by using a cement factor of over 8 bags per dubic yards and a water/ 
cement ration of 5 gallons per bag. Five of these 13 floating repair 
docks* were towed to advanced bases in the Pacific Ocean area. All 
proved water tight and required no maintenance during the war. The 
use of concrete for these ARDC's was based on the successful earlier 
performance of 400-ton capacity floating concrete docks, designed by 
the Bureau, for use in repairing small patrol craft. 
Another concrete vessel designed at BuDocks, and constructed early 
in 1944, was the prototype of the concrete LCT (Landing Craft Tank). 
The overall dimensions and capacity were identical to the steel LCT's 
in use at that time. The prototype was 112 feet long, 32 feet wide, 
and weighed 224 tons (in air). The construction involved precast 
slabs, precast cells, shotcrete, and cast-in-place concrete (MacLeay, 
1950). The cells were 4 by 7 by 5 feet in size and had wall thick- 
nesses of 3/4 inch (for the 4 foot sides) and 1-1/2 inches (for the 7 
foot sides). Reinforcement was wire fabric. Compressive strength of 
the concrete in the cells was 8500 psi at age 28 days; aggregate/cement 
ratio of the rather stiff mixture was about 2.5 for the cells and for 
the slabs which were 1-1/4 inches thick and also reinforced by wire 
fabric. The completed prototype was tested for 6 weeks, during which 
the vessel outrode a hurricane and underwent full-speed landings on 
gravelly beaches, without damage to the concrete. The cost of such 
concrete LCT's was deemed comparable to that of steel LCT's built under 
wartime conditions, but apparently the USN need for such landing craft 
diminished the following year, and no production was initiated. 
All of the concrete vessels constructed in America, Great Britain, 
and Europe during both World Wars I and II have been estimated to re- 
present a total displacement of 500,000 tons (Jackson and Sutherland, 
1969). These ocean going concrete ships and barges were structurally 
sound. Nevertheless, further development was apparently undesirable 
because conventionally reinforced thick concrete hulls are heavier 
than comparatively thin steel hulls. Assuming no shortage of steel 
plate in peacetime, the greater motive power requirements of a concrete 
ship preclude the comparatively economic operation that prevails among 
steel ships. This weight disadvantage might be overcome by resorting 
to prestressed concrete hulls, but such possible trend has not yet 
appeared among the steel-orientéd ship designers. 
The experienced gained in building concrete hulls during World 
War II subsequently led to improved methods of fabricating floating 
concrete platforms. A post-war example is the landing stage built 
in 1952 at Hamburg, Germany (Minetti, 1956). It consists of five com- 
partmentalized reinforced concrete pontoons, each 390 feet iong by 60 
feet wide by 13 feet high, having wall 10 inches thick (Billig, 1960). 
A floating highway, nearly 1-1/2 mile long, and known as the Hood 
Canal Bridge crosses a portion of Puget Sound about 35 miles north of 
Seattle. The structure, completed in 1960, consists of 23 floating 
reinforced concrete pontoon bolted together (Andrew, 1959). Water 
depths at mean low tide range from 70 to 340 feet, tidal range is 18 
* 
Designated ARDC during the war and in 1946 redesignated ARDL(C) which 
denotes Auxiliary Repair Drydock Little (Concrete). 
