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Accelerated loading evaluation of stabilized BCS layers in pavement performance.
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    Final report; 2005-2008.
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  • Abstract:
    BCS is short for blended calcium sulfate, a recycled fluorogypsum mixture that has been used in Louisiana as a roadway base for more than a decade.

    Without further chemical stabilization, the major concern of using raw BCS as a pavement structural layer is its moisture susceptibility.

    In order to verify the efficiency of laboratory-derived BCS stabilization schemes and further assess related field performance and potential cost

    benefits, an accelerated pavement testing (APT) experiment was recently conducted at Louisiana Transportation Research Center (LTRC) using the

    Accelerated Loading Facility (ALF). The APT experiment included three different base test sections: the first one contained a granulated ground blast

    furnace slag stabilized BCS base course (called BCS/Slag), the second used a fly ash stabilized BCS base course (called BCS/Flyash), and the third had a

    crushed limestone base. Except for using different base materials, the three APT sections shared a common pavement structure: a 2-in. asphalt wearing

    course, an 8.5-in. base course, and a 12-in. lime-treated working table layer over an A-6 soil 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). The

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

    surveys (for surface rutting and cracking) were performed at every 25,000 ALF load passes.

    The accelerated loading results generally indicated that the test section with a BCS/Slag base course outperformed the other two APT sections (i.e., the

    BCS/Flyash and the crushed stone sections) by a large margin. This was evidenced by all measurements in surface deflection, vertical compressive stress,

    rutting resistance, and pavement life. Post-mortem trench results revealed that the BCS/Slag base performed just like a lean concrete layer inside the

    pavement without any moisture-induced damage issues. The backcalculated layer moduli of the BCS/Slag base ranged from 1,190 ksi to 2,730 ksi, much

    higher than that of an asphalt concrete layer. In addition, the BCS/Flyash test section performed significantly better than the crushed stone test section in

    terms of the load carrying capacity, rutting resistance, and pavement life. However, post-mortem trench results showed a shear failure initialized inside the

    BCS/Flyash base layer on a failed station of the corresponding test section. Whether or not such a shear failure is indicative of a long-term moisturesusceptibility

    problem for the BCS/Flyash base layer, especially under a constantly wet environment, remains a concern due to the relatively short loading

    period associated with any APT experiment. Based on APT results, it was estimated that structural layer coefficients for the BCS/Slag and BCS/Flyash

    base courses used in this APT study would be 0.34 and 0.29, respectively.

    A cost-benefit analysis showed that the implementation of a slag stabilized BCS base in lieu of a crushed stone base will lead to a thinner asphalt

    pavement design, which can result in an initial construction cost reduction up to 16 percent without compromising future pavement performance. On the

    other hand, a 30-year life cycle cost analysis (LCCA) based on a typical Louisiana low volume road pavement structure indicated that using an 8.5-in. slag

    stabilized or 8.5-in. fly ash stabilized BCS base course, in lieu of a 8.5-in. crushed stone base, will potentially result in an LCCA cost savings up to 62

    percent and 56 percent per lane mile, respectively.

    Overall, it is concluded that both the slag and fly ash stabilized BCS materials evaluated in the study should be a good base material candidate for a

    flexible pavement design in Louisiana. However, caution should be made when using a fly ash stabilized BCS base under a constantly wet environment.

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