Aggregate angularity affects the shear strength properties of asphalt concrete and granular base layers in pavements. It also improves aggregate interlock and load transfer properties of jointed concrete pavements. The development of a quantifiable index based on image analysis to characterize the angularity of coarse aggregate used in pavement layers is described. The new angularity index (AI) was developed as part of the University of Illinois Aggregate Image Analyzer, and the procedure was calibrated for two aggregate samples, rounded gravel and crushed stone, which possess the two extremes of particle angularity. A statistical study demonstrated that the AI computation technique is not only able to distinguish crushed stone from gravel but also is robust enough to give similar AI values regardless of the particle size and orientation. Furthermore, the crushed stone and gravel samples together with a 50–50 blend of the two samples by weight were tested for shear strength under triaxial loading conditions. The AI value computed for these samples could be correlated to the angle of internal friction and thus the shear strength properties of the samples. The AI distributions of representative aggregate samples from Illinois, crushed gravel, limestone, and dolomite, were also computed. The newly developed index has also demonstrated the capability to distinguish between crushed stone and crushed gravel samples. With this AI value as a measure of aggregate angularity, pavement engineers can objectively quantify the influence of aggregate angularity on asphalt concrete, portland cement concrete, and granular mix performance and thereby establish meaningful criteria relating aggregate properties to performance indicators.
5-10한편 최근 교정영역에서 미니 임플란트와 miniplate 등과 같은 골내 고정원 장치(temporary skeletal
This paper presents research findings on the prediction performances and field validations of the recently developed granular base–subbase layer permanent deformation models using the full-scale pavement test section data from the FAA's National Airport Pavement Test Facility (NAPTF). The FAA-designated P209/P154 aggregate materials were used in the construction and testing of the NAPTF flexible pavement test sections with variable-thickness base and subbase courses. To account for the rutting performances of these substantially thick granular layers, a comprehensive set of repeated load triaxial tests, considering both constant and variable confining pressure (CCP and VCP) conditions, were conducted on the P209 base and P154 subbase granular materials. On the basis of the laboratory test results, both CCP- and VCP-type permanent deformation models were developed to predict maximum ruts that occurred at the NAPTF under both six-wheel and four-wheel gear loadings applied following a wander pattern. The developed rutting models were first calibrated for the field conditions and then evaluated for predicting the field accumulation of permanent deformations by properly taking into account the NAPTF trafficking data, effects of stress rotation due to moving wheel loads, and loading stress history effects. A comparison of the measured and predicted permanent deformations indicated that a good match for the measured rut magnitudes and the accumulation rates could be achieved only when the magnitudes and variations of stress states in the granular layers, number of load applications, gear load wander patterns, previous loading stress history effects, trafficking speed or loading rate effects, and finally, principal stress rotation effects due to moving wheel loads were properly accounted for in the laboratory testing and permanent deformation model development.
A systematic laboratory approach is established to evaluate shear stability or bearing capacity improvement of sand-geofiber stabilization for rapid road and airfield construction. The approach deals with the investigation of directional dependency, anisotropy, and modulus properties and links stability to shear stress levels typically applied on specimens during testing in relation to their strength. An advanced triaxial testing machine referred to as the University of Illinois FastCell is used together with direct shear tests for determining the anisotropic resilient moduli and the strength properties of two geofiber-reinforced sands (poorly and uniformly graded sands) prepared with three 51-mm geofibers: fibrillated, monofilament, and tape. The use of different geofiber types and the various amounts of clay and silt fines present in the sand mixtures significantly affected the recorded horizontal and vertical moduli and the shear stresses at applied stress states. Monofilament-type geofiber stabilization was found to be the most effective, with the recorded highest vertical moduli and the highest shear strength and stability improvement indicated by the lowest shear stress ratios, especially when mixed with 10% to 20% clay. The tape-type geofiber reinforcement generally was not very effective. For the geofiber stabilization of sands to be a viable construction alternative, the sand-geofiber mixtures should contain an optimal amount of fines needed for geofibers to mobilize the shear strength of the mix effectively and thereby improve the shear stability and resistance to permanent deformation.
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