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Accelerated loading evaluation of foamed asphalt treated RAP layers in pavement performance.
  • Published Date:
    2013-12-01
  • Language:
    English
Filetype[PDF-1.08 MB]


Details:
  • Publication/ Report Number:
    FHWA/LA.09/475
  • Resource Type:
  • Geographical Coverage:
  • Format:
  • Abstract:
    Due to a lack of locally produced high-quality stone base materials, the Louisiana Department of Transportation and Development (LADOTD) is

    continuously seeking alternative base materials in lieu of crushed stones used for roadway construction. This report documents the research efforts conducted

    at the Louisiana Transportation Research Center (LTRC) regarding foamed-asphalt treated reclaimed asphalt pavement (RAP) alternative base materials and

    provides detailed information on experiment design as well as conducted field and laboratory tests.

    An accelerated pavement testing (APT) experiment was conducted in this study using the Accelerated Loading Facility (ALF) at LTRC’s Pavement

    Research Facility (PRF) testing site. The APT experiment included three different base test sections: the first one contained a foamed-asphalt treated 100

    percent RAP base course (FA/100RAP), the second used a foamed-asphalt treated 50 percent RAP and 50 percent recycled soil cement base course

    (FA/50RAP/50SC), and the third had a crushed limestone base. Despite using different base materials, the three APT sections shared other pavement layers

    and had a common pavement structure: a 2-in. asphalt wearing course, an 8.5-in. base course, and a 12-in. cement-treated subbase course over an A-4 soil

    embankment subgrade. Each section was instrumented with one multi-depth deflectometer and two pressure cells for measuring ALF moving load induced

    pavement responses (i.e., deflections and vertical stresses). To expedite traffic-induced pavement deteriorations, two steel load plates of 2,300-lb. each were

    added to the ALF load assembly (with a self-weight of 9,750-lb.) specifically at the loading cycle numbers of 175,000 and 225,000, respectively. The

    instrumentation data was collected at approximately every 8,500 ALF load repetitions; whereas, non-destructive deflection tests (NDT) and surface distress

    surveys (for surface rutting and cracking) were conducted at every 25,000 ALF load passes. In addition, a series of laboratory engineering performance-based

    tests was performed to characterize the performance of utilized materials in the APT experiment.

    The overall APT results generally indicated that the two foamed-asphalt base materials did not perform better than or as well as the crushed stone base. All

    three test sections were failed primarily due to the development of surface rutting. I isolated fatigue cracks were observed in localized areas of each test

    section associated with excessive surface ruts. The crushed stone section reached a rutting failure limit of an average rut depth of 0.5 in. approximately at an

    ALF loading cycle of 282,000; whereas, the FA/100RAP and FA/50RAP/50SC sections reached the limit at 230,000 and 228,000 repetitions, respectively.

    However, further analyses based on field measurement results revealed that both foamed-asphalt test sections showed slightly less permanent deformation

    than the crushed stone section during the first 175,000 ALF load repetitions. The backcalculated in-situ moduli of the two foamed-asphalt base courses were

    higher than that of the crushed stone base during the loading period when the applied ALF load was at 9,750 lb. Loading was increased after this and

    unfortunately, as the ALF load levels increased, both foamed-asphalt sections suddenly displayed a significantly higher rate of rutting than the stone section

    and quickly developed a premature rutting failure.

    A Shakedown theory analysis indicated that both foamed-asphalt treated RAP base materials seemed to have a lower shakedown threshold stress than the

    crushed stone base. It was due to the increase of the ALF load levels after the 175,000 repetitions that caused pavement base stresses higher than the

    shakedown threshold stresses of the two foamed-asphalt treated RAP base materials and eventually resulted in a stage of incremental collapse (or a sudden

    rutting failure) for the two foamed-asphalt test sections. In addition, the shakedown analysis also suggested that, as long as keeping the traffic induced stress

    level below the corresponding threshold stresses (as shown in the case when the ALF load was at a 9,750-lb. level), both foamed-asphalt base materials would

    have continuously performed better than the stone base.

    Due to having excellent performance under a 9,750-lb. ALF load, the foamed-asphalt treated RAP mixtures evaluated in this study may be considered for

    low volume roads, where the percentage of overloaded heavy truck traffic is relatively low and the environment is relatively dry (or a good drainage system is

    provided).

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