Cement kiln dust and polypropylene fiber in expansive clay improvement

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lower stabilization costs, especially in road construction projects.To address these issues, an experiment was conducted to determine how locally obtained cement kiln dust (CKD), both alone and combined with polypropylene fibers, affected the properties of plastic clay soil, also referred to as expansive clay from Cheffia.The main objective of this study is to assess how well different CKD percentages (from 5% to 25%) stabilize soil while improving its mechanical and physical properties.The study also aims to explain how the addition of polypropylene fiber affects the unconfined compressive strength and compaction behavior of the soil in the optimal CKD-soil mixture.The results of the analysis show that the addition of cement kiln dust (CKD) significantly improved the studied soil's workability, compaction, and strength.Additionally, adding polypropylene fibers strengthens the clay's resistance to compression, which presents encouraging opportunities for reducing the difficulties brought on by expansive soils in civil engineering applications.

INTRODUCTION
Numerous towns, highways, and structures are situated atop clay-rich soils and rocks.These materials' clay can be quite dangerous for building since it can swell or shrink depending on the amount of water in them.The distribution of expansive soils is influenced by geology, climate, hydrology, geomorphology, and vegetation.Expansive soils are found in many parts of the world, especially in arid and semi-arid regions when rainy conditions follow protracted periods of drought.
In 2012, Jones, Lee D. Arid and semi-arid regions cover a large part of Algeria, soils from these areas, when used in major construction projects, especially infrastructures using large quantities of fill, can cause considerable damage, Chen (1988), Nelson (1992), Mohamed Khemissa et al. (2014).According to estimates, the average yearly cost of structural damage from shrinking and swelling is 400 million pounds in the United Kingdom, a total of $15 billion in the United States of America, and many billions of dollars globally. Lee D. Jones (2012).To solve this problem, these soils need to be treated to achieve the desired geotechnical properties.Several methods have been proposed to improve the physical and mechanical properties of poor soils, among which chemical stabilization is a technique mainly used to improve workability, bearing capacity, swelling/shrinkage potential, and permeability of problematic soils.Portland cement and quicklime are the two substances that are most frequently employed in soil stabilization.Since these two materials are produced commercially for numerous different industrial applications, they must be obtained for road construction projects at prices that are competitive.Project cost increases are unavoidable given the significant volumes of soils that need to be stabilized Nishantha Bandara et al. (2020).In order to develop a less expensive substitute material that contains the necessary quantity of calcium oxide or cementitious elements, which are found in lime and cement, researchers have been working on this project recently, which can react similarly with the clay minerals in the soil.Industrial waste materials are the focus of attention for this purpose, It's interesting to notice that the primary source of potential materials is the same industry that is, the manufacturing of quicklime and Portland cement.Cement kiln dust (CKD), which has a significant amount of cementitious materials and calcium oxide, is the ideal option for this investigation.
Additional methods of stabilizing soil involve the use of synthetic materials like nylon and polypropylene, natural materials like coconut and palm fiber, and additional materials like tires and shredded plastic strips.Alternative stabilization methods that can minimize or replace the usage of conventional cementitious agents are encouraged by the global community's shift towards a more sustainable attitude Soltani et al. (2018).Polypropylene fibers (FPP) are the second additive used for all the advantages they offer: ease of use, low cost, hydrophobicity, and chemical inertness.Unlike natural fibers, synthetic fibers do not absorb moisture from the soil or react with it Miller et al. (2004).Moreover, synthetic fibers can be produced with well-defined specifications, including geometric shapes, lengths, and even surface conditions, to improve their frictional properties.Changes in the environment, such as fluctuations in moisture, prevent the majority of synthetic fibers from biodegrading, sunlight, heat, or cold Krenchel (1973), Hoover et al. (1982).These two materials, CKD and FPP, have been chosen after an in-depth study of several investigations conducted by researchers in various countries worldwide, which have yielded very positive results.Some notable studies include Peethambaran et al. (2009),who investigated the efficacy of different CKDs in stabilizing expansive clay and demonstrated that clay treated with CKDs had noticeably higher compressive strength than clay left untreated.The importance of including CKD in the compaction parameters of black cotton soil was illustrated by Oriola and Moses (2011).According to Ismaiel (2013), adding CKD and CKD-lime decreased the maximum dry density and raised the ideal moisture content.Hashad and El-Mashad (2014) investigated the possibility of stabilizing soil using CKD.Ismail and Belal (2016) demonstrated that when the proportion of CKD rose in moderately compressible soil, the maximum dry density reduced and the optimal moisture content increased.The ideal moisture content and maximum dry density The findings demonstrated that swelling decreased and unconfined compressive strength increased as the proportion of additional FPP increased.It was discovered that the ideal fly ash and FPP percentages for UCS were 1.5% and 15%, respectively.Sharma (2017) investigated how introducing polypropylene fibers and cement kiln dust affected the properties of native soil.The findings showed that the unconfined compressive strength rose over the course of the curing time, peaking at 12% soil addition of cement kiln dust.The study also found that adding polypropylene fibers to cement kiln dust enhanced the properties of compaction and strength even further.This essay examines the technical characteristics of CKD, a regional byproduct of Hadjar Essoud cement (Skikda, Algeria), and polypropylene fibers  and Exact Sciences, Curitiba, v.5, n.1, p. 1771-1792, 2024 on how the curing period affects the UCS simple shear strength.The following parts contain a presentation, analysis, and commentary on the findings.

Soil:
The soil used in this study was taken from the El Tarf province's Cheffia district, which is situated in eastern Algeria 62 kilometers from the city of Annaba.At a depth of around two meters, soil samples were collected, and they were promptly sealed in plastic bags to avoid contamination from external substances.After that, the samples were shipped to the LMGE research lab at Badji Mokhtar University in Annaba, Algeria, where they were kept in safekeeping.

Cement kiln dust (CKD)
: is a by-product of making Portland cement that has the appearance of fine powder.It is removed from high-temperature rotary kiln chimneys by means of dust collection devices such bag filters, electrostatic precipitators, and/or cyclones.When clinker is produced using the dry process, a significant amount of cement kiln dust is produced.Due to variations in raw materials, operational procedures, dust collection systems, and fuel types used in various cement plants, the chemical and physical qualities of cement kiln dust might fluctuate greatly.Each plant's dust might have quite different physical characteristics, mineralogy, and chemical content.According to Table 1, which summarizes the cement kiln dust's characteristics, CKD has a noticeable CaO content.
Polypropylene fibers: Because of its great tensile strength, resistance to corrosion, and nontoxicity, fiber is one of the most often used synthetic materials for soil reinforcement.The Algerian business SIKA offers the polypropylene fibers utilized in this study for commercial application.Together with cement kiln dust, they serve as a stabilizing agent.The maximum length of polypropylene fiber employed in the next trials is 6 mm.Table 2 lists the mechanical and physical properties of the polypropylene fibers.

MTEST PROGRAM
The same laboratory procedures were performed on treated and untreated soil specimens in order to investigate the impact of cement kiln dust (CKD) on the mechanical and physical characteristics of soil.These tests included measuring the samples' specific gravities (Gs), sedimenting the untreated soil to analyze its Studies in Engineering and Exact Sciences, Curitiba, v.5, n.1, p. 1771-1792, 2024 particle size distribution, evaluating the plasticity of the soil to assess Atterberg limits, compaction to determine the ideal water content and maximum dry density, and performing unconfined compression tests to ascertain strength.It was also investigated how long the soil cured.The initial stage of soil stabilization involved applying the Eades and Grim (1966) approach, which was created for lime, to ascertain the minimum percentage of CKD necessary for long-term property improvement.The pycnometer method, as outlined in ASTM D 854-00, standard test, is the suitable technique for ascertaining the specific gravity of soil.The weight of a particular volume of soil solids divided by the weight of an equal volume of water is a specific gravity of soil particles.Soil specific gravity is a crucial statistic in soil mechanics since it makes it possible to calculate other physical parameters that are required for any geotechnical study.The distribution of bigger particles in the soil was ascertained by sieve analysis of particle size distribution, while the distribution of finer particles was ascertained by the hydrometer method in accordance with the standard test ASTM D 422-90.The liquid limit and plastic limit standard test technique ASTM D 4318, standard Test, was used to determine the Atterberg limits.According to the Casagrande device method, the water content of a remolded soil sample that causes a typical groove to close by 13 mm after 25 blows is known as the liquid limit of the soil (WL).When soil is rolled between fingers on a glass plate to create a 3 mm diameter thread, it reaches the plastic limit (WP), which is the water content at which the soil begins to crumble and exhibit a stiff stiffness.The plasticity index (PI) is the difference between the plastic limit WP and the liquid limit WL.Using the Proctor compaction test in accordance with ASTM D 698-91/98 standard test, the ideal water content and maximum dry density of the prepared soil were ascertained.Compaction of the soil at a set water content in roughly equal layers three in a standard Proctor mold was used to conduct the test.A 2.495 kg rammer descended freely from a height of 304.88 mm, compacting each layer with a standard number of strokes (25 blows) dispersed uniformly.The unconfined compressive strength of cohesive soil standard test, ASTM D 216, was followed in conducting the unconfined compression test.The main series of compositions used in this experiment were soil samples that had been left untreated and samples that had only been treated with CKD at varying percentages (5%, 10%, 15%, 20%, and 25% CKD).Later, 15% CKD was added Studies in Engineering and Exact Sciences, Curitiba, v.5, n.1, p. 1771-1792, 2024 to different proportions of polypropylene fibers (0.25%, 0.5%, and 1% FPP) in a second set of formulations.During the compaction test, all of these samples were compacted into three layers of identical thickness at the ideal moisture level.
Following their removal from their molds, all cylindrical soil specimens with roughly equal dimensions (diameter = 10.16 cm and height = 11.7 cm) were wrapped in plastic film and kept for 1, 7, 14, and 28 days at an average temperature of 20°C in a 100% humid environment.The cylindrical specimens were subjected to progressive axial compressive force till failure after reaching the designated curing period.A constant axial strain rate of 1% per minute was used to test each sample.

RESULTS AND DISCUSSIONS
Figure 2 illustrates the dispersed grain size distribution curve of the investigated soil, with 83% of the fines less than 75 µm and 33% of them composed of clay.This demonstrates the fine-grained nature of the soil.The soil has a specific gravity of 2.65 and less than 3% organic matter.Plotting the values of the Atterberg limits presented in Table 3 on the Casagrande plasticity chart reveals that the soil under investigation is classified by the USCS as a high plasticity inorganic clay (CH).alumina is also considerably enhanced at higher pH levels (pH > 12), which is essential for the sustained pozzolanic reaction in the treated soil.Long-term pozzolanic reactions can result in the formation of secondary cementitious products in cement-stabilized soil when hydrated silica and alumina combine with calcium ions generated during cement hydration.Gerald A. and others (2000), Bergardo DT and others (1996).While Eades and Grim (1966) proposed that soil stabilization requires the lowest lime percentage required to maintain a pH of 12.40, Davidson et al. (1965) advised a minimum pH of approximately 10.5 for the occurrence of the pozzolanic reaction.The fact that the pH of the treated soil would typically be higher than 12 even when only a little amount of lime is added to the soil was highlighted by Broms (1984).Figure 3 shows that if 10% of cement kiln dust (CKD) is applied to the soil, the pH would gradually rise to 12.07 and reach 12.25 when 15% of CKD is added.Regardless of the amount of hydraulic binder used, the rate of pH fluctuation becomes less significant above 15%, producing an almost constant curve.As a result, the starting percentage utilized in this study to treat the natural fine soil under inquiry was 10% of stabilizer (CKD) by dry weight.

INFLUENCE OF CEMENT KILN DUST ON ATTERBERG LIMIT
Figure 4 shows the findings of a study on the impact of CKD on the Atterberg limits of treated and untreated samples.The instantaneous drying reaction caused by the absorption and evaporation processes in the cement kiln dust (CKD)-treated samples showed a decrease in the liquid limit (WL) and a rise in the plastic limit (WP).The clay became friable and granular as a result of the quick ion exchange reactions between CKD and the organic minerals in the soil, which led to flocculation and agglomeration of the fine soil particles.This improved the soil's workability by lowering its plasticity index.This made it possible to labor longer hours all year round as opposed to just during the dry seasons.This result is consistent with research published in 2019 by Almurshedi et al. (2019), Rashed et al. (2019).

CEMENT KILN DUST'S (CKD) EFFECT ON COMPACTION PROPERTIES
For the purpose of creating a pavement that is both practical and longlasting, ideal ground is necessary for the development of some infrastructure, including roads, highways, and airport runways.The most crucial stage in making soils more resilient to adversity and weather is compaction.Consequently, it is crucial to research how the stabilizer affects the compaction curve.Figure 5 presents the findings from this investigation.We may deduce that as the amount of Ciment Kiln Dust (CKD) grows, the compaction curve becomes flatter, the dry bulk density falls, and the ideal water content increases.This is supported by the compaction curves for proportions of 0%, 5%, 10%, 15%, 20%, and 25% of the additive utilized.In fact, adding 25% CKD to the soil improved the ideal water content of the untreated soil from 20.38% to 29.5%, a 44.75% increase; with the same compaction effort, the maximum dry density dropped from 1.55 g/cm³ to 1.49 g/cm³, a 3.87% decrease.In Figure 6.This suggests that the compaction properties of the cement dust-stabilized soil have improved.Similar findings were obtained when polypropylene fibers and cement kiln dust were used to stabilize the soil.In this instance, adding 15% CKD + 1% FPP to the soil resulted in a 3.22% decrease in maximum dry density and an increase in water content of 18.54% (Figures 7 and 8).This plastic clay seems to benefit greatly from these additions.
The agglomerated and flocculated soil particles occupying larger spaces cause the reduction in dry density.Moreover, the CKD-induced particle aggregation leads to larger macropores within the soil, which decreases the dry density and improves the safety factor and structural stability.In terms of the rise in the ideal water content, more water is needed for cement dust to react instantly with the minerals in the soil, causing the clay to agglomerate and flocculate.This outcome is in line with studies that were published in 2019 by Langade and colleagues and in 2021 by Mohamedzein and colleagues.process.After compaction, another curing period of 1 day, 7 days, 14 days, and 28 days was provided for the samples to undergo a pozzolanic reaction, resulting in the stabilization of the treated samples.The influence of cement kiln dust on compressive strength is depicted in Figure 9, which clearly shows that the compression strength of the soil increases with an increase in the percentage of cement kiln dust.The variation in this resistance concerning the quantity of additive appears to be significant between 5 and 15%, reaching its peak at 15% CKD.
Subsequently, the unconfined compressive strength decreases with the addition of 20% and 25% CKD; it is lower than that of 15% CKD, which represents the peak but remains higher than the unconfined compressive strength of the untreated confined soil.The decrease in unconfined compressive strength is attributed to the excessive CKD content, creating heterogeneity in the soil+CKD mixture.The higher-than-optimum stabilizer content added to the soil leads to a lesser increase    (2017).This allows us to consider that the percentage of (15% CKD + 0.5% FPP) is the optimal quantity for this study.
Figure 12 shows that the effect of curing time remarkably increases the strength of the treated soil.Adding the optimal quantity (15% CKD + 0.5% FPP) to

CONCLUSIONS
This research aims to explore the ways in which locally produced cement kiln dust (CKD) from the Hadjer Soud SKIKDA cement plant enhances the mechanical and physical properties of Cheffia Clay, a fine natural soil.We looked at the unconfined compressive strength, plasticity, compaction, and particle size distribution of soil specimens stabilized with cement kiln dust (CKD alone) and CKD in combination with synthetic fibers (CKD + Polypropylene Fibers, FPP).
Drawing on the outcomes of this experimental investigation, the subsequent deductions can be made: 1.
For treating fine soils, the initial percentage of 10% CKD was applied.compressive strength of the soil improves more quickly and effectively when the amount of additive is increased.

7.
The effects of curing time were found to be similar when stabilizing Cheffia Clay using a mixture of polypropylene fibers and cement kiln dust.
The investigated soil's unconfined compressive strength significantly increased after the ideal amount of (15% CKD + 0.5% FPP) was added.
This improvement continued as the curing period increased.
The study showed that the incorporation of 15% CKD + 0.5% FPP into clay leads to improved performance characteristics, increased durability and loadbearing capacity, and the assurance of safe and stable constructions in geotechnical works.The economic advantages of employing cement kiln dust include lower costs for soil stabilization procedures and less fill material needed for foundation layers in road construction.
To gain a deeper understanding of how the low-bearing capacity swelling soil, improved by adding CKD and polypropylene fiber, behaves, it's essential to conduct thorough microstructural analysis.This involves using techniques like Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) to examine untreated soil samples, CKD-treated soil samples, and those treated with both CKD and polypropylene fiber.This analysis will provide insights into how these additives influence the soil's internal structure and composition, enhancing our understanding of their effects on soil stability and mechanical properties.
Abbas (2023) modified the OMC-MDD relationship, swell-collapse potential (SCP), and unconfined compressive strength (UCS) to assess the efficacy of CKD as a stabilizer for expansive soils.The experimental findings demonstrated that the addition of CKD resulted in a large improvement in unconfined compressive strength, a drop in maximum dry density, an increase in optimal moisture content, and a complete reduction in swell-collapse potential (SCP).Our attention has been drawn to several research studies that have utilized polypropylene fiber, either by itself or in conjunction with CKD, as an additive to enhance the properties of expansive soils.In order to determine the impact of adding a percentage of polypropylene fibers (0%-0.8%)randomly distributed on the properties of compaction, unconfined compressive strength (UCS), modulus of elasticity (E50), swelling, and consolidation of expansive clay, MuhammadHamza et al. (2022) carried out an experimental study.The studied parameters significantly improved, according to the experimental results.The impact of incorporating polypropylene fibers (FPP) on the behavior of artificial expansive soil made with 80% bentonite and 20% sand was investigated by Sarah A.Hussein and Haifaa A. Ali in 2019.

(
FPP).A battery of geotechnical laboratory tests was conducted to ascertain the effect of CKD alone on the plasticity, compaction, and shear strength (UCS) characteristics of a highly flexible clay soil.Additionally, research has been done Studies in Engineering

Figure 2 -
Figure 2 -Soil grain size distribution curve

Figure 3 -
Figure 3 -Determination of the initial proportion of CKD, or cement kiln dust

Figure 4 -
Figure 4 -Impact of Chronic Kidney Disease on Atterberg limits

Figure 5 -SOIL+15%CKD
Figure 5 -Impact of cement kiln dust (CKD) on the properties of compaction

Figure 6 -Figure 8 -
Figure 6 -MDD and OMC variations with CKD content in unconfined compressive strength (UCS) due to the loosening of the soil structure (indicating a brittle type of failure) caused by flocculation due to the presence of free calcium oxide in the cement kiln dust unreacted; a similar trend was observed by G.K. Moses and al (2012) S. Ghavami and M Rajab (2021) and R. K. Sharma (2017).The elevated stabilizer content added to the soil results in a lessened increase in unconfined compressive strength (UCS) because of the loosening of the soil structure (indicating a brittle type of failure) caused by flocculation due to the presence of free calcium oxide in the cement kiln dust unreacted.Actually, at 15% CKD, the clay's consistency gets even better; it gets very firm, has a tight texture, and has less interstitial voids.For this reason, we may conclude that this proportion is ideal for our study.Studies in Engineering and Exact Sciences, Curitiba, v.5, n.1, p. 1771-1792, 2024

Figure 9 -
Figure 9 -Influence of cement dust on simple compressive strength

Figure 10 -
Figure 10 -The impact of cement kiln dust and curing duration on compressive strength the studied soil led to an increase in the strength value from 273.35 kPa to 1831.93 kPa after 1 day of curing.Increasing the curing time from 1 to 28 days resulted in an increase in the unconfined compressive strength value to 3636.372 kPa for the same percentage of additives.It can be concluded that this increase in strength indicates a transition of the studied soil from a brittle (fragile) deformation state to a ductile deformation state.Studies in Engineering and Exact Sciences, Curitiba, v.5, n.1, p. 1771-1792, 2024

Figure 11 -
Figure 11 -Effects of FPP fiber and cement kiln dust (CKD) on basic compressive strength is raised by the addition of cement dust up to a saturation point of 15% CKD, at which time it reaches its maximum value and then gradually drops.Additionally, it raises the liquid limit, which lowers the plasticity index and improves the clay's workability, allowing building to continue all year round rather than just during dry seasons.3.Compaction using the standard Proctor test on Cheffia Clay shows that increasing the percentage of CKD and CKD combined with polypropylene fibers (FPP) flattens the compaction curve, allowing better control of water content on-site, as the optimum water content can vary.It also decreases the maximum dry bulk density, resulting in an improvement in the safety factor and, consequently, better stability of the structure, while increasing the optimum water content.These changes result from ion exchange and flocculation of the soil particles, making it more friable for compaction.4.The UCST simple compression test was used to calculate the larger percentage of CKD needed for the stabilization procedure compared to the modification process.The latter demonstrated how, after 24 hours of curing, raising the CKD percentage to 15% greatly improves the clay's consistency, which goes from an initial medium consistency to a very firm one for 15% of CKD; this raises the resistance to unconfined compression.When the clay reaches this point, it becomes solid (stiff) and loses some of its strength and consistency.Increased cement kiln dust content heterogeneously reduces the strength of the clay+CKD mixture.Therefore, the ideal percentage of CKD is 15%.5.For all three of the utilized additive compositions, the unconfined compression strength of the soil is greatly increased by the addition of polypropylene fibers to the ideal soil+CKD mixture; the maximum strength value is reached at a fiber concentration of 0.5%.The fibers tend to boost the unconfined compression strength at the interfaces by acting as tiny bonding components and preventing the formation of rupture fractures.6.The amount of cement kiln dust in the soil has a major impact on its unconfined strength over the course of the curing period, and the curing time has a notable effect on the soil's compressive strength.The unconfined Studies in Engineering and Exact Sciences, Curitiba, v.5, n.1, p. 1771-1792, 2024

Table 1 -
Chemical makeup of the soil under study and CKD

Table 2 -
The mechanical and physical characteristics of polypropylene fibers

Table 3 -
Atterberg limits for the natural soil