ultra thin whitetopping

7/28/2019 Ultra Thin Whitetopping

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CONCRETE INDUSTRY MANAGEMENT TECHNOLOGY

Whitetopping:1. Whitetopping

A. History

B. ThicknessC. Advantages

D. Design

2. Ultra-Thin Whitetopping

A. HistoryB. Bond and thickness

C. Joint Spacing

D. Construction

CONCRETE APPLICATIONS I

CIMT 210

Overlays_of_Asphalt_Pavement
http://www.pavement.com/Concrete_Pavement/Technical/Fundamentals/Overlays_of_Asphalt_Pavement.asphttp://www.pavement.com/Concrete_Pavement/Technical/Fundamentals/Overlays_of_Asphalt_Pavement.asp


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1. Whitetopping

A. HistoryPaved surfaces for roadways, both portland

cement concrete and asphalt, must withstand

very harsh conditions:

Wheel loads from moving vehiclesThe pavement must endure environmental effects.

Climatic changes

Moisture variations

Freezing and thawing temperature


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1. Whitetopping

A. History

Whitetopping is a portland cement concrete

overlay on existing asphalt concrete pavement. It

can be used as a road surface course where

traditional paving materials have failed due to

rutting or general deterioration.

There are three types of whitetopping:

Conventional (thickness greater than 8 inches)

Thin (thicknesses over 4 but less than 8 inches.)

Ultra-thin(2 to 4 inches) Ultra-thin

whitetopping (UTW) is a bonded, fiber reinforced

concrete overlay.


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1. Whitetopping

A. History

Whitetopping used in the United States

since 1918 and routinely used since mid-1970's.

Method of rehabilitating asphalt pavements

Was developed in the early 1990's.

Thicker bonded concrete overlays of existing

asphalt pavements have been built on

three major highways in the U.S.


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1. WhitetoppingB. Thickness

Unbonded, Classical WhitetoppingUntil 1991, most whitetopping projects in the

U.S. did not purposely seek bond between the

interface of the concrete overlay and the underlying

asphalt surface. Rather, the existing asphalt serves

as base for the new concrete overlay.

Defined as: "A concrete overlay, usually of

thickness of 100 mm(4 inches) or more

Unbonded PCC overlays, often called"classical whitetopping"

Bonded PCC overlays, often called

"thin composite whitetopping"


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1. WhitetoppingC. Advantages

Applicable where the depths of potholesare less than 50 mm (2 inches).

If rut or pothole depths are deeper, the potholes

are filled or the surface is milled.

All three types of rigid pavement (JPCP, JRCP

and CRCP) have been successfully used as

Classical whitetopping (McGhee, 1994).

The chief advantage of classical whitetoppingis that it requires minimal surface preparation

Minimum overlay thicknesses tend to be in the

125 - 175 mm (5 - 7 inch) range, which is quitethick and possibly unsuitable in situations

where a specific elevation must be maintained

such as in curbed areas or under bridges.


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1. WhitetoppingD. Design

The design procedure contained in the1993 AASHTO Guide is virtually identical

to the AASHTO empirical design for

new rigid pavements with one exception:

The effective modulus of subgrade reaction (k)

is determined based on the existing flexible

pavement resilent modulus.

Although perfectly acceptable, this methodgives little credit to the existing pavement's

remaining strength.


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1. WhitetoppingD. Design

The design procedure contained in the1993 AASHTO Guide is virtually identical

to the AASHTO empirical design for

new rigid pavements with one exception:

The effective modulus of subgrade reaction (k)

is determined based on the existing flexible

pavement resilent modulus.

Although perfectly acceptable, this methodgives little credit to the existing pavement's

remaining strength.


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A. History

Ultra-Thin Whitetopping "UTW"Emerges

Term was needed to differentiate this new

technology from classical whitetopping. Three

features differentiated the whitetopping of asphalt:(1.) The concrete overlay was substantially thinner

(2.) Bond between the concrete overlay and the

underlying asphalt created composite action.

(3.) Short joint spacing significantly improved

overlay performance.



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A. History

Ultra-thin whitetopping." requires bonding

a relatively thin layer of concrete to the

underlying asphalt

Over 200 ultra-thin whitetopping sectionshave been built, primarily on low-volume

roadways.


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B. Bond and Thickness

The concrete overlay and the underlying asphalt

act as a composite section rather than two

independent layers.

Significantly reduces the load-induced stressesThe concrete overlay can be significantly thinner

for the same loading as compared to a no bond

to the underlying asphalt.


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C. Joint Spacing

F igure : Shorter joint spacing reduces

slab-bending. Wheel loads cause bending in

concrete pavements with conventional

joint spacing. I n UTW, shorter joint

spacing casues more transfer of wheel loads

to the under lying asphalt through deflection.


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D. Construction

Constructing UTW Overlays Proper construction

of ultra-thin whitetopping consists of four

fundamental steps:

1. Prepare the asphalt surface by milling and

cleaning, or water or abrasive blasting.

2. Place, finish, texture, and cure using

conventional techniques and materials.

3. Saw joints to prevent cracking.

4. Open to traffic. A clean surface is requiredfor proper bond.



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D. Construction

Milling the surface followed by cleaning

improves bond because it exposes more of the

aggregate of the asphalt pavement.

The milling creates a rough surface the also

enhances the bond between the two layers.

If milling is not done, water or abrasive blasting

should be used to clean the asphalt surface.



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D. Construction

When water blasting is used, the surface must

be allowed to air dry before the concrete is placed.

Once a surface is cleaned it is important to keepit clean until the concrete overlay is placed.

Dust, dirt and debris that falls or blows onto

the asphalt surface must be removed.

If the surface is cleaned on the day prior to paving,

air cleaning may be required on the day of paving

to remove dirt and dust.



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D. Construction

If traffic is allowed on the milled surface, the

surface must be recleaned prior to paving.

Paving UTW is no different from paving anyother concrete pavement.

Conventional slip-form and fixed-form pavers,

as well as small equipment

- such as vibrating screeds



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D. Construction

Typical concrete finishing and texturing

procedures are appropriate for ultra-thin

whitetopping.

Proper curing is critical to avoiding shrinkage

cracking in the concrete overlay and to prevent

debonding between the asphalt and concrete.



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D. Construction

Because the overlay is a thin concrete slab,

it has high surface area to volume ratio and

can lose water rapidly due to evaporation.

Curing compound should be applied at twicethe normal rate.

Care must be used during application in order

to avoid spraying curing compound on a prepared

asphalt surface, which will decrease bonding.

Joints should be sawed with lightweight saws

as early as possible to control cracking.



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D. Construction

Saw-cut depth should be 1/4 - 1/3 of overlay

thickness.

Typically, the joints are not sealed. They have

performed well without sealant because the

short joint spacing minimizes joint movement.

Performance to date shows no benefit from

sealant use.


ultra thin whitetopping

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