In accordance with your request, I checked with Dr. Kitzes of ORNL and his assistant, Mr. Gallaher, on the Coleminite concrete. Their remarks and recommendations are reproduced below.

1. The basic problem in the setting of this concrete is that the boron compound dissolves in water, resulting in a solution that inhibits the action of Portland cement. The amount of water added must be carefully controlled, and the mix prepared in a much dryer state than is conventional in concrete practices, and in fact, giving such a constituency that contractors are very much alarmed. The added water should be as cold as possible because of the solubility problem.

2. The exact proportions at the various constituents have been established by experiment; once they are found and the procedure for preparation followed religiously, a reproducible satisfactory concrete is obtained. (To my untrained eyes the test blocks I was shown looked very good.)

3. The two mixes that have been used successfully were: a) that for which we have specifications: Barytes 3970 lbs, Coleminite 400 lbs, Portland cement (preferably type III) 830 lbs, water 310 lbs (maximum), which is designed for poured sections, using Coleminite sand. The aggregate size specifications are: 1" and 3/8" aggregate ASTM in the ratio at about 16:1 coarse/fine. All material of size passed by a 16 mesh screen is removed from the aggregate. The water content is best specified by the maxim of a 2" slump, rather than by the weight listed above. This test takes care of the tempera- ture and humidity conditions at the tine of pouring.