Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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2015 - 20202

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Subject: search.filters.subject.Digital image processing

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  • Doctoral Thesis
    Examination of Bonding Between Successive Lifts of Concretes Having Different Thixotropy Levels by Surface Scanning
    (Izmir Institute of Technology, 2020) Ersöz, Hasan Yavuz; Erdem, Tahir Kemal
    Unexpected delays in casting can result in strength losses and should be examined considering the thixotropy of the concrete. The effects of thixotropy and delays in casting (0, 45, and 90 min) on concrete bonding strength and on the surface properties were examined. Firstly, 15 self-consolidating concretes (SCC) having different compositions with three different water/cement ratios (0.36, 0.41 and 0.46) three different fine/all aggregate ratios (0.45, 0.50 and 0.55) and two slump flow diameters (60 cm and 70 cm) were produced. Slump flow, visual stability index, T50, V-funnel, static sieve segregation, rheology, and thixotropy tests were carried out on fresh concrete. Considering the results obtained so far, three mixtures were selected to have high, low, and moderate thixotropy for subsequent tests on hardened concrete specimens. Five different roughening patterns were applied on the concrete specimens' interlayer zones by using wooden frames. Slant shear, bi-surface shear, and pull-off tests were conducted on the cylindrical, cubic and drilled specimens to assess bond strength, respectively. Slant shear test gave the highest bonding test results. The lowest results were obtained for the pull-off test. Lateral surfaces of the specimens were scanned with two different lenses. 2D and 3D scanning procedures were adapted with those lenses. Pattern and thixotropy effect was investigated. Lowest void area was obtained for high thixotropy. Highest compressive strengths were obtained for mid thixotropy and high thixotropy for slant shear and pull-off tests respectively. Image J and Matlab were used to the analyze images of the surfaces. Ultrasonic pulse velocity test was conducted on all specimens, moderate thixotropy gave the highest results for Ultrasonic Pulse Velocity test.
  • Doctoral Thesis
    Joint Reconstruction of Surface Geometry and Reflection Properties by Using Image Based Methods
    (Izmir Institute of Technology, 2015) Ozan, Şükrü; Gümüştekin, Şevket
    In this thesis, we aim to capture realistic geometrical descriptions of real world scenes and objects with a special effort to characterize reflection properties. After a brief review of the stereo imaging literature, we show our contributions to enhance stereo matching performance by identifying and eliminating specular surface reflections. The identification of specular reflection can be done both passively and actively. We use dichromatic-based methods to identify and eliminate specular reflections passively. We utilize polarization imaging methods to do the same job actively. In this work we also study structured light based methods that can give better reconstruction results compared to stereo imaging methods. We propose three laser scanners equipped with a pair of line lasers and a method to calibrate these systems. Another convenient way to obtain good surface reconstruction results using structured light is to use projectors that can be used as a light source that project complicated patterns. We show our results from a digital camera-projector-based scanning system as well. This system can robustly generate a very dense reconstruction of surfaces. We also use the projector based scanning system to determine the surface reflection properties. Using high dynamic range imaging (HDRI) techniques makes it possible for us to estimate scene radiance values. Since we can determine the incoming and outgoing light directions, we are able to measure bidirectional reflectance distribution function (BRDF) values from reconstructed surface points for corresponding directions. If the sample surface have not only diffuse reflection components but also a sufficient amount of specular highlights, it is possible to approximate BRDF corresponding to a surface by fitting an analytical BRDF model to the measured data. In our work we preferred to use Phong BRDF model. Finally, we present results with rendered synthetic images where the parameter values of the Phong model were estimated using scans of real objects.