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Utilization of image and signal processing techniques for assessment of built heritage condition
Koudelka_ml., Petr ; Koudelková, Veronika ; Doktor, Tomáš ; Kumpová, Ivana ; Kytýř, Daniel ; Valach, Jaroslav
Historical buildings represent invaluable heritage from the past and therefore their protection is a very important task. Assessment of their condition must not cause damage accumulation thus the least possible volume removed from the structure is essential. As many historical buildings in the Czech Republic are built using sandstone that can be considered as a typical heterogeneous system, statistical signal processing is a promising approach for determination of the representative volume element (RVE) dimensions. Such calculations can be carried out on the domain of logical arrays representing binary images of the materials microstructure. This paper deals with processing of image data obtained using SEM-BSE and high resolution flatbed scanner for determination of RVE dimensions. Advanced image processing techniques are employed and results from calculation using grayscale data are presented and compared with results calculated on the basis of color input images.
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Crystallization force of sodium chloride
Koudelková, Veronika ; Wolf, Benjamin
Soluble salts are one of the most deteriorating factor causing damage of historical building materials due to generation of crystallization pressure inside pore space. Direct measurement of crystallization force is quite challenging, hence we developed at our institute a novel device able to detect the force of growing crystal. The device is based on the monitoring of force developed with upper microscopic glass on the growing crystal to maintain constant position. The crystal could generate force because of the existence of thin liquid layer of solution between both surfaces come into contact. The driving force for the subsequent growth of crystal against obstacle is supersaturation, which is mainly induced by evaporation of the salt solution. In this experiment, the crystal of sodium chloride generated force 16.8 mN and the corresponding crystallization pressure was equal to the value 0.48 MPa.
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Microscopic features of cement paste modified by fine perlite
Hrbek, V. ; Koudelková, Veronika ; Padevět, P. ; Šašek, Petr
The use of waste material and replacement of binder element in cementitious composites is in focus of material development. Perlite in the construction industry is usually used in form of lightweight aggregate enhancing the insulating performance of concrete. This paper focuses on integration of fine perlite into the cement matrix and possible replacement of the cement binder in the composition of the material. The macromechanical performance of the modified paste is tested on specimens with 5, 10, 15 and 20% fine perlite substitution and pure cement sample. To distinguish the effect of the perlite on the microstructural level, pure cement material and specimen containing 10% of fine perlite are investigated by the electron microscopy. Furthermore, the mechanical properties of individual phases are examined and compared on same samples by instrumented indentation. The presented results enabled estimation of fine perlite impact on the macro and microscopic performance of the material..
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Freeze-thaw durability of fiber-reinforced lime-based mortars
Přinosil, Michal
This paper presents results of experimental investigation focused on freeze-thaw\ndurability of fiber-reinforced lime-based mortars. Evolution of structural deterioration and frost resistance were evaluated using non-destructive testing (resonance method). In this study, we consider two types of lime-based matrices (pure lime, lime-metakaolin) and two types of polyvinyl alcohol fibers in several volume fractions. The results showed that the resistance against the frost depends mainly on the matrix type and on the amount of fibers.
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Designing of all-wooden carpentry joints for reconstruction of historical structures
Kunecký, Jiří ; Hasníková, Hana ; Fajman, P. ; Tippner, J.
The article introduces the new method „Lapped Scarf Joints for Repairs of Historical Structures“ that deals with the design of the lapped scarf joint suitable for the reconstruction of valuable historical timber structures, with help of making the prosthesis for the damaged parts of the beams. The method is the result of the four-year research project supported by the Czech Ministry of Culture within NAKI program. Institute of Theoretical and Applied Mechanics AS CR, Faculty of Civil Engineering CTU and Faculty of Forestry and Wood Technology of Mendel University participated on the research.
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Determination of drift distortion in SEM micrographs acquired at different magnifications and acquisition times
Petráňová, Veronika ; Koudelka_ml., Petr ; Valach, Jaroslav
In the experimental mechanics wide variety of optical methods including measurement of deformation at reduced length scales using combination of computer vision and scanning electron microscopy (SEM) have been recently applied. One of suitable methods for in-plane measurement of displacements and deformations in the micrographs obtained by SEM is the 2D digital image correlation. In contrast to images obtained in visible spectrum by classical optical devices temporally-varying distortions known as drift distortion are present in the SEM micrographs. These distortions are caused by positional errors of electron beam during scanning process. Magnitude of this effect decreases with higher conductivity of the sample and is also influenced by magnification and scanning time. For this purpose measurement of distortion was performed on a series of micrographs of conductive samples acquired at different magnifications and acquisition times. Surface of each sample was covered with liquid silver to ensure adequate contrast pattern necessary for determination of distortion’s magnitude and distortion magnitudes were assessed.
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