The purpose of this paper is to present the effectiveness of in-situ instrumentation on diagnosing the pavement layer conditions under full-scale accelerated traffic loading. The test section is an in-service pavement (US281) in Jacksboro, Texas. Multi-Depth Deflectometers (MDDs) are used to measure both permanent deformations and transient deflections, caused by accelerated traffic loading and Falling Weight Deflectometer (FWD) tests. Four different FWD loads of 25, 40, 52, and 67 kN were applied in close proximity to the MDDs at various traffic loading intervals to determine pavement conditions. It was found that the majority of rutting occurred in the newly recycled asphalt mix. The aged (> 40 years) underlying base and subgrade layers contributed less than 30% to overall rutting. Only the top recycled asphalt layer underwent notable deterioration due to traffic loading. Up to 1.5 million axle repetitions, the test pad responded to FWD load almost linearly, not only over the whole pavement system but also within individual layers. However, under higher FWD loads, the percentage of total deflection contributed by the subgrade increased.
The Dynamic Cone Penetrometer (DCP) is one of the least expensive testing devices able to characterize base and subgrade properties. To fully use the DCP in pavement evaluation, an empirical relationship between DCP penetration rate and layer modulus is required. However, the literature on this correlation is limited. This study incorporates a total of 198 DCP and Falling Weight Deflectometer (FWD) tests done over 8 years on various types of highways (Interstate Highway, US, and Farm-to-Market). The computer program MODULUS was employed to backcalculate the layer moduli from the FWD results to build a correlation with DCP results. A comparison was made with the widely-used model by Powell et al. (1984). It is found that the difference between the two models decreases as the Penetration Rate (PR) increases. For a PR of less than 10 mm/blow, the difference between these two models was over 10%. The difference is only about 1.7 % when the PR is 80 mm/blow. Without knowing the true moduli, it is impossible to tell which equation is better. The correlation developed here provides another option and allows researchers to recognize the range of variability.
A comprehensive evaluation of pavement condition and an understanding of the underlying causes of pavement distress is vital in selecting the optimal rehabilitation strategy. Three projects were investigated in this study to demonstrate the application of nondestructive testing technologies in this selection process. Ground Penetrating Radar (GPR), Falling Weight Deflectometer (FWD), and Dynamic Cone Penetrometers (DCP) were successfully used on these TxDOT projects. GPR was employed successfully to locate defects in the hot mix surface layer that were responsible for the chronic distress on US 69. This roadway was rehabilitated previously but the strategy used had not addressed the root cause of the pavement problem. FWD and DCP data were also used to determine the structural capacity or layer moduli of the pavement system that allows the designer to derive the overlay thickness. Coring and trenching were utilized to verify the defects detected in the GPR data. The advantage of nondestructive testing is that it provides a comprehensive evaluation of subsurface conditions throughout the entire project, not only at locations where coring and trenching are performed. Furthermore, GPR was employed to verify a rehab design of an old JCP pavement on SH 73. Originally, the plan called for pressure grouting to fill the subsurface voids. However, GPR found no voids under the JCP slab; this was validated in subsequent coring. Therefore the GPR results helped district personnel to eliminate the cost of the pressure grouting. For comparison purposes, GPR results from IH 45 and US 82 (where there were voids under JCP slabs) were utilized.
This study evaluates the use of 3D laser scanning technology to measure pavement roughness. Three 100 m test sections, ranging from smooth to very rough (with apparent cracks, areas of distress, and manholes) were selected to investigate the capability of the 3D laser scanning technology. Rod and level surveys were conducted to establish the reference profile for each test section. In addition, Multiple Laser Profiler (MLP) was employed to measure the multiple paths of each test section. Results from multiple paths of 3D laser scanning were compared with those from MLP and rod and level surveys. The 100 m reference profiles indicate similar results between the 3D laser scanning and rod and level survey. With 95% confidence, the statistical paired-samples T-test indicates that there is no significant variation between the results from rod and level surveys and 3D laser scanning. The data include IRI from 2.83 to 13.15 m/km such that they represent a wide spectrum of pavement conditions. The coefficient of correlation (R2) between the MLP and 3D laser scanning from 20 longitudinal profiles is 0.99. The 3D laser scanning is a static method and thus the data do not have to be filtered and therefore there is no associated cut-off wavelength problem. Based on the results gathered, the 3D laser scanner is able to collect reliable profile data and has high potential to be used as a QC/QA tool for construction acceptance. Through 3D laser scanning technology, pavement engineers are able to visualize the pavement roughness covering the entire pavement width in unprecedented detail that consists of extremely rich and accurate point-cloud data.
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