Polymer-modified asphalt (PMA) mixtures are routinely used today in flexible pavement structures or overlays carrying high volumes of traffic. Although there have been numerous laboratory and field studies comparing the performance of PMA and conventional hot-mix asphalt (HMA) mixtures, for example, Superpave® and Marshall, there has not been a concerted effort to quantify the benefits of using PMA mixtures or to develop guidance on when the use of PMA mixtures is cost-effective. An investigation of nearly three dozen real-world pavement sections in North America was conducted to quantify the benefits of using PMA mixtures. The test sections used in performance comparisons included both roadway and accelerated pavement test sections. Performance data for the test sections were derived from published literature or other public sources such as the Long-Term Pavement Performance or the National Center for Asphalt Technology databases. On the basis of the performance comparisons made between PMA and conventional sections, it was found that PMA mixtures significantly enhance not only the rutting performance of flexible pavements but also their fatigue and fracture performance. The examples used in this study show an extended service life for deep-strength HMA pavements of 5 to 10 years through the use of PMA mixtures, on the basis of the performance observations from the companion test sections, which were constructed mostly with older Marshall or Hveem mixtures. A definite bias exists between the predicted and measured distress values for the sections with PMA mixtures when using current mechanistic-empirical distress prediction models. This finding suggests a need for different calibration factors in PMA mixtures for use in rutting and fatigue cracking prediction equations.
One of the objectives for the Long-Term Pavement Performance (LTPP) program is to develop improved design methodologies for pavements. To achieve that objective, hundreds of hot-mix asphalt (HMA) test sections have been established and are being monitored to determine the performance characteristics of HMA pavements. The data from this program can be used to validate improved design methodologies and to establish the service life of HMA pavements. Specific findings are summarized from a study sponsored by the Asphalt Pavement Alliance to determine the expected service life of HMA or flexible pavements included in LTPP by using survivability analyses.
No abstract
In recent years, a significant percentage of coarse-graded Superpave® asphalt mixtures have exhibited tender mix behavior. Although the underlying causes of the phenomenon are not well understood, many experts believe the main cause of the tender zone problem is related to the amount of fluids, particularly excess moisture, in the asphalt mixture. Unfortunately, some asphalt technologists consider the accurate determination of moisture in an asphalt mixture to be a difficult prospect. The purpose of the present research was to determine if the tender mix behavior exhibited by some coarse-graded Superpave mixtures is related to moisture content and to develop procedures to accurately measure the moisture content in an asphalt mixture. The research indicated that conventional oven drying (110°C) was an acceptable alternative to the standard distillation procedure (ASTM D1461). The use of the microwave oven procedure for determination of moisture content also appeared to be acceptable, although in the present research there was a significant problem with breakage of the glass containers. The best sampling container for determination of the moisture content after a storage period was a 4-L aluminum paint can. When the paint can was used and sealed, the moisture content after 72 h of storage at room temperature was statistically equal to the moisture content determined immediately after sampling of the asphalt mixture. Other containers studied (paper grocery bag and plastic oven bag) indicated lower moisture content values after storage and a consistent loss of moisture the longer the sample was stored.
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