Sunday, March 31, 2019

The Bitumen Stabilised Materials Engineering Essay

The Bitumen stabilized Materials Engineering EssayThe pursuit character looks at what bitumen satbilised signifi nonifyts be and how they atomic number 18 implemented in twisting. As many aspects of bitumen photographic photographic emulsion and scintillateed bitumen overlap this section looks at them some(prenominal) together, which sub-sections outlining the differences betwixt the methods.IntroductionBitumen Stabilised literalsBitumen stabilized satisfyings argon tangibles which shit been breeded with either bitumen emulsion or foamed bitumen. When adding either grammatical case of bitumen the quantity of bitumen should non exceed more than 3% of the total masses of the dry merge, as this would conceive it is more than a stabilize agent. what is more in many situations an alert filler in the radiation pattern of cementum or hydrated lime arse in any case be added to the assortment. If it is added yet it should not exceed more than 1% of the bitumen stabilizer added. If it does the cloths is considered to be cement treated.It is similarly of import(prenominal) to business that this stabilisation agent does not the solid into solid pave like signifi cigargonttet. In under pass this discourse the poppycock go away remain in a granular state similar to how it was ahead stabilisation. It is yet its behavioral characteristics which allow change. The visible give experience an emergence in material effectuality and a diminution in dampure susceptibility as a result of the manner in which the bitumen is spread amongst the finer f do particles.The fact that the material bequeath remain in a granular state sum that this treatment method is dramatically polar from all other pavement materials. The dispersed bitumen changes the plume properties of the material by signifi empennagetly increasing the gumminess value whilst ca use minor change to the internal friction angle of the material. It exit in any cas e aim a void essence similar to that of a granular stratum, not like and asphalt.Bitumen emulsionAs the name suggest in this summons bitumen is emulsified in peeing. This way of life that bitumen is dispersed in water, with the knowledge that they go forth not desegregate overdue to the fact an emulsifying agent is use. The emulsifying agent depart also give the bitumen emulsion a charge, make the bitumen emulsion either cationic or anionic.This pre liquifyture is then added to the aggregate which testament make up a part of the pavement structure. As the bitumen droplets be charged, they ordain be attracted to the aggregate particles. In attraction they ordain be drawn to the littler particles as they have the greatest surface atomic number 18a and charge ingress features. For these reasons the type and moisture of the aggregate in the mix is crucial in efficiently dispersing the bitumen emulsion and precludeing premature separation of the bitumen from the w ater during variety. formerly it has been interracial the separation of the water from the bitumen needs to occur. This leave behind allow the bitumen to act as a binder. This separation should just occur after the material has been fully compacted.The change integrity bag process convolute with Bitumen emulsion occurs offsite in a manufacturing plant. here(predicate) it is can be stored for several months. The diagram below shows a simplified version of the manufacturing process.Foamed BitumenTo plead foamed bitumen water is injected into hot bitumen, which results in instant foamy of the bitumen. In the foaming process the hot bitumen is turned into vapour, which is trapped in thousands of tiny bitumen bubbles. These bubbles dissipate in less than a minute.When the bubbles burst they form tiny bitumen particles. These spread throughout the aggregate attaching themselves to the finer particles of the aggregate mixture. When the aggregate is compacted, the bitumen cover ed particles are pressed against the big particles in the aggregate. As a resultant of this localized non-continuous bonds are formed, like spot welds.BehaviourAs the material treated with bitumen leave behind remain in an unbound state, it will act similar to the original material. The scarce difference will be an improved cohesive dominance and reduced moisture aesthesia, which are both favorable outcomes. This is because the bitumen only disperses amongst the finer particles, which forms a bitumen-rich mortar between the gritty particles. This also means that opponent to the common misconception that the material will capture black and sticky like a hot-mix asphalt. The material will only slightly darken in colour.Through numerous tests around the area of bitumen stabilized pavements a number of initial observations on how the pavement will behave have been made. The following behaviours have been assumed.Materials treated with either bitumen methods will experience an increase in cohesion.The friction angle of the treated material will remain similar to the untreated material.They cause flexural strength. Which will mean the pavement is less likely to crack when subjected to pliant stresses. moisture sensitivity and durability are improved. This is due to the fact the finer particles are encapsulated and immobilized jam feast channels.The most common mode of failure is permanent deformation. all(prenominal) these behaviors will see on the followingThe local climate (Temperature, fair(a) rainfall, likeliness of frost or snow)The properties of the parent materialThe slow-wittedness of the layerThe quantity of binder addedThe use of any bustling fillersThe properties of the supporting materialIt is of import to note here that BSMs behave very different to asphalt and cement treated materials.BenefitsThere are a number of benefits associated with using BSMs. These embarrassIncreased strengthThe ability to replace b passage(prenominal)er role materials, meaning a cost saving modify durability modify moisture sensitivityCan provide cost and time savingsTypical failure mode is permanent deformation, which requires less effort to rehabilitate when compared to a material that will fail due to full-depth crackingThey are not temperature sensitiveIf the road requires rehabilitation BSMs propose little treat to the environmentThey are not overly sensitive, meaning the essence of bitumen added can vary slightlyThe process does not require heavy pull traffic. This limits the damage cause to newly constructed layers during constructionLimitationsWhen considering whether to use BSMs or not there are three main limitations. These should be guardedly considered when reservation the decision to use BSMs. The three limitations areEconomics Bitumen treatment can add significant costs to a project. Its use of lower caterogory roadstead should be carefully examined as it could not be worth it. formula expertise as they are cu rrently been developed and act other than from all other pavement materials careful objective is needful.Construction Expertise the construction process requires attention to detail. This means special training of the work out force is inevitable.along with this limitations the both bitumen emulsion and foamed bitumen have their own disadvantagesBitumen EmulsionWith bitumen emulsion come the following disadvantagesBy adding the water present in the emulsion process, the original material may go over its outflank water kernel. This will mean the material cannot be compacted properly.A fond setting time is required allow the material to gain sufficient strengththe construction process moldiness be completed with care. If the bitumen breaks prematurely it will not mix properly. If the material is to s add-in it can bring months for the bitumen to breakFoamed BitumenWith foamed bitumen come the following disadvantagesit requires sufficient fines. They required to ensure the bitumen mixes thoroughly. scintillating equipment needs to be up kept and be in remedy working order. The foamed bitumen needs to be sprayed in uniform, consistent manner.The process requires specialiser equipment, as the deuce liquid are not compatible.Materials Suitable for treatmentFor bitumen stabilisation to work a worthy material must be selected. First of all the material must be granular. For this reason materials that are suitable for treatment includeCrushed rockPreviously untreated natural gravels, such as basalt, granite, limestone, quartz, sandstone reclaim asphaltIt can also be said that calcrete gravels can be used for bitumen emulsion only it will not work with foamed bitumen.Design ApproachDesign sequenceThe first step in a distinctive normal for a BSM involves an investigation of the conditions. This includes expected traffic volumes, the materials visible(prenominal), the climate and the pavement structure for recycle projects.Once this has been done a lab oratory investigation of the proposed material leaves place. This involves find the materials class.The next step is to design the mix and make the final material classification.Once all of these steps are completed the structural design is completed. In this design if it is shown that the road is not economically viable the mix design will be redone and the steps repeated.Shown below is a flow chart of the steps involved. prance DesignIn using a stabilizer it is big that the stabilizer corresponds its intended purpose. The process of design the mix will be mainly symbiotic of the design traffic, the material available and the cost considerations. However n creating a mix design it is also important to consider the followingThe primary failure mode this will define the materials performance requirements.Appropriate laboratory tests tests need to be selected that will identify the key performance criteria and failure mechanisms.Identifying key mix properties and essential ma terial properties.Taking into account variability in material propertiesenvironmental factors clime and moisture conditions.The ability to effectively compact the material.In innovation the mix it is important to note that optimum bitumen content is not continuously selected for the mix design. This is because although the optimum bitumen content will provide the maximum material strength, this will mean other characteristics are forfeited. For example a high strength design will often lead to brittle sturdy pavement layers that are susceptible to cracking. In designing the mix it is important that the design is balance so that it will be suitable to it requirements. categorisation of BSMsCurrently South Africa has divided Bitumen Stabilised Materials into three classes. These classes are dependent on the quality of the original material and the design traffic. The three classes includeBSM1 The parent material has a high shear strength, and is normally the dwelling layer for large volumes of traffic. Source materials include well graded impoverished rock or acquire asphalt.BSM2 The parent material has a fairly high shear strength and is normally the bastardly layer for declare traffic loads. Source materials include graded natural gravel of reclaimed asphalt.BSM3 The parent material is soil-gravel and/or sand, stabilized with higher bitumen contents. It is a base layer that can only handle low traffic volumes.It is supposition that Australia will have a classification system similar to this.Mix designBSMs behave in a very complex manner, which gives engineers a great flexibility when it comes to designing a mix that will best meet the design conditions. The mix is made up of aggregate, bitumen and close totimes an quick filler where required.In design the mix there are two fundamental failure mechanisms that need to be designed for in the mix these arePermanent Deformation This is dependent on the materials shear properties as it is caused b y the accumulation of shear stresses. Resistance to permanent deformation as known as rutting is improved by repaird aggregate angularity shape, hardness and roughnessIncreased maximum particle sizeImproved compactionReduced moisture content addition of limited amounts of bitumen humanitarian of an active fillerMoisture Susceptibility this is the damage caused by the flick of a BSM to high moisture contents and pore-pressures caused by traffic. This then means a loss of adhesion between the bitumen and the aggregate. Due to water been involved in the mixing stage and the partially coated nature of the aggregate makes moisture susceptibility an important consideration in the evaluation of material performance. Moisture resistance is improved byIncreased bitumen contentAddition of an active fillerImproved compactionSmooth continuous razingIt is interesting to note here the difference in recommended bitumen content. To help foresee deformation limited amounts of bitumen are recomm ended. However to improve moister resistance change magnitude bitumen contents are recommend. This means that a compromise must be made, by using the laboratory examen to de nameine a bitumen content which will meet the demands of the design.Mix type selectionAs give tongue to in sectionXX the three main factors the influence the type of BSM used areThe design trafficThe quality of aggregate availableThe costOnce the type of BSM has been selected there are three main factors that affect the bitumen and active filler selection for the mix designTraffic design (volumes and loadings)Climate (particularly moisture considerations)Supporting layers (strength)The influence these factors have is demonstrated in the following figure. As it can be seen heavy traffic loads, a prankish climate and weak supporting layers all mean an increased amount of bitumen is required to ensure design requirements are meet.Mix Design appendageTo compose the best design mix possible several adjective st eps need to be done. This ensures that that every criteria is meet, as there are numerous variables that need to be checked.The first step of the mix design is to test the material which will be treated. This is done to ensure that the material is appropriate for testing. These tests include standard laboratory tests to determine the materials grading curve, moister, density and Atterberg limits.The next tests which are undertaken are the level 1 mix design tests. These provide an interpretation of the act rate of bitumen and active filler required to achieve an indicated class of BSM. direct 1 starts with the preparation of samples that will be used to manufacture the specimens required for all levels of mix design testings. testing at this level involves preparing centurymm diameter specimens which are compacted and cured for the purpose of under expiry substantiating pliant aptitude testing. These testing results are used toIndentify the preferred bitumen stabilizing agent Determine the optimum bitumen contentIdentify if there is a need for an active filler and its type canvasss after level 1 are done depending on the design traffic. The first of these are Level 2 mix design tests. The test at this level involves fashioning a sample which is clmm in diameter and 127mm in space. These are make using vibratory compaction and then cured at the vestibular sense moisture content. This sample then undergoes Indirect ductile Strength to optimize the required bitumen content.The level 3 mix design test is only recommended for high capacity roads. This test involves preparing 150mm diameter by 300mm in length specimens, which allows for a higher level of confidence. It then undergoes the same Indirect Tensile Strength test.Mix Constituents coreA wide range of mineral aggregates are suit for use with both types of bitumen treatment. These include aggregates ranging from sands to weather-beaten gravels to crushed stone and can either be virgin or recycled. These must however fall into certain quality standards to ensure the road will be at it required class.When examining a material its following properties will be checkedDurability characteristics of the untreated aggregate malleabilityGradingSpatial compositionWeathering characteristicsAggregate sourceThe aggregate used can come from three different sources, Virgin Aggregate, Recycled Granular Layers and Reclaimed AsphaltQuality of AggregateIn using bitumen to stabilize the material it is possible to use a poorer quality of aggregate. For virgin aggregates four tests are used to identify material limits.Soacked CBRGrading completing a grading will identify any deficiencies in the material voice passing through the 0.075mm sieve higher fines contents mean a higher need for bitumenPlasticity Index for bitumen emulsion the materials PI should be less than 7. For foamed bitumen the materials PI should be less than 10. Materials with a high PI can be treated with lime.For recycled gr anular layers the materials quality will depend onThe structure of the existing pavementConstruction variability judgment of recyclingAge of the pavementDegree of patching and repair on the existing pavementThickness and nature of old surfacing seals. apply reclaimed asphalt needs serious consideration as some material may not meet the quality standards required. This is particular important on highly used roads, where traffic loads are going to be large.When deciding whether the quality of the reclaimed asphalt will meet standards, the following needs to be considered.Climatic region if the material is going to be placed in a warm climate, shear tests must be carried out to represent that climateAxle loads high stresses will result in accelerated deformation of the road. This means that if the road is to exact heavy traffic its shear properties will need to be carefully consideredReclaimed Asphalt Composition if needed crusher dust can be added to the mix. This will provide an angular skeleton that will improve the mixes shear resistance.GradingThe grading requirements for both types of bitumen stabilisation is different. This is due to the fact that the bitumen will disperse differently. The graph and table below give an indication of the grading required for each type of stabilisation.XXXXXXBitumen EmulsionAs the above table shows a minimum filler content of 2% is required. This is because the bitumen emulsion will coat the large particles of the aggregate better than the foamed bitumen.Foamed bitumenFoamed bitumen requires more filler approximately 5% filler content is required. This is because the bitumen droplets disperse through the material, only partially coating the large particles. It uses the filler to create a spot welds connecting the larger particles using the fines.Bitumen SelectionThe bitumen selected plays an important part in how well the BSM works. incursion grade bitumen is used to produce both bitumen emulsion and foamed bitumen. In the next two sections the specific bitumen requirements for each form of stabilisation is given below.Bitumen EmulsionFor bitumen emulsion base bitumens with a penetration value between 80 and 100 are normally selected. In saying this around the macrocosm softer and harder grades of bitumen have successfully been used.In recent years there have been many technological advances which have allowed the bitumen emulsion to have improved stableness without prolonging the break time. However sufficient testing of the bitumen mix needs to take place both in the mix design phase and during construction trials. This will ensure the correct bitumen has been chosen.Another important consideration is the compatibility of the bitumen emulsion and the aggregate. This is because the type of bitumen chosen is influenced by the type of aggregate been treated. Certain materials are not suitable for catatonic treatment and others are not suitable for anionic treatment. The table below gives an indica tion of the compatibility of the emulsion with a aggregate.Aggregate TypeCompatible withCationic EmulsionAnionic EmulsionDoleriteYesYesQuartziteYesNoHornfels/GreywackeYesYesDolomiteYesYesGraniteYesNoTilliteYesVariableBasaltYesYesSyeniteYesNoAmphilboliteYesYesMarbleYesYesRhyoliteYesNoFelsiteYesNoSandstoneYesNoAndesiteYesYesFurthermore it is normally recommended that the undiluted bitumen emulsion is heat to between 50 and 60C. This will prevent premature breakage of the bitumen emulsion while pumping in the construction equipment. It is also important to note here that when diluting the emulsion the emulsion must be added to the water. This will prevent premature breaking.Foamed BitumenWhen it comes to foamed bitumen a softer grade of bitumen can be used without agree stability. This is because foamed bitumen only requires low percentages of bitumen in the mix. However like bitumen emulsion typical penetration values are between 80 and 100. Harder bitumen is normally avoided due t o the poor quality of foam it produces.There are two main properties that determine the suitability of the bitumen for foamed bitumen stabilisation. These are its Expansion Ratio and its Half-Life.The elaboration raito is a cake of the viscosity of the foam. This is what determines how well the bitumen will disperse through the mix. It is calculated by finding the ratio between the maximum volume of foam in kin to the original volume of bitumen.The half-life is a measure of the stability of the foam and provides an indication of the rate of take apart of the foam during mixing. It can be calculated by determining the time it takes for the foam to collapse to half its maximum volume. The table below shows the minum limits of the expansion ratio and the half-life of the bitumen.XXXThe greatest factor which will influencing the foam properties is the water injected into the expansion chamber. A greater injection of water will mean a higher expansion ratio, but this is offset by th e fact it will mean a short half-life as the foam will subsided faster. Furthermore a higher bitumen temperature is usually recommended as it will create a better quality foam.Active FillerThere are two types of fillers which can be used to improve the results of bitumen stabilisation these are active and natural fillers. An active filler is a filler which will chemically alter the mix properties. There are various active fillers which can be used, examples of these are cement hydrated lime and strike down ash. born(p) fillers are fillers such as rock flour.These fillers can be used either by themselves or in a combination with another filler. Their use will depend on their cost, efficacy during use and the materials availability. Research has shown that it is almost impossible to predict the effectiveness of a filler. The only way to gain an idea of their effect is to complete experiments using different mixes.Active fillers are added to the bitumen in order toIncrease the stiff ness of the mixIncrease the rate at which the mix will gain strengthImprove the dispersion of bitumen in the mixImprove adhesion between the bitumen and the aggregateImprove the lot time of the compaction mixAlong with these general improvements, there are specific benefits for both treatments. For Bitumen Emulsion a filler willControl the breaking time of the emulsionImprove the workability of the emulsionFor Foamed Bitumen a filler willAssist in dispersing the bitumen dropletsNatural fillers on the other hand only act as a supplement for a lack of fines in the material which is needed for dispersion.It is important to note that when adding an active filler the time between the bitumen is mixed and it application is dramatically reduced. When an active filler is added the reaction begings immediately when it comes into contact with moist material. The longer the delay between mixing and application the less the filler will work.WaterTo ensure a high quality harvest it is importan t that the water used in mixing meets certain standards. for each one technique requires different water qualities.Bitumen EmulsionFor bitumen emulsion the pH levels of the water are extremely important. For cationic bitumen the water cannot be alkaline. If it is hydrochloric acid can be used to decrease the waters pH.For anionic bitumen emulsion the opposite applies, the water cannot be too acidic. To make the water more alkaline lime or caustic soda can be added to the water.Foamed BitumenThe standards for foamed bitumen arent as high as they are for bitumen emulsion. It is acceptable for the water used to obligate some impurities, however this should be avoided. This is because the water can affect the mixing machinery.Specimen preparationMoistureMoisture plays an important part in using bitumen to stabilize material. The role that moisture plays in the two types of BSM is explained in the table below.ComponentBitumen EmulsionFoamed BitumenBitumenContributes to fluids for comp actionDoes not effectMoisture in aggregateReduces absorption of bitumen emulsion water into aggregateSeparates and suspends the fines making them available to bitumen during mixingPrevents premature breakingActs as a flattop for bitumen droplets during mixingExtends bent time and reduces early strengthReduces early strengthProvides workability at ambient temperaturesReduces friction angle and lubricates for compactionProvides shelf-life for the mixThe term for the best moisture content in the material is the optimum mixing moisture content or OMMC. It is important to note that for bitumen emulsion this moisture value is the moisture in the aggregate plus the moisture from the emulsion.The mental institution of modern rollers has allowed for high energy compaction. In the case of BSM this means a lower fluid content can be used to produce the same quality of compaction. This has the added benefit of increasing the strength of the BSM.Material PreparationBelow is the basic procedure for the material preparation involved in the mixing design.Determine the grading curve of the aggregate and its optimum moisture content of the natural materialDetermine the materials Atterberg LimitsDetermine the moisture and density relationship of natural material to obtain optimum moisture contentDetermine the moisture and density relationship of the treated material to obtain optimum moisture contentDetermine the moisture and density relationship using vibratory hammer compaction to obtain optimum moisture contentMixingIt is recommended that a pugmill mixer is used in both mixes. The use of different mixers can produce up to a 25% difference in strength. Experiments have found that the pugmill mixer provides the most general mix.CompactionCorrect compaction of the material is extremely important as it reduces the voids and improves particle contact. The use of bitumen emulsion will help improve the compatibility of the mix, while the use of foamed bitumen will promote the adh esion of the bitumen mastic to the stone.bandCuring is the process where the water is removed(p) from the compacted layer. Water can be removed from either evaporation, particle charge repulsion and pore-pressure induced flow paths. The reduction in moisture content will lead to an increased tensile and compressive strength as well as add stiffness to the mix. The band process is different for both methodsBitumen EmulsionIt is chemistry that controls the way bitumen emulsion treated material cures. By removing the water from the mix breaking of the emulsion occurs. To do this the water is removed by means of evaporation and migration. This curing will take longer than foamed bitumen curing, due to the higher moisture contents.Foamed BitumenThe curing of the foamed bitumen is a natural process. It is cured through the migration of water during compaction and continues as the water is evaporated.TestingThere are two main tests which are used to check the various mix designs, they are the Indirect Tensile Strength test and a Triaxial TestIndirect Tensile StrengthThis test is completed to measure the flexibility of the material and give an indication of its tensile strength. The table below gives a postulate for interpreting the results of the test.TestSpecimen Diameter (mm)BSM1BSM2BSM3PurposeITSdry (kPa)100225175-225125-175Indicates optimum bitumen contentITSwet (kPa)10010075-10050-75Indicates need for active fillerITSequil (kPa)150175135-17595-135Optimise bitumen contentITSsoaked (kPa)150150100-15060-100Check value on ITSwetTriaxial TestThis test is completed to meause the cohesion of the material, the friction angle and the retained cohesion. The table below gives a guide for interpreting the results of the test.Test or IndicatorBSM1BSM2BSM3Cohesion (kPa)250100-25050-100Friction slant ()4030-40Retained cohesion (MIST)7560-7550-60Structural DesignAs discussed in part XX the structural layers purpose is to protect the subgrade by dispersing the traffic loads. This means that the pavement structure and subgrade must work together to ensure the required design capacity.ConstructionFor both stabilizing methods once the material has been mixed into the material, the various construction operations are relavitivily the same as those if the material wasnt treat

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