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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 1
Construction
Methods and Materials II
Asphalt and Asphalt
Mixtures
Construction Methods & Materials II
2
Introduction
US petroleum consumption:
20 million barrels/day
149 operating refineries in the US
Over 600 million barrels/year of asphalt is produced and marketed.
About 85 to 90% of this is asphalt for paving.
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 2
Construction Methods & Materials II
Introduction One barrel of crude
oil equals 42 gallons (or 159 liters).
Typical products from a barrel of crude oil is shown here.
The amount of each product that can be derived from crude vary depending on the crude source.
3Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), aka propane or butane.
Construction Methods & Materials II
4
Bituminous Materials Topics History
Introduction
Refiners
ExxonMobil—a global supplier
Types of asphalt products
Uses of asphalt
HMA pavement construction
Characterization of asphalt binders
Superpave HMA mix design
Other asphalt uses
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 3
Construction Methods & Materials II
History of and Use of Bituminous Materials
Use in Ancient Times
From 6000 B.C. through Columbus voyage
Mastic in statuary, pottery, and ornaments -6000 B.C.
Caulking for ships - 600 B.C.
Embalming purposes - 2500 to 1500 B.C.
Paved streets and constructed walls of bricks set in asphalt - 600 B.C.
Medicinal - 1400 to 600 B.C.
New World - Christopher Columbus caulked the seams of the ship with Trinidad asphalt - 1498
5•Mastic asphalt is a sticky, black and highly viscous liquid.
Construction Methods & Materials II
History of and Use of Bituminous MaterialsUse in Modern Times
Began in 1700's Tar in roofing in Germany - 1730
Seyssel asphalt deposit - marketed for surfacing floors, bridges, sidewalks, and waterproofing - 1790
McAdam develops compacted layered rock design-unbound-1817
Coal tar used in tar-macadam pavement in Gloucestershire-1832
Rock asphalt from Europe used in New York - 1870
Barber Asphalt Paving Co. develops equipment and processes for sheet asphalt paving - 1899
Asphalt produced commercially from petroleum - 1902
Hot mix plants developed - 1910
Mix Designs developed - 1930's6
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 4
Construction Methods & Materials II
Terminology
Bitumen
Black or dark-colored cementitious substances
Solid, semisolid, or viscous
Natural or manufactured
High molecular weight (complex) hydrocarbons
Soluble in carbon disulfide
asphalt
tars
pitches7
Construction Methods & Materials II
Terminology
Asphalt Cement - asphalt refined to meet specifications
Asphalt Concrete - mixture of asphalt cement and aggregate
Cutback Asphalt - liquid asphalt - blend of asphalt cement and petroleum solvents
Emulsified Asphalt - liquid asphalt - blend of asphalt cement, water, and emulsifying agent
8
Bitumen Material
Hardness(Ambient Temp.) Source
Asphalt Variable Natural or Fractional Distillation of Petroleum
Tar Liquid or Semi-Liquid
Destructive Distillation of Coal or other Organic Matter
Pitch Hard - Liquefies with Heat
Fractional Distillation of Tar
Coal Tar Hard - Liquefies with Heat
Destructive Distillation of Coal
A suspension of tiny droplets of one liquid in a second liquid.
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 5
Construction Methods & Materials II
Tars and Pitches Most tars produced from coal
Coal heated to produce coke
Lighter fractions vaporized
These lighter fractions collected and distilled to create desired grades
Road Tars
Resistant to the dissolving actions of petroleums
Road tar concrete on airfields at refueling points
In emulsions, surface sealant on parking lots
Built-up roofing
Waterproofing of foundations, retaining walls, dams, etc.
9
Construction Methods & Materials II
Natural Asphalt Same material as petroleum
Lighter fractions removed by natural processes
Earliest use of asphalt were from natural deposits
1. Native or Lake Asphalts
Asphalt occurring in nature, open deposits
Up to 65% asphalt
Trinidad, West Indies
Bermudez, Venezuela
La Brea Atar@ pits near Los Angeles
2. Rock Asphalts
Porous rock impregnated with natural asphalt
sandstone
limestone
2 to 20% bitumen
Seyssel asphalts from France
Uvalde, Texas rock asphalt10
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 6
Construction Methods & Materials II
11
Natural sources
Trinidad Lake Asphalt
Primary world asphalt supplier 1875 - 1900
Construction Methods & Materials II
12
Natural sources
Gilsonite
Naturally occurring asphalt in Utah
Picture from Asphalt Associates, Ltd.
Gilsonite, also known as asphaltum, is a bitumen-impregnated rock (asphaltite) mainly found in the Uintah Basin of Utah and Colorado. It is a naturally occurring solid hydrocarbon bitumen.
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 7
Construction Methods & Materials II
Production of Asphalt from Petroleum
Most asphalts used in construction are from fractional distillation of crude oils in refineries
Common Refinery Products
Straight run gasoline
Naphtha
Kerosene distillate
Diesel fuel
Lubricating oils
Heavy residue
13
Construction Methods & Materials II
Production of Asphalt from Petroleum Asphalts
Come from heavy residue
Second stage distillation completed on heavy residue
vacuum tower fractionation
heavy residue again heated and distilled
Produces
additional lighter oils
asphalts of desired consistencies
Air Blowing Air-blowing modifies asphalt cements for roofing applications
Produces stiffer asphalt that retains that stiffness at higher temperatures
A type of polymerization
14
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 8
Construction Methods & Materials II
Asphalt Cement (aka Paving Asphalt)
Asphalt cement is a type of asphalt that is very sticky and highly viscous, specially prepared with the quality and consistency required in the manufacture of asphalt pavements (hot-mix pavements). Asphalt cements are used because
Ability to coat aggregate
Act as a binder between aggregate particles
Water resistance
Typical uses
road construction
roofing applications
roofing shingles
water proofing applications
coatings15
Construction Methods & Materials II
Liquid Asphalts Asphalt cements are stiff at normal temperatures
Softening by heating not feasible in all cases
Liquid asphalts are liquid at normal ambient temperatures
Two Types - both produced from asphalt cement
Cutback Asphalts
Emulsified Asphalts
1. Cutback Asphalts
Asphalt cement recombined with diluent (also called solvent, distillate, or cutter stock)
Diluent evaporates leaving original asphalt cement
Adding sufficient diluent produces liquid asphalt
Type of diluent determines how rapidly it will evaporate
16
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 9
Construction Methods & Materials II
Liquid Asphalts2. Emulsified Asphalts
Asphalt cements mixed with emulsifying agent and water in colloidal mill
Water is continuous phase (at least 25%)
Asphalt is the discontinuous phase
Emulsifying agent places electrical charge around each droplet of asphalt
negative (anionic)
positive (cationic)
Since like electrical charges repel, droplets stay suspended in continuous water phase
Stable situation until disrupted by
mixing with aggregates
evaporation of water17
Construction Methods & Materials II
ExxonMobil Complex—Baytown, Texas
Globally produces 6 million tons (or about 30 million barrels) of asphalt per year which is marketed in 30 countries.
Only 19 of ExxonMobil’s 49 refineries can produce asphalt.
18
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 10
Construction Methods & Materials II
ExxonMobil Complex—Baytown, Texas
19
Construction Methods & Materials II
ExxonMobil Complex—Baytown, Texas
20
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 11
Construction Methods & Materials II
ExxonMobil Tankers Offloading Crude —Baytown, Texas
21
Construction Methods & Materials II
22
Types of asphalt products
Distillation of crude oil
Asphalt cements
Cutback asphalts
Slow-curing
Medium-curing
Rapid-curing
Emulsified asphalts
Less used today due to environmental impacts.
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 12
Construction Methods & Materials II
Uses of asphalt
The primary one of interest for CM 323 is hot mix asphalt (or hot mix asphalt concrete).
WSDOT pavements (total of 18,000 lane-miles)
HMA 60%
Bituminous surface treatment (BST) 27%
PCC 13%
23
Construction Methods & Materials II
24
HMA pavement construction
Pavement cross sections
Overview of HMA plant operations
Trucks
Pickup machines
Laydown machines
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 13
Construction Methods & Materials II
Bituminous Surface Treatment
HMA
25
Pavement cross sections
HMA Bituminous Surface Treatment
12-ft
0.5 to 1-in.
Thickness ranges from 2 in. to over 1 ft.
Construction Methods & Materials II
HMA and Asphalt Binders
26
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 14
Construction Methods & Materials II
Bituminous Surface Treatment (BST)
(aka seal coat or chip seal)
Construction Methods & Materials II
Production of HMA (plant operations)
28
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 15
Construction Methods & Materials II
29
Plant—aggregate conveyors
Construction Methods & Materials II
30
Plant—mixing drum
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 16
Construction Methods & Materials II
31
Plant—mixing drum
Construction Methods & Materials II
32
Plant--burner
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 17
Construction Methods & Materials II
33
Plant—aggregate storage bins
Construction Methods & Materials II
34
Plant—adding RAP to drum and RAP stockpile
RAP: Recycled Asphalt Pavement
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 18
Construction Methods & Materials II
35
Plant—storage silos
Construction Methods & Materials II
36
Plant—control house
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 19
Construction Methods & Materials II
37
Trucks—Flowboy
Construction Methods & Materials II
38
Trucks—Belly Dump
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 20
Construction Methods & Materials II
39
Remixing—Blaw-Knox MC-30
Construction Methods & Materials II
40
Remixing—Roadtec Shuttle Buggy
Photo courtesy of Roadtec
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 21
Construction Methods & Materials II
41
Remixing—Roadtec Shuttle Buggy
Construction Methods & Materials II
42
Remixing—Roadtec Shuttle Buggy
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 22
Construction Methods & Materials II
43
Infrared Image—End Dump
Route: SR-203
Section:
King/Snohomish
Line to SR-2
Binder: PG 64-22
Mix: Class A
Haul Time: 30
minutes
Haul Length: 18
miles
Plant Temp: 290°F
Mat Temp: 255°F
Comments:
Thermal
differential of 140
degrees between
crust and internal
mix.
290.5
148.9
>302.0°F
<68.0°F
80 .0
100 .0
120 .0
140.0
160 .0
180 .0
200.0
220.0
240.0
260.0
280.0
300.0
Construction Methods & Materials II
Trucks—end dump into paving machine
44
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 23
Construction Methods & Materials II
Trucks—end dump into paving machine
45
Construction Methods & Materials II
Infrared Image—End Dump
46
Route: SR-203
Section: King/Snohomish Line to
SR-2
Binder: PG 64-22
Mix: Class A
Haul Time: 30 minutes
Haul Length: 18 miles
Plant Temp: 290°F
Mat Temp: 255°F
Comments: Temperatures and
corresponding densities.
94.6%
201.2
89.8%
154.392.7%
176.693.7%
194.992.4%
204.387.8%
206.0
*>237.6°F
*<68.0°F
80 .0
100 .0
120 .0
140.0
160 .0
180 .0
200.0
220.0
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 24
Construction Methods & Materials II
47
Finish roller on I-90 near Vantage
Construction
Methods and Materials II
HMA PLACEMENT
Hauling
Placement
Compaction
48
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 25
Construction Methods & Materials II
49
Different types of trucks are used
Construction Methods & Materials II
50
Self Propelled Paver
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 26
Construction Methods & Materials II
51
Self Propelled Paving Machine
THE BASIC PRINCIPLE HAS NOT CHANGED MUCH SINCE THE 1930’s
Construction Methods & Materials II
52
HMA Flow
Self Propelled Paving Machine
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 27
Construction Methods & Materials II
53
Compaction
GOOD COMPACTION LEADS TO GOOD PERFORMANCE
Compaction is the single most important factor that affects the ultimate performance of an HMA pavement.
Construction Methods & Materials II
Reason For Compaction
To prevent further compaction
To provide shear strength or resistance to rutting
To ensure the mixture is waterproof
To prevent excessive oxidation of the asphalt binder
54
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 28
Construction Methods & Materials II
55
Temperature is critical
Construction Methods & Materials II
One of the most important factors is the mix temperature
Too cold and the mix cannot be compacted
Too hot and the mix will not support the rollers
56
Temperature is critical
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 29
Construction Methods & Materials II
57
Vibratory Roller
Construction Methods & Materials II
Vibratory Roller Vibratory rollers come in a variety of configurations.
Single drum and double drum.
These rollers can be operated in any one of three modes:
static (with the vibrators off),
with one drum vibrating and one static, and
with both drums vibrating.
These rollers provide two types of compactive force to the HMA - static force and dynamic (impact) force.
The static force is caused by the weight of the roller and frame.
The dynamic force is caused by the impact produced by a rotating eccentric weight located inside the drum or drums. As the eccentric weight rotates about the shaft inside the drum, a dynamic force is produced.
58
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 30
Construction Methods & Materials II
59
Pnuematic Roller
Construction Methods & Materials II
Pnuematic Roller
Most pneumatic rollers are operated as intermediate rollers - behind a vibratory or static steel wheel breakdown roller and in front of a static wheel finish roller.
The compactive force is a function of the wheel load of the machine, the tire pressure, the tire design and the depth of penetration of the tires into the mix.
The tire pressures range from 60 to 120 psi and the minimum weight is 15 tons. For a tender mix a lower tire pressure should be used. For a stiff mix a higher tire pressure should be used.
60
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 31
Construction Methods & Materials II
61
Steel Wheeled Roller
Steel wheel rollers range from 3 to 14 tons.
They can either be three wheel here or tandem.
Construction Methods & Materials II
62
Extracting A Core
Cores are taken for density determination and thickness. They are usually cut to obtain a sample of the layer being
placed. The bulk specific gravity of the core is determined and
using that with the maximum specific gravity it is possible to determine the percent compaction.
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 32
Construction Methods & Materials II
63
Cost of HMA
Construction Methods & Materials II
64
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 33
Construction Methods & Materials II
Primary Reference Information
Pavement Interactive Asphalt
(http://www.pavementinteractive.org/article/materialsasphalt/)
Asphalt tests (http://www.pavementinteractive.org/category/testing/asphalt-tests/?show=all)
Superpave mix design (http://www.pavementinteractive.org/category/testing/asphalt-tests/?show=all)
Chip seals or BSTs (http://www.pavementinteractive.org/article/bituminous-surface-treatments/)
65
Construction Methods & Materials II
66
Characterization of asphalt binders
Prior to PG (Performance Graded) grades, asphalt binder specifications typically were based on measurements of viscosity, penetration, ductility, and softening point temperature.
Performance Graded (PG) Binder (a.k.a. Asphalt Cement)
Penetration Measurement
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 34
Construction Methods & Materials II
67
Characterization of asphalt binders
Softening Point TemperatureDuctility Test
Viscosity TestViscosity denotes the fluid property of bituminous material and it is a measure of resistance to flow.
Construction Methods & Materials II
Manufactured sources
Crude oil
Crude oil surpassed natural sources in 1907
Atmospheric
DistillationVacuum
Distillation
Vacuum
Residual
Conversion Unit
Asphalt
CrudeOil
PrincipalRefineryProducts
Lube oilsFuel oilsSolventsWaxesGrease
GasolineJet FuelDieselKeroseneChemicals
68
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 35
Construction Methods & Materials II
Crude oil make-up
26
28
30
7
10
16
14
20
21
33
58
27
1
6 3
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Boscan Venezuela Arabian Heavy Nigerian Light
Crude Oil Type
Perc
en
t
Gasoline
Kerosene
Light Gas Oil
Heavy Gas Oil
Bitumen Residuals
69
Construction Methods & Materials II
Crude oil
Utah West Texas North Sea
Sudan Illinois
Source: http://www.chevron.com 70
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 36
Construction Methods & Materials II
71
Asphalt characteristics
Thermoplastic material
Properties change with temperature
Important characteristics
High temperature: construction workability
Medium temperature: deformation resistance
Low temperature: thermal cracking resistance
Construction Methods & Materials II
72
Low Temp Test
Range
Middle Temp Test
Range
High Temp Test
Range
PG Test Temperatures
The properties of asphalt are susceptible to change as temperature changes.
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 37
Construction Methods & Materials II
Viscosity
Quantity that describes a fluid resistance to flow.
There exist several different test methods for measuring viscosity
73
Construction Methods & Materials II
What is a Poise?
74
It is a measure of viscosity.
Units: dyne-second/cm2
A dyne is 10-5 Newtons.
Named after a French physician, Jean Louis Poiseuille (1799-1869).
A commonly used measure is centipoises (or 1/100 P).
1 Pa·s = 1,000 cP or
1 Poise = 100 cP = 0.1 Pa·s
And centistokes = centipoises/specific gravity
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 38
Construction Methods & Materials II
75
A Sample of Viscosities in cP
Material Viscosity (cP)
PG Binders @ 135°C(AASHTO M320 and ASTM D4402)
3,000 max
Venezuelan Orinoco heavy oil @ 53°C
1,500—3,000
Motor oil @ SAE 10 @ 20°C 65
Motor oil @ SAE 30 @ 20°C 150—200
Motor oil @ SAE 40 @ 20°C 320
Bunker C Fuel Oil
(ocean vessels but often quoted in centistokes)
Gasoline 0.6
Water 1
Construction Methods & Materials II
76
Material Viscosity (cP)
Olive Oil @ 25°C 80
Peanut Butter 250,000
Tar @ 20°C 30,000,000
Blood @ 20°C 3 to 4
Honey @ 20°C 10,000
Ketchup @ 25°C 50,000 to 100,000
A Sample of Viscosities in cP
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 39
Construction Methods & Materials II
77
Asphalt grading
Grading
Shorthand way of describing asphalt physical properties
Performance Grading (PG) System
Specifications account for:
Local environment
Traffic loading (somewhat)
WSDOT asphalt binder grading in accordance with AASHTO M320 (or ASTM D 6373)
Construction Methods & Materials II
ASTM D6373
78
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 40
Construction Methods & Materials II
79
PG System
Nomenclature
PG 64-22
Performance grading
system
Expected average 7-day maximum
pavement temperature = 64°C
Expected minimum
pavement temperature =
- 22°C
Construction Methods & Materials II
80
PG Grades
Temperatures listed in Centigrade
Increments of 6°C
PG 46-34
PG 46-40
PG 46-46
PG 52-10
PG 52-16
PG 52-22
PG 52-28
PG 52-34
PG 52-40
PG 52-46
PG 58-16
PG 58-22
PG 58-28
PG 58-34
PG 58-40
PG 64-10
PG 64-16
PG 64-22
PG 64-28
PG 64-34
PG 64-40
PG 70-10
PG 70-16
PG 70-22
PG 70-28
PG 70-34
PG 70-40
PG 76-10
PG 76-16
PG 76-22
PG 76-28
PG 76-34
PG 82-10
PG 82-16
PG 82-22
PG 82-28
PG 82-34
Cold climate Hot climate
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 41
Construction Methods & Materials II
Washington Base PG Binders
PG 64-22
PG 64-28
81
Construction Methods & Materials II
82
California Base PG Binders
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 42
Construction Methods & Materials II
83
PG Binder Grade Determination
Must account for:
Expected traffic loading
Expected traffic speed
And…WSDOT uses 4 types of HMA mixes which are based on nominal maximum aggregate size (NMAS): 3/8-inch, ½-inch, ¾-inch, and 1-inch.
Construction Methods & Materials II
84
PG Binder Grade Determination
Base PG grades with no adjustment for traffic speed or ESAL level Western Washington: PG 64-22
Eastern Washington: PG 64-28
Adjustment for traffic speed Standing (0 to 10 mph): Increase PG high temperature by 2 grades (12°C)
Slow (10 to 45 mph): Increase PG high temperature by 1 grade (6°C)
Free flow (45+ mph): No adjustment
Adjustment for traffic loading (20 year basis) 10,000,000 ESALs: No adjustment
10,000,000 to 30,000,000 ESALs: Consider an increase in the PG high temperature by 1 grade (6°C)
30,000,000 ESALs: Increase PG high temperature by 1 grade (6°C)
Maximum PG high temperature: The maximum increase in the PG high temperature for any combination of conditions will not exceed a 2 grade increase (or 12°C) over the base PG grade.
Source: WSDOT Pavement Policy, June 2011
ESAL: Equivalent Single Axle Load
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 43
Construction Methods & Materials II
85
PG Specification Table
Construction Methods & Materials II
86
PG Table
Rutting
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 44
Construction Methods & Materials II
87
PG Table
Fatigue Cracking
Construction Methods & Materials II
88
PG Table
Low Temperature Cracking
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 45
Construction Methods & Materials II
89
Summary
Asphalt description
Asphalt sources
Asphalt characteristics
Temperature susceptibility
Binder grading
Performance Grading (PG) system
Construction
Methods and Materials II
90
Mix Design
Asphalt and Asphalt Mixtures
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 46
Construction Methods & Materials II
91
Photos fromChina by Yiming
Construction Methods & Materials II
92
Bituminous Materials Topics
Introduction
Refiners
US Oil and Refining—a producer of asphalt binders
ExxonMobil—a global supplier
Types of asphalt products
Uses of asphalt
HMA pavement construction
Characterization of asphalt binders
Superpave HMA mix design
Other asphalt uses
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 47
Construction Methods & Materials II
93
Superpave HMA mix design
Hot mix asphalt (HMA) description
HMA mixture design
Methods
Volumetrics
Job mix formula
Example
Construction Methods & Materials II
Hot Mix Asphalt (HMA)
94
Distinguished by: Materials (asphalt binder and
aggregate)
Mix design methods
Elevated mixing temperature
Other names: Asphalt concrete (AC)
Blacktop
Bitumen
Bituminous concrete
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 48
Construction Methods & Materials II
HMA Description (dense graded)
Construction Methods & Materials II
HMA Description
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 49
Construction Methods & Materials II
HMA Description
Construction Methods & Materials II
HMA Description
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 50
Construction Methods & Materials II
99
HMA Description
Construction Methods & Materials II
Types of HMA
(VMA = voids in the mineral aggregate)
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 51
Construction Methods & Materials II
101
This is the type of HMA you mostly see
in use in WA.
The best performing type of HMA as a surface (wearing)
course.
Open graded mixes great for safety but quickly damaged by studded tires and
chains.
Construction Methods & Materials II
Hot Mix Asphalt
Described by:
Maximum aggregate size
Aggregate gradation
Asphalt binder
Asphalt binder content
Section 1
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 52
Construction Methods & Materials II
Maximum Aggregate Size
Largest aggregate “diameter” as defined by:
Maximum SizeThe smallest sieve through which 100 percent of the aggregate sample particles pass
Nominal Maximum SizeThe largest sieve that retains some of the aggregate particles but generally not more than 10 percent by weight
103
Construction Methods & Materials II
Gradation
Dense graded
Most common
Gap graded
Stone matrix asphalt (SMA)
Open graded
Used as a surface course in many areas
Uniformly graded
Not used as a construction material
104
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 53
Construction Methods & Materials II
90105
Construction Methods & Materials II
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 54
Construction Methods & Materials II
Asphalt Binder
Choose asphalt binder grade
Select a grade based on:
Design pavement high temperature
Design pavement low temperature
Adjust based on reliability
Adjust based on traffic speed and loading
Add modifiers to achieve certain properties
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Construction Methods & Materials II
Asphalt Binder Content
Ratio of asphalt binder to aggregate
Determining this is a key component of mix design
Typical binder contents
Usually expressed as a percentage by weight of total mixture
Dense graded HMA = 4.5 to 6.0%
SMA = 6.0 to 8.0%
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 55
Construction
Methods and Materials II
Superpave Mix DesignProcedure
Construction Methods & Materials II
Superpave Asphalt Pavement
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 56
Construction Methods & Materials II
Superpave History
Under the Strategic Highway Research Program (SHRP), an initiative was undertaken to improve materials selection and mixture design by developing:
1. A new mix design method that accounts for traffic loading and environmental conditions.
2. A new method of asphalt binder evaluation.
3. New methods of mixture analysis.
When SHRP was completed in 1993 it introduced these three developments and called them the Superior Performing Asphalt Pavement System (Superpave).
Although the new methods of mixture performance testing have not yet been established, the mix design method is well-established.
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Construction Methods & Materials II
Superpave Procedure
The Superpave mix design method consists of 7 basic steps:
1. Aggregate selection.
2. Asphalt binder selection.
3. Sample preparation (including compaction).
4. Performance Tests.
5. Density and voids calculations.
6. Optimum asphalt binder content selection.
7. Moisture susceptibility evaluation.
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 57
Construction Methods & Materials II
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Asphalt-Aggregate Ratio
Mix Design = determining this ratio
Procedure:
Select aggregate gradation
Select asphalt binder
Make samples
Test samples for key parameters
Test results predict field performance
Construction Methods & Materials II
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Concepts
We design volume but measure mass
Specific gravity is important Converts mass to volume
Constituent
Typical Values
By Total Volume By Total Mix Weight
Air 4% 0%
Asphalt 10% 5%
(Range 4% to 6%)
Aggregate 86% 95%
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 58
Construction Methods & Materials II
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Variables
Aggregate
Asphalt binder
Ratio of aggregate to asphalt binder
Construction Methods & Materials II
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Goals
Stability (deformation resistance)
Durability
Fatigue resistance
Ductility (low temp. cracking resistance)
Moisture damage resistance
Skid resistance
Workability
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 59
Construction Methods & Materials II
Select Aggregate
Must meet:
Consensus requirements
Source properties
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Construction Methods & Materials II
Select Asphalt Binder
Almost always done to local standard as illustrated by WSDOT criteria
Easier to follow in specifications
Easier for suppliers
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 60
Construction Methods & Materials II
Select Aggregate Gradation
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Source: WSDOT SS, 9-03.8(6)
Construction Methods & Materials II
Design Aggregate Structure
Not many formal procedures to do this
Typical Superpave aggregate structures create quarry waste
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 61
Construction Methods & Materials II
Select Asphalt Binder Content
Level of sample compaction is critical
Bleeding Raveling122
Construction Methods & Materials II
First, define VMA and VFA
VMA: % of total volume in a compacted HMA mix due to
1) air voids and
2) the volume of the binder not absorbed into the aggregate (i.e., the space between the aggregate particles).
VFA: % of VMA filled with asphalt binder.
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VMA: Voids in the Mineral AggregateVFA: Voids Filled with Asphalt
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 62
Construction Methods & Materials II
VMA: Voids in the Mineral AggregateVFA: Voids Filled with Asphalt 124
Construction Methods & Materials II
125
VMA: Voids in the Mineral Aggregate
VFA: Voids Filled with Asphalt
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 63
Construction Methods & Materials II
Conduct Performance Tests
There are none for Superpave right now
Agencies typically use
Moisture susceptibility test
Laboratory wheel tracking devices
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Construction Methods & Materials II
Important Volumetric Properties
Tests run on compacted samples Mixture specific gravity (Gmb)
Test run on loose mix (uncompacted) Theoretical maximum specific gravity (Gmm)
Often called “Theoretical maximum density” Often called “Rice density”
Calculated volumes (based on above tests) Air voids (Va) Voids in the mineral aggregate (VMA) Voids filled with asphalt (VFA)
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 64
Construction Methods & Materials II
1. HMA Bulk Specific Gravity (Gmb) – Ratio of the weight of a unit volume of compacted HMA mixture to the weight of an equal volume of water (includes permeable voids as part of the volume).
2. HMA Maximum Theoretical Specific Gravity (Gmm) – Ratio of the weight of a unit volume of uncompacted HMA mixture to the weight of an equal volume of water (includes permeable voids as part of the volume). This value is often referred to as the “Rice” gravity.
3. Voids in the Total Mix (VTM) – Also known as air voids. Ratio of the volume of voids in a compacted mixture to the total compacted mixture volume.
4. Voids in the Mineral Aggregate (VMA) – Volume of voids and effective binder in a compacted HMA mixture.
5. Voids Filled with Asphalt (VFA) – The percentage of VMA that is filled with binder.
6. Total Binder Content (Pb) – Total amount of binder in an HMA mixture expressed as a percent of the total mixture weight. It can also be expressed as percent of aggregate weight.
7. Percent Binder Absorbed (Pba) – Amount of binder absorbed by the aggregate in an HMA mixture. It is usually expressed as a percentage of the total aggregate weight.
8. Effective Binder Content (Pbe) – Total binder content less the absorbed binder content.
9. Bulk Density – Terminology loosely used in the industry. To obtain the bulk density, multiply the Gmb by 62.4 pcf.
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Hot-Mix Asphalt Definitions
Construction Methods & Materials II
Hot-Mix Asphalt - Equations
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The pycnometer (from the Greek puknos, meaning "density", also called pycnometer or specific gravity bottle),
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 65
Construction Methods & Materials II
Hot-Mix Asphalt - Equations
130
Ps = % aggregate by weight of mix
Gsb = aggregate specific gravity
Gmb = mix specific gravity,
Gmm = theoretical maximum specific gravity
(zero air voids)
Construction Methods & Materials II
Hot-Mix Asphalt - Equations
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 66
Construction Methods & Materials II
Equations Air voids
VMA
VFA
100
mm
mbmm
aG
GGV
100
11
sb
bmb
G
PGVMA
sb
smb
G
PGVMA 100
VMA
VVMAVFA a
100T
V
aV
VV
Pb = % asphalt binder by weight of mix, Ps = % aggregate by
weight of mix
Gsb = aggregate specific gravity, Gmb = mix specific gravity,
Gmm = theoretical maximum specific gravity (zero air voids).132
Construction Methods & Materials II
Develop Job Mix Formula (JMF)
End result of mixture design
A specification (along with tolerances) used for plant production of HMA
Cannot be significantly altered without another mix design
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 67
Construction Methods & Materials II
Job Mix Formula (JMF)
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 68
Construction Methods & Materials II
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 69
Construction Methods & Materials II
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3 Basic Lab Compaction Methods
Marshall Method
Hveem Method
Superpave Method
All use the same basic procedure
This one exists in CM 323 lab
Most widely used today
No longer used—RIP
Construction Methods & Materials II
Prepare Trial Blends
Goal: usually about 4% air voids (why 4%?)
Achieves most objectives satisfactorily
Adding Asphalt Binder Pouring out the mix
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 70
Construction Methods & Materials II
Compact Samples
Simulates field compaction by rollers
Simulation is fair to poor
Marshall Method140
Construction Methods & Materials II
Compact Samples
Simulates field compaction by rollers
Simulation is fair to poor
Superpave MethodHveem Method 141
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 71
Construction Methods & Materials II
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Compact Samples
Height2.5 inches
Diameter4 inches
Marshall & HveemSuperpave
Height4.5 inches
Diameter6 inches
Construction Methods & Materials II
Test Samples
Measure volume properties (volumetrics)
Containers Used to Agitate and Draw a Vacuum on Submerged TMD Samples
TMD: Theoretical Mass Density 143
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 72
Construction Methods & Materials II
Predict how they will perform in the field
Marshall Stability and Flow Test
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Test Samples
Construction Methods & Materials II
Air voids = Va = VV/VT = (Gmm – Gmb)/Gmm = (2.513 –
2.371)/2.513 = 0.0565 or 5.6%
VMA = 1 – (Gmb(1 – Pb)/Gsb) = 1 – (2.371(1 - 0.049)/2.691)
= 0.162 = 16.2%
VFA = (VMA – Va)/VMA = (0.162 – 0.056)/0.162 = 0.654 =
65.4%
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Example AGiven:
Bulk specific gravity = 2.371 (Gmb)
Theoretical maximum specific gravity = 2.513 (Gmm)
Aggregate specific gravity = 2.691 (Gsb)
Asphalt content = 4.9% (Pb)
Find air voids, VMA and VFA.
VMA: Voids in the Mineral AggregateVFA: Voids Filled with Asphalt
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
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Winter Quarter 2019 73
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Example BAn HMA pavement was placed 6 months ago and is already
showing signs of rutting. Several cores were taken from the
pavement in question and the following values were
obtained from laboratory tests:
Asphalt content by ignition oven: 5.9% (Pb)
Theoretical maximum specific gravity: 2.567 (Gmm)
Bulk specific gravities on 3 cores: 2.498, 2.501, 2.490
Aggregate specific gravity = 2.690 (Gsb)
The job mix formula called for:
Asphalt content = 5.6 % ± 0.3%
VMA = must be > 14.0%
VFA = between 65% and 75%
Construction Methods & Materials II
Example B (continued)Pb: 5.9%
Gmm: 2.567
Gmb: 2.498, 2.501, 2.490
Gsb = 2.690
Job mix formula: Asphalt content = 5.6% ± 0.3%
VMA = must be > 14.0%
VFA = between 65% and 75%
Air voids = VV/VT = (Gmm – Gmb)/Gmm = (2.567 – 2.498)/2.567 = 0.0269 or
2.7% (others are 2.6% and 3.0%)
VMA = 1 – (Gmb(1 – Pb)/Gsb) = 1 – (2.498(1 - 0.059)/2.690) = 0.1262 =
12.6% (others are 12.5% and 12.9%)
VFA = (VMA – Va)/VMA = (0.1262 – 0.0269)/0.1262 = 0.7868 = 78.7%
(others are 79.5% and 76.7%)
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 74
Construction Methods & Materials II
Superpave Mix Design in the Pavement Interactive
Refer to the article “Superpave Mix Design” in the Pavement Interactive Webpage.
http://www.pavementinteractive.org/article/superpave-mix-design/
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Construction Methods & Materials II
Superpave Mix Design in the Pavement Interactive
149
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 75
Construction
Methods and Materials II
150
Asphalt and Asphalt
Mixtures
Other Uses
Construction Methods & Materials II
Latest paving costs for HMA
Washington Region Urban Rural
Western WA $270,000 lane-mile $207,000 lane-mile
Eastern WA $196,000 lane-mile $165,000 lane-mile
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Assumes a HMA overlay 45 mm thick along with traffic control, 12 ft. lane + shoulder, safety and drainage (12%), mobilization (6%), tax (8%), engineering and contingencies (19%), preliminary engineering (10%).
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 76
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Brief List
Mixtures
Cutbacks
Emulsions
Uses
Bituminous surface treatments
Fog Seals
Slurry seals
Tack coats
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Cutbacks
Asphalt cement dissolved in volatile solvent
Typically kerosene or naptha (gasoline)
Upon application, solvent evaporates
85% Asphalt
15% Solvent
TypicalConstituents
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 77
Construction Methods & Materials II
Cutbacks 3 basic types based on volatility of
solvent Rapid Curing (RC): 4 – 8 hours to cure
Medium Curing (MC): 12 – 24 hours to cure
Slow Curing (SC): 48 – 60 hours to cure
Type Components
Percent of Component by Grade
30 70 250 800 3000
RC Asphalt cement 65 75 83 87
Solvent (gasoline, naphtha) 35 25 17 13
MC Asphalt cement 54 64 74 82 86
Solvent (kerosene) 46 36 26 18 14
SC Asphalt cement 50 60 70 80
Solvent (fuel oil) 50 40 30 20
Viscosity
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Emulsion
Asphalt cement emulsified in water Emulsifying agent is essentially soap
Upon application to a surface (pavement), the water evaporates
65% Asphalt
35% Water
TypicalConstituents
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 78
Construction Methods & Materials II
156
Emulsions
4 types based on speed of setting (coalescing) Rapid Set (RS): 1 to 5 minutes
Medium Set (MS): 5 to 30 minutes
Slow Set (SS): 20 minutes to several hours
High float (HF): less drain-down (e.g., HFMS-1)
Asphalt globules can have + or – surface charges Anionic: net negative surface charge (RS, MS, SS)
Cationic: net positive surface charge (CRS, CMS, CSS)
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Emulsions
Viscosity grades
1 = low viscosity
2 = high viscosity
Base asphalt
“h” = harder residue (e.g., RS-1h)
“s” = soft residue (e.g., HFMS-2s)
CMS-2h RS-1
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 79
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158
Uses
Bituminous surface treatments (chip seals) CRS-2, RS-2
Fog seals Diluted with water (water:emulsion = 3:1 to 5:1)
MS-1, SS-1, SS-1h, CSS-1, CSS-1h
Slurry seals CSS-1, CSS-1h, SS-1, SS-1h
Tack coat Diluted with water (water:emulsion = 3:1 to 5:1)
SS-1, SS-1h, CSS-1, CSS-1h
Construction Methods & Materials II
Chip Seal
Chip seal is a pavement surface treatment that combines one or more layer(s) of asphalt with one or more layer(s) of fine aggregate.
In the United States, chip seals are typically used on rural roads carrying lower traffic volumes, and the process is often referred to as "asphaltic surface treatment“.
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 80
Construction Methods & Materials II
160Photo courtesy of MnDOT
Chip Seal
Construction Methods & Materials II
161Photo courtesy of MnDOT
Chip Seal
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 81
Construction Methods & Materials II
162
Chip Seal
Construction Methods & Materials II
Fog Seal
A fog seal is a light application of a diluted slow-setting asphalt emulsion to the surface of an aged (oxidized) pavement surface.
Fog seals are low-cost and are used to restore flexibility to an existing HMA pavement surface.
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 82
Construction Methods & Materials II
164Fog Seal
Construction Methods & Materials II
Slurry Seal
A slurry seal is the application of a mixture of water, asphalt emulsion, aggregate (very small crushed rock), and additives to an existing asphalt pavement surface.
A slurry seal is similar to a fog seal except the slurry seal has aggregates as part of the mixture.
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 83
Construction Methods & Materials II
166
Slurry Seal
Photo courtesy of WSDOT
Construction Methods & Materials II
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Slurry Seal
Photo courtesy of WSDOT
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 84
Construction Methods & Materials II
What is a “Tack Coat?”
A tack coat is sprayed on the surface of an existing asphalt or concrete pavement by a distributor truck immediately prior to placing an overlay.
The goal is to achieve uniform coverage over the entire surface to be paved.
Once the tack coat is in place it should be given time to cure and become tacky. Normally this would only require a few minutes.
Traffic should NOT be allowed on a tack coat, to avoid getting dust and dirt on the surface.
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Construction Methods & Materials II
169Tack Coat Photo courtesy of WSDOT
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 85
Construction Methods & Materials II
170Tack Coat Photo courtesy of WSDOT
Construction Methods & Materials II
171Tack Coat Photo courtesy of WSDOT
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 86
Construction Methods & Materials II
172Tack Coat Photo courtesy of WSDOT
Construction
Methods and Materials II
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Asphalt and Asphalt
Mixtures
Asphalt Pavement
Deterioration
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 87
Construction Methods & Materials II
Deterioration of Asphalt Pavement
Asphalt is one of the most durable building components.
The life of asphalt pavement can be cut short due to poor installation, or over exposure to the elements without proper asphalt pavement maintenance.
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Construction Methods & Materials II
Deterioration of Asphalt Pavement
Significant asphalt deterioration can begin to take place after the first two years. Around this time, asphalt starts to turn gray and begins cracking.
Water seeps into the cracks, freezes, and thaws during the yearly cycle, causing larger cracks.
The liquid asphalt binder starts to lose it’s water-resistance properties, and this is how water is able to penetrate the asphalt, causing it a great deal of wear and tear.
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 88
Construction Methods & Materials II
Deterioration of Asphalt Pavement
The water works down into the sub-surface and softens the base. The pavement begins to give way and buckles under the heavy loads.
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Construction Methods & Materials II
Deterioration of Asphalt Pavement
Pavement begins to separate and break up. Potholes are the result. Alligatoring spreads, asphalt mat looses all flexibility and dries out. Total structural failure results.
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Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 89
Construction Methods & Materials II
Crocodile or Alligator Cracking Crocodile cracking (aka fatigue or alligator
cracking), is a common type of distress in asphalt pavement.
Crocodile cracking is characterized by interconnecting or interlaced cracking in the asphalt layer resembling the hide of a crocodile.
Cell sizes can vary in size up to 12 inches across, but are typically less than 6 inches across.
Crocodile cracking is generally a loading failure. It is often a sign of sub-base failure, poor drainage, or repeated over-loadings.
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Crocodile or Alligator Cracking
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Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 90
Construction Methods & Materials II
Rutting Surface depression in the wheelpath.
Pavement uplift (shearing) may occur along the sides of the rut.
There are two basic types of rutting:
Mix rutting
Subgrade rutting
Mix rutting occurs when the subgrade does not rut yet the pavement surface exhibits wheelpath depressions as a result of compaction/mix design problems.
Subgrade rutting occurs when the subgrade exhibits wheelpath depressions due to loading.
In this case, the pavement settles into the subgrade ruts causing surface depressions in the wheelpath.
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Construction Methods & Materials II
Rutting
Severe Mix Rutting
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Rutting in outside wheelpathdue to subgrade rutting
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 91
Construction Methods & Materials II
Rutting – Possible Causes Permanent deformation in any of a pavement’s layers or
subgrade usually caused by consolidation or lateral movement of the materials due to traffic loading.
Specific causes of rutting can be:
Insufficient compaction of HMA layers during construction. If it is not compacted enough initially, HMA pavement may continue to densify under traffic loads.
Subgrade rutting (e.g., as a result of inadequate pavement structure)
Improper mix design or manufacture (e.g., excessively high asphalt content, excessive mineral filler, insufficient amount of angular aggregate particles)
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Construction Methods & Materials II
Raveling
The progressive disintegration of an HMA layer from the surface downward as a result of the dislodgement of aggregate particles.
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Raveling due to low density Raveling from snowplow operations
Construction Methods & Materials II
Asphalt and Asphalt Mixtures
Professor Kamran M. Nemati
Winter Quarter 2019 92
Construction Methods & Materials II
Raveling – Possible Causes Loss of bond between aggregate particles
and the asphalt binder as a result of:
A dust coating on the aggregate particles that forces the asphalt binder to bond with the dust rather than the aggregate.
Aggregate Segregation. If fine particles are missing from the aggregate matrix, then the asphalt binder is only able to bind the remaining coarse particles at their relatively few contact points.
Inadequate compaction during construction. High density is required to develop sufficient cohesion within the HMA.
Mechanical dislodging by certain types of traffic (studded tires, snowplow blades or tracked vehicles).
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Raveling due to inadequate
compaction caused by cold weather
paving