]M.\N'L'FACTURK OF CemEXT PipE 



97 



the sand. The usual ratio is 5 of sand to 3 of broken stone. A 

 larger proportion of stone might be stronger but there would be 

 some cavities, and more danger of seep spots. Broken stone give.«i 

 greater strength than gravel. If pipe is broken up for examination, 

 the pieces of broken stone are more often broken through, while the 

 breaks run around the gravel. Stone that passes through a ^-inch 

 screen is suitable for 12-inch pipe, and stone from a 1-inch screen 

 for 18-inch pipe. If it is possible to obtain broken stone that has 

 passed through a ^^ j-inch screen, it could be used in a limited way in 

 packer-head pipe. 



For tamped pipe, therefore, the most favorable proportions are 

 1 of cement, 2^ of sand, and 1^^ of J4 irich to ^ inch broken stone. 

 If no stone is available, the mix should be 1 of cement to 3 of sand. 

 For sewer pipe the proportions used in many cases are 1 :25^, but so 

 rich a mix is not necessary unless the sewer is laid very deep or is 

 in soil containing a high percentage of white alkali, particularly 

 sodium sulfate. 



Two samples of the sand being used at Continental were taken 

 on April 3, 1917, and two samples on June 26, 1918. They were 

 subjected to mechanical analysis. 



TABLE V. MECHANICAL ANALYSIS OF SCREENED SAND AT CONTINENTAL, 



ARIZONA 



A cement mixer of the batch type, such as the Blystone, should 

 be used at all cement pipe plants. The cement and sand should be 

 mixed dry for about a minute before the water is let in from a meas- 

 uring tank attached to a frame just over the mixer. Mixing is then 



