WO CHAPTER II. SECTION 18 phalts. The major testing equipment was in- stalled in the Elmer Laboratory although smail branch laboratories were established on various islands on both atolls as required. Site Tare had equipment for making determinations of coral aggregate sieve analyses and moisture content; site Fred had a small laboratory for testing asphalt. Aggregates for the concrete mixes were comprised of crushed cura: rock with the additic: of fine coral beach sand. Past experience in both OPERAIION GREENHOUSE and OPERATION IVY showed coral deposits had Wia. variations in their specific gravities and in their percentages of absorption. The testing and control of these two factors are most imp .tant in the economical production of 2500 to 3500 psi concrete. tested to destruction. Three and seven-day old cylinders were tested for comparative purposes and Figure 2-21 shows a seven-day break for aggregate procured at site Oboe. The length of the break is typical of coral rock. With a cement content of 6.5, 3430 psi was obtained in seven days. The lack of shear in the rock is likewise typical of seven-day tests. With the evaluation of these preliminary tests, final mixes «vere designed and tested. Figure 2-22 is a typical 28day test. This cylinder, with a cement content of 6.5, broke at 4527 psi; 95% of the rock had been sheared. With such excellent coral rock and improved test results, it was possible to reduce the cement factor from 7.0 (used in OPERATION IVY) to an average of 5.8. For OPERATION CASTLF, it was estimated in April 1953 that shout 20,000 cubic Bikini Atoll, and it was vlanned to stockpile the aggregate in about iu. - or five separate areas in that atoll. This included an estimated yardage of 14,000 for the Scientific Program, plus vardage for camp construction and miscellaneous work and wastage. On 25 April 1953, explorations of the Bikini Atoll were started to determine the locations, characteristics and amounts of coral aggregate available. Samples were obtained and tests on these samples were completed on 3 June 1953. Excellent grades of aggregates were found on exposed reefs in the top three to eight feet at sites Cnarlie, Easy, Nan, and Oboe andthese sites were selected as areas for stockpiles. Figure 2-19 shows the tvpe of coral ruck selected and used at Nan. The apparent specific gravity of this rock was 2.652 and the absorption was 1.00%. The heavier the rock, the denser the concrete. Absorption critically affects the ultimate strengih of the concrete and should be kept to a minimum. If the absorption is excessive, the strength will be reduced as much as 50°. As far as is known, including U.S. Navy and the U.S. Department of Interior sources, the rock on Nan represents the highest in specific gravity and the lowest percentage of absorption of coral rock tested to date. Figure 2-20 shows the type of corai ruck selected and used at Charlie. This rock was entirely different in appearance, structure and formation from the rock used on Nan. The apparent specific gravity for this rock was 2.63 and the absorption was 1.17%. As a yardstick for comparison, good structural coral cock will average Pn apparent specitic gravity of 2.33 and an absorption percentage of 6.66. The variations in the physical properties of coral rock, as noted above, required individual tests, computations and design mixes for each seiected site. For cot: nuting and checking these design mixes, 630 test cylinders were cast and TE NET aH ape aon PETAL ETE SPC yards of coral aggregate would be required for Figure 2-21. Seven Day Concrete Test Cylinder Page 2-47 s eues ws he ue naarsetninttensteal