Rhéologie de matériaux à base de ciment utilisés pour l'impression 3D à grande échelle

Abstract : Concrete 3D printing introduces a brand-new technic of concrete elements production. The advantages of this technic over the conventional formwork-based method are (1) easier and less costly production of the elements with complex geometry, (2) a higher level of customization, (3) lower concrete and formwork materials waste, and (4) lower rate of manpower injuries. However, there are still several challenges toward the industrialization of concrete 3D printing, one of which is materials engineering. The main objective of this study is to develop cementitious materials that fulfill the two important requirements of the large-scale 3D printing process namely extrudability and buildability. Additionally, this study aims to develop suitable testing methods to refine the optimized cement-based materials subjected to 3D printing. The development of novel test methods to evaluate the rheology of the 3D printing materials is necessary to overcome the inadaptability of the existing testing methods. Indeed, the 3D printing mixtures exhibit a behavior described as extrudable yet stable in shape, thus require customized and adapted test methods to quantify their properties. In addition, the interaction between the material and the robot (3D printer) must be considered. To address this matter, cement-based materials with adapted thixotropic behavior were developed using chemical and mineral additives. Indeed, these materials greatly contribute to solving the problems of extrudability and shape stability of printing materials which have proven to be a major challenge in the case of the material-robot interaction. This study was conducted in 4 different and complementary phases. Phase 1 involved a comprehensive literature review and scanning the major problematics in the field regarding the materials engineering. In addition, a buy-or-make decision analysis was conducted in this phase to evaluate various alternatives to develop a large-scale concrete 3D printer at the Université de Sherbrooke. Several options were considered, and a decision was made to design and conceptualize a cartesian 4-axis gantry robot for in-house fabrication. In the Phase 2, the effectiveness of the rheometric methods to evaluate the structural build-up of printing materials was investigated. For this purpose, empirical testing methods such as mini-slump cone as well as rheometric methods were evaluated. In the case of rheological properties, the modified Bingham model parameters were identified for a wide array of materials and used for optimization. The structural build-up of mixtures was consequently measured using the evolution of the static yield stress and dynamic rheological measurements. Various mortar mixtures were subjected to 3D printing trials using a custom-made printer to evaluate the effectiveness of rheometric and empirical methods in assessing the extrudability and shape stability of the optimized mixtures. In Phase 3, cement-based materials with adapted thixotropic behavior were developed using chemical and mineral admixtures. Several mixtures were subsequently investigated to optimize 4 mixtures based on a structural build-up rate criterion. A feasibility study was also conducted at this point to adapt a compressive testing set-up for fresh cement-based materials. For this purpose, a prototype testing device was fabricated. In the next step and after tuning the prototype, a uniaxial compression device was fabricated with unique features including programmable force application protocols, deformation monitoring accuracy of 1 micron, mobility (the system requires solely a compressed air unit), and user-friendly interface. Furthermore, the uniaxial compression test was used to develop a testing method to quantify the fresh properties of mixtures. This contributed to overcoming the existing challenges of the rheometric testing methods when measuring the properties of mixtures with excessive rigidity. Initially, rotational rheometric methods to assess the static yield stress were used to characterize the investigated mortar mixtures. Secondly, the squeeze flow test was used to obtain the compressional yield stress using the fabricated device. Finally, in Phase 4, the in-house-made 3D printer at Université de Sherbrooke fabricated in parallel to the activities of this study was used to perform large-scale 3D printing and to validate the performance of the testing methods and the optimized mixtures in terms of extrudability and buildability. In addition, the effect of pumping and extrusion on the shear history of the materials was investigated to help adapting the thixotropic responses of mixtures to the 3D printing process. The performance of the developed compressive testing machine was validated through obtaining the structural build-up of the mortars and experimental simulation of the 3D printing process. In addition, a numerical investigation was carried out to simulate the process-induced shape variations of cement-based 3D printing materials.L'impression 3D béton introduit une toute nouvelle technique de production d'éléments en béton. Les avantages de cette technique par rapport à la méthode de construction conventionnelle basée sur l’utilisation de coffrage sont (1) une production plus facile et moins coûteuse des éléments à géométrie complexe, (2) un niveau de personnalisation plus élevé, (3) moins de déchets de béton et de matériaux de coffrage, et (4 ) un faible risque de blessure de la main-d'œuvre. Cependant, il existe encore plusieurs défis vers l'industrialisation de l'impression 3D du béton, notamment l'ingénierie des matériaux. L'objectif principal de cette étude est de développer des matériaux cimentaires qui répondent aux deux exigences importantes du processus d'impression 3D à grande échelle, à savoir l'extrudabilité et la constructibilité. De plus, l'étude vise à développer des méthodes d'essai appropriées pour affiner les matériaux à base de ciment optimisés soumis à l'impression 3D. Le développement de nouvelles méthodes d’essais pour évaluer la rhéologie des matériaux d'impression 3D est nécessaire pour surmonter l'inadaptabilité des méthodes existantes. En effet, les matériaux imprimables doivent être extrudables (i.e. pompable), mais de forme stable, nécessitent donc des méthodes d’essais personnalisées et adaptées pour quantifier leurs propriétés. De plus, l'interaction entre le matériau et le robot (imprimante 3D) doit être prise en compte. Pour répondre à ce problème, des matériaux cimentaires ayant un comportement thixotropique adapté ont été développés à l'aide des adjuvants et additions minérales. En effet, ces matériaux contribuent grandement à résoudre les problèmes d'extrudabilité et de stabilité de forme des matériaux d'impression, qui se sont avérés être un défi majeur dans le cas de l'interaction matériau-robot. Cette étude est réalisée en quatre différentes phases complémentaires. La Phase 1 comporte une revue de littérature complète et une analyse des principales problématiques dans le domaine d’impression 3D des matériaux cimentaires. De plus, au cours de cette phase, une analyse de décision d'achat a été menée afin d'évaluer les alternatives pour s’équiper d’une imprimante 3D pour béton à grande échelle à l'Université de Sherbrooke. Plusieurs options ont été envisagées, un robot portique cartésien à 4 axes a été conçu et conceptualisé pour fabrication. Dans la Phase 2, l'efficacité des méthodes rhéométriques pour évaluer la structuration structurelle des matériaux cimentaires destinés pour une impression 3D a été étudiée. À cette fin, des méthodes d'essais empiriques, tel que le mini-cône d'affaissement, ainsi que des méthodes rhéométriques ont été adaptées. Dans le cas des propriétés rhéologiques, les paramètres rhéologiques ont été estimés en utilisant le modèle de Bingham modifié identifiés pour une large gamme de de matériaux et utilisés pour l’étude d'optimisation. La structuration structurale des mélanges a donc été mesurée en utilisant l'évolution des seuils d’écoulement statique et dynamique. Les formulations de mortier ont été soumis à des essais d'impression 3D à l'aide d'une imprimante à l'échelle de laboratoire pour évaluer l'efficacité des méthodes de caractérisation empiriques et rhéométriques sur l'extrudabilité et la stabilité de forme des mélanges optimisés. Dans la Phase 3, des matériaux à base de ciment ayant un comportement thixotropique élevé ont été développés à l'aide d'adjuvants et additions minérales. Plusieurs mélanges ont ensuite été optimisés sur la base d'un critère de taux de structuration. Une étude de faisabilité a été menée à ce stade pour adapter un dispositif d'essai de compression pour les matériaux cimentaires à l’état frais. A cet effet, un prototype permettant un contrôle adéquat de la pression appliqué et un suivi très précis de de la déformation a été fabriqué. À l'étape suivante et après le réglage du prototype, une machine de compression uniaxiale a été fabriquée avec des caractéristiques uniques, notamment le protocole d'application de force de compression automatisé, le suivi de la déformation à une bonne résolution de 1 micron, la mobilité (le système nécessite uniquement une unité d'air comprimé) et l’interface d’usage conviviale. De plus, l'essai de compression uniaxiale a été utilisé pour développer une méthode d'essai afin de quantifier les propriétés des formulations destinées pour une impression 3D à l’état frais. Ceci est réalisé afin de surmonter les défis existants des méthodes d'essai rhéométrique lors de la mesure des propriétés rhéologiques de mélanges ayant une rigidité excessive. Initialement, certaines méthodes rhéométriques existantes pour obtenir le seuil d’écoulement statique des matériaux ont été utilisées pour caractériser les mortiers sélectionnés. Deuxièmement, l’essai de compression uniaxiale développé a été utilisée pour proposer un nouveau type de limite d'élasticité, à savoir la limite d'élasticité en compression. Enfin, dans le Phase 4, l'imprimante 3D à grande échelle de l'Université de Sherbrooke, fabriquée en parallèle des activités de recherche, a été utilisée pour effectuer des impressions 3D à grande échelle et valider la performance des méthodes d'essais afin de caractériser les formulations optimisées en termes d'extrudabilité et de constructibilité. De plus, l'effet du pompage et de l'extrusion sur l’histoire de cisaillement des matériaux a été étudié afin de pouvoir ainsi l’adapter au processus d'impression 3D. Les performances de la machine d'essai de compression ont été validées par l'obtention de la structuration structurelle des mortiers. De plus, une étude numérique a été réalisée pour simuler les variations de forme des matériaux cimentaires induites par le processus d'impression 3D

Optical Signal Processing With Discrete-Space Metamaterials

As digital circuits are approaching the limits of Moore’s law, a great deal of efforthas been directed to alternative computing approaches. Among them, the old concept of optical signal processing (OSP) has attracted attention, revisited in the light of metamaterials and nano-photonics. This approach has been successful in realizing basic mathematical operations, such as derivatives and integrals, but it is difficult to be applied to more complex ones. Inspired by digital filters, we propose a radically new OSP approach, able to realize arbitrary mathematical operations over a nano-photonic platform. We demonstrate this concept for the case of spatial differentiation, image compression and color encoding through a heuristic design based on a waveguide with periodic arrays of input/output channels at its opposite walls

Theory borrowing in IT-rich contexts : lessons from IS strategy research

While indigenous theorizing in information systems has clear merits, theory borrowing will not, and should not, be eschewed given its appeal and usefulness. In this article, we aim at increasing our understanding of modifying of borrowed theories in IT-rich contexts. We present a framework in which we discuss how two recontextualization approaches of specification and distinction help with increasing the IT-richness of borrowed constructs and relationships. In doing so, we use several illustrative examples from information systems strategy. The framework can be used by researchers as a tool to explore the multitude of ways in which a theory from another discipline can yield the understanding of IT phenomena

Comparison of boric acid and combination drug of polymyxin, neomycin and hydrocortisone (Polymyxin NH) in the treatment of acute otitis externa

Acute otitis externa is an inflammation of the external auditory canal known as “swimmer's ear”. Direct costs including medical treatment, painkillers, antibiotics, steroids or both and indirect costs are also remarkable. Aim: The aim of this study was to compare the effect of boric acid and polymyxin, neomycin and hydrocortisone composition in the treatment of acute otitis externa. Materials and Methods: This randomized clinical trial was carried out on 80 patients aged more than 17-year-old who were referred to Kashani hospital clinic with a diagnosis of acute otitis externa by otolaryngologist. The patients were randomly allocated to two groups (A: Boric acid and B: polymyxin NH ear drops) and Painkiller was prescribed and administered orally for all patients and in the presence of fever, cellulitis around the ears and neck adenopathy, broad-spectrum systemic antibiotics were used besides topical treatment. Symptoms of patients who were evaluated by a physician includes pain, discharge from the ear, swelling of the ear canal, auricle swelling, tenderness, and ear itching. In addition, pain was evaluated in patients and was recorded by Macgill Pain Questionnaire, in the first, third, seventh and tenth days. Results: Results showed that itching on third day (p=0.007) and swelling of the ear canal in the examination of the third day (p=0.006) and the seventh day (p=0.001) in the polymyxin NH group is more than those of boric acid group. Overall mean pain based on McGill questionnaire was 11.10±1.49 in boric acid group in the examination on the first day and was 4.05±0.22 in the examination on the tenth day and in the polymyxin NH group, it was 10.9±0.99 on the first day and 4.20±0.40 on the tenth day. In both groups, pain relief was the same and there was no significant difference between two groups (p=0.075) Conclusion: The findings of this study showed slight differences in the effectiveness of the boric acid drug and combination of polymyxin, neomycin and hydrocortisone in the treatment of patients with acute otitis externa that is clinically of significance and considerable

Responding—or Not—to IT Project Risks: Conceptualizing Risk Response as Planned Behavior

Prior research suggests that IT project managers’ risk response behavior sometimes differs from the prescriptions in the literature. Conceptualizing performing a risk response as planned behavior, this study draws upon the theory of planned behavior (TPB) and develops a model to enrich the understanding of the relationship between perceiving risk and enacting—or not—a risk response. The model includes the TPB constructs—behavioral attitude, perceived pressure and perceived control. It also leverages the notion of ‘background factors’ in TPB that allows the inclusion of antecedents of behavioral attitude, in the present study, perceived risk of project without the risk response and perceived risk of enacting the risk response. The research design comprises three studies. Study 1 selected three specific risk responses. Study 2 elicited IT project managers’ beliefs about each risk response. Study 3 (in progress), tests the proposed model—enriched with the elicited beliefs—for each risk response

Effectiveness of Lasers in the Treatment of Dentin Hypersensitivity

Dentin hypersensitivity (DH) is a relatively common painful condition among dental problems. Although many studies have been performed regarding the diagnosis and treatment of DH, dental practitioners are still confused about the definite diagnosis and treatment.The use of lasers as a treatment for dentin hypersensitivity was first introduced in 1985. Laser treatment in dentin hypersensitivity is an interesting and controversial issue and many investigations have been done on its mechanism of action, advantages, and unclear points. The present literature review tries to go over the definition, diagnosis, etiology, predisposing factors, various laser types in the treatment of DH alone or in combination with topical desensitizing agents. Since a certain treatment has not yet introduced for dentin hypersensitivity, a combination of laser therapy and topical desensitizing factors, can increase the success of the treatment compared with either treatments alone

Understanding the Dynamic Nature of Contribution in Virtual Project Teams

Two dysfunctional contribution behaviors in virtual project teams are non-contribution (e.g., social loafing, free riding, and shirking) and over-contribution (e.g., being a lone wolf or a “diligent isolate”). To prevent these behaviors or mitigate them when they occur, some coping actions (e.g., increasing contribution visibility) can be undertaken. In this research-in-progress, we report on the findings of a pilot study run to increase our understanding of the dynamic nature of such dysfunctional contribution behaviors and coping actions. We also briefly explain our plans for the main study

Research-In-Progress: An Empirical Investigation of the Decision of Whether or Not to Perform Risk Mitigation in Software Projects

Although software project risk management has been found to positively affect project success, research suggests that software project risk management is not widely practiced. Addressing this issue, this research-in-progress paper focuses on the risk-response step of risk management and proposes a model that explains and predicts software project managers’ undertaking of risk-response actions. The theoretical model integrates behavioral decision making under uncertainty literature and the reasoned action approach. Especially, the availability heuristic (i.e., people’s reliance on the accessible information to make judgments) is used to explain the variation in the project managers’ beliefs about the outcomes of continuing-risk-inaction and undertaking risk-response actions. The paper presents the survey methodology that will be adopted to test the model