Curved concrete shells with automatic spraying

Curved concrete shells with automatic spraying

In a recent article published in the magazine additive manufacturingIn this article, the researchers discussed the utility of automated concrete spraying in the digital fabrication of ribbed concrete shells.

Stady: Digital fabrication of ribbed concrete shells using automated concrete spraying. Image credit: muratart / Shutterstock.com

background

Concrete stands out among other frequently used building materials due to its adaptability. Designers can produce highly efficient designs that reduce overall material costs and associated carbon emissions by taking advantage of the fluidity of the material. Thin-shell concrete structure is one such design that has been widely used to extend to large areas.

Engineers and architects devised techniques to make concrete formwork more straightforward after realizing the difficulties in producing curved concrete forms. However, the use of thin-shell concrete structures subsequently declined as labor prices rose globally. Thin-shell concrete structures have recently attracted renewed interest, in part due to the model’s ability to save on materials.

It has taken a lot of effort to evaluate the capabilities of thin-crust concrete structures. However, the process of building these thin concrete floors still required a lot of manual labor. Curved polygon shells are not compatible with this technology, although 3D printing of concrete may produce precise geometric shapes. As an alternative to 3D printing of concrete, several attempts have been made to combine shotcrete with automated assembly.

Automated spraying of concrete has been used extensively to produce delicate architectural features. To assess the possibility of automated spraying of concrete to create curved load-bearing structural parts, further research is needed. Various difficulties exist in creating ribbed concrete shells for structural application. Variable thickness distribution is required to optimize material placement. Finally, to scale up the manufacturing process for industrial application in a precast manufacturing facility, a high turnover rate and fast manufacturing speed are required.

About the study

In this study, the authors discuss an innovative fabrication technique known as Automated Spraying Concrete (ARCS), which uses glass fiber reinforced concrete (GFRC) to build thin components with a range of thicknesses by spraying them onto a curved mould. To build the components, the path layout and generation method created and implemented in ARCS are described.

A larger structural demonstration of the floor was created consisting of two sets of projectile prototypes, and another set was made of one component with deep ribs on a thin shell. Each prototype used two distinct methods for adding the ribs to the manufactured shells, with the sequence used to create the spray paths for each component. While the pin mold powering the flexible molds was used in conjunction with the fabrication process to build the spray deck, the path layout approach was flexible enough to work with any die casting.

The team concluded that concrete shells of variable thickness with distinct ribs could be rapidly produced by spraying GFRC on a curved base. The GFRC mix design was initially introduced to better contextualize the generation of the spray path. The proposed ARCS algorithm for automated code generation for the fabrication of concrete shells of various thicknesses is described in detail.

The researchers created two sets of prototypes using the ARCS process. The first was a 1.5m by 1.2m ribbed shell with highly prominent ribs and the second was a nine-part shell that served as the structural floor for a demonstration measuring 4.5m by 4.5m. The fabrication process for each prototype was described in detail, and the thickness distributions achieved were examined. The results showed that ARCS provided a method for accurate and rapid fabrication of concrete veneers with variable thickness ribs.

Notes

With a normalized variance of 0.0224 and a standard deviation of 0.472, the intended thicknesses were frequently interpolated. The manufacturing method successfully produced each piece of the intended thickness, with a mean standard variance of 0.195 and standard deviation of 0.202. The sections would not fit together due to problems with the tolerances of the timber frame, which resulted in variances of about 10mm in each section with an error rate of about 0.5%. The mixture was less dense than typical concrete and had a nominal density of 2000 kg/m3 As a result of the absence of coarse aggregate.

The HAL Robotics Framework and the built-in Grasshopper3D plug-in can be used to generate automated code that can accurately deposit GFRC into concrete formwork surfaces. Although only one physical fabrication setup was used in conjunction with the design process, it was broad enough to be applied to any automated assembly system connected to a concrete sprayer. The numerical control of the robot can be combined with the slurry output rate, calibration and air supply of the concrete sprayer to increase the repeatability, flexibility and accuracy of the manufacturing process. Compared with conventional concrete mixes, the higher cement content in the mortar resulted in a higher carbon value per weight of the material.

Conclusions

In conclusion, this study described two sets of prototypes manufactured from ARCS. Both models demonstrated the adaptability of the process and the increased production efficiency provided by automated concrete spraying. Geodesics as remote functions have been used to establish fixed distance boundaries on a surface in the new path planning and stacking approach proposed in ARCS.

The authors stated that it would be beneficial to use a gantry-mounted robotic arm in an off-site manufacturing facility, which would reduce size and reach the limitations imposed by a six-axis floor-mounted robot. They also stated that ARCS could make it possible to produce expressive, structurally and physically efficient ribbed concrete shells at an industrial pace, regardless of the mix design used.

The team believes the proposed study will make it easier to create resource- and carbon-efficient concrete structures.

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references

Noh, M, Oval, R, Orr, G, et al. Digital fabrication of ribbed concrete shells using automated concrete spraying. additive manufacturing, 103159 (2022). https://www.sciencedirect.com/science/article/pii/S2214860422005486

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