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  • Washington Asphalt Pavement Association |
    in any way with Read More Pavement Facts Posted by admin on Sep 18 2010 There are over 4 05 million public centerline road miles 8 52 million lane miles in the U S and of this 2 50 million miles or 63 percent are paved FHWA 2009 About 70 percent of Washington State roads are paved Pavement Purpose Typically pavements are built for three main Read More Member Benefits Posted by admin on Sep 13 2010 As a member of the Washington Asphalt Pavement Association WAPA you will have access to the latest technologies resources and innovations for the industry In addition to networking sessions where you can interact with your counterparts at local and state agencies WAPA plays an Read More Previous Next Economics Life Cycle Cost Posted by admin on Sep 15 2010 Today s current national and local economic conditions combining reduced funding with high infrastructure needs have elevated the importance of prudent spending Read More Environment Sustainable Pavement Posted by admin on Sep 13 2010 Asphalt is the sustainable material for constructing pavements From the production of the paving material to the placement of the pavement on the road to rehabilitation through Read More Engineering Perpetual Pavement Posted by admin on Sep 13 2010 The Perpetual Pavement concept was first articulated in 2000 and the concept has rapidly gained acceptance The APA s newest technical document on the subject is Perpetual Asphalt Read More Policy Livable Communities Posted by admin on Sep 12 2010 There is no doubt that societal trends and economic realities will shape the pavement market going forward Those driving factors include public funding issues an emphasis on Read More Recent Posts 28th Annual WSDOT WAPA LTAP Asphalt Pavement Joint Training Conference 2016 Archived Presentations 28th Annual WSDOT WAPA LTAP Joint Training

    Original URL path: http://www.asphaltwa.com/page/2/ (2016-04-26)
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  • Asphalt Pavement History | Washington Asphalt Pavement Association
    other natural pozzolans as binders Figure 2 shows a typical Roman road structure Figure 1 Roman Road Surface Figure 2 Roman Road Structure Telford Pavements Skipping forward several thousand years Telford pavements begin to show likeness to today s modern HMA pavements Thomas Telford born 1757 served his apprenticeship as a building mason Smiles 1904 Because of this he extended his masonry knowledge to bridge building During lean times he carved grave stones and other ornamental work about 1780 Eventually Telford became the Surveyor of Public Works for the county of Salop Smiles 1904 thus turning his attention more to roads Telford attempted where possible to build roads on relatively flat grades no more than a 1 in 30 slope in order to reduce the number of horses needed to haul cargo Telford s pavement section was about 14 to 18 inches in depth as shown in Figure 3 Telford pavements did not use any binding medium to hold the stones together Figure 3 Typical Telford Road after Collins and Hart 1936 Macadam Pavements Macadam pavements introduced the use of angular aggregates Figure 4 John McAdam born 1756 and sometimes spelled Macadam observed that most of the paved U K roads in early the 1800s were composed of rounded gravel Smiles 1904 He knew that angular aggregate over a well compacted subgrade would perform substantially better He used a sloped subgrade surface to improve drainage unlike Telford who used a flat subgrade surface onto which he placed angular aggregate hand broken maximum size 3 inches in two layers for a total depth of about 8 inches Gillette 1906 On top of this the wearing course was placed about 2 inches thick with a maximum aggregate size of 1 inch Collins and Hart 1936 Macadam who did not use any binding medium to hold the stones together realized that the layers of broken stone would eventually become bound together by fines generated by traffic The first macadam pavement in the U S was constructed in Maryland in 1823 Figure 4 Macadam Pavement Core Figure 5 Typical Macadam Road after Collins and Hart 1936 Tar Macadam Pavements A tar macadam road consists of a basic macadam road with a tar bound surface It appears that the first tar macadam pavement was placed outside of Nottingham Lincoln Road in 1848 Hubbard 1910 Collins and Hart1936 At that time such pavements were considered suitable only for light traffic i e not for urban streets Coal tar the binder had been available in the U K from about 1800 as a residue from coal gas lighting Possibly this was one of the earlier efforts to recycle waste materials into a pavement As a side note the term Tarmac was a proprietary product in the U K in the early 1900s Hubbard 1910 Actually it was a plant mixed material but was applied to the road surface cold Tarmac consisted of crushed blast furnace slag coated with tar pitch portland cement and a resin Today the

    Original URL path: http://www.asphaltwa.com/2010/10/18/welcome-asphalt-pavement-history/ (2016-04-26)
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  • Pavement Types | Washington Asphalt Pavement Association
    pavements which make up about 67 percent of U S roads and 70 percent of Washington State roads are typically categorized into flexible and rigid pavements Flexible pavements Those which are surfaced with bituminous or asphalt materials These types of pavements are called flexible since the total pavement structure bends or deflects due to traffic loads A flexible pavement structure is generally composed of several layers of materials which can accommodate this flexing Rigid pavements Those which are surfaced with portland cement concrete PCC These types of pavements are called rigid because they are substantially stiffer than flexible pavements due to PCC s high stiffness Each of these pavement types distributes load over the subgrade in a different fashion Rigid pavement because of PCC s high stiffness tends to distribute the load over a relatively wide area of subgrade Figure 1 The concrete slab itself supplies most of a rigid pavement s structural capacity Flexible pavement uses more flexible surface course and distributes loads over a smaller area It relies on a combination of layers for transmitting load to the subgrade Figure 1 This Guide focuses on flexible pavements Figure 1 Rigid and Flexible Pavement Load Distribution essay writing services

    Original URL path: http://www.asphaltwa.com/2010/09/18/pavement-types-pavement-types/ (2016-04-26)
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  • HMA Mix Types | Washington Asphalt Pavement Association
    1 Dense Graded Cores 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 Other Info Particulars about dense graded HMA are covered by the rest of this Guide Stone Matrix Asphalt SMA Stone matrix asphalt SMA sometimes called stone mastic asphalt is a gap graded HMA originally developed in Europe to maximize rutting resistance and durability Figure 2 and 3 The mix goal is to create stone on stone contact Since aggregates do not deform as much as asphalt binder under load this stone on stone contact greatly reduces rutting SMA is generally more expensive 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 Figure 2 SMA Surface Figure 3 SMA Lab Sample 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 Info 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 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

    Original URL path: http://www.asphaltwa.com/2010/10/17/pavement-types-hma-mix-types/ (2016-04-26)
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  • Superpave | Washington Asphalt Pavement Association
    overview and background of Superpave Strategic Highway Research Program SHRP In 1987 the U S Congress established a 5 year 150 million applied research program aimed at improving the performance durability safety and efficiency of the Nation s highway system Called the Strategic Highway Research Program SHRP this program was officially authorized by the Surface Transportation and Uniform Relocation Act of 1987 and consisted of research concentrated in four key areas FHWA 1998 Asphalt This area consists of research to develop a completely new approach to HMA mix design Concrete and structures This area consists of research in the areas of mix design and assessing protecting and rehabilitating concrete pavements and structures Highway operations This area consists of pavement preservation work zone safety and snow and ice control research Pavement performance This area consists of the Long Term Pavement Performance Program LTPP a 20 year study of over 2 000 test sections of in service U S and Canadian pavements to improve guidelines for building and maintaining pavements SHRP research activities were completed in 1992 and SHRP was closed down in 1993 To date SHRP has produced more than 100 new devices tests and specifications and perhaps more importantly has spawned a full scale on going implementation drive by such organizations as the FHWA AASHTO and TRB Superpave The SHRP asphalt research program the largest SHRP program at 53 million FHWA 1998 had three primary objectives NECEPT 2004 Investigate why some pavements perform well while others do not Develop tests and specifications for materials that will out perform and outlast the pavements being constructed today Work with highway agencies and industry to have the new specifications put to use The final product of this research program is a new system referred to as Superpave which stands for SUperior PERforming Asphalt

    Original URL path: http://www.asphaltwa.com/2010/09/18/pavement-types-what-is-superpave/ (2016-04-26)
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  • Asphalt Treated Base (ATB) | Washington Asphalt Pavement Association
    pavement loading can cause subgrade fines to migrate into the base and pavement structure This can clog the base layer which impedes drainage and create voids in the subgrade into which the pavement may settle An alternative to untreated base material Structurally ATB is about three times as strong as an untreated granular base such as crushed surface base or top course Therefore it is possible to use thinner layers for the same structural support which can save on excavation costs In some cases a layer of aggregate base is still needed to provide material to fine grade and to provide a smooth surface on which to pave The costs savings of using ATB can add up quickly On a site that must export material excess cut an ATB pavement design can save a considerable amount of excavation hauling and disposal costs On a site that must import material excess fill ATB can be used to build the pavement over more marginal subgrades i e a structure of gravel borrow and ATB can replace thicker crushed aggregate sections The most current ATB mix design specifications are maintained by the American Public Works Association of Washington APWA WA as a Local Agency General Special Provision GSP GSPs 4 SA1 and 9 03 6 are used together to define the current ATB specification These GSPs can be found on the Washington State Department of Transportation Local Agency GSP webpage at http www wsdot wa gov Partners APWA Important Considerations when Substituting ATB for Crushed Aggregate The minimum recommended crushed aggregate base thickness is 4 inches The minimum recommended ATB thickness is about 3 inches ATB gradation and nominal maximum aggregate size specifications are quite loose however pavement layers thinner than about 2 3 times the nominal maximum aggregate size may be difficult

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  • Standard Washington Mixes | Washington Asphalt Pavement Association
    is advantageous in many situations Old WSDOT Hveem Mix Designation Although WSDOT does not use these mixture classifications any more they may still exist in local city county specifications Class A Dense graded HMA with at least 90 percent of the coarse aggregate having at least one fractured face Its primary use is as a surface course for locations with high traffic levels or when the potential for rutting within the HMA layer exists Class B Dense graded HMA with at least 75 percent of the coarse aggregate having at least one fractured face Its primary use is as a leveling course or surface course because its nominal maximum aggregate size provides a good compromise between offering a smooth surface texture and low rut potential This is WSDOT s standard surface course paving mix Class D An open graded HMA Typically Class D mixes are placed as 0 70 inch thick wearing courses essentially an OGFC Proper maintenance requires a fog seal about every 5 years The performance of these mixes has varied on the state route system There is clear evidence that this type of wearing course is susceptible to studded tire wear Class E Dense graded HMA primarily intended for use as a base course This is WSDOT s standard base course paving mix Can also be used as a heavy duty mix Class F Dense graded HMA similar to Class B but with a wider gradation specification This is used in lieu of Class A B where aggregate sources properties cannot meet Class A B requirements generally limited to some areas of Eastern Washington Thus it has a higher performance risk Class G Dense graded HMA for thin lifts usually 1 inch or less The nominal maximum aggregate size is about 0 375 inches This small size

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  • Aggregate | Washington Asphalt Pavement Association
    1996 It is important to specify whether maximum size or nominal maximum size is being referenced Gradation WAPA Pavement Note on Aggregate Gradation Aggregate is typically crushed to certain size or gradation specifications Each crushed gradation is typically stored as a different aggregate stockpile While some standard mixes can possibly be met using a single aggregate stockpile with the possible addition of some blending sand Superpave mixes often require combinations of up to three or four different stockpiles to meet gradation requirements An aggregate s particle size distribution or gradation is one of its most influential characteristics In HMA gradation helps determine almost every important property including stiffness stability durability permeability workability fatigue resistance frictional resistance and resistance to moisture damage Roberts et al 1996 Because of this gradation is a primary concern in HMA mix design and thus most agencies specify allowable aggregate gradations Measurement Gradation is usually measured by a sieve analysis In a sieve analysis a sample of dry aggregate of known weight is separated through a series of sieves with progressively smaller openings Once separated the weight of particles retained on each sieve is measured and compared to the total sample weight Particle size distribution is then expressed as a percent retained by weight on each sieve size Results are usually expressed in tabular or graphical format The typical graph uses the percentage of aggregate by weight passing a certain sieve size on the y axis and the sieve size raised to the n th power n 0 45 is typically used as the x axis units The maximum density appears as a straight line from zero to the maximum aggregate size the exact location of this line is somewhat debatable but the location shown in Figure 2 is generally accepted Typical Gradations Figure 2 Dense or well graded Refers to a gradation that is near maximum density The most common HMA mix designs in the U S tend to use dense graded aggregate Gap graded Refers to a gradation that contains only a small percentage of aggregate particles in the mid size range The curve is flat in the mid size range These mixes can be prone to segregation during placement Open graded Refers to a gradation that contains only a small percentage of aggregate particles in the small range This results in more air voids because there are not enough small particles to fill in the voids between the larger particles The curve is flat and near zero in the small size range Uniformly graded Refers to a gradation that contains most of the particles in a very narrow size range In essence all the particles are the same size The curve is steep and only occupies the narrow size range specified Figure 2 Typical Aggregate Gradations Other Gradation Terms Fine aggregate sometimes just referred to as fines Defined by AASHTO M 147 as natural or crushed sand passing the No 10 sieve and mineral particles passing the No 200 sieve Coarse aggregate Defined

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