Asphalt and Asphalt Concrete

HistoryAsphalt and Tar MaterialEngineered Asphalt Cements Hot-mixed asphalt Cutbacks Emulsions

Properties of Asphalt

History

3500 B.C. natural bitumen used to line reservoirs by the Greeks

First US asphalt in NY and NJ

Automobile drove the ACC industry

Sources of “Natural” Asphalt Cement

Natural asphalts are refined by nature

Trinidad Lake asphalt

very hard, mined commercially

Washington, DC 1870’s

Gilsonite in Utah

very hard, mined commercially

contains fine sand

Rock asphalt Kentucky, Texas

sandstone impregnated with asphalt

“Tar“ sands

in Canada (Athabasca)

La Brea “tar” pits in California

Bitumen and Asphalt

Bitumen: non-volatile hydrocarbon, soluble in carbon disulfide, very complex material structure Coal tar, asphalt (processed oil residue)

Asphalt (combination of asphaltine, resin, oil) Asphaltine (C/H>0.8) Resin (0.8>C/H>0.6) Oil (C/H < 0.6)

Specific Gravity = 0.95 – 1.05

Composition of Asphalt Cement

Large organic molecules of varying size and polarityCarbon 80-87% Nitrogen 0-1%Hydrogen 9-11% Sulfur 0.5 -7% Oxygen 2-8% Heavy metals 0-0.5%

Heavy metals play important role

Contribute to polarity

Molecular structure very complex

Asphaltenes -largest and most polar

Resins -intermediate, also polar

Oils - smallest, paraffin -like, non-polar

Colloidal model

Asphaltenes surrounded by resins

Oils continuous medium

AsphaltenesResinsOils

Refinery Operation

FIELD STORAGE TANKS

PUMPINGSTATION

LIGHT DISTILLATE

HEAVY DISTILLATE

ASPHALTCEMENTS

STORAGE

TOWERDISTILLATION

RESIDUAL

CONDENSERS AND

COOLERS

TUBEHEATER

MEDIUM DISTILLATE

OIL WELL

SOLVENTS

GASOLENE

JET FUEL

LUBRICANTS

HEATING OIL

Lighter molecules vaporizeAsphalt cement remainsResidual varies in consistency

Asphalt Characterization

Flash Point: temperature at which a substance will ignite with a open flame

Rolling Thin-Film Oven: indicator of the aging effect of short term high temperatures when producing ACC.

Viscosity: rotational viscometer measures the viscosity at a standard temperature (135C)

Complex Shear Modulus: dynamic shear rheometer

Flexural Creep: bending beam rheometer measure creep stiffness

Tensile Strength

Engineered Asphalt Cement

Hot mixed asphalt (pavements) Viscous semi-solid Flows for heating into liquid range

Cutback asphalt Viscous liquid Cut with oil distillates

Emulsion asphalt Viscous liquid Cut with water

Emulsions Asphalt Binder Liquefied with Water -

Water -reduces viscosity

Emulsifier gives surface charge to asphalt droplets suspended in water medium

Anionic

ŸNegative charge

ŸAlkaline (Basic) aggregate

ŸGood with limestones (positive charge)

Cationic

ŸPositive charge

ŸAcidic aggregate

ŸGood with silica gravels (negative charge)

Consistency controlled by amount of water

Stability controlled by choicer of emulsifier

Environmentally correct

Water

Asphalt Binder

Properties of Asphalt Cement

Adhesion: property to connect dissimilar materials

Cohesion: property to connect similar materials

3M scotch tape is adhesive, not cohesive Silly putty is cohesive, not adhesive Asphalt is adhesive and cohesive

Flow properties

Consistency: measure of fluidity at a given temperature

Absolute Viscosity, poises

Kinetic Viscosity, centistokes

Penetration: empirical measure of ease to penetration Penetration of 1 mm diameter needle.

sPapoisesrateshear

stressshear 1.0

_

_

3/

viscosityAbsolute

cmgdensity

Performance-Graded Asphalt Binders

MaximumTemperature

(ºC)Minimum Temperature (ºC)

PG 46 -34 -40 -46

PG 52 -10 -16 -22 -28 -34 -40 -46

PG 58 -16 -22 -28 -34 -40

PG 64 -10 -16 -22 -28 -34 -40

PG 70 -10 -16 -22 -28 -34 -40

PG 76 -10 -16 -22 -28 -34

PG 82 -10 -16 -22 -28 -34

As an example, a PG 64-28 is acceptable for use in a climatic region where the maximum temperature is 64°C and the minimum temperature is -28°C.

Selection of Grading Temperatures

Temperature-28 -22 -16 64 70 76 82

Given that the minimum measured air temperature for a site is -21°C and the maximum 7-day average temperature is 73°C, which PG grade should be used for this site. Here, use PG 76-22.

Pavement Temperature

Air TemperatureMaximum 7-day

(Running Average)

Alternative Grading System

Grade Viscosity Abs., Poises Kinetic, cStokes

Penetration

Flash Point

°C

AC-2.5 250 125 220 163

AC-5 500 175 140 177

AC-10 1000 250 80 219

AC-20 2000 300 60 232

AC-30 3000 350 50 232

AC-40 4000 400 40 232

Asphalt and Asphalt Concrete

Asphalt Concrete Aggregates Properties

PavementsMixture Design

Asphalt Concrete

Aggregates clean and dry aggregates are necessary

for adhesion (no dust, no water) interlocking nature creates internal

friction which is important to the long-term properties of the asphalt concrete.

angular shape aggregates 50-80% with 2 angular faces

ACC: Importance of Aggregate

Asphalt cement has no strength at temperatures > 60CStability of pavements in hot weather is due to internal friction in the aggregates

-40 -20 0 20 40 60

Temperature, C

Modu

lus, P

a

Asphalt Concrete Mixtures

Mixtures of aggregate and asphalt cement binderabout 95% aggregate by weightabout 75% aggregate by volumeideally, 3-5% air voids

Asphalt Concrete

Flexibility high binder content low viscosity binder

Short-term Loadings elastic properties of binder-aggregate

matrix

Asphalt Concrete

Long-term Durability fluid properties of binder dry clean aggregates water causes “stripping” strong porous angular stone durable aggregates (LA abrasion)

Asphalt Concrete

Workability: Ease in which material is handled and laid and compacted. poor compaction leads to deformation

and the permeability of water and air. temperature affects workability

Strength high viscosity binder crushed stone aggregates (interlock)

Pavement Section

ACC Surface

ACC Base

Granular Subbase

Subgrade

Asphalt Pavement Distress

-40 -20 0 20 40 60

Temperature, C

Consi

sten

cy

Cracking

Rutting

Traffic Associated Fatigue

Asphalt Concrete Applications

Roofing, slurry composition shingles

Sealants waterproofing for foundations, etc electrical insulation

Asphalt Concrete Applications

Pavements Hot Mixed Asphalt Cement

(asphaltine, resin)

Emulsions (repairs, small jobs) moist or dry aggregates hot or cold applications no fuel or solvents anionic or cationic

Asphalt Concrete Applications

Cutbacks (on the way out) RC - flash point in 27°C !!!

hard base (hot regions) MC - safer

softer base (cold regions) SC - “Road Oils”

rural roads, sealants

Primary Distress Modes HMA Pavements

RuttingRutting

Fatigue CrackingFatigue Cracking5 -15 m

Thermal Cracking Moisture Damage?

Temperature Regimes where Distress Predominates

-25 7550250Approximate Temperature, C

Con

sist

ency

Low-temperature thermalShrinkage cracking

Intermediate-temperaturetraffic-associated fatigue

High-temperaturerutting

Plexiglas

Salt Water Taffy

Molasses