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- ItemGamma radiation attenuation, mechanical properties and microstructure of barite-modified cement and geopolymer mortars(Elsevier, 2024-10-30) Jóźwiak-Niedźwiedska, Daria; Rovnaník, Pavel; Dabrowski, Mariusz; Ośko, Jakub; Kuć, Michal; Maciak, MaciejThe present study contributes to the development of alternative materials for radiation shielding, focusing on environmental sustainability and material cost efficiency. The primary aim was to evaluate the compressive and flexural strength, mineral composition, microstructure, and gamma-ray attenuation properties of cement mortars and geopolymer mortars containing barite powder. Mortars based on ordinary Portland cement (OPC) and fly ash geopolymers with varying amounts of barite powder were assessed for their shielding properties at energy levels associated with the decay of 137Cs. From the results, key parameters such as the linear attenuation coefficient (µ), mass attenuation coefficient (µm), half-value layer (HVL), and tenth-value layer (TVL) were determined. The results showed that while cement based composites exhibited superior gamma radiation attenuation compared to fly ash geopolymer mortars, the latter had higher mass attenuation efficiency, meaning less material density was required for the same level of shielding. Additionally, cement mortars had 23–25% highermechanical strength thangeopolymermortars. Importantly, the inclusionof barite powder improved the radiation shielding performance of both materials by 7–10%, demonstrating itseffectiveness in enhancing the protective properties of these mortars. This research highlights the potential of fly ash geopolymer mortars as viable, eco-friendly alternatives to traditional cement mortars in radiation shielding applications.
- ItemImpedance Spectroscopy – comparison of experimental ceramic results with model parameters(IOP Publishing, 2024-08-25) Kusák, Ivo; Luňák, Miroslav; Dvořák, Richard; Nekorancová, Anna; Mizerová, Cecílie; Rovnaník, PavelImpedance spectroscopy is a non-destructive test method belonging to the group of electrical engineering measurements. The method is suitable for monitoring the quality of building materials even with low conductivity. Although the method focuses on the intrinsic conductivity of systems, most IS techniques, including data analysis methods, conceive of the material in terms of a lossy dielectric. In selecting the material for testing with the IS method, an attempt was made to bring the IS capabilities as close as possible to practical, real-world materials. This paper is devoted to a comparison of the impedance characteristics of ceramics with three types of dielectric models that are described in theory or referenced in the literature. The ceramic samples were fabricated using different material additions, such as bentonite, phosphoric acid, or sodium water glass. Experimental curves of the loss factor versus frequency for all samples are described and then approximations of selected samples are shown successively for all three models considered. Experimental results were obtained from more than 50 points in each characterization. Measurements were performed for frequencies from 40 Hz to 1 MHz.
- ItemEvaluation of durability-related field inspection data from concrete bridges under service(Polish Academy of Sciences, 2020-01-01) Konečný, Petr; Lehner, Petr; Vořechovská, Dita; Sadílková Šomodíková, Martina; Horňáková, Marie; Rovnaníková, PavlaThe level of de gradation of reinforced concrete bridges was evaluated based on the in-situ measurements performed on five reinforced concrete bridges under service located in the Czech Republic. The combined effect of carbonation and chlorides with respect to the corrosion of steel reinforcement, namely the pH and the amount of water-soluble chlorides, were evaluated on drilled core samples of concrete. Based on these parameters, the ratio between the concentrations of Cl– and OH, which indicates the ability of concrete to protect reinforcement, was calculated. All the data were statistically summarized and the relationships among them were provided. The main goal of this study is to evaluate the non-proportional effect of the amount of chlorides per mass of concrete on the risk of corrosion initiation and to localize the “critical” locations in the bridges that are the most affected by the degradation effects.
- ItemInfluence of rock inclusion composition on the fracture response of cement-based composite specimens(Elsevier, 2021-11-20) Vyhlídal, Michal; Čairović, Iva; Šimonová, Hana; Kucharczyková, Barbara; Vavro, Leona; Vavro, Martin; Němeček, Jiří; Rovnaníková, Pavla; Keršner, ZbyněkThis 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.
- ItemMicrostructure of biopolymer-modified aerial lime mortars(EDP Sciences, 2020-10-14) Žižlavský, Tomáš; Vyšvařil, Martin; Bayer, Patrik; Rovnaníková, PavlaCellulose-based viscosity-modifying admixtures are used on daily basis in a wide range of building materials, dominantly in pre-mixed mortar systems. Lately, alternative admixtures such as different “gums” have emerged. In building materials, the gums have similar viscosity-enhancingeffects as cellulose ethers with different efficiency. Various ways of production, as well as diverse working mechanisms of the biopolymers are to be considered while choosing the most suitable admixture for the intended use. Influence of alternative admixtures in several doses on the microstructure of lime mortars was studied in this paper. Mortars were prepared with the same workability and the air content in fresh mortar was determined, for it can have notable impact on microstructure of hardened mortar. Hydroxypropyl derivative of chitosan showed air entraining ability, while the carboxymethyl derivative reported slight decrease in amount of air entrained into the mixture. In the case of diutan gum, the most water-demanding admixture, the percentage of entrained air dropped with growing dose. Admixture addition increased the volume of pores in diameter lower than 0.1 m, and in region of pores around 10 m. Only the diutan gum affected the distribution of capillary pores, which are typical for lime mortars. Hygric properties were in correlation with air content values.