I read that the Hoover dam concrete was laid about a foot in each layer. There are myths that workers sank into the concrete and were never seen again, but that could not have happened.
What I would like to know is, did they really find the skeleton of a boy when they broke up The Great Eastern? Probably not, but it is a good story.
No reason why a concrete-making one couldn’t be built. Feeding in the correct raw materials in the required volume would be the biggest bottleneck for big projects.
The document referenced above describes this. QUOTE:
Don’t be fooled by the fact that the main construction medium here is concrete. This is high-tech work. The mobile concrete batch plant, for example, is loaded with sensors that weigh sand, stone and cement, measure the moisture content in the ingredients, and monitor the mixing torque, the rheology — the flow of the printing mixture — and other factors for each individual batch. Operators monitor and adjust the factors from a computer inside a glass cab in the middle of the trailer. “Once we mix it and make the concrete, we have only so much time to be able to print it,” Kenny says. “Based on a combination of testing, computer modeling and simulation work, the concrete is designed to develop strength at a certain rate to handle the layers above it and the weight of the rebar. This allows us to build the structure within our targeted time frame.”
The whole system is designed to work like this: The batch plant blends the cement from the storage tank and the stone, sand and water, and sends the concrete to the printer. The printer then extrudes layers of concrete in the desired shape through a special nozzle. Each layer is several inches thick. Like at the batch plant, the process is monitored by sensors and cameras.
