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ultra-high-strength concretes
Ambruz, Pavel ; Hubáček,, Adam (referee) ; Hela, Rudolf (advisor)
Thesis deals with summarizing knowledge about production methods of ultra – high – strength concrete (UHSC) and their possible use in practice, which is documented on the existing building. Further work shows suitable raw materials for production UHSC and their availability on the Czech market. The practical part results an experiment whose outcome should be concrete with a compressive strength of 150 MPa.
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Influence of Initial Conditions on the Modulus of Elasticity of Concrete for Bridges
Blažek, Michal ; Bílek,, Vlastimil (referee) ; Cikrle, Petr (advisor)
Beside the compressive strength of concrete, which is considered as the basic parameter parameter for design of concrete structures a modulus of the concrete elasticity should be set as well. This thesis deals with influences, which are acting on the concrete, particularly within the initial stage of its hardening (i.e. within 28 days after casting). Nowadays, when time is the most valuable factor, some knowledge is required about mechanical properties of concrete earlier than after above mentioned 28 days and to apply them advantageously. The concrete in initial stage of hardening is influenced by many factors that affect progress of the elasticity modulus during the course of the time. For understanding of these problems a literature search was performed, as well as the experiment demonstrating the effect of temperature on the modulus of the concrete elasticity. The effect of temperature on the modulus of elasticity of concrete in initial stage of hardening has not been intensively studied yet. Therefore, more attention is paid to it by this elaborate. The experiment investigated the static and dynamic elastic modulus of concrete, whose recipe is similar to one used for production of prefabricated and prestressed bridge girders.
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New devices for diagnostics of historical structures
Hasníková, Hana ; Kloiber, Michal ; Zíma, Pavel
The aim of the paper is to present a few new devices that were developed at ITAM AS CR for non-destructive testing of materials, especially those from historically valuable structures. So called microtube is a semi-automatic portable tool for water absorption measurements. It consists of box with microprocessor where the time is recorded and the plastic “pistol” – a part that is in contact with the material surface and where the scaled micro-tube is fixed on. The natural stones, mortars and other porous materials can be measured by the microtube; it is very useful to assess the efficiency of various hydrophobic treatments used within the restoration. The diagnostic device for in-situ assessment of timber in existing structures enables direct determination of conventional compressive strength and modulus of deformability in arbitrary depth along timber profile. The semi-destructive method causes a very gentle damage on the structural members.
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