A kind of alkali-activated soil solidifying agent and preparation method thereof

Abstract

The invention belongs to the field of building materials, and specifically relates to an alkali-activated soil curing agent and a preparation method thereof, which comprises the following raw materials by weight: 20-25 parts of cement, 70-80 parts of mineral admixture, 13-16 parts of alkaline activator, 4-8 parts of wollastonite powder, 0.3-0.8 parts of fiber, and 3-7 parts of modified chitosan. The alkali-activated soil curing agent obtained by the invention is suitable for engineering slag, has good curing effect, reduces cement consumption, is environmentally friendly, and has good ecological benefits.

Description

Technical Field

[0001] The invention belongs to the field of building materials, and particularly relates to an alkali-activated soil solidifying agent and a preparation method thereof. Background Art

[0002] There are a large number of underground projects in the process of urban construction, which will generate a large amount of construction waste. Most of the abandoned construction waste is piled up on the banks of urban rivers, depressions, vacant land, etc., or even on planned land. This treatment method occupies a large amount of land resources. In addition, the random stacking of waste is prone to landslides, collapses, mudslides and other hazards. In the process of stacking, a large amount of construction waste that cannot be used for engineering backfill is mixed with soil that can be used for engineering backfill without any treatment, resulting in the failure to reasonably utilize the construction waste that can be utilized as a resource, increasing social costs. The traditional method of treating construction waste is to use cement to solidify it. This treatment method requires a large amount of cement. Due to the strong alkalinity of cement, the alkalinity of the solidified engineering waste mud and waste is high. At the same time, the production of cement is a high-energy-consuming process. The firing of cement clinker requires a large amount of fossil energy. These fossil energy will emit a large amount of polluting gases and CO2 into the atmosphere during combustion, exacerbating the greenhouse effect. Therefore, environmentally friendly soil solidifiers that can reduce the amount of cement have become the research focus in this field.

[0003] Patent CN115806417B discloses a curing agent for construction slag, which uses solid wastes such as construction slag, desulfurization ash, industrial byproduct gypsum, slag powder, etc. as components of the curing agent, and makes rational use of waste resources. The alumina in the slag powder accelerates the transformation of calcium sulfate in the desulfurization ash to calcium sulfonite, and uses Al2O3, SiO2 and other components to improve the mechanical properties of the construction slag. Although the curing agent realizes the reuse of waste, it still requires the use of a large amount of cement, which aggravates the greenhouse effect. Patent CN113620655B discloses a curing agent for the base material of the water-stabilizing layer of tailings-based construction slag, which is composed of iron tailings mortar, slag powder, desulfurization gypsum powder, lime powder, and polycarboxylic acid high-efficiency water reducer. The curing agent has good consolidation performance for construction slag with high mud content, and realizes the comprehensive utilization of resources and reduces construction costs. In order to reduce the amount of water used, the invention needs to add a water reducer, which may cause the durability of the solidified slag to decrease.

[0004] Therefore, there is an urgent need to prepare a soil solidifying agent that reduces cement usage, is environmentally friendly, and has good durability of solidified slag. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides an environmentally friendly alkali-activated soil solidifier which is applicable to a variety of soils, has good solidification effect, and reduces cement usage.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The first aspect of the present invention provides an alkali-activated soil solidifier, which comprises the following raw materials by weight: 20-25 parts of cement, 70-80 parts of mineral admixtures, 13-16 parts of alkaline activator, 4-8 parts of wollastonite powder, 0.3-0.8 parts of fiber, and 3-7 parts of modified chitosan.

[0008] In some embodiments, the cement includes one or more of ordinary Portland cement, aluminate cement, and sulphoaluminate cement.

[0009] Preferably, the cement is 42.5 ordinary Portland cement.

[0010] In some embodiments, the mineral admixture includes one or more of coal gangue powder, slag, silica fume, and steel slag powder.

[0011] Preferably, the mineral admixtures are coal gangue powder and slag, with a mass ratio of 1:(0.8-1.1).

[0012] Further preferably, the coal gangue powder is activated coal gangue powder, and the preparation method of activated coal gangue powder comprises the following steps: placing coal gangue with a particle size less than 5 mm in a rapid heating box-type electric furnace, calcining at a temperature of 450-550°C for 2-3 hours, cooling to room temperature, and then grinding the calcined coal gangue with a ball mill, passing through an 8-8.5μm sieve, to obtain activated coal gangue powder.

[0013] The invention activates the coal gangue by means of calcination and grinding, thereby improving the volcanic ash activity of the material and enhancing the alkali excitation effect.

[0014] In some embodiments, the alkaline activator is one or more of CaO, Ca(OH)2, NaOH, Na2SO4, Na2CO3, and water glass.

[0015] Preferably, the alkaline activator is NaOH and Na2CO3, with a mass ratio of 1:(0.9-1.2).

[0016] In some embodiments, the wollastonite powder has a particle size of 500-900 mesh.

[0017] Preferably, the particle size of the wollastonite powder is 800 mesh.

[0018] Further preferably, the wollastonite powder is purified wollastonite powder, and the preparation method of purified wollastonite powder comprises the following steps: subjecting the wollastonite powder to ultrasonic treatment, the ultrasonic time is 4-6 minutes, the ultrasonic power is 100-250W, and then the ultrasonicated wollastonite powder is calcined at 600-800°C for 2-3 hours, and purified wollastonite powder is obtained after filtration, washing and drying.

[0019] The present invention uses ultrasound and calcination to treat wollastonite powder, providing sufficient silicon source and calcium source for the reaction system, increasing the amount of active silicon in the system, and effectively increasing the initial silicon-aluminum ratio and the number of Si-O-Si bonds. Under alkaline conditions, the active calcium content in the system increases, and calcium ions react with Si(OH)4, Al(OH)4 - The monomers combine to form CSH and CASH gels, which promote gel formation, increase the degree of polymerization of the gel network, make the structure denser, and help enhance the compressive strength.

[0020] In some embodiments, the fiber is one or more of corn straw fiber, polypropylene fiber and basalt fiber.

[0021] Preferably, the fiber is corn stover fiber.

[0022] Further preferably, the corn straw fiber is pretreated corn straw fiber, and the pretreatment steps are: soaking the corn straw fiber in 2-3wt% NaOH solution for 30-40min, then washing the straw fiber with water until neutral, and drying at 75-85°C to obtain pretreated corn straw fiber.

[0023] The invention adopts alkali activation to pretreat the straw fiber, solves the shortcomings of traditional soil solidifiers such as high brittleness and low toughness, and improves the bending strength and tensile strength of the solidified soil.

[0024] In some embodiments, the preparation method of the modified chitosan comprises the following steps: stirring acrylic acid and 2,4-hexadien-1-ol at a constant temperature of 70-80°C for 1-2 hours, then adding chitosan, toluene and concentrated sulfuric acid and stirring at a constant temperature of 60-70°C for 5-6 hours, and drying to obtain the modified chitosan.

[0025] In some embodiments, the mass ratio of acrylic acid, 2,4-hexadien-1-ol, and chitosan is (2.8-3):1:(0.8-1.2).

[0026] The present invention adds polymers to the soil, utilizes the steric shielding effect of organic polymer materials, reduces the adsorbed water in the soil, improves the soil's anti-permeability, forms a dense structure when the soil is compacted and formed to ensure good compressive strength, and improves the engineering properties of the soil. The applicant polymerizes acrylic acid and 2,4-hexadiene-1-ol, and then grafts it with chitosan. On the one hand, the gel property of chitosan is utilized to accelerate the solidification of sludge, and on the other hand, the dispersibility of chitosan in water is improved, the internal hardness unevenness after soil solidification is reduced, and the compressive resistance is enhanced. The possible reason is that by limiting the mass ratio of acrylic acid, 2,4-hexadiene-1-ol, and chitosan, the modified chitosan is still a hydrophobic structure, which is conducive to water loss during compaction, is not easy to enter the soil, reduces the pores in the soil, makes the solidified soil more resistant to compression and is not easy to crack, and the double bonds and hydroxyl groups on the chain segments can be complexed with metal ions in the soil, enhance the curing agent and the soil to form a whole to form a cementation, and make the soil more solidified.

[0027] In some embodiments, the alkali-activated soil solidifier further comprises 0.8-1.2 parts by weight of a solidification aid.

[0028] In some embodiments, the method for preparing the curing aid comprises the following steps: adding pentaerythritol and triphenylmethane triisocyanate into DMF, reacting at 60-70° C. for 5-6 hours, rotary evaporating, and drying to obtain the curing aid.

[0029] The present invention prepares a curing aid, which contains multiple isocyanate groups and benzene rings in a molecular structure. On the one hand, the hardness of the soil after curing is increased, and on the other hand, it can be cross-linked with modified chitosan to form a dense network structure to accelerate soil curing. At the same time, the isocyanate group reacts with water to produce carbon dioxide, so that Ca(OH)2 is converted into CaCO3, and the solid phase volume of CaCO3 is greater than that of Ca(OH)2, thereby reducing the pores in the soil and further improving the density of the soil after curing.

[0030] In some embodiments, the mass ratio of pentaerythritol to triphenylmethane triisocyanate is 1:(11-14).

[0031] The invention limits the mass ratio of pentaerythritol to triphenylmethane triisocyanate, so that the hydroxyl groups of pentaerythritol can react completely on the one hand, and on the other hand, a large amount of free triphenylmethane triisocyanate is provided so that each hydroxyl group of pentaerythritol reacts with a single triphenylmethane triisocyanate.

[0032] The second aspect of the present invention provides a method for preparing an alkali-activated soil solidifier, comprising the following steps: mixing cement, mineral admixtures, wollastonite powder, fiber and modified chitosan for 10-15 minutes, then adding an alkaline activator and continuing to stir for 20-30 minutes to obtain the soil solidifier.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The present invention obtains an alkali-activated soil solidifier by adding modified chitosan and a solidifying aid, which has a good solidifying effect. The solidified soil has a higher hardness and compressive strength, while reducing the amount of cement used and being environmentally friendly.

[0035] 2. The present invention polymerizes acrylic acid and 2,4-hexadiene-1-ol and then grafts them with chitosan. On the one hand, the gel property of chitosan is used to accelerate the solidification of sludge. On the other hand, the dispersibility of chitosan in water is improved, the uneven hardness of the soil after solidification is reduced, and the compression resistance is enhanced.

[0036] 3. The curing aid prepared by the present invention contains multiple isocyanate groups in one molecular structure, which are cross-linked with modified chitosan to form a dense network structure to accelerate soil curing. At the same time, the isocyanate groups react with water to produce carbon dioxide, converting Ca(OH)2 into CaCO3. The solid phase volume of CaCO3 is larger than that of Ca(OH)2, thereby reducing the pores in the soil and further improving the density of the soil after curing. DETAILED DESCRIPTION

[0037] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following examples and comparative examples are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0038] In order to facilitate those skilled in the art to implement the present invention, some raw materials and manufacturers of the embodiments and comparative examples are described as follows: the compounds and related reagents used in the present invention can be purchased from the market.

[0039] Preparation Example 1

[0040] The preparation method of activated coal gangue powder comprises the following steps: placing 10 g of coal gangue with a particle size of less than 5 mm in a fast heating box-type electric furnace, calcining at a temperature of 500° C. for 2.5 hours, cooling to room temperature, and then grinding the calcined coal gangue with a ball mill, passing through an 8.5 μm square hole sieve to obtain activated coal gangue powder.

[0041] Preparation Example 2

[0042] The preparation method of purified wollastonite powder comprises the following steps: subjecting the wollastonite powder to ultrasonic treatment, wherein the ultrasonic time is 5 minutes and the ultrasonic power is 200W, then calcining the ultrasonicated wollastonite powder at 700°C for 2.5 hours, and obtaining the purified wollastonite powder after filtration, washing and drying.

[0043] Preparation Example 3

[0044] The pretreated corn straw fiber comprises the following steps: soaking 5 g corn straw fiber in 100 ml 2 wt % NaOH solution for 35 min, then washing the straw fiber with water until the pH value of the solution is 7, and drying at 80° C. to obtain the pretreated corn straw fiber.

[0045] Preparation Example 4

[0046] The preparation method of modified chitosan-1 comprises the following steps: 2.9g acrylic acid and 1g 2,4-hexadiene-1-ol are stirred at 75°C for 1.5h, 1g chitosan, 50ml toluene and 0.5ml concentrated sulfuric acid are added, stirred at 65°C for 5.5h, and dried to obtain modified chitosan-1.

[0047] Preparation Example 5

[0048] The preparation method of modified chitosan-2 comprises the following steps: 3.5g acrylic acid and 1g 2,4-hexadiene-1-ol are stirred at 75°C for 1.5h, 1g chitosan, 50ml toluene and 0.5ml concentrated sulfuric acid are added, stirred at 65°C for 5.5h, and dried to obtain modified chitosan-2.

[0049] Preparation Example 6

[0050] The preparation method of modified chitosan-3 comprises the following steps: 2.9g acrylic acid and 1g 2,4-hexadiene-1-ol are stirred at 75°C for 1.5h, 2g chitosan, 50ml toluene and 0.5ml concentrated sulfuric acid are added, stirred at 65°C for 5.5h, and dried to obtain modified chitosan-3.

[0051] Preparation Example 7

[0052] The preparation method of curing aid-1 comprises the following steps: adding 1g of pentaerythritol and 12g of triphenylmethane triisocyanate into 20ml of DMF, reacting at 65°C for 5.5h, rotary evaporating, and drying to obtain curing aid-1.

[0053] Preparation Example 8

[0054] The preparation method of curing aid-2 comprises the following steps: adding 1g of pentaerythritol and 8g of triphenylmethane triisocyanate into 20ml of DMF, reacting at 65°C for 5.5h, rotary evaporating, and drying to obtain curing aid-2.

[0055] Example 1

[0056] An alkali-activated soil solidifier comprises the following raw materials, measured by weight: 23 parts of 42.5 ordinary Portland cement, 75 parts of mineral admixtures, 15 parts of alkaline activator, 6 parts of purified wollastonite powder, 0.5 parts of pretreated corn straw fiber, and 5 parts of modified chitosan-1.

[0057] The mineral admixtures are activated coal gangue powder and slag, with a mass ratio of 1:1; the alkaline activator is NaOH and Na2CO3, with a mass ratio of 1:1.

[0058] The preparation method of the alkali-activated soil solidifier of this embodiment comprises the following steps: 42.5 ordinary Portland cement, mineral admixture, purified wollastonite powder, pretreated corn straw fiber and modified chitosan-1 are mixed and stirred for 13 minutes, and then an alkaline activator is added and stirred for 25 minutes to obtain the soil solidifier.

[0059] Example 2

[0060] An alkali-activated soil solidifier comprises the following raw materials, measured by weight: 20 parts of 42.5 ordinary Portland cement, 70 parts of mineral admixtures, 13 parts of alkaline activator, 4 parts of purified wollastonite powder, 0.3 parts of pretreated corn straw fiber, and 3 parts of modified chitosan-1.

[0061] The mineral admixtures are activated coal gangue powder and slag, with a mass ratio of 1:0.8; the alkaline activator is NaOH and Na2CO3, with a mass ratio of 1:0.9.

[0062] The preparation method of the alkali-activated soil solidifier of this embodiment comprises the following steps: 42.5 ordinary Portland cement, mineral admixture, purified wollastonite powder, pretreated corn straw fiber and modified chitosan-1 are mixed and stirred for 10 minutes, and then an alkaline activator is added and stirred for 30 minutes to obtain the soil solidifier.

[0063] Example 3

[0064] An alkali-activated soil solidifier comprises the following raw materials, measured by weight: 25 parts of 42.5 ordinary Portland cement, 80 parts of mineral admixtures, 16 parts of alkaline activator, 8 parts of purified wollastonite powder, 0.8 parts of pretreated corn straw fiber, and 7 parts of modified chitosan-1.

[0065] The mineral admixtures are activated coal gangue powder and slag, with a mass ratio of 1:1.1; the alkaline activators are NaOH and Na2CO3, with a mass ratio of 1:1.2.

[0066] The preparation method of the alkali-activated soil solidifier of this embodiment comprises the following steps: 42.5 ordinary Portland cement, mineral admixture, purified wollastonite powder, pretreated corn straw fiber and modified chitosan-1 are mixed and stirred for 15 minutes, and then an alkaline activator is added and stirred for 20 minutes to obtain the soil solidifier.

[0067] Example 4

[0068] An alkali-activated soil solidifier comprises the following raw materials, measured by weight: 23 parts of 42.5 ordinary Portland cement, 75 parts of mineral admixtures, 15 parts of alkaline activator, 6 parts of purified wollastonite powder, 0.5 parts of pretreated straw fiber, 5 parts of modified chitosan-1, and 1 part of curing aid-1.

[0069] The mineral admixtures are activated coal gangue powder and slag, with a mass ratio of 1:1; the alkaline activator is NaOH and Na2CO3, with a mass ratio of 1:1.

[0070] The preparation method of the alkali-activated soil solidifier of this embodiment comprises the following steps: 42.5 ordinary Portland cement, mineral admixture, purified wollastonite powder, pretreated corn straw fiber and modified chitosan-1 are mixed and stirred for 13 minutes, and then an alkaline activator and curing aid-1 are added and stirred for 25 minutes to obtain the soil solidifier.

[0071] Example 5

[0072] An alkali-activated soil solidifier and a preparation method thereof. The specific implementation manner is the same as that of Example 4, except that an equal amount of modified chitosan-1 is replaced by modified chitosan-2.

[0073] Example 6

[0074] An alkali-activated soil solidifier and a preparation method thereof. The specific implementation manner is the same as that of Example 4, except that an equal amount of modified chitosan-1 is replaced by modified chitosan-3.

[0075] Example 7

[0076] An alkali-activated soil solidifier and a preparation method thereof, wherein the specific implementation manner is the same as that of Example 4, except that an equal amount of solidifying aid-1 is replaced by a solidifying aid-2.

[0077] Comparative Example 1

[0078] An alkali-activated soil solidifier and a preparation method thereof, wherein the specific implementation manner is the same as that of Example 4, except that an equal amount of modified chitosan-1 is replaced by chitosan.

[0079] Performance Testing

[0080] The soil sample used in the test is silty clay. The basic physical properties of the soil sample are shown in Table 1.

[0081] Table 1

[0082]

[0083] Take silty clay, add the soil solidifier in the above embodiments and comparative examples, the addition amount is 5wt% of the soil sample, make a Φ50cm×50cm cylindrical specimen, and compact it by static compaction at the optimal moisture content, the compaction degree is 95%, and according to JTG E51-2009 "Test Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering" standard, cure for 7 days and 28 days, and test the unconfined compressive strength for 7 days and 28 days.

[0084] The test results are shown in Table 2.

[0085] Table 2

[0086] serial number 7d unconfined compressive strength / MPa 28d unconfined compressive strength / MPa Example 1 3.32 3.84 Example 2 3.08 3.31 Example 3 3.12 3.57 Example 4 3.81 3.98 Example 5 2.63 2.69 Example 6 2.35 2.86 Example 7 2.71 2.73 Comparative Example 1 1.53 1.81

[0087] From the data comparison of Examples 1-3 in Table 1, it can be seen that the alkali-activated soil solidifier has a good curing effect by changing the ratio of each material; the addition of curing aid-1 in Example 4 accelerates soil curing and increases the compactness of the soil after curing; from the comparison between Example 5 and Example 4, it can be seen that the amount of acrylic acid in the modified chitosan-2 increases, which may lead to an increase in water absorption during the curing process, the generation of pores, and a decrease in compressive performance; from the comparison between Example 6 and Example 4, it can be seen that the amount of chitosan in the modified chitosan-3 increases, which may lead to a decrease in the dispersibility of the modified chitosan-3, resulting in uneven distribution during the curing process and a decrease in compressive strength; from the comparison between Example 7 and Example 4, it can be seen that the triphenylmethane triisocyanate in the curing aid-2 is reduced, resulting in a decrease in the degree of crosslinking and a slowdown in the conversion of Ca(OH)2 into CaCO3, resulting in a decrease in compressive strength; from the comparison between Example 4 and Comparative Example 1, it can be seen that the dispersibility of chitosan decreases and the compressive strength decreases.

[0088] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An alkali-activated soil stabilizer, characterized in that: The raw materials include, by weight: 20-25 parts of cement, 70-80 parts of mineral admixture, 13-16 parts of alkaline activator, 4-8 parts of wollastonite powder, 0.3-0.8 parts of fiber, and 3-7 parts of modified chitosan; The preparation method of the modified chitosan comprises the following steps: stirring acrylic acid and 2,4-hexadiene-1-ol at a constant temperature of 70-80° C. for 1-2 hours, adding chitosan, toluene and concentrated sulfuric acid, stirring at a constant temperature of 60-70° C. for 5-6 hours, and drying to obtain the modified chitosan; The mass ratio of acrylic acid, 2,4-hexadiene-1-ol and chitosan is (2.8-3):1:(0.8-1.2).

2. The alkali-activated soil solidifying agent according to claim 1, characterized in that: The cement includes one or more of ordinary Portland cement, aluminate cement and sulphoaluminate cement.

3. The alkali-activated soil solidifying agent according to claim 1, characterized in that: The mineral admixture includes one or more of coal gangue powder, slag, silica fume and steel slag powder.

4. The alkali-activated soil solidifying agent according to claim 1, characterized in that: The alkaline activator is one or more of CaO, Ca(OH)2, NaOH, Na2SO4, Na2CO3, and water glass.

5. The alkali-activated soil solidifier according to claim 1, characterized in that: The fiber is one or more of corn straw fiber, polypropylene fiber and basalt fiber.

6. The alkali-activated soil solidifying agent according to claim 1, characterized in that: The alkali-activated soil solidifier further comprises 0.8-1.2 parts by weight of a solidification aid.

7. The alkali-activated soil solidifying agent according to claim 6, characterized in that: The preparation method of the curing aid comprises the following steps: adding pentaerythritol and triphenylmethane triisocyanate into DMF, reacting at 60-70° C. for 5-6 hours, rotary evaporating, and drying to obtain the curing aid.

8. A method for preparing the alkali-activated soil solidifying agent according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: mixing cement, mineral admixture, wollastonite powder, fiber and modified chitosan for 10-15 minutes, adding alkaline activator and continuing to stir for 20-30 minutes to obtain soil solidifying agent.

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