Water-invasion-resistant quick-hardening curing agent and preparation method thereof

Abstract

The invention discloses a preparation method of a water-invasion-resistant quick-hardening curing agent, which comprises the following steps of: activating the surface of nano silicon dioxide to obtain surface-activated nano silicon dioxide, reacting the surface-activated nano silicon dioxide with chitosan phosphate to obtain nano silicon dioxide-chitosan phosphate, metering according to the molar ratio of MgO to MgCl2. 6H2O to H2O of 7: 1: 7, adding MgCl2. 6H2O into H2O, stirring, and reacting to obtain the water-invasion-resistant quick-hardening curing agent. The preparation method comprises the following steps: mixing MgO with nano-silica and chitosan phosphate, adding KH2PO4 accounting for 1% of the mass of MgO to prepare a premixed aqueous solution, taking out MgO accounting for 10% of the total mass of MgO, replacing and doping the MgO with red mud powder with the same mass as the MgO into the remaining MgO to obtain a red mud-magnesium oxide mixture, and finally stirring and mixing the red mud-magnesium oxide mixture with the premixed aqueous solution and the nano-silica and chitosan phosphate to obtain the product. Compared with the prior art, the rapid hardening curing agent disclosed by the invention has good water resistance and strength performance, and is particularly suitable for coastal soft soil foundation engineering.

Description

Technical Field

[0001] The invention belongs to the field of geotechnical technology, and in particular relates to providing a fast-hardening curing agent material that is resistant to water intrusion. Background Art

[0002] During the implementation of offshore soft foundation projects, coastal tidal flats will be encountered. The surface of most plots is silt or silty clay, and there is also a thick silt layer below the surface. This soil has the characteristics of high water content, low strength, and high compressibility. The bearing capacity is difficult to meet the design requirements of various foundation projects. In addition, due to the continuous erosion of coastal strata by seawater, the groundwater level is generally high and fluctuates significantly, and the soil is soaked in seawater for a long time. The deformation and stability of the foundation caused by construction on soft soil foundations are particularly prominent. Therefore, some effective curing agents are needed to reinforce the soft soil foundation.

[0003] At present, commonly used curing agents include cement, lime, alkali-activated curing materials. In coastal environments, the use of curing materials needs to consider special conditions such as alkali resistance, water intrusion resistance and settlement resistance, and cement and other curing materials are greatly affected by coastal environmental factors. For example, cement mainly relies on hydration reaction to produce strength, and the high alkali content in the coastal environment will destroy the cement's retarding mechanism, increase water demand, and be unfavorable to hydration. In addition, factors such as the groundwater level and tides in the coastal environment will also cause cement and other curing agents to be eroded by water for a long time, which will also lead to poor strength. Whether it is cement-based materials or alkali-activated materials, they are all achieved through the resistance of their own hydration reaction products. Therefore, the hydration process is significantly affected by the above-mentioned adverse conditions, which can easily cause insufficient hydration and imperfect product development. At the same time, adverse conditions will also affect the long-term durability of the solidified body.

[0004] At present, cement curing agents are mostly used in engineering projects from the perspectives of strength, environmental protection and economy. However, cement curing agents are greatly affected by their ability to resist water erosion, which limits their use in coastal environments.

[0005] Magnesium oxychloride cement is an environmentally friendly non-hydraulic cement that has gained widespread attention due to its many properties that are different from ordinary Portland cement. On the one hand, ordinary Portland cement has many adverse effects on the environment during production, including ozone depletion and increased global warming, highlighting the urgent need for more sustainable cement and production methods. On the other hand, the manufacture of its main raw material MgO requires lower temperatures, making it an energy-saving alternative. In addition, magnesium oxychloride cement has high early strength and good corrosion resistance, and has good bonding potential with various fillers. Therefore, its application prospects are huge. Although magnesium oxychloride cement has more advantages than Portland cement in reducing greenhouse gas emissions and low energy consumption. But so far, magnesium oxychloride cement can only replace Portland cement in limited application scenarios. The main reason is that magnesium oxychloride cement has poor water resistance. Studies have found that when the cured magnesium oxychloride cement is soaked in water for 28 days, its compressive strength loss exceeds 90%, which greatly limits the scope of application of magnesium oxychloride cement.

[0006] Therefore, the research on the modification of the waterproof performance of magnesium oxychloride cement is particularly urgent and critical. This modification can not only significantly improve the applicability of magnesium oxychloride cement, but also greatly expand its application range. Especially in the construction of coastal soft soil foundations, the application of this modified magnesium oxychloride cement will bring new changes. It will effectively solve the problem that traditional building materials are difficult to adapt to the special environmental conditions in coastal areas, thus providing a new and efficient solution for my country's coastal engineering construction.

[0007] Currently, phosphates and phosphoric acid have been used to improve the water resistance of magnesium oxychloride cement (MOC), but there are problems with long-term effect and durability. Due to its unusually large specific surface area and strong reactivity, nanosilica (nSiO 2 ) can be used as the core of the hydrated phase of cement materials, but due to the 2 Easy to self-aggregate, when n-SiO 2 When added to cement, the self-aggregated n-SiO 2 The formation of cavities leads to discontinuity inside the cement, uneven stress distribution, and stress concentration, which has an adverse effect on the compressive strength of the cement. Summary of the invention

[0008] The purpose of the present invention is to provide a fast-hardening curing agent that is resistant to water intrusion and has good strength and water resistance, in view of the fact that the curing agent currently used in the construction process of coastal soft soil foundation generally has the problems of low strength and poor water resistance in coastal environment.

[0009] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0010] A method for preparing a water-resistant fast-hardening curing agent comprises the following steps:

[0011] (1) adding nano-silicon dioxide to a hydrogen peroxide solution having a mass concentration of 30%, stirring for reaction, and drying to obtain surface-activated nano-silicon dioxide;

[0012] (2) dissolving chitosan phosphate in an acetic acid solution, adding surface-activated nano-silica under stirring, stirring for reaction, and drying to obtain nano-silica@chitosan phosphate;

[0013] (3) According to MgO, MgCl 2 6H 2 O and H 2 O in a molar ratio of 7:1:7. First, MgCl 2 6H 2 O joins H 2 O, and add KH2O accounting for 1% of the mass of MgO 2 PO 4 , stirring and mixing evenly to obtain a premixed aqueous solution;

[0014] (4) removing 10% of the total mass of MgO from step (3), replacing it with an equal mass of red mud powder, and adding it to the remaining MgO to obtain a red mud-magnesium oxide mixture;

[0015] (5) The premixed aqueous solution, the red mud-magnesium oxide mixture and the nano-silica@chitosan phosphate are stirred and mixed uniformly to obtain a fast-hardening curing agent that is resistant to water intrusion.

[0016] Furthermore, in step (1), the particle size of the nano-silicon dioxide is 20 to 60 nm, and 2 g of the nano-silicon dioxide is added to 20 to 30 mL of a hydrogen peroxide solution having a mass concentration of 30%.

[0017] Furthermore, in step (1), the stirring reaction is carried out at a temperature of 60° C. for a period of 2 to 5 hours.

[0018] Furthermore, in step (2), the preparation method of the chitosan phosphate is as follows: 5g of phosphorus pentoxide and 6g of chitosan are added to 100ml of a mixture of anhydrous ethanol, phosphoric acid and triethyl phosphate in a volume ratio of 4:1:1, the mixture is heated and stirred at 45°C for reaction, the reaction mixture is poured into anhydrous methanol for precipitation, the precipitate is filtered, and the precipitate is washed with anhydrous methanol until it is neutral, and dried to obtain the product.

[0019] Furthermore, in step (2), the mass ratio of the chitosan phosphate to the surface activated nano-silica is (0.3-0.5):1.

[0020] Furthermore, in step (2), the mass concentration of the acetic acid solution is 2%.

[0021] Furthermore, in step (2), the drying temperature is 40°C.

[0022] Furthermore, in step (5), the amount of nano-silica@chitosan phosphate added is 1wt% of the amount of MgO used.

[0023] Furthermore, in step (5), the stirring and mixing speed is 300 rpm.

[0024] The water-resistant rapid-hardening curing agent is prepared by the method.

[0025] Beneficial effects of the invention: The invention discloses a rapid-hardening curing agent that is resistant to water intrusion. Compared with the prior art, the invention has the following advantages:

[0026] 1) The present invention adopts magnesium oxychloride cement as a curing agent, which has the advantages of high strength, simple curing conditions, short setting time, light weight, and environmental friendliness. Magnesium oxychloride cement is also more advantageous than Portland cement in reducing greenhouse gas emissions and low energy consumption.

[0027] 2) The present invention uses nano-silica @ chitosan phosphate, red mud and phosphate to form a composite modified material to modify magnesium oxychloride cement, wherein the highly dispersed nano-silica @ chitosan phosphate improves the fluidity of magnesium oxychloride cement slurry and refines the pores of cement; red mud and KH 2 PO 4 The heat release rate and the total amount of hydration heat in the hydration process of the magnesium chloride slurry are reduced. By reducing the hydration heat and extending the setting time of magnesium chloride, the generation of temperature stress can be reduced, and the crack resistance and structural durability can be improved. The composite modifier of the present invention not only greatly improves the water resistance of magnesium chloride cement, but also improves its strength, so that it can be better applied in the soft soil foundation construction in the coastal environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The test results of the unconfined compressive strength of the water-resistant rapid-hardening curing agent prepared in Example 1 and Comparative Examples 1-2;

[0029] Figure 2 The water resistance test results of the water-resistant rapid-hardening curing agents prepared in Example 1 and Comparative Examples 1-2 are shown. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is clearly and completely described below in conjunction with the accompanying drawings and specific embodiments.

[0031] Example 1

[0032] A method for preparing a water-resistant fast-hardening curing agent comprises the following steps:

[0033] (1) 2 g of nano-silicon dioxide (particle size 30 nm, specific surface area 2 × 10 8 m 2 / g) was added into 25mL of a 30% hydrogen peroxide solution, stirred at 60°C for 3h, and then dried to obtain surface-activated nano-silica;

[0034] (2) Add 5 g of phosphorus pentoxide and 6 g of chitosan to 100 ml of a mixture of anhydrous ethanol, phosphoric acid and triethyl phosphate in a volume ratio of 4:1:1, heat and stir in a water bath at 45°C, and after sufficient reaction, pour the reaction mixture into excess anhydrous methanol for precipitation, filter the precipitate, wash it with anhydrous methanol until it is neutral, and dry it at 40°C to obtain chitosan phosphate;

[0035] 0.8 g of chitosan phosphate was dissolved in an acetic acid solution with a mass concentration of 2%, and 2 g of surface-activated nano-silica was added under stirring. After stirring for reaction, the mixture was dried at 40° C. to a constant weight to obtain nano-silica@chitosan phosphate;

[0036] (3) According to MgO, MgCl 2 6H 2 O and H 2 O in a molar ratio of 7:1:7. First, MgCl 2 6H 2 O joins H 2 O, and add KH2O accounting for 1% of the mass of MgO 2 PO 4 , stirring and mixing evenly to obtain a premixed aqueous solution;

[0037] (4) removing 10% of the total mass of MgO from step (3), replacing it with an equal mass of red mud powder, and adding it to the remaining MgO to obtain a red mud-magnesium oxide mixture (in the mixture, the mass ratio of magnesium oxide to red mud is 9:1);

[0038] (5) Using an electric mixer set at 300 rpm, the premixed aqueous solution, the red mud-magnesium oxide mixture and the nano-silica@chitosan phosphate (the added amount is 1 wt % of the actual amount of MgO) are stirred and mixed to obtain a water-resistant fast-hardening curing agent.

[0039] Comparative Example 1

[0040] A method for preparing a water-resistant fast-hardening curing agent comprises the following steps:

[0041] (1) According to MgO, MgCl 2 6H 2 O and H 2O in a molar ratio of 7:1:7. First, MgCl 2 6H 2 O joins H 2 O, and add KH2O accounting for 1% of the mass of MgO 2 PO 4 , stirring and mixing evenly to obtain a premixed aqueous solution;

[0042] (2) removing 10% of the total mass of MgO from step (1), replacing it with an equal mass of red mud powder, and adding it to the remaining MgO to obtain a red mud-magnesium oxide mixture (in the mixture, the mass ratio of magnesium oxide to red mud is 9:1);

[0043] (3) Using an electric mixer set at 300 rpm, the premixed aqueous solution and the red mud-magnesium oxide mixture were stirred and mixed uniformly to obtain a water-resistant fast-hardening curing agent.

[0044] Comparative Example 2

[0045] A method for preparing a water-resistant fast-hardening curing agent comprises the following steps:

[0046] (1) 2 g of nano-silicon dioxide (particle size 30 nm, specific surface area 2 × 10 8 m 2 / g) was added into 25mL of a 30% hydrogen peroxide solution, stirred at 60°C for 3h, and then dried to obtain surface-activated nano-silica;

[0047] (2) Add 5 g of phosphorus pentoxide and 6 g of chitosan to 100 ml of a mixture of anhydrous ethanol, phosphoric acid and triethyl phosphate in a volume ratio of 4:1:1, heat and stir in a water bath at 45°C, and after sufficient reaction, pour the reaction mixture into excess anhydrous methanol for precipitation, filter the precipitate, wash it with anhydrous methanol until it is neutral, and dry it at 40°C to obtain chitosan phosphate;

[0048] 0.8 g of chitosan phosphate was dissolved in an acetic acid solution with a mass concentration of 2%, and 2 g of surface-activated nano-silica was added under stirring. After stirring for reaction, the mixture was dried at 40° C. to a constant weight to obtain nano-silica@chitosan phosphate;

[0049] (3) According to MgO, MgCl 2 6H 2 O and H 2 O in a molar ratio of 7:1:7. First, MgCl 2 6H 2 O joins H 2 O, stirring and mixing evenly to obtain a premixed aqueous solution;

[0050] (4) Using an electric mixer set at 300 rpm, the premixed aqueous solution, MgO and nano-silica @ chitosan phosphate were stirred and mixed uniformly, and the amount of nano-silica @ chitosan phosphate added (nano-silica @ chitosan phosphate accounted for 1 wt% of the amount of MgO) to obtain a water-resistant fast-hardening curing agent.

[0051] The fast-hardening curing agent for water intrusion resistance prepared in Example 1 and Comparative Examples 1-2 was subjected to unconfined compressive strength and water resistance tests: the prepared fast-hardening curing agent for water intrusion resistance was poured into 20 mm and 40 mm cubes, cured in the air, and then demolded, and then the sample was placed in the air (temperature 20°C ± 2°C, humidity 60% ± 5%) for further curing for 28 days. The samples after curing were taken for unconfined compressive strength test, and the test method was based on the GB-T50123-2019 geotechnical test method standard; in order to systematically characterize the water resistance of the prepared fast-hardening curing agent for water intrusion resistance, the sample cured in the air for 28 days was completely immersed in water for 28 days, and then the sample was taken out, and the surface moisture was dried to test the residual compressive strength, and the softening coefficient Rw was introduced using the following formula:

[0052]

[0053] In the formula, C n It indicates the residual compressive strength of the rapid hardening curing agent for water intrusion resistance immersed in water after curing for 28 days. The compressive strength of the rapid hardening curing agent for water intrusion resistance after curing in air for 28 days is designated as C 28 (MPa). The test of water resistance softening coefficient refers to the method in GB / T 20473-2021 "Building Thermal Insulation Mortar".

[0054] Figure 1 The test results of the unconfined compressive strength of the water-resistant rapid-hardening curing agent prepared in Example 1 and Comparative Examples 1-2 are as follows: Figure 1 It can be seen that the unconfined compressive strength of magnesium oxychloride cement with phosphate and red mud (Comparative Example 1) is about 60 MPa, the unconfined compressive strength of nano-silica @ chitosan phosphate (Comparative Example 2) is 117 MPa, and when both are added together (Example 1), the unconfined compressive strength is 137 MPa, which is significantly higher than Comparative Examples 1 and 2. It proves the effectiveness of the composite modifier of phosphate, red mud and nano-silica @ chitosan phosphate in improving the strength of magnesium oxychloride cement after curing.

[0055] Figure 2 The water resistance test results of the water-resistant fast-hardening curing agent prepared in Example 1 and Comparative Examples 1-2 are as follows: Figure 2It can be seen that the softening coefficient of magnesium oxychloride cement (Comparative Example 1) with phosphate and red mud is about 0.88, the softening coefficient of nano-silica @ chitosan phosphate (Comparative Example 2) is 0.8, and when both are added together (Example 1), the softening coefficient reaches 0.94, which is higher than Comparative Examples 1 and 2. The larger the softening coefficient, the better its water resistance. Although phosphate, red mud and nano-silica @ chitosan phosphate are all beneficial to improving the water resistance of magnesium oxychloride cement. However, the results show that the composite treatment of phosphate, red mud and nano-silica @ chitosan phosphate is more effective in improving the water resistance of magnesium oxychloride cement.

Claims

1. A method for preparing a water-resistant rapid-hardening curing agent, characterized in that: The steps include: (1) adding nano-silicon dioxide to a hydrogen peroxide solution having a mass concentration of 30%, stirring for reaction, and drying to obtain surface-activated nano-silicon dioxide; (2) dissolving chitosan phosphate in an acetic acid solution, adding surface-activated nano-silica under stirring, stirring for reaction, and drying to obtain nano-silica@chitosan phosphate; (3) According to the molar ratio of MgO, MgCl2·6H2O and H2O being 7:1:7, MgCl2·6H2O is first added to H2O, and KH2PO4 accounting for 1% by mass of MgO is added, and the mixture is stirred and mixed to obtain a premixed aqueous solution; (4) removing 10% of the total mass of MgO from step (3), replacing it with an equal mass of red mud powder, and adding it to the remaining MgO to obtain a red mud-magnesium oxide mixture; (5) The premixed aqueous solution, the red mud-magnesium oxide mixture and the nano-silica@chitosan phosphate are stirred and mixed uniformly to obtain a fast-hardening curing agent that is resistant to water intrusion.

2. The method for preparing the water-resistant rapid-hardening curing agent according to claim 1, characterized in that: In step (1), the particle size of the nano-silicon dioxide is 20-60 nm, and 2 g of the nano-silicon dioxide is added to 20-30 mL of a hydrogen peroxide solution with a mass concentration of 30%.

3. The method for preparing the water-resistant rapid-hardening curing agent according to claim 1, characterized in that: In step (1), the stirring reaction is carried out at a temperature of 60° C. for 2 to 5 hours.

4. The method for preparing the water-resistant rapid-hardening curing agent according to claim 1, characterized in that: In step (2), the preparation method of chitosan phosphate is as follows: 5g of phosphorus pentoxide and 6g of chitosan are added to 100ml of a mixture of anhydrous ethanol, phosphoric acid and triethyl phosphate in a volume ratio of 4:1:1, and the mixture is heated and stirred at 45°C for reaction, and the reaction mixture is poured into anhydrous methanol for precipitation. After filtering, the precipitate is washed with anhydrous methanol until it is neutral, and dried to obtain the product.

5. The method for preparing the water-resistant rapid-hardening curing agent according to claim 1, characterized in that: In step (2), the mass ratio of the chitosan phosphate to the surface activated nano-silicon dioxide is (0.3-0.5):

1.

6. The method for preparing the water-resistant rapid-hardening curing agent according to claim 1, characterized in that: In step (2), the mass concentration of the acetic acid solution is 2%.

7. The method for preparing the water-resistant rapid-hardening curing agent according to claim 1, characterized in that: In step (2), the drying temperature is 40°C.

8. The method for preparing the water-resistant rapid-hardening curing agent according to claim 1, characterized in that: In step (5), the amount of nano-silica@chitosan phosphate added is 1wt% of the amount of MgO used.

9. The method for preparing the water-resistant rapid-hardening curing agent according to any one of claims 1 to 8, characterized in that: In step (5), the stirring and mixing speed is 300 rpm.

10. The water-resistant rapid-hardening curing agent prepared by the method according to any one of claims 1 to 9.

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