Rob Wolfs

• PhD
• Professor (Assistant) at Eindhoven University of Technology

Additive manufacturing is gaining ground in the construction industry. The potential to improve on current construction methods is significant. One of such methods being explored currently, both in academia and in construction practice, is the additive manufacturing of concrete (AMoC). Albeit a steadily growing number of researchers and private ent...

A numerical model was developed to analyse the mechanical behaviour of fresh, 3D printed concrete, in the range of 0 to 90 min after material deposition. The model was based on a time-dependent Mohr-Coulomb failure criterion and linear stress-strain behaviour up to failure. An experimental program, consisting of unconfined uniaxial compression test...

The technology of 3D Concrete Printing (3DCP) has progressed rapidly over the last years. With the aim to realize both buildings and civil works, the need for reliable mechanical properties of printed concrete grows. As a consequence of the additive manufacturing technique, 3D printed structures may consist of several layers that should exhibit bon...

In 3D concrete printing processes, two competing modes of failure are distinguished: material failure by plastic yielding, and elastic buckling failure through local or global instability. Structural analysis may be performed to assess if, and how, an object may fail during printing. This requires input in the form of transient material properties...

This contribution studies failure by elastic buckling and plastic collapse of wall structures during extrusion-based 3D printing processes. Results obtained from the parametric 3D printing model recently developed by Suiker (Int J Mech Sci, 137: 145–170, 2018), among which closed-form expressions useful for engineering practice, are validated again...

The technology of 3D concrete printing has seen a rapid growth in industrial applications and academic activities over the past decade. 3D Printing is being advertised to address the urgent sustainability and productivity challenges in the field of construction, by reducing the total amount of concrete in buildings or structures, and by producing t...

Existing databases containing measurements of crack width and spacing are usually limited in size and based on isolated experimental studies. These databases are used to develop new formulas to describe crack patterns in concrete structures. A database obtained from multiple sources of experimental programmes is required to quantify the accuracy of...

The quality control of digital fabrication with concrete has more stringent requirements than traditional casting. Firstly, since formwork is typically absent, or removed at an early stage in production, the material is exposed to external influences that can result in deformations, collapse, or deterioration. Therefore, the evolution of properties...

Over the last century, over one hundred crack width formulas have been developed to calculate the width and spacing of cracks in reinforced and pre-stressed concrete elements. It is unclear which formulas are the most accurate. An extensive comparison study is required to determine which formulas accurately describe the crack patterns, consisting o...

An accurate calculation of steel stresses is essential for assessing reinforced concrete structures’ serviceability limit state, e.g., assessing crack widths. The steel stresses in elements loaded in bending are not known but are estimated by steel stress calculations. To get a more accurate crack width prediction, the calculated steel stress shoul...

Crack width formulations, such as the one described in Eurocode 2, present a single value to describe the crack width in reinforced concrete structures, but provide limited insight into the uncertainty of the description of crack widths. This paper describes how the uncertainty in the descriptions of these crack widths can be calculated by construc...

Extrusion-based 3D Concrete Printing (3DCP) is rapidly gaining popularity in the construction industry. Trial projects are now being realized at an increasing rate around the world to test the viability of the technology against real-world requirements. This step, from the ‘simple’ deposition of filaments of self-stable concrete to its application...

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...

In this work, a framework for large-scale structural applications of 3D printed concrete is presented. The steps in this framework, consisting of a design phase, testing phase and manufactur-ing phase, towards a final output were presented and discussed theoretically. The framework was then applied to the case of a 29 m 3D printed bridge, construct...

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 formation of droplets near the nozzle exit gives information about the production process and extruded material properties, which can be used for quality control, and process and material optimization. Mass and length of these droplets, or “slugs”, have been measured in previous studies [1, 2]. In this study, the experiment is expanded by inclu...

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...

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,...

This article offers a comprehensive, systematic overview of the existing solutions for integrating reinforcement in digital concrete technologies with particular emphasis on Additive Manufacturing (AM) with concrete, also called 3D concrete printing (3DCP). While the functionalities of various types of reinforcement are briefly addressed, the major...

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...

This contribution studies failure by elastic buckling and plastic collapse during 3D concrete printing of wall structures. Four types of experiments were performed, which demonstrate the circumstances under which elastic buckling and plastic collapse occur, the effect of geometrical imperfections on the buckling response, the influence by the curin...

3D Concrete Printing (3DCP) is being used for off-site manufacture of many elements found in the built environment, ranging from furniture to bridges. The advantage of these methods is the value added through greater geometrical freedom because a mould is not needed to create the form. In recent years, research has focused on material properties bo...

This book gathers peer-reviewed contributions presented at the 2nd RILEM International Conference on Concrete and Digital Fabrication (Digital Concrete), held online and hosted by the Eindhoven University of Technology, the Netherlands from 6-9 July 2020. Focusing on additive and automated manufacturing technologies for the fabrication of cementiti...

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...

Due to the lack of formwork, a key issue in the novel technology of filament-based 3D concrete printing (3DCP) is the ‘buildability’: the capacity of the deposited dormant material to support itself during the print process. Since the strength and stiffness development of fresh concrete is determined by chemical and physical processes, it may be ex...

Case study projects based on Digitally Fabricated Concrete (DFC) are presented in an increasing pace around the globe. Generally, though, it is not reported what structural requirements (if any) these structures meet and how compliance to these requirements was established. Published material research is often not connected to the presented case st...

One of the geometrical restrictions associated with printed paste materials such as concrete, is that material must be self-supporting during printing. In this research paper a new methodology for 3D Printing Concrete onto a temporary freeform surface is presented. This is achieved by setting up a workflow for combining a Flexible Mould developed a...

3D printing of concrete and related digital fabrication techniques are enjoying rapid growth. For these technologies to be broadly accepted in structural applications and to be economically competitive, quality control methods of the process will be required. Additive concrete manufacturing processes are sensitive to process settings and conditions...

Recent years have seen a rapid growth of additive manufacturing methods for concrete construction. A recurring issue associated with these methods, however, is the lack of ductility in the resulting product. In cases this is solved by combining printing with conventional casting and reinforcing techniques. Alternatively, this paper presents first f...

Recent years have seen a rapid growth of additive manufacturing methods for concrete construction. Generally, these methods are based on a linear sequence of design → print path definition → actual printer actions in a print environment. However, printing experiments show that a large number of parameters influence the printing process. Not all of...

The magnetic orientation of steel fibres in transparent silicone oil and in fresh, self-compacting concrete (SCC) beams is studied experimentally. The effect of the generated fibre locations and orientations on the failure response of the SCC beams is determined by means of three-point bend tests. A relatively small coil was designed for the magnet...

The effect of scale on different parameters of the 3D printing of concrete is explored through the design and fabrication of a 3D concrete printed pavilion. This study shows a significant gap exists between what can be generated through computer aided design (CAD) and subsequent computer aided manufacturing (generally based on CNC technology). In r...

Robotically Driven Construction of Buildings (RDCB) is an exploration into design to production solutions for robotically driven construction of buildings initiated by the faculties of Civil Engineering and Architecture, TU Delft and Architecture, TU Eindhoven and implemented 2014 within the 3TU Lighthouse framework. The aim of was to involve the d...

Robotically Driven Construction of Buildings (RDCB) is an exploration into design to production solutions for robotically driven construction of buildings initiated by the faculties of Civil Engineering and Architecture, TU Delft and Architecture, TU Eindhoven and implemented 2014 within the 3TU Lighthouse framework. The aim of was to involve the d...