Chitin-silicon-calcium-based modified material for repairing rammed earth wall and weather resistance evaluation method of chitin-silicon-calcium-based modified material

Abstract

The invention discloses a chitin-silicon-calcium-based modified material for rammed earth wall repair and a weather resistance evaluation method thereof, and belongs to the technical field of rammed earth wall repair, the chitin-silicon-calcium-based modified material comprises metakaolin, calcium oxide, quartz and chitin; the ratio of chitin to metakaolin to calcium oxide to quartz is 1: 1: 2: 4; the method comprises the following steps: pre-treating at the earlier stage of a test, evaluating freeze-thaw cycle performance, evaluating dry-wet cycle performance, evaluating salt corrosion resistance, analyzing association between a microstructure and a strength performance, and finally, revealing a material degradation rule and mechanism by combining scanning electron microscope observation, unconfined compressive strength test and crack rate analysis. When the freezing and thawing cycle number N is less than or equal to 5, the dry and wet cycle number I is less than or equal to 9, and the salt solution concentration c is less than or equal to 0.3 mol / L, the characteristics of freezing and thawing resistance, dry and wet resistance, salt erosion resistance and the like of the modified material are obviously improved; after the modified material is added, internal pores of plain soil can be filled, unconfined compressive strength of a soil body is enhanced, and long-term durability of the soil body is improved.

Description

Technical Field

[0001] This invention relates to the field of rammed earth wall repair technology, and in particular to chitosan-silicon-calcium-based modified materials for rammed earth wall repair and their weather resistance evaluation methods. Background Technology

[0002] In the preservation of archaeological sites, research on reinforcement materials under different geological conditions has always been a challenge for those working on the preservation of earthen sites. Among the existing reinforcement materials, the mainstream restoration materials include: traditional inorganic materials, organic materials, microbial materials, and organic and inorganic materials. Inorganic materials mainly include calcium hydroxide, rammed earth, hydraulic lime, PS (potassium silicate), WD-10 (dodecyltrimethoxysilane), WD-S (polyoxymethoxysilane), and RTV (polyorganosiloxane and ethyl silicate). They are relatively inexpensive and have good applicability, but their restoration effect is poor and color difference is obvious. Organic materials such as glutinous rice mortar, egg white, and microbial restoration materials such as Bacillus pasteurellii and yeast also have good restoration effects, but they have certain toxicity. Microorganisms are prone to fungal contamination during reproduction. With the development of the concept of restoring old artifacts to their original state and sustainable development, nanomaterials are also being gradually promoted. For the characteristics of earthen site preservation in Xi'an, existing reinforcement materials are no longer suitable for reinforcing the original soil, and it is necessary to explore more environmentally friendly modified materials.

[0003] As research on modified materials deepens, studies on the weather resistance of modified materials to subgrade soil have also been extensively conducted. Current research includes the following: Using desalinated subgrade soil from the Xiaguanying Ancient City in Lanzhou as a case study, wet-dry cycle tests were conducted with NaCl and Na2SO4 solutions. The unconfined compressive strength tended to stabilize after 7-10 cycles. Triaxial experiments were performed using glutinous rice paste-modified materials under different wet-dry cycle conditions, showing that the dynamic shear modulus and damping ratio of the subgrade soil generally stabilized after 5 wet-dry cycles. Simultaneously, full-scale tests were conducted to study the erosion and damage modes of soil archaeological sites under the coupled effects of heat, water, and salt. The results indicate that the model exhibits a shear failure mode of upward tension and downward compression, and that this failure is progressive. This study investigated the effect of lime-metakaolin-modified soil on moisture content under freeze-thaw cycles. The effects on mass loss, unconfined compressive strength, color difference, and microstructure were studied at different moisture contents. The results showed that at lower moisture contents, compressive strength was directly proportional to the number of freeze-thaw cycles, but at higher moisture contents, the compressive strength was inversely proportional to the number of freeze-thaw cycles. While numerous studies have been conducted on weather resistance, they have all focused on single factors and have not considered the influence of salinity, wet-dry conditions, and freeze-thaw cycles.

[0004] In summary, current research focuses primarily on the short-term effects of modified materials in repairing rammed earth walls, with limited exploration of their long-term durability effects. Therefore, developing a novel modified restoration material that combines environmental friendliness, compatibility, and long-term durability, building upon traditional research, has become a critical technical challenge urgently needing resolution in the field of earthen heritage site preservation. Summary of the Invention

[0005] The purpose of this invention is to provide a chitosan-silicon-calcium-based modified material for repairing rammed earth walls and a method for evaluating its weather resistance, in order to solve the above-mentioned problems.

[0006] This invention provides a chitosan-silicon-calcium-based modified material for repairing rammed earth walls. The chitosan-silicon-calcium-based modified material includes metakaolin, calcium oxide, quartz, and chitosan. The ratio of metakaolin, calcium oxide, and quartz is 1:2:4. Metakaolin, calcium oxide, and quartz are mixed to obtain a silicon-calcium-based polymer. The mass ratio of the silicon-calcium-based polymer to chitosan is 1:1.

[0007] Preferably, the silicon-calcium-based polymer is mixed with chitosan to obtain a chitosan-silicon-calcium-based modified material, and the chitosan-silicon-calcium-based modified material is mixed with plain soil to prepare chitosan-silicon-calcium-based modified soil for rammed earth wall repair; the material mass ratio of chitosan-silicon-calcium-based modified soil is as follows: The ratio of the mass of chitosan-silica-calcium-based modified material to the mass of the raw soil is expressed as follows: In the formula: M 1 represents the mass of the chitosan-silicon-calcium-based modified material, in grams. M 2 represents the mass of the raw soil, in grams; the chitin-silica-calcium-based modifier is added to the modified soil at a rate of 20%.

[0008] Preferably, the chitosan-silicon-calcium-based modified material for rammed earth wall repair is prepared by: weighing silicon-calcium-based polymer and chitosan according to the mass ratio, mixing and stirring evenly under heating conditions to obtain the chitosan-silicon-calcium-based modified material, and then mixing the materials according to the mass ratio. Weigh out the corresponding mass of chitosan-silica-calcium-based modified material and the corresponding mass of raw soil. Mix the raw soil and chitosan-silica-calcium-based modified material mixture thoroughly, and then add water. Control the moisture content of the raw soil and modified material to the optimum moisture content. ω op =19.9%, dry density is the maximum dry density ρ dmax =1.65g / cm 3 The mixture was pressed into a diameter using a hydraulic jack. A sample with a diameter of 39.1 mm and a height of 8 cm was prepared. The compacted soil sample was then placed in a moisture-retaining container for 12 hours to allow for full consolidation, resulting in chitosan-silica-calcium-based modified soil for rammed earth wall repair. Preferably, the heating condition for mixing the silicon-calcium based polymer with chitosan is constant temperature water bath heating at 80°C.

[0009] A method for evaluating the weather resistance of the chitosan-silica-calcium-based modified material for rammed earth wall repair as described above is provided, including freeze-thaw cycle performance evaluation, wet-dry cycle performance evaluation, salt erosion resistance performance evaluation, and microstructure-performance correlation analysis test modules. The specific evaluation process is as follows: S1. Pre-experiment preparation: Plain soil and chitosan-calcium silicate-based material were mixed to prepare the soil sample to be tested. The plain soil and chitosan-calcium silicate-based modified soil were cured in a moisture-retaining container for 7 days. During curing, the soil sample was wrapped with plastic wrap to prevent moisture migration and evaporation. The temperature of the environmental chamber used in the experiment was calibrated. The thermocouple calibrator was placed in the low-temperature test chamber and the constant temperature chamber respectively. After setting the target temperature, the stable temperature within 24 hours was measured as the actual temperature of the environmental chamber. It was ensured that the deviation between the actual temperature and the target temperature did not exceed ±0.3℃. S2. Freeze-thaw cycle performance evaluation: The freeze-thaw environment was controlled using a low-temperature test chamber and a constant-temperature chamber. Cured soil samples were placed in the low-temperature test chamber and frozen at -20℃ for 4 hours, then transferred to a 20℃ constant-temperature chamber for 4 hours of curing, completing one freeze-thaw cycle. The number of freeze-thaw cycles is represented by the character symbol. N It is indicated that the number of freeze-thaw cycles for chitosan-silica-calcium-based modified soil is set to 0, 1, 3, 5, 7, 10, 13, 15, 16, 17, 20, 22, 25, 26, 27, 30, 33, 35, 37, 39, 40, 42, 45, 47, 50, 52, and 55, and the number of freeze-thaw cycles for plain soil is set to 0, 1, 3, 5, 7, and 10. However, since plain soil loses strength after 7 cycles, it is no longer included in the statistical results. But the results of the freeze-thaw experiment on plain soil in the 6th cycle without loss of strength are supplemented. S3. Evaluation of Wet-Dry Cycle Performance: Tests were conducted using a vacuum saturation device, a drying oven, and a stainless steel triaxial saturator (three-part mold). The vacuum saturation device included a vacuum pump, a transparent glass cylinder cover, a pressure valve, a water inlet valve, a silicone sealing ring, and a stainless steel vacuum cylinder. The triaxial saturator containing the soil sample was placed in the vacuum cylinder. Vaseline was applied to the sealing ring at the cylinder opening. The vacuum pump was turned on, the water inlet valve was closed, and the upper transparent glass cylinder cover was pressed for 2-3 minutes. After observing the pressure change at the glass cylinder cover, the pressing was stopped. When the air inside the cylinder was evacuated to -0.1 MPa, a complete vacuum was considered achieved. The water inlet valve was then slowly opened, and the pressure at the inlet valve was kept stable at -0.1 MPa during the water immersion process. After closing the inlet valve, the cylinder was immersed in water for 12 hours. The triaxial saturator was then removed and placed in a drying oven at 108℃ for 6 hours. The immersion and drying processes constituted one wet-dry cycle. The number of wet-dry cycles was represented by the number of characters. I It is indicated that the number of wet-dry cycles for chitosan-silica-calcium-based modified soil is set to 0, 1, 3, 5, 7, 9, 11, 13, and 15, and the number of wet-dry cycles for plain soil is set to 0, 1, 3, 5, 7, and 9. Plain soil loses stability after 9 cycles and is no longer included in the statistical results. S4. Salt resistance performance evaluation: A salt solution was prepared using anhydrous sodium sulfate, and a salt solution cycling test was conducted following the same procedure as the wet-dry cycle test, except that deionized water was replaced with the salt solution. The salt resistance performance test mainly included two types of variable factors: salt solution concentration... c Number of cycles of salt solution R This study investigated the changes in the mechanical properties of chitosan-silica-calcium-based modified soil under two different conditions. The salt solution concentrations for the chitosan-silica-calcium-based modified soil were set to 0, 0.1, 0.2, 0.3, and 0.4 mol. L -1 The salt solution was circulated 0, 1, 2, 3, 4, and 5 times; the salt solution concentration for the raw soil was only measured to be 0-0.3 mol. L -1 The experiment did not set a specific number of cycles for the clay-salt solution because the clay completely disintegrates at a salt solution concentration of 0.4 mol / L, and the number of cycles for the clay-salt solution is limited. R When the strength is greater than 1, it disintegrates rapidly, making it impossible to determine its unconfined compressive strength. S5. Correlation Analysis of Microstructure and Performance: Soil samples after the above tests were cut into specimens with a diameter <30mm and a height <13mm, dried, and sealed. A metal tray containing the specimens was placed on a gold plating machine for surface spraying. After completion, the microstructure was observed under a microscope. Based on the unconfined compressive strength data obtained from freeze-thaw cycles, wet-dry cycles, and salt erosion resistance tests, the unconfined compressive strength of the plain soil was plotted. q u-P Unconfined compressive strength of chitosan-silica-calcium-based modified soil qu-K Based on the curves showing changes in salt concentration, number of wet-dry cycles, and number of freeze-thaw cycles, the following intensity prediction formula is proposed: Formula for predicting the unconfined compressive strength of plain soil and modified materials as a function of freeze-thaw cycles: ; ; Formulas for predicting the unconfined compressive strength of plain soil and chitosan-silica-calcium-based modified soil with the number of wet-dry cycles: ; ; Prediction formulas for unconfined compressive strength of plain soil and chitin-silica-calcium-based modified soil as a function of salt concentration: ; ; The concept of crack ratio is used to characterize the number of cracks per unit volume. Based on the crack ratio, the degree of damage to soil samples under three environments—freeze-thaw cycle, wet-dry cycle, and salt concentration—is analyzed. The formula for calculating the crack ratio is: ,in : χ Crack rate, unit: cracks / cm 3 , L V represents the number of cracks, in cm³. 3 Based on the microstructure observation results, the deterioration process of chitin-silica-calcium-based modified soil is divided into compaction stage, new material formation stage and failure stage, and a comprehensive evaluation of weather resistance is completed.

[0010] Preferably, the three stages of the chitosan-silica-calcium-based modified soil degradation curve in step S5 are specifically divided as follows: Stage 1, the compaction stage, corresponds to the number of freeze-thaw cycles. N =1-5 times, Stage 2 of the new material formation stage corresponds to the number of freeze-thaw cycles. N =5-10 times, Stage 3 corresponds to the number of freeze-thaw cycles. N =10-55 times.

[0011] Preferably, in Stage 1, metakaolin, calcium oxide, quartz, and chitin materials fill the gaps as the number of freeze-thaw cycles increases; in Stage 2, chitin-silica-calcium-based modified materials undergo hydration and carbonization reactions to generate new hydrated calcium silicate substances, which continuously fill the pores from the inside; in Stage 3, tensile cracks appear on the soil surface as the number of freeze-thaw cycles continues to increase.

[0012] Preferably, the specific operation of the salt solution cycling test in step S4 is as follows: open the water inlet valve, replace the deionized water solution with a salt solution of a set concentration and immerse it in water for 12 hours to complete the salt solution saturation process; place the soil sample that has undergone 5 cycles and 4 soil samples of different concentrations in a drying oven and control the temperature at 108°C for 6 hours to complete one salt solution cycle.

[0013] Preferably, in step S5, microscopic structural observation reveals that: there are large pores in the plain soil, and the soil particles mainly have point contact; the hydrated calcium silicate material generated in the chitosan-calcium silicate-modified soil fills the large pores inside, making the pores compact from the inside, and the soil particles mainly have surface contact, which increases the friction between soil particles and thus improves the compressive strength.

[0014] Therefore, the present invention employs the above-mentioned chitosan-silicon-calcium-based modified material for rammed earth wall repair and its weather resistance evaluation method, which has the following beneficial effects: (1) Chitosan-silica-calcium-based modified materials can greatly improve the engineering performance of soil by adding a certain proportion of chitosan, metakaolin, quartz and calcium oxide to the soil. There are large pores in the soil, and the contact mode is mostly point contact. The newly generated substances in the chitosan-silica-calcium-based modified materials fill the internal large pores. As the number of freeze-thaw and wet-dry cycles increases, the internal pores gradually decrease. The chitosan-silica-calcium-based modified materials generate new hydrated calcium silicate substances through hydration and carbonization reactions, which continuously fill the pores from the inside, increase the form of surface contact between soil particles, and change the particle contact mode from point contact to surface contact, thereby filling the pores and strengthening the structure.

[0015] (2) The weather resistance evaluation method for chitosan-silica-calcium based modified materials integrates three typical environmental diseases in Northwest China—freeze-thaw cycles, wet-dry cycles, and salt erosion—into a single evaluation system. By simulating the combined effects of diurnal temperature variation (freeze-thaw), drought-rainfall alternation (wet-dry), and saline-alkali environment experienced by the material under long-term static conditions, it can comprehensively and realistically reflect the complex degradation process faced by the modified material in actual service environments, overcoming the limitations of single-factor evaluation. Through unconfined compressive strength testing, the change law of material performance with environmental effects is accurately quantified. The concept of crack rate is introduced, transforming the difficult-to-describe crack disease into a measurable and comparable quantitative indicator, realizing a rapid and objective assessment of the degree of damage to the material structure.

[0016] (3) The method has clear steps and specific equipment requirements. The strength prediction formula and crack rate development model established based on experimental data enable the prediction of long-term material performance to move from empirical judgment to modeling and semi-quantitative methods, providing a standardized process for the weather resistance assessment of rammed earth wall repair materials.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 Unconfined compressive strength and strain curves of chitosan-silica-calcium-based modified soil (q) u vs. ε); Figure 2 The relationship between unconfined compressive strength and optimal mix ratio of chitosan-silica-calcium-based modified soil ( q u vs. ); Figure 3 The curve showing the relationship between the unconfined compressive strength of plain soil and the number of freeze-thaw cycles (q) u vs. N) ; Figure 4 The curve showing the relationship between the unconfined compressive strength of chitosan-silica-calcium-based modified soil and the number of freeze-thaw cycles (q) u vs. N ); Figure 5 The number of wet-dry cycles of the plain soil and q u Result curve; Figure 6 The number of dry-wet cycles of chitosan-silica-calcium-based modified soil and q u Result curve; Figure 7 A comparison of the strength of chitosan-silica-calcium-based modified soil and plain soil under wet-dry cycles; Figure 8 Figure 1 shows the results of salt resistance tests on plain soil and chitosan-silica-calcium-based modified soil. Figure 9 The curve showing the predicted unconfined compressive strength as a function of the number of freeze-thaw cycles is shown. Figure 10 The curve showing the predicted unconfined compressive strength as a function of the number of wet-dry cycles is shown. Figure 11 The curve showing the predicted unconfined compressive strength as a function of salt concentration is shown. Figure 12 Crack rate curves for plain soil and chitosan-silica-calcium-based modified soil; Figure 13 Diagrams showing the crack failure modes of chitosan-silica-calcium-based modified soil under different concentrations of salt solution cycles; Figure 14 SEM images of chitosan-silica-calcium-based modified soil after different number of cycles; Figure 15 This diagram illustrates the reinforcement mechanism of chitosan-silica-calcium-based modified soil. Detailed Implementation

[0019] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0021] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0022] Example 1 Preparation of chitosan-silicon-calcium-based modified materials: Raw material preparation: Plain soil was taken from loess peeled off near a certain site in Xi'an City. After being naturally air-dried, it was sieved through a 2mm sieve to remove impurities; Chitosan: Industrial grade, purity ≥90%; Silicon-calcium based polymer was prepared by mixing metakaolin, calcium oxide and quartz in the optimal ratio of 1:2:4.

[0023] Preparation of modified soil: Mass ratio of modified soil materials Φ The calculation formula is as follows: In the formula: M 1 represents the mass of the chitosan-silicon-calcium-based modified material, in grams. M 2 represents the total mass of the soil, in grams; the dosage of modified materials is controlled at 20%, i.e. Φ =0.2, the specific preparation process is as follows: Chitosan-silicon-calcium based modified material is prepared by mixing the silicon-calcium based polymer with chitosan in a 1:1 ratio and heating in a constant temperature water bath at 80°C.

[0024] Based on the optimum moisture content ω, the plain soil is... op =19.9% ​​The required amount of deionized water is 1000×19.9%=199g. After spraying the water, stir it evenly, seal it and let it stand for 24 hours to allow the water to be evenly distributed.

[0025] The chitosan-silica-calcium-based modified material was thoroughly mixed with the pretreated clay, and a small amount of deionized water was added to ensure that the overall moisture content was maintained at 19.9%, and the dry density of the mixture was controlled to be the maximum dry density. ρ dmax =1.65g / cm 3 .

[0026] The above mixture was pressed into a specification using a hydraulic jack. Cylindrical samples measuring 39.1 mm × 8 cm were prepared; soil samples of the same specifications were also prepared. The plain soil sample and the chitin-silica-calcium-based modified soil sample were wrapped in plastic wrap and placed in a humidification tank for curing for 7 days. During the curing period, the humidity inside the tank was kept stable to prevent moisture migration and evaporation.

[0027] Using an LSY30-1 conventional stress-strain controlled triaxial apparatus, the specimen was placed on the base, and after adjusting the specimen to just contact the pressure plate, the displacement and stress data in the data acquisition device were zeroed. The specimen loading rate was set to 0.8 mm / min, and the pressurization time was controlled to 15-20 min. The displacement-stress curve was automatically collected and plotted by the computer to obtain the unconfined compressive strength parameters. Simultaneously, an optimal mix design test was conducted at room temperature to determine the optimal mix design of the modified material KMCS at room temperature. The scheme is set as 0:1:2:4, 1:1:2:4, 2:1:2:4, 3:1:2:4, and 4:1:2:4. For example... Figure 1-2 As shown, with the increase of chitin ratio, the unconfined compressive strength ( q u The trend is that it first increases and then decreases; when When increasing from 0:1:2:4 to 1:1:2:4, q u The pressure increased from 541.34 kPa to 749.55 kPa. q u (Increased by 38.5%), but when As the ratio of unconfined compressive strength increases from 1:1:2:4 to 6:1:2:4, the unconfined compressive strength gradually decreases, from 749.55 kPa to 416.42 kPa. q u (Reduced by 44.4%); Chitosan is a type of chitosan and has a certain carbonization effect. When a small amount of chitosan is added... When the ratio is 1:1:2:4, it combines with water to form aggregates, which can increase the soil's cohesive properties. It also quickly forms calcium carbonate precipitate with calcium ions in the MCS modified material, thereby reducing the internal porosity of the soil and achieving the effect of reinforcing the rammed earth wall.

[0028] Example 2 Methods for evaluating the weather resistance of chitosan-silicon-calcium-based modified materials: Plain soil and chitin-silica-calcium-based modified soil from the archaeological site were selected as the samples to be evaluated. The plain soil and chitin-silica-calcium-based modified soil were cured in a humidifying chamber for 7 days. During the curing period, the soil samples were wrapped with plastic wrap to prevent moisture migration and evaporation. The temperature of the environmental chamber used in the experiment was calibrated. The thermocouple calibrator was placed in the low-temperature test chamber and the constant temperature chamber respectively. After setting the target temperature, the stable temperature within 24 hours was measured as the actual temperature of the environmental chamber, ensuring that the deviation between the actual temperature and the target temperature does not exceed ±0.3℃. Freeze-thaw cycle performance evaluation: A low-temperature test chamber and a constant-temperature chamber were used to control the freeze-thaw environment. Cured soil samples were simultaneously placed in the low-temperature test chamber and frozen at -20℃ for 4 hours, then transferred to a 20℃ constant-temperature chamber for 4 hours to complete one freeze-thaw cycle. The number of freeze-thaw cycles is represented by the number of characters. N This indicates that the number of freeze-thaw cycles for chitosan-silica-calcium-based modified soil is set to 0, 1, 3, 5, 7, 10, 13, 15, 16, 17, 20, 22, 25, 26, 27, 30, 33, 35, 37, 39, 40, 42, 45, 47, 50, 52, and 55, while the number of freeze-thaw cycles for plain soil is set to 0, 1, 3, 5, and 7. Plain soil loses its strength after 6 cycles and is no longer included in the statistical results. With increasing freeze-thaw cycles, the unconfined compressive strength of plain soil decreases sharply, but the strength of chitosan-calcium silicate-modified soil shows a trend of first increasing and then decreasing. Its freeze-thaw stage is divided into three parts: Stage I, Stage II, and Stage III. When N increases from 0 to 10 cycles (Stage I), the unconfined compressive strength increases by 34.25%. This is because in the early freeze-thaw stage (Stage I), the high temperature forces water molecules to move rapidly and react with residual chitosan and MCS materials in the material, resulting in a volcanic ash reaction to generate hydrated calcium silicate, which reinforces the soil. Simultaneously, the early freeze-thaw stage causes aging, healing damaged structures in the soil and enhancing its freeze-thaw properties, resulting in a slight increase in strength. Surface cracks are mainly through cracks, with micro-cracks appearing around them. When the freeze-thaw stage is in Stage II... N When the freeze-thaw cycle reached 10-39 times, the unconfined compressive strength decreased by 37.59%, and small areas of spalling began to appear around the soil sample, mainly concentrated in the top and middle areas; at the same time, microcracks expanded into large cracks; and many small cracks extended around the cracks. When the freeze-thaw stage was in Stage III ( NWhen the unconfined compressive strength reaches 39-55 cycles, it gradually stabilizes. This is because the material used for the volcanic ash reaction is almost completely consumed over a long freeze-thaw period. Simultaneously, the ice crystals formed during freezing expand the soil pores, and the frost heave further applies tensile pressure to the pores, leading to a decrease in compressive strength and a gradual reduction in freeze-thaw resistance. The cracks exhibit a "reverse mountain" distribution; the cracks show a multi-grid intersection phenomenon; large areas of spalling occur, along with multiple sets of main cracks, indicating significant damage.

[0029] Evaluation of wet-dry cycle performance: A vacuum saturation device, drying oven, and triaxial saturator were used for testing. The triaxial saturator containing the sample was placed in a vacuum cylinder. Vaseline was applied to the sealing ring at the cylinder opening, the water inlet valve was closed, and the air inside the cylinder was evacuated to -0.1 MPa to ensure a complete vacuum. The water inlet valve was then opened, allowing the triaxial saturator to be completely immersed in water and evacuated for 2 hours. After closing the water inlet valve, it was immersed in water for 12 hours for saturation. Subsequently, the triaxial saturator was removed and placed in a drying oven at a controlled temperature of 108℃ for 6 hours. The immersion and drying processes constituted one wet-dry cycle, and the number of wet-dry cycles was represented by the character "I". The number of wet-dry cycles for chitosan-silica-calcium-based modified soil was set to 0, 1, 3, 5, 7, 9, 11, 13, and 15 times, and the number of wet-dry cycles for plain soil was set to 0, 1, 3, 5, 7, and 9 times. Plain soil lost stability after 9 cycles and was no longer included in the statistical results. With increasing wet-dry cycle count, the unconfined compressive strength of plain soil gradually decreases, while the strength of chitosan-silica-calcium-based modified soil first increases and then decreases; when the number of wet-dry cycles increases... I When the number of wet-dry cycles was 1, the strength of the chitosan-silica-calcium-based modified soil increased by 1.52 times compared to the strength of plain soil; when the number of wet-dry cycles was 1, the strength of the modified soil increased by 1.52 times. I When the KMCS modified soil was subjected to 9 cycles, the strength of the soil was increased by 3.41 times compared with the strength of the plain soil.

[0030] Salt erosion resistance evaluation: A salt solution was prepared using anhydrous sodium sulfate. The salt solution cycling test was conducted following the same procedure as the wet-dry cycle test, except that deionized water was replaced with the salt solution. The inlet valve was opened, and the deionized water solution was replaced with a salt solution of a set concentration, immersing the soil for 12 hours to complete the salt solution saturation process. Soil samples that had undergone 5 cycles and 4 soil samples with different concentrations were placed in a drying oven at 108℃ for 6 hours to complete one salt solution cycle. The salt solution concentrations for the chitosan-silica-calcium-based modified soil were set to 0, 0.1, 0.2, 0.3, and 0.4 mol. L -1 The salt solution was circulated 0, 1, 2, 3, 4, and 5 times; the salt solution concentration for the raw soil was only measured to be 0-0.3 mol. L -1 In the experiment, the native soil completely disintegrated at a salt solution concentration of 0.4 mol / L, and the number of salt solution cycles was [not specified]. RWhen the strength is greater than 1, it disintegrates rapidly, making it impossible to determine its unconfined compressive strength. As the salt solution concentration increases, the unconfined compressive strength initially increases and then decreases. c = At 0.3 mol / L, the unconfined compressive strength of KMCS increased by 4.5 times compared to that of plain soil. As the concentration increased, white precipitates floated on the surface of the soil sample, enhancing its resistance to salt erosion. However, due to the continuous increase in concentration, salt crystals gradually precipitated on the surface, resulting in a decrease in unconfined compressive strength. Compared to plain soil, the modified material exhibited stronger salt resistance.

[0031] With the number of dynamic circulation tests of salt solution R As the compressive strength increases, the unconfined compressive strength gradually decreases. A large amount of white salt particles adhere to the surface of the chitosan-calcium silicate-modified soil, and these salts invade the soil structure. Anhydrous Na2SO4 reacts with water to crystallize and form sodium sulfate (Na2SO4·10H2O). R When the content of sodium sulfate increases, it puts pressure on the pores inside the soil. When the soil sample is dried, sodium sulfate is converted into anhydrous sodium sulfate, which reduces the pore volume. Its crystalline salt fills the pores, causing the internal structure of the soil to deteriorate.

[0032] Microstructure and performance correlation analysis: Soil samples after the above tests were cut into specimens with a diameter <30mm and a height <13mm, dried and sealed. The metal tray containing the specimens was placed on a fine plating instrument for surface gold spraying. After completion, the microstructure was observed under a microscope. Based on the unconfined compressive strength data obtained from freeze-thaw cycle, wet-dry cycle, and salt erosion resistance tests, the unconfined compressive strength of the plain soil was plotted. q u-P Unconfined compressive strength of chitosan-silica-calcium-based modified soil q u-K Based on the curves showing changes in salt concentration, number of wet-dry cycles, and number of freeze-thaw cycles, the following intensity prediction formula is proposed: Formula for predicting the unconfined compressive strength of plain soil and modified materials as a function of freeze-thaw cycles: ; ; Formulas for predicting the unconfined compressive strength of plain soil and chitosan-silica-calcium-based modified soil with the number of wet-dry cycles: ; ; Prediction formulas for unconfined compressive strength of plain soil and chitin-silica-calcium-based modified soil as a function of salt concentration: ; ; The prediction formula shows that the compressive strength of plain soil gradually decreases with the increase of wet-dry cycles, freeze-thaw cycles, and salt concentration. However, the compressive strength of chitosan-silica-calcium-based modified materials first increases and then decreases with the increase of wet-dry cycles, freeze-thaw cycles, and salt concentration. Due to the formation of new mineral components, the internal structure of chitosan-silica-calcium-based modified materials develops microcracks and spalling after experiencing extreme environmental stimuli with the increase of freeze-thaw cycles and wet-dry cycles, and the strength gradually decreases.

[0033] The concept of crack ratio is used to characterize the number of cracks per unit volume. Based on the crack ratio, the degree of damage to soil samples under three environments—freeze-thaw cycle, wet-dry cycle, and salt concentration—is analyzed. The formula for calculating the crack ratio is: Where: χ is the crack rate, unit: cracks / cm 3 L represents the number of cracks, in units of cracks; V represents the volume of the soil sample, in cm³. 3 ; With increasing freeze-thaw and wet-dry cycles, the crack rate of plain soil gradually increases. However, the crack rate of chitosan-silica-calcium-based modified soil shows a trend of first decreasing and then increasing. When the number of freeze-thaw cycles... N After 6 freeze-thaw cycles, the plain soil lost its bearing capacity and collapsed. However, for chitosan-calcium silicate-modified soil, after 42 freeze-thaw cycles, the maximum crack rate was 0.197 cracks / cm. 3 When the number of dry and wet cycles I At 9 cycles, the soil structure became unstable, leading to soil disintegration, making it impossible to determine the crack rate. However, after 15 wet-dry cycles, the crack rate of the chitosan-calcium silicate-modified soil stabilized at 0.176 cracks / cm. 3 .

[0034] With increasing salt solution concentration, the crack rate of the native soil gradually increased, while the crack rate of the modified material showed a trend of first increasing and then decreasing. The chitin-silica-calcium-based modified soil exhibited a peak crack rate at a salt solution concentration of 0.1 mol / L. However, with increasing salt solution concentration, sodium sulfate (Na₂SO₄·10H₂O) crystallized during salt migration, filling soil pores and thus enhancing soil strength. The crack rate decreased with increasing number of dynamic cyclic salt solution tests. R As the number of cracks increases, the cracks gradually widen and grow larger. R When R=1, many micro-cracks appear around the Y-shaped main crack, and a large through crack appears from the top to the bottom of the soil sample. At the same time, many white crystals and uneven pits form on the surface of the soil sample. When R=5, the cracking phenomenon is more obvious, and it is accompanied by large-area spalling. The crack expansion law can demonstrate the salt solution migration law and the phenomenon of internal damage of the soil sample.

[0035] Based on microstructural observations, the degradation process of chitosan-silica-calcium-based modified soil was divided into three stages: compaction, new material formation, and failure, thus completing a comprehensive weather resistance evaluation. The specific division of the three stages in the chitosan-silica-calcium-based modified soil degradation curve is as follows: Stage 1 of the compaction stage corresponds to the number of freeze-thaw cycles. N =1-5 times, Stage 2 of the new material formation stage corresponds to the number of freeze-thaw cycles. N =5-10 times, Stage 3 corresponds to the number of freeze-thaw cycles. N =10-55 cycles. In Stage 1, metakaolin, calcium oxide, quartz, and chitin fill the gaps with increasing freeze-thaw cycles. In Stage 2, the chitin-calcium silicate-modified material undergoes hydration and carbonization reactions to generate new hydrated calcium silicate, continuously filling the pores from the inside. In Stage 3, tensile cracks appear on the soil surface as the number of freeze-thaw cycles continues to increase. It can be seen that there are large pores in the original soil, and the contact mode of soil particles is mostly point contact. The hydrated calcium silicate generated in the chitin-calcium silicate-modified soil fills the large pores inside, making the pores compact from the inside. The contact mode of soil particles is mainly surface contact, which increases the friction between soil particles and thus improves the compressive strength.

[0036] Therefore, this invention employs the aforementioned chitosan-calcium silicate-based modified material for rammed earth wall repair and its weather resistance evaluation method. The chitosan-calcium silicate-based modified material, by adding a certain proportion of chitosan, metakaolin, quartz, and calcium oxide to the subgrade, can significantly improve the engineering performance of the subgrade. Subgrade contains large pores, and its contact mode is mostly point contact. Newly generated substances in the chitosan-calcium silicate-based modified material fill the internal large pores. With the increase in freeze-thaw and wet-dry cycles, the internal pores gradually decrease. The chitosan-calcium silicate-based modified material generates new hydrated calcium silicate through hydration and carbonization reactions, continuously filling the pores from the inside, increasing the form of surface contact between soil particles, changing the particle contact mode from point contact to surface contact, thereby filling the pores and strengthening the structure. The weather resistance evaluation method of the chitosan-calcium silicate-based modified material integrates three typical environmental diseases in Northwest China—freeze-thaw cycles, wet-dry cycles, and salt erosion—into a single evaluation system. By simulating the combined effects of diurnal temperature variations, drought-rainfall cycles, and saline-alkali environments experienced by materials under long-term static conditions, this method comprehensively and realistically reflects the complex degradation process faced by modified materials in actual service environments, overcoming the limitations of single-factor evaluation. Through unconfined compressive strength testing, the method precisely quantifies the changes in material properties under environmental influences. The introduction of the crack rate concept transforms the difficult-to-describe cracking defects into measurable and comparable quantitative indicators, enabling rapid and objective assessment of the degree of structural damage to the material. This method features clear steps and well-defined equipment requirements. The strength prediction formula and crack rate development model established based on experimental data enable the prediction of long-term material performance to move from empirical judgment to model-based and semi-quantitative methods, providing a standardized process for assessing the weather resistance of rammed earth wall repair materials.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A chitin-silicocalcic based modified material for the restoration of adobe walls, characterized by, The chitin-silicon calcium-based modified material comprises metakaolin, calcium oxide, quartz and chitin; the mass ratio of the metakaolin, the calcium oxide and the quartz is 1:2:4, the metakaolin, the calcium oxide and the quartz are mixed to obtain a silicon calcium-based polymer, and the mass ratio of the silicon calcium-based polymer and the chitin is 1:

1.

2. The adobe wall restoration chitin-silicic calcium-based modified material according to claim 1, characterized by, The chitin-silicon calcium-based modified material is mixed with soil to prepare chitin-silicon calcium-based modified soil for repairing rammed earth walls. The ratio of the mass of the chitin-silicon calcium-based modified material to the mass of the soil is specifically expressed as follows: In the formula: M 1 is the mass of chitin-silicon calcium-based modified material, unit: g; M 2 is the total mass of soil, unit: g; the dosage of chitin-silicon calcium-based modified material in modified soil is 20%.

3. The adobe wall restoration chitin-silicic calcium-based modified material according to claim 2, characterized in that, The preparation method of the chitosan-silica-calcium based modified soil is as follows: Weigh the silica-calcium based polymer and chitosan according to the mass ratio, mix and stir evenly under heating conditions to obtain the chitosan-silica-calcium based modified material, and then mix according to the material mass ratio. Weigh out the corresponding mass of chitosan-silica-calcium-based modified material and the corresponding mass of raw soil. Mix the raw soil and chitosan-silica-calcium-based modified material mixture thoroughly, and then add water. Control the moisture content of the raw soil and modified material to the optimum moisture content. ω op =19.9%, dry density is the maximum dry density ρ dmax =1.65g / cm 3 The mixture was pressed into a diameter using a hydraulic jack. A sample with a diameter of 39.1 mm and a height of 8 cm was prepared. The pressed soil sample was placed in a moisturizing tank for 12 hours to allow the soil sample to fully consolidate, thus obtaining chitosan-silica-calcium-based modified soil for rammed earth wall repair.

4. The adobe wall restoration chitin-silicic calcium-based modified material according to claim 3, characterized in that, The suitable heating condition for mixing the silicon calcium-based polymer and the chitin is constant-temperature water bath heating at 80 DEG C.

5. A method for evaluating the weather resistance of a rammed earth wall repair chitin-silicic calcium-based modified material according to any one of claims 1 to 4, characterized in that, The test modules include a freeze-thaw cycle performance evaluation, a dry-wet cycle performance evaluation, a salt erosion resistance performance evaluation and a microstructure and performance correlation analysis test module, and the specific evaluation process is as follows: S1, test preparation: select the soil and the chitin-silicon calcium-based material mixed to prepare the soil sample to be tested, and the soil and the chitin-silicon calcium-based modified soil are cured in a humidifying jar for 7 days; during the curing, the soil sample is wrapped with a preservative film to prevent water migration and evaporation; the temperature of the environmental chamber used for the test is calibrated, the thermocouple verifier is placed in the low-temperature test chamber and the constant-temperature chamber, the target temperature is set, and the stable temperature within 24 hours is measured as the actual temperature of the environmental chamber to ensure that the deviation between the actual temperature and the target temperature is not more than ± 0.3 DEG C; S2, freeze-thaw cycle performance evaluation: using a low temperature test chamber and thermostat to control the freeze-thaw environment, the soil sample after curing is put into the low temperature test chamber, frozen at-20℃ for 4h, then transferred to the 20℃ thermostat for constant temperature curing for 4h, to complete one freeze-thaw cycle, the freeze-thaw cycle number is represented by the character N ; the freeze-thaw cycle number of chitin-silica calcium modified soil is set to 0, 1, 3, 5, 7, 10, 13, 15, 16, 17, 20, 22, 25, 26, 27, 30, 33, 35, 37, 39, 40, 42, 45, 47, 50, 52, 55 times, and the freeze-thaw cycle number of the soil is 0, 1, 3, 5, 7, 10 times, but the soil loses strength after 7 cycles and is no longer included in the statistical results, but the freeze-thaw test results of the soil that did not lose strength in the 6th cycle are supplemented; S3, dry-wet cycle performance evaluation: vacuum saturation device, drying oven and stainless steel triaxial saturator are used to carry out the test, the vacuum saturation device includes vacuum pump, transparent glass cylinder cover, air pressure valve and water inlet valve, silica gel sealing ring and stainless steel vacuum cylinder; the triaxial saturator with soil sample is put into the vacuum cylinder, vaseline is smeared on the cylinder port sealing ring, the vacuum pump is opened, the water inlet valve is closed, the upper transparent glass cylinder cover is pressed for 2-3 minutes, after the air pressure of the glass cylinder cover starts to change, the pressing is stopped, when the air in the cylinder is pumped to-0.1MPa, it is considered that the vacuum is complete; then the water inlet valve is slowly opened, the water flow is kept at-0.1MPa during the water infiltration process, the water inlet valve is closed after the water saturation for 12h; then the triaxial saturator is taken out, the triaxial saturator with soil sample is placed in the drying oven to control the temperature at 108℃ and continuously dry for 6h, the water immersion and drying process constitutes one dry-wet cycle, the dry-wet cycle number is represented by the character I ; the dry-wet cycle number of chitin-silicon calcium modified soil is set to 0, 1, 3, 5, 7, 9, 11, 13, 15 times, the dry-wet cycle number of the plain soil is set to 0, 1, 3, 5, 7, 9 times, the plain soil loses stability after 9 cycles and is no longer included in the statistical results; S4, salt erosion resistance performance evaluation: with anhydrous sodium sulfate solution, using the same steps as the dry-wet cycle test, only the deionized water is replaced by salt solution; salt erosion resistance performance test mainly contains two variable factors: salt solution concentration c and salt solution cycle number R , the mechanical properties of chitin-silicon calcium modified soil under the two changes were studied, and the salt solution concentration of chitin-silicon calcium modified soil was set as 0, 0.1, 0.2, 0.3, 0.4 mol L -1 , the salt solution cycle number was 0, 1, 2, 3, 4, 5 times; the test of soil only determined the salt solution concentration of 0-0.3 mol L -1 , the salt solution cycle number of soil was not set, because the soil completely disintegrated when the salt solution concentration was 0.4 mol / L, and the soil rapidly disintegrated when the salt solution cycle number R was greater than 1, so it was impossible to determine its unconfined compressive strength; S5, microstructure and performance correlation analysis: the soil sample after the above test is cut into a sample with a diameter of <30 mm and a height of <13 mm and dried and sealed, a metal carrier plate containing the sample is placed on a precision plating instrument for surface gold spraying treatment, and after completion, it is placed in a microscope to observe the microstructure; based on the unconfined compressive strength data obtained by freeze-thaw cycle, dry-wet cycle, salt erosion resistance test, the unconfined compressive strength of the soil is plotted q u-P and the unconfined compressive strength of the chitin-silicon calcium modified soil q u-K The strength prediction formula is as follows: The prediction formula of the unconfined compressive strength of the soil and the modified material with the number of freeze-thaw cycles is as follows: ； ； The prediction formula of the unconfined compressive strength of the soil and the chitin-silicon calcium-based modified soil with the number of dry-wet cycles is as follows: ； ； The prediction formula of the unconfined compressive strength of the soil and the chitin-silicon calcium-based modified soil with the salt concentration is as follows: ； ； The crack rate concept is cited to characterize the number of cracks in a unit volume. The damage degree of soil samples under freeze-thaw cycles, wet-dry cycles, and salt concentration is analyzed based on the crack rate. The crack rate calculation formula is: wherein : χ is the crack rate, with units of strips / cm 3 , L is the number of cracks, with units of strips, and V is the volume of the soil sample, with units of cm 3 . Combined with the microstructure observation results, the deterioration process of the chitin-silicon calcium modified soil is divided into a compaction stage, a new material formation stage, and a damage stage, and a comprehensive evaluation of the weather resistance is completed.

6. The method for evaluating the weather resistance of rammed earth wall repair chitin-silica calcium-based modified materials according to claim 5, characterized in that, The three stages of the chitin-silicon calcium-based modified soil deterioration curve in step S5 are specifically divided as follows: the compaction stage Stage 1 corresponds to the freeze-thaw cycle number N=1-5 times, the new material formation stage Stage 2 corresponds to the freeze-thaw cycle number N=5-10 times, and the damage stage Stage 3 corresponds to the freeze-thaw cycle number N=10-55 times.

7. The method for evaluating the weather resistance of rammed earth wall repair chitin-silica calcium-based modified materials according to claim 6, characterized in that, In Stage 1, the metakaolin, calcium oxide, quartz and chitin material fill the gaps as the number of freeze-thaw cycles increases; in Stage 2, the chitin-silicon calcium-based modified material undergoes hydration and carbonization reactions to generate new hydrated calcium silicate substances, which continuously fill the pores from the inside; in Stage 3, as the number of freeze-thaw cycles continues to rise, tensile cracks appear on the surface of the soil body.

8. The method for evaluating the weather resistance of a rammed earth wall repair chitin-silica calcium-based modified material according to claim 5, characterized in that, The specific operation of the salt solution circulation test in step S4 is as follows: open the water inlet valve, replace the deionized water solution with a salt solution of a set concentration, and immerse and saturate for 12 hours to complete the salt solution saturation process; place the soil samples after 5 cycle periods and the soil samples of 4 different concentrations in a drying oven and control the temperature to 108 DEG C for 6 hours to complete one salt solution cycle.

9. The method for evaluating the weather resistance of a rammed earth wall repair chitin-silica calcium-based modified material according to claim 5, characterized in that, In step S5, it can be known from the microstructure observation that there are larger pores in the soil, and the contact mode of the soil particles is mainly point contact; the hydrated calcium silicate substances generated in the chitin-silicon calcium-based modified soil fill the internal large pores, causing the pores to be compacted from the inside, the contact mode of the soil particles is mainly surface contact, the friction between the soil particles is increased, and thus the compressive strength is improved.

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