DlRAIillJTV 



141 



ing the least effect. The grand average crushing strength of the 16 

 kinds of tile in the eight locations has not diminished in the three 

 years, but many tile show alkali salts in the fracture. Some of the 

 tile, notably the leaner and drier mixtures, are partly disintegrated. 

 It is concluded tentatively that the injury to cement pipe is propor- 

 tional to the sulfate and magnesia present in the soil water and to 

 the degree of concentration of the salts. Hand-tamped tile are 

 not so resistant as machine-made tile, and tile made of sand cement 



Fig. 27. — Cement pipe, completely disintegrated while curing, due to unsound ce- 

 ment. This is not an argument against the use of cement pipe, but it demonstrates 

 that good material and skill must be utilized in its manufacture. 



have less resistance than those made with Portland cement. It is 

 recommended that tile should be made not leaner than 1 : 3, of quak- 

 ing consistency, and as dense as possible. 



In the Salt River Valley concrete structures in great numbers 

 have been built by the U. S. Reclamation Service and other parties, 



