Waterproof and shrinkage-resistant graphite tailing-saw mud road base material and preparation method thereof

Abstract

This invention belongs to the technical field of cement concrete, specifically relating to a waterproof and shrinkage-resistant graphite tailings-sawdust road base material and its preparation method. The graphite tailings-sawdust road base material comprises the following components by weight: 25-40 parts sawdust, 60-75 parts graphite tailings, 10-12 parts cement, 10-20 parts metakaolin, 0.5-1.5 parts solid NaOH, 0.5-1.5 parts sodium silicate, 0.01-0.03 parts polyester fiber, 0.02-0.04 parts modified MIL-125(Ti), and 15-17 parts water. This road base material can effectively solidify As… 5+ It contains heavy metal ions and can effectively block moisture transport to improve the water stability of the base material, thus greatly improving its resistance to drying shrinkage.

Description

Technical Field

[0001] This invention belongs to the technical field of cement concrete, specifically relating to a waterproof and shrinkage-resistant graphite tailings-sawdust road base material and its preparation method. Background Technology

[0002] Sawdust, a solid waste generated during stone processing, is primarily composed of cellulose, hemicellulose, and lignin, containing small amounts of ash (such as SiO2 and CaO). It exists in a fibrous or flocculent form, exhibiting high porosity and a loose texture, which presents several challenges in its application. Sawdust fiber agglomeration easily leads to uneven internal pores in products, and due to its high water absorption and poor durability, sawdust products are prone to volume shrinkage. Furthermore, the organic matter in sawdust lacks cementing properties, resulting in relatively low strength and slightly higher toughness, yet it remains difficult to maintain structural stability during long-term use.

[0003] Graphite tailings are the main solid waste generated during graphite mining and beneficiation.

[0004] Current technologies propose a research direction for the high-value utilization of sawdust and graphite tailings as solid waste, using sawdust and graphite tailings together as road concrete materials.

[0005] Patent CN117263638B discloses a graphite tailings-sawdust road subbase material, its preparation method, and its application. The subbase material comprises the following components by weight: 40-55 parts graphite tailings, 45-60 parts sawdust, 0.5-2 parts phase change microcapsules, 5-10 parts hydrated lime, 10-20 parts fly ash, 0.5-1.5 parts titanium gypsum, 0.5-2 parts steel slag powder, 5-15 parts water, and 0.05-0.2 parts dispersant. The 7-day unconfined compressive strength of the graphite tailings-sawdust road subbase material ranges from 2.64 to 3.87 MPa, and the loss of compressive strength (BDR) ranges from 82.1% to 86.2%. The graphite tailings-sawdust road subbase material provided by this method mainly uses Fe(OH)3 and Al(OH)3 colloids in titanium gypsum to adsorb and solidify heavy metal ions. However, the adsorption effect is limited and the stability is poor, posing a risk of desorption. Furthermore, the low water content (5-15 parts) in this system easily leads to the unhydrated cementitious material continuing to absorb water, thereby triggering secondary shrinkage. The added phase change microcapsules have poor adhesion between their wall material (such as polymer) and the inorganic matrix, which may form local weak areas that become crack initiation points under drying shrinkage stress.

[0006] Therefore, in order to better solve the solid waste problem of sawdust and graphite tailings, there is an urgent need to provide a graphite tailings-sawdust based road base material that can effectively solidify heavy metal ions in the material and inhibit the drying shrinkage of the material. Summary of the Invention

[0007] The purpose of this invention is to provide a waterproof and shrinkage-resistant graphite tailings-sawdust road base material and its preparation method. This road base material can effectively solidify As... 5+ It contains heavy metal ions and can effectively block moisture transport to improve the water stability of the base material, thus greatly improving its resistance to drying shrinkage.

[0008] In the research process, this invention fully considers the defects of sawdust in the system, such as high water absorption, easy decomposition by microorganisms, and poor durability, as well as the problem of heavy metal pollution in graphite tailings. Through formula design, while strengthening the solidification of heavy metals, it effectively solves the problems of high water absorption and poor water resistance of sawdust, and enhances the durability and structural stability of the material.

[0009] The technical solution of this invention is as follows:

[0010] A waterproof and shrinkage-resistant graphite tailings-sawdust road base material comprises the following components in parts by weight: 25-40 parts sawdust, 60-75 parts graphite tailings, 10-12 parts cement, 10-20 parts metakaolin, 0.5-1.5 parts solid NaOH, 0.5-1.5 parts sodium silicate, 0.01-0.03 parts polyester fiber, 0.02-0.04 parts modified MIL-125(Ti), and 15-17 parts water.

[0011] The modified MIL-125(Ti) was prepared by the following steps:

[0012] First, place MIL-125(Ti) in a vacuum reaction chamber; then place container A containing methyltrimethoxysilane and container B containing an aqueous ethanol solution in the vacuum reaction chamber. Take care to avoid direct contact between methyltrimethoxysilane and the aqueous ethanol solution and MIL-125(Ti).

[0013] Then, the vacuum reaction chamber was sealed, a vacuum was drawn, the temperature was set to 80°C, and deposition was carried out for 3 hours to obtain the modified MIL-125(Ti).

[0014] The volume ratio of methyltrimethoxysilane to ethanol aqueous solution is 1:1. The volume ratio of ethanol to water is 3:2.

[0015] The raw material MIL-125(Ti) is tetravalent titanium ions (Ti 4+ The core active site is terephthalic acid (H2BDC, 1,4-phthalic acid), which is the organic linking unit, and is linked to Ti via the carboxyl group (-COOH). 4+ Coordination connects the metal centers into a three-dimensional framework structure.

[0016] Hydrophobic groups were grafted onto the surface of MIL-125(Ti) using the above-described vapor deposition method.

[0017] Firstly, in the waterproof and shrinkage-resistant graphite tailings-sawdust road base material system described in this invention, the modified MIL-125(Ti) can directly form a stable chemical bond with the trivalent arsenic As(III) and pentavalent arsenic As(V) contained in the graphite tailings. At the same time, with the structural reconstruction of the material framework, the heavy metal arsenic is effectively and stably retained in the material, and will not easily desorb, thus solving the problem of low-concentration arsenic being difficult to remove and easy to desorb.

[0018] More importantly, the modified MIL-125(Ti) is uniformly dispersed and fixed on the pore surface of the alkali-activated gel formed by metakaolin, cement, solid sodium hydroxide and sodium silicate, forming a water-repellent interface on the surface, blocking the channels for water to enter and exit. This not only prevents the leakage of heavy metal ions, but also significantly reduces the evaporation rate and delays the appearance of the humidity gradient. It plays a dual role of water retention and slow release in the system, thereby inhibiting shrinkage cracking.

[0019] In the system, solid sodium hydroxide and sodium silicate work together on metakaolin (a highly active silica-alumina material), while synergistically activating small amounts of active components on the surface of cement hydration products, aggregate graphite tailings, and sawdust to generate stable cementitious products, providing the material with the required strength and densified structure.

[0020] In this invention, the graphite tailings in the waterproof and shrinkage-resistant graphite tailings-sawdust road base material have a particle size of 4-10.5 mm; the sawdust has a moisture content of 0.7%-0.8% and a pH value of 8-9.

[0021] In this invention, the cement in the waterproof and shrinkage-resistant graphite tailings-sawdust road base material has a fineness of 9.4%-9.8% and a specific surface area of ​​360-380 m². 2 / kg. Cement, along with graphite tailings and sawdust, forms an effective binder. It also provides a calcium source for the alkali-activated system.

[0022] In this invention, the metakaolin in the waterproof and shrinkage-resistant graphite tailings-sawdust road base material has a 28-day activity index ≥110% and an amorphous silica-alumina content >90%. The metakaolin provides an active silica-alumina source for the alkali-activated system, significantly reducing the chemical shrinkage and auto-shrinkage of the alkali-activated system, and works synergistically with modified MIL-125(Ti) to reduce shrinkage.

[0023] In this invention, the solid sodium hydroxide in the waterproof and shrinkage-resistant graphite tailings-sawdust road base material is a flaky solid with a purity ≥96%. The solid sodium hydroxide and sodium silicate together form a dual-alkali system, activating the material's activity.

[0024] In this invention, the modulus of sodium silicate in the waterproof and shrinkage-resistant graphite tailings-sawdust road base material is 2.8-3.0. Sodium silicate provides an activator for the alkaline activation system. The silicate ions in sodium silicate chemically bond with the hydroxyl groups in the sawdust, dehydrating and condensing to form a dense amorphous silicate gel film, which is beneficial for the corrosion prevention of the sawdust.

[0025] In this invention, the polyester fiber in the waterproof and shrinkage-resistant graphite tailings-sawdust road base material is a short-cut fiber of 16mm-18mm with a linear density of <100dtex.

[0026] The 7-day unconfined compressive strength of the graphite tailings-sawdust road base material ranges from 2.98 to 3.91 MPa.

[0027] The preparation method of the above-mentioned waterproof and shrinkage-resistant graphite tailings-sawdust road base material includes the following steps:

[0028] (1) Raw material pretreatment:

[0029] Pre-treat graphite tailings to control the moisture content to ≤4%. This can be done by natural air drying or low-temperature drying (drying temperature 60-80℃).

[0030] Pre-treat the sawdust to control its moisture content to 0.7%-0.8%. It can be dried using a dryer at a low temperature (60-80℃).

[0031] (2) Preparation of dispersion:

[0032] First, add the modified MIL-125(Ti) to water accounting for 30% of the total weight of water, and perform segmented sonication: first sonicate at 300W for 3-4 minutes, let stand for 1-2 minutes; then sonicate at 350W for 4-5 minutes to further improve the stability of the dispersion and ensure that the modified MIL-125(Ti) is fully dispersed to obtain dispersion A.

[0033] Then, solid NaOH is first added to water accounting for 30% of the total weight of water to dissolve it. Then, sodium silicate is added under stirring conditions, with the stirring speed controlled at 100-200 rpm and the stirring time at 3-5 min, to obtain solution B.

[0034] (3) Mixing materials:

[0035] First, put the cement and sawdust into the mixer and dry mix for 1-2 minutes. Then add the remaining 40% water and mix at 60-70 rpm for 4-5 minutes at room temperature.

[0036] Then, graphite tailings, metakaolin, and polyester fiber are added to a mixer and stirred to obtain a mixture.

[0037] Then, first add dispersion A to the obtained mixture, and stir at 60-70 r / min for 2-3 min at room temperature. Then add solution B and continue stirring at 60-70 r / min for 2-3 min at room temperature to obtain the graphite tailings-sawdust road base material.

[0038] The preparation method provided by this invention employs segmented ultrasound, involving three processes: ultrasound-static setting-ultrasound, which effectively avoids the agglomeration of modified MIL-125(Ti) material and further ensures that the modified MIL-125(Ti) material can fully play its role in the graphite tailings-sawdust road base.

[0039] The aforementioned graphite tailings-sawdust road base material can be applied to the base construction of Class II and above highways.

[0040] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0041] 1. This invention specifically addresses the environmental hazards associated with solid waste. Traditional base materials can only be treated through simple physical wrapping, which easily leads to excessive leaching of heavy metals, especially arsenic. However, the core of the modified MIL-125(Ti) in this invention is chemical adsorption. This chemical bonding ensures that heavy metal ions, especially arsenic, remain stably within the material and do not easily desorb, thus solving the problem of difficult removal of low-concentration arsenic and avoiding secondary pollution that may result from physical adsorption.

[0042] 2. Graphite tailings-sawdust materials exhibit significant shrinkage due to drying and thermal shrinkage. Traditional materials lack effective shrinkage compensation methods, making them prone to cracking. The addition of polyester fibers disperses the locally concentrated tensile stress caused by drying shrinkage throughout the entire structure, reducing the probability of microcracks initiation caused by stress concentration. Modified MIL-125(Ti) effectively inhibits moisture evaporation, resists drying shrinkage, and prevents pavement cracking. The components in the system work together to form a dense structure, reducing the pathways for moisture intrusion. Compared to traditional materials, the water absorption rate is significantly reduced, effectively preventing water immersion from causing softening of road materials, pumping, and other defects, thus extending the service life of roads.

[0043] 3. The present invention is composed of cement, metakaolin, sodium silicate and solid sodium hydroxide to form an alkali activation system, which has the properties of resisting dry and wet cycles, resisting sulfate corrosion and resisting shrinkage cracking; the silicate ions in sodium silicate will chemically bond with the hydroxyl groups in sawdust and form a dense amorphous silicate gel film on the surface of sawdust, effectively solving the problem of sawdust being easy to rot.

[0044] 4. In the preparation method provided by this invention, segmented ultrasonic dispersion is used to improve the dispersibility of modified MIL-125(Ti), effectively avoiding the reduction in mechanical properties caused by agglomeration of modified MIL-125(Ti). Since sawdust has strong water absorption, cement and sawdust are mixed first, and the cement hydration products (CSH gel) are used to fill the pores between sawdust particles. Detailed Implementation

[0045] The present invention will be further described below.

[0046] 1. In the following examples and comparative examples, the graphite tailings were sourced from the Pingdu section of National Highway 206 in Shandong Province; the sawdust was sourced from accumulated waste sawdust in Pingdu City; the cement used was P·O42.5 ordinary Portland cement produced by Shandong Cement Plant; and the metakaolin was sourced from Jinan Tianju New Materials Co., Ltd. Other experimental reagents were all commercially available and will not be described further here.

[0047] The graphite tailings have a particle size of 4-10.5 mm; the sawdust has a moisture content of 0.7%-0.8% and a pH value of 8-9.

[0048] The 28-day activity index of metakaolin is ≥110%, and the content of amorphous silica and aluminum is >90%.

[0049] Solid sodium hydroxide is a flaky solid with a purity of ≥96%.

[0050] 2. Compressive strength loss rate (BDR): The ratio of the compressive strength of the specimen before and after freeze-thaw.

[0051] 3. 7-day unconfined compressive strength: The specimens were placed in a standard curing chamber for 6 days, with the last day being water immersion curing.

[0052] 4. 30-day water absorption rate: The method of drying-soaking-weighing was used.

[0053] 5. The modified MIL-125(Ti) described below was prepared by the following steps:

[0054] First, place MIL-125(Ti) in a vacuum reaction chamber; then place container A containing 5 mL of methyltrimethoxysilane and container B containing 5 mL of an aqueous ethanol solution (ethanol:water volume ratio of 3:2) in the vacuum reaction chamber. Take care to avoid direct contact between the methyltrimethoxysilane and the aqueous ethanol solution and MIL-125(Ti).

[0055] Then, the vacuum reaction chamber was sealed, a vacuum was drawn, the temperature was set to 80°C, and deposition was carried out for 3 hours to obtain the modified MIL-125(Ti).

[0056] Example 1

[0057] The waterproof and shrinkage-resistant graphite tailings-sawdust road base material is composed of the following components in the indicated weight proportions: 30 parts sawdust, 70 parts graphite tailings, 11 parts cement, 15 parts metakaolin, 1 part solid NaOH, 1 part sodium silicate, 0.02 parts polyester fiber, 0.03 parts modified MIL-125(Ti), and 16 parts water.

[0058] The specific surface area of ​​cement is 364.2 m². 2 / kg.

[0059] Sodium silicate has a modulus of 3.0.

[0060] The polyester fiber is a 16mm short-cut fiber with a linear density of <100dtex.

[0061] The preparation method of the waterproof and shrinkage-resistant graphite tailings-sawdust road base material includes the following specific steps:

[0062] (1) Raw material pretreatment:

[0063] The graphite tailings were dried at a low temperature of 60℃ to control the moisture content to ≤4%.

[0064] The sawdust was dried using a dryer at a low temperature of 60℃ until the moisture content was 0.7%-0.8%.

[0065] (2) Preparation of dispersion:

[0066] First, 0.3g of modified MIL-125(Ti) was added to 48g of water and subjected to segmented sonication: first, sonication at 300W for 4min, followed by standing for 2min; then sonication at 350W for 4min to obtain dispersion A.

[0067] Then, 10g of solid NaOH was dissolved in 48g of water, and then 10g of sodium silicate was added under stirring conditions. The stirring speed was controlled at 200rpm and the stirring time was 3min to obtain solution B.

[0068] (3) Mixing materials:

[0069] First, put 110g of P·O 42.5 ordinary Portland cement and 300g of sawdust into the mixer, dry mix for 1 minute, then add the remaining 64g of water and mix at 60r / min for 5 minutes at room temperature.

[0070] Then, add 700g of graphite tailings, 150g of metakaolin and 0.2g of polyester fiber into a mixer and stir to obtain a mixture.

[0071] Then, first add dispersion A to the obtained mixture and stir at 60 r / min for 3 min at room temperature; then add solution B and continue stirring at 60 r / min for 3 min at room temperature to obtain the graphite tailings-sawdust road base material.

[0072] Example 2

[0073] The waterproof and shrinkage-resistant graphite tailings-sawdust road base material is composed of the following components in the indicated weight proportions: 25 parts sawdust, 75 parts graphite tailings, 10 parts cement, 10 parts metakaolin, 0.5 parts solid NaOH, 0.5 parts sodium silicate, 0.01 parts polyester fiber, 0.02 parts modified MIL-125(Ti), and 15 parts water.

[0074] The specific surface area of ​​cement is 378.9 m². 2 / kg.

[0075] Sodium silicate has a modulus of 2.8.

[0076] The polyester fiber is a short-cut fiber with a diameter of 18 mm and a linear density of <100 dtex.

[0077] The others are the same as in Example 1.

[0078] Example 3

[0079] The waterproof and shrinkage-resistant graphite tailings-sawdust road base material is composed of the following components in the indicated weight proportions: 40 parts sawdust, 60 parts graphite tailings, 12 parts cement, 20 parts metakaolin, 1.5 parts solid NaOH, 1.5 parts sodium silicate, 0.03 parts polyester fiber, 0.04 parts modified MIL-125(Ti), and 17 parts water.

[0080] The others are the same as in Example 1.

[0081] Comparative Example 1

[0082] The difference from Example 1 is that the ratio of sawdust to graphite tailings in this comparative example is not within the range described in this invention.

[0083] Specifically:

[0084] The graphite tailings-sawdust road base material is composed of the following components in the indicated weight proportions: 20 parts sawdust, 80 parts graphite tailings, 11 parts cement, 15 parts metakaolin, 1 part solid NaOH, 1 part sodium silicate, 0.02 parts polyester fiber, 0.03 parts modified MIL-125(Ti), and 16 parts water.

[0085] The others are the same as in Example 1.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that the amount of modified MIL-125(Ti) added in this comparative example is not within the range described in this invention.

[0088] Specifically:

[0089] The graphite tailings-sawdust road base material is composed of the following components in the indicated weight proportions: 30 parts sawdust, 70 parts graphite tailings, 11 parts cement, 15 parts metakaolin, 1 part solid NaOH, 1 part sodium silicate, 0.02 parts polyester fiber, 0.08 parts modified MIL-125(Ti), and 16 parts water.

[0090] The others are the same as in Example 1.

[0091] Comparative Example 3

[0092] The difference from Example 1 is that the graphite tailings-sawdust road base material described in this comparative example replaces polyester fibers with polypropylene fibers.

[0093] Specifically:

[0094] It is composed of the following components in the indicated weight proportions: 30 parts sawdust, 70 parts graphite tailings, 11 parts cement, 15 parts metakaolin, 1 part solid NaOH, 1 part sodium silicate, 0.02 parts polypropylene fiber, 0.03 parts modified MIL-125(Ti), and 16 parts water.

[0095] The others are the same as in Example 1.

[0096] Comparative Example 4

[0097] The difference from Example 1 is that the polyester fiber length in the graphite tailings-sawdust road base material described in this comparative example is 50 mm.

[0098] The others are the same as in Example 1.

[0099] Comparative Example 5

[0100] The difference from Example 1 is that the sodium silicate in the graphite tailings-sawdust road base material described in this comparative example is not within the scope of this invention.

[0101] The graphite tailings-sawdust road base material is composed of the following components in the indicated weight proportions: 30 parts sawdust, 70 parts graphite tailings, 11 parts cement, 15 parts metakaolin, 1 part solid NaOH, 5 parts sodium silicate, 0.02 parts polyester fiber, 0.03 parts modified MIL-125(Ti), and 16 parts water.

[0102] The others are the same as in Example 1.

[0103] Comparative Example 6

[0104] The difference from Example 1 is that the graphite tailings-sawdust road base material described in this comparative example does not contain metakaolin.

[0105] The graphite tailings-sawdust road base material is composed of the following components in the indicated weight proportions: 30 parts sawdust, 70 parts graphite tailings, 11 parts cement, 1 part solid NaOH, 1 part sodium silicate, 0.02 parts polyester fiber, 0.03 parts modified MIL-125(Ti), and 16 parts water.

[0106] The others are the same as in Example 1.

[0107] Comparative Example 7

[0108] The difference from Example 1 is that the graphite tailings-sawdust road base material described in this comparative example replaces modified MIL-125(Ti) with ZIF-8.

[0109] Specifically:

[0110] It is composed of the following components in the indicated weight proportions: 30 parts sawdust, 70 parts graphite tailings, 11 parts cement, 15 parts metakaolin, 1 part solid NaOH, 1 part sodium silicate, 0.02 parts polyester fiber, 0.03 parts ZIF-8, and 16 parts water.

[0111] The others are the same as in Example 1.

[0112] Comparative Example 8

[0113] The difference from Example 1 is that the solid NaOH in the graphite tailings-sawdust road base material described in this comparative example is not within the scope of this invention.

[0114] Specifically:

[0115] It is composed of the following components in the indicated weight proportions: 30 parts sawdust, 70 parts graphite tailings, 11 parts cement, 15 parts metakaolin, 5 parts solid NaOH, 1 part sodium silicate, 0.02 parts polyester fiber, 0.03 parts modified MIL-125(Ti), and 16 parts water.

[0116] The others are the same as in Example 1.

[0117] Comparative Example 9

[0118] The difference from Example 1 is that the mixing order of the material mixing in step (3) of the preparation method of graphite tailings-sawdust road base material described in this comparative example is different. Cement and sawdust are directly mixed with other materials.

[0119] Specifically as follows:

[0120] First, put 110g of P·O 42.5 ordinary silicate cement, 300g of sawdust, 700g of graphite tailings, 150g of metakaolin and 0.2g of polyester fiber into a mixer, dry mix for 1 minute, then add the remaining 64g of water and mix at 60r / min for 5 minutes at room temperature.

[0121] Then, first add dispersion A to the obtained mixture and stir at 60 r / min for 3 min at room temperature; then add solution B and continue stirring at 60 r / min for 3 min at room temperature to obtain the graphite tailings-sawdust road base material.

[0122] Comparative Example 10

[0123] The difference from Example 1 is that the order of adding dispersion A and solution B in step (3) of the preparation method of graphite tailings-sawdust road base material described in this comparative example is different. Specifically:

[0124] First, put 110g of P·O 42.5 ordinary Portland cement and 300g of sawdust into the mixer, dry mix for 1 minute, then add the remaining 64g of water and mix at 60r / min for 5 minutes at room temperature.

[0125] Then, add 700g of graphite tailings, 150g of metakaolin and 0.2g of polyester fiber into a mixer and stir to obtain a mixture.

[0126] Then, solution B is added to the resulting mixture and stirred at 60 r / min for 3 min at room temperature; then dispersion A is added and stirred at 60 r / min for 3 min at room temperature to obtain the graphite tailings-sawdust road base material.

[0127] The others are the same as in Example 1.

[0128] Table 1 Performance Indicators of Various Graphite Tailings-Sawdust Road Base Materials

[0129]

[0130] As shown in Table 1, the 7-day unconfined compressive strength of Examples 1-3 is greater than 2.0 MPa, which meets the strength requirements in the "Specifications for Design of Asphalt Pavement of Highways" JTGD50-2017.

[0131] In Comparative Example 1, the 7-day unconfined compressive strength did not meet the strength requirements and the BDR value was small, indicating poor frost resistance and insufficient strength. Comparative Example 1 illustrates the importance of the optimal gradation of the core material sawdust and graphite tailings. When the ratio of the core substrate exceeds the design range, the material's structural density, strength, and durability all decrease to varying degrees.

[0132] Compared with Example 1, the 30-day shrinkage strain in Comparative Example 2 was significantly higher, and the arsenic leaching concentration value increased sharply. The water absorption rate reached its peak at 30 days, and the shrinkage also increased. This shows that the amount of polyester fiber is not necessarily better the more it is used. Excessive polyester fiber will affect the water absorption rate of the material and increase the shrinkage.

[0133] In Comparative Example 3, polyester fiber was replaced with polypropylene fiber, which resulted in varying degrees of deterioration in various indicators, especially strength and 30-day shrinkage strain. This shows that polyester fiber has stronger resistance to shrinkage, and the different fiber types also have a significant impact on strength due to shrinkage cracks.

[0134] In Comparative Example 4, the polyester fiber length was changed to 50 mm, resulting in a 30-day shrinkage strain value that was about four times that of Example 1. This shows that the polyester fiber length is also an important factor affecting the system. The decrease in 7-day unconfined compressive strength is due to the longer polyester fiber length and poorer dispersibility, which affects the interaction between the various systems.

[0135] Comparative Example 5 showed that the sodium silicate content exceeded the range described in this invention, resulting in reduced strength and a lower corrosion resistance coefficient. This demonstrates that a higher sodium silicate content is not necessarily better.

[0136] In Comparative Example 6, due to the lack of metakaolin to provide a highly active silicon-aluminum source, the material's 30-day drying shrinkage strain increased, and its 7-day unconfined compressive strength decreased, which also affected the compressive strength and corrosion resistance coefficient.

[0137] Comparative Example 7 showed varying degrees of performance degradation in various aspects due to the replacement of MOFs materials, especially the excessively high arsenic leaching concentration. Therefore, modified MIL-125(Ti) is irreplaceable, and ZIF-8 cannot achieve good results in this invention.

[0138] In Comparative Example 8, the content of solid NaOH was changed. The increase in the content of solid NaOH caused all indicators to deviate from the normal standard values. This shows that the content of solid NaOH is quite important. The content in this invention is the optimal content.

[0139] In Comparative Example 9, the mixing order was changed. Instead of mixing the sawdust and cement first, they were mixed together. The purpose of mixing them first is to reduce the adverse effects of high water absorption. Therefore, not mixing them first will lead to an increase in the water absorption of the sawdust. The water absorption reaches its maximum value after 30 days. Excessive water absorption will reduce the road durability. Therefore, mixing the sawdust and cement first is a necessary step.

[0140] In Comparative Example 10, the arsenic leaching concentration increased and the 30-day drying shrinkage strain also increased due to the change in the order of adding the modified MIL-125(Ti) dispersion and NaOH and sodium silicate solution. This also had a significant impact on the 30-day water absorption rate and corrosion resistance coefficient. This is because the MOFs material takes effect first when the dispersion is added first. After changing the order of addition, this effect is greatly weakened. It can be seen that the order of addition in this invention cannot be changed.

Claims

1. A waterproof and shrinkage-resistant graphite tailings-sawdust road base material, characterized in that, The composition includes the following components by weight: 25-40 parts sawdust, 60-75 parts graphite tailings, 10-12 parts cement, 10-20 parts metakaolin, 0.5-1.5 parts solid NaOH, 0.5-1.5 parts sodium silicate, 0.01-0.03 parts polyester fiber, 0.02-0.04 parts modified MIL-125(Ti), and 15-17 parts water. The modified MIL-125(Ti) was prepared by the following steps: First, place MIL-125(Ti) in a vacuum reaction chamber; and place container A containing methyltrimethoxysilane and container B containing an aqueous ethanol solution in the vacuum reaction chamber. Then, the vacuum reaction chamber was sealed, a vacuum was drawn, the temperature was set to 80°C, and deposition was carried out for 3 hours to obtain the modified MIL-125(Ti). The polyester fiber is a short-cut fiber of 16mm-18mm with a linear density of <100dtex; The waterproof and shrinkage-resistant graphite tailings-sawdust road base material is prepared through the following steps: (1) Raw material pretreatment: Pre-treat graphite tailings to control the moisture content to ≤4%; Pre-treat the sawdust to control its moisture content to 0.7%-0.8%; (2) Preparation of dispersion: First, add the modified MIL-125(Ti) to water accounting for 30% of the total weight of water, and perform segmented sonication: first sonicate at 300W for 3-4 minutes, let stand for 1-2 minutes; then sonicate at 350W for 4-5 minutes to obtain dispersion A; Then, solid NaOH is first added to water accounting for 30% of the total weight of water to dissolve it. Then, sodium silicate is added under stirring conditions, with the stirring speed controlled at 100-200 rpm and the stirring time at 3-5 min, to obtain solution B. (3) Mixing materials: First, put the cement and sawdust into the mixer, dry mix for 1-2 minutes, then add the remaining 40% water and mix at 60-70 rpm for 4-5 minutes at room temperature. Then, graphite tailings, metakaolin, and polyester fiber are added to a mixer and stirred to obtain a mixture. Then, first add dispersion A to the obtained mixture and stir at 60-70 r / min for 2-3 min at room temperature; then add solution B and continue stirring at 60-70 r / min for 2-3 min at room temperature to obtain the graphite tailings-sawdust road base material.

2. The waterproof and shrinkage-resistant graphite tailings-sawdust road base material according to claim 1, characterized in that, The volume ratio of methyltrimethoxysilane to ethanol aqueous solution is 1:1; the volume ratio of ethanol to water is 3:

2.

3. The waterproof and shrinkage-resistant graphite tailings-sawdust road base material according to claim 1, characterized in that, The graphite tailings have a particle size of 4-10.5 mm; the sawdust has a moisture content of 0.7%-0.8% and a pH value of 8-9.

4. The waterproof and shrinkage-resistant graphite tailings-sawdust road base material according to claim 1, characterized in that, The specific surface area of ​​the cement is 360-380 m². 2 / kg.

5. The waterproof and shrinkage-resistant graphite tailings-sawdust road base material according to claim 1, characterized in that, The metakaolin has a 28-day activity index ≥110% and an amorphous silica-alumina content >90%.

6. The waterproof and shrinkage-resistant graphite tailings-sawdust road base material according to claim 1, characterized in that, The solid NaOH is a flaky solid with a purity of ≥96%.

7. The waterproof and shrinkage-resistant graphite tailings-sawdust road base material according to claim 1, characterized in that, The modulus of the sodium silicate is 2.8-3.

0.

8. The method for preparing the waterproof and shrinkage-resistant graphite tailings-sawdust road base material as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) Raw material pretreatment: Pre-treat graphite tailings to control the moisture content to ≤4%; Pre-treat the sawdust to control its moisture content to 0.7%-0.8%; (2) Preparation of dispersion: First, add the modified MIL-125(Ti) to water accounting for 30% of the total weight of water, and perform segmented sonication: first sonicate at 300W for 3-4 minutes, let stand for 1-2 minutes; then sonicate at 350W for 4-5 minutes to obtain dispersion A; Then, solid NaOH is first added to water accounting for 30% of the total weight of water to dissolve it. Then, sodium silicate is added under stirring conditions, with the stirring speed controlled at 100-200 rpm and the stirring time at 3-5 min, to obtain solution B. (3) Mixing materials: First, put the cement and sawdust into the mixer, dry mix for 1-2 minutes, then add the remaining 40% water and mix at 60-70 rpm for 4-5 minutes at room temperature. Then, graphite tailings, metakaolin, and polyester fiber are added to a mixer and stirred to obtain a mixture. Then, first add dispersion A to the obtained mixture and stir at 60-70 r / min for 2-3 min at room temperature; then add solution B and continue stirring at 60-70 r / min for 2-3 min at room temperature to obtain the graphite tailings-sawdust road base material.

Images