Construction has always been a three-dimensional activity. While the representation of the intent of construction has been liberated "virtually" into 3D digital models and rotatable 3D representations, accurate physical representations of design intent have been achieved, until only recently, either through the artistry and skill of a scale model-builder or by building full-scale mock-ups of the ideas captured by the design documentation.
But now 3D digital printing offers a third way to go from intent to reality. Like ink-jet printers, 3D printers deposit fine particles on a surface but then keep adding more passes and layers, bonding together the particles with various agents so that, guided by a 3D design file, they accumulate and rise into solid shapes. The process also is referred to as "additive printing." A 3D model printed from a digital design file may be the truest representation that can be achieved of the intended geometry. Unlike actual construction, the model is driven directly from the digital design file, with no teams of trades involved. "There is nothing that has quite the same impact as putting a physical object in front of people that they can touch and turn around," says James P. Barrett, head of integrated building solutions at Turner Construction.
Owners are starting to get that. So are stakeholders and constituents, architects, engineers and subs. Well-made, digitally printed 3D models have authority, and they can have more than a little job-winning charm, too, as some successful bidders have found. For many clients, the models convey a sense of physical relationships that are often difficult to understand from traditional representations. "They see the model, and they just get it," says Barrett. "Virtual is great, but there has to be a physical product—from bytes to atoms."
Not only is 3D printing catching on in the market, it is rapidly improving in terms of production speed, materials options, binding agents and scale. But it is the latter that really catches most people's imagination.
Scaling up 3D printing is the subject of research for Behrokh Khoshnevis, professor of industrial and systems engineering and civil and environmental engineering at the University of Southern California, in collaboration with scientists at the National Atmospheric and Space Administration.
Khoshnevis serves as the director of the university's Center for Rapid Automated Fabrication Technologies. While working to scale up a computer-guided, rolling-gantry-driven printer system to extrude extremely low-slump concrete according to digital model plans to print buildings, he found himself presenting at the same conference with NASA researchers who were developing technology to build on the Moon and Mars. They have been collaborating ever since.
Khoshnevis was the inventor of a lot of these large-scale printing processes, says Philip T. Metzger, a NASA physicist and manager of its Granular Mechanics and Regolith Operations Laboratory. "We want to adopt what he is doing, along with any solutions we develop, to use existing materials to make concrete on Mars and the Moon," Metzger says. One option is to "laser-sinter the soil without any binder. You heat it almost to the point of melting, and the grains become a little bit soft and weld together. That could save several billion dollars," he says.
Khoshnevis originally was looking at building structures, but building landing pads also is vitally important. "You really can't land a 40- to 50-ton spacecraft on Mars without building a landing pad first. That's the only way of putting humans safely on Mars," Metzger adds.
Khoshnevis' technology would let NASA do just that. "You could have a small vehicle put the robot printer on Mars and another digger that would go get dirt, and they would build for maybe a year," Metzger says. He envisions fitting Khoshnevis' printers with interchangeable heads to switch between sintering, sulpher-based or hydraulic concrete printing.
In addition to the NASA research, Khoshnevis also is doing work on earth-bound printing that he does not have permission to publicize, but he says the goal is to work out all the details for the process from end to end to create a fully reliable system before commercializing it, much less sending it into outer space.
