Compute Plant-Mix Materials

Several methods are used to calculate the amount of hot-mix material, required for paving projects; however, when the weight of a hot mix per square yard or cubic foot is not known, two equations are used in the NCF to compute the number of tons of asphalt, required for a project. These equations are as follows:

^{L =} length of project in feet.

^{W =} width of project in feet.

^{D =} depth or thickness of compacted mat. You must change inches into feet by dividing the number of inches by 12 (inches in 1 foot). For paver screed height, add 1/8 inch for each inch of the mat to be paved. (Example: For a 2-inch mat, two blocks of wood 2 1/4 inches thick will be required to set under the screed.) The blocks must be thicker than the finished compacted mat to allow for additional compaction by rollers.

^{146 =} This number represents the approximate weight of 1 cubic foot of compacted hot-mix asphalt. This number can vary from 140 to 160 pounds; however, 146 pounds equals the 110 pounds per square yard per l-inch depth of asphalt used in the second equation for figuring tons require for asphalt. (See table 16-2.)

^{WF =} Waste factor equals 5% or .05, or 10% or .10, depending on the experience of the screed operators and handwork required on the project.

^{2,000 =} 2,000 pounds is equal to one ton; therefore, you must divide the total weight of material by 2,000, giving tons required.

Table 16-2.-Weight and Volume Relations for Various Types of Compacted Asphalt Pavement

Where

^L= Length of project in feet.

^W= Width of project in feet.

^{110 =} Pounds per square yard of asphalt per 1-inch depth. (Example: A 2-inch mat will equal 220 pounds per square yard.)

^{9 =} To obtain square yards from square feet, divide by 9.

^{2,000 =} 2,000 pounds equal one ton; therefore, you must divide the total weight of material by 2,000, giving tons required.

^{WF =} Waste factor equals 5% or .05, or 10% or .10, depending on the experience of the screed operators and handwork required on the project.

Example: The specifications for a parking lot paving project are as follows:

L = 90 feet

W = 30 feet

D= 2 inches

WF = .10

Find the amount of asphalt required for this project.