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Keywords: roller types, roller coverages, roller patterns, chip seal, MMLS3.
This report presents an improvement in the rolling protocol for chip seals based on an evaluation of aggregate retention performance and aggregate embedment depth. The flip-over test (FOT), Vialit test, modified sand circle test, digital image processing technique, and the third-scale Model Mobile Loading Simulator (MMLS3) are employed to evaluate the effects of the various rolling parameters and to measure chip seal performance. The samples used to evaluate the chip seal rolling protocol were obtained directly from field construction. In order to determine the optimal rolling protocol, the effects of roller type, number of coverages, coverage distribution on the sublayers of a multiple chip seal (i.e., the split seal and triple seal), and rolling pattern are evaluated using the results of aggregate retention performance tests, the modified sand circle method, and the digital image process. It is found that two types of roller, the pneumatic tire roller and the combination roller, are recommended as the optimal rollers for the chip seal. In addition, it is found that the optimal number of coverages for the chip seal is three coverages. Moreover, the performance of the triple seal without coverage at the bottom layer does not affect the aggregate retention performance, although the split seal does require coverage at the bottom layer. Finally, it is found from the MMLS3 results that the delayed rolling time between the spreading of the aggregate and the initial rolling significantly affects the aggregate loss, and that the delayed rolling time is related to the aggregate moisture condition and the ambient temperature. Effects of different rolling patterns are investigated based on the delayed rolling time and roller speeds, and recommendations are developed for two- and three-roller scenarios.
TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 342: Chip Seal Best Practices examines ways to assist in the development and implementation of pavement preservation programs by identifying the benefits of using chip seal as part of a preventive maintenance program and by highlighting advanced chip seal programs in use around the world. The report includes approximately 40 best practices in the areas of chip seal design methods, contract administration, equipment practices, construction practices, and performance measures. According to the report, the increased use of chip seals for maintenance can be a successful, cost-effective way of using preventive maintenance to preserve both low-volume and higher-volume pavements.
Chip sealing typically consists of covering a pavement surface with asphalt emulsion into which aggregate chips are embedded. The asphalt emulsion cures through the evaporation of water, thus providing mechanical strength to adhere to the pavement while keeping the aggregate chips in place. The curing time for the chip seal depends on many factors, such as the asphalt emulsion and aggregate types, aggregate moisture content, emulsion and aggregate application rates, and environmental conditions (e.g., temperature, wind speed, relative humidity, and solar radiation). Currently, no field technique is available to quantify when sufficient mechanical strength has developed in the binder to allow traffic on a newly sealed roadway or to remove the surplus aggregate from a fresh chip seal through brooming. Instead such decisions are made by empirical factors that rely on the experience of field personnel.This study investigated the use of electrical resistance measurements to develop a quantitative method for determining the optimum curing time for chip seals. First, full frequency, two-point, uniaxial electrical impedance spectroscopy was used to characterize the electrical properties of asphalt emulsions and various asphalt emulsion-aggregate combinations. The laboratory test results suggest a relationship between the changes in the electrical resistance of an asphalt emulsion and the amount of curing that has occurred in the system. Additionally, standardized mechanical strength tests and full-scale field trials were conducted using a variety of materials. The electrical properties of the fresh seals were quantified using a handheld electrical device with a two-point probe to measure resistance. The findings suggest that chip seal systems gain significant mechanical strength when the initial electrical resistance measurement increases by a factor of 10. Finally, the implementation of the methodology for five full-scale chip seal projects in Indiana indicates that curing times for the chip seals range from 3.5 to 4.0 hours.
The purpose of this manual is to provide clear and helpful information for maintaining gravel roads. Very little technical help is available to small agencies that are responsible for managing these roads. Gravel road maintenance has traditionally been "more of an art than a science" and very few formal standards exist. This manual contains guidelines to help answer the questions that arise concerning gravel road maintenance such as: What is enough surface crown? What is too much? What causes corrugation? The information is as nontechnical as possible without sacrificing clear guidelines and instructions on how to do the job right.
This synthesis will be of interest to construction, maintenance, pavement design, and materials engineers, pavement contractors, and others interested in the use of open-graded friction courses (OGFC) as an asphalt concrete pavement wearing surface. Information is provided on performance benefits and limitations of OGFC, material and mixture properties, and current construction practices in use in the United States and Europe. Advances in mixture design and construction techniques have overcome several of the performance limitations identified in early applications of OGFC, as well as enhanced the performance benefits associated with OGFC use. This report of the Transportation Research Board describes the current state of the practice with respect to the use of OGFC. Experience with the design, construction, and performance of OGFC is summarized, based on a review of the literature, documentation of experience from applications in the U.S. and Europe, and site visits to several states.
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At long last, Sarah Britton, called the “queen bee of the health blogs” by Bon Appétit, reveals 100 gorgeous, all-new plant-based recipes in her debut cookbook, inspired by her wildly popular blog. Every month, half a million readers—vegetarians, vegans, paleo followers, and gluten-free gourmets alike—flock to Sarah’s adaptable and accessible recipes that make powerfully healthy ingredients simply irresistible. My New Roots is the ultimate guide to revitalizing one’s health and palate, one delicious recipe at a time: no fad diets or gimmicks here. Whether readers are newcomers to natural foods or are already devotees, they will discover how easy it is to eat healthfully and happily when whole foods and plants are at the center of every plate.