Abstract: The performance of geosynthetic stabilized flexible pavement systems is under investigation. Laboratory test sections were constructed and dynamically loaded to simulate a typical secondary road. The laboratory study demonstrated that geotextiles offer substantial improvement to the performance of pavements constructed over weak and moderate subgrade. The improvement was attributed to the separation capabilities of the geotextiles and their ability to prevent the development of a transition layer (intermixing layer). To verify the laboratory results, nine instrumented full-scale test sections were constructed as a part of a secondary road. Three groups, each group consisting of geotextile and geogrid stabilized and non-stabilized test sections, were constructed. The base course thickness varied between the three groups. Monitoring of the field test sections is currently in progress. This paper presents a summary of the laboratory results and describes the construction, monitoring, testing, and preliminary results of the field study. Preliminary field results support the separation mechanism theory and the development of a transition layer when a separator is absent.

Abstract: The aim of this research project is to develop an improved backcalculation procedure, for the determination of flexible pavement properties from the Falling Weight Deflectometer (FWD) test results. The conventional backcalculation methods estimate the pavement layer moduli assuming full adhesion exists between layers in the analysis process. The method developed in this research can predict the interface condition between the wearing and the base courses in addition to the layer moduli, which can be considered an improvement to the existing procedures. A two stage database procedure has been used to predict the above parameters and to facilitate the determination of the deflection insensitive parameters. The need for this improvement arises from the large number of debonding failures which have been reported in the literature between the wearing and base courses, and the theoretical studies which identified the significance of including the interface bonding condition in the analysis process. The validation of the improved method has been carried out firstly by comparing the backcalculated results for ninety theoretical pavements with their hypothetical values, and secondly by comparing the improved procedure results with other well known programs such as WESDEF and MODULUS. Full scale pavement testing using the FWD has been performed and the backcalculated results compared with measured values for the pavement materials. Indirect tensile tests for resilient modulus of bituminous materials were carried out on cores extracted for the pavements, whereas Dynamic Cone Penetrometer (DCP) tests were conducted for the unbound materials. The Backcalculated and the physically measured results correlated well, validating the improved procedure.

Abstract: A laboratory-scale pavement testing facility with a moving vehicle load can be used to simulate reliably the stresses caused by traffic in the road structure and is therefore well suited to the testing of materials and structures. The measuring system developed here can be used to determine reliably both elastic and permanent deformations within the structure, which, in turn, can be used to determine relative strains. The mechanical properties of the unbound base course and their significance for the performance of the whole road structure depend on the thickness of the bound layer and the quality of the material. When the asphalt concrete (AC) layer is thin, it would be good to have grading with Fuller's "n" value equal to 0.4 or 0.5 in the unbound base course. When the bound layer consists of very soft asphalt, in turn, it would be good to aim at a grading curve with "n" = 0.5. A large maximum grain size in the base course minimizes both permanent and elastic strains. Compaction of the unbound layers also has a distinct effect on the mechanical properties of the layer. A high degree of compaction minimizes permanent strains. Effective compaction, however, results in grinding of the materials. The compaction of unbound rough materials and their grinding during compaction can be evaluated with the Intensive Compaction Tester gyratory compactor both quickly and inexpensively.

Abstract: Full depth reclamation in the United States increasingly is being selected by cities, counties, state departments of transportation, federal agencies, airports and consulting engineers to reconstruct severely deteriorated asphalt pavements. This process allows complete reconstruction using 100% of existing pavement materials and grade, cross slope and underlying pavement problems can be corrected. A new base course is produced by the recycling of existing asphalt pavement materials and, when required, some underlying materials. This method of cold recycling an asphalt pavement has the environmental advantages of reduced energy consumption, greatly reduced use of new materials and depletion of their sources, little to no disposal of existing pavement materials (in landfills), and reduced air pollution. A thorough project evaluation is essential for project selection, design and construction. The procedures in the evaluation process that must be completed are (1) conducting a pavement condition survey, (2) pavement coring or placing test holes, (3) sampling of the asphalt pavement, any granular base and subgrade, (4) laboratory testing of materials, (5) pavement structural design, and (6) an economic analysis for initial and life cycle costs. Also, proper construction procedures and quality control are critical along with an experienced contractor that is committed to both.

Abstract: The study evaluates the performance of lime/fly ash stabilized base as an alternate to soil cement stabilized base for flexible pavement systems on reconstructed Louisiana highways. Louisiana has historically used soil cement for most flexible base construction due to its low cost, high compressive strength, and ease of construction. However, soil cement is subject to excessive cracking due to shrinkage, which may decrease the expected pavement life. Lime/fly ash bases exhibit many of the same properties as soil cement bases with potential for less shrinkage cracking.

Abstract: This paper describes the results of a comparative study of the performance of different pavement designs in North Carolina. Testing was carried out at an instrumented test facility constructed on the US 421 Bypass near Siler City, North Carolina. The experimental stretch was about 7.5 mi (12 km) long and was composed of 12 pavement section types, two of each type in two directions of traffic (having different expected traffic loads), for a total of 48 sections. Based on field measurements, such as stress, strain, and distress survey analysis, the performance of the various sections was analyzed. Subgrade stabilization was found to provide the maximum assistance to the pavement sections. Sections with asphalt concrete bases performed better than sections with aggregate base courses. Cement-treated base course sections performed the worst. Also, in this study, it was noticed that almost all of the rutting was limited to the asphalt concrete layers.

Abstract: Geosynthetics have been proposed and used to reinforce base course layers in flexible pavement sections to reduce base course thickness, or life-cycle costs, or both. Studies show conflicting results regarding the level to which geosynthetics can improve the performance of flexible pavements. To examine the reinforcement role of geosynthetics, a program of study has been initiated to define the mechanisms of base course reinforcement, to define and quantify the effect of site-specific parameters on the level of improvement observed, and to devise a design tool that can be readily applied in practice. This program will eventually involve the instrumentation of a full-scale pavement subjected to moving traffic loads, the success of which is essential to meeting the three objectives. As a first examination of the performance of proposed instruments, a pilot test section was constructed and monitored for approximately 3 months. The test section was chosen and constructed not necessarily to establish geosynthetic performance but rather to evaluate instrument installation techniques and subsequent instrument performance. Instruments designed to measure strain in the geosynthetics, base course, and asphalt concrete were included.

Abstract: PROBLEM TO BE SOLVED: To improve aesthetic properties of soil by mixing one or more materials selected from among decomposed weathered granite, sandy soil, soil, sand, volcanic ash, crusher-run, and screenings and an acrylic resin emulsion containing asphalt. SOLUTION: If the amount of an acrylic resin emulsion containing asphalt as a binder added to a raw material such as decomposed weathered granite is less than 1%, its water and wear resistance declines. When the binder accounts for more than 10%, water permeability decreases. Therefore, preferably the amount of the binder should be 1 to 10%. A soil pavement material obtained this way is spread on a base course and finished by rolling compaction. Therefore, the pavement retains its natural aesthetic properties, does not produce dust on fine days and the mud on rainy days, exhibits appropriate cushioning properties, the characteristic of soil, and provides foot-friendly walkability.

Abstract: The soundness or durability of aggregates has been conventionally determined by laboratory tests (e.g., Los Angeles Abrasion and Sulfate Soundness) that do not necessarily mimic the effects of physical and chemical degradation encountered under field conditions in Florida. For this reason, the research reported here was performed to identify and evaluate alternative test methods to measure aggregate quality in Florida materials. Part I of the research addressed the evaluation of aggregate soundness research and included an historical review of aggregate soundness research and an evaluation of alternative testing methods. Part II of the research examined the shear resistance and degradation characteristics of aggregates with the primary objective being to evaluate aggregate typically used in Florida for the purpose of developing a test method that relates to aggregate quality and potential for degradation during production of hot-mix asphalt and/or in its use for granular base course materials.

Abstract: A study was undertaken to determine the advantages of plant mix over road mix cement-treated aggregate base course (CTABC). Ten projects known to have cement-treated base course were selected. Each had been tested with a falling-weight deflectometer and had been cored to determine layer thicknesses and properties either in the past or as part of the current effort. Three possible benefits were considered: improved uniformity of material properties, reduced deflections, and increased strength or stiffness. Neither the coefficient of variation nor a developed uniformity coefficient showed a significant difference between plant mix and road mix. Plant mix resulted in lower average deflections and lower deflections when sites were compared with equal thicknesses of asphalt above the base course. However, road mix sites had higher compressive strengths than did plant mix sites. Backcalculated moduli for CTABC were higher for plant mix than for road mix, but the elastic moduli were similar for plant and road mix when determined by pulse-velocity testing. It was concluded that no clear benefit could be determined from using plant mix based on the sample of 10 projects, although the benefit of an adequate thickness of asphalt above the CTABC was clearly demonstrated.

Abstract: This article discusses a soil-related application of geotextiles in roadway systems, namely as a separator between a plastic subgrade and roadway base stone. The classic separation for a geotextile typically is related to seasonal trauma, such as freeze-thaw, which causes degradation of a plastic subgrade beneath the roadway. If the base course of a road section does not drain rapidly, or if fines from a plastic subgrade pump into the base stone, the resilient modulus of the base stone is dramatically reduced; stress from traffic loadings is transferred to the subgrade with little or no reduction, resulting in accelerated road failure. A geotextile's separation role requires it to allow the slow removal of water from the impacted subgrade. Geotextile separators are a simple subset of geotextile-soil filter systems. The author describes the design of geotextile separators with a focus on survivability and hydraulic requirements.

Abstract: Backcalculation method based on the least square mean concept is widely used to identify pavement structural adequacy from FWD deflection basin. However, it is often pointed out that this kind of calculation yields unsuitable layer moduli, when a) the surface layer is extremely thin, b) modulus of surface layer is significantly larger than that of base course, or c) modulus of surface layer is almost identical to that of base course.This study proposes a new backcalculation method based on Genetic Algorithm (GA) that determines the most suitable offset position of each sensor on such pavements. The deflection data given at the proposed positions reveals more stable solutions in calculation of layer moduli.

Abstract: In this and a companion paper, studies related to the use of geosynthetics in the base course layer of flexible pavements for the purpose of reinforcement are examined. The purpose of these papers is to provide a synthesis and evaluation of the literature focusing on this application. The companion paper is a review of studies involving physical experiments of reinforced roadways. The majority of the reviewed studies conclude that appreciable improvement can be realized by proper placement of a geosynthetic in the base course of a flexible pavement and that improvement is seen over the entire service life of the pavement and not only for conditions of excessive surface deformation. The companion paper demonstrates that these experimental results taken by themselves are insufficient for the development of an accepted design procedure due to the many dependent variables impacting the problem. It is concluded in the companion paper that the development of a comprehensive analytical model is a necessary step ...