PLAIN CONCRETE 243 



Let c be the number of parts of cement; s, the number of 

 parts of sand; g, the number of parts of gravel or broken 

 stone; C, the number of barrels of Portland cement required 

 for 1 cu. yd. of concrete; S, the number of cubic yards of 

 sand required for 1 cu. yd. of concrete; and G, the number 

 of cubic yards of stone or gravel 'required for 1 cu. yd. of 

 concrete. Then 



11 3.8 3.8 



C = ,S= Cs, and = Cg 

 c+s+g 27 27 



If the broken stone is of uniformly large size, with no 

 smaller stone in it, the voids will be greater than if the stone 

 were graded. Therefore, 5% must be added to each value 

 found by the preceding formulas. 



EXAMPLE. If a 1-2-4 mixture is considered, what will 

 be: (a) the number of barrels of cement, (fc) the number of 

 cubic yards of sand, and (c) the number of cubic yards of 

 stone required for 1 cu. yd. of concrete. 



SOLUTION. (a) Here c = l, s = 2, and g = 4. Substituting 

 these values in the first formula, 



(6) Substituting the values of C and s in the second 

 formula, 



3 8 



S = X1.57X2 = .44 



27 



(c) Substituting the values of C and g in the third 

 formula, 



= X1.57X4=.88 



Table of Quantities. The table on pages 244 and 245, giving 

 the quantities of ingredients for concrete of various pro- 

 portions, was prepared by Edwin Thacher. It will be noted 

 in this table that the difference in the character and size of 

 the stone or gravel used has been taken into account. These 

 values will be found to agree fairly well with values found 

 by Fuller's rule. 



