5.Paving and Surface Treatment Operations

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Dr. Khaled Hyari Department of Civil Engineering

Hashemite University

5. Paving and Surface Treatments Operations

Construction Methods 110401542

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• Paving and surface treatments are Used to: – Provide a roadway wearing surface – Protect the underlying material from moisture

• Two types of pavements: – Asphalt pavements (flexible pavements) – Concrete pavements (rigid pavements)

• Surface treatments: applying liquid asphalt or some other bituminous material to a roadway surface

Paving and Surface Treatment

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• Used to apply liquid bituminous materials • Utilized in almost all types of bituminous

construction • Rate of application (liters per square

meter) depends on: – Spray bar length (1.2 m to 7.3 m) – Travel speed (meters per minute) – Pump output (liter per minute)

• Pump output is measured by a pump tachometer in liter per minute

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The Bituminous Distributor

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The Bituminous Distributor II

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The Bituminous Distributor III Standard asphalt volume is measured in at a temperature of 15.5 C. A volumetric correction factor must be applied to convert asphalt volume at other temperatures to the standard volume

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• Bituminous surface treatments are used to: – Bond old and new surfaces or – Seal and revive old pavements or – Provide fresh waterproofing and wearing

surface


Bituminous Surface Treatments III

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• A wide variety of surface treatments are available: – Prime coats – Tack coats

– Dust palliatives – Seal coats

– Single-pass surface treatments – Multiple-pass surface treatments


Bituminous Surface Treatments III

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• What?: A coating of light bituminous material applied to a porous unpaved surface

• Why?: – To seal the existing surface – To provide a bond between the existing surface and

the new bituminous surface • The usual rate of application varies from 1.1 to

2.3 liters per square meter • All liquid bituminous should be absorbed within

24 hours and it should cure in about 48 hours


Prime Coats

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• Tack coat: Thin coating of light bituminous material applied to previously paved surface to act as a bonding agent – Usual rate of application is 0.45 liters per

square meter or less

– Tack coat must be allowed to cure to a tacky condition before the new surfacing layer is placed


Tack Coats

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• Dust palliative: A substance applied to an unpaved surface to reduce the amount of dust produced by vehicular traffic and wind – Bituminous dust palliatives are designed to penetrate

and bond particles in the unpaved surface and provide some waterproofing

– Other agents used as dust palliatives include water, acrylic copolymer, and petroleum resins

– Except water they are usually effective for 30 days or more


Dust Palliatives

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• Fog seal: A light application of a slow-setting asphalt emulsion diluted by 1 to 3 parts of water

– Used to seal small cracks and voids and to revive old asphalt surfaces

– Usual application rate is 0.4 to 0.9 liters per square meters

• Emulsion slurry seal: Composed of a mixture of slow-setting asphalt emulsion, fine aggregate, mineral filler, and water


Seal Coats

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• Emulsion slurry seal: Continued – Usual mixtures contain by weight 20-25%

asphalt emulsion, 50-65% fine aggregate, 3-10% mineral filler, and 10-15% water

– Slurry is placed in a layer 0.6 cm or less in thickness using slurry seal machines, spreader boxes

• Sand seal: Composed of a light application of a medium-viscosity liquid asphalt covered with fine aggregates – Rate of application

• Liquid asphalt: varies from 0.45 to 0.68 liters per square meters

• Fine aggregate: 5.4 to 8.1 kg per square meters


Seal Coats II

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• Sometimes called aggregate surface treatments • Made up of alternate applications of asphalt and

aggregate • Used to waterproof a roadway and to provide

improved wearing surface • Widely used because:

– They require a minimum of time, equipment, and material – They lend themselves to stage construction (successive

applications are repeated over a period of time to provide a higher level of roadway surface

• Single-pass surface treatment: constructed by spraying on a layer of asphalt and covering it with a layer of aggregate approximately one stone in depth


Single- and Multiple Pass Surface Treatments

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• The sequence of operations:

– Sweep the existing surface

– Apply prime coat and cure, if required

– Apply binder at the specified rate (1.1 to 1.4 liters/m2 )

• Type and quantity of binder depends on ambient temperature, aggregate absorbency, and aggregate size)

– Apply aggregate at the specified rate (13 to 16 kg/m2 of ½ in or smaller aggregate)


Single-pass Surface Treatments

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• The sequence of operations, continued:

– Roll the surface to imbed the aggregate in in the binder and to interlock aggregate particles

– Sweep again to remove loose stone that might cause damage when thrown by fast vehicles

• Spreading of aggregate must be follow immediately after binder application – Binder temperature has been found to drop to ambient

surface temperature in about 2 minutes – Every effort should be made to apply aggregate within 2

minutes after binder application


Single-pass Surface Treatments II

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• Two or more single surface treatments placed on top of each other

• Same construction as single pass surface treatments except applying more than one binder/aggregate layers

• The maximum size of aggregate used in each layer should be about one half the size used in the underlying layer

Multiple-pass Surface Treatments

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• Hot-mix asphalt (HMA) pavement: • Hot-mix paving operations include:

– Delivery of the asphalt mix – Spreading of the mix – Compacting the mix


Asphalt Paving

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• The primary purpose of the paver is to place the hot mix asphalt to the desired width, grade, cross slope, and thickness and to produce a uniform mat texture. The paver should also be able to place the HMA in a manner that results in improved ridability and smoothness of the roadway

• The paver consists of two primary parts: – The tractor unit, and – The screed unit

Asphalt Paver

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• Asphalt Truck, Tractor unit, and Screed unit This image cannot currently be displayed.

Asphalt Paver II

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Asphalt Paver III

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• Tractor unit – Provides the motive power to the paver – Pushes the haul truck in front of the paver

during the unloading process – receive the asphalt mixture directly from

the haul trucks, carry it through the machine back to the augers, and then distribute it across the width of the screed

Asphalt Paver IV

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• Tractor unit: The tractor unit has the following major components: – The truck push rollers – Material feed system consisting of:

• mix-receiving hopper • slat conveyors • material flow gates (usually) • a pair of augers

Asphalt Paver V

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• Truck push rollers – Located on the front of the paver hopper – Used to maintain contact with the tires of the

haul truck and to push that truck ahead of the paver

– The rollers must be clean and free to rotate in order to allow smooth forward travel of the paver

– If the push rollers are not cleaned periodically and do not rotate freely, the truck tires will slide on the rollers and increase the load on the paver. Moreover, if one roller rotates freely and the other does not, the paver may be more difficult to steer

Asphalt Paver VI

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• Truck push rollers, continued – Many pavers are equipped with a truck hitch that

is located underneath or incorporated into the push rollers on the front of the paver. The purpose of the hitch is to keep the truck in contact with the paver and thereby prevent the truck driver from pulling away from the paver and inadvertently dumping mix on the pavement in front of the paver

– Once the truck bed has been emptied of mix, the truck hitch is withdrawn, and the truck is able to pull away from the paver

Asphalt Paver VII

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• Paver hopper: – Used as temporary storage area for the asphalt

mix delivered from the haul vehicle, the window elevator, or the material transfer vehicle

– The amount of mix in the paver hopper should always be kept at a level above the top of the flow gates or tunnel openings at the back of the hopper. In order to keep the conveyors on the paver full and thus maintain a constant head of hot mix asphalt in front of paver screed, providing for a smooth mat behind the screed

Asphalt Paver VIII

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– The sides or wings of the hopper are movable. The mix is periodically moved from the sides of the hopper into the middle of the hopper by folding the wings (sides) and depositing the mix on top of the area of the conveyors. This is performed to avoid allowing mix to stand for a long period of time in the corners of the hopper since it will cool and appear as chunks of material in back of the screed when it passes through the paver.

Asphalt Paver IX

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• Slat Conveyors: – Located at the bottom of the paver hopper – Consist of heavy chains and flight bars – The slat conveyors are a continuous system,

with the slats being rotated back to the bottom of the hopper underneath the paver itself.

– Used to carry the asphalt mix from the hopper through the tunnels on the paver and back to the augers

– The slat conveyors should never be visible at any time during the paving operation

Asphalt Paver X

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• Flow Gates: – Located at the back of the paver hopper one over

each of the two slat conveyors – Used to regulate the amount of mix that can be

delivered by each slat conveyor to the corresponding auger on the paver

– The gates can be moved vertically, either manually or mechanically (electrically). Depending on the vertical setting of the gates, more or less mix is permitted to enter each paving tunnel.

– The paver should be stopped before the tunnel openings or flow gates are visible

Asphalt Paver XI

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• Augers: – The mix carried to the back of the tractor unit by

the slat conveyors is deposited in front of the augers

– Like the two slat conveyors, the augers on each side of the paver operated independently of one another

– The mix placed in the auger chamber from the slat conveyors is distributed across the width of the paver screed by the movement of the two independent augers

– The amount of mix carried in the auger chamber should be as constant as possible

Asphalt Paver XIII

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• Augers, continued – The proper depth of material on the augers is at

the center of the auger shaft. The level of material carried in front of the screed should not be so low as to expose the lower portion of the screw conveyor flights. Further, the level mix delivered to the screed should never be so high as to cover the upper portion of the auger

Asphalt Paver XIV

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• Screed unit: – Towed by the tractor unit – Attached to the tractor unit at only one point on

each side of the paver and “floats” on the HMA. – provides the initial texture and compaction to the

HMA as it passes out from under the unit – Establishes the thickness of the asphalt layer – The concept of free-floating screed allows the

paver screed to average out changes in grade or elevation experienced by the wheelbase (rubber tire or crawler tractor) of the tractor unit

Asphalt Paver XV

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• Screed Heaters: – The screed is equipped with two or more heaters

or burners to preheat the plate on the bottom of the screed to the temperature of the HMA being laid

– The screed must be at nearly the same temperature as the asphalt material passing under it to ensure that the mix does not stick to the screed plate and tear, imparting a rough texture to the mat

Asphalt Paver XVI

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• Screed Vibrators: – Approximately 75 to 85 percent of the theoretical

maximum density of the HMA are obtained when the mix passes out from under the paver screed

Asphalt Paver XVII

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• The consistency of the head of material (amount of HMA) in front of the paver screed is one of the primary factors affecting the consistency of the thickness of the layer being constructed

• The head of material in the auger chamber is directly affected by the operation of the slat conveyors and augers on each side of the paver

• When the slat conveyors and augers are operating, the mix is pulled from the paver hopper, through the tunnel, and is distributed across the front of the screed by the augers

Asphalt Paver XVIII

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• As long as this flow of material is relatively constant, the head of material pushing against the screed remains relatively constant as well, and the mat being placed has a smooth and consistent texture

Asphalt Paver XIX

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• Stringline

Asphalt Paver XX

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• Compaction is the process by which the asphalt mix is compressed and reduced in volume

• Compaction is the most important factor in the performance of a hot mix asphalt pavement

• Adequate compaction of the mix – Increases fatigue life – Decreases permanent deformation (rutting) – Reduces oxidation or aging – Decreases moisture damage – Increases strength and stability – Decreases low temperature cracking.

Asphalt Pavement Compaction

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• Compacting or rolling of the mix should begin immediately after it is placed by the paver


Asphalt Pavement Compaction II

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• Three primary types of compaction equipment: – Static steel wheel rollers – Pneumatic tire rollers – Vibratory steel wheel rollers


Steel wheel roller

Asphalt Pavement Compaction III

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• Pneumatic tire roller

• Roller tires

Asphalt Pavement Compaction IV

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• Finish roller This image cannot currently be displayed.

Asphalt Pavement Compaction V

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• Usual sequence of rolling involves – Breakdown rolling (vibratory or static steel

wheel rollers) – Intermediate rolling (Pneumatic rollers) – Final or finish rolling (static steel wheel

rollers) • Rollers need a number of passes over the

pavement to achieve the required density • Roller passes must be distributed uniformly

over the width and length of the mat

Asphalt Pavement Compaction VI

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• Core test

Asphalt Pavement Inspection

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• 4R construction – Resurfacing: involve surface treatments or

overlays of asphalt or concrete – Restoration: any work required to return the

highway to an acceptable condition. May require strengthening subgrade or base courses by soil stabilization or drainage improvements

– Rehabilitation: same as restoration – Reconstruction: complete removal of the old

pavement structure and construction of a new pavement

Pavement Repair and Rehabilitation

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• Milling: Mechanical removal of the upper portion of the pavement – Used to remove the high points in the existing

surface instead of placing a leveling course (filling in the low spots)

– Milling can be accomplished in any width necessary, from 150 mm (6 in.) to more than 4 m (13 ft)

– The resulting asphalt pavement produced by the milling process can be hauled back to the asphalt plant for future recycling

Pavement Repair and Rehabilitation II

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• Milling:

Pavement Repair and Rehabilitation III

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• Recycling: – Reduces cost – Reduces the demand for new aggregate sources – Reduces the problems associated with disposal

of the old material

Pavement Repair and Rehabilitation IV

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Nighttime Paving

5.Paving and Surface Treatment Operations

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