[ESTIMATING.]
ESTIMATING CONCRETE.
In estimating the amount of concrete in a given piece of work and the quantities of materials required, the unit of measurement is usually the cubic yard (27 cubic feet). The following examples will explain best the method of determining the quantities required:
Example 1.—A wall 9 inches thick, 12 feet high, and 30 feet long has a door opening 3 feet wide and 6 feet high, also a footing 18 inches wide and 9 inches deep. The concrete is to be mixed in the proportions of 1:2:4.
The volume of the footing is found by multiplying together the dimensions expressed in feet, thus, 11/2 ×3/4 × 30 = 333/4 cubic feet. Similarly, the volume in the wall is3/4 × 12 × 30, less the door opening3/4 × 3 × 6 = 2561/2 cubic feet.
The total volume in footing and wall is 2901/4 cubic feet = 103/4 cubic yards.
To find the quantity of cement, sand, and gravel, multiply the amounts for 1 cubic yard, indicated in line 7 of Table 1, by 103/4, and it will be found that 65 sacks of cement, 4.83 cubic yards of sand, and 9.56 cubic yards of gravel are necessary to build the wall.
Example 2.—A pavement 27 feet long, 4 feet wide, and 6 inches thick has a 5-inch base mixed in the proportions of 1:3:5 and a 1-inch surface mixed in the proportions of 1:2.
The volume in the base is 27 × 4 ×5/12 = 45 cubic feet = 12/3 cubic yards.