Construction Placement 1

Placement of HMA Mixes

Senior/GraduateHMA Course

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Safety - First, Last and Always...

Don’t depend on drivers to avoid you. Play it safe.

Watch your back and your buddies.

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Push Rollers

Tractor

Hopper

Tow Point

Side ArmsConveyors

Screed

Depth Crank

Augers

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TRACTORTRACTOR

HOPPERHOPPER

PUSH ROLLERPUSH ROLLER

TOW POINTTOW POINT

SIDE ARMSIDE ARM

SCREEDSCREED

DEPTH CRANKDEPTH CRANK

AUGERAUGER

CONVEYORCONVEYOR

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Tractor Unit

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Push Roller

Truck Hitch

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Truck hitch engaged

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Hopper Wings

Slat ConveyorsHopper GatesAugers

Screed Plate

ProportionalFeed Control

Material Flow

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Operational Principles of the Operational Principles of the ScreedScreed

• Self-leveling Concepts Self-leveling Concepts • Screed Response versus Distance Screed Response versus Distance • Forces Acting on a ScreedForces Acting on a Screed

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Self Leveling - Rubber Tired Paver

Rear Drive Tires Front Bogie Wheels

Line of Pull

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Detail of Screed PathDetail of Screed Path

Tow Point PathTow Point PathStep Amplitude = 100%Step Amplitude = 100%

L = Leveling Arm LengthL = Leveling Arm Length

Screed PathScreed PathDirection of PavingDirection of Paving

63%63% 87%87%

6L6L5L5L4L4L3L3L2L2L1L1L00

96%96% 98%98% 99%99%

L

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1 inch movement at Tow Point

1/8 inch movement at Leading Edge of Screed

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Main Forces Acting on Screed Main Forces Acting on Screed

1. Speed of Paver1. Speed of Paver

2. Head of Material2. Head of Material

- - Shear resistanceShear resistance

3. Angle of Attack 3. Angle of Attack

4. Other Forces 4. Other Forces – Pre-compaction Pre-compaction – Screed WeightScreed Weight

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Tow Point

Screed DepthCrank

Pivot Point

F1

F2

F3

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Constant Head of Material Volume

Head of Material Volume Too High

Head of Material Volume Too Low

Correct Depth ofMat Maintained

Screed Rises Due toExcess Material ForcedUnder Nose of Screed

Screed Settles Due toInadequate Supporting

Material

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Correct Correct ElevationElevation

Auger Auger OverloadedOverloaded

Auger Auger UnderloadeUnderloade

dd

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Travel

Angle of Attack

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HOT STOP ConceptHOT STOP Concept

• If constant material flow cannot be If constant material flow cannot be maintained, before HMA mix drops in maintained, before HMA mix drops in hopper below gates...hopper below gates...

• ““Hot Stop” the paver as quickly as Hot Stop” the paver as quickly as possiblepossible

• Wait for next truckWait for next truck• Pick up truck on run and resume speed as Pick up truck on run and resume speed as

quickly as possible.quickly as possible.

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Screed Control SystemsScreed Control Systems

• Who’s Responsible for Changes Who’s Responsible for Changes • Sticking the Mat Sticking the Mat • Manual Controls Manual Controls • Automatic Controls Automatic Controls

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Pavement ProfilePavement Profile

Direction of PavingDirection of Paving

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Detail of Screed PathDetail of Screed Path

Tow Point PathTow Point PathStep Amplitude = 100%Step Amplitude = 100%

L = Leveling Arm LengthL = Leveling Arm Length

Screed PathScreed PathDirection of PavingDirection of Paving

63%63% 87%87%

6L6L5L5L4L4L3L3L2L2L1L1L00

96%96% 98%98% 99%99%

L

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Types of Grade Reference Types of Grade Reference

• Stringline Stringline • Mobile referenceMobile reference• Joint matching shoe Joint matching shoe • Sonic sensorSonic sensor• LaserLaser

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Grade Sensor - Side Arm Mount

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Grade Sensor - Screed End Mount

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Ultrasonic Grade SensorUltrasonic Grade Sensor

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Balancing ProductionBalancing Production

TruckingTrucking CompactionCompaction

PavingPavingHMA HMA FacilityFacility

Construction Placement 47

QUESTIONS ?