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Early investigations demonstrated the usefulness of small additions of diatomite [or diatomaceous] earth in increasing the plasticity and decreasing the tendency towards segregation of concrete mixes. As a result of these findings and field experience, diatomaceous earth was processed by a number of manufacturers and came to be widely used as a concrete ad-mixture. The raw earth, after being dried, was usually pulverized in impact mills; and the product, though fine as compared with portland cement, was still largely composed of unfractured or partly fractured skeletons of diatoms and was therefore highly absorptive. Its unit weight was of the order of 10 lb. per cu. ft. It was generally believed that there was an advantage in this high absorption and low unit weight, though additions in excess of 2 or 3 per cent of the weight of the cement significantly increased the water requirement to produce concrete of a given consistency, and significantly increased the yield.
Professor of Civil Engineering and Director of the Engineering Materials Laboratory, University of California, Berkeley, Calif.
Research Engineer, University of California, Berkeley, Calif.