INTRODUCTION 
For centuries ships were “careened," or laid over on their sides, 
to remove fouling from their hulls and replace the materials then used 
as antifoulants. In 1495, the first dry dock was built for Henry VII at 
Portsmouth (Ref 1), and this method for removal of fouling has today 
replaced careening. Neither of those methods is presented as a possible 
way to keep an Ocean Thermal Energy Conversion (OTEC) facility free of 
fouling, but they are cited to present the difficulty man has encountered 
over the centuries in ridding his ocean-going vessels of accumulating 
biomass. 
This investigation was directed at the production of concrete which 
will resist the attachment of marine fouling organisms. Such a concrete 
is needed to form or line the hull and cold water pipe of the proposed 
OTEC structure. Growth of marine fouling organisms on a floating structure 
can add significantly to its weight, thus reducing freeboard. For 
instance, biomass has accumulated to 25 1lb/ft* on buoys in less than 3 
years (Ref 2, p. 17). The cold water OTEC pipe, when fouled, would 
provide a reservoir of adult organisms (Ref 2, pp 11-14) that could 
discharge eggs or larvae directly into the heat exchanger surfaces. 
Adult members of an established fouling community would be sloughed off 
in time, causing clogging of screens. Broken pieces of calcareous 
shells of adults carried in the cold water intake would present further 
problems. The Civil Engineering Laboratory (CEL) has undertaken an 
investigation of methods to make concrete that resists the attachment of 
marine fouling organisms. 
Ten years ago at CEL, James S. Muraoka prepared concrete incor- 
porating toxic chemicals as antifoulants (Ref 4,5). This method of 
incorporating oily toxicants into the concrete was patented (Ref 6). In 
this method, a porous, expanded shale aggregate was impregnated with 
such toxicants as bis-(tri-n-butyltin) oxide (TBTO) and creosote. 
Concrete was then prepared from the treated aggregate, cement, and 
water. Toxicants other then TBTO and creosote were evaluated. These 
included pentachlorophenol, quaternary amines, malachite green base, 
malachite green oxalate, tributyltin fluoride, nicotine, and copper 
naphthenate. Muraoka concluded that an impregnant consisting of a 
mixture of creosote and TBTO (3:1 by volume) yielded concrete having the 
best antifouling properties (Ref 5). Because the interest at that time 
was primarily in antifouling properties, sand was not used in the con- 
crete mix design. As a result, the compressive strength of the resulting 
product was lower than that of standard concrete. With the advent of 
the OTEC concept, an antifouling concrete with a higher compressive 
strength was required. The work described in this document is directed 
toward that objective. 
