Iman Harsini

Sensitivity of Input Variables for Flexible Pavement Rehabilitation Strategies in the M-E PDG

The Mechanistic-Empirical Pavement Design Guide (M-E PDG) can be used to design different flexible rehabilitation options; namely HMA over HMA (overlay), HMA over JPCP (composite), and HMA over JPCP fractured (rubblized). Each rehabilitation option has different input variables for new and existing layers. The type and magnitude of the input parameters have significant impact on the predicted flexible pavement performance. In order to evaluate the impact of various design inputs on the predicted performance for the rehabilitation options, one-variable-at-atime (OAT), and detailed sensitivity analyses were performed. While the OAT sensitivity analysis investigated the input variables specific to the existing pavement layers, it also determined the variable effects on the overall pavement performance. The OAT results identified the significant input variables of the existing pavement layers. Subsequently, based on the results of OAT sensitivity analysis, a detailed sensitivity analysis was performed. Full factorial matrices were designed to determine statistically significant main and interaction effects. This paper highlights the process of identifying the most sensitive input variables for flexible rehabilitation design options. The results of the sensitivity analyses show that the existing pavement condition rating and existing thickness for HMA over HMA overlays is critical for all performance measures. On the other hand, existing PCC modulus and thickness are important in determining the performance of HMA overlay over intact and rubblized JPCP. Keyword: Pavement rehabilitation, M-E PDG, Sensitivity analysis, Input variables

Robust, Carbon Nanotube/Polymer Nanolayered Composites with Enhanced Ductility and Strength

Robust, Carbon Nanotube/Polymer Nanolayered Composites with Enhanced Ductility and Strength A new class of robust, nanolayered, self-assembled composite was developed by sequential deposition of electrostatically dispersed negatively charged carbon nanotubes (CNT) (charges were introduced via polymer wrapping) and oppositely charged polyelectrolytes on a polyurethane scaffold and subsequent heating. Heat treatment allowed for the formation of amide bonds between carboxylic acid functionalities on CNT walls and amine groups of the polyelectrolyte resulting strong covalent bonded network (crosslinked) of self-assembled, nanolayered composite. This robust nanolayered composite demonstrated high tensile strength and enhanced ductility compared to that of original polyurethane scaffold. The self-assembled nanolayered composites, after complementary cross-linking steps, were found to provide a unique balance of strength and ductility, which surpassed those of conventional (micro-scale) composites.

Polymer nanocomposites processed via self-assembly through introduction of nanoparticles, nanosheets, and nanofibers

Nanocomposites offer the theoretical potential to achieve mechanical properties surpassing those of conventional (micro-scale) composites. The underlying reasons for the high potential of nanocomposites include the uniquely high mechanical attributes of nano-scale reinforcement, effective control of defect size and growth by nano-spaced interfaces, and interactions between the polymer matrix and the large surface areas of nanomaterials. Attempts to produce nanocomposites via conventional processing techniques have encountered challenges associated with thorough dispersion and effective interfacial interactions of nano-scale reinforcement with the polymer matrix. In order to address these challenges, materials were processed into polymer nanocomposites via electrostatically driven layer-by-layer self-assembly. Electrostatically dispersed nanomaterials and oppositely charged polyelectrolytes were sequentially built upon a substrate (cellular scaffold). The self-assembled nanocomposites, after complementary cross-linking, provided a unique balance of strength and ductility, which surpassed those of conventional (micro-scale) composites. Self-assembly was found to be an effective approach to producing nanocomposites embodying uniformly dispersed nanomaterials with controlled interfacial interactions. This approach is highly versatile and enables introduction of diverse nanomaterials into polymer nanocomposites. The work reported herein evaluated introduction of diverse categories of nanomaterials incorporating nanoparticles, nanosheets, nanotubes, and nanofibers. This investigation also evaluated the potential for a biomimetic approach to processing of light-weight structural systems by self-assembly of polymer nanocomposites onto cellular scaffolds.

Characterization of ASR in Concrete by ²⁹Si MAS NMR Spectroscopy

AbstractSi29 MAS NMR spectroscopy was employed for the evaluation of the alkali-silica reaction (ASR) in laboratory and field concrete specimens. A series of NMR data was collected on the individual constituents of cement as well as on samples subjected to accelerated aging in a carefully controlled laboratory setting. Peaks associated with ASR were assigned and quantified. In spite of the spectral complexity due to the diverse constituents and the heterogeneous nature of concrete, changes due to ASR, including increased polymerization of C-S-H and A-S-H formation, could be identified and quantified. The trends established through Si29 NMR spectroscopy of the laboratory specimens were used to identify the presence and extent of the alkali-silica reaction in samples from operational bridges. Both bridge samples exhibited spectral evidence of ASR. Fourier transform infrared spectroscopy was used to verify the Si29 NMR spectroscopy observations.

Surface grown copper nanowires for improved cooling efficiency

Abstract The interactions between heat sink surfaces and coolant play important roles in cooling methods. This study relies upon controlled nanostructuring of heat sink surfaces that produces orders of magnitude increases in surface area, excites local vortexes and improves the phase change mechanisms to enhance cooling efficiency. A scalable, economical and environmentally benign technique to grow copper nanowires with a strong/conductive base-anchorage on the surface of copper and related materials is described. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to monitor the reduction and morphology of the nanowires. Transmission electron microscopy (TEM), electron diffraction (ED) and X-ray diffraction (XRD) were employed to understand the structure of the as-grown copper hydroxide nanowires and reduced copper nanowires. The convective heat transfer of nanostructured surfaces was measured in the laboratory and compared to a theoretical treatment of the nanowire array effects on convective heat transfer. The various surface treatments tested showed heat transfer increases of up to 93% in good agreement with a theoretical analysis.