(fog) room overnight. The next morning, the molds were removed, and the 
specimens returned to the fog room to cure for 28 days. 
The mix design for the concrete was not changed when various amounts 
of dry toxicants were added. In one case, pea gravel was substituted for 
expanded shale aggregate to compare compressive strengths. This was 
done in such a way that the same volume of pea gravel was used as was 
occupied by 40.3 pounds of expanded shale aggregate; thus, 79.5 pounds 
of pea gravel were used in this mix. 
The first specimens for testing were formed in 1977. Antifouling 
concrete containing aggregate impregnated with TBTO and creosote (60:40 
by weight) was prepared (Ref 8,9). A set of control specimens was also 
prepared, using the same mix design, but with untreated aggregate. This 
first set of specimens is designated as Ul, U2, Cl, and C2 (see Table 2). 
Twelve replicates of each were placed in the channel at Port Hueneme 
harbor for 173 days. At periodic intervals during exposure, ratings 
were made of the types and approximate numbers of the types of fouling 
attached to the specimens. When the specimens were removed from the 
ocean they were weighed, dried, and scraped free of the accumulated 
biofouling. At this time, it was decided that the more objective gravi- 
metric ratings gave a better indication of the antifouling performance 
than the more subjective visual observations done periodically during 
the exposure (see Table 3). Subsequently, weighing was done on all 
specimens exposed. 
The remaining sets (2 through 5 of Table 2) were exposed both at 
Port Hueneme and from docks at the University of Miami in Biscayne Bay. 
Set no. 2 contained four types of concrete: one duplicated the TBTO/ 
creosote mixture from the first set, one contained TBTO alone as a 
toxicant, and the other two were controls: one prepared with pea gravel 
to compare its compressive strength with concrete made with treated and 
untreated expanded shale aggregate. Ten replicate specimens of each 
type of concrete were exposed at both sites. 
Cuprous oxide (Cu,0) was employed in set no. 3, both by itself and 
in combination with TBTO. The Cu,0 was simply added to the concrete mix 
and wasn't impregnated into aggregate. As in the second set, TBTO was 
used by itself, but in this set the concentration of TBTO was halved in 
all cases by substituting an equal amount of pea gravel for treated 
aggregate. It was felt that this would both reduce the cost and increase 
the compressive strength of the resulting concrete. Five replicates of 
this set were deployed at both sites. Also, five replicates of each 
member of the third set were placed in the submarine harbor at Key West, 
Fla. to determine the resistance of these concretes to attack by pholads. 
No weighings were done at Key West, but visual inspections were made and 
photographs taken. 
The effect of the chloro-organic compound methoxychlor was investi- 
gated in set no. 4. In two members of this set, the toxicants added to 
the concrete were dry powders and were incorporated into the concrete 
mix by simple addition. Methoxychlor was incorporated into the concrete 
by itself and in combination with triphenyltin hydroxide (TPTH) and 
cuprous oxide. One member of this set was not added to the concrete but 
consisted of an organotin-polysiloxane polymer coating brush-applied to 
otherwise untreated cylinders. Polymerization took place when the 
substance was exposed to atmospheric moisture. The coverage was deter- 
