Lesson 6/Learning Event 4
Step 10: Calibrate the Asphalt Metering Pump.
The amount of asphalt in a given specification is written as a percent of the total mix (plant
output). Since the final plant output is dependent on the amount of aggregates being processed
by the dryer, the amount of asphalt is regulated in direct proportion at the same time that the
amount of aggregates to be fed by the apron feeders is determined (Step 6). The asphalt flow is
controlled by the positive displacement, variable volume metering pump (Figure 26).
FIGURE 26. METERING PUMP
To calibrate the asphalt metering pump, it is necessary to establish the type of bituminous
material, specific gravity of bitumen material, and bitumen temperature near the metering pump.
The pump is calibrated to determine the setting which will deliver the required asphalt to the
mix. The pump may be calibrated by either the arithmetic method or the pump output method.
(1) Arithmetic method (Specific gravity and temperature known). Refer to Step 9. This
example will use 85-100 penetration asphalt cement having a specific gravity of 1.015. The
mixing temperature will be 300F.
a. Determine the lbs per rev of titumen to be used in the mix (9.3 from Step 6).
b. Calculate the lbs per gal at mixing temperature of the bitumen being used (refer to
Step 10). As established above, the mixing temperature of 85-100 penetration asphalt
cement is 300F. Refer to Table 18. In this table, "t" equals the mixing temperature
of the asphalt and "M" equals the multiplier to be used to convert the weight of one
gallon of asphalt at 60 to the weight of one gallon at mixing temperature. In Table
18 find 300 in the column headed "t." To the right of the column headed "M," it is
seen that the multiplier is 0.9187.