Bridges are a common sight in the Netherlands. But four bridges are particularly unusual: each 26-foot structure was fashioned from concrete by a giant robotic printer. They are part of a revolution (变革) that is seeing 3D printers move from the tabletop to the construction lot.
3D construction printers work a lot like home-office ones, except instead of ink they spit out concrete. Nozzles (喷嘴) run back and forth on rails, with computers controlling the time and speed, so that a layer of concrete is laid down where needed. By the time the slow-moving nozzle reaches the end of its path, the layer has usually hardened just enough to lay down another on top of the first, building up, layer-by-layer, a home-sized wall. With precise pattern of deposit, the nozzle can leave spaces for windows, doors, and other design and structural elements.
It takes about 24 hours of printing to build a 500-square-foot single-floor home. “The printing process delivers structure, wall-sheeting, inner and outer surface finishing, all at the same time,” says Jason Ballard, co-founder and CEO of ICON, an Austin, Texas company. “That normally takes 20 people representing five or six different trades working several days.”
3D construction printers are also less wasteful. A typical home construction site generates about four tons of waste. Because the concrete used in conventional construction is applied uniformly, regardless of whether it’s needed for structural support in a particular area or not, about half of the concrete is wasted. 3D printers, however, can vary the thickness of a structure with great precision, using concrete only where it is really needed.
So far, printed buildings have been modest, low-cost affairs. For instance, ICON printed a house in Austin, Texas, intended for families, at a cost of $10,000, and has a contract to print a total of six. Then it plans to take a printer down to Latin America to build 50 low-cost homes there.
【小题1】Why does the author discuss the nozzle in Paragraph 2?| A．To analyze why the nozzle is so important. | B．To confirm 3D construction printers are slow. |
| C．To explain how 3D construction printers work. | D．To argue the precision of the nozzle needs improving. |
| A．They are highly efficient. | B．They are a little complex. |
| C．They increase the building cost. | D．They will replace builders one day. |
| A．By making a contrast. | B．By giving examples. | C．By describing a process. | D．By analyzing causes. |
| A．Printed Bridges Become a Fashion in the Netherlands | B．3D Printing Technology is Key to Housing Problems |
| C．Your House is Going to Be Greener in the Future | D．Your Next House May Come Out of a 3D Printer |
