Curing test method for dredging sludge

Abstract

The invention discloses a solidification test method for dredged sludge, and relates to the technical field of dredged sludge solidification construction.The solidification test method for dredged sludge comprises the steps that wet dredged sludge is dried to constant weight, crushed and then sieved, and dried pretreated soil is obtained; doping carbide slag and rice hull ash into the pretreated soil to obtain a mixture; uniformly mixing the mixture to obtain a sludge solidified mixture; compacting the sludge solidified mixture in stages to form a cylindrical sample; sealing the cylindrical sample, placing the cylindrical sample in a constant-temperature and constant-humidity environment, and maintaining the cylindrical sample to a preset age; testing the compressive strength and the limit strain of the cylindrical sample by adopting an unconfined pressure meter; and cutting out a section from the cylindrical sample to obtain the distribution condition and pore structure of hydration products in the cylindrical sample, and obtaining a curing strength model of the dredged sludge. According to the method, the curing effect of the cured dredged sludge is predicted by establishing a strength prediction model for curing the dredged sludge by using the rice hull ash and the carbide slag.

Description

Technical Field

[0001] The invention relates to the technical field of dredged sludge solidification construction, in particular to a solidification test method for dredged sludge. Background Art

[0002] In dredging projects, silt solidification is a critical step in ensuring project stability and environmental safety. Traditional solidification methods rely on high-cost materials such as cement, which can easily lead to soil alkalinization and carbon emissions. Existing technologies lack systematic testing methods to determine the development of dredged silt solidification strength, making it difficult to predict the effectiveness of dredged silt solidification and thus impractical for practical application. Summary of the Invention

[0003] The main purpose of the present invention is to propose a solidification test method for dredged sludge, which aims to predict the solidification effect of dredged sludge solidified by rice husk ash and carbide slag, so as to apply it to the actual dredged sludge solidification construction process.

[0004] To achieve the above-mentioned purpose, the present invention proposes a solidification test method for dredged sludge, which comprises:

[0005] Drying the wet dredged sludge to a constant weight, crushing it and then sieving it to obtain dry pretreated soil;

[0006] adding carbide slag and rice husk ash to the pretreated soil to obtain a mixture;

[0007] mixing the mixture uniformly to obtain a sludge solidified mixture;

[0008] compacting the sludge solidification mixture into cylindrical specimens in stages;

[0009] The cylindrical sample is sealed and placed in a constant temperature and humidity environment for curing to a preset age;

[0010] Using an unconfined pressure instrument to test the compressive strength and ultimate strain of the cylindrical specimen;

[0011] Cutting a cross section from the cylindrical sample to obtain the distribution of hydration products and the pore structure in the cylindrical sample, and obtaining a solidification strength model of the dredged sludge;

[0012] The hydration products include needle-shaped, columnar and flocculent CSH gels.

[0013] In one embodiment, the step of uniformly mixing the mixture to obtain a sludge solidified mixture comprises:

[0014] adding water to the mixture to moisten the mixture;

[0015] The mixture is mixed uniformly to obtain the sludge solidification mixture.

[0016] In one embodiment, the step of adding water to the mixture to moisten the mixture comprises:

[0017] Obtaining the initial moisture content of the dredged sludge and the total mass of the pretreated soil;

[0018] Obtaining water demand based on the initial moisture content, the total mass of the pretreated soil, and the target moisture content;

[0019] Water is added to the mixture according to the required amount to moisten the mixture.

[0020] In one embodiment, the step of obtaining the water requirement according to the initial moisture content, the total mass of the pretreated soil and the target moisture content includes:

[0021] Using Formula 1, the water requirement is obtained according to the initial moisture content, the total mass of the pretreated soil and the target moisture content;

[0022] The formula 1 is:

[0023]

[0024] 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 pretreated soil, and K2 is the water requirement.

[0025] In one embodiment, 52.16%≤the target moisture content≤57.65%.

[0026] In one embodiment, the step of adding water to the mixture to moisten the mixture comprises:

[0027] Water was added to the mixture three times, and the mixture was stirred for 5 minutes after each addition. The mixture was allowed to stand for 10 minutes before the next addition of water to moisten the mixture.

[0028] In one embodiment, the step of compacting the sludge solidification mixture into cylindrical samples in stages includes:

[0029] The sludge solidified mixture is divided into three layers and compacted, with each layer compacted 25 times and each compaction pressure being 200 kPa, to obtain the cylindrical sample.

[0030] In one embodiment, there are multiple cylindrical specimens, and the step of sealing the cylindrical specimens and placing them in a constant temperature and humidity environment for curing to a preset age includes:

[0031] The cylindrical specimens were sealed and placed in a constant temperature and humidity environment for curing for 7 days, 14 days and 28 days respectively.

[0032] In one embodiment, the step of adding carbide slag and rice husk ash to the pretreated soil to obtain a mixture comprises:

[0033] 100 parts of the dredged sludge, 5 to 20 parts of the rice husk ash and 3 to 11 parts of the carbide slag are taken by mass and mixed to form the mixture.

[0034] In one embodiment, the mass ratio of the carbide slag to the rice husk ash is 1:2 to 1:3;

[0035] The steps of cutting a cross section from the cylindrical sample, obtaining the distribution of hydration products and the pore structure in the cylindrical sample, and obtaining a solidification strength model of the dredged sludge include:

[0036] cutting a cross section from the cylindrical sample to obtain the distribution of hydration products and the pore structure of the cylindrical sample;

[0037] According to Formula 2, the dosage of the rice husk ash and the actual curing age of the cylindrical specimen after sealing and placing it in a constant temperature and humidity environment, the curing strength model of the dredged sludge is obtained;

[0038] The second formula is:

[0039] Q=-72.8+38.93*T+46.69*a0+(-0.69)*T 2 +(-1.66)*a0 2 +0.08*T*a0

[0040] Wherein, T is the actual curing age, and a0 is the actual dosage of the rice husk ash.

[0041] The technical solution of the present invention establishes a strength prediction model for the use of rice husk ash and carbide slag to solidify dredged sludge by controlling the dosage of carbide slag and rice husk ash, compacting cylindrical specimens in stages, and observing their microstructure. This model provides reliable technical support for the efficient solidification and engineering application of dredged sludge. The prediction of the solidification effect of rice husk ash and carbide slag on dredged sludge can be applied to the actual dredged sludge solidification construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0043] Figure 1 A schematic flow chart of an embodiment of a solidification test method for dredged sludge provided by the present invention;

[0044] Figure 2 A graph showing the relationship between the strength of carbide slag soil, carbide slag content, and curing age involved in the present invention;

[0045] Figure 3 The present invention relates to a relationship diagram of the unconfined compressive strength of rice husk ash calcium carbide slag soil at different rice husk ash dosages;

[0046] Figure 4 This is a schematic diagram of the fitting curve of the unconfined compressive strength and the rice husk ash content at different curing ages involved in the present invention;

[0047] Figure 5 This is a relationship diagram of the unconfined compressive strength of rice husk ash calcium carbide slag at different curing ages involved in the present invention;

[0048] Figure 6 This is a relationship diagram of the ultimate strain of rice husk ash calcium carbide slag at different curing ages involved in the present invention;

[0049] Figure 7 A model diagram of the actual measurement of the unconfined compressive strength of rice husk ash calcium carbide slag soil involved in the present invention;

[0050] Figure 8 A strength model diagram of rice husk ash calcium carbide slag soil according to the present invention;

[0051] Figure 9 This is a schematic diagram of SEM analysis results showing the effect of rice husk ash dosage on the microstructure of solidified soil according to the present invention;

[0052] Figure 10 This is a schematic diagram of SEM analysis results of the microstructure of rice husk ash carbide slag solidified soil changing with age;

[0053] Figure 11 This is a schematic diagram of the microscopic evolution mechanism model of rice husk ash carbide slag solidified sludge involved in the present invention.

[0054] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0055] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0056] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0057] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0058] In dredging projects, silt solidification is a critical step in ensuring project stability and environmental safety. Traditional solidification methods rely on high-cost materials such as cement, which can easily lead to soil alkalinization and carbon emissions. Existing technologies lack systematic testing methods to determine the development of dredged silt solidification strength, making it difficult to predict the effectiveness of dredged silt solidification and thus impractical for practical application.

[0059] In order to solve this technical problem, the present invention proposes a solidification test method for dredged silt.

[0060] See also Figure 1 In one embodiment of the present invention, the solidification test method for dredged sludge includes:

[0061] Step S10, drying the wet dredged sludge to a constant weight, crushing it, and then sieving it to obtain dry pretreated soil;

[0062] Step S20, adding carbide slag and rice husk ash to the pretreated soil to obtain a mixture;

[0063] Step S30, mixing the mixture uniformly to obtain a sludge solidified mixture;

[0064] Step S40, compacting the sludge solidification mixture into cylindrical samples in stages;

[0065] Step S50, sealing the cylindrical sample and placing it in a constant temperature and humidity environment for curing to a preset age;

[0066] Step S60, using an unconfined pressure instrument to test the compressive strength and ultimate strain of the cylindrical specimen;

[0067] Step S70, cutting a cross section from the cylindrical sample to obtain the distribution of hydration products and pore structure in the cylindrical sample, and obtaining a solidification strength model of the dredged sludge;

[0068] The hydration products include needle-shaped, columnar and flocculent CSH gels.

[0069] Specifically, step S10 is to pre-treat the dredged sludge, wherein the dredged sludge having a moisture content of 54.9% is placed in a 105°C oven and dried to a constant weight (the difference between two consecutive weighings is ≤0.1%), crushed and sieved through a 2mm standard sieve to remove impurities and large particles, thereby obtaining the dry pre-treated soil. This is to eliminate the moisture fluctuation of the original dredged sludge, ensure that the amount of calcium carbide slag and rice husk ash is calculated based on the dry soil mass, and avoid the ratio error caused by moisture difference. After sieving, the particles are uniform (particle size ≤2mm), which improves the homogeneity of subsequent mixing and reduces internal defects of the sample.

[0070] Step S20: Add solidifying materials. Based on the dry soil mass, add 3% to 11% carbide slag (CaO content 67.87%) and 0% to 20% rice husk ash (SiO2 content 91.68%), and mechanically stir for 5 minutes until the mixture is uniform. Carbide slag provides a calcium source (CaO), and rice husk ash provides active silicon (SiO2). The two generate CSH gel in an alkaline environment, improving the soil's cementation strength. The dosage range was determined through orthogonal experiments. 3% to 11% carbide slag can trigger a full hydration reaction, and 0% to 20% rice husk ash balances the filling effect and porosity.

[0071] Step S30 and step S40, mixing and compacting, add distilled water to the mixture three times, stir for 5 minutes each time, let it stand for 10 minutes, and adjust to the target moisture content (52.16% to 57.65%). Fill the wet mixture into a cylindrical test mold with a diameter of 50mm and a height of 100mm in three layers, and compact each layer 25 times with a pressure of 200kPa, for a total of 75 compaction times. Add water in batches to avoid local accumulation of water, and let it stand to allow the water to evenly penetrate into the gaps between the particles (the strength discreteness in Example 2 is reduced by 8%). Layered compaction reduces the internal porosity of the sample, and the density reaches 1.66g / cm 3 , close to the maximum dry density.

[0072] Step S60, curing and testing, after demoulding, the sample is sealed with plastic wrap and placed in a constant temperature and humidity box at 20℃±2℃ and humidity>90% for curing for 7 days, 14 days and 28 days. A strain-type unconfined pressure gauge is used to load the sample at a rate of 2mm / min until it is destroyed, and the compressive strength and ultimate strain (with 80% of the peak strain as the limit value) are recorded. Sealed curing prevents water evaporation, and the constant humidity environment ensures that the hydration reaction continues (the 28-day strength in Example 1 increases by 67.2% compared to 7 days). The standard loading rate (2mm / min) avoids damage to the sample by impact load and ensures data comparability.

[0073] Step S70, microscopic analysis and model establishment, cut 0.5cm from the middle of the sample 3 Fresh cross section, observe the microstructure. Based on the compressive strength data, establish a multivariate regression model:

[0074] Q=-72.8+38.93*T+46.69*a0+(-0.69)*T 2 +(-1.66)*a0 2 +0.08*T*a0

[0075] SEM images show pores filled with needle-like and columnar CSH gels, confirming the microscopic mechanism of strength enhancement. A multivariate regression model can predict strength at any mix ratio and age, reducing engineering testing costs. It can also, to a certain extent, predict the solidification of actual dredged sludge with the addition of rice husk ash and carbide slag, providing data reference for similar projects.

[0076] The technical solution provided by this invention establishes a strength prediction model for the use of rice husk ash and carbide slag to solidify dredged sludge by controlling the dosage of carbide slag and rice husk ash, compacting cylindrical specimens in stages, and observing their microstructure. This model provides reliable technical support for the efficient solidification and engineering application of dredged sludge. The prediction of the solidification effect of rice husk ash and carbide slag on dredged sludge can be applied to the construction process of dredged sludge solidification.

[0077] In an embodiment of the present invention, the step of uniformly mixing the mixture to obtain a sludge solidified mixture comprises:

[0078] Step S31, adding water to the mixture to moisten the mixture;

[0079] Step S32: uniformly mix the mixture to obtain the sludge solidified mixture.

[0080] Specifically, in steps S31 and S32, distilled water is added to the dry pretreated soil, carbide slag, and rice husk ash mixture in three batches. Each addition of water is followed by mechanical stirring for 5 minutes, followed by 10 minutes of quiescence before the next addition of water. Adding water in batches avoids water concentration that can lead to localized overwetting or cracking, thereby improving mixing uniformity. Quiescence allows the water to fully penetrate the intergranular spaces, reducing the internal porosity of the compacted sample.

[0081] In an embodiment of the present invention, the step of adding water to the mixture to moisten the mixture comprises:

[0082] Step S311, obtaining the initial moisture content of the dredged sludge and the total mass of the pretreated soil;

[0083] Step S312, obtaining the water requirement according to the initial moisture content, the total mass of the pretreated soil and the target moisture content;

[0084] Step S313: adding water to the mixture according to the required water amount to moisten the mixture.

[0085] In an embodiment of the present invention, the step of obtaining the water requirement according to the initial moisture content, the total mass of the pretreated soil and the target moisture content includes:

[0086] Step S310, using Formula 1, the water requirement is obtained according to the initial moisture content, the total mass of the pretreated soil and the target moisture content;

[0087] The formula 1 is:

[0088]

[0089] 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 pretreated soil, and K2 is the water requirement.

[0090] Specifically, the water addition requirement is quantified using Formula 1 to ensure moisture content control, keeping the actual moisture content deviation less than 0.5%, thus avoiding sample softening due to excessive water addition or loose compaction due to insufficient water.

[0091] In an embodiment of the present invention, 52.16%≤the target moisture content≤57.65%.

[0092] Specifically, the target moisture content covers the optimal compaction range of dredged sludge, ensuring maximum sample density. Beyond this range (e.g., moisture content > 57.65%), the sample is prone to lateral expansion, and the compressive strength decreases by 12% to 18%.

[0093] In an embodiment of the present invention, the step of adding water to the mixture to moisten the mixture comprises:

[0094] Step S301 , adding water to the mixture three times, stirring for 5 minutes after each addition, and letting it stand for 10 minutes before adding water again, so as to moisten the mixture.

[0095] Specifically, the step-by-step process allows the water to gradually penetrate the interior of the particles, preventing crusting on the surface. The resting time allows the water to be evenly distributed, improving the overall homogeneity of the sample after compaction.

[0096] In an embodiment of the present invention, the step of compacting the sludge solidification mixture into cylindrical samples in stages includes:

[0097] Step S41 , dividing the solidified sludge mixture into three layers and compacting them, with each layer compacted 25 times and each compaction pressure being 200 kPa, to obtain the cylindrical sample.

[0098] Specifically, layered compaction reduced the porosity within the sample, increasing density by 12%. A pressure of 200 kPa balanced density with equipment load, preventing particle breakage caused by excessive pressure.

[0099] In an embodiment of the present invention, there are multiple cylindrical specimens, and the step of sealing the cylindrical specimens and placing them in a constant temperature and humidity environment for curing to a preset age includes:

[0100] Step S51 , sealing the plurality of cylindrical samples and placing them in a constant temperature and humidity environment for curing for 7 days, 14 days and 28 days respectively.

[0101] Specifically, multi-age testing revealed strength trends over time (508 kPa at 7 days, 849.6 kPa at 28 days), guiding the design of project maintenance cycles. Data showed that the strength at 14 days was 1.41 times that of 7 days, and 1.19 times that of 28 days, verifying the persistence of the hydration reaction.

[0102] In an embodiment of the present invention, the step of adding carbide slag and rice husk ash to the pretreated soil to obtain a mixture comprises:

[0103] Step S21 , taking 100 parts of the dredged sludge, 5 to 20 parts of the rice husk ash and 3 to 11 parts of the carbide slag by mass, and mixing them to form the mixture.

[0104] Specifically, the mass ratio was quantified to ensure test repeatability (7% carbide slag + 15% rice husk ash is the optimal ratio). 3% to 11% carbide slag balances reaction rate and porosity, and 5% to 20% rice husk ash optimizes the filling effect.

[0105] In an embodiment of the present invention, the mass ratio of the carbide slag to the rice husk ash is 1:2 to 1:3;

[0106] The steps of cutting a cross section from the cylindrical sample, obtaining the distribution of hydration products and the pore structure in the cylindrical sample, and obtaining a solidification strength model of the dredged sludge include:

[0107] Step S71, cutting a cross section from the cylindrical sample to obtain the distribution of hydration products and pore structure in the cylindrical sample;

[0108] Step S72, obtaining a curing strength model of the dredged sludge according to Formula 2, the amount of rice husk ash added, and the actual curing age of the cylindrical specimen after sealing and placing it in a constant temperature and humidity environment;

[0109] The second formula is:

[0110] y=-72.8+38.93*T+46.69*a0+(-0.69)*T 2 +(-1.66)*a0 2 +0.08*T*a0

[0111] Wherein, T is the actual curing age, and a0 is the actual dosage of the rice husk ash.

[0112] Specifically, the mass ratio controls the calcium-silicon molar ratio (Ca / Si≈1.5-2.0) to promote the full formation of CSH gel. Exceeding this ratio (e.g., 1:4) results in an incomplete reaction due to excessive SiO2, resulting in a 22% decrease in strength.

[0113] More specifically, Formula 2 was developed based on strength data. It inputs the curing age (T) and the rice husk ash content (a0) and outputs a predicted strength value. This model accounts for the interaction between mix ratio and time, accurately predicting strength under complex conditions. In an engineering application, using T = 28 days and a0 = 15%, the predicted strength was 849.6 kPa, with an error of less than 0.5% from the measured value.

[0114] As a specific implementation method, silt is obtained from the bottom of a lake. The basic physical indicators of the silt are shown in the following table:

[0115]

[0116] Rice husk ash and carbide slag are used as sludge solidification materials. Rice husk ash is made from rice husks produced by sintering at around 600°C and contains 90% SiO2. Carbide slag is primarily composed of CaO, which accounts for 67.87% of the total mass. The chemical composition of rice husk ash and carbide slag is shown in the table below:

[0117] 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

[0118] The experimental design was as follows: using silt soil prepared at the optimal moisture content as the control sample, five groups of carbide slag single-addition test groups were set up, with the addition gradient of 3%, 5%, 7%, 9%, and 11% (based on the dry soil mass, the same below); on this basis, five rice husk ash compounding ratios (0%, 5%, 10%, 15%, and 20%) were configured under each carbide slag addition. The test indicators included unconfined compressive strength at 7 days, 14 days, and 28 days, and the microstructural morphology was observed using scanning electron microscopy.

[0119] (1) Specimen preparation and maintenance:

[0120] The specific preparation process is as follows: first, the original silt sample is dried and crushed, and passed through a 2mm standard sieve for later use; then, according to the established test plan, the pretreated dry soil, calcium carbide slag and rice husk ash and other raw materials are weighed, fully mixed, and an appropriate amount of distilled water is added to adjust to the optimal moisture content and stirred evenly. The sample is prepared according to the maximum dry density by the compaction method, wherein the optimal moisture content and maximum dry density parameters are predetermined by the standard compaction test; the sample is formed using a 50mm×100mm cylindrical test mold. After the sample is compacted and formed, it is left to stand for 24 hours for preliminary curing and then demolded. A thin layer of vaseline is evenly applied to the inner wall of the test mold in advance to facilitate demolding; after demolding, the sample is sealed with plastic wrap to prevent moisture migration and placed in a constant temperature and humidity curing box for curing under standard conditions of temperature (20±2)℃ and relative humidity>90%.

[0121] (2) Unconfined compressive strength test:

[0122] The test used a strain gauge unconfined pressure instrument, loading the specimens at an axial strain rate of 2 mm / min until failure. Three specimens were collected for each mix ratio at each curing age, and the average value was taken to determine the unconfined compressive strength.

[0123] (3) Scanning electron microscope test:

[0124] The test was conducted using a German ZEISS Sigma 360 field emission scanning electron microscope. After the unconfined compressive strength test, a fresh section was cut from the middle of the specimen, and a volume of approximately 0.5 cm was selected. 3 Regular fragments of are used as observation samples.

[0125] Test results and analysis:

[0126] Unconfined compressive strength, unconfined compressive strength of calcium carbide slag:

[0127] Figure 2 This is a relationship diagram between the strength of carbide slag soil and the carbide slag content and curing age. It can be seen from the figure that the strength of carbide slag soil shows an upward trend with the increase of curing age. When the carbide slag content was less than 7%, the strength of carbide slag soil with a curing age of 14 days increased by 30% to 35% compared to the strength of the same carbide slag content with a curing age of 7 days. At a curing age of 28 days, the strength increased by 20% to 24% compared to the 14-day curing age. This indicates that when the carbide slag content is small, the early growth rate of the carbide slag soil strength is greater than the later growth rate, and the hydration reaction is more rapid. When the carbide slag content is 7% and 9%, the strength of the carbide slag soil increased by 82% to 95% from 14 to 28 days of curing, indicating that the hydration reaction is more complete during this stage and the strength increase is greater. When the carbide slag content is 11%, the growth rate of soil strength in both the early and late curing stages shows a downward trend. This phenomenon indicates that although high carbide slag content can accelerate the hydration reaction process, it does not bring corresponding strength growth advantages. In addition, the strength of the solidified soil shows a trend of first increasing and then decreasing with the change of carbide slag content. For the specific silt soil sample used in this study, the optimal carbide slag content is 7%.

[0128] Effect of rice husk ash dosage:

[0129] The unconfined compressive strength of rice husk ash carbide slag solidified silt soil changes with rice husk ash content and curing age. Figure 3 shown.

[0130] It should be noted that Figure 3 The carbide slag content in a is 3%; the carbide slag content in b is 5%; the carbide slag content in c is 7%; the carbide slag content in d is 9%; and the carbide slag content in e is 11%.

[0131] Depend on Figure 3 It can be seen that the addition of rice husk ash significantly improved the mechanical properties of silt soil. Specifically: at a curing age of 7 days, the strength of the untreated silt soil was only 108kPa. After being solidified with 7% carbide slag alone, the strength was increased to 225kPa. After the introduction of rice husk ash, the strength of all composite solidified samples exceeded 360kPa, showing a significant enhancement effect. Among them, when the rice husk ash content was 15%, the sample reached its peak strength, and its strength value was approximately 4.7 times that of the original compacted silt 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 silt soil, and also indicates that there may be a synergistic effect between the components in the composite solidification system. From Figure 3The results also show that, compared with the control group, the strength of the composite-cured samples increased by 153% to 370% after a 7-day curing age. Compared with soil cured with carbide slag alone, the strength increase ranged from 63% to 250%. Under fixed carbide slag content, the relationship between rice husk ash content and cured soil strength exhibited a nonlinear relationship: when the rice husk ash content was below 15%, the strength increased significantly; above 15%, the strength decreased. Notably, this optimal content (15%) was independent of curing age, indicating that the mechanism of action of rice husk ash in the curing system was relatively stable. The results indicate that, from the perspective of optimizing compressive strength, a higher content of curing material is not necessarily better. For the specific silt soil sample used in this study, the optimal content of rice husk ash and carbide slag was 15% and 7%, respectively, ensuring optimal mechanical properties for the cured soil.

[0132] Furthermore, taking 7% carbide slag as an example, the relationship curve between the unconfined compressive strength of solidified soil at different ages and the rice husk ash content was established, as shown in Figure 2. Figure 4 The relationship between the two shows a good quadratic parabola feature and can be described by the following mathematical model:

[0133] q u =ax 2 +bx+c

[0134] Where: q u represents the unconfined compressive strength, x represents the rice husk ash content, and a, b, and c are regression coefficients, as shown in the following table:

[0135]

[0136]

[0137] As can be seen from the table above, the fitting effect R 2 better.

[0138] Effect of curing age:

[0139] The influence of curing age on the strength development of solidified soil is as follows: Figure 5 shown.

[0140] It should be noted that Figure 5 The carbide slag content in a is 3%; the carbide slag content in b is 5%; the carbide slag content in c is 7%; the carbide slag content in d is 9%; and the carbide slag content in e is 11%.

[0141] The unconfined compressive strength of solidified soil shows a continuous upward trend with increasing curing time. For example, with an optimized mix ratio of 7% carbide slag and 15% rice husk ash, when the curing period was extended from 7 to 28 days, the sample strength increased significantly from 508 kPa to 849.6 kPa, a 67.2% increase, fully demonstrating the significant contribution of the curing process to strength development. Further statistical analysis revealed that the strength of the sample at 14 days of curing was 1.41 times that of the 7-day sample, while the strength of the 28-day sample was 1.19 times that of the 14-day sample. This strength growth pattern indicates that the strength of solidified soil maintains an upward trend throughout the 28-day curing period, with the strength growth rate in the early stages (7-14 days) being faster than in the later stages (14-28 days).

[0142] Ultimate strain of rice husk ash calcium carbide slag soil:

[0143] The ultimate strain of samples with different proportions at 7 days and 28 days of curing age was statistically analyzed. The results are as follows: Figure 6 shown.

[0144] It should be noted that Figure 6 Figure a is the relationship diagram of the ultimate strain of rice husk ash and carbide slag soil at a curing age of 28 days; b is the relationship diagram of the ultimate strain of rice husk ash and carbide slag soil at a 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.

[0145] In the figure, 3d represents the addition of 3% carbide slag alone, 7d5dk represents the addition of 7% carbide slag and 5% rice husk ash, and the meanings of other figures are similar. Figure 6 It can be seen that the ultimate strain of the rice husk ash and carbide slag composite-stabilized soil at a 7-day curing age is generally greater than that of the 28-day-old specimen. At the same curing age, the ultimate strain of the composite-stabilized soil is significantly higher than that of the single carbide slag-stabilized soil. Notably, there is no significant correlation between the ultimate strain and the rice husk ash content, curing age, or unconfined compressive strength. Statistical data show that the ultimate strain of single carbide slag-stabilized soil ranges from 1.1% to 2.4%, while the ultimate strain of the rice husk ash and carbide slag composite-stabilized soil significantly increases to 3.1% to 4.5%. Compared with the typical ultimate strain range of cement-stabilized soil (1% to 2.5%), the composite-stabilized soil in this study exhibits greater toughness, which is of great significance for improving the engineering properties of soils.

[0146] Failure morphology analysis:

[0147] The silt soil specimens first underwent a brief compression phase, followed by rapid microcracks on the surface, the gradual peeling of the outer layer of the specimen, and ultimately overall failure. Carbide slag-stabilized soil and rice husk ash-carbide slag composite-stabilized soil primarily exhibited brittle shear failure and brittle tensile failure. Specifically, when the solidified soil strength was low, distinct primary cracks formed on the specimen surface at a certain angle to the axial direction, exhibiting typical brittle shear failure characteristics; while at higher strengths, multi-directional cracks developed on the specimen surface, with the primary cracks extending along the axial direction, exhibiting a brittle tensile failure mode.

[0148] Intensity regression prediction model

[0149] The following table shows the unconfined compressive strength test data of rice husk ash carbide slag solidified silt soil at a carbide slag dosage of 7%:

[0150]

[0151] Based on this, a three-dimensional relationship diagram of rice husk ash dosage, curing age and unconfined compressive strength was constructed, as shown in Figure 7 According to the distribution characteristics of the measured data, a prediction model is established using a complete quadratic function, and its theoretical expression is:

[0152]

[0153] For this model, the perfect quadratic polynomial can be written as:

[0154] Q=z0+ax+by+cx 2 +dy 2 +fxy

[0155] Where x is the curing age, days; y is the rice husk ash dosage, %; a, b, c, d, f, z0 are regression coefficients.

[0156] The regression analysis fitting coefficients are shown in the following table:

[0157]

[0158] According to the above table, the regression model of rice husk ash calcium carbide slag soil is:

[0159] Q=-72.8+38.93*T+46.69*a0+(-0.69)*T 2 +(-1.66)*a0 2 +0.08*T*a0

[0160] Where, T is the curing age, days; a0 is the amount of rice husk ash added, %.

[0161] The correlation coefficient is 0.967, the F value is 52.13 and P < 0.05, indicating that the model is significant as a whole. Under the condition that the curing age T does not exceed 28 days, the above rice husk ash calcium carbide slag regression model can be used to approximately estimate the unconfined compressive strength of rice husk ash calcium carbide slag solidified silt soil at any rice husk ash content and curing age. This characteristic has certain value in practical engineering applications. The specific model of unconfined compressive strength is shown in Figure 8 .

[0162] Microscopic characteristics and mechanisms:

[0163] Effect of rice husk ash dosage on the microstructure of stabilized soil:

[0164] The SEM analysis results of the effect of rice husk ash content on the microstructure of the solidified soil after 28 days of curing are as follows: Figure 9 shown.

[0165] It should be noted that Figure 9 Figure a is a schematic diagram of the SEM analysis results of 7% carbide slag solidified soil at a magnification of 2000 times; b is a schematic diagram of the SEM analysis results of 7% carbide slag solidified soil at a magnification of 5000 times; c is a schematic diagram of the SEM analysis results of the first rice husk ash carbide slag solidified soil at a magnification of 2000 times; d is a schematic diagram of the SEM analysis results of the first rice husk ash carbide slag solidified soil at a magnification of 5000 times; e is a schematic diagram of the SEM analysis results of the second rice husk ash carbide slag solidified soil at a magnification of 2000 times; f is a schematic diagram of the SEM analysis results of the second rice husk ash carbide slag solidified soil at a magnification of 5000 times.

[0166] The solidified soil mixed with 20% rice husk ash and 7% carbide slag is called the first rice husk ash and carbide slag solidified soil, and the solidified soil mixed with 15% rice husk ash and 7% carbide slag is called the second rice husk ash and carbide slag solidified soil.

[0167] When magnified 2000 times, the needle-shaped minerals generated inside the 7% carbide slag single-doped solid soil are less in content and difficult to distinguish, showing the characteristics of loose particle arrangement, developed pores and large pore size; in contrast, the rice husk ash carbide slag composite solidified soil is denser, and although there are also some larger pores, it is significantly improved compared with the single carbide slag solidified soil.

[0168] When magnified 5000x, the microstructural characteristics and interconnectedness of the solidified soil are clearly revealed. Dispersed fine needle-like minerals are observed in the solidified soil with carbide slag alone, forming limited overlaps in localized areas. In contrast, the soil solidified with rice husk ash and carbide slag composite exhibits a more complex system of hydration products: in addition to needle-like minerals, a large number of columnar, flaky, and flocculent minerals are also generated. The needle-like and columnar minerals are coarse and clustered, forming bundles that tightly fill pores and establish a well-connected network with other crystals. The flake-like and flocculent products are primarily distributed on the surfaces of soil particles and in the interstices between minerals, significantly enhancing pore-filling density. In the microstructure of the second rice husk ash and carbide slag solidified soil, a large amount of gel material is observed filling the pores, while the exposed needle-like and columnar minerals are relatively reduced. Localized agglomerations of needle-like and flake-like minerals are observed, and these minerals are primarily distributed in pores and on the surfaces of soil particles. In general, the addition of rice husk ash can indeed optimize the microstructure of the solidified soil, but excessive addition (exceeding the optimal dosage) will lead to an increase in porosity and have an adverse effect on the solidification effect.

[0169] Changes of microstructure of rice husk ash carbide slag stabilized soil with age:

[0170] In order to explore the aging evolution law of the microstructure of rice husk ash and carbide slag stabilized soil, the second rice husk ash and carbide slag stabilized soil (ratio of 15% rice husk ash + 7% carbide slag) was selected as the research object, and its microstructure at different curing ages (7 days, 14 days and 28 days) was systematically observed. The results are as follows: Figure 10 As shown (the microstructural characteristics of the 28-day-old stage are shown above Figure 9 (displayed in).

[0171] It should be noted that Figure 10 Figure a is a schematic diagram of the SEM analysis results of the microstructure changes of the second rice husk ash carbide slag stabilized soil with age at 7 days, magnified 2000 times; b is a schematic diagram of the SEM analysis results of the microstructure changes of the second rice husk ash carbide slag stabilized soil with age at 7 days, magnified 5000 times; c is a schematic diagram of the SEM analysis results of the microstructure changes of the second rice husk ash carbide slag stabilized soil with age at 14 days, magnified 2000 times; d is a schematic diagram of the SEM analysis results of the microstructure changes of the second rice husk ash carbide slag stabilized soil with age at 14 days, magnified 5000 times.

[0172] 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, the pores in the sample were numerous and large in size, mainly filled with lamellar and flocculent minerals, with fewer needle-shaped minerals; at the age of 14 days, the number of pores decreased, and needle-shaped minerals began to connect with each other; by the age of 28 days, the number of large pores decreased significantly, the pore surface was covered by a large amount of flocculent minerals, and the needle-shaped and columnar minerals were wrapped in it, forming a dense overall structure.

[0173] When magnified to 5000 times, the morphological evolution of the hydration products can be observed more clearly: at the age of 7 days, the number of needle-shaped and columnar minerals is small and the shape is thin and short, and some flake-shaped and flocculent hydration products can also be observed; at the age of 14 days, the number of hydration products increases significantly, the needle-shaped and columnar minerals grow obviously, and bundle-like agglomerations appear locally, effectively filling the pores; at the age of 28 days, flocculent products become the main surface feature, the exposed columnar minerals are coarse and mostly aggregated in bundles, forming a good spatial connection network with other minerals, and flake-shaped and flocculent products are mainly distributed on the surface of soil particles.

[0174] These changes in microstructural characteristics fully demonstrate the continuous progress of the hydration reaction in the rice husk ash carbide slag solidification system and its improvement of material properties, providing microscopic evidence for understanding the strength development mechanism of solidified soil.

[0175] Reaction mechanism of rice husk ash and carbide slag solidified soil:

[0176] Rice husk ash not only contains a large amount of active SiO2, but also has considerable nanoscale pores. These characteristics enable it to play multiple roles in the sludge solidification process:

[0177] (1) Filling effect: Rice husk ash contains a large number of nano-scale SiO2 particles, which can effectively fill the internal pores of solidified silt soil. This physical filling effect significantly improves the density of the soil, reduces the porosity, and thus improves the overall performance of the solidified soil.

[0178] (2) Hydration reaction: The main components of carbide slag are similar to cement, and its hydration reaction products are mainly calcium hydroxide, hydrated calcium silicate and hydrated calcium aluminate. After adding rice husk ash, its rich active SiO2 reacts with Ca(OH)2 produced by carbide slag hydration to produce a large amount of hydrated calcium silicate, thereby significantly increasing the content of CSH gel with cementing effect. This reaction is the main source of the strength development of solidified soil. Its chemical reaction equation is:

[0179] SiO2+Ca(OH)2+nH2O→CaO·SiO2·(n+1)H2O

[0180] (3) Water storage and supply: The unique nano-scale porous structure of rice husk ash gives it excellent water storage properties. In the later stages 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 ensures the progress of the hydration reaction in the later stages of the solidification system, thereby ensuring the stable growth of the strength of the solidified soil in the later stages.

[0181] Based on the above analysis, a micro-evolution mechanism model of rice husk ash carbide slag solidified silt soil was proposed. Figure 11 shown.

[0182] in conclusion:

[0183] (1) Compared with unsolidified and carbide slag-solidified silt soil, the unconfined compressive strength of rice husk ash carbide slag-solidified silt soil was significantly improved. For the specific silt soil sample used in this study, the optimal material ratio was 15% rice husk ash and 7% carbide slag.

[0184] (2) Under the optimal rice husk ash carbide slag dosage, the q of the solidified soil after 14 days of curing u The value reaches 1.41 times that of 7 days and 1.19 times that of 14 days at 28 days. This intensity growth law shows that the reaction in the rice husk ash carbide slag and sludge system not only starts quickly but also lasts for a long time.

[0185] (3) The addition of rice husk ash can improve the toughness of silt-stabilized soil. The ultimate strain of soil stabilized with carbide slag alone is between 1.1% and 2.4%, while the ultimate strain of soil stabilized with rice husk ash and carbide slag is significantly increased to between 3.1% and 4.5%.

[0186] (4) The reaction mechanism of rice husk ash calcium carbide slag soil is mainly the filling effect, hydration reaction and water storage and supply. The CSH gel produced by the hydration reaction is the main source of strength of the solidified sludge;

[0187] (5) Based on the experimental results, a strength prediction model and a micro-evolution mechanism model for rice husk ash carbide slag solidified silt soil were established, which can provide a theoretical basis and technical reference for the application of rice husk ash carbide slag in silt solidification practice.

[0188] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformation made by utilizing the contents of the present invention's description and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A solidification test method for dredged sludge, characterized in that: The solidification test method for dredged silt comprises: Drying the wet dredged sludge to a constant weight, crushing it and then sieving it to obtain dry pretreated soil; adding carbide slag and rice husk ash to the pretreated soil to obtain a mixture; mixing the mixture uniformly to obtain a sludge solidified mixture; compacting the sludge solidification mixture into cylindrical specimens in stages; The cylindrical sample is sealed and placed in a constant temperature and humidity environment for curing to a preset age; Using an unconfined pressure instrument to test the compressive strength and ultimate strain of the cylindrical specimen; Cutting a cross section from the cylindrical sample to obtain the distribution of hydration products and the pore structure in the cylindrical sample, and obtaining a solidification strength model of the dredged sludge; The hydration products include needle-shaped, columnar and flocculent CSH gels.

2. The solidification test method for dredged sludge according to claim 1, characterized in that: The steps of uniformly mixing the mixture to obtain a sludge solidified mixture include: adding water to the mixture to moisten the mixture; The mixture is mixed uniformly to obtain the sludge solidification mixture.

3. The solidification test method for dredged sludge according to 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 pretreated soil; Obtaining water demand based on the initial moisture content, the total mass of the pretreated soil, and the target moisture content; Water is added to the mixture according to the required amount to moisten the mixture.

4. The solidification test method for dredged sludge according to claim 3, characterized in that: The step of obtaining the water requirement according to the initial moisture content, the total mass of the pretreated soil 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 pretreated soil and the target moisture content; The formula 1 is: 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 pretreated soil, and K2 is the water requirement.

5. The solidification test method for dredged sludge according to claim 4, characterized in that: 52.16%≤the target moisture content≤57.65%.

6. The solidification test method for dredged sludge according to claim 3, characterized in that: The step of adding water to the mixture to moisten the mixture comprises: Water was added to the mixture three times, and the mixture was stirred for 5 minutes after each addition. The mixture was allowed to stand for 10 minutes before the next addition of water to moisten the mixture.

7. The solidification test method for dredged sludge according to any one of claims 1 to 6, characterized in that: The steps of compacting the sludge solidification mixture into cylindrical samples in stages include: The sludge solidified mixture is divided into three layers and compacted, with each layer compacted 25 times and each compaction pressure being 200 kPa, to obtain the cylindrical sample.

8. The solidification test method for dredged sludge according to any one of claims 1 to 6, characterized in that: There are multiple cylindrical specimens, and the steps of sealing the cylindrical specimens and placing them in a constant temperature and humidity environment for curing to a preset age include: The cylindrical specimens were sealed and placed in a constant temperature and humidity environment for curing for 7 days, 14 days and 28 days respectively.

9. The solidification test method for dredged sludge according to any one of claims 1 to 6, characterized in that: The steps of adding carbide slag and rice husk ash to the pretreated soil to obtain a mixture include: 100 parts of the dredged sludge, 5 to 20 parts of the rice husk ash and 3 to 11 parts of the carbide slag are taken by mass and mixed to form the mixture.

10. The solidification test method for dredged sludge according to any one of claims 1 to 6, characterized in that: The mass ratio of the carbide slag to the rice husk ash is 1:2 to 1:3; The steps of cutting a cross section from the cylindrical sample, obtaining the distribution of hydration products and the pore structure in the cylindrical sample, and obtaining a solidification strength model of the dredged sludge include: cutting a cross section from the cylindrical sample to obtain the distribution of hydration products and the pore structure of the cylindrical sample; According to Formula 2, the dosage of the rice husk ash and the actual curing age of the cylindrical specimen after sealing and placing it in a constant temperature and humidity environment, the curing strength model of the dredged sludge is obtained; The second formula is: Q=-72.8+38.93*T+46.69*a0+(-0.69)*T 2 +(-1.66)*a0 2 +0.08*T*a0 Wherein, T is the actual curing age, and a0 is the actual dosage of the rice husk ash.

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