Microstructure and Strength Parameters of Cement-Stabilized Loess

: In this study, cement was used as a component to provide a stabilizing effect in order to evaluate the hardness and stability of loess soil. To evaluate the strength properties of loess soil reinforced with cement, samples with four distinct cement concentrations (3%, 5%, 7%, and 9%) and three distinct curing durations (7, 14, and 28 days) were generated. During a series of tests, the ﬂexural strength, direct shear strength, indirect tensile strength, and unconﬁned compressive strength were determined. An appropriate cement dosage was found, in addition to a durability index that could be used to quantify the effect of water absorption investigations on cement-stabilized loess. Both of these discoveries were made simultaneously. Scanning electron microscopy (SEM) and energy dispersive X-ray ﬂuorescence spectrometry (XRF) examinations were carried out so that the fundamental mechanics of the materials could be comprehended. The results show that the cohesion of cement-stabilized loess is much more sensitive to structure than the friction angle of the material. The increase in shear strength after remoulding is due to cohesion. The SEM study showed that the cement interacted with the loess particles to produce a thick cement network that successfully covered the voids and boosted the mixture’s strength parameters. The 28-days UCS for the samples containing 7% cement was the greatest, at 3.5 MPa, while the UCS for those containing 9% cement was 4.78 MPa. The highest ﬂexural tensile strength of 1.98 N/mm 2 was determined after 28 days. The tensile strength after 7 days in samples containing 3%, 5%, 7%, and 9% cement reached a maximum force of 0.15 MPa, 0.23 MPa, 0.27 MPa, and 0.37 MPa, respectively, and increased with each passing day. To achieve the desired level of strength, it is necessary to adjust the proportion of cement. In addition, as the curing period progressed, we observed an increase in the resistance and stiffness of the cement-stabilized loess due to the interactions that take place between the structure and the mineral composition. It is believed that this event was caused by naturally occurring cementation. As a consequence of this reaction, the production of new cementitious materials takes place. The cation exchange that causes the hydration and pozzolanic reaction that leads to the creation of aggregates and interparticle ﬂocculation is responsible for their production. These ﬁndings suggest that cement may be utilised as a simple and effective method of loess stabilization, ultimately resulting in improved performance of the loess. Therefore, this study revealed that cement may considerably enhance the microstructure and strength parameters of loess. This research provides important information on cement-stabilized loess that has ramiﬁcations for geotechnical investigation, construction, research, and testing to achieve a successful project.


Introduction
Loess is wind-blown sediment that occurs in arid and semi-dry areas where fine sand, silt, and clay accumulate. China has 640,000 km 2 of loess, accounting for 4.4% of its total land area. Most loess comes from the 317,000 km 2 Loess Plateau in the upper and middle Yellow River. According to Dalei Peng et al. [1], the Loess Plateau has around 300 million inhabitants. Loess is utilised in high-filled foundations, subgrades, and embankments because it is inexpensive and plentiful. Loess as a construction material, on the other physical and chemical interactions between cement and loess particles create configurational strength.

Raw Materials
China's Loess Plateau provided test soils. Four soil samples were assessed for specific gravity (Gs) using an ultra-pycnometer, and the average was considered typical ( Table 1). The soil compaction curve showed that 12.00% moisture was optimal and 1.82 g/cm 3 was the maximum dry density. The soil liquid limit (LL) was 31.33% and the plastic limit was 18.33%. ( Table 1). The particle size distribution is displayed in (Table 1). Clay, silt, and sand fraction sizes vary. Loess' chemical composition ( Table 2) varies based on its location and geological history. Silicon is a prevalent element found in loess, accounting for most of the sediment's mineral composition. Aluminium, iron, magnesium, calcium, and potassium are other frequent components found in loess. Table 1. Physical properties of loess.

Property Value
Gs 2.71 ρ max (g/cm 3 ) 1.82 w opt (%) 12.00 Atterberg limits Liquid limit (%) 31.33 Plasticity index (%) 15.00 Plastic limit (%) 18 Other elements (Table 3), like copper, zinc, and manganese, may be found at trace levels in loess. These trace elements may provide important details about the geological and environmental history of the location where the loess was formed.

Specimen Preparation
The mix ratios were compared to the cement, loess, and water masses. Dry cement and loess were thoroughly mixed. The water-to-loess ratio was 0.4. The original combinations all contained loess and varied in cement content (3%, 5%, 7%, and 9%). After adding water, they were mixed. We kept the mixtures in airtight plastic bags for 24 h to balance the moisture before compaction. The material was crushed in layers within a cylindrical steel mould with a 61.8 mm diameter and a 125 mm height to create a homogeneous cement-stabilized loess. GB/T50123 required 4 layers with 20 knocks each. The samples were 80mm long and 39.1mm wide. Compacted specimens were removed from the mould. They were labelled and sealed. Samples were made and cured for 7, 14, and 28 days.

Flexural Strength Test
Steel moulds with dimensions of 105 × 99.5 × 213 mm formed beams for the study (Figure 1a). Next, the flexural tensile strength of the beams was measured, and three homogenous cement-loess layers were moulded. After modification, the moulds were sealed in plastic ( Figure 1b) and left overnight. At this point, the samples could sustain their own weight. Demoulded samples were aged for 28 days at 20 • C, with 1 • C relative humidity and temperature. We measured the flexural tensile strength of the beams made from cement-stabilized loess in accordance with PN-EN 12390-5, the European standard for evaluating hardened concrete. According to [18], the flexural strengths of the test specimens were determined. Four different cement samples were used in the study. The samples were built around two 20 mm diameter steel shafts with a 30 cm base. Each beam's load shaft was placed in the centre of its length.

Specimen Preparation
The mix ratios were compared to the cement, loess, and water masses. Dry cement and loess were thoroughly mixed. The water-to-loess ratio was 0.4. The original combinations all contained loess and varied in cement content (3%, 5%, 7%, and 9%). After adding water, they were mixed. We kept the mixtures in airtight plastic bags for 24 h to balance the moisture before compaction. The material was crushed in layers within a cylindrical steel mould with a 61.8 mm diameter and a 125 mm height to create a homogeneous cement-stabilized loess. GB/T50123 required 4 layers with 20 knocks each. The samples were 80mm long and 39.1mm wide. Compacted specimens were removed from the mould. They were labelled and sealed. Samples were made and cured for 7, 14, and 28 days.

Flexural Strength Test
Steel moulds with dimensions of 105 × 99.5 × 213 mm formed beams for the study (Figure 1a). Next, the flexural tensile strength of the beams was measured, and three homogenous cement-loess layers were moulded. After modification, the moulds were sealed in plastic ( Figure 1b) and left overnight. At this point, the samples could sustain their own weight. Demoulded samples were aged for 28 days at 20 °C, with 1 °C relative humidity and temperature. We measured the flexural tensile strength of the beams made from cement-stabilized loess in accordance with PN-EN 12390-5, the European standard for evaluating hardened concrete. According to [18], the flexural strengths of the test specimens were determined. Four different cement samples were used in the study. The samples were built around two 20 mm diameter steel shafts with a 30 cm base. Each beam's load shaft was placed in the centre of its length.
The following formula was used to compute the flexural tensile strength of each sample: where: d1 = depth, d2 = width.  The following formula was used to compute the flexural tensile strength of each sample: (1) where: d 1 = depth, d 2 = width.

Unconfined Compression Test
Mechanical properties of stabilized soils are often evaluated by measuring their unconfined compressive strength ( Figure 2). The unconfined compressive strength test is used in soil stabilization applications to measure loess improvement after treatment. We examined the effect of Portland cement on loess by adding different percentages of cement by weight. Each cylindrical UCS test item was 39.9 mm wide and 80 mm high. The soil-cement samples were placed in a humid and temperature-controlled curing chamber. To characterise the mechanical characteristics of the loess specimens, we estimated their unconfined compressive strength (UCS) using the formula proposed in [19]. Direct compression was applied to the samples, and the displacement rate was measured at 0.01 mm/s. Mechanical properties of stabilized soils are often evaluated by measuring their unconfined compressive strength ( Figure 2). The unconfined compressive strength test is used in soil stabilization applications to measure loess improvement after treatment. We examined the effect of Portland cement on loess by adding different percentages of cement by weight. Each cylindrical UCS test item was 39.9 mm wide and 80 mm high. The soilcement samples were placed in a humid and temperature-controlled curing chamber. To characterise the mechanical characteristics of the loess specimens, we estimated their unconfined compressive strength (UCS) using the formula proposed in [19]. Direct compression was applied to the samples, and the displacement rate was measured at 0.01mm/s.

Compaction Test
Compaction tests indicate the appropriate moisture level per Chinese National Standard GB/T50123-2019. Three layers of loess samples with varied water contents filled the squeezed cylinder. Each layer of loess was pounded 25 times. Before compressing the samples, the cylinders were filled. The sample weight was divided by the compressed cylinder capacity to obtain the wet density. The following formula yields the dry density: The above approach correlates wet and dry densities for each category. The graphs show that the ordinate of the peak point ordinate has the highest water content, and the abscissa has the highest dry density.

Indirect Tensile Strength
The British Standards Institution's indirect tension test method was used to determine the indirect tensile strength of cement-stabilized loess specimens [20].
This test method determines hydraulically bound mixture indirect tensile strength ( Figure 3). The specimens analysed had a slenderness ratio of 2.05. Two plywood pieces with dimensions of 4 × 4 × 80 mm were used as bearing strips. Compressed samples were analysed at 0.002mm/s. A vertical force to two parallel sides of a horizontal cylinder was applied to measure the material's tensile strength, followed by a vertical sample split. This mathematical equation indirectly calculates tensile strength [20]. Indirect tension testing

Compaction Test
Compaction tests indicate the appropriate moisture level per Chinese National Standard GB/T50123-2019. Three layers of loess samples with varied water contents filled the squeezed cylinder. Each layer of loess was pounded 25 times. Before compressing the samples, the cylinders were filled. The sample weight was divided by the compressed cylinder capacity to obtain the wet density. The following formula yields the dry density: The above approach correlates wet and dry densities for each category. The graphs show that the ordinate of the peak point ordinate has the highest water content, and the abscissa has the highest dry density.

Indirect Tensile Strength
The British Standards Institution's indirect tension test method was used to determine the indirect tensile strength of cement-stabilized loess specimens [20].
This test method determines hydraulically bound mixture indirect tensile strength ( Figure 3). The specimens analysed had a slenderness ratio of 2.05. Two plywood pieces with dimensions of 4 × 4 × 80 mm were used as bearing strips. Compressed samples were analysed at 0.002 mm/s. A vertical force to two parallel sides of a horizontal cylinder was applied to measure the material's tensile strength, followed by a vertical sample split. This mathematical equation indirectly calculates tensile strength [20]. Indirect tension testing was utilised to evaluate the tensile strength of the stabilized loess specimens. "Test Method for Determining the Indirect Tensile Strength of Hydraulically Bound Mixtures". Geotechnics 2023, 3, FOR PEER REVIEW The slenderness ratio was 2.05 (low). The bearing strips were two 4 × 4 × 80 mm wooden pieces. Samples were compressed at 0.002 mm/s. This test measured the tensil strength of a horizontal cylinder using a vertical force on two parallel sides. The sampl was sliced vertically into equal parts. The following formula was used to determine ind rect tensile strength.
where R is the indirect tensile strength, F is the maximum applied force, H is the length o the sample, and D is the diameter of the sample.

Direct Shear Test
The direct shear test follows the [21] standard (1994). In this study, the shear ring i the cement-stabilized loess was 60 mm × 60 mm × 25 mm. The specimens were then re moved from the shear box. The shear strength was measured at 50, 100, 200, and 300 kPa with a horizontal displacement rate of 0.05 mm/min. Each mixture combination include three specimens, and the test data average was determined. Based on addition propor tions (3%, 5%, 7%, and 9%), the samples were divided into 4 groups to assess cohesivenes (c) and internal friction angle (ϕ). Curing took 7 days.

Water Absorption Test
The water absorption and softening coefficient were studied to assess the water re sistance of cement-stabilized loess. For the water absorption test, the specimens' dr weight was determined after 28 days, followed by their weight after 1 day in water. Th following approaches yielded water absorption: where Mn is the dry mass, and Mn is the water-immersed material. The compressiv strength of specimens after 28 days and after 1 day in water were assessed to establish th softening coefficient. The following equation was used to calculate the softening coeff cient: The slenderness ratio was 2.05 (low). The bearing strips were two 4 × 4 × 80 mm wooden pieces. Samples were compressed at 0.002 mm/s. This test measured the tensile strength of a horizontal cylinder using a vertical force on two parallel sides. The sample was sliced vertically into equal parts. The following formula was used to determine indirect tensile strength.
where R is the indirect tensile strength, F is the maximum applied force, H is the length of the sample, and D is the diameter of the sample.

Direct Shear Test
The direct shear test follows the [21] standard (1994). In this study, the shear ring in the cement-stabilized loess was 60 mm × 60 mm × 25 mm. The specimens were then removed from the shear box. The shear strength was measured at 50, 100, 200, and 300 kPa, with a horizontal displacement rate of 0.05 mm/min. Each mixture combination included three specimens, and the test data average was determined. Based on addition proportions (3%, 5%, 7%, and 9%), the samples were divided into 4 groups to assess cohesiveness (c) and internal friction angle (φ). Curing took 7 days.

Water Absorption Test
The water absorption and softening coefficient were studied to assess the water resistance of cement-stabilized loess. For the water absorption test, the specimens' dry weight was determined after 28 days, followed by their weight after 1 day in water. The following approaches yielded water absorption: where M n is the dry mass, and M n is the water-immersed material. The compressive strength of specimens after 28 days and after 1 day in water were assessed to establish the softening coefficient. The following equation was used to calculate the softening coefficient: where K is the softening coefficient, l 0 is the compressive strength after 28 days, and l 1 is the corresponding compressive strength after immersion in water.

Microstructural Analysis
Many investigations have shown that cementitious components influence the microstructure of compacted mixtures. After 28 days of curing with cement percentages of 3%, 5%, 7%, and 9%, SEM (Figure 4a) was employed. X-ray power diffraction (XRF) showed the usual quartz and clay composition of the loess. Many investigations have shown that cementitious components influence the microstructure of compacted mixtures. After 28 days of curing with cement percentages of 3%, 5%, 7%, and 9%, SEM ( Figure 4a) was employed. X-ray power diffraction (XRF) showed the usual quartz and clay composition of the loess.
An XRF spectrometer ( Figure 4b) was used to perform non-destructive chemical tests on rocks, minerals, sediments, and fluids. The behaviour of atoms in the X-rays allowed for XRF analysis of primary and trace elements in geological rocks.

Compaction Properties
The standard test approach for laboratory soil compaction characteristics was used to perform compaction tests with normal effort. Trace cement in loess soil affected its usual Proctor compaction curves ( Figure 5). The maximum dry unit weight decreased from 1.82 g/cm 3 to 1.48 g/cm 3 when the cement concentration was increased from 0% to 9% and the appropriate moisture level increased from 0.12% to 0.14%. The dry unit weight decreased steadily with cement concentration.  An XRF spectrometer (Figure 4b) was used to perform non-destructive chemical tests on rocks, minerals, sediments, and fluids. The behaviour of atoms in the X-rays allowed for XRF analysis of primary and trace elements in geological rocks.

Compaction Properties
The standard test approach for laboratory soil compaction characteristics was used to perform compaction tests with normal effort. Trace cement in loess soil affected its usual Proctor compaction curves ( Figure 5). The maximum dry unit weight decreased from 1.82 g/cm 3 to 1.48 g/cm 3 when the cement concentration was increased from 0% to 9% and the appropriate moisture level increased from 0.12% to 0.14%. The dry unit weight decreased steadily with cement concentration.
The standard test approach for laboratory soil compaction characteristics was used to perform compaction tests with normal effort. Trace cement in loess soil affected its usual Proctor compaction curves ( Figure 5). The maximum dry unit weight decreased from 1.82 g/cm 3 to 1.48 g/cm 3 when the cement concentration was increased from 0% to 9% and the appropriate moisture level increased from 0.12% to 0.14%. The dry unit weight decreased steadily with cement concentration.  It was shown that the ideal moisture content increased as a function of cement percentage because cement hydration necessitated an increasing amount of moisture [22]. "These changes may be related to the pozzolanic reaction, as occurs with related clay materials" [23]. The optimal water content increases together with the percentage of binder used to enhance loess [24].
The addition of cement increases flexibility, in agreement with the idea that the optimum water content should increase by around 10%. The inclusion of cement, which has a higher density relative to loess and soil skeletal stiffness, may explain the increased maximum dry density in loess cement mixtures. Cement-stabilized loess develops its final macrostructure as a result of primary cement linkages between aggregated loess and cement particles.

Shear Strength
The direct shear test was used to measure the shear strength parameter. After 7 days, cement-stabilized loess had a maximum shear strength (Figure 6a). In general, the microstructural modifications that take place in cement-stabilized loess after shear strength testing are complex and depend on a variety of characteristics, including soil composition, the kind and amount of cement used, and the testing circumstances. Shear strength increased steadily as cement content increased. These findings show how cement boosts peak shear strength. As illustrated, cement-stabilized loess strength envelopes determined their friction angle and cohesiveness (Figure 6b,c). The association between cement and friction angle dropped, demonstrating that soil structure had no effect at a certain cement concentration. The friction angle decreased from 27 • to 20 • as the cement percentage increased from 3% to 7%. The cement percentage increased with shear strength. The 7% cement composite was four times stiffer than the 3% composite. These data reveal that cohesion, which increases shear strength, is more structure-sensitive than friction angle. Remoulded samples with cement percentages under 9% demonstrated minimal friction angles. Cementitious linkages between loess mineral components create a matrix that encloses unbonded particles and aggregates, resulting in more complex engineering behaviours [25].
7% cement composite was four times stiffer than the 3% composite. These data reveal that cohesion, which increases shear strength, is more structure-sensitive than friction angle. Remoulded samples with cement percentages under 9% demonstrated minimal friction angles. Cementitious linkages between loess mineral components create a matrix that encloses unbonded particles and aggregates, resulting in more complex engineering behaviours [25].

Unconfined Compressive Test
The unconfined compressive strength (UCS) test is a typical technique for determining the strength of cement-stabilized soils. In this case, the loess was stabilized with different percentages of cement (3%, 5%, 7%, and 9%) and cured for varying lengths of time (3 days, 14 days, and 28 days). The UCS tests demonstrate that increasing the cement quantity and curing time enhanced the strength of the stabilized loess. Consoli et al. [26] discovered that the unconfined compressive strength of cement-stabilized soil improves proportionally as cement content increases. The UCS of cement stabilized-loess (Figure 7 The development of cementitious compounds in the microstructure of the stabilized loess was responsible for the increase in strength. When cement is mixed with loess, it interacts with water to generate cementitious compounds such as calcium silicate hydrates and calcium aluminate hydrates, which fill the pores and bind the soil particles together. These chemicals continue to develop and enhance the microstructure of the stabilized loess as the curing period advances. Moreover, the increased degree of compaction and decrease in the void ratio owing to the cement stabilization process might contribute to strength enhancement. The cement stabilizes soil particles by creating chemical links with the minerals in the soil, lowering the soil's sensitivity to moisture fluctuations and boosting its overall strength and durability.
Finally, the UCS test findings show that cement stabilization is a viable strategy to increase the strength of loess soils. The increased strength is attributable to the production

Unconfined Compressive Test
The unconfined compressive strength (UCS) test is a typical technique for determining the strength of cement-stabilized soils. In this case, the loess was stabilized with different percentages of cement (3%, 5%, 7%, and 9%) and cured for varying lengths of time (3 days, 14 days, and 28 days). The UCS tests demonstrate that increasing the cement quantity and curing time enhanced the strength of the stabilized loess. Consoli et al. [26] discovered that the unconfined compressive strength of cement-stabilized soil improves proportionally as cement content increases. The UCS of cement stabilized-loess (Figure 7)

Flexural Strength
The flexural strength of cement-stabilized loess is a measure of the material ability to resist bending or deformation under a load. The flexural strength parameters of cementstabilized soils were examined in [27]. Flexural strength is a crucial characteristic for the fatigue analysis of cement-stabilized loess. (Figure 8) shows the flexural strength of the cement-stabilized loess measured after 28 days for four different percentages of cement used in the stabilization process: 3%, 5%, 7%, and 9%. The results show an exponential increase in flexural strength as the percentage of cement increases. Cement strengthened the structure, as planned. Cement improved strength by 0.8 N/mm 2 , 1.1 N/mm 2 , 1.4 N/mm 2 , and 1.98 N/mm 2 for 3%, 5%, 7%, and 9%, respectively. An exponential increase in flexural strength means that the strength increases at an accelerating rate with increasing percentages of cement. Several microstructural changes happen when the flexural strength of cement-stabilized loess is tested. When water is added to cement-stabilized loess, it starts a chemical reaction called cement hydration. This process results in a complex network of crystals that fit together. This can make the material stronger and last longer. Secondly, as the loess is subjected to stress during the flexural strength test, the particles can rearrange themselves, causing a change in the microstructure of the material. This can lead to an increase in density and a reduction in pore space, which can improve the strength of the material. Ettringite and C-S-H gel provide strength, and humidity optimises hydration. Cementing loess modifies its failure mechanisms. Cement-stabilized loess samples maintained strength throughout the test.  The development of cementitious compounds in the microstructure of the stabilized loess was responsible for the increase in strength. When cement is mixed with loess, it interacts with water to generate cementitious compounds such as calcium silicate hydrates and calcium aluminate hydrates, which fill the pores and bind the soil particles together. These chemicals continue to develop and enhance the microstructure of the stabilized loess as the curing period advances. Moreover, the increased degree of compaction and decrease in the void ratio owing to the cement stabilization process might contribute to strength enhancement. The cement stabilizes soil particles by creating chemical links with the minerals in the soil, lowering the soil's sensitivity to moisture fluctuations and boosting its overall strength and durability.
Finally, the UCS test findings show that cement stabilization is a viable strategy to increase the strength of loess soils. The increased strength is attributable to the production of cementitious compounds in the microstructure of the stabilized loess, as well as an increase in compaction and a decrease in void ratio. The reported test findings may help engineers and construction professionals to plan and choose suitable stabilization techniques for loess soils in a variety of engineering applications.

Flexural Strength
The flexural strength of cement-stabilized loess is a measure of the material ability to resist bending or deformation under a load. The flexural strength parameters of cementstabilized soils were examined in [27]. Flexural strength is a crucial characteristic for the fatigue analysis of cement-stabilized loess. (Figure 8) shows the flexural strength of the cement-stabilized loess measured after 28 days for four different percentages of cement used in the stabilization process: 3%, 5%, 7%, and 9%. The results show an exponential increase in flexural strength as the percentage of cement increases. Cement strengthened the structure, as planned. Cement improved strength by 0.8 N/mm 2 , 1.1 N/mm 2 , 1.4 N/mm 2 , and 1.98 N/mm 2 for 3%, 5%, 7%, and 9%, respectively. An exponential increase in flexural strength means that the strength increases at an accelerating rate with increasing percentages of cement. Several microstructural changes happen when the flexural strength of cement-stabilized loess is tested. When water is added to cement-stabilized loess, it starts a chemical reaction called cement hydration. This process results in a complex network of crystals that fit together. This can make the material stronger and last longer. Secondly, as the loess is subjected to stress during the flexural strength test, the particles can rearrange themselves, causing a change in the microstructure of the material. This can lead to an increase in density and a reduction in pore space, which can improve the strength of the material. Ettringite and C-S-H gel provide strength, and humidity optimises hydration. Cementing loess modifies its failure mechanisms. Cement-stabilized loess samples maintained strength throughout the test. particles can rearrange themselves, causing a change in the microstructure of the material. This can lead to an increase in density and a reduction in pore space, which can improve the strength of the material. Ettringite and C-S-H gel provide strength, and humidity optimises hydration. Cementing loess modifies its failure mechanisms. Cement-stabilized loess samples maintained strength throughout the test.

Splitting Tensile Strength Test
According to the research conducted by Consoli et al. [28], the strength of stabilized soil improves as the volumetric binder concentration increases and declines as the porosity increased. The splitting tensile strength of cement-stabilized loess is defined as the amount of tensile stress that the loess can handle without cracking. The results show that the strength of cement-stabilized loess increased with the amount of cement and the curing time.
The splitting tensile strength (Figure 9) of 3% cement added after 7 days was 0.15 MPa, increasing to 0.23 MPa after 14 days and 0.37 MPa after 28 days. This increase in strength is attributable to the hydration of the cement, which leads to the development of hydrated compounds such as calcium silicate hydrate (C-S-H) gel, which is responsible for the increase in strength in the cement-stabilized loess.

Splitting Tensile Strength Test
According to the research conducted by Consoli et al. [28], the strength of stabilized soil improves as the volumetric binder concentration increases and declines as the porosity increased. The splitting tensile strength of cement-stabilized loess is defined as the amount of tensile stress that the loess can handle without cracking. The results show that the strength of cement-stabilized loess increased with the amount of cement and the curing time.
The splitting tensile strength (Figure 9) of 3% cement added after 7 days was 0.15 MPa, increasing to 0.23 MPa after 14 days and 0.37 MPa after 28 days. This increase in strength is attributable to the hydration of the cement, which leads to the development of hydrated compounds such as calcium silicate hydrate (C-S-H) gel, which is responsible for the increase in strength in the cement-stabilized loess.
Furthermore, the addition of 5%, 7%, and 9% cement led to an increase in splitting tensile strength with increasing curing time. After 28 days, the splitting tensile strength was 0.42 MPa for 5%, 0.48 MPa for 7%, and 0.57 MPa for 9% cement content. Notably, the appropriate cement concentration to obtain the necessary splitting tensile strength relies on a number of variables, including the features of the loess and the planned use of the stabilized material. The reported results show that higher cement concentrations usually lead to higher strength, although this is not always the case. High cement content may contribute to the production of shrinkage fractures caused by the excessive heat created during hydration, resulting in a reduction in splitting tensile strength. The microstructure of cement-stabilized loess is critical to the development of splitting tensile strength. The addition of cement enhances the concentration of C-S-H gel, which fills the pores and gaps of the loess to produce a more compact and dense microstructure. Increased splitting tensile strength is a result of a denser microstructure. Furthermore, the splitting tensile strength of cement-stabilized loess can be affected by the way in which it is compacted, how it is allowed to cure, and the presence of other materials, such as pozzolanic materials.
Understanding the splitting tensile strength and microstructural changes that occur throughout the stabilization process is crucial for developing and choosing cement compositions to stabilize loess materials that satisfy the requisite strength parameters.

Flexural-Compressive Strength Relationship
Flexural and indirect tensile strength are as important as unconfined compressive strength for assessment of material stabilization. Figure 10 shows flexural and unconfined compressive strengths at different cement concentrations (with an R value of 0.71). The material was homogeneous, since the UCS and flexural strength samples were different. The findings can be compared and connected, but they are not reliable. Furthermore, the addition of 5%, 7%, and 9% cement led to an increase in splitting tensile strength with increasing curing time. After 28 days, the splitting tensile strength was 0.42 MPa for 5%, 0.48 MPa for 7%, and 0.57 MPa for 9% cement content. Notably, the appropriate cement concentration to obtain the necessary splitting tensile strength relies on a number of variables, including the features of the loess and the planned use of the stabilized material. The reported results show that higher cement concentrations usually lead to higher strength, although this is not always the case. High cement content may contribute to the production of shrinkage fractures caused by the excessive heat created during hydration, resulting in a reduction in splitting tensile strength. The microstructure of cement-stabilized loess is critical to the development of splitting tensile strength. The addition of cement enhances the concentration of C-S-H gel, which fills the pores and gaps of the loess to produce a more compact and dense microstructure. Increased splitting tensile strength is a result of a denser microstructure. Furthermore, the splitting tensile strength of cement-stabilized loess can be affected by the way in which it is compacted, how it is allowed to cure, and the presence of other materials, such as pozzolanic materials.
Understanding the splitting tensile strength and microstructural changes that occur throughout the stabilization process is crucial for developing and choosing cement compositions to stabilize loess materials that satisfy the requisite strength parameters.

Flexural-Compressive Strength Relationship
Flexural and indirect tensile strength are as important as unconfined compressive strength for assessment of material stabilization. Figure 10 shows flexural and unconfined compressive strengths at different cement concentrations (with an R value of 0.71). The material was homogeneous, since the UCS and flexural strength samples were different. The findings can be compared and connected, but they are not reliable.

Water Resistance
Using different samples of cement and loess, the effect of curing time on how much water a material can hold was studied. The soaking process increased Rn from 30 min to 24 h, as seen in (Figure 11). The water absorption rate quantifies a material's capacity to resist water penetration. According to the result, the rate of water absorption decreases as the amount of cement increases. The water absorption rate was greatest with 9% cement content, at 2.7% for 30 min, 2.6% for 60 min, 2.6% for 90 min, and 3.5% for 24 h. The water absorption rate was 0.5% for 30 min, 1.1% for 60 min, 1% for 90 min, and 1.3% for 24 h for 3% cement. The microstructure of cement-stabilized loess is crucial in influencing the material's water resistance. The inclusion of cement in loess raises the material's density and provides a binding matrix that decreases the porosity. This causes a drop in the material's water absorption rate. With increasing cement content, the microstructure becomes denser and less porous, resulting in decreased water absorption rates. Calcium silicate hydrate (C-S-H) and calcium hydroxide (Ca(OH)2) must form, as cement hydrates during the curing process of cement-stabilized loess. The C-S-H gel fills the spaces between the particles and makes the material denser. Ca(OH)2 is forms as a by-product, which plugs the pores. The C-S-H gel continues to develop as the curing period continues, resulting in a denser microstructure with fewer holes. This leads to an increase in the material's water resistance.
The curing duration also significantly impacts the water resistance of cement-stabilized loess. After 24 h of curing, the water absorption rate rose dramatically for all cement percentages. This might be because the material was not completely cured and still had a large porosity, allowing it to absorb more water.
The ability of cement-stabilized loess to resist water can be improved by adding more cement and giving it more time to cure. A material's microstructure largely determines

Water Resistance
Using different samples of cement and loess, the effect of curing time on how much water a material can hold was studied. The soaking process increased R n from 30 min to 24 h, as seen in (Figure 11). The water absorption rate quantifies a material's capacity to resist water penetration. According to the result, the rate of water absorption decreases as the amount of cement increases. The water absorption rate was greatest with 9% cement content, at 2.7% for 30 min, 2.6% for 60 min, 2.6% for 90 min, and 3.5% for 24 h. The water absorption rate was 0.5% for 30 min, 1.1% for 60 min, 1% for 90 min, and 1.3% for 24 h for 3% cement. The microstructure of cement-stabilized loess is crucial in influencing the material's water resistance. The inclusion of cement in loess raises the material's density and provides a binding matrix that decreases the porosity. This causes a drop in the material's water absorption rate. With increasing cement content, the microstructure becomes denser and less porous, resulting in decreased water absorption rates. Calcium silicate hydrate (C-S-H) and calcium hydroxide (Ca(OH) 2 ) must form, as cement hydrates during the curing process of cement-stabilized loess. The C-S-H gel fills the spaces between the particles and makes the material denser. Ca(OH) 2 is forms as a by-product, which plugs the pores. The C-S-H gel continues to develop as the curing period continues, resulting in a denser microstructure with fewer holes. This leads to an increase in the material's water resistance.  Figure 11. Influence of soaking time on water absorption rate.

XRF Analyses
Cement-stabilized loess was analysed by XRF. Micro-XRF (M4 Tornado, German) was used to measure the elemental composition (Table 6, Figure 12). XRF (X-ray fluorescence) analysis is a non-destructive method for determining a material's elemental composition. XRF analysis can provide information regarding the distribution of elements in the microstructure of cement-stabilized loess.
XRF analysis shows ( Table 6) that the sample of cement-stabilized loess has the most of the elements Si, Ca, and Al. Si makes up 6.95% of the sample, which shows that the loess contains silica (SiO2). Calcium makes up 12.09% of the total, which shows that calcium carbonate (CaCO3) is present, which is a common mineral in loess. Al amounts to 1.72%, showing that aluminum silicates are present in the loess.
Along with the main elements, there are also smaller amounts of Fe, K, Mn, and Ti. Fe accounts for 7.54% of the total, showing that iron oxide (Fe2O3) is present in the loess. 2.31 percent K indicates the presence of potassium oxide (K2O). Mn and Ti are considerably less abundant, accounting for 0.15% and 0.61% of the sample, respectively. The curing duration also significantly impacts the water resistance of cement-stabilized loess. After 24 h of curing, the water absorption rate rose dramatically for all cement percentages. This might be because the material was not completely cured and still had a large porosity, allowing it to absorb more water.
The ability of cement-stabilized loess to resist water can be improved by adding more cement and giving it more time to cure. A material's microstructure largely determines how resistant it is to water, with a denser and less porous microstructure resulting in lower water absorption rates.

XRF Analyses
Cement-stabilized loess was analysed by XRF. Micro-XRF (M4 Tornado, German) was used to measure the elemental composition (Table 6, Figure 12). XRF (X-ray fluorescence) analysis is a non-destructive method for determining a material's elemental composition. XRF analysis can provide information regarding the distribution of elements in the microstructure of cement-stabilized loess. loess contains silica (SiO2). Calcium makes up 12.09% of the total, which shows that cal-cium carbonate (CaCO3) is present, which is a common mineral in loess. Al amounts to 1.72%, showing that aluminum silicates are present in the loess. Along with the main elements, there are also smaller amounts of Fe, K, Mn, and Ti. Fe accounts for 7.54% of the total, showing that iron oxide (Fe2O3) is present in the loess. 2.31 percent K indicates the presence of potassium oxide (K2O). Mn and Ti are considerably less abundant, accounting for 0.15% and 0.61% of the sample, respectively.  XRF analysis shows ( Table 6) that the sample of cement-stabilized loess has the most of the elements Si, Ca, and Al. Si makes up 6.95% of the sample, which shows that the loess contains silica (SiO 2 ). Calcium makes up 12.09% of the total, which shows that calcium carbonate (CaCO 3 ) is present, which is a common mineral in loess. Al amounts to 1.72%, showing that aluminum silicates are present in the loess.
Along with the main elements, there are also smaller amounts of Fe, K, Mn, and Ti. Fe accounts for 7.54% of the total, showing that iron oxide (Fe 2 O 3 ) is present in the loess. 2.31 percent K indicates the presence of potassium oxide (K 2 O). Mn and Ti are considerably less abundant, accounting for 0.15% and 0.61% of the sample, respectively.
The XRF analysis also provides information regarding the loess' mineral composition. The SiO 2 content of 14.86% indicates the presence of quartz, a common mineral found in loess. The Al 2 O 3 concentration of 3.25% indicates the existence of aluminum silicates, such as feldspar or mica. A CaO concentration of 16.92% shows calcium carbonate is present. The Fe 2 O 3 content of 10.79% suggests the presence of iron oxide. The K 2 O content of 0.37% suggests the presence of potassium feldspar. According to [29], the maximum SO 3 concentration is 4%.
Adding cement to the loess microstructure can result in a number of alterations. For instance, cement may serve as a binder, therefore increasing the material's strength. Additionally, cement can fill the spaces between soil particles, resulting in a decrease in porosity and permeability. This may increase the material's water resistance and longevity, which is especially important in construction situations where the material may be exposed to damp.
The XRF analysis of cement-stabilized loess tells us a lot about the elements and minerals that make up the material. This information can be used to learn about the microstructure of the material and how stabilization with cement changes the properties of loess. The XRF analysis can also be used to improve the design of cement stabilization processes and make sure that the final product is of high quality.

SEM Analyses
The SEM micrographs ( Figure 13) show the microstructure of cement-stabilized loess after 28 days with 3%, 5%, 7%, and 9% cement percentages. The dominant crystalline hydrates in the examined patterns were Ca(OH) 2 and ettringite [30,31] Reaction products and hydration affect loess matrix changes (Figure 13a). According to Angelova and Evstatiev [32], the particles and pores of the soil are partially covered and filled by fibrous phases of about 0.5-1.0 m in length. Fibrous growths can be seen in the sample because the loess matrix is porous and the composite mixture has a high water-to-cement ratio. At higher magnification, hydration product production was fast ( Figure 13c). As cement concentration increases, natural soil flocculations thicken. Cement-produced flocculations may create a stronger, more controllable loess structure with denser particles. Thus, increasing the cement dose improved flocculation and loess strength. This result may be explained by recognising that the flocculations are a consequence of the cement hydrating during the curing time and that additional cement would result in increased hydration, cementing weak soil particles and enhancing soil strength. C-S-H gel hydration products form the reticular fibrous network after 28 days (Figure 13d). Calcium silicate hydrate (C-S-H) is thought to boost Portland cement's strength when hydrated. Soil stabilized by Ca(OH) 2 from cement hydration may be further strengthened via C-S-H synthesis, which involves the ionisation of Ca 2+ and OH − . Calcium and alumina may produce a C-A-H cementitious complex. Ettringite grew with C-S-H phases (3CaO.Al 2 O 3 .3CaSO 4 .32H 2 O or C6AS3H323CaO). The cement-stabilized loess's strength is provided by additional cementation products created during curing. Cation exchange, pozzolanic reactions, and carbonation strengthen cement-stabilized loess. Cement-stabilized loess aggregates during short-term cation exchange, increasing its strength. Slow pozzolanic reactions and carbonation create new cementitious materials, make loess particles less porous, and bond soil particles. This makes cement-stabilized loess considerably stronger.

Conclusions
Loess from the "China Loess Plateau" was tested for geotechnical properties after being combined with different cements. The water resistance, density, and compressibility of cement-stabilized loess were measured. The direct shear, as well as the flexural, unconfined compressive, and tensile strengths, was also measured to compare strength at various curing stages. Results: (1) Cement minimises loess flexibility. Increasing shear strength correlated with changes in cohesiveness. This study shows that cohesiveness in cement-stabilized loess is more structure-sensitive than friction angle and that bonding is necessary for shear strength gain following remoulding. (2) The compressive strength increases without limit as the cement amount and curing time increase. The unconfined compressive strength of a given cement content increases as curing time increases. (3) With more cement added and the ideal moisture level decreased, the maximum dry density increases. (4) Tensile and bending strengths grow with the quantity of cement used and the curing period. (5) After 28 days, the specimens' flexural strength increased most when the cement concentration was between 7% and 9%. (6) Cement pozzolanic reaction enhanced the strength properties of the loess by creating ettringite and C-S-H gels.
The findings of this study require addition research into strength factors. Importantly, testing the long-term effectiveness of loess cement stabilization under varied conditions, such as high and low temperatures, would be beneficial. Lastly, since protecting the environment is becoming more important, more research should be done to find out how cement can be changed into a material that has less of an effect on the environment during loess stabilization.

Acknowledgments:
The authors acknowledge the practical support of Chang'an University.

Conflicts of Interest:
The authors declare that they have no known competing financial interest or personal relationship that could have appeared to influence the work reported in this paper.