IV Asphalt

CE 40/L Construction Materials and Testing Chapter IV - ASPHALT TECHNOLOGY

Chapter IV

ASPHALT TECHNOLOGY

4.1. Bituminous Material

Asphalt - is defined by the American Society for Testing Materials (ASTM) as a dark brown to black cementitious materials, solid or semi-solid in consistency in which the predominating constituents are bituminous which occur in nature as such or are obtained as residue in refining petroleum.

- derived from the Acadian term "Asphaltu" or "Sphallo"- earliest recorded use of asphalt by the human race was by the pre-Babylonian

inhabitants of Southeastern Mesopotamia, about 3800 BC.

Bitumen - is a term applied to native substances; petroleum, native asphalt, mineral, waxes, and asphaltites of variable colors, hardness and volatility

- in this note, the term bitumen is applied to that portion of an asphalt soluble in carbon disulfide

The success or failure of bituminous paving materials is more dependent upon the chemical characteristics of the actual bituminous portion of the asphalt than upon any other single factor.

Particular attention must be paid to the properties of the asphalt employed, for upon this depend the performance behavior of the finished pavement.

Two constituents of asphalt:1. asphaltene

- the dispersed phase of asphalt- is the substance which remains insoluble and precipitates or coagulates when

an asphalt is dissolved by a specific solvent (naphtha, ethyl ether, heptane)- responsible for the plastic properties of asphalts and imparts hardness to it

2. petrolene - term used by American author ormaltene - term used by European workers- constitute the dispersing medium- the substance soluble in petroleum solvents- it consists of two parts:

a. resins - is that portion of the petrolene which when absorbed by fullers earth remains insoluble in normal pentane but dissolves in ethyl ether

b. oily constituent - is that portion of the petrolene which when mixed with fullers earth is

soluble in N-pentane- responsible for the softness of the asphalt

For good adhesiveness the oily constituents should be low and the asphaltic resins high

4.1.1. Significant Properties:

1. Consistency - fluidity or degree of hardness. It varies with temperature and kind of fluxing agent, in the case of liquid asphalt

2. Durability - resistance to change in properties due to weathering or aging. Asphalts generally tend to become hard and brittle with age. Good quality asphalt is more weather-resistant

3. Adhesion - ability to adhere to aggregate in the presence of water4. Rate of Setting - rate of hardening or curing. It varies with the type of fluxing agent,

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5. Ductility - ability to stretch without breaking.

4.1.2. Types of Bituminous Materials

Natural Asphalt:1. Pure deposits - found in Trinidad, Bermudez2. Rock Asphalt

- refers to sandstone and limestone which is naturally impregnated with bitumen

- the only commercial source in the Philippines today is Villaba, Leyte

Manufactured Asphalt:1. Asphalt Cement

- also known as hot asphalt (135 175 oC), penetration grade asphalt or solid asphalt

- designated as AC- it is the basic cementing material and a constituent of all other asphalt types- it is black, has a consistency ranging from solid to semi-solid- it is heavier than water and practically odorless

2. Liquid Gradesa. Slow-curing cutback

- asphalt cement with slowly volatile and non-volatile oils- designated as SC- has a characteristic smell of oil

b. Medium-curing cutback - asphalt cement with light petroleum distillate, such as kerosene- has a characteristic smell of kerosene- it is black and varies from a light liquid at room temperature for lower MC to

an almost semi-solid for higher MCc. Rapid-curing cutback - asphalt with a low-boiling point petroleum distillate,

such as gasoline or naphtha.- has a characteristic smell of naphtha or gasoline

d. Emulsified Asphalt - asphalt cement dispersed in water with the aid of an emulsifying agent.- an asphalt emulsion is chocolate-colored before use, turning black when

emulsion is broken- It may be used without heating (15-50 oC) and will mix with water in all

proportions without difficulty.- It is characterized by a disagreeable odor which is evident even in the best

emulsionsThree classes of asphalt-emulsions:

d.1. quick-breaking or quick-settingd.2. medium settingd.3. slow-setting

Advantages over non-emulsified asphalt d.1. it can be used during damp weather with moist aggregatesd.2. control of the quantity is often automatic, any excess draining off

through the subgrade leaving only a thin film on the aggregate surface.

d.3. utilizes less of asphalt cement (about 60%)

3. Blown Asphalt - produced by oxidation of asphalt residue by blowing air after fractioning of

lighter constituents.

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- used for joint sealing, under-sealing of concrete pavements, water proofing and roofing.

4.1.3. Factors to be considered in the selection of type and grade of bituminous material:

1. type of construction equipment to be used2. climatic conditions3. nature and grading of aggregates available4. maintenance problems5. traffic requirements6. funds available

4.1.4. Significant Tests:

1. Penetration Test - is an arbitrary measurement of consistency and is the basis of the

classification of all solid and semi-solid asphalt- penetration is the depth in tenths of a millimeter

Procedure:A standard needle weighing 100 grams is allowed to penetrate into a sample at

25oC (77oF) for 5 seconds.

2. Ductility- this test represents the capacity of the bituminous material for elongating and

stretching- it is expressed as the distance in centimeters that a standard briquette of

asphalt with a minimum cross-section of 1 cm2 will stretch before breaking- high ductility asphalts usually are (a) more susceptible to temperature

changes (b) normally cementitious and adhere well to aggregates and desirable for paving purposes

- low ductility on the other hand, are desirable as joint and crack fillers- ductility is lowered during its use.

Procedure:A sample placed in a briquette with 25oC is pulled at a uniform rate of 5

cm/min. The initial distance until the specimen breaks is measured expressed in centimeters.

3. Viscosity - is a measure of the consistency of liquid asphaltic materials, determining their

fluidity or resistance to flow- it is measured as the time in seconds for the liquid asphalt to flow through a

standard orifice into a measured flask.- it is used to classify liquid asphalts into grades- it is useful as measure and control of consistency, particularly when run at the

temperature of intended application

Procedure:A 60 cubic centimeters of liquid asphalt is allowed to pass through a standard

orifice into a measured flask. The time it takes for the material to flow through this opening is recorded.

4. Flash Point - is used primarily for determining the adaptability of bituminous substances

for certain definite usage and serves as a criterion in eliminating fire hazards

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- it indicates the safe working temperature for an asphaltic material

Procedure:

It consists of heating the asphalt in an open cup and passing a small test flame across the surface of the material. The flash point is taken as the temperature at which a flash appears due to the ignition of the evolved vapors upon contact with the test flame.

5. Softening Point - is consistency test for ascertaining the adaptability of a bituminous material

for certain usage, including its resistance to heat.- it is the temperature at the instant the loaded sample falls through the ring and

touches the bottom of the beaker- result is particularly useful for asphalts to be used in thick films as in joint

and crack filling, but is of negligible importance in paving asphalt

Procedure:This is done by heating in a beaker the asphalt enclosed in a brass ring while

suspended in water and carrying a small steel ball on the upper surface.

6. Solubility - this test is useful for the following reasons:

a. for purposes of identificationb. for ascertaining the adaptability of bituminous substance for a given

purposec. for gauging uniformity of supply and as a criterion of its quality or

purity and consequently its intrinsic value- it determines the total bitumen content of asphaltic materials, which is the

actual cementing constituent of the material

% solubility = 100 - (c - b) x 100awhere: a - mass of sample, g

b - mass of crucible + filter paper, gc - mass of crucible + residue, g

Procedure:A one gram sample is dissolved in either carbon disulfide or carbon

tetrachloride. The solution is filtered off and the solubility determined from the insoluble material retained on the filter.

7. Loss on Heating- is an accelerated test to show the loss on volatiles- if loss is excessively high and the penetration after heating is low, it is

probable that it would harden materially when mixed with aggregate in thin films

Procedure:

The sample is heated at 163oC for five hours, and the loss due to volatilization is determined.

% loss on heating = b c x 100 %b a

where: a - mass of empty container, gb - mass of container + sample, g

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c - mass of container + sample after heating, g

8. Specific Gravity- it is of value in identification of the asphalt type- the higher the specific gravity the lower is the penetration- it is an indicative of the uniformity of the products supplied from a given

source- it is useful in making calculations needed for proper control during

construction

Specific Gravity = c a(b a) - (d c)

where: a - mass of the pycnometer ( plus stopper), gb - mass of pycnometer filled with water, gc - mass of pycnometer partially filled asphalt, gd - mass of pycnometer + asphalt + water, g

9. Distillation Test-measures the amount of the more volatile constituents in cut-back asphaltic

products- it gives information as to the actual amount of constituents removed at

definite temperatures.- the properties of the residue after distillation are not necessarily characteristic

of the bitumen used in the original mixture nor of the residue which may be left at any particular time after the application of the product

4.1.5. Sampling and Control (AASHTO Method Designation: T 40)

1. Samples should be sent to the laboratory for testing accompanied by completely filled out sample card as soon as shipment is received.

2. Visual examination should be conducted on all bituminous materials received on site: To identify material delivered whether it conforms to the type of asphalt required

(like color, consistency and odor). To reject immediately the materials found defective like presence of foreign

materials.3. Size of sample:

Minimum requirement 4 liters for a maximum of 200 liters or 40 tons4. For semi-solid materials, samples should be taken at the center of the containers at least

75 mm (3 in) below the surface and 75 mm (3 in) from the sides with the aid of a clean hatchet or putty knife

5. Hard asphalt should not be heated in sampling as excessive and uncontrolled heating will produce some changes in properties of the materials.

6. Care should be taken to insure no contamination in sampling.7. Clean and dry cans should be used as sample containers and these should be tightly

covered.

4.2. Bituminous Mixtures

- is a carefully proportioned combination of bituminous material and aggregate, with or without mineral filler.

- It is used as base or surface course in the construction of highways, airport runways and taxi-ways, and parking areas.

- The amount of bituminous material may vary widely from 3 15% by weight, depending on the aggregate gradation and specific use.

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Classification according to preparation:1. Road-mix mixed in place2. Plant-mix prepared in a central mixing plant

Classification according to grading of aggregates:

1. Dense-graded the aggregate is well graded from coarse to fine and contains appreciable amount of material passing the #200 sieve. A mineral filler like cement or lime is added if the available aggregate is deficient in fines.

2. Open-graded have a poor grading or it may differ from the dense-graded only in the amount of material passing the #200 sieve. It requires seal coat if use as surface course to provide necessary resistance to moisture and oxidation.

Advantages of dense-graded over the open-graded Is better in quality and uniformity due to closer control in batching and mixing. The cost is higher but is more than offset by better service and performance

4.2.1. Significant Properties

1. Stability resistance to displacement under sustained or repeated loading.- it implies resistance to shoving and rutting by the action of vehicular traffic

and resistance to shearing stress.

Factors influencing stability:a. Gradation of mineral aggregates

Stability of bituminous mixture is directly related to aggregate density, which in turn, has a direct relationship on gradation or particle-size distribution. In designing a mixture, aggregates available in a job shall be combined in the proportions that result in the maximum density.

b. Shape and surface texture of aggregate particles

Aggregates composed of angular and rough-textured particles are more desirable than round and smooth aggregate particles from the standpoint of stability. The aggregate component contributes internal friction to the shear strength and stability of the mixture. From this point of view, the shape and surface texture of the aggregate particles are of primary importance.

c. Hardness of aggregate particles

If soft and friable aggregates are used, the voids are greatly reduced by rolling during construction and by subsequent vehicular traffic, that there will be insufficient space for the bituminous binder, which results in bleeding and loss of stability.

d. Maximum size of coarse aggregate.

Higher stability is obtained by the use of coarser aggregates. However, with coarser aggregates, there is a tendency towards increasing harshness and segregation which results in unattractive surface appearance. The choice of maximum size of aggregate should depend on the relative importance of high stability versus workability and surface finish.

e. Quantity and consistency of bituminous binder.

The quantity of binder greatly affects stability of the mixture. Most mixtures have a critical bitumen content which if exceeded will result in over-lubrication of

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aggregates, thus causing instability. The critical bitumen content is about 5 to 7 % lower than the quantity of binder required to completely fill the voids in the compacted mineral aggregate.

f. Degree of compaction.Compaction is essential to produce maximum contact between the bitumen-coated

aggregates for the development of stability in the mixture. The degree of compaction is principally dependent upon the intensity and type of compactive effort, gradation and particle shape of aggregate, and consistency of binder at the time of compaction.

Tests for stability:a. Marshall stabilityb. Immersion-compression

2. Durability resistance to disintegration due to the detrimental effects of traffic, water, air and temperature changes. To be durable, a bituminous pavement must satisfactorily resist traffic loads during its lifetime.

Factors affecting durability:a. Density of compacted mixture

High-density pavement is highly resistant to the intrusion of water. High-density pavement has low air voids thus it is less exposed to detrimental

effects of water or air. Bituminous pavement should not be voidless, as this will result in bleeding and

instability. Allowable % air voids range is 5 7. b. Properties of mineral aggregate

Aggregates vary in their ability to retain the bituminous coating in the presence of water. Hydrophylic aggregates have affinity for water and should be avoided. The film stripping and immersion-compression tests have been developed to measure the loss of cohesion as a result of water action on the compacted bituminous mixture.

Absorption of moisture causes the mixture swell. A durable movement should be able to resist this swelling action.

Aggregates vary with respect to hardness and toughness. Soft aggregates at the exposed surface of bituminous pavements may be dislodged under traffic.

c. Properties of bituminous binder.

All bituminous road materials harden with age and weathering action. However, certain materials harden more rapidly than others. The thin-film oven test had been developed in order to differentiate bituminous materials with respect to hardening characteristics.

Asphalts also differ in their resistance to stripping from aggregates in the presence of water.

d. Quantity of bituminous binder

In order to preserve the plastic properties of the pavement, it is a good practice to use as much bituminous materials in the mixture as possible, consistent with stability requirements. If the coating in the aggregates is very thin, the pavement easily becomes brittle and is abraded more readily.

3. Flexibility the ability of the pavement to bend repeatedly without cracking and to conform to variations of the underlying base

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Factors affecting flexibilitya. Quantity of bituminous binderb. Quantity of mineral fillerc. Viscosity and temperature susceptibility of the binder

There should be flexibility without sacrificing stability Flexibility is improved by decreasing the mineral filler; this reduces surface area of

particles, thus permitting thicker asphalt films. But should not be overdone as it may result in reducing greatly the stability.

4. Skid Resistance is the resistance offered by the pavement to slipping or skidding of the vehicle tires.

Factors affecting skid resistance:a. Excess asphalt at pavement surface immediately after construction or after

densification by traffic or due to change in temperature.b. Surface roughness of aggregate particles

Certain types of rocks, as non-porous and hard limestone and serpentine, tend to become polished under traffic and cause a slick surface. It is helpful to incorporate angular silica sand in the mix in such proportions so that the finish is like sandpaper, instead of having the smooth stones predominate at the surface. Incorporation of granitic aggregates in the mix will also help in producing a skid-resistant surface.

5. Permeability porosity or perviousness of the mixture. It is principally dependent on pore size. A dense graded mix prevents water from entering the base through the surface.

4.2.2. Tests

1. Extraction is performed to determine whether paving mixtures conform to asphalt content requirement.

Procedure: A representative sample of about 1,000 gm bituminous mixture is weighed. Then placed in either a rotarex centrifuge or reflux extractor by dissolving the asphalt in the mixture using a suitable solvent.

Bitumen Content, % by weight of aggregate = 100 (A B)B

where: A oven-dry weight of sampleB oven-dry weight of aggregate after extraction

2. Density or Specific Gravity of Compacted Mixture- this data is important in the determination of the degree of compaction of a

newly constructed asphalt pavement.

Procedure: A sample from compacted pavement is weighed in air then in water. The loss in weight is the volume of compacted mixture.

Density = AA B

where: A weight in grams of sample in air

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B weight in grams of sample in water

Theoretical Maximum Density =100

% Bituminous Binder ( By wt) + % Aggregate (By Weight)S.G. of Bituminous Binder S.G. of Aggregate

Degree of Compaction, % = Density x 100%Theoretical Maximum Density

3. Voids in the Compacted Mixture

Percent Voids = 100 (D d)D

Where: D theoretical maximum densityd density of compacted mixtures

4. Swell determines the amount of water absorbed by bituminous mixture

Procedure: It is determined by placing bituminous mixtures in a mold, compressed it to specified load then immersed in a water bath with both ends of steel mold open. The amount of swelling is measured by a dial until the maximum swell is obtained.

1/16 inch mediocre mixture inch unsuitable mixture from service standpoint

% Swell = 100 (Final dial reading Initial dial reading)Original height

5. Film Stripping - it is used for measuring the relative adhesion of bituminous film to aggregate

particles in the presence of moisture- it is also of great value in predicting if the particular combination is

satisfactory or not.

Procedure: Prepare a mixture of aggregate and the bitumen proposed to be used with it. The mixture is heated for 24 hours, soaked under water for another 24 hours, then boiled for 5 minutes. An aggregate is considered satisfactory if at the end of the test, it is seen by visual inspection that there is no appreciable amount of uncoated particles.

6. Stability - these tests are very useful design tools especially if used by experienced engineers.a. Immersion-Compression test it measures the cohesion or viscous resistance

of the bituminous material in a dry or wet mixture

Procedure: At least two samples of the mixture are compacted in 100 mm diameter molds about 100 mm high, and removed from the mold after an application of 17,045 kg (37,500 lb) load. One specimen is soaked in water for four days after obtaining the weight, while the other is exposed in the air for the same length of time. Both specimens are tested in compression unsupported.

Wet or Dry Stability = Load at Failure

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Cross-sectional Area

Stability Ratio = Wet StabilityDry Stability

b. Marshall Test it measures resistance to displacement of a compacted bituminous

mixture. flow index is obtained to measure the diametric distortion required

to produce failure.

Procedure: Lateral pressure is applied with a zero normal load whish makes the test opposite of the unconfined compression test.

Recommended Marshall Stability Values at 60 oCa) 340 kg (750 lb) for light trafficb) 544 kg (1200 lb) for medium trafficc) 816 kg (1800 lb) for heavy traffic

Flow value for all traffic requirements for paving mixtures 16.0 when measured in a 0.25 mm gradation

4.3 Design of Bituminous Paving Mixtures

Essential Steps in Mix Design;

1. Selection of quality of aggregate.Important factors to be considered are shape, surface texture, and preferential

wetting characteristics of the aggregate particles.

2. Selection of gradation of aggregates.

Important factors to be considered are workability of mix, perviousness and surface texture of pavement, and overall economy. Generally it is more economical to include a maximum of coarse particles, without sacrificing workability.

3. Selection of type and grade of bituminous binders.

Important factors to be considered are workability, climatic conditions, aging considerations, and gradation of aggregate.

4. Determination of correct amount of bituminous binder by Marshall or Immersion-Compression test.

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IV Asphalt