This technical session is co-organized by ACI 564, ACI 236, and RILEM to disseminate information on scaling up of concrete 3D printing, with an emphasis on knowledge gained by the international community (in Europe, Asia etc. where concrete 3D printing is becoming more ubiquitous). These sessions are intended to: (i) disseminate the most recent information on scaling up of concrete 3D printing for different structural applications, and (ii) outline the challenges faced in printing real-world elements related to materials, printing system, architectural and design, structural testing, code compliance etc., and methodologies adopted to overcome those challenges. These sessions will incorporate international speakers who are at the cutting edge of research and development in concrete 3D printing, as well as practitioners who have implemented such structures in real world. The session is intended for professionals, students, and practicing engineers/architects.
Learning Objectives:
(1) Understand issues that are bottlenecks for scaling up 3D printing;
(2) Explore bioinspired design and applications for 3D printing;
(3) Introduce numerical modeling aspects related to scaled up 3D printing;
(4) Introduce special structural systems enabled by 3D printing.
Robustness of Digital Concrete, A Bottleneck for Scale-Up
Presented By: Matineh Mahmoudi
Affiliation:
Description: Automation has become an inevitable aspect of almost every industrial sector during the past decades. However, the construction sector is still mainly relying on skilled labor for the process. Considering the enormity of this sector, there is an insistent demand for automation in construction. This is why digital fabrication of concrete has been attracting researchers and industrial parties for more investigation and investment. Digital fabrication is also promising for improving the sustainability of the sector by means of design optimization and material consumption reduction. There has been great progress in this field of science in the past few years, however, the method does not constitute a major part of the sector. This is because of the scientific limitations towards scaling up the method. One of the important deficiencies of the digital concrete technology today is the robustness issue of it. The behavior of the material which must satisfy numerous limiting factors is in turn greatly sensitive to possible variations. The variations include variations in the type and dosage of the incoming material and/or environmental conditions such as temperature variations. In this work we examine some of these critical aspects in digital concrete for a 2-component (2K) rapid vertical buildrate system.
3D Printing of Concrete with Bioinspired Design: A Study on Impact Resistance
Presented By: Yu Wang
Affiliation: Purdue University - West Lafayette
Description: Concrete is widely utilized as a construction material, often in combination with steel reinforcing rebars and/or prestressing strands. These reinforcements play a pivotal role in enhancing the tensile and shear resistance capacity of concrete when exposed to quasi-static loading conditions. However, certain civil structures, such as bridge substructures, roadside barriers, or airport runways, regularly encounter extreme loading conditions, such as impacts or explosions from diverse sources. While ordinary concrete structures exhibit success under static conditions, studies have revealed their insufficiency under extreme loads due to the limited energy absorption capacity. Potential solutions to address this challenge lie in leveraging concrete 3D printing technology and integrating inventive design principles inspired by naturally occurring impact-resistant materials. Nature offers numerous examples of organisms and structures that exhibit exceptional resilience to impact forces (e.g. helicoidal, honeycomb, and lattice structures observed in such organisms as mantis shrimp, nacre, horseshoe, etc). The emergence of concrete 3D printing technology provides a cutting-edge approach to customizing structures with these intricate bio-inspired internal architectures. This presentation will cover the approach to developing bio-inspired architectures in 3D-printed concrete. The mechanical evaluation of 3D-printed concrete with selected bio-inspired architectures under impact load conditions will be discussed.
X-Ray Tomography and Impedance Spectroscopy to Elucidate Anisotropy in 3D Printed Concrete
Presented By: Sahil Surehali
Affiliation: Arizona State University
Description: Extrusion-based 3D concrete printing (3DCP), in which printable cementitious materials are deposited as a continuous filament from a nozzle in a layer-wise manner, results in two different interfaces – the interfilament interface between the adjacent layers and the interlayer interface between the layers printed on the top. The printing parameters, including the layer height, width, and print velocity, dictate the number and quality of interfaces, rendering direction dependence on the mechanical and transport properties in 3D printed elements. In addition to interface quality and numbers, microstructure in the interfacial regions, including porosity content and pore morphology, present a physical basis for the anisotropic behavior. This work focuses on the impact of layer heights (6, 13, and 20 mm), test directions (along the direction of printing, along the direction of layer build-up, and in the direction perpendicular to the above two directions), and fiber-reinforcements on the compressive strengths and non-steady state chloride migration coefficients of 3D printed concretes. Interface-parallel cracking is found to be the primary failure mechanism under compression loading. The inter-filament interfaces are shown to be more detrimental from an ionic transport standpoint. A thorough investigation of the porosity parameters in the bulk and interface regions via mercury intrusion porosimetry and X-ray computed tomography, respectively, compiled with electrical impedance spectroscopy, indicates higher porosity at interfacial regions. Overall, the work provides guidelines on furthering the use of 3D-printed concrete elements via simple process changes (choosing appropriate layer height and print direction or appropriately orienting weaker interfaces) and material modifications (such as fiber reinforcement) for desired end applications.
Numerical Simulation of Flow, Setting, and Hardening of 3D Printed Concrete
Presented By: Gianluca Cusatis
Affiliation: Northwestern University
Description: : 3D printed concrete as an innovative construction technology has been increasingly used for intricate and customized structural designs. This requires an improved comprehension of the material properties' transition from the flow stage to solidification in concrete. The primary objective of this study is to simulate the various phases of 3D-printed concrete, including the flow, setting, and hardening stages, and validate the modeling method. The fresh concrete was simulated using smoothed particle hydrodynamics (SPH) coupled with the discrete element method (DEM). DEM was employed to represent the aggregate, capturing the movements of discrete particles, while the SPH was utilized to simulate the cement paste, modeling the continuous property of the concrete mixture. After the concrete setting, the lattice discrete particle model (LDPM) was used to model the failure behavior of concrete at the meso-scale. The concrete setting process, which depicts the transition of concrete from a viscous fluid to a solid state, was also simulated. The evolution of material properties during the concrete setting was provided by experimental tests. The entire simulation was performed in Project Chrono which is an open-source multi-physics engine. The simulation was validated by comparing the numerical results with the experimental data of real 3D printed concrete.
Portside Large Scale Additive Manufacturing of Floating Off-Shore Wind Turbine Foundations Using Ultra-High Performance Concrete
Presented By: Mohammed Alnaggar
Affiliation: Oak Ridge National Laboratory
Description: Floating Off-shore Wind Turbine Foundations (FOWTFs) are very large structures that have been dominated by steel as their manufacturing material of choice given the large heavy steel manufacturing infrastructure in Europe and the traditional use of floating steel hulls in the oil and gas industry. Such infrastructure does not exist in USA and many other parts of the world, thus, innovative FOWTFs alternative designs are needed to achieve the government ambitious goals regarding renewable energy production from wind resources. Since 2013, the scaled concrete VolturnUS FOWTF has held the world record of being the first scaled FOWTF to be tested in real marine operational environments. With rapidly growing wind turbine capacities expected to pass 20 MW, the need to develop larger FOWTFs becomes even more demanding. This presentation will illustrate the ongoing research work on enabling the rapid 3D printing of FOWTFs using Ultra-High Performance Concrete at the portside. Our work encompasses the development of a second generation VolturnUS-3D FOWTF that can support 20 MW and larger wind turbines while being cost-effective and rapidly printable. This research combines advanced and scalable 3D printing techniques using novel UHPC delivery and extrusion systems as well as topology optimization of the FOWTF design to take advantage of 3D printing.
Additive Construction Program at US Army Corps of Engineers
Presented By: Eric Kreiger
Affiliation: U.S. Army Engineer Research and Development Center
Description: USACE ERDC’s Additive Construction program began in 2015 to determine the feasibility of placing concrete by adapting Additive Manufacturing technology for military construction. The program started with the premise that the equipment needed to be used in the field with easy to replace parts that would not be inhibited by dirty/wet environments and could use locally available materials. The first stage began by developing a simple lab based machine that was used to evaluate the equipment limits and a material design of a concrete mix with 3/8” nominal aggregate size. The program continued to evolve through various iterations to utilize a system that could place material using a 20 ft wide x 40 ft long x 10 ft height gantry style robot and developed material design and evaluation methods. Through this work several structures were constructed, including the first building in the US, the first bridge in the US, and several full scale test structures. Using these systems ERDC has trained military personnel to independently operate a deployable system that fits in a 20’ shipping container during demonstrations in Illinois, Missouri, California, Guam, and Indiana.