Jean-François Caron

École nationale des ponts et chaussées · Navier Laboratory, Architected Materials and Strucures team

Quality control (QC) is a key issue for extrusion-based additive manufacturing of concrete. The timely evolution of the material yield stress, called structuration, plays a key role in the stability of the printed part and its final mechanical performances [1]. With this regard, the authors have previously proposed an affordable and efficient struc...

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...

Geopolymer-based concretes have been elaborated among others for their potential to lower the environmental impact of the construction sector. The rheology and workability of fresh geopolymers make them suitable for new applications such as 3D printing. In this paper, we aim to develop a potassium silicate- and metakaolin-based geopolymer mortar wi...

High packing density is one of the key factors for obtaining ultra-high-performance cementitious materials in the hardened state. Packing density also plays a role in the fresh state, influencing various properties of dense suspensions, including rheological properties and stability, which are highly important in 3d printing applications. The maxim...

Significant developments in 3D concrete have been made over the past few decades. Yet, unreinforced printed components generally do not comply with existing construction standards or regulations and are therefore not used as load-bearing components. There is still a gap between research and use, and despite several proposals, standard commercial so...

The control of mortar rheology is of paramount importance in 3D printing concrete by extrusion. This is particularly sensitive for two-component (2K) processes that use an accelerator to switch the printed mortar very quickly from a liquid behavior to a sufficiently solid behavior to be able to be printed (i.e. structuration). After some main key p...

In recent years, significant progress has been made in modeling various additive manufacturing processes such as Fused Deposition Modeling (FDM) for polymers, Directed Energy Deposition (DED) for metals (including and Wire Arc Additive Manufacturing (WAAM) and Wire Laser Additive Manufacturing (WLAM)), or 3D Printed Concrete (3DPC). However, there...

The control of mortar rheology is of paramount importance in the design of systems and structures in 3D printing concrete by extrusion. This is particularly sensitive for two-component (2K) processes that use an accelerator to switch the printed mortar very quickly from a liquid behavior to a sufficiently solid behavior to be able to be printed. It...

This article investigates the application of a multi-robotic platform to the fabrication of complex “free-form” timber structures. A concept of “smart factory”, with a 13-DOF robotic cell combining robotic mobility with fixed workstations, is proposed. A computational workflow was implemented to allow for fast iterations during the early design sta...

Structures that are 3D printed by an extrusion process have periodic geometrical heterogeneity whose influence on the final stiffness properties is not extensively discussed in the existing literature. The objective of this article is to quantify the effect of local lace geometry on the anisotropy of extrusion-based 3d printed structures. A numeric...

The detection of anomalies is at the basis of any 3D printing control. In this paper, we propose a methodology for detection of anomalies based on computer vision. This methodology is composed of three modules: (1) image acquisition, (2) interlayer line and layer segmentation and (3) characterization of the local geometry and texture of the layers...

Various technologies of in-line reinforcement for extrusion-based 3D printing have been proposed in the recent years. With such techniques, knowledge of the dynamic rheological properties of the extruded material is a key point for several issues, such as its ability to properly impregnate reinforcement, and possibly to pull the reinforcement thank...

The issue of reinforcement for 3D concrete printing has received considerable attention, as constructions have to comply with reliability principles and building standards. Here a specific process called Flow-Based Pultrusion for additive manufacturing (FBP), inspired by pultruded composite manufacturing and built on existing extrusion-based 3D pri...

The adoption of FRP materials for the construction of new bridges has become a challenge to traditional bridge engineers who need to become familiar with the materials itself but also with the code to design efficient FRP structures. Today, there is various available FRP design guidelines all around the world and in Europe, thus, the CEN/TC 250 sho...

This study aims to design a topological interlocking structure which can be constructed without any formwork. According to studies, the cost of material and labour for formworks often consumes up to 50% of the total project cost (Hack et al)[1]. The construction industry, being one of the largest in the world economy with about 10 trillion USD (McK...

This study was undertaken in the context of Cigéo project to investigate the use of geopolymer for potential applications in high level waste cell. The aim was to evaluate the structural evolution of potassium metakaolin based geopolymer as a function of time and temperature for geological nuclear waste disposal applications. The evolution of mecha...

Important developments in additive manufacturing with concrete have been achieved in the past decades. Yet, printed components usually do not comply with building standards or basic reliability principles, and are not commonly used as load-bearing components. A gap between research and practice exists and despite several attempts, off-the-shelf com...

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...

An original experimental setup, dedicated to the measurement of the dynamic response of structures, is presented. Called the Robotized Laser Doppler Vibrometer (RLDV), it consists in the assembly of a fixed point Laser Doppler Vibrometer (LDV) on a 6-axis industrial robot arm. This allows to measure the 3D velocity on the surface of objects with a...

This work aims at proposing a strategy for 3D-printing geopolymer composite structures at a half-meter scale, without using organic additives. An original printing device based on cartridges is developed and adapted to a 6-axis robot. The yield stress, working time and apparent Young modulus of the extruded material are measured. A devoted software...

The vast majority of applications of extrusion-based concrete additive manufacturing deal with unreinforced mortar. The lack of reinforcement is a serious limitation for the industrial development of 3d printed concrete, because of the brittleness and lack of tensile strength of unreinforced mortar. In this paper, a new reinforcement method inspire...

This work aims to synthetize geopolymer composites and study the influence of the aluminum concentration, wollastonite and glass fibers on the properties of the fresh and hardened material. To this end, different metakaolin, wollastonite and glass fibers contents were used to synthesize geopolymer composites. The effect of reinforcement elements on...

This work aims to shape a hollow cylinder with a geopolymer and an additive manufacturing process (3D printing) without organic additives. The formulation of a geopolymer composite using only mineral parts is proposed and the parameters of the 3D printing process were optimized. The mechanical properties, the microstructure, and the adhesion of the...

This work aims to adapt a formulation of a geopolymer composite to elaborate complex shapes. Here a hollow cylinder is chosen to investigate different possible solutions: building process according to the formulation. To this end, different content of metakaolin, wollastonite, and glass fibers was used to identify the feasibility of shaping of the...

The embodied energy of a building is not only but essentially determined by the quantity of material in its structure. Current fabrication techniques of optimised reinforced concrete (RC) structural elements have not proved sufficient economic competitiveness to be broadly accepted by the construction industry. This partly explains why the construc...

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 proposes a specific extrusion method for 3D printing of mortar called free deposition by the authors. It consists in letting a fine mortar flow through a moving nozzle above a support, here EPS foam. The aim is to obtain a regular lace, thus to avoid instability phenomena like coiling, and ensure a regular diameter, without stretching th...

The paper presents new results about the geometry of topological interlocking masonries and some possibilities they present to build without formwork. Construction without the use of formwork may be an important issue concerning both productivity increase and decreasing of waste generated on a construction site. Due to the development of computatio...

For the last decades, new reparation or fabrication processes have been studied to replace traditional rebar by roving of different mineral or organic fibres to avoid corrosion issues. Such materials refer to the family of cementitious composite. Their tensile strength would directly depend on the proportion of reinforcement and strongly on the int...

For the tens past years, important development has been achieved on the adaptation of additive manufacturing to the construction industry using concrete. They mostly concerns control rheology at fresh state, setting time, and technology advances. Nevertheless, the reinforcement of 3D printed part remains an open question. Different reinforcement pr...

The goal of Zero Energy Buildings represents a challenge for designers: in order to meet required performance, a wide range of technologies and solutions is needed, and interactions with other stakeholders can limit productivity of building process. In this context, early-design stage plays a key role in building lifecycle: at this point, choices d...

City revegetation strategies seem appealing to mitigate urban heat island effects through shading and transpirational cooling. Moreover, other potential benefits that may derive, e.g. biodiversity enhancement, the reduction in buildings energy consumption, stormwater management, acoustic insulation or air purification, earned them the designation ‘...

The High Resolution Wavevector Analysis (HRWA) is presented and its application illustrated. Extending the High Resolution Wavenumber Analysis method [1] to 2D signals, it allows the wide-band and local characterization of the linear elastic behavior of anisotropic plates. The method belongs to the family of experimental wavenumber-based characteri...

The aim of this paper is to discuss the dialectic form-finding of a complex timber structure based on an innovative structural system: shell-nexorade hybrids. Nexorades, also known as reciprocal frames are elegant structures that suffer from a relatively poor structural behavior due to in-plane shear and bending of the members. Introducing plates a...

In the framework of sustainable development policies, it is essential that infrastructure owners can rely on effective repair or strengthening solutions, designed and tested in relevance to actual service conditions. In the case of steel structures, fatigue damage is a major concern that can significantly affect the lifespan of the structure, and s...

The High-Resolution Wavenumber Analysis (HRWA) is presented. It identifies complex wavenumbers and amplitudes of waves composing the harmonic response of a beam. Based on the frequency dependence of these wavenumbers, experimental dispersion equations of various beam mechanisms (e.g bending, torsion) can be retrieved. The HRWA method is compared to...

"Metal Euplectella Folie" is a prototype which explores an innovative design and manufacturing method for free-form architecture. Four 40m long by 0.4m wide by 1.5mm thick steel sheets, each cut to a unique pattern and then spiral-wrapped, form a sculptural tube assembled without the need for any adjustment, plans or jigs. This experimental constru...

Navier laboratory, a joint research unit between the Ecole des Ponts ParisTech, IFSTTAR, and CNRS, gathers about 50 permanent scientists, 120 Ph.D.’s and general skills in the mechanics and physics of materials and structures, in geotechnics, and their applications to, in particular, civil engineering and petroleum geophysics. For last 15 years, Na...

This study focuses on deployable systems actuated by shape memory alloys in the perspective of designing adaptive sun shading devices for building facades. We first set the context of smart materials for adaptive facades and underline the remarkable characteristics of shape memory alloys for mechanical actuation purposes. After outlining the constr...

Adhesive joints are increasingly used in bridges and buildings construction thanks to their high mechanical properties and their ease of implementation. However, the load transfer mechanism within adhesive joints is complex and has been the subject of several studies since 1938. Several models have been developed to quantify the stress distribution...

In the framework of sustainable development policies, it is essential that infrastructure owners can rely on effective repair or strengthening solutions, designed and tested in relevance to actual service conditions. In the case of steel structures, fatigue damage is a major concern that can significantly affect the lifespan of the structure, and s...

p>By reinforcing the links between mechanics of materials, structural engineering and applied mathematics at a sufficiently high level, new paths may be explored and building innovations proposed, making complex structures more affordable constructions. Three main keys are explained and illustrated with examples. The first key is a deep knowledge o...

p>“Metal Euplectella Folie” is a prototype which explores an innovative design and manufacturing method for free-form architecture. Four 40m long by 0.4m wide by 1.5mm thick steel sheets, each cut to a unique pattern and then spiral-wrapped, form a sculptural tube assembled without the need for any adjustment, plans or jigs. This experimental cons...

In this paper phenomenological observations of the creep rupture under maintained combined traction and torsion loading are first presented. They show the importance of the matrix's behavior in the long-term durability of the material. Understanding and foreseeing creep rupture of unidirectional fiber reinforced polymers (UD FRP) involves comprehen...

This study gives a detailed analysis on estimating the ultimate tensile strength of unidirectional fiber reinforced composites and its creep behavior under sustained tension load. We develop two different micromechanical models that allow us to estimate the longitudinal tensile strength and the evolution with time of fiber and matrix stresses aroun...

Gridshells are lightweight structures made of interconnected slender beams. Due to large displacements, high interaction between the beams, and bending–torsion coupling, modeling gridshells requires specific non-linear numerical tools to reach convergence within a reasonable time. In this article, the development of such a tool is presented. It is...

The aim of this paper is to present some innovative strategies for the design of plated shell structures. Fabrication constraints are carefully considered, as the obtained shapes are covered with planar quadrilateral facets only. Different corrugation strategies are investigated, and our method guarantees extension of the shape generation to comple...

This paper proposes a new layerwise model for multilayered plates. The model, called SCLS1 for Statically Compatible Layerwise Stresses with first-order membrane stress approximations per layer in thickness direction, complies exactly with the 3D equilibrium equations and with the free-edge boundary conditions. As in the LS1 model initially propose...

The Ephemeral Cathedral of Créteil at Paris, France, is a gridshell structure made of composite materials. Built in 2013, this 350 m2 religious edifice is a temporary church meant to gather the parishioners during the two year renovation of their permanent cathedral. This large-scale prototype represents a first in the building industry which still...

Over the last twenty years, many innovative solutions have confirmed the usefulness of composite structures realized with FRPs (Fibre Reinforced Polymer or Plastic). The need of European standards for use of fibre reinforced polymer composites in civil engineering was justified in 2007 in the JRC Report EUR 22864 EN. The new European technical rule...