CONCRETE 



13 



diameter of hole, and also illustrate how inefficient the screening 

 process may be. For example, if the sizes of the particles had 

 corresponded exactly to the diameters of the holes and the 

 screening had been more perfectly done, the curves would have 



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 6 

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had more nearly the direction and location of dotted lines No. 

 la and No. 2a. In combining these curves so as to obtain the 

 strongest and most impermeable concrete, it is quite clear that 

 the grains smaller than 0.10 in. diameter must be supplied 

 wholly from the portion Oa of the sand curve; while the larger 



