PHYSICAL AND MECHANICAL PROPERTIES OF MULTI-COMPONENT HARDENING ACCELERATOR CEMENT STONE

SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 10 OCTOBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 62 PHYSICAL AND MECHANICAL PROPERTIES OF MULTICOMPONENT HARDENING ACCELERATOR CEMENT STONE A.A. Bekmurodov1, F.S. Ismailov2 LLC “LUKOIL UZBEKISTAN OPERATING COMPANY”- a foreign enterprise. Chemicalanalytical laboratory assistant1 Senior researcher, doctor of technical sciences Tashkent Research Institute of Chemical Technology2 https://doi.org/10.5281/zenodo.17451693 Abstract. The article presents the results of studying the influence of a highly effective multi-component local additive that accelerates the hardening of cement concrete on the properties of cement and concrete. The effect of this additive on the cement hardening process, the kinetics of strength development, as well as on the structure and morphological characteristics of the hardening cement stone has been evaluated. Keywords: hardening and hardening accelerators; setting time; strength; heat release. Introduction Under conditions of high construction rates, accelerators of concrete setting and hardening are attracting increasing attention among the means that control the kinetics of cement hydration. Although their use is often necessary, in some cases it may lead to adverse effects on concrete. The use of chlorides can cause corrosion of steel reinforcement, while potassium and sodium salts may lead to alkali corrosion. There are also accelerators based on organic substances, such as diethanolamine and triethanolamine, calcium salts of formic and acetic acids, and various carboxylic acids [1–2]. The disadvantages of such accelerators include their relatively high cost and selective efficiency depending on the dosage and the type of cement used. Accelerators for shotcrete (sprayed concrete) possess specific properties. In the shotcreting process, the concrete mix is sprayed under pressure onto the treated surface using a special device (shotcrete machine) and is compacted by the impact energy [3]. To ensure high-quality shotcrete, accelerators that promote rapid setting and hardening play a decisive role. Unlike ordinary concrete, in shotcrete, accelerators are almost an integral component of the mix. The dosage of accelerators in shotcrete is higher than in conventional concreting and usually amounts to 3–6% of the cement mass. A distinctive feature of accelerators used for shotcrete is their ability to cause instant setting, which prevents the mixture from sliding and allows for the application of thicker layers. Figure 1. General structure of a polycarboxylate superplasticizer SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 10 OCTOBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 63 As noted in [4], the mechanism of action of polycarboxylate polymers in water–cement systems is associated with a “steric hindrance” effect that occurs during the coagulation of cement hydration products. Such superplasticizers have been proposed to be called “comb polymers.” These types of admixtures have been systematically studied over the past decade and have found widespread practical application. It should be emphasized that high-performance superplasticizers are produced based on polycarboxylates. At low concentrations and water–cement ratios, the strong dispersing (thinning) effect of polycarboxylates leads to an increase in the early strength of concrete and enables the production of self-compacting concrete without vibration. It should also be noted that the strong dispersing effect of polycarboxylate additives is achieved at significantly lower dosages compared to conventional superplasticizers. When polycarboxylates are introduced into concrete mixtures together with the mixing water, the workability of the mixture increases considerably, making them suitable for use in monolithic concrete production as well as in the manufacture of prefabricated reinforced concrete structures. The selection and use of such plasticizers represent an effective and progressive direction in the development of concrete plasticization technology [5]. In recent decades, significant advances have been achieved in concrete technology, associated with the development of new types of concrete possessing high performance characteristics — including high-strength, durable, and self-leveling concrete mixtures. In this progress, organic admixtures have played a crucial role, and according to some studies [6], they are considered even more important than the cement itself. The following materials were used in the study. Research Methodology. The synthesis of the superplasticizer was carried out at a reaction temperature of 70°C for 5 hours using a stirring apparatus. During the process, an initiator was added dropwise to the mixture. The reaction was maintained at 80°C in a thermostated water bath. The final product of the superplasticizer was obtained as a 35% aqueous solution, which was then cooled and neutralized with NaOH to achieve a pH of approximately 8. In these experiments, the 35% superplasticizer solution was added in an amount corresponding to 1% of the liquid phase, which equals 0.2–1% of the cement mass in terms of dry matter. The main purpose of the research was to determine the optimal dosage of the additive that provides the best strength characteristics of the concrete mixture. As the dosage of the plasticizer increased from 0.2% to 1%, the strength class of the concrete mixture improved from P2 to P5. The research results showed that when the amount of the superplasticizer was 1% (in solution form), the optimal effect on the mixture was achieved. Observations of the concrete strength at 3, 7, and 28 days demonstrated that samples containing 1% superplasticizer exhibited a continuous increase in strength up to 28 days. During this period, the reduction of water demand due to the presence of the superplasticizer led to a denser cement stone structure, which ultimately resulted in increased strength at 28 days. Results and Discussion. To analyze the changes in the workability of cement stones depending on the structure of polycarboxylate compounds, a PC polycarboxylate superplasticizer was synthesized. In this study, comparative tests were conducted between the synthesized polycarboxylate-based superplasticizer and the naphthalene–sulfonate–formaldehyde (NSF) superplasticizer produced from local raw materials. The flowability of the cement paste was determined using a slump cone test, while the workability of the concrete mixtures was observed after 30 and 60 minutes. The compressive strength of the samples was measured after 3, 7, and 28 days under standard pressing conditions. For testing, samples were prepared in molds measuring 10×10×10 mm. The concentration of the concrete mixture, water–cement ratio, as well as its rheological and strength characteristics, are presented in Table 1. SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 10 OCTOBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 64 1-table. Study of the strength properties of concrete with added superplasticizers № Name of Superplasticiz er Additiv e Amoun t, % Water/Ceme nt Ratio Slump, cm Densit y, kg/m³ Strength, MPa 0 mi n 30 mi n 60 mi n 3 daily 7 daily 28 daily 1 PK (Polycarboxyla te superplasticize r) 1% 0.42 28 19 17 2520 18.5 0 24.2 0 36.4 0 2 NSF (Naphthalene sulfonate formaldehyde superplasticize r) 1% 0.42 17 12 8 2240 19.0 2 15.6 10.5 The synthesis of the PK polycarboxylate superplasticizer allows for an increase in the water–cement ratio efficiency and workability, enabling the production of high-quality concrete products. The concrete mixture containing 1% NSF superplasticizer exhibited a slump of 17 cm, while the mixture with 1% PK superplasticizer achieved a slump of up to 28 cm, indicating improved flowability. At a water–cement ratio of 0.42, the concrete mixture with the PK polycarboxylate superplasticizer showed a slump decrease from 28 cm to 17 cm within 60 minutes, while the NSF-based mixture lost its workability completely after 30 minutes. The addition of superplasticizers reduces water demand, thereby contributing to a higher concrete strength. The increase in strength was studied at a water–cement ratio of 0.43, and after 3, 7, and 28 days, the compressive strengths were recorded as follows:  PK: from 18.50 MPa to 36.50 MPa  NSF: from 19.02 MPa to 10.50 MPa It should be noted that with the PK superplasticizer, the compressive strength increased steadily over time, reaching 6.7 MPa in daily growth rate, compared to 4.7 MPa for the NSF admixture. From an economic and technological standpoint, the synthesized PK polycarboxylate superplasticizer, being a water-soluble additive, provides better solubility and dispersion effects compared to conventional water-reducing admixtures. The fluidity of the concrete mixture improves proportionally with the polycarboxylate content. Materials used: 1. Portland cement 42.5 N, phase composition (wt.%):  Alite (3CaO·SiO₂): 52–53%  Belite (2CaO·SiO₂): 18–20%  Intermediate phases (3CaO·Al₂O₃ + 4CaO·Al₂O₃·Fe₂O₃): 20–22%  Gypsum (CaSO₄·2H₂O): 3–4%  Anhydrite (CaSO₄): 1% SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 10 OCTOBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 65  CaCO₃: 2%  Al₂O₃ content in cement: 4.9 wt.% 2. Fine aggregate (sand) with a particle size modulus Mk = 2.5. 3. Setting Accelerators: PK, Meycosa 167, Sigunite L-53, Relamix Torkret. Tests on the effectiveness of setting and hardening accelerators were carried out using a cement mortar mixture. The mix composition was 1:3 (cement:sand) with a water–cement ratio of 0.40. The additive contents, relative to the cement mass, were as follows:  PK superplasticizer: 0.4%  Setting accelerator: 6% Preparation procedure: The PK superplasticizer was first mixed with water. The remaining components were then added in the following order and mixed according to the set schedule:  Cement – 30 seconds  Sand – 60 seconds  Pause – 90 seconds  Final mixing – 30 seconds The slump flow of the mixture was observed to be 170–190 mm. Afterward, the setting accelerator was introduced, and the mixture was stirred for 10 seconds. Immediately after mixing, the mortar was placed into the ring of a Vicat apparatus and compacted on a vibration table for 10 seconds. Subsequently, the setting time was determined in accordance with GOST 310.3, and from the remaining mixture, samples measuring 40×40×160 mm were prepared. The samples were cured in a normal hardening chamber (at 100% relative humidity and 20°C) and tested for compressive strength after 6 hours, 1 day, and 28 days. 2-table. Effect of non-alkaline setting accelerators on cement mortar strength Sample Compressive Strength, MPa 6 hour 1 day 28 days Sample 0.40 12.6 45.3 PK 0.70 17.0 49.0 Meycosa 167, 0.70 16.0 45.0 Sigunite L-53 0.60 13.7 45.0 Effect on the Strength of Cement Stone. The study of cement stone hardening rate showed that clay containing montmorillonite causes the greatest reduction in strength at both the initial and final stages of setting. After 28 days of normal curing, the introduction of montmorillonite reduced the compressive strength of cement stone by 17%. According to the standard GOST 24211-2008 “Additives for Concretes and Mortar Mixtures: General Technical Requirements”, the use of superplasticizers to improve workability is permitted only when the strength reduction does not exceed 5%. Therefore, the use of polycarboxylate-based superplasticizers in concretes made with sands containing montmorillonitic clays is ineffective. Clays composed of hydromica and kaolinite minerals slightly reduce strength during the early stages of hardening (up to 7 days); however, no significant strength reduction is observed at later stages of hardening. In general, all studied clays, when treated with polycarboxylate superplasticizers, reduced the cement stone strength by up to 33% on the first day of hardening, similar to montmorillonitecontaining clays. Cement stone treated with hydromicas and ASE 430 superplasticizer showed a SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 10 OCTOBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 66 strength decrease of only 6.5% after 7 days and 3% after 28 days. Kaolinite clay caused a 11.7% decrease in strength after 7 days, but the reduction after 28 days did not exceed 3% for mixtures plasticized with ASE 430.Thus, the use of sands containing up to 2% kaolinite and hydromica clays does not adversely affect the efficiency of polycarboxylate superplasticizers in concrete production. When finely dispersed limestone was used as a mineral additive in self-compacting concrete and self-leveling floor mixtures, visible gas release was observed, leading to a reduction in strength compared to mixtures with other fillers. In contrast, mixtures containing micro-silica (silica fume) and stone powder derived from siliceous rocks did not exhibit this effect. This experiment confirms that limestone interacts with plasticizing additives, which in turn reduces the physical and mechanical properties of the resulting concretes. 3-table. Physical and mechanical properties of concrete Type of Filler Consumption of microfiller additive Compressive Strength, MPa (days) 3 7 28 Limestone powder 36 31.2 33.1 34.4 Crushed hard rock powder 37 33.8 37.0 41.8 The conducted studies have shown that the use of finely dispersed limestone as a mineral additive in concretes containing three main classes of plasticizing admixtures leads to gas formation. This effect is caused by the interaction between these components. The research identified the mechanism of this interaction, suggesting that the reactivity may be related to the carbonate components present in the limestone and the amount of mineral admixtures introduced into the mix. Conclusion In modern construction, mineral additives are regarded as an essential component of concrete used for high-performance and structural applications, as they help improve various technical properties. Crushed rocks, often considered inert fillers, such as finely dispersed limestone, may actually react when combined with superand hyperplasticizers, particularly in the hydrating cement environment, resulting in the formation of a gas phase. The rheology of the system influences gas evolution — as viscosity decreases, for instance, during the production of self-leveling mixtures, this process can become significantly more intense. In such cases, the microfiller function of fine additives may not be fully realized, and their optimal dosage might not yield the expected positive effects on the structure and properties of concrete. Therefore, it is crucial to evaluate the compatibility and interaction of mineral and chemical admixtures, especially since this aspect has not yet been sufficiently studied in current construction materials science. REFERENCES 1. Batrakov, V. G. Modified Concretes: Theory and Practice. Moscow: Stroyizdat, 1998. 768 p. 2. 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