Visited Knox Concrete Products, Inc., 4918 Kingston Pike, and talked with Mr. Amos Brown, plant superintendent. He had been in charge of coleminite block production for Oak Ridge, working with Mr. S. M. Barnes, was away at the time of my visit. Their procedure consists of mixing Sweetwater Barytes 3970 (3790 lbs, 100% through 1/2" screen, 90-95% retained on 16 mesh screen) Coleminite (400 lbs same specifications as ours) and type I cement (830 lbs) for about 10 minutes in the hopper of the block machine. A much shorter period, say 2 minutes, would be needed in an ordinary mixer, he states. Exact amounts of water, to within a pint determined by experience, are added. If the mix is too dry, the machine cannot handle it; if too wet, it balls up. For poured structures this may not be as critical. A minimum of water, however, is used less then 37.5 gal. (straight city water without special coaling).

The mix is dropped into the machine, vibrated, and pressed at 8000 lbs with mechanical means. The vibration is supposed to help strengthen the product, but no such virtue is claimed for the pressure, except to fill the mold well.

The blocks, of size 4" x 7 5/8" x 11 7/8", weight ≃ 40 lbs, are removed and let dry somewhat in the kiln. A fine water spray is applied 3 times a day for up to 3 days, depending on storage facilities. The first large batch, in the curing stags at the time of my visit, consisted of 7000 blocks. Test blocks made earlier looked very good. Samples were provided of the mortar only and of the mortar plus aggregate.

4 x 7 5/8 x 11 7/8 = 364in3 = 5930 cm3 40lb = 40(454) = 18100g ρ = 3.05