Investigations into the effect of the antifouling additives on the 
corrosion of reinforcing rods were performed. These tests indicated 
that those additives which proved efficacious retarded the corrosion of 
steel reinforcement. 
Biotoxicity tests revealed that the toxicants were lethal to test 
organisms in very small doses. Organotin (as TBTO) was found to remain 
bound in an organic molecule in concrete for 6% years in the ocean. 
Costs 
The cost of the toxicants employed is significant and will be a 
criterion in the selection of an antifouling system. The coating system 
consisting of the organotin-polysiloxane polymer is the least expensive, 
but insufficient data have been gathered to allow an estimation of its 
useful lifetime. At the coverage rate used in this investigation, the 
cost of this product was $0.10/ft?. 
The TBTO-impregnated rubber is higher in cost — cost increasing 
with increasing thickness. The 0.08-in.-thick sheet of this rubber 
product costs $4.85/ft? for material and adhesives. A 1-in.-thick panel 
has remained totally fouling free in Biscayne Bay for 7 years, according 
to the manufacturer. A 0.5-in.-thick sheet has an estimated antifouling 
life of 25 years in tropical waters. 
The cost of the two toxicant-bearing concretes described in this 
investigation depends upon the thickness of the treated concrete layer 
applied over the concrete structure. Assuming a 0.5-in. layer, the cost 
of the toxicant in the TBTO-creosote system is $1.64/ft*. This could be 
reduced (and perhaps an even better concrete prepared) by reducing the 
ratio of TBTO to creosote. The system employing TPTH, cuprous oxide, 
and methoxychlor carries a toxicant cost of $2.64/ft* when applied 
0.5-in. thick. Insufficient data are available to make it possible to 
speculate on whether this cost could be reduced significantly without 
losing the antifouling properties of the concrete. 
CONCLUSIONS 
Various candidate antifouling concretes were prepared and exposed 
in the ocean at two sites. The effects of the chemicals used as anti- 
foulants were investigated. Toxicity tests of the antifoulants on 
specific organisms were performed, and their effect on reinforcing rod 
was investigated. Results of these investigations are summarized as 
follows: 
1. Concrete into which toxicants were incorporated accumulated, at 
best, about half as much fouling as untreated controls. This ability to 
resist fouling is insufficient for practical use in the present form. 
Two systems in which toxicant-bearing coatings were applied to concrete 
show promise, but they have been under investigation for only a short 
time. 
2. A mixture of TBTO and creosote (60:40 by weight) impregnated into 
aggregate from which concrete is made yielded a product with better 
antifouling properties than concrete prepared from aggregate impregnated 
with TBTO only. This is highly significant from a cost standpoint. 
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