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Influence of the stress field on weathering and erosion of sandstone landforms
Řihošek, Jaroslav ; Bruthans, Jiří (advisor) ; Mikuláš, Radek (referee) ; Válek, Jan (referee)
The influence of mechanical stress on weathering and erosion has been overlooked in works focused on sandstone landforms formation, although stress has been shown to be a key factor in the formation of a number of different sandstone landforms recently. The main goal of the doctoral thesis is to understand the relationship between mechanical stress and weathering or erosion in the formation and development of sandstone landforms. The influence of mechanical stress on the mode of weathering and the rate of disintegration of the material forming historical monuments in Petra, Jordan was investigated on the site and on samples in laboratory. A negative exponential dependence has been proven between the speed of salt weathering and the magnitude of uniaxial compression of Petra sandstone samples. The role of mechanical stress as a mechanism controlling the formation and development of the shape of sandstone forms was further studied in rock overhangs, sandstone arcades and rock gates in the Czech Republic and the USA. The doctoral thesis presents and verifies a method using Střeleč sandstone as a natural analogue in physical models simulating weathering and erosion of cemented sandstone. These physical models usually take the form of a reduced initial shape of a sandstone object created in situ from...
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Determination of reference parameters for evaluating the strengthening of degraded sandstone masonry of the Cathedral of St. Vit at Prague Castle
Válek, Jan ; Kozlovcev, Petr ; Fialová, Anna ; Slížková, Zuzana ; Kotková, Kristýna ; Svoboda, Milan ; Koudelková, Veronika
Sandstone materials exposed to weather conditions degrade naturally, consequently consolidation of these materials is often required. The aim of this research was to evaluate the impact of four commercials organosilicate consolidants on degraded sandstones, which were used during the neogothic rebuilding of st. Vithus Cathedral at the turn of the 19th to 20th century. The depth of penetration of consolidants into the sandstone porous system and the impact of consolidants on the physical properties of sandstones, namely on the hydrofobicity, water absorption and evaporation, were evaluated primarily. According to the test results, all four consolidants should be suitable for consolidation of sandstones mentioned above even though the results varied slightly between consolidants. For final chose of appropriate consolidant, it is necessary to consider the properties of the treated sandstoned and the technological conditions of the application given by the manufacturer.
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Determination of the vaporization plane depth in sandstones and other porous materials: uranine-coated needles
Mareš, Jakub ; Weiss, Tomáš (advisor) ; Válek, Jan (referee)
Abstact The vaporization plane in porous materials separates the capillary zone, the area where water moves in liquid state, from the dry surface layer where water moves in the form of vapor. The depth of the vaporization plane and its geometry is essential for a large number of physical, chemical and biological processes in porous materials that can, for example, cause material degradation and decay. Mostly, the vaporization plane is not measured directly, but water content or suction pressure measurements are used instead, which are, however, not suitable for the plane's detection. Therefore, there was a need for a method that would be able to determine the depth of the vaporization plane in holes of small diameter (<1 cm). To fulfill this aim, I used a needle onto which I applied glue and uranine. Upon insertion, uranine on the needle dissolves in the capillary zone and changes its color from red to green, while remaining red in the dry zone. The boundary between the red and green parts thus accurately displays the vaporization plane. With this newly developed method, I subsequently measured the depth of the vaporization plane on natural outcrops as well as on buildings, where I tried to describe the vaporization plane's behavior.
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