermal effusivity. This variation in thermal properties as a function of bulk density is performed linearly. However, the bulk density should not decrease under certain minimum values below which the CEB lose their cohesion and compressive strength.

International audience; The objective of this work was to analyze the influence of compaction pressure on the intrinsic acoustic parameters (porosity, tortuosity, airflow resistivity, viscous and thermal characteristic lengths) of compressed earth blocks through their identification by solving an inverse acoustic wave transmission problem. A low frequency acoustic pipe (60-6000 Hz of length 22 m, internal diameter 3.4 cm) was used for the experimental characterization of the samples. The parameters were identified by the minimization of the difference between the transmission coefficients data obtained in the pipe with that from an analytical interaction model in which the compressed earth blocks were considered as having rigid frames. The viscous and thermal effects in the pores were accounted for by employing the Johnson-Champoux-Allard-Lafarge model. The results obtained by inversion for high-density compressed earth blocks showed some discordance between the model and experiment especially for the high frequency limit of the acoustic characteristics studied. This was as a consequence of applying high compaction pressure rendering them very highly resistive therefore degrading the signal to noise ratios of the transmitted waves. The results showed that the airflow resistivity was very sensitive to the degree of the applied compaction pressure used to form the blocks.

The present research studies the formulation and optimization of a self-leveling composition for floor toppings. This formulation is, in particular, based on a fluoroanhydrite which is a by-product of a Tunisian plant for fluorhydric acid preparation; it also contains aggregates, a neutralizing agent, a hydration accelerator and, especially, a plasticizer prepared by sulfonation of the lignin extracted from the black liquor of a Tunisian esparto grass soda pulping process. The optimization of four responses (plasticity, compressive strength, initial and final setting times) has been carried out in two steps. First, we obtain a coarse composition with a relatively acceptable rheological properties. Second, we carry out a mixture design in the surroundings of the retained composition aimed at obtaining a product with the required characteristics formulated by the users of this kind of materials. To this end, the evolution of the plasticity and the setting times of the fresh mortar and the compressive strength of the hardened mortar in a four-component system with constraints were analyzed using a mathematically independent variable approach. Finally, and in order to reach a near-optimal composition, we use the desirability functions to optimize the four responses simultaneously. This allows us to determine the coordinates of a composition which is characterized by high plasticity, acceptable compressive strength and relatively rapid setting times.

The objective of the work described in this first paper of a series is an investigation of the preparation of a sulfonated esparto grass lignin (SEL) and its behavior as a plasticizing–water-reducing agent for cement–water systems. SEL is prepared by extracting the lignin from the black liquor of a soda esparto grass pulping process and then sulfonating it with a mixture of sodium sulfite and formaldehyde. Analyses and characterization of SEL carried out with high-performance size exclusion chromatography (HPSEC), reversed phase chromatography (RPC), infrared spectrometry and chemical methods show that both the molecular weight average and the combined sulfur content are relatively high. Moreover, HPSEC shows that SEL has a relatively more uniform molecular weight distribution (MWD) than the commercial products obtained from the sulfite wood pulping process. On the other hand, SEL could reduce the water content, improve the workability and compressive strength of mortars. SEL also permits a very low rate of slump loss of cements without excessive extension of the final set time.