No men at work: these robots build houses

Concrete Producer, The, July, 2004 by Michael Leaverton

At first glance, it doesn't look like much. Just a concrete wall, 3 feet high and 5 feet long, sitting on the floor of a laboratory in Los Angeles. But this wall wasn't poured. It was "printed" by the machine next to it--a robot armed with a concrete pump and a pair of trowels. Although the wall is nicely crafted, with a uniform surface and smoothly rounded ends, it's just a trifle when compared to the robot's next job: building a 2000-square-foot house.

The man behind the robot is Dr. Behrokh Khoshnevis, a professor of engineering at the University of Southern California. Over the past several years, he's been developing Contour Crafting (CC), a fabrication technology for computer-generated designs. "It's really just three-dimensional printing," he says. "All geometries can be built with the process. Naturally, I thought about using it for construction of houses."

Those houses are on the way. Funded by grants from the National Science Foundation and the Office of Naval Research, Khoshnevis expects his robots to build their first multiroom, one-story, concrete house in 2005, potentially ushering in a new era of automated housing.

The layered approach

Khoshnevis' current robot--a 6-foot contraption with a cylindrical pump running along a large metal frame--"prints" by extruding 1-inch-thick strips of quick-setting concrete, like toothpaste squeezed from a tube, along a precise, computer-designed route, creating the outer and inner rims of a 6-inch-thick wall. Two trowels attached to the nozzle shape the material as it is laid down, producing exceptionally smooth and accurate free-form shapes in one go, free of surface defects such as voids and ready for paint.

Khoshnevis envisions CC being used for everything from "dignified low-income housing" and "track-home developments where no two houses look the same" to Frank Gehry-style curvilinear buildings and even to dwellings on the moon and Mars, where the machine could build autonomously using solar power and lunar regolith, or space dirt, as the basis of the construction material. Since the designs of the structures are limited only by the maneuverability of the nozzle, curved wails and abstract shapes will be as easy to create as straight walls.

The nearly complete absence of problems hampering construction--high accident rates, low labor efficiency, low work quality, the vanishing of a skilled work-force, and environmental impact--adds to its appeal. Robots can work day and night at a constant level of quality, and they can work fast--completing homes in hours rather than weeks or months. And it will be cheap. Khoshnevis puts the figure at $40 per square foot, or less than 1/3 of the cost of traditional construction.

From the ground up

Once in the plant or on the jobsite, Khoshnevis plans to use a gantry to hang the machine over the construction site. Running overheard, the nozzles will lay down the thin concrete strips, leaving gaps for doors and windows. A larger nozzle will periodically fill the wall cavities as the structure begins to rise. Utilizing the gantry, integrated robotic arms can lift and position support beams.

Reinforcing the concrete can be accomplished in a variety of ways: robotically imbedding modular steel mesh, creating ducts that can be fed with reinforcement epoxies or steel tendons for post-tensioning, or feeding fiber-reinforced plastics through the nozzle to form continuous reinforcement within the material.

Affixing nonstructural elements can also be automated. As the building inches higher, robotic arms can periodically fit sections of copper pipes pretreated with solder, which can be heated to bind the sections together. As the walls incrementally rise, the pipes can run vertically, then horizontally, depending on the plumbing design.

Electrical and communication components can be encased in nonconductive materials and fitted together within concrete hollows, behind prescribed openings in the walls for outlets. Even painting and tiling can be accomplished robotically, utilizing the gantry system.

The success of CC lies not so much in the mechanics--after all, robots can build structures far more intricate than houses--but in the construction formula itself. In the lab, Khoshnevis creates his walls using store-bought material, what he calls "regular, fast-setting concrete that we add accelerator to." But that's a far cry from what he'll need for commercial construction, since the process works without support forms, molds, or other structural aids.

That's where materials manufacturer Degussa AG comes in. In December 2003, Khoshnevis met with executives at Degussa's headquarters in Dusseldorf, Germany. The firm came away impressed. Dr. Gerhard Albrecht, head of research at Degussa's specialty-materials subsidiary, Admixture, says the process will be a "quantum leap in the modern construction industry." Degussa "is ready to develop special new construction chemicals in our own R&D labs fitted for the Contour Crafting process," he added.

Environmental versatility