Solid State Phenomena Vol. 296

Abstract: The paper presents the results of experiments carried out on test samples made from reinforced concrete. Within this experiment, concrete beams with steel reinforcement in the middle were made. The concrete samples were tested by a non-destructive acoustic Impact-echo method before and after high temperature loading (after cooling to room temperature). We focused on the dominant frequencies shift in the frequency spectra obtained by this method. The aim was to assess the ability of aforementioned acoustic method to detect the thermal damage of steel reinforced concrete.

Abstract: Carbon nanotubes (CNTs) are used for the application in concrete especially due to their excellent physical properties. In this study, CNTs were used as a conductive admixture to prepare composites with enhanced electrical properties that might be potentially used in smart concretes or structures. We assessed the changes in selected electrical properties of fly ash geopolymer mortars (conductivity, resistance, capacitance) depending on the concentration of CNTs that ranged from 0.05 to 0.20%. The most convenient CNTs concentration was discussed considering both the electrical and mechanical properties (compressive and flexural strength). Mercury intrusion porosimetry and scanning electron microscopy were used to observe the distribution of CNTs and porosity of the mortars.

Abstract: Nonlinear Ultrasonic Spectroscopy (NUS) methods investigates nonlinear phenomena that occur when the sound or ultrasound waves pass through the material. This paper focuses on the use of these methods for nondestructive testing of reinforced concrete damaged by high temperature. For this research, reinforced concrete beams with one steel rod were made and the NUS measuring equipment was assembled. An appropriate nonlinear parameter was selected to assess the damage. The nonlinear behavior of thermally damaged reinforced concrete was manifested by the deformation of ultrasound waves passing through the measured samples, resulting in nonlinear effects in the frequency spectra of the recorded signal.

Abstract: Fluid fuel combustion technology in coal-fired power plants is very popular in the Czech Republic, resulting in a relatively high production of a specific by-product - fluidized fly ash (class C according to ASTM definition), which differs from the classical high-temperature fly ash in mineralogical composition with a high sulphur content of anhydrite CaSO₄. Fluidized ash is not yet used in the production of fired building materials, where it could be used as a source of calcium oxide (for example, the production of porous ceramic tiles). However, high volume of sulphur dioxide emissions during the re-firing of fluidized fly ash in ceramic raw materials mixtures has been solved. The aim of the paper is definition of temperature ranges of anhydrite decomposition (formation of SO₂ emission) from pure class C (fluidized) fly ashes from different sources (power plants) depending on granulometry of fly ash especially.

Abstract: Concretes with high fly ash content are within a unified world nomenclature often referred to as HVFAC, resp. high volume fly ash concrete. These concretes are characterized by the percentage of fly ash as an active admixture relative to a cement dose of at least in a ratio of 1:1. The use of these concretes falls into the field of construction with the necessary reduction in the development of hydration heat. In the experiment, long-term monitoring of the development of important mechanical parameters, namely the static modulus of compressive elasticity and compressive strength, was performed. Both monitored parameters play a very important role in the design of buildings, for which construction is HVFAC often used. These parameters were monitored within the carried out research until the time of 360 days. The results of the experiment give an overview of the pozzolanic reaction progress over the in the long-term time horizon and its impact on the concrete parameters monitored. The results clearly show that even after 360 days the development of the strength parameters of these concretes is not stopped.

Abstract: Only a few types of commercially available high temperature ceramic abradable coatings are presented on the market and most of them consist of partially stabilized yttria zirconia with polymer porosity former agent and/or hBN solid lubricant. The basic demand placed on abradable coatings include balance between hardness and erosion resistance. The contribution focuses on the description of microstructure, phase composition and hardness of alternative atmospheric plasma sprayed ceramic abradable coatings deposited from four different experimental powder mixtures: (i) commercial yttria-zirconia + 5 wt. % of experimental BaF₂/CaF₂, (ii) commercial yttria stabilized zirconia + 10 wt. % of experimental BaF₂/CaF₂, (iii) R&D powder Sr_xTiO_y and (iv) R&D powder Sr_xTiO_y + 5 wt. % of polyester. The abradable coating systems were of ~ 150 μm thick CoNiCrAlY bond coat and of ~ 800-1000 μm thick ceramic top coat. The microstructure and phase composition of all atmospheric plasma sprayed coating systems were evaluated by the means of scanning electron microscopy and X-ray diffraction techniques. To estimate coatings basic parameters the Rockwell hardness HR15Y was measured.

Abstract: Aluminosilicate materials are generally considered electrical insulators. In order to achieve enhanced electrical conductivity these materials must doped with suitable conductive admixtures such as carbon black. These composites gain the importance in the new field of applications such as self-sensing materials or self-monitoring structures. This paper presents a study on self-sensing properties of alkali-activated slag composite with 2 and 4% of carbon black as conductive filler during repeated flexural and till fracture loading in the configuration of three-point bending test. The results showed that best performance of the self-sensing properties was achieved with 4% of carbon black, though both the compressive and flexural strengths were deteriorated.

Abstract: This paper is focused on the effect of treatment of fly ash after selective non-catalytic reduction (SNCR) with tannin on autoclaved aerated concrete (AAC) production in order to reduce or stop ammonia leakage from the fresh mixture due to its alkalinity. A pure form of tannin and a tannin-based product „Farmatan“ were used as a treatment in dosage ranging from 0,5 g – 3 g of agent per 1 kg of fly ash. Efficient dosage was determined at 2 wt.% of fly ash by the speed of an indicator change due to gaseous ammonia diluted in water. The rheological properties of fresh mixtures were observed by consistency test in Viskomat showing that Farmatan causes delay of hydration. The results of bulk density and compressive strength testing revealed that Farmatan causes an increase of bulk density and at higher amount decreases the compressive strength because of thermal crack formation due to combined effect of delayed hydration and thixotropy. Using x-ray diffraction (XRD) analysis there were no differences in phase composition observed.

Abstract: The aim of this article is to characterize the synthesis and properties of forsterite ceramics in dependence on different amount of fly ash in the raw material mixture. Forsterite ceramics is not currently produced in the Czech Republic. Forsterite is used in industry for its high refractoriness and for its coefficient of linear thermal expansion which is close to metals. The primary objective is to synthesize forsterite via solid state reaction using different amounts of fly ash in the raw material mixture. Fly ash is a secondary energy product from coal combustion in power plants. Therefore, it is inexpensive, and its recycling is important for the environment and sustainable development. Slovakia offers the import of talc, magnesite and its products. The article assessed the influence of different amounts of fly ash in the raw material mixture on the synthesis and properties of forsterite in terms of mineralogy, physico-mechanical properties of fired body and refractoriness.

Abstract: Clay plasters have been used extensively in the past. Later, these plasters were replaced with more modern materials. In recent years, however, they have come back and are being used primarily for new constructions. The interest in ecological constructions and natural materials was significantly influenced not only by experts but also by ordinary users. A significant disadvantage of clay plasters is poor durability in the exterior environment and in contact with water in the liquid state where the part of the clay product is leached. The paper deals with the modification of clay plasters with silicate-based hydrophobic agents. The aim of this experiment is to improve the durability of these plasters and to extend their application both indoors and outdoors while maintaining typical advantageous properties.