142 Bulletin 86 



but there is not a single instance of disintegration or weakening due 

 to alkali. Only one case has been observed by the author of pos- 

 sible deterioration from alkali. In that case the pipe was made by 

 a novice and was poorly tamped. The seepage through the porous 

 spots, which are usually narrow, perhaps one-half inch to an inch 

 along the pipe line, has apparently carried away the cement in solu- 

 tion. The intervening portions are still hard and ring when struck 

 with a hammer. This pipe line is ten years old. 



It has long been known that certain pozzuolanic cements are ex- 

 ceedingly resistant to the action of sea water and consequently to 

 similar soil alkalies. Some efforts are now being made to produce 

 a "marine cement" or "alkali-proof cement" by regrinding Portland 

 cement with pozzuolanic materials, especially diatomaceous earth. 

 Laboratory tests show such mixtures to be resistant to chemical 

 action and to be actually stronger in sea water than in soft water. 



Good cement pipe cannot be made from unsound cement. Fig. 

 27, reprinted from Bulletin 55, shows cement irrigation pipe which 

 disintegrated while curing and for which the cement manufacturers 

 paid damages. Cement should be purchased with the standard 

 specifications of the American Society of Civil Engineers. Unsound 

 cement is met with much less frequently than it was twenty years 

 ago. 



