Aggregate

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AggregateAggregate

Goh Boon Hoe

Senior University Teaching [email protected]. (office) : 6(03) – 8924 8182Room B1C20

Faculty of Engineering

Department of Civil Engineering

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Contents

• Aggregate Sources

o Mineral Properties

o Chemical Properties

� Stripping

o Physical Properties

� Gradation & Size

� Toughness & Abrasion Resistance

� Durability & Soundness

� Particle Shape & Surface Texture

� Specific Gravity

� Cleanliness & Deleterious Materials

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Introduction

• Aggregate is a collective term for the mineral materials suchas sand, gravel & crushed stone that are used with a bindingmedium (such as water, bitumen, portland cement, lime,etc.) to form compound materials (such as Asphalt Concrete& Portland cement concrete).

• By volume, aggregate generally accounts for 92 – 96% of hotmix asphalt (HMA) & about 70 – 80 % of Portland cementconcrete (PCC).

• Aggregate is also used for base & subbase courses for bothflexible & rigid pavements.

• Aggregates can either be natural or manufactured.

• Natural aggregates are generally extracted from larger rockformations through an open excavation (quarry).

• Extracted rock is typically reduced to usable sizes bymechanical crushing. Manufactured aggregate is often thebyproduct of other manufacturing industries.

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Mineral Properties

• An aggregate’s mineral composition largely determines its

physical characteristics & how it behaves as a pavementmaterial.

• Therefore, when selecting an aggregate source, knowledge ofthe quarry rock’s mineral properties can provide an excellent

clue as to the suitability of the resulting aggregate.

• The following slide shows some general guidelines for

aggregate used in HMA.

• In general, relationships between mineral & physical

properties are quite complex, making it difficult to accuratelypredict how a particular aggregate source will behave based

on mineral properties alone.

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Mineral Properties (continued)

Desirable Properties of Rocks for HMA

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Chemical Properties

• In HMA, aggregate surface chemistry can determine how well

an asphalt cement binder will adhere to an aggregatesurface.

• Poor adherence, commonly referred to as stripping, cancause premature structural failure.

• In PCC, aggregates containing reactive forms of silica can

react expansively with the alkalis contained in the cement

paste.

• This expansion can cause cracking, surface popouts &

spalling.

• Note that some aggregate chemical properties can changeover time, especially after the aggregate is crushed. A newly

crushed aggregate may display a different affinity for water

than the same aggregate that has been crushed & left in astockpile for a year.

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Stripping (for HMA)

• Although the displacement of asphalt on the aggregate particlesurface by water (stripping) is a complex phenomena & is not yetfully understood, mineralogy & chemical composition of theaggregate have been established as important contributing factors.

• In general, some aggregates have an affinity for water over asphalt(hydrophilic). These aggregates tend to be acidic & suffer fromstripping after exposure to water.

• On the other hand, some aggregates have an affinity for asphaltover water (hydrophobic). These aggregates tend to be basic & donot suffer from stripping problems.

• Additionally, an aggregate’s surface change when in contact withwater will affect its adhesion to asphalt cement & its susceptibilityto moisture damage.

• In sum, aggregate surface chemistry seems to be an importantfactor in stripping. However, specific cause-effect relationships arestill being established.

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Physical Properties

• Aggregate physical properties are the most readily apparent

aggregate properties & they also have the most direct effecton how an aggregate performs as either a pavement material

constituent or by itself as a base or subbase material.

• Commonly measured physical aggregate properties are:

1) Gradation & size

2) Toughness & abrasion resistance

3) Durability & soundness

4) Particle shape & surface texture

5) Specific gravity (particle density)

6) Cleanliness & deleterious materials

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Physical Properties (continued)

• These are not the only physical properties of aggregates but

rather the most commonly measured.

• Tests used to quantify these properties are largely empirical.

• The physical properties of an aggregate can change over

time.

• For instance, a newly crushed aggregate may contain more

dust & thus be less receptive to binding with an asphaltbinder than one that has been crushed & stored in a stockpile

for a year.

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Gradation and Size

• The particle size distribution (also named as gradation), of an

aggregate is one of the most influential aggregatecharacteristics in determining how it will perform as a

pavement material.

• In HMA, gradation helps determine almost every important

property including stiffness, stability, durability, permeability,

workability, fatigue resistance, frictional resistance &resistance to moisture damage.

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Gradation and Size (continued)

ASTM Sieve Opening (mm)

2 Inches 50.80

1 ½ Inches 37.5

1 Inch 25.40

¾ Inch 19.00

½ Inch 12.50

3/8 Inch 9.50

No. 4 4.75

No. 8 2.36

No. 16 1.18

No. 30 0.60

No. 50 0.30

No. 100 0.15

No. 200 0.075

Standard Sieve Number and Opening (ASTM standard)

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Maximum Aggregate Size

• Maximum aggregate size can affect HMA, PCC &

base/subbase courses in several ways.

• In HMA, instability may result from excessively small

maximum sizes; & poor workability and/or segregation mayresult from excessively large maximum sizes.

• ASTM C 125 defines the maximum aggregate size in one of

two ways:

o Maximum size. The smallest sieve through which 100 % of

the aggregate sample particles pass.

o Nominal maximum size. The largest sieve that retains

some of the aggregate particles but generally not morethan 10 % by weight (Size indicated in specification).

• Thus, it is important to specify whether "maximum size" or"nominal maximum size" is being referenced.

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Maximum Aggregate Size (continued)

ASTM Sieve

¾” (19 mm)

½” (12.5 mm)

3/8” (9.5 mm)

No. 4 (4.75 mm)

No. 8 (2.36 mm)

No. 16 (1.18 mm)

No. 30 (0.6 mm)

No. 50 (0.3 mm)

No. 100 (0.15 mm)

No. 200 (0.075 mm)

Pan

% Retained

0 %

0 %

4.3 %

7.7 %

12.6 %

13.4 %

17.1 %

18.9 %

16.1 %

7.9 %

2 %

TOTAL = 100%

% Passing

100 %

100 %

95.7 %

88 %

75.4 %

62 %

44.9 %

26 %

9.9 %

2 %

0 %

Maximum Size

Nominal Maximum

Size

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Gradation Test

• The gradation of a particular aggregate is most often

determined by a sieve analysis.

• In a sieve analysis, a sample of dry aggregate of known

weight is separated through a series of sieves withprogressively smaller openings.

• Once separated, the weight of particles retained on each

sieve is measured & compared to the total sample weight.

• Particle size distribution is then expressed as a percent

retained by weight on each sieve size.

• Results are usually expressed in tabular or graphical

format. PCC gradation graphs are traditionally semi-logarithmic (BS standard), while HMA graphs often employ

the standard 0.45 power gradation graph (ASTM Standard).

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Gradation Test (continued)

Logarithmic Graph (for PCC)

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FHWA 0.45 Power Graph (for HMA)

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• The previous slides show the typical gradation graphs, note

that sieve sizes are presented from smallest to largest, left toright. The number & size of the sieves used in a sieve

analysis depend upon specification requirements.

• For PCC, aggregate is typically classified as either "coarse" or

"fine". Coarse aggregate is generally the fraction retained on

the 4.75 mm (No. 4) sieve while fine aggregate is thefraction passing the 4.75 mm (No. 4) sieve.

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Desired Gradation

• Gradation has a profound effect on material performance.

• But what is the best gradation?

o This is a complicated question, the answer to which willvary depending upon the material (HMA or PCC), itsdesired characteristics, loading, environmental, material,structural & mix property inputs.

• Therefore, gradation requirements for specific HMA & PCCmixes are discussed in their respective pavement typesections. This section presents some basic guidelinesapplicable to common dense-graded mixes.

• It might be reasonable to believe that the best gradation isone that produces the maximum density.

• This would involve a particle arrangement where smallerparticles are packed between the larger particles, whichreduces the void space between particles.

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Desired Gradation (continued)

• This creates more particle-to-particle contact, which in HMA

would increase stability & reduce water infiltration.

• In PCC, this reduced void space reduces the amount of

cement paste required.

• However, some minimum amount of void space is necessaryto:

o Provide adequate volume for the binder (asphalt binder orportland cement) to occupy.

o Promote rapid drainage & resistance to frost action for

base & subbase courses.

• Therefore, although it may not be the "best" aggregategradation, a maximum density gradation does provide a

common reference.

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Desired Gradation (continued)

• A widely used equation to describe a maximum density

gradation was developed by Fuller & Thompson (1907). Theirbasic equation is:

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The 0.45 Power Maximum Density Curve

• In the early 1960s, the FHWA introduced the standard

gradation graph used in the HMA industry today.

• This graph uses n = 0.45 & is convenient for determining the

maximum density line & adjusting gradation.

• This graph is slightly different than other gradation graphsbecause it uses the sieve size raised to the nth power (usually

0.45) as the x-axis units.

• Thus, n = 0.45 appears as a straight diagonal line.

• The maximum density line appears as a straight line from

zero to the maximum aggregate size for the mixture being

considered.

• To illustrate how the maximum density curves are

determined, see the following slide for the associatedcalculations for a maximum aggregate size of 19.0 mm.

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The 0.45 Power Maximum Density Curve (continued)

Maximum Density Curves for 0.45 Power Gradation Graph (each curve is for a different maximum aggregate size)

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The 0.45 Power Maximum Density Curve (continued)

Calculations for a 0.45 Power Gradation Curve Using 19.0-mm (0.75-inch) Maximum Aggregate Size

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Gradation Terminology

FHWA Gradation Graph Showing Representative Gradations

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Gradation Terminology (continued)

1) Dense or well-graded

o Refers to a gradation that is near the FHWA’s 0.45 power curvefor maximum density. Typical gradations are near the 0.45power curve but not right on it.

o Generally, a true maximum density gradation (exactly on the0.45 power curve) would result in unacceptably low VMA.

2) Gap graded

o Refers to a gradation that contains only a small percentage ofaggregate particles in the mid-size range.

o The curve is flat in the mid-size range.

o Some PCC mix designs use gap graded aggregate to provide amore economical mix since less sand can be used for a givenworkability.

o HMA gap graded mixes can be prone to segregation duringplacement.

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3) Open graded

o Refers to a gradation that contains only a smallpercentage of aggregate particles in the small range.

o This results in more air voids because there are notenough small particles to fill in the voids between thelarger particles.

o The curve is near vertical in the mid-size range, and flatand near-zero in the small-size range.

4) Uniformly graded

o Refers to a gradation that contains most of the particlesin a very narrow size range.

o In essence, all the particles are the same size.

o The curve is steep & only occupies the narrow size rangespecified.

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5) Fine gradation

o A gradation that, when plotted on the 0.45 powergradation graph, falls mostly above the 0.45 powermaximum density line.

o The term generally applies to dense graded aggregate.

6) Coarse gradation

o A gradation that, when plotted on the 0.45 powergradation graph, falls mostly below the 0.45 powermaximum density line.

o The term generally applies to dense graded aggregate.

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Toughness and Abrasion Resistance

• Aggregates undergo substantial wear & tear throughout their

life.

• In general, they should be hard & tough enough to resist

crushing, degradation & disintegration from any associatedactivities including manufacturing, stockpiling, production,

placing, compaction (in the case of HMA) & consolidation (in

the case of PCC).

• Furthermore, they must be able to adequately transmit loadsfrom the pavement surface to the underlying layers (&

eventually the subgrade).

• Aggregates not adequately resistant to abrasion & polishing

will cause premature structural failure and/or a loss of skid

resistance.

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Toughness and Abrasion Resistance (continued)

• Common tests are ;

1) Los Angeles Abrasion test (ASTM C131)

2) Aggregate Impact Test (BS 812 : Part III)

3) Aggregate Crushing Test (BS 812 : Part III)

4) Ten percent fines (BS 812 : Part III)

5) Aggregate Polishing Test (BS 812 : Part III)

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Los Angeles Abrasion Test

• For the L.A. abrasion test, the

portion of an aggregate sampleretained on the 1.70 mm (No. 12)

sieve is placed in a large rotating

drum that contains a shelf plateattached to the outer wall.

• A specified number of steel spheresare then placed in the machine &

the drum is rotated for 500

revolutions at a speed of 30 – 33revolutions per minute (RPM).

Los Angles Abrasion Test Apparatus

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Los Angeles Abrasion Test (continued)

• The material is then extracted & separated into material

passing the 1.70 mm (No. 12) sieve & material retained onthe 1.70 mm (No. 12) sieve.

• The retained material (larger particles) is then weighed &compared to the original sample weight.

• The difference in weight is reported as a percent of the

original weight & called the "percent loss".

• Aggregate with high L.A. abrasion loss values will tend to

create dust during production & handling, which may produce

environmental & mixture control problems.

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Aggregate Impact Test

• This test is designed to evaluate the

resistance of an aggregate to suddenimpact.

• Since vehicle loads cause impact, thistest gives an indication of the

performance of aggregates to resist

crushing under impact.

• The test consists of subjecting asample (passing 12.5 mm sieve &

retained on 10 mm sieve) filled into a

cylindrical mould 7.5 cm internaldiameter & 5 cm height.

• The impact is provided by dropping ahammer of weight 13.5 kg through a

height of 38 cm.Aggregate Impact

Test Equipment

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Aggregate Impact Test (continued)

• Aggregates passing fully through 12.5 mm sieve & retained

on 10 mm sieve are filled in the cylindrical measure in 3layers, each layer being given 25 strokes with a rod.

• The sample is then transferred to the cup of the aggregateimpact testing machine & tapped 25 times with the rod.

• After subjecting the specimen to 15 blows through the

hammer, the crushed aggregate is sieved on 2.36 mm sieve.

• The weight materials passing through this sieve expressed as

a percentage of the total weight of the sample gives the

Aggregate Impact Value (AIV).

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Aggregate Crushing Test

• One of the modes in which a

pavement material can fail is bycrushing under severe stresses.

• This test consist of subjecting thespecimen of aggregate in a

standard mould to a compression

test under standard loadingconditions.

• Dry aggregates passing through

12.5 mm sieve & retained on 10

mm sieve are filled in a cylindricalmeasure 11.5 cm diameter & 18

cm high, in 3 layers, each layer

being tamped with a standard rod25 times.

Aggregate Crushing Test Apparatus

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Aggregate Crushing Test (continued)

• The sample is then transferred to the cup of the aggregate

crushing testing machine & tapped 25 times with the rod.

• The specimen is subjected a compressive load of 400 kN

gradually applied in 10 times.

• The material passing through 2.36 mm sieve is separated.

• The weight of this material (fines) is expressed as a

percentage of the weight of the total sample gives theAggregate Crushing Value (ACV).

• A value of less than 10 signifies an exceptionally strong

aggregate, while above 30 would normally be regarded as of

weak aggregate.

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Ten Percent Fines

• This is normally is carried out after the aggregate impact &

crushing tests.

• The purpose of this test is to determine the force required to

produce the 10% fines value.

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Aggregate Polishing Test

• The resistance of aggregates to

polishing under traffic determines itskid resistance.

• The standard method for testing isto embed the aggregates in a

curved mould in cement-sand

mortar & subject the sample toaccelerated polishing caused by a

rotating pneumatic wheel.

• The specimens are mounted on a

circular frame 40 cm diameter. Thesize of each specimen is 45 mm

wide x 90.5 mm long.

Accelerated Polishing Machine

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Aggregate Polishing Test (continued)

• The rubber wheel is 20 cm diameter & 5 cm broad, loadedwith 40 kg load at a tire pressure of 3.15 ± 0.15 kg/cm2.

• Sand & water are fed to the machine when it’s rotated at an

RPM of 320 – 325 for 3 hours 13 minutes.

• The specimens are thereafter tested for their polishing valueon a British portable pendulum tester.

Road Wheel & Samples

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• This machine consists of a rubber sliding shoe which is

mounted at the end of a pendulum. The slider, whenreleased, brushes past the specimen & comes to a halt.

British Portable Pendulum Tester

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• The specimen directly measures the Polishing Stone Value

(PSV) on a graduated scale.

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Durability and Soundness

• Aggregates must be resistant to breakdown & disintegrationfrom weathering (wetting/drying & freezing/thawing) or theymay break apart & cause premature pavement distress.

• Durability & soundness are terms typically given to anaggregate’s weathering resistance characteristic.

• Aggregates used in HMA are dried in the production process& therefore should contain almost no water.

• Thus, for aggregate used in HMA, freezing / thawing shouldnot be a significant problem.

• However, this is not true for aggregate used in PCC or asbase and/or subbase courses. These aggregates typicallycontain some water (on the order of 0.1% to 3% usually) &are not dried prior to use.

• Soundness test (ASTM C88) is used to determine thesoundness loss of the aggregate.

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Durability and Soundness (continued)

• The most common soundness test involves repeatedly

submerging an aggregate sample in a saturated solution ofsodium or magnesium sulfate.

• This process causes salt crystals to form in the aggregatepores, which simulate ice crystal formation.

Aggregate Before Soundness Test

Aggregate After Soundness Test

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Durability and Soundness (continued)

• The basic procedure is as follows :

o Oven dry the sample & separate it into specific sieve sizes.

o Immerse the sample in a saturated solution of sodium ormagnesium sulfate & let it remain at a constanttemperature for 18 hours.

o Remove the sample from the solution & dry to a constantweight at 110 ± 5oC (230 ± 9oF).

o Repeat this cycle five times.

o Wash the sample to remove the salt; then dry.

o Determine the loss in weight for each specific sieve size &compute a weighted average percent loss for the entiresample.

• The maximum loss values typically range from 10 – 20percent for every five cycles.

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Particle Shape and Surface Texture

• Particle shape & surface texture are important for proper

compaction, deformation resistance, HMA & PCC workability.

• However, the ideal shape for HMA & PCC is different because

aggregates serve different purposes in each material.

• In HMA, since aggregates are relied upon to provide stiffness& strength by interlocking with one another, cubic angular-

shaped particles with a rough surface texture are best.

• However, in PCC, where aggregates are used as an

inexpensive high-strength material to occupy volume,

workability is the major issue regarding particle shape.Therefore, in PCC rounded particles are better.

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Particle Shape and Surface Texture (continued)

• Relevant particle shape / texture characteristics are :

1) Particle shape

� Rounded particles create less particle-to-particle

interlock than angular particles & thus provide better

workability & easier compaction.

� However, in HMA less interlock is generally a

disadvantage as rounded aggregate will continue tocompact, shove & rut after construction.

� Thus angular particles are desirable for HMA (despite

their poorer workability), while rounded particles are

desirable for PCC because of their better workability(although particle smoothness will not appreciably

affect strength).

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2) Flat or Elongated particles

� These particles tend to impede compaction or break

during compaction & thus, may decrease strength.

3) Smooth-surfaced particles

� These particles have a lower surface-to-volume ratio

than rough-surfaced particles & thus may be easier to

coat with binder.

� However, in HMA asphalt tends to bond more

effectively with rough-surfaced particles, & in PCCrough-surfaced particles provide more area to which

the cement paste can bond.

� Thus, rough-surface particles are desirable for both

HMA & PCC

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• There are several common tests used to identify & quantify

aggregate particle shape & surface texture. Among the mostpopular are ;

1) Angularity number (BS 812 : Part I)

2) Flakiness and elongation tests (BS 812 : Part III)

3) Others test (for Superpave technology)

� Particle index (ASTM D 3398)

� Coarse aggregate angularity / Percent fractured face

(ASTM D 5821)

� Fine aggregate angularity (AASHTO T304 & ASTM

C1252)

� Flat or Elongated Particles (ASTM D 4791)

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Angularity Number

• The angularity of an aggregate can be estimated indirectly from thefact that the degree of packing of particles of the same size,compacted in a specified way, depends on the shape.

• The angularity number of an aggregate is the difference by whichthe percentage void exceed 33 after being compacted in aprescribed manner.

• If one conducts a test on the most rounded gravel, 67% of thevolume of the vessel is filled by the solid volume of aggregate. Thepercentage voids will then be 33, making the angularity numberzero, as per definition.

• The higher the number, the more angular the aggregate, the usualrange being 0 – 11.

• The apparatus for testing the angularity number consists of a metalcylinder of capacity 3 liter, tamping rod & a metal scoop.

• The test is sieved & a specified size range of the sample is used forthe test.

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Angularity Number (continued)

• A scoop full of this single size aggregate is placed in a cylinder &tamped 100 times.

• A 2nd & 3rd layers are placed & tamped similarly & the excessaggregate is struck off level to the top surface of the cylinder.

• The weight of aggregate is found (W).

• Then the cylinder is emptied & weight of water filing the cylinder isfound (C).

• The specific gravity of aggregate also determined (GA).

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Flakiness and Elongation Tests

• These tests are conducted on coarse aggregates to assess

the shape of aggregate.

• Aggregates which are flaky or elongated are detrimental to

the higher workability & stability of mixes.

• They are not conductive to good interlocking & hence themixes with an excess of such particles are difficult to compact

to the required degree.

Metal thickness & length gauges

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Flakiness and Elongation Tests (continued)

• The flakiness index is defined as the percentage by weight of

aggregate particles whose least dimension is less than 0.6 oftheir mean size.

• The elongation index of aggregate is the percentage byweight of particles whose greatest dimension (length) is

greater than one & four-fifths times their mean dimension.

• Both tests are not applicable to aggregates smaller than 6.3

mm.

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Specific Gravity

• Aggregate specific gravity is useful in making weight-volumeconversions & in calculating the void content in compactedHMA.

• In general, specific gravity & water absorption tests areconducted together.

• The specific gravity of aggregates is an indirect measure ofits strength. The higher the specific gravity, the denser therock is & stronger is the aggregate.

• Water absorption depends on the pores & voids in the rock.The more water absorption, the higher the voids.

• Generally, there are 3 different aggregate specific gravitiesused in association with pavements:

1) Bulk specific gravity

2) Apparent specific gravity

3) Effective specific gravity

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Specific Gravity (continued)

Vpp

Vs

Vap

Vpp – Vap

Goh B.H. 54


• Apparent Specific Gravity (Gsa)

o Includes only the volume of the aggregate particle.

o It does not include the void volume that becomes filled withwater during the test soak period.

o Ideally, it would not include any void volume but in reality somevoids may not become entirely filled with water during the testsoak period.

o The void volume that does not become filled with water is thuscounted with the solid volume.

o Since it is intended to only measure the specific gravity of thesolid volume, it will be the highest of the 3 aggregate specificgravities.

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• Bulk Specific Gravity (Gsb)

o Includes the volume of the aggregate particle plus the voidvolume that becomes filled with water during the test soakperiod.

o Since it includes the void volume, bulk specific gravity will beless than apparent specific gravity.

o It is very important to measure Gsb as accurately as possible.

o Since it is used to convert weight measurements to volumes,any small errors in Gsb will be reflected in significant volumeerrors, which may go undetected.

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• Effective Specific Gravity (Gse)

o Typically used with HMA.

o The ratio of the mass in air of a unit volume of a permeablematerial (excluding voids permeable to asphalt) at a statedtemperature to the mass in air (of equal density) of an equalvolume of gas-free distilled water at a stated temperature.

o Gse includes the volume of the aggregate particle plus the voidvolume that becomes filled with water during the test soakperiod minus the volume of the voids that absorb asphalt.

o Effective specific gravity lies between apparent & bulk specificgravity.

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• Specific gravity & absorption tests can be carried out for

both;

1) Coarse aggregate (AASHTO T85 & ASTM C127)

2) Fine aggregate (AASHTO T84 & ASTM C128)

Goh B.H. 58

Specific Gravity & Absorption

of Coarse Aggregate (continued)

• Approximately 5 kg of

thoroughly washed aggregateretained on a No. 4 (4.75 mm)

sieve is oven-dried to a constant

weight.

• The dried sample is then

immersed in water for 24 hours.

• The aggregate is removed fromthe water, drained, & surface-

dried until all visible films of

water are removed (The surfaceswill still appear damp).

• The weight of the sample in thesurface-dry condition is then

obtained & recorded as B.

Buoyancy Balance & Wire Basket

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• The saturated surface-dry sample is placed in a wire basket,

submerged in water, & the submerged weight determined &recorded as C.

• The sample is then removed from the water, dried & placedin an oven & dried to a constant weight.

• The oven-dried weight is recorded as A.

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• The specific gravity & absorption are calculated as follows:

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Specific Gravity & Absorption of Fine Aggregate

• The flask (pycnometer) to be used to measure specificgravity is filled with water & the weight recorded as B.

• Approximately 1,000 g of fine aggregate is oven-dried to aconstant weight.

• The dried sample is then immersed in water for 24 hours.

• The fine aggregate is spread on a clean flat surface &exposed to a gently moving current of warm air until asaturated surface dry condition is achieved.

• A saturated surface-dry condition is reached at the moisturecontent at which the lightly compacted material in a cone 1st

slumps when cone is removed.

• The aggregate has some cohesion as long as there is surfacemoisture but has no cohesion when the surface moistureevaporate; hence, the fine aggregate slumps when the coneis removed.

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Specific Gravity & Absorption of Fine Aggregate (continued)

• The cone test must be repeated several times to ensure that

the highest moisture content (saturation) at which theaggregate will slump is determined.

• Approximately a 500 g sample of the saturated surface drymaterial is placed in the flask & the actual weight of the

sample recorded as D.

• The flask is then filled with water, using a specified

procedure, & the weight recorded as C.

• The fine aggregate is removed from the flask, oven-dried to a

constant weight, & the weight recorded as A.

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Specific Gravity & Absorption of Fine Aggregate (continued)

• The specific gravity & absorption are calculated as follows:

Goh B.H. 64

Cleanliness & Deleterious Materials

• Aggregates must be relatively clean when used in HMA or

PCC.

• Vegetation, soft particles, clay lumps, excess dust &

vegetable matter are not desirable because they generallyaffect performance by quickly degrading, which causes a loss

of structural support and/or prevents binder-aggregate

bonding.

• Tests commonly carried out are;

1) Tests for Deleterious Materials: Sand Equivalent

2) Tests for Deleterious Materials: Clay Lumps & Friable

Particles

Goh B.H. 65

Sand Equivalent

• The sand equivalent test is a rapid field test to show the

relative proportions of fine dust or claylike materials inaggregate (or soils).

• A sample of aggregate passing the 4.75 mm (No. 4) sieve &a small amount of flocculating solution are poured into a

graduated cylinder & are agitated to loosen the claylike

coatings from the sand particles.

• The sample is then irrigated with additional flocculationsolution forcing the claylike material into suspension above

the sand.

• After a prescribed sedimentation period, the height of

flocculated clay & height of sand are determined.

Goh B.H. 66

Sand Equivalent (continued)

• The sand equivalent is determined from the following

equation.

• Cleaner aggregates will have higher sand equivalent values.

• Agencies often specify a minimum sand equivalent around 25

to 35

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Goh B.H. 67

Clay Lumps & Friable Particle

• To test for clay lumps or friable particles, a sample is first

washed & dried to remove material passing the 0.075 mm(No. 200) sieve.

• The remaining sample is separated into different sizes & eachsize is weighed & soaked in water for 24 hours.

• Particles that can be broken down into fines with fingers are

classified as clay lumps or friable material.

• The amount of this material is calculated by percentage of

total sample weight.

• Specifications usually limit clay & friable particles to a

maximum of 1%.

Goh B.H. 68

The EndTHANK YOU

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