The quality of constructed pavement foundation layers was studied with rapid and near-continuous soil stiffness measurements as alternatives to traditional nuclear gauge moisture–density measurements. Sixteen sections of stabilized pavement foundations covering 4.8 mi, with ground conditions ranging from soft to very stiff, were studied. Measurements from falling weight deflectometer, light weight deflectometer, dynamic cone penetrometer, and roller-integrated compaction monitoring systems were used to assess soil stiffness. Statistical analyses of the results were reported in the form of coefficient of variation and empirical correlations between measurements. Results of soil stiffness were compared with two independent groups of nuclear moisture–density measurements to demonstrate some of the shortcomings of traditional nuclear-gauge testing for quality assessment. The findings from this paper show the value in using soil stiffness measurements to characterize ground variations. Cost data are also reported for the stabilized sections.
This paper describes results from a study comparing the performance of side-by-side test sections of pavement foundation layers constructed with on-site recycled materials and surfaced with hot-mix asphalt (HMA). Test sections included recycled materials blended with subgrade to create a mechanically stabilized subgrade layer and recycled materials placed in an overexcavated subgrade layer. In situ falling weight deflectometer (FWD), dynamic cone penetrometer (DCP), and laboratory freeze–thaw tests were used to assess the performance of the test sections, in comparison with a control section where recycled materials were not used. Field testing was conducted at seasonal intervals over 2 years after construction, and the results were statistically analyzed with two-tailed Welch's t-tests to account for unequal variances. Findings indicated that test sections with on-site recycled materials provided improved support conditions for the pavements during both before and after freeze–thaw conditions, when compared with the control section. FWD and DCP test results indicated that recycled material blended with sub-grade showed more thaw-weakening compared with recycled material alone. Laboratory freeze–thaw test results corroborated the comparisons observed in the field test results. Correlations between FWD test measurements on the foundation layer and on the pavement yielded a statistically significant regression relationship, which indicated the importance of support conditions on the surface layer performance. Analysis of bid prices to construct the test sections indicated no statistical evidence to suggest that the unit costs for the test sections were different from one another.
In Maryland, persons engaged in the work of the treatment and care of trees for compensation must be licensed by the Department of Natural Resources. The Department of Natural Resources—Forest Service, the Mid- Atlantic Chapter of the International Society of Arboriculture, the Maryland Arborist Association, and the Maryland Community Forest Council cosponsored a survey of Licensed Tree Experts (LTEs). The survey's purposes were to estimate the total number of jobs and gross dollar revenue that the arboricultural industry provides to the state of Maryland; to identify the tree care industry as a constituency in the business community; to identify training resources and trade affiliations most used by LTEs; to identify business type, geographic concentration, and client type; and to provide input into agency regulations affecting the industry. It is estimated that the tree care industry in Maryland employs 2,841 individuals and generates more than $134.5 million in annual gross revenue.
The fundamentals of rutting behavior for thin full-depth flexible pavements (i.e., asphalt thickness less than 12 inches) are investigated in this study. The scope incorporates an experimental study using full-scale Accelerated Pavement Tests (APTs) to monitor the evolution of each pavement structural layer's transverse profiles. The findings were then employed to verify the local rutting model coefficients used in the current pavement design method, the Mechanistic-Empirical Pavement Design Guide (MEPDG). Four APT sections were constructed using two thin typical pavement structures (seven-and ten-inches thick) and two types of surface course material (dense-graded and SMA). A mid-depth rut monitoring and automated laser profile systems were designed to reconstruct the transverse profiles at each pavement layer interface throughout the process of accelerated pavement deterioration that is produced during the APT. The contributions of each pavement structural layer to rutting and the evolution of layer deformation were derived. This study found that the permanent deformation within full-depth asphalt concrete significantly depends upon the pavement thickness. However, once the pavement reaches sufficient thickness (more than 12.5 inches), increasing the thickness does not significantly affect the permanent deformation. Additionally, for thin full-depth asphalt pavements with a dense-graded Hot Mix Asphalt (HMA) surface course, most pavement rutting is caused by the deformation of the asphalt concrete, with about half the rutting amount observed within the top four inches of the pavement layers. However, for thin full-depth asphalt pavements with an SMA surface course, most pavement rutting comes from the closet sublayer to the surface, i.e., the intermediate layer. The accuracy of the MEPDG’s prediction models for thin full-depth asphalt pavement was evaluated using some statistical parameters, including bias, the sum of squared error, and the standard error of estimates between the predicted and actual measurements. Based on the statistical analysis (at the 95% confidence level), no significant difference was found between the version 2.3-predicted and measured rutting of total asphalt concrete layer and subgrade for thick and thin pavements.
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