Principles of paving
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Principles of Paving. Paver System Five. Grade Control Systems Tremendous benefits to the paving contractor: Increase efficiency and productivity Control Material Quantities Improve smoothness and rideability Increase jobsite safety. Control Sensors. Slope Control. Laser Control.

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Principles of paving

Principles of Paving


Paver system five

Paver System Five

  • Grade Control Systems

  • Tremendous benefits to the paving contractor:

  • Increase efficiency and productivity

  • Control Material Quantities

  • Improve smoothness and rideability

  • Increase jobsite safety

Control Sensors

Slope Control

Laser Control

= Theanswer for perfect, smooth paving?

Sonic Control

Smoothtrac

Sonic Averaging System


Paver system five1

Paver System Five

Good Paving Practice

Grade Control

Decent paving

Control Sensors

Control Sensors

Control Sensors

=

+

Fair paving

=

+

Great paving!

=

+


Principles of paving1

Principles of Paving

  • Good principles of paving must come BEFORE Grade Control

  • Paving is a TEAM project

  • Grade control is a great tool to help the paving team:

    • be more efficient

    • control material quantities

    • provide a smoother surface

Train the entire TEAM!


Paver components

Paver Components

  • Asphalt Paver

  • The paver has two primary components:

  • Tractor

  • Screed


Paver tractor

Paver Tractor

  • Tractor has two primary functions

  • Material Handling

  • Forward Movement


Paver tractor1

Paver Tractor

  • Asphalt distribution

  • The paver typically receives the asphalt:

  • directly from a truck

  • by a pickup machine (windrow elevator)


Paver tractor2

Paver Tractor

  • Asphalt distribution

  • The asphalt is received into the paver’s hopper

  • Hopper is a holding station for the asphalt

  • The operator tilts the hopper to deliver material into the feeder conveyor


Paver tractor3

Paver Tractor

  • Asphalt distribution

  • Feeder conveyors distribute the asphalt to the augers

  • The augers spread the asphalt in front of the screed

  • End gates contain the material at the outer edge of the screed


Screed components

Screed Components

  • Paver Screed

  • Function of the screed is mat laydown

  • Screed has several components


Screed concept

Screed concept

  • The screed floats on the asphalt as it passes under the screed plate

  • The screed will “self-level” and maintain a thickness based on the forces acting on the screed.

Floating, Self-Leveling Screed


Screed concept1

Screed Concept

  • The desired thickness is controlled by the screed angle of attack

  • As the angle of attack is increased or decreased, the screed will float up or down changing the thickness

Screed angle of attack…

…controls mat thickness


Changing angle of attack

Changing Angle of Attack

  • The angle of attack can be changed by:

  • The manual crank

  • The hydraulic cylinder at the tow point


Screed concept2

Screed Concept

If the angle of attack is…

increased,

decreased,

Mat thickness decreases

Mat thickness increases


Floating self leveling screed

Floating, Self-Leveling Screed

  • The paver tractor, and therefore the screed tow point, travel over the existing “rough” surface

  • The floating screed doesn’t react immediately to the variations in the tow point path

  • The floating screed seeks it’s own level, smoothing out small humps and bumps.


Floating self leveling screed1

Floating, self-leveling screed

  • The floating screed naturally cuts off high spots and fill in low spots.

Cuts off high spots

Fills in low spots


Screed reaction

Screed Reaction

  • Tow point “step disturbance” and screed reaction

  • Two point is changed by a unit of one (1)

  • Net effect = the angle of attack has been changed


Screed reaction1

Screed Reaction

  • Example of tow point “step disturbance” and screed reaction

  • Two point is changed by a unit of one (1)


Screed reaction2

Screed Reaction

Example of change in angle of attach by turning manual crank and screed reaction.


Checking mat depth

Checking Mat Depth

  • Goal is to “average” a particular paving thickness

  • Always check several places, horizontally and laterally


Adjusting mat depth

Adjusting Mat Depth

  • Once an adjustment is made – GIVE THE SCREED TIME TO REACT!


Adjusting mat depth1

Adjusting Mat Depth

Goal – Provide smoothness and compaction, while hitting target tonnage for entire project!

  • Determine average depth by measuring tons/mile

  • Make small adjustments based on calculation


Floating self leveling screed2

Floating, Self-Leveling Screed

Left alone, the screed will self-level and assume a thickness based on forces that are acting on the screed.

  • What are these forces?


Forces acting on the screed

Forces Acting on the Screed

There are four major forces acting on the screed


Forces acting on the screed1

Forces Acting on the Screed

  • If any one of these forces change, the mat thickness will change.

  • But in “real life” job applications, these forces cannot always remain constant.


Tow point force

Tow Point Force

If the forward speed…

increases;

mat thickness will decrease

decreases;

mat thickness will increase

Goal - Non-stop, continuous paving!


Tow point force1

Tow Point Force

Goal - Non-stop, continuous paving!

  • Determine paving speed based on plant supply in tons/hour

  • Regulate trucks to the paving supply and operation, not the paving operation to the trucks

Plant supply = 210 tons/hour

Paving speed = 25’/minute


Tow point force2

Tow Point Force

Maintain smooth truck exchange!

Bump in matat every truck exchange

(probably “caused by faulty grade control!”)


In motion switches

In Motion Switches

  • While stopped waiting for trucks, the screed will settle slightly

  • Screed goes down, the tracker will also go down slightly


In motion switches1

In Motion Switches

  • Grade control would want to drive the tow cylinder up to compensate

  • The paver’s In-Motion switch stops the valve electrical signal

  • A timer initiates the electrical signal after the paver is in-motion

X


Head of material force

Head of Material Force

Maintain a CONSISTANT head of material


Head of material force1

Head of Material Force

Maintain a CONSISTANT head of material


Head of material force2

Head of Material Force

Maintain a CONSISTANT head of material


Reaction of material force

Reaction of Material Force

  • Mix Characteristics

  • Gradation

  • Segregation

  • Mix Temperature


Weight of the screed force

Weight of the Screed Force

Compaction Force = Pounds per square inch


Weight of the screed force1

Weight of the Screed Force

  • Compaction Force = Pounds per square inch

  • How can the weight force change? (lbs per square inch)

  • People climbing on and off the screed can have a small effect on overall screed weight


Weight of the screed force2

Weight of the Screed Force

  • Screed extension

  • Changing screed width changes the compaction force - Lbs per square inch


Roller compaction

Roller Compaction

  • Good rolling practice is critical to the quality of the mat


Roller compaction1

Roller Compaction

  • A freshly laid, smooth mat will reflect some of the original surface after rolling

  • Quality of the base being paved affects smoothness

  • Multiple lifts help to minimize these effects


Mechanical condition of the paver

Mechanical condition of the Paver

  • The paving machine itself needs to be in good shape and adjusted correctly

  • Feeder system

    • Hopper, flight chain operation and adjustment, augers, etc.

    • Operation and adjustment of feeder controls

  • No excessive wear on screed components

    • Screed plates

    • Thickness control screws, bearings, and bushings

    • Screed pivot point bushings

  • Screed adjustment

    • Strike off plates

    • Screed flatness

    • Screed extensions adjusted properly, elevation and slope


Paver system five2

Paver System Five

Good Paving Practice

Grade Control

Decent paving

Control Sensors

Control Sensors

Control Sensors

=

+

Fair paving

=

+

Great paving!

=

+


Paver system five3

Paver System Five

  • Tow point is smoothly controlled to a desired path:

  • Curb

  • Stringline

  • SAS smoothing out existing surface

Then let the floating, self-leveling screed do it’s job!


Best paving practices

Best Paving Practices

  • Good mechanical condition of the paver

  • Minimize changes in the natural forces on the screed

  • Non-stop, continuous paving

  • Good, smooth truck exchange

  • Constant paving speed

  • Constant head of material

  • Consistent mix characteristics

  • Good rolling techniques

  • Good quality of sub-base

  • Understand proper setup and operation of Grade Control


Principles of paving2

Principles of Paving


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