http://www.press.ierek.com ISSN (Print: 2537-0154, online: 2537-0162) Proceedings of Academic Research Community pg. 1 Research Paper Received: 27 May 2024, Accepted: 4 August 2024, Published online: 29 August 2024 DOI: 10.21625/archive-sr.v8i2.1086 Life Cycle Analysis Comparison of Stabilizing Materials for Expansive Soils Zied Benghazi1, Rima Tobal2, Adel Djellali3 1,2,3 Environment Laboratory, Department of Mining and Geotechnology, Mining Institute, Echahid Cheikh Larbi Tebessi University, Algeria Abstract Expansive soils present significant challenges to infrastructure stability, necessitating the use of stabilizing materials. This study conducts a comprehensive life cycle analysis (LCA) research design to evaluate the environmental sustainability of various stabilizing materials for expansive soil. The study uses a quantitative analysis assessing materials, including cement, limestone, natural pozzolana, iron ore tailings, and geopolymers (especially alkali- activated slag cement). The method involves a comprehensive LCA, considering phases from raw material extraction through production, use, and disposal. The analysis reveals distinct differences in environmental impact. Cement and lime, common stabilizers, show a high carbon footprint. Natural pozzolana and iron ore tailings exhibit potential as supplementary cementitious materials with reduced environmental impact. Geopolymers, particularly alkali-activated slag cement, offer promising alternatives with lower carbon emissions. This research contributes insights into sustainable geotechnical practices, guiding material selection aligned with environmental goals for effective expansive soil stabilization. © 2024 The Authors. Published by IEREK Press. This is an open-access article under the CC BY license (https://creativecommons.org/licenses/by/4.0/). Peer review under the responsibility of ARChive-SR’s International Scientific Committee of Reviewers. Keywords Environmental Sustainability; Expansive Soil; Stabilizing Materials; Life Cycle Analysis 1. Introduction Expansive soils (ES) pose serious challenges to the stability of infrastructures worldwide due to the presence of clay minerals susceptible to volume changes under moisture content variation. These soils undergo significant swell-shrink behavior when they are exposed to alternate periods of wetness and dryness, leading to severe structural damage to civil engineering works. This dynamic behavior makes the ES significantly impact the durability and safety of infrastructures. In response to these challenges, geotechnical engineers have adopted various soil stabilization techniques to prevent the damaging effect of ES. Stabilizing materials, such as binders and pozzolanic materials, are commonly used to enhance the ES properties and minimize volume changes over time. The utilization of materials that minimize the environmental impact of ES stabilization contributes to sustainable construction practices. Numerous studies have investigated the environmental effects of traditional stabilizing agents, such as cement and lime. Cement, a widely employed stabilizer, has been subjected to examination due to its high carbon footprint during production (Ellis et al., 2020). Previous research by Chang et al. (2019) and Garcez et al. (2024) have explored the https://crossmark.crossref.org/dialog/?doi=10.21625/archive-sr.v8i2.1086&domain=press.ierek.com http://www.press.ierek.com/ https://creativecommons.org/licenses/by/4.0/ Benghazi/ Proceedings of Academic Research Community pg. 2 carbon footprint associated with cement-based stabilization and emphasized the need for alternative materials with lower environmental impact. On the other hand, the literature suggests that natural pozzolana (NP) and iron ore tailings (IOT) can be used as supplementary cementitious materials with reduced environmental impact. Studies by Ghadir & Ranjbar (2018), Bahadori et al. (2018), and Soğancı et al. (2023) demonstrated the viability of these materials in enhancing the mechanical properties of ES while minimizing their environmental footprint. Geopolymers, particularly alkali-activated slag cement, have garnered attention as a promising alternative with lower carbon emissions (Zeghichi & Benghazi, 2011; Benghazi et al., 2022). The work of Disu & Kolay (2021) shows the potential of geopolymers in sustainable soil stabilization. Understanding the environmental advantages offered by these newer materials is important to guide geotechnical practices toward more sustainable solutions. In that context, researchers have also conducted several studies on the possibility of recycling mine ore tailings to use them as stabilizing materials, such as lead-zinc ore tailing (Odumade et al., 2022) and IOT (Osinubi et al., 2015). However, their environmental sustainability has not been comprehensively explored. As infrastructure development continues to escalate globally, understanding the ecological impact of soil stabilization becomes a necessity. This study aims to investigate the sustainability of different stabilizing materials, contributing valuable insights into sustainable geotechnical practices. A life cycle analysis (LCA) is conducted to evaluate and compare the environmental impacts of IOT with natural pozzolana and alkali-activated slag cement, as well as with high carbon footprint conventional materials: cement and lime. The LCA provides a holistic approach by considering the environmental implications of these materials, from extraction to their final disposal after use. This work’s findings provide recommendations for environmentally sustainable geotechnical techniques. 2. Materials and Methods The LCA is led on one tonne of ordinary Portland cement (OPC), Lime (LL), IOT, NP, and alkali-activated slag cement (AASC), with a specific surface area ranging from 3000 to 3500 cm2/g. Tables 1 and 2 illustrate the physical properties and chemical composition of the studied materials. As their production process varies, their environmental impact also varies (Fig. 1). The LCA encompasses the different life cycle phases of each stabilizing material. This includes raw material extraction, energy consumption, transportation, water consumption, and carbon footprint. Table 1: Provenance and physical properties of studied materials. Material Provenance Color Bulk density (kg/m3) Specific gravity Surface area (cm²/g) OPC (CEM II/A) Cement plant of Tebessa, Algeria Grey 1371 3.18 3500 LL Eastern cement & derivatives company, Constantine, Algeria White 791 3,345 3080 NP Beni Saf, Algeria Brown 1030 2.72 3430 AASC Granular blast furnace slag of El Hadjar steel factory, Annaba, Algeria Greyish 927 1.85 3350 IOT Boukhadra Iron Mine, Tebessa, Algeria Brown 1853 3.95 3410 Table 2: Chemical composition of studied materials (% wt.). Material SiO2 Al2O3 Fe2O3 CaO MgO K2O SO3 Na2O Cl- LOI OPC 27,430 05,400 03,480 53,710 01,410 00,920 02,590 00,160 00,004 01.790 LL 01.400 03.540 00.790 81.860 02.130 00.190 00.160 00.062 - 00.270 Benghazi/ Proceedings of Academic Research Community pg. 3 NP 46,250 17,340 10,260 10,180 02,900 01,640 00,800 03,640 00,010 04.480 AASC 39,700 09,260 01,470 40,250 04,130 00,890 00,590 00,140 00,004 01.590 IOT 20.010 06.000 43.160 02.540 00.390 00.280 01.330 - - 02.420 Figure 1: The studied materials’ manufacturing flow chart: (a) OPC production; (b) LL production; (c) NP powder, AASC, and IOT powder production 3. Life cycle analysis and discussion 3.1. Raw materials extraction OPC primarily comprises 80% limestone and 20% clay (Aïtcin, 2016; Benghazi et al., 2022). The extraction of limestone, a pivotal component, poses a significant environmental impact during quarrying due to processes like blasting and haulage, leading to the emission of dust and CO2. Similar environmental implications arise in the extraction of LL and NP. Conversely, IOT are byproducts of iron mining activities and are not extracted independently. The IOT from the Boukhadra mine consists of rocks and particles of varying sizes, with a substantial content of low-grade ore exceeding 30 million tonnes (Rouaiguia et al., 2017). Granulated blast furnace slag (GBFS) is also a byproduct that results from the steel manufacturing process and does not directly contribute to pollution. Consequently, the transportation phase becomes the focal point for potential pollution of IOT and GBFS in this life cycle phase. In optimizing this transportation stage, the utilization of rail transport emerges as a more advantageous choice than trucks. This choice not only proves economically advantageous but also aligns with low carbon emissions practices. By prioritizing rail transport, we can mitigate the environmental impact associated with the movement of raw materials, thereby fostering a more sustainable and eco-friendly approach. 3.2. Raw materials grinding and calcination Both grinding and calcinating of the different raw materials for OPC are electricity-consuming processes. The calcination of the clinker in kilns (about 1450°C) is the most polluting phase in OPC manufacturing, with about 0.83 tonnes of CO2 per tonne of clinker (Antunes et al., 2022) due to both the fuel combustion and the decomposition of calcium carbonates (CaCO3) lime during this phase. The same for the Limestone calcination at a temperature of 900 to 1200 °C, with 1.8 tonnes of CO2 per tonne of LL (Greco-Coppi et al., 2023). in the case of this work’s chosen materials, the complete decomposition of LL calcium carbonates (CaCO3) would produce about 50% more CO2 per tonne (≈ 1.251 tonnes CO2/tonne) compared to clinker. The (CaCO3) occurs at a minimum temperature of 900°C (Fig. 2). Benghazi/ Proceedings of Academic Research Community pg. 4 Figure 2: Transformation of raw meal into clinker (Aïtcin, 2016) 3.3. Final Grinding During this stage in OPC manufacturing, the amalgamation of final ingredients (mineral additions and clinker) takes place, which is accomplished through the grinding and mixing process utilizing ball mills. Clinker demands approximately 40 kWh/tonne to achieve a specific surface area (SSA) of 3500 cm²/g, which is approximately equal to 60% of the total energy consumption in OPC plants (Benghazi et al., 2022). In contrast, the entire manufacturing process of GBFS cement consumes 43.52 kWh/tonne (Ciments Lafarge, 1999). This divergence in energy consumption underscores the distinctive energy profiles associated with these materials, emphasizing the importance of considering energy efficiency in the manufacturing process. In this study, both IOT and NP underwent laboratory grinding. Notably, IOT exhibited a grinding time comparable to that of GBFS, indicating similar processing requirements. Conversely, NP necessitated a more extended grinding duration, approximately 1.5 times longer than GBFS, to achieve the targeted SSA. This difference in grinding times depends on the material's chemical composition, porosity, and mineralogical properties. Tables 3 and 4 present the energy consumption and the carbon footprint of the studied stabilizing materials, respectively. Table 3: Energy consumption estimation of studied stabilizing materials based on Wächter et al. (2021) and Simoni et al. (2022) work Material Energy Consumption (kWh/tonne) OPC 110,28 LL 20 to 50 NP 62.64 AASC 46.32 IOT 46.34 Table 4: Carbon footprint estimation of studied stabilizing materials based on Wächter et al. (2021) and Simoni et al. (2022) work Material Carbon footprint (tonnes CO2/tonne) OPC 0.834 LL 1.0 to 1.8 NP 0.150 AASC 0.140 IOT 0.150 Benghazi/ Proceedings of Academic Research Community pg. 5 3.4. Water consumption Water consumption in OPC manufacturing plants varies widely, spanning from 0.14 to 1.28 L/kg of cement (Nydrioti et al., 2023). As depicted in Figure 3, the water demand of the investigated stabilizing materials is showcased. OPC demands 28% of water to achieve normal consistency, a factor that significantly influences its water consumption. Pozzolanic materials exhibit a positive impact on reducing water demand, particularly evident in the cases of NP and Industrial IOT. Additionally, AASC, formulated using NaOH as an activator with a concentration of 5 mol/L, demonstrates a lower water demand compared to OPC. This is attributed to the small Ca/Si ratio (Zeghichi & Benghazi, 2011), signifying a crucial aspect of environmental stabilization. The diminished water demand implies that less water is required for the stabilization process when employing AASC, NP, and IOT, compared to OPC and LL. While geopolymers and pozzolanic materials (AASC, NP, and IOT) exhibit a slower development of early mechanical strength in comparison to soil stabilized with cement, it is notable that these materials continue to enhance their long- term mechanical strength beyond the conventional 28-day period (Zeghichi & Benghazi, 2011; Ahmed et al., 2019). This characteristic highlights the enduring and sustainable nature of these alternative materials in the stabilization context, emphasizing their potential for long-term infrastructure resilience. Figure 3: Water demand of the different studied stabilizing materials Table 5 provides a comparative overview of the environmental impact of OPC, LL, NP, and AASC based on data from existing literature. It can be noticed that the current study values from Tables 3 and 4 are generally consistent with those found in the literature. However, it is important to note that some values are not reported in the literature, particularly those for IOT. This gap is attributed to the relatively nascent stage of research in utilizing IOT as a stabilizing material. Therefore, the current findings of the present paper contribute valuable preliminary data, offering a foundation for further exploration and validation. Table 5: Summary of literature review on OPC, LL, NP, and AASC as stabilizing materials Material Reference Energy consumption (kWh/tonne) Carbon footprint (tonnes CO2/tonne) Water demand (%) OPC Wächter et al. (2021) 110.28 0.834 - Simegn et al. (2021) - - 0.26 to 0.33 LL Simoni et al. (2022) 20 to 50 1.0 to 1.8 0.40 NP Heath et al. (2014) - 0.004 to 0.435 - AASC Black (2016) - 0.052 to 0.143 - Zeghichi et al. (2011) - - 0.19 Benghazi/ Proceedings of Academic Research Community pg. 6 4. Conclusions This life cycle analysis (LCA) compares the environmental impact of expansive soil stabilizing materials, emphasizing the need for sustainable geotechnical practices. Traditional stabilizers like cement and lime exhibit high carbon footprints, prompting the exploration of alternative materials. NP and IOT emerge as eco-friendly options, offering reduced environmental impact as supplementary cementitious materials. Geopolymers, especially alkali-activated slag cement, present lower carbon emissions The LCA encompass and diminished water demand, making them promising alternatives for environmental stabilization. Consideration of energy efficiency during raw material extraction, grinding, and final manufacturing stages underscores the importance of sustainable material selection. While geopolymers and pozzolanic materials exhibit slower early mechanical strength development, they compensate with continued long-term mechanical strength enhancement, showcasing their potential for enduring infrastructure resilience. Acknowledgments The abstract of this paper was presented at the Geographic Perspectives on Climate Change Mitigation in Urban and Rural Environments (GCUE) Conference – 1st Edition which was held on the 25th-27th of June 2024. Funding declaration This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors/individuals. Ethics approval Not applicable. Conflict of interest The authors declare that there is no competing interest. References Aïtcin PC. Portland cement. In: Science and Technology of Concrete Admixtures. 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