This article deals with the possibility of assessing the k-value of power plant fly ash using durability. For cement mortars with replacement of 10, 20 and 30 % of Portland blended cement with fly ash, compressive strengths, efficiency indices, depth of talc water seepage and depth of carbonation were determined for ages of 7, 28, 60 and 90 days. For individual cement substitutes, k-values were determined for a given age using the relationship between water coefficient and compressive strength. According to the results of the hardness tests, the determined k-values were assessed and the k-values that are safe for the use of power plant fly ash in the aggressive environment XC and XD were determined.

This article follows up on Part 1, which dealt with the theoretical knowledge of partial fire protection of steel structures. It focuses on experimental work and numerical models, supplemented by parametric studies. Experiments were conducted on four steel samples, each subjected to a standard fire temperature curve for 60 minutes. The samples were tested with various thicknesses of coatback to determine its impact on the thermal behavior of steel. Numerical models were developed based on the experimental data and used for parametric studies, which examined the impact of various variables, such as the length and thickness of fire protection, on the temperature at the junction of the beam and column. The results show that the thickness and length of fire protection significantly influence the thermal stability of steel structures and can be used to design effective fire protection measures.

This article focuses on the partial fire protection of steel structures and provides a theoretical review of current methods and materials used in this area. Various types of passive fire protection systems are introduced, including intumescent coatings and their influence on heat transfer between protected and unprotected parts of the structure. The article deals with analytical and mathematical methods for determining the thermal properties and fire resistance of the materials used, with an emphasis on those that undergo thermal degradation. This article offers a comprehensive view of the theoretical foundations of partial fire protection of steel structures and proposes directions for further research in this area, providing a basis for Part 2: Experiments, Numerical Models, and Comparisons.

The article is focused on the issue of traditional timber joist floor structures and floor compositions from the period up to the first half of the 20^th century. In building practice, we very often encounter these structures in residential buildings that are the subject of structural changes. During these interventions, the basic ideas of the original technical solution are not always respected and some physical parameters of building are degraded. The article describes the principles that were devoted to these types of structures in historical legislative and standard regulations and further in professional literature. The original historical solutions are presented on a practical example. In relation to building interventions in historic timber joist floor structures, current legislative and standard regulations are described, as well as examples of modern solutions and their limitations.

The article is focused on the issue of traditional timber joist floor structures and floor compositions from the period up to the first half of the 20^th century. In building practice, we very often encounter these structures in residential buildings that are the subject of structural changes. During these interventions, the basic ideas of the original technical solution are not always respected and some physical parameters of building are degraded. The article describes the principles that were devoted to these types of structures in historical legislative and standard regulations and further in professional literature. The original historical solutions are presented on a practical example. In relation to building interventions in historic timber joist floor structures, current legislative and standard regulations are described, as well as examples of modern solutions and their limitations.

The prepared experimental program focused on the shear resistance of presstressed beams with bonded tendons needed to develop a parametric study, focused on the shear resistance of the designed beams. In the contribution, a parametric study of beam with I - cross section type DPS VP I/10 with total length of 7,0 m and a height of 0.6 m with different levels of prestress and different levels of shear reinforcement is processed. The standardized reinforcement of the cross-section used in practice is supplemented by longitudinal bars. Different design approaches were used to determine the shear resistance of the beam.

This paper deals with the effect of recycled aggregate in concrete beams that are subjected to flexural and shear stresses. The beams are reinforced with two types of longitudinal bearing reinforcement. The reliability factor is slightly reduced. For concrete with recycled aggregate, it is 3 % for EC2 and 5 % for prEC2. For concrete with recycled aggregate, brick aggregate it is 13 % for EC2 and 14 % for prEC2.
The reduced modulus of elasticity does not affect the results. The coefficient of variation for reinforced beams GFRP reinforcement is 6.98 % for beams with 10 mm reinforcement and 9.40 % for beams with 16 mm reinforcement. The coefficient of variation for beams reinforced with 10 mm diameter steel reinforcement is 16,79 %, and for beams reinforced with 16 mm diameter steel reinforcement is 9,87 %

Modern trends in civil engineering are focused at reducing the comprehensive carbon footprint. One way to reduce a building structure's carbon footprint is to replace conventional building materials with suitable alternatives from recycled materials. These products also include recycled steel fibers from waste tires, which have a great potential for use in the form of dispersed reinforcement in concrete. Waste material from industrial production thus creates the possibility of its transformation into a recovered raw material within the so-called circular economy. This paper is focused on evaluation of the fibers in terms of geometric and mechanical properties, as well as experimental research on the properties of fresh and hardened concrete with different doses of recycled steel fibers.

This paper deals with the study of the effect of the use of styrene in a polyester resin as a polymer binder in a trenchless rehabilitation composite. The different formulations also contain secondary raw materials as waste foam glass, basalt frit, waste glass from solar panels and fly ash. In the development of the formulations, which are subsequently used to saturate the polymer sleeves, the influence on the mechanical properties of the whole composite is mainly investigated. The mechanical parameters investigated include mainly the flexural modulus, the stress at first failure, the flexural deformation, adhesion of the lining to the pipe. The work found that the decrease in mechanical properties for the non-styrene variant is not so significant as to prevent its effective use in the composite.

In the past, natural stone was among the most used building materials in the Renaissance and Gothic periods. On the territory of the Slovak Republic, sandstone was used for its suitable properties, good compressive strength, appearance, and good machinability. Sandstones still form the supporting elements of sacral and public historical buildings. These building structures are exposed to the weather because the surface finish consists of capillary-active materials or none. From the point of view of monument protection, it is not possible to propose hydrophobic modifications and therefore water coming from driving rain can be absorbed into these structures of historical buildings. This article describes the absorption and redistribution of water in structures using one-dimensional computational simulations of liquid water transfer in selected sandstones from eastern Slovakia using a simulation tool. The results are compared with German sandstones.

In the Czech Republic, a preparation of high-speed lines construction according to principles adopted from France is currently in process. Its substructure is among others to be made of an asphalt concrete layer. Nevertheless, the requirements on asphalt mixture properties cannot simply be taken from the French standards, as a different procedure for the compaction of test specimens, which are used for mechanical and functional tests, is used in the Czech Republic. This paper presents the results of an experimental study that compares the impact of test specimen compaction methods used in the Czech Republic and in France on selected properties of asphalt concrete. As a part of the study evaluation, a mutual correlation between individual compaction methods is identified and discussed.

This article deals with the issue of the use of construction and demolition waste in concrete. Primarily with regard to the testing of recycled fine aggregates using today's current standards for concrete aggregate. Three main representatives of recycled aggregates are tested, namely concrete aggregate, brick aggregate and mixed recycled aggregate. Subsequently, recycled aggregate is used for concrete production where it forms a substitute for fine aggregate at 33, 66 and 100 wt%. A series of tests were carried out on 150 × 150 × 150 mm concrete test speciement to determine basic properties such as bulk density, water absorption and compressive strength.

One of the possible solutions for using up used tires is the construction industry. By incorporating waste rubber and reinforcement from tires into concrete, it is possible to partially replace natural aggregate and manufactured reinforcement. This solution should help reduce the negative impact of waste tire disposal on the environment.

Alkali-silica reaction of aggregate with components of cement (AE - Alkaline Expansion) are among the factors causing degradation of concrete. Within a few years or decades of concrete aging, at the surface of aggregates containing reactive form of silica, a cover layer occurs. This layer is capable of expansion due to water absorption. The process is called alcali-silica reaction (ASR).

Contemporary architecture often works with glass facades, roofs or even glass columns and beams. The problematic part of a glass structure design is usually a connection between the glass elements and the rest of structure. In order to achieve as much transparency as possible, various mechanical point fixing systems, adhesive connections and their combinations were developed. Although being widely used, the design procedure is mostly based on experiments. There is ongoing research at the Czech Technical University in Prague focusing on characteristics of an embedded laminated connection under various types of loads. Within the initial phase of experiments, small scale specimens consisting of different glass and foil types were tested. The experiments revealed the tensile, eccentric shear and compressive short-term load-bearing capacity of the connection and a dominant mode of failure. Data obtained from the tests are going to be used for further numerical simulations and a parametrical study.

The test results show that both TORRENT and ISAT methods can be used to assess the durability of both concrete and fibre concrete with dense aggregate. In the case of concrete containing concrete recyclate, however, the TORRENT method was not effective. Also the method of determining the permeability for CO₂ was not suitable for the concrete with concrete recyclate.

The rapid growth of the world's population and its concentration in large cities represents a major impact on the construction industry and the production of building materials. It is the recycling of building materials that is an effective solution to meet the requirements for the construction of new buildings and at the same time achieve sustainable development on earth.

The article deals with the issue of punching shear of flat slabs without shear reinforcement weakened by openings near the supports. The paper compares the predictions of punching shear resistance of flat slabs weakened by openings and supported by square and wall columns. The predictions were calculated using the design model prEC2 for prediction punching capacities that are introduced in the second generation of Eurocode 2. The obtained results of punching shear capacities were compared with experimentally measured results. The standard-recommended model of reduction of the control perimeter length using steering by a radial projection of the opening show that the prEC2 model significantly underestimates punching capacity when the opening is located at the face of support or near the shorter side of the wall column.

The article presents individual procedures for the selective demolition of a panel house intended for demolition. The procedure for inspecting the building for the purpose of identifying waste materials or end-of-life products intended for recycling is given. Furthermore, the contents of the project documentation for the demolition work and the progress of the preparatory work associated with the dismantling of the building are presented. The following is a description of the prefab house intended for selective demolition, the procedure for the demolition work and a sample of the summary list of waste during the selective demolition of the prefab house.

The article provides an overview of the development of construction and demolition waste recycling in the Czech Republic in the period between 2007 and 2020. Waste group 1701 concrete, bricks, tiles and ceramics analyzed in more detail. Recycled C&DW from this group are assessed in terms of the possibility of their use as concrete filler. Attention is also paid to group 170504 – soil and stones without hazardous substances. A significant increase in recycling has been demonstrated for this group in recent years. In conclusion, the ratio of recycled C&DW and extracted natural mineral raw materials in the construction industry is analyzed.