Lesson 6/Learning Event 4
Learning Event 4
PLANT CALIBRATION AND OUTPUT
A necessary step in the production of asphalt mixes is the calibration of the mixing plant. During
the calibration process the components of the plant are adjusted to feed the proper amounts of
aggregate and asphalt cement to meet the mix specifications.
The following list contains essential preliminary information for plant calibrations:
Mix specifications limits
- percent and type of bitumen
- aggregate gradation limits
Gradation of the available aggregates
Number of bins to be used for dry aggregate
Screen sizes available
Aggregate moisture content
The recommended sequence in calibrating the high type asphalt plant is as follows:
Determine the proper aggregate blend.
Select the screen sizes to be used in the gradation unit.
Determine the dryer capacity.
Determine the smallest screen size capacity.
Determine the plant output.
Determine the feeding rate.
Determine the gradation unit feeder speeds.
Calibrate the gradation unit feeder gates.
Calibrate the fines feeder.
Calibrate the asphalt metering pump.
Determine the initial cold feed settings.
Check all settings.
The procedures for calibrating the above items are:
Step 1. Determine the Proper Aggregate Blend
There are various methods used for determining the aggregate blend proportions. To date,
however, the trial and error method is most workable for field engineers. The procedures for this
method of blending was discussed in Lesson 5, Learning Event 2. The information required is a
sieve analysis performed on each stockpile of aggregate, as specified gradation of blend
(gradation selected), and the quantity of materials available (Table 12).