Within a couple of years, researchers at the University of Southern California believe 3D printing techniques will be used to construct entire buildings in less than a day.
As outrageous as it sounds, such machines can already extrude concrete walls with internal reinforcement fast enough to complete the shell of a 2,000-sq. ft. house in under 20 hours.
The technology was demonstrated this week at the Inside 3D Printing Conference and Expo here.
The robotic extruding method, called Contour Crafting, is comparable to its smaller 3D desktop printer counterparts in that it takes its orders from CAD software, which stores and executes the architectural designs. The designs can be customized on a construction site even as work is underway.
The machines can also automatically embed all the conduits for electrical, plumbing and air-conditioning, as well as place electronic sensors to monitor the building's temperature and health over time.
Behrokh Khoshnevis, a professor of industrial and systems engineering at the USC's Viterbi School of Engineering, is leading the effort to perfect the Contour Crafting construction technology.
Khoshnevis said that he expects the technology will be commercially viable within two years.
Contour Crafting could help solve one of the largest problems facing the world today, a lack of decent housing for more than a billion people, Khoshnevis said.
Today, construction is slow, labor intensive, inefficient -- and the most hazardous job in the world, with 400,000 people injured 6,000 to 10,000 killed in construction accidents every year in the U.S. alone.
"It is wasteful and emission causing and corruption prone. And, the cost is always over budget," Khoshnevis said. "What we aspire to do is create neighborhoods that are dignified at a fraction of the cost, a fraction of the time and far more safety with beautiful architectural designs."
Structures not only can be constructed of concrete but also of hybrid materials. For example, the outer shell of a wall can be plaster with polymer or cement filler. Steel reinforcement in for form of coils can also be added to the mix.
A Contour Crafting-machine, which is made up of a metal gantry frame, along with the robotic extruding system, weighs about 500 pounds. It comes in two pieces and can be quickly erected on a construction site, Khoshnevis said.
The gantry frames can be modified to climb structures, creating one story at a time until it reaches the top of a building. Then the robotic gantry could climb back down the sides of the building.
Each layer of concrete extruded by the machine is four inches thick and about six inches in height. Using special hardeners in the concrete, the material is hard enough to support the next layer by the time the machine circumnavigates the outside perimeter of a structure.
Because the materials are extruded through a nozzle, the walls of a building can take any form - thus the name "Contour Crafting."
The structures can look like the Adobe structures made of mud, clay and straw (or other domestic materials) in Africa, West Asia, and more arid parts of the Americas. Adobe structures have been a construction method for thousands of years; and can last hundreds of years.
"The reason they last is not the material. The strength comes from the geometry," Khoshnevis said. "The worst structures you can use are planar [flat] walls."
Khoshnevis demonstrated the strength of a contoured structure by holding a sheet of paper up and blowing on it, which bent if over. He then rolled the paper in a semi-circle and blew on it again; it remained upright.
Using Contour Crafting on the Moon and Mars
Khoshnevis, also a professor of aerospace and mechanical engineering at USC, is also working with the National Aeronautics and Space Administration (NASA) on a plan for creating structures on the Moon and Mars.
"The proposal we have is rather than take segments of buildings and transport them there, just take the machinery there ... and use the local material and make them there," Khoshnevis said.
The USC team is in phase two of an advanced concept for the off-world structures.
"The objective of NASA is to build settlements, outposts," he said. "Nothing's been said about human operated missions. Those can come later."
One problem with constructing landing pads, roads, or blast walls to protect living quarters on other planets is that water cannot be used. Because of the thin atmosphere on Mars, and lack thereof on the moon, water would evaporate from cement or concrete, leaving it to return to its origin of dust and rocks.
The USC researchers solved that problem by melting sulfur for use as a binder, binding the sand like cement.
"We have already shown the ability to build using Martian materials," he said.
The USC team also came up with a plan to combat the high temperatures on the sunny areas of the Moon -- creating interlocking ceramic tiles that can resist temperatures of up to 2,000 degrees Celsius. The tiles can be locked together to create structures. The machines could not only extrude the ceramic material, but a separate component could them assemble them into structure.
Another method of building structures is to use lithium disilicate, a glass-ceramic material that can be heated and poured out like molten lava to form structures on off-planet worlds.
While robotics could handle construction off world, here on Earth Contour Crafting would require far fewer laborers to build houses and other structures. Labor makes up 45% to 55% of construction costs, Khoshnevis said.
"It could be much cheaper than prefab structures and much, much cheaper than conventional construction," he said. "Nothing beats contour construction on cost."
The labor issue has already become a point of controversy -- some observers have have complained that machines would replace construction workers, leaving them without jobs, Khoshenevis said.
"My response to that is it's not going to happen overnight," he said. "Second, this is not a new question. When the steam engine was invented they said what's going to happen to carriage drivers?"
Khoshenevis pointed out that at the end of the 19th century in the U.S. 62.5% of Americans were farmers. Today, less than 1% work to grow our produce. "The world did not come to a standstill from such a major change," he said.