BFC31802 Handout Chapter2a

8/17/2019 BFC31802 Handout Chapter2a

1/26BDD/HANDOUT/2A

Wearing course

Binder course

Base

Sub-base

Sub-grade

A typical flexible pavement structure:


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In road construction, one or more layers of material are placed immediately abovethe subgrade.

The unbound pavement course ensures that the courses above are adequatelysupported so that their full potential is achieved.

Unbound pavement courses are extraordinarily strong when properly compactedand confined.

The unbound pavement courses are the:

• BASE COURSE• SUB-BASE COURSE

Granular Materials

The base course lies immediately above the sub-base.

If a sub-base course is not used, the base is placed immediately above the sub-

grade.

This course usually consists of granular materials such as crushed stone, crushed

or uncrushed slag, crush or uncrushed gravel and sand.

The specifications for base course materials usually include stricter requirementsthan those for sub-base materials, particularly with respect to their plasticity,gradation and strength.

BASE COURSE


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Materials that do not have the required properties can be used as base materials ifthey are properly stabilised with Portland cement, asphalt or lime.

In some cases, high-quality base course materials may also be treated with asphaltor Portland cement to improve the stiffness characteristics of heavy-dutypavements.

The base course helps to distribute the load.

While distributing the load, the base course itself must not be a cause of failure.

Therefore, it must be strong enough to carry the load without shear failure andresultant rutting.

In order to ensure that its strength is maintained, the base course must allow waterdrainages to the sides of the pavement structure.

If the base becomes saturated, high stresses may be created in the wateroccupying the pore spaces, resulting in less frictional strength between particles.

The materials must be durable, that is, resistant to degradation or breakdown tosmaller sizes from wear and weathering.

The base course must also prevent infiltration of sub-grade material.


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The base material shall be:

crushed rock or crushed gravel, or a mixture of crushed andnatural aggregates,

which are:

hard, durable, clean and essentially free from clay and other

deleterious materials.

The material shall conform with the following physical and mechanical qualityrequirements:

The plasticity indexshall be not more than

6.

The aggregate crushingvalue shall be not more

than 30.

The flakiness indexshall be not more than

30.

Not less than 80% ofparticles retained on theB.S 4.75 mm sieve shall

have at least onefractured face.

The weighted averageloss of weight in thesodium sulphate

soundness test (5cycles) shall be not

more than 12%.

The material shall havea CBR value of not lessthan 80 when

compacted to 95% ofthe maximum dry

density.

The gradation shallcomply with the

envelope shown inTable 2-1 for type

specified.


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Table 2-1: Gradation Limit for Crushed Aggregate Road-Base

B.S Sieve% Passing by Weight

Type I Type II

50.0 mm37.5 mm28.0 mm20.0 mm10.0 mm5.00 mm2.36 mm2.00 mm600 µm425 µm75 µm

10095 – 100

-60 – 8040 – 6025 – 4015 – 30

-8 – 22

-0 – 8

10085 – 10070 – 10060 – 9040 – 6530 – 55

-20 – 40

-10 – 252 – 10

TESTING

The materials used to construct this layer are consists of the mixing ofcrushed aggregates with the size from 50 mm to dust.

All road base materials shall fulfill the testing listed below:

CaliforniaBearing

Ratio (CBR)

PlasticityIndex (PI)

AggregateImpact

Value (AIV)

FlakinessIndex (FI)

Soundness Sieve


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Located immediately above the sub-grade, the sub-base component consists ofmaterial of a superior quality to which is generally used for sub-grade construction.

The sub-base must drain readily.

Strength is not as important, however, since the course is lower in the pavementstructure and therefore is subjected to much smaller loads.

The requirements for sub-base materials are usually given in terms of thegradation, plastic characteristics and strength.

SUB-BASE COURSE

The functions of sub-base are:

To support the base layer and distribute load from vehicles.

As a drainage layer (if the materials used are capable ofdraining the water)

Used as a temporary road during the construction

To protect the sub-grade from failure due to climatic effect

As a barrier layer to avoid the mixing of sub-grade andbase materials


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TESTING

When the quality of the sub-grade material meets the requirements of thesub-base material, the sub-base component may be omitted.

In cases where suitable sub-base material is not readily available, theavailable material can be treated with other materials to achieve thenecessary properties.

The most suitable sub-base materials should meet these requirements:

The liquid limit shallbe not more than

25%.

The plasticity indexshall be not more

than 6%.

The aggregatecrushing value shall

be not more than35%.

The material shall havea CBR value of 30 or

more when compactedto 95% of the maximum

dry density.

The gradation shall conform to one of theenvelopes shown in Table 2-2 with the

fraction passing the B.S. 75 µm sieve notgreater than 2/3 of the fraction passing the

B.S. 425 µm sieve.

For lateritesand –

CBR value> 20 %

Crushed aggregates – with the size

ranging from 75 mmto dust and the CBR

value > 30%

Sub-base material should fulfill the test ofCBR, Liquid Limits, Plastic Limits,Aggregate Impact Value (AIV), Los

Angeles Abrasion (LAA) and Sieving


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Table 2-2: Gradation Limits for Sub-base Material

B.S.Sieve Size (mm)% Passing By Weight

A B C D E F

50.025.09.54.752.0425 µm75 µm

100-

30 - 6525 – 5515 – 408 – 202 – 8

10079 – 9540 – 7530 – 6020 – 4515 – 305 – 20

-100

50 – 8535 – 6525 – 5015 – 305 – 20

-100

60 – 10050 – 8540 – 7025 – 455 - 20

-100

-55 – 10040 – 10020 – 506 – 20

-100

-70 – 10055 – 10030 – 708 – 25

The sub-grade is the part of embankment ornatural soil under the sub-base.

This layer is the first phase of the roadconstruction. The surface of sub-grade is

identified as a formation level.

The formation level is the soil surface after the earthwork, consolidation,compaction and stabilisation works are completed.

The primary function of the sub-grade is to support load from the surfaces above.

SUB-GRADE

Soil


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The selection of suitable soils to be used as the foundation for the highwaypavement surface is of primary importance in the design and construction of anyhighway.

A good sub-grade should have these properties:

Should bestable under

vehicle loadingand climatic

conditions.

The strengthshould remainthroughout the

design period.

Should have theability to drain

water.

There are some soils which are identified as unsuitable materials for the sub-grade and road embankment.

These materials are not capable to sustain load from the above layer and traffic.

Unsuitable soils include:

• Soils which consists of organic clays or silts.

• The value of Liquid Limits (LL) > 80 % or Plasticity Index (PI) > 55 %• The value of Loss On Ignition (LOI) > 2.5 %

• Soils consist of roots, grass or other plants, toxic, peat or mud.


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Material for the top 300 mm of sub-grade shall have a minimum California BearingRatio (CBR) as required in the specification when compacted to 95% of themaximum dry density determined in the B.S 1377 Compaction Test.

Throughout the top 300 mm of sub-grade, the material shall be compacted to not

less than 95% (for cohesive material) or 100% (for cohesionless material) of themaximum dry density.

In cut area, the top 300 mm of the sub-grade shall be scarified and re-compactedto 95% (for cohesive material) or 100% (for cohesionless material) of the maximum

dry density.

However, for the sub-grade in its natural state possesses a density exceeding therequirements, then the surface of the sub-grade shall be trimmed and rolled toobtain smooth finish.

Where the material in cut area is found to be unsuitable for use in the top 300 mm

of sub-grade, it shall be removed and replaced with suitable material which shall becompacted as indicated above.


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TESTING

The factors which influence to the strength of the sub-grade are listed as follows:

Types of soils – The most suitable soil are granular soil and the most unsuitable

material for the sub-grade is the peat soils.

Water content – the suitable moisture content of soil is determined through thelaboratory compaction test.

The method and compaction effort – the strength of soil also depends on thesefactors and at site the type of machinery used for the compaction and thenumber of repetition of compaction also been considered.

Therefore, testing need to be conducted to the soil to determine the suitability ofsoils as a sub-grade.

The tests which are usually conducted to the soils for sub-grade and roadembankment are listed as follows:

• Loss On Ignition (LOI) – BS 1377: Part 3: 1990• Liquid Limit (LL) and Plastic Limit (PL) – BS 1377: Part 2: 1990• Compaction – BS 1377: Test 13: 1975 (Part 4: 1990)• California Bearing Ratio (CBR) – BS 1377: Test 16: 1975 (Part 4: 1990)


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In Malaysia, the term of asphalt refers to the bindermaterial, which is produced from crude oil.

The mixture of asphalt and aggregates is calledasphaltic concrete (AC).

The chemicalcomposition ofasphalt:

Minerals Percentage Content (%)

Carbon 80 – 85

Hydrogen 10

Sulfur 1 – 5

Nitrogen 1

Oxygen < 1

Asphalt (Bitumen)

Asphalt can be obtained from two main sources:

Natural sources – asphalt which is located in geological stratum and can beobtained in the hard and soft form.

Petroleum – asphalt in colloidal form obtained from crude oil (widely used in roadconstruction).

Asphalt can be classified into four types as listed as follows:

Penetrationasphalt

Cutbackasphalt

Emulsifiedasphalt

Blown asphalt


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Penetration Asphalt

The grade of penetration asphalt classified according to the

• penetration test : 40 – 300• viscosity test: 5 – 40

Cutback Asphalt

Cutback asphalt is produced based on the asphalt with the percentage rangingfrom 50 – 80 % mixed with the petroleum-based solvents. When it is mixed with

aggregate, the petroleum will evaporate and it allows for the asphalt to bind withthe aggregate.

Cutback asphalt can be classified into three types according to the rate ofevaporation:

Produced bymixing asphaltwith petrol.

Used for tackcoat andsurfacetreatment.

RapidCuring(RC)

Produced bymixing asphaltwith kerosene.

Used forprime coatand cold mixfor patchingwork.

MediumCuring(MC) Produced by

mixingasphalt withdiesel.

Used forprime coatand cold mixfor patchingwork and dustcontrol.

SlowCuring(SC)


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Emulsified asphalt

Emulsified asphalt is produced by mixing the asphalt (55 – 65%) with waterand an emulsifier in a colloidal rotor.

This will reduce the viscosity of asphalt and allow them to be used at the lowtemperatures.

The type of asphalt depends on the emulsifying agent used.

The two types of emulsified asphalt are:1) Anionic

2) Cationic

AnionicContains the negative asphalt globule.This asphalt is produced when a positive emulsifying agent is used – alkali.It is suitable to be used with the aggregates that have positive charges likelimestone.

CationicContains the positive asphalt globule.

This asphalt is produced when a negative emulsifying agent is used – acid.It is suitable to be used with the aggregates that have negative charges like

sand, quartz and silica.


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Emulsified asphalt can be classified into three categories based on setting time:

Used forsurfacetreatment andtack coat.

RapidSetting

(RS)

Used forMacadampenetrationand opengraded cold

mix.

MediumSetting

(MS)

Used for tackcoat, densegrade coldmix, crackpatching and

slurry mixture

SlowSetting

(SS)

Emulsified asphalt is most widely used compared to cutback asphalt due toseveral factors:

Environmental regulation – emulsified asphalt contains water while cutbackasphalt contains materials which can evaporate and pollute the air when it has

been used.

The wastage of petroleum – cutback asphalt uses petroleum solvents.

Safety – emulsified asphalt is safer to be used.

Low temperature of mixing – this reduces the cost of fuel consumption.Besides that, emulsified asphalt can be used on damp surfaces while cutbackasphalt needs dry condition.


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Blown asphalt

Produced by heating the asphalt at high temperature. Air is allowed through theasphalt, making the asphalt harder.

Used for building materials especially for roofs.

TESTING

In order to ensure the asphalt fulfills the specification, a series of tests isconducted as follows:

PenetrationSoftening

PointDuctility

Flash andFire Point

Viscosity

Loss onHeating

Thin FilmOven Test

SpecificGravity

Solubility


17/26BDD/HANDOUT/2A

The bituminous pavement layer is constructed ofasphaltic concrete, which is the mix of aggregatesand binder (asphalt).

The surface layer consists of two layers known as the binder course and the

wearing course. The surface layer should be able to:

Asphaltic Concrete

Withstand hightyre pressure

Resist theabrasive forcedue to traffic

Provide a skid-resistant drivingsurface

Prevent theinfiltration ofsurface water

The quality depends on the mix design of the asphalt concrete used.

The materials used to construct this layer are aggregates, asphalt and filler.

Aggregates Asphalt FillerAsphalt

Concrete


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Aggregates – provide interlocking structure, and supports and distributes loadto the layer beneath.

Asphalt – the binder material that binds the aggregates to produce a strongand stable mixture.

Filler – fills the voids in the mix, improves the elasticity of the asphalt toproduce a durable mix, and reduces bleeding of the bituminous mixture.

Binder Course

This layer is used to distribute load to theroad base and provide a flat surface forthe construction of the wearing course.

The maximum size of aggregates usedis 28 mm.

The asphalt content of the mix generally

ranges between 4 and 6 %.

BinderWearing


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Wearing Course

The top layer that functions to:

The maximum size of aggregate is 20 mm and mixed with asphalt with thepercentage ranging from 4.5 – 7 %.

Provide skidresistance

Protect the roadsurface

Provide a safe andcomfortable riding

surface

Sustain abrasionfrom traffic

Act as a drainage system byproviding a waterproof layer, andeliminating surface run-off to the

side drain.

Aggregates

Most of the aggregates used in road construction are natural aggregates.

Aggregates can be classified into three groups according to the size as follows:

Coarse aggregates – retained on the sieve 2.36 mm.

Fine aggregates – passing sieve 2.36 mm and retained at 75 µm sieve size.

Filler – the dust passing sieve size 75 µm (eg. quarry dust and Portland cement).


20/26BDD/HANDOUT/2A 2

Coarse aggregates shall be screened crushed hard rock, angular in shape andfree from dust, clay, vegetative and other organic matter and other deleterioussubstances.

In order to ensure the properties of aggregate fulfill the requirement of bituminous

mixture, they need to satisfy the following requirements:

The aggregatedcrushing value shall

be not more than 30.

The weighted average loss ofweight in the sodium sulphatessoundness test (5 cycles) shall

be not more than 12%.

The flakiness indexshall be not more than

30

The water absorptionshall be not more than

2%.

The polished stone value shallbe not less than 40 (only

applicable to aggregates forwearing course)

Fine aggregates shall be clean natural sands, screened quarry fines or miningsand. Mining sand shall be thoroughly washed before use.

They shall be non-plastic and free from clay, loam, aggregations of material,vegetative and other organic matter and other deleterious substances.

They shall conform to the following requirements:

Notwithstanding compliance with the requirements, limestone aggregates shallnot be permitted for use in wearing course.

The weighted average loss of weight in thesodium sulphate soundness test (5 cycles) shall

be not more than 12%.

The water absorption shall be not

more than 2%.



The gradation of the combined course and fine aggregates, together with ordinaryPortland cement added as an adhesion and anti-stripping agent and if necessaryany other mineral filler shall conform to the appropriate envelope shown below:

Mix Type Wearing Course Binder Course

Mix Designation ACW 14 ACB 14 ACB 28

B.S. Sieve Size % Passing By Weight

37.5 mm

28.0 mm20.0 mm14.0 mm10.0 mm

5.0 mm

3.35 mm1.18 mm425 µm150 µm

75µm

-

-100

80 – 9568 – 90

52 – 72

45 – 6230 – 4517 – 307 – 16

4 – 10

-

-100

70 – 9556 – 81

40 – 65

32 – 5820 – 4212 – 286 – 16

4 – 8

100

80 – 10072 – 9358 – 8250 – 75

36 – 58

30 – 5218 – 3811 – 255 – 14

3 – 8

Aggregate Selection

• determine physical properties

• perform blending calculationsto achieve aggregate gradation

Binder Selection

• determine appropriate binder

Sample Preparation

• 5 blends with 3 samples each

• mixing and compaction

Stability Determination

• Marshall stability and flow test

Density & Voids Calculation

• Bulk density, Theoretical Max. SG

• VTM, VFB & VMA

Optimum Binder Content Selection

• based on the combined results of Marshallstability and flow, density analysis and voidsanalysis

• OBC is determined through graphical method

Marshall Mix Design



The most used method for the mixture design is the Marshall Method (ASTM D

1559).

The objective of the Marshall design is to determine the mixing ratio ofaggregates and optimum asphalt content to produce durable, stable andadequate of voids, workable, flexible, economy and quality.

The most common method used to determine the optimum asphalt content isthe method proposed by the Asphalt Institute. The procedure of this method isgiven as follows:

1. Determine

- asphalt content for the maximum stability- asphalt content for the maximum density- asphalt content at the median of the specification of VTM- asphalt content at the median of the specification of VFB

2. Calculate the mean value from these 4 values.

3. Based on this mean value, determine the following values from theMarshall property curves:

Stability (S)Flow (F)Stiffness (S/F)Void in Total Mix (VTM)Void Filled with asphalt (VFB)

4. Compare the values obtained from (3) with the specification values. If itfulfills the specification, the asphalt can be considered as the optimum asphaltcontent. If it does not fulfill the requirement, the mixture needs to beredesigned.



Table 2-6: Test and Analysis Parameters for Asphaltic Concrete

Parameter Wearing Course Binder Course

Stability

Flow

Stiffness

Air voids in mix (VTM)

Voids in aggregates filled with asphalt(VFB)

>500kg

>2.0mm

>250kg

3.0%-5.0%

75-85%

>450kg

>2.0mm

>225kg

3.0%-7.0%

65-80%



Conventional asphalt content ranges used for mix design

Wearing Course ACW 14 5.0 – 7.0%

ACW 20 4.5 – 6.5%

Binder Course ACB 14 4.5 – 6.5%

ACB 20 4.0 – 6.0%

ACB 28 4.0 – 6.0%

EXAMPLE OF MARSHALL MIX DESIGN (for Binder Course)

% AC Density Stability Flow Stiffness VTM VFB

4.0 2.259 1339.2 2.62 511.8 6.49 57.96

4.5 2.270 1469.3 2.79 526.0 5.33 65.50

5.0 2.289 1551.0 3.19 486.2 3.86 74.59

5.5 2.272 1321.3 3.25 407.0 3.89 76.06

6.0 2.260 1196.7 3.70 323.1 3.70 78.40

2.00

2.20

2.40

2.60

2.80

3.00

3.20

3.40

3.60

3.80

3.5 4.0 4.5 5.0 5.5 6.0 6. 5

%AC

F l o w

200.0

250.0

300.0

350.0

400.0

450.0

500.0

550.0

3.5 4.0 4.5 5.0 5.5 6.0 6.5

%AC

S t i f f n e s s



2.255

2.260

2.265

2.270

2.275

2.280

2.285

2.290

2.295

3.5 4.0 4.5 5.0 5.5 6.0 6. 5

%AC

D e n s i t y

1000.0

1100.0

1200.0

1300.0

1400.0

1500.0

1600.0

3.5 4.0 4.5 5.0 5.5 6.0 6.5

%AC

S t a b i l i t y

3.00

3.50

4.00

4.50

5.00

5.50

6.00

6.50

7.00

3.5 4.0 4.5 5.0 5.5 6.0 6. 5

%AC

V T M

50.00

55.00

60.00

65.00

70.00

75.00

80.00

3.5 4.0 4.5 5.0 5.5 6.0 6.5

%AC

V F A

Average = (5.02 + 4.85 + 4.55 + 4.98) / 4 = 4.85 %

1000.0

1100.0

1200.0

1300.0

1400.0

1500.0

1600.0

3.5 4.0 4.5 5.0 5.5 6.0 6.5

%AC

S t a b i l i t y

2.00

2.20

2.40

2.60

2.80

3.00

3.20

3.40

3.60

3.80

3.5 4.0 4.5 5.0 5.5 6.0 6.5

%AC

F l o w

200.0

250.0

300.0

350.0

400.0

450.0

500.0

550.0

3.5 4.0 4.5 5.0 5.5 6.0 6.5

%AC

S t i f f n e s s

3.00

3.50

4.00

4.50

5.00

5.50

6.00

6.50

7.00

3.5 4.0 4.5 5.0 5.5 6.0 6.5

%AC

V T M


26/26

50.00

55.00

60.00

65.00

70.00

75.00

80.00

3.5 4.0 4.5 5.0 5.5 6. 0 6.5

%AC

V F A

Parameter Results Specification

(Binder course, JKR 1988)

Remarks

StabilityFlow

Stiffness

VTMVFB

1530 kg3.04 mm

495 kg/mm

4.42 %71.1%

> 450 kg> 2.0 mm

> 225 kg/mm

3.0 – 7.0%65 – 80%

OKOK

OK

OKOK

Optimum Binder Content, OBC = 4.85%

BFC31802 Handout Chapter2a

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