SECTION 401
3.3.2 Suitable means shall be provided, either by steam or oll jacketing or insulation, for maintaining the specified
temperatures of the asphalt binder in the pipelines, meters, weigh buckets, spray bars, and other containers or flow line.
3.4 Baiching Pianis — General.
3.4.1 All aggregate shall be delivered by belt driven feeders. All feeders shall provide for adjustment of the cold feed and
shall be capable of being secured in any position.
3.4.2. Dryers shall continuously agitate the aggregate during the heating and drying process without leaving any visible
unburned oily residue on the aggregate when it is discharged from the dryer. If unusually wet aggregate is being used, the input
to the dryer shal! be reduced to that amount which the dryer is capable of drying. Aggregates shall be free from coatings of dust
after drying.
3.4.3 Plant screens shall be constructed and operated in such manner that all aggregates will be uniformly separated into
the sizes required for proportioning. They shall have sufficient capacity to furnish the necessary quantity of each aggregate size
required for continuous operation. Screen cloth that has become broken or has worn sufficiently to affect the gradation shall be
replaced.
3.4.4 Thermometric equipment shall be provided as follows:
(a) An armored thermometer of suitable range shall be fixed in the asphalt binder feed line at a suitable location near
the discharge at the mixer unit.
(b) The plant shall be further equipped with an approved thermometer, pyrometer, or other approved thermometric
instrument that continuously indicates the temperature of the heated aggregate at the discharge chute of the dryer.
3.4.5 Hot bins shall consist of at least four separate aggregate compartments. One compartment shall be reserved for fine
aggregate, and when required, one additional compartment shall be added for dry storage of mineral filler. Alternate bin systems
may be utilized with prior approval from the Department. Provision shall be made for accurate proportioning. Each compartment
shall contain the following features:
(a) Sufficient volume to supply the mixer at full rated capacity.
(b) An overflow pipe that shall be of such size and at such a location as to prevent any backing up of material into
other bins or into contact with the screen. Overflow apparatus shall be equipped with a telltale device that alerts
the operator and the inspector when the overflow equipment is full.
(c) Adequate telltale devices to indicate the position of the aggregate in the bins at the lower quarter points.
(d) Gates that cut off quickly and completely with no leakage.
(e) Adequate and convenient facilities including safe platforms for obtaining representative samples from each bin,
3.4.6 | Weigh boxes shail be of sufficient size to hold the maximum required weight of aggregate for one batch without hand
raking or running over, The weigh box shall be supported on fulerums and knife edges so constructed that they remain in
alignment or adjustment. All parts of the weigh box shall be free from contact with any supporting rods, columns, or other
equipment that affects the proper functioning of the hopper or scale. Gates on both bins and weigh hopper shall be constructed
to prevent leakage when closed.
3.4.7. Aggregate scales for any weigh box or hopper shall be of standard make and design and shall be accurate to 0.5
percent of the indicated load. The weight shail be indicated on a digital display. Scales shall be substantially constructed and
shall be installed in such a manner as to be free from vibration. The display shall be in full view of the operator, and the numerals
shall be of such a size that they can be easily read by the inspector. If the digital display is so located that it is not easily accessible
to the inspector, a duplicate display will be required for exclusive viewing by the inspector. The job mix formula target weights
shall continuously be part of the digital display during plant operations. The digital scale weight indications shall be displayed
adjacent (in juxtaposition) to each target weight for easy comparison to the job mix formula. It shall be the responsibility of the
Contractor to ensure that all scales are tested and sealed according to provisions as shown in the National Institute of Standards
and Technology Handbook 44, at least on an annual basis. The work shall be accomplished by a competent commercial scale
company prior to the start of the construction season, Scales shall be re-tested prior to use, after they have been moved. The
Contractor shall have readily available at least ten standard 50 Ib weights, for checking the scales during operations.
3.4.8 The batch mixer shall be of an approved pug mill type, hot oil or steam jacketed, or heated by other approved means
and capable of producing uniform mixtures within the specified tolerances. The mixer shal! have a batch capacity of not less
than 4,000 lb and be constructed so as to prevent leakage during the mixing cycle. The amount of material that may be mixed
per batch shall not exceed the manufacturer's rated capacity. If the mixer does not mix properly at the rated capacity, or if its
production does not coordinate with the other plant units, the Department reserves the right to reduce the size of the batch until
the desired efficiency is obtained. The pug mill shall be equipped with a sufficient number of paddles operated at such speed as
2016 NHDOT
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