Investigation of Stability and Underlying Mechanism of Unstable Subgrades Loess Modified by Carbide Slag in Road Construction Projection

Abstract

The repurposing of carbide slag (CS) coupled with the advancement of eco-friendly engineering methodologies promises a novel approach to addressing the technical challenges inherent in loess refinement. This inquiry delves into the feasibility of employing CS as an economically viable and ecologically sustainable remedy to amplify the engineering attributes of loess within the context of optimal preservation. In this investigation, assorted quantities of CS, spanning from 1% to 6%, were infused into the loess. The efficacy of CS as an additive was ascertained through a comprehensive array of tests administered across varied curing durations (0, 5, 10, 20, and 30 days), concentrating on its influence over the soil’s mechanical attributes. The study conducted various tests such as dual hydrometer, Attberg limit, specific gravity, compaction, unconfined compressive strength (UCS), consolidation, physico-chemical properties (pH, conductivity), and chemical analysis (sodium percentage and sodium adsorption rate). The study demonstrated that the incorporation of CS into loess resulted in an increase in hydraulic conductivity, UCS, and optimum water content while reducing maximum dry density, plasticity, and compressibility. Specifically, the application of 6% CS resulted in a significant 6.7-fold increase in UCS from 226.8 (kPa) to 1508.8 (kPa) over a 30-day curing period. It was also observed that the addition of CS and curing period resulted in a decrease in soil pH from 8.5 to 7.5 and an increase in electrical conductivity (EC) from 250 to 490 μs/cm. When the CS concentration was increased to 6%, the amount of Na⁺ ions, the total soluble salts, and the percentage of Na in the loess decreased. The phenomenon can be ascribed to the replacement of Ca²⁺ for Na⁺, leading to a more slender, diffuse double layer and heightened stability. The application of calcium silicate in loess subgrades enhances their stability and potency, concurrently providing an ecologically sound waste management resolution. Consequently, it emerges as a profoundly viable choice for ameliorating loess within the realm of the construction sector.

1. Introduction

Loess, a unique geological carrier, is widely distributed in Northwest China and poses a serious threat to the safety of people’s lives and properties as the most serious geological disaster in the region [1,2,3,4]. As a result, it emerges as an imperative task within the realm of engineering to be promptly attended to. Loess manifests traits akin to those of engineering calamities, including laxity and porosity, thereby engendering challenges in fulfilling the mechanical requisites of tangible engineering endeavors [5,6]. Consequently, it stands as one of the imminent engineering quandaries necessitating resolution in the sphere of geotechnical engineering. Loess sites frequently encounter predicaments such as subgrade degradation, instability in excavation engineering, and seepage-related impairments, all stemming from the inherent attributes of loess [7,8,9]. These potential characteristics can result in uneven settlement of loess subgrade, instability, and damage, posing a threat to the progress of road construction and the safety of people’s lives and properties. The endeavor of constructing highways within regions dominated by loess is often beset by the recurrent influence of subgrade collapsibility, a predicament acutely pronounced in nascent loess terrains. The traditional method of treating loess subgrades involves using inorganic materials such as cement and lime to improve the soil’s stability [10,11,12,13]. With the ascendancy of environmental preservation as an escalating imperative, and the inception of imperatives such as “carbon peak” and “carbon neutrality,” the generation of pivotal constituents for road construction, encompassing sand, gravel, and cement, finds itself increasingly constrained. This circumstance has engendered a paucity in the reservoir of elemental substances requisite for the realization of road construction undertakings. Hence, it assumes paramount importance to discern apt substances capable of elevating the caliber of the loess subgrade, thereby transmuting it into a proficient filler [14,15,16]. This will adeptly confront the momentous technical quandaries that arise in the course of loess subgrade construction.

Numerous scholarly investigations have been conducted previously, aimed at the remediation of soil through diverse assortments of chemical agents and additives [17,18,19]. Faruk et al. [20] and Savas et al. [21] employed fly ash for the amelioration of dispersed soil, noting that a stabilization efficacy necessitated 9% and 10% fly ash, respectively. Vakili et al. [22] ascertained that an incorporation of 8% ZELIAC (a new additive) content sufficed to mitigate the potential for dispersion. Reddy et al. [19] found that maximum dry density (MDD) decreased with increasing doses of xanthan gum. But as the amount of xanthan gum increased, optimum moisture content (OMC) and unconfined compressive strength (UCS) increased. Savas et al. [21] employed 2% lime and 3% natural zeolite to diminish dispersiveness, consolidation, and swell traits. Chemical agents have demonstrated efficacy in the stabilization of disseminated soils. Although these agents may refine the performance of dispersion, their repercussions on the environment are adverse, necessitating the exploration of eco-friendly alternatives for stabilizing agents. The novel approach entails substituting ecologically detrimental agents with environmentally friendly counterparts. Among these, calcium-based substances demonstrate the utmost efficacy in remediating disseminated soils. These compounds adeptly induce rapid agglomeration and flocculation of soil particles, leading to the formation of a cementitious matrix by substituting Ca²⁺ ions in lieu of Na⁺.

In recent years, a surge of interest has been witnessed in the realm of repurposing industrial solid waste and the propagation of eco-conscious engineering methodologies. This shift has led to a burgeoning sphere of investigation and application [23,24]. Various scholarly inquiries have highlighted that the utilization of traditional soil amendments, encompassing cement, lime, and fly ash, can engender intricate engineering predicaments [25,26]. These predicaments encompass substantial costs linked with cement, limited efficacy in enhancing exceptionally plastic soil, as well as issues such as fissuring, the generation of particulate matter, gradual fortification, and suboptimal water resistance often associated with lime-stabilized soil [27,28,29,30]. Furthermore, the utilization of fly ash-infused soil can be intricate and often beset by challenges such as initial strength deficiency and susceptibility to desiccation. It is widely acknowledged that carbide slag emerges as a residue resulting from the synthesis of acetylene via calcium carbide, comprising primarily Ca(OH)₂ and CaCO₃ as its principal constituents [31]. Given the predominant presence of Ca(OH)₂ within carbide slag, the prospect arises for its potential application in soil stabilization. Left unchecked and allowed to amass through the passage of time, this refuse possesses the potential to induce land calcification, thereby precipitating grave contamination of the surrounding aqueous and terrestrial milieu. Nevertheless, the carbide slag, replete with an abundance of Ca(OH)₂ and diverse chemical constituents, presents an opportunity for repurposing to elevate the engineering attributes of fillers. Instances of such repurposing involve its integration as a component in the composition of road sub-base materials. The scrutiny of calcium carbide slag’s efficacy in augmenting the quality of loess roadways promises to introduce an innovative resolution to technical quandaries associated with the enhancement of loess soil integrity. Moreover, this approach holds the capability to address the ecological apprehensions linked with waste proliferation, thereby engendering favorable ecological consequences and auspicious implementations near Tongchuan in the Shaanxi Province of China. This research employs carbide slag (CS) as a transformative agent for loess. The physical and mechanical attributes of the enhanced loess have been scrutinized through a sequence of controlled assessments. Furthermore, the inquiry delved into the mechanism underpinning the reinforcement and proffered parameters conducive to future scientific exploration and engineering applications.

Most existing studies have a focus on the deterioration of soil matrices and enhancement of soil characteristics by traditional soil additives, while few studies investigate the chemo-mechanical processes of loess modified by CS from the perspectives of the microscale structural and macroscale mechanical. This offers engineers a pragmatic recourse to contend with the prevalent obstacles entwined with disseminated soil compositions. In consideration of the aforementioned, the objectives of this study are as follows: (1) To investigate the microstructure evolution of loess modified by CS using microscopic tests including SEM, XRD, and XRF; (2) to evaluate the enhancement behavior of the strength properties using the dual hydrometer, Attberg limit, specific gravity, compaction, unconfined compressive strength (UCS), consolidation, and physico-chemical properties (pH, conductivity) tests; and (3) to explore the underlying mechanism of the microstructure evolution of loess modified by CS with the enhancement of the macroscale mechanical properties.

2. Materials and Methods

2.1. Study Area and Samples

In Northwest China, wind-blown sand is deposited on the Loess Plateau, and loess is formed by wind-blown sandy materials through three stages: leaching, erosion, and accumulation. The Loess Plateau consists of three primary geomorphic features: Loess ridges, loess hills, and stone ditches. Drilling data indicate that the upper layer of the sandstone bedrock consists of a 20–30 m and 2–5 m-thick paleosol and overlying Malan loess (Q₃), respectively. The undisturbed loess was retrieved from Tongchuan, Shaanxi Province, which is approximately 46 km southeast of Xi’an, with a sampling depth of 3.0–4.5 m, as shown in Figure 1. The physical properties of the loess samples were measured, and the results are shown in

Table 1. Geotechnical properties of the loess.

Properties	Loess	CS
Specific gravity, Gs	2.72	2.32
Dry density, ρdmax/(g/cm3)	1.78	1.49
initial water content, wn/%	16.5	-
The Atterberg limit
Liquid limit, wL/%	35.43	-
Plastic limit, wP/%	21.42	-
Soil classification	CL	-

. The water content (ω) and dry density (ρ_d) of the samples were determined by the dry method, and the specific gravity (G_s) of the samples was determined by the hydraulic method. The particle size distribution of the samples was measured with a WJL-602 laser particle size analyzer (Jinko, China), indicating that 86.64% of particles were silt, as well as 9.16% clay and 4.20% sand [32,33,34]. It should be emphasized that sodium hexametaphosphate was used as a dispersant to avoid mistaking clay aggregates for large particles [1]. According to the Unified Soil Classification System, loess belongs to low-plasticity (CL) clay. Table 1 lists the geotechnical properties of dispersive soil, and

Table 2. Physiochemical properties of loess.

Properties	Value
pH	8.83
Electrical conductivity, EC (ds/m)	24.6
Sodium cations, Na+ (mg/L)	185
Total dissolved salts, TDS (mg/L)	234
BET specific surface area (m2/g)	24.43
Organic matter (mg/g)	4.4

lists the physiochemical properties. The mineral composition of loess was analyzed by a Bruker AXS D8 Advance X-ray powder diffractometer (XRD). Figure 2 shows the results obtained by semiquantitative XRD analysis [32]. The mineral composition is mainly quartz, and there are other minerals such as calcite, chlorite, potassium feldspar, and montmorillonite. Further, the major element compositions were analyzed through the scanning electron microscope (SEM) images.

While the usage of CS for soil modification has been previously documented, its role as a stabilizing agent in the context of loess treatment is held in high regard. The elemental composition of CS, as deduced through X-ray fluorescence (XRF) analysis, is delineated in

Table 3. Composition analysis of the Tongchuan loess specimen and carbide slag (CS).

Concentration of Oxides	Loess (%)	CS (%)
CaO	14.47	68.10
SiO2	55.08	2.48
Al2O3	13.58	1.96
SO3	-	0.78
Fe2O3	7.73	0.15
MgO	2.63	0.11
K2O	3.36	-
Na2O	1.41	0.07
Others	1.74	26.35

, revealing calcium as its primary metallic oxide. The qualitative test results of the XRD test conducted on the loess used in the experiment, as described in Figure 2, confirm the mineral composition of the loess. Additionally, Table 3 presents the XRF quantitative study results of both loess and CS, indicating the composition of oxides. These results are found to be in good agreement with the quantitative results obtained for the loess. The selection of this waste material for the study was predicated on its distinctive attributes and ready availability. As a preliminary facet of the soil treatment protocol, CS underwent comminution into a fine powder, which was subsequently sieved through mesh No. 200. The objective underlying this procedure was to yield an optimal amalgamation of minute particles poised to instigate reactions with the clay constituents.

2.2. Measurements of Mechanical and Physical Properties of Modified Loess

First, loess specimens and CS used in this study were oven-dried for one day and pulverized into fine form. After that, CS were passed through the sieve, and then the quantity of CS was correctly mixed for each batch. The test amounts of CS were 1, 2, 3, 4, 5, and 6% of the dry weight of soil. The curing times for the test were 0, 5, 10, 20, and 30 days. All tests applied to the present work had three replicates.

For the purpose of examining the influence of CS upon the liquid plastic limit of loess specimens, the Attberg limit test, in accordance with ASTM D4318 [35], was duly conducted. In order to ascertain whether CS wrought any alteration in the specific gravity of the soil samples, analyses were executed as per the Standard for Geotechnical Test Methods (2019) [36]. Distinct allotments of CS were employed in the compaction of the loess samples through conventional methodologies, facilitating a comparative assessment of their attributes. The methodology for this analysis has been elucidated in ASTM D698 [37]. Moreover, in alignment with ASTM D2166 [38], a subset of chosen loess specimens underwent UCS experiments to unveil the repercussions of CS on both their dispersive tendencies and strength characteristics.

2.3. Measurements of Physiochemical and Chemical Properties of Modified Loess

Subsequently, the loess specimens underwent a series of geotechnical evaluations. The double hydrometer test, meticulously conducted in accordance with the Standard for Geotechnical Test Methods (2019), was employed to assess the intrinsic dispersive potential (DP) within the soil samples. It is established that soil is bereft of dispersive tendencies if its DP remains below 30. If it falls within the range of 30 to 50, the soil is deemed moderately dispersive, whereas it is classified as overtly dispersive if its DP surpasses the threshold of 50. Concomitantly, physicochemical analyses, encompassing assessments of soil pH, electrical conductivity (EC), percentage sodium (PS), and sodium adsorption ratio (SAR), were conducted to discern the intricate chemical interplay between the soil samples and the incorporated additive, CS. The parameters of pH, EC, PS, and SAR were expeditiously quantified, immediately after a 24 h duration, while maintaining a steady laboratory temperature of 25 °C.

3. Results and Discussion

3.1. Effect of CS on the Mechanical and Physical Properties of Modified Loess

The alteration in plasticity index (PI) for specimens subjected to different concentrations of calcium silicate (CS) and durations of curing is illustrated in Figure 3. With the augmentation of both CS concentration and curing duration, a substantial reduction in the PI of the specimens was observed. The zenith of adsorption capacity within the loess substrate for Si²⁺, Ca²⁺, or Al³⁺ was discernible at a concentration range of 4–5% CS, as the plasticity index (PI) exhibited a decline at elevated CS concentrations. The incorporation of CS engendered a reduction in the PI of the treated loess, heralding a favorable advancement that amplifies the soil’s workability owing to its solid nature. It remains imperative to underscore that the treated loess undergoes manifold chemical reactions encompassing cation exchange, flocculation, coagulation, and calcification responses, all of which collectively contribute to the geotechnical excellence of the soil. Various authors [5,39,40] have deliberated upon the merits inherent in diminishing pliancy as the valency of cations or the concentration of electrolytes experiences augmentation. While the plasticity index (PI) is profoundly influenced by interparticle interactions, it regrettably falls short of identifying dispersion phenomena. Nonetheless, in the course of the stabilization phase, a decline in flexibility serves as an indicator of the attenuation of loess dispersibility. The introduction of calcium silicate (CS) augments the allure of interfacial forces, thereby elevating the impediment between surfaces and diminishing the plasticity index (PI) within the dispersed soil specimens. Consequently, a transformation from dispersive to non-dispersive soil attributes transpires. Furthermore, the soil substrate may encounter a decline in its elasticity as a consequence of the cement infusion, provoking the aggregation of particles. Elaboration on this matter will follow in subsequent discourse.

The influence of calcium silicate (CS) on the specific density of dispersed soil is elucidated in Figure 4. The incorporation of CS into the loess substrate engendered a marked reduction in the specific density of the soil. The specific gravity (Gs) of the soil diminished from 2.72 to 2.62 upon the infusion of 6% CS. With the escalation of CS content within the loess, the specific density of the soil exhibited a consistent descent. This occurrence can be ascribed to the inherent characteristic of CS particles possessing a lower specific gravity compared to their loess counterparts.

The relationship between MDD and OMC is elegantly showcased across a spectrum of diverse CS concentrations and curing durations, as artfully depicted in Figure 5. The intrinsic MDD of unadulterated loess material stands at 2.18 g/cm³, coinciding with an OMC value of 18.1%. As the CS concentration undergoes elevation, reaching a pinnacle of 6%, the zenith of dry weight attains diminishment. The inquiry has revealed that the zenith of water content finds augmentation in tandem with the ascension of CS concentration, reaching an apogee at the 6% mark. These findings harmoniously resonate with antecedent inquiries into the treatment of clays employing cement, lime, or calcium-based compounds, all of which corroborate the trend of lower MDD and heightened OMC. The subdued dry weight attributed to CS, registering at 2.32 in comparison to the soil’s specific gravity of 2.72, potentially expounds the rationale behind the MDD decrease, as CS supplants a portion of the soil within any given volume.

Within the realm of soil stabilization research, the UCS magnitude serves as a paramount litmus test, wielded to ascertain the efficacy of soil adjuncts. In the grand pursuit of road construction and the orchestration of earthwork endeavors, the UCS attains a status of utmost significance, encapsulating one of the cardinal design benchmarks. Furthermore, the realm of cohesive soils finds the evaluation of bearing capacity encapsulated within the concept of undrained shear strength, a parameter that mirrors half the quantitative measure of UCS. The comprehensive investigation, undertaken, delves into the intricate dynamics of strength modulation through the prism of diverse CS concentrations and their corresponding curing durations. The outcomes unveiled within Figure 6 unfurl a compelling narrative: A 6% infusion of CS ushered forth a momentous upsurge in the UCS parameter. From a modest inception of 196.6 kPa, the UCS value burgeoned to a majestic 1415.8 kPa after a span of 20 days, encapsulating a remarkable growth of approximately 7.2-fold. Furthermore, after 30 days, this ascending trajectory persisted, propelling the UCS to 1508.8 kPa, an ascent equivalent to 6.7-fold from its initial value of 226.8 kPa. Discernibly, the temporal evolution of strength unravels across three discernible epochs, intrinsically linked to the passage of curing time. Initially, the process of hydration ignited a transient surge in sample resilience, thereby culminating in a surge of strength within the embryonic timeframe of zero to 10 days. Amidst the interval from the 10th to the 20th day, scant accumulative or diurnal increments in strength became discernible. The striking augmentation in UCS, materializing between the 20th and 30th days, finds its mooring in the expansive tapestry of prolonged chemical reactions. An observant note beckons, heralding that the nexus between curing duration and the cadence of strength amplification eclipses the resonance of cementitious material content in its impact.

The inherent compressibility inherent within the dispersed soil entity underwent notable enhancement subsequent to the intervention of CS. As the quantum of CS was progressively augmented to reach the zenith of 6%, a discernible nosedive in the compressibility index emerged, a tangible testament to the ascendancy of resistance against compression phenomena (as discerned in Figure 7). This intensification in resistance can be attributed to the orchestrations of flocculation and agglomeration amidst the particles within the treated soil. The intricate process of cation exchange orchestrates the evolution of more intricately flocculated structures, thus engendering a transformation of fabric composition from sodium dominance to a calcium-infused narrative. When introduced to loess terrains, the influence of CS on compressibility stands juxtaposed to the impact registered by the introduction of lime-stabilized clay.

3.2. Effect of CS on the Physiochemical and Chemical Properties of Modified Loess

The dispersed potential (DP) inherent within diverse loess samples, characterized by their varying concentrations of calcium silicate (CS), finds its nexus within the interplay of dry soil mass and the passage of curing time. This intricate interdependence finds its captivating portrayal within the visual realm of Figure 8. In instances where the CS concentration remains confined below the threshold of 6%, a pronounced decrement in DP is manifested as the concentration attains amplification. Conversely, an ethereal transformation befalls this pattern when the concentration ascends above 6%, heralding an augmentation in DP with the intensification of concentration. Moreover, the chronicle of DP unravels an enthralling chapter after the span of 30 days within the crucible of curing. Emanating from the embrace of 6% CS and a temporal span of 20 and 30 days, a conspicuous diminishment in DP becomes evident, a pivotal juncture that crystallizes the point of CS fixation at 6%. The infusion of CS wields the power to orchestrate a metamorphosis, transmuting the tapestry of deflocculated structures nestled within the loess particles into an era dominated by more intricate, flocculated formations. This orchestration, intrinsically correlated to the celestial ballet of ion exchange processes, is believed to have contributed to the dwindling of bilayer thickness, thus consecrating the descent of DP within soil substrates boasting variable CS content.

When the CS concentration is below 6%, DP decreases considerably as the concentration increases. However, when the concentration is above 6%, the trend changes, and DP increases as the concentration increases. Additionally, DP decreases significantly after 30 days of curing. After being exposed to 6% CS and cured for 20 and 30 days, there was a significant decrease in DP. The point of fixation for CS was found to be 6%. The addition of CS caused a transition from deflocculated to more flocculated structures in loess particles. It is possible that the decrease in bilayer thickness due to ion exchange processes caused the decrease in DP in soils with different amounts of CS. CS is a type of waste material that contains calcium and divalent cations such as Ca²⁺. When sodium cations (Na⁺) are introduced, which are only found in loess, the dispersed structure of the material changes to a flocculent structure. The CS application resulted in a reduction of Na⁺ content in loess. Specifically, a 6% concentration of CS was found to significantly decrease the concentration of Na⁺. Moreover, the percentage of sodium (PS) decreased significantly, indicating a complete transition from a dispersed sample to a non-dispersed and erosion-resistant sample, thus reducing repulsion between ingredients. The Ca²⁺ levels in the CS samples suggest that a successful cation exchange reaction occurred, wherein Na⁺ was replaced by Ca²⁺. This resulted in a thinner diffuse double layer and lower dispersion. The study’s findings demonstrate that CS significantly alters the dispersion resistance of loess. Moreover, aggregate development analysis indicates that CS-treated loess has greater strength. The effects of CS on the concentration and percentage of Na in loess were examined and presented in Figure 9. The addition of CS led to a decrease in both the Na⁺ concentration and the Na percentage. This decrease was accompanied by a reduction in the total dissolved salts in the soil solution. As the CS content was reduced, the sodium ion concentration in the loess also decreased, resulting in a lower total dissolved salt value. This, in turn, led to the loess being considered non-dispersed, as illustrated in Figure 10.

The demeanor of soil is profoundly swayed by the intricate tapestry of its mineral constitution. Table 2 unveils the tapestry of physicochemical attributes that define the essence of unaltered loess. However, when graced by the ministrations of a 6% infusion of CS, the pH of the loess solution embarks on a subtle descent, as gracefully portrayed in the tableau of Figure 11. The reduction in pH precipitated a metamorphosis in the oriented arrangement of loess constituents from their pristine condition to a state of flocculation. The diminution of hydroxide ions ensues with the decline in pH, engendering a reduction in surface charge density. Furthermore, the application of CS induces a pH reduction, culminating in the emergence of affirmative edges along the surface of negatively charged clay particles. This instigates the genesis of flocculated configurations, thereby mitigating soil dispersal tendencies. Upon juxtaposing treated specimens with their indigenous counterparts, it was discerned that conductivity had escalated within all treated instances. Notably, the specimen possessing 6% CS content exhibited a substantial elevation in electrical conductivity vis-à-vis other samples stabilized with CS. This phenomenon can be ascribed to the augmented concentration and valency of cations preexistent within the bilayer matrix, along with the observation of a slender bilayer.

3.3. Discussion

In the context of infusing calcium silicate (CS) into the loess matrix, a notable augmentation unfolded across hydraulic conductivity, unconfined compressive strength (UCS), and the optimal moisture content. Simultaneously, there transpired a discernible diminution in the utmost dry mass, plasticity, and compressibility. The pursuit of discerning enhanced methodologies and temporal parameters emerges as an indispensable facet in the endeavor of stabilizing this intricate process. When the CS concentration reached a maximum value of 6%, the OMC value increased. These results are consistent with previous studies on clays treated with cement, lime, or calcium-based compounds, which have shown lower MDD and higher OMC. CS had a lower specific gravity value of 2.32 compared to 2.72 for soil. This difference can be attributed to the fact that CS displaces part of the soil in a given volume, which may explain the reduction in MDD. The optimum moisture content of soil is determined by the concentration of Na⁺ ions in soil pore water. The increase in Na⁺ ions helps increase the osmotic potential and reduce the van der Waals attraction between soil particles, leading to an increase in OMC. The incorporation of a 6% composition of CS into the soil specimens yielded a substantial surge in UCS by a factor of 6.7, escalating from 226.8 (kPa) to 1508.8 (kPa) subsequent to a curing period of 30 days. The investigation has ascertained that the apogee concentration of CS materialized at 6%, thereby alluding to its prodigious potential as a roadbed filler while concurrently preserving its robustness. The amplification of UCS is ascribed to both transient phenomena, such as ion interchange that culminates in the flocculation of soil microparticles, and enduring processes involving volcanic ash that engender an array of binding compounds. This augmentation in structural integrity equips the soil to more resolutely endure augmented loads, consequently mitigating its vulnerability to structural distortion.

The intricate physicochemical attributes of soil and interstitial fluid stand as pivotal determinants dictating the permeability of the soil medium. The permeability thereof is intricately influenced by parameters such as the sodium uptake ratio, the magnitude of exchanged sodium, the proportion of sodium content, and the concentration of ions within the aqueous matrix. Within the realm of soil permeability, the exchangeable sodium quotient and the holistic ionic composition within the aqueous milieu wield a marked influence. Notably, an elevated sodium uptake ratio instigates a decline in permeability as clay microparticles effuse in the presence of aqueous constituents, thereby instigating the occlusion and impediment of fluidic flux. In a contrasting vein, the introduction of CS into the soil matrix engenders a discernible augmentation in the liberated calcium inventory and a concomitant curtailment in the sodium absorption ratio. These shifts orchestrate the coalescence of soil particulates, thus effectuating the amelioration of surface occlusion and the elevation of permeability. The introduction of CS furnishes the soil milieu with unbound calcium ions, which in turn supplant the incumbent sodium ions through cationic interchange. This infusion of calcium ions engenders a mitigation of repulsive forces operative among clay particles, culminating in the genesis of more expansive aggregates characterized by a flocculated architecture.

The infusion of CS along with the temporal phase of maturation orchestrated a discernible decline in the pH of the soil matrix, concurrently ushering forth an augmentation in EC. Specifically, the incorporation of CS at a proportion of 6% ushered in a notable abatement in the concentration of Na⁺ ions, the cumulative tally of soluble salts, and the proportion of Na⁺ within the loess substrate. This phenomenon is ascribable to the incursion of Ca²⁺ in lieu of Na⁺, thereby instigating a tenuity within the diffuse double layer and auguring heightened stability, as delineated in Figure 9. The microstructural constitution of unaltered loess and CS-molded loess underwent meticulous scrutiny via the scanning electron microscopy (SEM) technique, thereby discerning disparities subsequent to a 20-day maturation period. The scrutiny unveiled that the supplementation of CS to the loess conglomerate prompted the agglomeration of clay microparticles through the introduction of calcium, as poignantly illustrated in Figure 12. The intricate architecture of the unadulterated disintegrated soil, as vividly portrayed in Figure 12, predominantly embodies structures that exist in a state of destabilization and dispersion. Moreover, conspicuous voids and interstices permeate the soil matrix, serving as eloquent indicators of a configuration characterized by looseness and a paucity of density. However, with the infusion of CS, the microstructural ensemble of the soil undergoes a seamless metamorphosis, transiting from a state of deflocculation to a realm typified by enhanced flocculation. This transformative process begets the origination of novel cohesive entities, which are impeccably delineated in Figure 12. As previously alluded to, the aggregation of soil particulates finds its origins in the transient phenomenon of cationic interchange reactions. Upon the mingling of CS with the soil medium, a release of calcium cations transpires, effectuating the consolidation of clay constituents. Subsequently, a volcanic sequence of reactions unfolds, culminating in the ultimate amalgamation of the soil with CS. This intricate process begets a spectrum of distinct calcium silicate hydrates and calcium aluminate hydrates. The pozzolanic sequence of reactions amplifies the vigor of the attractive forces, thereby catalyzing a diminution in the thickness of the diffusive double layer as well as the diffusive potential intrinsic to the clay particles. The process of calcification augments the adhesive interactions binding clay particulates, engendering a discernible attenuation in their propensity for dispersion. This consequential alteration subsequently gives rise to a diminishment in the dimensions characterizing the diffusive double layer.

4. Conclusions

Dispersive soils have the potential to cause severe issues with construction. However, in this investigation, the cost-effective additive CS was used to successfully treat the dispersivity characteristics of loess. When adding CS to loess, the hydraulic conductivity, UCS, and OMC all increased, while the MDD, PI, and compressibility decreased. The decrease in dispersivity was due to cation exchange, agglomeration, and flocculation reactions where the soil structure was changed from a deflocculated to a flocculated state. The supplementation of 6% CS into the soil samples occasioned a remarkable amplification in UCS, by a factor of 6.7, escalating from 226.8 (kPa) to 1508.8 (kPa) following a 30-day curing phase. The inquiry disclosed the zenith of CS concentration to reside at 6%, serving as a testament to its prospective utilization as a roadbed filler without forsaking its tenacity. The confluence of CS addition and the temporal maturation period gave rise to a decline in soil pH coupled with a rise in electrical conductivity. Specifically, with a 6% CS admixture rate, there was a discernible abatement in the presence of Na⁺ ions, cumulative soluble salts, and the proportion of Na within the loess. This occurrence finds its origins in the substitution of Na⁺ with Ca²⁺, precipitating a refinement of the diffusive double layer thickness and, concomitantly, an upsurge in stability. The attenuation in dispersal propensity was a consequence borne from the interplay of cationic interchange, agglomeration, and flocculation reactions, whereby the structural configuration of the soil underwent a paradigmatic shift from a deflocculated to a flocculated state. The quest for innovative methodologies and temporal considerations remains of paramount importance in the endeavor to stabilize this intricate process.