SECTION 401
3.5 Drum Mix Plants — General.
3.5.1 The plant shall be specifically designed for the process and shall be capable of satisfactorily heating, drying, and
uniformly mixing the bituminous material and aggregate in accordance with the job mix formula. The rate of flaw through the
drum shall be controlled in order that a homogeneous mixture is obtained with all particles uniformly coated. In no case shall
the quantity of mix produced exceed the manufacturer’s rated capacity. If the percent of moisture in the mixture exceeds 1.0
percent by weight, the right is reserved to decrease the rate of production. The plant shall be equipped with automatic burner
controls.
3.5.2 The cold bins shall be divided in at least five compartments and shall be designed to prevent the overflow of material
from one bin to another. When reclaimed pavement is used, an additional bin designed for this purpose will be required. In
event of an emergency this bin may be used to feed aggregate in an amount not to exceed 15% of material to complete the days
production. Each cold bin shall be equipped with an orifice to feed the aggregate accurately and uniformly. The feeding orifice
shall be adjustable, and indicators shall be provided to show the gate opening. An automatic plant shutoff device shall be provided
to operate when any aggregate bin becomes empty or the flow from any bin gate becomes restricted. A vibrator or other suitable
means may be required in order to ensure a uniform flow of materials. The order of aggregate feed onto the composite cold feed
belt shall be from coarse to fine.
3.5.3 The total cold aggregate feed shall be weighed continuously by an approved belt scale. The weighing system shall
register within +0.5 percent of the indicated load.
3.5.4 Proportioning controls for aggregate and asphalt binder shall be located at the panel that also controls the mixture and
the temperature. The panel shall be equipped with automatic controls that shall display, in digital form, the percentages of asphalt
binder, mineral filler if required, and each aggregate in the job mix formula. The panel shall also be equipped to raise and lower
the production rate without having to reset the individual controls for each change in production rate. The controls shall maintain
aggregate flow accuracy such that the total variation of all materials being drawn per interval of time shall not exceed an amount
equal to 1.5 percent of the total weight of bituminous mixture per interval of time.
3.5.5 Provisions shall be made for introducing the moisture content of the total cold feed into the belt weighing system and
correcting the wet aggregate weight to dry aggregate weight. The system shall be capable of adjusting the flow of bituminous
material to compensate for any variation in the dry weight of the aggregate flow. It shall be the responsibility of the Contractor
to monitor and determine accurate moisture contents of the aggregate and RAP stockpiles used for production of hot mixed
asphalt. Accurate moisture contents shall be determined at a minimum every other day of production. In the event of rain,
moisture contents shall be determined for all aggregates and RAP to be utilized before the next day's production.
3.5.6 The dry weight of the aggregate flow shall be displayed by automatic digital readout in units of weight per interval of
time.
3.5.7 | When mineral filler is specified, a separate bin and feeder shall be provided with a variable drive interlocked with the
aggregate feeders. Mineral filler shall be introduced and uniformly dispersed into the mixture without loss to the dust collection
system. A device shall be provided to indicate when the flow of filler into the delivery system stops or its specified volume is
out of job mix tolerance. The rate of flow shall be accurate to within 0.5 percent by weight, of the total mix. Means shall be
provided to readily divert the flow of mineral filler into a container for measurement.
3.5.8 The asphalt binder shall be introduced through a continuously registering cumulative indicating meter by a pump
specifically designed for the plant. The meter shall be located in the asphalt line so that it continuously registers the asphalt
discharge to the mixer and so that the discharge through the meter can be readily diverted into a suitable container for
measurement by actual weight. The meter shall indicate accurately to within 1.0 percent the amount of asphalt binder being
delivered. The accuracy of the pump and meter shall be verified at periodic intervals as designated by the Engineer.
3.5.9 Satisfactory means shall be provided to ensure positive interlock between dry weight of aggregate flow and the flow
of bituminous material through an approved meter.
3.5.10 The flow of bituminous material shall be displayed by automatic digital readouts in terms of volume or intervals of
weight and time.
3.5.11 The plant shall have a means of diverting mixes at start up and shut down or where mixing is not complete or uniform.
3.5.12 A surge or storage system complying with 3.7 shall be provided.
2016 NHDOT
GoTo=9)> TOC Division 100 Division200 Division 300 Division 400 Standard
Division 500 Division 600 Division 700 Specifications
