Appendix C 

 COMPRESSIVE STRENGTH OF CONCRETE FOR SPHERE 3 



Even though Sphere 3 imploded on descent to the seafloor, the control block of concrete was not 

 retrieved until 340 days later. This control block was fabricated of the same concrete as One of the sphere's 

 hemispheres, W-16. This concrete experienced a history of 172 days of on-land field curing and 340 days of 

 in-ocean field curing. 



The other hemisphere, W-15, had a corresponding control block that was continuously stored 

 out-of-doors; hence, this concrete underwent a continuous 514 days of on-land field curing. Simulta- 

 neously, three 6 x 12-inch-long cylinders for both hemispheres underwent continuous fog room curing. 



The compressive strengths for the concrete are shown in Table C-1 and Figure C-1. The fog-cured 

 concrete increased 23 percent in average strength, from 8,460 to 10,420 psi. The on-land field-cured 

 concrete leveled off in strength at an average of 8,650 psi after 134 days. The in-ocean field-cured concrete 

 decreased in strength from an average of 9,650 psi after 132 days of on-land curing to an average of 7,600 

 psi after 340 days in the ocean; this was a 21 percent decrease in strength. Wetting of the dry concrete 

 would account for 10 percent of the decrease [8] ; perhaps under the long-term hydrostatic pressure the 

 total decrease in strength was due to saturation of the concrete. Previous work by Russians [13] showed a 

 decrease in compressive strength of 28 percent due to saturating dry concrete under high hydrostatic 

 pressure; however, the test procedure used to obtain the saturated concrete was not discussed. 



Concrete from block W-16 was analyzed by x-ray diffraction techniques. It was found that the 

 concrete was not attacked by the seawater. 



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