Porous solidified soil as well as preparation method and use method thereof

Abstract

The invention discloses porous solidified soil as well as a preparation method and a use method thereof. The porous solidified soil is prepared from the following components in parts by weight: 300 to 500 parts of ground dry soil, 20 to 40 parts of cement, 50 to 70 parts of mineral powder, 5 to 15 parts of gypsum, 0.01 to 0.3 part of early strength agent, 0.01 to 0.3 part of foaming agent, 0.03 to 0.08 part of foam stabilizer and 200 to 300 parts of water, and the ground dry soil is obtained by drying and grinding engineering soil; the early strength agent is at least one of triethanolamine, triisopropanolamine and diethanolisopropanolamine; the foaming agent is a hydrogen peroxide solution and azodicarbonamide, and the mass ratio of the hydrogen peroxide solution to the azodicarbonamide is 1: (1.4-1.6); the foam stabilizer is nano silicon dioxide. According to the porous solidified soil, the backfilling strength is guaranteed, meanwhile, bubbles in the soil can be reserved, the soil is not prone to hardening, the growth condition of vegetation is guaranteed, and therefore the porous solidified soil serves as an ecological restoration material.

Description

Technical Field

[0001] This invention belongs to the field of building materials, and in particular relates to a porous solidified soil and its preparation and application methods. Background Technology

[0002] Solidified soil is a self-compacting and self-leveling cementitious backfill material used to replace traditional compacted filling materials. Its main applications include trench backfilling, structural filling, pavement foundation filling, and slope stabilization. Compared to traditional compacted soil and granular backfill materials, it has many advantages, including: fast construction speed, commercial availability, self-leveling, designable early strength, and usability in narrow or restricted spaces. While traditional compacted filling and soil solidification significantly improve soil strength, they reduce soil porosity. Reduced porosity leads to severe soil compaction, making it difficult for vegetation to grow or even survive. In the long run, without vegetation consolidation and protection, simple soil compaction or solidification by solidifying agents is insufficient to resist water and wind erosion, which contradicts the concept of sustainable development. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a porous solidified soil and its preparation and use methods, which can retain air bubbles inside the soil while ensuring backfill strength, making it less prone to compaction, so as to ensure the growth conditions of vegetation, and thus serve as an ecological restoration material.

[0004] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0005] A porous solidified soil comprises the following components in parts by weight: 300-500 parts finely ground dry soil, 20-40 parts cement, 50-70 parts mineral powder, 5-15 parts gypsum, 0.01-0.3 parts early-strength agent, 0.01-0.3 parts foaming agent, 0.03-0.08 parts foam stabilizer, and 200-300 parts water;

[0006] The finely ground dry soil is obtained by drying and grinding the engineering soil.

[0007] The early strength agent is at least one of triethanolamine, triisopropanolamine, and diethanol monoisopropanolamine;

[0008] The foaming agent is hydrogen peroxide solution and azodicarbonamide, with a mass ratio of 1:(1.4-1.6).

[0009] The foam stabilizer is nano-silica.

[0010] As a further improvement, the cement is at least one selected from silicate cement, ordinary silicate cement, slag silicate cement, pozzolanic silicate cement, fly ash silicate cement, and composite silicate cement, with a cement strength grade of 42.5 and a specific surface area of ​​350 m². 2 / kg~400m 2 / kg.

[0011] As a further improvement, the mineral powder grade is S95 or higher.

[0012] As a further improvement, the gypsum is desulfurized gypsum or phosphogypsum, with a calcium sulfate content of not less than 85 wt%.

[0013] As a further improvement, the alkanolamine content in the early strength agent is not less than 85 wt%.

[0014] As a further improvement, the concentration of the hydrogen peroxide solution is 20–30 wt%.

[0015] As a further improvement, the mass ratio of hydrogen peroxide solution to azodicarbonamide in the foaming agent is 1:1.5.

[0016] The present invention provides a method for preparing the porous solidified soil, comprising: mixing cement, mineral powder and gypsum with finely ground dry soil, then adding foaming agent, early strength agent and water, mixing and stirring evenly to form a uniform solidified soil mixture.

[0017] As a further improvement, the foam stabilizer is added in three parts during the stirring process, with each addition being 1 / 3 of the total dosage.

[0018] The present invention provides a method for using porous solidified soil obtained by the preparation method described above, comprising: pumping the porous solidified soil to the surface of a backfill pit or slope, and then curing it after hardening.

[0019] The principle of this invention:

[0020] To reduce the cost of solidified soil, this invention utilizes a large amount of mineral powder, making its proportion exceed that of cement. Cement and gypsum, on the one hand, together with the mineral powder, form a cementitious material; on the other hand, both act as activators for the mineral powder. The calcium hydroxide and ettringite produced during cement hydration, and the calcium ions and sulfate ions formed by the dissolution of gypsum, activate the reactivity of the mineral powder, enabling it to rapidly hydrate and generate hydration products that bind soil particles, thereby forming a load-bearing skeleton structure. Therefore, after the solidified soil is mixed with water, cement, mineral powder, and gypsum undergo a series of hydration reactions, and the resulting hydration products bond with soil particles to form a stable and strong skeleton.

[0021] The present invention differs from traditional solidified soil in that it introduces a large number of air bubbles into the solidified soil and retains these air bubbles after hardening, thus making it suitable for vegetation growth. To achieve this goal, the present invention includes components of an early-strength agent and a foaming agent.

[0022] During the hydration process, alkanolamines, as early strength agents, play a role in two aspects: firstly, promoting cement hydration, stimulating the reactivity of mineral powder, improving the early strength of solidified soil, and shortening its setting time; secondly, as a surface-active substance, alkanolamines have a certain air-entraining ability, introducing some air bubbles during the mixing of solidified soil, thereby improving the foaming ability of the curing agent.

[0023] The main function of the combination of hydrogen peroxide and azodicarbonamide is to introduce a large number of air bubbles during the mixing and curing process of the solidified soil through synergistic foaming. This results in a continuously distributed multi-level porous structure within the solidified soil, reducing soil compaction and hindering vegetation growth. The synergistic foaming effect is mainly reflected in two aspects: foaming time and foam size. Regarding foaming time, azodicarbonamide decomposes upon heating to produce nitrogen gas, resulting in rapid foaming with a short duration, which can form the initial porous structure during the mixing stage. Hydrogen peroxide, as an oxidizing foaming agent, decomposes upon heating to produce oxygen, resulting in gentle and long-lasting foaming, which can continue foaming in the subsequent curing stage, consolidating the already formed porous structure. The two work together to ensure that pores are continuously generated in the solidified soil from the end of mixing until before hardening, compensating for lost porosity. Regarding foam size, azodicarbonamide forms larger main pores with a diameter of approximately 100–300 μm, while hydrogen peroxide forms smaller interconnected pores with a diameter of approximately 10–50 μm. The co-generation of these two pore sizes constructs a continuous multi-level porous structure within the solidified soil system.

[0024] The nano-silica added during the mixing process acts as a bubble stabilizer. On one hand, the nanoparticles adsorb at the interface of air bubbles in the solidified soil, forming a dense protective layer to prevent bubble collapse. On the other hand, the nano-silica increases the apparent viscosity of the slurry, slowing down the rise rate of air bubbles. Furthermore, the nanoparticles fill the capillary channels in the solidified soil slurry, reducing the number of interconnected pores and increasing the number of closed pores, which not only reduces the rate of water evaporation but also improves the system's resistance to freeze-thaw damage.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The solidified soil of the present invention is a new type of backfill material that can be applied to a completely new field. It is no longer limited to the traditional solidified soil field, but can be used as an ecological restoration material. While ensuring the backfill strength, it also ensures the growth conditions of vegetation.

[0027] (2) Compared with traditional backfill solidified soil, the solidified soil of the present invention has the characteristics of high porosity, suitable for vegetation growth, and initial air content of more than 35%.

[0028] (3) The solidified soil of the present invention has a certain air-entraining property and the foam stability is also guaranteed. The air content can reach more than 30% in 1 hour and the air content after solidification can reach more than 30%.

[0029] (4) The solidified soil of the present invention has a 28-day strength of more than 8.0 MPa under the premise of satisfying high porosity and being suitable for vegetation growth, which meets the backfill strength requirements.

[0030] (5) The porous solidified soil of the present invention, compared with traditional backfill materials, maximizes the environmental friendliness of the soil. The main backfill material can be sourced locally, with less cement used, and is low-carbon, environmentally friendly and inexpensive.

[0031] (6) The porous solidified soil of the present invention introduces a large number of air bubbles to play a lubricating role compared with traditional solidified soil, making the solidified soil more fluid and easier to construct.

[0032] (7) The porous solidified soil of the present invention, compared with the traditional solidified soil, introduces a large number of closed pores, which can improve the solidified soil's resistance to freeze-thaw damage. Detailed Implementation

[0033] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0034] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] In some specific embodiments, the porous solidified soil of the present invention comprises the following components in parts by weight: 300-500 parts finely ground dry soil, 20-40 parts cement, 50-70 parts mineral powder, 5-15 parts gypsum, 0.01-0.3 parts early-strength agent, 0.01-0.3 parts foaming agent, 0.03-0.08 parts foam stabilizer, and 200-300 parts water. The cementing material therein can solidify the soil and generate stable and uniform air bubbles.

[0037] In some embodiments, the engineering soil sample is dried and ground to obtain finely ground dry soil. The engineering soil sample is taken according to the engineering requirements, and should be as free of impurities as possible, such as large pieces of gravel and domestic waste, but retain residual vegetation roots and other humus in the soil sample. In some embodiments, the soil sample is dried at 105°C, and then ground finely using a high-power pulverizer or ball mill, and sieved with a sieve aperture diameter of 1 mm.

[0038] In some embodiments, the cement is at least one selected from silicate cement, ordinary silicate cement, slag silicate cement, pozzolanic silicate cement, fly ash silicate cement, and composite silicate cement, and the cement strength grade is 42.5, with a specific surface area of ​​350 m². 2 / kg~400m 2 / kg.

[0039] In some embodiments, the mineral powder grade is S95 or higher.

[0040] In some embodiments, the gypsum is desulfurized gypsum or phosphogypsum, and the calcium sulfate content is not less than 85 wt%.

[0041] In some embodiments, the early strength agent is at least one of industrial triethanolamine, triisopropanolamine and diethanol monoisopropanolamine, wherein the content of the alcohol amine is not less than 85 wt%.

[0042] In some embodiments, the foaming agent is a mixture of hydrogen peroxide solution and azodicarbonamide, wherein the mass ratio of hydrogen peroxide solution to azodicarbonamide is 1:(1.4-1.6), preferably 1:1.5. The concentration of the hydrogen peroxide solution is 20-30 wt%, and in the examples below, the concentration is 30 wt%.

[0043] In some embodiments, the foam stabilizer is nano-silica.

[0044] In some specific embodiments, the method for preparing porous solidified soil of the present invention involves simply weighing out solidified soil raw materials and stirring them evenly to form a mixture.

[0045] In some embodiments, cement, mineral powder and gypsum are first mixed with finely ground dry soil, and then foaming agent, early strength agent and water are added and mixed evenly by a soil hardening mixing device to form a uniform soil hardening mixture.

[0046] In some embodiments, the foam stabilizer is added in three parts during the stirring process, with each addition being 1 / 3 of the total dose.

[0047] In some embodiments, the stirring speed is 800 rpm, the stirring time is 15 min, and the temperature of the stirring chamber is controlled at 50°C during the stirring process.

[0048] In some embodiments, the solidified soil is subjected to ultrasonic treatment after mixing. The ultrasonic treatment frequency is 40 kHz and the ultrasonic treatment time is 10 min.

[0049] In some specific embodiments, the method of using the porous solidified soil of the present invention includes: after the solidified soil is mixed, the porous solidified soil is pumped to the backfill pit or slope surface, and after hardening and curing for a period of time, a porous solidified soil with strength and suitable for vegetation growth is formed.

[0050] In some embodiments, the pumping pressure is 1 MPa to 3 MPa.

[0051] In some embodiments, the mixture is pumped to the backfill location, and after hardening, it forms an integral backfill with a certain strength. It begins to set after 16 hours, begins to show strength after 24 hours, and reaches a strength of over 8.0 MPa after 28 days. After 50 freeze-thaw cycles, the strength retention rate is over 50%, and after 100 freeze-thaw cycles, the strength retention rate is over 25%. The initial air content can reach over 35%, the air content can reach over 30% after 1 hour, and the air content can reach over 30% after condensation.

[0052] The significant feature of the solidified soil of this invention is that a large number of air bubbles are introduced into the soil after solidification, making the solidified soil still suitable for vegetation growth. After backfilling, it contains a large number of stable and uniformly distributed air bubbles, and is a self-compacting and self-leveling cementitious backfill material, requiring no compaction treatment during use.

[0053] Experimental tests show that the porous solidified soil backfilled by this invention has suitable strength, high air content, high air bubble retention rate, and is suitable for vegetation growth. Furthermore, because the solidified soil contains low amounts of cementitious materials and uses little cement itself, replacing it with mineral powder and phosphogypsum, the overall price of the solidified soil is low, and the solid waste utilization rate is high, which aligns with the concept of sustainable development.

[0054] Example 1

[0055] The solidified soil provided in this embodiment comprises the following components: 30 parts of 42.5 grade silicate cement; 60 parts of S95 mineral powder; 10 parts of 85% phosphogypsum; 0.02 parts of 85% triethanolamine; 0.12 parts of hydrogen peroxide solution; 0.18 parts of azodicarbonamide; 0.08 parts of nano-silica; 250 parts of water; 400 parts of finely ground dry soil; and a pumping pressure of 1 MPa.

[0056] The method for preparing finely ground dry soil is as follows: the engineering soil sample is dried at a temperature of 105℃, and then the soil sample is ground finely using a high-power pulverizer or ball mill and sieved through a sieve with a sieve hole diameter of 1mm to obtain finely ground dry soil.

[0057] Cement, mineral powder, and gypsum are first mixed with finely ground dry soil. Then, foaming agent, accelerator, and water are added and mixed thoroughly using a soil hardening mixing device to form a homogeneous solidified soil mixture. The foam stabilizer is added in three stages during mixing, each time adding one-third of the total dosage. The mixing speed is 800 rpm, and the mixing time is 15 minutes, while the temperature of the mixing chamber is controlled at 50℃. After mixing, the solidified soil is ultrasonically treated. The ultrasonic treatment frequency is 40 kHz, and the ultrasonic treatment time is 10 minutes.

[0058] Example 2

[0059] The solidified soil provided in this embodiment comprises the following components: 20 parts of 42.5 grade ordinary silicate cement; 50 parts of S95 mineral powder; 5 parts of 90% phosphogypsum; 0.02 parts of 95% triethanolamine; 0.06 parts of hydrogen peroxide solution; 0.09 parts of azodicarbonamide; 0.05 parts of nano-silica; 300 parts of water; 500 parts of finely ground dry soil; and a pumping pressure of 2 MPa.

[0060] The preparation method is as described in Example 1.

[0061] Example 3

[0062] The solidified soil provided in this embodiment comprises the following components: 40 parts of 42.5 grade fly ash silicate cement; 70 parts of S95 mineral powder; 15 parts of 90% phosphogypsum; 0.04 parts of 95% triethanolamine; 0.04 parts of hydrogen peroxide solution; 0.06 parts of azodicarbonamide; 0.03 parts of nano-silica; 200 parts of water; 300 parts of finely ground dry soil; and a pumping pressure of 2 MPa.

[0063] The preparation method is as described in Example 1.

[0064] Example 4

[0065] The solidified soil provided in this embodiment comprises the following components: 30 parts of 42.5 grade slag silicate cement; 60 parts of S95 mineral powder; 10 parts of dihydrate gypsum; 0.04 parts of 99% triethanolamine; 0.02 parts of hydrogen peroxide solution; 0.03 parts of azodicarbonamide; 0.08 parts of nano-silica; 250 parts of water; 400 parts of finely ground dry soil; and a pumping pressure of 3 MPa.

[0066] The preparation method is as described in Example 1.

[0067] Comparative Example 1

[0068] The solidified soil (without early strength agent) provided in this comparative example comprises the following components: 30 parts of 42.5 grade silicate cement; 60 parts of S95 mineral powder; 10 parts of 90% phosphogypsum; 0.12 parts of hydrogen peroxide solution; 0.18 parts of azodicarbonamide; 0.08 parts of nano silica; 250 parts of water; 400 parts of finely ground dry soil; and a pumping pressure of 2 MPa.

[0069] The preparation method is as described in Example 1 (without adding early strength agent).

[0070] Comparative Example 2

[0071] The solidified soil provided in this comparative example (without foaming agent and foam stabilizer) comprises the following components: 30 parts of 42.5 grade silicate cement; 60 parts of S95 mineral powder; 10 parts of 90% phosphogypsum; 0.02 parts of 85% triethanolamine; 250 parts of water; 400 parts of finely ground dry soil; and a pumping pressure of 2 MPa.

[0072] The preparation method is as described in Example 1 (without adding foaming agent and foam stabilizer).

[0073] Comparative Example 3

[0074] A conventional solidified soil comprises the following components: 30 parts of 42.5 grade silicate cement; 60 parts of S95 mineral powder; 10 parts of 90% phosphogypsum; 250 parts of water; 400 parts of finely ground dry soil; and a pumping pressure of 2 MPa.

[0075] Comparative Example 4

[0076] The solidified soil (without hydrogen peroxide) provided in this comparative example comprises the following components: 30 parts of 42.5 grade silicate cement; 60 parts of S95 mineral powder; 10 parts of 90% phosphogypsum; 0.02 parts of 85% triethanolamine; 0.18 parts of azodicarbonamide; 0.08 parts of nano-silica; 250 parts of water; 400 parts of finely ground dry soil; and a pumping pressure of 2 MPa.

[0077] The preparation method is as described in Example 1 (without hydrogen peroxide).

[0078] Comparative Example 5

[0079] The solidified soil provided in this comparative example (without azodicarbonamide) comprises the following components: 30 parts of 42.5 grade silicate cement; 60 parts of S95 mineral powder; 10 parts of 90% phosphogypsum; 0.02 parts of 85% triethanolamine; 0.12 parts of hydrogen peroxide solution; 0.08 parts of nano-silica; 250 parts of water; 400 parts of finely ground dry soil; and a pumping pressure of 2 MPa.

[0080] The preparation method is as in Example 1 (without doping with azodicarbonamide).

[0081] Comparative Example 6

[0082] The solidified soil (without silica) provided in this comparative example comprises the following components: 30 parts of 42.5 grade silicate cement; 60 parts of S95 mineral powder; 10 parts of 90% phosphogypsum; 0.02 parts of 85% triethanolamine; 0.12 parts of hydrogen peroxide solution; 0.18 parts of azodicarbonamide; 250 parts of water; 400 parts of finely ground dry soil; and a pumping pressure of 2 MPa.

[0083] The preparation method is as described in Example 1 (without silicon dioxide).

[0084] The composition of the solidified soil in the examples and comparative examples is shown in Table 1.

[0085] Table 1. Composition (parts) of the solidified soil in the examples and comparative examples.

[0086]

[0087]

[0088] The above comparative and example samples were thoroughly mixed using a concrete mixer to form a solidified soil mixture. This mixture was pumped into a pre-prepared mold and cured for 28 days. The compressive strength was then measured, along with the compressive strength after 50 and 100 freeze-thaw cycles after 28 days of curing (see Table 2). Simultaneously, the air content of the mixture was measured at the initial time, 1 hour, and after setting (see Table 1). The air content of the mixture was determined according to the American ASTM C185-2020 standard.

[0089] Table 2 shows the remaining compressive strength of the test blocks after 28 days and 50 and 100 freeze-thaw cycles.

[0090]

[0091] Table 3 Initial time, 1 hour, and air content after solidification of solidified soil

[0092]

[0093]

[0094] The test results above show that in Examples 1-4, the 28-day strength of all solidified soils reached over 8.0 MPa, the initial air content reached over 35%, the 1-hour air content reached over 30%, and the post-condensation air content reached over 30%. On the other hand, the addition of foaming agents and foam stabilizers did not affect the strength; on the contrary, it improved the residual strength after 50 and 100 freeze-thaw cycles. After 50 cycles, the retained strength reached over 50%, and after 100 cycles, the retained strength reached over 25%. The beneficial effects of foaming agents and foam stabilizers improved the freeze-thaw resistance of the solidified soil. The improvement in freeze-thaw resistance was mainly closely related to the increase in the amount of foaming agent, while the foam stabilizer, by supporting and strengthening the formed foam structure, was crucial to this freeze-thaw resistance. Data from Examples 1 to 4 showed a strong correlation between the decreasing trend of residual strength after freeze-thaw cycles and the reduction in the amount of foaming agent. Although the amounts of other components (such as cement, water, early strength agent and foam stabilizer) were also adjusted in each embodiment, the significant reduction in the amount of foaming agent was the main reason for the systematic decline in antifreeze performance.

[0095] In addition, the comparative group, which did not contain early strength agent or foaming agent, had a much lower air content than the example group, and could not meet the requirements of porous solidified soil.

[0096] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A porous solidified soil, characterized in that, It comprises the following components by weight: 300-500 parts finely ground dry soil, 20-40 parts cement, 50-70 parts mineral powder, 5-15 parts gypsum, 0.01-0.3 parts early strength agent, 0.01-0.3 parts foaming agent, 0.03-0.08 parts foam stabilizer, and 200-300 parts water; The finely ground dry soil is obtained by drying and grinding the engineering soil. The early strength agent is at least one of triethanolamine, triisopropanolamine, and diethanol monoisopropanolamine; The foaming agent is hydrogen peroxide solution and azodicarbonamide, with a mass ratio of 1:(1.4-1.6). The foam stabilizer is nano-silica.

2. The porous solidified soil according to claim 1, characterized in that, The cement is at least one of silicate cement, ordinary silicate cement, slag silicate cement, pozzolanic silicate cement, fly ash silicate cement, and composite silicate cement, with a strength grade of 42.5 and a specific surface area of ​​350 m². 2 / kg~400m 2 / kg.

3. The porous solidified soil according to claim 1, characterized in that, The mineral powder grade is S95 or higher.

4. The porous solidified soil according to claim 1, characterized in that, The gypsum used is desulfurized gypsum or phosphogypsum, with a calcium sulfate content of not less than 85 wt%.

5. The porous solidified soil according to any one of claims 1 to 4, characterized in that, The accelerator contains no less than 85 wt% alcohol amines.

6. The porous solidified soil according to claim 1, characterized in that, The concentration of the hydrogen peroxide solution is 20–30 wt%.

7. The porous solidified soil according to claim 1 or 6, characterized in that, The mass ratio of hydrogen peroxide solution to azodicarbonamide in the foaming agent is 1:1.

5.

8. A method for preparing the porous solidified soil according to any one of claims 1 to 7, characterized in that, include: Cement, mineral powder, and gypsum are first mixed with finely ground dry soil, and then foaming agent, early strength agent, and water are added and mixed evenly to form a uniform solidified soil mixture.

9. The preparation method according to claim 8, characterized in that, The foam stabilizer is added in three parts during the stirring process, with each addition being 1 / 3 of the total dosage.

10. A method for using porous solidified soil obtained by the preparation method according to claim 8 or 9, characterized in that, include: Porous solidified soil is pumped to the backfill pit or slope surface, hardened, and then cured.

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