Optimization of fly ash and cement for stabilizing clay soil

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Robiul Hoque, Shriful Islam, Sourav Ray, Shuva Sarker, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4679698/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Fly ash and cement are commonly used as soil stabilizers, offering environment friendly solutions for soil improvement. This study aims to determine the ideal combination of fly ash and cement to improve the geotechnical behavior of clay soil collected from a future building construction project in Sylhet, Bangladesh. Strength development in soil was assessed across a wide range of fly ash (0–25%) and cement (0–18%) during 3-, 7-, 14-, and 28-day curing periods. Tests included in this research are: Atterberg limits test, standard Proctor tests, unconfined compressive strength (UCS) and scanning electron microscopy tests. Incorporating fly ash, cement, or both decreased maximum dry density (MDD) and increased optimum moisture content (OMC) of the soil, while soil classification remained consistent. The investigation revealed that fly ash initially had a higher reduction rate in MDD of the mixtures up to around 7% binder content, before cement took precedence. Optimal soil-binder strength was achieved at 5% fly ash and 8% cement after curing for 28 days individually. However, the optimal combination of the binders was identified as 6% (3% fly ash and 3% cement), yielding a 99.51% increase in UCS compared to untreated soil after 28 days. Scanning electron microscopy tests show that the compactness of clay soil increases due to the addition of fly ash and cement. This binder combination (3% fly ash and 3% cement) could be suitable for stabilizing clay soil beneath the shallow foundation of a residential building in the study area. Clay soil fly ash stabilization cement stabilization maximum dry density unconfined compressive strength Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction Bangladesh encompasses a total area of 147,570 km 2 , with approximately 75,350 km 2 dedicated to wetlands [ 1 ]. The Haor basin, covering around 24,500 km 2 , is a significant portion of this wetland, including areas such as Baor and Beel. Particularly noteworthy is the Sylhet division, often referred to as the 'Home of Haor,' where a substantial amount of silt and clay soil is prevalent on or near the surface. Alam et al. [ 2 ] classifies the Sylhet division’s ground as acid basin clay and grey piedmont soil. In this region, silt and clay content ranges from 9.9–21% and 3–78.5%, respectively. These clay deposits, known for their soft characteristics, pose challenges in geotechnical engineering applications [ 3 ] when designing roads and shallow foundations for various structures because of low shear strength and high consolidation settlement. Consequently, soil improvement techniques have become imperative to mitigate construction costs and to reduce possibility of post-construction failure of the structures. One soil improvement method involves utilizing stabilizing agents like fly ash, lime, cement, either individually or in combinations, to enhance soil characteristics. While many researchers have extensively studied the efficacy of these stabilizing agents individually [ 4 ], only a few have explored the possibility of using fly ash and cement together for soil strength development of soil [ 3 , 5 – 9 ]. In one of the earliest studies, Indraratna et al. [ 5 ] demonstrated the feasibility of using fly ash with cement in certain proportions for soil strength development. Another study found that a 10% fly ash content, when combined with cement, could provide soil strength comparable to that of cement alone over a longer curing period [ 7 ]. Sumesh et al. [ 9 ] reported the maximum unconfined compressive strength (UCS) of 628.82 kPa with 35% fly ash content for a 28-day curing period, noting lower strength when 1% or 2% cement was added to the same amount of fly ash (35%). Cristelo et al. [ 3 ] applied alkaline-activated fly ash and cement separately and found similar UCS results of soil samples after 28 days of curing. However, alkali-activated fly ash exhibited significantly higher strength results in long-term curing compared to cement stabilizers. Rai et al. [ 8 ] studied the clay soil stabilization using cement and fly ash, achieving effective strength of 167.75 kPa, which is 48.20% higher than the original soil, with a combination of 8% cement and 20% fly ash. In a recent 2023 study, researchers used coal ash (a combination of bottom ash and fly ash) and ordinary Portland cement as additives for soil stabilization. They concluded that a 15% additive (13% coal ash and 2% cement) resulted in a stabilized soil strength of 536 kPa after 180 days of curing [ 6 ]. Despite these efforts, there remains a gap in the research regarding how strength develops with increasing cement content gradually with fly ash and cement content, and how soil-fly ash-cement mixtures change their characteristics in terms of Atterberg limits and dry density. The Barapukuria coal field, the sole active one among six potential coal fields in Bangladesh, produces approximately 1 million tons of coal annually. Notably, 65% of this coal is utilized in the Barapukuria coal-fired thermal power plant [ 10 ], generating about 52,000 tons of fly ash each year. While the disposal of fly ash can pose environmental challenges [ 9 ], its potential as a stabilizing agent for soil improvement is significant [ 11 ]. Pozzolanic and hydration reaction of fly ash and cement, respectively, enhances the shear strength of clay soil [ 9 ]. Furthermore, the use of fly ash results in lower lateral and overburden pressure due to its reduced dry density compared to other stabilizing agents [ 9 ]. This characteristic makes it particularly effective in reducing structural loads in construction projects such as highway embankments, pavements, and backfilling for retaining walls. In addition to its engineering advantages, integrating fly ash into diverse projects shows potential for efficiently handling and diminishing the substantial quantities of fly ash generated. This dual benefit highlights the possibilities for sustainable and eco-friendly practices in construction and infrastructure development. In this study, clay soil strength maximization was achieved with the inclusion of fly ash. Subsequently, cement, known for its rapid stabilizing properties, was employed to optimize its content for soil strength enhancement. Fly ash is relatively more affordable than cement but doesn't provide the same level of strength enhancement. This investigation seeks to determine the optimal ratio of fly ash and cement to achieve higher strength in the clay soil compared to using fly ash alone. Thus, the study evaluates the strength enhancement potential of combining fly ash and cement with the same soil. Addressing the existing research gap, the study also evaluated soil-binder characteristics in the presence of individual binder or both fly ash and cement. 2. Binder material and experiment methods 2.1. Investigational plan The primary objective is to identify the optimal combination of fly ash and cement to achieve maximum unconfined compressive strength (UCS). The investigational plan was implemented in three steps to achieve the objectives as follows: 1. Maximize UCS using fly ash as a stabilizer; 2. Optimize UCS using cement as a binder; 3. Determine the optimal fly ash and cement ratio for UCS development. 2.2. Sample collection, preparation, and laboratory test The investigated soil was obtained from a future building construction projects near Shahjalal University of Science and Technology (SUST), Sylhet, Bangladesh, at a 3 m depth, as referenced in earlier studies [ 11 , 12 ], ensuring a natural and uniform soil composition. Various geotechnical properties, including field moisture content [ 13 ], particle size analysis [ 14 ], specific gravity [ 15 ], X-ray diffraction (XRD), Atterberg limits [ 16 ], and compaction parameters [ 17 ], were determined for the collected soil sample. For this investigation, fly ash and cement were utilized as additives in different combinations (mass/mass 1 ). The fly ash, obtained from the Barapukuria thermal power plant at Fulbari, Dinajpur, Bangladesh, was classified as Class F fly ash [ 10 ]. On the other side, ordinary Portland cement (OPC) produced in Bangladesh served as the cement-based stabilizer. Both binding materials were applied individually and in various compositions, as detailed in Table 1 . To assess changes in geotechnical properties, the Atterberg limits test and the standard Proctor test were carried out on all soil-binder-mixed samples. The standard Proctor test was particularly significant for determining the optimum moisture content (OMC) employed to formulate the soil-binder samples [ 11 ]. Throughout the experiment, a room temperature of about 22–23°C was maintained. The strength development was assessed through the unconfined compressive test carried out on all the soil-binder compositions at various curing periods, following ASTM Standard [ 18 ]. Initially, the collected sample was oven-dried for 24 hours and subsequently pulverized with a wooden hammer. Adequate soil was then obtained for the mold passing through sieve No. 10 (2 mm). These extracted soil samples were blended with different binding compositions (refer to Table 1 ) by dry mass in the presence of OMC [ 9 , 11 , 19 ] to achieve the maximum density of the mold. Molds around 38.405 ± 0.055 mm in diameter and 77.9 ± 0.6 mm in height [ 20 ], were prepared for all percentages of binding composition (Table 1 ). Curing was performed at 3, 7, 14, and 28 days under controlled temperature and humidity [ 21 ]. This is crucial, as curing time significantly contributes to the strength development of the soil-cement and soil-fly ash mixtures [ 9 , 11 , 22 ] in the presence of sufficient moisture [ 23 ]. Subsequently, all molds were tested in the UCS machine using the test method of ASTM Standard D5102 [ 18 ]. Furthermore, scanning electron microscopy (SEM) tests were also carried out only for the samples that yielded optimum strength. Table 1 Details of binder compositions of cement and fly ash in soil Sample ID Fly ash [%] Cement [%] Binder [%] S 0 0 0 SF2 2 2 SF4 4 4 SF5 5 5 SF8 8 8 SF10 10 10 SF15 15 15 SF20 20 20 SF25 25 25 SC2 0 2 2 SC4 4 4 SC6 6 6 SC8 8 8 SC10 10 10 SC12 12 12 SC14 14 14 SC16 16 16 SC18 18 18 SF2C2 1 1 2 SF4C4 2 2 4 SF6C6 3 3 6 SF8C8 4 4 8 SF10C10 5 5 10 SF12C12 6 6 12 SF14C14 7 7 14 SF16C16 8 8 16 SF18C18 9 9 18 Note: S = Clay soil; F = Fly ash; C = Cement 3. Results and discussion 3.1 Characterization of paddy field soil The collected soil sample was classified as fined-grained, consisting of 1.40% gravel-sized, 40.40% sand-sized, and 6.80% silt-sized particles, along with 51.40% clay-sized particles (Fig. 1 ), following ASTM Standard D422 [ 14 ]. X-ray diffraction analysis with the courtesy of previous research by Islam et al. [ 11 ], carried out on soil passing through a #200 sieve (74 µm), following Terzano et al. [ 24 ], results are plotted in Fig. 2 , indicating the presence of quartz, orthoclase, illite, and kaolinite. Table 2 Geotechnical properties of soil used in the investigation. Properties Test values Specific gravity (-) 2.58 Field moisture content (%) 43.13 Gravel (%) 00.83 Sand (%) 37.76 Silt (%) 45.04 Clay (%) 16.37 Liquid limit, LL (%) 54.48 Plastic limit, PL (%) 29.68 Plasticity index, PI (%) 24.79 Optimum moisture content, OMC (%) 20.30 Maximum dry density, MDD (g/cm 3 ) 1.615 pH (-) 6.7 Liquid limit (LL) and plastic limit (PL) tests were carried out by following the four-point method and hand-rolling method, respectively, according to ASTM Standard D4318 [ 16 ]. The values of LL and PL for the soil sample are 54.48% and 29.68%, respectively (Table 2 ). The specific gravity of the soil was measured as 2.58, following ASTM Standard D854 [ 15 ]. In accordance with the Unified Soil Classification System (USCS), the collected soil is classified as inorganic silts of high plasticity (MH) or organic clays of medium to high plasticity (OH). 3.2 Behavioral changes of stabilized soil in the presence of fly ash and cement 3.2.1 Influence on the Atterberg limits of the soil The Atterberg limits test demonstrates unique effects of cement and fly ash on the soil's properties, as illustrated in Fig. 3 . In both liquid limit and plastic limit cases, soil-fly ash mixtures exhibit a higher slope. For nearly all binder combinations, the liquid limit decreases, and the plastic limit increases (Fig. 3 ) with the rising binder content, whether it be fly ash, cement, or a combination of both. Up to approximately 7% binder content, the slope of the liquid limit curve for the soil-cement mixtures exceeds that of the soil-fly ash mixtures. However, beyond 7% binder content, the situation reverses. Meanwhile, the plasticity limit remains relatively constant for the soil-cement mixtures up to 15% (Fig. 3 ). Figure 4 illustrates that all data points consistently fall within the regions of MH or OH for all binder content combinations in this study. 3.2.2 Impact on maximum dry density (MDD) and optimum moisture content (OMC) of the soil The impact of fly ash and cement on the compaction efficacy of soil was illustrated through the standard proctor test as depicted in Fig. 5 . The MDD of the soil-binder mixtures reduced with an increase in all combinations of binder content (Fig. 5 ), and the slope exhibited an opposite trend to that of the liquid limit (Fig. 3 ). Specifically, the slope of the curve for soil-fly ash mixtures was steeper than that of soil-cement mixtures until around 7% binder content in soil, after which the situation reversed. However, the overall reduction in MDD can be explained by the incremental addition of fly ash and cement in soil, as their specific gravity is relatively low compared to the original clay soil [ 9 , 11 , 25 , 26 ]. The MDD of 10% binder content was 1.56 g/cm 3 , 1.52 g/cm 3 , and 1.54 g/cm 3 for soil-fly ash mixture, soil-cement mixture, and soil-fly ash-cement mixture, respectively, where unstabilized soil’s MDD was 1.62 g/cm 3 . In both individual and combined addition of binders to the soil, a decrease in MDD was observed, consistent with findings from previous research [ 6 , 9 , 27 – 29 ]. Conversely, the OMC rises with higher binder content in all combinations (Fig. 5 ). The increasing rate is higher for soil-cement mixtures than the soil-fly ash mixtures. The OMC for soil-cement mixtures is almost constant throughout the range of 14–18%. The OMC of 10% binder content was 21.4%, 27.5%, and 24.4% for soil-fly ash mixture, soil-cement mixture, and soil-fly ash-cement mixture, respectively, where unstabilized soil’s OMC was 20.3%. The increase in OMC is typically associated with the presence of finer particles and the bonding formed between soil particles and binders, leading to greater water retention and plasticity in the soil-binder mixtures [ 11 , 19 , 25 , 27 , 28 ]. Additionally, another study observed that the presence of large, hollow spheres in fly ash leads to a rise in the OMC value as the binder content in the soil increases [ 26 ]. 3.3 Optimum fly ash and cement content for maximum unconfined compressive strength of clay soil The test results presented in Figs. 6 and 8 illustrate the progression of UCS of soil-binder against curing time for various ratios of fly ash and cement content. The UCS of untreated soil samples are 270.99 kPa and 289.07 kPa after 7 and 28 days of curing, respectively. The plots indicate that the soil's strength increased with curing time when fly ash and cement were added individually, as expected. Interestingly, it was observed that the strength improvement rate increased until reaching a specific percentage of fly ash and cement content. This phenomenon was also evident when both fly ash and cement were used in the soil. The UCS of the soil exhibited a rising trend with the rise in fly ash content up to a certain percentage, specifically 5% (Fig. 6 ). For 7- and 28-day curing periods, this binder (5% fly ash) provided UCS of 349.15 kPa and 430.96 kPa, respectively, representing a notable increment of 28.84% and 49.08% compared to untreated soil. However, beyond the 5% fly ash content, a considerable depletion in strength was observed. These results delineate two distinct zones (Fig. 7 ): an active zone (0–5% fly ash) and a deterioration zone (above 5% fly ash) [ 11 ]. Other researchers have observed this phenomenon across varying percentages of fly ash in several kinds of soil [ 26 , 30 – 32 ]. The impact of the deterioration zone is significant, resulting in a reduction in the soil's strength below its normal level. Notably, at 3 and 7 days of curing, 20% (SF20) and 25% (SF25) fly ash content provided less strength than the original soil's strength alone. Similar observations of a deteriorating phenomenon in different percentages of fly ash content in clay soil have been reported by other researchers [ 9 , 29 ]. The decline in strength can be attributed to two main factors. Firstly, the limited strengthening capacity of fly ash is a critical factor contributing to its inability to enhance the strength of this type of soil. Secondly, insufficient coverage of contact points between the soil and fly ash further exacerbates the soil-fly ash particles bonding [ 11 , 30 ]. While adding fly ash to a maximum of 5% may adequately cover all available contact points in the soil, exceeding this percentage results in a decline in strength. The strength results from the experiment demonstrate that the use of cement as a binder material in soil leads to a better strength development compared to fly ash, as depicted in Fig. 8 - a result consistent with Sumesh et al. [ 9 ]. However, the findings reveal that the rate of development for soil-cement mixtures decreases beyond a certain binder content for this specific soil type. With an 8% cement content, the soil-cement mixture generates a UCS of 775.45 kPa over 28-day curing periods, representing a significant increment of 168.26% compared to the unstabilized soil strength. The increment rate remains substantial up to 12% cement content, yielding a UCS of 883.42 kPa. However, beyond 8% cement content, the rate slows down, reaching 933.28 kPa for 18% cement content. Consequently, these results delineate two distinct zones (refer to Fig. 9 ): an active zone (0–8% cement) and an inert zone (above 8% cement). While a comparable active zone was identified for soil-cement mixtures as seen with soil-fly ash mixtures, a new inert zone emerges, differentiating it from soil-fly ash mixtures, where no significant strength development occurs. This observation aligns with a similar zone pattern reported by Horpibulsuk et al. [ 12 ], where an active zone was identified up to 10% cement content. In the context of combining both fly ash and cement binder (Fig. 10 ), the strength increment of soil was smooth for the entire curing period up to 10% binder content (SF5C5: 5% fly ash and 5% cement). At 10% binder content (SF5C5), the produced UCS of soil-binder was 689.60 kPa, which was 90.21% higher than the unstabilized soil’s strength for the 28-day curing period. Beyond 10% binder (SF5C5), slightly irregular strength development occurred throughout the entire curing period. The maximum increase of 34.42% increment rate was found for 6% binder content (SF3C3) in soil, generating 520.47 kPa UCS. The increment rate remained favorable up to 12% binder content (SF6C6). Starting from 12% binder content (SF6C6), the strength increment rate decreased rapidly and continued until 16% binder content (SF8C8). Beyond 16% binder content (SF8C8), the strength started to diminish. Overall, the stabilized soil strength for the 28 days produces three zones for different binder contents (Fig. 11 ): an active zone (0–12% binder content: fly ash and cement), an inert zone (12–16% binder content: fly ash and cement), and a deterioration zone (above 16% binder content: fly ash and cement). A group of researchers have found similar results, indicating that strength develops up to 25% fly ash content, irrespective of the amount of cement mixed [ 33 ]. This study demonstrates that all soil samples treated with fly ash and cement exhibit enhanced UCS compared to untreated soil. This strength improvement is attributed not only to the pozzolanic [ 29 ] and hydration reactions [ 7 ] but also to the presence of iron and aluminum oxides in the soil [ 9 ]. Interestingly, approximately 50% of the strength increase occurs within the first 7 days of curing. Several factors influence the rate and level of strength development, including the type of clay minerals present, the type of fly ash, the proportion of fly ash and cement, ambient temperature, and curing environment [ 34 ]. Figures 6 , 8 , and 10 illustrate that the UCS of the soil increases over curing time. This is primarily due to the pozzolanic reaction of fly ash and the hydration reaction of cement. While the hydration reaction is faster, the pozzolanic reaction requires more time to develop a bond [ 35 ]. The free lime in fly ash reacts with alumina and silica in the existence of water to form calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) gels, which act as binders connecting soil particles [ 9 ]. Similarly, the hydration and pozzolanic reactions of cement also contribute to the binding of soil particles, resulting in a higher UCS compared to fly ash alone [ 36 ]. 4. Verification of binder effects on soil stabilization by SEM image analyses The interaction between soil and optimum composites of cement and fly ash used in this research are closely observed in scanning electron microscopy (SEM) test. Figures 12 (a)-(d) show the SEM images of soil (S), soil + 5% fly ash (SF5), soil + 8% cement (SC8), and soil + 3% fly ash + 3% cement (SF3C3), composites. As described in the Fig. 12 (a), the fine-sized particles of the clay soil sample look clotted or aggregated together and form an irregular appearance on the surface with significant pores. On the other hand, the sample with 5% fly ash after 28 days of curing gives a different appearance with more filled-up pores (Fig. 12 (b)), and the pozzolanic behavior of fly ash with clay particles is indirectly revealed in the firm and stabilized surface of the voids previously appeared in the untreated soil sample. Again, the soil sample with 8% cement, as shown in Fig. 12 (c), has a more filled surface, the voids are better covered, and the soil seems to be stabilized more than the two cases shown in Figs. 12 (a) and 12 (b). As per the different mechanical properties test results discussed above, although the cement and fly ash both gave the characteristics of stabilizing clay soil, the cement is far more effective in treating soil, which is also observed through the SEM test results. In the SEM image shown in Fig. 12 (d), the soil sample with optimum mixed additive percentages of 3% cement and 3% fly ash (SF3C3) shows a mostly stabilized condition with limited visible voids in the surface and the soil mass seems to be stiff enough. The UCS test of 28 days-soaked soil sample also revealed that the soil sample with 3% cement and 3% fly ash has the most satisfying strength which justifies the stiffness of the soil sample resulted in UCS test through the dense-looked surface of the soil sample in SEM image in Fig. 12 (d). Islam et al. [ 37 , 38 ] also experienced good bearing capacity and lower consolidation settlement in clayey soil using recycled concrete aggregates as an additive and revealed the interaction through a similar case of SEM analysis. Yoobanpot et al. [ 36 ] discussed the microstructural behavior of treated clay soil with both cement kiln dust and fly ash, and found the filled-up pores with denser conditions in between clay particles due to the continuous growth of hydration of cement and fly ash particles during curing period and made the clay stiffer and increased strength. 5. Conclusion This study aimed to identify the optimal fly ash and cement content for maximizing the strength of clay soil. The laboratory investigation unveiled the alterations in the characteristics of the soil-binder mixtures. These findings provide valuable insights for stabilizing clay soil, guiding the selection of the optimal ratio of fly ash and cement to achieve desired strength in applications such as foundation bases, embankments, and sub-bases for pavements. The key findings are summarized below. Soil-binder mixtures consistently exhibit MH or OH across various binder content ranges. The MDD of soil-binder mixtures tends to decrease as the binder combination increments increases, while the OMC exhibits an increasing trend with the rise in binder content. Notably, the decreasing trend in MDD of soil-binder mixtures is more pronounced for fly ash as a binder compared to cement, especially up to around 7%. However, beyond this point, the trend reverses, indicating a higher rate of decrease in MDD for cement as the binder content continues to increase. Fly ash as the sole binder in soil attains the highest unconfined compressive strength (UCS), reaching 430.96 kPa at a 5% binder content. In contrast, the optimal cement content, set at 8%, yields a UCS of 775.45 kPa after curing for 28 days. The peak strength of soil-binder mixtures increment is observed at 6% binder content (SF3C3), resulting in a UCS of 520.47 kPa after a 28-day curing period. Beyond 6% binder content in soil, the strength increment begins to decrease. Consequently, the identified optimal fly ash and cement content for maximum strength is 3% for both binders. The presence of both cement and fly ash in soil results in active, inert, and deterioration zones during strength development, depending on the specific binder content. SEM image analyses conducted on original soil, soil-5% fly ash (SF5), soil-8% cement (SC8), and soil-3% fly ash-3% cement (SF3C3) composites validate the findings of standard compaction and unconfined compression tests results. Overall, the stabilization effects of fly ash, cement and fly ash-cement on the studied soil can be ranked as: soil-5% fly ash (SF5) < soil-8% cement (SC8) < soil-3% fly ash-3% cement (SF3C3) composites. Declarations Acknowledgment The authors extend sincere appreciation for the invaluable support received from the Department of Civil and Environmental Engineering (CEE) at Shahjalal University of Science and Technology (SUST), which provided essential laboratory services for the successful execution of the current investigation. Funding No funding was received for conducting this study. Conflicts of interest/Competing interests The authors have no relevant financial or non-financial interests to disclose. Data availability All necessary data will be available upon request. Code availability Not applicable. Authors' contributions N. M. R. Hoque participated in the conceptualization, methodology, and writing—original draft, including all the tables and figures. S. Islam took part in the conceptualization, methodology, and writing—review, including all the figures. S. Ray contributed to the research's methodology, writing, and supervision, including all the tables. S. 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Horpibulsuk S, Rachan R, Suddeepong A. Assessment of strength development in blended cement admixed Bangkok clay. Construction and Building Materials. 2011;25(4):1521–31. Reema T, Kalita A. STRENGTH CHARACTERISTICS OF RED SOILS BLENDED WITH FLY ASH AND. IJIRSET. 2013;3(4):270–3. Zeng Q, Li K, Fen-chong T, Dangla P. Determination of cement hydration and pozzolanic reaction extents for fly-ash cement pastes. Construction and Building Materials. 2012;27(1):560–9. Yoobanpot N, Jamsawang P, Horpibulsuk S. Strength behavior and microstructural characteristics of soft clay stabilized with cement kiln dust and fly ash residue. Applied Clay Science. 2017;141:146–56. Islam S, Islam J, Hoque NMR, Hasan K. Improving geotechnical properties of soil of hillock slope using crushed recycled concrete aggregates. Journal of Engineering Research. 2023;11(4):293–300. Islam S, Islam J, Robiul Hoque NMd. Improvement of consolidation properties of clay soil using fine-grained construction and demolition waste. Heliyon. 2022;8(10):e11029. Footnotes Percentage of binder = (mass of binder) / (mass of binder + mass of soil) * 100. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4679698","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":335681616,"identity":"b0b775db-c594-4135-bdb8-956d7e338891","order_by":0,"name":"Nur Md. Robiul Hoque","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzklEQVRIiWNgGAWjYBACAziLvQHEtSBFC88BEFeCFC0SCWCSsBZz9uZtEh8Y7OT4JZ9f3fCjQIKBv707Aa8Wy55jZZIzGJKNJWfnlN3sATpM4szZDfgddiPHTJqH4UDihts5aTd4gFoMJHKJ0PKH4UD9/ptn0m7+IVoLA8OBBAMJ9mO3ibPlzLFiyx6DZMMZZ3LYbssYSPAQ9svx5o03flTYyfO3H392880fGzn+9l78WhjAUQOOHR4ISUg5VAsYsD8gRvUoGAWjYBSMQAAAwGFEOsrYD2oAAAAASUVORK5CYII=","orcid":"","institution":"Shahjalal University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Nur","middleName":"Md. Robiul","lastName":"H","suffix":"Md."},{"id":335681617,"identity":"446ff2e8-79d2-45bf-bcbf-a384c274170b","order_by":1,"name":"Shriful Islam","email":"","orcid":"","institution":"Shahjalal University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Shriful","middleName":"","lastName":"Islam","suffix":""},{"id":335681618,"identity":"8b454028-da21-4fdd-b42c-8f42bbb08d8b","order_by":2,"name":"Sourav Ray","email":"","orcid":"","institution":"Shahjalal University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Sourav","middleName":"","lastName":"Ray","suffix":""},{"id":335681619,"identity":"8223396f-b6d8-4991-bc9f-6470aa467884","order_by":3,"name":"Shuva Sarker","email":"","orcid":"","institution":"Shahjalal University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Shuva","middleName":"","lastName":"Sarker","suffix":""},{"id":335681620,"identity":"2946ff26-528e-4f9b-8287-9359be01d3d8","order_by":4,"name":"Junaidul Islam","email":"","orcid":"","institution":"Shahjalal University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Junaidul","middleName":"","lastName":"Islam","suffix":""}],"badges":[],"createdAt":"2024-07-03 10:31:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4679698/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4679698/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":61838578,"identity":"f90a8539-d76f-40ee-8bb6-ee2c24e7736d","added_by":"auto","created_at":"2024-08-06 06:14:11","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":20479,"visible":true,"origin":"","legend":"\u003cp\u003eGrain size distribution of soil used in the investigation\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/4455189704444b30cb11e6cc.png"},{"id":61838585,"identity":"8e8d928e-c32f-4b42-ae4a-efc1d318137a","added_by":"auto","created_at":"2024-08-06 06:14:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":29355,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffraction of pulverized soil sample [11]\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/b84828b21b70f7cf2dda742c.png"},{"id":61839859,"identity":"e21ac47a-b261-4488-aaa2-d5babbc2965b","added_by":"auto","created_at":"2024-08-06 06:30:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":64310,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of liquid limit and plastic limit in presence of different percentages of fly ash, cement, or both in soil\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/323e1b3ed2fb2629dee722c0.png"},{"id":61839316,"identity":"89f4462f-c17d-4ff7-9420-25a1d732fa71","added_by":"auto","created_at":"2024-08-06 06:22:12","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":46811,"visible":true,"origin":"","legend":"\u003cp\u003eClassification of various soil-binder mixture samples on the plasticity chart according to USCS (CH: Inorganic clays of high plasticity CL: Low to medium plasticity; MH: Inorganic silts of high plasticity; ML: Inorganic silts or clayey silts with slight plasticity; OH: Organic clays of medium to high plasticity; OL: Organic silts and organic silty clays of low plasticity)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/21e7a6d4d9eb60f9a3138b09.png"},{"id":61839322,"identity":"09073fb3-b765-4448-9136-f9ea163032bf","added_by":"auto","created_at":"2024-08-06 06:22:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":69989,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of maximum dry density (MDD) and optimum moisture content (OMC) in presence of different percentages of fly ash, cement, or a combination of both in soil\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/31c367f6fbe6553082bb0574.png"},{"id":61838588,"identity":"ac6a5a0d-f0af-4e84-a02a-79b5400c8849","added_by":"auto","created_at":"2024-08-06 06:14:12","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":85131,"visible":true,"origin":"","legend":"\u003cp\u003eUnconfined compressive strength development with curing time for soil stabilized using \u003cem\u003efly ash\u003c/em\u003e as a binder\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/a3bb7adf487b7468b7564aef.png"},{"id":61838584,"identity":"75c6edc2-c807-4ad0-96db-bd1f8c9c484a","added_by":"auto","created_at":"2024-08-06 06:14:12","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":33527,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in the development of unconfined compressive strength over 28 days of curing in the presence of different \u003cem\u003efly ash\u003c/em\u003e content\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/be18a7a2abb1dfd95f266670.png"},{"id":61839320,"identity":"1542cc7b-52f6-4bde-8354-868fefc4b265","added_by":"auto","created_at":"2024-08-06 06:22:12","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":70701,"visible":true,"origin":"","legend":"\u003cp\u003eUnconfined compressive strength development with curing time for soil stabilized using \u003cem\u003ecement\u003c/em\u003eas a binder\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/c6cbb255066efe841215fb15.png"},{"id":61838582,"identity":"a6bffc0e-9e95-4c9c-bd84-503f2099e83c","added_by":"auto","created_at":"2024-08-06 06:14:12","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":37232,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in the development of unconfined compressive strength over 28 days of curing in the presence of different \u003cem\u003ecement\u003c/em\u003e content\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/e5484bb91b7823e4822ebf2b.png"},{"id":61839318,"identity":"249289e7-7d52-45de-bddc-54b232c049f1","added_by":"auto","created_at":"2024-08-06 06:22:12","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":72225,"visible":true,"origin":"","legend":"\u003cp\u003eUnconfined compressive strength development with curing time for soil stabilized using \u003cem\u003efly ash\u003c/em\u003e\u003cstrong\u003e \u003c/strong\u003eand\u003cstrong\u003e \u003c/strong\u003e\u003cem\u003ecement\u003c/em\u003e as a binder\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/ac4bd3bffa70531bd2a1d27d.png"},{"id":61838580,"identity":"281cee69-70ea-4626-9a8c-83f27041a5be","added_by":"auto","created_at":"2024-08-06 06:14:12","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":44425,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in the development of unconfined compressive strength over 28 days of curing in the presence of different \u003cem\u003efly ash\u003c/em\u003e\u003cstrong\u003e \u003c/strong\u003eand\u003cstrong\u003e \u003c/strong\u003e\u003cem\u003ecement\u003c/em\u003econtent\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/683a4334cb0d2b48fa846533.png"},{"id":61839861,"identity":"11a9b525-fe0e-4b77-9717-cf140270a1a1","added_by":"auto","created_at":"2024-08-06 06:30:12","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":361453,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscopic (SEM) images of a) Clay soil (S), b) Soil + 5 % fly ash (SF5), c) Soil + 8% cement (SC8), d) Soil + 3% fly ash + 3% cement (SF3C3)\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/048a697b6a1edc029c0108e6.png"},{"id":63041117,"identity":"0248f84b-a2df-4003-8707-73d5f14f0185","added_by":"auto","created_at":"2024-08-22 11:32:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1574641,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4679698/v1/d2415942-e22e-40b8-b8c5-f2e9761619d1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Optimization of fly ash and cement for stabilizing clay soil","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eBangladesh encompasses a total area of 147,570 km\u003csup\u003e2\u003c/sup\u003e, with approximately 75,350 km\u003csup\u003e2\u003c/sup\u003e dedicated to wetlands [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The Haor basin, covering around 24,500 km\u003csup\u003e2\u003c/sup\u003e, is a significant portion of this wetland, including areas such as Baor and Beel. Particularly noteworthy is the Sylhet division, often referred to as the 'Home of Haor,' where a substantial amount of silt and clay soil is prevalent on or near the surface. Alam et al. [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] classifies the Sylhet division\u0026rsquo;s ground as acid basin clay and grey piedmont soil. In this region, silt and clay content ranges from 9.9\u0026ndash;21% and 3\u0026ndash;78.5%, respectively. These clay deposits, known for their soft characteristics, pose challenges in geotechnical engineering applications [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] when designing roads and shallow foundations for various structures because of low shear strength and high consolidation settlement. Consequently, soil improvement techniques have become imperative to mitigate construction costs and to reduce possibility of post-construction failure of the structures.\u003c/p\u003e \u003cp\u003eOne soil improvement method involves utilizing stabilizing agents like fly ash, lime, cement, either individually or in combinations, to enhance soil characteristics. While many researchers have extensively studied the efficacy of these stabilizing agents individually [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], only a few have explored the possibility of using fly ash and cement together for soil strength development of soil [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan additionalcitationids=\"CR6 CR7 CR8\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. In one of the earliest studies, Indraratna et al. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] demonstrated the feasibility of using fly ash with cement in certain proportions for soil strength development. Another study found that a 10% fly ash content, when combined with cement, could provide soil strength comparable to that of cement alone over a longer curing period [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Sumesh et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] reported the maximum unconfined compressive strength (UCS) of 628.82 kPa with 35% fly ash content for a 28-day curing period, noting lower strength when 1% or 2% cement was added to the same amount of fly ash (35%). Cristelo et al. [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] applied alkaline-activated fly ash and cement separately and found similar UCS results of soil samples after 28 days of curing. However, alkali-activated fly ash exhibited significantly higher strength results in long-term curing compared to cement stabilizers. Rai et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] studied the clay soil stabilization using cement and fly ash, achieving effective strength of 167.75 kPa, which is 48.20% higher than the original soil, with a combination of 8% cement and 20% fly ash. In a recent 2023 study, researchers used coal ash (a combination of bottom ash and fly ash) and ordinary Portland cement as additives for soil stabilization. They concluded that a 15% additive (13% coal ash and 2% cement) resulted in a stabilized soil strength of 536 kPa after 180 days of curing [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Despite these efforts, there remains a gap in the research regarding how strength develops with increasing cement content gradually with fly ash and cement content, and how soil-fly ash-cement mixtures change their characteristics in terms of Atterberg limits and dry density.\u003c/p\u003e \u003cp\u003eThe Barapukuria coal field, the sole active one among six potential coal fields in Bangladesh, produces approximately 1\u0026nbsp;million tons of coal annually. Notably, 65% of this coal is utilized in the Barapukuria coal-fired thermal power plant [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], generating about 52,000 tons of fly ash each year. While the disposal of fly ash can pose environmental challenges [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], its potential as a stabilizing agent for soil improvement is significant [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePozzolanic and hydration reaction of fly ash and cement, respectively, enhances the shear strength of clay soil [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Furthermore, the use of fly ash results in lower lateral and overburden pressure due to its reduced dry density compared to other stabilizing agents [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. This characteristic makes it particularly effective in reducing structural loads in construction projects such as highway embankments, pavements, and backfilling for retaining walls. In addition to its engineering advantages, integrating fly ash into diverse projects shows potential for efficiently handling and diminishing the substantial quantities of fly ash generated. This dual benefit highlights the possibilities for sustainable and eco-friendly practices in construction and infrastructure development.\u003c/p\u003e \u003cp\u003eIn this study, clay soil strength maximization was achieved with the inclusion of fly ash. Subsequently, cement, known for its rapid stabilizing properties, was employed to optimize its content for soil strength enhancement. Fly ash is relatively more affordable than cement but doesn't provide the same level of strength enhancement. This investigation seeks to determine the optimal ratio of fly ash and cement to achieve higher strength in the clay soil compared to using fly ash alone. Thus, the study evaluates the strength enhancement potential of combining fly ash and cement with the same soil. Addressing the existing research gap, the study also evaluated soil-binder characteristics in the presence of individual binder or both fly ash and cement.\u003c/p\u003e"},{"header":"2. Binder material and experiment methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Investigational plan\u003c/h2\u003e \u003cp\u003eThe primary objective is to identify the optimal combination of fly ash and cement to achieve maximum unconfined compressive strength (UCS). The investigational plan was implemented in three steps to achieve the objectives as follows: 1. Maximize UCS using fly ash as a stabilizer; 2. Optimize UCS using cement as a binder; 3. Determine the optimal fly ash and cement ratio for UCS development.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Sample collection, preparation, and laboratory test\u003c/h2\u003e \u003cp\u003eThe investigated soil was obtained from a future building construction projects near Shahjalal University of Science and Technology (SUST), Sylhet, Bangladesh, at a 3 m depth, as referenced in earlier studies [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], ensuring a natural and uniform soil composition. Various geotechnical properties, including field moisture content [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], particle size analysis [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], specific gravity [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], X-ray diffraction (XRD), Atterberg limits [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], and compaction parameters [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], were determined for the collected soil sample.\u003c/p\u003e \u003cp\u003eFor this investigation, fly ash and cement were utilized as additives in different combinations (mass/mass\u003csup\u003e1\u003c/sup\u003e). The fly ash, obtained from the Barapukuria thermal power plant at Fulbari, Dinajpur, Bangladesh, was classified as Class F fly ash [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. On the other side, ordinary Portland cement (OPC) produced in Bangladesh served as the cement-based stabilizer. Both binding materials were applied individually and in various compositions, as detailed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eTo assess changes in geotechnical properties, the Atterberg limits test and the standard Proctor test were carried out on all soil-binder-mixed samples. The standard Proctor test was particularly significant for determining the optimum moisture content (OMC) employed to formulate the soil-binder samples [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Throughout the experiment, a room temperature of about 22\u0026ndash;23\u0026deg;C was maintained.\u003c/p\u003e \u003cp\u003eThe strength development was assessed through the unconfined compressive test carried out on all the soil-binder compositions at various curing periods, following ASTM Standard [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Initially, the collected sample was oven-dried for 24 hours and subsequently pulverized with a wooden hammer. Adequate soil was then obtained for the mold passing through sieve No. 10 (2 mm). These extracted soil samples were blended with different binding compositions (refer to Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) by dry mass in the presence of OMC [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] to achieve the maximum density of the mold. Molds around 38.405\u0026thinsp;\u0026plusmn;\u0026thinsp;0.055 mm in diameter and 77.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 mm in height [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], were prepared for all percentages of binding composition (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Curing was performed at 3, 7, 14, and 28 days under controlled temperature and humidity [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. This is crucial, as curing time significantly contributes to the strength development of the soil-cement and soil-fly ash mixtures [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] in the presence of sufficient moisture [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Subsequently, all molds were tested in the UCS machine using the test method of ASTM Standard D5102 [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Furthermore, scanning electron microscopy (SEM) tests were also carried out only for the samples that yielded optimum strength.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDetails of binder compositions of cement and fly ash in soil\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample ID\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFly ash [%]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCement [%]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBinder [%]\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"8\" rowspan=\"9\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSC2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"8\" rowspan=\"9\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSC4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSC6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSC8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSC10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSC12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSC14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSC16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSC18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF2C2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF4C4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF6C6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF8C8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF10C10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF12C12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF14C14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF16C16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSF18C18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003eNote: S\u0026thinsp;=\u0026thinsp;Clay soil; F\u0026thinsp;=\u0026thinsp;Fly ash; C\u0026thinsp;=\u0026thinsp;Cement\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Characterization of paddy field soil\u003c/h2\u003e \u003cp\u003eThe collected soil sample was classified as fined-grained, consisting of 1.40% gravel-sized, 40.40% sand-sized, and 6.80% silt-sized particles, along with 51.40% clay-sized particles (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), following ASTM Standard D422 [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. X-ray diffraction analysis with the courtesy of previous research by Islam et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], carried out on soil passing through a #200 sieve (74 \u0026micro;m), following Terzano et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], results are plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, indicating the presence of quartz, orthoclase, illite, and kaolinite.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eGeotechnical properties of soil used in the investigation.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProperties\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTest values\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecific gravity (-)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eField moisture content (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e43.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGravel (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e00.83\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSand (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e37.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSilt (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eClay (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16.37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLiquid limit, LL (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e54.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlastic limit, PL (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlasticity index, PI (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24.79\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOptimum moisture content, OMC (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaximum dry density, MDD (g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.615\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epH (-)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eLiquid limit (LL) and plastic limit (PL) tests were carried out by following the four-point method and hand-rolling method, respectively, according to ASTM Standard D4318 [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The values of LL and PL for the soil sample are 54.48% and 29.68%, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The specific gravity of the soil was measured as 2.58, following ASTM Standard D854 [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. In accordance with the Unified Soil Classification System (USCS), the collected soil is classified as inorganic silts of high plasticity (MH) or organic clays of medium to high plasticity (OH).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Behavioral changes of stabilized soil in the presence of fly ash and cement\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Influence on the Atterberg limits of the soil\u003c/h2\u003e \u003cp\u003eThe Atterberg limits test demonstrates unique effects of cement and fly ash on the soil's properties, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. In both liquid limit and plastic limit cases, soil-fly ash mixtures exhibit a higher slope. For nearly all binder combinations, the liquid limit decreases, and the plastic limit increases (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) with the rising binder content, whether it be fly ash, cement, or a combination of both. Up to approximately 7% binder content, the slope of the liquid limit curve for the soil-cement mixtures exceeds that of the soil-fly ash mixtures. However, beyond 7% binder content, the situation reverses. Meanwhile, the plasticity limit remains relatively constant for the soil-cement mixtures up to 15% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e illustrates that all data points consistently fall within the regions of MH or OH for all binder content combinations in this study.\u003c/p\u003e\u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 Impact on maximum dry density (MDD) and optimum moisture content (OMC) of the soil\u003c/h2\u003e \u003cp\u003eThe impact of fly ash and cement on the compaction efficacy of soil was illustrated through the standard proctor test as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The MDD of the soil-binder mixtures reduced with an increase in all combinations of binder content (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), and the slope exhibited an opposite trend to that of the liquid limit (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Specifically, the slope of the curve for soil-fly ash mixtures was steeper than that of soil-cement mixtures until around 7% binder content in soil, after which the situation reversed. However, the overall reduction in MDD can be explained by the incremental addition of fly ash and cement in soil, as their specific gravity is relatively low compared to the original clay soil [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The MDD of 10% binder content was 1.56 g/cm\u003csup\u003e3\u003c/sup\u003e, 1.52 g/cm\u003csup\u003e3\u003c/sup\u003e, and 1.54 g/cm\u003csup\u003e3\u003c/sup\u003e for soil-fly ash mixture, soil-cement mixture, and soil-fly ash-cement mixture, respectively, where unstabilized soil\u0026rsquo;s MDD was 1.62 g/cm\u003csup\u003e3\u003c/sup\u003e. In both individual and combined addition of binders to the soil, a decrease in MDD was observed, consistent with findings from previous research [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eConversely, the OMC rises with higher binder content in all combinations (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The increasing rate is higher for soil-cement mixtures than the soil-fly ash mixtures. The OMC for soil-cement mixtures is almost constant throughout the range of 14\u0026ndash;18%. The OMC of 10% binder content was 21.4%, 27.5%, and 24.4% for soil-fly ash mixture, soil-cement mixture, and soil-fly ash-cement mixture, respectively, where unstabilized soil\u0026rsquo;s OMC was 20.3%. The increase in OMC is typically associated with the presence of finer particles and the bonding formed between soil particles and binders, leading to greater water retention and plasticity in the soil-binder mixtures [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Additionally, another study observed that the presence of large, hollow spheres in fly ash leads to a rise in the OMC value as the binder content in the soil increases [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.3 Optimum fly ash and cement content for maximum unconfined compressive strength of clay soil\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eThe test results presented in Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e illustrate the progression of UCS of soil-binder against curing time for various ratios of fly ash and cement content. The UCS of untreated soil samples are 270.99 kPa and 289.07 kPa after 7 and 28 days of curing, respectively. The plots indicate that the soil's strength increased with curing time when fly ash and cement were added individually, as expected. Interestingly, it was observed that the strength improvement rate increased until reaching a specific percentage of fly ash and cement content. This phenomenon was also evident when both fly ash and cement were used in the soil.\u003c/p\u003e \u003cp\u003eThe UCS of the soil exhibited a rising trend with the rise in fly ash content up to a certain percentage, specifically 5% (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). For 7- and 28-day curing periods, this binder (5% fly ash) provided UCS of 349.15 kPa and 430.96 kPa, respectively, representing a notable increment of 28.84% and 49.08% compared to untreated soil. However, beyond the 5% fly ash content, a considerable depletion in strength was observed. These results delineate two distinct zones (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e): an active zone (0\u0026ndash;5% fly ash) and a deterioration zone (above 5% fly ash) [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Other researchers have observed this phenomenon across varying percentages of fly ash in several kinds of soil [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The impact of the deterioration zone is significant, resulting in a reduction in the soil's strength below its normal level. Notably, at 3 and 7 days of curing, 20% (SF20) and 25% (SF25) fly ash content provided less strength than the original soil's strength alone. Similar observations of a deteriorating phenomenon in different percentages of fly ash content in clay soil have been reported by other researchers [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The decline in strength can be attributed to two main factors. Firstly, the limited strengthening capacity of fly ash is a critical factor contributing to its inability to enhance the strength of this type of soil. Secondly, insufficient coverage of contact points between the soil and fly ash further exacerbates the soil-fly ash particles bonding [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. While adding fly ash to a maximum of 5% may adequately cover all available contact points in the soil, exceeding this percentage results in a decline in strength.\u003c/p\u003e \u003cp\u003eThe strength results from the experiment demonstrate that the use of cement as a binder material in soil leads to a better strength development compared to fly ash, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e - a result consistent with Sumesh et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, the findings reveal that the rate of development for soil-cement mixtures decreases beyond a certain binder content for this specific soil type. With an 8% cement content, the soil-cement mixture generates a UCS of 775.45 kPa over 28-day curing periods, representing a significant increment of 168.26% compared to the unstabilized soil strength. The increment rate remains substantial up to 12% cement content, yielding a UCS of 883.42 kPa. However, beyond 8% cement content, the rate slows down, reaching 933.28 kPa for 18% cement content. Consequently, these results delineate two distinct zones (refer to Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e): an active zone (0\u0026ndash;8% cement) and an inert zone (above 8% cement). While a comparable active zone was identified for soil-cement mixtures as seen with soil-fly ash mixtures, a new inert zone emerges, differentiating it from soil-fly ash mixtures, where no significant strength development occurs. This observation aligns with a similar zone pattern reported by Horpibulsuk et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], where an active zone was identified up to 10% cement content.\u003c/p\u003e\u003cp\u003eIn the context of combining both fly ash and cement binder (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e), the strength increment of soil was smooth for the entire curing period up to 10% binder content (SF5C5: 5% fly ash and 5% cement). At 10% binder content (SF5C5), the produced UCS of soil-binder was 689.60 kPa, which was 90.21% higher than the unstabilized soil\u0026rsquo;s strength for the 28-day curing period. Beyond 10% binder (SF5C5), slightly irregular strength development occurred throughout the entire curing period. The maximum increase of 34.42% increment rate was found for 6% binder content (SF3C3) in soil, generating 520.47 kPa UCS. The increment rate remained favorable up to 12% binder content (SF6C6). Starting from 12% binder content (SF6C6), the strength increment rate decreased rapidly and continued until 16% binder content (SF8C8). Beyond 16% binder content (SF8C8), the strength started to diminish. Overall, the stabilized soil strength for the 28 days produces three zones for different binder contents (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e): an active zone (0\u0026ndash;12% binder content: fly ash and cement), an inert zone (12\u0026ndash;16% binder content: fly ash and cement), and a deterioration zone (above 16% binder content: fly ash and cement). A group of researchers have found similar results, indicating that strength develops up to 25% fly ash content, irrespective of the amount of cement mixed [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis study demonstrates that all soil samples treated with fly ash and cement exhibit enhanced UCS compared to untreated soil. This strength improvement is attributed not only to the pozzolanic [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] and hydration reactions [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] but also to the presence of iron and aluminum oxides in the soil [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Interestingly, approximately 50% of the strength increase occurs within the first 7 days of curing. Several factors influence the rate and level of strength development, including the type of clay minerals present, the type of fly ash, the proportion of fly ash and cement, ambient temperature, and curing environment [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Figures\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, and \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e illustrate that the UCS of the soil increases over curing time. This is primarily due to the pozzolanic reaction of fly ash and the hydration reaction of cement. While the hydration reaction is faster, the pozzolanic reaction requires more time to develop a bond [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The free lime in fly ash reacts with alumina and silica in the existence of water to form calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) gels, which act as binders connecting soil particles [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Similarly, the hydration and pozzolanic reactions of cement also contribute to the binding of soil particles, resulting in a higher UCS compared to fly ash alone [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Verification of binder effects on soil stabilization by SEM image analyses","content":"\u003cp\u003eThe interaction between soil and optimum composites of cement and fly ash used in this research are closely observed in scanning electron microscopy (SEM) test. Figures\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e (a)-(d) show the SEM images of soil (S), soil\u0026thinsp;+\u0026thinsp;5% fly ash (SF5), soil\u0026thinsp;+\u0026thinsp;8% cement (SC8), and soil\u0026thinsp;+\u0026thinsp;3% fly ash\u0026thinsp;+\u0026thinsp;3% cement (SF3C3), composites. As described in the Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e (a), the fine-sized particles of the clay soil sample look clotted or aggregated together and form an irregular appearance on the surface with significant pores. On the other hand, the sample with 5% fly ash after 28 days of curing gives a different appearance with more filled-up pores (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e (b)), and the pozzolanic behavior of fly ash with clay particles is indirectly revealed in the firm and stabilized surface of the voids previously appeared in the untreated soil sample. Again, the soil sample with 8% cement, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e (c), has a more filled surface, the voids are better covered, and the soil seems to be stabilized more than the two cases shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e (a) and 12 (b). As per the different mechanical properties test results discussed above, although the cement and fly ash both gave the characteristics of stabilizing clay soil, the cement is far more effective in treating soil, which is also observed through the SEM test results. In the SEM image shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e (d), the soil sample with optimum mixed additive percentages of 3% cement and 3% fly ash (SF3C3) shows a mostly stabilized condition with limited visible voids in the surface and the soil mass seems to be stiff enough. The UCS test of 28 days-soaked soil sample also revealed that the soil sample with 3% cement and 3% fly ash has the most satisfying strength which justifies the stiffness of the soil sample resulted in UCS test through the dense-looked surface of the soil sample in SEM image in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e (d). Islam et al. [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] also experienced good bearing capacity and lower consolidation settlement in clayey soil using recycled concrete aggregates as an additive and revealed the interaction through a similar case of SEM analysis. Yoobanpot et al. [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] discussed the microstructural behavior of treated clay soil with both cement kiln dust and fly ash, and found the filled-up pores with denser conditions in between clay particles due to the continuous growth of hydration of cement and fly ash particles during curing period and made the clay stiffer and increased strength.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThis study aimed to identify the optimal fly ash and cement content for maximizing the strength of clay soil. The laboratory investigation unveiled the alterations in the characteristics of the soil-binder mixtures. These findings provide valuable insights for stabilizing clay soil, guiding the selection of the optimal ratio of fly ash and cement to achieve desired strength in applications such as foundation bases, embankments, and sub-bases for pavements. The key findings are summarized below.\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eSoil-binder mixtures consistently exhibit MH or OH across various binder content ranges.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe MDD of soil-binder mixtures tends to decrease as the binder combination increments increases, while the OMC exhibits an increasing trend with the rise in binder content. Notably, the decreasing trend in MDD of soil-binder mixtures is more pronounced for fly ash as a binder compared to cement, especially up to around 7%. However, beyond this point, the trend reverses, indicating a higher rate of decrease in MDD for cement as the binder content continues to increase.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eFly ash as the sole binder in soil attains the highest unconfined compressive strength (UCS), reaching 430.96 kPa at a 5% binder content. In contrast, the optimal cement content, set at 8%, yields a UCS of 775.45 kPa after curing for 28 days.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe peak strength of soil-binder mixtures increment is observed at 6% binder content (SF3C3), resulting in a UCS of 520.47 kPa after a 28-day curing period. Beyond 6% binder content in soil, the strength increment begins to decrease. Consequently, the identified optimal fly ash and cement content for maximum strength is 3% for both binders.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe presence of both cement and fly ash in soil results in active, inert, and deterioration zones during strength development, depending on the specific binder content.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eSEM image analyses conducted on original soil, soil-5% fly ash (SF5), soil-8% cement (SC8), and soil-3% fly ash-3% cement (SF3C3) composites validate the findings of standard compaction and unconfined compression tests results. Overall, the stabilization effects of fly ash, cement and fly ash-cement on the studied soil can be ranked as: soil-5% fly ash (SF5)\u0026thinsp;\u0026lt;\u0026thinsp;soil-8% cement (SC8)\u0026thinsp;\u0026lt;\u0026thinsp;soil-3% fly ash-3% cement (SF3C3) composites.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors extend sincere appreciation for the invaluable support received from the Department of Civil and Environmental Engineering (CEE) at Shahjalal University of Science and Technology (SUST), which provided essential laboratory services for the successful execution of the current investigation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003eNo funding was received for conducting this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest/Competing interests\u0026nbsp;\u003c/strong\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003eAll necessary data will be available upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode availability\u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u0026nbsp;\u003c/strong\u003eN. M. R. Hoque participated in the conceptualization, methodology, and writing\u0026mdash;original draft, including all the tables and figures. S. Islam took part in the conceptualization, methodology, and writing\u0026mdash;review, including all the figures. S. Ray contributed to the research\u0026apos;s methodology, writing, and supervision, including all the tables. S. Sarker participated in the laboratory work and writing. J. Islam conducted the formal analysis.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eNishat A, Hussain Z, Roy MK, Karim A. Freshwater wetlands in Bangladesh: issues and approaches for management. In IUCN; 1993 [cited 2024 Feb 4]. p. 9\u0026ndash;22. 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Geotechnical Properties of Fly Ash and Soil Mixtures for Use in Highway Embankments. In Denver, CO, USA; 2011. p. 11.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTuran C, Javadi AA, Vinai R. Effects of Class C and Class F Fly Ash on Mechanical and Microstructural Behavior of Clay Soil\u0026mdash;A Comparative Study. Materials. 2022;15(5):1845.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAxel M, Li X, Wen F, An MX. Microstructure and Strength Parameters of Cement-Stabilized Loess. Geotechnics. 2023;3(2):161\u0026ndash;78.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGhavami S, Rajabi M. Investigating the Influence of the Combination of Cement Kiln Dust and Fly Ash on Compaction and Strength Characteristics of High-Plasticity Clays. 2021;5:9\u0026ndash;16.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNoaman MF, Khan MA, Ali K, Hassan A. 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Assessment of strength development in blended cement admixed Bangkok clay. Construction and Building Materials. 2011;25(4):1521\u0026ndash;31.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReema T, Kalita A. STRENGTH CHARACTERISTICS OF RED SOILS BLENDED WITH FLY ASH AND. IJIRSET. 2013;3(4):270\u0026ndash;3.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZeng Q, Li K, Fen-chong T, Dangla P. Determination of cement hydration and pozzolanic reaction extents for fly-ash cement pastes. Construction and Building Materials. 2012;27(1):560\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYoobanpot N, Jamsawang P, Horpibulsuk S. Strength behavior and microstructural characteristics of soft clay stabilized with cement kiln dust and fly ash residue. Applied Clay Science. 2017;141:146\u0026ndash;56.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIslam S, Islam J, Hoque NMR, Hasan K. Improving geotechnical properties of soil of hillock slope using crushed recycled concrete aggregates. Journal of Engineering Research. 2023;11(4):293\u0026ndash;300.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIslam S, Islam J, Robiul Hoque NMd. Improvement of consolidation properties of clay soil using fine-grained construction and demolition waste. Heliyon. 2022;8(10):e11029.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Footnotes","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e Percentage of binder = (mass of binder) / (mass of binder\u0026thinsp;+\u0026thinsp;mass of soil) * 100.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Clay soil, fly ash stabilization, cement stabilization, maximum dry density, unconfined compressive strength","lastPublishedDoi":"10.21203/rs.3.rs-4679698/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4679698/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFly ash and cement are commonly used as soil stabilizers, offering environment friendly solutions for soil improvement. This study aims to determine the ideal combination of fly ash and cement to improve the geotechnical behavior of clay soil collected from a future building construction project in Sylhet, Bangladesh. Strength development in soil was assessed across a wide range of fly ash (0\u0026ndash;25%) and cement (0\u0026ndash;18%) during 3-, 7-, 14-, and 28-day curing periods. Tests included in this research are: Atterberg limits test, standard Proctor tests, unconfined compressive strength (UCS) and scanning electron microscopy tests. Incorporating fly ash, cement, or both decreased maximum dry density (MDD) and increased optimum moisture content (OMC) of the soil, while soil classification remained consistent. The investigation revealed that fly ash initially had a higher reduction rate in MDD of the mixtures up to around 7% binder content, before cement took precedence. Optimal soil-binder strength was achieved at 5% fly ash and 8% cement after curing for 28 days individually. However, the optimal combination of the binders was identified as 6% (3% fly ash and 3% cement), yielding a 99.51% increase in UCS compared to untreated soil after 28 days. Scanning electron microscopy tests show that the compactness of clay soil increases due to the addition of fly ash and cement. This binder combination (3% fly ash and 3% cement) could be suitable for stabilizing clay soil beneath the shallow foundation of a residential building in the study area.\u003c/p\u003e","manuscriptTitle":"Optimization of fly ash and cement for stabilizing clay soil","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-06 06:14:07","doi":"10.21203/rs.3.rs-4679698/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"786c01dc-a9c8-4a49-995b-1972578e9f83","owner":[],"postedDate":"August 6th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-08-22T11:23:55+00:00","versionOfRecord":[],"versionCreatedAt":"2024-08-06 06:14:07","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4679698","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4679698","identity":"rs-4679698","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}