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33 In a research report for VDOT (Diefenderfer and Bry- pavement product is achieved after the pavement work has ant 2005), pavement warranty contracts are suggested for been performed" (Frabizzio et al. 2002). future rehabilitation projects. VDOT considered requiring pavement contractors to enter into warranty contracts. Such In Kentucky, a 5.1 km (3.17 mi) section of Interstate 265 warranties ensure quality pavements over the course of a was examined following a pavement reconstruction project. pavement's design life. In some cases, however, competition In addition to FWD data, ground-penetrating radar (GPR) between contractors was reduced. As a potential study case, testing and coring were completed along the segment. The an AC overlay project was chosen. FWD data were employed PCC slabs showed transverse cracks and differential settle- in the AC overlay design phase and before acceptance. FWD ment. The FWD data were used to determine layer stiffness data collection included using four load levels spaced at loca- and LTE. Although the Kentucky Transportation Cabinet tions 22.9 m (75 ft) apart. accepts LTE values of 90% or greater, all slabs in the study area had less than 90% LTE (Rister et al. 2003). After a jointed reinforced concrete pavement rehabilita- tion was completed along Interstate 287 in New Jersey, FWD data were used for "assessing the existing condition of the CASE 12. Conversion of Data From Other NONDESTRUCTIVE TESTING Devices mainline pavement, investigating the causes of premature distresses in the mainline pavement, and monitoring the effectiveness of slab undersealing at joint locations." For FDOT elected to replace its entire Dynaflect fleet with example, after a pavement rehabilitation project was com- FWDs. This decision is attributable to FWD providing a plete, low- to medium-severity transverse cracks appeared. more accurate simulation of actual traffic loads, its use as a "The FWD, DCP, and compressive strength test results were pavement research tool, and its adoption by LTPP. Because used to evaluate the condition of the various pavement lay- FDOT testing data were collected by means of Dynaflect ers. A normalization load of 40 kN (9,000 lbf) was used before FWD adoption, conversion from Dynaflect to FWD for the analysis of the FWD test results. That is, the FWD was needed. A linear correlation was found to make the deflections from the actual applied loads were normalized conversion, and this study refines this correlation. FWD, or adjusted to the values that would have resulted if a 40 Seismic Pavement Analyzer, and Dynaflect data were col- kN (9,000 lbf) loading had been applied." The FWD and lected at pavement sites throughout Florida, and statistical compressive strength test results revealed that the PCC layer correlations were determined. Additionally, the researchers was in fair-to-good condition. The average backcalculated conducted a state-of-the-practice literature review, as well PCC layer modulus (E PCC) was almost 34,500 MPa (5,000 as a survey of SHAs. FWD data were processed into Mr ksi), whereas the average compressive strength of the PCC and soil support value using MODULUS, EVERCALC, the layer was 60 MPa (8,700 psi). The FWD results indicated AASHTO method, and a finite-element modeling program. that the support to the PCC layer was adequate at midslab FWD Mr data backcalculated through MODULUS showed a locations, because the average backcalculated modulus of strong correlation to Mr values collected by the Dynaflect (R2 subgrade reaction (k) value was 5.5 kg/cm3 (200 pci), a "fair = 0.867). Similarly, Dynaflect Mr values correlated strongly value." However, the DCP test results indicated low Cali- with FWD data processed through EVERCALC (R2 = 0.742) fornia Bearing Ratio (CBR) values (average CBR = 46%) and through the AASHTO method (R2 = 0.925) along 483 for the nonstabilized open graded (NSOG) layer. Notwith- km (300 mi) pavement sections. In cases in which pavement standing the LTE values (92% on average), the FWD joint testing had been performed by LTPP, the LTPP database was test results indicated that the pavement was not performing "found to be the best database available to deduce general well at joint locations. The joint deflection (i.e., deflection patterns of the pavement behavior during field testing." The directly beneath the center of the FWD load plate during researchers reached 16 conclusions. The following 11 con- joint testing) and joint intercept values (indicative of slab clusions were relevant to this synthesis (Tawfiq 2003): support) were fairly high--average values of 9.6 mils and 2.1 mils, respectively. These results suggest that voids likely FWDs accurately simulated vehicle loads on exist beneath the slabs near joints, and excessive vertical slab pavements. movement consequently occurs at these locations. These Other NDT devices did not accurately simulate vehicle voids were promptly undersealed. Additionally, high degrees loads. of nighttime slab curl were confirmed by FWD testing, exac- Thick AC layers, very thin AC layers, shallow bedrock, erbated by the nonstabilized open graded base layer instead and heavier loads may have given unrealistic data and of a more densely graded base material. The researchers should be compensated for before performing back- concluded that "the FWD can thus act as an evaluative and calculation. investigative tool during the early stages of a project and as Calibration was crucial. a quality control instrument to ensure that the desired final