Appendix B 
MATER [ALS 
by W. R. Lorman 
According to Morgan (1970), "Large concrete vessels have in the 
past behaved extremely well under impact and proved their seaworthiness 
in severe weather, but it must be remembered that all these vessels 
were grossly overdesigned. As design methods and constructional 
techniques become more sophisticated and critical, the previous record 
of good behaviour of concrete vessels ceases to be valid. It must not 
be assumed that modern vessels will be as sound as their predecessors 
which had very large factors of safety inherent in their design. Float- 
ing structures, especially large prestressed powered vessels, present 
complex problems in both design and construction over and above those 
met in land-based structures and the prospects are exciting." 
Deterioration of reinforced concrete in maritime structures occurs 
mostly above the high-water mark and sometimes anywhere within the tidal 
range. Deterioration occurs also on horizontal surfaces, above sea 
level, that are subject to seawater spray. The deleterious effects 
begin as the seawater evaporates, creating concentrated solutions of 
magnesium sulfate which usually attack most of the constituents of the 
hardened cement paste matrix in the concrete. The sodium chloride con- 
centrations promote corrosion of the steel reinforcement. The alkalies 
(sodium and potassium) present in the concentrated solutions may react 
with the aggregate in the concrete. The reaction between calcium 
hydroxide crystals, formed in the hydration of portland cement, and the 
magnesium sulfate (from the seawater) results in the formation of calcium 
sulfate and magesium hydroxide. The insoluble products of this reaction 
occupy a greater volume than do the calcium hydroxide crystals that are 
replaced; consequently these products are the cause of disruptive forces 
which are evidenced by cracking of the concrete cover over the steel and 
subsequent spalling. The situation is worsened by the corroding steel 
and possibly by the alkali-aggregate reaction. To minimize these problems, 
the concrete must incorporate a sulfate-resistant portland cement (ASTM 
Type V preferably or Type II) and the steel reinforcement must be covered 
with at least 3 inches of watertight concrete (i. e., low permeability). 
In warm seawater, the deterioration is usually due to chemical action; 
in cold seawater, due to thermal changes. 
Steel reinforcement embedded in concrete is at first in an alkaline 
environment which inhibits corrosion of steel. To minimize the possible 
adverse effect of chlorides present in the seawater, not only is a 
watertight concrete mandatory but supplementary alkalinity is needed to 
protect the embedded steel. This protection can be attained by using 
lime-saturated freshwater in the concrete mixture; 5 grams of calcium 
hydroxide per liter of water is known to prevent corrosion of steel in 
concrete containing as much as 7% calcium chloride admixture (by weight 
of cement). 
