asphalt seal coats

7/30/2019 Asphalt Seal Coats

1/33

Washington State Department of Transportation

Revised - March 2003

Technology Transfer (T )

As haltea oats


2/33

Contents

Why Seal Coat?.................................................................

Types of Seals....................................................................2

Fog Seal.........................................................................2

What is it? ................................................................2

Purpose .....................................................................2

How is it done?.........................................................2

onstruction Seal (Fog Seal) ....................................... 2

What is it? ................................................................2

Purpose .....................................................................2

How is it done?.........................................................2

Sand Seal ......................................................................3

What is it? ................................................................3

Purpose .....................................................................3

How is it done?.........................................................3

Slurry Seal.....................................................................3What is it? ................................................................3

Purpose .....................................................................3

How is it done?.........................................................4

ape Seal ......................................................................4

What is it? ................................................................4

Purpose .....................................................................4

How is it done?.........................................................4

hip Seal ......................................................................4

What is it? ................................................................4

Purpose .....................................................................4

How is it done?.........................................................5Effects of Weather ............................................................6

ool Temperatures........................................................6

Hot Temperatures .........................................................6

Rain...............................................................................7

Wind.............................................................................7

Humidity...................................................................... 7

Seasonal Restrictions....................................................7

Surface for a Chip Seal.....................................................8

Untreated Base .............................................................8

Dry or Open Pavement.................................................8

Fat (Flushing) Pavement ..............................................8Patched Pavement........................................................9

Heavily Shaded Areas ..................................................9

Grades of Asphalt for Seals ........................................... 0

Paving Grade Asphalts ............................................... 0

utback Asphalts ....................................................... 0

Asphalt Emulsions...................................................... 0

Advantages and Disadvantages .................................. 1

Paving Grades......................................................... 1

Cutbacks................................................................. 2


3/33

Asphalt Emulsions.................................................. 3

Storage and Handling of Asphalts ................................. 4

Types of Asphalt Storage ............................................ 4

Insulation of Asphalt Tanks ....................................... 4

Heating of Asphalt Storage Tanks ............................. 4

Electric Heat............................................................... 4

Flue Type Heaters or Coils ......................................... 4

Extended Storage and Heating of Asphalts ............... 5With Paving Grades or Cutbacks............................... 5

With Emulsions .......................................................... 5

o-Mingling of Asphalts............................................ 6

Types & Sizes of Rock for Seal Coat Cover Aggregate 7

Surface Texture........................................................... 7

Volume of Trafc ........................................................ 7

Economics or Availability .......................................... 7

Uniform Appearance.................................................. 7

Turning of Cover Stone.............................................. 7

Durability of a Seal ..................................................... 7

rushed or Natural Rock............................................ 7ne-Sized Rock .......................................................... 8

Dust and Moisture ...................................................... 8

radation.................................................................... 8

Application Rates for Asphalt and Rock ...................... 8uide to Application Rates........................................ 8

Asphalt ....................................................................... 8

Methods for Determining Asphalt Application Rate 9

Amount of Aggregate Cover ...................................... 9

Equipment for Applying the Asphalt and the Rock.....20

Distributor...................................................................20

Proper Bar Height.......................................................21

hip Spreader.............................................................22Coordination of the Operation ......................................23

Pre-Application Preparation ...................................... 23

Application of the Asphalt ........................................ 23

Application of the Rock.............................................23

hoke .........................................................................24

Rolling ........................................................................24

Application of the Second Lane ................................24

Trafc Control ............................................................25

Brooming ....................................................................25

Post-Seal Inspection .......................................................26

Miscellaneous Seal Coat Information ...........................27Asphalt Additives for Seal Coat Asphalts ................. 27

Anti-Strip Additives ..................................................27

Polymers......................................................................27

Marking Centerlines...................................................27

Seasonal Protection Seal Coats..................................27

Relative Cost .............................................................. 27

Glossary...........................................................................28

Bibliography ....................................................................29


4/33

Why Seal Coat?

Sea to esta is a weat er sur aces t at are

maintenance free,

ust free.

Sea to maintain t e existin avement in its resent con ition

elaying or eliminating ur er ag ng ue o wa er an sun.

Sea to c ange t e texture o t e roa to e

non-skid

smoother

uniform in appearance

Seal to change the color

by sealing the shoulder or emarcat on rom t e ma npavement

of the entire pavement surface and to improve light reection.

Sea to supp y minima a itiona stren t to t e avement

Seal to provide a moisture barrier

Sea to give etter resistance to stu e tires

Seal to correct existing pavement roblems b

waterproo ng openness

enriching under-asphalted pavement eitherasphalt concrete or seal coats

performing minor levelling

sealing cracks either temporarily or permanently,

depending on the cause

Sea or economic reasons

a seal can be less expensive than continualmaintenance of a gravel road

a seal can be an interim step to an asphalt mixedpavement

a seal can economically prolong the life of anexisting pavement


5/33

Types of Seals

Fog Seal

What is it?It is an application of a dilute emulsion without an aggregate cover.

Purpose

Its purpose is to seal and enrich an under-asphalted surface or to tightenand waterproof an open texture pavement. Fog seals can also be used aspre-seals.

How is it done?

Generally a Cationic Slow Seal (CSS-1) or CSS-1h emulsion is diluted upto 50/50 with water. The CSS-1 can be diluted by either adding the waterto the emulsion or the emulsion to the water. The former method usually

generates more foam, depending on the drop from the ll stem and thewater pressure. It is applied at .1 to .15 gallons of dilution per square yard.(Application can vary depending on pavement texture, local conditions,and trafc.) It is desirable to keep trafc off the fog seal until the emulsioncures (turns black). However trafc can use it immediately but at a reducedspeed to prevent skidding and/or splashing on the cars. The skid resistanceof the pavement may be reduced until trafc wears some of the asphaltfrom the surface.

Construction Sea (Fog Sea )

What is it?

It is an application of a dilute emulsion, usually the same material used forthe tack coat.

Purpose

It is to enrich or tighten a new asphalt concrete surface to provideresistance to the entrance of moisture and/or to prevent raveling undertrafc. This treatment is particularly helpful with late season paving.

How is it done?

The most satisfactory method is to apply the same product used for thetack coat to the new asphalt concrete immediately following the nalrolling while the pavement is still warm. The emulsion (a 50/50 dilution of

CSS-1) should be applied at a rate of .05 to .12 gallons of the dilution persquare yard. (Application can vary depending on pavement texture, localconditions and trafc.)


6/33


7/33

How is it done?

Aggregates are generally selected using the International Slurry SealAssociation (ISSA) grading specication (below). The largest aggregatevaries from 1/4 inch to 3/8 inch, depending on the application.

Aggregates, which are entirely manufactured, seem to give a better endproduct and a more durable slurry seal. The aggregate is mixed with a CSS-1, CSS-1h or Cationic Quick Set (CQS-1h) asphalt emulsion. The percent

of emulsion is determined by specications and tests set forth by the ISSA.Slurries are produced in transit mix trucks or specially designed slurry sealequipment and are laid through a drag box with a rubber squeegee strikeoff. Trafc must be kept off the slurry until it is cured.

Cape Sea

What is it?

A cape seal is a chip seal topped with a slurry seal.

Purpose

A cape seal produces a seal with no loose cover stone. The maximum sizeof a chip used for the seal coat will establish the depth of the mat. This sealmay be the best suited for roads with high trafc volumes.

How is it done?

A chip seal is laid in the conventional manner. After the chip seal hascured, the loose cover stone is removed. Then the slurry is applied over theseal to ll the voids between the cover stones.

C ip Sea

What is it?

A chip seal is an application of asphalt followed with an aggregate cover.

Purpose

A chip seal is constructed to produce an initial pavement or maintain anexisting asphalt pavement.


8/33

How is it done?

The technique of constructing a chip seal and its success are inuenced bya number of factors.

the weather

the surface on which a chip seal is laid

the grade of asphalt used

the method of storing and handling the asphalt

the type and size of rock used as cover aggregate and the dustand moisture on the stone

the application rate of the asphalt and the rock

the adjustment and operation of the equipment for applying theasphalt and rock

the coordination of the operation

the rolling

the trafc control during and after the seal coat is laid

the broomingthe post-seal inspection and the application of a fog seal, ifnecessary


9/33

Effects of Weather

Weat er can ave a mar e e ect on t e qua ity o a sea coat. T esevariations can e coo temperatures, ot temperatures, rain, win , andumi ity.

Coo Temperatures

Cool air or pavement tempera ures un er - can a ec e binding characteristics of the asphalt by making it less tacky (sticky)and/or increasing its viscosity. This can result in a poorer bond betweenthe existing pavement, the asphalt, and the rock. Further, it can reducethe embedment of the rock into the asphalt. In either case, it can result inextensive rock loss. A moderate increase of the asphalt application rate incooler conditions seems to improve the rock retention. An asphalt withsome petroleum solvent (cutter) remains tackier in these cooler conditions.However, with the higher shot rate and the cutter, there is the possibility of

ushing or bleeding when the weather warms.

ot emperatures

Sealing in hot weather (air temperatures o an g er can a socreate some construction problems with a seal coat. Pavement temperaturecan be 150 F or higher. At these elevated temperatures, the asphalt is lessviscous (more uid) and does not have its full strength (adhesiveness). Thisis particularly true with the cutbacks. The cutbacks contain a petroleumsolvent (cutter). While the cutter remains, the cutback is more uid andhas less strength at these elevated temperatures. A better choice may be apaving grade asphalt or an emulsion. The asphalt in these forms can be less

susceptible to hot weather. Trafc control and a dry choke also help protectthe new seal in hot weather.


10/33

Rain

Seal coating must be postpone , t ere s ra n or t e t reat o ra n. ecutbacks can oat up through the aggregate cover in a rain and be pickedup on the tires of the vehicles. The paving grades and the emulsions requireless curing time to be resistant to rain, which may occur shortly after theseal is laid.

If a seal is caught with an early rain, several steps may help save the seal:close the road to trafc (which is usually impractical)

reduce the speed of trafc

apply additional cover stone.

Win

Sealing during high winds s ou e scourage . g w n s can stortthe spray pattern from the distributor and prevent a uniform asphaltapplication. further, high winds can blow dust onto the road surface to besealed or onto freshly laid asphalt before the cover rock can be applied.

Humi ity

The cure time for asphalt emu s ons s exten e w en t e um ty s g .

Seasonal Restrictions

Late spring to early fall is the season most e y to ave weat er t at smost favorable for seal coat construction. Generally there are more daylighthours during this time of the year.

Although daytime temperatures may be warm, cool overnight temperatures,typical during the spring and the fall and in mountainous areas, will extend

the cure time for asphalt emulsions.


11/33

Surface for a Chip Seal

Seals can be successfully constructed on a variety of surfaces:

Untreate Base

An untreated base should be a equate y strong to carry t e ant c patetrafc and should be constructed with proper drainage. It should beprepared with a uniform texture and grade on which to apply the seal.

The asphalt can be applied to either a dampened thin layer of loosened topcourse (oat) or a moist, tightly bound surface. Each has its advantages.

shooting into oat can result in better penetration of theasphalt into the base rock and possibly a thicker mat

tight bound base gives uniform surfaces on which to shoot.his tight surface contributes to uniform rock retention. Mat

thickness is obtained by inverted penetration into the coverrock

ither method results in approximately the same matethickness using the same asphalt application rates

If the untreated base has been carrying trafc, all rutting andcorrugations much be removed before the surface is shot.

Dry or Open Pavement

Dry or open pavement will a sor some o t e asp a t nten e or t e newseal coat. Thus, a higher application rate or a pre-seal must be considered.

Fat (Flushing) Pavement

It is difcult to determine t e proper asp a t app cat on rate on a at(ushing) pavement. The surplus asphalt in the underlying pavement maycome up through and embed in the new chips. The cutter remaining in theoriginal fat pavement may penetrate and soften the asphalt in the new seal.It may be necessary to remove these fat areas prior to placing the chip seal.


12/33

Patched Pavement

Frequently, the patches are more open a sor ent t an t e surroun ngpavement. Either the patch must be pre-sealed or the asphalt applicationrate increased to avoid rock loss in the patched areas.

Heavi y S a e Areas

Seal coating pavements in heav y s a e areas can resu t n roc osswhen ordinary asphalt application rates are used. A heavier applicationfrequently helps. Asphalt containing a cutter is more tacky, which seemsto give better adhesion under these conditions. The use of a cutback ora Cationic Medium Set (CMS-2) emulsion in heavily shaded areas canminimize rock loss.


13/33

Grades of Asphalt for Seals

There are three basic types of asphalt used for seals.

Paving Grade AsphaltsThe paving grade asphalts (asphalt cements) are straight rened asphalts.They are rened to a specic hardness or viscosity.

Cutback Asphalts

The cutback asphalts (liquid asphalts) are asphalts that are dissolved in apetroleum solvent (cutter).

he hardness of the asphalt selected is based on thetemperatures the asphalt will be subjected to on the roadway.

he type of solvent controls the curing time of the cutback andthus when the cutback will obtain its ultimate strength. The

apid Curing (RC) cutbacks with naphtha (gasoline) cuttercure more rapidly than the Medium Curing (MC) cutbacksith the kerosene cutter.

he amount of cutter affects the viscosity of the cutbackasphalt. The higher the cutter content, the lower the viscosityand the more uid it will be.

Asphalt Emulsions

The asphalt emulsions are a suspension of asphaltin water.

Emulsions are made with different grades(hardnesses) of asphalt for varying climatic

conditions.The emulsions are manufactured withseveral different formulae for use in theconstruction of seals or mixes.

The anionic and cationic emulsions havedifferent electrical charges. The choice ofwhich type of emulsion to use depends uponthe electro-chemical characteristics of therock available.

Varying amounts of cutter are used to alterthe emulsion for specic applications.

The grades of emulsions are manufacturedto have different viscosities and curing timesto meet specic construction needs.


14/33

A vantages an Disa vanta es

Paving Grades

The paving grades have the advantages of:

eing made of pure asphalt

requiring little or no curing period. As soon as they havecooled, they obtain their full strength (holding power)

The paving grades have several disadvantages:

hey require high application temperatures (250 to 450 F) tomake them uid enough to handle well.

The cover stone must be applied rapidly into the asphaltcement before it becomes less uid (too stiff). If there is aelay, it is difcult to completely embed the rock into the

asphalt. Heating the cover stone is a means of improving theembedment. However the disadvantages of this are heatingcosts and generation of nes.

orking at these high application temperatures, handling theasphalt cement becomes hazardous.

It may be difcult to maintain the application temperatureithout reheating.


15/33

Cut ac s

Cutbacks have several advantages

hey are uid at lower application temperatures (50 to 250).

hey remain uid for a longer period after they have beenapplied to the road, which permits some latitude between theiristribution and the application of rock.

ome of the cutter remains in the cutback seal to remainexible to conform to some movement in the underlyingavement and base. A cutback can have self-healing

characteristics with minimal cracking.

he cutback can tolerate some nes in the cover aggregate.he kerosene cutter is more tolerant than the naphtha to these

nes.

Mixes can be made with unheated aggregates and somecutbacks.

The disadvantages of cutbacks are as follows:

he cutbacks do not obtain their ultimate strength until aood part of the solvent has escaped (evaporated). During the

curing period, the rock can be displaced under heavier trafc,articularly in warm weather. During this same period, early

rain can oat the cutback to the top of the rock and can betracked away under trafc. The type of cutter solvent affects thecuring period.

here is a potential re hazard using cutbacks that containetroleum solvents.

In certain areas, air pollution is a concern as the solventevaporates into the atmosphere.

xcessive moisture on either the pavement to be sealed or thecover rock can hinder good adhesion with a cutback.


16/33

Asp a t Emu sions

Asphalt emulsions have the following advantages:

hey are handled at cooler temperatures (50 to 150 F).

Mixes can be made with damp and cool aggregates.

Most emulsions contain an anti-strip additive.

he seal coating grades of CRS-2 and CMS-2 cure more rapidlythan the cutbacks under most conditions.

he emulsions can be made with a high viscosity to resistrunoff on supers, crowns, and grades.

hey are made with selected grades of asphalt cement for useunder different temperature conditions.

he water phases make them less of a re hazard to use.Lower handling temperatures results in less burn hazard.

he emulsions can be manufactured with varied percentages ofsolvent. The selection of the appropriate solvent and contentcan:

affect the curing characteristics of the emulsion, affect the exibility and self-healing characteristics of the

seal coat, and permit the use of cover aggregates containing nes.

he grades of CSS-1, CMS-2, and some high oat (HF)emulsions can be diluted with most waters to change theiriscosity and asphalt content.

The asphalt emulsions have several disadvantages:

If they are overheated (boiled) or frozen, they can break andecome unusable.

mulsions are not compatible with cutbacks or asphaltcements.

nionic and cationic emulsions are not compatible and shouldnot be mixed.


17/33

Storage and Handling of Asphalts

Types o Asp a t Storage

Most asphalt storage tanks are or zon a . s can ma e em por a e

and easy to move.However, vertical tanks

conserve space,

are more economic to construct,

are more efcient for maintaining heat on the asphalt, and

may expose less asphalt to the air, depending on theconguration of the tank.

Insulation of Asphalt Tanks

Insulation helps maintain a more un orm temperature t roug out t etank, saves heating costs, and reduces and delays coke (carbon) buildup onheating tubes.

Heating o Asp a t Storage Tan s

Electric Heat

Electric heating units are a popular method for maintaining thetemperature in an asphalt tank, particularly in areas of inexpensive electricpower.

Low density heating (3 watts per square inch of heating surface) reducesthe tendency of hot spots around the heating tube and reduces the cokebuildup.

Flue Type Heaters or Coils

These are acceptable methods for heating asphalts.

If the asphalt can be circulated during heating, more efciency can beaccomplished and spot overheating can be reduced or eliminated. This isparticularly true with the ue heaters and coils.

The asphalt level in the tank should be maintained above the coils or tubesduring the heating process.

There is a close relationship between storage and application temperatures.Asphalt held in storage at spray temperatures maintains a uniform viscosity,

handles well, and gives a good spray pattern through the distributor.Temperature viscosity curves can establish the optimum temperature thatwill give a consistent viscosity. There are variances within the specicationlimits from different suppliers. The Washington State DOT 2002 StandardSpecications can be used as a guide. At right are its recommendations forapplication temperatures


18/33

It may be desirable to maintain the temperature somewhat below themaximum recommendation to reduce re hazards with the cutbacks andthe danger of breaking the emulsions by overheating.

Overheating is undesirable because

additional heating costs;

the paving grades will become harder with extended heating;

higher heating temperatures can drive off (evaporate) solventsrom the cutbacks, make them more viscous, and change their

handling and performance characteristics; and

moderate overheating of an emulsion will drive off some ofthe water, make the emulsion more viscous, and change itserformance. More severe overheating can break the emulsion.

Exten e Storage an Heatin o As a ts

If the asphalt must be store or exten e per o s, o ow t ese precaut ons.

With Paving Grades or Cutbacks

It is desirable to lower the storage temperature to prevent theloss of light ends or solvents.

he storage tank should be equipped with a n vent, which willcondense the light ends or solvents back into the tank, ratherthan losing them into the atmosphere.

With Emulsions

lower storage temperature is desirable.

ith extended storage, a skin will form on top of the emulsionhere it is in contact with the air. Floating a layer of solvent

such as a naphtha or kerosene on the surface of the storedemulsion will prevent or reduce this formation of skin.

Occasional circulation is helpful.

It is desirable to ll and load out of the storage tank from the

ottom.If the storage tank is lled through the top, any skin that mayhave formed can break up into small chunks of asphalt that canlug pumps and snivies.


19/33

Co-Mingling of Asphalts

Co-mingling of grades of asp a t s a pract ca necess ty; owever, t ere arecertain limitations.

mall amounts of different cutbacks or cutbacks and pavingrades can be co-mingled. However, the resulting product will

assume some of the characteristics of each product, such as

iscosity and curing time.mulsions are not compatible with cutbacks or paving grades.

ven small amounts of cutbacks or paving grades in anemulsion will result in slugs of asphalt, which can causeumping problems and plugged snivies.

If emulsion remains in a tank, putting hot cutbacks or pavingrades in on top can cause the mixture to foam and boil overecause of the rapid expansion of the retained water.

Generally, cationic (+) and anionic (-) emulsions are notcompatible. Their mixture will cause the emulsions to breakand become unusable.

herefore, to prepare tanks or equipment for alternate usesith emulsions, paving grades or cutbacks, they should berained and thoroughly ushed with a petroleum solvent. The

ushing solvent should be drained before relling the tank.


20/33

Types and Sizes of Rock

for Seal Coat Cover AggregateSeal coats are constructed with a variety of chip (rock) sizes, shapes, and gradings.Several factors inuence the choice of seal rock.

Surface Texture

The desired surface texture can e o a ne y us ng a max mum s ze o3/4 inch or 1/2 inch for coarse texture and 3/8 inch or 1/4 inch for nertexture.

Vo ume o Tra c

The volume of trafc can in uence t e aggregate s ze c o ce. g tra cvolume conditions favor the use of a smaller sized rock, which is easier to

stick and less likely to break windshields and headlights.

Economics or Avai a i ity

Economics or availability can c a e e use o aggrega es w more nes.

Uni orm Appearance

Uniform appearance and the es nons c arac er s cs are o a ne wan aggregate with few nes.

The removal of the nes fraction (usually 1/4 inch to 0) from the chipsresults in a uniform mosaic surface.

Turning o Cover Stone

A choke stone can help prevent t e cover stone rom turn ng over on anew seal under early trafc.

Dura i ity o a Sea

The durability of a seal is a ecte y t e ar ness o t e sea roc . tis desirable to have a rock which will not crush or degrade under initialconstruction or later trafc.

Crushed or Natural Rock

Both crushed and natural grave roc are use . e uncrus e naturarock is generally less expensive than crushed. With its rounded faces, it hasless surface area in contact with old pavement surface and asphalt, thus itis more easily displaced under trafc. Generally, it requires more asphalt tohold it. Therefore, a crushed, well-graded aggregate is preferred.


21/33

One-Sized Rock

A one-sized rock surface pro uces a un orm mosa c sur ace. owever,without the ner rock matrix, the one-sized rock has a tendency to turn(roll) under trafc. A choke stone applied after the rolling, but before the

seal is opened to trafc, can prevent this rock displacement.

Dust an Moisture

The cover aggregate for a sea coa s ou no ave a us coa . e erresults are obtained if the rock is damp when it is applied. The aggregateshould be dampened in the stock pile.

Gra ation

The gradation of cover aggrega e s ou e e erm ne y we s ev ng.This procedure is important to determine and maintain control on the nes

passing the No. 200 sieve.

Application Rates for Asphalt and Rock

Gui e to App ication Rates

The Washington State Department o ransportat on s tan arSpecications contains a guide to application rate ranges.

Asp a tSeveral basic factors affect the application rate. The amount to applydepends on:

he size of the rock use or t e cover aggregate;

he grading of the rock;

Finer graded aggregates require lessasphalt,

Open graded or one-sized aggregatesneed a heavier shot of asphalt;

the surface texture of the existingpavement; and

Trafc volumes and seasonaltemperature ranges.

The asphalt application rate isincreased slightly for roads with lowertrafc volumes and in areas that havecooler summers.

Other factors may require adjusting theapplication rates of the asphalt.

A lication RateAsphalt Aggregates

(gal. per sq. yd.) Aggregate (lbs. per sq. yd.)Applied Size (In.) Applied

ass A

Prime Coat 0.35-0.55 - or - 25-40Tack Coat 0.35-0.50 - 25-35

-0 4-6lass B 0.40-0.60 ?- 25-40

-0 4-6lass C 0.35-0.50 - 20-30

-0 4-6ass D 0.20-0.35 ?-#10 18-25

Pre-Sea 0.15-0.20 -0 8-15


22/33

sually an increase in rates is required for

ow air or pavement temperatures,

Pavements in heavily shaded areas,

Recently patched areas, and

Open or dry pavements.

hots are reduced for fat or ushing pavements.sphalt emulsions will be applied at higher rates than cutbacks

under the same conditions. Some feel this is an advantage.

Met o s or Determining As a t A ication Rate

The most common way to e erm ne e amoun o asp a o app y s ouse past experience. There is a simple test to determine if the applicationrate used is correct. After the seal coat has been completed (preferablywithin a day or two), remove a random sampling of the largest sized rocksfrom the newly completed seal and determine the embedment of rock intothe asphalt. An embedment of 50 percent to 70 percent is desirable.

Amount o Aggregate Cover

There are several methods o eterm n ng t e proper amount o coveraggregate.

he spread rate can be based on experience.

simple method to determine the application rate for aspecic rock is by laying the rock one stone deep, on a one-square-yard surface, and then weighing it.

he proper rock cover is when 10 percent to 15 percent black

(asphalt) can be seen through the newly laid rock.nough cover aggregate should be spread to prevent pickup

under trafc.

here should not be a surplus of rock on the shoulders, after thesurface has been broomed and is being used by trafc.


23/33

Equipment for Applying

the Asphalt and the RockThe equipment required to do a seal includes a distributor, chip spreader, trucks,roller(s), and hand tools (broom, shovels, and agger tools). A second chip spreaderor a winter sander to apply the choke, a power broom, and a pilot car are optionalbut desirable equipment.

Distri utor

It is most important that the distributor be properlyadjusted and operated to uniformly apply the properamount of asphalt.

The bar and its snivies (nozzles) must be properly setto obtain a uniform shot (application). The snivy size,spacing, and angle in relation to the bar determine the

height of the bar.

Streaking will occur

If the asphalt is too cold;

When the viscosity of the asphalt is too high;

If a snivy or snivies are plugged;

If the aperture of the snivies is wornexcessively;

If the snivies are not all at the same angle;

When the bar is too high;


24/33

When the bar is too low;

When the bar pressure is too high. It cutsurrows because the snivies are too small and/or there is too much pump pressure.

When the bar varies in height from a full

to an empty distributor, blocking or lockingagainst the overload springs will reduce oreliminate this variance in height.

When the bar is too long and/or the snivyopenings are too large for the pump capacity,this results in narrow and uttering fans.Smaller snivies and/or higher pump capacitywill correct this.

If the pump pressure is too low it will create narrower sprayans and uttering.

If the distributor tank is allowed to run completely empty,

an irregular pattern of misses and uttering will occur acrossthe bar. For this reason, the shot should be terminated whileapproximately 100 gallons are left in the distributor.

Proper Bar Heig t

To etermine proper bar heig t,

Make sure the asphalt is at the proper temperature;

Install the right sized snivies;

Make sure the snivies are at the proper angle;

Met the proper pump pressure (or output);

Cut off (turn off) the snivies to produce a single lap, everyother snivy for 6-inch spacing and two snivies for every three

with 4-inch spacing;

If the bar is too low, there will be whitestreaks (areas of no asphalt coverage);


25/33

If the bar is too high, black (double-application) streaks will appear.

This is perfect coverage. Then turn on the remainingsnivies and shot.

C ip Sprea er

The chip spreader should be c ec e .he gates should be adjusted to apply a uniform rock spread.

However, frequently the gates in line with the wheel path ofthe spreader will be opened slightly more to give a heaviercover in these areas. This is the area of the greatest initial

heel loading. A slightly heavier aggregate cover prevents pickup on the wheels of the chip spreader and aggregate trucks.

he auger roller in the aggregate hopper should not be bent orout of round. This can cause corrugations.


26/33

Coordination of the Operation

Pre-App ication Preparation

All equipment necessary for e pro ec s ou e on e s e e ore eseal coat begins.

There should be enough loaded aggregate trucks standing by to cover thelength of the asphalt spread (or the spread should be shortened for theamount of rock available).

The distributor may shoot the lane with trafc or in the lane opposingtrafc. Both have proven satisfactory.

Consider whether to seal toward the stock pile site or away from it. Thereare advantages and disadvantages to each. Most engineers prefer to shoottoward the stock pile. This keeps most of the construction trafc off thefresh seal and avoids damage to the newly laid surface.

The surface to be sealed should be properly prepared (patched andcleaned).

App ication o t e Asp a t

The distributor should start an n s eac s ot on paper. s assures auniform application of asphalt for the entire shot and minimizes gaps ordouble applications at the ends of a shot.

The shot plan should be adjusted so the longitudinal joint (meet-line) is onthe center line or in the center or edge of the driving lanes.

After each shot, the distance, the width, and the amount of asphalt usedshould be determined. From this, the gallons per square yard should becalculated to assure that the proper application rate has been met.

Application of the Rock

The rock application shoul o ow as rap y as poss e, pre era y w none minutes. The asphalt will never be as uid as when it rst leaves thedistributor. The asphalt must be uid so the rock will be embedded by thedisplacement of the asphalt. This displacement is similar to the rise in thewater level when a person sits down in a bathtub full of water. For example,a 0.5 gallon/square yard shot is only 3/32-inch thick. It is necessary todisplace the asphalt while it is uid to get the desired 50 percent to 70percent embedment.

A wave of asphalt can form in front of the rock spread when a negraded aggregate is being laid on an emulsion. This is not desirable becausetransverse ridges may form and affect the ride and appearance of the seal.A slight delay of a minute or so in covering or a reduction in shot rate willreduce or eliminate the wave. The delay in covering is preferable. As thetemperature increases during the day, this waiting period can usually bereduced or may become unnecessary.

Trucks must back into the spreader. They should break the track (not alltravel in the same wheel path) to accomplish some initial rolling. Thetrucks should not cross over any exposed asphalt such as the open meet line


27/33

going into the chip spreader. It may be necessary for them to cross over themeet line as they leave the chip spreader.

The speeds and loads of the trucks hauling the seal rock should be regulatedto prevent damage to the new seal. They should turn around as little aspossible on the new seal.

The chip spreader should be operated at a speed that will prevent the coveraggregate from being rolled as it is being applied. Abrupt stops and startsshould be avoided. The aggregate supply should be controlled to assure auniform distribution across the entire box, so no section in the hopper isstarved for rock.

The aggregate should be spread on the rst half of the roadway so that a4-inch to 6-inch strip of asphalt is left exposed along the centerline. Thiswill form a lap for the application of the asphalt on the second half of theroadway.

If an excess of aggregate has been spread in some areas, it should beuniformly distributed on the adjacent roadway surface or picked up. Areasthat have received an aggregate cover that is too light should be hand-spotted (hand-covered).

C o e

A dry choke cover is a san or nc o . s requen y use o prevena new seal coat rock from being turned under early trafc.

The choke is applied after the seal rock has been rolled but preferablybefore trafc is allowed to use the road. It is applied at the rate of 4 lbs. to 6lbs. per square yard. It is better if the choke is rolled before trafc is allowedon the surface but not entirely necessary.

The choke cover usually produces a tighter seal coat surface.

Ro ingSteel wheeled rollers are frequent y use on t e pr me t e sea on a newbase). Pneumatic rollers are preferred for rolling seal coats laid on existingpavements because they will not fracture the rock and will roll into thedepressions. Rolling of a seal coat is done to orient the rock (get the atsides down).

Rollers should be operated at slow speeds (4 to 6 mph) so the rock is set,not displaced.

The number of rollers required for a seal coat project depends on the spreadof the operations. It takes two to four passes of the roller to set the rock.These rollers should have tire pressures of 45 psi or more.

Application of the Second Lane

After the rst lane has been s ot, covere , an t e ro ng as egun, t eequipment is pulled back for the second lane. The operation is the same ason the rst shot. The open meet line of the asphalt should receive a secondshot.


28/33

Trafc Control

Even the faster curing aspha ts use or sea coats ave a ten er per o .Some form of trafc control is desirable to keep the initial trafc speedbelow 25 mph. Flaggers or signs help, but the most positive means is apilot car. The primary purpose of the pilot car is to control the speed of thetrafc through the project. In addition, the pilot car can move trafc backand forth across the roads to prevent travelling in the same wheel paths.

This trafc will supply some secondary pneumatic tired rolling.

Brooming

Brooming is done at the comp et on o t e sea coat process or t efollowing reasons:

hen a cutback is used, there may be an advantage to bringingthe cover stone from the shoulder area back onto the newlysealed surface. It is possible an additional amount of rock cane stuck. This procedure can serve as a blotter for areas that

may blacken or bleed. This brooming is generally done with aroom (turkey tail) on the moldboard of a motor patrol.

emoval of the surplus aggregate from the surface of a new sealcoat will reduce ying rock, which can break windshields andheadlights. This loose surplus aggregate can grind and loosensome of the rock set in the seal coat. Brooming can be donethe next day or several weeks later, depending on trafc andthe curing characteristics of the asphalt used. It is desirable toroom during the cool period of the day (early morning). If the

rock is being dislodged, the brooming should be delayed untilthe asphalt has cured further or the weather is cooler. A rotaryower broom is generally used. The gutter broom on a pick-up

sweeper should not be used because it can exert such severerooming action.


29/33

Post-Seal Inspection

T e em e ment o t e aggregate into t e asp a t s ou e c ec e a ayor so a ter t e construction o t e sea coat. emove severa o t e argeststones an etermine i t e percent to percent em e ment as eeno taine .

If an inadequate application of asphalt was applied, a fog seal can enrichand tie down the seal rock. A diluted CSS-1 (usually 50/50) is applied atthe rate of .1 to .2 gallons per square yard of the dilution. (Application canvary depending on pavement texture, local conditions, and trafc.) Nocover aggregate is required; however, if a tighter seal is desired, a sand or1/4 inch to 0 cover may follow. Trafc should be controlled until the CSS-1has cured.


30/33

Miscellaneous Seal Coat Information

Asphalt Additives for Seal Coat As halts

nti-Strip AdditivesSome aggregates have a strong electro-chemical make-up and tend to repelthe asphalt, particularly in the presence of water. Under these conditions,the asphalt strips from the rock and the rock loses its bond. This is wherethe anti-strip additive may prove benecial, particularly for paving gradesand cutbacks. Most of the emulsiers in asphalt emulsions are an anti-stripadditive. A rather simple laboratory test such as AASHTO T-182 (ASTMD1664) can indicate the need for an anti-strip additive.

Polymers

A polymer can be blended with an asphalt to alter the physicalcharacteristics of the asphalt. It must be an individual decision as to the

need, benets, and additional cost justication of the polymer.

Mar ing Center ines

Marking centerlines before app y ng a sea coa can save e cos o re-engineering the location of the centerline. These markers can serve as atemporary centerline. The two most popular markers are

he polypropylene stake chaser, and

he stick-on reectorized stand-up tabs.

Seasona Protection Sea Coats

Seal coats, as with all aspha t pavements, s ou e protecte ur ng t etime of year when bases are weakened. This weakness occurs when frost iscoming out. Weight restrictions should be posted as necessary and enforcedto preserve the seal coat surface.

Excessive pressure applied to the plow blade during snow removal canresult in the loss of seal coat rock.

Re ative Cost

The relative cost of the var ous sea treatments orm t e east to t e mostexpensive are as follows:

he fog seal (construction seal),he sand seal,

he chip seal,

he slurry seal, and

he cape seal, which combines the cost of a chip and a slurryseal.


31/33

Glossary

Breakin emulsionse separation of the asphalt and water, which generally makes the

emulsion unusa e.

Breakin trackW en ve icles do not travel in the same wheel path.

ChokeA sand or manufactured 1/4 inch to 0 that is applied after the primarycover stone to sur ace voi s, to prevent roc turning, an to serve as a

otter.

Cokecarbon formed by overheating of the asphalt.

Cuttera petroleum solvent.

Floatloose cover stone on a granular base.

Hand-spottedhan -covered.

Inverte penetrationpenetration t at is upward into the cover stone.

Matrixthe ne aggregates surrounding the larger rock in the asphalt mix.

Meet linethe exposed asphalt strip left undercovered along the center line on the

rst a o t e sea .

Na hthaa type of gasoline.

rime coatan application of asphalt on an untreated or granular surface.

Pre seafog seal to tighten a surface before a seal coat.

S ugs in asp a tpieces o semi-solid asphalt.

Snivt e spray nozzle on an asphalt distributor.

Strippingw en asphalt loses its bond with the seal coat aggregate.

Track coata light application of asphalt between an existing pavement and an overlay.It can also be second shot on a bituminous surface treatment.

Tackystic y.

iscosityt e egree of uidity.


32/33

Bibliography

As a t Tec no ogy an Construction Instructors Gui e (ES01), Asp a t

nstitute.

Asp a t Sur ace Treatment Construction Tec nique (ES-12), Asp a tInstitute.

Field Manual on Design and Construction of Seal Coats, July 1981, TexasState Department o Hig way an Pu ic Transportation.

Guide Specication A105, International Slurry Seal Association.

Inspectors Training Manua Sea Coats an Sur ace Treatments, 1984,Texas State Department o Hig ways an Pu ic Transportation.

Road and Bridge Guide Book, Oklahoma State University Center for LocalGovernment Tec no ogy.

Slurry Seal (CL22), Asphalt Institute.

The Economics of Seal Coating, APWA Reporter, October 1983.

Was ington State Department o Transportation Stan ar Speci cations oroa , ri ge, an unicipa onstruction .


33/33

asphalt seal coats

Documents