Chapter - 7 Bitumen Bound Materials

7/24/2019 Chapter - 7 Bitumen Bound Materials

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B I T UMEN -

BOUNDM ATER I A L S


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B I T UM EN BOUND M ATER I A L S

Def i n i t i o n s a n d t er m i n o l o 2

A sp h a l t o r b i t um en : e res uum pro uce rom e s a on o cru e pe ro eum a

atmospheric and under reduced pressures in the presence orabsence of steam. As halt is a black or dark brown solid or viscous li uid at room

temperature; insoluble in water at 20 C; partially soluble inaliphatic organic solvents; and soluble in carbon disulfide,

chloroform, ether, and acetone.

It is naturally occurring deposits of asphalt-like material. While these deposits have physical properties that are similar to

those of etroleum-derived as halt the com osition is different.

Natural asphalt deposits occur in various parts of the world, mainlyas a result of mineral oil seepage from the ground. The best knownnatural deposit is Trinidads Pitch Lake; asphalt deposits can also be

, , ,oil sands in northeastern Alberta.


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Asph a l t cem en t :

It is an asphalt that is refined to meet specifications forpaving, roofing, industrial, and special purposes.

the mixture) in hot-mix asphalts and serve to hold the

aggregate together.

Pen et r a t i o n -g r a d e a sp h a l t s :

It is asphalt that that are further processed by air-lowin solvent reci itation or ro ane deas haltin .

A combination of these processes may be used to producedifferent grades that are classified according to their

.


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Cu t b a ck a sp h a l t : sp a a s que e y e a on o uen s yp ca y

petroleum solvents). It is used in both paving and roofing operations, depending on

whether a avin or roofin as halt is li uefied. It is further classified according to the solvent used to liquefy the

asphalt cement to produce rapid-, medium-, or slow-curing asphalt. Rapid-curing cutback asphalts are made by adding gasoline or

nap a an are ma n y use as sur ace rea men s, sea coa s, antack coats.

Medium curing cutback asphalts are made by the addition ofkerosene and slow-curin cutback as halts are made b theaddition of diesel or other gas oils.

Medium- and slow-curing cutback asphalts are mainly used assurface treatments, prime coats, tack coats, mix-in-place road

, .


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Em u l si f i ed a sph a l t : s a m x ure o wo norma y mm sc e componen s

(asphalt and water) and an emulsifying agent (usually soap). It is used for seal coats on asphalt pavements, built-up roofs,

. Emulsified asphalts are further graded according to their

setting rate (i.e., rapid, medium, and slow).- ,

coating, and penetration macadams; medium-setting gradesare used for patch mixtures; and slow-setting grades are usedfor mix-in- lace road mixtures atch mixtures tack coats fo

coats, slurry seals, and soil stabilization. H o t -m i x a sp h a l t : avin material that contains mineral a re ate coated and

cemented together with asphalt cement.


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T es o f B i t u m i n ou s M a t er i a l 6

Bitumen is a petroleum product obtained by the distillationo petro eum cru e

Bitumen is a hydrocarbon material of either natural orro enous ori in, found in aseous, li uid, semisolid or

solid form

Highway construction: hydrocarbon material which are

Natural product (lake asphalt, rock asphalt)

Fractional distillation of petroleum

sp a cemen ene ra on gra eOxidized asphalt (softening point grade)

Liquid asphalt

Tar: destructive distillation of coal


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Production

The portion of bituminous material present inpetroleum may widely differ depending on thesource

Almost all the crude petroleum's containconsiderable amounts of water along with crude oil

Hence the petroleum should be dehydrated before

t e isti ation


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Petroleum Bitumen Flow Chart8


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Types of Distillation Processes ract ona st at on:

In the fractional distillation the various volatile constituentsare separated at successively higher temperatures without

The fractions obtained yield gasoline, naphtha, kerosene and

lubricating oil In destructive distillation material undergoes chemical

changes under the application of extreme heat and pressure

Steam distillation is employed to produce steam refined

petroleum bitumen without causing chemical change

further treatment it is called asStraight-run Bitumen


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Desirable Properties of Bitumen

It should befluid enough at the time of mixing to coat theaggregate evenly by a thin film

It should have low temperature susceptibility

It should show uniform viscosity characteristics

Bitumen should have good amount of volatiles in it, and itshould not lose them excessivel when sub ected to hi hertemperature

The bitumen should be ductile and not brittle

temperature at which it can be easily mixed without any firehazards

should not be stripped off in the continued presence off water


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T est s f o r B i t u m i n o u s M a t er i a l s 11

ualit control tests for Bitumen

Penetration Ductility

Softening point

Specific gravity oss on eat ng

Flash & Fire point

Solubility


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Penetration test for Bitumen12

Significance

The bitumen grade is specified in terms of the penetration value 30/40 and 80/100 grade bitumen are commonly used

versa Consistency of bitumen varies with temperature, constituents, refining

process, etc. scos ty s an a so ute property, ut cou not e eterm ne eas y

Viscosity of cutback bitumen by indirect method (orifice viscometer) Too soft for penetration, too hard for orifice then perform float test

of 1/10th of a mm of a standard needle of 100 gm in a bitumen samplekept at 25C for 5 seconds

Higher penetration implies softer grade Purpose is classification


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Procedure 0

Pour the bitumen into the container at least 10 mm above the expectedpenetration Place all the sample containers to cool in atmospheric temperature for 1

our Place the sample containers in temperature controlled water bath at a

temperature of 250 C 1o C for a period of 1 hour Fill the transfer dish with water from the water bath to cover the container

completely Take off the sample container from the water bath, place in transfer dish

and place under the middle of penetrometer See the dial reading and release the needle exactly for 5 seconds Note the final reading Difference between the initial and final readings is taken as the penetration

va ue n 1 10t o mm


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Discussion

Test is highly influenced by the pouring temperature, size ofneedle, weight of needle, test temperature, duration of

High penetration grade is desirable in colder regions

Penetration below 20 will result in crackin

For lower penetration, bonding is difficult, but onceachieved will remain for a long time


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D u ct i l i t Test 18

Significance

The ductility of bitumen improves the physical interlocking ofthe aggregate bitumen mixes

deformation. The binder material of low ductility would crack

and thus provide pervious pavement surface e es s e eve o measure e a es ve proper y o umen

and its ability to stretch

Ductility and penetration go together, in general, but exception

can happen Ductility is the distance in cm to which a standard briquette of

bitumen can be stretched before the thread breaks

Ductile materials is one which elongates when held in tension


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Procedure o .

softening point until it is fluid It is strained through IS sieve 30, poured in mould assembly and placed on a brass

plate, after a solution of glycerine or dextrine is applied over all surfaces of themould exposed to bitumen

Thirty to forty minutes after the sample is poured into the moulds, the plateassembly along with the sample is placed in water bath maintained at 27oC for 30minutes

The sample and mould assembly are removed from water bath and excess bitumen

After trimming the specimen, the mould assembly containing sample is replaced inwater bath maintained at 27oC for 85 to 95 minutes

The slides of the mould are then removed and the clips are carefully hooked on the

The pointer is set to read zero The machine is started and the two clips are thus pulled apart horizontally While the test is in operation, it is checked whether the sample is immersed in water

The distance at which the bitumen thread breaks is recorded (in cm) and reported

as ductility value


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Discussion

Ductility of bitumen is affected by the pouring temperature,briquette size, placement of briquette, test temperature,

Ductility value ranges from 5-100. Low value implies

cracking. Some minimum ductility is needed for flexuralstrength

The lack of ductility does not necessarily indicate poor.


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So f t en i n Po i n t Test 26

Significance

Bitumen does not melt, but change gradually from solid toliquid

o en ng po n s e empera ure a w c e umenattains particular degree of softening under specified test

conditions Ring and ball apparatus is used for the test


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Procedure

Heat the bitumen to a temperature between 125oC to 150oC

Heat the rings at the same temperature on a hot plate & place onglass plate coated with glycerin

Fill up the rings with bitumen

Cool for 30 minutes in air and level the surface with a hot knife

distilled water at 5oC and maintain that temperature for 15minutes

at 5oC per minute till the ball passes trough the rings Note the temperature at which each of the ball and sample

Temperature shall be recorded as the softening point of bitumen


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Discussion

Test is affected by quality of liquid, weight of ball, rate ofheating etc

g ves an ea o e empera ure a w c e um nousmaterial attains a certain viscosity

Bitumen with hi her softenin oint is used in warmerplaces

Softening point is very critical for thick films like joint and

crac ers, to ensure t ey w not ow


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T est s f o r B i t u m i n o u s M a t er i a l s 31

Assi nment

Specific gravity Loss on heating

Flash & Fire point

Viscosity

o u ty


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B I T UM EN BOUND M ATER I A L ST est s f o r B i t u m i n o u s M a t er i a l s

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Quality control tests for Bitumen Consistency tests

Saybolt Fural Viscosity test

Float test

Tests for Rate of Curing

Specific gravity test

Loss on heating test

Flash & Fire point testViscosity test

o u y es


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Quality control tests for Bitumen

Saybolt Fural Viscosity test

Kinematic Viscosity test Penetration test Float test Softening point test

Ductility test Thin Film Oven test

Tests for Rate of Curing st at on test or cut ac an emu s ons

Softening point test Specific gravity test Ductility test Loss on heating test Flash & Fire point test Viscosity test Solubility test


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Bituminous materials, commonl referred to as

premixes, are manufactured in asphalt mixing plantsand laid hot (hence the other used designation, hot-m x .

In-situ mixing can also be used for making base.


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B I T UM EN BOUND M ATER I A L SCom onents of a Mix

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The coarse aggregates for premixes should be produced by crushingsound unweathered rock or natural ravel. The a re ate must beclean and free of clay and organic material; the particles should be

angular and not flaky. Aggregates for wearing course must also be resistant to abrasion

.where possible, but otherwise the absorption of bitumen must betaken into account in the mix design procedure.

Hydrophilic aggregates which have a poor affinity for bitumen inthe presence of water should also be avoided. They may beacceptable only where protection from water can be guaranteed.

The filler (material passing the 0.075 mm sieve) can be crushed, .

Portland cement or hydrated lime is often added to natural filler (1-2 % by mass of total mix) to assist the adhesion of the bitumen tothe aggregate. Fresh hydrated lime can help reduce the rate of

ar en ng o tumen n sur ace ress ngs an may ave a s m areffect in premixes.


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Table 7-1: Coarse Aggregate for Bituminous Mixes


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Table 7-2: Fine Aggregate for Bituminous Mixes


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To perform satisfactorily as road surfacing, bitumenaggregate mixes need to possess the following

characteristics: .

High resistance to fatigue and the ability to withstand highstrains i.e., they need to be flexible.

underlying pavement layers.

High resistance to environmental degradation i.e. good.

Low permeability to prevent the ingress of water and air.

Good workability to allow adequate compaction to be obtainedur ng cons ruc on


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The requirements of a mix which will ensure each of these.

Mixes suitable for areas carrying heavy, slow-moving traffic, such ason climbing lanes, or areas where traffic is highly channeled, will beunsuitable for flat, open terrain where traffic moves more rapidly.

A mix suitable for the latter is likely to deform on a climbing laneand a mix suitable for a climbing lane is likely to possess poordurability in flat terrain.

,bitumens in the surface of wearing courses all tend to harden to asimilar viscosity within a short time.

It is therefore recommended that 60/70 penetration bitumen is

used to provide a suitable compromise between workability,deformation resistance and potential hardening in service. If possible, a bitumen should be selected which has a low

.


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B I T UM EN BOUND M ATER I A L ST es of a PreMix

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The main types of premix are asphaltic concrete, bitumenmaca am an o ro e asp a .

Each type can be used in surfacings or base courses. ASPH AL T I C CONCRETE

Asphaltic concrete (AC) is a dense, continuously graded mixwhich relies for its strength on both the interlock between

a re ate articles and to a lesser extent on the ro erties ofthe bitumen and filler.

The mix is designed to have low air voids and low

behavior. The particle size distributions for wearing course material

-not generally suffered from deformation failures.


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Table 7-3: Asphaltic Concrete Surfacing


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It is common ractice to desi n the mix usin theMarshall Test (ASTM D1559) and to select the design

binder content by calculating the mean value of then er con en s or

a) maximum stability,

,

c) the mean value for the specified range of void contents and

d) the mean value for the specified range of flow values.

Compliance of properties at this design bindercontent with recommended Marshall Criteria is theno a ne a e 7-4 .


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Table 7-4: Suggested Marshall Test Criteria


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A good method of selecting the Marshall Design binder

to examine the range of binder contents over which each property issatisfactory,,

and then choose a design value near the center of the common range.

If this common ran e is too narrow the a re ategrading should be adjusted until the range is wider andtolerances less critical.

To ensure that the com acted mineral a re ate in

continuously graded mixes has a void content largeenough to contain sufficient bitumen, a minimum valueof the voids in the mineral aggregate (VMA) is specified,as s own in Ta e 7-5.


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Table 7-5: Voids in the Mineral Aggregate


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BITUMENMACADAM

Close graded bitumen macadams are continuously graded

mixes similar to asphaltic concretes but usually with a lessdense aggregate structure.

Their suitability for different conditions and with differentmaterials may be questioned but, in practice, numerous

materials including crushed gravels have been usedsuccessfully.

The advantage of this method is that quality control testing issim lified and this should allow more intensive com liance

testing to be performed. Aggregates which behave satisfactorily in asphaltic concrete

specifications for a base course mix are given in Table 7-6.



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Table 7-6: Bitumen Macadam



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When gravel other than limestone is used, the anti-strippingproper es w e mprove y nc u ng 2 or an cemen

or hydrated lime in the material passing the 0.075 mm sieve. For aggregate with fine micro texture e.g. limestone, the

itumen content s ou e re uce y 0.1 to 0.3%. 60/70grade bitumen is preferred.

In practice the upper limit has been exceeded by 20% with noadverse effect.

Limestone and gravel are not recommended for wearingcourses where hi h skiddin resistance is re uired.

Close graded bitumen macadam mixes offer a good basis forthe design of deformation resistant materials for severe sites,

their refusal density.



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Marshall Design criteria in Table 7-7 should be used.

At the time of construction the air voids content is virtuallycertain to be in excess of five per cent and therefore a

.

Table 7-7: Suggested Marshall Criteria for Close Graded BitumenMacadams



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B I T UM EN BOUND M ATER I A L SB I TUM I NOUS SURFACI NG

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B I TUM I NOUS SURFACI NG

It s essent a t at t e t n tum nous sur ac ngs

(50mm) recommended for flexible structures. This is particularly important for surfacing laid on

granular base courses. Mixes which are designed to have good durability rather

than hi h stabilit are flexible and are likel to havesand and bitumen contents at the higher end of thepermitted ranges.

In areas where the roduction of sand-sized material is

expensive and where there is no choice but to use higherstability mixes, additional stiffening through the agingand embrittlement of the bitumen must be prevented byapp y ng a sur ace ress ng.



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B I T UM EN BOUND M ATER I A L SDESIGN TO REFUSAL DENSITY

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DESIGN TO REFUSAL DENSITY

Under severe loading conditions asphalt mixes must be

expected to experience significant secondary compaction inthe wheel paths.

Severe conditions cannot be precisely defined but will consistof a combination of two or more of the following:

High maximum temperatures Very heavy axle loads

Very channeled traffic

Stopping or slow moving heavy vehicles

Failure by plastic deformation in continuously graded mixesoccurs very rapidly once the VIM is below 3 per cent.

refusal there is still at least 3 per cent voids in the mix.



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B I T UM EN BOUND M ATER I A L SDESIGN TO REFUSAL DENSITY

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DESIGN TO REFUSAL DENSITY ere ore e a m o re usa ens y es gn s o ensure a a

refusal there is still at least 3 per cent voids in the mix. For sites which do not fall into the severe category, the

content for good durability is obtained. This may be higher than the Marshall optimum but the

maintained. Where lower axle loads and higher vehicle speeds are

involved the minimum VIM at refusal can be reduced to 2 er

cent. Refusal density can be determined by two methods: Extended Marshall Compaction Compaction by vibrating hammer



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B I T UM EN BOUND M ATER I A L SBituminous Base Courses

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Bituminous Base Courses

Satisfactory bituminous base courses can be madeusing a variety of specifications.

ey s ou possess proper es s m ar obituminous mix surfacings but whenever they are

used in con unction with such a surfacin the loadinconditions are less severe, hence the mixrequirements are less critical.

ever e ess, e empera ures o ase courses maybe high and the mixes are therefore prone todeformation in earl life, and a in andembrittlement later.



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PR I N CI PA L M I X TYPES

Particle size distributions and general specificationsfor continuously graded mixes are given in Table 7-8.

No formal design method is generally available fordetermining the optimum composition for thesemater a s ecause t e max mum part c e s ze anproportions of aggregate greater than 25 mm

.



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Table 7-8: Bitumen Macadam Base Course



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The following principles should be adopted for allbituminous layers but are particularly important for

recipe type specifications: ,

carried out to determine suitable mix proportions andprocedures.

best achieved by specifying density in terms of maximumtheoretical density of the mix.

required to achieve good coating of the aggregates andsatisfactory compaction.

stability should be used



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SAND-BITUMENMIXES For g t an me um tra c e roa s an n areas

lacking coarse aggregates, bitumen stabilized sands arean alternative. Best results are achieved with well-graded angular sands

in which the proportion of material passing the 0.075mm

sieve does not exceed 10% and is non plastic. The bitumen can range from a viscous cutback that will

require heating to a more fluid cutback or emulsion thatcan be used at ambient temperatures.

The most viscous cutbacks that can be properly mixed atambient temperatures are RC or MC 800 or equivalents.In general, the more viscous the bitumen the higher will

e e s a y o e m x.


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B I TUM EN BOUN D M ATER I A L S58

SAND-BITUMENMIXES

The amount of bitumen required will generally lie between3 and 6 per cent by weight of the dry sand, the higherpropor ons e ng requ re w e ner-gra nematerials.

The Marshall Test ASTM D1 can be used fordetermining the amount of bitumen required.

Table 7-9: Criteria for Sand-Bitumen Base Course Materials



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MANUFACTURE AND CONSTRUCTION

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It is normal practice to carry out preliminary design testing to

determine the suitability of available aggregates and theirmost economical combination to produce a job mix formula.

The importance of detailed compaction trials at the beginningof asphalt construction work cannot be over emphasized.

,the production-run asphalt with the job-mix formula should

be established.

- , ,

redesign of the mix are carried out at this stage to ensure thatthe final job mix satisfies the mix design requirements and

.



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Tolerances are specified for bitumen content and for theaggrega e gra ng o a ow or norma var a on n p an

production and sampling. Good quality control is essential to obtain durable asphalt and

t e mean va ues or a series o tests s ou e very c ose to t ejob-mix formula which, in turn, should have a grading entirely

within the specified envelope. Mixing must be accomplished at the lowest temperatures and

in the shortest time that will produce a mix with completecoating of the aggregate and at a suitable temperature toensure proper compaction.

Very little additional compaction is achieved at the minimumrolling temperatures shown in the table and only pneumatictired rollers should be used at these temperatures.



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Table 7-10: Job-Mix Tolerances for a Single Test

Table 7-11: Manufacturing and Rolling Temperatures (oC)

B I TUM EN BOUND M ATER I A L S


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Rolled asphalts are relatively easy to compact but bitumen

compactive effort is required.

Heavy pneumatic tired rollers are usually employed, the kneadingaction of the tires being important in orientating the particles.

Vibratory compaction has been used successfully but care is neededin selecting the appropriate frequency and amplitude of vibration,and control of mix temperature is more critical than with pneumatic

Steel-wheeled deadweight rollers are relatively inefficient and giverise to a smooth surface with poor texture but are required to obtainsatisfactory joints.

Rolling usually begins near the shoulder and progresses towards thecenter.

It is important that directional changes of the roller are made only

slightly different length to avoid the formation of ridges.



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The number of joints to cold, completed edges should be minimized-

joints between adjacent layers.

If this is not possible, repositioning of the paver from lane to lane atfrequent intervals is another option.

If a layer is allowed to cool before the adjacent layer is placed, thenthe edge of the first layer must be roller over and thoroughlycompacted. Before laying the second lane, the cold joint should be

The paver screed should be set to overlap the first mat by asufficient amount to allow the edge of the rolled over layer to bebrought up to the correct level.

Coarse aggregates in the material overlapping the cold joint shouldbe carefully removed.

The remaining fine materials will allow a satisfactory joint to be.



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SURFACE TREATMENTS

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SURFACE TREATMENTS sur ace rea men s a s mp e, g y e ec ve an nexpens ve

road surfacing if adequate care is taken in the planning andexecution of the work.

roads, an also as a maintenance treatment for roads of all kinds.

A surface treatment comprises a thin film of binder, generallybitumen or tar, which is sprayed onto the road surface and thencovere w a ayer o s one c pp ngs.

The thin film of binder acts as a waterproofing seal preventing theentry of surface water into the road structure.

vehicle tires, and form a durable, skid-resistant and dust-freewearing surface. In some circumstances the process may be repeated to provide

ou e or r p e ayers o c pp ngs.

B I TUM EN BOUND M ATER I A L S S C S


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SURFACE TREATMENTS

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SURFACE TREATMENTS oa s carry ng n excess o 1000 ve c es ane ay, ave een

successfully surfaced with multiple surface treatments. If traffic growth over a period of several years necessitates a

,bituminous overlay can be laid over the original surfacetreatment when the need arises.

technique, which is capable of greatly extending the life of astructurally sound road pavement if the process is undertakenat the optimum time.

Under certain circumstances a surface treatment may alsoretard the rate of failure of a structurally inadequate roadpavement by preventing the ingress of water and preserving

subgrade.

B I TUM EN BOUND M ATER I A L S SURFACE TREATMENTS


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SURFACE TREATMENTS

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SI NGLE SURFACE TREATM ENT

s ng e sur ace treatment wou not norma y e use on anew roadbase because of the risk that the film of bitumen willnot give complete coverage.

future maintenance and a double dressing should beconsiderably more durable than a single dressing.

- ,new roadbase which has a tightly knit surface because of theheavier applications of binder which is used with this type ofsingle dressing.

When applied as a maintenance operation to an existingbituminous road surface a single surface treatment can fulfillthe functions required of a maintenance re-seal, namely

, ,restoring skid resistance.

B I TUM EN BOUN D M ATER I A L S


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B I TUM EN BOUN D M ATER I A L S67



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SURFACE TREATMENTS

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DOUBLE SURFACE TREATMENT

Double surface treatments should be used when:

A new road base is surface treated. Extra cover is re uired on an existin bituminous road surface

because of its condition (e.g. slightly cracked or patched surface).

There is a requirement to maximize durability and minimize the

frequency of maintenance and resealing operations. The quality of a double surface treatment will be enhanced of

traffic is allowed to run on the first treatment for a minimumeriod of 2-3 weeks before the second treatment is a lied.

This allows the chippings of the first treatment to adopt astable interlocking mosaic, which provides a firm foundationfor the second treatment.



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SURFACE TREATMENTS

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DOUBL E SURFACE TREATM ENT

However, traffic and animals may cause contamination of the

surface with mud or soil during this period and this must bethoroughly swept off before the second treatment is applied.

Such cleaning is sometimes difficult to achieve and the earlyapplication of the second seal to prevent such contamination

may give a better result. Sand may sometimes be used as an alternative to chippings

for the second treatment.

the surfacing, the combination of binder and sand provides auseful grouting medium for chipping of the first seal and helps

A slurry seal may also be used for the same purpose.



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SURFACE TREATMENTS

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TR I PL E SURFACE TREATM ENT

A triple surface treatment may be used to advantage where

a new road is expected to carry high traffic volumes.

e app ca on o a sma c pp ng n e r sea w

reduce noise generated by traffic and

-free service life



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SURFACE TREATMENTS

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RACK ED -I N SURFACE TREATM ENT

s treatment s recommen e or use w ere tra c sparticularly heavy or fast.

A heavy single application of binder is made and a layer of

coverage. This is followed immediately by the application of smaller

- a stable mosaic.

The amount of bitumen used is more than would be used witha sin le seal but less than for a double seal.

The main advantages of the racked-in surface treatment are: Less risk of dislodged large chippings.

. Good surface texture.



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SURFACE TREATMENTS

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OTH ER TYPES OF SU RFACE TREATM ENT

Pad coats are used where the hardness of the existing

road surface allows very little embedment of the first

cement stabilized roadbase or a dense crushed rock base.

A first layer of nominal 6mm chippings will adhere well

10mm or 14mm chippings in the second layer of thetreatment.

Sandwich surface treatments are principally used onexisting binder rich surfaces and sometimes on gradientsto reduce the tendenc for the binder to flow down theslope.



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SURFACE TREATMENTS

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Chippings for Surface Treatments

The selection of chipping sizes is based on the volume of

commercial vehicles having weight of more than 1.5

Ideally, chippings used for surface treatment should besingle sized, cubical in shape, clean and free from dust,

, ,the action of traffic.

It is recommended that chippings used of surfacetreatment should comply with the requirements of Table7-12 for higher levels of traffic, and to the requirementsof Table -1 for li htl trafficked roads of u to 2 0vehicles per day:



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SURFACE TREATMENTS

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Table 7-12: Grading Limits, Specified Size and Maximum Flakinessn ex or ur ace reatment ggregates



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Table 7-13: Grading Limits, Specified Size and Maximum Flakinessn ex or ur ace reatment ggregates or g t y ra c e oa s



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Samples of the chippings should be tested for grading, flakiness, , ,

stone value and aggregate abrasion value.

Specifications for maximum aggregate crushing value (ACV) forsurface treatment chippings typically lie in the range 20 to 35. Forg t y tra c e roa s t e g er va ue s e y to e a equate ut

on more heavily trafficked roads a maximum ACV of 20 isrecommended.

primary purpose of the surface treatment is to restore or enhancethe skid resistance of the road surface.

The PSV required in a particular situation is related to the nature ofe roa s e an e spee an n ens y o e ra c.

The resistance to skidding is also dependent upon the macro textureof the surface which, in turn, is affected by the durability of theex osed a re ate.



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Table 7-14: Recommended Polished Stone Values of Chippings



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The nominal sizes of chippings normally used for surface treatment, , .

Flaky chippings are those with a thickness (smallest dimension) less

than 0.6 of their nominal size. The ro ortion of flak chi in s clearl affects the avera e

thickness of a single layer of the chippings, and it is for this reasonthat the concept of the average least dimension (ALD) of chippingswas introduced.

,chippings when they have bedded down into their final interlockedpositions.

The amount of binder required to retain a layer of chippings is thusrelated to the ALD of the chippings rather than to their nominal

size. The most critical period for a surface treatment occurs immediately

.



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79

Dusty chippings can seriously impede adhesion and can cause.

The effect of dust can sometimes be mitigated by dampening them

prior to spreading them on the road. The chi in s dr out uickl in contact with the binder and when a

cutback bitumen or emulsion is used, good adhesion develops morerapidly than when the coating of dust is dry.

Most aggregates have a preferential attraction for water rather than

. Hence if heavy rain occurs within the first few hours when adhesion

has not fully developed, loss of chippings under the action of trafficis possible.

Where wet weather damage is considered to be a severe risk, anadhesion agent should be used.

An adhesion agent can be added to the binder or, used in a dilute.



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80

Improved adhesion of chippings to the binder film canalso be obtained by pre-treating the chippings before

spreading. s s e y o e mos ene c a e ava a e

chippings are very dusty or poorly shaped, or if traffic

conditions are severe. There are basically two ways of pre-treating chippings:

Spraying the chippings with a light application of creosote,ese o , or erosene a am en empera ure.

Pre-coating the chippings with a thin coating of hard bitumensuch that the chippings do not stick together and can flowfreely.



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81

Chippings which are pre-coated with bitumen enable the

can provide early strong adhesion and thus help to obtainhigh quality dressings.

e n er use or pre-coa ng nee no necessar y ethe same kind as that used for the surface treatment; forexample, tar-coated chippings adhere well to a sprayed

. Pre-coating is usually undertaken in a hot-mix plant and

the hardness of the coating, and thus the tendency for the,

the mixing temperature and/or the duration of mixing;typical coating temperatures are about 140oC for bitumeno .



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82

Table 9-4: Binder Contents for Lightly-Coated Chippings

Pre-coated chippings should not be used with emulsions becausethe breaking of the emulsion will be adversely affected.

Adhesion agents or pre-treatment chippings are often used in anattempt to counteract the adverse effect of some fundamentalfault in the surface treatment operation.

If loss of chippings has occurred, it is advisable to check whetherthe viscosity of the binder was appropriate for the ambient roadtemperature at t e t me to spray ng.



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83

Bitumens

It is essential that good bonding is achieved between the

surface treatment and the existing road surface.

This means that non-bituminous materials must beprimed before surface treatment is carried out.



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84

PR I M E COATS W ere a sur ace treatment is to e app ie to a previous y

untreated road surface it is essential that the surface shouldbe dry, clean and as dust-free as possible.

e unct ons o a pr me coat s summar ze as o ows: maintain adhesion between the roadbase and a surface

treatment by pre-coating the roadbase and penetrating surface

. seal the surface pores in the roadbase thus reducing the

absorption of the first spray of binder of the surface treatment.

particles of aggregate together. If the application of the surface treatment is delayed for some

reason it provides the roadbase with a temporary protectionagainst rainfall and light traffic until the surfacing can be laid.



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85

The depth of penetration of the prime should be between 3-

surface is dry within a few hours.

The correct viscosity and application rate are dependent

primed. The application rate is, however, likely to lie within the range

0. -1.1k m2. Low viscosity cutbacks are necessary for dense cement or

lime-stabilized surfaces, and higher viscosity cutbacks foruntreated coarse-textured surfaces.

It is usually beneficial to spray the surface lightly with water

before applying the prime coat as this helps to suppress dustand allows the primer to spread more easily over the surface

.



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86

Bitumen emulsions are not suitable for priming as they tendto form a skin on the surface.

Low viscosity, medium curing cutback bitumens such as MC- - -, , ,

prime coats.

Table 9-5: Kinematic Viscosities of Current Cutback Binders


8


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87

B I TUM ENS FOR SU RFACE TREATM ENTS

T e tumen must u a num er o mportantrequirements. It must: be capable of being sprayed; wet the surface of the road in a continuous film; not run off a cambered road or form pools of binder in local

depressions;

wet an a ere to t e c pp ng at roa temperature; be strong enough to resist traffic forces and hold the chippings

at the highest prevailing ambient temperatures; rema n ex e a e owes am en empera ure, ne er

cracking nor becoming brittle enough to allow traffic to pick-off the chippings; and .


88


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88

At the lower road temperatures cutback grades of bitumen are,

penetration grade bitumens can be used.

The temperature/viscosity relationships shown in Figure 7-2.

These have a relatively low viscosity and wet the chippingsreadily, after which the emulsion breaks, the water

eva orates and articles of hi h viscosit bitumen adhere tothe chippings and the road surface. Depending upon availability and local conditions at the time

of construction, the following types of bitumen are commonlyuse : Penetration grade Emulsion

Modified bitumens

Figure 7-2: SurfaceTemperature/Choice of

89B n er or Sur aceT


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89Treatments

In Ethiopia, daytime road

25oC and 50oC, normallybeing in the upper half ofthis range.

or t ese temperaturesthe viscosity of the bindershould lie betweenapproximately 104 and7x105 centistokes.

At the lower roadtemperatures cutback

most appropriate, whilstat higher roadtemperatures penetrationgra e umens can eused


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91


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91

B I T UM EN EM U LSI ON

per cent is recommended for most surface treatment work.

This type of binder can be applied through rotating spray jets at atemperature between 70 and 85oC and, once applied, it will breakrap y on contact w t c pp ngs o most m nera types.

The cationic emulsifier is normally an anti-stripping agent andthis ensures good initial bonding between chippings and the

. When high rates of spray are required, the road is on a gradient,

or has considerable camber, the emulsion is likely to drain fromthe road or from hi h arts of the road surface before breakoccurs.

In these cases it may be possible to obtain a satisfactory result ifthe bitumen application is split, with a reduced initial rate of

applied.


92


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92

B I T UM EN EM ULSI ON

e n en on was o cons ruc a s ng e sea en e seconapplication of binder will have to be covered with sand or

quarry fines to prevent the binder adhering to roller and.

If a double dressing is being constructed then it should bepossible to apply sufficient binder in the second spray to give

the re uired total rate of s ra for the finished dressin . If split application of the binder is used care must be takenwith the following: The rate of application of chippings must be correct so that there

is a minimum of excess chippings.

The second application of binder must be applied before traffic isallowed onto the dressing.

or a s ng e sea w e necessary o app y gr or san a er esecond application of binder.


93


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93

CUTBACK B I TUM ENS xcep or very co con ons, or 3000 gra e cu ac s norma y

the most fluid binder used for surface treatments.

This grade of cutback is basically an 80/100 penetration grade bitumenblended with approximately 12 to 17 percent of cutter. It may be necessary to blend two grades together or to cut-back a supplied

grade with diesel oil or kerosene in order to obtain a binder with therequired viscosity characteristics.

Diesel oil which is less volatile than kerosene and is enerall more easilavailable, is preferable to kerosene for blending purposes.

Only relatively small amounts of diesel oil or kerosene are required tomodify a penetration grade bitumen such that its viscosity is suitable forsurface treatment at road tem eratures in Ethio ia.

For example, Figure 7-3 shows that between 2 and 10 per cent of diesel oil

was required to modify 80/100 pen bitumen to produce binders withviscosities within the range of road temperatures of between 40 60.

-blends made for trials in Kenya.


94


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94

Figure 7-3: Blending Characteristics of 80/100 Pen Bitumen withese ue


95


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95

Figure 7-4: Viscosity/Temperature Relationahips for Blends of0 100 en tumen w t ese ue


96


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9

D et er m i n i n g t h e a v er a g e l ea st d i m en si o n o f

c h i p p i n g s

The ALD of chippings is a function of both the average size,

sieves, and the degree of flakiness.

The ALD may be determined in two ways.

A grading analysis is performed on a representative sample of thechippings

The sieve size throu h which 0 er cent of the chi in s ass isdetermined (i.e. the median size').

The flakiness index is then also determined.

in Figure 7-5.


97


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97

Figure 7-5

Determination of average

least dimension


98


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Det er m i n i n g t h e o v er a l l w ei g h t i n g f a ct o r

The ALD of the chippings is used with an overall weighting

factor to determine the basic rate of spray of bitumen. e overa we g ng ac or s e erm ne y a ng

together four factors that represent: the level of traffic, thecondition of the existing road surface, the climate and thetype of chippings that will be used.

Factors appropriate to the site to be surface dressed are- .


99


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Table 7-6: Weighting factors for surface dressing design


100


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For example, if flaky chippings (factor -2) are to be used at a roadsite carrying medium to heavy traffic (factor - 1) and which has avery rich bituminous surface (factor -3) in a wet tropical climate

(factor +1) the overall weighting factor 'F' is: -2-1-3 + 1 = -5

The rating for the existing surface allows for the amount ofbinder which is required to fill the surface voids and which is

retains the chippings.

If the existing surface of the road is rough, it should be rated as' '

bitumen. Similarly, when determining the rate of spread of binder for the

second layer of a double surface dressing, the first layer shouldalso be rated 'very lean bituminous'.


101


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Det er m i n i n g t h e b a si c b i t um en sp r a y r a t e

Using the ALD and 'F' values in the following equation will

give the required basic rate of spread of binder.= 0. 25+ 0.023 + 0.0375+ 0.0011

Where

=ALD = the average least dimension of the chippings (mm)

R = Basic rate of spread of bitumen (kg/m2)


102


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Alternatively, the two values can be used in the design chartgiven in Figure 7-6.

The intercept between the appropriate factor line and the

then read off directly at the bottom of the chart.

The basic rate of spread of bitumen (R) is the mass of

MC3000 binder per unit area on the road surfaceimmediately after spraying.

.

and the spread rate can therefore also be expressed in1/m2, however, calibration of a distributor is easier to do bymeasuring spray rates in terms of mass.


103


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Figure 7-6:

Surface dressing

design chart


104


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The basic rate of spread of binder must also be modified toallow for the type of binder used. The following

modifications are appropriate:

per cent.

Cutback binders: for MC/RC 3000 no modification is

requ re . n e rare cases w en cu ac s w ower v scos yare used the rate of spread should be increased to allow for theadditional percentage of cutter used).

Emulsion binders: multiply the rate of spread given in the

chart by 90/bitumen content of the emulsion (per cent). Thiscalculation includes a reduction of ten per cent for the residualpenetration grade bind


105


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Sp r ea d r a t e o f ch i p p i n g s

An estimate of the rate of application of the chippings

assuming that the chippings have a loose density of. ,

Chipping application rate (kg/m2) = 1 .364*ALD

Table 8 Suggested maximum increases in bitumen spray rate for low

volume roads


106


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The chipping application rate should be regarded as aroug gu e on y.

It is useful in estimating the quantity of chippings that isre uired for a surface dressin ro ect before crushin andstockpiling of the chippings is carried out.

A better method of estimating the approximate application

taken from the stockpile on a tray of known area.

The chippings are then weighed, the process repeated ten, .

An additional ten per cent is allowed for whip off. Storage and handling losses must also be allowed for when

stockpiling chippings.


107

h i hi i li i b d i d


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The precise chipping application rate must be determinedy o serv ng on s te w et er any expose n er rema ns

after spreading the chippings, indicating too low a rate of

application of chippings, or whether chippings are restingon top o eac ot er, in icating too ig an app icationrate.

Best results are obtained when the chi in s are ti htlpacked together, one layer thick.

To achieve this, a slight excess of chippings must be.

Some will be moved by the traffic and will tend to fill smallareas where there are insufficient chippings.

oo great an excess o c pp ngs w ncrease t e r s owhip-off and windscreen damage.

The quantity of

108

sufficient to cover theentire surface of the


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entire surface of then er m a er

rolling.

The rate at whichchippings should bespread depends on

,specific gravity, butrates can be estimatedus ng F gure 7-7.


109

POL YM ERM OD I F I E D B I T UM ENS


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POL YM ERM OD I F I E D B I T UM ENS

,cutback bitumens and emulsions.

Usually these modified binders are used at locations where the roadgeometry, traffic characteristics or the environment dictate that theroa sur ace exper ences g stresses.

Generally the purpose of the polymers is to reduce binder temperaturesusceptibility so that variation in viscosity over the ambienttem erature ran e is as small as ossible.

Polymers can also improve the cohesive strength of the binder so that itis more able to retain chippings when under stress from the action oftraffic.

the road to be reopened to traffic earlier than may be the case with

conventional unmodified binders. Other advantages claimed for modified binders are improved elasticity

n r g ng a r ne crac s an overa mprove ura ty.


110

POLYM ERM OD I F I E D B I T UM ENS


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xamp es o po ymers a may e use o mo y umens areproprietary thermoplastic rubbers such as Styrene-Butadiene-Styrene(SBS), crumb rubber derived from waste car tires and also glove rubberfrom domestic gloves. Latex rubber may also be used to modifyemu s ons. n ers o s ype are es app e y s r u ors e

with slotted jets of a suitable size. Rubber modified bitumen may consist, typically, of a blend of 80/100

penetration grade bitumen and three per cent powdered rubber.

B en ng an gest on o t e ru er w t t e penetrat on gra ebitumen should be carried out prior to loading into a distributor.

Cationic emulsion can be modified in specialized plant by the additionof three er cent latex rubber.

One of the advantages of using emulsions is that they can be sprayed at

much lower temperatures than penetration grade bitumens, whichreduces the risk of partial degradation of the rubber which can occur at.


111



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temperatures while having a rubbery nature at lower ambienttemperatures.

With three per cent of SBS, noticeable changes in binder viscosity and

is achieved. SBS can be obtained in a carrier bitumen in blocks of approximately 20kg

mass.

e oc s can e en e , a a concen ra on recommen e y emanufacturer, with 80/100 penetration binder in a distributor. In thisprocedure it is best to place half of the required polymer into the emptydistributor, add hot bitumen from a main storage tank and then circulate

. The remaining blocks are added after about 30 minutes and then about 2

hours is likely to be required to complete blending and heating of themodified binder.

very e ort s ou e ma e to use t e mo e tumen on t e ay t sblended.


112

ADH ESI ON AGENTS


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ADH ESI ON AGENTS

res y ra e me can e use o en ance a es on. It can be mixed with the binder in the distributor before spraying or

the chippings can be pre-coated with the lime just before use, bys ra in with lime slurr . The amount of lime to be blended with the bitumen should be

determined in laboratory trials but approximately 12 per cent bymass of the bitumen will improve bitumen aggregate adhesion.

Propr etary a t ves, nown as a es on agents, are a so ava a efor adding to binders to help to minimize the damage to surfacetreatments that may occur in wet weather with some types of stone.

enhance adhesion between the binder film and the chippings even

though they may be wet. Cationic emulsions inherently contain an adhesion agent and lime

s ou no e use w s ype o n er.

B I T UM EN BOUND M ATER I A L SM I X DESI GN

113

Th M h ll i d i th d i t f 6 b i


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The Marshall mix desi n method consists of 6 basicsteps:

Aggregate selection.Asphalt binder selection.

Sample preparation (including compaction).

a y e erm na on. Density and voids calculations.


114

Aggregate Selection


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Aggregate Selection

Determine aggregate physical properties.

This consists of running various tests to determine

Toughness and abrasion

Durability and soundness

Cleanliness and deleterious materials Particle shape and surface texture

Specific gravity and absorption

Perform blending calculations to achieve them x es gn aggrega e gra a on.


115

Asphalt Binder Evaluation


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Asphalt Binder Evaluation

The Marshall test does not have a common generic

asphalt binder selection and evaluation procedure. ac spec y ng en y uses e r own me o w

modifications to determine the appropriate binderand if an modifiers.

Binder evaluation can be based on local experience,previous performance or a set procedure.

Once the binder is selected, several preliminary tests

are run to determine the asphalt binder's-


116

Sample Preparation


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Sample Preparation T e Mars a met o , e ot er m x es gn met o s,

uses several trial aggregate-asphalt binder blends

(typically 5 blends with 3 samples each for a total of 15spec mens , eac w a eren asp a n er con en .

Then, by evaluating each trial blend's performance, anoptimum asphalt binder content can be selected.

In order for this concept to work, the trial blends mustcontain a range of asphalt contents both above and belowthe optimum asphalt content.

Therefore, the first step in sample preparation is to

estimate an optimum asphalt content. Trial blend as halt contents are then determined from

this estimate.


117

O timum As halt Binder Content Estimate


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O timum As halt Binder Content Estimate

The Marshall mix design method can use any

suitable method for estimating optimum asphaltcontent and usually relies on local procedures orexperience.

amp e sp a t n er ontents Based on the results of the optimum asphalt binder

,

0.5 percent by weight of mix increments, with atleast two sam les above the estimated as halt bindercontent and two below.


118

Compaction with the Marshall Hammer


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Compaction with the Marshall Hammer

Each sample is then heated to the anticipated

compaction temperature and compacted with a Marshallammer, a ev ce a app es pressure o a samp e

through a tamper foot. Some hammers are automaticand some are hand o erated. Ke arameters of the

compactor are: Sample size = 102 mm (4-inch) diameter cylinder 64 mm (2.5

heights)

Tamper foot = Flat and circular with a diameter of 98.4 mm3.875 nc es correspon ng to an area o 76 cm2 11.8 n2 .


119 Compaction with the


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Number of blows = Typically

35, 50 or 75 on each side

traffic loading.

Simulation method = Thetam er foot strikes thesample on the top andcovers almost the entiresample top area. After aspecified number of blows,

the sample is turned overand the procedure repeated.


120

The Marshall Stability and Flow Test


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y

The Marshall stability and flow test provides the performanceprediction measure for the Marshall mix design method.

The stabilit ortion of the test measures the maximum loadsupported by the test specimen at a loading rate of 50.8mm/minute (2 inches/minute).

Basicall the load is increased until it reaches a maximumthen when the load just begins to decrease, the loading isstopped and the maximum load is recorded.

,specimen's plastic flow as a result of the loading (Figure 2).

The flow value is recorded in 0.25 mm (0.01 inch) increments.


121

Fi ure 2. Marshall stabilit testin a aratus.


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Fi ure 2. Marshall stabilit testin a aratus.


122

The Marshall Stabilit and Flow Test


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The Marshall Stabilit and Flow TestTable 1. Typical Marshall Design Criteria (from Asphalt Institute, 1979)

Mix Criteria

Light Traffic

(< 104 ESALs)

Medium Traffic

(104 - 106 ESALs)

Heavy Traffic

(> 106 ESALs)

Compaction

(number of blows35 50 75

sample)

Stability 2224 N

3336 N

6672 N

. . .

Flow (0.25

mm (0.01inch))

8 20 8 18 8 16

ercent r

Voids3 5 3 5 3 5


123

Densit and Voids Anal sis


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All mix design methods use density and voids to

determine basic HMA physical characteristics. Twodifferent measures of densities are typically taken: Bulk specific gravity(Gmb).

, mm . These densities are then used to calculate the volumetric

parameters of the HMA. Measured void expressions are usually:

Air voids (Va), sometimes expressed as voids in the total mix

(VTM) Voids in the mineral a re ate VMA

Voids filled with asphalt (VFA)


124

Generall , these values must meet local or State


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,criteria..

Table 2. Typical Marshall Minimum VMA

(from Asphalt Institute, 1979)

Nominal Maximum

Particle Size Minimum VMA (percent)

(mm) (U.S.)

63 2.5 inch 11

50 2.0 inch 11.5

37.5 1.5 inch 12

25.0 1.0 inch 13

19.0 0.75 inch 14

12.5 0.5 inch 15

9.5 0.375 inch 16

4.75 No. 4 sieve 18

. o. s eve

1.18 No. 16 sieve 23.5


125

Selection of Optimum Asphalt Binder


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Content

The optimum asphalt binder content is finally

stability and flow, density analysis and void analysis.

O timum as halt binder content can be arrived at in

the following procedure: Plot the following graphs: Asp a t n er content vs. ens ty. Dens ty w genera y

increase with increasing asphalt content, reach a maximum,then decrease. Peak density usually occurs at a higher asphalt.


126

Selection of Optimum Asphalt Binder ContentA t t t M t t T


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Asp a t n er content vs. Mars a sta ty. T s s oufollow one of two trends:

Stability increases with increasing asphalt binder content, reaches a

Stability decreases with increasing asphalt binder content and doesnot show a peak. This curve is common for some recycled HMAmixtures.

. . Asphalt binder content vs. air voids. Percent air voids should

decrease with increasing asphalt binder content.. .

decrease with increasing asphalt binder content, reach a

minimum, then increase. As halt binder content vs. VFA. Percent VFA increases with

increasing asphalt binder content.


127

Selection of Optimum Asphalt Binder Content


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Determine the asphalt binder content that correspondsto the specifications median air void content (typically

This is the optimum asphalt binder content.

Determine properties at this optimum asphalt binder

content y re err ng to t e p ots. Compare each of these values against specification values

and if all are within s ecification then the recedinoptimum asphalt binder content is satisfactory.

Otherwise, if any of these properties is outside the.


128


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Chapter - 7 Bitumen Bound Materials

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Transcript of Chapter - 7 Bitumen Bound Materials