STEWART FIELD SPHERES
	The spheres represented 10 aggregate combinations; water-cement ratios ranged from 4.5 to 5.5 gal per bag; cement factors ranged from 5.1 to 7.4 bag per cu yd; air content ranged from 2.3 to 7.7 percent. Table 1-SF of TR 6-553 lists these specimens and gives their exposure record along with other pertinent information. The test data obtained indicate that changes in the condition of concrete spheres can be evaluated by pulse velocity measurements provided adequate steps are taken to ensure that pulse velocity readings are taken through the same path each time the spheres are tested. The three specimens that remain under test all contain the fine-coarse aggregate combination of crushed (fine) and natural gravel A (coarse). This seems to be the variable which has the most effect on durability in this study.
The purpose of this program was to determine if it was possible to evaluate changes in condition of concrete spheres by pulse velocity measurements. In May 1994, 24 air-entrained concrete spheres were installed at half-tide elevation. These spheres were 12 in. in diameter and had been previously exposed to 600 cycles of freezing and thawing. This previous exposure had no appreciable effect on the spheres. Five of the specimens are still under test after 28 winters of exposure.

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