280 FARM BUILDINGS IN SOUTH AFRICA 



(2) Referring to the table on p. 130 we find that the quantity of 

 cement required for 1 cubic yard of 1 : 2i : 5 concrete is 

 1*29 barrels. Hence — 



Amount of cement required for 33*3 cubic) Q ft „ • 



yards of concrete ) 



= 43 barrels 

 which are equivalent to 86 bags. 



Again referring to the table we find that 045 cubic yard of sand will 

 be required for 1 cubic yard of this concrete. Hence : — 



Amount of sand required for 33*3 cubic) . ._ on ■ 



\ = 0*4:5 X 65'6 

 yards of concrete ) 



= 15 cubic yards. 



The same method might be employed to calculate the amount of stone, 

 but it is evident that just twice as much broken stone as sand 

 will be required, or — 



Amount of broken stone required = 30 cubic yards. 



Example. — Calculate the approximate amounts of cement, sand, and 

 broken stone required for the reinforced concrete silo illustrated on p. 217. 



For purposes of calculation we will look upon the silo as having no 

 emptying doors. The materials which are saved by the presence of the 

 emptying doors will approximately be sufficient for the cornice, and to 

 allow for the richer concrete which is used around the emptying doors. 



The only formula which it is necessary to employ is that for the 

 volume of a cylinder, viz. : — 



V=^yj ........ (I.) 



where tt = 3f or 314, 



d = diameter of cylinder, 



h = height or length of cylinder. 



(a) The wall of the silo may be treated as a hollow cylinder, its 

 volume being equal to the difference between the volume of a 

 cylinder of diameter equal to the external diameter of the silo 

 (15' 10"), and that of a cylinder of diameter equal to the 

 internal diameter of the silo (15' 0"), the height of both 

 cylinders being 30 feet (see Fig. 166). 



