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Article

Effect of Magnesium Chloride Solution as an Antifreeze Agent in Clay Stabilization during Freeze-Thaw Cycles

by
Amin Yeganeh Rikhtehgar
* and
Berrak Teymür
Soil Mechanics and Geotechnical Engineering Program, Department of Civil Engineering, Istanbul Technical University, 34485 Istanbul, Türkiye
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(10), 4140; https://doi.org/10.3390/app14104140
Submission received: 30 March 2024 / Revised: 3 May 2024 / Accepted: 7 May 2024 / Published: 13 May 2024
(This article belongs to the Special Issue New Trends in Sustainable Geotechnics—Volume II)
Browse Figures
Versions Notes

Abstract

:
Freeze-thaw cycles significantly impact construction by altering soil properties and stability, which can lead to delays and increased costs. While soil-stabilizing additives are vital for addressing these issues, stabilized soils remain susceptible to volume changes and structural alterations, ultimately reducing their strength after repeated freeze-thaw cycles. This study aims to introduce a different approach by employing magnesium chloride (MgCl2) as an antifreeze and soil stabilizer additive to enhance the freeze-thaw resilience of clay soils. We investigated the efficiency of MgCl2 solutions at concentrations of 4%, 9%, and 14% on soil by conducting tests such as Atterberg limits, standard proctor compaction, unconfined compression, and freeze-thaw cycles under extreme cold conditions (−10 °C and −20 °C), alongside microstructural analysis with SEM, XRD, and FTIR. The results showed that MgCl2 reduces the soil’s liquid limit and plasticity index while enhancing its compressive strength and durability. Specifically, soil treated with a 14% MgCl2 solution maintained its volume and strength at −20 °C, with similar positive outcomes observed for samples treated with 14% and 9% MgCl2 solutions at −10 °C. This underlines MgCl2’s potential to enhance soil stability during initial stabilization and, most importantly, preserve it under cyclic freeze-thaw stresses, offering a solution to improve construction practices in cold environments.

1. Introduction

The construction industry faces significant challenges due to adverse weather conditions, which can profoundly impact project timelines and costs. Approximately 45% of construction projects globally experience disruptions caused by weather events, leading to billions of dollars in additional costs annually. These challenges are intensified by certain factors, such as the need to halt earthwork in subfreezing temperatures, adding complexity to projects [1,2,3].
One specific phenomenon is the freeze-thaw (F-T) effect, particularly affecting road construction projects. The F-T effect poses a threat during cold weather, potentially causing delays or even halting the project to prevent complications related to freezing and thawing. This underscores the industry’s ongoing struggle with the limitations imposed by unfavorable weather conditions, especially in subfreezing temperatures. The interruptions not only contribute to project delays but also increase costs as construction professionals navigate the complexities introduced by adverse weather, further emphasizing the need for effective strategies to mitigate weather-related risks in construction [4,5].
F-T cycles significantly alter the soil properties crucial for engineering applications, especially in geotechnical and road construction [6]. They pose risks to embankment soils’ stability [7] and durability, particularly in regions with mid-high latitudes and high altitudes, inducing substantial changes in geotechnical properties [8,9]. Research spanning six decades, particularly since the 1950s in the United States and Canada, has revealed how these cycles impact soil structure [10]. They disrupt soil stability and permeability by causing desiccation cracks, increasing pore space, and challenging water retention and drainage. Additionally, F-T cycles reduce soil strength and cohesion, making it more susceptible to erosion and runoff [11,12,13].
Furthermore, F-T cycles trigger volume and density changes in susceptible soil, a significant factor in soil embankment damage. Loose soils contract in volume, while dense soils expand, intensifying the risk to soil structures [14,15]. The phenomenon also accelerates weathering processes, leading to structural failures, such as uneven frost heave [16], thaw subsidence [17], compromised foundation integrity [18], and slope destabilization [19]. Material properties, including stress-strain behavior, failure strength, shear strength, and elastic modulus, exhibit variability under the influence of F-T cycles. Research by Kamei et al. [20] highlighted a reduction in both the strength and durability index of soft soils subjected to cyclic F-T processes. Similarly, Lu et al. [21] observed a decrement in the resilient modulus of expansive soils with increasing F-T cycles, thereby affecting their deformation characteristics [21]. Given the intricate effects of F-T cycles, meticulous consideration of engineering design is crucial, especially concerning the unsuitability of fine-grained soils for construction with regard to their low bearing capacity and shear strength [22,23].
To lessen the adverse effects of F-T cycles on the mechanical properties of soil, the traditional method involves mixing these soils with cement [24] or lime [25,26]. Additionally, scientists have conducted extensive research to explore non-traditional additives to minimize the damage in recent years. These include using fly ash [27], alkali-activated volcanic ash, and slag [28], biological approaches such as microbial-induced biopolymers [29], phase change material (PCM) [30], recycled ash along with natural fibers [31], mixing fibers with cement and soil [32], employing chemicals and polymers like polyacrylamide (PAM) [33], utilizing recycled materials [20,34], or incorporating materials such as rice husk ash [35]. However, despite all these methods increasing the ultimate strength of the soils after F-T cycles compared to untreated soil, a common characteristic among all these stabilizers is a subsequent loss of strength after successive cycles compared to their initial strength before experiencing F-T cycles. This weakening suggests alterations to the embankment soil structure, accompanied by continuous ongoing volume changes during F-T cycles. This loss of strength, especially when coupled with volume changes, presents significant challenges for the stability of soil embankments and infrastructure.
Another method to cope with the damages caused by F-T cycles is by using antifreeze materials in the soil. This approach prevents the soil moisture from freezing, thereby avoiding the development of ice lenses and the subsequent induced cracking, while maintaining the integrity of the compacted soil structure.
Research on the impact of diverse antifreeze agents on soils is relatively scarce. Among these agents is monoethylene glycol (MEG), a type of ethylene glycol with various applications. While ethylene glycols are used in different fields, monoethylene glycolhas garnered significant attention from scientific communities for its applications, notably as an antifreeze agent [36,37,38]. However, a study has shown that MEG is not a favorable material for use as an antifreeze because it has adverse effects on clays, leading to a decrease in the compressive strength of the clay. The results of this study indicate that the strength and stiffness of soils contaminated with MEG are progressively diminished by the level of contamination [39]. Therefore, using it as an antifreeze agent in cold weather would not be feasible due to this effect.
Consequently, our search for an alternative additive with antifreeze properties that does not compromise the strength of clay led us to magnesium chloride (MgCl2), a chemical salt. Some theoretical studies on the modeling of freeze-thaw effects on soil have demonstrated the impact of salt in water on lowering the freezing point within the modeling process, highlighting the significance of salt in the freeze-thaw process [40,41]. Additionally, there have been studies examining the effects of a magnesium chloride (MgCl2) solution on the mechanical properties of soil as a stabilizer, which have shown improvements in soil engineering properties [42,43,44,45].
However, the impact of MgCl2 as an antifreeze agent on the properties of soils under freeze-thaw conditions remains unexplored. This study aims to explore how water-soluble magnesium chloride (MgCl2) impacts the physical and mechanical properties of clay soil under unfrozen conditions and after undergoing freeze-thaw cycles. The research incorporates various experiments, such as Atterberg limits, standard proctor compaction, unconfined compressive strength (UCS), and freeze-thaw (F-T) cycles, performed on soil specimens treated with different concentrations of MgCl2 solution. To gain insights into the interaction of MgCl2 solution with soil at the microstructural level, the research also includes microstructural analysis using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR).

2. Materials and Methods

2.1. Materials

2.1.1. Soil

The fine-grained soil sample utilized in this investigation was sourced from the northern region of Istanbul. A comprehensive characterization of the soil sample was conducted through a series of tests, including hydrometer analysis [46], Atterberg limits [47], and specific gravity tests [48]. Figure 1 presents the X-ray diffractogram (XRD) pattern, indicating presence of Quartz (2θ = 20.8°, 26.6°, 36.5°, 39.4°, 42.4°, 45.7°, 50.1°, 59.9°, 67.7°, 68.2°) and Kaolinite (2θ = 12.3°, 19.8°, 24.8°, 34.9°, 42.3°, 50.2°, 55°) as the major constituents, with Muscovite (2θ = 8.7°, 17.6°, 25.4°, 40.2°, 54.8°, 60.1°, 67.9°, 68.1°) present in minor quantities. Furthermore, based on the unified soil classification system, the sample can be categorized as low plasticity clay (CL) [49]. The detailed physical properties of the soil used in research are shown in Table 1.

2.1.2. Magnesium Chloride

Magnesium chloride, known for its water solubility, serves as an effective antifreeze agent. It has applications in various industries but is primarily used for deicing and controlling dust. When sprayed in solid or liquid form onto road surfaces, magnesium chloride prevents snow and ice accumulation, ensuring safer travel conditions [50]. A 21.6% magnesium chloride solution can withstand temperatures as low as −33 degrees Celsius, making it an invaluable tool for combating freezing conditions [51]. The sample used in this study was obtained from Dead Sea Works Ltd., Beer Sheva, Israel. Table 2 displays the general characteristics of the MgCl2 utilized in this investigation based on the data sheet provided by the producer company.

2.2. Sample Preparation

The soil sample underwent drying at a temperature of 105 °C using an oven. Post-drying, it was subjected to fine grinding and passed through sieve No. 4, ensuring uniformity in particle distribution. A methodical process was utilized to prepare the samples, aiming to examine the properties of the soil after mixing it with a magnesium chloride (MgCl2) solution. Firstly, the MgCl2 was dissolved in distilled water to achieve 4%, 9% and 14% solutions. Subsequently, the dry soil was mixed with the MgCl2 solutions to create the desired soil samples.
Manual mixing was carefully executed to ensure uniformity at every stage. To enhance the absorption of the solution and to achieve a homogeneous mixture, the prepared mixtures were sealed in plastic bags and allowed to rest for about 24 h before compaction. This resting period allowed for the thorough absorption of the solution by the soil particles.
After compacting the treated and untreated samples to at least 98.0% of the maximum dry density (MDD) and the optimum water content (OWC) as obtained by the standard Proctor test (ASTM D-698) [52], each sample was wrapped in plastic film to avoid moisture loss. The samples were then divided into three groups with two designated for curing (one set for 7 days and another for 28 days) to study the effect of curing time on soil properties in a controlled environment. The third group was used for immediate testing to compare the soil characteristics directly with and without the curing process. Following preparation, all samples, both cured and uncured, were subjected to unconfined compression testing to evaluate the effect of curing on the samples’ strength. Additionally, only the samples cured for 28 days were tested for freeze-thaw cycles to assess their mechanical properties and durability.

2.3. Conducted Tests

Understanding the behavior of fine-grained soils, such as clay, necessitates the assessment of their Atterberg limits, which comprise the liquid limit (LL), plastic limit (PL), and plasticity index (PI). This assessment was carried out through liquid and plastic limit tests on all samples in accordance with the ASTM D4318 standards [47]. Additionally, standard Proctor compaction tests, guided by the ASTM D698 guidelines [52], were performed on soil samples treated with various concentrations of magnesium chloride (MgCl2) solution. These tests aimed to determine the samples’ maximum dry density (MDD) and optimum water content (OWC). To explore the effect of the MgCl2 solutions on the strength of treated samples, unconfined compressive strength (UCS) tests were conducted following ASTM D2166M [53] on samples cured for 7 and 28 days in a humidity-controlled environment, as well as on uncured samples for baseline strength comparison.
This study further investigated the impact of F-T cycles on the mechanical properties of soil stabilized with a MgCl2 solution at concentrations of 4%, 9%, and 14% under different freezing temperatures (−20 °C and −10 °C), using an experimental setup compliant with the ASTM D560 standards [54]. The experiment aimed to determine whether adjustments in the MgCl2 solution concentration are necessary to optimize soil stabilization effectiveness in response to different temperature exposures and to assess the treated soil’s response to various environmental freeze conditions.
Two identical sets of soil specimens, including both treated and untreated samples, were prepared as per guidelines and underwent a 28-day curing period before freeze-thaw testing. These specimens were measured for height, diameter, and weight, enabling an analysis of volume changes and an assessment of mechanical behavior after F-T cycles.
In the initial phase, one set of specimens was exposed to −10 °C for 24 h in a controlled freezer to simulate moderate freeze conditions, while the other set was subjected to −20 °C to represent severe freeze scenarios. After each freeze phase, the specimens were moved to a humidity chamber maintained at 23 °C with 100% relative humidity for 24 h, completing one 48-h F-T cycle. This process was repeated up to 7 times for both sets.
Following the 1st, 3rd, 5th, and 7th cycles, unconfined compressive strength tests were conducted, providing insights into the samples’ mechanical strength through repeated cycles. Volume changes were also measured after each freezing and thawing stage to evaluate the F-T cycles’ effect on soil volume. This approach facilitated the evaluation of the MgCl2 solution’s effectiveness in soil stabilization under varying temperature conditions, intending to develop more durable infrastructure solutions in cold climates.
Additionally, a subset of the samples underwent microstructural analysis using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) tests. This provided more profound insights into the microstructural changes made by the freeze-thaw cycles.

3. Test Results and Discussion

3.1. Atterberg Limits Tests

This study explored the effects of different concentrations of MgCl2 solution (4%, 9%, and 14%) on the liquid limit (LL), plastic limit (PL), and plasticity index (PI) of the soil (Figure 2). The results demonstrate a consistent decline in these parameters with an increase in MgCl2 concentration. The reduction is significant in soil mixtures treated with a 14% MgCl2 solution, showcasing decreases of 14% in the liquid limit, 9% in the plastic limit, and 19% in the plasticity index. These results align with previous research by Venkatabor Rad (1977) [55], suggesting that the decrease is likely due to a thinning of the diffuse double layer (DDL). This process is believed to be driven by the cation exchange with divalent magnesium ions and a subsequent rise in electrolyte concentration, given the complete solubility of MgCl2 in water.

3.2. Compaction Tests

The influence of different MgCl2 solution concentrations on the soil’s compaction characteristics is shown in Figure 3 and Table 3. The addition of a MgCl2 solution is observed to enhance the maximum dry density (MDD) while decreasing the optimum water content (OWC), especially at higher MgCl2 solution concentrations. These findings agree with the observations made by Randolph (1997) [56]. The increase in dry density is attributed to particle flocculation and aggregation, a consequence of rapid cation exchange within the soil–MgCl2 solution mixture. Notably, the application of a 14% MgCl2 solution increased the MDD to 17.89 kN/m3 from the initial value of 17.4 kN/m3 noted in untreated soil and reduced the OWC from 19% in untreated soil to 17.7%. These results suggest that increasing the concentration of the MgCl2 solution, and thus the rate of cation exchange process in the mixture of soil and MgCl2 solution, reduces the ability of clay surfaces to absorb water, resulting in an observed increase in dry density values.

3.3. Unconfined Compression Tests

The unconfined compression test was conducted to assess the effectiveness of a magnesium chloride (MgCl2) solution in improving the soil’s compressive strength. Figure 4 displays the stress-strain behavior of both untreated and MgCl2-treated soil samples, with curing periods of 7 and 28 days, as well as those without any curing. The results suggest that adding a MgCl2 solution generally leads to an increase in soil strength across all curing durations, and this enhancement is directly proportional to the concentration of the MgCl2 solution.
Figure 5a shows the unconfined compressive strength (UCS) enhancements as the MgCl2 solution concentration increases, highlighting the effect of curing time on treated samples with various concentrations. For instance, uncured samples showed UCS improvements of 9%, 26%, and 38% with 4%, 9%, and 14% MgCl2 solution concentrations, respectively, leading to UCS values increasing from 223.5 kPa to 244, 281, and 308 kPa.
Additionally, the data indicates a slight enhancement in UCS values associated with extended curing periods. For example, a 28-day curing of soil treated with a 14% MgCl2 solution resulted in a 5% improvement in UCS values. Additionally, Figure 5b demonstrates that an increase in the MgCl2 concentration reduces the failure strain for treated soils. Consequently, soils with higher MgCl2 levels become less deformable.

3.4. Freeze-Thaw Cycles Tests

F-T cycle tests were conducted to investigate the antifreeze and stabilizing properties of MgCl2 solution on clay to analyze its impact on the stress-strain behavior of MgCl2-treated soils. Experiments were carried out at both −10 °C and −20 °C on 28 days cured samples to evaluate the necessity for adjusting the MgCl2 solution concentrations in response to varying temperatures. These tests aimed to understand how different concentrations of MgCl2 can maintain soil integrity under mild and extremely cold conditions, providing valuable insights into their adaptability under different thermal stress levels. The samples used for these tests were subjected to a curing period of 28 days.
Moreover, to show the durability characteristics of the samples subjected to treatment, a durability index (DI) was established. This index is derived by calculating the ratio of the unconfined compressive strength (UCS) of a sample following the freeze-thaw (F-T) cycle (UCSi) to its corresponding UCS after the curing period (UCS0), as delineated in Equation (1) [57]. This metric is a critical indicator for assessing the material’s stability post-treatment under F-T conditions.
D I = U C S i U C S 0

3.4.1. Results at −10 °C

Figure 6 clarifies the impact of F-T cycles at −10 °C on the stress-strain characteristics of both untreated and treated samples. Observations indicate a significant reduction in strength for untreated samples during F-T cycles (Figure 6a). However, Figure 6c,d demonstrate that the application of 9% and 14% MgCl2 solutions results in a notable antifreeze effect, preserving the samples’ stress-strain behaviors. A lower concentration of 4% MgCl2 solution exhibits a minor yet observable impact, slightly reducing the extent of strength loss and displaying a reduced decrement in strength after 7 cycles, compared to untreated samples (Figure 6b).
The change in the unconfined compressive strength (UCS) values with the addition of a MgCl2 solution suggests that, for a given F-T cycle, the stabilizer enhances the soil’s strength (Figure 7a). For example, after the third freeze-thaw cycle, the untreated soil exhibits a strength of 145.84 kPa, while soil samples treated with 4%, 9%, and 14% MgCl2 solutions show increased strengths of 220.35 kPa, 289.62 kPa, and 331.24 kPa, respectively. The effect of a 4% MgCl2 solution on enhancing soil strength diminishes with the progression of cycles. Nevertheless, the strength improvements provided by 9% and 14% solutions endure even after the cycles progress.
The fluctuation in the durability index (DI), represented in Figure 7b, shows an apparent decrease in DI values for both untreated and 4% treated samples, with untreated samples exhibiting a notably sharp decline during the first F-T cycle. This highlights the critical role of the first F-T cycle in affecting the durability of soil samples. Notably, after 7 F-T cycles, the DI decreases to 0.41 for untreated samples and to 0.59 for samples treated with a 4% MgCl2 solution, underscoring the severe impact of F-T cycles on soil durability. In contrast, DI values for samples treated with 9% and 14% MgCl2 solutions exhibit stability, remaining consistent before and after 7 F-T cycles.

3.4.2. Results at −20 °C

To study the efficacy of magnesium chloride (MgCl2) solutions as antifreeze agents in soil stabilization under extreme cold conditions, F-T tests were repeated at −20 °C. The stress-strain properties of both the untreated and treated soil samples across 7 F-T cycles are illustrated in Figure 8. The results indicate that the untreated samples and those treated with a 4% MgCl2 solution exhibit significant strength reductions across F-T cycles (Figure 8a,b). However, the samples treated with a 9% MgCl2 solution show a less severe decline in strength at −20 °C (Figure 8c), indicating a concentration-dependent response to freezing conditions. It is evident that the samples treated with a 14% MgCl2 solution maintain consistent strength across the F-T cycles (Figure 8d).
At −20 °C, similar to the findings at −10 °C, the treated samples consistently demonstrate higher unconfined compressive strength (UCS) compared to the untreated samples across all F-T cycles, as illustrated in (Figure 9a). For example, after the third cycle, the untreated soil exhibited a strength of 121.42 kPa, whereas the soil treated with 4%, 9%, and 14% MgCl2 solutions demonstrated strengths of 202.52 kPa, 238.03 kPa, and 318.38 kPa, respectively. An essential distinction at −20 °C was observed in the performance of the samples treated with a 9% MgCl2 solution, which, unlike their behavior at −10 °C, exhibited a reduction in strength with an increasing number of cycles. However, this decline was less significant than the 4% treated and untreated samples. The samples treated with a 14% MgCl2 solution maintained a consistent strength throughout the cycles.
Regarding DI values, in contrast to the experiments at −10 °C, where the durability index (DI) values for samples treated with a 9% MgCl2 solution remained stable across seven freeze-thaw (F-T) cycles, a different trend was observed at −20 °C (Figure 9b). Both untreated and 4% MgCl2 solution-treated samples, as well as those treated with a 9% solution, exhibited a decline in DI. Specifically, after 7 F-T cycles, the DI values decreased to 0.31 for untreated samples and 0.55 and 0.70 for samples treated with 4% and 9% MgCl2 solutions, respectively. In contrast, the DI values for the samples treated with a 14% MgCl2 solution showed stability, as was the case for the tests at −10 °C, maintaining consistent levels before and after 7 F-T cycles. This difference in performance underscores the pivotal influence of MgCl2 concentration on enhancing the stability of soil samples under severe thermal conditions. It highlights the importance of carefully tailoring antifreeze treatments to meet specific environmental demands, demonstrating the complex interplay between additive concentration and soil durability.

3.5. Effect of Freeze-Thaw Cycles on Soil Volume Alterations

This study also examines the volumetric variations in materials subjected to F-T cycles, highlighting the mitigating effects of MgCl2. It has been documented that the volume of the samples expands during freezing due to water within the pores turning into ice, which is about 9% larger than its liquid form, causing soil particle displacement. Upon thawing, the volumes do not fully revert, leading to increased pore sizes and a reduced failure strength. This irreversible expansion and the consequent strength reduction are attributed to the structural alterations within the sample matrix, as outlined by Wang et al. [58] and further supported by Lu et al. [21] and Jamshidi et al. [59].
The observations from this study not only verify this pattern through experimental testing but also effectively demonstrate the critical role of MgCl2 solution concentrations in controlling this phenomenon. At −10 °C, untreated samples and those treated with 4% MgCl2 solution exhibited volume expansion proportional to the number of F-T cycles. Notably, the expansion was less pronounced in the samples treated with 4% MgCl2, suggesting a mitigating effect of the solution. Samples with 9% and 14% MgCl2 concentrations showed no volumetric changes, indicating MgCl2 solution effectiveness in stabilizing volume against F-T-induced expansion (Figure 10a).
At −20 °C, a similar pattern emerged; this trend extends to the samples treated with 9% MgCl2, which expanded less than those treated with 4% MgCl2, underscoring the concentration-dependent efficacy of MgCl2 in reducing expansion. Samples with a 14% MgCl2 maintained their volume, supporting the stabilizing role of the MgCl2 solution (Figure 10b). These results align with observed trends in F-T cycles tests, wherein higher MgCl2 concentrations effectively prohibited strength loss. These observations collectively affirm the potential of a MgCl2 solution, at specific concentrations, to function as an antifreeze stabilizer, thereby minimizing the detrimental impacts of F-T cycles on soil properties.
Furthermore, it should be emphasized that because the samples were wrapped in plastic films, it was observed that they did not experience significant weight loss or moisture change during measurements.

3.6. Microstructural Analyses

3.6.1. XRD & FTIR Analysis

X-ray diffraction (XRD) analysis serves as a crucial method for detailing alterations in material properties, interactions among interlayers, and the impact of added particles, providing an extensive set of data for interpretation regarding soil minerals. Figure 11 displays the XRD outcomes for samples that are both untreated and those treated with a MgCl2 14% solution. Upon comparison, there is no noticeable difference in the diffraction patterns between the untreated and treated samples. Specifically, no new peaks were observed in the diffraction pattern of the treated soil, and the peak positions, indicated by the 2θ values, remained unchanged for both sets of samples. This constancy suggests that the interlayer spacing remained unaltered, no new chemical bonds were formed, and the MgCl2 solution did not replace the interlayer cations within the clay structure. The primary mechanism for the observed phenomena is likely attributed to electrostatic exchanges between the clay particles and the charges of the MgCl2 solution, which contributes to an enhancement in the soil strength.
Fourier-transform infrared (FTIR) spectroscopy was employed to detect functional groups within untreated and treated soil minerals. Samples’ FTIR spectrum shows different peaks that are indicative of the many functional groups and bonding interactions that are typical of clay minerals (Figure 12). The spectra included bands at 688.16 cm−1 and 776.98 cm−1, which are likely indicative of metal-oxygen bonds, suggesting the presence of inorganic components or impurities within the clay matrix. Additionally, peaks at 910.10 cm−1 and 997.46 cm−1 were observed, indicating Si-O stretching vibrations and supporting the presence of silicate minerals such as quartz and potentially muscovite in the clay. The peak at 1634.69 cm−1 is due to bending vibrations of water molecules (H-O-H bend), which indicate moisture content in the clay. Peaks at 3620.48 cm−1 and 3694.75 cm−1 were recognized for the presence of O-H stretching vibrations from hydroxyl groups. The first peak is typical of phyllosilicates, while the second peak is specific to kaolinite, implying a rich composition that includes kaolinite and possibly other phyllosilicate minerals. Overall, comparisons of the FTIR spectra of untreated and 14% MgCl2 solution-treated soils showed no significant differences, indicating that MgCl2 does not significantly affect the soil’s functional groups. The only difference observed was the emergence of a peak at 3371.95 cm−1, which suggests enhanced O-H stretching vibrations, possibly due to new or altered hydroxyl groups or changes in hydrogen bonding influenced by interactions with Mg2+ ions. This comparison also suggests that the treatment mechanism is based on physical (electrostatic) interactions.

3.6.2. SEM Analysis

Scanning electron microscopy (SEM) was utilized to examine untreated and 14% MgCl2 treated samples for microstructural modifications in the soil’s composition. Figure 13 displays SEM images of untreated and treated samples after 28 days of curing. Applying a 14% solution of MgCl2 resulted in the reorganization of the particles, which led to a more cohesive structure and an improved structural integrity compared to the untreated sample. This aggregation transformed the geotechnical properties by reducing interactions between surface areas and water, with changes proportionate to the concentration of MgCl2 solution. This observation can be attributed to the increased salt concentration after adding MgCl2 solution, which facilitated the rapid flocculation and subsequent substantial particle size increase. In this regard, the sample treated with a 14% MgCl2 solution exhibited the highest strengths, indicating improved structural integrity and larger particle size.

4. Conclusions

Irrespective of the level of stabilization, stabilized soil embankments in cold climates are inherently vulnerable to freeze-thaw cycles, which ultimately cause strength loss and volume change. To address this, our study explored the use of a MgCl2 solution as an antifreeze and stabilizing agent for fine-grained soils. The experimental investigation assessed the effects of MgCl2 on the plasticity, strength, and durability properties during freeze-thaw cycles.
At a 14% concentration, MgCl2 not only enhances soil compaction and dry density but also reduces the optimum water content while increasing the unconfined compressive strength by up to 38% without curing. However, it also reduces soil deformability. Additionally, the results show that 28 days of curing increases the UCS values by 5%.
F-T cycle tests were conducted on 28-day cured clay samples at −10 °C and −20 °C. At −10 °C, MgCl2 solutions at 9% and 14% concentrations maintained their strength and durability indices and volume through seven cycles, outperforming both the 4% solution and the untreated samples. At −20 °C, samples with 14% MgCl2 maintained their strength and volume, whereas those with 9% showed less volume expansion and strength reduction compared to the lower concentrations and untreated samples. These results underscore the importance of a proper MgCl2 concentration in preserving soil stability and durability under cold conditions and thermal stress. This ability to preserve soil integrity and volume under severe thermal stress is critical for extending the construction and maintenance season in cold regions, thereby offering additional potential cost and time savings.
Further, the microstructural analyses through SEM, XRD, and FTIR showed that while there were no chemical changes in the soil, physical modifications occurred that improved soil performance. These changes were associated with increased concentrations of MgCl2, which enhanced the soil’s strength and durability.
Finally, this study identifies MgCl2 as a compelling antifreeze and stabilizing agent, significantly enhancing the durability and reliability of soil embankments in cold climates. We hope this research will open up new avenues for investigating the use of MgCl2 in geotechnical engineering, particularly in regions with severe winters. We recommend that future work should include site-specific studies to optimize the MgCl2 concentrations based on local weather conditions, soil types, and construction materials. Additionally, conducting large-scale field experiments will further our understanding of its practical applications for stabilizing soils against freeze-thaw challenges in cold regions.

Author Contributions

Conceptualization, A.Y.R.; Methodology, A.Y.R. and B.T.; Investigation, A.Y.R.; Writing—original draft, A.Y.R.; Writing—review & editing, B.T.; Visualization, A.Y.R.; Supervision, B.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Research Fund of Istanbul Technical University, under project number MDK-2021-43154, and forms part of the Ph.D. thesis of Amin Yeganeh Rikhtehgar.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in the current study are available on request from the authors.

Acknowledgments

The authors extend their gratitude to the authorities of Istanbul Technical University for their support in this study.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 14 04140 g001
Figure 1. X-ray diffraction (XRD) pattern.
Figure 1. X-ray diffraction (XRD) pattern.
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Figure 2. Effect of MgCl2 solution on the Atterberg limits of used soil.
Figure 2. Effect of MgCl2 solution on the Atterberg limits of used soil.
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Figure 3. The impact of MgCl2 solution on the dry density and water content of soil.
Figure 3. The impact of MgCl2 solution on the dry density and water content of soil.
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Figure 4. Stress-Strain diagrams for untreated and treated samples over various curing periods: (a) uncured, (b) 7 days cured, and (c) 28 days cured.
Figure 4. Stress-Strain diagrams for untreated and treated samples over various curing periods: (a) uncured, (b) 7 days cured, and (c) 28 days cured.
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Figure 5. Influence of MgCl2 solution on: (a) Unconfined compressive strength (UCS) values and (b) strain at failure.
Figure 5. Influence of MgCl2 solution on: (a) Unconfined compressive strength (UCS) values and (b) strain at failure.
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Figure 6. Stress-strain relations for treated and untreated samples at −10 °C with different MgCl2 solution: (a) Untreated, (b) treated with 4% MgCl2, (c) treated with 9% MgCl2, and (d) treated with 14% MgCl2.
Figure 6. Stress-strain relations for treated and untreated samples at −10 °C with different MgCl2 solution: (a) Untreated, (b) treated with 4% MgCl2, (c) treated with 9% MgCl2, and (d) treated with 14% MgCl2.
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Figure 7. Impact of MgCl2 solution at −10 °C on: (a) Unconfined compressive strength (UCS) values and (b) durability index values.
Figure 7. Impact of MgCl2 solution at −10 °C on: (a) Unconfined compressive strength (UCS) values and (b) durability index values.
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Figure 8. Stress-strain relations for treated and untreated samples at −20 °C with different MgCl2 solution: (a) Untreated, (b) treated with 4% MgCl2, (c) treated with 9% MgCl2, and (d) 14% MgCl2.
Figure 8. Stress-strain relations for treated and untreated samples at −20 °C with different MgCl2 solution: (a) Untreated, (b) treated with 4% MgCl2, (c) treated with 9% MgCl2, and (d) 14% MgCl2.
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Figure 9. Impact of MgCl2 Solution at −20 °C on: (a) Unconfined compressive strength (UCS) values and (b) durability index values.
Figure 9. Impact of MgCl2 Solution at −20 °C on: (a) Unconfined compressive strength (UCS) values and (b) durability index values.
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Figure 10. F-T cycle effects on samples’ volume alteration at: (a) −10 °C and (b) −20 °C.
Figure 10. F-T cycle effects on samples’ volume alteration at: (a) −10 °C and (b) −20 °C.
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Figure 11. XRD profiles or untreated and 14% MgCl2-treated soil.
Figure 11. XRD profiles or untreated and 14% MgCl2-treated soil.
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Figure 12. FTIR spectrums for untreated and 14% MgCl2-treated soil.
Figure 12. FTIR spectrums for untreated and 14% MgCl2-treated soil.
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Figure 13. SEM images: (a) 28 days cured untreated sample and (b) 28 days cured MgCl2 14% solution treated sample.
Figure 13. SEM images: (a) 28 days cured untreated sample and (b) 28 days cured MgCl2 14% solution treated sample.
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Table 1. Physical properties of used soil.
Table 1. Physical properties of used soil.
Physical PropertiesValues
Silt (%)61
Clay (%)39
Specific gravity2.72
Maximum dry density (kN/m3)17.4
Optimum water content (%)19
Liquid limit (%)37.2
Plastic limit (%)19.7
Plasticity index (%)17.5
pH8.1
Table 2. General properties of used MgCl2.
Table 2. General properties of used MgCl2.
ConstituentsSpecification
Magnesium Chloride (MgCl2)Min 46.5%
Calcium Chloride (CaCl2)Max 2.2%
Sodium Chloride (NaCl)Max 0.9%
Potassium Chloride (KCl)Max 0.6%
Water of CrystallizationBalance to 100%
Sulfates (SO4)Max 0.025%
Iron (Fe)Max 5 ppm
Mercury (Hg)Max 0.2 ppm
Lead (Pb)Max 0.1 ppm
Arsenic (As)Max 0.1 ppm
Cadmium (Cd)Max 0.1 ppm
pH of aqueous Solution8.0–9.5
Table 3. OWC and MDD of soil with different MgCl2 solution concentrations.
Table 3. OWC and MDD of soil with different MgCl2 solution concentrations.
MgCl2 Solution Concentration (%)Optimum Water Content (%)Maximum Dry Density (kN/m3)
0%1917.4
4%18.917.52
9%18.317.68
14%17.7117.89
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Yeganeh Rikhtehgar, A.; Teymür, B. Effect of Magnesium Chloride Solution as an Antifreeze Agent in Clay Stabilization during Freeze-Thaw Cycles. Appl. Sci. 2024, 14, 4140. https://doi.org/10.3390/app14104140

AMA Style

Yeganeh Rikhtehgar A, Teymür B. Effect of Magnesium Chloride Solution as an Antifreeze Agent in Clay Stabilization during Freeze-Thaw Cycles. Applied Sciences. 2024; 14(10):4140. https://doi.org/10.3390/app14104140

Chicago/Turabian Style

Yeganeh Rikhtehgar, Amin, and Berrak Teymür. 2024. "Effect of Magnesium Chloride Solution as an Antifreeze Agent in Clay Stabilization during Freeze-Thaw Cycles" Applied Sciences 14, no. 10: 4140. https://doi.org/10.3390/app14104140

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