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The stabilized waste dust as a constituent modifying properties of wood-cement composites
(CEMC - České ekologické manažerské centrum, 2024-03-08) Melichar, Tomáš; Vasas, Silvestr; Keprdová, Šárka; Bydžovský, Jiří; Schmid, Pavel; Tuscher Hájková, Iveta
The research presented in this paper deals with the effect of stabilized waste dust (from cement-bonded particleboard processing) on the properties of wood-cement composites. The attention was paid to sorption characteristics and mechanical properties. The goal of the research presented was to study the properties and behaviour of wood-cement composites containing an alternative raw material once stabilised. To evaluate this aspect, composites of modified composition (filler and matrix - based on Portland and mixed cement, substitution with waste dust) were exposed to variable relative humidity ranging from 0 to 96% (increase/decrease in 10% increments). Specimens were always exposed to a given humidity (0, 10, 20, etc.) for a period of time sufficient to stabilize their weight. Absorption and then desorption took place. After the exposure to moisture was completed, the bending strength and modulus of elasticity in bending, tensile strength perpendicular to the plane of the board were tested. In this way, the effect of stabilization of spruce chips in terms of the different matrix composition of the materials was indirectly analyzed in a partial way. Sorption isotherms demonstrate the different behaviour of the materials during varying ambient air humidity. The composition of the wood-cement composites affecting the stabilization of the spruce chips (contained in the composites), among others. In case of the physical and mechanical properties a slight increase was observed.
Experimental Study of Mechanical Wave Propagation in Solidifying Cement-Based Composites
(MDPI, 2024-12-06) Jakubka, Luboš; Topolář, Libor; Nekorancová, Anna; Dvořák, Richard; Hrabová, Kristýna; Černý, Felix; Skibicky, Szymon; Pazdera, Luboš
In this paper, a new measurement procedure is presented as an experimental study. In this experimental study, a measurement system using the pass-through pulsed ultrasonic method was used. The pilot application of the measurement setup was to monitor mechanical wave changes during the solidification and hardening of fine-grained cement-based composites. The fine-grained composites had different water–cement ratios. The measured results show apparent differences in the recorded mechanical wave parameters. Significant differences were observed in the waveforms of the amplitude increase in the passing mechanical waves. At the same time, the frequency spectra of the five most dominant frequencies are presented, where the frequency lines are clear, indicating the quality of the hydration process. Based on the results, it can be concluded that the new method is usable for fine-grained cement-based materials but is not limited to that. The advantages of this method are its high variability and non-destructive character. The experimental study also outlines the possible future applications of the pulsed passage ultrasonic method.
Optimisation of fine RCA content in mortar mixture based on the long-term fracture and fatigue tests
(Elsevier, 2025-05-06) Miarka, Petr; Šimonová, Hana; Kucharczyková, Barbara; Seitl, Stanislav; Poletanovic, Bojan; Merta, Ildiko
This paper presents the results of an experimental study with a focus placed on the long-term mechanical-, fracture- and fatigue analysis of mortar, in which natural aggregates (NA) were partially substituted with fine recycled concrete aggregates (RCA). Long-term tests were done at 28, 145 and 255 days under natural aging conditions. Fracture and fatigue experimental analysis took place for tensile mode I, which was enriched by fracture tests performed under a combination of tensile and shear load – mixed-mode I/II loading conditions. In total, four mixtures (reference and three with fine RCA) were tested to examine the influence of the aggregate replacement on the fracture and fatigue properties of the material. The experimental results showed that 25% of replacement seems to be an optimum dosage of fine RCA, which improves both the fracture and fatigue properties of tested mixtures.
Physical-mechanical and durability properties of concrete with lightweight artifical aggregate produced by controlled self-burning of waste coal tailings
(Faculty of Civil Engineering of The Slovak University of Technology, 2024-10-04) Stehlík, Michal; Batelka, Michal; Heřmánková, Věra; Anton, Ondřej
The goal of this research focusing on the burning of coal tailings to produce a lightweight artificial aggregate is to compare the physical-mechanical and durability properties of concrete containing this new type of artificial aggregate with those of the reference concrete. The following parameters are measured on all the samples: compressive strength, volume mass, the static modulus of elasticity in compression, the frost resistance of this new type of concrete, and the resistance to CO2. All the concretes tested with the new artificial aggregate exceeded the characteristic strength values in all the strength classes monitored. The volume mass of the concrete with the new artificial aggregate is tens of percentages lower than that of the conventional reference concrete. The frost resistance of the concrete tested was reliably proven by the non-destructive resonance method. It was also found that at the lower strength classes of concrete, carbonation occurred earlier, but there was no obvious direct relation to the porosity of the new artificial aggregate. The tests performed showed that it is possible to produce high - quality concrete using a new lightweight artificial aggregate produced from coal tailings
Hybrid Geopolymer Composites Based on Fly Ash Reinforced with Glass and Flax Fibers
(MDPI, 2024-10-26) Šimonová, Hana; Bazan, Patrycja; Kucharczyková, Barbara; Kocáb, Dalibor; Lach, Michal; Dariusz, Mierzwiński; Setlak, Kinga; Nykiel, Marek; Nosal, Przemysław; Korniejenko, Kinga
This article’s aim is to analyze physical, mechanical, and fracture properties as well as the thermal investigation of geopolymer composites reinforced with flax, glass fiber, and also the hybrid combination of fibers. Two types of matrices were considered as composites matrices. The first composition was based on fly ash and river sand. The second matrix composition contained fly ash and glass spheres. The content of reinforcement was 1% by mass. Compressive strength and three-point bending fracture tests were performed. The values of fracture toughness and fracture energy were determined. The resonance method was used to verify the dynamic characteristics, such as the dynamic modulus of elasticity and the dynamic Poisson ratio. The results show that single-type fibers in composites based on fly ash and glass spheres did not affect compressive strength. However, introducing hybrid reinforcement increased compressive strength by about 10% compared to the reference specimens. Flax fibers and hybrid reinforcement ensured higher fracture toughness and energy. The results also revealed great potential for glass sphere application to geopolymer materials in terms of fracture mechanics and thermal properties. Despite the lower strength properties in relation to geopolymers based on sand aggregate, applying reinforced fibers into the composite with glass spheres enhanced the compressive strength compared to other materials. Materials modified with glass spheres have a thermal conductivity twice as low as that of materials containing river sand.

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