sprayed onto the concrete. Many air pockets were not coated; approxi- 

 mately one pinhole per 2 in. 2 (1300 mm^) existed in the final water- 

 proofing coating. 



The concrete structure was instrumented with a total of 40 electri- 

 cal resistance strain gages to monitor hull response under long-term 

 loading. Half of the gages were placed diametrically opposed to each 

 other on the structure. The data were stored on magnetic tape inside 

 the structure and were recovered when the structure was retrieved 

 after 10 months. 



The concrete material for the cylinder portion of the structure 

 consisted of portland cement type II, sand, and coarse aggregate in the 

 proportions of 1.0:1.4:2.5 by weight, respectively. The water-to- 

 cement ratio was 0.40 by weight, and a water- reducing admixture was 

 used; the slump was 1.25 inch (32 mm). The average compressive 

 strength at 28 days of the 6-inch (152-mm) diameter by 12-inch 

 (305-mm) long control cylinders was 7,800 psi (53.8 MPa). 



Mix designs of different proportions were used for the hemi- 

 spheres: cement-to-sand-to-coarse-aggregate ratio of 1.0:1.95:2.3 by 

 weight; water-to-cement ratio of 0.38 by weight; and a water- reducing 

 admixture. Slump was again 1.25 inch (32 mm). The average compres- 

 sive strength at 28 days was 8,170 psi (56.3 MPa). 



Of the 15 cores taken from the cylinder wall just prior to the 

 implosion test, 7 were subsequently cut into 3.25-in. (83-mm) diameter 

 by 6-in. (152-mm) long cylinders, which were tested under uniaxial 

 compression. Compressive strengths of the cores and from a number of 

 6xl2-inch (152x305-mm) control cylinders at various ages are presented 

 in Table A-1. 



Three of the core specimens were instrumented with strain gages 

 to obtain stress-strain data for the concrete. Curves of this relation- 

 ship up to about 90% of the compressive strength are shown in Figure 

 A-3. The secant modulus of elasticity to about 40% of f was 4.4x10^ 

 psi (30.4 GPa), and Poisson's ratio was 0.20. 



32 



