Technologie hmot a dílců AdMaS

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Study of Possibilities of Using Special Types of Building and Demolition Waste in Civil Engineering
(Budapest University of Technology and Economics, 2020-01-15) Drochytka, Rostislav; Dufek, Zdeněk; Michalčíková, Magdaléna; Hodul, Jakub
Construction and demolition waste makes up a substantial part of all waste produced in Europe. Its impact on the environment may be relatively small, but it exists in large amounts and holds many options of re-use. This is why it remains a frequently discussed topic of European policy. As part of circular economy, the European Commission has already proposed new goals and strategies for existing types of waste. However, they are not entirely clear on the usage of new kinds of building and demolition waste, as they are yet to be specified by existing legislation. This paper discusses new kinds of building and demolition waste and the basic principles (new technology) of their use. The possibilities of utilizing new kinds of waste are based on a multicriteria optimization calculation, specifying each material and proposing ways of its further use. Recent findings can expand the choice of new uses of construction and demolition waste and reduce their impact on the environment (less waste, better properties and more effective processing, reducing transportation needs, maximizing re-use and recycling).
Metal matrix to ceramic matrix transition via feedstock processing of SPS titanium composites alloyed with high silicone content
(Elsevier, 2018-06-15) Tkachenko, Serhii; Čížek, Jan; Mušálek, Radek; Dvořák, Karel; Spotz, Zdeněk; Montufar Jimenez, Edgar Benjamin; Chráska, Tomáš; Křupka, Ivan; Čelko, Ladislav
Titanium silicides are promising candidates for use as a reinforcement in advanced light-weight composites due to their excellent mechanical properties and oxidation resistance at high temperatures, sufficient wear resistance, and high chemical stability in various corrosion environments. Direct in-situ synthesis of such composites from titanium-silicon (Ti-Si) powder feedstock by spark plasma sintering (SPS) was used in this study with a particular attention on the effect of the powder processing parameters (blending, co-milling, milling blending) on the microstructure formation and mechanical properties of the sintered composites. As opposed to the previous silicide-reinforced Ti studies, this was done for high silicone content (20 wt%). It was found that, despite the powders initial identical composition, the microstructure and phase content of the compacts varied significantly with the used powder fabrication route. Taking advantage of this, composites ranging from relatively soft metal-matrix (52 vol% metallic Ti; using non-milled Ti and coarse or fine-milled Si) to hard ceramic-matrix (11 vol% metallic Ti, using fine-dispersed joint-milled mixture of Ti and Si) were obtained. Due to in-situ formation of various TiSi2, TiSi, Ti5Si4 and Ti5Si3 silicide reinforcement phases contents with high hardness and stiffness, all the sintered composites showed superior hardness and wear resistance (an increase as much as 44) in comparison to pure Ti. Importantly, hardness and elastic modulus of intermediate compounds TiSi2, TiSi, Ti5Si4 and Ti5Si3 were measured using instrumented indentation technique for the first time and are presented in the paper.
Strength and fracture mechanism of iron reinforced tricalcium phosphate cermet fabricated by spark plasma sintering
(Elsevier, 2018-05-01) Tkachenko, Serhii; Horynová, Miroslava; Casas Luna, Mariano; Díaz de la Torre, Sebastian; Dvořák, Karel; Čelko, Ladislav; Kaiser, Jozef; Montufar Jimenez, Edgar Benjamin
The present work studies the microstructure and mechanical performance of tricalcium phosphate (TCP) based cermet toughened by iron particles. A novelty arises by the employment of spark plasma sintering for fabrication of the cermet. Results showed partial transformation of initial alpha TCP matrix to beta phase and the absence of oxidation of iron particles, as well as a lack of chemical reaction between TCP and iron components during sintering. The values of compressive and tensile strength of TCP/Fe cermet were 3.2 and 2.5 times, respectively, greater than those of monolithic TCP. Fracture analysis revealed the simultaneous action of crack-bridging and crack-deflection microstructural toughening mechanisms under compression. In contrast, under tension the reinforcing mechanism was only crack-bridging, being the reason for smaller increment of strength. Elastic properties of the cermet better matched values reported for human cortical bone. Thereby the new TCP/Fe cermet has potential for eventual use as a material for bone fractures fixation under load-bearing conditions.
Effect of wood chips properties on mineralogical composition and microstructure of silicate matrix based composites
(IOP Publishing, 2018-07-16) Melichar, Tomáš; Bydžovský, Jiří; Dufka, Amos
The research presented in this article was focused on proving the effect of wood chips parameters on the hardening process of silicate matrix in cement-bonded particleboard. Namely content of humidity in the chips (in range 30 to 90%) was significant. This amount of humidity was chosen with respect to real conditions of cement-bonded particleboards production. Influence of humidity could be reflected in the content of sugar (cellulose etc.) in wooden chips. The sugars affect the hardening of matrix negatively. Thus, phase composition and microstructure of matrix of cement-bonded particle boards were analysed during 2 to 28 days. Investigation of physico-chemical parameters and microstructure was also supplemented by verification of the basic material characteristics of cement-bonded particleboards (strength and modulus of elasticity in bending, transverse tensile strength perpendicular to the plane of the board, etc.).
Development of Crystallinity of Triclinic Polymorph of Tricalcium Silicate
(MDPI, 2020-08-24) Ravaszová, Simona; Dvořák, Karel
Tricalcium silicate phase is one of the main components of modern Portland cements. One of the major industrial challenges in the field of cement production is mapping the influence of individual clinker minerals and their polymorphs on the properties of industrially produced clinkers. The primary goal of this work is to improve the fundamental knowledge of understanding the process of alite formation and development from a crystallographic point of view. This study focuses on the observation of the crystallization process of triclinic alite during the firing process, which to date has not been thoroughly described. The effects of a wide range of temperatures and sintering periods on crystallinity were assessed on samples fired in platinum crucibles in a laboratory furnace. X-ray analysis—together with calculation of crystallinity using Scherrer’s equation—was used for observing the crystallite size changes of T1 alite polymorph. According to the acquired results, among the most technologically and economically advantageous regimes of production of a high-quality triclinic alite is the temperature of 1450 °C and sintering time of two hours. The most significant changes in the crystallite size occurred within the first hour of sintering for the whole investigated temperature range.

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