Pavement Engineering

M. Kharabsheh 1

A/P Pavement Design

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Wheel Loads & Design Factors

Load characterization

Tire loads

Axle and tire configurations

Load repetition

Traffic distribution

Vehicle speed

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Wheel Configuration (Airplane)

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Tire Imprint

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Wheel Loads & Design Factors

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Variability of material available , Traffic

load, and Environment in pavement

construction have a major influence on

Design.

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Definition of Pavement Types

Flexible

Flexible pavements are so named because the

total pavement structure deflects, or flexes,

under loading. A flexible pavement structure is

typically composed of several layers of

materials.

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Definition of Pavement Types

Flexible

In order to take maximum advantage of

this property, layers are usually arranged

in the order of descending load bearing

capacity with the highest load bearing

capacity (equals to tire pressure)material

(and most expensive) on the top and the

lowest load bearing capacity material

(and least expensive) on the bottom

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Pavement Engineering

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Definition of Pavement Types

Rigid

Rigid Pavements are made up of Portland

cement concrete and may or may not

have a base course between the

pavement and the subgrade.

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Definition of Pavement Types

Rigid Vs Flexible

The essential difference between the two

pavements is in the manner in which they

distribute the load over the subgrade.

The RIGID Pavement, because of its rigidity and

the high modulus of elasticity, distributes the

load over a relatively wide area of soil; and

thus a major portion of the structural capacity

is supplied by the slab itself.(Carries the load

by Deflection)

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Definition of Pavement Types

Rigid Vs Flexible

In FLEXIBLE Pavement, each layer

receives loads from the above layer,

spreads them out, and passes on these

loads to the next layer below. Thus the

stresses will be reduced, which are

maximum at the top layer and minimum

on the subgrade. (Carries the load by

strain)

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Environment

Temperature extremes

Frost action

Frost heave

Thaw weakening

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Pavement Types

Flexible Pavement A relatively thin wearing surface built over a

base course and subbase course.

Hot mix asphalt (HMA) pavements

Called "flexible" since the total pavement structure bends (or flexes) to accommodate traffic loads

About 82.2% of paved U.S. roads use flexible pavement

Rigid Pavement Portland cement concrete (PCC) pavements

Called “rigid” since PCC’s high modulus of elasticity does not allow them to flex appreciably

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Pavement Engineering

M. Kharabsheh 13

Flexible Pavement

Structure

Surface course

Base course

Subbase course

Subgrade

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Rigid Pavement

Structure

Surface course

Base course

Subbase course

Subgrade

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Types of Rigid Pavement

Jointed Plain Concrete Pavement

(JPCP)

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Types of Rigid Pavement

Continuously Reinforced Concrete

Pavement (CRCP)

Photo from the Concrete Reinforcing Steel Institute 12/29/2016 16

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Pavement Design

Several typical methods

Design catalog

Empirical

1993 AASHTO method

Mechanistic-empirical

New AASHTO method

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Design of Flexible Pavement

Example design catalog from the Washington Asphalt

Pavement Association (WAPA) for residential streets

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Asphalt Cement

" Asphalt" is a dark brown to black, highly viscous Bitumen, hydrocarbon that may be produced from petroleum distillation residue. This distillation can occur naturally, resulting in asphalt lakes, or occur in a petroleum refinery using crude oil.

In 2001, the U.S. produced almost 35 million tons of asphalt at a rough value of around $6 billion. Roads and highways constitute the largest single use of asphalt at 85 percent of the total (Asphalt Institute, 2002).

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Asphalt Cement

In HMA, asphalt functions as a waterproof,

thermoplastic, viscoelastic adhesive. By

weight, asphalt generally accounts for

between 4 and 8 percent of HMA and makes

up about 25 - 30 percent of the cost of an

HMA pavement structure depending upon the

type and quantity. The paving industry also

uses asphalt emulsions, asphalt cutbacks and

foamed asphalt.

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Asphalt Cement Lake (Trinidad)

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Penetration Grading

One penetration unit = 0.1 mm of

penetration by the standard needle).

Typical asphalt binders used are 65-

70 pen and 85-100 pen.

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Penetration Grading

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Source: Pavement Interactive

Load = 100 grams

Temperature = 25° C (77° F)

Time = 5 seconds

Penetration Grade Comments

40 – 50 Hardest grade.

60 – 70 Typical grades used

in the U.S. 85 – 100

120 – 150

200 – 300 Softest grade. Used

for cold climates

such as northern

Canada (Roberts et

al., 1996[1])

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Viscosity Test (Absolute Viscosity)

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AASHTO T 202 and ASTM D 2171: Viscosity of

Asphalts by Vacuum Capillary Viscometer

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Viscosity Test (Kinematic Viscosity)

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AASHTO T 201 and ASTM D 2170: Kinematic

Viscosity of Asphalts (Bitumen)

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Viscosity Grading

Measures an asphalt binder's viscosity at

140°F (60°C) and 275°F(135°C). Testing can

be done on virgin (AC) or aged (AR) asphalt

binder. Grades are listed in poises (cm-g-s =

dyne-second/cm2) or poises divided by 10.

Typical asphalt binders used are AC-10, AC-

20, AC-30, AR-4000 and AR-8000. Viscosity

grading is a better grading system

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40

50

60

70 85

100

120

150 200

300

Penetration Grades

AC 40

AC 20

AC 10

AC 5

AC 2.5

100

50

10

5

Vis

cosity,

60C

(140F

)

AR 16000

AR 8000

AR 4000000

AR 2000

AR 1000

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Asphalt Grading

Viscosity Grading