asphaltic mixtures

8/11/2019 Asphaltic Mixtures

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Ways of Communication Presentation


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Asphaltic mixtures are construction materials made of admixturesobtained from preset dosages of natural or artificial aggregatesand mineral dust, agglomerate with bitumen, using an advancedtechnology. They are multipurpose, being used especially forpaving asphalts blankets and basic layers.

The most common aggregates for asphaltic mixtures processingare:

all types of broken stone; natural and crushed sand; crushed and uncrushed gravel and ballast; artificial aggregates like flying ash, whitestone etc.

The natural aggregated have to satisfy several conditionsregarding shape and size of the grains, type of the rock,granularity etc. They have to be clean, good adhesive towards theused bitumen and to have corresponding mechanical resistances,to endure ageing.


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The most used mineral dust, which has the best results,is made by crushing limestone. Others like deadlimepowder, cement etc can be used.

The used bitumen in asphaltic mixtures processing ishighly important in their behavior; its type is chosentaking into consideration the desired mechanical andphysical properties of the asphaltic mixture. Purebitumen, modified bitumen, doped bitumen, cut

bitumen, asphaltic emulsion can be used.


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Meaning: right proportions between materials -> best phys-mech.characteristics

Composition of asphaltic mixtures:

a. natural aggregates (crushed stone-criblura-, sand)

with clean, homogenous, origin: basaltic rocks or neutral rockswith high compression resistances

b. Filer (Mineral dust) - dry and having the necessarydelicacy(finite-min 80%), increases the plastic domain of thebitumen and the adhesiveness of the natural aggregate, preventsthe aging of bitumen

c. Bitumen(binding properties) - assures the cohesion andimpermeability of the asphaltic mixtures, must assure theadhesiveness and resistance to water

Ration Filer-Bitumen 0.5-> 3.0


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Corresponding asphaltic mixture (examination of the qualityconditions):

Workability: property of punere in opera in best condition

Depends on: FluidityGranularity of natural aggregates

Natural and shape of aggregates

Filer dosage

Binding dosage

Toughness(Compactitate) The proper dosage of binding depends ongranularity of aggregates.

Mechanical stability depends on binding dosage and its viscosity.

bitumen excess -> waves in the clothing of bitumen

insufficient binder-> porous surfaces (Check Turda city where youcant hear yourself inside the car when riding in the T9

hood) Impassibility at water action - Influenced by: adhesiveness of binder

to aggregates, clay presence inside the mass of asphaltic mixture =>swelling in contact with water


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Establishing optimum dosage of binder

Curve 1- concrete asphalt- compression resistancesincrease until certain % for dosage of binderWhen this % is exceeded -> decreased resistancemeaning that bitumen is in excess => increasedplastic deformationCurve 2 shows that to optimum dosage of bindercorresponds to an apparent maximum density ro

app.Curve 3- at a low % of bitumen the waterabsorption increases over 10%

With these rules and graphical analysis severalmethods are developed for proper dosage like:

a. Method of void volumeb. Method of specific surfacec. Kraemer methodd. Asphalt Institute Method etc.


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In order to establish the quality of asphaltic mixtures andbituminous coating several tests have been developed, usingtesting samples both in laboratory and at the site.

First of all, an important part of these tests is actually the sampletaking and sample preparation. These actions are regulated by

specific norms. There are 3 types of specimen test shapes.

Cube for testing apparent density, water absorbtion, swelling,compression resistance and thermo-stability coefficient

Cylindrical Marsall Test (stability, fluency, apparent density,water absorbtion)

- Triaxial Testing (internal friction angle, cohesion)

- Brazilian testing ( traction and compression resistance)

Prism for testing flexibility, fissure, fatigue resistance


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Some of the testing procedures Water content(W) will be determined on test samples from the

present bituminous coating by drying or distilling with a solvent.

This will be expressed in percentage and will represent the waterquantity in relation with the initial weight of the sample.

Asphaltic mixture compositionis given by the content of bitumenand natural aggregates and their granulosity.

Binder content is usually determined by extracting bitumen from

the asphaltic mixture using an organic solvent. This can beachieved by several different methods.

Extraction centrifugal device, Soxhlet apparatus usingchloroform and benzene.


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Marshall stabilityserves us in determining optimal compositionof asphaltic mixtures in order to achieve the required stabilityunder traffic and high temperatures.

For testing, we use Marshall cylindrical testing samples withd=100mm and 63.5mm length.

We determine the tensile strength by applying a force on ageneratrix at a temperature of 60 degrees Celsius. The Marshallstability is in fact the load reached when the specimen fails.

Fatigue resistanceof bituminous coating gives us details abouthow they behave under alternative loading simulating traffic. Inlaboratory the specimen is subjected to a sinusoidal deformationuntil failure. This resistance is actually defined by the number ofcycles of loads which the mixture can undertake until failure.

Bending moment resistanceis determined on prismatic samplesby applying a concentrated load in the middle of the span andincreasing it until failure occurs.


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Producing the asphaltic mixture has to be done in a special mechanical

plant called asphaltic plant. There are two types of plants - the batch plant and the drum mixer plant.

Both batch plants and drum mix plants are designed to accomplish thispurpose. The difference between the two plants is that the batch plantsdry and heat the aggregate and then in a separate mixer blend theaggregate and asphalt one batch at a time; drum mix plants dry theaggregate and blend it with asphalt in a continuous process and in the

same piece of equipment.

BATCH DRUM MIXER


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StorageSilo

BatchTower

Dryer

Conveyor Belt

Burner

Asphalt Storage

Hot elevator


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Drying, heating and dust removal of the aggregates are veryimportant operations as they need a certain temperature to bemixed with the bitumen, so that the whole composition stays fluid

during the execution. Then the aggregates are passed through thedryer. When they are removed from the dryer the aggregates musthave a temperature between 165-190 degrees. The most importantfactors to be considered in these operations are: humidity of theagg., granulosity, temperature.

A constant quality control of the plant and of the asphaltic mixtureis to be done.

Transportation of the asphaltic mixtures:

Trucks for use in hauling come in many sizes. The key isthat they have metal beds, be cleaned of foreign material

and hardened asphalt. It is a practice within the industry tocoat the beds with a release agent. For many years thisrelease agent was diesel fuel - the diesel fuel will soften theasphalt binder and can result in soft spots in the pavement.


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Different types of truck s are Used

The mix is placed with a self-propelled paver. It can be done with amotor grader; but, that is seldom done. The purpose of the paver isto place the HMA to the desired width and thickness and toproduce a satisfactory mat texture. The mix is usually placed at 3times the thickness of the nominal aggregate size.


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The basic principle behind the pavers has notchanged much since the 1930s.


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Prior to paving startup, equipment should bechecked to assure its suitability and proper

function. Paving startup should begin with a test strip

section. This will allow for minor problems tobe solved, establishment of roller patterns andnumber of passes, and will assure that properplacement and compaction can be attained.Inorder to assure proper placement and

compaction, it is essential that the materialshould be placed hot


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Reason for compaction

- To provide shear strength or resistance to rutting

- To ensure the mixture is waterproof- To prevent excessive oxidation of the asphalt binder

- Rezistence to high compressions

- Minimum deformation

- Obtaining the maximum density, that means that the voidvolume is minimum

- Uniform texture and a better running surface

After compaction cores are taken for density determination

and thickness. They are usually cut to obtain a sample ofthe layer being placed. The bulk specific gravity of the coreis determined and using that with the maximum specificgravity it is possible to determine the percent compaction.


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Machines used for compaction : pneumaticrollers, Steel wheel rollers and Vibratory rollers


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5.1 Materials ControlThe materials used in asphaltic mixtures processing will be checked according to thespecific national standards. During the works, the checks and the tests will be done inthe site laboratory on every hand and also weekly, from aggregates warehouses andbitumen tank.

5.2 Processing and Placing Control of the Asphaltic MixturesWithin the site, the processing and placing of the asphaltic mixtures must be checked,including: asphaltic mixture processing appliance (accurate functioning of thevolumetric graduation, weighing- daily), thermal regime of the asphaltic mixtureprocessing, technological process of the bituminous layer execution, keeping the pre-

established asphaltic mixture composition.Consolidation checking must be done permanently, during the consolidation works, bythe contractor, and occasionally by the engineer, which has the right to stop the siteworks, in care of irregularities.The checking of the consolidation level must be made by the contractor, duringexecution on the bituminous clothing, by insitu or laboratory tests.

5.3 Contours Control During Execution(a)Surface Control- the medium material quantity placed on the surface must be equalwith the one from the prescriptive book with a 10% tolerance.(b)Leveling Control- the tolerances for the measured elevations in proportion to the pre-established ones are 1,5 cm; if the tolerances are kept in 95% of the examined points, thealignment is considered convenient.


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5 Geometric Elements ControlThe geometric elements checking includesaccomplishment of the quality conditions for thesupport layer, before placing the asphaltic mixtures, in

conformity with the articles STAS 6400. 6 Physical-Mechanical Characteristics and

Composition of the Asphaltic Mixtures ControlThe Physical-Mechanical Characteristics andComposition of the Asphaltic Mixtures Control is

made in different stages:-initial probations for establishing the asphalticmixture composition-checking of the asphaltic mixture characteristics, madeon sampling tests sampled during the works

-checking of the executed bituminous layercharacteristics.


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7. Frequency of checks


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Introduction Warm mix asphalt (WMA) technologies are being

promoted throughout the United States for their abilityto lower the production and placement temperatures ofconventional hot mix asphalt (HMA). From an

environmental standpoint WMA has the potential tolower asphalt production temperatures which canequate to reduced energy consumption, and emissions,as well as a smaller carbon footprint.

Although Europe is credited with many of the recent

developments in WMA technologies one of the firstprocesses used to foam asphalt and reduce mixingtemperature was patented in the United States in 1956.This process was later purchased and refined by MobilOil of Australia in 1968.


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The first WMA project paved in Washington Statewas constructed on Interstate 90, West of George in2008, since that time interest has grownsubstantially.


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The interest in producing mixtures with WMA technologies hasoutpaced the implementation of specifications and modification oftest procedures. While most modifications of specifications andtest procedures are minor, there are several issues pertaining to

simulated testing time and temperature that regulatory agenciesare faced with when attempting to make WMA a viablealternative to HMA.


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Chemical foaming technologies release water in the HMA, whichcause the asphalt to foam. Foaming expands the binder therebyreducing asphalt viscosity which allows a reduction in theproduction and placement temperatures of asphalt mixtures.

Advera, Aspha-min and WAM Foam are all examples ofwater carrying chemicals. To date, WSDOT has not constructed aproject using any of the chemical foaming technologies.Mechanical water foaming technologies foam the hot asphaltbinder at the HMA plant. The foaming process typically injects

water into the hot binder, which in turn reduces the asphalt binderviscosity and allows a reduction in the temperatures typicallyobserved for production and placement of asphalt mixtures. AstecDouble Barrel Green, Gencor Green Machine Ultrafoam GXand Maxam Equipment Inc. AQUABlack are examples offoaming systems currently in use. Low Energy (emission) Asphalt(LEA), marketed by Suit-Kote Corporation, is another foamingsystem that adds moisture to the fine aggregate instead of directlyinto the asphalt binder. With the exception of two projectsconstructed prior to 2010, all WMA produced for WSDOTcontracts have utilized the mechanical water foaming technology.


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asphaltic mixtures

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