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32 to significant seasonal variation. FWD data were gathered CASE 10. Experimental Paving Materials at varying sites throughout the year. The model was then built using backcalculated FWD moduli. Additionally, the Crushed aggregate, a popular base course for pavements, seasonal model was used to design a 20-year AC overlay in became progressively more expensive. To save money on Arcadia, New York. base courses, FDOT has sponsored recycling concrete aggregate (RCA) research. FWD data were used to test vari- ous RCA mixes and the results show RCA to be a viable base CASE 8. Nonresilient Pavement Layer course for roadway pavements ("Guidelines and Specifica- Behavior tions for the Use of Reclaimed Aggregates . . ." 2001). Because the FWD has replaced the Benkelman beam as the Ultra-thin whitetopping (UTW) was evaluated using primary pavement analysis and design device, measured FWD data in Minnesota. FWD data were collected one year layer moduli now include plastic deformations as well as after an experimental UTW pavement test section was con- recoverable deformations. Mechanistic design practices structed at the Minnesota Road Research test facility. PCC assume that all layers behave resiliently. In the past, these thickness varied from section to section; the study's intent is additional plastic deformations were assumed negligible; to determine an ideal PCC thickness. Strain data captured however, nonresilient behavior may be observed given a by the FWD showed a good bonding condition between the load of significant magnitude. The practice of "16 (FWD lower bituminous surface and the new PCC wearing course. weight) drops at four load levels with four replicates at each Although an optimal UTW overlay design is not yet deter- drop height or load level" may result in nonresilient behav- mined, "the dynamic strain measurements indicate that there ior. Such behavior can be detected by statistical tests. Two is a better bond between the asphalt and the overlay in the statistical methods of nonresilient behavior detection were thinner sections." It was also observed that the magnitude tested using FWD tests at Cornell University. Tests were of the strains in the thinner sections were more dependent performed from February until May 2003. No trends were on the stiffness of the asphalt than the number of equivalent observed through ANOVA (analysis of variance) tests but single axle loads accumulated (Vandenbossche and Rettner chi-squared variance tests on the center sensor data revealed 1998). nonresiliency during the spring-thaw season. ANOVA tests "will detect systematic variations; however, if the deflec- tions are not always generally increasing or decreasing for CASE 11. Project Acceptance and Evaluation a given load level, the test does not detect when nonresilient behavior is occurring" (Orr 2003). FWD tests have potential for use during construction. FWD data may be used for the following (Clark 2005): CASE 9. Utility Cuts · Subgrade strength improvements before structural sec- The Iowa DOT sought to improve utility cut repair tech- tion construction. niques. Utility cuts often settle over time, which leads to · Subbase and base layer monitoring after structural sec- "uneven pavement surfaces, annoyance to drivers and, tion construction. ultimately, further maintenance." Causes of the settlement · LTE on jointed plain concrete pavement. include differing backfill material between jurisdictions, · Baseline development. excessive volumes of backfill materials "placed at bulking moisture contents," and the lack of quality assurance or con- As an example, FWD tests on Virginia State Highway trol. FWD data showed that backfill materials within utility 288 showed where a cement-treated base needed to be placed cuts--as well as an area 0.6 to 0.9 m (2 to 3 ft) beyond the cut during construction. A second example, where CRCP was perimeter--were susceptible to settlement. The Iowa DOT placed, showed deflections greater than 0.14 mm (5.5 mils). will continue to monitor its utility cuts using FWD tests, as These deflections indicated poor construction joints, and well as nuclear gauges, dynamic cone penetrometers (DCPs), further investigation showed reinforcing steel at the wrong Clegg hammers, and laboratory tests. These data "will be depth. FWD was again used as a diagnostic tool along U.S. studied with the goal of increasing pavement patch life and Highway 29, where two stations showed poor support. reducing the maintenance of the repaired areas" (Research Although FWD could be used as an acceptance criterion, News 2007). contractors would have to be familiar with their use and be able to afford one.