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The 4 foot by 10 inch model has been successfully constructed using the materials and assembly techniques largely as planned. This page is a report on what has been learned in this phase of the project. The information is in three parts. First a series of photos of the assembly process. Second a list of problems encountered in the construction, how they were resolved, how we will modify the assembly process for the 12 foot ¼ scale model in the next phase. Last is a report on the results of testing on the completed 4 foot model. That testing has not yet begun.
Ready to rock
Wired-up cell remesh to floor.
Added floor and wall poly sheet. Setup wall form and spacers.
Poured normal concrete floor layer.
Placed and filled water bags. Poured cellular concrete inner partitions.
Placed roof remesh. Removed outer wall spacers.
Poured normal concrete outer walls and roof. Removed form. Water bags have not yet been removed
Problems Encountered in Assembly
Wrinkles in poly sheet put 1/2” grooves in walls, weakening them.
This will be less of an issue at larger scales. Still, need more care pulling out slack before setting.
Rough floor punctured water bags.
This will not be a problem with 6 mil poly (vs 2 mil).
Slack in bags blocked pump-out tubes.
Wrap tube ends with a fragment of open-cell foam or equivalent.
Constructing bags and hex wire cells was very labor-intensive.
Serious issue. Needs more thought.
Floor mesh must be placed before wall spacers.
Need jig for bending wire cells.
Cells were slightly too big.
Larger scale and wire cell jigs should fix this.
Bags were filled before pouring cellular concrete. (Won't work with 10 ft high cells).
Cell crete was poured in at several points, flowed very well. Coordinating bag filling with the pour remains to be tried.
Sloppy placement of floor concrete left sharp crust on hex cell walls, puncturing bags.
So be neater about it next time.
Water tubes made it hard to smooth down the roof concrete layer.
Not much to be done about this. Will be a `little better at larger scales.
Negative meniscus of roof concrete against poly wall sheet left ugly sharp edge.
After set but before cure, this edge was dressed with a wood scaper.
Hard to control thickness on this small scale. Normal concrete outer skin ended up almost twice as thick as planned, using more materials, and making the model twice as heavy, too heavy to float.
Underscores importance of controlling thickness. Should be less a problem at larger scales.
Bags should be removed after set, but before cure.
Weight and bouyancy determination. TBD
Airbag lifting and launching technique.TBD
Lift model by 4 inches.
Transfer to an adjascent bag.
Airbag punctures or leaks.
Floats at all.
Freeboard compared to design.
Porosity, seapage, leaks.
Autopsy, inspection of internal structure.TBD
Thickness of roof.
Thickness of floor.
Thickness of outer wall.
Thickness of cell walls.
Cell corners and edges.
Roof layer leakage into cells.
Exposure of cell remesh.
Strength test to destruction.TBD
Crush-test model at center, over 1-cell area.(how to generate such a load?)
Compression test sample of outer skin.
Compression test sample of cell walls.
Break-over test across diameter.