lec.8. paving equipment

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[Lecture 8]

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You want to construct a road in your area Asphalt batch plant provided you the right

mix in the desired quantity

No

w what? You need to somehow spread that mix on the

ready roadbase and then compact it.

An HMA Pavement l ayi ng operation i nvol ves sweepi ng, material transfer , spreadi ng and

compacti ng

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To place materials onto the existing surfaceat predetermined widths

to a designated thickness

to a required smoothness

all ready f or final compaction

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You want to lay bricks f orconstructing a wall

Place the right amount of

mortar on the lower brick

Spread it using screed

and then compact using

the brick



Pavers do the same! They take up the material, spread it to the

existing surface and then compact it

But f

or each

of ab

ove functi

ons there aredesignated parts which work in conjunction

with each other

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Two main partsTractor Unit

Provides f orward propulsion and motive power

Acts as a delivery conveyor to screed

Accepts the HMA at the front of the paver, moves it to the rear and spreads it out to the desired width in

preparation f or screed leveling and compaction

Screed

The screed takes the head of HMA from the materialdelivery system, strikes it off at the correct thickness

and provides initial mat compaction

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TRACTOR

SCREED



Push Roll er and T r uck Hitch

The push roller is the portion of the paver that contacts

the transport vehicle and the truck hitch holds the

transport vehicle in contact with the paver

They are located on the front of the hopper

Hopper

The hopper is used as a temporary storage area f or HMA

delivered by the transport vehicle.

Theref ore, the paver can accept more material than is

immediately needed and can use the volume in thehopper to compensate f or fluctuating material demands

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Hopper



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C onveyor

The conveyor mechanism carries the HMA from thehopper

The amount of HMA carried back by the conveyors is

regulated by either variable speed conveyors and augers or

flow gates, which can be raised or lowered by the operator

It can also be controlled by an automatic feed control

system

Auger

The auger receives HMA from the conveyor and spreads itout evenly over the width to be paved

There is one auger f or each side of the paver and they can

be operated independently

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Conveyors



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Screed pl ate

The flat bottom portion of the screed assembly that

flattens and compresses the HMA

Screed angl e ( angl e of attack)

The angle the screed makes with the ground surface

Strike-off pl ate

The vertical plate just above the leading edge of the screed

used to strike off excess HMA and protect the screeds

leading edge from excessive wear

Screed arms

Long beams that attach the screed to the tractor unit

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T ow poi nt

Point at which the screed arm is attached to the tractorunit (see Figure 7.43).

Depth crank

The manual control device used to set screed angle and

ultimately, mat thickness

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Towing f orce

Force from the HMA head resisting the towing

f orce

Weight of the screed acting vertically downward

Resistive upward vertical f orce from the materialbeing compacted under the screed

Additional downward f orce applied by the

screeds tamping barso

rvibrat

ors

Frictional f orce between the screed and the HMA

under the screed

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Speed

Material Feed Rate

Tow Point Elevation

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Material is discharged from adelivery lorry (truck) while the

paver moves f orward

Material is drawn along the

conveyors at the rear of the

hopper to be deposited at

augers

Augers distribute mix to full

width of screed

Screed further spreads the

material and partially compacts

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