Bituminous Materials

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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


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