Bituminous Materials
What specification is used to control HMA compaction in the field?
%Gmm
What is a typical target as-built density?
%Gmm = 91%
Screed
Controls the thickness of the mat. Provides initial compaction.
Vibratory roller
Good intermediate roller. Kneading plus static weight provides good compaction.
Penetration Test - ASTM D5
Measure distance needed penetrates AC Determines relative hardness or consistency of asphalt Five penetration grades - (40-50 = stiffest), (200-300 = softest)
Bending Beam Rheometer (BBR)
Measure low temperature properties. Test is done on aged binder. Calculate beam creep stiffness with time.
Finish Rolling
Remove roller marks and other blemishes
Bending Beam Rheometer
Thermal cracking
Pba
Absorbed asphalt percent, by weight of aggregate
Drum Mix Plant
Agg. bins > conveyor > burner > dryer & mix with asphalt > storage silo
Batch Plant
Agg. bins > conveyor > dryer > flame burner > mixing screens > hot bins
Define VTM
Air voids. The empty space in mix
Why are asphalt emulsions preferable to asphalt cutbacks
An emulsion is preferable because there are less environmental hazards with fumes/ ground water contamination
Two types of emulsions
Anionic Cationic
Gsa
Apparent specific gravity of solids
Penetration grading
As penetration increases, flash point decreases (more volatiles = lower flash point) As penetration increases, retained penetration decreases
Emulsions
Asphalt based product that is liquid at room temperature Produced by separating hot asphalt cement into small gobules and dispersing them in water treated with emulsifying agent (soap)
How is an asphalt emulsion liquified at room temperature
Asphalt cement is separated into small gobules and dispersed into water treated with emulsifying agent like soap
Penetration Specification - ASTM D946
Asphalts specified according to penetration tests but adds some other requirements: Flash point (safety) Ductility (flexibility) Solubility (purity) Thin film oven aging (penetration, ductility)
How do temperatures effect asphalt
At colder temperatures, the asphalt stiffens, and may be prone to cracking At higher temperatures, the asphalt softens, and may be prone to rutting
Why are batch plants better to handle mixture changes than drum mix plants?
Because the sieves and hot bins located in the plants allow for quick changes in the gradation of the blend
How do lake asphalts vary within a single source?
Bitumen content and inorganic material
Asphalt cement properties at room temperature
Black, sticky, semi-solid, highly viscous
What material property is being used to separate components of crude oil in the fractional distillation process?
Boiling point temperature
Compare drum mix and batch mix asphalt plants
Both plants have: •Aggregate separated into different bins and use a conveyor system •Have an asphalt cement supply line that adds asphalt with the aggregate when it is mixing
Compaction phases
Breakdown rolling Intermediate rolling Finish rolling
Rotational Viscometer common name
Brookfield Viscometer
Gsb
Bulk specific gravity of solids
How is a asphalt cutback liquified at room temperature
By adding a petroleum based solvent to the asphalt cement at room temperature
What pavement distress is the Creep Stiffness test meant to control in the Superpave binder specification?
Cold weather cracking
Breakdown Rolling
Compaction beyond that imparted by the paver
Disadvantages of original viscosity grading
Cost (labor intensive) Testing time is limited More technician skill required Only newtonian material can be tested May have wide range of properties for same grade
Medium Curing (MC)
Cut with Kerosene Moderate volatility Used for prime coats and pot hole repairs
Rapid Curing (RC)
Cut with NAPHTHA or gasoline High solvent volatility Used for tack coats or surface treatments
Slow Curing (SC)
Cut with low viscosity oil Used for prime coat and dust control
Asphalt cement definition
Dark brown to black cementious material that is either naturally occurring or produced from petroleum distillation; Soluble in petroleum products
Compaction measurement
Density. Measured in terms of air voids
Three classes of cutbacks
Depend on time to evaporate •Rapid curing •Medium curing •Slow curing
Rotational Viscometer (test)
Determine capability to pump and handle asphalt
Asphalt testing is needed to
Determine engineering properties Characterize desirable properties Use testing as a basis for payment
Auger
Distributes the mix evenly over paving width of screed.
What mixer does a Drum mix plant use
Drum mixer
What mixture problem is commonly associated with Hveem mixes?
Durability
Gse
Effective specific gravity of aggregate
Disadvantages of penetration grading
Empirical Shear rate dependent - response is variable depending on stiff or soft AC Mixing and compaction temperatures cannot be determined
Hveem Method disadvantages
Expensive and non-portable equipment. Less focus on volumetrics. Mixes may be non-durable due to too little asphalt.
Steel-wheel rollers
For breakdown and finish Vibe and static rolling
Superpave considers
Fundamental properties as related to pavement performance. Environmental factors. Various temperatures. Aging.
Intermediate Rolling
Further densification and sealing
Emulsifier
Gives surface charge to asphalt
Advantages of penetration grading
Grades AC near service temperature Fast Can be done in field Low cost Temperature susceptible
Pressure Aging Vessel (PAV)
High pressure and aging. 20 hours of testing. Uses RTFO asphalt specimens. Residue used for further testing.
Disadvantages of aged residue testing (AR)
Highly regional, no widespread experience Requires different testing equipment Longer testing time No consistency test on original AC Only used on Newtonian fluid Can have wide range of properties for same grade
Why are asphalts sometimes modified with polymer
Increase the elasticity Increase the bond between the asphalt cement and the aggregates. Increase the stiffness of the mix
What is the function of the reformer in fractional distillation?
Increase the hydrocarbons in NAPTHA
Ductility test
Indicates flexibility Sample stretched until breakage, and elongation is recorded Less ductility means more cracking •Historically, this test has resulted in poor precision
During which phase of construction is a rubber tire roller usually used during asphalt pavement construction?
Intermediate
Gobbles in emulsion
Kept apart until: •Charge is neutralized due to contact with aggregate •Water evaporates •Known as breaking or setting
Hveem Method advantages
Kneading compaction. Better measure of stability.
Gilsonite
Like rock asphalt but found in veins Hard, brittle, pure asphalt Can be economically extracted
Cutbacks
Liquid asphalt at room temperature; Produced by cutting with a petroleum solvent. Due to environmental regulations - have little use
Hveem Method (Mix design)
Mainly used in U.S.
Tar definition
Manufactured from destructive distillation of bituminous coal
Mix Design Methods
Marshall. Hveem. Superpave.
Gmm
Maximum specific gravity of mixture
Advantages of original viscosity grading
Measures a fundamental property Covers a wide range of temperatures Specifications based on maximum service temperatures Wide range of testing equipment available Test method precision well-established Temperatures susceptibility controlled Places limits on aging Yields information on mixing and compaction temperatures
Solubility test
Measures levels of impurities Sample of asphalt is dissolved in solvent then filtered Amount of insoluble material retained = impurities
Viscosity graded specification - ASTM D3381
Measures viscosity = resistance to flow Absolute and Kinematic
Kinematic Viscosity - ASTM D2170
Measures viscosity in units of (mm^2 /second) Measured with a U-tube at 135º celsius
Absolute Viscosity - ASTM D2171
Measures viscosity in units of poise (pascal seconds) Measure with u tube at 60º celsius
Marshall Method disadvantages
Method of compaction does not simulate field compaction. Marshall stability test does not measure actual shear strength of the HMA
Pneumatic tire rollers
More kneading action. Operate between breakdown and finish.
Conveyor
Moves material from hopper through control gates
Anionic emulsions
Negative charge Alkaline Works well with limestone aggregate (positively charged)
Compaction mechanism
Overcome shear strength of mixture when hot
What asphalt binder test was used to determine the relative hardness of asphalt cement?
Penetration test
Ps
Percent aggregate by total weight of mixture
Pmm
Percent total weight of mixture = 100%
PG
Performance graded binders
Cationic emulsions
Positive charge Acidic Good with silica gravel (negatively charged)
What is the mixing equipment used at a batch plant?
Pugmill
Rolling Thin Film Oven (RTFO)
Purpose: •Age binder for further testing •Determine loss of volatiles as an indication of aging
Push rollers
Pushes dump truck while unloading material into hopper
RAP
Reclaimed asphalt pavement
Advantages of aged residue testing (AR)
Represents AC properties after mixing Measures fundamental properties Covers a wide range of temperatures Places limits on aging
Superpave equipment for testing
Rolling thin film oven. Pressure aging vessel. Rotational viscometer. Dynamic shear rheometer. Bending beam rheometer. Direct tension tester.
Air blow asphalt cements are typically used for
Roofing
Dynamic Shear Rheometer
Rutting and fatigue cracking
What type of asphalt aging is the Rolling Thin Film Oven (RTFO) meant to simulate?
Short term
Rolling thin film oven
Short term aging
Roller patterns
Should be established on test strips. Density in transverse direction should be consistent. Usually the outside of the paving pass has adequate density.
Thin film oven aging (TFO)
Simulates aging due to: mixing, storage, and construction Measures loss of volatile material due to aging process •Determine properties before and after aging of sample
Pressure aging vessel
Simulates long term aging
Gb
Specific gravity of asphalt
Hopper
Storage bin in transport truck
Superpave
Superior performing asphalt pavements
What are the three major asphalt specification systems?
Superpave binder Penetration Viscosity
Three main types of asphalt recycling
Surface recycling Central plant recycling In-place recycling
How is tar different from asphalt cement?
Tar is manufactured from the destructive distillation of bituminous coal; Asphalt cement is either naturally occurring or produced from petroleum distillation
Flash Point test
Test performed for safety purposes Determines temperature at which asphalt will flash or ignite
Dynamic Shear Rheometer (DSR)
Testing done on: •Original AC •RTFO AC (short term) •PAV AC (long term) -Asphalt sandwiched between two metal plates -Variable test temperatures
How can the different types of aging of asphalt cement be simulated in the laboratory?
The Thin Film Oven Test, Rolling Thin Film Oven Test, and Pressure Aging Vessel
What is meant by temperature susceptibility of asphalt
The asphalt properties, such as viscosity, change with temperature
What is the function of a prime coat in an asphalt pavement
The prime coat acts as an adhesive between the aggregate base layer and the first layer of asphalt
What distresses is the asphalt binder dynamic shear modulus meant to control in the superpave binder specification?
The shear stresses that is a result of pavement rotting and cracking
Superpave concept
The specified criteria remain constant, but the temperatures at which those criteria are met depend on the environment where the binder will be used.
Describe the process for determining the stripping potential for an asphalt concrete mix
The specimens are divided into two groups: reference and conditioned specimens. A strength test determines the strength of the specimen before and after it is conditioned. The retained strength, which is the ratio of the conditioned strength and the reference strength is computed. Criteria is used to determined if the retained strength is adequate.
Direct Tension Tester
Thermal cracking
Superpave Method (Mix design)
Three intended levels: 1. Volumetric only 2. Volumetric and some performance testing 3. Volumetric and extensive performance testing
How are asphalt roller patterns usually established for asphalt pavement construction?
Through test patterns
Most common type of polymer modifier
Tire rubber
Compaction purpose
To prevent further compaction under traffic. To provide shear strength or resistance to rutting. To ensure the mixture is water proof. To prevent excessive oxidation of the asphalt binder.
Compaction temperature
Too cold = compaction can not be achieved Too hot = mat will not support rollers
What mixer does a Batch mix plant use
Tower mixer
N_design is a function of what?
Traffic level, NMAS, and geographic location
Direct tension tester
Used as a backup test when asphalt does not pass BBR test. Measure strain at failure.
Rotational Viscometer
Used to measure asphalt viscosity at various temperatures
Dynamic shear rheometer
Used to measure dynamic shear modulus and phase angle of binder. These properties are used to control cracking and rutting potential
Marshall Method advantages
Uses volumetrics Inexpensive Portable equipment
Drum Plants
Usually have a much higher production rate.
Batch Plants
Usually have better control of the final product. Can handle mix changes better.
Where is the Bermudez deposit located?
Venezuela
Define VFA
Voids filled with asphalt. The voids in mineral aggregate filled with asphalt
Define VMA
Voids in mineral aggregate. The empty space between aggregate particles
Superpave aging mechanism
Volatilization of light oils. Hardening and agitating during production at high temperatures. Oxidation in field at lower temperatures
Pb
Weight percent of asphalt in mixture
How does aging occur in asphalt cement?
Whenever it is subjected to wind and solar radiation. This occurs in the asphalt plant during production, during placement, and when the asphalt is exposed to the environment
Marshall Method (Mix design)
Widely used; laboratory equipment based primarily on volumetrics
PG XX-YY
XX = Average 7 day high temperature for site YY = One day low temperature
Three advantages of asphalt recycling
• Lowering the dead load on bridges due to overlays • Energy saving in manufacturing and transporting materials • Economic saving of around 25% of the price of materials
Lake asphalts
•Bermudez deposit in Venezuela •Trinidad Lake •La Brea pits
Natural asphalts
•Lake asphalts •Rock asphalts •Gilsonite
Advantages of using Warm Mix Asphalt (WMA)
•Less oxidation of the asphalt binder •Paving can be done at lower temperatures •Longer haul distances
Bituminous materials characteristics
•Strong cement •Durable •Waterproof •Adhesive •Resistant to most acids, bases, and salts
