ANTIFOULING MATERIALS 
Three methods of preparing antifouling concrete were investigated. 
In the first method, a porous expanded shale aggregate was impreg- 
nated with liquid toxicants, and concrete was prepared in an otherwise 
normal manner. In another method, dry toxicants were added directly to 
the concrete mix. The toxicants employed as additives in this investi- 
gation were organotin compounds, creosote, cuprous oxide, and a chlo- 
rinated organic insecticide. These were evaluated alone or in certain 
combinations. The third method involved the application of a special 
coating to otherwise untreated concrete. Two antifouling coating systems 
were investigated, both containing organotin toxicants. 
All of the materials investigated were incorporated into or were 
applied to 3-in.-diam x 6-in.-long concrete cylinders. The test cylinders 
were then exposed in the ocean at Port Hueneme, Calif., and Key Biscayne, 
Fla. The cylindrical shape was chosen so that compressive strength 
determinations could be made according to methods stipulated by the 
American Society for Testing and Materials (ASTM) (Ref 7). The anti- 
fouling properties of candidate concretes were measured by periodically 
weighing the specimens and attached fouling organisms. This resulting 
weight increase was compared with that of untreated controls which were 
similarly weighed to determine, by difference, the weight of accumulated 
biomass. 
Treated Aggregate 
Liquid toxicants were impregnated into porous, expanded shale 
aggregate to establish a reservoir of these antifouling chemicals in the 
finished concrete. The aggregate was first dried at 110°C to remove 
moisture. A list of the materials used in this work is presented in 
Table 1. 
Two methods of incorporating liquid toxicant into the aggregate 
were evaluated. 
In the first, the aggregate was placed in a container, covered with 
creosote, and allowed to stand 48 hours. The creosote was poured off, 
and the treated aggregate was allowed to drain, then spread on newspapers 
overnight to remove excess creosote from the surface. Using this method, 
an uptake of creosote equal to 16.0% of the weight of the aggregate was 
realized. 
Vacuum impregnation of the aggregate was then evaluated. In this 
procedure, the dried aggregate was placed in a vacuum chamber from which 
the air was removed. Creosote was admitted until the aggregate was 
covered, whereupon air was allowed to return the pressure in the chamber 
to atmospheric, forcing the creosote into the pores of the aggregate. 
After a 1- to 2-hour soaking time, the creosote was removed and the 
aggregate dried in the same manner as before. This impregnation method 
yielded a creosote uptake of 36.8% of the weight of the aggregate and 
was used in all subsequent work. Toxicants used to treat aggregate by 
the vacuum impregnation method were bis-(tri-n-butyltin) oxide (TBTO) 
alone and 60 parts TBTO mixed with 40 parts creosote by weight (Table 2). 
The average uptake of TBTO alone by the aggregate was 40%, while the 
average uptake of the TBTO/creosote mixture was 38%. 
