United States Department of Transportation
i
Construction comparison of Louisiana's conventional and alternative base courses under accelerated loading : final report.
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2001-11-01
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[PDF-5.37 MB]
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Alternative Title:Construction comparison of Louisiana's conventional and alternative base courses under accelerated loading.
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Abstract:This report describes the test results of the first project at the Louisiana Transportation Research Center's Accelerated Loading Facility (ALF). In 1995, 9 test lanes were constructed at the Louisiana Pavement Research Facility in Port Allen. These test lanes consisted of 3.5 in. of type 8 wearing and binder course and crushed limestone or soil cement bases made with either 4% or 10% cement and either plant-mixed or mixed in-place courses. These mixed courses had the same structural capacity but with variable shrinkage cracking potentials. The lanes were loaded to failure using the ALF and the results were used to compare the performance of the various base materials.
The experiment was organized into three phases. Phase I of the program evaluated a flexible pavement with a typical crushed stone base and compared it to two innovative flexible pavement designs. Phase II compared plant mix stabilized soil bases. Phase III compared other stabilized pavement layer configurations, including the conventional (benchmark) pavement.
Pavement condition was monitored by measuring surface deformation, cracking, and falling weight deflectometer surface deflection. A number of lined bores allowed monitoring of moisture content by down-the-hole meters. Ambient climate was recorded and "in pavement" temperatures were measured. Since traffic loading on each section stopped at different distress levels, all test sections were compared at a standard failure level for rutting. Regression models were developed for each test lane in order to be able to predict the number of equivalent single axle loads carried to a standard rutting failure level of 0.75 in. (19 mm). A post-mortem was conducted after loading to investigate the pavement failure modes and base conditions. A pavement performance comparison among various lanes and survival analysis on pavement life was conducted. The relative performance comparisons showed that the stone base performed as well as the soil cement base and that the stone over a cement stabilized base performed best of all. Using an A-4 soil, the 4% cement treated bases performed as well as the 10% cement stabilized bases and the mixed-in-place bases performed similarly to the plant-mixed bases.
The Phase I test results suggested a layer coefficient for the stone stabilized soil of 0.10. Estimating the Present Serviceability Index from the roughness, fatigue cracking, and rutting results provides a reasonable relationship for lanes with crushed stone or cement-stabilized soil bases that could be applied in pavement management systems models. Phase II and III test results suggested a layer coefficient for the cement stabilized subbase of 0.16. Performance of the stone over cement stabilized base ("inverted" design) pavement structure was significantly different from that of the other lanes in both failure mode and fatigue life. Cracking was found to initiate at the bottom of the asphalt layer or to reflect into the asphalt layer from the soil cement bases in all pavements except for the "inverted" base pavement where cracking initiated at the surface.
A literature survey was conducted to identify analytical pavement models that could be used to predict the performance of the test lanes using pavement material properties, layer thicknesses, and wheel loads applied by the ALF. The VESYS 3A-M and FLEXPASS models were used to predict rutting, cracking, and roughness development with traffic loads and to predict the performance of the test lanes with granular bases. Both of the control section, which consisted of an 8.5 in (216 mm) limestone base over geofabric, while FLEXPASS predictions matched the performance of a test section consisting of 4 in (102 mm) of limestone over (152 mm) stone-stabilized soil. In addition, Jameson and Asphalt Institute models were used to adequately predict the pavement fatigue life for three of the four cement stabilized base layers but not for the “inverted” base. The fatigue prediction model for cement-stabilized base asphalt pavement with a stone interlayer should be further investigated.
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