Values of 3,500 psi in the compressive strength test are considered 

 satisfactory for certain purposes. Thus, even though the results of the 

 tests indicate that the antifouling concrete is weaker than most struc- 

 tural concrete, it would be an acceptable material for construction 

 requiring no more than 3,500-psi compressive strength. 



Rather coarse expanded shale aggregates of 1/4- and 3/8-inch mesh 

 sizes were employed in making the antifouling concrete panels that were 

 evaluated in the CEL investigation. No sand was employed. It is well 

 known that concrete made with aggregates of mixed sizes ranging from 

 fine to coarse is stronger than concrete made with only a coarse aggre- 

 gate. Also, the addition of river sand improves the strength of an 

 expanded shale concrete. It should be possible to markedly increase the 

 strength of the CEL antifouling marine concrete by employing both fine 

 and coarse impregnated expanded shale aggregate and by employing some 

 unimpregnated river sand. 



Shear Strength Tests 



If the antifouling concrete is to be employed as a protective 

 covering over existing concrete structures made of portland cement and 

 gravel, it must adhere to previously cured concrete. Attempts were made 

 to cast 1- by 3- by 3-inch blocks of the antifouling concrete on the 

 surfaces of previously cured concrete panels made of Type III portland 

 cement and gravel (Figure 3) . Some difficulty was encountered in 

 securing a bond, especially with the controls. The small blocks cracked 

 loose when the molds were removed. This problem was overcome, and 

 several control specimens and several test specimens were successfully 

 bonded and tested. The results are given in Table 3. 



The shear tests indicate that a layer of concrete made from portland 

 cement and a porous shale aggregate impregnated with an oily mixture of 

 creosote and toxic chemicals can be bonded to a previously cured concrete 

 base. However, considerable care and skill are required for bonding 

 together two layers of any portland cement concrete. 



Antifouling Tests 



The effectiveness of the antifouling concrete panels was tested at 

 various sites in the ocean. Tests were made at depths of 120 and 600 

 feet in the ocean a few miles off shore from Port Hueneme. Tests were 

 also made near the surface at Point Mugu, Port Hueneme, and Guantanamo 

 Bay, Cuba. The bulk of the tests and the longest term tests were per- 

 formed in the harbor at Port Hueneme, but tests at the other sites 

 confirmed the universal effectiveness of the antifouling concrete. 



Six-Hundred-Foot Depth . The tests at a depth of 600 feet were 

 conducted in the vicinity of the STU structure, an ocean-bottom rack or 

 frame on which numerous devices and materials were fastened for ocean 

 exposure tests. The STU structure was emplaced on the seafloor in the 

 Santa Barbara Channel at a depth of 600 feet. The antifouling concrete 

 panels exposed at the STU site were made of porous aggregate impregnated 



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