Geotechnical Performance of Red Soil Stabilized with Fly Ash and Reinforced with Polypropylene Fibres

Geotechnical Performance of Red Soil Stabilized with Fly Ash and Reinforced with Polypropylene Fibres | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Geotechnical Performance of Red Soil Stabilized with Fly Ash and Reinforced with Polypropylene Fibres Nekibuddin Ahmed, Abhijit Deka This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8369111/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 The environmentally conscious and viable alternative to the traditional binders like lime and cement includes the sustainable use of industrial by-products for soil stabilization. This study proposes an innovative solution beyond the sole use of fly ash for geotechnical applications such as Class F fly ash (15–30%) and polypropylene fibres (0.5–2%) in high-plasticity red soils. The laboratory testing, including compaction, Unconfined Compressive Strength (UCS), stiffness, and strength ratio, allows us to discern the changes in density, strength, and ductility. The findings from the study showed that the addition of fly ash to the mixtures increased the strength and stiffness significantly, with the best result obtained using 20% fly ash. The reasons for such an increase in properties are the pozzolanic reactions taking place and causing the soil to become denser. Polypropylene fibres improved ductility, crack resistance, and post-peak performance but diminished the efficiency of compacting and stiffness at high dosages (> 1.5%). The optimum mix was 20–25% fly ash with 1% polypropylene fibre, which significant combined improvement in strength, ductility, and workability. Such results of combining fly ash and artificial fibres in the stabilization will have practically resulted in the application of poor-quality road sub-grades and other infrastructure projects on poor soils. Red Soil (RS) Fly ash (FA) Stiffness Strength ratio Unconfined Compressive Strength (UCS) Polypropylene fibre Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Introduction One major factor leading to the ever-increasing cost of high-quality construction materials was the fact that they were widely used in various geotechnical applications. To overcome this, engineers are always looking at different soil improvement techniques for the enhancement of the Engineering characteristics of the native soils [1]. The primary objective of soil improvement is to enhance the shear strength of the soil, reduce settlement, and improve resistance to harsh environmental conditions like the ones caused by repeated freeze-thaw cycles and to minimize or eliminate all problems connected with weak soils [2].Mechanical and chemical methods are available for the treatment of both sandy and clayey soils [3].The already existing and well-documented methods in the literature for both mechanical and chemical soil enhancement have been successfully adopted in many cases to improve the soil properties [4]. The use of fibre reinforcement in soil stabilization became a widely noticed field in recent years and is known as fibre-reinforced soil (FRS). Fibres in different sizes and aspect ratios are commercially available and can be randomly mixed with soil to be used in an almost exact manner to any other traditional Stabilizing agents such as cement and lime [5]. The isotropic strength characteristics arise from the random orientation of fibres within the soil mass, which prevents the formation of weak planes that could otherwise develop due to preferential fibre alignment, which could be weakened by applying strong moment forces. In sands and clays, the cited results of the investigations conducted on discrete fibre-reinforced systems have directed more appropriate applications of these fibres in geotechnical structures-consequently, in embankments, retaining walls, pavement subgrades, and landfill liners & covers [6]. From a construction standpoint, soft clays and other problematic soils often result in excessive settlement and structural distress, this behaviour is primarily attributed to their low shear strength and high compressibility [7,8 Expansive soils, in particular, are widely recognized for causing significant damage to structures and the surrounding environment when they are not adequately treated or stabilized [9].These soils have been identified as a major cause of damage to light buildings and pavements, exceeding the impact of other natural hazards such as earthquakes and floods. Over the past few decades, swelling-induced damage has been widely observed in semi-arid regions, Such effects are manifested as cracking and deformation in roadways, building foundations, slab-on-grade structures, canal linings, reservoirs, irrigation systems, and underground utility networks. [10,11]. Thus, it is pivotal that soil properties are improved prior to construction. The available ground improvement techniques include among others soil replacement, dynamic compaction, stone columns, lime or cement columns, and fibre reinforcement. The choice of a particular method will depend on the soil quality, its effectiveness, how easy it is to build and affordable it is. Apart from mechanical reinforcement, compaction techniques and the use of chemicals are also very popular practices in soil stabilization. The most commonly employed materials for soil stabilization include lime, cement, fly ash, blast furnace slag, steel slag, rice husk ash, and natural or synthetic fibres.[12]. Stabilization methods based on cement and lime are well established; however, they are still limited in application, mainly due to their high costs and environmental concerns, particularly carbon dioxide emissions during cement production. Besides, cement-treated soils may swell with the formation of expansive minerals like ettringite and thaumasite in sulphate-rich soils [13]. Therefore, industrial by-products such as fly ash, blast furnace slag, rice husk ash, and steel slag have emerged as more sustainable and environmentally friendly alternatives [14,15]. The present exploratory effort is a detailed appraisal of polypropylene fibre (PPF) and fly ash (FA) for improving the strength and compressibility of red soil (RS). This study is anticipated to provide significant insight into these improvements to render greater confidence in the wider application of PPF and FA in geotechnical engineering, thereby making red soil an even more worthwhile material for foundations and other infrastructure project. Materials Red Soil The soil used for the investigation was red soil silt obtained from the nearby hilly region of Guwahati in Assam, India. The sieving analysis of soils was carried out according to IS: 2720 (Part 4)–1985. Water content-dry density relationship was determined by light compaction as per IS: 2720 (Part 7)–1983. In the determination of Atterberg limits by the same procedure, IS: 2720 (Part 5)–1985 was followed. According to Indian standards of soil classification, the soil can be classified as CH (high plasticity clay). A summary of the engineering properties of the soil is presented in Table 1. Fly ash Fly ash is a non-crystalline pozzolanic and slightly cementitious material. The physical properties of fly ash used in the study are given in Table 1 and the chemical properties of fly ash in Table 3. The fly ash was collected from the National thermal power plant in Salakati, Kokrajhar, Assam, India as shown in Fig 1(b). From the chemical composition in Table 3, it is seen that the CaO content of fly ash was only 2.6% [17]. The specific gravity of the fly ash was 2.13, which was lower than the value of 2.54 of the red soil. The constituent of fly ash is mainly of the silt-sized fraction (60.12%). Polypropylene fibre Polypropylene fibre is a synthetic thermoplastic polymer produced from propylene monomer through the process of polymerization. It is composed mainly of carbon and hydrogen atoms, making it a non-polar, hydrophobic, and chemically inert material. The fibre has a low density, high tensile strength, and excellent resistance to moisture and most chemicals [18]. Due to its lightweight and durable nature, polypropylene fibre is widely used in civil engineering applications for soil stabilization, concrete reinforcement, and geotextiles. The fibres, supplied by a commercial vendor, are elongated and measure 12 mm in length as shown in fig1. For the tests, fibres passing through a 4.75 mm sieve but retained on a 2 mm sieve were selected. The physical properties of the polypropylene fibre, as presented in Table 2, were provided by the supplier.” Table 1. Engineering Properties of Red Soil and Fly Ash Soil Property Fly Ash (FA) Red soil (RS) Specific Gravity 2.13 2.54 Particle size distribution Coarse sand(4.75mm-2mm) Medium Sand (2 mm–0.425 mm) Fine Sand(0.425mm-0.075mm) Silt+Clay(<0.075mm) 0.19 0.83 38.12 60.12 0 0 0 100 Atterberg’s limit Liquid limit, % Plastic Limit, % Plasticity index, % Non-Plastic 65.05 21.71 43.34 USCS Classification ML CH Maximum dry density g/cm³ Optimum moisture content (%) 1.39 18.25 1.78 18.36 Table 2. Physical Properties of Polypropylene Fibre Fibre Characteristics Test Standard Result Fibre cross section Round Compressive strength ASTM C 39 5.40% Cut length, mm 12 Tensile strength ASTM D 638 7.90% Tear strength, N/mm² ≥ 400 Flexural strength ASTM C 1018 / ASTM C 1399 11.40% Elongation at break, % ≤ 80 Flexural toughness ASTM C 1018 / ASTM C 1399 improved Fibre dispergation excellent Melting Point, °C 163 – 170 Diameter, μm 18 Density, g/cm³ 0.91 Table 3. Chemical properties of fly ash Oxide Chemical characteristics SiO₂ 55.5 Al₂O₃ 23.5 Fe₂O₃ 2.5 MnO 1.4 MgO 0.9 CaO 2.6 Na₂O 0.7 K₂O 0.9 TiO₂ 3.7 P₂O₅ 2.0 SiO₂ + Al₂O₃ + Fe₂O₃ 81.5 Loss on ignition, LOI (%) 5.8 Classification (ASTM C618-05) F Methods Preparation of Fly ash blended red soil The red soil and fly ash used in this study were air-dried, pulverized, and sieved to ensure uniformity, after which fly ash was mixed with red soil in proportions of 15%, 20%, 25%, and 30% by dry weight. Each mix was thoroughly blended in the dry state to obtain a homogeneous mixture, and Standard Proctor compaction tests were conducted as per IS 2720 (Part 7) to determine the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC). Water was added in stages and compaction was carried out using standard Proctor energy, and the MDD and OMC were obtained from the respective compaction curves for each mix[19]. Based on the identified MDD and OMC values, specimens were prepared for the Unconfined Compressive Strength (UCS) test by compacting the red soil–fly ash mixtures in UCS molds at the corresponding MDD and OMC, followed by careful extrusion and testing in accordance with IS 2720 (Part 10) to evaluate the strength behaviour of the stabilized soil. Preparation of Fly ash blended red soil reinforced with Polypropylene fibre The red soil and fly ash were air-dried, pulverized, and sieved to ensure uniformity, after which fly ash was added to red soil in proportions of 15%, 20%, 25%, and 30% by dry weight to obtain homogeneous red soil–fly ash (RS–FA) mixtures. Polypropylene fibre (PPF), cut into 12 mm lengths, was then blended with each RS–FA mix in proportions of 0.5%, 1%, 1.5%, and 2% by dry weight and uniformly distributed through thorough dry mixing to avoid fibre balling. Standard Proctor compaction tests were conducted on all RS–FA–PPF mixes as per IS 2720 (Part 7) to determine the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC).As the MDD and OMC values were evaluated, the specimens were made compact by compacting the mixtures at MDD and OMC and extruded from the molds for testing in UCS mould in accordance with IS 2720 (Part 10) then the strength behaviour and other behaviour like strength ratio(SR),Stiffness of polypropylene fibre-reinforced red soil-fly ash mixtures was evaluated[20]. Sample Preparation for Strength Test For the Preparation Strength test, both the mixtures used in unconfined compression testing, red soil-fly ash (RS-FA) and fly ash-red soil-polypropylene fibre (RS-FA-PPF), were prepared on the basis of Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) values obtained from the Standard Proctor compaction tests. The materials were hand-mixed with care to achieve uniform and consistent blending. Cylindrical test specimens having dimensions of 38 mm diameter and 76 mm height were prepared using a standard UCS mold, each specimen compacted in three equal layers to achieve the desired MDD at the OMC. The UCS behaviour of RS-FA mixes with and without polypropylene fibre reinforcement is observed and externally evaluated. Three identical specimens were in general tested for each mix condition, and an average UCS value for this mix condition was reported. The mass of fly ash-red soil-polypropylene fibre dry was calculated using a general equation. $$\:W={W}_{RS}+{W}_{FA}+{W}_{PPF}\dots\:\dots\:\left(1\right)$$ Where \(\:{W}_{RS}\) , \(\:{W}_{FA}\) , and \(\:{W}_{PPF}\) denote the weights of red soil, fly ash, and polypropylene fibre, respectively. Table 4 Details of red soil–fly ash–polypropylene fibre mixtures for tests conducted Designation (W = W RS + W FA +W PPF ) Variation of RS (% by total dry weight) Variation of FA (% by total dry weight) Variation of PPF ((% by total dry weight)) 100RS-0FA-0PPF 100 0 0 0RS-100FA-0PPF 0 100 0 85RS-15FA-0PPF 85 15 0 80RS-20FA-0PPF 80 20 0 75RS-25FA-0PPF 75 25 0 70RS-30FA-0PPF 70 30 0 85RS-15FA-0.5PPF 84.58 14.93 0.5 85RS-15FA-1PPF 84.15 14.85 1 85RS-15FA-1.5PPF 83.73 14.78 1.5 85RS-15FA-2PPF 83.3 14.70 2 80RS-20FA-0.5PPF 79.6 19.9 0.5 80RS-20FA-1PPF 79.2 19.80 1 80RS-20FA-1.5PPF 78.8 19.70 1.5 80RS-20FA-2PPF 78.4 19.60 2 75RS-25FA-0.5PPF 74.63 24.88 0.5 75RS-25FA-1PPF 74.25 24.75 1 75RS-25FA-1.5PPF 73.88 24.63 1.5 75RS-25FA-2PPF 73.5 24.50 2 70RS-30FA-0.5PPF 69.65 29.85 0.5 70RS-30FA-1PPF 69.30 29.70 1 70RS-30FA-1.5PPF 68.95 29.55 1.5 70RS-30FA-2PPF 68.60 29.40 2 Result and Discussions Compaction Characteristics Compaction Characteristics of RS, RS-FA mixes The compaction features of red soil (RS), fly ash (FA), and their mixes reveal major patterns in Maximum Dry Density (MDD) and Optimum Moisture Content (OMC). As shown in Fig. 2 , MDD of pure red soil is at 1.78 g/cc, the highest in the group which indicates it is very compactable and goes along with its very good quality to be compacted. On the contrary, fly ash is quite the opposite; its MDD is only at 1.39 g/cc due to being light and very porous. As fly ash is being mixed with red soil in a portion of 15%, 20%, 25%, and 30%, the MDD goes down from 1.76 g/cc to 1.65 g/cc in a progressive manner. The reason for this is that heavier soil particles have been replaced with lighter fly ash particles, thus leading to less packing density and lower dry weight per unit volume. As for OMC, it shows the same pattern in the beginning for red soil and fly ash which is around 18.3%. But as the fly ash content in the mix goes up, the OMC slowly rises and it eventually touches the maximum of 19.52% at 30% fly ash. The reason for this is that the fly ash particles have a higher surface area and are more absorptive, thus they require more water to aid in lubrication and compaction. The combination of decreasing MDD and increasing OMC is clearly indicates that although fly ash can be used for the improvement of red soil, there is a compromise. More fly ash lead to lower density and higher water demand which may not help with strength and stability. Consequently, it seems that up to 20% fly ash content is the best choice according to the trends because it still gives a high MDD and does not ask for a lot of water. Past this point, the benefits are not significant anymore and the mix could easily be less durable and strong for geotechnical applications. Effect of PPF on RS-FA-PPF mixture The detailed evaluation and thorough examination of the compaction data show that the addition of polypropylene fibre (PPF) to fly ash (FA)-stabilized red soil changed its densification behaviour as shown in Fig. 3 . The major factor in this change was the particle-disruption mechanism, while another factor was the increased moisture requirement. For the entire range of FA contents (15–30%), the maximum dry density (MDD) not only decreases, but also the PPF dosage goes up, with the most intensive reducing point at 2% PPF where MDD values drop down to 1.453–1.483 g/cc, meaning 5–6% less than for the mixtures with 0.5% PPF. This drop is because of the fibre working as a low-density, high-aspect-ratio component that limits optimal particle packing, causes continuous voids, and then caps the energy of compaction through the creation of the bridging effect. At the same time, the optimum moisture content (OMC) keeps on being quite constant at low PPF volumes (0.5–1.5%) but shows a steep rise at 2% PPF, going beyond 24.7% in all mixes, with the reason being the increased hydrophobic surface area and the demand for extra water to make the fibrous matrix smooth. The presence of PPF also affects the moisture content needed to keep the soil in the best condition for compaction. Fly ash has a moderating effect on these trends as it consistently lowers the baseline MDD due to its lower specific gravity, yet it is predominately the fibre concentration that governs the adverse compaction effects. Recognizing 2% PPF as a critical point, where compaction efficiency is significantly reduced, thus compaction dosage optimization is essential, particularly with the 0.5–1.5% PPF range at 1% PPF combined with 20–25% FA giving a more practical and feasible balance between reaching the density requirement and obtaining the strength from fibres for geotechnical applications. Strength Characteristics Effect of fly ash on RS-FA mixes on UCS Initially, the stress-strain behaviour of red soil (RS) mixed with different amounts of fly ash (FA) has shown that the maximum stress and ductility of the soil were increased as the amount of fly ash reached the optimum. The graph in Fig. 5 shows that the red soil that has not been treated (RS) has the lowest peak stress and a quite brittle reaction, that is, it breaks easily and at lower strain values. The peak stress and the post-peak strain behaviour have been increased markedly by the addition of fly ash, especially in case of the specimen RS-20FA which shows the highest peak stress of about 510 kPa at a strain of nearly 3.4%, that is, the best performance is signified. The initial linear portion of the stress-strain curves (up to ~ 2% strain) for all mixes suggests similar stiffness in the early loading stages. The peak strength, however, rises considerably with the addition of 15% and 20% FA, which can be ascribed to the pozzolanic reaction between the calcium in the soil and the siliceous/aluminous fly ash, creating cementitious compounds like C–S–H gels. This reaction not only solidifies but also bonds the particles of the soil better. The RS-20FA's improved ductility and strain tolerance at peak stress indicate the enhanced energy absorption capacity which is advantageous for the geotechnical applications that experience dynamic loading. Specimens with 25% and 30% fly ash have less peak stress and more strain softening than those with 20% FA. This behaviour indicates that the presence of too much fly ash might cause the soil-fly ash matrix to be demolished due to the unavailability of enough calcium or moisture for sustaining the pozzolanic reaction, therefore leading to incomplete bonding and a weaker structure. Even though RS-25FA has much better strength than untreated RS, the little extra strength over RS-15FA is not worth the increased fly ash content from both the performance and sustainability point of view. The RS-30FA sample has shown a strength reduction, which ratifies that too much of a non-reactive filler material can dilute the phases that contribute to strength. In conclusion, the study indicates that the addition of fly ash has significantly improved the strength and ductility of red soil, with 20% fly ash content being the optimum. This not only increases the soil's structural performance but also provides an environmentally friendly way of reusing industrial by-products through soil stabilization as shown in Fig. 4 . Effect of PPF on RS-FA-PPF mixes on UCS The behaviour of unconfined compressive strength (UCS) of red soil that was treated with both fly ash and polypropylene fibre is a good example of the interaction between the two additives in strength enhancement. To ensure consistency in the experiments, all the specimens were compacted at their corresponding maximum dry density and optimum moisture content obtained from the Standard Proctor test. The data showed from the that UCS increased at first with the increase of polypropylene fibre content for a specific fly ash amount, peaked around 1% PPF and then gradually fell. Looking at the Fig. 7 , the UCS at 20% fly ash was 481.04 kPa at 0.5% PPF, went up to the highest 508.14 kPa at 1% PPF and then got lower again when more fibres were used. This pattern means that there is a certain fibre content that gives the best result, where the effective stress transfer and the crack-bridging mechanisms are fully engaged, on the other hand, more fibres will result in poor distribution, fibre clumping and more voids which will therefore reduce the compressive strength. Also, at a constant fibre content of 1% PPF, UCS went up with fly ash till 20% and then it went down. The very first increase in UCS was due to the pozzolanic reactions of fly ash and soil that made the bonding of the particles and the densifying of the matrix stronger, on the contrary, if too much fly ash is used, it may just spread around the soil matrix without being effectively bonded as shown in Fig. 6 . The highest UCS value that is 508.14 kPa, was for the mix of 80RS–20FA–1PPF which meant that there was a combined action of fly ash-induced cementation and fibre strengthening. In conclusion, it is concluded that the results demonstrate that fly ash and polypropylene fibre, when added in controlled amounts, would make a significant difference to the compressive strength of red soil and this not only stresses the importance of optimizing both fly ash and fibre contents for the application of sustainable ground improvement but also the need to continue to do so. Effect of FA on strength ratio of RS-FA mixes The evaluation of the strength ratio of red soil-fly ash mixes was done in order to measure the compressive strength improvement of red soil that was not treated. The enhancement in UCS resulting from the mixing of FA can be represented by the strength ratio (SR) defined as $$\:SR=\frac{UC{S}_{RS-FA\:}}{UCS}$$ 2 …… where UCS RS - FA is the UCS of RS-FA mixes and UCS is the UCS of only red soil. The findings suggest that the incorporation of fly ash greatly improves the strength ratio up to an ideal amount, after which the strength ratio starts to decrease as shown in Fig. 8 . Specifically, the untreated red soil's strength ratio was raised from 1.00 to 1.10 and 1.17 with the addition of 15% and 20% fly ash, thus clearly indicating even more the improvement in load-bearing capacity. One of the reasons for this increase is better packing of the particles and the commencement of pozzolanic reactions, the fly ash Class F siliceous and aluminous components reacting with the calcium in the soil and thus making the interparticle bonding stronger. However, when fly ash content was further increased, there was a consistent decline in strength ratio to 1.14 and 1.08 for 25% and 30% fly ash, respectively. One possible reason for the lower strength ratio at higher fly ash content is that the soil matrix has been diluted and not enough calcium is available to support the pozzolanic bonding. The overall results point to 20% fly ash as the ideal content for obtaining the best strength ratio for red soil-fly ash mixtures, thereby emphasizing the beneficial role of regulated fly ash use in environmentally friendly soil stabilization processes. Effect of PPF on RS-FA-PPF mixes on SR The strength ratio of red soil-fly ash-polypropylene fibre (RS-FA-PPF) mixtures was measured to assess the strength enhancement in comparison to untreated red soil. The raise in UCS caused by the incorporation of FA can be expressed in terms of strength ratio (SR) defined as: $$\:SR=\frac{UC{S}_{RS-FA-PPF\:}}{UCS}\dots\:\dots\:$$ 3 where UCS RS−FA−PPF is the UCS of RS-FA-PPF mixes and UCS is the UCS of only red soil. The study results illustrate that the combination of fly ash and polypropylene fibre consistently results in the strength ratio upgrade until the optimal ratio is reached, afterward, the reduction is seen in Fig. 9 . The strength ratios have all increased for the fly ashes at first, then the FIBRE content increase, and finally, the maximum strength ratios are 1–1.5% PPF. The topmost strength ratio recorded was approximately 1.26 for the 80RS–20FA–2PPF mix, which was then the 75RS–25FA–2PPF and 80RS–20FA–1PPF mixes. The significant synergistic activity of fly ash and FIBRE reinforcement has been indicated by this. The strength ratio improvement was grounded on the factors of the mixed fly ash matrix that was updated by the ash and the gradual pozzolanic bonding and the Fibres that amplified the stress transfer as well as the halt of crack initiation and propagation. But when the FIBRE contents turned high (especially for the case of 2% PPF in some mixes) the strength ratio was cut down at fly ash contents such as 30% where the strength ratio was close to unity. The reduction in the strength ratio may be attributed to the fibre issues like agglomeration, poor dispersion and an increase in voids which are all working against the reinforcement benefits. In conclusion, the results are suggestive that RS–FA–PPF mixes are stronger than RS–FA mixes, with the optimal combination being of 20–25% fly ash and 1–1.5% polypropylene fibre, thus amplifying the significance of dosage optimization in maximizing strength enhancement for sustainable soil stabilization applications. Effect of stiffness of PPF on RS-FA-PPF mixture Stiffness modulus is used to measure the ability of soil to resist deformation. According to Tang et al. [21], the modulus is expressed as the slope of the linear portion of the stress–strain curve. From Fig. 7 , the connecting line segment BA is selected for each curve, and the modulus (E) is expressed using the following formula: $$\:E=\frac{\varDelta\:\sigma\:}{\varDelta\:\epsilon\:}=\frac{{\sigma\:}_{A}-{\sigma\:}_{B}}{{\epsilon\:}_{A}-{\epsilon\:}_{B}}$$ 4 …… To evaluate the axial loading deformation response of RS-FA-PPF composites, a study was performed to show the impact of fly ash and polypropylene fibre inclusion on the stiffness characteristics of red soil. It was found that the stiffness was greatly affected by both the fly ash content and the fibre dosage, which showed a clear optimum combination in Fig. 11 . Generally, fly ash usage transformed the soil into a denser and stronger mass which contributed a lot to stiffness, while polypropylene fibres did good by providing even stress distribution and resisting deformation. The admixture of stiffness values met with an upward trend as the fibre increment was made until it reached the optimum range of about 1-1.5% PPF, thereafter a downward shift was noticed. For example, the composites with 25% fly ash showed a great increase in softness, which at last got the peak value of about 139.5 for the 75RS-25FA-2PPF blend, and that too was the case of a significant improvement in being rigid due to significant improvement effective fibre support and nice soil-fly ash interaction. Likewise, combinations with 15% fly ash saw a rise in stiffness with average fibre usage, which was particularly the case of improved bonding and crack-bridging provided by the fibres as shown in fig .10 But, at high fibre contents, especially in 2% PPF in some mixes, a drop in stiffness was noticed, particularly for the cases of 20% and 30% FA mixes which had either lower or higher fly ash contents. The reason might be the same as that the fibres got stuck together, were not evenly dispersed, and thus there were more voids, which led to less matrix continuity and stiffness. All in all, opting for the combined use of fly ash and polypropylene fibre in red soil leads to a considerable enhancement of the soil stiffness when they are employed in the right proportions. Fly ash by pozzolanic and filler effects strengthens the matrix and at the same time fibres help to make deformation harder, thus RS-FA-PPF composites are perfect for the tasks needing heightened stiffness and diminished compressibility. Conclusion Based on the thorough laboratory study, it was concluded that the joint use of fly ash (20–25%) and polypropylene fibres (1%) performed very well and were especially advantageous for the red soil with high plasticity, thus giving the right strength, stiffness, ductility, and compaction characteristics. Fly ash through its pozzolanic reactions contributes to strength and matrix densification while polypropylene fibres help to the ductility, crack resistance, and post-peak performance. The best mix proportion (20–25% FA plus 1% PPF) produced the maximum unconfined compressive strength of 508.14 kPa, an improved strength ratio, and increased stiffness, though too much fibre content (> 1.5%) or higher fly ash dosage meant reduced compaction efficiency and material stiffness. These results certify that the use of industrial by-products and synthetic Fibres as a stabilization method for weak subgrade soils in infrastructure projects is a sustainable and effective practice that not only benefits engineering performance but also helps the environment. Declarations Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contribution Author ContributionsNekibuddin Ahmed: Conceptualization, methodology, experimental investigation, data curation, formal analysis, visualization, and original draft preparation.Abhijit Deka: Supervision, validation, resources, critical review and editing of the manuscript, and overall guidance.All authors have read and approved the final version of the manuscript. References Fondjo, A. A., Theron, E., & Ray, R. P. (2021). Stabilization of expansive soils using mechanical and chemical methods: a comprehensive review. Civ Eng Archit, 9(5), 1295-1308. https://doi.org/10.13189/cea.2021.090503. Abdel-Rahman, M. (2020). Review of Soil Improvement Techniques. https://doi.org/10.1007/978-3-030-62908-3_14 Al-Naje, F. Q., Abed, A. H., & Al-Taie, A. J. (2020). A review of sustainable materials to improve geotechnical properties of soils. Al-Nahrain Journal for Engineering Sciences, 23(3), 289-305. https://doi.org/10.29194/njes.23030289 Sabzi, Z. (2018). 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(2017). Effect of fly-ash on strength behaviour of clayey soil. International Research Journal of Engineering and Technology (IRJET), 4(7), 5-7. Li, L., Zhang, J., Xiao, H., Hu, Z., & Wang, Z. (2019). Experimental Investigation of Mechanical Behaviours of Fibre-Reinforced Fly Ash-Soil Mixture. Advances in Materials Science and Engineering, 2019(1), 1050536. https://doi.org/10.1155/2019/1050536 Tang L, Cong S, Geng L, Ling X, Gan F (2018) The effect of freezethaw cycling on the mechanical properties of expansive soils. Cold Reg Sci Techno 145:197–207 Nguyen, T. T., & Indraratna, B. (2023b). Natural fibre for geotechnical applications: Concepts, achievements and challenges. Sustainability , 15 (11), 8603. https://doi.org/10.3390/su15118603 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. 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7","display":"","copyAsset":false,"role":"figure","size":1105086,"visible":true,"origin":"","legend":"\u003cp\u003eStress vs strain relationship of RS-FA-PPF mixture\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-8369111/v1/442bd72dbf5f5802db88f767.png"},{"id":99313069,"identity":"2c314633-7127-4a8e-b273-48b63479b9fe","added_by":"auto","created_at":"2025-12-31 16:19:44","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":194932,"visible":true,"origin":"","legend":"\u003cp\u003eStrength Ratio of RS-FA mixture\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-8369111/v1/bcdb02ef2aea0e32cb3878e8.png"},{"id":99313280,"identity":"30defbdf-600d-45de-b81e-ca67e89488c6","added_by":"auto","created_at":"2025-12-31 16:19:57","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":270762,"visible":true,"origin":"","legend":"\u003cp\u003eStrength Ratio of RS-FA-PPF mixture\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-8369111/v1/f9a94aa4c1bb4f66bbb1d6fa.png"},{"id":99313294,"identity":"e9320f9a-48bf-47a6-af60-5b45c4336a53","added_by":"auto","created_at":"2025-12-31 16:19:58","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":398132,"visible":true,"origin":"","legend":"\u003cp\u003eBridge effect of fibre on soil mass [21]\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-8369111/v1/e2520de2e4583ab07d28244b.png"},{"id":99025680,"identity":"ad8b196a-7b1d-426d-a751-d223adbc7fde","added_by":"auto","created_at":"2025-12-26 07:03:27","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":249451,"visible":true,"origin":"","legend":"\u003cp\u003eStiffness characteristics of RS-FA mixture on PPF reinforcement\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-8369111/v1/a2ebf2cd17081838e27e066e.png"},{"id":99788481,"identity":"16126ef0-702e-43ae-86b9-c326a40f650d","added_by":"auto","created_at":"2026-01-08 12:46:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5795435,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8369111/v1/c53b9ab8-054c-4f8f-86d0-60ffcf643311.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Geotechnical Performance of Red Soil Stabilized with Fly Ash and Reinforced with Polypropylene Fibres","fulltext":[{"header":"Introduction","content":"\u003cp\u003eOne major factor leading to the ever-increasing cost of high-quality construction materials was the fact that they were widely used in various geotechnical applications. To overcome this, engineers are always looking at different soil improvement techniques for the enhancement of the Engineering characteristics of the native soils [1]. The primary objective of soil improvement is to enhance the shear strength of the soil, reduce settlement, and improve resistance to harsh environmental conditions like the ones caused by repeated freeze-thaw cycles and to minimize or eliminate all problems connected with weak soils [2].Mechanical and chemical methods are available for the treatment of both sandy and clayey soils [3].The already existing and well-documented methods in the literature for both mechanical and chemical soil enhancement have been successfully adopted in many cases to improve the soil properties [4].\u003c/p\u003e \u003cp\u003eThe use of fibre reinforcement in soil stabilization became a widely noticed field in recent years and is known as fibre-reinforced soil (FRS). Fibres in different sizes and aspect ratios are commercially available and can be randomly mixed with soil to be used in an almost exact manner to any other traditional Stabilizing agents such as cement and lime [5]. The isotropic strength characteristics arise from the random orientation of fibres within the soil mass, which prevents the formation of weak planes that could otherwise develop due to preferential fibre alignment, which could be weakened by applying strong moment forces. In sands and clays, the cited results of the investigations conducted on discrete fibre-reinforced systems have directed more appropriate applications of these fibres in geotechnical structures-consequently, in embankments, retaining walls, pavement subgrades, and landfill liners \u0026amp; covers [6]. From a construction standpoint, soft clays and other problematic soils often result in excessive settlement and structural distress, this behaviour is primarily attributed to their low shear strength and high compressibility [7,8 Expansive soils, in particular, are widely recognized for causing significant damage to structures and the surrounding environment when they are not adequately treated or stabilized [9].These soils have been identified as a major cause of damage to light buildings and pavements, exceeding the impact of other natural hazards such as earthquakes and floods. Over the past few decades, swelling-induced damage has been widely observed in semi-arid regions, Such effects are manifested as cracking and deformation in roadways, building foundations, slab-on-grade structures, canal linings, reservoirs, irrigation systems, and underground utility networks. [10,11]. Thus, it is pivotal that soil properties are improved prior to construction. The available ground improvement techniques include among others soil replacement, dynamic compaction, stone columns, lime or cement columns, and fibre reinforcement. The choice of a particular method will depend on the soil quality, its effectiveness, how easy it is to build and affordable it is. Apart from mechanical reinforcement, compaction techniques and the use of chemicals are also very popular practices in soil stabilization. The most commonly employed materials for soil stabilization include lime, cement, fly ash, blast furnace slag, steel slag, rice husk ash, and natural or synthetic fibres.[12]. Stabilization methods based on cement and lime are well established; however, they are still limited in application, mainly due to their high costs and environmental concerns, particularly carbon dioxide emissions during cement production. Besides, cement-treated soils may swell with the formation of expansive minerals like ettringite and thaumasite in sulphate-rich soils [13]. Therefore, industrial by-products such as fly ash, blast furnace slag, rice husk ash, and steel slag have emerged as more sustainable and environmentally friendly alternatives [14,15].\u003c/p\u003e \u003cp\u003eThe present exploratory effort is a detailed appraisal of polypropylene fibre (PPF) and fly ash (FA) for improving the strength and compressibility of red soil (RS). This study is anticipated to provide significant insight into these improvements to render greater confidence in the wider application of PPF and FA in geotechnical engineering, thereby making red soil an even more worthwhile material for foundations and other infrastructure project.\u003c/p\u003e"},{"header":"Materials","content":"\u003cp\u003e\u003cstrong\u003eRed Soil\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe soil used for the investigation was red soil silt obtained from the nearby hilly region of Guwahati in Assam, India. The sieving analysis of soils was carried out according to IS: 2720 (Part 4)\u0026ndash;1985. Water content-dry density relationship was determined by light compaction as per IS: 2720 (Part 7)\u0026ndash;1983. In the determination of Atterberg limits by the same procedure, IS: 2720 (Part 5)\u0026ndash;1985 was followed. According to Indian standards of soil classification, the soil can be classified as CH (high plasticity clay). A summary of the engineering properties of the soil is presented in Table 1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFly ash\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFly ash is a non-crystalline pozzolanic and slightly cementitious material. The physical properties of fly ash used in the study are given in Table 1 and the chemical properties of fly ash in Table 3. The fly ash was collected from the National thermal power plant in Salakati, Kokrajhar, Assam, India as shown in Fig 1(b). From the chemical composition in Table 3, it is seen that the CaO content of fly\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eash was only 2.6% [17]. The specific gravity of the fly ash was 2.13, which was lower than the\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003evalue of 2.54 of the red soil. The constituent of fly ash is mainly of the silt-sized fraction (60.12%).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePolypropylene fibre\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePolypropylene fibre is a synthetic thermoplastic polymer produced from propylene monomer through the process of polymerization. It is composed mainly of carbon and hydrogen atoms, making it a non-polar, hydrophobic, and chemically inert material. The fibre has a low density, high tensile strength, and excellent resistance to moisture and most chemicals [18]. Due to its lightweight and durable nature, polypropylene fibre is widely used in civil engineering applications for soil stabilization, concrete reinforcement, and geotextiles. The fibres, supplied by a commercial vendor, are elongated and measure 12 mm in length as shown in fig1. For the tests, fibres passing through a 4.75 mm sieve but retained on a 2 mm sieve were selected. The physical properties of the polypropylene fibre, as presented in Table 2, were provided by the supplier.\u0026rdquo;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u0026nbsp;\u003c/strong\u003eEngineering Properties of Red Soil and Fly Ash\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"539\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 58.5502%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSoil Property\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20.4461%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFly Ash (FA)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21.0037%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRed soil (RS)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 58.5502%;\"\u003e\n \u003cp\u003eSpecific Gravity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20.4461%;\"\u003e\n \u003cp\u003e2.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21.0037%;\"\u003e\n \u003cp\u003e2.54\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 58.5502%;\"\u003e\n \u003cp\u003eParticle size distribution\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; Coarse sand(4.75mm-2mm)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; Medium Sand (2\u0026nbsp;mm\u0026ndash;0.425 mm)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; Fine Sand(0.425mm-0.075mm)\u003c/p\u003e\n \u003cp\u003eSilt+Clay(\u0026lt;0.075mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20.4461%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e0.19\u003c/p\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003cp\u003e38.12\u003c/p\u003e\n \u003cp\u003e60.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21.0037%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 58.5502%;\"\u003e\n \u003cp\u003e\u003cu\u003eAtterberg\u0026rsquo;s limit\u003c/u\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Liquid limit, %\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Plastic Limit, %\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Plasticity index, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20.4461%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eNon-Plastic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21.0037%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e65.05\u003c/p\u003e\n \u003cp\u003e21.71\u003c/p\u003e\n \u003cp\u003e43.34\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 58.5502%;\"\u003e\n \u003cp\u003eUSCS Classification\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20.4461%;\"\u003e\n \u003cp\u003eML\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21.0037%;\"\u003e\n \u003cp\u003eCH\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 58.5502%;\"\u003e\n \u003cp\u003eMaximum dry density\u0026nbsp;g/cm\u0026sup3;\u003c/p\u003e\n \u003cp\u003eOptimum moisture content (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20.4461%;\"\u003e\n \u003cp\u003e1.39\u003c/p\u003e\n \u003cp\u003e18.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21.0037%;\"\u003e\n \u003cp\u003e1.78\u003c/p\u003e\n \u003cp\u003e18.36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u0026nbsp;\u003c/strong\u003ePhysical Properties of Polypropylene Fibre\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"504\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 198px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eFibre Characteristics\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTest\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 118px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eStandard\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eResult\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003eFibre cross section\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003eRound\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003eCompressive strength\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003eASTM C 39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e5.40%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003eCut length, mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003eTensile strength\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003eASTM D 638\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e7.90%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003eTear strength, N/mm\u0026sup2;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e\u0026ge; 400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003eFlexural strength\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003eASTM C 1018 / ASTM C 1399\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e11.40%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003eElongation at break, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e\u0026le; 80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003eFlexural toughness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 118px;\"\u003e\n \u003cp\u003eASTM C 1018 / ASTM C 1399\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eimproved\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003eFibre dispergation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" style=\"width: 378px;\"\u003e\n \u003cp\u003eexcellent\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003eMelting Point, \u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" style=\"width: 378px;\"\u003e\n \u003cp\u003e163 \u0026ndash; 170\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003eDiameter, \u0026mu;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" style=\"width: 378px;\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003eDensity, g/cm\u0026sup3;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" style=\"width: 378px;\"\u003e\n \u003cp\u003e0.91\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3.\u003c/strong\u003e Chemical properties of fly ash\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOxide\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eChemical characteristics\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eSiO₂\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e55.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eAl₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e23.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eFe₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eMnO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eMgO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eCaO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e2.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eNa₂O\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eK₂O\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eTiO₂\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e3.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eP₂O₅\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eSiO₂ + Al₂O₃ + Fe₂O₃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e81.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eLoss on ignition, LOI (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003e5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eClassification (ASTM C618-05)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 186px;\"\u003e\n \u003cp\u003eF\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003ch3\u003eMethods\u003c/h3\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Fly ash blended red soil\u003c/h2\u003e \u003cp\u003eThe red soil and fly ash used in this study were air-dried, pulverized, and sieved to ensure uniformity, after which fly ash was mixed with red soil in proportions of 15%, 20%, 25%, and 30% by dry weight. Each mix was thoroughly blended in the dry state to obtain a homogeneous mixture, and Standard Proctor compaction tests were conducted as per IS 2720 (Part 7) to determine the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC). Water was added in stages and compaction was carried out using standard Proctor energy, and the MDD and OMC were obtained from the respective compaction curves for each mix[19]. Based on the identified MDD and OMC values, specimens were prepared for the Unconfined Compressive Strength (UCS) test by compacting the red soil\u0026ndash;fly ash mixtures in UCS molds at the corresponding MDD and OMC, followed by careful extrusion and testing in accordance with IS 2720 (Part 10) to evaluate the strength behaviour of the stabilized soil.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Fly ash blended red soil reinforced with Polypropylene fibre\u003c/h2\u003e \u003cp\u003eThe red soil and fly ash were air-dried, pulverized, and sieved to ensure uniformity, after which fly ash was added to red soil in proportions of 15%, 20%, 25%, and 30% by dry weight to obtain homogeneous red soil\u0026ndash;fly ash (RS\u0026ndash;FA) mixtures. Polypropylene fibre (PPF), cut into 12 mm lengths, was then blended with each RS\u0026ndash;FA mix in proportions of 0.5%, 1%, 1.5%, and 2% by dry weight and uniformly distributed through thorough dry mixing to avoid fibre balling. Standard Proctor compaction tests were conducted on all RS\u0026ndash;FA\u0026ndash;PPF mixes as per IS 2720 (Part 7) to determine the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC).As the MDD and OMC values were evaluated, the specimens were made compact by compacting the mixtures at MDD and OMC and extruded from the molds for testing in UCS mould in accordance with IS 2720 (Part 10) then the strength behaviour and other behaviour like strength ratio(SR),Stiffness of polypropylene fibre-reinforced red soil-fly ash mixtures was evaluated[20].\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSample Preparation for Strength Test\u003c/h3\u003e\n\u003cp\u003eFor the Preparation Strength test, both the mixtures used in unconfined compression testing, red soil-fly ash (RS-FA) and fly ash-red soil-polypropylene fibre (RS-FA-PPF), were prepared on the basis of Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) values obtained from the Standard Proctor compaction tests. The materials were hand-mixed with care to achieve uniform and consistent blending. Cylindrical test specimens having dimensions of 38 mm diameter and 76 mm height were prepared using a standard UCS mold, each specimen compacted in three equal layers to achieve the desired MDD at the OMC. The UCS behaviour of RS-FA mixes with and without polypropylene fibre reinforcement is observed and externally evaluated. Three identical specimens were in general tested for each mix condition, and an average UCS value for this mix condition was reported. The mass of fly ash-red soil-polypropylene fibre dry was calculated using a general equation.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:W={W}_{RS}+{W}_{FA}+{W}_{PPF}\\dots\\:\\dots\\:\\left(1\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{W}_{RS}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{W}_{FA}\\)\u003c/span\u003e\u003c/span\u003e, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{W}_{PPF}\\)\u003c/span\u003e\u003c/span\u003edenote the weights of red soil, fly ash, and polypropylene fibre, respectively.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDetails of red soil\u0026ndash;fly ash\u0026ndash;polypropylene fibre mixtures for tests conducted\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\u003eDesignation\u003c/p\u003e \u003cp\u003e(W\u0026thinsp;=\u0026thinsp;W\u003csub\u003eRS\u003c/sub\u003e+ W\u003csub\u003eFA\u003c/sub\u003e+W\u003csub\u003ePPF\u003c/sub\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVariation of RS (% by total dry weight)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVariation of FA (% by total dry weight)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eVariation of PPF ((% by total dry weight))\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e100RS-0FA-0PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\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\u003e0RS-100FA-0PPF\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\"\u003e \u003cp\u003e100\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\u003e85RS-15FA-0PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15\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\u003e80RS-20FA-0PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20\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\u003e75RS-25FA-0PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25\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\u003e70RS-30FA-0PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30\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\u003e85RS-15FA-0.5PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e84.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e85RS-15FA-1PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e84.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e85RS-15FA-1.5PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e83.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e85RS-15FA-2PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e83.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.70\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\u003e80RS-20FA-0.5PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e79.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e80RS-20FA-1PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e79.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e80RS-20FA-1.5PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e78.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e80RS-20FA-2PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e78.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.60\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\u003e75RS-25FA-0.5PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e74.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e75RS-25FA-1PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e74.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e75RS-25FA-1.5PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e73.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e75RS-25FA-2PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e73.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.50\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\u003e70RS-30FA-0.5PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e69.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e70RS-30FA-1PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e69.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e70RS-30FA-1.5PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e68.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e70RS-30FA-2PPF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e68.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Result and Discussions","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eCompaction Characteristics\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003eCompaction Characteristics of RS, RS-FA mixes\u003c/h2\u003e \u003cp\u003eThe compaction features of red soil (RS), fly ash (FA), and their mixes reveal major patterns in Maximum Dry Density (MDD) and Optimum Moisture Content (OMC). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, MDD of pure red soil is at 1.78 g/cc, the highest in the group which indicates it is very compactable and goes along with its very good quality to be compacted. On the contrary, fly ash is quite the opposite; its MDD is only at 1.39 g/cc due to being light and very porous. As fly ash is being mixed with red soil in a portion of 15%, 20%, 25%, and 30%, the MDD goes down from 1.76 g/cc to 1.65 g/cc in a progressive manner. The reason for this is that heavier soil particles have been replaced with lighter fly ash particles, thus leading to less packing density and lower dry weight per unit volume. As for OMC, it shows the same pattern in the beginning for red soil and fly ash which is around 18.3%. But as the fly ash content in the mix goes up, the OMC slowly rises and it eventually touches the maximum of 19.52% at 30% fly ash. The reason for this is that the fly ash particles have a higher surface area and are more absorptive, thus they require more water to aid in lubrication and compaction. The combination of decreasing MDD and increasing OMC is clearly indicates that although fly ash can be used for the improvement of red soil, there is a compromise. More fly ash lead to lower density and higher water demand which may not help with strength and stability. Consequently, it seems that up to 20% fly ash content is the best choice according to the trends because it still gives a high MDD and does not ask for a lot of water. Past this point, the benefits are not significant anymore and the mix could easily be less durable and strong for geotechnical applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eEffect of PPF on RS-FA-PPF mixture\u003c/h2\u003e \u003cp\u003eThe detailed evaluation and thorough examination of the compaction data show that the addition of polypropylene fibre (PPF) to fly ash (FA)-stabilized red soil changed its densification behaviour as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The major factor in this change was the particle-disruption mechanism, while another factor was the increased moisture requirement. For the entire range of FA contents (15\u0026ndash;30%), the maximum dry density (MDD) not only decreases, but also the PPF dosage goes up, with the most intensive reducing point at 2% PPF where MDD values drop down to 1.453\u0026ndash;1.483 g/cc, meaning 5\u0026ndash;6% less than for the mixtures with 0.5% PPF. This drop is because of the fibre working as a low-density, high-aspect-ratio component that limits optimal particle packing, causes continuous voids, and then caps the energy of compaction through the creation of the bridging effect. At the same time, the optimum moisture content (OMC) keeps on being quite constant at low PPF volumes (0.5\u0026ndash;1.5%) but shows a steep rise at 2% PPF, going beyond 24.7% in all mixes, with the reason being the increased hydrophobic surface area and the demand for extra water to make the fibrous matrix smooth. The presence of PPF also affects the moisture content needed to keep the soil in the best condition for compaction. Fly ash has a moderating effect on these trends as it consistently lowers the baseline MDD due to its lower specific gravity, yet it is predominately the fibre concentration that governs the adverse compaction effects. Recognizing 2% PPF as a critical point, where compaction efficiency is significantly reduced, thus compaction dosage optimization is essential, particularly with the 0.5\u0026ndash;1.5% PPF range at 1% PPF combined with 20\u0026ndash;25% FA giving a more practical and feasible balance between reaching the density requirement and obtaining the strength from fibres for geotechnical applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eStrength Characteristics\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003eEffect of fly ash on RS-FA mixes on UCS\u003c/h2\u003e \u003cp\u003eInitially, the stress-strain behaviour of red soil (RS) mixed with different amounts of fly ash (FA) has shown that the maximum stress and ductility of the soil were increased as the amount of fly ash reached the optimum. The graph in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows that the red soil that has not been treated (RS) has the lowest peak stress and a quite brittle reaction, that is, it breaks easily and at lower strain values. The peak stress and the post-peak strain behaviour have been increased markedly by the addition of fly ash, especially in case of the specimen RS-20FA which shows the highest peak stress of about 510 kPa at a strain of nearly 3.4%, that is, the best performance is signified. The initial linear portion of the stress-strain curves (up to ~\u0026thinsp;2% strain) for all mixes suggests similar stiffness in the early loading stages. The peak strength, however, rises considerably with the addition of 15% and 20% FA, which can be ascribed to the pozzolanic reaction between the calcium in the soil and the siliceous/aluminous fly ash, creating cementitious compounds like C\u0026ndash;S\u0026ndash;H gels. This reaction not only solidifies but also bonds the particles of the soil better. The RS-20FA's improved ductility and strain tolerance at peak stress indicate the enhanced energy absorption capacity which is advantageous for the geotechnical applications that experience dynamic loading. Specimens with 25% and 30% fly ash have less peak stress and more strain softening than those with 20% FA. This behaviour indicates that the presence of too much fly ash might cause the soil-fly ash matrix to be demolished due to the unavailability of enough calcium or moisture for sustaining the pozzolanic reaction, therefore leading to incomplete bonding and a weaker structure. Even though RS-25FA has much better strength than untreated RS, the little extra strength over RS-15FA is not worth the increased fly ash content from both the performance and sustainability point of view. The RS-30FA sample has shown a strength reduction, which ratifies that too much of a non-reactive filler material can dilute the phases that contribute to strength. In conclusion, the study indicates that the addition of fly ash has significantly improved the strength and ductility of red soil, with 20% fly ash content being the optimum. This not only increases the soil's structural performance but also provides an environmentally friendly way of reusing industrial by-products through soil stabilization as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eEffect of PPF on RS-FA-PPF mixes on UCS\u003c/h2\u003e \u003cp\u003eThe behaviour of unconfined compressive strength (UCS) of red soil that was treated with both fly ash and polypropylene fibre is a good example of the interaction between the two additives in strength enhancement. To ensure consistency in the experiments, all the specimens were compacted at their corresponding maximum dry density and optimum moisture content obtained from the Standard Proctor test. The data showed from the that UCS increased at first with the increase of polypropylene fibre content for a specific fly ash amount, peaked around 1% PPF and then gradually fell. Looking at the Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the UCS at 20% fly ash was 481.04 kPa at 0.5% PPF, went up to the highest 508.14 kPa at 1% PPF and then got lower again when more fibres were used. This pattern means that there is a certain fibre content that gives the best result, where the effective stress transfer and the crack-bridging mechanisms are fully engaged, on the other hand, more fibres will result in poor distribution, fibre clumping and more voids which will therefore reduce the compressive strength. Also, at a constant fibre content of 1% PPF, UCS went up with fly ash till 20% and then it went down. The very first increase in UCS was due to the pozzolanic reactions of fly ash and soil that made the bonding of the particles and the densifying of the matrix stronger, on the contrary, if too much fly ash is used, it may just spread around the soil matrix without being effectively bonded as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The highest UCS value that is 508.14 kPa, was for the mix of 80RS\u0026ndash;20FA\u0026ndash;1PPF which meant that there was a combined action of fly ash-induced cementation and fibre strengthening. In conclusion, it is concluded that the results demonstrate that fly ash and polypropylene fibre, when added in controlled amounts, would make a significant difference to the compressive strength of red soil and this not only stresses the importance of optimizing both fly ash and fibre contents for the application of sustainable ground improvement but also the need to continue to do so.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eEffect of FA on strength ratio of RS-FA mixes\u003c/h2\u003e \u003cp\u003eThe evaluation of the strength ratio of red soil-fly ash mixes was done in order to measure the compressive strength improvement of red soil that was not treated. The enhancement in UCS resulting from the mixing of FA can be represented by the strength ratio (SR) defined as\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:SR=\\frac{UC{S}_{RS-FA\\:}}{UCS}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u0026hellip;\u0026hellip;\u003c/p\u003e \u003cp\u003ewhere UCS\u003csub\u003eRS\u003c/sub\u003e-\u003csub\u003eFA\u003c/sub\u003e is the UCS of RS-FA mixes and UCS is the UCS of only red soil.\u003c/p\u003e \u003cp\u003eThe findings suggest that the incorporation of fly ash greatly improves the strength ratio up to an ideal amount, after which the strength ratio starts to decrease as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. Specifically, the untreated red soil's strength ratio was raised from 1.00 to 1.10 and 1.17 with the addition of 15% and 20% fly ash, thus clearly indicating even more the improvement in load-bearing capacity. One of the reasons for this increase is better packing of the particles and the commencement of pozzolanic reactions, the fly ash Class F siliceous and aluminous components reacting with the calcium in the soil and thus making the interparticle bonding stronger. However, when fly ash content was further increased, there was a consistent decline in strength ratio to 1.14 and 1.08 for 25% and 30% fly ash, respectively. One possible reason for the lower strength ratio at higher fly ash content is that the soil matrix has been diluted and not enough calcium is available to support the pozzolanic bonding. The overall results point to 20% fly ash as the ideal content for obtaining the best strength ratio for red soil-fly ash mixtures, thereby emphasizing the beneficial role of regulated fly ash use in environmentally friendly soil stabilization processes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eEffect of PPF on RS-FA-PPF mixes on SR\u003c/h2\u003e \u003cp\u003eThe strength ratio of red soil-fly ash-polypropylene fibre (RS-FA-PPF) mixtures was measured to assess the strength enhancement in comparison to untreated red soil. The raise in UCS caused by the incorporation of FA can be expressed in terms of strength ratio (SR) defined as:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:SR=\\frac{UC{S}_{RS-FA-PPF\\:}}{UCS}\\dots\\:\\dots\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere UCS\u003csub\u003eRS\u0026minus;FA\u0026minus;PPF\u003c/sub\u003e is the UCS of RS-FA-PPF mixes and UCS is the UCS of only red soil.\u003c/p\u003e \u003cp\u003eThe study results illustrate that the combination of fly ash and polypropylene fibre consistently results in the strength ratio upgrade until the optimal ratio is reached, afterward, the reduction is seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The strength ratios have all increased for the fly ashes at first, then the FIBRE content increase, and finally, the maximum strength ratios are 1\u0026ndash;1.5% PPF. The topmost strength ratio recorded was approximately 1.26 for the 80RS\u0026ndash;20FA\u0026ndash;2PPF mix, which was then the 75RS\u0026ndash;25FA\u0026ndash;2PPF and 80RS\u0026ndash;20FA\u0026ndash;1PPF mixes. The significant synergistic activity of fly ash and FIBRE reinforcement has been indicated by this. The strength ratio improvement was grounded on the factors of the mixed fly ash matrix that was updated by the ash and the gradual pozzolanic bonding and the Fibres that amplified the stress transfer as well as the halt of crack initiation and propagation. But when the FIBRE contents turned high (especially for the case of 2% PPF in some mixes) the strength ratio was cut down at fly ash contents such as 30% where the strength ratio was close to unity. The reduction in the strength ratio may be attributed to the fibre issues like agglomeration, poor dispersion and an increase in voids which are all working against the reinforcement benefits. In conclusion, the results are suggestive that RS\u0026ndash;FA\u0026ndash;PPF mixes are stronger than RS\u0026ndash;FA mixes, with the optimal combination being of 20\u0026ndash;25% fly ash and 1\u0026ndash;1.5% polypropylene fibre, thus amplifying the significance of dosage optimization in maximizing strength enhancement for sustainable soil stabilization applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eEffect of stiffness of PPF on RS-FA-PPF mixture\u003c/h2\u003e \u003cp\u003eStiffness modulus is used to measure the ability of soil to resist deformation. According to Tang et al. [21], the modulus is expressed as the slope of the linear portion of the stress\u0026ndash;strain curve. From Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the connecting line segment BA is selected for each curve, and the modulus (E) is expressed using the following formula:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:E=\\frac{\\varDelta\\:\\sigma\\:}{\\varDelta\\:\\epsilon\\:}=\\frac{{\\sigma\\:}_{A}-{\\sigma\\:}_{B}}{{\\epsilon\\:}_{A}-{\\epsilon\\:}_{B}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u0026hellip;\u0026hellip;\u003c/p\u003e \u003cp\u003eTo evaluate the axial loading deformation response of RS-FA-PPF composites, a study was performed to show the impact of fly ash and polypropylene fibre inclusion on the stiffness characteristics of red soil. It was found that the stiffness was greatly affected by both the fly ash content and the fibre dosage, which showed a clear optimum combination in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. Generally, fly ash usage transformed the soil into a denser and stronger mass which contributed a lot to stiffness, while polypropylene fibres did good by providing even stress distribution and resisting deformation. The admixture of stiffness values met with an upward trend as the fibre increment was made until it reached the optimum range of about 1-1.5% PPF, thereafter a downward shift was noticed. For example, the composites with 25% fly ash showed a great increase in softness, which at last got the peak value of about 139.5 for the 75RS-25FA-2PPF blend, and that too was the case of a significant improvement in being rigid due to significant improvement effective fibre support and nice soil-fly ash interaction. Likewise, combinations with 15% fly ash saw a rise in stiffness with average fibre usage, which was particularly the case of improved bonding and crack-bridging provided by the fibres as shown in fig .10 But, at high fibre contents, especially in 2% PPF in some mixes, a drop in stiffness was noticed, particularly for the cases of 20% and 30% FA mixes which had either lower or higher fly ash contents. The reason might be the same as that the fibres got stuck together, were not evenly dispersed, and thus there were more voids, which led to less matrix continuity and stiffness. All in all, opting for the combined use of fly ash and polypropylene fibre in red soil leads to a considerable enhancement of the soil stiffness when they are employed in the right proportions. Fly ash by pozzolanic and filler effects strengthens the matrix and at the same time fibres help to make deformation harder, thus RS-FA-PPF composites are perfect for the tasks needing heightened stiffness and diminished compressibility.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eBased on the thorough laboratory study, it was concluded that the joint use of fly ash (20\u0026ndash;25%) and polypropylene fibres (1%) performed very well and were especially advantageous for the red soil with high plasticity, thus giving the right strength, stiffness, ductility, and compaction characteristics. Fly ash through its pozzolanic reactions contributes to strength and matrix densification while polypropylene fibres help to the ductility, crack resistance, and post-peak performance. The best mix proportion (20\u0026ndash;25% FA plus 1% PPF) produced the maximum unconfined compressive strength of 508.14 kPa, an improved strength ratio, and increased stiffness, though too much fibre content (\u0026gt;\u0026thinsp;1.5%) or higher fly ash dosage meant reduced compaction efficiency and material stiffness. These results certify that the use of industrial by-products and synthetic Fibres as a stabilization method for weak subgrade soils in infrastructure projects is a sustainable and effective practice that not only benefits engineering performance but also helps the environment.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eDeclaration of competing interest\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthor ContributionsNekibuddin Ahmed: Conceptualization, methodology, experimental investigation, data curation, formal analysis, visualization, and original draft preparation.Abhijit Deka: Supervision, validation, resources, critical review and editing of the manuscript, and overall guidance.All authors have read and approved the final version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eFondjo, A. A., Theron, E., \u0026amp; Ray, R. P. (2021). Stabilization of expansive soils using mechanical and chemical methods: a comprehensive review. Civ Eng Archit, 9(5), 1295-1308. https://doi.org/10.13189/cea.2021.090503.\u003c/li\u003e\n\u003cli\u003eAbdel-Rahman, M. (2020). Review of Soil Improvement Techniques. https://doi.org/10.1007/978-3-030-62908-3_14 \u003c/li\u003e\n\u003cli\u003eAl-Naje, F. Q., Abed, A. H., \u0026amp; Al-Taie, A. J. (2020). A review of sustainable materials to improve geotechnical properties of soils. Al-Nahrain Journal for Engineering Sciences, 23(3), 289-305. https://doi.org/10.29194/njes.23030289 \u003c/li\u003e\n\u003cli\u003eSabzi, Z. (2018). Environmentally friendly soil stabilization materials available in Iran. Journal of Environmental Friendly Materials, 2(1), 33-39.\u003c/li\u003e\n\u003cli\u003eShukla, S. K. (2017). Applications of fibre-reinforced soil. In Fundamentals of Fibre-Reinforced Soil Engineering (pp. 145-180). Singapore: Springer Singapore.\u003c/li\u003e\n\u003cli\u003eKanchi, G. M., Neeraja, V. S., \u0026amp; Sivakumar Babu, G. L. (2015). Effect of anisotropy of fibres on the stress-strain response of fibre-reinforced soil. International Journal of Geomechanics, 15(1), 06014016.\u003c/li\u003e\n\u003cli\u003eKumar, P. S., \u0026amp; Baleshwar, S. (2015). Review of predictive models for shear strength behaviour of fibre reinforced soils. Journal of Environmental Research and Development, 10(1), 161.\u003c/li\u003e\n\u003cli\u003eDeb, K., \u0026amp; Narnaware, Y. K. (2015). Strength and compressibility characteristics of fibre-reinforced subgrade and their effects on response of granular fill-subgrade system. Transportation in Developing Economies, 1(2), 1-9.\u003c/li\u003e\n\u003cli\u003eShafiqu, Q. M., Ali, A. S., \u0026amp; Al-Hassany, H. N. (2015). Enhancement of Expansive Soil Properties Using Lime Silica-Fume Mixture. International Journal of Scientific \u0026amp; Engineering Research, 6(10), 1239-1257.\u003c/li\u003e\n\u003cli\u003eEldemary, I. F. (2023). A Broad Review on Treatment of Expansive Soils Using Mixing and Reinforcement Inclusion Treatment Techniques: A Comprehensive Review. ERU Research Journal, 2(2), 331-370. https://doi.org/10.21608/erurj.2023.293645\u003c/li\u003e\n\u003cli\u003eAli1a, M., Aziz, M., Hamza1c, M., \u0026amp; Madni3d, M. F. (2020). Engineering properties of expansive soil treated with polypropylene fibres. Geomechanics and Engineering, 22(3), 227-236. https://doi.org/10.12989/GAE.2020.22.3.227\u003c/li\u003e\n\u003cli\u003eJayanthi, P. N., \u0026amp; Singh, D. N. (2016). Utilization of sustainable materials for soil stabilization: state-of-the-art. Advances in Civil Engineering Materials, 5(1), 46-79\u003c/li\u003e\n\u003cli\u003eAshfaq, M., Baig Moghal, A. A., Munwar Basha, B., \u0026amp; Baig Moghal, A. A. (2021). Carbon footprint analysis on the expansive soil stabilization techniques. In IFCEE 2021 (pp. 213-222).\u003c/li\u003e\n\u003cli\u003eHasan, U., Chegenizadeh, A., Budihardjo, M. A., \u0026amp; Nikraz, H. (2015). A review of the stabilisation techniques on expansive soils.\u003c/li\u003e\n\u003cli\u003eShinde, B., Sangale, A., Pranita, M., Sanagle, J., \u0026amp; Roham, C. (2024). Utilization of waste materials for soil stabilization: A comprehensive review. Progress in Engineering Science, 1(2-3), 100009\u003c/li\u003e\n\u003cli\u003eDevapriya, A. S., \u0026amp; Thyagaraj, T. (2024). Evaluation of red soil-bentonite mixtures for compacted clay liners. Journal of Rock Mechanics and Geotechnical Engineering, 16(2), 697-710. https://doi.org/10.1016/j.jrmge.2023.04.006\u003c/li\u003e\n\u003cli\u003eReddy, C. S., Mohanty, S., \u0026amp; Shaik, R. (2018). Physical, chemical and geotechnical characterization of fly ash, bottom ash and municipal solid waste from Telangana State in India. International Journal of Geo-Engineering, 9(1), 23. https://doi.org/10.1186/s40703-018-0093-z\u003c/li\u003e\n\u003cli\u003ePatro, B. J., \u0026amp; Senapti, S. (2020). Stabilization of clayey soil by using polypropylene fibre. Int Res J Eng Technol, 7(8), 3439-3443.\u003c/li\u003e\n\u003cli\u003eKalita, T., Saikia, A., \u0026amp; Das, B. (2017). Effect of fly-ash on strength behaviour of clayey soil. International Research Journal of Engineering and Technology (IRJET), 4(7), 5-7.\u003c/li\u003e\n\u003cli\u003eLi, L., Zhang, J., Xiao, H., Hu, Z., \u0026amp; Wang, Z. (2019). Experimental Investigation of Mechanical Behaviours of Fibre-Reinforced Fly Ash-Soil Mixture. Advances in Materials Science and Engineering, 2019(1), 1050536. https://doi.org/10.1155/2019/1050536\u003c/li\u003e\n\u003cli\u003eTang L, Cong S, Geng L, Ling X, Gan F (2018) The effect of freezethaw cycling on the mechanical properties of expansive soils. Cold Reg Sci Techno 145:197\u0026ndash;207\u003c/li\u003e\n\u003cli\u003eNguyen, T. T., \u0026amp; Indraratna, B. (2023b). Natural fibre for geotechnical applications: Concepts, achievements and challenges. \u003cem\u003eSustainability\u003c/em\u003e, \u003cem\u003e15\u003c/em\u003e(11), 8603. https://doi.org/10.3390/su15118603\u003c/li\u003e\n\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":"Red Soil (RS), Fly ash (FA), Stiffness, Strength ratio, Unconfined Compressive Strength (UCS), Polypropylene fibre","lastPublishedDoi":"10.21203/rs.3.rs-8369111/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8369111/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe environmentally conscious and viable alternative to the traditional binders like lime and cement includes the sustainable use of industrial by-products for soil stabilization. This study proposes an innovative solution beyond the sole use of fly ash for geotechnical applications such as Class F fly ash (15\u0026ndash;30%) and polypropylene fibres (0.5\u0026ndash;2%) in high-plasticity red soils. The laboratory testing, including compaction, Unconfined Compressive Strength (UCS), stiffness, and strength ratio, allows us to discern the changes in density, strength, and ductility. The findings from the study showed that the addition of fly ash to the mixtures increased the strength and stiffness significantly, with the best result obtained using 20% fly ash. The reasons for such an increase in properties are the pozzolanic reactions taking place and causing the soil to become denser. Polypropylene fibres improved ductility, crack resistance, and post-peak performance but diminished the efficiency of compacting and stiffness at high dosages (\u0026gt;\u0026thinsp;1.5%). The optimum mix was 20\u0026ndash;25% fly ash with 1% polypropylene fibre, which significant combined improvement in strength, ductility, and workability. Such results of combining fly ash and artificial fibres in the stabilization will have practically resulted in the application of poor-quality road sub-grades and other infrastructure projects on poor soils.\u003c/p\u003e","manuscriptTitle":"Geotechnical Performance of Red Soil Stabilized with Fly Ash and Reinforced with Polypropylene Fibres","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-26 07:03:21","doi":"10.21203/rs.3.rs-8369111/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":"ed29d619-73d5-4907-b958-27b7b3ed7442","owner":[],"postedDate":"December 26th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-03T08:39:33+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-26 07:03:21","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8369111","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8369111","identity":"rs-8369111","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}