Key Engineering Materials Vol. 808

Abstract: At present, efflorescence formation on the surface of brickwork is a problem for many buildings under construction and those already built. Efflorescence not only spoil the external appearance of the facades, but in rare cases can even lead to peeling of the brick and reducing its durability. The conducted researches show that in most cases efflorescence on the facades of buildings under construction is formed by sodium sulfate and calcium carbonate. Sources of these salts are masonry cement mortars with plasticizing additives containing sodium salts. In this case, the porous structure of bricks contributes to its water saturation and the migration of soluble salts, leading to the formation of efflorescence on the masonry surface. This article suggests the criteria for selecting mortar composition that excludes the appearance of soluble salts, and introduces results of the research on the resistance of ceramic bricks modified with multilayer carbon nanotubes to salt corrosion.

Abstract: The paper deals with the properties, quality and durability of the exposed concrete. The main part of this paper are characteristic of architectural (sometimes called visible or naked) concrete and the criterion of the quality evaluation of the performed work. This is mainly the colour balance of the subject area, the quantity and the size of the pores, the quality of the raw material and the surface structure. Achieving the quality of architectural concrete is considerably more technologically demanding compared with conventional concrete. This is reflected also in its cost. In conclusion, the problems of surface layers of architectural concrete are summarized. Especially environments can cause faster degradation, reducing the lifetime of the whole construction, but also pointing to one of the main problems in construction, which is technological discipline.

Abstract: The Broumov group of churches was designed for the governing Benedictine abbey of St. Wenceslaw in Broumov by the famous Dientzenhofer family of architects, which helped define the Bohemian baroque style in the early 18th century. The paper shows numerical estimation of the bearing capacity. For the analysis were chosen the parts of enclosure walls from the selected Broumov Churches. The study summarizes the visual investigation and structural investigation using ATENA 2D software, to assess and verify the safety of the church walls regarding to the damages which currently suffers.

Abstract: The article deals with the methodology of the assessment of the state of the external facade of the outer cladding façade from the fiber cementitious boards in view of meeting the conditions of the technical legislation valid in the Czech Republic. On a particular case, the methodology of the procedure from the visual assessment of the facade facing plates to the requirements of their mechanical and physical properties is described. The object under consideration is a civic building in a climatically challenging location in the Beskydy foothills, whose facade is completely lined with fiber-cement boards. The assessment is based on the provisions of ČSN ISO 13822 (73 0038): Design principles for structures - Evaluation exists. construction and ČSN P 74 7251: 2015 Folded cladding, tiles and panel cladding - Requirements for casting accuracy, quality and appearance. For the assessment of mechanical and physical properties, the provisions of ČSN EN 12467 - Fiber-cement flat plates - Specimen specification and test method are used. Limit values ​​of individual parameters are taken into account in the technical sheets of the manufacturer of fiber-cement boards.

Abstract: The paper deals with preliminary construction-technical survey of the underpass at Hlučínská Street in Ostrava - Přívoz. The survey describes the location of the monitored object, the connection to the other roads and the construction system of the underpass. On individual structural elements all the defects found are summarized.

Abstract: The paper focuses on the analysis of reconstruction in terms of CO₂ concentration. The reconstruction at the university included the exchange of windows. The original windows were exchanged for the modern wood tight windows. Providing CO₂ concentration in the interiors of a university is immensely important for the students of the university. Not exceeding CO₂ concentration limits is necessary not only for the physiological needs of students but also for the required performance of students. Teaching is conducted during the whole day in the researched university schoolroom. The short-term natural ventilation during the breaks is noticeably not sufficient. After 15 minutes from the beginning of the lesson, students started complaining about the air quality and they had to open the windows. To point out the unsustainable state of the poor air quality during the day-long teaching and to be able to prove the officials the importance of the continuation of the reconstruction by building mechanical ventilation or air conditioning system, there were carried out the experimental measurements in the schoolroom. The device Testo 480 was used for the measurements. Obtained values of CO₂ concentration are presented in the charts. Interestingly, this reconstruction significantly decreased the air quality. The admissible values of CO₂ concentration were exceeded after the first hours of teaching. These values were worsening with each additional hour of teaching. Therefore, another reconstruction is needed to enable the transition from natural ventilation to the mechanical ventilation system. In the conclusion of this paper, there are principles how to design new schoolrooms. Furthermore, there are presented recommendations how to operate the existing schoolrooms.

Abstract: The unique water systems of the Baroque monasteries are shown and rehabilitation of historic structures are analysed. In historical buildings, it is desirable within the investigation to identify, properly understand and restore the frequently faulty or damaged original ventilation or drainage systems, which ingeniously took advantage of many-year experience of traditional building. The understanding of the original or older solution, its technical parameters and performance is the first step towards restoration and reliability of the buildings.

Abstract: Wood is preferably used in civil engineering for load bearing structures and facing elements. However, its disadvantage is low resistance to degradation factors, even when exposed to high temperature. Mineralization of wood matrix, for example by organosilanes, is one possibility of increasing the durability against weathering and against water exposition. In this work, the influence of the mentioned mineralization substances on the thermal degradation of solid wood is verified by means of thermal analysis.

Abstract: This paper focuses on the use of nonlinear acoustic spectroscopy with one excitation signal for NDT of concrete parts exposed to high temperature. The rate of the temperature rise, the highest achieved temperature, time of exposure to elevated temperature and the cooling rate has an influence on the overall damage of concrete structures affected by fire. The test specimens described in this paper have been heated for various periods of time and at a different temperature. Nonlinear acoustic spectroscopy method was performed before and after heat load.