Fly ash-based water-stable materials and their preparation methods

Abstract

The present invention discloses a water-stable material based on fly ash and its preparation method, belonging to the technical field of concrete. The water-stable material based on fly ash of the present invention comprises the following raw materials: cement, coal gangue, fly ash, sand, desulfurized gypsum, modified nano-material, water, water reducer, dispersant, activator. Using fly ash as an additive in the water-stable material can reduce the demand for traditional stone materials, thus helping to conserve natural resources. Fly ash has a fine powder-like particle morphology, which can fill the pores of the water-stable material, reduce the porosity during the compaction process of the material, and thus improve the working performance of the material, such as reducing shrinkage, increasing plasticity and fluidity. The acquisition cost of fly ash is relatively low, and its use can reduce the demand for other raw materials, further reducing the production cost.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and in particular to a water-stable material based on fly ash and a preparation method thereof. Background Art

[0002] Water stability is the abbreviation of the cement-stabilized crushed stone layer, that is, cement is used to consolidate graded crushed stone and is completed through compaction and curing. Cement-stabilized crushed stone, as a semi-rigid material, is widely used in the base course and sub-base course of high-grade highways in China. The cement-stabilized crushed stone base course has the characteristics of high strength, good plate property, strong bearing capacity and strong anti-deformation ability, and is more suitable for the heavy traffic conditions in China. Moreover, the raw materials of the cement-stabilized crushed stone base course are widely available. Therefore, at present, the base courses of the vast majority of high-grade highways in China are made of cement-stabilized crushed stone materials.

[0003] During the development of expressways, the problems of early pavement damage and insufficient durability are very common. To make the capital investment in highway construction and the consumption of raw material resources play a greater benefit, it is necessary to improve the durability of the roadbed and pavement and extend the service life of the road. Among the high-grade highways built in China, semi-rigid base asphalt pavements account for about ninety percent, and most of the semi-rigid bases are made of cement-stabilized crushed stone materials. Although the cement-stabilized crushed stone mixture has high strength, strong bearing capacity and good plate property, it also has the problems of easy generation of thermal shrinkage and dry shrinkage cracks, causing base course cracking, and thus leading to the generation of reflection cracks. Moreover, the water-stable base course has problems of poor water stability and insufficient durability. In the inspections of many roads during major and medium repairs, it has been found that the original cement-stabilized crushed stone base course has been in a loose state. Therefore, it is necessary to study and improve the durability of cement-stabilized crushed stone base course materials, such as anti-cracking performance, anti-freezing performance and fatigue performance.

[0004] There are many factors affecting the durability of the cement stabilized macadam base course, including aggregate gradation, cement dosage, mixing method, etc. Therefore, to improve the durability of the cement stabilized macadam material, it is necessary to analyze many influencing factors: (1) Mixing method: The mixing method of the cement stabilized macadam material has an impact on its road performance and durability. The main reason is that different mixing methods result in different degrees of mixing uniformity of the cement stabilized macadam mixture. Currently, the mixing machinery used for mixing the cement stabilized macadam mixture mainly adopts the continuous forced mixing technology based on the application of forced mixing technology. However, when its rotational speed exceeds the critical rotational speed, due to the existence of centrifugal force, the materials will adhere to the cylinder wall. And when the rotational speed of the mixer is too fast, the components in the cement stabilized macadam mixture will be thrown off by the mixing blades at different speeds due to different inertia, resulting in segregation of the mixed mixture and low mixing uniformity. The principle of the vibration mixing technology is to install a vibrator on the mixing device, which will make the mixing structure mix forcibly while vibrating. The mixture will also obtain vibration energy while being mixed. The fine cement clumps aggregated together will be dispersed into tiny cement particles in the flutter state, and the cement particles can be more evenly distributed on the surface of the aggregate; (2) The influence of cement dosage on the durability of the cement stabilized macadam is that increasing the cement dosage can enhance the cementitious performance of the cement stone, making the bonding performance between the cement stone and the aggregate surface stronger, and improving the strength and deformation resistance of the cement stabilized macadam; (3) The durability of the cement stabilized macadam material is also related to the gradation structure of its aggregate. The gradation structure of the cement stabilized macadam mixture includes suspended dense structure, skeleton dense structure, and skeleton void structure. For the cement stabilized macadam material with a suspended dense gradation, the aggregate particles are suspended in the cement stone structure and cannot effectively form interlock. The cement stone occupies most of the volume of the mixture, so there are more microcracks and micropores in the structure, and the fatigue performance of the mixed material basically depends on the fatigue performance of the cement stone. For the cement stabilized macadam material with a skeleton dense structure, the aggregate particles form a skeleton through multi-level interlock. On the one hand, the cement stone after cement hydration fills the skeleton formed by the aggregate interlock; on the other hand, the aggregate particles have a larger internal friction angle and stronger deformation resistance; (4) Adding appropriate amounts of other materials such as fiber, expansive agent, and nano-materials to the cement stabilized macadam can also improve its road performance and durability, and the reason is also related to the properties of the added materials.

[0005] Patent CN111960772 A discloses a modified anti-cracking cement-stabilized recycled base mixture and its preparation method. It aims to solve the technical problem of significantly improving the mechanical strength and durability of the base material while taking into account the anti-cracking effect of high-dosage RMAP water-stabilized recycled base materials. The inventive mixture is made of the following raw materials: mixed aggregate, cement, nano-magnesium oxide, graphene oxide nanosheets, carbon nanotubes, water reducer, and dispersant. The inventive mixture adds the three nanomaterials to the recycled base material after synergistic dispersion treatment, which greatly improves its mechanical properties and antifreeze ability while ensuring its good anti-cracking effect, so that the overall road performance of the recycled base material is significantly improved; using high-dosage waste pavement materials, the raw materials are widely available, recycled on-site, saving construction costs, environmentally friendly, and having good economic and ecological benefits.

[0006] Patent CN113603411 A discloses an environmentally friendly composite admixture modified cement stabilized gravel mixture, which is made of the following raw materials in parts by weight: 75-90 parts of gravel, 0.3-1.5 parts of modified rubber powder, 0.3-1.0 parts of nanographene microsheets, 3-8 parts of cement, 0.02-0.10 parts of retarder, 9-16 parts of ceramic fragments, 0.3-2.2 parts of coconut shell fiber, and 0.5-1.9 parts of tamarisk fiber; the amount of water added accounts for 4.2-6.5% of the mass of dry materials. The environmentally friendly composite admixture modified cement stabilized gravel mixture of the invention has excellent road performance, simple preparation process, non-toxic and harmless raw materials, and can improve the antifreeze performance and shrinkage performance of the road base, which plays a significant role in extending the service life of asphalt pavement; the environmentally friendly composite admixture modified cement stabilized gravel mixture of the invention is environmentally friendly and low-carbon, and the raw materials are widely available, the production process is pollution-free, and the price is low, the cost is low, and it has good economic and social benefits.

[0007] At present, adding nanomaterials is a widely used method. Adding nanomaterials to cement-stabilized gravel base can greatly improve the anti-cracking and anti-freezing properties of the cement-stabilized gravel base. However, the agglomeration of nanomaterials in the cement-stabilized gravel layer is very obvious, and the agglomeration will affect the strength of the cement-stabilized gravel layer. Not only will it not improve the performance, but it will also affect its performance. Therefore, it is necessary to modify the added nanomaterials to improve their dispersibility. Such modified nanomaterials not only have good dispersibility, but also play a very important role in improving the performance of the cement-stabilized gravel layer. Summary of the invention

[0008] In view of the above-mentioned defects in the prior art, the technical problem to be solved by the present invention is to provide a water-stable material with excellent compression and crack resistance and a preparation method thereof.

[0009] In the present invention, the inventors used lipoic acid and nano-silica as raw materials to synthesize a modified nano-material with a linear polymer structure. Due to the nano-scale effect of the nano-composite material, they can serve as a matrix and nucleation sites during the nucleation and growth of cement hydration products. Calcium ions are important factors affecting cement hydration and the composition of hydration products, and the prepared modified nano-materials have a strong adsorption effect on calcium ions, which can promote the formation of cement hydration products Ca(OH)2 and C-S-H. As the cement hydration progresses, the alkalinity of the cement pore solution also gradually increases. At the same time, the alkalinity promotes the hydrolysis of S-S bonds in the modified nano-materials into smaller mercapto acid nano-silica molecules, which have more carboxyl groups and can bind more Ca 2+ . The binding between a large number of carboxyl groups in the modified nano-materials and calcium ions mainly relies on electrostatic adsorption, which may lead to the nucleation and growth of hydration products Ca(OH)2 and C-S-H. At the same time, a large amount of Ca(OH)2 is consumed by the pozzolanic reaction of nano-silica, which may also be beneficial to the formation of additional C-S-H. These factors combined promote the improvement of the mechanical properties of the cement stabilized macadam layer. The modified nano-materials with a linear polymer structure have good self-healing properties due to the presence of hydrogen bonds, coordination bonds, and dynamic covalent S-S bonds, and this property can help improve the frost resistance of the cement stabilized macadam layer.

[0010] In the present invention, the water stable material made of gangue, desulfurized gypsum, fly ash, and cement forms strength by the close embedding and extrusion between the coarse aggregate gangue. The pores are filled with cement, fly ash, and desulfurized gypsum. After hardening, it can not only improve the macroscopic strength of the base material, but also improve its road performance including dry shrinkage and temperature shrinkage performance. In the initial stage of compaction and forming, the strength of the mixture comes from the internal frictional resistance between the skeletons and the filling of fly ash and desulfurized gypsum, and the molecular attraction between the water film and adjacent fine particles; after high-temperature calcination and mechanical activation, the original crystalline phase of the gangue is decomposed and destroyed, generating amorphous non-crystalline SiO2 and Al2O3, which react with Ca + in the mixture to produce C-S-H gel substances such as 3CaO·2SiO2·H2O and 3CaO·Al2O3·3CaSO4·32H2O, filling the voids and cracks in the mixture and making the mixture more dense; the CaO content in the gangue is very low, but the reaction consumes a certain amount of Ca(OH)2, while the cement undergoes a hydration reaction to produce Ca(OH)2, which can promote the reaction of the active substances in the gangue. As the curing age increases, the colloidal products generated by the hydration of the binder in the water stable material further increase the bonding strength between the aggregates, and the strength of the water stable material is enhanced.

[0011] FlyAsh is a by-product formed by fine particulate matter in the flue gas of coal-fired power plants. Using fly ash as an additive in water-stabilized materials can reduce the demand for traditional stone materials, thus helping to conserve natural resources. Fly ash has a fine powder-like particle morphology, which can fill the pores of water-stabilized materials, reduce the porosity during the compaction process of the materials, and thus improve the working performance of the materials, such as reducing shrinkage, increasing plasticity and fluidity. Compared with traditional water-stabilized materials, using fly ash as an additive can reduce the cost of the materials. The acquisition cost of fly ash is relatively low, and its use can reduce the demand for other raw materials, further reducing the production cost.

[0012] The technical solution of the present invention:

[0013] A water-stabilized material based on fly ash, comprising the following raw materials in parts by weight: 1-5 parts of cement, 50-70 parts of coal gangue, 4-8 parts of fly ash, 5-15 parts of sand, 5-10 parts of desulfurized gypsum, 1-3 parts of modified nano-material, 4-10 parts of water, 0.1-0.3 part of water reducing agent, 0.1-0.3 part of dispersant, and 0.1-0.2 part of activator.

[0014] The preparation method of the modified nano-material comprises the following steps:

[0015] S1 Weigh 5-15 parts by weight of nano-silica and add it to 50-100 parts by weight of absolute ethanol, and ultrasonically disperse for 30-60 min to obtain solution A; weigh 0.8-1.2 parts by weight of KH-540, 3.5-4.5 parts by weight of absolute ethanol, and 0.2-0.6 parts by weight of water, and prepare solution B; heat solution A to 40-60 °C and then add solution B to it. After adding, raise the temperature to 70-90 °C and stir for 2-4 h. After the reaction is completed, centrifuge and dry to obtain amino-modified nano-silica;

[0016] S2 Weigh 10-30 parts by weight of lipoic acid, heat it to 140-160 °C to obtain linear lipoic acid polymer, add the amino-modified nano-silica obtained in step S1, then add 60-100 parts by weight of toluene, cool to 100-140 °C and stir for 2-4 h. After the reaction is completed, centrifuge and dry to obtain a modified nano-material with a linear polymer structure.

[0017] Preferably, the water reducing agent is one of lignosulfonate water reducing agents, fatty acid water reducing agents, and polycarboxylic acid water reducing agents.

[0018] Preferably, the dispersant is one of silicates, alkali metal phosphates, cellulose derivatives, or paraffins.

[0019] Preferably, the activator is one or two of sodium sulfate, triethanolamine, calcium hydroxide, and sodium silicate.

[0020] A preparation method of a water-stable material based on fly ash, comprising the following steps:

[0021] X1 Crush and screen the coal gangue, then calcine and grind it.

[0022] X2 Mix and stir the coal gangue, fly ash, sand, desulfurized gypsum, and modified nanomaterial in step X1 until uniform to obtain a preliminary mixture.

[0023] X3 Add water, cement, water reducer, dispersant, and activator to the preliminary mixture prepared in X2, mix and stir evenly to prepare the water-stable material.

[0024] Preferably, the preparation method of the water-stable material based on fly ash comprises the following steps:

[0025] X1 Crush 50 - 70 parts by weight of coal gangue and screen it through a 2-mm square-hole sieve, calcine it at 600 - 800 °C for 1 - 3 h, and then grind it for 2 - 4 min.

[0026] X2 Mix and stir the coal gangue obtained in step X1 with 4 - 8 parts by weight of fly ash, 5 - 15 parts by weight of sand, 5 - 10 parts by weight of desulfurized gypsum, and 1 - 3 parts by weight of modified nanomaterial until uniform, with a stirring speed of 30 - 50 r / min, to obtain a preliminary mixture.

[0027] X2 Add 4 - 10 parts by weight of water, 1 - 5 parts by weight of cement, 0.1 - 0.3 parts by weight of water reducer, 0.1 - 0.3 parts by weight of dispersant, and 0.1 - 0.3 parts by weight of activator to the preliminary mixture prepared in X2, mix and stir evenly, with a stirring speed of 30 - 50 r / min, to prepare the water-stable material.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) After being activated by the activator, the fly ash added in the present invention reacts with the hydration product Ca(OH)2 of cement to generate CaSO4·2H2O (gypsum) and NaOH. The specific surface area of the generated gypsum is large, which can accelerate the hydration of C3A while promoting the formation of calcium sulfoaluminate, thereby accelerating the cement hydration process; the formation of calcium sulfoaluminate leads to the volume expansion of the composite system, reducing the pores and increasing the density of the cement-fly ash composite system.

[0030] (2) The added coal gangue has a relatively low density after activation and crushing, which can reduce the internal pores of the base course, decrease the expansion effect and capillary action of water, increase the particle contact area, enhance the connectivity and integrity between particles, reduce the solid shrinkage and liquid shrinkage of the base course, and form a good skeleton-type structure inside the base course. The chemical product crystals of cement, coal gangue, and fly ash can form a network structure covering the gaps between the base course particles, improve the compactness of the base course, thereby enhancing the mechanical properties of the base course and reducing the possibility of moisture migration and shrinkage inside the base course;

[0031] (3) For the prepared modified nano-materials with a linear polymer structure, due to the nano-scale effect of the nano-composite materials, they can serve as the matrix and nucleation points during the nucleation and growth process of cement hydration products. Moreover, the prepared modified nano-materials have a strong adsorption effect on calcium ions, which can promote the formation of cement hydration products Ca(OH)2 and C-S-H, and this plays an important role in improving the mechanical properties. In addition, the modified nano-materials with a linear polymer structure have good self-healing properties due to the presence of hydrogen bonds, coordination bonds, and dynamic covalent S-S bonds, and this property can help improve the frost resistance of the cement stabilized macadam layer. Specific embodiments

[0032] Next, the technical solutions of the present invention will be described in detail through specific embodiments. However, it should be clearly stated that these embodiments are used for illustrative purposes only and are not construed as limiting the scope of the present invention.

[0033] The parameters of some raw materials in the embodiments of the present invention are as follows:

[0034] Nano-silica, particle size: 20 nm, model: PST-G02, Nanjing Baokete New Materials.

[0035] Polycarboxylate superplasticizer: SPC-100, solid content: 21.0 ± 1.0%, Liaoning Kelong Fine Chemicals.

[0036] Coal gangue, Lingshou Yuteng Mineral Products Factory.

[0037] Fly ash, 200 mesh, Hebei Chuangtian Engineering Materials.

[0038] Sand, 50 - 100 mesh, Jiangxi Kangrong Environmental Protection Materials.

[0039] Desulfurized gypsum, 325 mesh, model: 2546856, Shandong Pengzhan Chemical Industry.

[0040] Cement, product number: CX-1000, Wuxi Jianghuai Building Materials Technology.

[0041] Crushed stone, apparent density: 1800 kg / m 3 , Lingshou Jinhong Mining Co., Ltd.

[0042] Control Example 1

[0043] A preparation method of a fly ash-based water-stable material and its preparation method includes the following steps:

[0044] X1 Crush 60 kg of coal gangue and pass it through a 2 mm square-hole sieve, calcine it at 700 °C for 2 h, and then grind it for 3 min;

[0045] X2 Mix and stir the coal gangue obtained in step X1 with 6 kg of fly ash, 10 kg of sand, 7.5 kg of desulfurized gypsum, and 2 kg of nano-silica until uniform, with a stirring speed of 40 r / min to obtain a preliminary mixture;

[0046] X3 Add 7 kg of water, 3 kg of cement, 0.2 kg of polycarboxylate water reducer, 0.2 kg of carboxymethyl cellulose, and 0.12 kg of sodium sulfate to the preliminary mixture obtained in X2, mix and stir evenly, with a stirring speed of 50 r / min, to obtain the water-stable material.

[0047] Example 1

[0048] A preparation method of a fly ash-based water-stable material and its preparation method includes the following steps:

[0049] X1 Crush 60 kg of coal gangue and pass it through a 2 mm square-hole sieve, calcine it at 700 °C for 2 h, and then grind it for 3 min;

[0050] X2 Mix and stir the coal gangue obtained in step X1 with 6 kg of fly ash, 10 kg of sand, 7.5 kg of desulfurized gypsum, and 2 kg of modified nano-material until uniform, with a stirring speed of 40 r / min to obtain a preliminary mixture;

[0051] X3 Add 7 kg of water, 3 kg of cement, 0.2 kg of polycarboxylate water reducer, 0.2 kg of carboxymethyl cellulose, and 0.12 kg of sodium sulfate to the preliminary mixture obtained in X2, mix and stir evenly, with a stirring speed of 50 r / min, to obtain the water-stable material.

[0052] The preparation method of the modified nano-material includes the following steps:

[0053] S1 Weigh 9 kg of nano-silica and add it to 90 L of absolute ethanol, ultrasonically disperse it at 400 W and 45 kHz for 45 min to obtain solution A; take 1 kg of KH-540, 3 L of absolute ethanol, and 0.4 L of water, and prepare solution B; heat solution A to 50 °C and then add solution B to it. After adding, raise the temperature to 80 °C and stir for 3 h. After the reaction ends, centrifuge at 5000 rpm for 10 min, and then dry at 60 °C for 4 h to obtain amino-modified nano-silica;

[0054] Weigh 20 kg of lipoic acid, heat it to 150 °C to obtain a linear lipoic acid polymer, add the amino-modified nano-silica obtained in step S1, then add 100 L of toluene, cool down to 120 °C and stir for 3 h. After the reaction ends, centrifuge at 5000 rpm for 10 min, and then dry at 60 °C for 8 h to obtain a modified nano-material with a linear polymer structure.

[0055] Example 2

[0056] A preparation method of a water-stable material made from coal gangue, desulfurized gypsum and cement includes the following steps:

[0057] X1 Crush 60 kg of coal gangue and pass it through a 2-mm square-hole sieve, calcine it at 700 °C for 2 h, and then grind it for 3 min;

[0058] X2 Mix and stir evenly the coal gangue, 10 kg of sand, 7.5 kg of desulfurized gypsum and 2 kg of modified nano-material obtained in step X1, with a stirring speed of 40 r / min to obtain a preliminary mixture;

[0059] X3 Add 7 kg of water, 3 kg of cement, 0.2 kg of polycarboxylate superplasticizer and 0.2 kg of carboxymethyl cellulose to the preliminary mixture prepared in X2, mix and stir evenly, with a stirring speed of 50 r / min, to obtain the water-stable material.

[0060] The preparation method of the modified nano-material includes the following steps:

[0061] S1 Weigh 9 kg of nano-silica and add it to 90 L of absolute ethanol, ultrasonically disperse it at 400 W and 45 kHz for 45 min to obtain solution A; take 1 kg of KH-540, 3 L of absolute ethanol and 0.4 L of water, and prepare solution B; heat solution A to 50 °C and then add solution B to it. After adding, raise the temperature to 80 °C and stir for 3 h. After the reaction ends, centrifuge at 5000 rpm for 10 min, and then dry at 60 °C for 4 h to obtain amino-modified nano-silica;

[0062] S2 Weigh 20 kg of lipoic acid, heat it to 150 °C to obtain a linear lipoic acid polymer, add the amino-modified nano-silica obtained in step S1, then add 100 L of toluene, cool down to 120 °C and stir for 3 h. After the reaction ends, centrifuge at 5000 rpm for 10 min, and then dry at 60 °C for 8 h to obtain a modified nano-material with a linear polymer structure.

[0063] Example 3

[0064] A preparation method of a water-stable material made from desulfurized gypsum, fly ash and cement includes the following steps:

[0065] X1 mixes 60 kg of crushed stones with 6 kg of fly ash, 10 kg of sand, 7.5 kg of desulfurized gypsum, and 2 kg of modified nano-material and stirs them until uniform at a stirring speed of 40 r / min to obtain a preliminary mixture;

[0066] X2 adds 7 kg of water, 3 kg of cement, 0.2 kg of polycarboxylate water reducer, 0.2 kg of carboxymethyl cellulose, and 0.12 kg of sodium sulfate to the preliminary mixture prepared by X1, mixes and stirs them evenly at a stirring speed of 50 r / min to obtain a water-stabilized material.

[0067] The preparation method of the modified nano-material includes the following steps:

[0068] S1 Weigh 9 kg of nano-silica and add it to 90 L of absolute ethanol, ultrasonically disperse it at 400 W and 45 kHz for 45 min to obtain solution A; take 1 kg of KH-540, 3 L of absolute ethanol, and 0.4 L of water, and prepare them into solution B; heat solution A to 50 °C and then add solution B to it. After adding, raise the temperature to 80 °C and stir for 3 h. After the reaction is completed, centrifuge at 5000 rpm for 10 min, and then dry at 60 °C for 4 h to obtain amino-modified nano-silica;

[0069] S2 Weigh 20 kg of lipoic acid, heat it to 150 °C to obtain linear lipoic acid polymer, add the amino-modified nano-silica obtained in step S1, then add 100 L of toluene, cool it to 120 °C and stir for 3 h. After the reaction is completed, centrifuge at 5000 rpm for 10 min, and then dry at 60 °C for 8 h to obtain a modified nano-material with a linear polymer structure.

[0070] Test Example 1

[0071] The mixtures prepared in the control example and the examples are subjected to ordinary forced stirring to make medium-sized beam specimens (size: 100 mm × 100 mm × 400 mm). The formed specimens need to be carefully moved to prevent the generation of sediment from affecting the test results. The specimens are made into medium-sized beam specimens through a temperature shrinkage test by pressing and molding, and cured in a marked curing room for 90 d. Then, after drying both sides of the specimens, resistance strain gauges are pasted on them, and then they are placed in a multi-purpose high and low temperature box and kept at a constant temperature for 2 h and heated by 5 °C every 2 h. When the data at each temperature segment is stable, the corresponding readings are read by an automatic data acquisition instrument. The evaluation index, the temperature shrinkage coefficient, is the linear shrinkage coefficient of the material change per unit temperature: α t = β m1 =(Δε / ΔT + β m2 ):

[0072] Where: α t - Average temperature shrinkage coefficient (1×10 -6 / °C);

[0073] β m1- Coefficient of shrinkage of the test specimen (1×10 -6 / °C);

[0074] β m2 - Coefficient of shrinkage of the standard specimen (1×10 -6 / °C);

[0075] Δε - Temperature shrinkage strain of the test specimen / 1×10 -6 ;

[0076] ΔT - Temperature variable of the test / °C.

[0077] Table 1 Test results of temperature shrinkage performance

[0078]

[0079] The temperature shrinkage coefficient is represented by α t to analyze the temperature shrinkage law of the water-stabilized material. At the same time, the temperature shrinkage coefficient α t also indirectly reflects the ability of the material to maintain its volume unchanged against temperature changes; compared with structural materials with a smaller temperature shrinkage coefficient, those with a larger temperature shrinkage coefficient are more sensitive to volume changes caused by temperature changes. Therefore, for water-stabilized materials, materials with a smaller temperature shrinkage coefficient are beneficial to crack resistance. The gangue selected in Example 1 has a smaller density after activation and pulverization, which can reduce the internal pores of the base layer, reduce the expansion effect and capillary action of water, increase the particle contact area, enhance the connectivity and integrity between particles, reduce the solid shrinkage and liquid shrinkage of the base layer, and form a good skeleton structure inside the base layer. The chemical product crystals of cement, gangue, and fly ash can form a network structure covering the gaps between the base layer particles, improve the compactness of the base layer, thereby enhancing the mechanical properties of the base layer and reducing the possibility of moisture migration and shrinkage inside the base layer. In addition, the products reacting with cement can offset the deformation of the base layer caused by temperature shrinkage to a certain extent, thereby improving the temperature shrinkage performance of the base layer. The prepared modified nano-material with a linear polymer structure has good self-healing properties due to the presence of hydrogen bonds, coordination bonds, and dynamic covalent S-S bonds. When facing temperature changes, the deformation of the base layer caused by temperature shrinkage can be more easily restored due to self-healing, so it has good frost resistance.

[0080] Test Example 2

[0081] The unconfined compressive strength test was carried out on the waterstabilized materials prepared in the control examples and the examples. The specimens (Φ150mm×150mm cylindrical) were prepared according to the static compaction method in the "Test Regulations for Inorganic Binding Material Stabilized Materials in Highway Engineering" (JTG E51-2009). After the formed specimens were demolded, they were covered with plastic bags and transferred to a standard curing room at a temperature of 20°C and a relative humidity of more than 95%. After curing for 28 days, the unconfined compressive strength test was carried out. The unconfined compressive strength test was carried out on the standard specimens cured to the specified age according to the specification. 6 specimens to be tested were set in each group. The specimens should be immersed in water for 24 hours before reaching the age. Before the test started, the surface moisture of the specimens was wiped dry, the height of the specimens was measured, and then the specimens were placed on the press. During the test, the loading rate of the press was kept at 1mm / min. Record the maximum pressure P when the specimens were damaged. The unconfined compressive strength of the specimens was calculated according to R c =P / A, where R c is the unconfined compressive strength of the specimen (MPa), P is the maximum pressure when the specimen is damaged (N), and A is the cross-sectional area of the specimen. The specific test results are shown in Table 2.

[0082] Table 2 Unconfined Compressive Strength Test and Self-healing Test Results

[0083] Experimental scheme 28-day compressive strength / MPa Control Example 1 4.5 Example 1 5.3 Example 2 4.4 Example 3 4.6

[0084] It can be seen from the compressive strength test that compared with Example 1 and Example 2, due to the addition of fly ash and activator Na2SO4, it reacts with the cement hydration product Ca(OH)2 to generate CaSO4·2H2O (gypsum) and NaOH. The specific surface area of the generated gypsum is large, which promotes the formation of calcium sulfoaluminate while accelerating the hydration of C3A, and then accelerates the cement hydration process; the formation of calcium sulfoaluminate leads to the volume expansion of the composite system, reducing the pores and increasing the density of the cement-fly ash composite system. The hydration product C-S-H gel is obtained by the reaction of the cement hydration product Ca(OH)2 with Al2O3 and SiO2 released inside the fly ash particles. The pores in the cement fly ash structure are filled, the porosity is reduced, and the structure is more dense, so the compressive strength is higher. Compared with Example 3 and Example 1, after the coal gangue in Example 1 was calcined at high temperature and mechanically activated, the original crystalline phase of the coal gangue was decomposed and destroyed, generating amorphous non-crystalline SiO2 and Al2O3, which reacted with Ca in the mixture +The reaction produces C-S-H gel substances such as 3CaO·2SiO2·H2O and 3CaO·Al2O3·3CaSO4·32H2O, which fill the voids and cracks in the mixture, making the mixture more dense. The modified nanomaterials with a linear polymer structure added in Example 1, due to the nanoscale effect of the nanocomposite materials, can serve as the matrix and nucleation sites during the nucleation and growth processes of cement hydration products. Moreover, the prepared modified nanomaterials have a strong adsorption effect on calcium ions, which can promote the formation of cement hydration products Ca(OH)2 and C-S-H, and this plays an important role in improving the mechanical properties.

Claims

1. A water-stable material based on fly ash, characterized in that It comprises the following raw materials in parts by weight: 1 - 5 parts of cement, 50 - 70 parts of coal gangue, 4 - 8 parts of fly ash, 5 - 15 parts of sand, 5 - 10 parts of desulfurized gypsum, 1 - 3 parts of modified nano - material, 4 - 10 parts of water, 0.1 - 0.3 part of water - reducing agent, 0.1 - 0.3 part of dispersant, 0.1 - 0.2 part of activator; the coal gangue is obtained by crushing, sieving, then calcining and grinding; The preparation method of the said modified nano - material comprises the following steps: S1 Weigh 5 - 15 parts by weight of nano - silica and add it into 50 - 100 parts by weight of absolute ethanol, ultrasonically disperse for 30 - 60 min to obtain solution A; weigh 0.8 - 1.2 parts by weight of KH - 540, 3.5 - 4.5 parts by weight of absolute ethanol, 0.2 - 0.6 parts by weight of water, and prepare solution B; heat solution A to 40 - 60 °C and then add solution B to it, after adding, raise the temperature to 70 - 90 °C and stir for 2 - 4 h, after the reaction ends, centrifuge and dry to obtain amino - modified nano - silica; S2 Weigh 10 - 30 parts by weight of lipoic acid, heat it to 140 - 160 °C to obtain linear lipoic acid polymer, add the amino - modified nano - silica obtained in step S1, then add 60 - 100 parts by weight of toluene, cool down to 100 - 140 °C and stir for 2 - 4 h, after the reaction ends, centrifuge and dry to obtain the modified nano - material with a linear polymer structure.

2. The water-stable material based on fly ash according to claim 1, characterized in that: The water - reducing agent is one of lignosulfonate water - reducing agent, fatty acid water - reducing agent, polycarboxylate water - reducing agent.

3. The water-stable material based on fly ash according to claim 1, characterized in that: The dispersant is one of silicate, alkali metal phosphate, cellulose derivative or paraffin.

4. The water-stable material based on fly ash according to claim 1, characterized in that: The activator is one or two of sodium sulfate, triethanolamine, calcium hydroxide, sodium silicate.

5. The preparation method of the fly ash-based water-stable material according to any one of claims 1 to 4, characterized in that, It comprises the following steps: X1 Crush and sieve the coal gangue, then calcine and grind it; X2 Mix and stir the coal gangue, fly ash, sand, desulfurized gypsum, and modified nano - material in step X1 until uniform to obtain a preliminary mixture; X3 Add water, cement, water - reducing agent, dispersant, and activator into the preliminary mixture prepared in X2, mix and stir evenly to obtain the water - stable material.

6. The preparation method of the fly ash-based water stable material according to claim 5, characterized in that: In step X1, the calcination temperature is 600 - 800 °C, calcine for 1 - 3 h, and grind for 2 - 4 min.

7. The preparation method of the fly ash-based water-stable material according to claim 5, characterized in that: In steps X2 and X3, the stirring speed is 30 - 50 r / min.

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