Dynopac Performance Handbook

8/19/2019 Dynopac Performance Handbook

1/921 ATLAS COPCO | COMPACTION, PAVING AND MILLING

COMPACTION,PAVING AND

MILLINGTheory and practice


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2 ATLAS COPCO | COMPACTION, PAVING AND MILLING


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COMPACTION,

PAVING ANDMILLING

Theory and practice

Copyright Atlas Copco Road Construction Equipment, Sweden 2014Production Happiend Reklambyrå, SwedenPhoto Atlas Copco, iStockphoto, Dreamstime, Fotolia

We reserve the right to change specifications without notice. Photos and illustrations donot always show standard versions of machines. The information is a general descriptiononly, all information is supplied without liability.


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This handbook presents a general overview of soil and asphalt materials, andsuitable methods and equipment for their compaction. It also deals with asphalt paving

as well as cold milling techniques and equipment. The principle purpose of the book is

to assist that important group of authority employees, contractors and consultants who

are concerned with compaction, paving and milling. It should also be useful to students

and others looking for an introduction to these subjects.

Dynapac has been at the forefront

of vibratory compaction and paving technology for many years.Its growth as an internationalorganization has been based on thesolid foundation of its research andtechnical expertise. This experien-ce, now gathered under the bannerof its Technology and ApplicationCenter (TAC), has provided thecompany with the knowledge andtools to design and manufacturecompaction equipment, pavingmachines and milling machines

that not only ensure that a jobis done satisfactorily, but also,

signicantly, that the equipment

remains on the job.Through the TAC, Atlas Copco

has developed CompBase, a uniquetool to predict the most suitablechoice of equipment for a given job with given specications. Ineffect, it is a bank of compactionand equipment-related data, basedon full-scale tests carried out undercontrolled conditions on Dynapaccompaction equipment working onvarious soil types. The test materialcomprises hundreds of thousands

of measurements. For givenconditions, CompBase suggests

the optimum type of equipment

and the suitable number ofmachines required. In practice,the CompBase predictions have proved to be very useful witha high degree of accuracy.

The TAC has developed anequivalent program for asphalt paving applications, PaveComp,which helps asphalt contractors andothers involved in the surfacing business to select not only the rightmachines for a given lay-down rateand given type of asphalt bitumen

mix but also the best combinationof paver and roller train to achieve

COMPACTION,

PAVING ANDMILLINGTHEORY AND PRACTICE


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the specied density cost efciently

and using the best asphalt surfacing practices.

Dynapac offers the market acomplete range of vibratory rollersfrom the largest asphalt tandemrollers in the world to smallerrepair work rollers. Vibratory singledrum rollers are available for allsoil applications. The roller rangealso comprises static smooth drumrollers and pneumatic tyred rollers.

Atlas Copco compaction equip-ment is supplemented by a range of

tracked and wheeled asphalt pavers,material feeders and planers. The

pavers are available with a full

range of screeds designed to handleall paving applications.

Atlas Copco has compaction, paving and milling equipmentmanufacturing facilities in Sweden,Germany, Brazil, China and India.The Atlas Copco products are soldthrough Customer Centers anddistributors in all major areas ofthe world.

The Atlas Copco world-widenetwork runs a global parts andservice back-up to maintain product

integrity over a long productivelife.


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Applications for compaction and paving techniques 8

Soil compaction

Type of soil 12

Compaction methods 18

Compaction equipment 20

Compaction properties of different soils 22

Special applications 25

Specifications and filed control methods 27

Field control methods 28

Asphalt paving, compaction and milling

Asphalt paving and compaction 32

Quality and functional requirements for asphalt pavements 34

Type of surfacing 35

Mixed asphalt components 37

Mix design proportioning 40

Properties of asphalt mixes 41

Manufacturing process and transportation 42

Asphalt pavers 44

Paving operations 47

Asphalt compaction 50

Rolling procedures 52

Choice of asphalt compactors 56

Specifications and field control 57

Cold milling applications 58

What to look for in ...

... a vibratory roller 63

... a static smooth drum roller 70

... a pneumatic tyred roller (PTR) 74

... cold milling equipment 78

... asphalt paving equipment 82

CONTENT


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Compaction is defined as the process of increasing the density and load-bearing

properties of a material through the application of either static or dynamic external

forces. It is required in many areas of the construction industry. The following pages

describe in brief the most common applications – roads, streets, motorways, airfields,earth dams, railway embankments and foundations for buildings. Other applications

include parking areas, storage yards, sports areas, industrial and residential areas,

harbour constructions, reservoirs and canal linings.

In the construction eld, the load bearing properties and stability ofrock ll, soil, asphalt and concrete,their impermeability and their

ability to withstand loads are allcorrelated to the adequacy of thecompaction of the material. Toillustrate the importance of compaction, a one-percent increasein density normally correspondsto at least a 10–15% increase in bearing capacity.

Although compaction may onlyaccount for some 1–4% of the totalconstruction costs, its role in thequality and life span of a nished project is immeasurable. If compac-tion is inadequate or incorrectly performed, settlement and other

failures are likely to occur withresultant high rehabilitation and/ormaintenance costs.

In a number of the above appli-

cations, principally roads, aireldsand parking and storage areas,the life span of the construction isalso dependent on the quality ofthe surfacing. For asphalt concretethe degree of compaction is decisi-ve to strength, wearing resistance,impermeability and durability.In addition, correct surface even-ness, uniform layer thicknessand the correct grades and cross-slopes are all necessary for a long,low-maintenance service life.As a consequence, the perfor-mance of the paving equipment

is in many aspects crucial to thequality of the nished surfacing.

Soil and asphalt

structuresThe design of a soil structure hasto take into account a number offactors such as loading, environme-ntal conditions, material availableas well as climate. The loads mayvary depending on the type ofstructure, but the main aim is todistribute them down through thestructure. The most common typesof load are trafc, buildings andwater pressure.

In a road, for example, the loadis distributed through the differentlayers. The greatest load distri-

APPLICATIONS FOR

COMPACTION ANDPAVING TECHNIQUES

APPLICATONS


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bution is to be found in the upperlayer and this diminishes the deeperyou get into the road. The variouslayers have to bear the weight ofthe layer above as well as the trafcload.

Any structure has an effect onand is affected by its environment,and this must be taken into consi-deration during the construction phase. Today, contractors try torecycle material which is on-siteto reduce the pressure on quar-ries as well as the need to exploitvirgin sites. As far as possible, theywill choose local material as llmaterial and to produce the asphalt.

Bringing in material from outsidenot only has repercussions on costs but also on the environment. Some-times it is unavoidable to transportmaterial when, for example, theasphalt mix needs to have special properties.

The effect of the climate mustalso be taken into considerationduring the actual construction period and the service life of thestructure. In cold climates, conside-ration must be given to frost and

the risk of low temperature crack-ing in asphalt. In hot climates, due

consideration should be given tothe stability of the asphalt layers tominimize the risk of deformation.

In all these conditions, compac-tion has a major signicance on thefunction of the structure, its servicelife and the maintenance costs.

Roads There are many types of road fromsmall secondary country roads tolarge multi-lane motorways. Themain criterion placed on a road isthat it should be able to transport people and goods in a safe, rapid,economic and comfortable manner.In order to full this, certain

demands are placed on where theroads are built, their surface even-ness and surface friction.

A road is built on an embank-ment or in a cut and is made up ofa number of layers – embankment, base course, binder course andwearing course. (See diagram.)Sometimes there is a need forcement-reinforced base course toenhance the load bearing capacityof the road.

APPLICATONS

Roads

Material description, see p. 11.Cut

APPLICATONS


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Railways In many parts of the world, rail-ways are still the major form oftransport for goods and passengers.

The transport of heavy materialssuch as ore, coal and other minerals places great stress on the railwayembankments.

Railways are built according tothe same principles as a road exceptfor the bound upper layers. The ballast bed on top serves to keepthe sleepers in place. Bitumen bound top layer ar also used tokeep the sleepers in place. Forthe construction of high speedrailways, considerably stricterrequirements are being imposedon embankments and ballast beds.

Airfields Runways, taxiing areas and apronsare all exposed to heavy loads inairport complexes. They are builtup in the same way as roads but thespecications are more stringent.In addition to this, under no circum-stances may the surface break up sothat loose stones can end up in the

airplane engines.

APPLICATONS

Foundations forbuildings and or/bridges Foundations are essentially built inthe same way as roads up to the basecourse. Layer thickness can differdepending on the nature of the loadthe structure is expected to carry.

Railways

Airfields

Foundations forbuildings, bridges etc.

Cut


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APPLICATONS

Canals Canals have to be designed and built to withstand enormous water pressure. In addition, they have to be water tight so that they don’tleak and they have to be able offer protection from the risk of erosioncaused by the owing water.

The bottom of the canal is level-led off and compacted. A lter layercomprising sand and gravel is then put in place and, on top of that,a sealing layer of ne soil, cementor asphalt. There is always a certainamount of leakage through the seal-ant and the lter ensures that thesealant does not get washed away.If ne soil is used as the sealing

layer, it must be covered by anerosion resistant layer. It is highlyimportant that the various layersare correctly compacted to avoidcracks in the sealing layer.

Earth dams There are certain similarities between the functional propertiesof canals and earth dams but theyare built in different ways.

An earth dam has a core ofimpermeable material, for example,ne soil or asphalt. On either side ofthe core there is a lter and, outside

that, a shoulder. The impermeablecore and lter full the same func-tion as the sealing layer and lterin a canal, while the shoulder keepsthe various layers in place. The damwall surface is exposed to enormouswater pressure – some dams aremore than 100 m high. The shoul-der also offers protection againsterosion. An alternative constructionallows for a layer of concrete orasphalt upstream instead of usingan impermeable core.

The core comprises an imperm-eable soil (silt and clay) or asphalt.It is important to use soil with

similar properties and that no lami-nation (layering) takes place duringcompaction.

The lter consists of sandand gravel and serves to keep thecore material in place as the waterforces its way through the core. Itis unavoidable that water will seepthrough the core but it is importantto keep the rate low.

The shoulder can consist of practically any type of ll material but rock ll is the most common.It is important that the surfacesup and downstream are protectedagainst erosion.

Canals

Earth dams

Asphalt wearing course

Asphalt base course

Sub-base

Shoulder/Erosion protection

Ballast

Asphalt binder course

Base course

Embankment

Core/lining

Filter

Natural ground


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Grain-size distributionGrain-size distribution is of greatimportance for the mechanical properties for a soil and for theselection of compaction equipment.

The grain-size distribution isdetermined by a sieve test anda sedimentation test if necessary.Ocular analysis can also be used

to categorize coarse-grained soil.

Sieve test The dried soil sample is passedthrough a number of standardsieves which differ in mesh size.The amount of material remainingon each sieve is calculated as a percentage of the total weight ofthe sample. The gures are plottedon a graph in a cumulative curveshowing the grain-size distributionof the material.

Sedimentation test A sedimentation test should be performed if the amount ofnes exceeds a certain level, forexample, 15%. In a sedimentationtest the soil sample (approximately40–60 grams) is mixed with waterand chemicals. After careful mix-ing, the density of the solution is

measured using a hydrometer after1, 2, 4, etc. minutes. Afterwardsthe grain-size distribution can becalculated and plotted.

Soil is categorized into differentfractions according to grain sizeas follows (from the smallest tothe largest): clay, silt, sand, gravel,cobbles and boulders. The differentfractions rarely occur individual-ly in nature. They usually occurin combinations of two or moredifferent fractions, for example

sandy gravel, silty sand, silty clay,sandy-silty clay, etc.

TYPE OF SOIL

SOIL COMPACTION

Sieve test

Soils may be divided into a number of different

categories depending on their composition,

geological history and physical properties.



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Gradation of Sand and Gravel

Gradation is an important factor forload bearing properties and for thecompaction and is determined fromthe grain-size distribution curve.

Cu=d60/d10 where d60 and d10 arethe particle diameters correspon-ding to values of 60 and 10 percent

on the grain-size distribution curve.

If Cu is less than 6 the soil isconsidered uniformly graded andif Cu is greater than 15 the soil isconsidered well-graded. In betweenthese two, the soil is medium-graded.

The limits differ from one classi-cation system to another.

In well-graded material, repre-sented by a curve covering a fullrange of grain-sizes, the voids left by the large particles are lled by

the smaller ones. This results in

a dense structure and good load bearing properties.

A curve showing grains of moreor less the same size indicates auniformly graded material. In thiscase, there are no smaller particlesto ll the voids. Consequently, itis harder to achieve high densityand load bearing properties inuniformly graded material thanin well-graded material.

SOIL COMPACTION

d60d10

Cu =


Well-graded material

Uniformly graded material


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Consistency Consistency is important in a ne-grained soil.The consistency of any ne-grained (plastic)soil may be soft, rm, or hard depending on theamount of water. As the soil changes consistency,

so do its mechanical properties.There are certain limits of soil consistency

which are the basis for differentiation amonghighly plastic, slightly plastic and non-plasticmaterial. These limits are designated Liquid Limit(LL), Plastic Limit (PL) and Shrinkage Limit (SL).Plasticity Index (PI) is dened as the difference between liquid and plastic limit.

The liquid limit is dened as the water contentat which the soil just begins to ow when lightly jarred 25 times in a standard cup.

The plastic limit is dened as the water contentat which soil can be rolled into a strand without breaking until it is only 3 mm in diameter.

The shrinkage limit is dened as the water con-tent at which the soil does not shrink any longerwhen being dried. The soil also changes colour and becomes lighter as the water content decreases.

A soil with a low plasticity index is very sensi-tive to changes in the water content. If the watercontent increases, the load bearing properties ofthe soil decreases.

Origin of soilsThe composition of a soil and the way that it was formedaffect its suitability for use as a construction material. Soilscan be split into two main categories: mineral and organic.Soil structures use only mineral soils. Organic soils such asearth and peat are not suitable or even allowed as they areconstantly decomposing and their load bearing propertiesis low and unpredictable.

Mineral soils are formed through weathering and naturalmechanical effect. They can also be formed articially by blasting and crushing. Their durability depends on the mine-ral composition and the way in which the rock was formed.There are three types of formation: igneous, sedimentary

and metamorphic.

Igneous rockIgneous rock types are formed from the cooling processof magma, a natural solution of high-temperature, rock-forming constituents under high pressure. Magma containsa large amount of water vapor and other gases and is alwaysunderground. Liquid rock that reaches the surface and losesits water and gases becomes lava. In general magma thatis formed about 10 km below the earth’s surface containslarge amounts of silica and is rich in sodium, potassiumand aluminium and tends to form granitic rocks. Magmaoriginating between 10 and 40 km below the surface tends

to form gabbroid rocks while, deeper down, it tends to form peridotitic rocks.

SOIL COMPACTION

Boulders

Gravel

SiltCobbles

Sand

Clay

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Sedimentary rock In time, rock, when exposed to theatmosphere, will be broken up ordissolved by weathering and ero-sion. The material is re-deposited

by wind, water and glaciers and builds into sedimentary rocks.The fragmented material, movingas loose particles, settles out byweight, smaller particles travellonger distances. The most distin-ctive characteristic of sedimentaryrock is its layering or stratica-tion. The most abundant typesof sedimentary rock are shale,sandstone and limestone. Thematerial ranges from very softto being as hard as some of theigneous rock types.

Metamorphic rock Metamorphic rock is formed bythe changes in texture of igneous

or sedimentary rock caused by heatand pressure. The transition fromone stage to another is gradual. Asa result of this, all intermediate sta-ges are represented. Eventually the

metamorphism may be thoroughenough to destroy all evidenceof the original state. Metamorphicrock is usually harder than the ori-ginal rock type. Gneiss is a typicalexample.

Grain shapeThe shape of the grain has a cer-tain inuence on the compactabili-ty and load bearing capacity of thesoil in question. The grain shapeis related to the way in which therock was formed and how it has been affected over the years. Grainshape can be divided into six cate-gories ranging from well roundedto very angular.

Well-rounded grains are foundin soils that have been formed bythe affect of wind and weather.The particles grind against eachother under the inuence of water

and wind. This type of soil is mostcommonly found in river deposits,lake sediment, dunes, loess andglaciuvial deposits.

Angular grains are formed bymechanical inuence on the rock by glaciers. Moraine is typicalexample of soils with this graintype, although the whole rangeof grain shapes can be present.

Very angular grains are artici-ally manufactured by the blastingand special crushing processes.

SOIL COMPACTION

Classification of soil types

Mineral soil types are generallyclassied by grain-size fractions.

The determination of the rangeof grain-sizes in the material is the basis for the classication of thesoil. Grain-size classication sys-tems vary from country to country.The classication of cohesive soilsalso involves determining theirconsistency.

One of the most commongrain-size classication systems

is the Unied Soil Classication

System (USCS) established in

USA, which categorizes soils in 15groups identied by name and lettersymbols. The AASHTO Classica-tion System (American Associationof Highway and TransportationOfcials) intended for road con-struction was also developed in theUSA. The grain-size classicationsystems used in different Europeancountries are the same except whenit comes to the classication oflarger particles.

Soils can also be generally

classied in larger groups, for

example, as coarse-grained or ne- grained, granular or non-granularand cohesive or non-cohesive soils.

There are no general rules thatgovern the permitted maximumcontent of nes in coarse-grainedand granular types of soils. Valuesvary between 15–50% dependingon the classication system. A coar -se grained soil is generally regardedas free-draining if it contains amaximum of 5–10% nes (silt andclay).


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SOIL COMPACTION

Resistance to compactionThere are four types of resistanceto compaction in soil and rockll:friction, cohesion, apparent cohe-sion and particle mass.

Friction is caused by the interaction

between the particles and is the main

resistance in a coarse-grained soil.

Cohesion is caused by molecularforces between the smallest partic-les and constitutes the main source

of resistance in a ne-grained soil.

Apparent cohesion is caused by the capillary forces of the waterin the soil and occurs more or lessin all soils. If water is added, thewater will nally also act as a lubri-cant between the soil particles.

Particle Mass. Heavy particlesrequire compaction of heavy equip-ment in order to be able to relocateto a denser state.

Most soils attain their highest drydensity at a certain optimum watercontent¹ for a given compactioneffort. In simple terms, a soil withwater content below the optimumrequires more compaction effort toreach the same density as soil at op-timum water content, whereas a wetsoil is soft and easier to compact.The highest dry density is obtainedat the optimum water content,

between the wet and dry states. Themost common method for determi-ning this state is the Proctor test.

Clean sand and gravel, as wellas other free-draining coarse mate-rials, are less sensitive to variationsin water content, and can attainmaximum density in a completelydry or in a water-saturated state aslong as the internal resistance tocompaction is overcome duringthe compaction process.

1 In some literature water content is expressed asmoisture content. This book has chosen to use watercontent.

Internal friction in a soil is a result of the forces acting

at the contact points between the individual particles.

Cohesion appears in clay as a result of the molecularforces acting between the miniscule particles. The stronger the

cohesion, the greater the compaction effort required.

Apparent cohesion is caused by the capillary forces created inthe water that partially fills the void in the soil. The apparentcohesion holds the particles together with “elastic” ties. The

smaller the particles – the greater the apparent cohesion.


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Laboratory compaction tests

The optimum water content can be determined in a laboratorycompaction test. There are two basic types of laboratory compac-tion test. One employs a standardweight falling onto a soil sample ina mold; the other is a standardizedvibro-compaction test.

The most common method isthe Proctor test which relies on afalling weight. The Proctor test isrecognized as the most common

laboratory method for determiningthe relationship between densityand water content. The test establi-shes the optimum water content fora soil as well as the reference densi-ty. The density is expressed as drydensity, which is the ratio betweenthe weight of the dried soil particlesand the volume of the sample.

Proctor test A sample of the soil to be tested is placed in a cylindrical mould and

compacted with a falling weight.Maximum particle size is limitedto one-tenth of the diameter of themould. If there is a low percentageof large particles, the maximum particle size is limited to one-fthof the diameter of the mould.The size of the mould is 4” (102mm), and 6” (153 mm) for larger particles.

The Proctor test can be carriedout in one of the variants known

as Standard and Modied Proctor.The compaction effort is 4,5 timesgreater for Modied Proctor thanStandard.

SOIL COMPACTION

The Modified Proctor uses a 10 lb

(approx. 4,5 kg) rammer with a fallheight of 18” (457 mm). The soil sampleis compacted in five separate layers.

The Standard Proctor test uses a

5,5 lb (approx. 2,5 kg) rammer witha fall height of 12” (305 mm). The soilsample is compacted in three separate

layers.


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Compaction equipment for soil materials is based on three main principles:

static load, vibration and impact. Different factors influence the selection

of compaction method and the compaction result:

• type of soil

• water content

• layer thickness

• stiffness of underlying layer

Static compactionStatic compactors were the rstreal mechanical compactionmachines. Static compactionequipment uses the dead weightof the machine to apply pressureto a particular surface and com- press the underlying particles.The only way to vary the pressureexerted on the surface is to alterthe weight or the contact area of

the equipment. Static equipmentwill normally achieve adequatecompaction on thin layers. Time,a function of the speed of the sta-tic compactor and the number of passes, also affects the nal result.Conventional types of static compactors include static three-wheelrollers, static tandem rollers and pneumatic tyred rollers (PTR).

Vibratory compactionVibratory compactors delivera rapid succession of impactsagainst the underlying surface from

COMPACTION

METHODS

SOIL COMPACTION


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where the vibrations, or pressurewaves, are transmitted through thematerial to set the soil particles inmotion. This reduces or practicallyeliminates the internal friction, andfacilitates the rearrangement ofthe particles into positions whichincrease the density. The simul-taneous increase in the number ofcontact points between the particlesleads to increased load-bearing

properties.Vibration is most effective

friction soils. Even though it hasless effect on cohesive soils, itstill improves the efciency whenthese types of soil are compacted.

Vibratory compaction achieveshigher densities and better deptheffect than static compaction onall materials, and nal density can be attained with fewer passes. Allof which explains why vibratoryequipment is more efcient andeconomical than heavy static equip-ment in almost all situations.

Vibratory compaction causes loose-ning of the uppermost surface ofa layer. The depth of the surfaceloosening depends on the soil type,its gradation and the water content.On a coarse-grained, uniformlygraded soil compacted on highamplitude; there will be a more pronounced loosening effect. Theloose soil on the surface is compac-ted as the next layer is placed on

top of it and compacted.

Impact compactionImpact compaction relies on a highimpact force. It generates a greaterforce on the surface than a staticcompactor. The force of the impact produces a pressure wave in thesoil which generates high pressureat depth as well. Tampers andtamping rollers work on the impact principle.

In certain cases, rollers with tri-angular, rectangular or pentagonaldrums may be used with relative

good depth effect. As this type ofcompactor will leave a non-compacted area between each impact,many passes are required to ensureuniform compaction.

Impact rollers must be operatedat signicantly higher speeds thanstatic or vibratory compactors torealize their full effect. They aremost economic on large areas.

The importance of the stiffness ofthe surface underneathThe compaction effect is inuenced by the stiffness of the underlyingground. Compaction cannot be fullyachieved if the underlying surfaceyields. It is often impossible to achi-eve a high degree of compactionin a ll resting on an underlyinglayer with low bearing capacity,for example, a ne-grained soilwith high water content.

SOIL COMPACTION

Static compaction Vibratory compaction Impact compaction


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COMPACTIONEQUIPMENT

SOIL COMPACTION

Vibratory tandem rollersp

Normally with vibration and drive on both drums. Mainly designed for asphalt com-

paction but sometimes also used for compaction of base course, sand and gravel.

Weight range: 1–18 tons.The most important compaction parameters are the static linear load, amplitude,

frequency and the speed. A higher static linear load gives a better compaction effect

and the amplitude controls the compaction depth. The frequency should match the

amplitude chosen for the current layer thickness. The speed should not exceed 6 km/h

otherwise there will be a noticeable decrease in the compaction effect.

Most suitable on thin to medium layer thicknesses on coarse-grained soils.

Choice of compaction equipment must take into consideration the type of soil,

the layer thickness, compaction specifications and the size of the job.

The most important consideration is the ability of the machine to fulfil

the compaction specifications in a cost-effective manner. You do not

select the largest roller for a small job such as a driveway. Converselyyou wouldn’t choose a small single drum roller for a dam job,

other than as a complement to other equipment.

There are a number of machine types in current use

for soil compaction. The most common ones, and their

generally accepted designations, are presented below.


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SOIL COMPACTION

Static three-wheel rollers p

Two driving steel drums and a steering drum with rigid frame, or

three-wheel drive and an articulated frame. The compaction effort canbe varied by ballasting. Weight range: 8–15 tons.

The most important compaction parameter is the static linear load

and the speed. A higher static linear load gives a better compactioneffect. The speed should not exceed 6 km/h otherwise there will be a

noticeable decrease in the compaction effect.Most suitable on thin layers of coarse-grained soils such and sand

or gravel.

Static tamping rollers

Four pad-foot drums. Articulated steering. Run at faster speeds thanvibratory rollers. Used for impact compaction. Effective on cohesive soils.

Weight range: 15–35 tons.The most important compaction parameters are the wheel load, width

of wheel, shape of pads and the speed. A higher wheel load

gives a better compaction effect. The speed should exceed10 km/h otherwise there will be a noticeable decrease in thecompaction effect.

Most suitable on thin layers and large surfaces.

Pneumatic tyred rollers p

Normally with 7–11 pneumatic tyres. Front and rear

tyres overlap. The compaction effort can be varied byballasting with water, sand or special cast-iron weights.

Weight range: 10–35 tons.The most important compaction parameters are

the wheel load and speed. A higher wheel load gives a

better compaction effect. The speed should not exceed6 km/h otherwise there will be a noticeable decrease inthe compaction effect. Most suitable on thin layers.

Self-propelled single-drum vibratory rollersp

With one vibrating drum and pneumatic drive wheels. Used on rock fill andsoil. Special pad-foot versions are very effective on clay. Weight range: 4–27 tons.

The most important compaction parameters are static linear load, amplitude, frequ-ency and speed. A high static linear load gives a better compaction effect. The amplitude

helps determine the compaction depth. The frequency should correspond to the amplitu-de and the material to be compacted. The speed should not exceed6 km/h otherwise there will be a noticeable decrease in the compaction effect.

Suitable on all kind of soils in relatively thick layers. On rock fill, only the heaviestrollers are suitable.


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The choice of compaction equipment must

take into account a number of factors.

These factors include:

• type of work and size of work-site

• type of soil and water content• layer thickness

• stiffness of underlying layer

• compaction specifications

• capacity requirements

• climatic conditions

The following section looks at different

types of soils and their compaction

properties.

Rock fill (Boulders and Cobbles)Rock ll includes boulders and cobbles which varyin size from a chicken’s egg up to around 1,5 meters(5 ft). Rock ll, blasted rock, crushed rock or naturalmaterial. Boulders and cobbles are the dominant frac-tion although small fractions may also occur.

The maximum stone size and gradation of rockll is determined by the type and quality of the rockand the rock blasting procedure. Primary rock such as basalt, gneiss and granite, have a high strength, and blasted rock ll with a size of up to 1.0–1,5 m has asmall amount of nes. When rock ll consist of limeor sand stone, the maximum stone size is smaller andthe amount of nes can be such that considerable sett-lement will occur if the ll is not properly compacted.

The maximum particle size permitted is normallytwo-thirds of the layer thickness but, from a compac-tion point of view, it is advantageous if the maximum boulder size does not exceed one-third of the layer

thickness. This reduces the risk of rock crushingduring compaction.

COMPACTION

PROPERTIES OFDIFFERENT SOILS

SOIL COMPACTION

22


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Vibratory equipment has provento be the most suitable and cost-effective method for compaction.Static and impact compaction arenot really well suited to rock ll.Impact compaction can be usedif a heavy falling weight is used.However, heavy falling weightsincrease the risk of crushing.

Medium-heavy and heavy vibra-tory compaction equipment is requi-red for rock ll in order to relocatethe large boulders and achieve thenecessary density and stability.

The risk of crushing the rocksmust be observed and may inuen-ce the choice of roller size, ampli-tude and the number of passes.

Rock ll compaction exertsextreme loads on the compactionequipment which is why it is important to select machines that arespecially designed for this purpose.

Gravel and Sand

Gravel and sand range in size froma chicken’s egg down to 0,063 mmor in some cases 0,075 mm. Theycan include fractions of other soiltypes which will affect their compaction properties.

The compaction properties ofgravel and sand are inuenced by the water content; compactionis most effective at the optimumwater content.

If the nes content is less than5–10%, the soil is classied asfree-draining. In free-draininggravel and sand, excess water is

drained out during compaction. Thismeans that the compaction workcan continue also when it is rainingor then the surface is ooded.

If the soil is not free-draining, problems are likely to occur ifattempts are made to compact thematerial above the optimum watercontent. The soil will becomeelastic and springy. It may be impossible to achieve the compactionrequirements as the soil becomeswater saturated at a lower densitythan the one specied.

When sand and gravel areuniformly graded it is difcult toobtain high density close to the sur-face (top 10–15 cm) owing to thelow shear strength of the material.The material tends to get pressedup behind the roller drum and thesurface therefore attains compara-tively low density. This has nogreat signicance in practice. Whencompacting in layers, the loose top

surface is compacted as the nextlayer is rolled.

The surface loosening should be considered when carrying outcompaction tests.

As a rule, all types and sizes ofmachines can be used for compac-tion of gravel and sand. The choicewill depend on compaction andcapacity requirements. Medium toheavy vibratory rollers will achievecompaction on thick layers whereassmaller roller is more suitablefor limited layer thicknesses andvolumes.

SiltSilt varies in grain size from0,063 mm down to 0,002 mm,although these limits may varyslightly according to soil classi-cation system. It can include frac-tions of other soil types which willaffect its compaction properties.

In pure silt or silt that is mixedwith coarse-grained fractions, thereis little cohesion. With higher claycontent, cohesion will increase.

As with all ne-grained soils,the compaction of silt is heavilydependent on water content. Forgood compaction effect the watercontent should not diverge toomuch from the optimum.

At optimum water content,silt is relatively easy to compact.At high water content and underthe inuence of vibration or trafc,silt is transformed into a more orless uid state.

Vibratory equipment is the

most effective for silt. Layerthickness can be almost the sameas for gravel and sand if the claycontent is not too high. If the claycontent is higher than 5% (butless than 15%) large machinesand thinner layers are requiredto overcome the cohesion in thematerial. In such cases, a pad-footdrum may give better results thana smooth drum. In addition, vibra-tory plates and smooth drum rol-

lers may have traction problemsespecially when the water contentis a little higher.

Boulders Gravel Silt

Cobbles Sand Clay

SOIL COMPACTION


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ClayClay consists of the smallest particles from around 0,002 mmand downward. The particles are sosmall that they cannot be discerned by the human eye. A clay contentof 15% is sufcient for the soil todisplay the properties of clay wherecohesion and apparent cohesionare the main resistance factors.The effect of cohesion dependson the clay content, the grain sizeand shape as well as the mineralcomposition of the clay. It can varywidely between two different clayswith the same grain distributioncurve but different grain shapesand mineral composition.

The water content has a greateffect on the compaction resistan-ce of the material. Compaction iseasiest at or above the optimum

water content.Clay requires a relatively high

compaction effort (compared withcoarse-grained soils). Vibratory pad-foot rollers are very suitablefor compaction of clay at watercontents below the optimum. Theycan transmit the high pressures andshear forces needed to compact hismaterial at or below the optimumwater content. Here the compres-sive strength is the highest. Layerthicknesses are normally restrictedto 15–40 cm depending on themachine size.

High speed tamping rollers arealso suitable for compaction ofclay. They are very economical onlarge clay lls. In such cases theclay is placed in 15–20 cm layers.

Clay with a water content abovethe optimum has less compressivestrength and can be compactedusing vibratory smooth drums orwith pneumatic tyred rollers.

Lime stabilizationCohesive soils are not possible tocompact when the water content ishigh. Stabilization of the materialusing lime is one way of improvingthe compactablity and the stability ofthe material. Lime is spread on thesurface and mixed into the materialusing a rotary soil stabilizer. The lime

binds part of the water and in time it

also creates a chemical binding that

substantially increases the strengthof the clay. Vibratory pad-foot rollers

are often the best choice for compac-

tion of stabilized materials.

Sub-base andbase courseSub-base and base course are selec-ted materials and should be withinspecied limits of a gradation curve. The main fraction consists of gra-vel. In certain countries relativelyhigh amounts of nes are allowed

in the sub-base, but it then loses itsfree-draining properties.

Sub-bases and base coursesnormally have high compactionspecications and require a highercompaction effort than ll materialfor the same layer thickness.

Vibratory equipment is the mosteffective on sub-base and basecourse. Impact compaction is notsuitable.

In some cases, where the base

course is thin (less than 10–15 cm)static rollers can be used. Theyare especially suitable if materialloosening is to be avoided. A basecourse should always be nishedoff with a couple of static passes before surfacing work can begin.

StabilizationSub-base and base courses cansometime consist of granular mate-rials mixed with cement, y-ash or

even bitumen. This is done in orderto increase the load bearing properties of the material. Stabilized base course material is often placedusing a paver in order to achievethe best possible evenness.

SOIL COMPACTION

Soil volumes

Soils have different densities depending on whether they arein situ , loose or compacted. The compacted layer thickness is alwaysstated in the design of new structures.Soil volume can be defined under different conditions• in natural state (in situ)• loose state (un-compacted)• compacted

The table below gives the relative volumes of different soil types.

Compaction properties of soil

A summary of the compaction properties offine-grained and coarse-grained soils.

Coarse-grained materialsRelatively easy to compact, especiallyby vibration. High bearing capacity.Free-draining soils are not susceptibleto soaking and frost.

Maximum permissible content of fines in free-draining soils: 5–10%

Fine-grained materialsWater content, and thus weatherconditions, are important to com-paction results. To be compacted inrelatively thin layers.

Sub-base and base course

1,0 m3 1,0 m3 1,0 m3 1,0 m3 1,0 m3

Rock fill

(blasted)

Bouldersand

Cobbles

(not blasted)

Graveland

Sand Silt Clay

1,75 m3 1,2 m3 1,2 m3 1,3 m3 1,5 m3

1,4 m3 0,9 m3 0,9 m3 0,85 m3 0,85 m3

Gravel Sand Silt Clay


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SOIL COMPACTION

There are a number of applications (see below) that re-

quire a special approach and methods and where general

guidelines for compaction do not apply.

Slopecompaction

Slope compaction can berequired for the constructionof dams and canals. Dams withan impervious upstream surface ofasphalt or cement concrete are oneexample where good slope compaction is especially desirable.

A self-propelled single-drumvibratory roller is the most suitabletype of machine for slope compac-tion. Whether the roller needs to be winch-aided or not depends onthe incline. When compacting, the

vibration should be switched onfor the upward journey and off for

the downwardone. If the roller

is winched a strongmesh should be used to

protect the operator and asafety wire should be attached to

the machine. Always use a roll over protection system (ROPS). Priorto using machines on slopes checkwith the manufacturer that themachines can operate continuouslyon the incline in question.

Dry compaction

Normally all types of soil are compacted most efciently at optimumwater content. However, in someareas such as arid or semi-aridareas, it may be impractical or toocostly to water the soil. In suchcases gravel and sand can be compacted in a dry state (water content


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Roller Compacted ConcreteIn contrast to cement stabilized base courses, roller compactedconcrete (RCC) is earth-moistconcrete with a 5–6% water contentthat is pre-mixed, transported to thesite and laid using standard hauling

and spreading equipment. It is thencompacted with vibratory rollers.

RCC is used in concrete damsas a ll and in industrial and portareas where heavy vehicles traveland maneuver at low speed. Asp-halt is not suitable for this kind ofapplications.

In dam construction the concre-te has low cement content (4–7%)and is normally spread in layers of20–30 cm.

Other suitable applications in-clude paving in tunnels and mines.

Test areas At the start of a road construction project, test strips are often set upto establish suitable compaction procedures which meet compactionspecications.

On large compaction jobs, forexample the construction of a dam,a full scale compaction test may becarried out employing a number of

different types of roller to establishthe best compaction practice.

One way of setting up a test isto lay down a strip where the layerthickness increases from virtually

zero to the thickest required. Thespecied measurements can bemade on the different thicknessesas the compaction process pro-ceeds. In this way, the maximumlayer thickness can be determinedfor the job in question.

Ground vibrations A vibratory roller in operationgenerates pressure and shear wavesas well as surface waves. Thesesurface waves are of primary con-cern for structures on or near thesurface of the soil.

An approximate and generalrule has been established statingthat ground vibrations that do notexceed 10mm/s do not cause anydamage to building with founda-tions on soil. Considerably highersafety limits, around 50 mm/s,applies to blasting operations. Itis also worth noting that a simul-taneous measurement of ground

vibrations in a building structureand the surrounding ground showsa signicant difference in wavevelocity. A velocity of 10 mm/sin the ground corresponds to2–5 mm/s in the actual structure.

Practical research has led to thefollowing recommended safetydistances resulting in a wave velo-city not exceeding 5 mm/s in the building foundation.

SOIL COMPACTION

Please note that the below infor-mation is to be seen as a generalrecommendation and that AtlasCopco does not accept any respon-sibility to any actual damage thatmay occur even if these recommen-

dations are followed.As all materials behave different-

ly it is recommended that vibrationmonitoring equipment is installedin any building where structuraldamage must be avoided.

Safety distances for vibratory rollers (including a safety factor of 2)

Self-propelled vibratory roller with pneumatic drive wheels (high amplitude)

Safety distance in meters = 3 times the drum module weight (in tons)

Vibratory tandem rollers (high amplitude setting)

Safety distance in meters = 2 times the drum module weight.

Common setup for a test areaon site. Maximum acceptable

layer thickness and the suita-

ble number of passes can bedetermined.


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There are three types of main specification, which sometimes can

be combined – method, end result and function.

Irrespective of the type of speci-cation, there is a call from govern-ments, governmental agencies, private owner-operators as well ascontractors themselves for effectivequality assurance methods.

Method specifications Method specications stipulatedetailed rules for type of equipmentto be used, number of roller passes,

roller speed, layer thickness, typeof soil and water content of the soil.The contractor is required to followthese rules in the compaction work.

End-result specifications End-results are specied for themajority of the compaction workinvolved in the construction of ro-ads, railways, dams and foundationsworld-wide. The specication mayinclude minimum densities or mini-mum load bearing properties. The

trend towards end-result specica-tions is universal. They offer more

leeway in the choice of equipment,and lend themselves to the mosteconomical method of achievingspecied densities. Often, vibratoryequipment enables the contractor towork to the best margins.

Functional specifications A third type of specication isknown as the function specica-tion where specied functions, for

example the settlement, evennessand friction, have to be fullledfor a certain contractual period.The contractor is free to use thematerials, layer thicknesses andequipment of his choice as long asa specied quality can be achieved.This type of contract is often linkedto a Build-Own/Operate-Transfer,BOT, contract where the contractorassumes operation of the highwayor other structure for a certain time – including maintenance and other

work – before transferring it backto the local road authority.

SPECIFICATIONS

AND FIELD CONTROLMETHODS

SOIL COMPACTION

METHOD SPECIFICATION

HOW COMPACTION WORKSHOULD BE CARRIED OUT

• Material and layer thickness• Machine type and size• Machine settings and number of

passes

The contractor must sign off on thatthe stipulated method was followed.

END-RESULT SPECIFICATION WHAT COMPACTION RESULTSSHOULD BE ACHIEVED

• Compaction result

• Control method

The compaction method is decidedby the contractor. The end result must betested and reported to the project ownerfor approval.

FUNCTIONAL SPECIFICATION FUNCTION OF THE COMPLETED

STRUCTURE OVER TIME

• Traffic volumes• Expected life time• Minimum acceptable road quality

(for example evenness, friction,rut depth etc)

The contractor designs and buildsthe road to meet the functional

requirements, maintenance responsibilityis also included in the contract.


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There are a number of methods of controlling specifications on soil in thefield. These include density tests, load bearing tests, levelling tests, and

others, all of which are spot measurements. Another method is the

roller-mounted compaction meter linked to a documentation system that

continuously controls the compaction process and the results.

FIELD CONTROL METHODS

SOIL COMPACTION


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Replacement method The sand replacement and water balloon methods are used asreplacement methods. A small hole

is dug in the soil. The contents areweighed and the volume of thehole is determined by lling it withcalibrated dry sand or with thewater balloon.

Tube sampling For ne-grained soils, especiallyclay, a tube is pressed down intothe material to remove a coresample for density tests.

Nuclear gauge method A nuclear density gauge providesan immediate indication of thedensity of the compacted layer.It also measures the water content.It works on the principle that radi-ation from a radioactive isotopethrough a material is attenuatedin proportion to its density. Bestresults are obtained in homoge-neous soils.

Static plate load test Static plate load test is performedon the surface of the compactedmaterial. By measuring the defor-

mation under the plate (with aknown area and load) it is possibleto calculate the modulus of elasti-city of the compacted soil.

The load bearing properties ofthe underlying layers will have aninuence on the measurement. Thedegree of inuence depends on thethickness of the compacted layer.

Falling-weight test Falling-weight test units are an ef-fective and rapid way of measuringthe load bearing properties of the

surface of the construction layerson site. The test can normally behandled by one operator. The unitmeasures the surface deectioncaused by a falling weight and fromthat calculates a dynamic modulusof elasticity. There are both lightand heavy falling weights.

Levelling ofsurface settlementThis method is mostly used on rockll, cobbles and boulders. The levelof a number of reference points ischecked with a levelling instrument

before and after compaction. It does not provide a direct measurementof the density.

Proof rolling This is a test where a very heavy pneumatic-tyred roller is run overthe compacted surface and the in-dentation may not exceed a certaindepth.

Penetration test There are several types of pene-tration tests which represent anattempt to quantify the behaviorof a soil. One of the most common

is the California Bearing Ratio(CBR) test.

The CBR test is an arbitrarytest. It does not attempt to measuredirectly any of the fundamental properties of the soil sample. Inessence, it consists of driving astandard cylindrical plunger intothe soil sample at a standard rateof penetration and measuring theresistance to penetration offered by the soil. This resistance is then

compared with certain standardresults. The ratio of the result forthe soil to the standard result isreported as the CBR.

The California Bearing Ratiotest is mostly used on ne-grainedsoils.

SOIL COMPACTION


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Continuous compaction control (CCC)

Many highway and other specifying agencies ask for documented proof that a contract has been completed as specied over the entiresurface in question and not only at a number of random sampling

spots. The demand for Quality Assurance has led to the developmentof sophisticated documentation (control and monitoring) systems that plot and record the result from a compaction meter using the roller asa measuring device.

The instantaneous and continuous registration of the entire compacted surface provides major benets compared with conventionalcontrol methods which may disrupt and delay the compaction work.Conventional testing methods for soil compaction may in somecases result in costs which are greater than for the compaction jobitself.

The compaction meter has proven to be a very cost-effectivecontrol method. The use of the compaction meter and documentationsystem, in combination with a limited number of density/load-bearingtests, is included in specications in a number of countries mainly forcoarse-grained soils.

The documentation of the compaction results gives all stake-holders valuable information regarding the quality and uniformityobtained.

Even if the use of a compaction meter not is included in the spe-cications, it will help operators to identify weak spots which needmore roller passes, and, in general, to optimize the number of passesto avoid over-rolling.

Compaction meter anddocumentation systems

Principle and functionA roller-mounted compactionmeter consists of an accelerometermounted on the vibrating drum.

The accelerometer readings aresent to processor and the readingsare presented to the operator onthe control panel of the roller. Thesignals from the accelerometer areconverted to values that indicatea measure of the stiffness of theground. The system records condi-tions at certain depths. The actualdepth depends on the size of theroller and amplitude selected.

A computer documents and presents the measured values ona screen which can be placed inview of the roller operator. The

documentation system enables theentire area that has been rolled to be presented on the screen. Use ofcolour and other graphics make itimmediately apparent which areasrequire additional compaction.

A GNSS receiver provides

accurate positioning and speedinformation to the on-board system.The documented result can then

be transferred to the ofce for nalanalysis and storage.

Applications The compaction meter (with or with-

out the documentation system) is

most suitable on coarse-grained soil

and rock lls. A soft, un-compacted

soil gives little response while a hard,well compacted soil will give a better

response. The stiffness increases in proportion to the bearing capacity.

CCC can be used and specied asone or more of the four differentmethods described below.

Weak area analysis The CCC values are used to deneone or more areas where the soil

stiffness is the lowest. These areasare the subjected to directed testing.If the areas pass the test this meansthe rest of the area is okay.

SOIL COMPACTION


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Calibrated target valueThe CCC values are calibrated tocreate a correlation to the accep-tance control method, typicallystatic plate load tests. Using this

correlation a corresponding CCCvalue is determined and used asthe target value for the area.

Pass count Using the CCC system to countand document the number of passesmade helps the operator achieveeven compaction results and provi-des documentation that the job wasdone according to the specication.

Progress The CCC values increase withevery compaction pass, a higherincrease for the rst passes and alower increase for the later passes.Once then increase from one passto the next is below a certain levelthere is very little more compaction

to be achieved. This is one measurethat can be used to determine whenthe compaction is nished.

The operator runs six vibratory

passes with the roller. When thisis completed, change view to look

at the compaction meter value and

locate the two weakest areas. Check

if the compaction increase from the

previous pass is less than 5%. If it is

more than ve percent it is still pos-

sible to increase the stiffness on the-se areas, compaction is not nished

here. Make more passes and review

where the weak areas are to be found

now. Check the increase percentage;

if it less than ve percent from the previous pass this means that the rol-ler that is being used cannot achieve

more compaction.

It is then suitable to run accep-

tance testing on these areas. If thetest fails it is most likely a material problem as the machine is not ableto achieve a higher stiffness.

A successful procedure used inroad and aireld constructions has been to rst register the compactionmeter values over the compactedareas, and then perform static load bearing tests in a limited numberof points, selected where thelowest compaction meter valueswere measured. This procedure

should give a good certainty thata prescribed load bearing capacity

is attained over the entire area of,for example a base course.

On ne-grained soils the bea-ring capacity is, to a high degree,related to the water content. As

the compaction meter indicates theload bearing properties, no directrelationship exists between thecompaction meter value and thesoil density. The compaction metercan therefore not be used to directlyguide the compaction work as oncoarse-grained soil. Informationgiven by the compaction meter onthe level and uniformity of the load bearing properties may, however beof great value.

A useful application of thecompaction meter is to detect softand weak spots of ne-grainedsoils with high water content. Suchspots are found in ll materials aswell as in natural ground. Rollersequipped with compaction metershave therefore, with good results, been used to survey the groundsurfaces on which road and railwayembankments shall be built. Evenif the use of a compaction meter isnot included in the specications, it

will help operators to identify areaswhich need more roller passes, and,in general, to optimize the numberof passes to avoid over-rolling.

31

SOIL COMPACTION

It is also possible to use several

methods in combination, this is oneexample:

Target number of passes: 6Weak area analysis: 2 areas

Progress: Maximum 5%


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A road traffic system is multifaceted. It comprises roads,

the people who use those roads and vehicles.

How well the system functions as a whole depends on

the individual components’ characteristics, how

they interact, and the impact of outside factors

such as climate, light conditions, etc.

Road surfacing has a decisive impact on trafc.The type of wearing course and the condition it isin affect the behaviour of the vehicles using the roadand, thereby, road safety. They also affect the cost oftravelling as well as the environment.

The majority of all paved roads are surfaced withasphalt¹. Concrete is also used but is, in general, lesscommon, although there are some countries whereconcrete is the preferred material. Asphalt is used inthe wearing, binder and base courses.

ASPHALT PAVING,COMPACTION

AND MILLING

ASPHALT PAVING, COMPACTION AND MILLING

1 Asphalt refers to a mixture of bitumen binder with mineral aggregate and filler.

1

2

3


33/92


The wearing course (1) provides an even,weather-resistant and high-friction runningsurface which can withstand abrasive forces.

It makes the road safe and the ride comforta-ble. In combination with the other layers inthe pavement, the wearing course helps to

distribute the traffic loads to avoid excessiveloading of the entire pavement.

The binder course (2) fulfils the same loaddistributing function and provides an even,

level surface to carry the wearing course.

The base course (3) is the main componentwhich provides the strength and loaddistributing properties of the pavement. On

roads with light traffic, it is usually madefrom graded crushed stone. On more heavilytrafficked roads, a fully bituminous road base

or cement stabilised granular base may beemployed to achieve the required strength

and durability.

In the design of the pavement (the part of a

road above the embankment) the choice of

material and the thickness of each layer inthe pavement are critical to good service life.

Correct design requires knowledge of thematerials’ different properties and theexpected load and intensity of the traffic.

In addition, it must take into account localclimatic conditions as well as the economic

constraints.


1

2

3

The image has been manipulated to highlight the three separate layers.


34/92


An asphalt surfacing is normally built to last for

a certain period of time, for example 20 years.

Its durability will depend on the quality of the

components, the mix design, and the manu-

facturing process from asphalt mixing to final

compaction.

The quality of an asphalt surfacing can be

measured against a number of properties.The most important include:• Resistance to plastic deformation,

which can be expressed as stability• Trafc and temperature related fatigue• Load distribution• Sensitivity to water • Ageing

QUALITY AND FUNCTIONALREQUIREMENTS FOR

ASPHALT PAVEMENTS

1. Evenness

If a road is to function satisfactorily over a givenperiod of time, the surface has to be even.

Unevenness reduces traffic speed and prolongs journeys. It reduces riding quality and increases

vehicle and tyre wear. It also increases theimpact effect of vehicles on the road, which inturn accelerates road wear and thus shortens

the service life. Transversal unevenness refersto rutting as a result of wear on the wearing

course or deformation in one or more of theunderlying layers. A measure of this is oftenthe depths of the ruts. Longitudinal unevenness

refers to lengthways unevenness of the road

or road section. Different methods are used tomeasure its occurrence, such as the Internatio-

nal Roughness Index (IRI).

1.

2.

3.

4.

THERE ARE A

NUMBER OF

FUNCTIONAL

REQUIREMENTS

THAT A ROAD

SURFACE HAS TO

COMPLY WITH TOMAKE IT USABLE.




35/92


The choice of surfacing

and its qualities depend on

the weight and intensity of

traffic as well as the climatic

conditions that the road is

expected to be subjected to

within the given period.

If the surfacing is to function asintended, the various ingredients – binder, aggregate and ller – needto be selected carefully with a viewto optimising the nal mix. Goodquality material and good design

are not enough to guarantee a longservice life. Just as vital are theway the material is manufacturedand the way it is laid down andcompacted. The benets of rst- class material can quickly disap- pear if the quality in one of thestages in the production chain failsto come up to standard.

The three main components in anasphalt mix are binder, aggregateand ller. In many cases, the binderwill also contain additives. In prac-tice, there are two main types ofasphalt, mixed asphalt and surface

treatments.

Mixed asphaltAlthough there is a wide variationof mixed asphalt there is no gene-rally acknowledged classicationsystem. The most common way tocategorise them is by mix tempe-rature: Hot Mix Asphalt (HMA),

Warm Mix Asphalt (WMA) andCold Mix Asphalt (CMA). HMAas well as WMA is a mixture ofheated aggregate, bitumen andller. It is manufactured in batchor drum mix plants at high tempe-

ratures i.e. 130–180 °C (HMA).The penetration value of the bitumen is determined by outsidefactors such as climate and trafc.Hot climates and heavy trafcrequire a high penetration value,for example. The binder can bemodied with different additivessuch as polymers.

TYPE OF SURFACING

>

2a. Texture

Texture refers to the surface roughness.

Texture is broken down into varying

degrees: macro- (0.5–50 mm) and micro-

texture (


36/92



Hot Mix Asphalt. Surface sealing.

Cold Mix Asphalt (CMA)CMA is produced using coldaggregates and a pre-heated binder(75–85°C). It is used as base, binderand/or wearing course for roads

with a low trafc volume.

Warm Mix Asphalt (WMA)WMA is produced at a lower temperature than HMA, 100–140 °C.A lower temperature means that lessenergy is consumed in producingthe asphalt. Less energy used meanlower emissions from the produc-tion. The application for WMA is basically the same as for HMA.

Hot Mix Asphalt (HMA)HMA is produced as Dense asphaltconcrete for use as a base, binder orwearing course or as Stone Masticasphalt (SMA) or Porous asphalt for use as wearing course. The aggre-gate in a dense mix or an asphalt base has a dense gradation whileSMA and Porous Asphalt are bothopen graded.

Dense Asphalt displays goodageing resistance thanks to its lowair-void content. Dense asphalt is

suitable for all asphalt pavementapplications. It is less abrasionresistant and stable than SMA.

The main characteristics of SMA are the gap in the ne end of thecurve, a high content of coarseaggregate and the high ller con-

tent. The coarse material builds askeleton of aggregate in the mix.

The binder content in SMA issomewhat higher than in DenseAsphalt which in turn has higher

binder content than Porous Asphalt.Fibres are sometimes used as acarrier for the binder to ensuresufcient high binder content inSMA and Porous Asphalt.

The air void content in DenseAsphalt and SMA is usually 2–5%(Asphalt Base: 4–7%), while inPorous Asphalt it is considerablyhigher at around 15–20%.

SMA is well suited for wearingcourses on high volume roadsowing to the high stone contentwhich provides good resistanceagainst abrasion as well as goodstability.

As the name implies, Porous (or

drainage) asphalt has good draining properties. This reduces the risk

of water spray and aquaplaning. It

has good retro-reective properties

in darkness and rain and tyre noise

is lower than on other types ofsurfacing. These benets diminish

relatively quickly as the pores in the

surface get clogged with other par -ticles and dirt. Owing to its structure,

Porous Asphalt is more susceptible

to climatic effects. This can have a

negative effect on the water resistan-

ce and the ageing properties of the binder and shorten the service life.

Surface treatmentSurface treatment is the processof laying binder and aggregateseparately. Examples of coatinginclude surface sealing, penetration

macadam and slurry seal.

Surface sealingSurface sealing prevents waterfrom penetrating the road. Theamount of binder is important fora long service life of the surfacetreatment. The aggregate needsto be uniform in size and washedto remove the nes to ensure goodadhesion.

Penetration macadamPenetration macadam is sometimesused as a base and wearing course.It comprises a layer of aggregateover which a layer of bituminous binder is spread. If the binder isa bitumen emulsion, the viscosityand dispersion properties should be such that the binder does not penetrate more than 50% of theaggregate’s layer thickness.

Slurry seal

Slurry seal involves spreading a binder and then laying sand on top.Pre-manufactured emulsion slurrycan also be used. Slurry seal is usedto ll cracks and other cavities to prevent water penetrating the roadsurface.

Dense asphalt concrete

Stone mastic asphalt

Porous asphalt


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Binders

BitumenThe binder in an asphalt mix is

referred to as bituminous, i.e. itcontains bitumen in some form.Bitumen is a thermo-plastic mate-rial which means that it becomessofter and more uid when heatedand hardens when cooled. The process is repeatable.

It can also be described as avisco-elastic material which meansthat its stiffness is a function oftemperature as well as loadingtime. From the gure below you

can see that the stiffness at a givenloading time decreases when thetemperature increases. The gurealso shows that at a given tempe-rature stiffness decreases as theloading time increases.

When the bitumen is mixed with

aggregate, it must be sufcientlyviscous to cover the surface of theaggregate. However, it cannot betoo uid as the binder will drain off

from the surface of the aggregateduring storage or transportation.The viscosity must also facilitatethe paving and compaction process.The binder should provide stabilityto avoid excessive deformation, butit must be exible enough to avoidthe risk of cracking. The adhesivequalities of the binder determinehow much aggregate loosens fromthe surface (ravelling).

Cutback and emulsionCutback is a mixture of bitumenand solvent, for example naphtha,while emulsion is a mix of bitumen,an emulsier and water. They bothenhance the uid properties of amix at low temperatures. When the

solvent or water evaporates, the bitumen retains its original proper-ties. The properties of the binder inthe road are mainly determined by

the constituent bitumen. The use ofcutback is on the decline, owing toenvironmental concerns, while theuse of emulsion is increasing. Themost common areas of applicationinclude, surface treatment, CMA,tack-coating, slurry sealing and penetration.

Specifications and test methodsfor bitumenIn most countries bitumen isclassied according to viscosityor penetration. Ageing propertiesare determined by the measurementof one or several parameters beforeand after ageing in the laboratoryaccording to stipulated methods.


Bitumen stiffness as a function of temperature and loading time for a100 Pen bitumen.

Specifications and test methods for bitumen -Determination of penetration.

S t i f f n e s s m o d u

l u s ( M P a )

Loadingtime (S)

mm x 10

25°C

Asphalt normally consists of three material components, the binder, the

aggregate and the filler. Some surfacing material includes additives such as

adhesives, polymers, fibres and recycled material.

MIXED ASPHALT

COMPONENTS


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Bitumen Test Data Chart The Bitumen Test Data Chart (BTDC) is used to predict the temperature/viscosity relationship of the bitumen over a wide range of temperatures, and is veryuseful to ensure the appropriate viscosity for any gradeof bitumen. The BTDC consists of a horizontal temperature scale and two vertical scales for penetrationand viscosity. The temperature scale is linear while the penetration scale is logarithmic. The viscosity scale has been designed so that penetration classied bitumenwith normal temperature susceptibility or penetrationindex will give straight-line relationships.

There are optimum bitumen viscosities for themanufacturing and compaction of bituminous mixes.Excessive viscosity during mixing, results in the aggre-gate not being coated properly while if the viscosity istoo low, the bitumen will easily coat the aggregate butmay subsequently drain off the aggregate. If the visco-sity is too low during compaction, the mix will be ex-tremely soft and workable. This may result in shovingor transversal movement of the mix. High viscositywill signicantly reduce the workability of the mixand consequently make it more difcult to compact.

Performance Grade (PG)The United States uses Superpave to specify asphaltmaterials. Asphalt binders are specied according toa performance based specication. The temperature ofthe pavement in which the binder is going to be useddetermines the choice of binder. Performance graded bitumen is classied according to the highest andlowest pavement temperature at which the bitumenmust have the ability to avoid rutting and low-tempe-rature cracking. For example, a PG 64–22 (sixty-fourminus twenty-two) is designed to prevent rutting ona hot summer day where the temperature is +64 °C20 mm below the surface and to counteract low tempe-rature cracking in the winter at -22 °C at the surface.

AggregateAggregate is a general term for all the mineral consti-tuents of an asphalt mix. It includes crushed stone,gravel, sand, slag and nes. In asphalt, the weightof the aggregate accounts for about 85% of the totalweight of the mix. The quality of the aggregate isdependent on both the origin of the aggregates as wellas the production method (natural or crushed material).The properties of an aggregate that directly or indirect-ly inuence the functional properties of the surface aregrain-size distribution, porosity, grain shape, durability,abrasion resistance, polish resistance and resistance toweathering. A number of these are interrelated.

Particle properties The most important physical properties of a mineral arestrength and shape. The quality of a rock material can be partially improved in the production stage. In prin-ciple, each crushing stage can improve the materials’mechanical properties. Shaping, for example, increasesthe abrasion resistance of the aggregate as well as thestability of the mix in a wearing course and therefore prolongs the service life of the road.

Grain-size distributionGrain-size distribution is the basic property of an aggre-gate. The grain-size distribution of a given sample isdetermined by a sieve test where the dried sample is passed through a number of standard sieves which

This modified Bitumen Test DataChart shows the maximum and

minimum mixing and compac-tion temperatures for a 100 penbitumen with the softening point

of 50 °C.



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differ in screen size. The grain-sizedistribution is described graphicallyin the form of a gradation curve.The grain-size distribution deter-mines the type of mix. Varying thegrain-size distribution for a givenmix type will inuence the functio-nal properties of the asphalt.

Filler The ller is used to ll the voids

between the coarser particles andto stiffen the binder. It therebycontributes to the stability of theasphalt mix. The ller (particles


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Design involves the choice of mate-rial (binder, aggregate, ller andadditives) with properties suitedto the nal required results and themixing of these ingredients in thecorrect proportions. Outside factorssuch as climate and trafc intensityand volumes must also be takeninto consideration. The tempera-ture span determines the choice of bitumen. The types of aggregateand binder must relate to the trafcload. The greater the intensity,the higher these requirements are.

The type and volume of trafchas a strong bearing on choice ofaggregate and binder as well asthe design of the mix. Weight, axlecongurations and tyre pressuresshould also be considered.

Once the choice of ingredientshas been made, the aggregatewith the required gradation curvemust be produced, A number ofaggregate samples are mixed withdifferent amounts of the selected binder to give a variation of bindercontent within given limits. One of

the samples should be the bindercontent recommended in the high-way authority’s own technicalspecications. The binder contentof the other samples should be insuitable intervals above and belowthis nominal content. The mixes arethen compacted using a Gyratorycompactor or Marshall apparatus.The compacted samples are thenanalysed for air void content,strength, etc. and the optimal mixis chosen.

Correct mix design is essential to a durable road.

MIX DESIGN

PROPORTIONING

Marshall compaction of asphalt sample.Gyratory compaction of asphalt sample.



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Asphalt and soil have a lot in common; however, a major distinction between them lies in

the adhesive properties of the bitumen used to bind the particles in an asphalt mix.

Asphalt mixes show wide variations in composition and properties. Their properties and compactability are primarily a function of:

• Internal friction

• Adhesion

• Viscous resistance/temperature

Internal frictionThe rst of these, internal friction,is determined mainly by the aggre-gate properties, and is more appa-rent in a well-graded mix than in an

open-graded one. A mix containingnatural round aggregate, where the particles can move past each otherrelatively easily under compaction,has less internal friction than a mixwith angular, crushed aggregate.The mix with crushed aggregateconsequently needs a higher compaction effort and also gives anasphalt surfacing of higher strengthand stability. High stone contentand large maximum stone size areother factors that result in stablemixes.

AdhesionAdhesion is what makes the binderattach itself to the aggregate.

Viscous resistanceViscous resistance is a function ofthe viscosity of the bitumen and theactual temperature of the mix. Theviscous resistance works againstthe rearrangement of the particlesunder compaction, and the lowerthe temperature the greater thisresistance is.

PROPERTIES OF

ASPHALT MIXES

Dense asphalt concrete. Stone mastic asphalt (SMA).

Mix proportions of two differentasphalt mixes with a maximumaggregate size of 16 mm. On the

left is a dense asphalt concrete andon the right a stone mastic asphalt(SMA). Note the high content of

large aggregate in the SMA.

Internal friction Adhesion



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Mixing Asphalt mixes are normallymanufactured in either continuousor batch-type asphalt works. The

asphalt plant can be mobile or sta-tionary. Capacity normally varies between about 100 and 300 tonnes per hour in batch plants while con-tinuous asphalt plants are used forthe production of larger volumes ofthe same type of mix. Here capacityvaries between 50 and 600 tonnes per hour.

Naturally, the constituentcomponents of an asphalt mix allhave a decisive inuence on thenal quality of the mix. As morethan 90% of the mix comprisesaggregate, the quality of the mix is

highly dependent on the quality ofthe aggregate which is a functionof the crushing process. It is alsoimportant to handle the aggregate

in the correct manner to avoiddeterioration of the gradation curveand exposure to moisture. A dry,well-graded aggregate is the foun-dation of a good asphalt mix.

In modern plants, the propor-tioning of the aggregate is largelygoverned by automatic processcontrollers according to pre-pro-grammed recipes. The aggregateis dried and heated in dryer drums.In the actual manufacturing pro-cess, bitumen and ller are addedto the aggregate to form the mix.There are different types of ller

according to the desired propertiesof the mix. Amines are added toimprove adhesives qualities, bresare used to allow higher volumes of

bitumen, while polymers improvethe binder properties.

The constituents are mixedaccording to a set pattern in themixer to achieve a homogenousasphalt mix. Mixing time will varyaccording to mix and type of mixer.It is important to nal quality thatthe time is neither too short nor toolong. Once ready the mix is transported to insulated and/or heatedstorage silos to reduce the cool offeffect. Measures also have to betaken to ensure that the asphalt mixdoes not oxidise or segregate.

MANUFACTURING

PROCESS ANDTRANSPORTATION



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TransportationTransportation of the mix fromthe asphalt plant to the site goesthrough three stages before it is laiddown on the road surface: loadingat the asphalt plant, transport to thesite and tipping into the hopper ofthe paver. To avoid disruption thetransportation must be well plannedand carried out correctly.

During loading it is importantto minimise the risk for segregation.Loading must be quick and the load

should be distributed as evenly as possible over the whole trailer. Asteep-sided pile will cause the mixto segregate. The transport to thesite must be well-planned. If a paverhas to stop to wait for a new load,the quality of the surfaced road willsuffer. It can lead to unevenness andreduced compaction both of whichmay shorten the service life of theroad. On the other hand, a convoyof waiting lorries should be avoidedat the site. The asphalt mix maycool off while waiting, which maylead to unsatisfactory compaction

results or having to discard the mix.The unloading of the asphalt massrequires skill to avoid segregationand to avoid stoppages.

A large quantity of asphaltmix retains the heat for a longer period than a smaller amount. If itis placed on an insulated truck andcovered properly, the chance of de-livering at the correct temperatureincreases signicantly. A rounded bed on the truck or trailer is alsoan advantage as the cold corners

on a regular truck can be avoided.There are various mathemati-

cal formulae for working out thecost of transport of asphalt mix.The overriding aim of any suchcalculation must naturally be toachieve cost-effective transport andmaintain the quality of the asphaltmix.

Tack coatingTack coating is the use of an asp-halt emulsion or cutback to “glue”

or bind together two surface layers – for instance when adding a new

wearing

Dynopac Performance Handbook

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