Trailblazing Mit Team Demos 3d-printed, Recycled Plastic Floor Truss

The vast majority of floor trusses in homes are made with wood, at least in part due to its strength, light weight, cost efficiency and ease of installation.

Engineers at the Massachusetts Institute of Technology are taking an alternative approach. The research team is exploring the use of another building material – one that they say could provide a low-cost, sustainable alternative as the need for more housing grows exponentially across the globe. 

Engineers from the MIT HAUS (Homes Architecture Universal Sustainability) team published a paper earlier this month announcing that they designed and delivered a prototyped 3D-printed floor truss system made from recycled plastic. The team also wants to use recycled plastic to create construction-grade beams and other structural elements using the same 3D printing method.

The researchers report that they can use recycled “dirty” plastic, which can be reused without cleaning or preprocessing. Using this material to build home elements, they argue, would reduce and repurpose waste while protecting vulnerable lands from deforestation. 

How the process works

The MIT team is using large-scale additive manufacturing – i.e. 3D printing – to develop and test the effectiveness of plastic floor trusses, which are designed to look similar to conventional floor trusses. Before printing full-scale parts, the team prototypes and runs tests and simulations to ensure the design is robust and minimizes material use.

The team produces the trusses using an industrial-scale 3D printer that melts recycled plastic mixed with glass fibers and extrudes it layer by layer. Each truss is printed as a continuous piece, naturally fusing the joints together without bolts or connectors. The engineers then assemble the printed trusses into floor panels, which are tested under load to verify compliance with residential building standards. 

The MIT team’s floor system is comprised of four trusses, each of which is about eight feet long, one foot high and an inch wide. At about 13 pounds, each plastic truss weighs less than a comparable wood-based truss. A single truss takes roughly 13 minutes to produce, and the entire floor system assembles in about an hour. 

The floor, using plastic trusses, bears a load of more than 4,000 pounds, ultimately failing at 4,480 pounds, well above the HUD load-bearing standard of 300 pounds for a truss of that size. This experiment shows that the plastic trusses are comparatively lighter, can be produced relatively quickly and can withstand heavy loads. 

The team imagines a future in which the repurposed plastic composite parts could be easily transported to a construction site, where parts could be assembled rapidly into a strong, efficient housing frame.

However, the research remains at a preliminary stage, and the authors note potential improvements, particularly in reducing costs and scaling production.

“The as-built truss cost is still high owing to the use of expensive material and modest production rates. The former can be reduced by creating a material stream from a tailored recycling process that is attuned to the needs of these structures, while the latter can be addressed by using high-capacity LSAM equipment,” the paper read. 

Why MIT is using recycled plastic

The United Nations estimates that only 10% of the more than 400 million tonnes of plastic that is produced every year across the world is recycled. About 11 million tonnes of that plastic ends up in rivers, lakes and oceans. 

The World Green Building Council also estimates that approximately 80% of cities worldwide lack sufficient affordable housing and that the world will need to build 2 billion homes over the next 75 years, or 96,000 homes every day, to accommodate population growth. 

The MIT team sees the potential of plastic trusses to accommodate the global need for affordable housing in a sustainable, waste-reducing manner. AJ Perez, a lecturer at MIT’s School of Engineering and one of the paper’s authors, told MIT News that his team estimates the need for approximately 1 billion new homes worldwide by 2050. 

“If we try to make that many homes using wood, we would need to clear-cut the equivalent of the Amazon rainforest three times over,” he claimed. 

Companies in North America are already testing the commercial viability of homes built primarily with recycled plastics. 

Los Angeles-based Azure Printed Homes, which uses 3D printing and robotic technology to build ADUs and backyard studios, is perhaps the most prominent example. The company offers tiny home models built primarily from recycled plastic. One model, a 120-square-foot ADU, is built with a shell made from recycled plastic that is equivalent to about 100,000 bottles. 

The recycled plastic, provided by a dedicated supplier, is blended with fiberglass and other compounds to form a strong building material. Once built, the unit is coated with a fire-resistant treatment and a UV stabilizer. 

However, using recycled plastic to 3D print homes and structural home elements is not yet a common practice. Whether this building method gains significant steam in the United States or abroad is yet to be determined. However, the MIT researchers seem to have displayed potential — and a persuasive rationale — that is worth further research and discovery.