SECTION 503 – PLANTS & EQUIPMENT
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Material Proportioning–All materials used, such as aggregates, asphalt cement, mineral
filler, hydrated lime, fibers, and RAP shall be proportioned by fully integrated measuring
systems that maintain the required proportions in conformance with the approved mix design.
Cold Bins–Cold feed apparatus shall conform to Subsection 503.03.2 and shall be inspected
routinely. Bins shall be of the proper size to accommodate loader bucket size and plant
production. They shall also be of a configuration that will not contribute to segregation and be
in good condition. There shall be no holes in any bin. The bin separating partitions shall not
be worn or broken. If a partition is damaged to the point that this specification is not met, the
Contractor/Producer shall replace the damaged part. Cold feed bins shall be loaded in a
manner that will not contribute to segregation. Aggregates shall be dumped into the center of
each bin. Bins shall be kept adequately filled with a relatively constant level of material with
uniform moisture content.
Belt feeders shall be in good condition, not worn or broken. Gate openings and belt speeds
shall be set to distribute the appropriate gradation for the job mix formula being produced. The
gate openings and belt speeds shall be periodically inspected to ensure that they remain
properly set. Aggregates shall flow uniformly onto the belt. Clogged gates, bridging or
excessive moisture can cause non-uniform flow.
Truck Loading–The loading of trucks will be observed to ensure that loading techniques or
discharge equipment is not contributing to mixture segregation. Equipment that drops a large
amount of mixture at a time into the truck will tend to generate less segregation than compared
to equipment that discharges a small flow/stream. The material dropped into the front and
back should be placed as close as possible to the front and back of the bed to minimize
segregation caused by the rolling of large aggregates. The intent of this truck loading
procedure is to minimize the roll down of coarse aggregate at the front and back of the truck
and to concentrate any roll down in the center of the load, where it will be more readily mixed
with the mass of material during discharge into the paver or MTV. When equipment
necessitates deviating from this procedure, the Producer may modify this procedure as long
as segregation does not occur.
Drum mix plants will be checked for satisfactory performance by inspecting the material
exiting the drum mixer. It will be checked for temperature, coating [Ross Count, (AASHTO T
195), if questionable], moisture, and segregation. If segregation is occurring during the mixing
process, one side of the material coming out of the dryer/drum will usually be fine and the other
coarse. Such segregation is often caused by improper drum operation.
Material produced at the beginning or termination of production periods shall be diverted
from DOTD projects. During startup, the Contractor shall observe the mixture coming out of
the diversion chute during these periods to determine that proper mixing and coating are being
achieved before allowing the asphalt mixture to enter the surge or storage silos.
The surge or storage silos in use at all plants are components that must be carefully and
routinely inspected. The batcher on the top of the silo must operate properly and at all times.
The gates must close tightly so that material cannot dribble through. The storage silo or surge
silo should maintain the proper cone shape of the material in storage to reduce the height of
mix drop, thereby helping to prevent segregation.