78 



Storage. Cement must be stored under a weath- 

 erproof cover on a platform raised a sufficient height 

 above the ground to prevent any dampness reaching 

 the cement. Only unbroken packages will be stored. 

 Broken packages must be put to one side during the 

 work of unloading, until the count of the car can be 

 verified. If undamaged, they will be used as promptly 

 as possible. 



Sand. The sand should be clean and coarse. The 

 cleaner the better. Fine sand should be avoided; it is 

 difficult to mix evenly and this may lead to poor re- 

 sults. If the sand is too coarse, it is not of the best 

 quality, but it is not as likely to cause trouble as a 

 fine sand. 



A rough test for cleanliness of the sand is to rub 

 it between the hands ; it will not soil them if it is clean. 

 A more accurate method is to put a sample of the 

 sand in a bottle, fill it with water nearly to the top, 

 then shake the bottle thoroughly. The sand will settle 

 to the bottom with the dirt on top of it when the mix- 

 ture is allowed to settle. The amount of dirt can be 

 measured approximately. Sand containing 5 per cent 

 or more of foreign matter should be rejected. 



In sampling the sand, care should be used to obtain 

 an average sample. 



Gravel. Gravel is not to be used, except when spe- 

 cial permission is obtained. It must conform to the 

 specifications and be screened when it contains a large 

 percentage of sand, or the amount of sand used in 

 mixing the concrete must be reduced. The amount of 

 sand in the gravel can be estimated by sifting samples 

 of it. 



Broken Stone. Broken trap rock forms a desirable 

 aggregate. Limestone must be avoided in work ex- 

 posed to high temperatures. Stone must comply with 

 the specifications in regard to size. Each lot of stone 

 must be inspected to see that it does not contain 

 quantities of stone dust. Many quarries prefer to de- 



