Robots Optimize Sustainable Concrete Prefabrication

By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Sep 18 2024

A recent article presented at the Digital Concrete 2024 conference introduced a novel automated design and production method aimed at enhancing resource efficiency in concrete prefabrication. The design utilizes automated topology optimization, supported by a strut-and-tie model, while the production process involves a modular assembly of robotic production islands.

Background

Reinforced concrete is the most widely used building material globally due to its excellent mechanical properties, ease of processing, and low cost. However, cement, a key component of concrete, contributes to over 4 % of global anthropogenic CO₂ emissions during its production.

It is important to note that the concrete itself is not inherently problematic. Lifecycle assessments indicate that concrete is the most ecological option for load-bearing applications. The real issue lies in its large-scale consumption, particularly in industrialized nations where labor costs are prioritized over material use. As a result, oversized designs that save time are favored over labor-intensive, custom designs optimized for structural performance.

To minimize the environmental footprint of concrete, it is essential to consider the entire life cycle—from design and production to end-of-life scenarios, with an emphasis on reuse—instead of focusing on individual sub-processes. This study, therefore, proposes a redesign of the prefabrication industry, leveraging automated and optimized precast construction within the framework of a circular economy.

Methods

This research focused on three main aspects: architectural design, automated optimization and structural dimensioning, and robot-assisted production.

A case study was conducted to assess the environmental potential of reusing precast concrete elements (Variant 3) compared to new constructions (Variant 1) and those made with 100% recycled aggregates (Variant 2). The analysis considered various phases, including manufacturing, transport and installation, and end-of-life.

The design process employed automated structural optimization using a strut-and-tie model, aiming to minimize material use by eliminating non-load-bearing elements, thus improving ecological efficiency. Importantly, the optimization was closely tied to the production process, ensuring that the designs could be seamlessly manufactured using automated production islands with a newly developed reusable shuttering system.

Production was centered around modular assembly, achieved through robot-assisted production islands that could be used individually or in groups, either offsite or on-site. To further enhance sustainability and efficiency, a reusable shuttering system was introduced, offering flexibility in producing various void shapes for beams and slabs.

The shuttering system consisted of multiple elements, or a "shuttering kit," designed to create different shapes. These elements were positioned on a shuttering table by a six-axis robot through a pick-and-place process and secured with magnets. The geometric alignment and magnetic attachments provided stability while offering the flexibility needed to handle varying curing loads.

Results and Discussion

The architectural design study revealed that using recycled aggregates (Variant 2) had a relatively minor impact on concrete's global warming potential (GWP), as cement remained the main contributor. In contrast, reusing building components allowed for up to a 75 % reduction in GWP. As a result, the proposed design focused on reusing entire building elements, incorporating a modular node design with steel connections.

The newly developed shuttering system demonstrated greater flexibility in shaping concrete compared to state-of-the-art formwork. Early prototypes were tested for their feasibility, compatibility with a six-axis robot, and precision throughout the production process, including concrete placement, casting, vibration, and de-shuttering. The system also offered enhanced geometric freedom in creating void shapes and sizes, although some boundary conditions were necessary to maintain structured void designs.

Unlike conventional conveyor or carousel production lines, the modular, robot-assisted production islands allowed for the simultaneous processing of complex, individualized components, resulting in greater overall efficiency. These islands could independently handle all production steps for precast elements, such as formwork and reinforcement placement, concreting, vibration, and de-shuttering.

The researchers suggest that increasing the number of production islands could further enhance efficiency, contributing to the construction industry’s shift toward Industry 4.0. Additionally, the islands can be integrated into existing workflows at manufacturing plants, enabling a gradual and seamless transition to more advanced production methods.

Conclusion

In conclusion, the researchers presented a comprehensive strategy for transforming the prefabrication industry through automated and optimized precast construction within the framework of a circular economy. By showcasing preliminary findings and prototypes, they highlighted the potential for more efficient and sustainable practices.

The proposed approach addressed the entire life cycle of construction, from architectural design based on segmentation and modularization, to structural optimization and robot-assisted manufacturing, all while promoting the reuse of building elements. Central to this strategy is the automated shuttering system, which is adaptable to different concrete mixtures and materials. Combined with a modular component kit, this system offers a higher-value circular economy by facilitating the reuse of building components, contributing to a more sustainable future for the construction industry.

Journal Reference

Kromoser, B., Gappmaier, P., Ahmed, I., & Reichenbach, S (2024). A new approach for automated design and robot-assisted production of structurally optimised reusable concrete building elements. Digital Concrete 2024, Munich, Germany. DOI: 10.24355/dbbs.084-202408141320-0, https://www.researchgate.net/publication/383871569

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