SYNTHESIS OF SULFATE-RESISTANT CEMENT THROUGH "GREEN" TECHNOLOGY USING KARAKALPAKSTAN RAW MATERIALS

RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 85 DOI: https://doi.org/10.5281/zenodo.17607432 SYNTHESIS OF SULFATE-RESISTANT CEMENT THROUGH “GREEN” TECHNOLOGY USING KARAKALPAKSTAN RAW MATERIALS Khadzhiev Azamat Shamuratovich Urgench State University named after Abu Rayhon Beruni, Urgench, H. Olimjon Street 14, 220100, Uzbekistan. [email protected] ABSTRACT This study investigates the synthesis and performance of sulfate-resistant Portland cement (SRC) clinker using local mineral resources from the Karakalpakstan region, emphasizing its technological, economic, and environmental importance. The raw mix—comprising limestone, barxan sand, kaolin, and iron-rich by-products— yielded a clinker with balanced oxide composition (LSF = 0.82, SR = 2.15, AR = 0.94). XRD analysis identified dominant alite (C₃S ≈ 38.6%) and belite (C₂S ≈ 41.0%) phases that ensure high mechanical strength, while the low tricalcium aluminate content (C₃A < 5%) and ferrite (C₄AF ≈ 16.2%) improved sulfate resistance and phase stability. Sulfate resistance tests (ASTM C1012/C1012M) confirmed that SRC cement showed the lowest expansion under 5% Na₂SO₄ exposure, indicating superior durability compared to ordinary Portland cement (OPC) and blended variants. These results demonstrate the effectiveness of local raw materials in producing high-quality SRC clinker suitable for the sulfate-rich conditions of the Aral Sea basin. Economically, the use of regional resources reduces production costs and reliance on imports, strengthening the competitiveness of the local cement industry. Environmentally, SRC’s longer service life and utilization of industrial by-products align with green and circular economy principles, reducing waste and promoting sustainable development. Keywords: sulfate-resistant Portland cement, clinker synthesis, mineral resources, sulfate resistance, green economy, sustainability. RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 86 QORAQALPOG‘ISTON XOM ASHYOLARI ASOSIDA “YASHIL” TEXNOLOGIYA BO‘YICHA SULFATGA BARDOSHLI SEMENT SINTEZI Xadjiyev Azamat Shamuratovich O‘zbekiston fanlar akademiyasi umumiy va noorganik kimyo instituti, 77 Mirzo Ulug‘bek ko‘chasi, 100170, Toshkent. [email protected] ANNOTATSIYA Ushbu tadqiqot Qoraqalpog‘iston mintaqasining mahalliy mineral resurslaridan foydalangan holda sulfatga chidamli portlandsement (SRC) klinkerining sintezi va uning xossalarini o‘rganishga bag‘ishlangan bo‘lib, texnologik, iqtisodiy va ekologik ahamiyatini yoritadi. Ohaktosh, barxan qumi, kaolin va temirga boy texnogen mahsulotlardan iborat xom aralashma natijasida oksid tarkibi muvozanatlangan klinker (LSF = 0,82; SR = 2,15; AR = 0,94) olindi. Rentgen fazoviy tahlil (XRD) natijalariga ko‘ra, klinker tarkibida alit (C₃S ≈ 38,6%) va belit (C₂S ≈ 41,0%) fazalari ustunlik qiladi, bu esa yuqori mexanik mustahkamlikni ta’minlaydi. Shu bilan birga, uch kalsiyli alyuminat miqdorining pastligi (C₃A < 5%) va ferrit fazaning (C₄AF ≈ 16,2%) mavjudligi sulfatga chidamlilik va fazaviy barqarorlikni oshirdi. ASTM C1012/C1012M standarti bo‘yicha olib borilgan sinovlar natijasida, 5% Na₂SO₄ eritmasida saqlangan namunalar orasida SRC sementida eng past kengayish kuzatildi, bu esa oddiy portlandsement (OPC) va aralash variantlarga nisbatan yuqori chidamlilikni ko‘rsatdi. Tadqiqot natijalari mahalliy xom ashyolardan foydalanib, Aralbo‘yi mintaqasining sulfatga boy sharoitlariga mos yuqori sifatli SRC klinker ishlab chiqarish imkonini tasdiqladi. Iqtisodiy jihatdan, mahalliy resurslardan foydalanish ishlab chiqarish tannarxini kamaytiradi va importga qaramlikni qisqartiradi, bu esa hududiy sement sanoatining raqobatbardoshligini oshiradi. Ekologik tomondan, SRC sementining uzoq xizmat muddati va sanoat chiqindilaridan foydalanish “yashil” va aylanma iqtisodiyot tamoyillariga mos kelib, chiqindilarni kamaytiradi va barqaror rivojlanishni qo‘llab-quvvatlaydi. Kalit so‘zlar: sulfatga chidamli portlandsement, klinker sintezi, mineral xom ashyo, sulfatga bardoshlilik, yashil texnologiya, barqaror rivojlanish. INTRODUCTION In recent years, the rapid development of the construction industry, particularly in the expansion of hydraulic structures, industrial facilities, and residential infrastructure, has significantly increased the demand for durable and long-lasting RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 87 types of cement and concrete. However, specific natural and geographical conditions in some regions pose unique challenges for construction materials. In the Republic of Karakalpakstan, especially in the Aral Sea region, soils and groundwater are characterized by high salinity, where the presence of sulfate ions (SO₄²⁻) poses a serious threat to concrete and reinforced concrete structures. Ordinary Portland cement-based concretes, when exposed to sulfate ions over a long period, form expansive products such as ettringite, which induce internal stresses, leading to cracking and deterioration. Therefore, the production of durable, long-lasting sulfateresistant Portland cement (SRC) has become a pressing necessity for the region. According to international and regional standards, strict requirements are imposed on the mineral composition of cement clinker to ensure sulfate resistance. One of the most critical parameters is the content of tricalcium aluminate (C₃A), which largely determines the sulfate resistance of cement. For instance, under O‘zM St 337:2024, the C₃A content in SRC should not exceed 5%, while according to GOST 22266-2013, it may be limited to as low as 3% in certain cases. Consequently, minimizing the C₃A phase—either by reducing the Al₂O₃ content or by increasing the Fe₂O₃ content in the clinker—represents one of the most effective approaches to enhance sulfate resistance. The Republic of Karakalpakstan possesses substantial scientific and practical potential in this regard. The region has large deposits of raw materials essential for cement production, including limestone (CaCO₃ ≈ 85–90%), kaolin (Al₂O₃ ≈ 36–38%), basalt, and iron-rich rocks. Rational utilization of these resources allows not only for achieving economic efficiency but also for producing high-quality SRC clinker adapted to the aggressive sulfate environments of the region. Consequently, the production and application of sulfate-resistant cement has become a critical requirement for the construction of buildings, reservoirs, sewage systems, and other engineering structures in the Aral Sea region. In international and regional standards, specific requirements are imposed on the mineralogical composition of cement clinker in order to ensure sulfate resistance. Among these, one of the most critical parameters is the content of tricalcium aluminate (C₃A). Studies have shown that the higher the proportion of the C₃A phase in cement, the more rapidly it reacts with sulfate ions, forming expansive products in concrete. For this reason, the C₃A content in sulfate-resistant Portland cement (SRC) is strictly limited to no more than 5%, and in some cases, it is required to be reduced to as low as 3%. Thus, in the production of sulfate-resistant cement, it is of great importance to control clinker composition—specifically, to minimize the C₃A phase either by RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 88 reducing the Al₂O₃ content or by increasing Fe₂O₃. This, in turn, requires careful selection of raw materials and precise proportioning of the raw mix. The Republic of Karakalpakstan possesses substantial opportunities for such scientific and practical work. The region contains large reserves of raw materials essential for cement production, including limestone, clay, basalt, and iron-rich rocks. Rational utilization of these mineral resources makes it possible not only to achieve economic efficiency but also to produce stable, high-quality sulfate-resistant Portland cement clinker that is well adapted to the aggressive sulfate environments of the region. The primary objective of this study is to synthesize sulfate-resistant Portland cement clinker based on the mineral raw materials of the Republic of Karakalpakstan, to determine its chemical and mineralogical composition, and to evaluate the influence of its phase structure on the sulfate resistance of the cement. The issue of producing sulfate-resistant Portland cement (SRC) has been at the center of attention for many researchers worldwide, since concrete made from ordinary Portland cement deteriorates rapidly under the action of sulfate ions, significantly reducing the service life of structures [1]. Consequently, most studies have focused on optimizing the mineralogical composition of SRC clinker, particularly by reducing the content of tricalcium aluminate (C₃A) [2, 3]. International research has demonstrated that minimizing the C₃A phase in clinker can be achieved either by reducing the Al₂O₃ content or by increasing Fe₂O₃. Shao et al. synthesized clinker dominated by ferrite phases due to a high Fe/Al ratio, showing a significant reduction in C₃A content and improved sulfate resistance of the cement [4]. Labidi, in his studies based on local resources, scientifically substantiated that optimization of the raw mix design can reduce C₃A content to below 5% [5, 6]. Khalifa and AlSadig tested the use of laterite additions to decrease C₃A, achieving effective results [7]. Costa et al. employed thermodynamic modeling to study clinker phase stability and demonstrated that high-ferrite cements are more advantageous in terms of sulfate resistance [8]. Furthermore, Santhanam, Cohen, and Olek carried out detailed investigations into the mechanism of external sulfate attack, with their two-stage studies confirming that the C₃A phase reacts with sulfate ions to form expansive products [9, 10]. Whittaker et al. observed microstructural changes in concrete under long-term sulfate exposure and reported that cements with lower C₃A contents exhibited superior durability [11]. González analyzed the behavior of cements incorporating limestone powder, highlighting the influence of mineral additions in SRC systems. Higgins, through long-term testing of cements blended with GGBFS (ground granulated blast furnace slag), demonstrated a substantial improvement in sulfate resistance [12, 13]. RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 89 Abubaker, however, noted that even SRC cements could deteriorate under extreme sulfate conditions during long-term storage in humid environments. It is evident that scientific efforts to improve sulfate resistance propose multiple approaches: increasing the Fe/Al ratio to enhance ferrite phase formation, reducing C₃A through laterite and other mineral additions, and employing supplementary mineral components such as slag and limestone. These methods have been extensively addressed in previous studies, and their findings can be effectively applied in the synthesis of SRC clinker [14]. Martínez Infante et al., in their research conducted in Spain, evaluated the technical and environmental efficiency of SRC clinkers incorporating novel auxiliary mineral components (iron-rich sand, slag, and “albero”) [15]. Their results indicated that partial replacement with up to 30% slag did not compromise the mechanical properties of cement but, in fact, enhanced its sulfate resistance. Similarly, Tiburzi et al. established that in Portland–limestone cements, the resistance to sulfate attack can be improved by the optimal incorporation of supplementary cementitious materials (SCMs) [16]. Neto et al. studied the interactions between clinker and gypsum, as well as other sulfate-containing additives, demonstrating that the SO₃ content significantly influences the sulfate resistance of cement [17]. These studies demonstrate that, in practice, the production of SRC clinker can be achieved not only through optimization of raw material composition but also through the rational use of supplementary mineral components and secondary materials. This approach contributes to improving ecological efficiency in the cement industry, reducing production costs, and lowering the carbon footprint. Research conducted in Uzbekistan, Kazakhstan, and neighboring regions has thoroughly examined the possibilities of producing sulfate-resistant cement from local mineral raw materials. These investigations have mainly focused on optimizing raw mix composition, controlling phase assemblage, and enhancing cement durability under sulfate environments. Studies based on local raw materials have scientifically substantiated that the synthesis of SRC can be achieved by incorporating basalt, kaolin, sandstone, and other silicate rocks into the raw mix, with Bogue calculations applied to maintain the C₃A content in the 3–5% range. Khadzhiev et al. analyzed the influence of sandstone additions on cement compositions and demonstrated that this leads to an increase in the belite (C₂S) phase while reducing the C₃A phase. Iskandarova et al. investigated the potential of using natural silicate rocks to reduce the carbon footprint in cement production, highlighting both ecological and economic advantages [18]. RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 90 The synthesis of sulfate-resistant Portland cement (SRC) clinker using local raw materials from the Republic of Karakalpakstan is of great importance not only from a technological perspective but also from economic and environmental standpoints. From an economic perspective, the use of limestone, barxan sand, kaolin, and iron-rich industrial by-products reduces dependence on imported raw materials and lowers production costs. This, in turn, enhances the competitiveness of the regional cement industry. The utilization of local raw materials not only improves technical efficiency but also reduces manufacturing expenses and contributes to the sustainable development of regional industry. Furthermore, reliance on local resources creates new investment opportunities and strengthens economic stability. Economic research also highlights that such approaches play a vital role in ensuring the effective use of resources in the development of the national economy [19]. From an environmental standpoint, SRC clinker demonstrates higher sulfate resistance compared to ordinary Portland cement (OPC), ensuring longer service life. This property is particularly beneficial in sulfate-rich environments, such as the Aral Sea region, where it helps to reduce frequent repairs or reconstructions of construction structures. As a result, resource consumption decreases and environmental impact is minimized. From the perspective of green economy principles, the long-term durability of SRC clinker and the effective utilization of industrial by-products ensure environmental sustainability. Moreover, these processes are consistent with modern economic approaches—particularly the concepts of the “green economy” and the “circular economy” [20]. In addition, the incorporation of iron-rich industrial by-products into the raw mix promotes the recycling of industrial waste, thereby putting into practice the principles of the “green economy” and “circular economy.” This process aligns with modern approaches to sustainable production and contributes to reducing the carbon footprint of the cement industry. Overall, the production of SRC clinker not only provides technological advantages but also ensures economic efficiency and environmental sustainability, demonstrating its potential as a promising material at both regional and national levels. METHODS The synthesis of sulfate-resistant Portland cement (SRC) clinker was conducted using locally available raw materials from the Republic of Karakalpakstan. The raw mix included limestone, barxan sand, kaolin, and an iron-rich by-product as the main components, with basalt and laterite as corrective additives. Laboratory-scale samples were produced at “Karakalpak Cement” LLC, and analyses were carried out at the RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 91 “STROM” Research and Testing Center, Institute of General and Inorganic Chemistry, Academy of Sciences of Uzbekistan. Chemical Composition: The chemical composition, determined according to O‘zM St 337:2024 and GOST 5382-2019 using classical titration and gravimetric methods, was as follows (wt.%): CaO – 61.09, SiO₂ – 22.10, Al₂O₃ – 4.98, Fe₂O₃ – 5.32, MgO – 2.07, SO₃ – 0.80, LOI – 1.14, Free CaO – 0.94. Calculated module values were: LSF = 0.82, SR = 2.15, AR = 0.94 — all within SRC normative limits. Mineralogical Composition (XRD): X-ray diffraction (Rigaku MiniFlex, Cu-Kα radiation) and Rietveld refinement identified the main clinker phases as: C₃S – 38.6%, C₂S – 38.0%, C₃A – 4.2%, and C₄AF – 14.8%, consistent with Bogue calculations and standard SRC composition. Testing Conditions: All analyses followed O‘zM St 337:2024 and GOST 5382-2019 [21,22]. Sulfate resistance was evaluated per ASTM C1012/C1012M by immersing specimens in 5% Na₂SO₄ solution and comparing their expansion to control samples stored in distilled water [23]. Duplicate control specimens ensured statistical reliability and isolated the effect of sulfate ions on dimensional stability and durability. RESULTS AND DISCUSSION The selection of raw materials for the synthesis of sulfate-resistant Portland cement clinker (SRC) has particular scientific and practical importance. In this context, the rational use of local resources is of great relevance. Within the Republic of Karakalpakstan, barxan sands, iron-rich by-product, kaolin, and limestone deposits represent promising sources. By analyzing their chemical composition, their role in shaping the mineralogical composition of SRC clinker can be assessed. In the synthesis of SRC clinker, the ratio of the major oxides in the raw mix is a key factor. Calcium oxide (CaO) contributes to the formation of alite (C₃S) and belite (C₂S) phases; silicon dioxide (SiO₂) provides the basis for silicate phases; aluminum oxide (Al₂O₃) promotes the formation of tricalcium aluminate (C₃A). At the same time, limiting the C₃A content to ≤5% is crucial for ensuring sulfate resistance. Iron oxide (Fe₂O₃) contributes to the ferrite phase (C₄AF) and plays an important role in reducing C₃A content. Thus, achieving the correct balance of oxides is decisive for enhancing the durability of cement in sulfate environments and ensuring long-term stability. The chemical composition of local raw materials by major oxides is summarized in (Table 1). RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 92 Table 1 Chemical composition of local raw materials selected for the synthesis of sulfateresistant portland cement Raw Material Chemical composition by major oxides (wt.%) SiO₂ Al₂O₃ CaO MgO Fe₂O₃ Na₂O K₂O TiO₂ SO₂ LOI Limestone – 0.15 53.14 2.56 0.12 – – – – 42.49 Barxan sand 89.22 3.15 0.68 2.32 0.97 0.94 0.70 0.24 0.20 1.61 Kaolin 54.07 16.47 0.85 2.57 9.93 1.72 – 0.17 – 9.23 Iron-rich byproduct 40.40 6.00 2.05 4.00 45.24 – 0.40 – 0.22 3.10 The chemical composition of these raw materials is suitable for ensuring the optimal balance required in the synthesis of sulfate-resistant Portland cement clinker. Barxan sands are characterized by a very high SiO₂ content (89.22%), which provides a primary source for silicate phases (e.g., C₃S and C₂S) and contributes to improved mechanical strength of clinker. However, due to their relatively low Al₂O₃ (3.15%) and Fe₂O₃ (0.97%) contents, these sands are mainly useful for increasing the silica modulus (SM). The iron-rich by-product contains a high Fe₂O₃ content (45.24%), which plays a critical role in forming the ferrite phase (C₄AF) and thus contributes to sulfate resistance by reducing C₃A content. Meanwhile, its SiO₂ (40.40%) and Al₂O₃ (6.00%) levels are moderate, allowing adjustment of the iron modulus (IM) in the raw mix. The low concentrations of alkali oxides such as Na₂O and K₂O (0 and 0.40%, respectively) reduce adverse effects during clinker hydration. Kaolin is enriched in Al₂O₃ (16.47%) and SiO₂ (54.07%) and serves as a key component in the formation of aluminate phases, including C₃A. However, because of its relatively high Al₂O₃ content, kaolin dosage must be carefully controlled to ensure that C₃A does not exceed 5% in clinker. Its Fe₂O₃ content (9.93%) and Na₂O (1.72%) levels are moderate, making it useful for adjusting the alumina modulus (AM). The low levels of SO₂ and TiO₂ (0 and 0.17%) do not compromise clinker quality. Limestone represents the primary source of CaO (53.14%), which is essential for the formation of alite and belite phases. Its negligible SiO₂ and Al₂O₃ contents (0 and 0.15%, respectively) make it an almost pure calcium source. The MgO (2.56%) and Fe₂O₃ (0.12%) levels are low and do not cause complications during clinker hydration. The high loss on ignition (LOI, ~42.49%) confirms the carbonate nature of limestone and indicates CO₂ release during calcination. RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 93 Overall, the mixture of these raw materials ensures the required oxide ratios for SRC clinker production, such as silica modulus (SM ≈ 2.0–2.5), alumina modulus (AM ≈ 1.0–1.5), and iron modulus (IM ≈ 1.0–2.0). However, to determine the optimal formulation, laboratory trials with raw mix proportions (e.g., barxan sand 15–20%, iron-rich by-product 5–10%, kaolin 10–15%, limestone 60–70%) are recommended. This approach maximizes the use of local resources and can potentially improve cement durability in sulfate environments by 20–30%. The successful balance of these raw materials is directly reflected in the chemical-mineralogical composition of the synthesized SRC clinker, since the oxide ratios strongly influence the resulting clinker phases (Table 2). As shown in the table, the overall clinker composition is dominated by CaO (61.09%), originating primarily from limestone, which provides the main portion of alite (C₃S) and belite (C₂S) phases that govern the strength and hydration characteristics of the cement. The SiO₂ content (22.1%) is at a moderate level and plays a crucial role in forming silicate phases, mainly derived from barxan sands and kaolin. Al₂O₃ (4.98%) and Fe₂O₃ (5.32%), contributed by kaolin and the iron-rich by-product, are responsible for the formation of aluminate and ferrite phases, respectively. Minor oxides such as MgO (2.07%) and SO₃ (0.80%) are present in low amounts, which helps to improve the stability of clinker in sulfate environments by minimizing undesirable reactions. The absence of Cl⁻ (0.0%) and the low content of free CaO (0.935%) enhance clinker resistance to corrosion, while the loss on ignition (1.14%) confirms the quality of the raw materials used. The total oxide balance (100.0%) indicates a well-optimized and complete composition. Table 2 Chemical and mineralogical composition of sulfate-resistant Portland cement clinker Material name LOI SiO₂ Al₂O₃ Fe₂O₃ CaO MgO SO₃ Cl⁻ CaO (Free CaO) Σ Portland cement clinker 1.14 22.1 4.98 5.32 61.09 2.07 0.8 0.0 0.935 100.0 Mineralogical composition (%) and module indices C₃S=38,64; C₂S=41,03; C₃A=4,17; C₄AF=16,16; CaO/SiO₂=2,76; LSF=0,86; SR=2,15; AR=0,94 In the mineralogical composition, the clinker is dominated by C₃S (38.64%) and C₂S (41.03%) phases, which primarily determine its mechanical properties. However, the relatively low content of C₃A (4.17%, ≤5%) is a key indicator of sulfate resistance, as it reduces the formation of ettringite. This is directly related to the limited proportion of Al₂O₃ in the raw materials. The presence of C₄AF (16.16%) reflects the high ferrite RESEARCH AND EDUCATION ISSN: 2181-3191 VOLUME 4 | ISSUE 9 | 2025 Multidisciplinary Scientific Journal October, 2025 100 formation of cement composite. 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