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This recipe will make 2 gallons of concrete with a density of slightly greater than 1.0:
In a concrete mixer, add in this order:
5 Liters water
6 Liters sand
6 Liters type I-II portland cement
Mix to a homogenous mud (2-3 minutes)
Add 11 Liters foam.
Mix to a homogenous light grey liquid (1-2 minutes)
The foam contains 1 part detergent solution to 20 parts air. The solution is one part safeway select concentrated diswashing liquid to 36 parts water. For the highest rate of flow, open the air valve a turn or two, the open the liquid valve completely, then set the air as high as possible without 'sputtering'.
The foam generator is made from 1” pcv pipe plus pvc and brass fittings. It injects a stream of detergent solution into a section of plastic scouring pad and forces compressed air at 80 psi through the pad. Another foot of scouring pad material wadded into the pipe whips the foam into a shaving-cream-like consistency.
The reservoir in the design drawing below was made from 4” pvc pipe and brass fittings. All materials were purchased at “Home Depot” at a cost of about $25. A used compressor cost us $60. This design produces 100 liters of foam on a filling, at 25 liters/minute. The flow rate is acceptable for pouring the ¼ scale model, but not enough for a full size platform. The reservoir will need to be inlarged even for the ¼ scale model.