1

1

Asphalt Materials 101

Aggregates and Mixes

Scott Shuler

2

The MIXWhat is It?

About 86%

About 10%

4%

Rocks

Asphalt

Air

3

Where We Get Rocks

Natural– Sand and Gravel– Quarry Stone

Artificial

Geology Sedimentary Igneous Metamorphic

How Rocks are Formed

1

2

3

2

4

Sedimentary Rock

Sedimentary

• Conglomerate• Sandstone• Siltstone• Shale

5

Igneous Rocks

Liquid Silicate – Magma– Extrusive

– Intrusive

6

Extrusive Igneous Rocks

4

5

6

3

7

Metamorphic Rocks

Formed from Sedimentary or Igneous Rocks

Re-crystallized by high temperature and pressure

8

Metamorphic Equivalents

Sediment Sedimentary Rock Metamorphic Rock

GravelSandClayLime deposits

ConglomerateSandstoneShaleLimestone

Gneiss and SchistQuartziteSlate and SchistMarble

Granite, Syenite Gneiss

Andesite Slate and Schist

Basalt Schist

Sedimentary

Igneous Metamorphic

9

Sand and Gravel

Water Deposits– Glacial – Alluvial – stream and river– Lacustrine - lakes– Marine – oceans

Wind Deposits– Eolian

7

8

9

4

10

Sand and Gravel Pit

11

Stone Quarry

12

Aggregate Sources

Colorado

Crushed Stone – 16 Locations

Sand & Gravel – 101 Locations

10

11

12

5

13

River Gravel Partially Crushed River Gravel

Crushing

14

Aggregate Gradation– The distribution of particle sizes expressed as a

percent of total weight.

– Determined by sieve analysis

Aggregate Sizes, aka. Gradation

15

Sieves Used for Construction

Opening is ¾” wide

4 Openings per inch

Dimensionedin Inches or mm

Numbered

13

14

15

6

Plotting Sizes

Grading Curves

0

20

40

60

80

100

0.001 0.01 0.1 1 10

Particle Size, mm

Pa

ss

ing

, %

Poorly graded

Well graded

200 4 3/8”

17

Better Asphalt Roads are:

Coarse

Medium

Fine

A Combination of an Asphalt Binder

And Crushed Rocks

18

These Individual Rock Sizes Will Not Make a Good Asphalt Mix Alone

but

A Combination Might

Coarse

Medium

Fine

16

17

18

7

19

What Combination Works?

Coarse Intermediate Fines

33.3% 33.3% 33.3%

20

Maximum Density for Aggregates

Goode and Lufsey, Bureau of Public Roads

p = 100d

D

0.45 p = percent material passing a given sieve d

D = Maximum aggregate size

21

To Build Better RoadsPurpose of Mixture Design

19

20

21

8

22

What a Mixture Design Does

Creates a Strong Pavement – HOW?– The Right Volumes of

About 86%

About 10%

4%

Rocks

Asphalt

Air

23

Rocks

Traffic Affects the Air Voids

Asphalt

86%

10%

Air 4%

Minivans, Cars

Heavier Traffic Squeezes Air Out

Air 3%

Light Trucks, Vans

2%

Semis

Until There is Less, and Less

24

And Finally…..

Rutting

22

23

24

9

25

Rocks

Asphalt

86%

10%

Air 4%

CarsLight Trucks Semis

Adjust Asphalt and Rocks for Traffic

4%4%

9% 8%

88%87%

26

Simulate Traffic in the Laboratory

Low Gyrations - Cars

Med Gyrations – Lt Trucks

High Gyrations - Semis

27

How Much Asphaltto get 4% Air Voids ??????

10

8

6

4

2

0

4.5 5.0 5.5 6.0 6.5

Air

Voi

ds,

%

Asphalt, %

5.0 5.3 5.7

As Traffic Increases

Decreases

The Key to Mixture Design

25

26

27

10

28

We Must Know TrafficTo Know Asphalt %

10

8

6

4

2

0

4.5 5.0 5.5 6.0 6.5

Air

Voi

ds,

%

Asphalt, %

5.7

Let’s Design for Residential Streetwith 100 cars per day

29

Would this DesignWork on I-25??????

10

8

6

4

2

0

4.5 5.0 5.5 6.0 6.5

Air

Voi

ds,

%

Asphalt, %

5.7

1.8

NO!1.8% Air Voids Is Too Low

5.0

Decrease AC%

30

Superpave Mix Design

Gyratory Compactor Simulates Traffic Better Than Hammer

Volumetric Analysis (Voids)

Adjusts AC% to Traffic and Climate

28

29

30

11

31

Volumetric Analysis

Air VoidsVMA (Voids in Mineral AggregateVMA Filled with AC%Absorption

32

VMA Concept

Durability – Enough Binder… Not Too Much

About 86%

About 10%

4%

Rocks

Asphalt

Air

VMA = Effective Asphalt + Air

Voids are Just Full Enough

33

If VMA Too Low

Durability Suffers…Not Enough Coating

About 88%

About 8%

4%

Rocks

Asphalt

Air

VMA = Effective Asphalt + Air

Voids are Not Full Enough

31

32

33

12

34

If VMA Too High

Stability Suffers…Too Much Coating

About 84%

About 12%

4%

Rocks

Asphalt

Air

VMA = Effective Asphalt + Air

Voids are Too Full of Asphalt

35

Select Asphalt and Aggregates

Aggregates

1. Coarse Aggregate Angularity (fractured faces)2. Fine Aggregate Angularity3. Flat and Elongated Particles4. Clay Content (sand equivalent)5. Toughness (LA Abrasion)6. Soundness7. Deleterious Stuff8. Gradation

36

Evaluate Compaction

Air

Vo

ids,

%

0

Low Med High

Compaction

Ninit

Ndes

Nmax

11

5

2

3

34

35

36

13

37

StabilityPressure

Load

RubberAllows LateralMovement

38

Optimum AC%

5.3

6

4

2

0

45

35

25

% Voids

Stability, %

4.5 5.0 5.5 6.0

minimum

39

Verify 5.3% AC

VMA OK?

VFA OK?

Stability OK?

Moisture Sensitivity OK?

37

38

39

14

40

Let’s Pave!

41

Questions...

40

41