Ústav technologie stavebních hmot a dílců

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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.
Durability of Wood–Cement Composites with Modified Composition by Limestone and Stabilised Spruce Chips
(MDPI, 2024-12-23) Melichar, Tomáš; Dufka, Amos; Dvořák, Karel; Bayer, Patrik; Vasas, Silvestr; Nováková, Iveta; Schwarzová, Ivana; Bydžovský, Jiří
Limestone (LS) and stabilised secondary spruce chips (SCs) utilisation in wood–cement composites is still an unexplored area. Therefore, the main objective of the research presented here is the assessment of the long-term behaviour of cement-bonded particleboards (CBPs) modified by LS and SCs. Cement (CE) was replaced by 10% of LS, and spruce chips by 7% of SCs. The test specimens were stored in a laboratory and exterior environment (Middle Europe) for up to 2 years. The density, strength, and modulus of elasticity were evaluated after 28 days, and then in 6-month periods. The hygrosco-picity was analysed separately. The mineralogical composition and microstructure were analysed due to possible LS participation during hydration. SC synergic behaviour in CBPs was also studied. After 2 years, the microstructure of the CBP was more compact, and denser. Strong carbonatation contributes to the improvement of CBP properties. The products of carbonatation were present in both the matrix and wood chips. The hydration of the matrix was almost finished. LS has a positive effect on the matrix microstructure development. LS acts both as an active component participating in the formation of the cement matrix structure and as an inert microfiller, synergic with hydration products. SCs have a positive effect on the hygroscopic behaviour of CBPs and slightly negative effect on the tensile strength.
Optimizing Indoor Microclimate and Thermal Comfort Through Sorptive Active Elements: Stabilizing Humidity for Healthier Living Spaces
(MDPI, 2024-11-29) Peterková, Jitka; Zach, Jiří; Novák, Vítězslav; Korjenic, Azra; Sulejmanovski, Abdulah; Sesto, Eldira
This paper investigates the potential use of natural materials and elements for stabilizing indoor humidity levels, focusing on creating healthier living environments in buildings. Unstable indoor microclimates, particularly extreme humidity levels, can negatively affect human health by causing issues such as condensation, mold growth, or dry mucous membranes. In this work, we explore how sorptive materials can maintain indoor humidity within the optimal range of 40-50%. The aim is to identify optimal solutions for moisture control using passive elements, such as unfired ceramic components, which demonstrate high sorption activity within the 35-55% relative humidity range. These elements can effectively absorb moisture from, or release it back into, the indoor environment as needed. Five clay types based on different clay minerals were analyzed in the research in order to assess how their structures influence moisture adsorption behavior. These elements can be combined with green/active elements and standard measures, such as ventilation or targeted room air exchange, to improve indoor humidity regulation. The evaluation of the results so far indicates that the use of clay-based elements in the interior offers a sustainable and natural approach to maintaining optimal indoor microclimate conditions. The slab elements from all 5 clay formulations investigated effectively support indoor humidity stabilization.
Utilization of Alternative Fibres Manufactured from Recycled PET Bottles in Concrete Technology for the Improvement of Fire Resistance
(MDPI, 2024-11-12) Sedlmajer, Martin; Zach, Jiří; Bubeník, Jan; Bydžovský, Jiří; Novák, Vítězslav
This article addresses the potential use of secondary polymer fibres in the field of structural concrete as a replacement for primary polymer fibres (mainly polypropylene/PP/), which are used in concrete to enhance its resistance when exposed to high temperatures (especially in the case of fire). Research has shown that, in addition to PP fibres, polyethylene terephthalate/PET/fibres, produced by recycling packaging materials (mainly PET bottles), can also be used as an alternative. These fibres are industrially produced in similar dimensions as PP fibres and exhibit similar behaviour when added to fresh and hardened concrete. In terms of their effect on increasing resistance to extreme heat loads, it has been found that despite a higher melting point (Tm), concrete with these fibres demonstrates comparable fire resistance. Therefore, it can be concluded that secondary PET fibres represent an interesting alternative to primary PP fibres from the perspective of a circular economy, and their use in construction represents a potentially valuable application for PET obtained through the collection and recycling of PET packaging materials.
Study on the use of glass by-products for sustainable polymer-modified mortars
(Springer Nature, 2024-11-09) Žižková, Nikol; Hodul, Jakub; Drochytka, Rostislav
This investigation is focused on the observation of changes in the properties of polymer-modified cement mortars caused by the addition of recycled glass. The current requirements for reducing CO2 emissions in the production of cement composites, are also forcing the producers of polymer-modified mortars (PMMs) to use alternative materials, such as silica-rich supplementary materials. Selected types of recycled glass with pozzolanic behavior were specifically ground (particle size below 63 m) and used as a partial cement substitute (10wt.%, 20wt.% and 30 wt.% substitution of Portland cement). In order to explain the obtained results and garner new knowledge of the microstructure of the mixtures being studied, the following tests were performed: scanning electron microscopy (SEM) observation, differential thermal analysis (DTA) and high-pressure mercury intrusion porosimetry. The findings show that the finely ground recycled glass has high potential to be used as an effective cement replacement for PMM materials, that are currently used in large amounts, mainly in the rehabilitation of concrete structures.

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