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    Physico-Mechanical Properties and Hydration Processes of Cement Pastes Modified with Pumice, Trass and Waste Chalcedonite Powder
    (MDPI, 2023-12-31) Spychal, Edyta; Vyšvařil, Martin
    In this article, the physico-mechanical properties and hydration processes of cement pastes containing three additives are introduced. Cement was replaced with pumice, trass, waste chalcedonite powder at 30% by mass and a combination of pumice or trass and waste chalcedonite powder in the amounts of 15% each. The main aim of this research was to assess the properties of two- or three-component binders to save cement in these binders. Rheological properties such as consistency, yield stress, viscosity and thixotropy were determined, in addition to porosity, 7-day and 28-day flexural and compressive strength and bulk density. Additionally, the heat evolution and degree of hydration of the tested pastes were compared. The use of all additives resulted in a reduction in the consistency of the tested pastes. The highest compressive strength measured after 28 days was observed for the cement paste with a 30% content of waste chalcedonite powder, which is related to it having the best pozzolanic activity of the materials used. The results of this research have confirmed that pumice, trass and waste chalcedonite powder can be used as components of blended Portland cements.
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    Impedance spectroscopy – comparison of dielectric model with experimental results
    (IOP Publishing, 2023-08-25) Kusák, Ivo; Luňák, Miroslav; Mizerová, Cecílie; Rovnaník, Pavel
    Impedance measurements of building materials have been gaining popularity especially in the last twenty years. No electrical component has only resistance, capacitance or inductance, as there is an interplay of these parameters. This is compounded in the case of building materials, which contain a significant number of different phases that vary in chemical composition, crystalline structure and properties. It is, therefore, necessary to choose a connection and measurement system that provides the most accurate information about the building material. This information is primarily meant to include the complex impedance, its components and the quantities derived from them. The derived quantities are electrical resistance or electrical capacitance. Using these quantities we can point out the composition of the material, its conductivity and identify the percolation threshold or describe its sensory properties in more detail. For measurements, an alternating electric field is crucial, and the range of frequencies depends on the instruments used. For materials characterization, the most used frequency range is 100 Hz to 100 kHz; however, we can measure down to 1 MHz.
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    Effect of De-Icing Chemicals on Concrete Scaling: The Role of Storage Water
    (MDPI, 2023-07-10) Misák, Petr; Kocáb, Dalibor; Bayer, Patrik; Vymazal, Tomáš; Rovnaníková, Pavla
    This paper deals with the effect of the character of the water used for the water storage of concrete test specimens on the results of tests for resistance to de-icing chemicals. Two experiments were conducted to investigate the effect of the content of free CO2 in water and leaching of calcium hydroxide from concrete on the test results. In the first experiment, the resistance of mortars to water and de-icing chemicals was investigated. It was found that the character of the water storage, i.e., fresh water vs. previously used water, can significantly affect the test results. The second experiment focused on investigating the effect of the content of free CO2 in water on the test results. It was found that the content of free CO2 in the water can statistically significantly influence the test results. In conclusion, the paper shows that the character of the water used for water storage of concrete test specimens and the content of free CO2 in water are essential factors that can significantly affect the results of concrete resistance tests to de-icing chemicals. Further research is needed to understand these influences and their potential use to improve the resistance of concrete.
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    Physico-Chemical Properties of Lithium Silicates Related to Their Utilization for Concrete Densifiers
    (MDPI, 2023-03-08) Kalina, Lukáš; Bílek, Vlastimil; Sedlačík, Martin; Cába, Vladislav; Smilek, Jiří; Švec, Jiří; Bartoníčková, Eva; Rovnaník, Pavel; Fládr, Josef
    Protection of concrete against aggressive influences from the surrounding environment becomes an important step to increase its durability. Today, alkali silicate solutions are advantageously used as pore-blocking treatments that increase the hardness and impermeability of the concrete’s surface layer. Among these chemical substances, known as concrete densifiers, lithium silicate solutions are growing in popularity. In the present study, the chemical composition of the lithium silicate densifiers is put into context with the properties of the newly created insoluble inorganic gel responsible for the micro-filling effect. Fourier-transform infrared spectroscopy was used as a key method to describe the structure of the formed gel. In this context, the gelation process was studied through the evolution of viscoelastic properties over time using oscillatory measurements. It was found that the gelation process is fundamentally controlled by the molar ratio of SiO2 and Li2O in the densifier. The low SiO2 to Li2O ratio promotes the gelling process, resulting in a rapidly formed gel structure that affects macro characteristics, such as water permeability, directly related to the durability of treated concretes.
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    Effect of petrographic composition and chemistry of aggregate on the local and general fracture response of cementitious composites
    (Gruppo Italiano Frattura, 2022-03-25) Vyhlídal, Michal; Rozsypalová, Iva; Šimonová, Hana; Kucharczyková, Barbara; Vavro, Leona; Vavro, Martin; Němeček, Jiří; Rovnaníková, Pavla; Keršner, Zbyněk
    This paper concerns the results of research into the influence of the composition of rock inclusions on the fracture response of cement-based composite specimens. Specially designed specimens of the nominal dimensions 40 × 40 × 160 mm with inclusions in the shape of prisms with nominal dimensions of 8 × 8 × 40 mm were provided with an initial central edge notch with a depth of 12 mm. These specimens, which were made of fine-grained cement-based composite with different types of rock inclusion – amphibolite, basalt, granite, and marble – were tested in the three-point bending configuration. Fracture surfaces were examined via scanning electron microscopy and local response in the vicinity of rock inclusions was characterized via the nanoindentation technique. The aim of this paper is to analyse the influence of the chemical/petrographic composition of rock inclusions on the effective mechanical fracture parameters of cement-based composites, as well as on the microstructural mechanical parameters of the interfacial transition zone. The results of this research indicate the significant dependence of the effective fracture parameters on the petrographic and related chemical composition of the rock inclusions.