Olga Zemskova

Nowadays, mortars are building materials with various properties that can be achieved through the careful selection of components and the introduction of different modifying additives. An additive based on the TiO₂–Bi₂O₃ oxide system can be considered a modifying component with photocatalytic and biocidal properties capable of decomposing organic pollutants, viruses, bacteria, and fungal spores. The purpose of the work was to obtain cement compositions containing the additive, study their physical and mechanical properties, evaluate their photocatalytic activity in accordance with the UNI 11259-2016 standard, and assess their resistance to mold fouling. In this study, samples of cement–sand plaster with the TiO₂–Bi₂O₃ additive synthesized via citrate-based technology at 1.7 and 5.0 wt.% were prepared, and their physical, mechanical, photocatalytic, and biocidal properties were examined. As a result, the authors identified photocatalytic activity in both the UV and visible spectra, achieving 69% after 26 hours of UV irradiation. The samples demonstrated 100% resistance to mold fouling. The compressive strength of the modified samples increased by 32.0–39.0%; bending strength by 33–38.0%; and adhesion strength to the base by 60–70%. The cost calculation also confirmed the feasibility of introducing the additive at 1.7 wt.% into the cement composition. The resulting cement material formula can be recommended for designing fungi-resistant, self-cleaning plasters.

The use of superplasticizers in a self-compacting concrete mix without the addition of a foaming agent in practice leads to a well-known problem associated with increased air entrainment and promotes the formation of harmful large bubbles, high-void content, and ununiform appearance. This paper presents research on the properties of cement paste consisting of Ordinary Portland Cement (OPC), powder based on ground granulated blast furnace slag (GBBS), and superplasticizer. The methodology of this study was the estimation of flow diameter and flow time, as well as the evaluation of the rheological characteristics. The influence of ground granulated blast furnace slag and polycarboxylate plasticizer on the flowability and viscosity of cement paste was studied. The effect of superplasticizer (SP) based on polycarboxylate esters (PCE) anti-foaming agent (AFA) based on a glycol ester and air-entraining admixture (AEA) based on an amphoteric surfactant on flowability, viscosity, rheological properties and the strength of the cement paste was evaluated. It was found that the increase of slag content in cement paste (25%) with the presence of superplasticizer (0.64%) significantly changes the flowability and viscosity. It was stated that the addition of 0.04% anti-foaming agents increases flowability (20%) and reduces viscosity (44%) of cement paste. It was stated that the addition of small dosages of glycol ester-based anti-foaming agent (0.02 and 0.04%) significantly changes the rheological properties, decreases the shear yield stress by 2.1–2.8 times, the plastic viscosity by 2.4–2.6 times and apparent viscosity 1.6–2.5 times, improves the compressive strength at the age of 1 and 7 days by 2.5 and 1.4 times, respectively. The addition of air-entraining admixture led to a decrease in the plastic viscosity by 1.2–1.4 times. It was stated that the presence of air-entraining admixture assists in increasing the apparent viscosity by 1.7–2.4 times. It was shown that the presence of complex admixtures of various origins, purposes, and mechanisms of action would assist in predicting the behavior of concrete mixtures under the conditions of the building site and reduce the consumption of polycarboxylate esters due to the enhancing plasticizing effect of anti-foaming agent and air-entraining admixture.

To solve a number of problems in construction materials science, composites with nano and ultrafine admixtures were analyzed. Their properties were studied, taking into account the variants of homogenization and stabilization of the system. To characterize the processes of the structure formation of a new material, mathematical methods were also applied. According to the literature review, the aim of the work was formulated. The subject of this research is to conduct physico-chemical studies that characterize the processes occurring during the homogenization and stabilization of the cement system with GGBS components and to establish the effect of the admixture on the properties of the composite. To achieve this goal, an ultrafine admixture based on GGBS was obtained, and the possibility of its introduction into the cement system in the form of a stabilized suspension instead of mixing water was considered. To provide increased characteristics of cement stone modified with the ultrafine admixture, a number of tests were carried out to study homogenization and stabilization of fine slag particles in suspension. The ultrasonic processing parameters were defined to provide uniform distribution of fine slag additive in the suspension: the processing time is 15–20 min, the frequency of ultrasonic vibrations is 44 kHz, the temperature of the dispersed medium is 25 ± 2 °C. To define physical and chemical processes appearing during the introduction of fine slag into water and water-polymer dispersed medium, the mechanism of interaction between fine slag and water was studied. In addition, the mechanism of chemisorption on the surface of fine slag particles and the stabilization mechanism of ultrafine slag particles with a plasticizer was studied to form the concept of aggregate and sedimentation stability of slag particles in suspension. It was found that the stabilization of fine slag particles by a plasticizer is significantly influenced by the hardness of water. The higher the water hardness, the more plasticizer required to stabilize the fine slag particles. At the same time, it was established that the concentration of the plasticizer should not exceed the critical micelle concentration value. If it is exceeded, the plasticizer solution transforms into the micellar colloidal system, and the stabilization of fine slag suspension will not occur. The studies of homogenization and stabilization of the slag suspension allowed the authors to substantiate the possibility of uniform distribution of fine particles in the cement matrix, followed by the formation of a denser and stronger cement stone structure. Cement-sand samples based on Portland cement (OPC) and slag-Portland cement (SPC) with GGBFS admixture showed higher compressive and flexural strength characteristics in the initial hardening periods and at 28 days. It was found that modified samples are more stable in an aggressive medium. On the 90th day of exposure, the resistance coefficient was 0.9 for a modified sample based on OPC and 0.98 for a modified sample based on SPC. The increased sulfate attack resistance of the samples is due to the formation of a dense stone with reduced porosity. It is noted that the porosity of modified OPC samples decreases by 14% and by 18% for SPC-based modified samples compared to the control sample at 28 days. Due to the fact that pores in the cement stone are blocked with hydration products, which make the structure of the cement stone denser, the filtration of aggressive solutions deep into its structure is difficult. Thus, the obtained concrete based on a cement composite with ultrafine slag can be applied as a protective layer of steel reinforcement in a reinforced concrete structure.

The possibility of using a nano-aluminum component in the cement composition has been considered. To ensure uniform distribution of the nano-aluminum component throughout the cement matrix, its suspension was stabilized using a sulfonaphthalene formaldehyde-based plasticizer and acoustic cavitation. It has been established that the nano-Al₂O₃ suspension is best stabilized when adding a plasticizer in an amount of 3-5 g/l and after an acoustic exposure at the optimal dispersion parameters: dispersion temperature–25±2 °C (the process is thermostated); dispersion time–20 minutes; and oscillation frequency-44 kHz. The study has shown that the compositions modified with a nano-aluminum component have improved strength and structural properties. On the first day of hardening, the compressive strength of the modified specimens increased by 20-24 % and at the grade age–by 31-35 % compared to the reference one. Introducing the stabilized nano-Al2O3 particles reduces the porosity for the first day of hardening by 12-13 % and at the grade age–by 27-29 %. It is recommended to add a nano-aluminum component as a stabilized suspension in an amount of 0.5-1.0 g/l to the cement composition.

The paper discusses the relevance of the use of metallurgical wastes crushed to a fine state in the production of building materials. Domain granulated slag (DGS) was used as a research object. A method for introducing fine ground slag (FGS) into the cement composition in the form of a slag suspension instead of mixing water has been developed. To establish the uniform distribution of FGS particles in the cement matrix, the behavior of slag particles in an aqueous dispersion medium was previously studied. The optimal parameters of ultrasonic dispersion of slag suspensions are established: the frequency of ultrasonic vibrations is 44 kHz; temperature of dispersion - 25±2°C; dispersion time - 15 min. It has been established that the application of UST to slag suspensions with the observance of optimal dispersion parameters can increase the aggregative and sedimentation stability of the FGS suspension by 2–3 times as compared with mechanical mixing, accelerate the micelle formation process, and enhance the electrostatic factor of aggregative stability.