ASU Electronic Theses and Dissertations

The current method of measuring thermal conductivity requires flat plates. For most common civil engineering materials, creating or extracting such samples is difficult. A prototype thermal conductivity experiment had been developed at Arizona State University (ASU) to test cylindrical specimens but proved difficult for repeated testing. In this study, enhancements to both testing methods were made. Additionally, test results of cylindrical testing were correlated with the results from identical materials tested by the Guarded Hot&ndashPlate; method, which uses flat plate specimens. In validating the enhancements made to the Guarded Hot&ndashPlate; and Cylindrical Specimen methods, 23 tests were ran on five different materials. The percent difference shown for the Guarded Hot&ndashPlate; method was less than 1%. This gives strong evidence that the enhanced Guarded Hot-Plate apparatus in itself is now more accurate for measuring thermal conductivity. The correlation between the thermal conductivity values of the Guarded Hot&ndashPlate; to those of the enhanced Cylindrical Specimen method was excellent. The conventional concrete mixture, due to much higher thermal conductivity values compared to the other mixtures, yielded a P&ndashvalue; of 0.600 which provided confidence in the performance of the enhanced Cylindrical Specimen Apparatus. Several recommendations were made for the future implementation of both test methods. The work in this study fulfills the research community and industry desire for a more streamlined, cost effective, and inexpensive means to determine the thermal conductivity of various civil engineering materials.

The use of reinforcing fibers in asphalt concrete (AC) has been documented in many studies. Published studies generally demonstrate positive benefits from using mechanically fiber reinforced asphalt concrete (M-FRAC); however, improvements generally vary with respect to the particular study. The widespread acceptance of fibers use in the asphalt industry is hindered by these inconsistencies. This study seeks to fulfill a critical knowledge gap by advancing knowledge of M-FRAC in order to better understand, interpret, and predict the behavior of these materials. The specific objectives of this dissertation are to; (a) evaluate the state of aramid fiber in AC and examine their impacts on the mechanical performance of asphalt mixtures; (b) evaluate the interaction of the reinforcement efficiency of fibers with compositions of asphalt mixtures; (c) evaluate tensile and fracture properties of M-FRAC; (d) evaluate the interfacial shear bond strength and critical fiber length in M-FRAC; and (e) propose micromechanical models for prediction of the tensile strength of M-FRAC. The research approach to achieve these objectives included experimental measurements and theoretical considerations. Throughout the study, the mechanical response of specimens with and without fibers are scrutinized using standard test methods including flow number (AASHTO T 378) and uniaxial fatigue (AASHTO TP 107), and non-standard test methods for fiber extraction, direct tension, semi-circular bending, and single fiber pull-out tests. Then, the fiber reinforcement mechanism is further examined by using the basic theories of viscoelasticity as well as micromechanical models.

The findings of this study suggest that fibers do serve as a reinforcement element in AC; however, their reinforcing effectiveness depends on the state of fibers in the mix, temperature/ loading rate, properties of fiber (i.e. dosage, length), properties of mix type (gradation and binder content), and mechanical test type to characterize M-FRAC. The outcome of every single aforementioned elements identifies key reasons attributed to the fiber reinforcement efficiency in AC, which provides insights to justify the discrepancies in the literature and further recommends solutions to overcome the knowledge gaps. This improved insight will translate into the better deployment of existing fiber-based technologies; the development of new, and more effective fiber-based technologies in asphalt mixtures.