Fluidic solidified soil composite anti-cracking agent for compensating shrinkage and preparation method thereof

Abstract

The invention discloses a shrinkage-compensating fluid stabilized soil composite anti-cracking agent and a preparation method thereof. The composite anti-cracking agent is prepared from the following raw materials in parts by mass: 50 to 70 parts of cement, 20 to 30 parts of superfine slag powder, 0.5 to 1.2 parts of nano flaky kaolin, 3 to 5 parts of expanding agent, 1 to 2 parts of temperature-sensitive polymer microcapsule and 0.1 to 0.4 part of additive. The performance indexes of the shrinkage-compensating composite anti-cracking agent for the fluid-state solidified soil meet the actual requirements of a current curing agent for the fluid-state solidified soil, the early-stage (3d) unlateral compressive strength is improved by 7 times or above compared with the effect of a conventional curing agent on the market, and the consolidation shrinkage rate of the fluid-state solidified soil is reduced by 70% or above compared with the consolidation shrinkage rate of the conventional curing agent; and no macroscopic crack exists on the surface 7 days after visual inspection construction, and the working performance is excellent.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ore pulp, concrete or similar building materials, and particularly relates to a shrinkage-compensating fluidized soil composite anti-cracking agent and a preparation method thereof. BACKGROUND

[0002] Existing fluidized soil mostly uses a single cement-based solidifying agent as the main component, which has the problems of large hydration shrinkage and serious early plastic cracking. Most of the traditional solutions compensate for shrinkage by adding fibers or expanding agents, for example, basalt short fibers are mixed into the solidifying agent of CN109053096A to delay cracking and improve the impermeability of the solidified soil, but only the internal cracks can be partially improved, surface cracking is difficult to achieve, and the fluidity in the construction process is easily lost. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a shrinkage-compensating fluidized soil composite anti-cracking agent and a preparation method thereof, which can significantly improve the surface cracking performance of fluidized soil, make the fluidized soil have the characteristics of early strength and low shrinkage, and have no visible cracks on the surface after solidification.

[0004] The present application provides a shrinkage-compensating fluidized soil composite anti-cracking agent, the raw materials and mass fraction ratio of which are as follows: cement 50-70 parts, ultra-fine slag powder 20-30 parts, nano-sheet kaolin 0.5-1.2 parts, expanding agent 3-5 parts, temperature-sensitive polymer microcapsule 1-2 parts, and additive 0.1-0.4 parts.

[0005] According to the above scheme, the cement is a 42.5 grade sulphoaluminate cement, the 28d strength of which is 45-60 MPa, the specific surface area is 360-450 m 2 / kg, and the initial setting time is 30-60 min.

[0006] According to the above scheme, the specific surface area of the ultra-fine slag powder is 600-920 kg / m 3 , the 28d activity index is greater than 100%, and the glass content is greater than 90%.

[0007] According to the above scheme, the nano-sheet kaolin has a diameter of 50-120 nm, a thickness of 5-20 nm, and an interlayer spacing of 0.7-1.2 nm.

[0008] According to the above scheme, the expanding agent is a calcium-magnesium composite expanding agent, the content of magnesium oxide in which is 30-50%, and the 21d restrained expansion rate in air at 20℃ is ≥-0.015%.

[0009] According to the above scheme, the temperature-sensitive polymer microcapsule is obtained by wrapping sodium sulfate with a gelatin shell, and has a particle size of 50-200 μm.

[0010] According to the above scheme, the preparation method of the temperature-sensitive polymer microcapsule is as follows: gelatin powder is added into warm water at 50-55 DEG C, and stirred until completely dissolved to obtain a colloidal solution, anhydrous sodium sulfate is added into the obtained colloidal solution, and stirred and dispersed uniformly to obtain a mixture, the obtained mixture is added dropwise into edible oil in an ice water bath, and the liquid droplets are quickly solidified into microspheres after contacting the cold oil, the microspheres in the oil are collected, washed with cold deionized water to remove surface oil, laid on filter paper, and dried at room temperature to obtain the temperature-sensitive polymer microcapsule.

[0011] According to the above scheme, the concentration of the colloidal solution is 0.08-0.15 g / mL, and the mass ratio of the gelatin powder to the anhydrous sodium sulfate is 1:0.4-0.8.

[0012] According to the above scheme, the additive is an aqueous solution of hydroxypropyl methyl cellulose, and the concentration is 0.02-0.04 wt%, the water retention rate of the hydroxypropyl methyl cellulose is ≥90% in 24 hours, and the viscosity is 40,000-80,000 mPa.s. The hydroxypropyl methyl cellulose is used to regulate the rheological properties of the slurry of the composite anti-cracking agent in the cured soil, and on the other hand, can be used to strengthen the directional arrangement of the nanosheet-shaped kaolin in the system, form a layered crack resistance barrier, and effectively play an internal and external anti-cracking effect.

[0013] The application also includes a preparation method of the shrinkage-compensated fluidized cured soil composite anti-cracking agent, and the specific steps are as follows: 1) the raw materials are weighed according to the proportion and prepared; 2) the weighed cement, superfine slag powder and expanding agent are premixed in a three-dimensional motion mixer to obtain a mixture A, then the nanosheet-shaped kaolin is uniformly dispersed in the mixture A by using a double-planetary mixer to obtain a mixture B, then the temperature-sensitive polymer microcapsule is added into the mixture B to obtain a mixture C, and finally, the mixture C is sprayed with the atomized liquid obtained by atomizing the additive to obtain the shrinkage-compensated fluidized cured soil composite anti-cracking agent.

[0014] According to the above scheme, the premixing process condition in step 2) is that the rotation speed is 30-40 r / min, and the mixing time is 15 min.

[0015] According to the above scheme, in step 2), the nanosheet kaolin is uniformly dispersed in the mixture A by using a double planetary mixer, and the specific steps are as follows: the nanosheet kaolin is preheated at 110-120 DEG C for 2-4 hours (to ensure the dispersion effect), then 10-20 wt% of the mixture A and all the nanosheet kaolin are poured into the double planetary mixer, mixed at a speed of 100-150 r / min for 5-8 min to obtain a kaolin-carrier premix, and finally the remaining mixture A is poured in and continuously mixed at a speed of 300-500 r / min for 15-20 min. This incorporation method can reduce the interaction force between particles, reduce the agglomeration phenomenon, improve the uniformity of the dispersion of the nanosheet kaolin, and strengthen the interfacial bonding force between the nanosheet kaolin and the hydration product CSH gel.

[0016] According to the above scheme, in step 2), the method for incorporating the temperature-sensitive polymer microcapsules into the mixture B is as follows: a bottom-spraying fluidized bed with an air distribution plate and an atomizing nozzle is selected, the mixture B is added to the fluidized bed hopper, the fluidized bed fan is turned on to introduce clean compressed air, the air flow rate is adjusted to 1.2-1.8 m / s, and after the mixture B is stably fluidized, the temperature-sensitive polymer microcapsules are sprayed into the fluidized bed through the atomizing nozzle at a rate of 0.5-1.0 kg / min, and the temperature-sensitive polymer microcapsules are fully contacted and mixed with the fluidized mixture B by using the air flow turbulence, and after the temperature-sensitive polymer microcapsules are sprayed, the fluidized state is maintained for 5-8 min. This method can balance the dispersion effect and the integrity of the temperature-sensitive polymer microcapsules to a certain extent.

[0017] According to the above scheme, in step 2), the atomized liquid obtained by spraying the admixture into the mixture C, and the specific process conditions are as follows: under the conditions of temperature 20-25 DEG C and relative humidity 40-60%, the mixture C is stirred at a speed of 30-60 r / min while spraying the atomized liquid. After the admixture is atomized, the molecular level droplets are self-assembled into a molecular level coating film on the surface of the powder particles through hydrogen bonds and van der Waals forces, which can enhance the bonding force between the powder particles, and also provide a physical barrier for the temperature-sensitive polymer microcapsules to reduce the interference of the core material release.

[0018] The application also includes the application of the shrinkage-compensating fluidified soil composite anti-cracking agent in the field of fluidified soil. The shrinkage-compensating fluidified soil composite anti-cracking agent is mixed with soil and water, and the amount of the shrinkage-compensating fluidified soil composite anti-cracking agent is 8-25% of the mass of the soil, so that the fluidified soil is obtained.

[0019] The application uses sulphoaluminate cement and superfine slag powder as a base to play a role of early strength, low shrinkage and delayed hydration shrinkage compensation curing system, and realizes early-late shrinkage stress dynamic balance. The addition of appropriate amount of calcium-magnesium composite expansion agent and temperature-sensitive polymer microcapsules in the system can trigger directional expansion at the initial curing stage (within 24h) and when the ambient temperature changes, respectively, accurately compensating the shrinkage stress. The temperature-sensitive polymer microcapsules wrap sodium sulfate inside, and when the ambient temperature slowly rises above 32℃, the capsules rupture to release sodium sulfate, which can react with Ca(OH)2 in the system to generate ettringite to produce delayed expansion, which can dynamically adapt to the shrinkage caused by day and night temperature difference. In addition, hydroxypropyl methylcellulose can effectively regulate the rheological properties of the slurry, and can induce the directional arrangement of nanosheet kaolin along the horizontal direction during the construction vibration process, forming a layered crack barrier, which can effectively play a crack resistance effect from the inside to the outside.

[0020] The beneficial effects of the application are: 1. The performance indicators of the shrinkage-compensating flow-state cured soil composite anti-cracking agent provided by the application meet the actual needs of current flow-state cured soil curing agents. The early (3d) side compressive strength is improved by more than 7 times compared with conventional curing agents on the market, the flow-state cured soil consolidation shrinkage rate is reduced by more than 70% compared with conventional curing agents, and no visible cracks are observed on the surface 7d after construction. The working performance is excellent. 2. The preparation method provided by the application is easy to implement, green and environmentally friendly, and no toxic and harmful substances are generated. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The photos taken on the 7th day of the cured soil experiment of the composite anti-cracking agent prepared for the application comparative example 4 (left) and example 1 (right). DETAILED DESCRIPTION

[0022] In order for those skilled in the art to better understand the technical solutions of the application, the following examples are used to further describe the application in combination with the drawings.

[0023] The cement used in the following examples and comparative examples is 42.5 grade sulphoaluminate cement, the 28d compressive strength is 51.6MPa, the specific surface area is 361m 2 / kg, the initial setting time is 38min; the specific surface area of the superfine slag powder used is 642kg / m 3 , the 28d activity index is 104%, the glass content is 93.2%; the average diameter of the nanosheet kaolin used is about 70nm, the average thickness is about 12nm, and the average interlayer spacing is 0.9nm; the expansion agent used is a calcium-magnesium composite expansion agent, the magnesium oxide content of which is 39%, and the 21d restricted expansion rate in air at 20℃ is-0.006%; the 24h water retention rate of the hydroxypropyl methylcellulose used is 93.2%, and the viscosity value is about 58000mPa.s.

[0024] The preparation method of the temperature-sensitive polymer microcapsule used in the examples and comparative examples of the present application is as follows: 5 g of gelatin powder is added to 50 mL of warm water at 50°C, and stirred until completely dissolved to obtain a colloidal solution, 3 g of anhydrous sodium sulfate is added to the obtained colloidal solution, and stirred for 1 min to disperse uniformly to obtain a mixed solution, the obtained mixed solution is added dropwise into 100 mL of edible oil in an ice water bath, the liquid droplets are quickly solidified into microspheres after contacting the cold oil, the microspheres in the oil are collected by filtration, washed with cold deionized water to remove surface oil, laid flat on filter paper, and dried at room temperature to obtain temperature-sensitive polymer microcapsules, and the average particle size of the capsules is 66 μm.

[0025] Examples 1-3 The specific steps for preparing the shrinkage-compensating fluidified solidified soil composite anti-cracking agent are as follows: 1) The raw materials are weighed according to the mass ratio in Table 1, and prepared for use; 2) The weighed sulphoaluminate cement, superfine slag powder and expanding agent are premixed in a three-dimensional motion mixer at a rotation speed of 35 r / min for 15 min to obtain a mixture A, the nanosheet kaolin is preheated at 110°C for 2 h, then 20 wt% of the mixture A and all of the nanosheet kaolin are poured into a double-planetary mixer, mixed at a rotation speed of 150 r / min for 5 min to obtain a kaolin-carrier premix, and finally the remaining mixture A is poured in, and mixed at a rotation speed of 300 r / min for 15 min to obtain a mixture B, the mixture B is placed in the hopper of a bottom-spraying fluidized bed with an air distribution plate and an atomizing nozzle, the fluidized bed fan is turned on to introduce clean compressed air, the air flow speed is adjusted to 1.3 m / s, after the mixture B is stably fluidized, the temperature-sensitive polymer microcapsules are sprayed into the fluidized bed through the atomizing nozzle at a rate of 0.6 kg / min, the air flow turbulence is used to make the temperature-sensitive polymer microcapsules fully contact and mix with the fluidized mixture B, after the temperature-sensitive polymer microcapsules are sprayed in, the fluidized state is maintained for 5 min, to obtain a mixture C, and finally the mixture C is stirred at a rotation speed of 60 r / min while spraying 0.02 wt% of an atomized solution of hydroxypropyl methyl cellulose in water at a temperature of 25°C and a relative humidity of 50%, to obtain the shrinkage-compensating fluidified solidified soil composite anti-cracking agent.

[0026] Table 1

[0027] Comparative Example 1 A composite anti-cracking agent is prepared by substantially the same method as in Example 1, except that no nanosheet kaolin is added.

[0028] Comparative Example 2 A composite anti-cracking agent is prepared by the method substantially the same as that of Example 1, except that the temperature-sensitive polymer microcapsules are replaced by equal mass of ordinary expanding agent (SY-K expanding agent provided by Wuhan Yuanjin Building Material Technology Co., Ltd.).

[0029] Comparative Example 3 A composite anti-cracking agent is prepared by the method substantially the same as that of Example 1, except that the sulphoaluminate cement is replaced by equal mass of ordinary Portland cement.

[0030] Comparative Example 4 A commercially available solidifying agent, a fluid solidifying soil solidifying agent from Huangshi Qinhe New Material Co., Ltd.

[0031] Comparative Example 5 A composite anti-cracking agent is prepared by the method substantially the same as that of Example 1, except that 0.02wt% hydroxypropyl methylcellulose aqueous solution is directly added to the mixture C.

[0032] The composite anti-cracking agents (solidifying agents) prepared in the above Examples 1-3 and Comparative Examples 1-5 are measured for initial setting time, initial neat cement paste fluidity, 30min neat cement paste fluidity and 60min neat cement paste fluidity according to the standard of CJ / T526-2018 Soft Soil Solidifying Agent; the prepared composite anti-cracking agents are mixed into soil at a dosage of 10% for solidifying soil experiments, wherein the soil is taken from the vicinity of Wulijie Street, Jiangxia District, Wuhan City, the unconfined compressive strength of the solidifying soil at 3d and 28d is measured according to the standard of CJ / T526-2018 Soft Soil Solidifying Agent, the expansion degree is measured according to the method in T / CECS1037-2022 Pre-mixed Fluid Solidifying Soil Filling Technology Standard, the solidifying soil consolidation shrinkage rate is measured according to the method in DB42 / T1218-2016 Shield Tunnel Synchronous Grouting Material, and the surface cracks are observed by naked eye at 7d. The experimental results are shown in Table 2 below.

[0033] Table 2

[0034] As can be seen from the data in Table 2, through the technical improvement of the present application, the initial, 30min and 60min neat cement paste fluidity and setting time of the solidifying agent fully meet the requirements of the standard of CJ / T526-2018 Soft Soil Solidifying Agent, and compared with the commercially available solidifying agent, the composite anti-cracking agent prepared in the present application significantly improves the early strength of the fluid solidifying soil and greatly reduces the crack problem caused by shrinkage.

[0035] Figure 1The photos of the cured soil of Comparative Example 4 (left) and Example 1 (right) taken on the 7th day after the curing soil experiment can be seen in the photos, and it can be seen that the cured soil added with the commercial curing agent of Comparative Example 4 has obvious cracks on the surface, and the cured soil added with the composite anti-cracking agent of Example 1 has a smooth surface and no cracks visible to the naked eye.

[0036] The present application is not limited to the above-mentioned embodiments, and for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements are also considered to be within the scope of protection of the present application. The contents not described in detail in the specification belong to the prior art known to those skilled in the art.

Claims

1. A shrinkage-compensating fluidized solidified soil composite anti-cracking agent, characterized in that: The raw materials and their mass proportions are as follows: 50-70 parts of cement, 20-30 parts of ultrafine slag powder, 0.5-1.2 parts of nano-flaky kaolin, 3-5 parts of expansion agent, 1-2 parts of temperature-sensitive polymer microcapsules, and 0.1-0.4 parts of admixture.

2. The shrinkage-compensating fluidized solidified soil composite anti-cracking agent according to claim 1, characterized in that: The cement is 42.5 grade sulphoaluminate cement, with a 28d strength of 45-60 MPa and a specific surface area of ​​360-450 m 2 / kg, the initial setting time is 30~60min; the specific surface area of ​​the ultrafine slag powder is 600~920kg / m 3 , 28d activity index is greater than 100%, and vitreous content is greater than 90%.

3. The shrinkage-compensating fluidized solidified soil composite anti-cracking agent according to claim 1, characterized in that: The nano-flaky kaolin has a diameter of 50-120 nm, a thickness of 5-20 nm, and an interlayer spacing of 0.7-1.2 nm. The expander is a calcium-magnesium composite expander, wherein the magnesium oxide content is 30-50%, and the limited expansion rate in air at 20°C for 21 days is ≥-0.015%.

4. The shrinkage-compensating fluidized solidified soil composite anti-cracking agent according to claim 1, characterized in that: The temperature-sensitive polymer microcapsule is obtained by wrapping sodium sulfate with a gelatin shell, and has a particle size of 50-200 μm.

5. The shrinkage-compensating fluidized solidified soil composite anti-cracking agent according to claim 4, characterized in that: The preparation method of the thermosensitive polymer microcapsules comprises the following steps: adding gelatin powder to warm water at 50-55° C., stirring until completely dissolved to obtain a colloidal solution, adding anhydrous sodium sulfate to the obtained colloidal solution, stirring and dispersing the mixture to obtain a mixed solution, adding the obtained mixed solution dropwise to edible oil kept warm in an ice water bath using a dropper, causing the droplets to rapidly solidify into microspheres upon contact with the cold oil, collecting the microspheres in the oil by filtration, rinsing with cold deionized water to remove surface grease, spreading the microspheres on filter paper, and air-drying at room temperature to obtain the thermosensitive polymer microcapsules.

6. The shrinkage-compensating fluidized solidified soil composite anti-cracking agent according to claim 1, characterized in that: The admixture is an aqueous solution of hydroxypropyl methylcellulose with a concentration of 0.02-0.04 wt %. The hydroxypropyl methylcellulose has a 24-hour water retention rate of ≥90% and a viscosity of 40,000-80,000 mPa.s.

7. A method for preparing the shrinkage-compensating fluidized solidified soil composite anti-cracking agent according to any one of claims 1 to 6, characterized in that: The specific steps are as follows: 1) Weigh the raw materials according to the ratio and set aside; 2) Weighed cement, ultrafine slag powder, and an expansion agent are premixed in a three-dimensional motion mixer to obtain a mixture A. Nano-flaky kaolin is then uniformly dispersed in the mixture A using a double planetary mixer to obtain a mixture B. The temperature-sensitive polymer microcapsules are then incorporated into the mixture B to obtain a mixture C. Finally, an atomized liquid obtained by atomizing the admixture is sprayed into the mixture C to obtain a fluidized solidified soil composite anti-cracking agent that compensates for shrinkage.

8. The method for preparing the shrinkage-compensating fluidized solidified soil composite anti-cracking agent according to claim 7, characterized in that: The process conditions of the premixing in step 2) are: mixing at a speed of 30 to 40 r / min for 15 minutes; step 2) using a double planetary mixer to uniformly disperse the nano-flaky kaolin in the mixture A, specifically the following steps: pre-drying the nano-flaky kaolin at 110 to 120° C. for 2 to 4 hours, then pouring 10 to 20 wt% of the mixture A and all the nano-flaky kaolin into the double planetary mixer, mixing at a speed of 100 to 150 r / min for 5 to 8 minutes to obtain a kaolin-carrier premix, and finally pouring the remaining mixture A into the mixture, and continuing to mix at a speed of 300 to 500 r / min for 15 to 20 minutes.

9. The method for preparing the shrinkage-compensating fluidized solidified soil composite anti-cracking agent according to claim 7, characterized in that: The method for incorporating the temperature-sensitive polymer microcapsules into the mixture B in step 2) is as follows: a bottom-spray fluidized bed with an air distribution plate and an atomizing nozzle is selected, the mixture B is added to the fluidized bed hopper, the fluidized bed fan is turned on to introduce clean compressed air, and the air flow velocity is adjusted to 1.2-1.8 m / s. After the mixture B is fluidized and stabilized, the temperature-sensitive polymer microcapsules are sprayed into the fluidized bed through the atomizing nozzle at a rate of 0.5-1.0 kg / min, and the air flow turbulence is used to fully contact and mix the temperature-sensitive polymer microcapsules with the fluidized mixture B. After the temperature-sensitive polymer microcapsules are sprayed, the fluidized state is maintained for mixing for 5-8 minutes. In step 2), the atomized liquid obtained by atomizing the admixture is sprayed into the mixture C. The specific process conditions are: at a temperature of 20-25° C. and a relative humidity of 40-60%, the mixture C is stirred at a speed of 30-60 r / min while spraying the atomized liquid.

10. Use of the shrinkage-compensating fluidized soil composite anti-cracking agent according to any one of claims 1 to 6 in the field of fluidized soil.

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