This document discusses highway construction methods for plant operations and mix transport. It describes the two main types of asphalt plants - batch plants and drum mix plants. Batch plants produce asphalt in individual batches while drum plants operate continuously. The choice between plant types depends on business factors like cost and production needs. The document also outlines the different methods for transporting asphalt from plants to paving sites, including end dump trucks, bottom dump trucks, and live bottom dump trucks. The goal of transport is to maintain mix quality during hauling. Proper transport practices can significantly impact mix temperature and prevent segregation issues.

1. HIGHWAY CONSTRUCTION METHODS
PLANT OPERATION & MIX TRANSPORT
ENG. S.A.S.T SALAWAVIDANA
CEng FIESL, MCIHT, MEng (Highway & Traffic), BSc.Eng (Hons)

2. PLANT OPERATIONS
• HMA production is the first step in construction. The
basic purpose of an HMA plant is to properly proportion,
blend, and heat aggregate and asphalt to produce an
HMA that meets the requirements of the job mix
formula (JMF).
• There are two basic types of HMA plants commonly in
use today: the batch plant, and the drum mix plant.
• Batch plants produce HMA in individual batches while
drum plants produce HMA in a continuous operation.
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3. PLANT OPERATIONS
• Each type of plant can produce the same types of HMA and
neither type of plant should impart any significant plant-specific
HMA characteristics.
• The choice of a batch or drum mix plant depends upon business
factors such as purchase price, operating costs, production
requirements and the need for flexibility in local markets; both can
produce quality HMA.
• This section gives a brief overview of batch and drum mix plants.
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4. Batch Plants
• Batch plants, which produce HMA in
individual batches, are the older of the two
types of HMA production facilities.
• HMA was originally made in batches; it was
not until the 1970s that drum plants became
a popular HMA production option.
• Typical batch quantities range from 1.5 to 5
tons of HMA.
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5. Drum Plants
• Drum plants, which produce HMA in a
continuous manner, generally offer higher
production rates than batch plants for
comparable cost.
• Typical production rates for drum plants vary
between about 100 tons/hr up to over 900
tons/hr depending upon drum design.
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6. MIX TRNASPORT
• Mix transport involves all actions and equipment
required to convey HMA from a production facility to
a paving site including truck loading, weighing and
ticketing, hauling to the paving site, dumping of the
mix into the paver or material transfer vehicle
hopper, and truck return to the HMA production
facility.
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7. MIX TRNASPORT
• Ideally, the goal of mix transport
should be to maintain mix
characteristics between the
production facility and the paving
site.
• Transport practices can have a
profound effect on mix temperature at
the paving site, aggregate and/or
temperature segregation of the mix
and mat quality.
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8. End Dump Truck
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9. End Dump Truck
• End dump trucks unload their payload by
raising the front end and letting the
payload slide down the bottom of the bed
and out the back through the tailgate.
• End dump trucks are the most popular
transport vehicle type because they are
plentiful, maneuverable and versatile.
• Some general considerations associated
with end dump trucks are:
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10. End Dump Truck
• When the bed is raised it should not contact the paver.
– Bed contact with the paver may affect the screed tow point elevation,
which can affect mat smoothness.
• The truck bed should be raised slightly before the tailgate is
opened.
– This allows the HMA to slide back against the tailgate, which will cause it
to flood into the paver hopper when the tailgate is opened.
– HMA that trickles into the paver hopper is more susceptible to
aggregate segregation.
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11. End Dump Truck
• Truck-paver contact should be established by allowing the paver to
move forward into a stationary truck.
– This ensures that the truck does not bump the paver too hard and
cause the paver to lurch to a sudden stop, which could cause a
rough spot in the mat.
• Once the paver and truck are in contact, they should remain in contact.
– This ensures that no HMA is accidentally spilled in front of the
paver because of a gap between the truck and paver.
– Usually the truck driver will apply the truck’s brakes hard enough
to offer some resistance to the paver but light enough so as not to
cause the paver tracks to slip from excessive resistance.
– Most pavers can also be coupled to an unloading truck using truck
hitches located on or near the push rollers.
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Salawavidana
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12. Bottom Dump Truck
• Bottom dump trucks unload their payload by
opening gates on the bottom of the bed.
• Internal bed walls are sloped to direct the entire
payload out through the opened gates.
• Discharge rates can be controlled by the degree of
gate opening and the speed of the truck during
discharge.
• The discharge is usually placed in an elongated pile,
called a windrow, in front of the paver by driving
the truck forward during discharge.
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13. Bottom Dump Truck
• A windrow elevator is used to pick up HMA
from the windrow and feed it into the paver
hopper.
• Windrow elevators do not have any method
of regulating material flow, which makes it
necessary to place the correct amount of
HMA in the windrow to match the paving
width and depth being placed without
allowing the paver hopper to run out of mix
or become overloaded.
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14. Live Bottom Dump Truck
• Live bottom (or flo-boy) dump trucks have a conveyor system
at the bottom of their bed to unload their payload.
• HMA is discharged out the back of the bed without raising the
bed.
• Live bottom trucks are more expensive to use and maintain
because of the conveyor system but they also can reduce
segregation problems (because the HMA is moved in a large
mass) and can eliminate potential truck bed – paver contact
(because the bed is not raised during discharge).
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15. Live Bottom Dump Truck
• Each truck type is capable of adequately delivering
HMA from a production facility to a paving site.
• However, certain situations such as the ones listed
in Table below, may make one truck type
advantageous over another.
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16. Eng. Suneth Thushara Salawavidana 16

17. Eng. S.A.S.T Salawavidana