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Publications (224)
The rapid development of 3D concrete printing now offers mechanical efficiency and freedom to push the limits of construction design. The digital manufacturing process holds potential for reducing carbon footprints through design optimization. Printable concrete, which is a mix of cement (based on ordinary Portland cement), aggregates, and admixtur...
Tomorrow's mineral binders are called on to integrate a growing proportion of mineral powders other than Portland clinker. This impacts most properties of industrial interest including fresh state properties, the focus of this paper. We discuss the physical, physico-chemical and chemical changes that such an evolution in mix design is expected to i...
Among the most significant causes of concrete degradation is ESA (external sulfate attack). The majority of studies are currently conducted on samples that have been saturated and matured. Concrete structures, however, are exposed to the environment once the formwork has been removed. The purpose of this study is to determine what effects early exp...
We study here the imbibition of a nanosilica-based product in a hardened cement-based material along with the consequences of the product on transport properties. We use X-ray microtomography to assess the liquid ingress in the cement-based matrix as a function of time. We moreover measure the consequences of the nanosilica treatment on water absor...
We analyze different flow regimes of a filament formed by extrusion of a material through a cylindrical die. We deduce that the elongational yield stress of a simple yield stress fluid (i.e., with negligible thixotropy effects) can be determined from the mass of the droplet after filament breakage and an estimation of the critical radius at pinch-o...
Besides the fact that concrete recycling allows to avoid landfills disposal and contributes to a closed-cycle economy, such option may be very much in demand in war struck regions such as Ukraine, which after the end of the war, are faced with the problem of rebuilding and reconstructing. Beyond this emergency, even in peacetime extensive parts of...
Purpose
3D printing has been put forward for its supposed environmental benefit, yet to be confirmed. This article describes an environmental assessment of a 3D printing process that represents one of the most commonly used technologies in the field. It then suggests a generic framework to evaluate the environmental impact of 3D concrete printing t...
Digital fabrication processes with concrete require a specific yield stress evolution after placing. This paper shows that this goal can be achieved with displacement controlled continuous slow penetration methods, and gives a model understanding and specific suggestions for measurement. It is found that the force recorded in continuous and point-w...
We focus in this paper on the embodied and operational contribution to climate change of a concrete-printing robotic cell. We first propose, in the case of extrusion-based additive manufacturing, a simple functional unit that relates a volume-based material impact and a time-based process impact through the printing head velocity and the filament c...
In the absence of a formwork, printable materials are expected to quickly increase their consistency in order to resist the self-weight of the structure being printed. Resolving this rheological requirement with the printing process is the key to successful printing. It is therefore necessary, from a material design, from a process design and from...
The Layer Pressing Strategy is widely used in large-scale concrete 3D Printing for its capacity to provide good control over the layer cross-section geometry and, consequently, the final overall printed element geometry. However, although layer pressing ensures exact positioning of the extruded layer upper surface, it may be at the origin of some d...
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This paper focuses on material-process interactions in particle bed binding. After a classification of particle bed binding techniques currently available for cement-based materials, the most important material-process interactions and their underlyin...
This paper deals with the control of the net geometry of a printed object in the case of powder-bed or particle bed binding technologies. We first measure and compare water penetration in one-dimensional experiments for various powder-beds. Our results, despite the simplicity of the experimental set-up, show a feature that has not been reported in...
It is well known in cement technology that the particle size distribution of cement particles significantly influence the rheology of the suspension, the hydration kinetics and microstructure development. Although much work has been done to develop protocols for the measurement of the particle size distribution of mineral particles, the characteriz...
Viscosity modifying agents (VMAs) are essential ingredients for the production of flowable cement-based materials. This paper presents an overview of commonly used VMAs and attempts to shed some light on the underlying physics at the origin of their mechanisms of action. The main molecular parameters of VMA controlling the rheological properties of...
The use of blended cements has attracted much interest in the quest to overcome the environmental challenges facing the concrete industry. However, partially replacing cement with supplementary cementitious materials (SCMs) can result in complex rheological behavior that is influenced by the type of SCM and the replacement percentage, as well as th...
The objective of this paper is the formulation of fat-reduced chocolate without affecting the viscosity of chocolate suspension. To achieve this objective, we control the rheological behaviour of dark chocolate suspension by optimizing the morphological properties (particle size distribution and maximum packing fraction) of sugar and cocoa powders....
In the last decade, the potential of 3D printing (and more generally of digital manufacturing) in the construction industry has been widely reported in the media. In 2017, CNN website posed the question “Will the world next megacity drip out of a 3D printer?”.
3D printing is offering a totally new construction method, but an in-depth understanding of the consequences of the different production conditions compared to traditional formwork-based casting operations is required. Bulk material properties (intrinsic strength and durability) will follow the same fundamental material laws. However, in printed st...
The comprehending of the processes’ physics is a prerequisite for the purposeful design and optimization of digital fabrication systems, as well as their efficient and robust process control. This chapter presents an overview of the underlying physics relevant to an understanding of the processing of cement-based materials during various production...
Digital fabrication with cementitious materials is a rapidly growing field of research in which the evolution of strength during the various processes, such as 3D printing, is the key controlling parameter. The strength evolves over multiple orders of magnitude during the process, and thus, it is essential to properly characterize the strength evol...
The need for methods for forming concrete has existed for as long as concrete has been used in constructing the built environment. Creating flat, rectilinear formers have traditionally been the cost and time efficient default for the majority of applications. The desire for greater design freedom and the drive to automate construction manufacturing...
This book presents the work of the RILEM Technical Committee 276-DFC: Digital fabrication with cement-based materials. The most important outcomes of the technical committee are presented. First, a unified process classification for digital fabrication with concrete is proposed, discussed and illustrated. Then, a state of the art of the testing met...
Materials’ requirements for 3D concrete printing centre around printability and buildability. The concrete must be pumpable, extrudable, yet retain its shape after extrusion (fresh state) and stack over each other without yielding and buckling failure (plastic state). The nature of 3D printed concrete materials has driven research into adapting var...
Control of filament geometry in extrusion based additive manufacturing is essential to guarantee the desired quality of the printing process and the final product. Depending on the selected process parameters, material strategy and geometrical features, the printing process can however be susceptible to filament tearing or filament buckling. In thi...
In order to measure the extensional rheological properties of yield stress fluids, we developed a rheometrical approach based on the analysis of the deformations of a fluid extrudate flowing downward and breaking in successive elongated drops due to gravity. Assuming the gradients of longitudinal velocity in radial planes are negligible, the local...
For the first time, a first-order physical correlation between pumping parameters (pressure and flow rate), granular skeleton properties (particle diameter and packing properties) and LL properties (thickness and viscosity) is proposed. This correlation is derived from the analysis of the equations driving shear-induced particle migration in dense...
This paper compiles selected predictive analytical and numerical tools which can be used to model and understand the mechanisms of importance at different stages during and immediately after extrusion-based 3D printing of cementitious materials. The proposed toolbox covers different aspects of the process including mixing, material transportation,...
In this work, we study the effect of mixing intensity on the size and concentration of nanoparticles in quartz and cement systems. We vary the local shear rate in the studied suspensions induced by mixing by either changing solid volume fraction or mixing speed. Our results obtained on quartz, cement and quartz-cement suspensions provide a master c...
Although in academic and industrial practice polymers are typically described by their average molecular parameters, most often they display a polydispersity both in size and in properties. In this paper, we focus on the influence of polydispersity on the adsorption of polycarboxylate ester on cement grains and on its influence on the definition of...
This paper introduces a novel rheological technique allowing for the assessment of printable materials yield stress at nozzle exit in the case of extrusion-based 3D printing. This technique is derived from the analysis of the specific gravity-induced non-Newtonian flow that takes place at nozzle exit, which is at the origin of the formation of mate...
The idea behind the present work is to assess robustness of fresh cement-based materials (i.e. their ability to display the same properties when submitted to variations in the way they are produced) from a generic and analytical point of view. First, analytical models from literature relating components proportions and yield stress are combined int...
In the present work, we aim at improving our understanding of the effect of synthetic flexible fibers on the rheology of fresh cement-based suspensions. We first measure the way that synthetic fibers do increase the yield stress of various fresh cement pastes and mortars. We then measure, using micro CT, the way these fibers are deformed in a fresh...
Recycled Concrete Aggregates are highly porous and may therefore absorb more water than natural aggregates. Several methods allow for the measurement of water absorption requiring drying at temperature above ambient conditions. We show here that, for temperatures above the ambient temperature (> 30°C) and at low relative humidity, the drying of rec...
The concrete industry is facing new digital shaping processes that still have to be optimized and that require cement-based materials, for which fresh properties requirements are yet to be defined. In this paper, we first present the state of the art in the field of numerical simulations of concrete flow. We then focus on the literature on numerica...
3d printing of cementitious material is a relatively new additive manufacturing process whose growing interest and fast development is mainly due to the digitalised manufacturing, allowing the disposition of material where it pleases. Yet, due to the properties of the fresh material and the difficulty to generate paths for the robots, the printed g...
Digital Fabrication with Concrete (DFC) encompasses 3D Concrete Printing (3DCP) and many other methods of production. DFC is emerging from an era of invention and demonstration to one where the merits of one principle over another needs to be quantified systematically. DFC technologies vary in characteristics, complexity and maturity which hampers...
3d printing of cementitious material by pressing layers during the extrusion is a strategy that requires a rather low initial yield stress so the material can deform without cracking. It allows to perfectly control the height of the layer and gives freedom in the orientation of the printing head and of the layer allowing for a wider range of printa...
3D extrusion-based additive manufacturing is known as the most widely applied printing strategy for digital fabrication of civil engineering materials. This construction method does not only require specific rheological properties and structural build-ups rates, but also mechanical properties comparable to conventional materials. In the current wor...
Successful and efficient fabrication using robotic extrusion of cementitious materials mainly relies on the mastering of the printable material fresh state behavior. This paper tackles this aspect by introducing a novel rheological apparatus dedicated to the yield stress measurement at nozzle exit in extrusion-based manufacturing. It is based on th...
This paper presents an environmental assessment of a 6-Axis robotic Arm for extrusion-based 3D Concrete Printing technology using Life Cycle Assessment method. In addition, the other components of a printing cell are assembled within a life cycle model and the relative contribution of the cell to the printing process is evaluated. The results show...
Powder-bed 3D printing technology is attractive as it allows to build complex structures and optimize cost and time. The liquid is sprayed to bond the powder bed at pre-determined positions layer by layer. After print, the non-bonded particles are removed during post-processing. From a material point of view, it is crucial to understand the interac...
Yield stress of aerated cement paste is studied. Samples are prepared by mixing aqueous foam with cement paste, which allows controlling bubble size, gas volume fraction and yield stress of the cement paste. Two distinct behaviors are observed depending on the surfactant used to prepare the precursor aqueous foam: (i) For a surfactant with low adso...
We prepare and study cement foam samples with well-controlled structure, i.e. containing monodisperse bubbles. We observe that the foam structure often changes before cement setting and identify ripening as the major destabilization mechanism at stake. Drainage plays only a minor role in cement foam destabilization except when bubble size is large....
Yield stress of aerated cement paste is studied. Samples are prepared by mixing aqueous foam with cement paste, which allows controlling bubble size, gas volume fraction and yield stress of the cement paste. Two distinct behaviors are observed depending on the surfactant used to prepare the precursor aqueous foam: (i) For a surfactant with low adso...
The interest in the elastic and yielding properties of fresh cement-based materials has recently grown due to the development of new processing techniques, which avoid the use of standard formworks. Without support, the material shaping relies only on the mechanical properties of the fresh material. Within this frame, the point of this paper is to...
This paper describes an approach of a process-aware exploration of the design space of building components constructed by extrusion of cementitious material (or concrete 3d printing). In an attempt to broaden the geometries that are being printed today, and to build cantilevers, vaults and domes without using temporary support, we look back at cons...
In this work, the influence of diameter of polypropylene (PP) fiber on the spalling of concrete was studied. Concrete prisms of 20 x 20 x 10 cm 3 containing 2 different diameters of fibers (32 and 20 µm) were tested under ISO 834-1 fire curve. In addition to this, tests of residual radial permeability to nitrogen were performed for the same mixes a...
Numerous studies conducted by researchers have indicated a positive effect of polypropylene fibers (PP fibers) in terms of the reduction of concrete spalling due to fire. Variation of test parameters such as concrete composition, curing conditions, heating curve, aggregate nature and size, etc. creates a challenge for identification of optimal fibe...
Production of morphology-controlled cement foams remains challenging, mainly due to bubble stability issues during cement setting. The use of cement paste with high yield stress is expected to promote stability by damping intrinsic bubble kinetics. Here we show however that for given W/C ratio, fresh foam stability can be achieved instead by decrea...
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Digital fabrication techniques with concrete and cementitious materials have seen a large amount of research and industrial activity recently, with industrialization of techniques such as 3D printing becoming more of a reality. The potential to revolutionize construction is real, not only through reducing costs, but also bringing more sustainabilit...
Requirements on material properties for extrusion-based additive manufacturing mostly focus on the rheological behavior of the cementitious material being printed. The layer interface strength is therefore often considered to result from a proper mixing or remixing of two consecutive layers induced by the deposition process itself and therefore fro...
We show that the rheological characteristics of a fresh cement paste can be determined from inclined plane tests. The apparent flow curve measured from inclined plane flows coincides with the apparent rheogram from classical rheometer tests and the flow curve obtained from local Couette flow measurements with magnetic resonance imaging (MRI). In or...
Particle fluid separation is studied in the case of slow squeezing flow of dense clay suspensions. The fluid pressure gradient generated by the test induces heterogeneity in the sample. Experimental water content measurements at different time points through the test allow the quantification of this separation phenomenon. The problem equations are...
In this paper after a presentation of the compression test and its classical references in the rheological literature a behaviour parameter identification method is introduced using simple compression tests on concentrated geo-suspensions with a plastic fluid behaviour. The obtained theoretical test response is validated for several materials (natu...
We prepare and study cement foam samples with well-controlled structure, i.e. containing monodisperse bubbles. We observe that the foam structure often changes before cement setting and identify ripening as the major destabilization mechanism at stake. Drainage plays only a minor role in cement foam destabilization except when bubble size is large....
Production of morphology-controlled cement foams remains challenging, mainly due to bubble stability issues during cement setting. The use of cement paste with high yield stress is expected to promote stability by damping intrinsic bubble kinetics. Here we show however that for given W/C ratio, fresh foam stability can be achieved instead by decrea...
Sulfate ions in seawater or underground can attack the cement paste leading to expansion and strength loss. This expansion is usually related to ettringite and gypsum precipitation. This study aims to characterize the possible altered zone and to identify the mechanisms of degradation under such conditions. For this study, cement pastes
manufacture...
Our results show that the storage elastic modulus as a function of time increases at a higher rate for cement paste mixed at higher vesus lower mixing intensity. Hence, higher mixing appears to be enhancing thixotropy. Using calorimetry analysis we find that higher mixing decreases the setting time and enhances the peak of the heat flow. By analyzi...
In this paper, we compare the drying of non-reactive materials (glass beads packing) with the one of fresh mortars. Through the sample drying process, the existing literature on the general underlying physical processes involved in drying of porous media allows for the identification of two distinct regimes. These regimes drive the drying kinetics....
Polypropylene fibers are accepted in many studies as an effective preventative measure against concrete spalling due to fire exposure. A high dosage of the fibers enhances this effect but reduces the flowability of fresh concrete. Due to a lack of literature, it is hard to identify optimal fiber dosage and geometry. This paper is aimed at understan...
Polypropylene fibers are accepted in the literature as an efficient preventative measure for concrete spalling due to fire. Use of the high dosage of fibers enhances this effect but drastically reduces the workability of concrete. A lack of the literature on the rheological behavior of fresh cementitious materials with flexible fibers prevents from...
Les fibres en polypropylène sont connues pour être une mesure préventive efficace contre l'écaillage du béton dû à l'exposition au feu. Un dosage élevé de fibres renforce cette protection mais réduit la maniabilité du béton frais. En raison d'un manque d'études, il est difficile d'identifier le dosage et la géométrie optimale des fibres. Cet articl...
The advent of digital fabrication for concrete calls for advancing our understanding of the entanglement of processing technology, rheology, admixture use and hydration control, in addition to developing novel measurement and control techniques. We provide an overview of recently proposed building processes, defining the type and range of yield str...
We study in this paper the rheological requirements for printable concrete in terms of yield stress, viscosity, elastic modulus, critical strain, and structuration rate. We first discuss the extrusion/deposition process at the level of the nozzle from a material perspective. We then focus on the rheological requirements needed to prevent the flow o...
In this work, we study the effect of non-adsorbing polymers with molar masses varying over several decades in both dilute and semi-dilute regimes on the yield stress of cement and calcite pastes. In both suspensions, we measure an increase of yield stress, the magnitude of which mainly depends on the polymer concentration regimes. From interparticl...
This work is focused on understanding the origin of the lower robustness detected in self-compacting recycled concretes and on identifying the parameters affecting this property to a greater extent. A reference concrete (0%) and three recycled concretes were studied. The replacement percentages of natural with recycled coarse aggregate were 20, 50...
Assessment of the so-called "saturated-surface-dried" state shows a strong dependency on the test operator in the case of fine porous aggregates. This leads to low reliability and reproducibility of water absorption measurement for this family of particles. Evaporative methods for water absorption measurements seem to be a promising alternative. In...
We focus in this paper on the bleeding of cement pastes. Our experimental results suggest that bleeding cannot be simply considered as the consolidation of a soft porous material but is of an obvious heterogeneous nature. It indeed leads to the formation of preferential water extraction channels. We measure here the existence of an induction period...
Digital fabrication has been termed the “third industrial revolution” in recent years, and promises to revolutionize the construction industry with the potential of freeform architecture, less material waste, reduced construction costs, and increased worker safety. Digital fabrication techniques and cementitious materials have only intersected in a...
Smart Dynamic Casting (SDC) explores the well-known construction method of slip forming, in which concrete is poured into an automated short formwork, which moves at a speed set according to the hardening rate of concrete. Formwork translation speed must stay between two critical boundaries. If it is too high, the column collapses, as the material...
First, we define in this paper two benchmark flows readily usable by anyone calibrating a numerical tool for concrete flow prediction. Such benchmark flows shall allow anyone to check the validity of their computational tools no matter the numerical methods and parameters they choose. Second, we compare numerical predictions of the concrete sample...
From rational and micromechanical arguments on energy levels of particle/particle and particle/ fluid interactions, we first provide here a conceptual diagram of predominant interactions within flowing cement pastes under simple shear in steady state as a function of shear rate and solid volume fraction. We focus then on what is universal and commo...
By going through rational and micro-mechanical arguments on particle/particle and particle/fluid interactions, we first provide here a conceptual diagram of predominant interactions within flowing cement pastes under simple shear in steady state as a function of shear rate and solid volume fraction. Within this frame, we then focus on the last four...
In this work, we measure and compare the rheological behavior of suspensions of limestone calcined clays cement paste and pure Portland cement pastes at the same solid volume fraction. The limestone calcined clays cement pastes are prepared with two different calcined clays. We first focus on the influence of clay particles on the suspensions yield...
9 Geopolymers are inorganic binders obtained by alkali activation of aluminosilicates. While the structure of 10 geopolymers is now well understood, the details of the geopolymerisation reaction and their impact on the rheology 11 of the paste remain uncertain. In this work, we follow the elastic properties of a paste made with metakaolin and 12 so...
Fibers are added to cementitious materials to enhance their mechanical behavior in hardened state. This reinforcement is strongly influenced by the fiber preferred orientation induced by casting flow. In this paper, a model derived from the evolution of a single rigid fiber orientation in a Newtonian medium is proposed to numerically predict fiber...
