Construction Material 2005 - Asphalt.pptmucc.mahidol.ac.th/~egpcp/Handout271/27110 - Asphalt.pdf · Bitumen Asphalt (cement) Thick black substance which is the ... Penetration and

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C O N S T R U C T I O N M A T E R I A L SASPHALT

© 2010 Praveen Chompreda, Mahidol University 2

A S P H A L T A T A G L A N C E

• Asphalt or Bitumen is a hydrocarbon product primarily obtained from the distillation of petroleum

• The major application of asphalt is in pavements• There are 3 main types of asphalt products

– Asphalt Cement (Solid)– Cutback Asphalt (Liquid)– Asphalt Emulsions (Liquid)

• Asphalt products are graded based on their consistency using various systems

• Various tests are available for safety and quality control of asphalts since their property may vary greatly among the sources

• Asphalt products are often mixed with aggregates to make layers of flexible pavements, each with different properties

• Failures of asphalt pavement often occurred due to inappropriate grade of asphalt or improper mixture proportion

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D I S A M B I G U O U S

• Please note the differences between the British English (UK, European countries) and American English (North America, Thailand) usages of some terms

British English American English Explanation of Terms

Bitumen Asphalt (cement) Thick black substance which is the residue of distillation

Bituminous ~ Asphaltic~ or Bituminous~

Adjective for all things relating to asphalt

Asphalt (Hot Mixed) Asphalt Concrete Pavement

A kind of mixture of asphalt and aggregates for use in road paving

Macadam Macadam A kind of mixture of asphalt and aggregates for use in road paving

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O U T L I N E

• Introduction– Components of Asphalt– Sources of Asphalt– Applications

• Types/ Grades/ Tests– Asphalt Cement– Cut-Back Asphalt– Emulsified Asphalt

• Asphalt Mixture– Asphalt Pavement– Asphalt Mixture Design– Manufacturing

• Deterioration of Asphalt & Prevention

Source: Wikipedia

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I N T R O D U C T I O NComponent of AsphaltSources of AsphaltDistillation of Crude OilApplications

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C O M P O N E N T S O F A S P H A L T

• Asphalt (or bitumen) is a complicated system of hydrocarbons soluble in trichloroethylene. In general, it is made up of 3 groups of hydrocarbons– Asphaltenes (C/H > 0.8) – provides the body of the asphalt– Resins (0.6 < C/H < 0.8) – contribute to adhesiveness and ductility– Oils (C/H < 0.6) – contribute to viscosity and flow

• The fractions that are not soluble in trichloroethylene are called carbenes.• They are hard at normal temperature but soften when heated. They are

mixed with aggregates and allowed to cool to form a pavement surface

0.6 0.8

CarbonHydrogen

AsphaltenesResinsOils

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S OU R C E S O F A S P H A L T

1. Native Asphalt or Natural Asphalt – they are asphalt materials found in natural states. Only few native sources in the world can produce enough asphalt to have economical importance.– Asphalt Lake – The area may be the bottom of a lake in prehistoric times.

Asphalt may be separated or mixed with water.– Tar Pit (e.g. Rancho La Brea Tar Pit in Los Angeles)– Rock Asphalt – Asphalt impregnated within sedimentary rocks (limestone,

shale, or sandstone). Usually used by crushing the rock and asphalt together.

Asphalt Lake in Trinidad Rancho La Brea Tar Pit Bituminous Sandstone

Source: Wikipedia Source: Wikipedia Source: Wikipedia

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2. Tar – it is a liquid by-product from the distillation of coal to make coke (which is used as smokeless fuel in stove or blast furnace). The use of tar (mostly in the UK) has been declined dramatically because its vapor was found to cause cancer

Coal Coke + Coal Tar


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Bituminous Coal Layer

Source: Wikipedia

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3. Refinery Asphalt or Petroleum Asphalt – from distillation of crude oil. It is the most popular type.• Asphalt based crude oil (easiest to obtain asphalt from)• Paraffin-based crude oil• Mixed-based crude oil

Source: Wikipedia

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D I S T I L L A T I O N O F C R U D E O I L

• Asphalt cement from residue of crude oil distillation

Hig

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A P P L I C A T I O N S

• Pavement/ Runway• Roof Shingles (not commonly found

in Thailand)• Waterproof Coating• Expansion Joints• Joint and Crack Sealant


Source: Wikipedia

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T Y P E S O F A S P H A L T P R O D U C T S

• There are three main types of asphalt products used in constructions

– Asphalt Cement (Penetration Grade Bitumen)• Product from distillation of petroleum• Solid

– Cutback Asphalt • Asphalt Cement + Hydrocarbon Solvent• Liquid

– Emulsified Asphalt or Asphalt Emulsions • Asphalt Cement + Emulsifier + Water• Liquid

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A S P H A L T C E M E N TAsphalt CementGrades of Asphalt CementProperties and Tests

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A S P H A L T C E M E N T

• Asphalt cement is the direct product from distillation of petroleum• It is solid at room temperature• To use it, we need to heat it until it becomes soft enough. Then we mix it

with hot aggregates, lay on the road, and compact. It becomes solid again once it is cool. We call the product “Hot Mix Asphalt Concrete (HMAC)”

Asphalt Cement

Aggregates

Mixer or Paving Machine

Heat to about 90 °C

Heat to about 150 °C

RoadSurface

Compact

Cool to ambient temperature

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A S P H A L T C E M E N T

Hot Mix Asphalt Paving Machine

Compaction of Asphalt Surface

Source: Wikipedia

Source: Wikipedia

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G R A D E S O F A S P H A L T C E M E N T

• Asphalt cement can be manufactured to have different consistency or fluidity –from hard to soft

• Why do we need different consistencies of asphalt?– Softer asphalt is suitable to colder climate to avoid excessive brittleness during

winter– Harder asphalt is suitable to hot climate as to avoid softening in summer– Asphalt that is too soft will not provide uniform film to bind all the aggregates– Asphalt that is too hard is difficult to mix and the resulting mixture will be

nonuniform

Too hard asphalt may crack Too soft asphalt may deformSource: Wikipedia Source: Wikipedia

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• A different consistency can be achieved by 2 means– Lower the temperature during the distillation to get more oils in the residue

softer asphalt– Diluting (fluxing) some lighter oils with asphalt cement (not good)

• Asphalt cement is primarily graded by its consistency using one of these systems:– Penetration (in unit of 0.1 mm) – this is the oldest and most popular grading of

asphalt cement– Absolute Viscosity (in poise)– Kinematic Viscosity (in stoke)

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• Penetration (ASTM D 5) is an measure of hardness/softness of asphalt cement by dropping a standard needle to an asphalt surface for 5 sec at temperature of 25 °C

– Higher value indicates softer asphalt– Common penetration grades are AC 40-50, AC 60-70, AC 70-80, AC 80-100,

AC 120-150 (example: AC 60-70 has the penetration between 60 and 70)– This grading has been used for a very long time– There is a trend to substitute the penetration with viscosity grading system

Penetration Distance Drop (in mm) 10

Source: http://www.soiltest.com

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• Viscosity is a more direct measurement of the fluidity of asphalt cement• Measured by counting the time it takes for a standard amount of hot asphalt (in liquid

state at standard temperature) to flow through a standard orifice• Absolute viscosity has the unit of poise (g /cm /sec)• Kinematic viscosity has the unit of stoke (cm2/sec) or centistoke (0.01 cm2/sec = 1

mm2/sec)• Absolute viscosity (ASTM D 2171) and kinematic viscosity (ASTM D 2170) differ by

the type of viscometer used but can be related (for the same test temperature).

• The density of AC is about 1 g/cm3. Therefore, absolute viscosity in poise is approximately numerically equal to kinematic viscosity in stoke

• Higher viscosity value means that the asphalt does not flow well (i.e. “harder” asphalt)

Absolute ViscosityKinematic Viscosity =

Density of Asphalt Cement

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P R O P E R T I E S & T E S T S

• Once we classify asphalt cement based on its consistency, the asphalt cement must have some other properties met the standard specifications

• Standard Specifications:– ทล. ก. 401/2531– มอก. 851-2542– ASTM D 946 Standard Specifications for Penetration-Graded Asphalt Cement

for Use in Pavement Construction

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A C S P E C I F I C A T I O N S

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• Other relevant tests for asphalt cement:

Property to be Measured Test Method

Fluidity (or consistency) Penetration Test (ASTM D 5), Viscosity Tests (ASTM D2170, 2171)

How well asphalt can bind aggregate Ductility Test (ASTM D 113)

Temperature we need to make it sufficiently soft

Softening Point Test (ASTM D 36, E 28)

Maximum temperature that we can heat it without catching fire

Flash Point Test (Cleveland Open-Cup or Pensky-Marten Closed Tester) (ASTM D 92, 93)

How much impurities there are Solubility Test (ASTM D 4, D 2042)

How much volatile constituents are presented

Loss on Heating (ASTM D 6), Thin-Film Oven Test (ASTM D 1754)

Specific Gravity and Density Specific Gravity Test (ASTM D 70)

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• In ductility test, we pull the sample of AC apart in a temperature-controlled bath and see how much it can stretch without breaking, the higher the better.

• In softening point test, we use “ring and ball” apparatus. The softening point is defined as the temperature at which the asphalt sample in the ring becomes soft enough that the asphalt stretches

to the reference plate under the weight of the metal ball

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• In the flash point test, the asphalt sample is heated. A pilot flame is passed over at regular interval. The flash point is defined as the temperature at which the vapor above the surface begin to ignite.

• In the solubility test, the asphalt sample is dissolved in Trichloroethylene (it used to be carbon disulfide) and filtered. The materials retained on the filter are the impurities.

• In the loss on heating and thin-film oven test, we put samples in the oven for several hours. The volatile oils will evaporate. We can weight the sample before and after to see how much loss there is. We can also perform Penetration and Ductility test on the residue material.

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C U T B A C K A S P H A L TCutback AsphaltGrades of Cutback AsphaltProperties and Tests

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C U T B A C K A S P H A L T

• Cutback asphalt is a liquid asphalt product. It is obtained by diluting asphalt cement in volatile oils.

• It is liquid at room temperature so it can be sprayed and mixed easily• The solvent (oils) will eventually evaporated, leaving the asphalt cement on

the road• Due to the pollution and health risk of the evaporation solvent, cutback

asphalt is no longer permitted in the USA, but it is still in use in many parts of the world, including Thailand.

Cutback Asphalt

Mixer or Sprayer

Room Temperature

Asphalt Cement on Road

Compact

Evaporation

Solvent

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G R A D E S O F C U T B A C K A S P H A L T

• Since cutback asphalt is obtained by mixing asphalt cement with solvents, it is therefore classified based on the solvent used– Rapid Curing (RC) – use gasoline as solvent + low-penetration AC– Medium Curing (MC) – use kerosene as solvent + higher-penetration AC– Slow Curing (SC) – use heavy oils as solvent + very high-penetration AC

or obtained directly from the distillation by cutting off early to get residue + heavy oils

• The choice of curing rate depends on:– The time desired for curing– The penetration grade of the finished pavement (after solvent has

evaporated); for example, MC will result in softer finished pavement compared with RC due to the higher-penetration AC used, which is good for colder climates)

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• For each type, the cutback asphalt is graded by kinematic viscosity (in centistoke = 0.01 stoke) or Saybolt-Furol viscosity (ASTM D 88) (in seconds; 1 SSF = 0.02 stoke)

• Different viscosity is obtained by changing the amount of solvent• Common grades are RC-70, RC-250, RC-800, RC-3000, MC-30, MC-70

(example: RC-70 has kinematic viscosity between 70 and 140, MC-30 has kinematic viscosity between 30 and 60 etc…)

• The choice of viscosity depends on– Application (spraying requires lower viscosity)– Aggregate used (smaller aggregates requires lower viscosity)– Cost (lower viscosity requires more solvent and cost more but it

requires less heat which saves the fuel cost)

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Saybolt – Furol Viscosity Test

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• Kinematic viscosity is in stoke or centistoke (1 centistoke = 0.01 stoke)

• Saybolt-Furol viscosity is measured in second

• 1 SFS = 0.02 stoke = 2 centistoke

Saybolt-Furol Second Grade

15-30 0

40-80 1

100-200 2

250-500 3

600-1200 4

1500-3000 5

Flow Easily

Difficult to Flow 32

C U T B A C K S P E C I F I C A T I O N S

• Standard Specifications:– ทล. ก. 402/2531– มอก. 865-2544– ASTM D 2028 Standard Specifications for Cut-Back Asphalt (Rapid Curing Type)

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C U T B A C K S P E C I F I C A T I O N S

• Standard Specifications:– ทล. ก. 403/2531– มอก. 865-2544– ASTM D 2027 Standard Specifications for Cut-Back Asphalt (Medium Curing Type)

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• Other relevant tests for Cut-Back Asphalt

Property to be Measured Test Method

Fluidity (or consistency) Viscosity Tests (ASTM D 88, 2170, 2171)

Maximum temperature that we can heat it (if needed) without catching fire

Flash Point Test (Cleveland Open-Cup or Tag Open Cup) (ASTM D 92, 1310)

Amount of water presented (impurity) Water Content Test (ASTM D 95)

Amount of asphalt cement Distillation (ASTM D 402)

Fluidity (or consistency) of residue Penetration Test (ASTM D 5), Float Test (ASTM D 139), Viscosity Tests

How well asphalt residue can bind aggregate

Ductility Test (ASTM D 113)

How much impurities there are in the residue

Solubility Test (ASTM D 4, D 2042)

How much asphalt binder is presented (for SC only)

Residue of Specified Penetration Test (ASTM D 243)

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• The distillation test is used to see how much asphalt cement there is. After the test, we can perform tests, such as penetration and ductility, on the asphalt residue as well

• The flash point test using the tag open cup is similar to the cleveland open cup.

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E M U L S I F I E D A S P H A L TEmulsified AsphaltEmulsifierGrades of Emulsified AsphaltProperties & Tests

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E M U L S I F I E D A S P H A L T

• Emulsified Asphalt or Asphalt Emulsion is a liquid asphalt product. It is a colloidal mixture obtained by mixing asphalt cement in water, with the help of the emulsifier.

• It is liquid at room temperature so it can be sprayed and mixed easily• The water will eventually evaporated, leaving the asphalt cement on the road• It is an alternative to cutback asphalt

Emulsified Asphalt

Mixer or Sprayer

Room Temperature

Asphalt Cement on Road

Compact

Evaporation

Water

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E M U L S I F I E R

• The emulsifier is a long hydrocarbon chain with ionic part at the end

• The hydrocarbon end attached to the asphalt particle

• The ionic end has an affinity for water

• The same ions repel each other, allowing the asphalt particle to suspend in water without sticking to each other

Source: Illston and Domone (2001)

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G R A D E S O F E M U L S I F I E D A S P H A L T

• Since Emulsified Asphalt is obtained by mixing the asphalt cement with water and emulsifier, they are graded by the types of emulsifier.– Anionic Emulsions – the asphalt cement particle has negative (-) charge

(good for limestone aggregate, which has positive charges)• Rapid Setting (RS)• Medium Setting (MS)• Slow Setting (SS)

– Cationic Emulsions – the asphalt cement particle has positive (+) charge (good for silica aggregate, which has negative charges)

• Rapid Setting (CRS)• Medium Setting (CMS)• Slow Setting (CSS)

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G R A D E S O F E M U L S I F I E D A S P H A L T

• For each type, the emulsified asphalt is graded by kinematic viscosity (in centistoke = 0.01 stoke) or Saybolt-Furol viscosity (ASTM D 88)

• Common grades are: CRS-1, CRS-2, CMS-2, CSS-1

Saybolt-Furol Second Grade

15-30 0

40-80 1

100-200 2

250-500 3

600-1200 4

1500-3000 5

Flow Easily

Difficult to Flow

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• Other relevant tests for Emulsified AsphaltProperty to be Measured Test Method

Fluidity (or consistency) Viscosity Tests (ASTM D 88, 2170, 2171)

Amount of water presented Water Content Test (ASTM D 244)

Amount of asphalt cement Distillation (ASTM D 6997), Residue by Evaporation (ASTM D 6394)

Fluidity (or consistency) of residue Penetration Test (ASTM D 5), Viscosity Tests

How much impurities there are in the residue Solubility Test (ASTM D 4, D 2042)

How well it can coat aggregate and withstand washing of water

Coating Ability and Water Resistance (ASTM D 244)

How well asphalt residue can bind aggregate Ductility Test (ASTM D 113)

How fast the emulsified asphalt will set Demulsibility Test (ASTM D 6936), Cement-Mixing Test (ASTM D 6935), Silica Sand Coating Test (ASTM D 244)

How well it withstand the addition of water Miscibility in Water Test (ASTM D 6999)

Stability during storage Sieve Test (ASTM D 6933), Settlement Test (ASTM D 244), Freezing Test (ASTM D 244)

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• In the water content test, the emulsified is heated in a closed container. The water will evaporate, condense in a condenser, and be collected in the trap. The water content is the percentage of the total water collected to the original weight of sample.

• In particle charge test, electrodes are inserted into the liquid asphalt. If it is a cationic emulsified asphalt (positive charge), the asphalt particles will adhere to the cathode (negative side). There will be nothing on the anode side.

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E M U L S I F I E D A S P H A L T S P E C I F I C A T I O N S• Standard Specifications:

– ทล. ก. 404/2531– มอก. 371-2530– ASTM D 977 Standard Specification for Emulsified Asphalt– ASTM D 2397 Standard Specification for Cationic Emulsified Asphalt

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S U M M A R Y O N A S P H A L T P R O D U C T SProperties & TestsAdvantages & Disadvantages

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P R O P E R T I E S & T E S T S S U M M A R Y

Asphalt Cement Cut-Back Asphalt Emulsified Asphalt

Penetration On distillate residue On distillate residue

Kinematic Viscosity

Saybolt-Furol Viscosity

Softening Point (Ring and Ball) On distillate residue On distillate residue

Flash Point

Ductility On distillate residue On distillate residue

Solubility On distillate residue On distillate residue

Loss on Heating

Thin-film Oven

Specific Gravity On distillate residue On distillate residue

Residue by Distillation

Residue by Evaporation

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P R O P E R T I E S & T E S T S S U M M A R Y

Asphalt Cement Cut-Back Asphalt Emulsified Asphalt

Float Test On distillate residue On distillate residue

Water Content Occasionally

Residue of Specified Penetration On SC only

Demulsibility

Cement-Mixing Test

Silica Sand Coating Test

Miscibility in Water Test

Sieve Test

Settlement Test

Freezing Test

Particle Charge Test

• Continued…

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U S A G E & A P P L I C A T I O N S

Advantages Disadvantages

Asphalt Cement

Strong and durable Require high heat to mixMust use with dry aggregates

Cut-Back Asphalt

Does not require high heat to use Highly flammableEvaporated fume is toxicSolvent can be expensive Must use with dry aggregates

Emulsified Asphalt

Does not require high heat to useUse with wet or dry aggregatesLess toxicNon-flammable

Can be washed off by rain quite easily

• Advantages & Disadvantages for each type of asphalt for pavement applications

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A S P H A L T M I X T U R E STypes of Asphalt PavementApplications in PavementRequired Properties of PavementAsphalt Concrete MixtureMarshall MethodManufacturing

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T Y P E S O F A S P H A L T P A V E M E N T S

• There are many types of asphalt pavement construction, ranging from low-cost, lightly traveled roads to heavily traveled highways. We first consider 2 extremes of asphalt construction, hot-mix asphalt concrete (or just “asphalt”) and macadam.

• Macadam

Source: Illston and Domone (2001) 50


• Hot Mix Asphalt Concrete


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• Asphalt concrete uses more asphalt and gap-graded aggregates. It is denser and more durable, but also more expensive because more asphalt is needed. It is typically used for heavily-traveled roads.

• Macadam uses asphalt just enough to coat aggregates and provide adhesion. Dense-graded aggregate is needed for strength. It is porous and not very durable, but cheaper because it needs only little asphalt. It is generally used for lightly traveled roads.

• Actually, there are ranges of asphalt pavement that are somewhere between asphalt concrete and macadam

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A P P L I C A T I O N S I N P A V E M E N T S

Subgrade

Wearing Course

Basecourse

Roadbase

Sub-Base

Capping

Typical Pavements

Foundation

Surfacing

Asphalt Materials

Soil

Granular Materials

• In typical asphalt pavement, the road structure has several layers, each having a specific function. Different asphalt products and different mixtures are used for different layers.

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A P P L I C A T I O N S I N P A V E M E N T S

• Asphalt Cement (Hot-Mixed or Hot-Rolled Asphalt)– Wearing surface of new road

construction– Resurfacing or overlaying of

existing road– Surface Dressing – hot asphalt is

sprayed over compacted base, followed by a layer of graded crush stone, and then rolled together. Another layer may be put on top.

– Patching of surface damages

• Liquid Asphalt (Cutback or Emulsified)– Patching of minor surface

damages– Surface Dressing – Tack Coat - to provide adhesion

between old and new layers– Prime Coat to prepare (base)

surface for new asphalt layer– Slurry Seal– Soil Stabilization

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A S P H A L T C O N C R E T E M I X T U R E

• Generally, hot-mix asphalt concrete mixture consists of asphalt cement (AC 60/70 or AC 80/100 are most common), fine aggregate (sand), and coarse aggregate (crushed limestone)

• The quality and proportion of each of these components plays an important role in the property and durability of the finished asphalt pavement

Source: Wikipedia56

P R O P E R T I E S O F P A V E M E N T S

Required properties of the pavement are:

• Stability – is the strength of the pavement to resist deformation under traffic load. It comes from aggregate interlocking and asphalt cohesions

• Durability – is the resistance of the pavement against disintegration either by weathering of asphalt or mechanical breakdown of aggregate.

• Flexibility – is the ability to withstand deformations without cracking• Skid Resistance – is the ability of the pavement to provide long-lasting

nonskid surface. Pavement bleeding and aggregate polishing is the two main sources of slippery surface

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A S P H A L T C O N C R E T E M I X T U R E

• Compromise is needed for the property of asphalt, aggregate, and the amount of air voids in the asphalt mixture

Property Asphalt Aggregate Air Void

Stability Just enough to coat the aggregate

Angular shapesRough textureDense graded

Durability Need a lot of asphalt to coat the aggregate and completely fill out the voids

Need minimal air void to prevent oxidation and entrance of water

Flexibility Open graded

Skid Resistance Just enough to coat the aggregate

Aggregate containing many minerals in it

Need some void space to prevent bleeding

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M I X T U R E P R O P O R T I O N I N G

• Factors affecting asphalt concrete pavement are:– Quality of Asphalt Binder– Quality of Aggregates (gradation, strength, texture, shapes, etc…)– Construction Processes– Mixture Proportions

• We want to know the optimum content of asphalt for a given type and gradation of aggregate, and the asphalt cement used to provide the best stability, durability, flexibility, and skid resistance

• There are several methods developed. Some of the more popular mix-design methods are:– Hubbard-Field (Asphalt Institute)– Marshall (U.S. Army Corps of Engineer)– Stabilometer or Hveem (California Highway Department)

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M A R S H A L L M E T H O D

• Using 4” diameter and 2.5” high cylindrical specimen. Specimens are compacted using a standard hammer

• Stability (i.e. maximum load) and flow (i.e. deformation) is measured using Marshall apparatus

Mold

Hammer



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Breaking HeadMarshall Stability Testing Machine



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• Stability is the maximum load, which indicates the strength of the asphalt mix

• Flow is the deformation at the maximum load, which indicates the flexibility of the asphalt mix

• Durability of the asphalt mix is measured through the determination of air voids in the specimenSource: Illston and Domone (2001)

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Typical procedures for Marshall method:1. Select aggregate proportions to meet specific requirements2. Estimate optimum asphalt content for a given aggregate type3. Prepare few asphalt concrete specimens with asphalt content above

and below the estimated optimum content according to the mix design method used

4. Test the specimens for physical properties such as specific gravity, air voids, stability, etc…

5. Plot the above properties with asphalt content and use a guideline to determine the range of acceptable asphalt content

6. Optimum asphalt content can be selected from that range - usually it is the content that gives highest stability value or the most economical one

7. The process may be repeated with different aggregate blends

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• We try several mixtures with different amount of asphalt and test the sample for– Density of Mix (or unit

weight)– Compacted Aggregate

Density (may be plotted as Voids in Mineral Aggregate)

– Marshall Stability– Flow

Source: Illston and Domone (2001) 64


• The following observations can be made:– Mix Density initially increases with asphalt content because asphalt fill

out the air voids and lubricates the aggregate movement (allow for denser compaction). However, too much asphalt replaces the heavier aggregates.

– Stability follows the same trend as density since it is mainly a function of aggregate interlock and, hence, the density

– Compacted aggregate density (i.e. how much aggregate can be packed in the volume) follows approximately the density curve because volume of aggregate is the main volume of the mix

– Flow increases with an increase in asphalt content because friction between aggregate particles decreases with thicker asphalt films

• It can be seen that the optimum asphalt content for density and stability are NOT the same so we generally average them to get the design asphalt content. We read the flow from the flow curve.

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Too little asphalt: have a lot of unfilled voids

Too much asphalt: lighter asphalt replaces the heavier aggregate, leading to lower density

Asphalt completely fills the voids

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Too little asphalt: mix is dry and difficult to

compact Too much asphalt: asphalt replaces the aggregate, leading to lower compacted aggregate density

Optimum asphalt content to lubricate the mix and make it easy to compact

67



Too little asphalt: not enough adhesions

between aggregateToo much asphalt reduces friction between aggregates

Optimum asphalt: enough asphalt to coat aggregate

Flow increases as asphalt content increases

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M A N U F A C T U R I N G

• Asphalt is typically manufactured (i.e. hot mixed) at a plant and transport by truck to the construction site

• The plant should be close to the construction site to avoid the hardening of asphalt during transit

• Two main types of asphalt manufacturing plants:– Batch Plant– Continuous Plant

Source: Wikipedia70

M A N U F A C T U R I N G / B A T C H P L A N T

– Batch Plant – produce one mix at a time

Aggregates are weighted and mixed according to the gradation needed

Aggregates are heated to remove moisture

Hot asphalt is mixed with hot aggregate and fillers in a mixer

The mixture is loaded in a truck to be used or stored in a silo

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– Continuous Plant – produce asphalt mixture continuously

Graded aggregates are continuously loaded into a drum.

The hot asphalt is mixed with the heated aggregate in the final portion of the drum

At the end of the drum, the mixture is loaded in a truck to be transported or stored in a silo

The first portion is the drying of aggregates.


• The choice of mixing process depends on:– Production Capacity (Continuous plant is good for large production of

one material specification whereas Batch plant is good for small productions of different mix proportions)

– Maintenance Cost (Continuous plant has lower maintenance cost)

– Cost of Construction (Continuous plant has lower construction cost)

– Environmental Issues (dusts, fumes, noise, etc…)

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D E T E R I O R A T I O N O F A S P H A L TDesign Life of Pavement Failure ModesDeterioration of SurfaceDeterioration of StructurePreventionsRemedies

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D E S I G N L I F E O F P A V E M E N T

• Asphalt pavement has a design life of 40 years (concrete structures have about 75 years). This is the life after which we need to replace the whole thing.

• However, we need to do some maintenances periodically to get that design life.


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F A I L U R E S O F A S P H A L T P A V E M E N T

• The failure of asphalt pavement is a little tricky to define because when the pavement “fails” it does not collapse

• So we define failure in terms of serviceablity (ability to service) or repairability (ability to repair vs. rebuilt)

• Examples of criteria – Riding Comfort (surface too rough, uneven surface, excessive noise) – Safety of Drivers on the road (slippery road, potholes)– Crack widths– Permanent deformations

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M O D E S O F F A I L U R E S

• The asphalt may fail in one of the two main forms• Deterioration of Road Surface – the damages occur at the top of the

wearing course (top layer) of the pavement– Bleeding of asphalt– Breakdown of surface materials– Polishing of surface– Fuel spillage

• Deterioration of Road Structure – the damages occurs on the pavement as a whole– Permanent Deformation– Fatigue Cracking

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D E T E R I O R A T I O N O F S U R F A C E

• Bleeding of asphalt to the surface (and sinking of aggregates to the bottom). This occurs under traffic pressure due to too little air voids. This leads to reduced skid-resistance of the road surface.

• Aggregate breakdown – weak aggregate may break into pieces under traffic and separated from asphalt

• Aggregate polishing – soft aggregate may become polished under traffic, resulting in slippery road surface

Aggregate polishing

Surface Bleeding

Source: www.asphaltwa.com


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• Aging of Asphalt – this is the hardening of asphalt (decrease in penetration or increase in viscosity) when exposed to the atmosphere. The asphalt becomes more brittle and cracks more easily.– Oxidation of asphalt in which resins was

converted into asphaltenes. Because the resin provides ductility and adhesiveness, loosing it results in a harder material. The pavement also turns grey

– Loss of volatile constituents – lighter oils evaporated, leaving only the heavy oils on the road. In asphalt cement, this is often caused by too much heat during mixing.

• Fuel spillage – oil spills from vehicles may dilute asphalt cement

Fuel Spillage

Oxidation Damage



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• Low Temperature Crack – this occurs in cold climates when the asphalt is too hard. When the asphalt shrinks under low temperature, it cannot deform enough, so it cracks.

Crack from low temperature and binder hardening


80

D E T E R I O R A T I O N O F S T R U C T U R E

• Structure failures consists of two main types– Permanent Deformation– Fatigue Failure


81

D E T E R I O R A T I O N O F S T R U C T U R E

Deformation due to foundation settlement

Deformation due to high stress

• Permanent Deformations – it is the deformation of the whole pavement structure (affect several layers, not just the surface). Possible causes are:– Foundation settlement due to

insufficient compaction or water scour

– Rutting under High Stress + High temperature – this occurs under heavy traffic on hot days when too soft asphalt is used. The asphalt deforms permanently in the form of wheel track. Once it is occurred, vehicles tends to lock into the wheel track, accelerating the process.



82

D E T E R I O R A T I O N O F S T R U C T U R E S

• Fatigue Failures – this occurs under repetitive stresses from traffic. – Cracking usually starts at the base

of top layer– By the time it reaches the surface,

a lot of damage has occurred– Characterized by “alligator skin”

cracking pattern– Occurs from the use of asphalt

that is too hard

Fatigue cracking


83

P R E V E N T I O N S

• To prevent or delay the failure, the followings must be done:– Use of strong and durable aggregates– Use asphalt binder with grade suitable for the geographical area to

prevent cracking– Control maximum temperature during mixing to prevent excessive

evaporation of lighter constituents, which may result in premature hardening

– Control maximum air voids in the mix to prevent water permeation and oxidation

– Control minimum air voids to prevent bleeding and slippery surface– Control the amount of asphalt in the mix (not too low and not too

high)

84

R E M E D I E S

• When the pavement has deteriorated, we need to do some maintenances. The maintenance of roads may fall into one of these categories:

• Patching– It is the repairs of potholes and minor damages

• Surface Treatments– It is the application of liquid asphalt onto small sized stone on the

existing surface– To improve skid resistance or prevent further deterioration of the

existing pavement – We do this when the structure of the pavement is still OK– Also known as Surface Dressing, Chip Seal, Slurry Seal, etc…

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R E M E D I E S

• Pavement Resurfacing / Overlay– This involves the laying of the new surface layer (usually hot rolled

asphalt) either after removal of the existing surface or on top (overlay)– May be laid on top of existing asphalt surface or concrete surface– Restore ride quality, skid resistance, and road profile – To prevent further deterioration of the existing pavement– Also increase the strength of the pavement due to increase thickness– Usually the most cost-effective method

• Reconstruction – This involves the removal of the construction depth and construct a

newly designed pavement– Only used at the end of service-life or when overlay is not possible

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M O D I F I E D A S P H A L T

• In recent years, modified asphalt material has becoming more popular. Additives are added to the asphalt binder for the purpose of:– Improve durability (reduce oxidation)– Increase stability/ stiffness / fatigue resistance– Improve aggregate adhesion– Improve workability/ viscosity/ ductility– Improve elasticity/ reduce permanent deformation– Reduce bleeding– Reduce fuel and oil damage

• Dosage varies from less than 1% of the total mix to more than 20%, depending on the additive

• Examples: tar, gilsonite, carbon black, sulfur, ethylene vinyl acetate, polyethylene, polypropylene, natural rubber, styrene-butadiene rubber-synthetic latex, styrene-butadiene-styrene, manganese catalyst, epoxy-resin, etc…

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R E C A P

• Introduction– Components of Asphalt– Sources of Asphalt

• Natural, Tar, Petroleum

– Applications– Types

• Asphalt Cement • Cutback Asphalt • Emulsified Asphalt

• Grading of Asphalt– Penetration– Kinematic, Absolute, and Saybolt-

Furol Viscosity– Curing Rate (Cutback), Setting

Rate (Emulsified)

• Properties & Tests– Ductility, Solubility, Softening Point,

Flash Point, Loss on Heating, Distillation, Solubility, Miscibility, etc…

• Asphalt Mixture– Properties Required– Design Methods

• Marshall Design Method– Applications

• Deterioration of Asphalt & Prevention– Causes of Failure– Prevention– Remedies

• Modified Asphalt Products

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R E F E R E N C E S

• ASTM (1996), Annual Book of ASTM Standards, West Conshohocken, PA.• Atkinson, K. (1990), Highway Maintenance Handbook, Thomas Telford, London,

460 pp.• Hunter, R. N. (2000), Asphalt in Road Construction, Thomas Telford, London, 563

pp.• Illston, J. M., and Domone, P. L. J. (2001), Construction Materials Their Nature and

Behavior, 3rd Edition, Spon Press, London.• Krebs, R. D. and Walker, R. D. (1971), Highway Materials, McGraw Hill, New York• http://www.asphaltwa.com• http://www.doh.go.th

Documents

Construction Material 2005 - Asphalt.pptmucc.mahidol.ac.th/~egpcp/Handout271/27110 - Asphalt.pdf · Bitumen Asphalt (cement) Thick black substance which is the ... Penetration and