Robotic Path Planning for Concrete Printing

Three-dimensional concrete printing (3DCP) is an innovative digital fabrication and automation technique based on additive manufacturing that enables the creation of complex and customized structures in the architecture and construction industry. Its most notable advantages include eliminating formwork costs and labor (Buswell et al., 2020; Lyu et al., 2021; Kaliyavaradhan et al., 2022) and facilitating the fabrication of structural elements with complex curvatures, particularly in printing systems utilizing industrial robotic arms (Alabbasi et al., 2023; De Soto et al., 2018). In addition, it offers significant potential for reducing material waste, shortening construction time, and establishing a workflow integrated with digital design. Furthermore, life cycle assessment (LCA) studies demonstrate that 3DCP can reduce environmental impacts such as Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP), Water Depletion (SFP), and Fossil Fuel Depletion (FFD) (Mohammad et al., 2020). One of the earliest studies in 3DCP research literature is an undergraduate project conducted by Pegna (1997) at Rensselaer Polytechnic Institute. In parallel with academic studies, experimental construction applications over the past two decades have introduced pioneering examples. Although discrepancies exist among sources reviewing the history of this field, some of the frequently cited pioneering patents and construction companies are summarized below:

Contour Crafting: A 3DCP patent reported to have been developed by Behrokh Khoshnevis at the University of Southern California in 1998 (Khoshnevis, 2001; Khoshnevis and Dutton, 1998). This method enables the construction of structures through layer-by-layer deposition of concrete using a 3D printer-like device (Buswell et al., 2022; Mohammad et al., 2020; Habibi et al., 2024; Paul et al., 2018; Labonnote et al., 2016; Lyu et al., 2021; Tu et al., 2023). In this technique, smooth surfaces are achieved through trowel-like surfaces integrated into the printhead.

D-Shape (Monolite): One of the earliest 3DCP technologies, reported to have been developed by Enrico Dini in 2005. This method enables the construction of concrete structures using large-scale printers. D-Shape involves depositing layers of a specialized concrete mixture containing sand, water, and binder materials through a nozzle onto a surface, followed by spraying a liquid binder to solidify each layer (Buswell et al., 2020, 2022; Alabbasi et al., 2023; Forcael et al., 2023; Labonnote et al., 2016; Tu et al., 2023).

WinSun: A construction company based in China reported to build large-scale 3DCP buildings. It primarily produces prefabricated concrete structures and residential units (Ramakrishnan et al., 2021; Balázs and Thajeel, 2024; Cabibihan et al., 2023; Li et al., 2023; Tu et al., 2023). Scientific publications regarding the proprietary technology remain limited. The company is reported to have been constructing buildings using 3DCP since 2014.

Apis Cor: Among the companies constructing both small- and large-scale structures using 3DCP (Tu et al., 2023; Duarte et al., 2024; De Soto et al., 2018; Cabibihan et al., 2023; Batikha et al., 2022; Ramakrishnan et al., 2021). Its most prominent feature is a mobile printer capable of constructing a residential unit in less than 24 hours.

HuaShang Tengda: A Chinese company constructing structures using 3DCP. In 2015, it reported the completion of a two-story, 400-square-meter building within 45 days (Buswell et al., 2022; Placzek and Schwerdtner, 2024; Batikha et al., 2022).

Tecla: A 3DCP residential project developed in 2019 by Mario Cucinella Architects and WASP (World’s Advanced Saving Project) (Alami et al., 2023; Duarte et al., 2024). The material utilized in this project is a clay-based natural mixture.

Additionally, various companies worldwide—such as Peri 3D (Germany), ICON (USA), and XtreeE (France)—are executing construction projects utilizing 3DCP technology (Placzek and Schwerdtner, 2024). In Turkey, research and implementations in this field are ongoing across several universities and institutions such as İSTON.

When additive construction techniques, which encompass 3DCP, are classified, five primary systems emerge: gantry (crane) systems (Heras Murcia et al., 2020; Lin et al., 2022; Zhang and Sanjayan, 2024; Marais et al., 2021; Wang et al., 2020; Dey et al., 2023), cable-suspended systems, swarm systems, robotic arm systems (De Soto et al., 2018; Balázs and Thajeel, 2024; Farahbakhsh et al., 2022; Xu et al., 2022; Alabbasi et al., 2023; Forcael et al., 2023; Duarte et al., 2024; Dielemans et al., 2021; Huang et al., 2023; Xu et al., 2020; Põldaru et al., 2023), and combined folding systems. Systems other than gantry and robotic arms remain largely experimental. For instance, an early example of cable-suspended printing systems is the C4 system developed by Bosscher et al. (2007). Aside from these experimental setups, the majority of research focuses on adapting conventional industrial robot systems to 3DCP. In terms of material deposition methods, extrusion, spraying (Dörrie et al., 2023), and particle bed (Placzek and Schwerdtner, 2024) techniques represent the most prevalent approaches.

Studies comparing 3DCP with conventional construction methods suggest substantial time and cost advantages in the structural shell construction phase, particularly for structures with complex geometries (Xu et al., 2022; De Soto et al., 2018; Buswell et al., 2020; Batikha et al., 2022; Forcael et al., 2023). In a comparative study evaluating cast steel, forged steel, reinforced concrete, 3DCP, and precast concrete construction methods, Batikha et al. (2022) argue that 3DCP ranks second in terms of duration, yet represents the most economical method when time and cost are evaluated together. The same study also indicates that 3DCP delivers the best results in terms of CO2 emissions. Investigating the impact of construction scale, Forcael et al. (2023) demonstrated that robotic-arm 3DCP is 45% faster than conventional formwork methods for small-scale construction; however, as the construction scale expands, this ratio shifts in favor of traditional methods, requiring an increase in the number of robotic arms (and associated capital cost) to maintain the time advantage.

On the other hand, despite these potential advantages, high material and equipment costs (Alami et al., 2023; Batikha et al., 2022), the requirement for specialized expertise, technical challenges hindering process standardization (ambient conditions, humidity, curing duration, chemical admixtures), potential social impacts (displacement of manual construction labor, environmental effects of certain specialized materials), and the lack of established building codes and regulatory standards (Alami et al., 2023; Alabbasi et al., 2023) negatively affect the feasibility of 3DCP and hinder its widespread adoption.

The concrete printing experiments we conduct with Assoc. Prof. Dr. Büşra Aktürk in the Department of Civil Engineering at Istanbul Bilgi University are small-scale and material science-oriented. I developed the Grasshopper Kuka-PRC code shown below for this purpose. To achieve low-cost and rapid printing without an extruder, we utilize a battery-powered caulking gun, which I observed in 2023 at the Delft University of Technology Laboratory. These guns can dispense material with a volume of 600 ml at variable speeds and allow nozzle replacement. In our experiments, we use two types of nozzle tips: circular and rectangular profiles. I have also attached the model files of these tips, which I produced with PETG on my 3D printer. The dispensing gun used in the printing process is mounted to a Kuka KR-20 robotic arm via a custom wooden housing. The Grasshopper script is capable of printing beam or cylinder specimens of specified dimensions at adjustable speeds and layer heights. We have executed numerous print runs using this code, which continues to be utilized across various publications and research projects. The latest version is shared below, illustrating the toolpath strategy and the optimal angle of approach that allows the robot to support the gun without inducing vibrations.

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