Guidelines for Marine Artificial Reef Materials, Second Edition

Lime (calcium hydroxide) in "green" or uncured cement may have surface pH levels of 10 to 11,
which is significantly more basic than seawater, which has a pH of 8.3. This can make the surface
of uncured concrete toxic to invertebrate organisms for 3 to 12 months. Pozzalanic materials can
help to neutralize the surface pH by combining with the free lime. Such materials include coal
combustion fly ash, diatomaceous earth, clays, shales, pumicites, micro-silica, among others. A
pozzalanic material reacts with the free lime, lowering the pH and also providing for better bonding
between aggregates, thus making the concrete stronger. The majority of concrete used in reef
applications is not used in the “green” or uncured form. Most imperfect culvert, bridge or road
decking or demolition debris has aged and cured for many months or years prior to deployment as
reefs. An estuarine reef made from concrete culvert in Delaware Bay exhibited the rapid
development of an epifaunal community, dominated by the polychaete worm, Sabellaria vulgaris.
Biomass and species diversity equaled that of the adjacent infaunal community less than two months
after deployment.
Research and development studies, conducted by the Portland Cement Association, have
characterized the long- term performance of concrete exposed to sea water (Stark 1995). Where
freezing and thawing is not an issue, as is the case with reef materials, the report concludes “Based
on the 32 to 34 year performance observations… All concretes exhibited a high level of durability
in seawater exposure, regardless of ASTM type of Portland cement. The ratio of water to total
cementitious material and quantity of air entrainment and pozzolans appears to be of little or no
significance in the observed durability of concrete.” Other studies have tested strength of concrete
in seawater over a 30-50 year period. In all tests, concrete of various types continued to gain
compressive strength which continued to increase over the period of observation (Portland Cement
Association, personal communication). This increase in strength is due to the continuing hydration
of the cement on a molecular level. The duration of these studies has not been sufficient to measure
how long this strengthening process may continue, but estimates range from many decades to
hundreds of years.
In a search of the available literature, the earliest reports regarding the use of concrete for artificial
reefs was 1962 (Martinez 1964); however, while not reported in the literature, in 1962, 300 tons of
concrete pipe were sunk off Perdido Pass, Alabama, in approximately 60 feet of water. Similarly,
concrete pipes were utilized for Alabama offshore reefs in 1964, 1970, 1971, and 1977 (Walter
Tatum, personal communication). During the 1980s, three bridges were replaced in the Alabama
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