Monday, November 30, 2015

Earthside - Simple arched structures using preformed blocks

This is an example of Earthside technology that could be applied to building structures on bodies with gravity, particularly the Moon or Mars.

Lock Block is a company that makes custom-engineered concrete blocks for building arched tunnels or structures. They do other things, but their zipper truck arch process is what interests me.
Here's a video of the process in action; there's no explanation in the audio track.
Here's a somewhat longer video with explanation.

In case you don't want to watch some random youtube videos I'll explain the concept after the jump:

1. Prefabricated concrete blocks are engineered to fit together in an arch shape. As with bricks or cinderblocks, each block will connect to two blocks below it and two above. These blocks will spend their entire working lives under compression, so no steel reinforcement is required.
2. A build site is excavated and leveled. Footings may be required for some soils.
3. A specialized 'zipper' truck is moved into position. This truck provides the support to hold blocks in place as the arch is being constructed. It is made of steel rails with rollers, overall in the shape of a tapering cone.
4. Heavy equipment (such as a backhoe) places these blocks in order. In the videos above a human is required to assist with fine positioning of the blocks; this is because the equipment has only one attachment point to the block and no control over rotation. A fully automated or remote solution would use two attachment points to gain control over the block and enable fine positioning.
5. As each course of blocks reaches the key stone, the zipper truck is moved forward. The rails taper to the back of the truck, so this causes the two arms of the arch to close. The load is transferred to the key stone and work begins on the next course.

There are some enormous advantages to this concept:
A small number of large block shapes are required
No tensile reinforcement needed
No mortar; blocks can shift in a quake without failing (up to a point) and return to proper alignment
Very rapid construction; Earth equipment can lay a 1.5m course in about five minutes. A two-team crew can build over 400m of structure per day.
Resulting structures are strong enough to drive eight-tonne earthmovers over them; can easily be buried for radiation protection.
Blocks can be built on site using local soil, a few forms and the user's choice of process (microwave sintering, steam hydration, molten basalt casting, aluminum encapsulation, etc.)
As long as the soil overburden is heavy enough, the structure can be sealed and pressurized while still operating in compression
Other than the zipper truck, construction requires only some kind of heavy lifting equipment with enough capacity for a single block. The zipper structure could be mounted to another earthmover or a heavy cargo rover as an attachment.
With appropriate design changes to the attachment method this could be a remote-operated or even fully automated process.

NASA has plans for heavy utility platforms with exchangeable payload modules. Adding a lift arm or bucket, a zipper rail kit and block casting equipment would allow the construction of sturdy shelters quickly with no on-site human assistance and minimal unique equipment. Standard airtight doors would be shipped from Earth or built with local metals and integrated into the structures as they are built. The interiors could be sealed with a variety of substances, but for best results should include a reinforcing fiber mat and a flexible polymer or metal layer, with a cut and abrasion resistant outer (or rather inner) lining. Existing fabrics for transhab / Bigelow modules could be used; that could even go so far as to ship pre-built and pre-tested liners with integrated attachment rings to connect to the doors. To minimize penetrations, any service lines that need to reach unpressurized space (power, coolant, data) would go through the frame of a door.

Initially this would be useful for constructing a habitat. After that is done there would be little use for the zipper, but it would be stored in case of later expansion. The excavating equipment would remain useful for mining and soil moving operations. Block casting equipment would be used to make blocks as counterweights for tethers or as pavers for a road.

Assuming the equipment can only handle one course per hour, a structure of nearly 2,600m² could be built in twelve days. Using the traditional estimate of 40m² growing area per person, such a structure could feed 64 people once outfitted as a greenhouse.

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