Evaluating the Strength and Durability of Eco-Friendly Stabilized Soil Bricks Incorporating Wood Chips

Abstract

The production of commercially used cement-based bricks has significant environmental implications, necessitating the development of robust, environmentally friendly alternatives. This study assesses the strength and durability of soil bricks by utilizing an eco-friendly stabilizer, which includes lime and natural-fiber-derived staple fibers. Soil bricks, each sized 50 mm × 100 mm and featuring varying proportions of stabilizer and wood chips, were subjected to unconfined compression and bending strength tests, permeability assessments, steel ball/golf ball (SB/GB) evaluations, and wetting–drying tests. The results demonstrated that higher stabilizer ratios and lower wood chip ratios led to enhanced unconfined compressive strength. Additionally, repeated wetting–drying cycles reduced the strength by up to 63%, while the relative dynamic modulus of elasticity decreased by as much as 45% with increasing wetting–drying cycles. Notably, the eco-friendly stabilizer significantly improved soil shear strength, ultimately enhancing the durability of the soil bricks.

1. Introduction

Over the past few years, there has been a growing concern about the harmful effects of traditional chemical stabilizers such as cementitious materials on the environment, leading to increased research and development activities focused on finding sustainable and eco-friendly alternatives. Cement, a widely used and popular soil stabilizer, emits up to 0.55 metric ton of carbon dioxide per metric ton of cement produced, contributing significantly to greenhouse gas emissions and climate change [1]. In particular, the cement industry is a major contributor to global carbon dioxide emissions, responsible for up to 8% of total emissions, with particulate air emissions in the form of cement dust presenting another potential environmental problem. These processes (sometimes called “industry” or “industrial” processes) and energy emissions are most often reported separately in global emissions inventories [2,3,4]. The development of eco-friendly stabilizers and related technologies is one such alternative that can help mitigate the harmful effects of cement on the environment [5].

The major issues of structures associated with soft soil materials used in rammed earth construction include low strength, low durability, and high compressibility. Therefore, it is crucial to enhance the geotechnical characteristics, particularly the mechanical properties and durability, of these materials [6]. The use of soil as the primary component in structures offers the advantage of low environmental impact. However, it is accompanied by drawbacks such as low strength, limited durability, and vulnerability to cracking caused by shrinkage during drying. Several research studies have introduced environmentally friendly materials for soil stabilization, aiming to promote soil preservation, sustainable development, and the reduction of greenhouse gas emissions [7,8,9,10,11,12,13]. Yang et al. (2006) performed a study to evaluate the compressive strength and drying shrinkage of mortar that does not contain cement but is instead based on Hwangtoh (red clay) with various mixing ratios; the aim was to explore the possibility of using Hwangtoh-based mortar as a sustainable and eco-friendly alternative to conventional cement-based materials [9]. Kwon and Oh (2012) conducted a study to assess the strength characteristics of soil-based cement mixed with an eco-friendly stabilizer made primarily from short fibers extracted from natural sources and lime. The study also investigated the mechanical properties of weathered clay soil-based cement, varying the content of the eco-friendly stabilizer [10]. Hence, the novel eco-friendly stabilizer, an inorganic chemical substance, was formulated through the utilization of specialized technologies and manufacturing processes. This study aimed to investigate the feasibility of the eco-friendly stabilizer as a solution to address issues such as low strength, limited durability, and susceptibility to cracking due to shrinkage during drying.

Earth-based structures are susceptible to climatic influences, such as wet–dry cycles, which can significantly impact their structural stability and safety [14]. To ensure the stability and safety of earth-based structures in the face of climatic influences, it is crucial to conduct extensive research into the short- and long-term impacts of climate, identify the signs of structural destabilization, and develop technologies that can account for these effects in current designs. Allam and Sridharan [15] established a basic theoretical framework regarding the impact of recurring wet–dry cycles on the shear strength of soil. Rajaram and Erbach [16] conducted a study to examine the effect of repeated wet–dry cycles on the mechanical properties and stress resistance of soil-based structures. The researchers conducted experiments using clay soils and reported physical changes that occurred in the soil structure, which ultimately affected its strength due to alternating wet and dry conditions. A study conducted by Yoo [17] investigated the impact of recurrent wet–dry phases on the compressive strength of weathered granite soil. The study involved conducting plane strain experiments to identify the changes in strength characteristics caused by forced wetting–drying cycles on molded samples with varying fine granule contents.

The vulnerability of earth-based structures to climatic influences such as wet–dry cycles has been reported in several papers [14,15,16,17]. This body of work underscores the critical need for investigating both short- and long-term impacts of climate change, recognizing early indicators of structural instability, and devising innovative technologies to incorporate these considerations into design practices. While significant attention has been given to studying weather-related effects on the strength of earth-based structures, there remains a noticeable research gap in understanding the behavior of these structures in the absence of cementitious stabilizers, which is the focus of this paper.

The objective of the present investigation is to expand the body of data and provide new insights on effects of wet–dry cycles and the SB/GB factor, along with the fundamental mechanical properties, on soil bricks that have been stabilized with the new eco-friendly stabilizer and wood chips. Soil brick specimens were fabricated using various ratios of eco-friendly stabilizers and wood chips, in relation to a mixture consisting of weathered granite soil. These specimens were then tested for wet–dry cycles, SB/GB factor, and fundamental mechanical properties.

2. Materials

2.1. Characteristics of Eco-Friendly Stabilizer

The eco-friendly stabilizer used in this study aims to enhance the shear strength of the soil, improve its bearing capacity, and increase its durability. Additionally, it serves to prevent damage caused by seepage and freezing. This eco-friendly material is composed mostly of lime and natural staple fibers, which have no harmful effects unlike other soil stabilizers. The stabilizer consists of various substances, including carbon, oxygen, aluminum, and others, as shown in

Table 1. Chemical compositions of the eco-friendly stabilizer used in this study.

Substance	Weight (%)	Atomic (%)
C	7.02	11.97
O	49.31	63.15
Al	4.01	3.04
Si	5.75	4.19
S	2.49	1.59
Ca	31.42	16.06
Total	100.00	100.00

with their corresponding amounts in percentages. Therefore, it can be easily applied to various types of pavements, including managed roads in forest parks, promenades, and bike lanes. This is because it can be laid on all types of soil, making it a flexible and practical solution for various construction projects [18].

Since the soil brick stabilized with the eco-friendly stabilizer is used in soil pavement for areas such as forest parks, promenades, and bike lanes, it is essential that the stabilizer contain no toxic chemicals to ensure public safety. In order to assess the environmental impact of the eco-friendly stabilizer, a TCLP (toxicity characteristic leaching procedure) method was conducted using an inductively coupled plasma spectrometer to measure the amount of hazardous substances in the eluted solution. The amounts of lead (Pb) and cyanide (CN) eluted from the stabilizer were found to be lower than their respective limit values (

Table 2. Elution test results for the eco-friendly stabilizer used in this study.

Substance	Limit Value (mg/L)	Results (mg/L)
Cd	0.3	Not Detected
Pb	3.0	0.04
Cu	3.0	Not Detected
Fg	0.005	Not Detected
CN	1.0	0.004
Cr6+	1.5	Not Detected
As	1.5	Not Detected

). This indicates that the stabilizer poses no significant environmental risks in terms of heavy metals.

The eco-friendly stabilizer should have the ability to effectively harden the soil brick by binding it with other materials, forming a solid mass. It is important to ensure that there is early development of strength to shorten the curing period [19]. The curing period of a stabilizer is dependent on the grain size. In this study, the eco-friendly stabilizer used had a specific area of 5293 cm²/g, which is 1.6 times that of ordinary Portland cement (OPC) 3260 cm²/g, indicating faster solidification performance and meeting the required criterion as shown in

Table 3. Comparison of setting time between the eco-friendly stabilizer and Ordinary Portland Cement (OPC).

Properties	Fineness (cm2/g)	Setting Time Test
		Water Content	Start Time (h/min)	End (h/min)
Eco-friendly stabilizer	5293	33.0%	00:16	02:20
OPC	3260	27.5%	02:31	03:45

.

2.2. Physical Properties of Weathered Granite Soil

Table 4. Physical properties of the weathered granite soil.

Substance	Results
Moisture content (%)	14.0
Unit weight (kN/m3)	19.8
Liquid limit (%)	29.2
Plastic limit (%)	NP
Plastic index (%)	NP
Specific gravity	2.60
Cu	10.19
Cc	1.15
USCS	SW

presents the physical properties of the weathered granite soil used in the experiments, including its specific gravity of 2.60, liquid limit of 29.2%, plastic limit of NP (non-plastic), and unified soil classification system (USCS) of SW (well-graded sand). Based on the indoor compaction test, the maximum dry unit weight and optimum water content of the soil were determined to be 19.8 kN/m³ and 14%, respectively. Test specimens were then fabricated to a dry unit weight of 16.8 kN/m³, which is 85% of the maximum dry unit weight, for the purpose of evaluating the strength characteristics of the soil brick through a wetting–drying test.

3. Experimental Program

A comprehensive series of material tests was executed to assess the engineering attributes of soil bricks comprising weathered granite, soil stabilizer, and wood chips, with a focus on mechanical properties, durability, and serviceability. Figure 1 illustrates the experimental program’s flow chart.

3.1. Mechanical Tests

3.1.1. Unconfined Compressive Strength Test

A series of unconfined compressive strength (UCS) tests was conducted to evaluate the engineering characteristics of soil bricks made of weathered granite, soil stabilizer, and wood chips. Soil specimens were fabricated with varying ratios of soil stabilizer and wood chips as well as different curing periods, as shown in

Table 5. Experimental parameters for USC tests.

Unit Weight (kN/m3)	Stabilizer (%)	Wood Chip (%)	Curing Period (Days)
16.8	5	0.5	7, 14, 28
		1.0
		1.5
	10	0.5
		1.0
		1.5
	15	0.5
		1.0
		1.5

, in accordance with the testing methods specified in KSF 2314 [20]. A total of eighty-one 50 × 100 mm cylinders were fabricated for UCS tests, allowing for three test repetitions for each condition. The mixing ratio of stabilizer to soil mix was varied at 5%, 10%, and 15%, while the ratio of wood chips was set at 0.5%, 1.0%, and 1.5% for each stabilizer content level. The specimens were cured for 7, 14, or 28 days. In order to produce homogeneous specimens, the soil mix was adjusted to reach an optimum moisture content of 14% by adding water and was mixed thoroughly by hand.

3.1.2. Bending Strength Test

Soil brick samples were fabricated to assess the bending strength of the specimen mix, with the ratio of stabilizer varied at 5%, 10%, and 15%. The bending strength test was conducted in compliance with the testing method outlined in KS F 2408 [21]. Soil brick samples (200 mm × 180 mm × 50 mm) for bending strength testing were fabricated using a compression method. The press-type brick machine was designed to apply biaxial compression pressure, and the samples were prepared by subjecting them to a pressure of 100 MPa for 1 min.

3.2. Wet–Dry Cycle Test

The wetting–drying test was carried out on the soil bricks to assess their durability, following the testing methods specified in KSF 2330 [22]. The specimens were fabricated and cured at room temperature for 28 days. Subsequently, the specimens were subjected to 0, 3, 6, or 12 cycles of wetting and drying, with each cycle comprising immersion in water for 24 h and drying in a 20 °C oven for 24 h. After completing their respective cycles, the specimens underwent an unconfined compression test to determine any changes in strength compared to the reference strength.

3.3. Dynamic Elasticity Test

In this study, a nondestructive dynamic elasticity test was utilized to quantify the resonance frequencies of vibrating elastic bodies as illustrated in Figure 2. By analyzing the obtained vibration waveforms using frequency scanning circuits, the dynamic modulus of elasticity and Poisson’s ratio were calculated based on the measured resonance frequencies [23]. Specifically, the relative dynamic modulus of elasticity was measured to assess changes in specimen strength under varying wetting–drying cycle numbers. The relative dynamic modulus of elasticity was calculated from the dynamic modulus of elasticity using Equation (1):

$$P_c={\left(n_1/n\right)}^2\times 100$$

(1)

where Pc is the dynamic modulus of elasticity (%) following wet–dry cycles, n is the 1st resonance frequency (Hz) with no wet–dry cycles, and n₁ is the 1st resonance frequency (Hz) following wet–dry cycles.

3.4. Permeability Test

The permeability test was conducted on the soil bricks, which were fabricated by mixing weathered granite soil with eco-friendly stabilizer and wood chips. An onsite permeability tester was used to evaluate the permeability, following the method outlined in KSF 2394 for testing the onsite permeability of permeable brick pavements [24]. The test required measuring the time taken for 400 mL of water to permeate through a single brick. To prevent water loss due to water pressure at the joint part, fat clay was applied along the gap between the tester and the specimen. Each specimen underwent five consecutive measurements at 1 min intervals, and the mean value was determined by averaging the results.

3.5. SB/GB Ratio Test

The SB/GB tests were conducted to evaluate the pedestrian serviceability of the soil brick when applied onsite. The ground reaction force of the soil bricks was compared with different stabilizer and wood chip contents using SB/GB tests. The test results were presented in terms of SB and GB factors as defined by Equation (2). During the SB/GB tests, the height of rebound of a one inch steel ball (66.7 g) and a golf ball (45.9 g) were measured after they were dropped from a height of 100 cm (free fall). Figure 3 illustrates the schematics of the SB/GB tester and illustrates the procedure of the test. The experiment was conducted multiple times for each paving material, specifically five repetitions. From these repetitions, the three rebound heights that exhibited the most similarity were chosen for further analysis. The mean value of these selected rebound heights, denoted as H₀, was calculated. Using Equation (2), the SB and GB factors were then determined based on the calculated H₀ value.

$$\mathrm{SB} \mathrm{or} \mathrm{GB} \mathrm{factor} (\%)=\frac{H_0}{H}\times 100$$

(2)

The GB factor is considered to reflect the ability of a material to absorb impact, while the SB factor represents its resilience in rebound. Generally, smaller values of these factors indicate reduced bodily impact on pedestrians. A smaller value of SB and GB factors indicates less impact on a pedestrian’s body [17]. All the tests were conducted following the guidelines outlined in the Handbook of Pavement Survey and Testing [25].

Figure 3. SB/GB factor test: schematics [26] (left) and photos (right).

Figure 3. SB/GB factor test: schematics [26] (left) and photos (right).

As per the findings reported by the PWRI (Public Works Research Institute) [27], the values of the SB/GB factors for different types of surfaces were determined. The SB/GB factor is a measure of the dynamic interaction between a tire and a pavement surface, where SB represents the braking force and GB represents the grip force. For natural stone surfaces, the SB/GB factor is in the range of 55–85 and 77–87, respectively. Concrete surfaces exhibit a lower SB factor range of 25–35 but a wider GB factor range of 75–92. Asphalt concrete surfaces have even lower SB factors, ranging 5–12, but a higher GB factor range of 57–72. On the other hand, soil pavement using stabilizer has a relatively lower SB factor range of 3–8 but a higher GB factor range of 50–62. The lowest SB factor range, 3–12, was observed for natural soil surfaces, along with a minimal GB factor range of 7–27. These findings provide valuable insights for pavement design and selection of materials based on their expected performance in terms of tire–pavement interaction. It should be noted that the reported ranges are based on the data provided by PWRI [27].

4. Experimental Results and Discussions

4.1. Mechanical Tests

4.1.1. Results of Unconfined Compressive Strength Test

Tests were conducted to evaluate the effects of different ratios of eco-friendly stabilizer and wood chips, as well as varying curing times, on the unconfined compressive strength of soil bricks that had been stabilized with this mixture. The data presented in Figure 4 indicate a direct relationship between stabilizer content and unconfined compressive strength, as an increase in stabilizer content results in a higher strength. Based on multiple preliminary experiments, it was observed that a 14 day curing period is sufficient to achieve 90% of the reference strength when the 28 day strength is used as the reference. The moisture content for developing 90% of the reference strength was found, as a result of multiple preliminary experiments, to exhibit the maximum strength in the wetting phase, and was higher than the optimum water content of weathered granite soil.

A soil brick reference strength of 2.0 MPa was achieved with a 7 day curing period when the stabilizer content was set at 15% or higher as shown in Figure 5. Therefore, if time is a constraint, a stabilizer content of 15% or higher can be utilized to attain the required brick strength within 7 days.

The unconfined compressive strength of the soil bricks varied with changes in the wood chip content. It was observed that a lower wood chip content is positively correlated with a higher unconfined compressive strength, as shown in Figure 6. Specifically, the strength of soil bricks with 0.5% wood chip content was up to 1.3 times greater than that of soil bricks with 1.5% wood chip content, and this trend diminished as the stabilizer content increased.

In conclusion, the integration of wood chips into soil brick pavement systems has been demonstrated to enhance pedestrian comfort. However, it is important to note that an increase in wood chip content coupled with a low stabilizer ratio can lead to a reduction in the pavement’s overall strength. To overcome this limitation, it is recommended to maintain a stabilizer ratio of 10% or greater, regardless of the wood chip content. This approach ensures that the soil brick pavement achieves its target strength within a curing period of 28 days, thus maintaining structural integrity while providing a comfortable walking surface.

4.1.2. Results of Bending Strength Tests

Bending strength tests were conducted to evaluate the effect of wood chip and stabilizer content on bending strength. Figure 7 illustrates that an increase in wood chip content resulted in a decrease in bending strength, with a maximum reduction of 24%. Conversely, the addition of more stabilizer content led to an improvement in bending strength, with values increasing up to 2.9 times between 5% and 15% stabilizer content.

4.2. Wet–Dry Cycle Test

The effect of various wetting–drying cycles on the unconfined compressive strength of soil brick specimens was evaluated through a combined test that included wet–dry cycle and uniaxial compressive tests. The specimens were first cured at room temperature for 28 days, then subjected to 0, 3, 6, or 12 wetting–drying cycles, and their unconfined compressive strength was measured at each cycle level. The goal was to determine the patterns of change in the unconfined compressive strength of the specimens with respect to the different wetting–drying cycles. The experimental results, presented in Figure 8, demonstrate that the unconfined compressive strength of soil brick specimens decreased with an increasing number of wetting–drying cycles. Specifically, the strength showed a gradual decrease over the first three cycles, followed by a steep decline of 63% between cycles three and six. However, as the number of cycles came closer to the termination point of 12 cycles, the decrease became smoother, averaging less than 15%.

The experimental results, as illustrated in Figure 8, depict the ratio of unconfined compressive strength at each cycle to the initial strength. The test-to-baseline strength ratios indicate a gradual decline up to three cycles, followed by a steep drop between cycles three and six. Notably, at a stabilizer content of 5%, the strength decreased by up to 43% during this period. The experiment revealed a strength change pattern that varied with the stabilizer content of the soil brick specimens. As the stabilizer content increased, the test-to-baseline strength ratio decreased. Notably, at a stabilizer content of 5%, the strength decreased by as much as 32%. However, at stabilizer contents of 10% and 15%, the strength decrease was 25% or less, which was significantly lower than the decrease observed with cementitious stabilizer (60%).

The study reveals that stabilizer content significantly affects the performance of soil brick structures under wet–dry conditions. While eco-friendly stabilized soil bricks exhibit reduced sensitivity to climate-induced effects when compared to conventional stabilizers, they are sensitive to the number of wetting–drying cycles. Thus, careful stabilizer selection is crucial for optimal performance. Overall, the study indicates that the soil bricks used in this research are considerably less susceptible to climate-induced effects than conventional stabilizers.

4.3. Dynamic Elasticity Test

Dynamic modulus of elasticity tests were performed on eco-friendly stabilized soil bricks with different stabilizer contents at each wet–dry cycle. The results, presented in Figure 9, demonstrate that the relative dynamic modulus of elasticity decreased by up to 45% at the test termination point of the 12th cycle. The experiment revealed that no significant stabilizer content-dependent changes were observed in the relative dynamic modulus of elasticity during the first three cycles. However, a steeper decrease in the relative dynamic modulus of elasticity was observed as the stabilizer content decreased after three cycles. At the 12th cycle, the relative dynamic modulus of elasticity was 1.15-fold higher at a stabilizer content of 15% compared to 5%, indicating a lower rate of decrease in the dynamic modulus of elasticity with increasing stabilizer content. These observations underscore the importance of stabilizer content in determining the dynamic behavior of eco-friendly stabilized soil bricks and provide valuable insights for their design and optimization.

4.4. Permeability Test

The permeability test, conducted in accordance with the specifications outlined in KS F 2394, aimed to determine the permeability characteristics of the soil brick [24]. The results of the test revealed a permeability coefficient for the soil brick ranging from 1.5 to 1.9 × 10⁻² cm/s. This coefficient is higher than that observed in conventional cementitious bricks. The permeability coefficient was found to increase by up to 1.13 times as the wood chip content increased from 0.5% to 1.5%, as shown in Figure 10. In contrast, an increase in the stabilizer content resulted in a decrease in the permeability coefficient by as much as 7%. Considering the quality standards stated in KS F 4419 [28], which indicate that permeable bricks should have a permeability coefficient of 0.01 cm/s and soil–concrete bricks should have a permeability coefficient of 1.0 × 10⁻³ cm/s, the soil brick employed in this study satisfies the requirement for a permeable brick.

4.5. Comfort Level of Pedestrian Walking

A golf ball (GB) and a steel ball (SB) were dropped from a height of 100 cm (H) onto the paved surface in order to evaluate the rebound characteristics of different paving materials. The resulting rebound heights were recorded. Figure 11a shows that the GB factor increased with an increase in stabilizer content, while it decreased with an increase in wood chip content. Specifically, the maximum GB factor increased 2.34-fold from 35 to 82 when the stabilizer content increased from 5% to 15%. Additionally, the GB factor decreased by up to 31% when the wood chip content increased from 0.5% to 1.5%. In conclusion, the GB test, conducted to assess walking comfort, demonstrated that lower stabilizer content and higher wood chip content resulted in better impact absorbance. According to Figure 11b, the SB factor followed a similar trend to the GB factor. It increased with higher stabilizer content and decreased as the wood chip content increased. Specifically, the maximum SB factor showed a significant increase from 9 to 18 when the stabilizer content increased from 5% to 15%. Conversely, the SB factor experienced a substantial 64% decrease when the wood chip content increased from 0.5% to 1.5%. In conclusion, the SB test, which evaluated walking comfort, revealed that lower stabilizer content and higher wood chip content resulted in improved impact absorbance, leading to a better walking experience.

It is commonly believed that the GB factor reflects impact absorbance, while the SB factor represents rebound resilience. It is widely held that smaller values of these factors correspond to a lower risk of significant bodily impact for pedestrians. The SB/GB ratio, which indicates the walking comfort level, was analyzed to compare the impact load experienced by the human body in relation to stabilizer and wood chip contents. It was found that the SB/GB ratio decreased with higher wood chip content while maintaining a constant stabilizer content, as shown in Figure 12. Notably, when conducting a comparison to 0.5% wood chip content with stabilizer content 5%, a significant decrease in the SB/GB ratio was observed at a wood chip content of 1.5%. This suggests that higher wood chip content in the soil brick leads to greater walking comfort. The analysis results indicate that the soil brick used in this study greatly improves walking comfort compared to cementitious soil paving materials by achieving lower rebound resilience (0.012–0.020) and higher impact absorbance (0.055–0.167). In conclusion, the SB/GB testing performed to assess the walking comfort level of soil bricks verifies that the soil brick used in this study has superior impact absorbance compared to cementitious bricks. It is expected to significantly reduce the impact load on the human body when used as paving material for pedestrian paths such as promenades, hiking trails, and sports facilities.

5. Conclusions

The compressive strength and strength characteristics of soil bricks made with eco-friendly stabilizer and wood chips were evaluated through unconfined compression tests, where the stabilizer and wood chip contents were varied. In addition, wetting–drying tests, permeability tests, and SB/GB tests were conducted to further assess the properties of the soil bricks. The findings of this study can be summarized as follows:

• It was found that a minimum stabilizer content of 10% and a curing period of 14 days were required to achieve a target strength of 2.0 MPa for the soil brick. An increase in the mixing ratio of the stabilizer resulted in higher unconfined compressive strength. Additionally, at a curing period of 7 days, the maximum strength achieved was 81% compared to the 28 day strength, indicating excellent early strength.
• The bending strength of the soil brick increased proportionally to the stabilizer content, and the bending strength was found to develop up to 30% of the unconfined compressive strength.
• The wetting–drying test showed that the strength of the soil brick gradually decreased over the initial 3 cycles, sharply decreased (up to 63%) between cycles 3 and 6, and decreased by up to 15% between cycles 6 and 12 (test termination), indicating its vulnerability to weather conditions. However, the strength ratio analysis indicated that the change in strength was not significant compared to conventional cement bricks.
• The dynamic elasticity test revealed that with an increased number of wetting–drying cycles, the relative dynamic modulus of elasticity decreased by up to 45%, while higher stabilizer content resulted in a smaller rate of decrease in the dynamic modulus of elasticity of the soil brick.
• The permeability test showed excellent permeability (1.5–1.9 × 10⁻² cm/s) for the soil brick. GB/SB tests revealed higher factors with increased stabilizer content (up to a 2.3-fold increase) and lower rebound resilience with lower stabilizer content and higher wood chip content, indicating better walking comfort. Further field tests are necessary to assess performance under freezing and thawing conditions.