A small 3D-printed concrete bridge demonstrates a possible way to build with less material. Researchers from MIT designed a 2.3-meter-long structure, then printed and tested it.
Concrete is the most widely used construction material in the world. Its production is also a major source of carbon emissions. 3D printing could reduce this impact by depositing material only where the structure needs it, without traditional molds.
Hajin Kim-Tackowiak (left), a postdoctoral researcher in MIT's Department of Civil and Environmental Engineering, and Zane Schemmer, a graduate student, pose with the 3D-printed concrete bridge they designed and load-tested.
Photo: MIT
In practice, the optimal shapes calculated by software are often too complex to manufacture. Optimization methods can imagine very light structures, almost like spider webs. But a concrete printer must work with the thickness of its nozzle and the paths it can actually follow.
The team therefore integrated these constraints from the start of the mathematical design. The software accounts for the width of concrete layers, possible turns, and the need to print a continuous path. The model thus produces a shape that can be directly made by the machine.
The structure was printed with a standard mortar in about 30 minutes. It weighed approximately 408 kg. During tests, it supported 907 kg of blocks distributed over its surface, with no measurable deflection according to the researchers.
Construction of a 2.3-meter concrete bridge, 3D-printed layer by layer.
Video: MIT Department of Civil and Environmental Engineering
The test revealed an important point. For the expected loads, the amount of material needed depended more on the printer's capabilities than on the concrete's strength. A machine capable of depositing thinner layers or following tighter curves could therefore produce even more economical structures.
The method also saves time when adapting a project. The researchers indicate that a new printable design can be obtained in minutes on a laptop. This speed can facilitate adjustments on a construction site or for elements of different sizes.
This prototype does not announce an immediate replacement of traditional methods. It does, however, show how design tools and machines can evolve together. The challenge is to build safe, feasible elements that are less material-intensive, without sacrificing their mechanical performance.