lab lecture 2 fin

7/27/2019 Lab Lecture 2 Fin

1/66

1

All about gradation

Lecture 2


2/66

2

Aggregates

"Aggregate" is a collective term for the

mineral materials such as sand, gravel and

crushed stone that are used with an asphalt

binding medium to form compound

materials like hot mix asphalt (HMA).

Aggregate accounts for about 92 to 96

percent by total weight of HMA mixture.


3/66

3

Aggregates

Aggregate properties of concern in mix design aregenerally physical in nature and can be divided upinto three major categories:

Gradation and sizeParticle size distribution. Physical attributes requirements Properties

associated with physical shape and contaminationmeasurements that can at least partially be

controlled during production. Source properties Properties inherent in the rock

source for the aggregate
http://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_overview.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/aggregate_intro/agg_consensus.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/aggregate_intro/agg_source.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/aggregate_intro/agg_source.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/aggregate_intro/agg_consensus.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/aggregate_intro/agg_consensus.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_overview.htm


4/66

4

Physical attributes requirements

Physical attributes requirements requirements are:

Coarse Aggregate Angularity (CAA) Fine Aggregate Angularity (FAA)

Flat & Elongated Particles

Sand Equivalent
http://training.ce.washington.edu/VSL/aggregate_tests/caa/caa_overview.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/faa/faa_overview.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/fe/fe_overview.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/se/se_overview.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/se/se_overview.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/fe/fe_overview.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/faa/faa_overview.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/caa/caa_overview.htm


5/66

5

Coarse Aggregate Angularity (CAA)

The coarse aggregate angularity (CAA) test is a

method of determining the angularity ofcoarse

aggregate. Coarse aggregate angularity is important to

ensure better aggregate interlock and prevent

excessive HMA deformation under load (rutting).

Aggregate angularity test conducted by visually

inspecting of a small sample
http://training.ce.washington.edu/VSL/aggregate_tests/caa/caa_overview.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/caa/caa_overview.htm


6/66

6

Aggregate Angularity


7/66

7



8/66

8


This test is used to help ensure that the

resulting HMA mixture will be resistant to

deformation under repeated loads.


9/66

9

Fine aggregate angularity (FAA) test

The fine aggregate angularity (FAA) test is

an indirect method of assessing the

angularity offine aggregate. Fineaggregate angularity is important because

an excess of rounded fine aggregate (often

in the form of natural sand) can lead toHMA rutting.
http://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htm


10/66

10

Fine aggregate angularity (FAA) test

The FAA test estimates fine aggregate

angularity by measuring the loose un-

compacted void content of a fine aggregatesample.

The higher the void content, the higher the

assumed angularity and rougher thesurface.


11/66

11

FAA test

Calculate the Un-compacted Voids as follows:

U = V(F/G) x 100

V

Where:

U = Un-compacted Voids

V = Volume of Measure

F = Net mass of fine aggregate in the measureG = Bulk Dry Specific Gravity of the Blend of

fine aggregate


12/66

12

The flat and elongated particle test

The flat and elongated particle test is used to

determine the dimensional ratios for aggregate

particles of specific sieve sizes.

Flat or elongated particles tend to lock up morereadily during compaction making compaction

more difficult. They also have a tendency to

fracture during compaction along their weak,

narrow dimension, which can effectively make

aggregate gradation finer and possibly cause

lower-than-expected HMA.


13/66

13

The flat and elongated particles


14/66

14

The flat and elongated particles

This flat and elongated particle test uses a

proportional caliper to help measure

dimensional ratios. The specified ratio isset on the caliper and then about 100

particles are tested for each specified sieve

size.


15/66

15

Calipers for the flat and elongated particle

test


16/66

16

Sand equivalent test

The sand equivalent test is a rapid field test toshow the relative proportions of fine dust or clay-like materials in fine aggregate (or granular

soils). The term "sand equivalent" expresses the concept

that most fine aggregates are mixtures ofdesirable coarse particles (e.g., sand) andgenerally undesirable clay or plastic fines anddust. These materials can coat aggregate particlesand prevent proper asphalt binder-aggregate

bonding.


17/66

17

Sand Equivalent Test Apparatus


18/66


19/66

19

Why Gradation in the Lab???


20/66

20

Gradationhow much imp???

The particle size distribution or gradation of

aggregate is one of the most influential

characteristics in determining how an HMA

mixture will perform as a pavement material.Aggregate gradation influences almost every

important HMA property including stiffness,

stability, durability, permeability, workability,

fatigue resistance, skid resistance and resistance

to moisture damage
http://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_vo.htm


21/66

21

PROPERTIES CONSIDERED IN MIX

DESIGN


22/66

22

PROPERTIES CONSIDERED IN MIX DESIGN

Good HMA pavements function well because they aredesigned, produced and placed in such a way as to givethem certain desirable properties. There are several

properties that contribute to the quality of HMApavements.They include

stability,

durability,

impermeability,

workability,

flexibility, and

fatigue resistance


23/66

23

STABILITY

Stability of a HMA pavement is the abilityof the mixture to resist shoving and rutting

under loads (traffic). A stable pavement

maintains the shape and smoothnessrequired under repeated loading; an

unstable pavement develops ruts

(channels), raveling and other signs ofshifting of the HMA.


24/66

24

Shoving at a busy intersection
http://www.pavementinteractive.org/wp-content/uploads/2006/10/Shoving.jpg


25/66

25

Ravelingdislodgement of aggregate particles


26/66

26

Rutting


27/66

27

STABILITY

The stability of a mix depends on internal friction andcohesion. Internal friction among the aggregate particles(inter-particle friction) is related to aggregate

characteristics such as shape and surface texture.Cohesion results from the bonding ability of the binder.

A proper degree of both internal friction and cohesion inHMA prevents the aggregate particles from being moved

past each other by the forces exerted by traffic.

In general, the more angular the shape of the aggregateparticles and the more rough their surface texture, the

higher the stability of the HMA


28/66

28

DURABILITY

The durability of a HMA pavement is the abilityof the HMA pavement to resist changes in the

binder oxidation and disintegration of the

aggregate. These factors may be the result of

weather, traffic, or a combination of the two.Generally, durability of a HMA may be enhanced

by three methods. They are:

using maximum binder content,

using a sound aggregate, and

designing and compacting the HMA for

maximum impermeability


29/66

29

Max binder content & durability

Maximum binder content increases durabilitybecause thick binder films do not age and hardenas rapidly as thin films. Consequently, the binder

retains the original characteristics longer. Also, maximum binder content effectively seals

off a greater percentage of interconnected airvoids in the pavement, making the penetration ofwater and air difficult.

A certain percentage of air voids is required to beleft in the pavement to allow for expansion of the

binder in hot weather.


30/66

30

Dense gradation & durability

A dense gradation of sound, tough aggregate

contributes to pavement durability by

providing closer contact between aggregateparticles that enhances the impermeability

of the HMA, and resists disintegration

under traffic.


31/66

31

IMPERMEABILITY

Impermeability is the resistance of a HMA pavementto the passage of air and water into or through themixture. This characteristic is related to the voidcontent of the compacted HMA, and much of thediscussion on voids in the mix design relates to theimpermeability. Even though void content is anindication of the potential for passage of air and waterthrough a pavement, the character of these voids ismore important than the number of voids.

The size of the voids, whether or not the voids areinterconnected, and the access of the voids to thesurface of the pavement all determine the degree of

impermeability.


32/66

32

WORKABILITY

Workability describes the ease with which a paving HMAmay be placed and compacted. Workability may beimproved by changing mix design parameters, aggregatesources, and/or gradation.

Harsh HMA (HMA containing a high percentage of

coarse aggregate) has a tendency to segregate duringhandling and also may be difficult to compact.

Through the use of trial mixes in the laboratory,additional fine aggregate and perhaps binder may beadded to a harsh HMA to make the mixture moreworkable. Care is required to be taken to ensure that thealtered HMA meets all the other design criteria


33/66

33

WORKABILITY

Excess fines may also affect workability.

Depending on the characteristics of the

fines, the fines may cause the HMA to

become tough or gummy, making the

mixture difficult to compact


34/66

34

FLEXIBILITY

Flexibility is the ability of a HMA pavement toadjust to gradual settlements and movements inthe sub-grade without cracking. Since virtuallyall sub-grades either settle (under loading) or rise(from soil expansion), flexibility is a desirablecharacteristic for all HMA pavements.

An open graded HMA with high binder content isgenerally more flexible than a dense graded, low

binder content HMA. Sometimes the need forflexibility conflicts with stability requirements,so much care need to be taken.


35/66

35

FATIGUE RESISTANCE

Fatigue resistance is the pavement's resistance to repeatedbending under wheel loads (traffic). Air voids (related tobinder content) and binder viscosity have a significant

effect on fatigue resistance. As the percentage of air voids in the pavement increases,

either by design or lack of compaction, pavement fatiguelife (the length of time during which an in-service

pavement is sufficiently fatigue-resistant) is drastically

shortened. Likewise, a pavement containing binder that has aged and

hardened significantly has reduced resistance to fatigue.


36/66

36

Thickness & Strength of pavement

The thickness and strength characteristics of the

pavement and the supporting strength of the sub-

grade also have an effect on the pavement lifeand prevention of load associated cracking.

Thick, well supported pavements do not bend as

much under loading as thin or poorly supported

pavements. Therefore, thick well supportedpavements have longer fatigue lives.


37/66

37

Gradationhow much imp???

Theoretically, there exists a particular

gradation that, for a given maximum

aggregate size, will produce the maximumdensity. This gradation would involve a

particle arrangement where successively

smaller particles are packed within thevoids between larger particles


38/66

38

Smaller particles are packed within the voids

between larger particles


39/66


40/66

40

Three different aspects


41/66

41

what is the best gradation?

Gradation has a profound effect on material

performance. But what is the best gradation? This

is a complicated question, the answer to which

will vary depending upon the material (HMA)

its desired characteristics,

loading, environmental


42/66

42

what is the best gradation?

It might be reasonable to believe that the best

gradation is one that produces the maximum

density. This would involve a particle

arrangement where smaller particles are packedbetween the larger particles, which reduces the

void space between particles. This creates more

particle-to-particle contact, which in HMA would

increase stability and reduce water infiltration


43/66

43

But we require space/voids

However, some minimum amount of void

space is necessary to:

Provide enough volume for the binder(asphalt binder) to occupy.

Promote rapid drainage and resistance to

frost action for base and sub-base courses
http://www.pavementinteractive.org/article/gradation-and-size/frost-actionhttp://www.pavementinteractive.org/article/gradation-and-size/frost-action


44/66

44

Fuller and Thompson Eq

A widely used equation to describe a maximum

density gradation was developed by Fuller and

Thompson in 1907. Their basic equation is:


45/66

45

Maximum density curves for 0.45 Power gradation graph

each curve is for a different maximum aggregate size)


46/66

46

Gradation types

Dense or Well-Graded

Refers to a gradation that is near the FHWAs

0.45 power curve for maximum density. Themost common HMA mix designs tend to use

dense graded aggregate. Typical gradations are

near the 0.45 power curve but not right on it.

Its primary use is as a surface course for locationswith high traffic levels or when the potential for

rutting within the HMA layer exists.
http://training.ce.washington.edu/wsdot/modules/02_pavement_types/02-2_body.htmhttp://training.ce.washington.edu/wsdot/modules/09_pavement_evaluation/09-7_body.htmhttp://training.ce.washington.edu/wsdot/modules/09_pavement_evaluation/09-7_body.htmhttp://training.ce.washington.edu/wsdot/modules/02_pavement_types/02-2_body.htm


47/66

47

Dense-graded mix

A dense-graded mix is a well-graded HMA

mixture intended for general use. When

properly designed and constructed, a dense-

graded mix is relatively impermeable.

They can further be classified as eitherfine-

graded or coarse-graded. Fine-graded mixes

have more fine and sand sized particles thancoarse-graded mixes
http://training.ce.washington.edu/wsdot/modules/03_materials/03-2_body.htmhttp://training.ce.washington.edu/wsdot/modules/03_materials/03-2_body.htmhttp://training.ce.washington.edu/wsdot/modules/03_materials/03-2_body.htmhttp://training.ce.washington.edu/wsdot/modules/03_materials/03-2_body.htm


48/66

48

Gap gradedMIX

Gap graded. Refers to a gradation that contains

only a small percentage of aggregate particles in

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

size range. Some PCC mix designs use gap

graded aggregate to provide a more economical

mix since less sand can be used for a given

workability. HMA gap graded mixes can beprone to segregation during placement.


49/66

49

A gap-graded HMA

SMA is a gap-graded HMA that is designed tomaximize deformation (rutting) resistance anddurability by using a structural basis of stone-on-

stone contact. Because the aggregates are all in contact, rut resistance

relies on aggregate properties rather than asphalt binderproperties. Since aggregates do not deform as much asasphalt binder under load, this stone-on-stone contact

greatly reduces rutting. SMA is generally moreexpensive than a typical dense-graded HMA because itrequires more durable aggregates, higher asphalt contentand, typically, a modified asphalt binder.
http://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htm


50/66

50

Use

Improved rut resistance and durability.

Therefore, SMA is almost exclusively used

for surface courses on high volume

interstates ROADS


51/66

51

SMA Gap graded


52/66

52

Open-graded HMA

An open-graded HMA mixture uses open-

graded aggregate and is designed to be

water permeable (dense-graded and SMAmixes usually are not permeable)

Typically result in smoother surfaces than

dense-graded HMA. Their high air voidstrap road noise and significantly reduce

tire-road noise.
http://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htmhttp://training.ce.washington.edu/VSL/aggregate_tests/gs/gs_background.htm


53/66

53

Dense vs Open graded mix


54/66

54

(NMAS)

Nominal maximum aggregate size

(NMAS). The largest sieve that retains

some of the aggregate particles butgenerally not more than 10 percent by

weight. We can define nominal maximum

aggregate size as "one sieve size largerthan the first sieve to retain more than 10

percent of the material"


55/66

55

Gradation Specification

Gradation and size are specified by a series of

gradation control points

Control points give the allowable percent passing

(or retained) range for given sieve sizes. For instance, the gradation control points for a

0.5 inch (12.5 mm) mix specify a maximum of

58% passing and a minimum of 28% passing on

the No. 8 (2.36 mm) sieve.


56/66


57/66

57

HMAVariables

HMA is a rather complex material.

It must resist deformation and cracking, be

durable over time, resist water damage,provide a good tractive surface, and yet be

inexpensive, readily made and easily

placed


58/66

58

A HMA roadis it real??? Maui


59/66

59

Qualities of a well-made HMA mix Deformation resistance (stability). HMA

should not distort (rut) or deform (shove) undertraffic loading. HMA deformation is related toone or more of the following:

Aggregate surface and abrasion characteristics.Rounded particles tend to slip by one anothercausing HMA distortion under load while angular

particles interlock with one another providing a

good deformation resistant structure. Brittleparticles cause mix distortion because they tendto break apart under agitation or load.


60/66

60

Aggregate gradation

Gradations with excessive fines (either

naturally occurring or caused by excessive

abrasion) cause distortion because the largeamount of fine particles tend to push the

larger particles apart and act as lubricating

ball-bearings between these larger particles


61/66

61

Asphalt binder content

Excess asphalt binder content tends

to lubricate and push aggregate

particles apart making theirrearrangement under load easier.

The optimum asphalt binder content

as determined by mix design shouldprevent this.
http://training.ce.washington.edu/VSL/mix_design/bc/bc_overview.htmhttp://training.ce.washington.edu/VSL/mix_design/bc/bc_overview.htmhttp://training.ce.washington.edu/VSL/mix_design/bc/bc_overview.htmhttp://training.ce.washington.edu/VSL/mix_design/bc/bc_overview.htm


62/66

62

Asphalt binder viscosity

In the hot summer months, asphalt binder

viscosity is at its lowest and the pavement willdeform more easily under load. Specifying an

asphalt binder with a minimum high

temperature viscosity ensures enough high

temperature viscosity.


63/66

63

Fatigue resistance

HMA should not crack when subjected to repeated loadsover time. HMA fatigue cracking is related to asphalt

binder content and stiffness.

Higher asphalt binder contents will result in a mix that

has a greater tendency to deform elastically (or at leastdeform) rather than fracture under repeated load.

The use of an asphalt binder with a lower stiffness willincrease a mixture's fatigue life by providing greaterflexibility. However, the potential for rutting must also be

considered in the selection of an asphalt binder. Note thatfatigue resistance is also highly dependent upon therelationship between structural layer thickness andloading


64/66

64

Durability

HMA durability is related to one or more of thefollowing

oAsphalt binder film thickness around each

aggregate particle. If the film thicknesssurrounding the aggregate particles isinsufficient, it is possible that the aggregatemay become accessible to water through holesin the film. Water will displace the asphaltfilm and asphalt-aggregate cohesion will belost. This process is typically referred to asstripping.
http://training.ce.washington.edu/VSL/mix_design/bc/bc_background.htmhttp://training.ce.washington.edu/VSL/mix_design/bc/bc_background.htmhttp://training.ce.washington.edu/VSL/mix_design/bc/bc_background.htmhttp://training.ce.washington.edu/VSL/mix_design/bc/bc_background.htm


65/66

65

Air voids

Excessive air voids (on the order of 8

percent or more in a dense-graded HMA)increase HMA permeability.

oHMA mix design seeks to adjust items such as

asphalt content and aggregate gradation toproduce design air voids of about 4 percent.
http://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_wv.htmhttp://training.ce.washington.edu/VSL/introduction/intro/pvmt_mixtures.htmhttp://training.ce.washington.edu/VSL/introduction/intro/pvmt_mixtures.htmhttp://training.ce.washington.edu/VSL/introduction/intro/pvmt_mixtures.htmhttp://training.ce.washington.edu/VSL/introduction/intro/pvmt_mixtures.htmhttp://training.ce.washington.edu/VSL/mix_design/fundamentals/fundamentals_wv.htm


66/66

lab lecture 2 fin

Documents