PART TWO - HISTORY OF CONCRETE STRUCTURES 
IN A MARINE ENVIRONMENT 
by W. R. Lorman 
SIGNIFICANT FIXED STRUCTURES 
The earliest known use of concrete in a marine environment is an 
ancient waterfront structure, the remnants of which are in evidence 
today on the Italian coast near Naples. Early in the lst century, 
sometime between 12 and 41 A.D., the Romans constructed concrete pillars 
as supports for a large wharf in the Bay of Pozzuoli. In 1954, after 
19 centuries of submergence in seawater, the concrete was considered 
still serviceable on the basis of scientifice examination of various 
samples retrieved from the structure. This installation is believed 
to be the oldest known example of concrete in seawater. The Roman 
engineers utilized the fact that pozzolanic material, in the form of 
volcanic ash from nearby Mt. Vesuvius, reacts with lime to create a 
cementitious compound that hardens underwater. Along the coast between 
Naples and Gaeta to the north there are great masses of Roman concrete 
still extant, as evidence of the resistance of plain (non-reinforced) 
concrete to the action of the sea. 
According to Vitruvius, Roman concrete structures consisted of 
a calcareous mixture, which actually was a combination of lime, natural 
pozzolana, and water, placed over and around broken stone (rubble) and 
built up as layers of concrete. Wooden formwork was sometimes used. 
The usual mix proportions of the solids in the mortar were 2 parts 
of lime and 5 parts of pozzolana. 
As the result of the demise of the Roman Western Empire in 476, 
the use of pozzolanic mixtures declined by the end of the 5th century 
and the knowledge was forgotten during the dark ages. During the mid- 
dle ages the mortars used in stone masonry construction were usually 
mixtures of lime, sand, and water, but such construction was limited to 
structures on land. 
In the 18th century the Italian and French engineers followed the 
principles laid down by Vitruvius. In 1748 one of the jetties at 
Toulon, France, was made entirely of concrete; in 1774 the drydock at 
Toulon was constructed of similar materials (Rennie, 1857). In 1756 
the concrete used in constructing the base of the stone lighthouse on 
Eddystone Rock, situated on the Cornish coast of England, consisted of 
pozzolana mixed with hydraulic lime containing a considerable amount 
of clay. This was the first instance of an improvement (Lea, 1956) 
on the Roman mixture of lime and natural pozzolana, up to that time the 
only suitable cementitious material for structures under or exposed to 
water. The base and first floor of the Eddystone lighthouse still 
remain today althoughthe lighthouse proper was dismantled and relocated 
at nearby Plymouth where it now stands. 
