METHOD OF CONSTRUCTION OF CONCRETE SHIPS. 15 



either brick or cement kilns to such a temperature that it bloats. After cooling it is 

 crushed, screened and used as any normal aggregate. The fines passing a i/io 

 or 3/16-inch screen are used as sand, and the coarse from i/io or 3/16 to J^ inch is 

 used as coarse aggregate. 



This aggregate, being porous and ver'y sharp, was not as workable in the plastic 

 concrete as might have been desired, particularly if the fines lacked in content of 

 dust. The gradation of the fines varied, depending in part upon the type of crush- 

 ing equipment employed. 



In order to increase the workability of the plastic concrete in such cases, a very 

 small quantity (i^ per cent by weight or about 12 per cent by volume of cement) 

 of celite was employed. This material is a very light-weight (about 12 pounds to 

 the cubic foot) natural silica product of the following composition: — 



Silica (SiOa) 86.00* 



Ferric oxide (Fe203) 1.61 



Alumina (AI2O3) 2.99 



Lime (CaO) 44 



Magnesia (MgO) 72 



Sulphuric anhydride (SO3) Trace. 



Ignition loss 7.90 



Alkali by difiference 34 



100.00 



The addition of this material also tended to prevent segregation of the coarser 

 particles in the concrete. 



The concrete mixture employed was usually composed of one part by volume of 

 cement to two parts of total aggregate. The proportion of coarse and fine in the 

 aggregate varied from % part fine to iVs part coarse to i part fine to i part coarse. 

 Table 5, Plate 4, gives a summary of some of the tests made from concrete used in 

 the hulls. 



EQUIPMENT USED TO TRANSPORT CONCRETE TO FORMS. 



A dififerent type of concreting plant was used at each yard. At Oakland the 

 plant consisted of two 24-cubic feet Koehring mixers set in pits. The aggregate 

 and cement was brought to the mixers in buggies. A 90-foot elevator tower with 

 one cubic yard automatic dumping buckets was set over each mixer. The buckets 

 dumped into a hopper at the top of the tower. One double drum electrically oper- 

 ated hoist served both elevators. The forward tower distributed concrete through 

 three main chutes, which terminated in one yard, distributing hoppers on the center 

 line of the ship about 40 feet apart. The after tower supplied three similarly located 

 distributing hoppers in the after end. These distributing hoppers were arranged 

 with four outlets, and from them the concrete was passed through chutes to buggies 

 and distributed by the buggies to the forms. 



*16.76 is soluble in 10 per cent HCl and 11.24 is soluble in S per cent NaiCOs. 



