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Polymer-silicate composite based on alternative raw materials under conditions of increased temperature
(Elsevier, 2016-08-03) Melichar, Tomáš; Bydžovský, Jiří
The paper presents research into studying the properties of composite materials with polymer-silicate matrix and porous (lightweight) filler. Specifically, the matrix based on cement substituted by 35% of alternative raw material was considered. In case of filler aggregate based sintered ash was used. Investigated materials were exposed at high temperatures. Thermal loading took place gradually in temperature increments of 22 °C (reference conditions), 400, 600, 800 and 1000 °C with subsequent controlled cooling. Attention was also focused on various ways of cooling – slow in the furnace (1 °C/min) and immersion in water (bath temperature c. 18 °C). Suitability of matrix modification and use of porous fillers based on alternative raw materials was proved by set of analyses. After exposure in an environment with a temperature of 1000 °C followed by quench cooling was set residual compressive strength of about 40%, which is relatively high for this type of the matrix. The curves of residual strength with different types of cooling are intriguing too. Selected samples were also investigated by using micro/structural techniques, where the emphasis was placed on the formation of any defects related.
Cementotřískové desky s vyšším obsahem netradičních alternativních surovin substituujících pojivo a třísky
(CEMC - České ekologické manažerské centrum, 2021-12-01) Melichar, Tomáš; Bydžovský, Jiří; Keprdová, Šárka; Dufka, Amos
Článek prezentuje laboratorní výzkum zaměřený na posouzení vlastností a mikrostruktury cementotřískových desek modifikovaných alternativními surovinami. Konkrétně bylo modifikováno složení pojiva jemně mletým vápencem a škvárou. Současně byla provedena úprava složení plniva, tj. substituce smrkových třísek. Jako substituent byly využity druhotné třísky získané úpravou odřezků, které vznikají jako vedlejší produkt výroby cementotřískových desek. Pojivo bylo nahrazováno v množství do 10 % a smrkové třísky substituovány v množství 10 % až 20 %. Vlastnosti cementotřískových desek byly analyzovány po 28 dnech zrání v laboratorních podmínkách vč. ověření mrazuvzdornosti (100 cyklů). Výsledky prezentovaného výzkumu lze shledat jako přínosné. Využitím alternativních surovin, které jinak nejsou využity (vyjma vápence) a představují tak odpad, dojde k snížení zátěže životního prostředí a současně zachování užitných vlastností cementotřískových desek bez negativního vlivu na jejich mikrostrukturu.
Long-term durability of cement-bonded particleboards with modified composition by waste dust
(CEMC - České ekologické manažerské centrum, 2021-12-01) Melichar, Tomáš; Bydžovský, Jiří; Dufka, Amos
This paper presents research on long-term behaviour of cement-bonded particleboards exposed to adverse conditions. The boards were subjected to frosting / defrosting cycles, up to 300 cycles. Specifically, 100, 200, 300 cycles were performed at the age of 28 days, 6 months, 12 months, 18 months and 24 months. Compositoin of the particleboards was modified by by-product, which has its origin in production of cement-bonded particleboards. Dust from cutting and grinding of the particleboards was used in amount of 7% as a partial substituent of cement (6%) and spruce chips (1%). The goal of presented research is the assessing the effect of adverse conditions at different age of cement-bonded particleboards (with modified composition), when attention is paid to mechanical properties and microstructure, respectively. Bending strength, modulus of elasticity in bending, transverse tensile strength perpendicular to the plane of the board and microstructure (SEM) were studied with respect to the changes in time (up to 2 years).
Immobilization of Heavy Metals in Natural Zeolite-blended Cement Pastes
(Elsevier, 2016-09-26) Vyšvařil, Martin; Bayer, Patrik
This paper deals with the investigation of efficiency of natural zeolite-blended cement pastes for the immobilization of heavy metals. Natural zeolite was used to partially replace ordinary Portland cement (OPC) at rates of 0% and 20% by weight of a binder and soluble heavy metal salts were added to a mixing water in an amount of 1% and 5% by weight of the binder. The flexural and compressive strength of the cement pastes were investigated, while the leachability of the heavy metals was determined. Additionally, scanning electron microscopy was performed to investigate the microstructure of the cement pastes, while the pore size distribution was analyzed with mercury intrusion porosimetry. The results indicated that the flexural and compressive strengths of the pastes containing 20 wt.% of natural zeolite were higher than those with OPC alone. It was also found out that the effectiveness in reducing the leachability of Ba, Cd, Cu, Ni and Pb was better for the natural zeolite-blended cement pastes.
Wear of grinding rotors with thermally-sprayed coatings in a high-speed mill
(Elsevier, 2018-10-15) Tkachenko, Serhii; Dvořák, Karel; Jech, David; Slámečka, Karel; Klakurková, Lenka; Paloušek, David; Čelko, Ladislav
In this paper, the erosion behavior of three types of protective thermally-sprayed coatings and non-coated substrate steel was investigated under semi-industrial test conditions using a laboratory high-speed pin mill DESI-11. The grinding in the mill was performed by two counter rotors, on which protective coatings were deposited either by atmospheric plasma spraying (APS) (Cr3C2-NiCr and NiCrBSi coatings) or by high velocity oxy-fuel (HVOF) process (WC-CoCr coating). The grinding rotors with deposited coatings were used for milling of the Portland cement, and rotors' weight loss was monitored after milling of 1, 3, 5, 10, and 15 kg of this material. The lowest weight loss in the mixed impact erosion conditions was exhibited by WC-CoCr coating, which was followed by Cr3C2-NiCr and NiCrBSi coatings. The greatest material removal on the anterior and the right lateral faces of rotor pins was a result of erosion damage at high impact angles through surface fatigue wear and the following failure of protective coatings down to the substrate. In contrast, the top and the left lateral faces of the pins were subjected mostly to the ploughing and microcutting at oblique impact angles that resulted in significant erosive damage only if hardness of the pin was lower than that of the Portland cement (Cr3C2-NiCrcoated and non-coated steel pins). The study also found a significant disproportion between the volumetric wear losses of various rows of pins of grinding rotors. The central part of the grinding tool consisting of two counter rotors (both rows of 2-row rotor and a middle row of 3-row rotor) suffered more intensive erosion wear than the external part (outer rows of 3-row rotor). The design of the mill and the resulting variability in parameters of milled powder particles at different sites of the grinding tool (such as particle size, particle flux and particle velocity) were considered as main reasons of this phenomena.

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