A high-molecular polymer doped calcareous sand and a preparation method thereof

Abstract

The application provides a calcareous sand doped with a polymer and a preparation method thereof, and the preparation method comprises the following steps: taking the calcareous sand and performing an activation reaction by using a hydrochloric acid solution; adding polyethylene glycol polymer and anhydrous ethanol into the activated calcareous sand powder; adjusting the pH value to 9-10; stirring; and drying to obtain the calcareous sand; and the polyethylene glycol polymer is obtained by the reaction of polymethyl methacrylate and polyethylene glycol with a methacrylic acid group. The polyethylene glycol polymer is used for doping the calcareous sand, and the doped calcareous sand is obtained. Compared with the untreated calcareous sand, the calcareous sand doped with the polymer has improved unconfined compressive strength, increased shear strength, and a cohesion of 28.8-30.5 kPa, which is helpful to improve the soil structure and enhance the soil strength.

Description

Technical Field

[0001] This invention relates to the field of geotechnical materials preparation technology, and in particular to a polymer-doped calcareous sand and its preparation method. Background Technology

[0002] Coral reef calcareous sand is widely distributed in tropical coasts and oceans between the Tropic of Cancer and the Tropic of Capricorn. It is found in the South China Sea islands, the southern Arabian Gulf, the Red Sea, the western Indian Ocean, the western continental shelf of Australia and the Bass Strait, the Java Sea, the waters off Florida in North America, the Central American waters, and Barbados. It is a special type of marine biogenic soil with a calcium carbonate content greater than 50%. Its main source is the skeletal remains of reef-building corals, coral algae, and other marine organisms, deposited in situ or transported near-source. Based on grain size, it can be classified into coral reef nodules, gravelly sand, coarse sand, and fine sand. Because coral reef calcareous sand is mostly not transported long distances during deposition, it retains the fine pores of the protozoan skeleton. Its particles are characterized by high porosity, irregular shape, large angularity, low strength, easy breakage, and easy cementation, resulting in engineering mechanical properties that differ from conventional terrigenous sand.

[0003] The construction of offshore infrastructure in the South China Sea has encountered various geotechnical engineering problems related to islands and reefs. Using locally sourced calcareous sand for land reclamation is an economical and effective method. However, in the process of reclamation in the open sea, the large cutter suction dredgers commonly used do not uniformly crush coral reefs. The finer, more uniform calcareous sand particles, due to their smaller weight, are pumped to locations farther from the pump and have a slower deposition rate, resulting in uneven distribution of the reclaimed soil in both horizontal and vertical spaces. This situation is often unavoidable. Furthermore, in actual projects, reclamation is not done in one go but in layers, leading to the formation of interlayers of calcareous sand in various locations on the artificial islands. Because calcareous sand pumped from seawater often has a high water content and a small particle size, its permeability coefficient is reduced, slowing down drainage and consolidation. This results in uneven hardness of the calcareous sand foundation on the reclaimed islands, posing a risk of uneven settlement for structures built upon it. This indicates that the spatial variability of calcareous sand materials and construction uncertainties exist during the construction of calcareous sand foundations for island and reef reclamation, which are the main sources of engineering uncertainty. Therefore, to address the shortcomings of calcareous sand in South China Sea land reclamation, a new type of calcareous sand suitable for calcareous sand reclamation in the South China Sea should be provided. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a polymer-doped calcareous sand and its preparation method to solve the above problems.

[0005] The technical solution of this invention is implemented as follows:

[0006] A method for preparing polymer-doped calcareous sand includes the following steps:

[0007] S1: Take calcium sand and activate it with hydrochloric acid solution, then dry it to obtain activated calcium sand;

[0008] S2: Polyethylene glycol polymer and anhydrous ethanol are added to activated calcium sand, the pH is adjusted to 9-10, stirred, and dried to obtain the calcium sand.

[0009] The polyethylene glycol polymer is obtained by reacting polymethyl methacrylate with polyethylene glycol containing methacrylic acid groups.

[0010] A further embodiment is that the preparation method of the polyethylene glycol polymer includes: using N-methylpyrrolidone as a solvent, mixing polymethyl methacrylate and polyethylene glycol with methacrylic acid groups, and initiating the reaction with an azo initiator to obtain the polyethylene glycol polymer; wherein the mass ratio of polymethyl methacrylate to polyethylene glycol with methacrylic acid groups is 0.3 to 0.5:1.

[0011] A further embodiment is that the polyethylene glycol with methacrylic acid groups has a molecular weight of 500-900; the polymethyl methacrylate has a molecular weight of 80,000-90,000; the initiation reaction temperature is 50-60°C; and the initiation reaction time is 5-8 hours.

[0012] A further embodiment is that, in step S2, the mass-to-volume ratio of the activated calcium sand powder, polyethylene glycol polymer, and anhydrous ethanol is 100g: 6-12g: 200-250mL.

[0013] A further embodiment is that, in step S2, the mass-to-volume ratio of the calcareous sand and the hydrochloric acid solution is 1g:5-6mL; and the concentration of the hydrochloric acid solution is 0.5-0.6M.

[0014] A further option is that, in step S2, the drying temperature is 80–100°C and the drying time is 30–40 minutes.

[0015] A further option is that, in step S2, sodium hydroxide solution is used to adjust the pH value; and in step S2, the stirring time is 10 to 30 minutes.

[0016] A further embodiment is that, in step S1, the temperature of the stirring reaction is 50-60°C and the stirring reaction time is 1-2 hours; in step S1, the drying temperature is 120-180°C and the drying time is 1.5-3 hours.

[0017] This invention provides a calcareous sand doped with a polymer.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The present invention provides a method for doping calcareous sand with polyethylene glycol polymer to obtain polymer-doped calcareous sand. Compared with untreated calcareous sand, the unconfined compressive strength of polymer-doped calcareous sand is improved, the shear strength of polymer-doped calcareous sand is increased, and the cohesion is 28.8-30.5 kPa. This method helps to improve soil structure and enhance soil strength. Detailed Implementation

[0020] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0021] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0022] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0023] Based on the background of the coral reef reclamation project in the South China Sea, the study uses calcareous sand from the reclamation site as raw material.

[0024] Example 1 - Polyethylene glycol polymer

[0025] Using N-methylpyrrolidone as a solvent, 40g of polymethyl methacrylate with a molecular weight of 80,000 to 90,000 and 100g of polyethylene glycol with a molecular weight of 500 to 900 containing methacrylic acid groups were mixed, and azobisisobutyramidine hydrochloride was added. The mixture was reacted at 55°C for 6 hours to obtain a polyethylene glycol polymer.

[0026] Example 2 - Polymer-doped calcareous sand

[0027] Take 100g of calcium sand, add 500mL of 0.5M hydrochloric acid solution, stir and react at 50-60℃ for 1.5h, filter, rinse repeatedly with deionized water until the pH of the washing solution is 7, and dry at 160℃ for 2h to obtain activated calcium sand.

[0028] Take 100g of activated calcium sand, add 8g of polyethylene glycol polymer and 200mL of anhydrous ethanol, adjust the pH to 9-10 with 0.1M sodium hydroxide solution, stir, and dry at 90℃ for 40min to obtain the target calcium sand.

[0029] Example 3 - Polymer-doped calcium sand

[0030] Take 100g of calcium sand, add 500mL of 0.5M hydrochloric acid solution, stir and react at 50-60℃ for 1.5h, filter, rinse repeatedly with deionized water until the pH of the washing solution is 7, and dry at 120℃ for 3h to obtain activated calcium sand.

[0031] Take 100g of activated calcium sand, add 10g of polyethylene glycol polymer and 200mL of anhydrous ethanol, adjust the pH to 9-10 with 0.1M sodium hydroxide solution, stir, and dry at 90℃ for 40min to obtain the target calcium sand.

[0032] Example 4 - Polymer-doped calcareous sand

[0033] Take 100g of calcium sand, add 500mL of 0.5M hydrochloric acid solution, stir and react at 50-60℃ for 1.5h, filter, rinse repeatedly with deionized water until the pH of the washing solution is 7, and dry at 180℃ for 1.5h to obtain activated calcium sand.

[0034] Take 100g of activated calcium sand, add 6g of polyethylene glycol polymer and 200mL of anhydrous ethanol, adjust the pH to 9-10 with 0.1M sodium hydroxide solution, stir, and dry at 90℃ for 40min to obtain the target calcium sand.

[0035] Comparative Example 1 - Polymer-doped calcium sand

[0036] Take 100g of calcareous sand, add 8g of polyethylene glycol polymer and 200mL of anhydrous ethanol, adjust the pH to 9-10 with 0.1M sodium hydroxide solution, stir, and dry at 90℃ for 40min to obtain the target calcareous sand.

[0037] Experimental Example 1

[0038] Under a confining pressure of 400 kPa, an unconsolidated undrained rapid shear test was conducted using a ZJ-type strain-controlled direct shear apparatus. The shear rate was set to 1 mm / min. Calcium sand with different treatment groups was added to the shear chamber for sample preparation. Under high confining pressure, all treatment groups exhibited strain hardening. According to Mohr-Coulomb strength theory: T f Let σ be the shear strength of the soil (shear stress on the fracture surface), σ be the normal stress on the fracture surface, and c be the cohesion of the soil. Calculate the shear strength index based on the internal friction of the soil. And c, the results are as follows:

[0039] Table 1 Shear strength parameters of calcareous sand in different treatment groups

[0040]

[0041] As shown in Table 1 above, the cohesion of the calcareous sand obtained by the treatment in Examples 2 to 4 is 28.8 to 30.5 kPa. Calcareous sand itself has no cohesion. However, the calcareous sand doped with polymer exhibits a certain degree of cohesion between coarse particles, which helps to improve the soil structure and increase the soil strength. The internal friction angle of the calcareous sand obtained by the treatment in Examples 2 to 4 does not change significantly.

[0042] Example 5 - Polymer-doped calcium sand

[0043] Take 100g of calcium sand, add 500mL of 0.5M hydrochloric acid solution, stir and react at 50-60℃ for 1.5h, filter, rinse repeatedly with deionized water until the pH of the washing solution is 7, and dry at 160℃ for 2h to obtain activated calcium sand.

[0044] Take 100g of activated calcium sand, add 10g of polyethylene glycol polymer and 200mL of anhydrous ethanol, adjust the pH to 9-10 with 0.1M sodium hydroxide solution, stir, and dry at 90℃ for 40min to obtain the target calcium sand.

[0045] Example 6 - Polymer-doped calcium sand

[0046] Take 100g of calcium sand, add 500mL of 0.5M hydrochloric acid solution, stir and react at 50-60℃ for 1.5h, filter, rinse repeatedly with deionized water until the pH of the washing solution is 7, and dry at 160℃ for 2h to obtain activated calcium sand.

[0047] Take 100g of activated calcium sand, add 12g of polyethylene glycol polymer and 200mL of anhydrous ethanol, adjust the pH to 9-10 with 0.1M sodium hydroxide solution, stir, and dry at 90℃ for 40min to obtain the target calcium sand.

[0048] Experimental Example 2

[0049] The unconfined compressive strength test was conducted using an LDF unconfined compressive strength tester from Zhejiang Geo Technology Co., Ltd., with a loading rate set to 1 mm / min. The specimen was placed in the center of the instrument, and pressure was applied to the specimen using the computer system. Untreated calcareous sand was used as a control. The results are as follows:

[0050] Table 2. Unconfined compressive strength results of calcareous sand in different treatment groups.

[0051]

[0052] As shown in Table 2 above, the compressive strength of the calcareous sand obtained by treatment in Examples 2 to 4 is 711.0 to 788.5 kPa. Compared with the control, the unconfined compressive strength of the calcareous sand doped with polymers is improved compared with that of the untreated calcareous sand.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing polymer-doped calcareous sand, characterized in that, Includes the following steps: S1: Take calcium sand and activate it with hydrochloric acid solution, then dry it to obtain activated calcium sand; S2: Polyethylene glycol polymer and anhydrous ethanol are added to activated calcium sand, the pH is adjusted to 9-10, stirred, and dried to obtain the calcium sand. The polyethylene glycol polymer is obtained by reacting polymethyl methacrylate and polyethylene glycol with methacrylic acid groups.

2. The method for preparing polymer-doped calcareous sand according to claim 1, characterized in that, The method for preparing the polyethylene glycol polymer includes: using N-methylpyrrolidone as a solvent, mixing polymethyl methacrylate and polyethylene glycol with methacrylic acid groups, and initiating the reaction with an azo initiator to obtain the polyethylene glycol polymer; the mass ratio of polymethyl methacrylate to polyethylene glycol with methacrylic acid groups is 0.3~0.5:

1.

3. A method for preparing polymer-doped calcareous sand according to claim 2, characterized in that, The polyethylene glycol with methacrylic acid groups has a molecular weight of 500-900; the polymethyl methacrylate has a molecular weight of 80,000-90,000; the initiation temperature is 50-60 °C, and the initiation time is 5-8 h.

4. A method for preparing polymer-doped calcareous sand according to claim 1, characterized in that, In step S2, the mass-to-volume ratio of the activated calcium sand, polyethylene glycol polymer, and anhydrous ethanol is 100 g: 6~12 g: 200~250 mL.

5. A method for preparing polymer-doped calcareous sand according to claim 1, characterized in that, In step S2, the mass-to-volume ratio of the calcareous sand and the hydrochloric acid solution is 1 g: 5~6 mL; the concentration of the hydrochloric acid solution is 0.5~0.6 M.

6. A method for preparing polymer-doped calcareous sand according to claim 1, characterized in that, In step S2, the drying temperature is 80~100 ℃ and the drying time is 30~40 min.

7. A method for preparing polymer-doped calcareous sand according to claim 1, characterized in that, In step S2, sodium hydroxide solution is used to adjust the pH value; in step S2, the stirring time is 10~30 min.

8. The polymer-doped calcareous sand prepared by the method for preparing polymer-doped calcareous sand according to any one of claims 1 to 7.

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