3. Concrete prepared using TBTO-impregnated aggregate and cuprous oxide 
possesses some antifouling properties. Cuprous oxide, when employed as 
the sole antifoulant (at 2% by weight of the total) did not provide 
antifouling properties. 
4. Concrete containing methoxychlor, TPTH, and cuprous oxide demonstrated 
antifouling properties, while concrete prepared using methoxychlor alone 
exhibited none. These specimens have been exposed for only five months. 
5. A proprietary organotin-polysiloxane polymer coating was under 
evaluation for 5 months. Preliminary data indicate that this coating 
prevents fouling and is low in cost. 
6. A proprietary organotin-impregnated rubber sheeting demonstrated 
excellent antifouling properties for 2 months at Port Hueneme. Its cost 
is significantly greater than that of the organotin-polysiloxane coating 
both for materials and application. 
7. The cost of the various antifouling concretes varies considerably 
and will be an important consideration in the selection of one system 
versus another. 
8. Structurally sound concrete can be prepared using aggregate impreg- 
nated with the antifoulants employed in this investigation. The com- 
pressive strength of these concretes was greater after 9 months of ocean 
exposure than after the 28-day curing period. 
9. All of the candidate antifoulants considered for possible use caused 
a reduction in the corrosion rate of simulated steel reinforcing rods. 
10. Some of the candidate antifouling concretes were exposed in an area 
of the ocean where rock-boring clams (pholads) are known to exist. In 
the 1-1/2 years this test has been under way, none of these concretes 
(including the untreated controls) has shown evidence of attack by the 
pholads. 
11. Biotoxicity tests were performed with certain of the toxicants on 
the eggs and larvae of the red abalone Haliotis rufescens. All of the 
toxicants proved to be fatal to this organism at all concentrations 
tested. 
12. A TBTO-containing antifouling concrete panel prepared in an earlier 
investigation and exposed in the ocean 6-1/2 years had a tin concentration 
essentially the same at both the surface and the interior. The tin at 
the interior was shown to still exist in an organic molecule. 
RECOMMENDATIONS 
Concrete made with aggregate impregnated with a TBTO/creosote 
mixture exhibits antifouling properties after 1-1/2 years of exposure. 
The ratio of TBTO to creosote might well be lowered to reduce the cost 
of the impregnant. Because it has been shown that this mixture of 
impregnants displays a latent period before the best antifouling prop- 
erties are realized, this effect of time should be considered. If it is 
determined that creosote should not be used in concrete for an OTEC 
structure, other hydrocarbon vehicles for TBTO should be investigated. 
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