archive-com.com » COM » A » ASPHALTWA.COM

Total: 206

Choose link from "Titles, links and description words view":

Or switch to "Titles and links view".
  • Structural Design Methods | Washington Asphalt Pavement Association
    historical experience When using a design catalog it is important to be aware of the author s assumptions and design procedure Often assumptions and design procedures are based on extremely local conditions which may not be transferable For instance basic Snohomish County structural designs may not be appropriate for Spokane County and vice versa WAPA Pavement Note on Design Catalogs See the WAPA Design Catalog for recommended structural designs Often the required level of design does not warrant the use of advanced equations or models For instance a local residential road subject to only a few heavy loads per week i e school bus garbage truck does not warrant the expense and time of a mechanistic empirical design approach However many cities counties and private owners do not have specified standard pavement structural designs Empirical Design Many pavement structural design procedures use an empirical approach This means that the relationships between design inputs e g loads materials layer configurations and environment and pavement failure were determined using experience experimentation or a combination of both Although the scientific basis for these relationships is not firmly established they can be used with confidence as long as the limitations with such an approach are recognized Specifically it is not prudent to use an empirically derived relationship to describe phenomena that occur outside the range of the original data used to develop the relationship WAPA Pavement Note on Empirical Design WSDOT uses the 1993 AASHTO Guide for Design of Pavement Structures method for new HMA pavement design The most common empirical design method is the equation contained in the 1993 AASHTO Guide for Design of Pavement Structures use the equation here This equation was developed from experimental data at the AASHO Road Test a 27 million 1960 dollars road experiment conducted in Ottawa IL from 1956 1961 The AASHO Road Test was a complex study of the performance of highway pavement structures of known thickness under moving loads of known magnitude and frequency Highway Research Board 1961 The test studied both portland cement concrete and asphaltic concrete pavements as well as certain types of short span bridges The resultant design equation remains a popular method for pavement structural design Expert knowledge is required to use the 1993 AASHTO empirical equation a pavement design expert should be consulted if you are considering its use Mechanistic Empirical Design The most advanced pavement structural design uses a mechanistic empirical approach Unlike an empirical approach a mechanistic approach seeks to explain phenomena only by reference to physical causes In pavement design the phenomena are the stresses strains and deflections within a pavement structure and the physical causes are the loads and material properties of the pavement structure The relationship between these phenomena and their physical causes is typically described using a mathematical model Various mathematical models can be used WAPA Pavement Note on Mechanistic Empirical Design WSDOT uses a mechanistic empirical software package for pavement rehabilitation structural design This software package called the Everseries Pavement Analysis Programs Sivaneswaran

    Original URL path: http://www.asphaltwa.com/2010/09/17/methods/ (2016-04-26)
    Open archived version from archive


  • Manufacturing | Washington Asphalt Pavement Association
    asphalt to produce an HMA that conforming to JMF requirements There are two basic types of HMA plants commonly in use today the batch plant and the drum mix plant Batch plants produce HMA in individual batches while drum plants produce HMA in a continuous operation Each type of plant can produce the same types of HMA and neither type of plant should impart any significant plant specific HMA characteristics The choice of a batch or drum mix plant depends upon business factors such as purchase price operating costs production requirements and the need for flexibility in local markets both can produce quality HMA Batch Plants Batch plants which produce HMA in individual batches are the older of the two types of HMA production facilities it was not until the 1970s that drum plants became a popular HMA production option Currently about 70 percent of all operational HMA plants in the U S are batch plants while only about 5 percent of all newly manufactured plants in the U S are batch plants Roberts et al 1996 This means that as older batch plants are retired they are more than likely to be replaced by new drum plants which can

    Original URL path: http://www.asphaltwa.com/2010/09/17/manufacturing/ (2016-04-26)
    Open archived version from archive

  • Transport | Washington Asphalt Pavement Association
    and the discharge is usually placed in an elongated pile called a windrow in front of the paver by driving the truck forward during discharge Windrows require a special MTV to feed the HMA into the paver Live bottom or flo boy Live bottom dump trucks see Figure 3 have a conveyor system at the bottom of their bed to unload their payload HMA is discharged out the back of the bed without raising the bed Live bottom trucks are more expensive to use and maintain because of the conveyor system but they also can reduce segregation problems and can eliminate some detrimental types of truck bed paver contact because the bed is not raised during discharge Figure 1 End Dump Truck Figure 2 Bottom Dump Truck Video 1 End Dump Truck Video 2 Bottom Dump Truck Figure 3 Live Bottom Truck best pc antivirus software Transport Considerations There are several mix transport considerations or best practices that are essential to maintaining HMA characteristics between the production facility and the paving site These considerations can generally be placed into four categories Loading at the Production Facility Truck beds should be clean and lubricated with non petroleum products to prevent the HMA from sticking to the truck bed Petroleum based products such as diesel fuel should not be used because of environmental issues and because they tend to break down the asphalt binder HMA should be discharged into the truck bed so as to minimize segregation Dropping HMA from the storage silo or batcher for batch plants in one large mass creates a single pile of HMA in the truck bed Large sized aggregate may roll off this pile and collect around the base Dropping HMA in several smaller masses three is typical at different points in the truck bed will

    Original URL path: http://www.asphaltwa.com/2010/09/17/transport/ (2016-04-26)
    Open archived version from archive

  • Laydown | Washington Asphalt Pavement Association
    forces back into equilibrium Therefore changing the following paver characteristics will affect these forces and thus mat thickness in the described manner Paver speed If a paver speeds up and all other forces on the screed remain constant the screed angle decreases to restore equilibrium which decreases mat thickness think of what happens to the ski angle of a water skier as boat speed increases Material head If the material head increases either due to an increase in material feed rate or a reduction in paver speed screed angle will increase to restore equilibrium which increases mat thickness Tow point elevation As the tow point rises in elevation the screed angle increases resulting in a thicker mat As a rule of thumb a 1 inch movement in tow point elevation translates to about a 0 125 inch movement in the screed s leading edge Without automatic screed control tow point elevation will change as tractor elevation changes due to roughness in the surface over which it drives Locating the screed tow point near the middle of the tractor significantly reduces the transmission of small elevation changes in the front and rear of the tractor to the screed Because the screed elevation responds slowly to changes in screed angle the paver naturally places a thinner mat over high points in the existing surface and a thicker mat over low points in the existing surface TRB 2000 Screed angle can also be adjusted manually by using a thickness control screw or depth crank Screed angle adjustments do not immediately change mat thickness but rather require a finite amount of time and tow distance to take effect Figure 6 shows that it typically takes five tow lengths the length between the tow point and the screed after a desired level is input for a screed to arrive at the new level Because of this screed reaction time a screed operator who constantly adjusts screed level to produce a desired mat thickness will actually produce an excessively wavy unsmooth pavement Figure 6 Screed Reaction to a Manual Decrease in Screed Angle after TRB 2000 Automatic Screed Control Since it is not practical to manually control tow point elevation pavers usually operate using an automatic screed control which controls tow point elevation using a reference other than the tractor body Since these references assist in controlling HMA pavement grade they are called grade reference systems and are listed below Roberts et al 1996 Erected stringline This consists of stringline erected to specified elevations that are independent of existing ground elevation Most often this is done using a survey crew and a detailed elevation grade plan Although the stringline method provides the correct elevation to within surveying and erecting tolerances stringlines are fragile and easily broken knocked over or inadvertently misaligned Lasers can be used to overcome the difficulties associated with stringlines because they do not require any fragile material near the pavement construction area Lasers can establish multiple elevation or grade planes even in dusty

    Original URL path: http://www.asphaltwa.com/2010/09/17/laydown/ (2016-04-26)
    Open archived version from archive

  • Quality Assurance | Washington Asphalt Pavement Association
    and acceptance as its three key components TRB 1999 Quality assurance All those planned and systematic actions necessary to provide confidence that a product or facility will perform satisfactorily in service Quality assurance addresses the overall problem of obtaining the quality of a service product or facility in the most efficient economical and satisfactory manner possible Within this broad context quality assurance involves continued evaluation of the activities of planning design development of plans and specifications advertising and awarding of contracts construction and maintenance and the interactions of these activities Quality control Those quality assurance actions and considerations necessary to assess production and construction processes so as to control the level of quality being produced in the end product This concept of quality control typically includes sampling and testing by the contractor to monitor the process but usually does not include acceptance sampling and testing by the agency owner Also called process control Acceptance Sampling testing and the assessment of test results to determine whether or not the quality of produced material or construction is acceptable in terms of the specifications Independent assurance A management tool that requires a third party not directly responsible for process control or acceptance to provide an independent assessment of the product and or the reliability of test results obtained from process control and acceptance testing The results of independent assurance tests should not be used as a basis of product acceptance Figure 1 Checking Mat DensityFigure 2 Truck Sampling During Night Paving WAPA Pavement Note on Quality Assurance On State jobs WSDOT performs acceptance testing while the contractor may choose to sample and test at any level for their own quality control Acceptance testing is not always used on local or private jobs If used it is often performed by an independent consultant working

    Original URL path: http://www.asphaltwa.com/2010/09/17/quality-assurance/ (2016-04-26)
    Open archived version from archive

  • Specifications | Washington Asphalt Pavement Association
    WA RD 517 1 Washington State Department of Transportation Transportation Center TRAC Seattle WA http www wsdot wa gov ppsc research CompleteReports WARD517 1HotMixAsphalt pdf Proprietary Product Specifications A proprietary product specification is used when a generic description of a desired product or process cannot be easily formulated It usually contains an or equivalent clause to allow for some measure of competition in providing the product It is generally acknowledged that such a specification severely limits competition increases cost provides little latitude for innovation and puts substantial risk on the owner for product performance Most agencies avoid this type of specification whenever possible however private owners often use them Method Specifications A method specification outlines a specific materials selection and construction operation process to be followed in providing a product In the past many construction specifications were written in this manner A contractor would be told what type of material to produce what equipment to use and in what manner it was to be used in construction In its strictest sense only the final form of the structure can be stipulated for instance the thickness of the pavement layers This type of specification allows for a greater degree of competition than the proprietary product specification but as long as the structure is built according to the materials and methods stipulated the owner bears the responsibility for the performance Although widely used method specifications have several key disadvantages First they tend to stifle contractor innovation because there is virtually no incentive to develop better more efficient construction methods Second since they are not statistically based and 100 percent compliance is usually not possible method specifications usually required substantial compliance a purposely vague and undefined term that can lead to disputes Finally spot checks of material quality which are often used in method specifications do not reflect overall material quality because they are taken from subjectively determined non random locations Since they are not random these spot checks have no statistical validity and therefore do not reflect overall material quality Despite their flaws method specifications are still widely used on the local agency level e g counties small cities towns etc In general this is because they are familiar straightforward to write and can be implemented with minimal agency involvement Local agencies often lack the expertise and resources required to use statistical specifications or warranties End Result Specifications An end result specification is one in which the final characteristics of the product are stipulated and the contractor is given considerable freedom in achieving those characteristics In their roughest form they specify minimum maximum or a range of values for any given characteristic and base acceptance on conformance to these specifications For instance they may state a minimum layer thickness or a range of in place air voids Since it is impractical to measure every square foot of constructed pavement end result specifications use statistical methods to estimate overall material quality based on a limited number of random samples Therefore end result specifications

    Original URL path: http://www.asphaltwa.com/2010/09/17/specifications/ (2016-04-26)
    Open archived version from archive

  • Construction | Washington Asphalt Pavement Association
    Residential Driveways Pathways Recreational Facilities Heavy Industrial Facilities Airfields Site Paving Awards Winners How To Apply Calendar Industry Events WAPA Events Home Construction Segregation and Temperature Differentials Segregation and temperature differentials are construction related HMA pavement problems that can lead to early pavement failure Washington State has been a leader in researching identifying and combating these problems adobe photoshop software Read More Compaction Compaction is the process by which the

    Original URL path: http://www.asphaltwa.com/category/6/66-wapa-construction/page/2/ (2016-04-26)
    Open archived version from archive

  • Condition Rating Systems | Washington Asphalt Pavement Association
    help manage pavement networks By carefully choosing the rating scale called the condition index pavement condition scores can be used to Deighton 1997 Trigger treatment For instance once a pavement s condition rating reaches a certain level it can be scheduled for maintenance or rehabilitation Determine the extent and cost of repair A pavement condition score is a numerical representation of a pavement s overall condition and can thus be used to estimate the extent of repair work and the likely cost Determine a network condition index By combining pavement condition scores for an entire road network a single score can be obtained that gives a general idea of the network condition as a whole Allow equal comparison of different pavements Since a pavement condition score accounts for all types of pavement performance measures it can be used to compare two or more pavements with different problems on an equal footing A pavement condition index is simply the scale or series of numbers used to describe a pavement condition Typical pavement condition indices may be based on a scale of 0 to 5 or perhaps 0 to 100 The proper pavement condition index depends upon the objectives of whatever system is used to manage a particular pavement network called a Pavement Management System or PMS This section will present two example pavement condition indices Present Serviceability Index PSI The Present Serviceability Index PSI is a 0 to 5 scale that was originally based on a panel of raters who between 1958 and 1960 rated various roads in the states of Illinois Minnesota and Indiana PSI ranges from 5 excellent to 0 essentially impassable and is still used today throughout the country It is often a good choice for a smaller less sophisticated pavement rating system WSDOT s Pavement Rating System

    Original URL path: http://www.asphaltwa.com/2010/10/01/pavement-evaluation-condition-rating-systems/ (2016-04-26)
    Open archived version from archive



  •