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An idea I had back in late 1960's of how to automatically build a concrete house, 

using a temporary containing structure and balancing wet sand's mass to transfer positioning over to the constraining shell

A large cylindrical steel form would be set up around the construction site, then inside it a pair of nozzles would scan back and forth across the insides of the cylinder, everywhere either putting down cement or wet sand of similar density, building it up layer by layer. The sand would couple the lateral pressure to the cylindrical wall around the site, holding the areas that got the cement in place. A computer program would define the sites for the cement put down instead of wet sand. When it all had time to set up solid, the steel cylinder would be unlatched and disassembled for use at next site, and the sand hosed out to leave the three dimensional structure there in place. In reality there would need to be plumbing and electrical conduit put in, and probably the cement laced with nail-like steel fibers for reinforcing, details. Since the structural form would be controlled by the computer program's placement list, identical copies could be made, or each house could be a different design made by the programming.

Was a fun idea back then. I played with it a bit with the kids, each using a pail in which the layering of sand and cement went in, to harden the 3-dimensional shape in place and see what it looked like the next visit, when all the sand was washed out. 

Here are photos of one of the resulting artifacts made back then during a sand-balance casting experiment. Somehow this artifact has survived all the moves and struggles of the past 35 years, possibly because it also sometimes serves as an interesting flowerpot holder. I made it circa 1973 as my demonstration part of showing the kids how to do theirs creatively too, being a weekend daddy. Somewhat explaining its rather rough and clumsy-looking quality, this was a creation made after about a year of self-recovery following the leaving by my wife and the severe neuro and physical damage I was self-recovering from due to poorly understood factors associated with that. When this artifact was made, I was in the apartment life mode yet was still somewhat remembering the creative construction mode I had established when living in the canyon where I had had to build a 40 foot long car-carrying bridge and rebuild after flood and landslide damages to house etc. Visiting at my apartment, we (kids and I) each had a pail, wet sand, and wet topping concrete mix, and objects of choice, and following each person's creative urge of the moment, used the placement of concrete and using wet sand to transfer shape-holding pressure over to sides of pails, building up layer by layer (like the larger house-building computer-controlled house building idea I mentioned, only on small scale.) This particular artifact's creative making also explored the use of some bent heavy wire and the use of filling sandwich baggies with cement to also help define the shape of the concrete segments and smooth its surface, yet used the pressure from wet sand to hold it all in shape in the sand-filled pail while hardening. Part of the fun was in the discovery of what they exactly looked like the next weekend when extracting the resulting hardened objects out of the sand. 

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In this example, the heavy steel wire that links the two flat sections can be best seen in the second and fourth photos above. The fourth photo also gives a sense of the smoothness (wondering about potentials for use as a shaped mirror substrate) imparted by the sandwich baggies used to contain the two concrete portions. The whole object shape is of course illustrative of how use of wet sand in a constrained container can support the weight of irregular concrete in place while it goes through the hardening process.

Although this was not made by use of a computer-controlled area scanning nozzle pair, this illustrates some of the principles that would be used in the above-mentioned computer-controlled building of concrete shell houses, or other concrete-based items such as large art sculpture structures.

A different sort of sand casting itself has been used since ancient times, of course; but required first making a full sized model to shape the sand, then be melted out (as in wax) then filling the vacated space with the final material, such as melted metal. Other ways to shape concrete are of course by use of forms and shaped molds. In the technique here, however, neither wooden forms nor initial model have to be made and discarded. Even the washed-out sand could be re-used in the next house construction project, just as also reusing the hinged large steel cylinder sections that surrounds the construction site while the house is being built by the computer-controlled scanning nozzle inside, in which the concrete left to harden.

An Excalator Hi page titled SandbalanceCasting by J E D Cline started on Saturday, May 24, 2008 12:07:13 PM US/Pacific

Copyright © 2008 James E. D. Cline. Permission granted to reproduce providing inclusion of a link back to this site and acknowledgment of the author and concept designer James E. D. Cline.