Formulation of a composite of date palm wood-cement

This work reports the results of an experimental study on the incorporation of wood waste date palm reduced in particles for the manufacture of wood – cement composites. These materials are chipper than the conventional insulator material and environmental friendly. Five types of wood – cement composites with various concentrations of the wood particles, ie. 2, 4, 6, 8 and 10% of total volume, were made according to defined protocol and mix design. Their thermal and mechanical properties were measured and compared to other conventional materials. The obtained results show that the thermal conductivity is positively correlated to the content of particles in the mixture. The compressive strength of composites decreases where the content of particles increase. However, taking account of the ASTM C 109 / C109-95 standard, the wood – cement composite contained 10% of wood particles, considered as lightweight concrete, could be used as non-structural material in construction

Simulation de l'écoulement des pâtes cimentaires par un modèle diphasique

La modélisation de l'écoulement des pâtes cimentaires est un problème difficile car le matériau a non seulement un comportement rhéologique complexe mais il peut également présenter des hétérogénéités induites par l'écoulement. L'apparition de ces hétérogénéités résulte de la filtration de phases fluides au travers de phases solides et peut conduire au blocage de l'écoulement. Pour modéliser l'écoulement d'un tel matériau il est nécessaire de prendre en compte la présence d'au moins deux phases. Dans notre modélisation nous considérons que les deux phases sont continues et admettent un comportement rhéologique en loi de puissance. Le couplage entre les deux phases est pris en compte au moyen d'une loi de Darcy généralisée à un fluide en loi de puissance. Le modèle est résolu par la méthode des éléments finis et validé dans le cas d'un test d'écrasement. Nous montrons que ces simulations permettent d'établir des diagrammes d'ouvrabilité des pâtes cimentaires

Etude du comportement visqueux-visco-plastique de suspensions sédimentaires multi-échelle

International audienc

Comportement Rhéologique des mortiers industriels

Les mortiers industriels sont composés d'un liant (ciment et/ou chaux), de granulats de différentes tailles, formes et nature (sables, charges, pigments colorants, etc.) et d'adjuvants organiques ou minéraux. Les mélanges sont effectués en usine et le produit est conditionné en sacs. L applicateur rajoute la quantité d eau nécessaire avant une mise en place qui s effectue le plus souvent par pompage-projection (enduits de façade et certains mortiers techniques). Lors d un tel procédé le matériau est soumis à une suite complexe de différents types d écoulement. Par ailleurs, compte tenu de la composition granulaire du produit plusieurs problèmes sont rencontrés lors des applications sur chantier. Cela inclut le bouchonnage, le mauvais entrainement au niveau de la pompe ("effet tunnel"), fluage une fois sur le support, etc. Il est évident que les propriétés de mise en place de ces matériaux sont déterminées par leur comportement rhéologique. L objectif de ce travail de thèse était de relier de manière claire les problèmes liés au procédé de pompage-projection aux propriétés rhéologiques des matériaux. Les mortiers industriels sont caractérisés par des seuils d écoulement et des consistances relativement élevés. Par ailleurs, ils sont constitués de différentes phases qui peuvent éventuellement se séparer lors des mesures. Ainsi il a fallu développer une méthodologie spécifique pour ce type de matériaux. Pour caractériser les problèmes de blocage d écoulement nous avons utilisé l essai d écrasement (squeeze test). Cela a permis de déterminer des diagrammes séparant les zones dans lesquelles le matériau peut être déformé en restant homogène de celles où l on a apparition d une séparation liquide-granulats aboutissant éventuellement au blocage. Nous avons considéré tout d abord le cas de mortiers modèles pour lesquelles on a fait varier aussi bien la rhéologie de la phase liquide que la perméabilité du squelette granulaire. Il a été montré que pour minimiser les risques de blocage on peut aussi bien augmenter la consistance de la phase liquide (effet des épaississants) que diminuer la perméabilité du réseau granulaire. Des simulations numériques basées sur un modèle diphasique ont été développées. Les simulations ont permis de reproduire qualitativement la plupart des observations expérimentales. Les courbes d écoulement des matériaux obtenues en rhéométrie (avec le système Vane) ont généralement des allures très complexes. Elles présentent souvent un profond minimum signe d une forte localisation du cisaillement. Par ailleurs les matériaux sont soit thixotropes soit rhéopexies, selon la gamme de taux de cisaillement considérée. Ces comportements rhéologiques sont discutés ici en relation avec les propriétés de mise en place par pompage-projection. En particulier, il est montré qu il est possible de prévoir la plupart des problèmes d application à partir des courbes d écoulement. En s inspirant des résultats de rhéométrie nous avons développé un test simple pour caractériser la pompabilité des mortiers. Ce test peut être utilisé directement sur chantier ou pour une aide à la formulation en usine ou au laboratoire.Industrial mortars are roughly composed of a binder (cement and/or lime), sand, granular charges and different polymer and organic admixtures. They are provided to the construction sites as ready-mix powders to which a given dosage rate of kneading water is added to obtain a homogeneous paste. This mortar paste is then placed following processing involving in general highly complex flows (pumping, spaying, etc.). A number of practical problems can be encountered during the placement process (in particular in machinery applications), including flow-blockage, lack of worm drive, creeping, etc. It is clear that all these issues are closely related to the rheological behaviour of the mortar paste. The primary objective of this thesis program is to relate the properties of pumping-spaying of render mortars to their rheological behaviour. These materials are actually characterised by a quite high yield stress and they are composed of different granular phases that may separate under flow. It is then necessary to develop specific procedures to characterise their flow. One of the origins of flow blockage in machinery applications may be attributed to solid-liquid separation under compressional flow. In this investigation we use the squeeze test to mimic and consider quantitatively this situation. The squeeze tests are performed either at controlled velocities or fixed applied normal forces. Flow diagrams separating flow zone parameters and blockage are then determined. It is shown with model suspensions that the flowability zone can be extended both by increasing the consistency of the fluid phase and by decreasing the permeability of the granular skeleton. This shows that the flow blockage issue is controlled by the competition between the suspension flow as a whole and the filtration of the fluid phase through the porous media made up by the solid particles. Numerical simulations based on a diphasic model taking into account filtration are then conducted. Our numerical simulations are in qualitative agreements with all the experimental observations. The flow curves of the render mortars as determined with a 4-blade vane geometry are quite complex, in particular at controlled shear-rates. In this case deep minima are observed indicating that we may have strong localisation. In addition, the materials display both thixotropy and rheopexy, depending upon the shear-rate interval considered. Other rheological properties are also investigated, including transient properties (thixotropy), yielding and creep. These properties are discussed in relation with the practical problems encountered in pumping applications. Finally a simple test procedure, based on slump determination of cylindrical samples subjected to different shear histories, is suggested to characterise pumpability of render mortars. More calibration investigation is needed in order to use this test in practise as a mixdesign aid or as a control-test for render mortars.CACHAN-ENS (940162301) / SudocSudocFranceF

Contributions of Information and communication technologies to industrialization of additive manufacturing

Additive manufacturing is in clear progress in the field of civil engineering construction, essentially boosting by the development of new information and communication technologies. For better industrialization of the use of this technique, in-situ control of products manufactured along the production line is a major issue. In this work we were able to supervise the quality of printed object along the process by comparing the target values and those measured by image processing obtained by a camera installed in the printing device. We have developed a program that allows us to measure the deformations of the different layers and thus to assess the difference between the values of the target ratings and those achieved. This deviation is defined as a criterion for validating piece conformity and can also be used to adapt the process parameters

Effect of entrapped and entrained air on the workability and rheology of cementitious materials

The influence of air on the fresh properties of cementitious materials is still a point of discussion in concrete research. On the one hand, fluctuations of entrapped air can change the predicted properties in an undesirable way. On the other hand, it is known that the addition of air entrainment changes the rheology significantly. A profound research on the impact of different methods to change the air content, is necessary. We investigated the influence of vacuum mixing and air entrainment on the workability of paste and mortar. For self-compacting mortar also the influence on the rheology was examined. For vibrated paste and self-compacting mortar a clear decrease of the workability is determined when air is added. This was also found for the rheology of self-compacting mortar. In case of vibrated mortar an overall increase of the workability occurred, when the air content increased. In conclusion, vacuum mixing can control the air content and changes the workability and rheology in an acceptable way. A more important change of the slump flow and, if determined, the rheology, is obtained by air entrainment. Further research should be performed on the influence of air on the worability and the rheology of ultra-high performance concrete

Bamboo Sawdust as a Partial Replacement of Cement for the Production of Sustainable Cementitious Materials

This paper reports on the utilization of recycled moso bamboo sawdust (BS) as a substitute in a new bio-based cementitious material. In order to improve the incompatibility between biomass and cement matrix, the study firstly investigated the effect of pretreatment methods on the BS. Cold water, hot water, and alkaline solution were used. The SEM images and mechanical results showed that alkali-treated BS presented a more favorable bonding interface in the cementitious matrix, while both compressive and flexural strength were higher than for the other two treatments. Hence, the alkaline treatment method was adopted for additional studies on the effect of BS content on the microstructural, physical, rheological, and mechanical properties of composite mortar. Cement was replaced by alkali-treated BS at 1%, 3%, 5%, and 7% by mass in the mortar mixture. An increased proportion of BS led to a delayed cement setting and a reduction in workability, but a lighter and more porous structure compared to the conventional mortar. Meanwhile, the mechanical performance of composite decreased with BS content, while the compressive and flexural strength ranged between 14.1 and 37.8 MPa and 2.4 and 4.5 MPa, respectively, but still met the minimum strength requirements of masonry construction. The cement matrix incorporated 3% and 5% BS can be classified as load-bearing lightweight concrete. This result confirms that recycled BS can be a sustainable component to produce a lightweight and structural bio-based cementitious material

Estimation of the Pumping Pressure from Concrete Composition Based on the Identified Tribological Parameters

A new method is proposed to estimate pumping pressure based on concrete composition without experimental measurements. Previous studies show that the pumping pressure depends on the interface friction between concrete and the wall of the pumping pipes. This friction is determined by the thickness and the rheology of the boundary layer formed at the interface. The latter is mainly formed by water, cement, and fine sand particles which come from concrete. Hence, interface parameters, which are the viscous constant and the interface yield stress, are directly related to concrete composition. In this work, at the first time the interface yield stress model is suggested and validated thanks to an experimental database also carried out in this study with a precision of around 13%. Then, the pressure estimation method is proposed using the two models to calculate the interface parameters. The validation of the method is carried out basing on the comparison with real measurements on the building site. This method enables the calculation of the pumping pressure with a precision of around 15%