An Investigation of the Effectiveness of Super White Cement in Improving the Engineering Properties of Organic Soils by Laboratory Tests

Abstract

In this study, the efficacy of super white cement (SWC) to improve organic soils was researched. For stabilization, 10%, 15%, and 20% proportions of SWC were added to organic soil. After improvement with SWC, Atterberg limit testing, standard Proctor tests, triaxial compression tests, and swelling and compressibility tests were performed on the organic soil. Proctor tests showed that stabilization of organic soil with SWC increased maximum dry density (MDD) and optimum moisture content (OMC) values. After stabilization, the unconfined compressional strength values of the soil increased. This increase continued until the 28th day and had a reducing trend after improvement with SWC, linked to time. In addition to the reaction between SWC and OS, the time-dependent behavior of OS also contributed to this behavior. With the increase in SWC proportions, the cohesion intercept and internal friction angle values rapidly increased until the 56th day. This increase began to reduce after the 56th day. After stabilization, the swelling percentage and compressibility values for the soil reduced. The addition of SWC within organic soil appeared to improve the engineering properties of the soil.

1. Introduction

In geotechnical engineering, highly organic soil is referred to as difficult soil because it is composed of decomposing materials like shells and plants that are deficient in silica, alumina, iron, and calcium [1]. Urbanization is increasing around the world, leading to new construction on greenfield sites, including alluvial floodplains and areas with challenging soils, such as highly compressible organic clays. To enable building in these difficult ground conditions, ground improvement techniques are essential [2]. Organic soils are known as problematic soils in geotechnical engineering, and bearing capacity, strength, stiffness, settlement, and slope problems are experienced with organic soils [3]. Organic soils cover nearly 8% of the Earth’s surface [4,5]. Due to the high-compressibility features in organic soils, high rates of secondary consolidation settlement occur. Soils with less than 75% dry matter are called organic soils, while soils with dry matter above 75% are called peat soils. Organic soils have low strength values, along with their high compressibility and high rates of secondary consolidation.

Organic soils have a fibrous structure. As organic soils have a fibrous structure, they have high void ratios and a high cation exchange capacity. This situation causes an increase in the adhesion of water molecules within soil. Additionally, soils with a fibrous structure have high permeability and compression features [6]. Water is generally held within fibers in soil. In addition, water may be held in voids in soil and in the cells of plant remains [7,8]. The water content values of organic soils may reach up to 500%. This proportion may reach 700% in peat soils. Water content values are generally above 70% in silt soils and may reach above 100% in soft soils [7,8].

Commonly used binders include cement, lime, fly ash, rice husk, or combinations of these materials. It is important to note that compared to inorganic soils, organic soils typically provide more challenges for chemical stabilization. In addition, chemical stabilization stands out as a cost-effective alternative [9,10,11,12,13,14,15,16,17,18,19,20,21,22]. This process involves blending a binder into soft soils to enhance their strength and stiffness through chemical reactions. The objective is to cement the soil solids, thereby increasing overall strength and stiffness. Binders are typically added as dry solids, a practical approach given the challenges and time constraints associated with reducing water content in high-water-content soils to their optimum levels. Consequently, the addition of dry solids and cementitious materials is preferred, reducing water content while binding soil particles, resulting in increased strength and stiffness.

Several researchers have performed experimental studies about stabilization of organic soils. Kalantari [23] applied ordinary Portland cement (OPC) as a binder and blast furnace slag (BFS) as an additive to tropical fibrous peat soil. The strength properties of the stabilized soil were evaluated in a laboratory using unconfined compressive strength (UCS) and California bearing ratio (CBR) tests. Dehghanbani et al. [24] investigated the stabilization of peat soil using cement and various natural fillers. The strength properties of these soils, which were stabilized by mixing natural fillers with cement in various proportions, were evaluated using UCS tests. Various peat soil stabilization methods, such as mechanical, chemical, electrical, and biological techniques, are currently used to improve their engineering properties and make peatland usable [25,26,27,28]. Hashim and Islam [29] improved peat soils obtained from the west coast of the Malaysian peninsula with Portland cement, bentonite, and sand and observed the geotechnical properties of soil improved after stabilization. Deboucha et al. [30] stabilized peat soils with cement, bentonite, and sand and observed an increase in the unconfined compressive strength values. Kalantari and Huat [31] observed that California bearing ratio (CBR) and unconfined compressive strength (UCS) increased after stabilizing peat soils with Portland cement. Tastan et al. [32] performed an improvement study on organic soil using fly ash. The study observed that fly ash increased the strength and elasticity modulus; however, the type of fly ash affected the improvement. Kalantari and Prasad [33] studied the effect of different curing types on peat soil samples. They discovered that applying moist curing with a surcharge load led to the greatest increase in UCS. Ahmad et al. [34] suggested utilizing ordinary Portland cement (OPC) and filler materials to fill the voids in tropical peat soil with cement-based products. They also highlighted the importance of determining the stabilizer dosage for treating organic soil by taking into account the indexed properties and the presence of humus.

In more recent times, cements with different chemical contents have been produced. One of these is super white cement (SWC). Çimsa super white cement (CEM I 52.5R) is a cement with high early and final strength, high whiteness, and a low alkali content that is fast to produce. It is widely used in precast manufacturing, glass fiber-reinforced concrete manufacturing, terrazo tile manufacturing, stair step manufacturing, aerated concrete manufacturing, pumice manufacturing, and exposed concrete manufacturing.

This experimental study targeted improvement of organic soil (OS) from the Söğüt region of Bilecik province, with a low bearing capacity and high amount of settlement problems, using super white cement (SWC). It is quite difficult to improve the engineering properties of organic soils with cementitious materials. SWC is a newly generated cement. This study focuses on improving the engineering properties of organic soils with SWC. After improvement, the efficacy of the stabilization of OS with SWC was researched via unconfined compression, triaxial strength, and swelling and compressibility tests. There are no studies in the literature on the improvement of the engineering properties of organic soils using SWC. In this respect, our study is a pioneering investigation.

2. Materials and Methods

2.1. Soil

In this research study, organic soil (OS) samples were procured by excavating to depths ranging from 3.0 to 6.0 m below the soil surface in Söğüt county, Bilecik province. The obtained OS samples underwent a 24 h drying process at 80 ± 5 °C, followed by placement in a desiccator until reaching room temperature. Subsequently, the soil samples underwent analysis for particle size distribution, organic matter content, and specific gravity.

Particle size distribution for the OS was determined in accordance with ASTM D6913-17 [35] and ASTM D7928-21 [36]. Sieve analysis tests were conducted on soil samples retained after applying the #200 sieve, while hydrometry tests were performed on soil samples passing the #200 sieve size. The granulometry curve of the soil, obtained as a result of sieve analysis and hydrometer testing, is given in Figure 1. The resulting granulometry curve reveals that over 68% of the soil remained above the #200 sieve, indicating a predominant sand-sized composition.

Tests for organic matter content followed ASTM D2974-20 [37] standards, utilizing heat-resistant porcelain containers placed in an oven at 440 °C. Soil sample weights were recorded at two-hour intervals until a constant weight was achieved, concluding the 24 h test duration. Calculations revealed an organic matter content of 52%, classifying the sample as organic soil per ASTM D2974-20 [37] criteria, given the content was below 75%. The specific gravity of the OS was determined using ASTM D0854-23 [38]. The test was conducted 6 times, and the mean of the results yielded a specific gravity (Gs) value of 2.16 for the OS.

2.2. Super White Cement (SWC) and Pozzolanic Cement (PC)

In this experimental study, super white cement (SWC; CEM I 52.5R type) was added as stabilizer within cement. Some physical and chemical features of SWC are given in

Table 1. Physical and chemical properties of SWC.

Chemical properties	SiO2	21.6
	Al2O3	4.05
	Fe2O3	0.26
	CaO	65.7
	MgO	1.30
	SO3	3.50
	Na2O	0.30
	K2O	0.35
	Ignition loss	3.50
Physical properties	Specific gravity	3.06
	Fineness (cm2/g)	4600
Neat UCS	2-day strength (MPa)	37.0
	7-day strength (MPa)	50.0
	28-day strength (MPa)	60.0
	90-day strength (MPa)	66.0

. When the neat unconfined compressive strength (UCS) values are examined, it appears SWC gains strength early. SWC has early strength due to its chemical structure. Table 1 shows that Neat SWC has early strength in unconfined compression tests. The stabilized specimens behaved like Neat SWC and had early strength.

2.3. Specimen Preparation Procedure

Before beginning the experiments, first, the SWC and OS samples were dried in an oven at 105 °C for 24 h. After drying, the samples were formed by adding the desired proportions of the materials (OS and SWC) and mixing homogeneously using a mixer with low rotational speed. SWC was added to the mix at rates of 10%, 15%, and 20% per weight of OS. Previously in experimental studies performed by researchers, the cement proportions used varied from 6% to 20% [39,40,41]. It is not economically viable for the cement proportion to exceed 20%. If this proportion is less than 5%, the cement is not effective. When cement is added at low proportions, effective improvement cannot be provided, while at high proportions, improvements are not economic.

2.4. Determination of Atterberg Limits

The liquid and plastic limits of both the OS and the specimens treated with SWC were assessed following the guidelines outlined in the ASTM D4318-17 [42] standard. The liquid limit (LL), plastic limit (PL), and plasticity index (PI) values for OS without additives and with SWC are given in Figure 2.

2.5. Determination of Compaction Characteristics

In the pursuit of establishing the maximum dry density and optimum moisture content for mixtures of SWC and OS, standard Proctor tests were conducted. These tests adhered to the guidelines outlined in the ASTM D0698-12 [43] standard. Initially, dry SWC and OS were uniformly mixed using a mechanical mixer. Various water proportions were subsequently introduced to the mixtures, and the compaction process ensued. Following each compaction cycle, the soil’s water content was measured, dry unit weight values were calculated, and the Proctor curve was plotted. After completing the experiments, standard Proctor curves were drawn for samples of OS without additives and with SWC, and these curves are shown in Figure 3.

2.6. Preparation of the Amended Soil Samples for Unconfined Compressive Strength (UCS) and Triaxial (TA) Tests

To systematically prepare samples for unconfined compressive strength (UCS) and triaxial (TA) tests, a custom stainless-steel mold was fabricated. The mold, designed with an internal diameter of 50 mm and a height of 100.5 mm, adhered to the recommended height-to-diameter ratio of 2.01. To facilitate sample removal, the mold was greased. Samples, prepared at optimum moisture content, were arranged in three equal layers, each 33.5 mm in height, within the mold. Each layer was compressed to a diameter of 49.2 mm and a height of 105.5 mm with a steel hammer to achieve maximum density at Proctor compression. There are two notches on the handle of the steel hammer. The distance between each notch is 33.5 mm. During compression, it is checked, by means of notches, whether sufficient compression is achieved. The mold consists of one piece. The samples placed in the mold were removed from the mold with an extraction jack.

Half of the OS samples stabilized with SWC were air-dried at 25 °C until the day of the UCS and TA tests, while the other half were placed in a curing tank at 25 °C in a wet-cured environment. These distinct curing conditions mirrored situations where material is exposed to the atmosphere (road fill) or isolated from it (under building foundations). Furthermore, to assess stabilization efficacy, UCS and TA tests were conducted on clay soil before stabilization to determine soil strength and shear strength values. UCS tests were conducted in accordance with the ASTM D2166M-16 [44], and ASTM D2850-23 [45] standards on the 7th, 28th, 56th, and 90th days, for both cure conditions. The test results are given in Figure 4, Figure 5 and Figure 6.

2.7. Swell Potential

In order to assess the swelling potential of OS with and without SWC, the samples, prepared through the standard Proctor compression test, were positioned within consolidation rings and subjected to two contrast curing conditions until the testing day. In the lab, half of the samples were air-dried at 25 °C, and the other half were wet-cured using plastic wrap at 25 °C. Tests to determine the time-linked swelling percentage were conducted in accordance with ASTM D4546-21 [46] on days 0, 7th, 28th, and 56th. The variation in the swelling percentages with the curing period is shown in Figure 7.

2.8. Compressibility

The samples required for the compressibility tests of OS without and with SWC additives were prepared via the same procedure as for the swelling test. The compressibility tests were conducted on days 0, 7th, 28th, and 56th, corresponding to two different curing conditions. These compressibility tests adhered to the ASTM D0698-12R21 [43] standard, being conducted at a temperature of 25 °C. The variation in the volumetric strain percentages with the curing period is given in Figure 8.

3. Results and Discussion

3.1. Atterberg Limits

Looking at Figure 2, for organic soil (OS), the LL value was 37.9%, the PL value was 24.2%, and the PI value was 13.7%. For the 10%, 15%, and 20% cement proportions for organic soil stabilized with SWC, the LL values were 43.10%, 41.84%, and 40.42%, and the PL values were 27.28%, 26.26%, and 25.28%, respectively. For OS stabilized with SWC, the LL, PL, and PI values increased. For soil stabilized with SWC at 10% cement proportion, the LL, PL, and PI values increased, while a reduction occurred after 10%.

3.2. Compaction Characteristics

Proctor curves were drawn for OS stabilized with SWC. Looking at Figure 3, the optimum moisture content (OMC) value for OS was 22.5%, and the maximum dry density (MDD) value was 12.79 kN/m³. For OS stabilized with SWC using cement contents of 10%, 15%, and 20%, the OMC values were 24.95%, 26.20%, and 27.52%, while the MDD values were 12.86 kN/m³, 12.92 kN/m³, and 13.04 kN/m³, respectively. For OS stabilized with SWC, with the increase in cement content, the Proctor curves were observed to move up toward the right. As the cement ratio increases, the amount of water required for the reaction that will occur after mixture will also increase. Therefore, as the cement ratio increases, the OMC values also increased. With the increase in the cement ratio, the MDD values increased as well. This is due to the cement’s outstanding flocculation characteristics. Flocculation improves in mixtures with SWC addition, and when the flocs are packed, they readily reorient to their new positions and become more compact.

3.3. Unconfined Compressive Strength

The UCS values for OS subjected to a wet-cured environment were 398 kPa, 470 kPa, 505 kPa, and 300 kPa on the 7th, 28th, 56th, and 90th days, respectively. Conversely, for OS left in an air-dried environment, the UCS values were 543 kPa, 638 kPa, 653 kPa, and 527 kPa on the corresponding days. The UCS values for both curing conditions increased until the 56th day and subsequently showed a decreasing trend after the 56th day. It was found that the strength values of OS samples kept in an air-drying environment were 60% higher than those kept in a wet curing environment.

For soils stabilized with SWC and subjected to a wet-cured environment, the UCS values ranged from 1180 to 1365 kPa on the 7th day, 1368 to 1680 kPa on the 28th day, 1295 to 1435 kPa on the 56th day, and 839 to 995 kPa on the 90th day. In the air-dried environment, the UCS values were 1575 to 1822 kPa on the 7th day, 1836 to 2318 kPa on the 28th day, 1715 to 2287 kPa on the 56th day, and 1398 to 1993 kPa on the 90th day. The UCS values for SWC-stabilized soils rapidly increased until the 28th day, followed by a declining trend after the 28th day. Based on this behavior, in addition to the interaction between SWC and OS, the time-dependent behavior of OS also has an effect. Between the 7th and 28th days, the samples in the air-dried environment exhibited a 23% increase in strength, while those in the wet-cured environment demonstrated a 22% increase. Between the 28th and 90th days, the samples in the air-dried environment exhibited a 21% decrease in strength, while those in the wet-cured environment demonstrated a 41% decrease. Soils stabilized with SWC gained rapid strength. The UCS values of the SWC-stabilized soils increased with increasing cement content. In the stabilization experiment performed on OS samples with SWC, the UCS values of the soils left in the air-dried environment were higher than those left in the wet-cured environment. The strength values of the soil stabilized with SWC and left in the air-dried environment were 51% higher than those of the soil left in the wet-cured environment. In addition to the reaction between OS and SWC, the time-dependent behavior of OS also affects in the time-dependent change in strength.

Figure 9 illustrates the typical failure forms in UCS tests for OS without additives and stabilized with SWC. During OS failure, a shortening of the sample length was observed, while soil stabilized with SWC exhibited failure with a 45° fracture angle (Figure 9). The variations in water content over time for OS without additives and with SWC are given in Figure 10. As shown in Figure 10a, the water contents in both OS without additive and with SWC reduced until day 28 when left in the wet-cured environment and then appeared to increase after day 28. The reason for this variation in water content, linked to time, is the water absorption over time by the soil particles, followed by the release of absorbed water after a certain duration. Additionally, it is considered that the water content in OS with added SWC is affected by the hydration reaction occurring after stabilization.

For the OS samples without additives and those with SWC that were left in the air-dried environment, the water content reduced up to day 28, then increased from day 28 to day 56, and then reduced again after day 56 (Figure 10b). Water was absorbed within the cavities between soil particles in the samples left in the air-dried environment and released again over time. Additionally, the variation in water content is affected by the humidity of the environment due to the open-air conditions of the soil samples. The water content of the samples left in the air-dried environment was lower than the water content of the samples left in the wet-cured environment. The decrease in moisture content under air-dried conditions is more significant compared to the wet-cured condition and can be attributed to the depletion of water during the chemical reaction, as well as the evaporation of water in the open air.

3.4. Triaxial Tests

For the OS samples left in the wet-cured environment, the cohesion intercept values were 119.86 kPa, 122.68 kPa, 136.58 kPa, and 112.67 kPa, and the internal friction angle values were 42.22°, 43.16°, 47.93°, and 41.98°, respectively, on days 7, 28, 56, and 90. Similarly, for the OS left in the air-dried environment, the cohesion intercept values were 112.65 kPa, 116.68 kPa, 127.43 kPa, and 105.67 kPa, and the internal friction angle values were 41.98°, 42.18°, 43.82°, and 41.65°, respectively, on days 7, 28, 56, and 90. For the OS left in both the wet-cured and air-dried environments, the cohesion intercept and internal friction angle values increased until day 56 and then tended to reduce after day 56. For OS left in the air-dried environment, the cohesion intercept and internal friction angle values were higher than the values for the OS left in the wet-cured environment.

For the OS stabilized with SWC and left in the wet-cured environment, the cohesion intercept values were 232.25 kPa to 387.39 kPa at the end of 90 days. The internal friction angles varied from 49.32° to 53.22°. Similarly, for the OS stabilized with SWC and left in the air-dried environment, the cohesion intercept values varied from 376.32 kPa to 521.28 kPa, and the internal friction angle values varied from 50.29° to 55.67° at the end of the 90 days. OS stabilized with SWC in both the wet-cured and air-dried environments had increases in cohesion intercept and internal friction angle values until day 28, and then a reducing tendency after 28 days. The OS stabilized with SWC and left in the air-dried environment had 31% higher cohesion intercept values than the samples left in the wet-cured environment. Similarly, OS left in the air-dried environment had internal friction angles values that were, on average, 4% higher than the internal friction angle values for OS left in the wet-cured environment. With the increase in cement proportion in OS stabilized with SWC, the internal friction and cohesion intercept values increased.

3.5. Swelling

The swelling values for OS left in the wet-cured environment were 9.68%, 5.98%, 4.91%, and 4.82% on days 0, 7, 28, and 56. The swelling values for OS left in the air-dried environment were 9.79%, 6.18%, 5.21%, and 5.04% on days 0, 7, 28, and 56. For OS left in both wet-cured and air-dried environments, the swelling values rapidly reduced until day 7, and then the reduction in swelling values slowed after day 7. The swelling values for OS left in the wet- cured environment were 4% higher than the swelling values for OS left in the air-dried environment.

For samples stabilized with SWC and left in the wet-cured environment, the swelling values were 9.79% to 9.62% on day 0, 2.95% to 1.51% on day 7, 2.13% to 1.22% on day 28, and 1.63% to 1.01% on day 56. For samples stabilized with SWC and left in the air-dried environment, the swelling values were 9.55% to 8.04% on day 0, 1.52% to 1.31% on day 7, 1.13% to 0.82% on day 28, and 0.80% to 0.53% on day 56. Linked to time, the swelling values for samples stabilized with SWC decreased rapidly up to day 7, and then this reduction slowed after day 7. From day 0 to day 56, the swelling values reduced by 93% for samples in the air-dried environment, with an 86% reduction for swelling values of samples left in the wet-cured environment.

The increase in cement content from 10% to 20% for OS stabilized with SWC caused a 39% reduction in compressibility (volumetric strain) values. The swelling values for soils stabilized with SWC and subjected to the wet-cured environment exceeded the swelling values for soils subjected to the air-dried environment. The swelling values of the OS stabilized with SWC and subjected to the air-dried environment were 52% higher on average than those in the wet-cured environment.

3.6. Compressibility Tests

The compressibility values for OS left in the wet-cured environment were 17.45%, 18.6%, 19.1%, and 19.2% on days 0, 7, 28, and 56, respectively. The compressibility for OS left in the air-dried environment was 8.53%, 9.63%, 9.82%, and 9.62% on days 0, 7, 28, and 56, respectively. The compressibility values for OS left in both the wet-cured and air-dried environments increased until day 7, and then this increase slowed after day 7. The compressibility values for OS left in the wet-cured environment were 49% higher than compressibility values of the samples left in the air-dried environment.

For samples stabilized with SWC and left in the wet-cured environment, the compressibility varied from 0.32% to 0.18% on day 0, from 3.51% to 2.81% on day 7, from 4.75% to 3.15% on day 28, and from 4.85% to 3.36% on day 56. For the samples stabilized with SWC and left in the air-dried environment, the compressibility varied from 0.31% to 0.16% on day 0, 2.05% to 1.45% on day 7, 3.15% to 2.04% on day 28, and 3.25% to 2.15% on day 56. The compressibility values for samples stabilized with SWC increased until day 7, and then this increase slowed after day 7, with this effect being linked to time.

The increase in cement proportions from 10% to 20% for OS stabilized with SWC reduced the compressibility values by 34%. For SWC stabilization, the compressibility values of the samples left in the air-dried environment were, on average, 30% higher than the compressibility values for the samples left in the wet-cured environment.

3.7. Microstructural Analysis

The results of our scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analyses for OS stabilized with SWC and without additives cured for 90 days are given in Figure 11 and Figure 12. In Figure 11a, the presence of wrinkled fibrous structures and long flat particles, characteristic of organic soil, is evident. Significant voids are observed, directly linked to the inherent high compressibility of organic soil. The use of scanning electron microscopy (SEM), as advocated by Taylor [47], has been instrumental in understanding the hydration process of Portland cement (PC). SEM provides visual micro-characteristics of hydration products resulting from different cementitious binders and demonstrates the development of these products over time. Figure 11b highlights the main hydration product as minute needle-shaped ettringite crystals (calcium sulphoaluminate), abundantly present around the organic soil particles. Notably, the poor development of ettringite around small wood fibers, as indicated within the circled area, serves as evidence of the influence of organic matter on strength enhancement.

Conversely, Figure 11b illustrates a denser region primarily composed of calcium silicate hydrate (C-S-H) gel, with visible crystals of ettringite within a circumscribed mark. The denser the area, the stronger the material becomes, as observed in Figure 11b. This correlation is attributed to the development of hydration products filling voids across all specimens, resulting in a more compact material.

As shown in Figure 12a, elemental analysis of OS revealed that its composition was as follows: 11.97% carbon (C), 39.15% oxygen (O), 15.78% aluminum (Al), 28.54% silicon (Si), 2.12% potassium (K), 2.12% titanium (Ti), and 1.54% iron (Fe). For OS stabilized with SWC, increased amounts of O and Fe are observed, while the Al and K amounts decrease. The introduction of calcium (Ca) after stabilization with SWC supports the formation of C-S-H gel, demonstrating improvement in material properties through stabilization.

4. Conclusions

The following are the principal findings of this study:

• Stabilization of OS with SWC increased the LL, PL, and PI values. This situation can be explained by the increasing amount of SWC in the OS with the addition of SWC and the resulting flocculation.
• The increase in cement proportions in OS stabilized with SWC increased the OMC and MDD values. With the increase in cement proportion in OS stabilized with SWC, the Proctor curves were observed to move up toward the right. As the cement ratio increases, the amount of water required for the reaction that will occur after mixture will also increase. Therefore, as the cement ratio increased, the OMC values also increased. With the increase in the cement ratio, the MDD values increased as well. This is due to the cement’s outstanding flocculation characteristics. Flocculation improves in mixtures with added SWC, and when the flocs are packed, they readily reorient to their new positions and become more compact.
• The unconfined compressive strength values for OS left in both the wet-cured and air- dried environments rapidly increased until day 56 and then had a reducing tendency after 56 days.
• Linked to time, the unconfined compressive strength values of the samples stabilized with SWC increased rapidly until day 28, and then, there was a reducing tendency after day 28. The reaction between SWC and OS, as well as the time-dependent behavior of OS, played a role in this type of behavior.
• Samples stabilized with SWC gained strength rapidly.
• The unconfined compressive strength of OS stabilized with SWC increased with the increase in cement proportion.
• Due to the stabilization of OS with SWC, the unconfined compressive strength of the samples left in the air-dried environment was higher than the strength of the samples left in the wet-cured environment.
• The cohesion intercept and internal friction angle values for OS left in both the wet-cured and air-dried environments increased until day 56 and then had a reducing tendency after day 56.
• The cohesion intercept and internal friction angle values for OS left in the air-dried environment were higher than the cohesion intercept and internal friction angle values for OS left in the wet-cured environment.
• For both the wet-cured and air-dried environments, OS stabilized with SWC had increases in cohesion intercept and internal friction angle values until day 28, with a reducing trend after day 28. With the increase in cement proportion in OS stabilized with SWC, the internal friction angle and cohesion intercept values increased.
• After stabilization of OS with SWC, the UCS and shear strength values increased. The reason for this increase is the chemical reaction that occurs between SWC and OS. The fact that SWC is an early and high-strength cement contributed to the increase in these parameters.
• Addition of SWC within OS reduced the swelling percentage and compressibility values of the samples. Cation replacement between monovalent cations, like sodium and potassium, present in the OS and higher-valence calcium cations due to hydration has reduced the swelling potential and compressibility by decreasing the attraction of water molecules.

As a result of this study, SWC appears to be an effective stabilizer for stabilization of organic soils.