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Article

Research on the Anti-Erosion Capacity of Aeolian Sand Solidified with Enzyme Mineralization and Fiber Reinforcement Under Ultraviolet Erosion and Freeze–Thaw Erosion

by
Jia Liu
1,
Qinchen Zhu
1,
Gang Li
1,*,
Jing Qu
1 and
Jinli Zhang
2
1
Shaanxi Key Laboratory of Safety and Durability of Concrete Structures, Xijing University, Xi’an 710123, China
2
State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(11), 5053; https://doi.org/10.3390/su17115053 (registering DOI)
Submission received: 22 April 2025 / Revised: 22 May 2025 / Accepted: 26 May 2025 / Published: 30 May 2025
(This article belongs to the Special Issue Freeze-Thaw Cycles of Rock and Soil in the Sustainable Ecological Environment and Engineering Safety)
Browse Figures
Versions Notes

Abstract

:
Aeolian sand is susceptible to wind and water erosion, which seriously restricts the ecological restoration and sustainable development in desert areas. Traditional solidification methods have characteristics of high cost, easy pollution, and unstable solidification. Enzyme-induced calcium carbonate precipitation (EICP) is an emerging method that has advantages in terms of cost-effectiveness, environmental friendliness, and durability, and, especially when coupled with fiber reinforcement (FR), it can significantly prevent brittle fracture. In this paper, ultraviolet (UV) erosion and freeze–thaw (FT) erosion tests were conducted to investigate the anti-erosion capacity of aeolian sand solidified by EICP and basalt fiber reinforcement (BFR) or wool fiber reinforcement (WFR). According to the analysis of the variation laws of sample appearance, quality losses, and unconfined compressive strength (UCS) during the UV and FT erosion process, the erosion mechanism was revealed, and the UCS models considering the damage effects were established. The research results indicated that the UCS of aeolian sand solidified by MICP and FR was significantly improved under UV and FT erosion. The strength loss rates of aeolian sand solidified by EICP, EICP–BFR, and EICP–WFR reached 45.4%, 46.6%, and 51.6%, respectively, under 90 h UV erosion. When the FT cycles reached 8, the strength loss rate of aeolian sand solidified by EICP, EICP–BFR, and EICP–WFR attained 41.0%, 49.2%, and 55.8%, respectively. The determination coefficients of the UCS models were all greater than 0.876, indicating that the experimental results were in good agreement with the predicted results, verifying the reliability of the established models. The research results can offer reference values for windproof and sand fixation in desert areas.

1. Introduction

Wind erosion is a key factor in desertification. It causes soil degradation, sand dune formation, and the appearance of desert gravel layers through surface creep, jumping, and suspension. Therefore, it seriously threatens ecological balance and economic development in desert and semi-desert areas [1,2,3]. At present, approximately 500 million people worldwide are affected by desertification, with the most populous regions being South and East Asia, North Africa, and the Middle East [4]. The results of China’s sixth national survey on desertification and desertification show that as of 2019, the area of desertified land is 2.57 × 105 km2, accounting for 26.8% of the total land area [5]. Compared with the 2014 survey results, desertification in China has gradually decreased [6], but the overall form is still severe. The traditional mechanical, biological, and chemical sand fixation methods have problems such as regional limitations, long construction periods, high costs, and environmental pollution [7,8,9]. Enzyme-induced calcium carbonate precipitation (EICP) technology, a novel biomineralization technique, has received widespread attention in desert management and soil remediation recently due to its environmentally friendly, easy-to-operate, and low-cost advantages [10,11]. EICP is not only applied in reinforcement but also in repairing high-temperature damaged concrete [12], repairing and reinforcing ancient buildings [13], and repairing contaminated soil [14]. The principle of mineralization is to extract enzymes from plants, which then catalyze the decomposition of urea into carbonate ions. Subsequently, carbonate ions combine with calcium sources in the environment to form calcium carbonate precipitates, which cement sand particles into a cohesive whole [15,16,17].
Many scholars have found that EICP technology can significantly improve sandy soil’s mechanical and erosion properties and effectively solve the disadvantages of traditional reinforced sandy soil, such as easy pollution, high cost, and the unstable curing effect. In the constant temperature test, the solidification time of EICP for aeolian sand reached 96 h, and the CaCO3 precipitation rate reached 77.7% [18]. In EICP-cured clay, the increase of 0.5 mol/L cementation concentration gradually increases the content of CaCO3, which greatly improves the UCS of rubber particles mixed with clay [19]. When EICP synergistic fibers are used to reinforce desert sand, with the increase in fiber content and urease concentration, the CaCO3 increases, and the UCS gradually increases [20]. When the EICP-reinforced soil had 16 bonding cycles, the calcium carbonate content and chemical conversion efficiency could reach 15.8% and 85.7%, respectively, reflecting high strength and good permeability [21]. During the process of reinforcing sea sand with EICP, the UCS increased, but after 15 wet–dry cycles, the UCS decreased by 63.7% [22]. Adding sodium alginate biopolymer to EICP resulted in a 100% increase in the erosion rate compared to untreated samples, demonstrating excellent resistance to wind erosion [23]. When the cementation concentration was 1.0 M, the corrosion resistance of the EICP solidified the surface sand layer in the enzyme, the 1.0 M cementation solution injections were significantly enhanced, and the content of the precipitated calcium reached 18.8% [24]. In the SEM experiments, the CaCO3 produced by EICP can effectively repair 0.35 mm cement-based materials, exhibiting a more organized and densely packed crystal structure, thereby reducing cement usage [25]. EICP has strengthened the municipal solid waste cultivation bottom ash (MSWIBA), improved its shear strength, elastic modulus, and permanent deformation, and reduced environmental impact [26]. In microexperiments, it was found that EICP produced many calcite crystals, and the enhanced particle binding resulted in a tighter soil skeleton, improving wind erosion resistance [27].
EICP technology significantly improves sand strength, and coupling it with fiber reinforcement (FR) can effectively prevent brittle fracture. However, the erosion capacity of sand subject to ultraviolet (UV) and freeze–thaw (FT) erosion needs further exploration. This paper explores the changes in sample appearance, quality loss, and UCS during UV erosion testing. Based on the results of UV and FT experiments, the erosion mechanism was revealed, and the model was established, with determination coefficients of the UCS models all greater than 0.876, indicating that the experimental results were in good agreement with the predicted results, verifying the reliability of the established models. The research results provide a scientific basis for sand fixation in desert areas.

2. Materials and Methods

2.1. Test Materials

The experimental enzyme extraction was obtained from soybeans (Suihua City, Heilongjiang Province). The soybeans were crushed and sieved using a grinder, and deionized water was added to prepare a 100 g/L mixture. The mixture was then stirred for 30 min using a magnetic stirrer to obtain the soybean liquid. The soy sauce was centrifuged at a speed of 400 r/min for 15 min using a high-speed centrifuge, and the supernatant was removed from the centrifuge tube to obtain enzyme. The curing solution consists of calcium chloride solution and urea solution. Calcium chloride and urea solution are uniformly prepared with deionized water in the presence of anhydrous calcium chloride and urea, with a concentration of 1.25 mol/L. As shown in Figure 1 and Figure 2, the primary material used in this experiment, aeolian sand, was taken from the Maowusu Desert in Yulin City, Shanxi Province. Aeolian sand is yellow, free of impurities, and has a uniform texture. The basalt fiber (BF) and Australian sheep wool fiber (WF) used in the experiment were produced in Suihua City, Heilongjiang Province, and Tongliao City, Inner Mongolia, respectively. Basalt fiber, characterized by its sleek brown or antique bronze surface, is a novel inorganic, eco-friendly, and high-performance fiber material. Wool fiber is milky white, a natural protein fiber often clustered together and exhibiting good softness, elasticity, and wear resistance. The physical properties of aeolian sand were tested strictly by the “Standard for Soil Test Methods” (GB/T 50123-2019) [28], and the non-uniformity coefficient Cu and the curvature coefficient Cc of aeolian sand were calculated to be 2.30 and 0.85, respectively. Aeolian sand can be classified as poorly graded fine sand. Table 1 shows the fundamental physical property indicators of the aeolian sand used in the experiment.

2.2. Sample Preparation

According to the “Standard for Soil Test Methods” (GB/T 50123-2019) [28], during the preparation process of enzyme mineralization combined with fiber-reinforced aeolian sand, a semi-separable PVC pipe with an inner diameter of 39.1 mm and a height of 150 mm was selected. The PVC pipe connection was fixed with a hot melt glue gun, the bottom of the pipe was blocked with a rubber stopper, and a small hole was reserved for the solution to flow out. The aeolian sand was mixed evenly with fibers (based on the experimental results, basalt fiber and wool fiber content of 0.75% of the total sample mass, basalt fiber length of 6 mm, and wool fiber length of 9 mm), and then they were divided into four layers and loaded into the mold. A layer of Vaseline on the inner wall of the mold was applied, and a layer of filter paper was placed at the bottom of the sample. The experimental urease extraction was obtained from soybeans (origin: Suihua City, Heilongjiang Province). The soybeans were crushed and sieved using a grinder, and deionized water was added to prepare a 100 g/L mixture. The mixture was then stirred for 30 min using a magnetic stirrer to obtain the soybean liquid. We centrifuged the soy sauce at a speed of 400 r/min for 15 min using a high-speed centrifuge, and we removed the supernatant from the centrifuge tube to obtain urease. The curing solution consists of calcium chloride solution and urea solution. Calcium chloride and urea solution are uniformly prepared with deionized water in the presence of anhydrous calcium chloride and urea, with a concentration of 1.25 mol/L. After the sample preparation, a two-stage method injects enzyme and curing solutions into the sample. A specific volume of enzyme solution is first injected according to the enzyme gel ratio set in the plan. After the solution is wholly immersed, 10 mL of calcium chloride and 10 mL of urea solution are injected. After 24 h, the next round of injections is carried out. After completing all infusion cycles and reaching the settling time, we rinsed the sample with deionized water three times to terminate the internal reaction. After completion, we removed the mold and placed the sample in an 80 °C oven for 36 h for drying treatment. The specific sample preparation process is shown in Figure 3.

2.3. Test Methods

According to solar shortwave radiation conversion, 1 W/m2 = 31.536 MJ/m2/year. As shown in Table 2, based on the basic meteorological data of Yulin, Shanxi Province, in the China Meteorological Yearbook 1986–2022, it was found that the annual total solar radiation in desert areas was about 10% higher than that in areas of the same latitude. The calculated annual solar radiation in the Mu Us Desert area was 5127.8 × (1 + 10%) = 5640.58 MJ/m2. Because the total amount of ultraviolet radiation is about 7% of the total amount of solar radiation, the annual ultraviolet radiation in the Mu Us Desert area is about 394.84 MJ/m2. The experiment is based on the energy equivalence principle: the annual natural ultraviolet radiation = annual indoor ultraviolet radiation = indoor ultraviolet box irradiation intensity x irradiation duration. The ultraviolet erosion test of this experiment is conducted, and the ultraviolet irradiation box irradiation intensity is 0.68 W/m2/340 nm. The irradiation amount in the box for 1 h is 0.68 × 31.536 = 21.44 MJ/m2, and it takes about 18.42 h to achieve the natural annual average ultraviolet irradiation amount. For the convenience of the experiment, 18 h were selected for the test.
The UV erosion test in the experiment was conducted in a QUV UV aging test chamber (Shenzhen Xinmingfan Technology Co., Ltd., Shenzhen, China). Two UVA-340 type lamps are installed on the top of the test chamber, which can emit an ultraviolet light that simulates the solar spectrum. The wavelength range is between 315 nm and 400 nm, with a peak wavelength of 340 nm, similar to the peak intensity of sunlight at noon in summer, effectively simulating the sunlight conditions at noon in summer. The illumination intensity of the lamp tube is set to 0.68 W/m²/nm, and the closest parallel distance to the surface of the lamp tube is approximately 50 mm. According to the preset exposure standard, the test chamber can simulate a year’s ultraviolet exposure by working continuously for 18 h, which is 21.44 × 18 = 385.92 MJ/m². The experimental plan is shown in Table 3. A total of 21 experiments were conducted, and each experiment had a replicate group.

3. Results and Analysis of UV Erosion Test

3.1. Analysis of Sample Appearance

The apparent condition has a significant impact on UV erosion testing. Table 4 shows the state of EICP synergistic fiber-reinforced solidification under aeolian sand UV erosion. The table shows that the original sample (0 h) cured well, with a uniform and normal surface without apparent unevenness, accompanied by a small amount of CaCO3 crystal precipitation. Compared with the original sample, the EICP-cured aeolian sand sample exhibited a large amount of CaCO3 crystal precipitation on the surface after 18 h of UV irradiation, and the UV irradiation had no significant effect on the appearance of the EICP-cured aeolian sand sample. However, ultraviolet irradiation for 36–90 h had no significant effect on the appearance of aeolian sand samples cured by EICP. When the aeolian sand samples cured by EICP–BFR were exposed to ultraviolet light for 18–36 h, there was no noticeable change on the surface of the samples. After the aeolian sand cured by EICP–BFR was subjected to ultraviolet erosion for 72–90 h, the surface shedding slag increased, and pores were visible. Compared with the original samples, the wind–sand samples cured by EICP–WFR showed the most severe apparent erosion. There was no noticeable change in the sample after ultraviolet irradiation from 0 to 16 h. When the self-irradiation time starts at 36 h, the color of the sample gradually deepens. When the duration of ultraviolet erosion reached 90 h, more severe holes appeared on the surface of the sample than those of the aeolian sand sample cured by EICP–BFR, and it became rough compared with the original sample. This situation is because, under ultraviolet erosion conditions, ultraviolet rays significantly impact the CaCO3 crystals on the surface of the sample. Among them, the main component of wool fibers is protein, which is prone to deterioration under ultraviolet radiation. The “flake structure” on the surface of wool fibers will be gradually eroded under ultraviolet erosion, and the surface will become smooth, causing the CaCO3 crystals and sand particles attached to the surface to fall off the sample together without a point of contact. This is also the most important reason for the most severe erosion phenomenon on the surface of aeolian sand samples cured by EICP–WFR. This is consistent with the research conclusion in [29], which is that in UV erosion tests, the surface of the sample will be eroded and damaged as the erosion time increases. However, the difference is that (Microbially Induced Carbonate Precipitation) MICP technology is used to reinforce aeolian sand in the literature, which requires the consideration of many factors for microbial cultivation.

3.2. Analysis of Quality Losses

Quality losses can reflect the degree of damage caused by ultraviolet erosion to the sample. Figure 4 shows the variation curve of the mass loss of aeolian sand cured by EICP synergistic fiber reinforcement with UV erosion duration. As shown in the figure, the mass loss of the three samples increases continuously with the increase in UV erosion duration. The experiment considered that there is a specific drying effect due to the close-range irradiation of the lamp tube, and the reason for the mass loss of the sample is most likely due to the evaporation of internal moisture. When the erosion time is 6 h, the moisture evaporation is complete, and, at this time, the mass of the aeolian sand samples solidified by EICP, EICP–BFR, and EICP–WFR is lost by 20.33 g, 18.43 g, and 20.16 g, respectively. When subjected to UV erosion for up to 90 h, the mass loss of aeolian sand samples cured by EICP, EICP–BFR, and EICP–WFR was 26.96 g, 27.64 g, and 33.14 g, respectively. From this, it can be concluded that the mass loss of the sample, mainly under UV erosion, is 6.63 g for EICP, 9.21 g for EICP–BFR, and 12.98 g for EICP–WFR. This is because the radiation erosion of ultraviolet radiation affects the CaCO3 crystals on the sample’s surface, resulting in a decreased bonding ability of CaCO3. Therefore, the reason for the quality loss of the sample comes from the detachment of sand particles and CaCO3 crystals. The EICP–BFR-cured aeolian sand sample also has the detachment of basalt fibers so the quality loss is greater than that of the EICP-cured aeolian sand sample. The main component of wool fiber is protein, and the EICP–WFR-cured aeolian sand sample is most severely eroded under UV irradiation, resulting in the highest quality loss. In Ref. [30], it is pointed out that in UV testing, the initial quality loss may be due to water evaporation caused by the heating of ultraviolet lamps. However, the difference is that the literature explores the effect of a strong ultraviolet radiation environment on the shrinkage deformation of cement paste. Ref. [31] points out that UV erosion can weaken the ability of CaCO3 to bond soil particles in MICP-reinforced soil. However, the difference is that MICP technology heavily relies on specific temperature and humidity conditions for microbial cultivation environments.

3.3. Analysis of UCS

The change in intensity is an important indicator of the degree of ultraviolet erosion. Figure 5 shows a bar chart of the variation of the UCS of aeolian sand reinforced with EICP fibers with UV erosion duration. The ratio of the difference between the UCS value of the sample after UV erosion and the UCS value of the control group to the UCS value of the control group is defined as the UCS loss rate of the sample under UV erosion, represented by β1, as shown in Equation (1).
β 1 = q 1 q 0
In which, β1—strength loss rate; q1—the difference between the UCS value of the sample after erosion and the UCS value of the control group, kPa; q0—the UCS value of the control group, kPa.
The larger the β1, the smaller the UCS value of the sample after UV erosion, and the worse the sample’s resistance to UV erosion. Conversely, the sample’s resistance to UV erosion is better. As shown in Figure 5, the UCS of the three samples decreases continuously with the increase in UV erosion duration, and β1 gradually increases, indicating that the anti-UV erosion performance of the samples is worsening. Among them, when the UV erosion duration was 90 h, the UCS of the aeolian sand sample cured by EICP was 285.85 kPa, with a strength loss rate of 45.4% compared to the control group of 523.19 kPa. The UCS of the aeolian sand sample cured by EICP–BFR was 519.72 kPa, with a strength loss rate of 46.6% compared to the control group of 972.83 kPa. The UCS of the aeolian sand sample cured by EICP–WFR was 488.64 kPa, with a strength loss rate of 51.6% compared to the control group of 1010.42 kPa. The reason for this situation is that under UV irradiation, the internal pores of the sample will change, and CaCO3 crystals will appear with pores, which proves that long-term UV irradiation weakens the performance of CaCO3 and reduces its bonding ability, resulting in a decrease in the UCS of the cured sample. Among them, with the increase in UV erosion duration, wool fibers are most affected because the “scale tissue” on the fiber surface is destroyed, and the original frictional advantage between the fiber and sand particles is no longer significant, resulting in a loss of its tensile strength. Among them, the UV erosion test mainly leads to the destruction of the internal structure of EICP and the increase in internal voids, which is consistent with the conclusion of the literature [32]. However, the difference is that the literature also points out the potential environmental pollution problem for MICP technology, while EICP technology relatively does not have this problem. Ref. [33] points out that in the UV erosion test, the surface roughness of wool fibers decreases. However, the difference is that the results of UV erosion on wool in the literature benefit the dyeing process.

3.4. Analysis of UV Erosion Mechanism

To analyze the mechanism of EICP and EICP synergistic FR solidification of aeolian sand under UV erosion environment, as well as the changes in the action mode of CaCO3 crystals before and after UV erosion, Figure 6 shows the schematic diagram of the UV erosion process of aeolian sand. As shown in the figure, for the aeolian sand sample solidified by EICP, the CaCO3 crystals generated by EICP have their CaCO3 bonding surface, filling, and coating effects destroyed by ultraviolet radiation. The CaCO3 crystals bonded and filled between the sand particles fracture and peel off, and the CaCO3 crystals covering the surface of the sand particles show noticeable pores [34]. After adding BFR and WFR to EICP, more nucleation sites can be provided for the generation of CaCO3 crystals, and CaCO3 crystals are more “anchored” near the fibers, resulting in significantly higher strength of aeolian sand solidified by EICP synergistic fiber reinforcement than by EICP. However, after UV erosion, when CaCO3 crystals break due to increased porosity, they will also detach along with the fibers. Unlike basalt fiber, wool fiber undergoes changes in its surface “scale” structure under ultraviolet irradiation, from rough to smooth [35]. The CaCO3 crystals attached to it not only have pores but also fall off directly due to the deterioration of wool fiber α—keratin, and this is the main reason for the maximum loss of aeolian sand strength caused by the solidification of EICP–WFR.

3.5. UCS Model Establishment and Verification

By comparing the UCS test results of aeolian sand specimens cured with EICP, EICP–BFR, and EICP–WFR with the control group, it can be seen that the influence of UV erosion is significant, and the UCS of the three specimens decreases continuously with the increase in UV erosion duration. The main consideration is establishing the UCS model for cured aeolian sand specimens under UV erosion conditions, considering the influence of UV erosion duration. Assuming the duration of UV erosion as a variable, the UCS of solidified aeolian sand is assumed to be as follows:
U = f ( t Z )
In which, U—UCS of cured aeolian sand after UV erosion, kPa; tZ—UV erosion duration, h.
Because the UCS of aeolian sand specimens after UV erosion decreases with increasing tZ, the relationship between the two can be expressed as a linear function:
U = x t z + y
In which, x is a parameter related to tZ; Y is a constant, which can be obtained through regression analysis.
Figure 7 shows the relationship curves between UE, UB1, UW1, and tZ, while Table 5 presents the parameter values for the three samples. As shown in Figure 6 and Table 5, the model’s determination coefficients reached 0.936, 0.970, and 0.876, respectively, indicating strong correlations between UE, UB1, UW1, and tZ. We substituted the existing data and obtained parameters x and y into Equation (3) to calculate the UCS (UE, UB1, and UW1) that varies with tZ. Figure 8 compares the measured and calculated values of UCS of aeolian sand specimens concerning tZ after UV erosion. The experimental results indicate that the calculated results of the experimental model have a high degree of agreement with the experimental data.

4. Results and Analysis of Freeze–Thaw Erosion Test

4.1. Analysis of Sample Appearance

The apparent condition has a significant impact on freeze–thaw erosion tests. Table 6 shows the observable condition changes under the freeze–thaw erosion of aeolian sand reinforced with EICP fibers. As shown in the table, EICP-cured aeolian sand underwent four freeze–thaw cycles, aeolian sand shedding. When subjected to eight freeze–thaw cycles, cracks appeared in the sample. When subjected to 12 freeze–thaw cycles, after being lightly touched, the sample fractured. The EICP–BFR-curled aeolian sand underwent eight freeze–thaw cycles, with a slight shedding of aeolian sand. When subjected to 12 freeze–thaw cycles, cracks appeared in the sample. When subjected to 16 freeze–thaw cycles, the sample fractured. Therefore, only partial results are reported in the table and subsequent test results. EICP–WFR-cured aeolian sand underwent 12 freeze–thaw cycles, aeolian sand shedding. When subjected to 16 freeze–thaw cycles, cracks appeared in the sample. When subjected to 20 freeze–thaw cycles, the sample fractured. The above reasons are under the freeze–thaw erosion environment; as the number of freeze–thaw cycles increases, the water inside the sample will crystallize and expand, and the volume will increase. This affects the CaCO3 crystal detachment inside the sample; the aeolian sand sample cured by EICP–BFR is more resistant to damage than the aeolian sand sample cured by EICP due to the tension and interlocking of basalt fibers inside, while the aeolian sand sample cured by EICP–WFR relies on the advantage of the rough surface of wool fibers so it is relatively more resistant to damage. This is consistent with the results of the frost heave force generated by the sample in the freeze–thaw cycle in Ref. [36], but the difference is that the research object of the reference is the surrounding rock. Ref. [37] points out that as the number of freeze–thaw cycles increases, the pore size distribution inside the sample becomes more discrete, but the difference is that the research object of the reference is foam concrete.

4.2. Analysis of Quality Losses

Quality loss can reflect the degree of damage caused by freeze–thaw erosion to the sample. Figure 9 shows the mass change curve of fiber-reinforced EICP-solidified aeolian sand sample loss under freeze–thaw cycles. As shown in the figure, when the freeze–thaw cycle is 12 times, the maximum mass loss of the EICP-cured aeolian sand sample is 5.85 g; when the freeze–thaw cycle is 16 times, the mass loss of the EICP–BFR-cured aeolian sand sample is 2.93 g, and when the freeze–thaw cycle is 20 times, the minimum mass loss of the EICP–WFR-cured aeolian sand sample is 2.69 g. The maximum mass loss of EICP-cured aeolian sand samples is because, after freeze–thaw erosion, due to water phase changes and migration, the internal structure of the samples will change [38], while EICP-FR-cured aeolian sand samples have the load-bearing effect of fibers inside, which to some extent reduces the erosion phenomenon of the samples [39]. As a result, the surface of wool fiber is rougher than that of basalt fiber, which increases the friction with sand particles and CaCO3 crystals. Therefore, the EICP–WFR-cured aeolian sand sample has the most minor mass loss. This situation is because, during the freeze–thaw cycle, the water inside the sample freezes and expands, causing an increase in volume. The freeze–thaw force is generated at this time, and the sand particles are squeezed tightly. The bonding ability of CaCO3 crystals between particles is weakened and even broken and deformed. When the temperature rises to the point where the ice begins to melt, the liquid water slowly migrates, causing disturbance and structural reorganization [40].

4.3. Analysis of UCS

The change in intensity is an important indicator of the degree of ultraviolet erosion. Figure 10 shows a bar chart of the variation of the UCS of the aeolian sand specimen reinforced with EICP fibers with freeze–thaw cycles. The ratio of the difference between the UCS value of the sample after freeze–thaw erosion and the UCS value of the control group to the UCS value of the control group is defined as the UCS loss rate of the sample under freeze–thaw erosion, represented by β2. As shown in the figure, the UCS of the three samples decreases continuously with the increase in freeze–thaw cycles. On the other hand, the progressive increase in β2 indicates a growing deterioration in the samples resistance to freeze–thaw erosion, indicating that the anti-freezing sample sand thawing erosion performance is worsening. At eight freeze–thaw cycles, the UCS of the aeolian sand sample cured by EICP was 265.76 kPa, with a loss rate of 41.0% compared to the control group at 450.18 kPa. At 12 freeze–thaw cycles, the UCS of the aeolian sand sample cured by EICP–BFR was 465.78 kPa, with a loss rate of 49.2% compared to the control group at 916.27 kPa. At 16 freeze–thaw cycles, the UCS of the aeolian sand sample cured by EICP–WFR was 433.15 kPa, with a loss rate of 55.8% compared to the control group of 980.15 kPa. This situation is because freeze–thaw erosion mainly changes the stability and content of sand particle aggregates, thereby damaging the basic internal structure of the sample [41]. After being subjected to freeze–thaw cycles, the internal structure of EICP-cured aeolian sand was damaged, and CaCO3 crystals detached from the sand particles, affecting the curing effect and decreasing the sample’s strength. This is consistent with the research conclusion of reference. Ref. [42] indicates that in the FT cycle test, the UCS of the specimen decreases, but the difference is that the literature uses EICP-reinforced soil.

4.4. Analysis of Freeze–Thaw Erosion Mechanism

To analyze the mechanism of aeolian sand solidification by EICP, EICP–BFR, and EICP–WFR under a freeze–thaw erosion environment, Figure 11 shows the schematic diagram of the freeze–thaw erosion process of aeolian sand solidification by EICP, EICP–BFR, and EICP–WFR. As can be seen from the figure, after freeze–thaw erosion, the aeolian sand sample solidified by EICP showed significant cracks between the CaCO3 crystals that were initially bonded to the surface and between the sand particles [43]. The aeolian sand sample reinforced and solidified with EICP fibers has a fiber-bearing effect inside so the CaCO3 crystals attached to the fibers will first detach, which partially mitigates erosion of the sample. The surface of wool fiber is rougher than that of basalt fiber, resulting in a better reinforcement effect of EICP–WFR than EICP–BFR. At the same time, the diameter of wool fiber is more evident than basalt fiber, which also leads to a better reinforcement effect of EICP–WFR than EICP–BFR. This is because, during the freezing process, the water inside the sample will crystallize and expand, increasing the volume and forcing the CaCO3 crystals to detach from the sand particles or fibers. Therefore, this affects the solidification effect of CaCO3 inside the sample, leading to cracks or even fractures and affecting the overall strength of the sample [44].

4.5. UCS Model Establishment and Verification

Both linear and logarithmic models were tested to demonstrate the linear trend of UCS and erosion frequency and to capture the different attenuation patterns of material strength in the early and late stages of erosion frequency. We compared and analyzed the UCS test results of aeolian sand samples cured by EICP–BFR and EICP–WFR with the control group and established a model for the UCS of aeolian sand cured by EICP synergistic fiber reinforcement under freeze–thaw erosion conditions. The primary consideration is the number of freeze–thaw cycles, and the assumed UCS of the solidified aeolian sand is as follows:
U = f ( n D )
In which, U—the UCS of solidified aeolian sand after freeze–thaw erosion, kPa; nD—the number of freeze–thaw cycles.
Because the UCS of aeolian sand specimens decreases with increasing nD after freeze–thaw erosion, the relationship between the two can be expressed as linear and logarithmic functions, respectively:
U B 2 = x 1 n D + c 1
U W 2 = x 2 ln ( n D + y ) + c 2
In which, UB2—the UCS of EICP–BFR-cured aeolian sand specimens under freeze–thaw erosion, kPa; UW2—the UCS of EICP–WFR-cured aeolian sand specimens under freeze–thaw erosion, kPa; x1, x2, and y are parameters related to nD; c1 and c2 are constants that can be obtained through regression analysis.
Figure 11 shows the relationship curves between UB2, UW2, and nD, and Table 7 shows the parameter values of the two sample models. Figure 12 and Table 7 show that the determination coefficients reached 0.998 and 0.927, respectively, indicating strong correlations between UB2, UW2, and nD. We substitute the existing data and obtained parameters x1, x2, y, c1, and c2 into Equations (5) and (6) and calculate the UCS UB2 and UW2 of EICP–BFR and EICP–WFR-cured aeolian sand samples after freeze–thaw erosion. Figure 13 compares the aeolian sand samples calculated and measured UCS values after freeze–thaw erosion and changes with nD. The experimental results indicate that the calculated results of the experimental model have a strong agreement with the experimental data. The model results established by Ref. [45] under freeze–thaw cycles are consistent. As the number of cycles increases, the sample’s UCS decreases. However, the difference is that the literature did not consider comparing the model’s calculated results with the experimental results.

5. Conclusions

The control of desertification and soil loss is of great significance to the ecological environment. In this paper, the ultraviolet (UV) erosion and freeze–thaw (FT) erosion tests were conducted to investigate the anti-erosion capacity of aeolian sand solidified by EICP and basalt fiber reinforcement (BFR) or wool fiber reinforcement (WFR). Based on the test results, the erosion mechanism of UV and FT was revealed, and the UCS models considering the damage effects were established. The main conclusions are as follows:
  • Under UV erosion, the apparent conditions of the three samples show different patterns with the increase in ultraviolet erosion duration. After 18 h, a large amount of CaCO3 crystals precipitated on the surface of the EICP sample, but there was no significant effect on the appearance of the sample with increasing time. After 36 h, sand particles and CaCO3 crystals fell off the surface of the EICP–BFR sample. After 36 h, the color of the EICP–WFR sample gradually deepened, and the sand particles, CaCO3 crystals, and wool fibers on the sample’s surface gradually fell off.
  • Under UV erosion, the mass loss of the three samples increases continuously with the increase in UV erosion duration. When the UV erosion duration was 90 h, the mass loss measurements of the aeolian sand samples cured by EICP, EICP–BFR, and EICP–WFR were 26.96 g, 27.64 g, and 33.14 g, respectively. Due to the leading cause of mass loss in the early stage of the sample being the evaporation of internal moisture, the mass lost under UV erosion was 6.63 g for EICP, 9.21 g for EICP–BFR, and 12.98 g for EICP–WFR.
  • Under UV erosion, the UCS of the three samples decreases continuously with increased ultraviolet erosion duration. At UV erosion duration of 90 h, the UCS of the aeolian sand specimens cured with EICP, EICP–BFR, and EICP–WFR reached 285.85 kPa, 519.72 kPa, and 488.64 kPa, respectively. Compared to the UCS of the control group, the loss rates were 45.4%, 46.6%, and 51.6%, respectively.
  • Under FT erosion, the apparent conditions of the three samples showed the phenomenon of sand particle detachment and CaCO3 crystal slagging in the freeze–thaw erosion test. When the EICP-cured aeolian sand sample reaches 12 freeze–thaw cycles and the EICP–BFR-cured aeolian sand sample reaches 16 freeze–thaw cycles, cracks or fractures may occur upon light touch. The EICP–WFR-cured aeolian sand sample relies on the advantage of the rough surface of wool fibers and is the least susceptible to erosion and damage.
  • Under FT erosion, the mass loss of the three samples increases continuously with the increase in freeze–thaw cycles. When the number of freeze–thaw cycles is 12, the maximum mass loss of the EICP-cured aeolian sand sample is 5.85 g; when the number of freeze–thaw cycles is 16, the mass loss of the EICP–BFR cured aeolian sand sample is 2.93 g; when the number of freeze–thaw cycles is 20, the mass loss of the EICP–WFR-cured aeolian sand sample is 2.69 g.
  • Under FT erosion, the UCS of the three specimens decreases continuously with the increase in freeze–thaw cycles. When subjected to eight freeze–thaw cycles, the UCS of the aeolian sand specimen cured by EICP was 265.76 kPa; when subjected to 12 freeze–thaw cycles, the UCS of the aeolian sand specimen cured by EICP–BFR was 465.78 kPa; when subjected to 16 freeze–thaw cycles, the UCS of the aeolian sand specimen cured by EICP–WFR was 433.15 kPa. The loss rates of the UCS of the three samples relative to the control group were 41.0%, 49.2%, and 55.8%, respectively.
  • Based on the UV erosion and FT erosion tests, the UCS model considering the damage effects was established, respectively. The determination coefficients of the UCS models were more than 0.876, indicating that the test results were in good agreement with the predicted results and verifying the reliability of the established models.
  • The experimental process of EICP collaborative fiber reinforcement for aeolian sand is limited to the indoor testing stage. Due to the complexity and variability of the desert environment, this technology has not yet been applied in practical conditions. Looking ahead, whether the EICP collaborative fiber reinforcement method is suitable for on-site environments will become the main research direction. This has profound implications for the stability or environmental restoration of sand dune edges.

Author Contributions

Conceptualization, G.L. and J.L.; methodology, G.L. and J.L.; validation, J.Q. and J.Z.; writing—original draft, Q.Z.; writing—review and editing, Q.Z.; funding acquisition, G.L. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the Scientific Research Program Funded by Education Department of Shaanxi Provincial Government (23JS061) and the Special Fund for Scientific Research by Xijing University (XJ24B11).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data generated or analyzed during this study are included in this published article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Experimental materials: (a) aeolian sand; (b) basalt fiber; (c) wool fiber.
Figure 1. Experimental materials: (a) aeolian sand; (b) basalt fiber; (c) wool fiber.
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Figure 2. The geographical location of aeolian sand.
Figure 2. The geographical location of aeolian sand.
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Figure 3. Flow chart of sample preparation: (a) weigh aeolian sand; (b) add fibers; (c) stir evenly; (d) load into mold; (e) inject enzyme solution; (f) inject calcium chloride solution; (g) inject urea solution; (h) form removal; (i) high-temperature drying; (j) retain as a backup.
Figure 3. Flow chart of sample preparation: (a) weigh aeolian sand; (b) add fibers; (c) stir evenly; (d) load into mold; (e) inject enzyme solution; (f) inject calcium chloride solution; (g) inject urea solution; (h) form removal; (i) high-temperature drying; (j) retain as a backup.
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Figure 4. Variation curve of quality loss of aeolian sand with UV erosion duration.
Figure 4. Variation curve of quality loss of aeolian sand with UV erosion duration.
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Figure 5. Variation curve of UCS of aeolian sand with UV corrosion duration: (a) EICP; (b) EICP–BFR; (c) EICP–WFR.
Figure 5. Variation curve of UCS of aeolian sand with UV corrosion duration: (a) EICP; (b) EICP–BFR; (c) EICP–WFR.
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Figure 6. Schematic diagram of UV erosion process of aeolian sand.
Figure 6. Schematic diagram of UV erosion process of aeolian sand.
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Figure 7. Relationship curve between UE, UB1, UW1, and tZ.
Figure 7. Relationship curve between UE, UB1, UW1, and tZ.
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Figure 8. Comparison between UCS measured and calculated values under UV erosion.
Figure 8. Comparison between UCS measured and calculated values under UV erosion.
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Figure 9. Variation curve of quality loss of aeolian sand with the number of freeze–thaw cycles.
Figure 9. Variation curve of quality loss of aeolian sand with the number of freeze–thaw cycles.
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Figure 10. Variation curve of UCS of aeolian sand with the number of freeze–thaw cycles: (a) EICP; (b) EICP–BFR; (c) EICP–WFR.
Figure 10. Variation curve of UCS of aeolian sand with the number of freeze–thaw cycles: (a) EICP; (b) EICP–BFR; (c) EICP–WFR.
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Figure 11. Schematic diagram of freeze–thaw erosion process of aeolian sand.
Figure 11. Schematic diagram of freeze–thaw erosion process of aeolian sand.
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Figure 12. Relationship curves between UB2, UW2, and nD.
Figure 12. Relationship curves between UB2, UW2, and nD.
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Figure 13. Comparison between UCS measured and calculated values under freeze–thaw erosion.
Figure 13. Comparison between UCS measured and calculated values under freeze–thaw erosion.
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Table 1. Fundamental physical properties of aeolian sand.
Table 1. Fundamental physical properties of aeolian sand.
Specific Gravity GsDensity ρ (g/cm3)Water Content w (%)Void Ratio ePlastic Limit wP (%)Liquid Limit wL (%)Plasticity Index IPCoefficient of Uniformity CuCoefficient of Curvature Cc
2.651.592.600.6719.625.05.42.300.85
Table 2. Basic meteorological data of Yulin City, Shaanxi Province.
Table 2. Basic meteorological data of Yulin City, Shaanxi Province.
AreaAnnual Mean
Temperature (°C)		Sunshine Duration
(h)		Sun Annual
Exposure level
(MJ/m2)		Ultraviolet Ray Annual
Exposure Level
(MJ/m2)
Yulin, Shaanxi8.527505127.8358.95
Table 3. UV erosion test scheme.
Table 3. UV erosion test scheme.
Sample TypeDuration of Irradiation (h)Exposure (MJ/m2)
EICP
EICP–BFR
EICP–WFR		18385.92
36771.84
541157.76
721543.68
901929.60
Table 4. Appearance of aeolian sand treated by EICP and FR under UV erosion.
Table 4. Appearance of aeolian sand treated by EICP and FR under UV erosion.
Aeolian SandErosion Time
0 h18 h36 h54 h72 h90 h
EICPSustainability 17 05053 i001Sustainability 17 05053 i002Sustainability 17 05053 i003Sustainability 17 05053 i004Sustainability 17 05053 i005Sustainability 17 05053 i006
EICP–BFRSustainability 17 05053 i007Sustainability 17 05053 i008Sustainability 17 05053 i009Sustainability 17 05053 i010Sustainability 17 05053 i011Sustainability 17 05053 i012
EICP–WFRSustainability 17 05053 i013Sustainability 17 05053 i014Sustainability 17 05053 i015Sustainability 17 05053 i016Sustainability 17 05053 i017Sustainability 17 05053 i018
Table 5. Parameter values of the UCS model under UV erosion.
Table 5. Parameter values of the UCS model under UV erosion.
SamplexyR2
EICP−2.43507.550.9356
EICP–BFR−4.74996.870.9702
EICP–WFR−5.861036.310.8764
Table 6. Appearance of aeolian sand treated by EICP and FR under FT erosion.
Table 6. Appearance of aeolian sand treated by EICP and FR under FT erosion.
Aeolian SandNumber of Freeze–Thaw Cycles
0 Times4 Times8 Times12 Times16 Times20 Times
EICPSustainability 17 05053 i019Sustainability 17 05053 i020Sustainability 17 05053 i021Sustainability 17 05053 i022------
EICP–BFRSustainability 17 05053 i023Sustainability 17 05053 i024Sustainability 17 05053 i025Sustainability 17 05053 i026Sustainability 17 05053 i027---
EICP–WFRSustainability 17 05053 i028Sustainability 17 05053 i029Sustainability 17 05053 i030Sustainability 17 05053 i031Sustainability 17 05053 i032Sustainability 17 05053 i033
Table 7. Parameter values of UCS model under freeze–thaw erosion.
Table 7. Parameter values of UCS model under freeze–thaw erosion.
Samplex(1,2)yc(1,2)R2
EICP–BFR−36.76—904.000.9977
EICP–WFR−11,328.82344.1267132.670.9272
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Liu, J.; Zhu, Q.; Li, G.; Qu, J.; Zhang, J. Research on the Anti-Erosion Capacity of Aeolian Sand Solidified with Enzyme Mineralization and Fiber Reinforcement Under Ultraviolet Erosion and Freeze–Thaw Erosion. Sustainability 2025, 17, 5053. https://doi.org/10.3390/su17115053

AMA Style

Liu J, Zhu Q, Li G, Qu J, Zhang J. Research on the Anti-Erosion Capacity of Aeolian Sand Solidified with Enzyme Mineralization and Fiber Reinforcement Under Ultraviolet Erosion and Freeze–Thaw Erosion. Sustainability. 2025; 17(11):5053. https://doi.org/10.3390/su17115053

Chicago/Turabian Style

Liu, Jia, Qinchen Zhu, Gang Li, Jing Qu, and Jinli Zhang. 2025. "Research on the Anti-Erosion Capacity of Aeolian Sand Solidified with Enzyme Mineralization and Fiber Reinforcement Under Ultraviolet Erosion and Freeze–Thaw Erosion" Sustainability 17, no. 11: 5053. https://doi.org/10.3390/su17115053

APA Style

Liu, J., Zhu, Q., Li, G., Qu, J., & Zhang, J. (2025). Research on the Anti-Erosion Capacity of Aeolian Sand Solidified with Enzyme Mineralization and Fiber Reinforcement Under Ultraviolet Erosion and Freeze–Thaw Erosion. Sustainability, 17(11), 5053. https://doi.org/10.3390/su17115053

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