Batching and Mixing

2 parts sand to 1 part cement to 1/2 part; to test.

Tony,

Sorry for the late reply. Our system wasn't working well and your question has been floating in cyberspace!

Cast stone is an emerging field--with some big corporations in the thick of it like OwensCorning, Headwaters, Oldcastle and others.

Most ulitize a latex liner that goes face down into a casting box about large enough for 4-6 stones. The stones are cast face down and pigments, paints, imperfections, etc. are brushed into the empty latex form randomly to give a natural effect.

Most make cast stones with the lightest possible weight aggregate available: pumice or even styrofoam pellets. Fly ash and slag are used in a mix that produces approximately 1,000 psi compressive strength. A high-shear mixer is used like a planetary vertical type, but just about any wet cast mixer can work.

This is a growing field, but the enemy is redundancy--don't make the stones look too uniform!

I would recommend conctacting concrete.org and click on the student section as well as research/technical.

A recirculating high-shear vortex or impeller pump works well. For cement and water it is important to remember we are actually emulsifying the powder and water, dissolving the finest powder materials and creating a solution or paste--depending on the viscosity required. For very thick pastes, a pump is not reccommended, but rather a high-shear mixer should be utilized.

The best way to do this is to use a mid-range water reducing agent in the mix at the plant to establish an initial 100mm slump at the plant with the W/C slightly lower than specified. Then on site add a small amount of prescribed high-range water-reducing agent after dosing the small amount of yet-to-be-added water.