Houston, Tampa, San Francisco, and National City, adjacent to San Diego 
(Tuthill, 1945). During the period 1942 and 1945 a total of 104 con- 
crete hulls were built; 24 of these were for self-propelled dry cargo 
ships (McLaughlin, 1944) each 350 feet long by 54 feet wide by 35 feet 
high; the remainder were for barges (Engineering News-Record, 1943) or 
lighters which were designed for towing and which ranged from 265 to 
366 feet in length, 48 to 56 feet in width, and 18 to 38 feet in 
height. The concrete in all of these vessels incorporated lightweight 
aggregate (maximum size 1/2 inch) modified portland cement (ASTM Type 
II), and in some cases a set-retarding admixture. Average slumps 
were seldom over 4 inches. Cement factor was 9 bags in most cases. 
Minimum compressive strength required at age 28 days was 5,000 psi. 
The average water/cement ratio ranged between 0.45 and 0.50 (by weight). 
Hull thickness of the concrete vessels was 6-1/2 inches. 
Among the 80 ship-shaped concrete barges, 26 were built at the 
Delair shipyard of Barret & Hilp, contractors, at San Francisco Bay 
under contract for the U. S. Maritime Commission. The first of these 
366-foot barges was floated in its graving dock in June 1943. The 
barges were designed for loads of 2,368 pounds per square feet of ship 
bottom and 416 pounds per square feet of deck. The superstructure was 
designed so that vertical bulkheads would resist horizontal forces, due 
to waves arriving aft on the deck, as high as 950 pounds per square 
feet. Reinforcement was heaviest in the midsection where steel amounted 
to 35 pounds per cubic feet of concrete. Reinforcing bars were positioned 
carefully to specified clearances which, at certain locations, were 
within 1/2 inch of the concrete surface. The bottom was 7 inches thick 
and the sides 6 inches thick. Each longitudinal reinforcing bar was 
welded into one piece 366 feet long, dragged into the formwork, and 
laid in proper position. Unit weight of freshly mixed concrete was 126 
pounds per cubic feet initially, but was later reduced to 116 pounds 
per cubic feet. Wooden forms for the hulls were erected in 6 graving 
docks. The completed concrete hulls were floated into the Bay by 
flooding the graving docks. 
Early in the U. S. Maritime Commission's concrete shipbuilding 
program, an investigation of concrete vessels built previously during 
World War I revealed that reinforcing steel rarely corroded or became 
exposed due to spalling wherever the concrete cover over steel was 
greated than 3/8 inch. 
In addition to the U. S. Maritime Commission's program during World 
War II, the Bureau of Yards and Docks in 1943 undertook the construction 
of 13 auxiliary reinforced concrete floating repair docks (ARDC), each 
of 2800 ton capacity (Anon., 1947). These were 389 feet long, 84 feet 
wide, and had an overal height of 40 feet which included 14 feet high 
bottom pontoons (compartmental); the 26 feet high wing walls tapered 
from 14 feet at the base to 10 feet at the top deck. Eight of these 
were built at Wilmington, North Carolina and five at San Pedro, Califor- 
nia in dry basins. Each required 3300 cubic yards of concrete which was 
designed to have a 28 day compressive strength of 4000 psi, obtained 
