Browsing by Author "Dr. Akhtarhusein A. Tayebali, Committee Member"

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    Mechanical Response of Crushed Stone Mixtures
    (2009-11-20) Cunningham, Charles Noel; Dr. Akhtarhusein A. Tayebali, Committee Member; Dr. Mo A. Gabr, Committee Member; Dr. T. Matthew Evans, Committee Chair
    A study was conducted in order to see the effects on material performance from varying the gradation of aggregate base course material. Five different gradations were selected which followed along the North Carolina Department of Transportation’s guidelines for acceptable aggregate base mixtures, specification section 1010. Experimental trials were performed in order to classify the material of aggregate base course and to judge the performance differences between five gradations. Those experiments included grain size distribution tests, specific gravity testing, Atterberg limits testing, particle shape analysis, compaction testing, both standard (3 in. diameter) and large (6in. diameter) unconsolidated undrained compression testing, and resilient modulus testing. Generally it was found that aggregate base course acts as a well graded gravel or sand with clay like fines. The gradation was found to affect the performance of the aggregate slightly in that coarser gradations gave better strength and resilience values under conditions most similar to those found in the field. From research and experience during the lab testing it was concluded that the coarsest blends became too difficult to realistically work with and they also lacked the stability of the more well graded gradations. It was also found that as the amount of fines in the specimens exceeded around 8% by mass, those fines governed the behavior of the material. Several recommendations are proposed for the adoption of new standards and for conducting future testing on aggregate base course material. It was concluded that the current standard was sufficient in providing fairly uniform and desirable behavior. It is recommended that the gradation be narrowed and shifted toward the lower bound of the current NCDOT standard in order to have even more predictable material behavior as well as to have the benefit of higher strength and resiliency.
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    Performance Based Evaluation of Asphalt Surface Treatment using Third Scale Model Mobile Loading Simulator
    (2007-06-04) Lee, Ju Sang; Dr. Y. Richard. Kim, Committee Chair; Dr. Ranji S. Ranjithan, Committee Member; Dr. Akhtarhusein A. Tayebali, Committee Member; Dr. Mohammed A. Gabr, Committee Member; Dr. Roy H. Borden, Committee Member
    This dissertation presents the research efforts to evaluate the characteristics of asphalt surface treatment (AST) performance including aggregate retention, bleeding, and skid performance using the third-scale Model Mobile Loading Simulator (MMLS3). A new test protocol is developed that uses the MMLS3 and incorporates the digital image processing technique and British Pendulum Test (BPT) for the performance evaluation of ASTs. In this study, the new MMLS3 AST performance test method is applied to evaluate the effects of fines content, aggregate gradation, and aggregate type (i.e., granite vs. lightweight) on aggregate retention performance. It is confirmed that aggregate retention performance is improved as the fines content decreases and the gradation becomes more uniform. Moreover, it is found that the aggregate gradation factor plays a critical role in the aggregate retention performance regardless of the type of aggregate. This research also develops a performance-based uniformity coefficient as an AST performance indicator. A methodology is developed to determine the optimum application rate based on AST performance in laboratory tests; this methodology is then extended to the field application. Based on the characteristics of AST performance determined by MMLS3 tests with various AST application rates, the AST design equation as a function of the voids at the loose aggregate state is developed. This research also develops a correlation that converts skid resistance laboratory results to field results. The ability of the MMLS3 test to simulate the texture of ASTs in the field is confirmed by finding the same trends in skid resistance characteristics of the two aggregate types for both laboratory and field results.