查看更多>>摘要：A two-step method—wavelet transform followed by Radon transform— is proposed for pavement distress classification. First, a pavement image is decomposed into different frequency subbands by wavelet transform. Distress is transformed into the high-amplitude wavelet coefficients, which are referred to as the details, in the high-frequency subbands. The wavelet modulus is calculated by combining the horizontal, vertical, and diagonal details. Since distress, especially crack, has dominant orientations in both the space domain and the wavelet domain, Radon transform is then applied to the wavelet modulus to transform cracks into peaks in the Radon domain. The patterns and parameters of the peaks are finally used for distress classification. Both simulated and experimental results demonstrate that the proposed two-step method is an effective method for pavement distress classification.
查看更多>>摘要：Many automated systems for crack analysis have been developed to measure the extent and severity of pavement cracking objectively. However, the accuracy of such an automated crack analysis system has not been satisfactory. This paper presents a crack type index (CTI) that can be easily adopted to determine the crack type objectively as longitudinal, transverse, and alligator cracking. The CTI is based on the spatial distribution of the image tiles rather than image pixels, where a tile is defined as a subimage of a whole digital image. The spatial distribution of image tiles is analyzed vertically and horizontally, with a resulting single index, which can be used to identify a spatial orientation of cracking. To determine the accurate CTI threshold values for longitudinal, transverse, and alligator cracks, 150 pavement images were captured with a digital video camera mounted on a sport-utility vehicle: 50 images for each of three types of cracking. These 150 images were analyzed automatically to compute the CTI values that correlate with crack types. To validate the CTI system, another 150 pavement images were captured. The CTI system identified 150 images as proper crack types with an 86% accuracy for alligator cracking, 92% accuracy for transverse cracking, and 94% accuracy for longitudinal cracking. The CTI system is further validated against images of block cracking and multiple cracks. The validation result against block cracking and multiple cracks indicates that the proposed CTI system in conjunction with UCI is robust and can be extended to identify block cracking and multiple cracks. The CTI method can be used to determine crack types from the digital images automatically without any human intervention.
Chul SuhJeffrey L. Y. LeeDavid W. FowlerKenneth H. Stokoe II...
p.113-124页
查看更多>>摘要：Several full-scale rigid pavement slabs were constructed and tested under constant cyclic loading for fatigue. To provide the comparable maximum applied stress to number of cycles to failure (S-N) relationships for the full-scale field slabs, laboratory beam fatigue testing was conducted before field testing with the use of the same concrete mix designs. The superaccelerated pavement testing technique that was developed at the University of Texas was used in the field. The stationary dynamic deflectometer (SDD) was used to load the full-scale concrete slabs. To monitor the response of the rigid pavements, accelerometers and linear variable differential transformers were installed, and dynamic and permanent displacements of slabs were recorded during the entire testing period. All test slabs reached fatigue failure under the interior loading configuration using the SDD. This field loading system was found to be a practical and effective tool for testing the full-scale rigid pavement system. During fatigue loading, cracks began at the bottom of the slabs at the loading locations and propagated along the bottom of the slab centerline, which was the maximum stress path. Vertical crack propagation at the edge and stress redistribution occurred for the part of the slab's fatigue life. The concept of equivalent fatigue life was applied to correct the effect of the different stress ratios between the field and the laboratory testing. The laboratory beams and full-scale field slabs showed an almost identical S-N relationship after the correction for the variance of stress ratio.
Mostafa A. ElseifiImad L. Al-QadiPyeong J. YooIbrahim Janajreh...
p.125-135页
查看更多>>摘要：A study conducted in 2001 on the heavily instrumented Virginia Smart Road measured pavement responses to a new generation of single wide-base tire (445/50R22.S) and to dual tires (275/80R22.5). The new single wide-base tire has a wider tread and a greater load-carrying capacity than conventional wide-base tires. The potential fatigue damage resulting from different tire configurations was evaluated. After successful field testing, a finite element (FE) parametric study was conducted to investigate different failure mechanisms that were not evaluated in the field. In this study, dual tires and two new generations of wide-base tires (445/50R22.5 and 455/55R22.5) were evaluated. The main difference between the two generations of wide-base tires is that the 455/55R22.5 is wider than the 445/50R22.5; hence, it further reduces the contact stress at the pavement surface under the same nominal tire pressure. In the developed FE models, geometry and dimensions were selected to simulate accurately the axle configurations typically used in North America; actual tire tread sizes and applicable contact pressure for each tread were considered; laboratory-measured pavement material properties were incorporated; and models were calibrated and properly validated against stress and strain measurements obtained from the experimental program. Four failure mechanisms were considered: fatigue cracking, primary rutting, secondary rutting, and top-down cracking. Results indicated that the new generations of wide-base tire would cause the same or relatively greater pavement damage than conventional dual tires. Because overall truck weight is reduced by approximately 450 kg when wide-base tires are used, it is reasonable to implement the load limits currently applied to the dual-tire assembly on the 455/55R22.5 wide-base tire.
查看更多>>摘要：The Florida Department of Transportation (FDOT) conducted an experiment to address the effects of polymer modifiers on the performance of Superpave~® mixes by using a heavy vehicle simulator. Two fine-graded Superpave mixes were considered. One mix included a virgin binder meeting the requirements of PG 67-22, and the other contained a styrene-butadiene-styrene polymer (SBS)-modified binder meeting those of PG 76-22. Both respective mixes contained the same effective binder content, aggregate components, and gradation. The mixes were designed for 10 million to 30 million equivalent single-axle loads with the use of the standard Superpave mix design methodology. During placement of these mixes, all standard FDOT density requirements and acceptance criteria were applicable. The subsequent investigation showed that the sections with SBS-modified mixture significantly outperformed those with the unmodified mixture. It was also determined that rutting in the unmodified mixture was primarily a function of shear flow, whereas rutting in the SBS-modified mixture was caused mainly by densification. This paper presents a description of the testing program, the data collection effort, and the subsequent analyses and findings, focusing primarily on the initiation mechanisms of rutting in asphalt mixtures as generated and observed under accelerated pavement testing.
查看更多>>摘要：Field cores were taken in 1995 and 2002 from eight asphalt pavements constructed in 1993 at FHWA's pavement testing facility to evaluate in situ pavement aging. Dynamic mechanical properties of these cores were evaluated by using the Superpave~® shear tester. The moduli of aged pavements were also predicted from binder, aggregate, and mixture properties with available prediction models, and the aging severity levels of all pavements were compared between the lab-measured and model-predicted. Eight pavements with two polymer-modified and six unmodified binders were evaluated in this study. Polymer-modified asphalt pavements showed comparatively lower aging than unmodified asphalt pavements. For unmodified asphalt pavements, stiffer asphalts tended to have higher aging indices. The binder aging index was found to be inversely proportional to the loading frequency, and differences between the aging indices for different binders were higher at lower frequency. Comparison of lab-measured and model-predicted binder aging indices showed similar rankings for all binders. Low stiffness binders, for example, AC-5, showed higher aging indices than high stiffness binders, for example, Styrelf. Pavement depth significantly affected binder aging. The aging index near the surface (6.35 mm) was found to be about four to five times the aging index at a depth of 139.7 mm in pavement. Comparison of lab-measured and model-predicted mixture aging indices showed large variations, from overpredicted to quite underpredicted, depending on the binder type and nominal maximum aggregate size.
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