ITEM 402 ASPHALT CONCRETE MIXING PLANTS
402.01
Description
402.02
Calibration
402.03 Polymer
Binders
402.04 Water
Injection System for Warm Mix Asphalt
402.01 Description. This specification consists of the
minimum requirements for an asphalt concrete mixing plant to produce asphalt
concrete mixes according to Department specifications.
Ensure asphalt
concrete mixing plants conform to the requirements of Supplement 1101 in addition to the
following.
402.02 Calibration. Ensure the plant is calibrated
according to Supplement
1101 when producing any asphalt concrete for the Department. Ensure that
the calibration is accurate within 1.0 percent. When performing a complete
calibration for ODOT projects notify the ODOT district 24 hours in advance of
the calibration.
402.03 Polymer Binders. If an asphalt binder is
modified by SBR at an asphalt concrete mixing plant,
equip the plant with an automated SBR flow control
and monitoring system. Obtain the Department’s approval of the system before
operating and demonstrate the system calibration to the District. If the
District waives the demonstration, provide a letter documenting calibration
data for the flow system to the DET for each project.
Obtain written approval from the Laboratory for the use of SBR
and ensure the QCP contains methods for properly
controlling SBR.
For
drum mix plants, introduce the SBR directly into the
asphalt binder line through means of an in-line motionless blender or other
device approved by the Laboratory which is able to provide a homogeneous blend.
Locate a sampling valve between the in-line blender and the plant drum.
For
batch plants, add the SBR after the aggregate has
been completely coated with asphalt binder. Continue mixing for a minimum of 20
seconds after SBR is added and long enough to provide
a uniform mixture.
Ensure
the SBR pumping and metering system is capable of
adding the SBR within the limits of 702.01. For drum plants ensure the SBR pump is automatically controlled by an independent
computer and interfaced with the asphalt binder flow to automatically maintain
the SBR flow within specification limits. Produce
asphalt mixtures for placement in automatic SBR
control mode only.
Ensure
the SBR meter is accurate to ± 2.0 percent over a
flow range typical of that used at the asphalt plant (typically 0.8 to 12 gpm at drum plants and 10 to 25 gpm
at batch plants). Ensure the SBR meter is a magnetic
flow meter consisting of a metering flow tube which utilizes Faraday’s Law of
Induction to measure the flow and includes a transmitter to transmit the flow
signal to a totalizer located in the control room of the asphalt plant. Locate
the SBR meter downstream of any recirculation lines.
Provide a means for removing the SBR line at the
in-line blender to be able to obtain a sample of the SBR
for calibration purposes.
Obtain
Laboratory approval for use of any other type of SBR
meter. Ensure the totalizer displays total volume measured and flow rate in
standard engineering units. Ensure the totalizer is interfaced with a data
logger which produces printouts of the logged data every five minutes for a drum
plant or every batch for a batch plant. Ensure the logged data includes time,
date, flow rate, and flow total except flow rate is not necessary for batch
plant production.
Balling
or wadding of SBR or uncoated aggregate indicates
improper mixing; cease production immediately and until corrected to District
satisfaction.
402.04 Water Injection System for Warm Mix Asphalt.
When
allowed by specification use a water injection system
approved by the Department for the purpose of foaming the asphalt binder and
lowering the mixture temperature. Only use equipment that has been proven
stable and effective through project use on non-ODOT projects. Ensure equipment
for water injection meets the following requirements:
1. Injection
equipment computer controls are in the plant control room and are tied to the
plant computer metering.
2. Injection
equipment has variable water injection control controlled by the plant
operation rate and the water injection can never exceed 1.8 percent by weight
of asphalt binder.
3. Water injection
rate cannot be manually overridden by the plant operator once in the computer.
4. Injection
equipment stops water flow when a control or equipment failure in the injection
system occurs.
5. The water
injects into the asphalt binder flow before the asphalt binder spray hits
aggregate. Do not allow water to touch aggregate before the binder spray.
6. Injection
equipment includes water storage and pump control tied to the injection
computer controls.
7. Water storage
low water alarm installed in the control room.
8. Provide a PG
binder sampling valve between the last piping tee on the tank side of the line
and the injection equipment to sample PG binder before water is injected.