Rostislav Drochytka

This article presents research focusing on the analysis of lightweight polymer–cement mortar using combined impact-echo (IE) and computed tomography (CT) methods after exposure to extreme temperatures. Lightweight mortar based on blended cement and waste cellulose fibers was developed for this purpose. The mortar consisted of a polymer–cement matrix (60% Portland cement, 40% blast furnace slag and polymer modifier) and porous aggregate (expanded clay with grain size from 0 to 2 mm) including other minor components (superplasticizer) and admixtures (silica fume). Mortars with two types of dispersed reinforcement based on waste cellulose (G-500T and G-700T) in amounts ranging from 0.5 to 1.5 kg/m³ were analyzed. The materials were tested at the age of 28 days upon exposure to 20 °C (storage in laboratory conditions), 600 °C, 800 °C and 1000 °C. Aside from IE and CT, the outputs were supplemented by testing basic physical and mechanical parameters (strength, volume changes, etc.), as well as microstructure analysis, specifically testing of microcracks using SEM. The purpose of the CT and SEM was confirmation of cracks, specifically microcracks (including their character and areas of appearance), along with possible anomalies occurring during high-temperature stress of polymer–cement composites.

The cement industry is one of the largest environmental polluters, responsible for approximately 7–8% of global CO ₂ emissions. The search for more sustainable alternative binders and innovative composites is therefore becoming a key direction in the development of building materials. This paper investigates the effect of cement type and CO ₂ cured alternative binder on the resistivity of a silicate composite with carbon-based filler. The amount of electrically conductive filler was kept below the percolation threshold to observe changes in the electrical properties of the material due to chemical and microstructural modifications, and for the same reason the porosity of the material was maintained. The alternative binder was a 50/50 mixture of cement and grounded ladle slag, cured in a controlled CO ₂ climatic chamber. The results show that the use of CO ₂ cured binder not only helps to reduce the environmental footprint of the material but also contributes to the electrical conductivity parameters in the saturated state, which may be important for outdoor applications. The results further indicate that composites based on conventional CEM I and CEM II cements provide relatively good electrical conductivity, while furnace slag-rich CEM III cements show significantly reduced ionic conductivity and higher impedance, making them less suitable for electro-conductive applications. In contrast, the CO ₂ -cured cement/ladle slag system demonstrated the highest leachate conductivity and the lowest impedance in the saturated state, confirming its potential as the most efficient and environmentally beneficial binder for outdoor electro-conductive composites. The study thus confirms that combining alternative binders with electrically conductive fillers can lead to more sustainable and functionally advanced building materials of the future.

The aim of this research was to examine the effect of water-based hydrophobic impregnations on concrete in order to improve its durability, chemical resistance, and physical–mechanical parameters. The purpose of this research was to prevent as much water evaporation as possible during concrete hydration, which resulted in the improvement in concrete properties including strength, durability, resistance of concrete in high-pressure water, water tightness, etc. Water-based hydrophobic impregnations based on silane and siloxane, epoxy resin, and oil were chosen to achieve improvements in concrete parameters. The comparison of water-based hydrophobic impregnations with solvent-based hydrophobic impregnations was also performed using the determination of absorbency, water pressure penetration depth, watertightness, concrete penetration depth, and resistance to aggressive environment. The concrete microstructure was observed using a digital microscope and a scanning electron microscope (SEM). Samples with hydrophobic agents exhibited a higher contact angle, lower absorbency, and higher resistance to aggressive environment, when compared to the untreated surfaces, confirming the water repellency of the water-soluble hydrophobic impregnations. The positive effect of hydrophobic agents in the compressive strength was also recorded. Furthermore, the benefit of the addition of 0.1 wt.% of nanocellulose into the hydrophobic impregnations was observed. Based on the obtained results, it was found that the addition of nanocellulose to water-soluble hydrophobic impregnations reduced the depth of pressurized water seepage and increased the compressive strength of the concrete after 28 days by 2 MPa.

This paper aims to verify the effect of water-soluble hydrophobisations on cementitious composites such as concrete (S1) and cement-bonded particle boards (S2). The research was focused on the water-soluble hydrophobisations based on methylsilanolate (MS), a mixture of silanes and siloxanes (SS) and alcohol with the addition of nano-silica (N). The results provide a comprehensive overview of the benefits and effectiveness of water-soluble hydrophobisations in the context of building materials, outlining a direction towards the development of new, more environmentally friendly solutions in the construction industry. For this reason, alternative raw materials (brick recyclate and brick dust) were used for S1 substrate preparations. How the water-soluble hydrophobisations, including hydrophobisations with the addition of nano-silica (N), affect the process of water evaporation during hydration and the resulting water repellence of the S1 and S2 substrates were experimentally verified through a series of tests, e.g., measurement of the contact angle and depth of water penetration under pressure. The evaluation of the effect of hydrophobisations on the resistance of substrate to aggressive gaseous and liquid environments was observed by the determination of the resistance to carbonation and sulphation processes and the resistance of the concrete to aggressive liquid media (10% H₂SO₄, 10% CH₃COOH). Although the hydrophobisations did not have a significant effect on some aspects of S1, such as the resistance to carbonation and sulphate attack, improvement was observed in other areas, such as the quadrupling increase in contact angle of the surface and 9 mm decrease in water pressure penetration into the concrete substrate.

The reconstruction of buildings is a complex process that often requires the consideration of the construction load when selecting correct building materials. Autoclaved aerated concrete (AAC)—which has a lower bulk density (compared to traditional masonry materials)—is very beneficial in such applications. A current trend in AAC development is the utilization of secondary raw materials in high-performance AAC, characterized by higher bulk density and compressive strength than regular AAC. The increase in bulk density is achieved by increasing the content of quartz sand in the mixing water. In this study, part of the siliceous component was replaced by ladle slag, foundry sand, furnace lining, and chamotte block powder. These materials are generated as by-products in metallurgy. The substitution rates were 10% and 30%. The samples were autoclaved in a laboratory autoclave for 8 h of isothermal duration at 190 °C with a saturated water vapor pressure of 1.4 MPa. The physical–mechanical parameters were determined, and the microstructure was described by XRD and SEM analyses. The results were compared with traditional AAC, with silica sand being used as the siliceous component. The measurement results show that sand substitution by the secondary raw material is possible, and it does not have a significant impact on the properties of AAC, and in a proper dosage, it can be beneficial for AAC production.

In this study, the suitability of waste from glass fibre production as a secondary filler for a polymeric durable hydrophobic coating, based on an innovative polyurethane organic–mineral base, was experimentally verified. The main aim of this work was to develop a basic formulation for a polymeric hydrophobic coating designed primarily for usage in aggressive environments. For this purpose, a total of four formulations were tested with different weight percentages of waste glass fibre, i.e., from 30 to 60%. The basic properties in the fresh state, such as the coating workability and kinematic and dynamic viscosity, were verified, and an application test was performed. The formulations were also verified after the polymerisation of the coating. Adhesion on a concrete substrate and the tensile properties and hardness of the coating were tested. Chemical resistance to liquid aggressive media and the microstructure of the coating after exposure to SO₂ were also tested, as these are critical properties. All the formulations showed better workability than the reference coating without a filler, and the formulation with the highest filling (60%) appeared to be optimal. The maximum adhesion on the concrete substrate (11.9 MPa) and tensile strength (21.6 MPa) were recorded for the formulation with 60% waste fibreglass. It can be concluded that with an increase in the waste glass content, there was a significant improvement in the properties of the coatings. Additionally, the waste fibreglass did not have a significant negative impact on chemical resistance.

Silicate composites have very low conductivity in general. It is possible to achieve an electrical resistivity decrease by adding an electro-conductive filler. The conductive mixture consists of cementitious binder, various types of silica sand, and graphite-based conductive fillers. One of the research focusses is partial substitution of ordinary raw materials by alternative components (waste materials by-products and secondary raw materials) and its influence on composite properties. The alternative components studied were fly ash as a partial binder replacement, waste graphite from two different sources and steel shavings as a substitute for conductive filler. Resistivity of cured conductive silicate-based specimens was analysed in relation to changes in physico-mechanical properties in context of microstructural changes in the hardened cementitious matrix (by optical and scanning electron microscopy with energy disperse analysis). Partial substitution of cement by fly ash was found to reduce the electrical resistivity of the composite. Some of the waste graphite fillers significantly reduce the resistivity of the cement composite and increase the compressive strength. It was proven, that is possible to replace primary conductive fillers by secondary raw materials.

Cement composite materials with reduced resistivity are specialized building materials, which are constantly pushing their limits. Research into these composites requires a study of the influences of exposure conditions on resistivity. The mixes selected for the purpose of the research included the reference, pure cement mix, and mixes with proportions of graphite under and above the percolation threshold, with two different types of graphite. It was found that the resistivity of all the tested mixes decreases if moisture grows; the influence of moisture is more significant for mixes with graphite proportions below the percolation threshold. The resistivity of all the tested mixes decreases with increasing temperatures; the influence of a higher temperature (50 °C) is more significant for mixes with graphite proportions above the percolation threshold; however, these mixes are, at the same time, more resistant to permanent changes in resistivity caused by frost (−10 °C). It was found that the action of CO₂ causes a reduction in resistivity. Mixes with proportions of graphite above the percolation threshold show higher stability when exposed to CO₂. Mixes with proportions of graphite below the percolation threshold are extremely sensitive to horizontally oriented pressure loads. Increases in resistivity caused by vertical pressure loads were by 20–40%. The resistivity of the mixes with proportions of graphite above the percolation threshold was less sensitive to the pressure load.

New types of highly chemically resistant coating systems, primarily intended for concrete and metal substrates, were designed and experimentally verified in the paper. Secondary raw materials in optimal amounts, including solidified hazardous waste (e.g., end product and cement bypass dust), were used as microfillers. The polymer coating systems, containing pre-treated hazardous waste (HW), showed high abrasion resistance and excellent adhesion to metal and concrete surfaces. Based on polyurethane and epoxy resins, the coatings can be used in environments where aggressive chemical media act, such as sewers and the chemical industry. The developed polymeric coating systems showed even better properties than the compared reference coating systems. The chemical resistance of the three-layer coating systems was evaluated both visually and based on changes in mechanical properties, such as hardness and adhesion. The microstructure of the coating systems was also monitored using a digital optical microscope and a scanning electron microscope with energy dispersive X-ray analysis (SEM-EDX) after chemical stress. It was observed that the particles of HW were fully incorporated into the polymer matrix of the coating systems.