Robot-assembled building blocks may be a more environmentally cordial method of building large-scale structures than some existing construction techniques, according to a fresh study by MIT researchers.
The team conducted a feasibility study to evaluate the effectiveness of constructing a plain building using “voxels,” which are modular 3D subunits that can be assembled into convoluted, tough structures.
After examining how multiple voxels work, scientists have developed three fresh designs to improve building design. They also created a robotic assembler and a user-friendly interface for generating voxel-based building plans and instructing the robots.
Their results indicate that this voxel-based robotic assembly system can reduce carbon content – all the carbon emitted over the life cycle of building materials – by as much as 82 percent compared to popular techniques such as 3D concrete printing, modular precast concrete and steel frames. The system would also be competitive in terms of costs and construction time. However, the choice of materials used to produce voxels plays a major role in their carbon footprint and costs.
While scalability, durability, long-term reliability and essential issues such as fire resistance still need to be investigated before such a system can be widely deployed, the researchers say these preliminary results highlight the potential of this approach for automated on-site construction.
“I’m particularly excited about how robotic assembly of discrete meshes can practically apply digital manufacturing to the built environment in a way that will allow us to build much more efficiently and sustainably,” says Miana Smith, a graduate student at MIT’s Center for Bits and Atoms (CBA) and lead author of the study.
She is joined in this article by Paul Richard, a graduate of École Polytechnique Fédérale de Lausanne in Switzerland and former visiting scientist at MIT; Alfonso Parra Rubio, CBA graduate; and senior author Neil Gershenfeld, MIT professor and director of CBA. Tests appears in .
Designing better building blocks
Over the past few years, researchers from the Bits and Atoms Center have been developing voxels, i.e. components with a mesh structure that can be used to assemble objects with high strength and stiffness, such as aircraft wings, wind turbine blades and space structures.
“Here we take aviation principles and apply them to buildings. Why don’t we build buildings as efficiently as we make airplanes?” Gershenfeld says it builds on his lab’s previous work on voxel assembly with NASA, Airbus and Boeing.
To investigate the feasibility of a voxel-based building assembly strategy, researchers first evaluated the mechanical performance and durability of eight existing voxel designs, including a cuboid made of glass-reinforced nylon and a Kelvin grid made of steel.
Based on these evaluations, they developed a set of three voxels using fresh geometry that can be more easily assembled automatically into a larger structure. The fresh structure, based on a high-strength and high-stiffness octet mesh, mechanically self-adjusts to inflexible structures.
“The interlocked nature of these voxels means we can achieve good mechanical properties without having to use multiple joints in the system, so the build process can be much faster,” Smith says.
To speed up construction, they designed robotic assembly system based on robots resembling inchworms crawl through the voxel structure anchoring and stretching their bodies. These modular Inchworm Lattice Assembler robots, or MILAbots, operate grippers at each end to place voxel building blocks and enable snap-in connections.
“Robots can assemble voxels by dropping them into place and then stepping on them to make the pieces engage. We can perform precise maneuvers based on the mechanical connections between the robots and the voxels,” explains Smith.
The team examined the inherent carbon needed to create fresh voxel designs using three materials: plastic, plywood and steel. They then assessed the throughput and cost of using a robotic assembly system to construct a plain, single-story building. The researchers compared these estimates with the performance of other construction methods.
Potential environmental benefits
They found that most existing voxels, especially those made of plastic, performed poorly compared to existing methods in terms of sustainability, while the steel and wood voxels they designed offered significant environmental benefits.
For example, using their steel voxels would only generate 36 percent of the embodied carbon required for 3D concrete printing and 52 percent of the embodied carbon in precast concrete. Plywood voxels had the lowest carbon footprint, requiring approximately 17 percent and 24 percent of the embodied carbon needed, respectively.
“There is still a potential viable option for the plastic-based voxel approach, we just need to be a little more strategic in the types of plastics, infills and geometries we use,” Smith says.
Additionally, the expected on-site assembly time for the steel and wood voxels averaged 99 hours, while existing construction methods took an average of 155 hours.
These speed benefits are based on the distributed nature of voxel-based assembly. While one MILAbot working alone is significantly slower than existing techniques, with a team of 20 robots working in parallel, the system equals or exceeds existing automation methods at a lower cost.
“One of the advantages of this method is its gradual nature. You can start building, and if it turns out you need a new room, you can simply add to the structure. The method is also reversible, so if you change how it is used, you can dismantle the voxels and change the structure,” says Gershenfeld.
The researchers also developed an interface that allows users to enter or manually design the voxelized structure. The automated system determines the paths MILAbots should follow during construction and sends commands to the assemblers.
The next step for this project will be a larger testbed in Bhutan that will operate the “superfabricated lab” that CBA helped set up there to replicate robots to test the design of the planned sustainable city, Gershenfeld says.
Additional areas for future work include investigating the stability of voxel structures under lateral loads, refining the design tool to account for system physics, improving MILAbot robots, and evaluating voxels with integrated electrical and hydraulic covering, insulation, or routing.
“Our work helps explain why this type of distributed robot assembly could be a practical way to bring digital manufacturing to construction,” Smith says.
This work was funded in part by the MIT Center for Bits and Atoms consortium.