Maintenance method for exciting and solidifying sludge through rice hull ash modified carbide slag

Abstract

The invention discloses a maintenance method of rice hull ash modified carbide slag excited and solidified sludge, and relates to the technical field of dredged sludge solidification construction.The maintenance method of the rice hull ash modified carbide slag excited and solidified sludge comprises the steps that dredged sludge, rice hull ash and carbide slag are taken by mass and mixed to form a solidified base material; adding water into the curing base material to form a mixture; uniformly stirring the mixture to form a sludge solidified mixture; compacting the sludge solidified mixture to form a sludge solidified body; curing the sludge solidified body by adopting the environment temperature P1 and the first relative environment humidity I1; curing the sludge solidified body by adopting the environment temperature P1 and the second relative environment humidity I2; and curing the sludge solidified body by adopting the environment temperature P1 and the third relative environment humidity I3. According to the method, the rice hull ash and the carbide slag are compositely doped into the dredged sludge, the staged maintenance process is combined, and the maintenance period is divided into three stages, so that the curing strength of the dredged sludge is improved, and the actual use requirements of engineering are met.

Description

Technical Field

[0001] The present invention relates to the technical field of dredged sludge solidification construction, and particularly relates to a curing method for rice husk ash modified carbide slag activated solidified sludge. Background Art

[0002] In dredging projects, the solidification treatment of sludge is a key step to ensure project stability and environmental safety. In existing dredged sludge solidification processes, curing usually takes 28 days as a unified cycle, without distinguishing the temperature and humidity adaptation requirements of the early (7 - 14 days) rapid hydration period and the late (14 - 28 days) slow release reaction period, resulting in the inhibition of the early reaction rate or insufficient water supply in the late stage, and the uneven growth of the strength of the solidified soil, resulting in low solidification strength of the dredged sludge and unable to meet the actual use requirements of the project. Summary of the Invention

[0003] The main object of the present invention is to propose a curing method for rice husk ash modified carbide slag activated solidified sludge, aiming to improve the solidification strength of dredged sludge to meet the actual use requirements of the project.

[0004] To achieve the above object, the curing method for rice husk ash modified carbide slag activated solidified sludge proposed by the present invention includes:

[0005] Taking 100 parts of dredged sludge, 5 - 20 parts of rice husk ash and 3 - 11 parts of carbide slag by mass, and mixing them to form a solidification base material;

[0006] Adding water to the solidification base material to form a mixture;

[0007] Stirring the mixture evenly to form a sludge solidification mixture;

[0008] Compacting the sludge solidification mixture to form the sludge solidified body;

[0009] Within 7 days, curing the sludge solidified body with an environmental temperature P1 and a first relative environmental humidity I1; wherein, 18°C ≤ P1 ≤ 22°C, I1 > 95%;

[0010] Within 7 to 14 days, curing the sludge solidified body with the environmental temperature P1 and a second relative environmental humidity I2; wherein, 92% ≤ I2 ≤ 94%;

[0011] Within 14 to 28 days, curing the sludge solidified body with the environmental temperature P1 and a third relative environmental humidity I3; wherein, 90% < I3.

[0012] In an embodiment, the step of mixing the mixture evenly to form a sludge solidification mixture includes:

[0013] Add water to the mixture to moisten the mixture;

[0014] Mix the mixture evenly to obtain the solidified sludge mixture.

[0015] In one embodiment, the step of adding water to the mixture to moisten the mixture includes:

[0016] Obtain the initial water content of the dredged sludge and the total mass of the solidifying base material;

[0017] Obtain the required water amount according to the initial water content, the total mass of the solidifying base material and the target water content;

[0018] Add water to the mixture according to the required water amount to moisten the mixture.

[0019] In one embodiment, the step of obtaining the required water amount according to the initial water content, the total mass of the solidifying base material and the target water content includes:

[0020] Use Formula 1 to obtain the required water amount according to the initial water content, the total mass of the solidifying base material and the target water content;

[0021] The Formula 1 is:

[0022]

[0023] Wherein, the target water content is greater than the initial water content, W1 is the initial water content, W2 is the target water content, K1 is the total mass of the solidifying base material, and K2 is the required water amount.

[0024] In one embodiment, 52.16% ≤ the target water content ≤ 57.65%.

[0025] In one embodiment, the mass ratio of the rice husk ash to the carbide slag is 15:7.

[0026] In one embodiment, the porosity of the nanopores of the rice husk ash is

[0027] In one embodiment, the specific surface area of the rice husk ash is SSA, 200m 2 / g ≤ SSA ≤ 500m 2 / g.

[0028] In one embodiment, the content of CaO in the carbide slag is B, 65% ≤ B ≤ 70%; the content of SiO2 in the carbide slag is C, 1% ≤ C ≤ 2%; the content of Al2O3 in the carbide slag is D, 1.5% ≤ D ≤ 2.5%.

[0029] In one embodiment, the content of SiO2 in the rice husk ash is A, where 90% ≤ A ≤ 95%; the content of Fe2O3 in the rice husk ash is E, where 0.5% ≤ E ≤ 1%.

[0030] The technical solution of the present invention is to compound and incorporate 15% rice husk ash and 7% carbide slag into the dredged silt, and in combination with a staged curing process, the curing period is divided into three stages: 7 days, 14 days, and 28 days. In the early stage (7 days), 20 ± 2°C and humidity > 95% are used to accelerate the initial hydration of CaO; in the middle stage (14 days), the humidity is adjusted to 92% - 94% to promote the secondary reaction between SiO2 in the rice husk ash and Ca(OH)2; in the later stage (28 days), the humidity is maintained > 90% and the curing duration is extended, and the nano-pores in the rice husk ash are used to slowly release water to continuously generate C-S-H gel. This method enables the unconfined compressive strength of the composite solidified soil of 7% carbide slag and 15% rice husk ash to reach 849.6 kPa after 28 days, which is 67.2% higher than that of the traditional single-stage curing, and the porosity is reduced to 12%; at the same time, the staged humidity control ensures the directional growth of needle-shaped / columnar C-S-H gel, the ultimate strain is increased to 4.5%, and the microstructure presents a bundled dense network, realizing the ternary synergistic optimization of strength, toughness, and durability. The curing strength of the dredged silt is improved to meet the actual engineering usage requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the structures shown in these drawings.

[0032] Figure 1 It is a schematic flow chart of an embodiment of the curing method for rice husk ash-modified carbide slag-activated solidified silt provided by the present invention;

[0033] Figure 2 It is a relationship diagram between the strength of carbide slag soil and the carbide slag content and the curing age related to the present invention;

[0034] Figure 3 It is a relationship diagram between the unconfined compressive strength of rice husk ash carbide slag soil under different rice husk ash contents related to the present invention;

[0035] Figure 4 It is a schematic diagram of the fitting curve between the unconfined compressive strength and the rice husk ash content under different curing ages related to the present invention;

[0036] Figure 5 It is a relationship diagram between the unconfined compressive strength of rice husk ash carbide slag soil under different curing ages related to the present invention;

[0037] Figure 6 It is a relationship diagram of the ultimate strain of rice husk ash carbide slag soil under different curing ages related to the present invention;

[0038] Figure 7 It is a model diagram of the measured unconfined compressive strength of rice husk ash carbide slag soil related to the present invention;

[0039] Figure 8 It is a strength model diagram of rice husk ash carbide slag soil related to the present invention;

[0040] Figure 9 It is a schematic diagram of the SEM analysis results of the influence of the rice husk ash content on the microstructure of solidified soil related to the present invention;

[0041] Figure 10 It is a schematic diagram of the SEM analysis results of the change of the microstructure of rice husk ash carbide slag solidified soil with age related to the present invention;

[0042] Figure 11 It is a schematic diagram of the model of the microscopic evolution mechanism of rice husk ash carbide slag solidified silt related to the present invention.

[0043] The realization, functional characteristics and advantages of the object of the present invention will be further described with reference to the accompanying drawings in combination with the embodiments. Detailed Embodiments

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] It should be noted that if there are directional indications (such as up, down, left, right, front, back...) involved in the embodiments of the present invention, the directional indications are only used to explain the relative position relationship and movement conditions between components in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0046] In addition, if there are descriptions such as "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, if "and / or" or "and / or" appears throughout the text, its meaning includes three parallel scenarios. Taking "A and / or B" as an example, it includes Scenario A, or Scenario B, or the scenario where both A and B are satisfied simultaneously. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0047] In dredging engineering, the solidification treatment of silt is a key step to ensure the stability of the project and environmental safety. In the existing dredged silt solidification process, the curing usually takes 28 days as a unified cycle, without distinguishing the temperature and humidity adaptation requirements in the early (7 - 14 days) rapid hydration period and the late (14 - 28 days) slow release reaction period, resulting in the inhibition of the early reaction rate or insufficient water supply in the late stage, and the uneven growth of the strength of the solidified soil, resulting in low solidification strength of the dredged silt and unable to meet the actual use requirements of the project.

[0048] To solve this technical problem, the present invention proposes a curing method for rice husk ash modified carbide slag activated solidified silt.

[0049] Please refer to Figure 1 , in an embodiment of the present invention, the curing method for rice husk ash modified carbide slag activated solidified silt includes:

[0050] Step S10, taking 100 parts of dredged silt, 5 - 20 parts of rice husk ash, and 3 - 11 parts of carbide slag by mass, and mixing them to form a solidification base material;

[0051] Step S20, adding water to the solidification base material to form a mixture;

[0052] Step S30, stirring the mixture evenly to form a silt solidification mixture;

[0053] Step S40, compacting the silt solidification mixture to form the silt solidified body;

[0054] Step S50, curing the silt solidified body with an environmental temperature P1 and a first relative environmental humidity I1 within 7 days; wherein, 18°C ≤ P1 ≤ 22°C, I1 > 95%;

[0055] Step S60, cure the silt solidified body at the environmental temperature P1 and the second relative environmental humidity I2 within 7 to 14 days; wherein, 92% ≤ I2 ≤ 94%;

[0056] Step S70, cure the silt solidified body at the environmental temperature P1 and the third relative environmental humidity I3 within 14 to 28 days; wherein, 90% < I3.

[0057] Specifically, by mass, take 100 parts of dredged silt, 5 to 20 parts of rice husk ash, and 3 to 11 parts of carbide slag, and mix them to form a solidification base material. The dredged silt needs to be dried, crushed, and passed through a 2 mm sieve to ensure uniform particles; the rice husk ash is an active powder obtained by calcining rice husks at 600 °C for 2 hours and then grinding to a particle size ≤ 0.075 mm; the carbide slag is an industrial by-product with a CaO content ≥ 65%, and it needs to pass through a 0.15 mm sieve. When mixing, use a mixer and stir at a speed of 60 rpm for 10 minutes. If there are no lumps visually, it is considered uniform.

[0058] Add distilled water to the solidification base material and adjust it to the optimal moisture content (15% - 25%), which is specifically determined by a standard compaction test. After stirring, use the layered compaction method to fill the mixture into a cylindrical mold with a diameter of 50 mm and a height of 100 mm, and compact it in 3 layers, with 30 compaction times for each layer, to ensure a maximum dry density of 1.6 - 1.8 g / cm 3 . Let it stand for 24 hours before demolding. Apply vaseline evenly on the inner wall of the mold (with a thickness of 0.1 - 0.3 mm) to prevent the specimen from sticking.

[0059] The curing process is divided into three stages, with the temperature kept constant at 20 ± 2 °C and the humidity regulated in gradients:

[0060] Stage 1 (0 - 7 days): The humidity I1 > 95%, and a saturated KNO3 salt solution is used to maintain high humidity to accelerate the initial hydration of CaO to generate Ca(OH)2;

[0061] Stage 2 (7 - 14 days): The humidity I2 = 92% - 94%, and an NaCl salt solution is used instead to promote the reaction between active SiO2 in the rice husk ash and Ca(OH)2 to generate C-S-H gel;

[0062] Stage 3 (14 - 28 days): The humidity I3 > 90%, and the nano-pores in the rice husk ash are used to slowly release moisture to maintain the late hydration reaction.

[0063] In the technical solution provided by the present invention, by compounding and incorporating 15% rice husk ash and 7% carbide slag into the dredged silt, combined with a staged curing process, the curing period is divided into three stages of 7 days, 14 days, and 28 days. In the early stage (7 days), 20 ± 2 °C and humidity > 95% are used to accelerate the initial hydration of CaO; in the middle stage (14 days), the humidity is adjusted to 92% - 94% to promote the secondary reaction between SiO2 in the rice husk ash and Ca(OH)2; in the later stage (28 days), the humidity is maintained > 90% and the curing duration is extended, and the nano-pores in the rice husk ash are used to slowly release water to continuously generate C-S-H gel. This method enables the unconfined compressive strength of the 7% carbide slag and 15% rice husk ash composite solidified soil to reach 849.6 kPa at 28 days, which is 67.2% higher than that of the traditional single-stage curing, and the porosity is reduced to 12%; at the same time, the staged humidity control ensures the directional growth of needle-like / columnar C-S-H gel, the ultimate strain is increased to 4.5%, and the microstructure presents a bundled dense network, realizing the ternary synergistic optimization of strength, toughness, and durability. The curing strength of the dredged silt is improved to meet the actual engineering usage requirements.

[0064] In an embodiment of the present invention, the step of mixing the mixture uniformly to form a silt solidification mixture includes:

[0065] Step S31, adding water to the mixture to moisten the mixture;

[0066] Step S32, mixing the mixture uniformly to obtain the silt solidification mixture.

[0067] Specifically, in step S31 and step S32, distilled water is added to the mixture of dry solidification base material, carbide slag, and rice husk ash in three times. After each addition of water, mechanical stirring is carried out for 5 minutes, and after standing for 10 minutes, the next addition of water is carried out. Adding water in batches avoids local over-wetting or cracking caused by concentrated water, and improves the mixing uniformity. Standing allows the water to fully penetrate into the particle gaps and reduces the internal porosity of the specimen after compaction.

[0068] In an embodiment of the present invention, the step of adding water to the mixture to moisten the mixture includes:

[0069] Step S311, obtaining the initial moisture content of the dredged silt and the total mass of the solidification base material;

[0070] Step S312, obtaining the required water amount according to the initial moisture content, the total mass of the solidification base material, and the target moisture content;

[0071] Step S313, adding water to the mixture according to the required water amount to moisten the mixture.

[0072] In an embodiment of the present invention, the step of obtaining the water demand according to the initial moisture content, the total mass of the solidifying base material, and the target moisture content includes:

[0073] Step S301, using Formula 1, obtain the water demand according to the initial moisture content, the total mass of the solidifying base material, and the target moisture content;

[0074] The Formula 1 is:

[0075]

[0076] wherein, the target moisture content is greater than the initial moisture content, W1 is the initial moisture content, W2 is the target moisture content, K1 is the total mass of the solidifying base material, and K2 is the water demand.

[0077] Specifically, the water addition requirement is quantified through Formula 1 to ensure the control of the moisture content, so that the deviation of the actual moisture content < 0.5%. This avoids the softening of the specimen caused by excessive water addition or the incomplete compaction caused by insufficient moisture.

[0078] In an embodiment of the present invention, 52.16% ≤ the target moisture content ≤ 57.65%.

[0079] Specifically, the target moisture content covers the optimal compaction interval of the dredged silt to ensure the maximization of the specimen density. When exceeding this range (such as the moisture content > 57.65%), the specimen is prone to lateral expansion, and the compressive strength decreases by 12% - 18%.

[0080] In an embodiment of the present invention, the mass ratio of the rice husk ash to the carbide slag is 15:7.

[0081] Specifically, the mass ratio of the rice husk ash to the carbide slag is 15:7 to ensure the efficient generation of C-S-H gel and avoid the reaction imbalance caused by excess or deficiency; at this ratio, the nano-pore filling and the distribution of hydration products are uniform, significantly reducing the porosity (< 20%), which can further improve the anti-seepage property and durability of the soil body; and it can adapt to different moisture content silts, and the strength stability of the solidified soil is better than that of traditional cement-based materials (the 28-day UCS fluctuation range < 10%).

[0082] In an embodiment of the present invention, the porosity of the nano-pores of the rice husk ash is

[0083] Specifically, measured by thermogravimetric analysis (TGA), the rice husk ash with a porosity of can adsorb 23.7% mass of water under the condition of a relative humidity of 95%, and the continuous release rate reaches 82% during the 28-day curing period. And, The interfacial binding energy between C-S-H gel and rice husk ash in the sample reaches 2.1 nN / nm, which is 160% higher than that of the sample.

[0084] In the embodiment of the present invention, the specific surface area of the rice husk ash is SSA, and 200 m 2 / g ≤ SSA ≤ 500 m 2 / g.

[0085] At a carbide slag content of 7%, when the SSA increases from 150 m 2 / g to 200 m 2 / g, the 28-day UCS value jumps from 420 kPa to 580 kPa; when the SSA reaches 500 m 2 / g, the UCS value can reach 820 kPa, but when it continues to increase to 550 m 2 / g, the strength drops to 780 kPa. Scanning electron microscopy shows that the filling rate of C-S-H gel in the sample with SSA = 350 m 2 / g reaches 82%, and the pore tortuosity coefficient reaches 4.7, which is significantly better than that of the sample with a low specific surface area. Moreover, after 10 freeze-thaw cycles, the mass loss rate of the sample with SSA = 200 m 2 / g is 3.2%, while that of the sample with SSA = 500 m 2 / g is only 1.8%, showing better structural stability.

[0086] In the embodiment of the present invention, the content of CaO in the carbide slag is B, and 65% ≤ B ≤ 70%; the content of SiO2 in the carbide slag is C, and 1% ≤ C ≤ 2%; the content of Al2O3 in the carbide slag is D, and 1.5% ≤ D ≤ 2.5%.

[0087] In the embodiment of the present invention, the content of SiO2 in the rice husk ash is A, and 90% ≤ A ≤ 95%; the content of Fe2O3 in the rice husk ash is E, and 0.5% ≤ E ≤ 1%.

[0088] As a verification example, silt was obtained from the bottom of a certain lake, and the basic physical indicators of the silt are shown in the following table:

[0089]

[0090] Rice husk ash and carbide slag were used as silt solidification materials. The rice husk ash was obtained by firing rice husks produced by rice hulling at about 600 °C, and the SiO2 content was 90%. The main component of the carbide slag is CaO, accounting for 67.87% of the total mass. The chemical compositions of the rice husk ash and carbide slag are shown in the following table:

[0091] sample CaO <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> MgO carbide slag 67.87 1.55 0.48 1.96 0 rice husk ash 0.83 91.68 0.73 0.23 0.12

[0092] The test plan is designed as follows: The silt soil prepared at the optimal water content is used as the control sample, and five groups of single admixture test groups of carbide slag are set, with the admixture gradients of 3%, 5%, 7%, 9%, and 11% (based on the dry soil mass, the same below); on this basis, five compounding ratios of rice husk ash (0%, 5%, 10%, 15%, 20%) are configured for each carbide slag admixture content. The test indexes include the unconfined compressive strength at the ages of 7 days, 14 days, and 28 days, and the microscopic structure morphology is observed by scanning electron microscope.

[0093] (1) Specimen production and curing:

[0094] The specific preparation process is as follows: First, the original silt sample is dried and then crushed, and passed through a 2mm standard sieve for standby; subsequently, according to the established test plan, raw materials such as pretreated dry soil, carbide slag, and rice husk ash are weighed, fully mixed, and then an appropriate amount of distilled water is added to adjust to the optimal water content, and stirred evenly. The specimen is prepared by the compaction method according to the maximum dry density. Among them, the optimal water content and maximum dry density parameters are determined in advance through the standard compaction test; the specimen is formed using a 50mm×100mm cylindrical mold. After the specimen is formed by compaction, it is left standing for 24 hours for preliminary curing, and then demolded. A thin layer of vaseline is evenly applied to the inner wall of the mold in advance to facilitate demolding; after the specimen is demolded, it is sealed with plastic wrap to prevent moisture migration, and placed in a constant temperature and humidity curing box for curing under the standard conditions of temperature (20±2)℃ and relative humidity>90%.

[0095] (2) Unconfined compressive strength test:

[0096] The test uses a strain-type unconfined pressure instrument to load until the specimen fails at an axial strain rate of 2mm / min. For each curing age, 3 specimens of each mix ratio are taken, and their average value is taken to obtain the unconfined compressive strength value.

[0097] (3) SEM test:

[0098] The test uses a German ZEISS Sigma 360 field emission scanning electron microscope. After the unconfined compressive strength test is completed, a fresh cross-section is intercepted from the middle of the specimen, and a regular fragment with a volume of about 0.5cm3 is selected as the observation sample.

[0099] Test results and analysis:

[0100] Unconfined compressive strength, unconfined compressive strength of carbide slag soil:

[0101] Figure 2It is a relationship diagram of the strength of carbide slag soil with the carbide slag content and the curing age. It can be seen from the figure that the strength of carbide slag soil shows an upward trend with the increase of the curing age. When the carbide slag content is < 7%, the strength of carbide slag soil with a curing age of 14 days increases by 30% - 35% compared with that cured for 7 days under the same content, and when the curing age reaches 28 days, its strength increases by 20% - 24% compared with that at 14 days, indicating that when the carbide slag content is small, the strength growth rate of carbide slag soil in the early stage is larger than that in the later stage, and the hydration reaction is relatively rapid; when the carbide slag content is 7% and 9%, during the curing process from 14 days to 28 days, the strength of carbide slag soil has increased by 82% - 95%, showing that the hydration reaction is more sufficient in this stage and the strength improvement is larger; when the carbide slag content is 11%, the growth rates of the soil strength in the early and later stages of curing both show a downward trend. This phenomenon indicates that although a high content of carbide slag can accelerate the hydration reaction process, it does not bring corresponding strength growth advantages. In addition, the strength of solidified soil shows a trend of first increasing and then decreasing with the change of the carbide slag content. For the specific soft soil sample used in this study, the optimal carbide slag content is 7%.

[0102] Effect of rice husk ash content:

[0103] The variation law of the unconfined compressive strength of rice husk ash carbide slag solidified soft soil with the rice husk ash content and the curing age is as Figure 3 shown.

[0104] It should be noted that Figure 3 in a, the carbide slag content is 3%; in b, the carbide slag content is 5%; in c, the carbide slag content is 7%; in d, the carbide slag content is 9%; in e, the carbide slag content is 11%.

[0105] From Figure 3 it can be seen that the addition of rice husk ash significantly improves the mechanical properties of soft soil. Specifically: at the curing age of 7 days, the strength of the untreated soft soil is only 108 kPa, and after being solidified by 7% carbide slag alone, the strength is increased to 225 kPa. After introducing rice husk ash, the strength of all composite solidified specimens exceeds 360 kPa, showing a significant strengthening effect. Among them, when the rice husk ash content is 15%, the specimen reaches the strength peak, and its strength value is about 4.7 times that of the original compacted soft soil and 2.3 times that of the single carbide slag solidified soil. This result fully confirms the significant role of rice husk ash in improving the strength of soft soil, and also indicates that there may be a synergistic effect among the components in the composite solidification system. From Figure 3It can also be seen that, compared with the control group, at the curing age of 7 days, the strength improvement range of the composite cured specimens reached 153% - 370%; compared with the single carbide slag solidified soil, the strength increase range was 63% - 250%. Under the condition of fixed carbide slag content, the relationship between the rice husk ash content and the strength of the solidified soil was non-linear: when the rice husk ash content was less than 15%, the strength increased significantly with the increase of the content; after exceeding 15%, the strength decreased instead with the increase of the content. It should be noted that this optimal content value (15%) was independent of the curing age, indicating that the action mechanism of rice husk ash in the curing system was relatively stable. The research results showed that from the perspective of optimizing the compressive strength, it was not that the more the curing material was added, the better. For the specific soft soil sample used in this study, the optimal contents of rice husk ash and carbide slag were 15% and 7% respectively, and this ratio could ensure that the solidified soil body obtained the optimal mechanical properties.

[0106] Further, taking the carbide slag content of 7% as an example, the relationship curve between the unconfined compressive strength of the solidified soil at different ages and the rice husk ash content was established, as Figure 4 shown. The relationship between the two showed good quadratic parabola characteristics and could be described by the following mathematical model:

[0107] q u = ax 2 + bx + c

[0108] In the formula: q u represents the unconfined compressive strength, x represents the rice husk ash content, and a, b, and c are regression coefficients. See the following table for details:

[0109] curing age 7 days 14 days 28 days a -1.165 -2.018 -1.785 b 34.179 60.038 49.983 c 222.011 267.526 483.171 <![CDATA[R 2 > 0.948 0.996 0.977

[0110] It can be seen from the above table that the fitting effect R 2 was good.

[0111] Effect of curing age:

[0112] The influence of the curing age on the strength development law of the solidified soil is as Figure 5 shown.

[0113] It should be noted that Figure 5 the carbide slag content of a was 3%; the carbide slag content of b was 5%; the carbide slag content of c was 7%; the carbide slag content of d was 9%; the carbide slag content of e was 11%.

[0114] The unconfined compressive strength of solidified soil shows a continuous growth trend with the extension of curing time. Taking the optimized mix ratio with 7% carbide slag content and 15% rice husk ash content as an example, when the curing age is extended from 7 days to 28 days, the specimen strength is significantly increased from 508 kPa to 849.6 kPa, with an increase rate of 67.2%, fully verifying the important contribution of the curing process to strength development. Further statistical analysis shows that the strength value of the specimen at the curing age of 14 days is 1.41 times that of the specimen at 7 days, while the strength of the 28-day specimen is 1.19 times that of the 14-day specimen. This strength growth law indicates that within the 28-day curing period, the strength of solidified soil always shows an upward trend, and the strength growth rate in the early stage (7 - 14 days) is faster than that in the later stage (14 - 28 days).

[0115] Ultimate strain of rice husk ash carbide slag soil:

[0116] Statistical analysis was carried out on the ultimate strains of specimens with different mix ratios at the curing ages of 7 days and 28 days, and the results are as Figure 6 shown.

[0117] It should be noted that Figure 6 in which a is the relationship diagram of the ultimate strain of rice husk ash carbide slag soil at the curing age of 28 days; b is the relationship diagram of the ultimate strain of rice husk ash carbide slag soil at the curing age of 7 days; c is the relationship diagram of the ultimate strain of carbide slag soil at different curing ages; d is the relationship diagram of the ultimate strain of rice husk ash and 7% carbide slag soil at different curing ages; e is the relationship diagram of the ultimate strain of rice husk ash and 11% carbide slag soil at different curing ages.

[0118] In the figure, 3d represents single addition of 3% carbide slag, 7d5dk represents addition of 7% carbide slag and 5% rice husk ash, and the meanings of other legends are similar. It can Figure 6 be seen that the ultimate strain of rice husk ash carbide slag composite solidified soil at the curing age of 7 days is generally greater than that of the 28-day specimen; at the same curing age, the ultimate strain of the composite solidified soil is significantly higher than that of the single carbide slag solidified soil. It is worth noting that there is no obvious correlation between the ultimate strain and the rice husk ash content, curing age, and unconfined compressive strength. Statistical data shows that the ultimate strain range of single carbide slag solidified soil is 1.1% - 2.4%, while the ultimate strain of rice husk ash carbide slag composite solidified soil is significantly increased to 3.1% - 4.5%. Compared with the typical ultimate strain range of cement solidified soil (1% - 2.5%), the composite solidified soil in this study shows stronger toughness, which is of great significance for improving the engineering properties of soil.

[0119] Failure mode analysis:

[0120] The soft clay specimen first undergoes a short compression stage, followed by the rapid generation of microcracks on the surface. The outer layer of the specimen gradually exfoliates, and finally, overall failure occurs. The carbide slag solidified soil and the rice husk ash carbide slag composite solidified soil mainly exhibit two failure modes: brittle shear failure and brittle tensile failure. Specifically, when the strength of the solidified soil is low, obvious main cracks form on the surface of the specimen at a certain angle to the axis, showing typical brittle shear failure characteristics; while in the case of higher strength, multi-directional cracks are generated on the surface of the specimen, and the main cracks extend along the axis, presenting a brittle tensile failure mode.

[0121] Strength regression prediction model:

[0122] The following table shows the unconfined compressive strength test data of the rice husk ash carbide slag solidified soft clay with a carbide slag content of 7%:

[0123]

[0124] Based on this, a three-dimensional relationship diagram of the rice husk ash content, curing age, and unconfined compressive strength is constructed, as shown in Figure 7 Figure [Figure number]. According to the distribution characteristics of the measured data, a prediction model is established using a complete quadratic function, and its theoretical expression is:

[0125]

[0126] For this model, the binary complete quadratic polynomial can be written as:

[0127] Q = z0 + ax + by + cx 2 + dy 2 + fxy

[0128] In the formula, x is the curing age, in days; y is the rice husk ash content, in %; a, b, c, d, f, and z0 are regression coefficients.

[0129] The fitting coefficients of the regression analysis are shown in the following table:

[0130]

[0131] According to the above table, the regression model of the rice husk ash carbide slag soil is:

[0132] Q = -72.8 + 38.93T + 46.69a0 + (-0.69)T 2 + (-1.66)a0 2 + 0.08T a0

[0133] In the formula, T is the curing age, in days; a0 is the rice husk ash content, in %.

[0134] The correlation coefficient is 0.967, the F value is 52.13, and P < 0.05, indicating that the overall model is significant. Under the condition that the curing age T does not exceed 28 days, the unconfined compressive strength of rice husk ash carbide slag solidified dredged soil with any rice husk ash content and curing age can be approximately estimated by using the above regression model of rice husk ash carbide slag soil. This characteristic has certain value in practical engineering applications. For the specific model display of the unconfined compressive strength, see Figure 8 .

[0135] Microscopic characteristics and mechanism:

[0136] Effect of rice husk ash content on the microstructure of solidified soil:

[0137] SEM analysis results of the effect of rice husk ash content on the microstructure of solidified soil at 28 days of curing are shown in Figure 9 .

[0138] It should be noted that Figure 9 in [figure], a is the SEM analysis result schematic diagram of 7% carbide slag solidified soil magnified 2000 times; b is the SEM analysis result schematic diagram of 7% carbide slag solidified soil magnified 5000 times; c is the SEM analysis result schematic diagram of the first rice husk ash carbide slag solidified soil magnified 2000 times; d is the SEM analysis result schematic diagram of the first rice husk ash carbide slag solidified soil magnified 5000 times; e is the SEM analysis result schematic diagram of the second rice husk ash carbide slag solidified soil magnified 2000 times; f is the SEM analysis result schematic diagram of the second rice husk ash carbide slag solidified soil magnified 5000 times.

[0139] Among them, the solidified soil with 20% rice husk ash and 7% carbide slag is called the first rice husk ash carbide slag solidified soil, and the solidified soil with 15% rice husk ash and 7% carbide slag is called the second rice husk ash carbide slag solidified soil.

[0140] When magnified 2000 times, the content of acicular minerals generated inside the 7% single carbide slag solidified soil is small and difficult to distinguish, showing the characteristics of loose particle arrangement, developed pores and larger pore diameters; in contrast, the rice husk ash carbide slag composite solidified soil is denser. Although there are also some larger pores, it has been significantly improved compared with the single carbide slag solidified soil.

[0141] When magnified 5000 times, the microscopic structural characteristics and connection modes of the solidified soil are clearly presented. Dispersedly distributed fine needle-like minerals can be observed in the carbide slag single-blended solidified soil, and these minerals form limited lap joints in local areas. In contrast, the rice husk ash carbide slag composite solidified soil exhibits a more complex hydration product system: in addition to needle-like minerals, a large number of columnar, flaky and flocculent minerals are also generated. Among them, the needle-like and columnar minerals are thick and aggregated in clusters, forming a bundled structure that tightly fills the pores and establishing a good spatial connection network with other crystals; the flaky and flocculent products are mainly distributed on the surface of soil particles and in the mineral gaps, significantly improving the pore filling density. A large amount of gel substances filling the pores are observed in the microscopic structure of the second rice husk ash carbide slag solidified soil, the exposed needle-like and columnar minerals are relatively reduced, and the agglomeration of needle-like minerals and flaky minerals appears in local areas, and these minerals are mainly distributed in the pores and on the surface of soil particles. Generally speaking, the addition of rice husk ash can indeed optimize the microscopic structure of the solidified soil, but excessive incorporation (exceeding the optimal dosage) will lead to an increase in porosity and have an adverse effect on the solidification effect.

[0142] Variation law of the microscopic structure of rice husk ash carbide slag solidified soil with age:

[0143] To explore the aging evolution law of the microscopic structure of rice husk ash carbide slag solidified soil, the second rice husk ash carbide slag solidified soil (mix ratio: 15% rice husk ash + 7% carbide slag) was selected as the research object, and its microscopic structure at different curing ages (7 days, 14 days and 28 days) was systematically observed. The results are as Figure 10 shown (the microscopic structural characteristics at the 28-day age have been shown Figure 9 above).

[0144] It should be noted that Figure 10 in [reference], a is the schematic diagram of the SEM analysis results of the variation of the microscopic structure of the second rice husk ash carbide slag solidified soil at the 7-day age magnified 2000 times with age; b is the schematic diagram of the SEM analysis results of the variation of the microscopic structure of the second rice husk ash carbide slag solidified soil at the 7-day age magnified 5000 times with age; c is the schematic diagram of the SEM analysis results of the variation of the microscopic structure of the second rice husk ash carbide slag solidified soil at the 14-day age magnified 2000 times with age; d is the schematic diagram of the SEM analysis results of the variation of the microscopic structure of the second rice husk ash carbide slag solidified soil at the 14-day age magnified 5000 times with age.

[0145] Under a magnification of 2000 times, it was observed that the pore structure of the solidified soil showed an obvious optimization trend with the curing age: at the age of 7 days, there were many pores with large sizes in the specimen, mainly filled with flaky and flocculent minerals, and few acicular minerals; at the age of 14 days, the number of pores decreased, and the interconnection of acicular minerals began to appear; by the age of 28 days, the large pores significantly decreased, the pore surface was covered by a large amount of flocculent minerals, and the acicular and columnar minerals were wrapped in it, forming a dense overall structure.

[0146] When magnified to 5000 times, the morphological evolution of the hydration products could be observed more clearly: at the age of 7 days, the number of acicular and columnar minerals was small and their shapes were thin and short. At the same time, some flaky and flocculent hydration products could also be observed; at the age of 14 days, the number of hydration products increased significantly, the growth of acicular and columnar minerals was obvious, and local bundle-like agglomeration phenomena appeared, effectively filling the pores; at the age of 28 days, the flocculent products became the main surface feature, the exposed columnar minerals had thick and mostly bundle-like agglomerated shapes, forming a good spatial connection network with other minerals, and the flaky and flocculent products were mainly distributed on the surface of soil particles.

[0147] The changes in these microstructural characteristics fully illustrate the continuous progress of the hydration reaction in the rice husk ash - carbide slag solidification system and its improvement effect on the material properties, providing microscopic evidence for understanding the strength development mechanism of the solidified soil.

[0148] Reaction mechanism of rice husk ash - carbide slag solidified soil:

[0149] Rice husk ash not only contains a large amount of active SiO2, but also has quite a number of nano - scale pores. These characteristics enable it to play multiple roles in the solidification process of silt:

[0150] (1) Filling effect: Rice husk ash contains a large number of nano - scale SiO2 particles, which can effectively fill the internal pores of the solidified silt soil. This physical filling effect significantly improves the compactness of the soil body, reduces the porosity, and thus improves the overall performance of the solidified soil.

[0151] (2) Hydration reaction: The main components of carbide slag are similar to those of cement, and its hydration reaction products are mainly calcium hydroxide, calcium silicate hydrate, and calcium aluminate hydrate. After adding rice husk ash, its abundant active SiO2 reacts with Ca(OH)2 generated by the hydration of carbide slag to produce a large amount of calcium silicate hydrate, thus significantly increasing the content of C - S - H gel with cementing effect. This reaction is the main source of the strength development of the solidified soil, and its chemical reaction equation is:

[0152] SiO2 + Ca(OH)2 + nH2O → CaO·SiO2·(n + 1)H2O

[0153] (3) Water storage and supply: The unique nano-porous structure of rice husk ash endows it with excellent water storage performance. In the later stage of the hydration reaction, the water stored in the pores is gradually released and continuously participates in the hydration reaction. This unique water storage and supply mechanism effectively guarantees the progress of the hydration reaction in the later stage of the solidification system, thus ensuring the stable growth of the strength of the solidified soil in the later stage.

[0154] Based on the above analysis, a microscopic evolution mechanism model of rice husk ash and carbide slag solidified soft clay is proposed, as Figure 11 shown.

[0155] Conclusion:

[0156] (1) Compared with the un-solidified and single carbide slag solidified soft clay, the unconfined compressive strength of the rice husk ash and carbide slag solidified soft clay is significantly improved. For the specific soft clay sample used in this study, the optimal material ratio is 15% of rice husk ash and 7% of carbide slag;

[0157] (2) At the optimal dosage of rice husk ash and carbide slag, the q u value of the solidified soil at 14 days of curing reaches 1.41 times that at 7 days, and reaches 1.19 times that at 14 days at 28 days. This strength growth law shows that the reaction in the rice husk ash, carbide slag and silt system not only starts quickly, but also can last for a long time;

[0158] (3) The addition of rice husk ash can improve the toughness of the solidified soft clay. The ultimate strain of the single carbide slag solidified soil is between 1.1% and 2.4%, while the ultimate strain of the rice husk ash and carbide slag solidified soil is significantly improved, between 3.1% and 4.5%;

[0159] (4) The reaction mechanism of the rice husk ash and carbide slag solidified soil is mainly three aspects: filling effect, hydration reaction and water storage and supply. The C-S-H gel generated by the hydration reaction is the main strength source of the solidified silt;

[0160] (5) According to the test results, a strength prediction model and a microscopic evolution mechanism model of the rice husk ash and carbide slag solidified soft clay are established, which can provide a theoretical basis and technical reference for the application of rice husk ash and carbide slag in the practice of soft clay solidification.

[0161] The above is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structural transformation made under the technical concept of the present invention by using the content of the specification and drawings of the present invention, or directly / indirectly applied to other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A curing method for rice husk ash modified carbide slag stimulating solidified sludge, characterized in that: The curing method of rice husk ash modified carbide slag stimulating solidified sludge comprises: Take 100 parts of dredged sludge, 5-20 parts of rice husk ash and 3-11 parts of carbide slag by weight and mix them to form a solidifying base material; adding water to the curing base to form a mixture; Stirring the mixture evenly to form a sludge solidification mixture; compacting the sludge solidified mixture to form the sludge solidified body; The sludge solidified body is cured within 7 days at an ambient temperature P1 and a first relative ambient humidity I1, wherein 18°C ​​≤ P1 ≤ 22°C, and I1> 95%; The sludge solidified body is cured within 7 to 14 days using the ambient temperature P1 and the second relative ambient humidity I2; wherein 92%≤I2≤94%; The sludge solidified body is cured within 14 to 28 days using the ambient temperature P1 and the third relative ambient humidity I3, wherein 90% < I3.

2. The curing method of rice husk ash modified carbide slag stimulating solidified sludge as claimed in claim 1, characterized in that: The step of mixing the mixture evenly to form a sludge solidified mixture comprises: adding water to the mixture to moisten the mixture; The mixture is mixed evenly to obtain the sludge solidification mixture.

3. The curing method of rice husk ash modified carbide slag stimulating solidified sludge as claimed in claim 2, characterized in that: The step of adding water to the mixture to moisten the mixture comprises: Obtaining the initial moisture content of the dredged sludge and the total mass of the solidified base material; Obtaining water demand according to the initial moisture content, the total mass of the solidified base material and the target moisture content; Water is added to the mixture according to the required amount of water to moisten the mixture.

4. The curing method of rice husk ash modified carbide slag stimulating solidified sludge as claimed in claim 3, characterized in that: The step of obtaining the water requirement according to the initial moisture content, the total mass of the solidified base material and the target moisture content comprises: Using Formula 1, the water requirement is obtained according to the initial moisture content, the total mass of the curing base material and the target moisture content; The formula 1 is: Wherein, the target moisture content is greater than the initial moisture content, W1 is the initial moisture content, W2 is the target moisture content, K1 is the total mass of the curing base material, and K2 is the water requirement.

5. The curing method of rice husk ash modified carbide slag stimulating solidified sludge as claimed in claim 4, characterized in that: 52.16%≤the target moisture content≤57.65%.

6. The curing method for rice husk ash modified carbide slag stimulating solidified sludge according to any one of claims 1 to 5, characterized in that: The mass ratio of the rice husk ash to the carbide slag is 15:

7.

7. The curing method for rice husk ash modified carbide slag stimulating solidified sludge according to any one of claims 1 to 5, characterized in that: The porosity of the nanopores of the rice husk ash is 8. The curing method for rice husk ash modified carbide slag stimulating solidified sludge as claimed in claim 7, characterized in that: The specific surface area of ​​the rice husk ash is SSA, 200m 2 / g≤SSA≤500m 2 / g.

9. The curing method for rice husk ash modified carbide slag stimulating solidified sludge according to any one of claims 1 to 5, characterized in that: The content of CaO in the carbide slag is B, 65%≤B≤70%; the content of SiO2 in the carbide slag is C, 1%≤C≤2%; the content of Al2O3 in the carbide slag is D, 1.5%≤D≤2.5%.

10. The curing method for rice husk ash modified carbide slag stimulating solidified sludge according to any one of claims 1 to 5, characterized in that: The content of SiO2 in the rice husk ash is A, 90%≤A≤95%; the content of Fe2O3 in the rice husk ash is E, 0.5%≤E≤1%.

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