124 CONCRETE OR CEMENT SILOS. 



"To obtain best results in concrete it is necessary first 

 to use good cement, and, second, the work must be care- 

 fully and skillfully done. This is particularly true of re- 

 inforced concrete. The mixing of the concrete requires 

 skill as well as does the tamping of the concrete in the 

 forms. The proportion of sand to mix with the gravel or 

 crushed stone will vary somewhat with the character of 

 the gravel and the sand and it requires experience to 

 know just the right proportions to use. The proportion of 

 cement to sand will vary with the cement and with the 

 sand. This again involves skill. The amount of water to 

 use will vary considerably with circumstances. If the 

 cement is too wet or too dry best results will not be ob- 

 tained. Experience and skill are again involved here. 



"If it were possible to have the work skillfully done 

 a cement silo 16 feet in diameter and 35 feet high could 

 be built of reinforced concrete with walls only 2 or 3 

 inches thick and be abundantly strong. But labor suffi- 

 ciently skilled to do this would cost too much, so that 

 it would be cheaper to use twice as much cement; make 

 wall 6 or 8 inches thick and use less skilled labor. If the 

 work is carefully done using ordinary labor it is prac- 

 ticable to build silos 16 feet in diameter and 35 feet high 

 with 6 or 8 inch walls if the steel rod is laid in the wall 

 every 2 or 3 feet." 



Reinforced concrete offers great possibilities for silo 

 building. The lateral pressure on the walls when the silo 

 is filled is very great, but the circular shape renders it 

 very easy to reinforce. The freezing of the silage has 

 heretofore been the one disadvantage of solid walls, espe- 

 cially in cold climates, but this has been largely overcome 

 by machines now on the market that easily and success- 

 fully build reinforced and continuous hollow walls. (See 

 pages 165 and 166 for special articles on frozen silage.) 



The foundation, as in all other concrete structures, is 

 very important. Not only must it serve as an anchor to 

 protect the structure against wind pressure, but it must 

 also be very strong and firm or the great weight upon it 



