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by:-MUBAREK ZEYNE E-mail: zemubarek@yahoo Office: Informatics BLDG no. 305

by:-MUBAREK ZEYNE E-mail: zemubarek@yahoo Office: Informatics BLDG no. 305

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  1. DEPARTMENT OF CIVIL ENGINEERING COURSE:-HIGHWAY ENGINEERING II by:-MUBAREK ZEYNEE-mail: zemubarek@yahoo.comOffice: Informatics BLDG no. 305

  2. 5. PAVEMNET MATERIALS - UNBOUND GRANULAR MATERIALS • Pavement design requires the efficient use of locally available materials if economically constructed roads are to be built. • Pavement materials include: • Granular materials (aggregates):crushed rock aggregates obtained from hard rock sources, natural (pit-run) gravels, gravel-sand-soil mixtures • Binders :bitumen and cement are a binder used for stabilizing or modifying the properties of subgrade/subbase/base such as lime, cement, foam bitumen, etc.

  3. 5.2 Sources of Aggregates • Hard rock sources (crushed quarried rock)– hard sound bed rock exposures that need blasting and crushing. Crushed aggregates- Hard rocks are important sources of aggregates. -Extrusive (volcanic) igneous rocks (Basalts, Rhyolite, Trachyte) – which formed on or near the surface of the earth’s crust due to rapid cooling of magma and hence rocks are fine grained (glassy or vitreous/like a glass (without crystal) or partly vitreous and partly crystalline (with small grain sizes)). -Intrusive (Plutonic) igneous rocks (Granite, Gabbro) – formed by the cooling of magma below the earth’s surface, and hence are crystalline (the crystals may be big enough to be visible by the naked eye). • Acidic Rocks – igneous rocks with high silica (Sio2) content > 63%. (granite, rhyolite) • Intermediate rocks – igneous rocks with intermediate silica content, Sio2between 52% - 62%. (andesite, diorite) • Basic rocks – igneous rocks with low silica content, Sio2between 45 – 52%. (Basalt, gabbro). • Generally speaking, igneous rocks with medium grain sized particles are preferable as source for aggregates

  4. 5.2 Sources of Aggregates…. • Sedimentary rocks may be siliceous rocks – formed from disintegrated rock sediments transported by wind or water, re-deposited as sediments, then consolidated or cemented in to a new rock type (e.g. conglomerate (consolidated gravel), sand stone (consolidated sand), shales (consolidated mud/clay, rich in organic matter: silt stone or clay stone). Calcareous rocks – rocks formed by chemical deposition of organic remains in water (Gypsum, chalk, Limestone) • Metamorphic rocks are igneous or sedimentary rocks thathave been changed (metamorphosed) due to intense heat and pressure into new rocks by the recrystallization of their constituents (e.g.Quartzite, Gneiss, Schist, Slate, marble, etc.). Schist and slate are highly foliated rocks which are not desirable as they are fissile and liable to be crushed when compacted with rollers. Schist and slate are highly foliated rocks which are not desirable as they are fissile and liable to be crushed when compacted with rollers. Quartzite and gneisses can furnished good aggregates.

  5. 5.2 Sources of Aggregates…. • Naturally occurring gravels– which includes alluvial deposits, and highly weathered and fractured residual formations (rippable or can be worked using earth moving machinery such as Dozers) • Natural sand and gravel pits have been used extensively as sources of road aggregates. Sand or gravel pit is first stripped of topsoil, vegetation, and other unsuitable material from the surface of the deposit to obtain pit run materials. • Recycled material- the use of pulverized concrete from pavements, sidewalks, and buildings being demolished is growing in other countries both due to the increased cost of natural aggregates and the desire to recycle rather than landfill these materials. Aggregate production from bedrock (quarries):- Aggregate production involves extraction (blasting and breaking to pieces), crushing (reduction to size using compression/impact crushers) and screening. After stripping and opening the quarry, holes are drilled from the surface. Then dynamite is placed and detonated in these holes to break the rock into sizes that can be transported. The rock is then fed to crushers which reduce it (crush it) to the required sizes in various types of rock crushers. The aggregates are then screened to the various required sizes.

  6. 5.3 Aggregate tests • The properties of aggregate that are important for road construction include its cleanliness (contamination with dust and other deleterious materials), particle size and shape, gradation, toughness - resistance to crushing, abradability - wearing/abrasion resistance, durability/soundness, specific gravity and water absorption, surface texture, tendency to polish, bonding property with bitumen. Aggregate tests are necessary to determine the suitability of the material for a specific use and to make sure that the required properties are consistently within specification limits. These tests include: • Gradation(grading) test:- sieve analysis performed to evaluate the suitability of the aggregate materials with respect to their grain size distribution for a specific use. • Aggregate Crushing Value (ACV) Test:- evaluates the resistance of aggregates against the gradually applied load. The test is used to evaluate the crushing strength of available supplies of rock, and in construction ,to make sure that minimum specified values are maintained. The test is undertaken using a metal plunger to apply gradually a standard load of 400kN to a sample of the aggregate (10 – 14 mm) contained in a standard test mould. The amount of material passing 2.36 mm sieve in percentage of the total weight of the sample is referred to as the Aggregate Crushing value (ACV). Over the range of normal road making aggregates, ACVs vary from 5 percent for hard aggregates to 30 percent for weaker aggregates.

  7. 5.3 Aggregate tests cont… 3) Ten Percent Fines value(TFV):- For weaker aggregates (usually ACV<30%), the apparatus of ACV is used to evaluate the Ten Percent Fines value i.e. the load which produces 10 percent of fines passing 2.36 mm sieve. The value is obtained by interpolating of the percentage of fines produced over a range of test loads. 4) Aggregate Impact Test:-evaluates the resistance of aggregates to sudden impact loading. It is carried out by filling a steel test mould with a sample of aggregate (10 – 14 mm) and then the impact load applied is by dropping hammer at a height of 380 mm. The Aggregate Impact Value (AIV) is the percentage of fines passing 2.36 mm sieve after 15 blows. This test produces results that are normally about 105 per cent of the ACV. 5) Abrasion Test:- is the test used to know how the aggregate is sufficiently hard to resist the abrasive effect of traffic over its service life. The most widely used abrasion test is the Los Angeles Abrasion Test which involves the use of a steel drum, revolving on horizontal axis, into which the test sample of chippings is loaded together with steel balls of 46.8 mm diameter. The Los Angeles Abrasion Value (LAV) is the percentage of fines passing the 1.7 mm sieve after a specified number of revolutions of the drum at specified speed. For bituminous surface dressings, chippings with an ACV less than 30 are desirable and the stronger they are the more durable will be the dressings.

  8. 5.3 Aggregate tests cont… 6)Soundness Test:- is useful in both survey and design for the evaluation of aggregates to resist disintegration due to weathering. A sample of aggregate is saturated in a solution of magnesium sulphate or sodium sulphate, and then removed and dried in an oven. This process is repeated for five cycles. On completion, the percentage lost gives the durability of the material. 7) Specific Gravity and Water Absorption:-These tests are likely to be used both in surveys of aggregate resources and in design, particularly in the interpretation of compaction tests and in the design of bituminous mixtures. In the tests, a 4 kilogram sample of the crushed rock of specific nominal size chippings is soaked in distilled water for 24 hours, weighed in water (WW), surface dried and weighed in air (WS). It is then oven dried at 105oC for 24 hours and weighed again in air (WD). The specific gravity and the water absorption are then obtained as follows: 8) Shape Tests. Three mechanical measures of particle shape which may be included in the specifications for aggregates for road construction, are the flakiness index, elongation index and angularity number.

  9. 5.3.1Blending aggregates • To meet the gradation requirements of aggregates for particular uses in pavement construction, it is often necessary to blend two or more aggregates together. Chart sand diagrams are available to do this blending, but the trial-and-error method is simpler and just about as fast as more complex methods. • Example: Three aggregates are to be blended to meet a specification. The aggregates, gradations, and the specification are given in the Table below

  10. Solution: - • Most of coarse aggregate will come from aggregate A and most of the fines will be obtained from aggregate C. To obtain a mixture that is approximately in the middle of the specification, • we first use the equation and continue with more trials. The equation can be written to blend aggregate A, B, and C for retained on 9.5 mm sieve and passing 75 μm sieve as follows: where, A ,B & C are percentages from aggregates A,B and C to be blended for satisfying the specification limits. a, b and c are the respective sieve analysis values for a given sieve X, expressed as a decimal fraction, and T is the sieve analysis value in the blended aggregate. • For retained materials on 9.5 mm sieve, the known variables are ar= 0.38, br = 0, cr = 0 and Tr= 20%, which implies that A = 53%. • Similarly, for passing 75 μm, the known variables are ap = 0, bp = 0, cp = 0.18 and Tp= 4.5%, which results C = 25%, and B = 100 – 53 – 25 = 22%. The first trial blend as seen in the Table above is within the specification limit, but on the coarse side. Reducing the contribution of aggregate A and increasing B, or C or both for the second and the subsequent trials can result in a blend more close to the middle of the specification.

  11. 5.4 Unbound Base and Subbase Materials (ERA Pavement Design Manual Requirements) • Unbound base and subbase courses in pavement structures are granular materials from sand or gravel deposits or crushed rock from quarries without admixtures. A. Base course:- For Graded crushed aggregate:- • Grading requirement • After crushing, the material should be angular in shape with a Flakiness Index of less than 35%, and preferably of less than 30% • ACV should preferably be less than 25 and in any case less than 29

  12. A. Base coursecont… • TFV requirement:- • Construction requirement:-The in situ dry density of the placed material should be a minimum of 98% of the maximum dry density obtained in the Heavy Compaction. The compacted thickness of each layer should not exceed 200 mm. Crushed stone base materials described above should have CBR values well in excess of 100 percent, and fines passing 0.425 mm sieve should be non plastic. Requirements for natural gravels and weathered rocks:-A wide range of materials including lateritic, calcareous and quartzitic gravels, river gravels, boulder sand other transported gravels, or granular materials resulting from the weathering of rocks can be used successfully as base course materials. • CBR requirement :-depending on traffic and rainfall, minimum CBR value of 60-80% is required. • The fines of these materials should preferably be nonplastic but should normally never exceed a PI of 6. If the PI approaches the upper limit of 6, it is desirable that the fines content be restricted to the lower end of the range. To ensure this, a maximum Plasticity Product (PP) of 60 is recommended or alternatively a maximum Plasticity Modulus (PM) of 90 where:

  13. B. Sub-base course materials:- • The sub-base is an important load spreading layer which enables traffic stresses to be reduced to acceptable levels on the subgrade. It also acts as a working platform for the construction of the upper pavement layers separating the subgrade and base course. Under special circumstances, it may serve as a filter or as a drainage layer. In the construction of low-volume roads, where cost savings at construction are particularly important, local experience is often invaluable and a wider range of materials may often be found to be acceptable. In Ethiopia, laterite is one of the widely available materials and can be used as a sub-base material. Laterite meeting the gradation requirements of Table 5-7can be used for traffic levels up to 3x106ESA provided the following criteria is satisfied:

  14. C. Selected subgrade materials and capping layers • These materials are often required to provide sufficient cover on weak subgrades. They are used in the lower pavement layers as a substitute for a thick sub-base to reduce costs, and a cost comparison should be conducted to assess their cost effectiveness. • A minimum CBR of 15 per cent is specified at the highest anticipated moisture content measured on samples compacted in the laboratory at the specified field density. This density is usually specified as a minimum of 95 per cent of the MDD in the Heavy Compaction.

  15. 6. STABILIZED PAVEMENT MATERIALS • The term ‘soil stabilization’ may be defined as the alteration of the properties of an existing soil either by blending (mixing) two or more materials and improving particle size distribution or by the use of stabilizing additives to meet the specified engineering properties. • Quite often soils are stabilized for road construction in most parts of the world for the following one or more objectives: • Improve the strength (stability and bearing capacity) for subgrade, subbase, base, and low-cost road surfaces, • Improve the volume stability – undesirable properties such as swelling, shrinkage, high plasticity characteristics, and difficulty in compaction, etc. caused by change in moisture, • Improve durability – increase the resistance to erosion, weathering or traffic,and • Improve high permeability, poor workability, dust nuisance, frost susceptibility, etc • The factors that should be considered include physical and chemical composition of the soil to be stabilized, availability and economical feasibility of stabilising agents, ease of application, site constraints, climate, curing time, and safety. Such factors should be taken into account in order to select the proper type of stabilization.

  16. Soil stabilization techniques • Basically four techniques of soil stabilization are commonly practiced in pavement construction. These are: - • ƒ Mechanical stabilization, • ƒ Cement stabilization, • ƒ Lime stabilization, and • ƒ Bitumen stabilization • Mechanical stabilization is a method by which a soil or gravel is mixed with the original soil in order to improve the grading and mechanical characteristics of the soil. • Other methods of stabilization use additives such as cement, lime and bitumen to improve strength, workability or waterproofing. • Portland cement has been used with great success to improve existing gravel roads, as well as to stabilize natural soils. It can be used for base courses and subbases of all types. It can be used in granular soils, silty soils, and lean clays, but it cannot be used inorganic materials.

  17. Mechanical Stabilization :- is an improvement of an available material by blending it with one or more materials in order to improve the particle size distribution and plasticity characteristics. Typical materials used for mechanical stabilization include river deposited sand, natural gravel, silty sands, sand clays, silt clays, crushed run quarry products and waste quarry products, volcanic cinders and scoria, poorly graded laterites and beach sands, etc. • Cement Stabilization:- Cement is an effective stabilizing agent which has two important effects on soil behaviours: • Reduces the moisture susceptibility of soils ⎯cement binds the particles greatly and reduces moisture induced volume change (shrinkage and swell) and it also improve strength stability under variable moisture, • Develop inter-particle bonds in granular materials ⎯increased tensile strength and elastic modulus. • Soil properties progressively change with increasing cement contents. For practical reasons, two categories of cement stabilised materials have been identified.

  18. 2. Cement Stabilization cont… -Cement modified materials ⎯cement is used to reduce plasticity, volume-change, etc, and the inter-particle bonds are not significantly developed. Such materials are evaluated in the same manner as conventional unbound flexible pavement materials. -Cement bound materials ⎯cement is used to sufficiently enhance modulus and tensile strength. Cement bound materials have practical application in stiffening the pavement. There are no established criteria to distinguish between modified and bound materials, but an arbitrary limit of indirect tensile strength of 80kN or unconfined compressive strength of 800 kPa after seven days moist curing has been suggested. • A number of factors influence the quality of the cement-soil interactions:- • Nature and type of soil • Cement content:- 3-16% by weigh depending on soil class eg. For A-1-a 3-5% by weight is recommende d by ERA. • Moisture content and • Pulverization, mixing, compaction, and curing conditions

  19. 3) Lime stabilization :- • Lime is a broad term which is used to describe calcium oxide (CaO) – quick lime; calcium hydroxide Ca(OH)2– hydrated lime, and calcium carbonate (CaCO3) – carbonate of lime. Out of these, calcium oxide and calcium hydroxide react with soil and calcium carbonate is of no value for stabilization. The most commonly used products are hydrated calcitic lime (Ca(OH2)), monohydrated dolomitic lime (Ca (OH2) MgO), calcitic quick lime (CaO), dolomitic quick lime (CaO MgO). They are available as commercial and waste lime. Lime can be applied as dry hydrated lime, quick lime or slurry lime. The reaction between soil and lime are complex and still not completely understood. Basically four different factors are involved in the soil-lime reaction which are: cation exchange, flocculation, pozzolanic reaction, and carbonation. Cation exchange is an immediate reaction and unlike pozzolanic reaction, it isnot significantly dependent on temperature in which cations such as sodium and hydrogen are replaced by calcium ions for which the clay mineral has a greater affinity.

  20. 4. Bituminous Stabilization:- Bituminous stabilization is used with : -non-cohesive granular materials where the bitumen adds cohesive strength; and -cohesive materials where the bitumen “waterproofs” the soil thus reducing loss of strength with increase in moisture content. • Both effects take place partly from the formation of bitumen film around the soil particles which bonds them together and prevents the absorption of water, and partly from simple blocking of the pores, preventing water from entering the soil mass. • The bituminous materials that are used for stabilization works are mostly penetration grade bitumen and cutback bitumen and bitumen emulsion. • Because more care is necessary in bituminous stabilization to achieve satisfactory mixing, its use has not been as widespread as cement and lime stabilizations.

  21. 7. Bituminous materials and mixtures7.1 bituminous binders and properties • Bituminous material (or bitumen), also known as asphalt cement in the US: –a viscous liquid or solid material black or dark brown in colour, having adhesive properties, consisting essentially of hydrocarbons which are soluble in carbon disulphate. –They are usually fairly hard at normal temperatures. –When heated they soften and flow. –When mixed with aggregates in their fluid state, and then allowed to cool they solidify and bind the aggregates together, forming a pavement surface. –They are used on all types of roadway –from multiple layers of asphalt concrete on the highest class of highways to thin, dust-control layers on seldom-used roads. • Based on their sources there are two main categories of bitumens namely, –those which occur naturally and –those which are by-products of the fractional distillation of petroleum at refinery. • Refinery bitumens are by far –the greater proportion of road bitumen used all over the world.

  22. 7.1.1Types of bituminous binders • Native asphalts are obtained from –asphalt lakes in Trinidad and other Caribbean areas, and –were used in some of the earliest pavements in North America after softening with petroleum fluxes.

  23. 7.1.1Types of bituminous binders conti… • Refinery Bitumen:-is a Bitumen artificially produced by the industrial refining of crude petroleum oils are known under a number of names depending on the refining method used such as –residual bitumens–straight-run bitumens –steam-refined bitumens and –as is now most commonly accepted • Petroleum crudes are complex mixtures of hydrocarbons differing in molecular weight and consequently in boiling range. • Before they can be used, crudes have to be –separated, purified blended, and sometimes chemically or physically changed. • The primary processing involved in the production of bitumen from petroleum is fractional distillation. In this process, part of the hydrocarbon materials in the crude oil are vaporized by heating them above their boiling points under pressure. • The lightest fractions of the crude remain as a vapour and are taken from the top of the distillation column, heavier fractions are taken off the column as side-streams with the heaviest fractions remaining as a liquid and therefore left at the base of the column

  24. Penetration Grade Bitumen:- Penetration grade bitumen or asphalt cements are in consistency from semi-solid to semi-liquid at room temperature. Such bitumen are graded according their viscosity (mainly used in the US) and penetration. • Penetration is the depth in 0.1 mm that a specified needle is able to penetrate the samples when standard penetration tests are carried out. • They are produced in various viscosity grades, the most common being AC 2.5, AC 5, AC 10, AC 20, and AC 40. These viscosity grades indicate the viscosity in hundreds of poises ± 20% measured at 60oC (140oF). For example, AC 2.5 has a viscosity of 250 poises ± 50. AC 40 has a viscosity of 4000 poises ± 800. • These roughly correspond to penetration grades 200-300, 120-150, 85-100, 60-70, and 40-50, respectively. • The majority of penetration grade bitumens is used in road construction, the harder grades, 35 pen to 100 pen, being used in asphalt where bitumen stiffness is of primary importance and the softer grades, 100 pen to 450 pen, in macadams where the lubricating properties during application and bonding of the aggregate in service are more important. During construction asphalt cements require to be heated to varying degrees before mixing with hot or warm aggregates and the mixed material must be laid while hot within a few hours of mixing.

  25. Liquid Bitumen:- liquid binders are preferable to handle at relatively low temperatures and mixed with aggregates either when cold or only warmed sufficiently to make them surface-dry. The two forms of liquid bitumen generally, are those which are prepared by dissolving the asphalt cement in a suitable volatile solvent and known as cutback bitumen, and those which are prepared by emulsifying the asphalt cement in an aqueous medium and called bitumen emulsions. • Cutback Bitumen:- are prepared by dissolving penetration grade bitumen in suitable volatile solvents to reduce their viscosity to make them easier to use at ordinary temperatures. They are commonly heated and then sprayed on aggregates. The curing period depends on the volatility of solvents. -Cutback bitumen are grouped into three types based on the type of solvent, which governs the rates of evaporation and curing, namely, slow-curing (SC), medium-curing (MC), and rapid-curing (RC). Each type of cutback bitumen is subdivided into several grades characterized by their viscosity limits. - Slow-Curing (SC) Cutbacks: Slow-curing asphalts can be obtained directly as slow-curing straight-run asphalts through the distillation of crude petroleum or as slow-curing cutback asphalts by "cutting back" asphalt cement with a heavy distillate such as diesel oil. They have lower viscosities than asphalt cement and are very slow to harden. they designated as SC-70, SC-250, SC-800, or SC-3000, where the numbers are related to the approximate kinematic viscosity in centistokes at 60oC (140oF). They are used with dense-graded aggregates and on soil-aggregate roads in warm climates to avoid dust.

  26. Medium-Curing (MC) Cutbacks: Medium-curing asphalts are produced by fluxing, or cutting back, the residual asphalt (usually 120-150 penetration) with light fuel oil or kerosene. The term medium refers to the medium volatility of the kerosene-type dilutent used. The fluidity of medium-curing asphalts depends on the amount of solvent in the material. MC-3000, for example, may have only 20 percent of the solvent by volume, whereas MC-70 may have up to 45 percent. These medium-curing asphalts can be used for the construction of pavement bases, surfaces, and surface treatments. • Rapid-Curing (RC) Cutbacks: Rapid-curing cutback asphalts are produced by blending asphalt cement with a petroleum distillate that will easily evaporate, thereby facilitating a quick change from the liquid form at time of application to the consistency of the original asphalt cement. Gasoline or naphtha generally is used as the solvent for this series of asphalts. The grade of rapid-curing asphalt required dictates the amount of solvent to be added to the residual asphalt cement. For example, RC-3000 requires about 15 percent of distillate, whereas RC-70 requires about 40 percent. • These grades of asphalt can be used for jobs similar to those for which the MC series is used, but where there is a need for immediate cementing action or colder climates.

  27. Asphalt emulsions • Emulsified asphalts are produced by breaking asphalt cement, usually of 100-250 penetration range, into minute particles and dispersing them in water with an emulsifier, These minute particles have like electrical charges and therefore do not coalesce. They remain in suspension in the liquid phase as long as the water does not evaporate or the emulsifier does not break. Asphalt emulsions therefore consist of asphalt, which makes up about 55 percent to 70 percent by weight,up to 3% emulsifying agent, water and in some cases may contain a stabilizer. • Two general types of emulsified asphalts are produced, depending on the type of emulsifier used: -cationic emulsions, in which the asphalt particles have a positive charge; and -anionic, in which they have a negative charge. Each of the above categories is further divided into three subgroups,based on how rapidly the asphalt emulsion will return to the state of the original asphalt cement .These subgroups are rapid setting (RS), medium-setting (MS), and slow setting (SS). A cationic emulsion is identified by placing the letter "C" in front of the emulsion type; no letter is placed in front of anionic and nonionic emulsions. For example, CRS-2 denotes a cationic emulsion, and RS-2 denotes either anionic or nonionic emulsion. • The anionic and cationic asphalts generally are used in highway maintenance and construction.

  28. 7.1.2 Tests on Bituminous Materials • Consistency Tests are:- • Saybolt Furol Viscosity Test • Kinematic Viscosity Test • Penetration Test • Float Test • Ring-and-Ball Softening Point Test II. Durability Tests :- • Thin-Film Oven Test (TFO) III. Distillation Test for Cutbacks IV. Distillation Test for Emulsions General Tests include:- • Specific Gravity Test • Ductility Test • Solubility Test • Flash-Point Test • Loss-on-Heating Test • The consistency of bituminous materials is important in pavement construction because the consistency at a specified temperature will indicate the grade of the material. As stated earlier, asphaltic materials can exist in either liquid, semisolid, or solid states. • The property generally used to describe the consistency of asphaltic materials in the liquid state is the viscosity, which can be determined by conducting either the Saybolt Furol viscosity test or the kinematic viscosity test. Tests used for asphaltic materials in the semisolid and solid states include the penetration test and the float test. • The ring-and-ball softening point test may also be used for blown asphalt.

  29. 7.2 Types of Asphalt Mixtures • There are different types of asphalt mix. Some of the common mixes are the following: • Hot mix asphalt concrete (HMAC) –is produced at 1600c –This high temperature serves to decreaseviscosity and moisture during the manufacturing process, resulting in a very durable material. –HMAC is most commonly used for high-traffic areas, such as busy highways and airports. • Warm mix asphalt concrete (WAM or WMA) • –reduces the temperature required for manufacture by adding asphalt emulsions, waxes, or zeolites. • –This process benefits both the environment and the workers, • as it results in less fossil fuel consumption and reduced emission of fumes.

  30. cold mix asphalt concrete, –the asphalt is emulsified in soapy waterbeforemixing it with the aggregate, • eliminating the need for high temperatures altogether. –However, the asphalt produced is not nearly as durable as HMAC or WAM, and cold mix asphalt is typically used for low traffic areas or to patch damaged HMAC. • Cut-back asphalt concrete • –has been illegal in the United states since the 1970s, but many other countries around the world still use it. • –This type of concrete is the least environmentally friendly option, resulting in significantly more air pollution than the other forms. • –It is made by dissolving the asphalt binder in kerosene before mixing it with the aggregate, reducing viscosity while the concrete is layered and compacted. • –The lighter kerosene later evaporates, leaving a hardened surface.

  31. Mastic asphalt, also called sheet asphalt –has a lowerbitumen content than the rolled asphalt forms discussed above. –It is used for some roads and footpaths, but also in roofing and flooring. –Stone mastic asphalt (SMA), another variety, is becoming increasingly popular as an alternative to rolled asphalt. –Its benefits include an anti-skid property and the absence of air pockets, but if laid improperly, • it may cause slippery road conditions.

  32. Asphalt Concrete • Asphalt concrete –A uniformly mixed combination of • asphalt cement • course aggregate • fine aggregate and • other materials, depending on the types of asphalt concrete • the different types of asphaltic concretes commonly used in pavement construction are –hot mix, hot laid –cold-mix, cold laid • when used in the construction of highway pavements –it must resist deformation from imposed traffic loads –be skid resistant even when wet and –not be easily affected by weathering forces. • the degree to which an asphalt concrete achieves these characteristics is mainly dependent on the design of the mixused in producing the concrete.

  33. Hot-Mix, Hot-Laid Asphalt Concrete(HMA) • Produced by properly blending –asphalt cement –coarse aggregate –fine aggregate and –filler (dust) at temperature ranging from about 175oF to 325oF, depending on the type of asphalt cement used. • Suitable types of asphaltic materials include AC-20, AC-10 and AR-1000 with penetration grades of 60-70, 85-100, 120-150 and 200-300. • Hot-mix, hot laid asphaltic concrete is normally used for high-type pavement construction and the mixture can be described as • –open graded –course graded –dense graded and –fine graded

  34. Dense-Graded Mixes • A dense-graded mix –is a well-graded HMA intended for general use. –When properly designed and constructed, a dense-graded mix is relatively impermeable. –Dense-graded mixes are generally referred to by their nominal maximum aggregate size. –They can further be classified as either fine-graded or coarse-graded. –Fine-graded mixes have more fine and sand sized particles than coarse-graded mixes. –Dense-graded mixes are used extensively in Washington State for all purposes. • Purpose: –Suitable for all pavement layers and for all traffic conditions. –They work well for structural, friction, leveling and patching needs. • Materials: –Well-graded aggregate, asphalt binder (with or without modifiers), RAP

  35. Stone Matrix Asphalt (SMA) • Stone matrix asphalt (SMA), sometimes called stone mastic asphalt, is a gap-gradedHMA originally developed in Europe to maximize rutting resistance and durability. • The mix goal is to create stone-on-stonecontact. • Since aggregates do not deform as much as asphalt binder under load, this stone-on-stone contact greatly reduces rutting. • SMA is generally moreexpensive than a typical dense-graded HMA because it requires more durable aggregates, higher asphalt content, modified asphalt binder and fibers. • In the right situations it should be cost-effective because of its increased rut resistance and improved durability. • SMA, has been used in the U.S. since about 1990, although it has only been used in Washington State on several pilot projects. • Purpose: –Improved rut resistance and durability. –SMA is almost exclusively used for surface courses on high volume interstates and U.S. roads. • Materials: –Gap-graded aggregate, modified asphalt binder, fiber filler –Other reported SMA benefits include wet weather friction (due to a coarser surface texture) and less severe reflective cracking. –Mineral fillers and additives are used to minimize asphalt binder drain-down during construction, increase the amount of asphalt binder used in the mix and to improve mix durability.

  36. Open-Graded Mixes • Unlike dense-graded mixes and SMA, an open-graded HMA mixture is designed to be water permeable. • Open-graded mixes use only crushed stone (or gravel) and a small percentage of manufactured sands. • The two most typical open-graded mixes are: –Open-graded friction course (OGFC). • Typically 15 percent air voids and no maximum air voids specified. –Asphalt treated permeable bases (ATPB). • Less stringent specifications than OGFC since it is used only under dense-graded HMA, SMA or PCC for drainage.

  37. HMA -FUNDAMENTALS • HMA consists of two basic ingredients: –aggregate and asphaltbinder. • HMA mix design is the process of determining --what aggregate to use, –what asphalt binder to use and –what the optimum combination of these two ingredients ought to be. • HMA mix design has evolved as a laboratory procedure that uses several critical tests to make key characterizations of each trial HMA blend. • Although these characterizations are not comprehensive, –they can give the mix designer a good understanding of how a particular mix will perform in the field during construction and under subsequent traffic loading. • This section covers mix design fundamentals common to all mix design methods.

  38. Conti… • HMA is a rather complex material upon which many different, and sometimes conflicting, performance demands are placed. • It must –resist deformation and cracking, –be durable over time, –resist water damage, –provide a good tractive surface, and yet be inexpensive, –readily made and easily placed. • In order to meet these demands, the mix designer can manipulate all of threevariables: –Aggregate. • Items such as type (source), • gradation and size, toughness and abrasion resistance, • durability and soundness, • Shape and texture as well as cleanliness can be measured, judged and altered to some degree.

  39. HMA conti… –Asphalt binder • Items such as type, • durability, • rheology, • purity as well as additional modifying agents can be measured, judged and altered to some degree. –The ratio of asphalt binder to aggregate. • Usually expressed in terms of percent asphalt binder by total weight of HMA, • this ratio has a profound effect on HMA pavement performance. • Because of the wide differences in aggregate specific gravity, –the proportion of asphalt binder expressed as a percentage of total weight can vary widely even though the volume of asphalt binder as a percentage of total volume remains quite constant.

  40. Objectives of Mix Design • Before embarking on a mix design procedure it is important to understand what its objectives. • This section presents the typical qualities of a well-made HMA mix. • By manipulating the variables of aggregate, asphalt binder and the ratio between the two, mix design seeks to achieve the following qualities in the final HMA product: –Deformation resistance (stability) –Fatigue resistance –Low temperature cracking resistance –Durability –Moisture damage resistance –Skid resistance. –Workability • Knowing these objectives, the challenge in mix design is then to develop a relatively simple procedure with a minimal amount of tests and samples that will produce a mix with all the above HMA qualities.

  41. Basic Procedure of Mix Design • HMA mix design is the process of determining –what aggregate to use, –what asphalt binder to use and –what the optimum combination of these two ingredients ought to be. • In order to meet the demands placed by the preceding desirable HMA properties all mix design processes involve three basic steps: –Aggregate selection. • No matter the specific method, the overall mix design procedure begins with evaluation and selection of aggregate and asphalt binder sources. • Different authorities specify different methods of aggregate acceptance. • Typically, a battery of aggregate physical tests is run periodically on each particular aggregate source. • Then, for each mix design, gradation and size requirements are checked. • Normally, aggregate from more than one source is required to meet gradation requirements.

  42. BASIC PROCEDURE Conti.. –Asphalt binder selection. • Although different authorities can and do specify different methods of asphalt binder evaluation, the Superpave asphalt binder specification has been or will be adopted by most State DOTs as the standard (NHI, 2000). –Optimum asphalt binder content determination. • Mix design methods are generally distinguished by the method with which they determine the optimum asphalt binder content. • This process can be subdivided as follows: –Make several trial mixes with different asphalt binder contents. –Compact these trial mixes in the laboratory. »It is important to understand that this step is at best a rough simulation of field conditions. –Run several laboratory tests to determine key sample characteristics. »These tests represent a starting point for defining the mixture properties but they are not comprehensive nor are they exact reproductions of actual field conditions. –Pick the asphalt binder content that best satisfies the mix design objectives.

  43. The Job Mix Formula • The end result of a successful mix design is –a recommended mixture of aggregate and asphalt binder. • This recommended mixture, which also includes aggregate gradation and asphalt binder type is often referred to as –the job mix formula (JMF) or recipe. • For HMA manufacturing, –target values of gradation and asphalt binder content are specified based on the JMF along with allowable specification bands to allow for inherent material and production variability. • It bears repeating that these target values and specification bands are based on the JMF and not any general HMA gradation requirements. • Thus, the mix designer is allowed substantial freedom –in choosing a particular gradation for the JMF and then the manufacturer is expected to adhere quite closely to this JMF gradation during production.

  44. HMA -MARSHALL METHOD • The basic concepts of the Marshall mix design method were originally developed by –Bruce Marshall of the Mississippi Highway Department around1939 and then refined by the U.S. Army. • Procedure –The Marshall mix design method consists of6 basic steps: • Aggregate selection. • Asphalt binder selection. • Sample preparation (including compaction). • Stability determination using the Marshall stability and flow test. • Density and voids calculations. • Optimum asphalt binder content selection.

  45. Aggregate Evaluation • Although neither Marshall nor Army Waterways Experiment Station (WES) specifically developed an aggregate evaluation and selection procedure, –one is included here because it is integral to any mix design. • A typical aggregate evaluation for use with either the Hveem or Marshall mix design methods includes three basic steps (Roberts et al., 1996): –Determine aggregate physical properties. • This consists of running various tests to determine properties such as: –Toughness and abrasion –Durability and soundness –Cleanliness and deleterious materials –Particle shape and surface texture

  46. CONTI… –Determine other aggregate descriptive physical properties. • If the aggregate is acceptable according to step #1, additional tests are run to fully characterize the aggregate. • These tests determine: –Gradation and size –Specific gravity and absorption –Perform blending calculations to achieve the mix design aggregate gradation. Often, aggregates from more than one source or stock pile are used to obtain the final aggregate gradation used in a mix design. • Trial blends of these different gradations are usually calculated until an acceptable final mix design gradation is achieved. • Typical considerations for a trial blend include: –All gradation specifications must be met. »Typical specifications will require the percent retained by weight on particular sieve sizes to be within a certain band. –The gradation should not be too close to the FHWA's 0.45 power maximum density curve. »If it is, then the VMA is likely to be too low. »Gradation should deviate from the FHWA's 0.45 power maximum density curve, especially on the 2.36mm (No. 8) sieve.

  47. Asphalt Binder Evaluation • The Marshall test does not have –a common generic asphalt binder selection and evaluation procedure. • Each specifying entity uses their own method with modifications to determine –the appropriate binder and, if any, modifiers. • Binder evaluation can be based on local experience, –previous performance or a set procedure. • Perhaps the most common set procedure now in use is –based on the SuperpavePGbinder system. • However, before this system –there was no nationally recognized standard for binder evaluation and selection. • Once the binder is selected, several preliminary tests are run to determine –the asphalt binder's temperature-viscosity relationship.

  48. Sample Preparation • The Marshall method, like other mix design methods, –uses several trial aggregate-asphalt binder blends (typically 5 blends with 3 samples each for a total of 15 specimens), –each with a different asphalt binder content. –Then, by evaluating each trial blend's performance, an optimum asphalt binder content can be selected. • In order for this concept to work, –the trial blends must contain a range of asphalt contents both above and below the optimum asphalt content. • Therefore, the first step in sample preparation is –to estimate an optimum asphalt content. • Trial blend asphalt contents are then determined from this estimate. • Optimum Asphalt Binder Content Estimate –The Marshall mix design method • can use any suitable method for estimating optimum asphalt content and • usually relies on local procedures or experience. • Sample Asphalt Binder Contents –Based on the results of the optimum asphalt binder content estimate, • samples are typically prepared at 0.5 percent by weight of mix in crement • with at least two samples above the estimated asphalt binder content and two below.

  49. Compaction with the Marshall Hammer –Each sample is then heated to the anticipated compaction temperature and compacted with a Marshall hammer, • a device that applies pressure to a sample through a tamper foot (see Figure ). –Some hammers are automatic and some are hand operated. –Key parameters of the compactor are: • Sample size = 102 mm (4-inch) diameter cylinder 64 mm (2.5 inches) in height (corrections can be made for different sample heights) • Tamper foot = Flat and circular with a diameter of 98.4 mm (3.875 inches) corresponding to an area of 76 cm2(11.8 in2). • Compaction pressure = Specified as a 457.2 mm (18 inches) free fall drop distance of a hammer assembly with a 4536 g (10 lb.)sliding weight. • Number of blows = Typically 35, 50 or 75 on each side depending upon anticipated traffic loading.