Rice hull ash and carbide slag composite curing agent and preparation method thereof

Abstract

The invention discloses a rice hull ash and carbide slag composite curing agent and a preparation method thereof, and relates to the technical field of dredged sludge curing construction, the rice hull ash and carbide slag composite curing agent comprises 10-30 parts by mass of rice hull ash and 5-15 parts by mass of carbide slag; wherein the content of SiO2 in the rice hull ash is A1, A1 is larger than or equal to 85%, the content of CaO in the carbide slag is B1, and B1 is larger than or equal to 60%. According to the invention, 10-30 parts by mass of rice hull ash and 5-15 parts by mass of carbide slag are compounded for use, so that efficient solidification of dredged sludge is realized. Industrial and agricultural wastes are used for replacing traditional cement, waste raw materials are used for improving the strength of a soil body after dredged sludge solidification, energy consumption and carbon emission are reduced, and the environment requirements of complex engineering can be better met.

Description

Technical Field

[0001] The invention relates to the technical field of dredged sludge solidification construction, and in particular to a rice husk ash and carbide slag composite solidifying agent and a preparation method thereof. Background Art

[0002] In dredging projects, silt solidification is a critical step in ensuring project stability and environmental safety. While traditional solidification materials (such as cement and lime) can effectively improve the strength of solidified silt, their production is energy-intensive, resulting in significant carbon emissions. Their long-term use can lead to resource waste and increased environmental burden. Furthermore, cement-based materials have poor compatibility with silt, resulting in low early strength and insufficient durability after solidification. Summary of the Invention

[0003] The main purpose of the present invention is to provide a rice husk ash carbide slag composite curing agent and a preparation method thereof, aiming to utilize waste raw materials to improve the soil strength after dredging silt curing.

[0004] To achieve the above-mentioned purpose, the rice husk ash and carbide slag composite curing agent proposed in the present invention is used for dredging silt. The rice husk ash and carbide slag composite curing agent comprises 10 to 30 parts by mass of rice husk ash and 5 to 15 parts by mass of carbide slag; wherein the SiO2 content in the rice husk ash is A1, A1≥85%, and the CaO content in the carbide slag is B1, B1≥60%.

[0005] In one embodiment, the mass ratio of the rice husk ash to the carbide slag is 15:7.

[0006] In one embodiment, the porosity of the nanopores of the rice husk ash is

[0007] In one embodiment, the specific surface area of the rice husk ash is SSA, 200m 2 / g≤SSA≤500m 2 / g.

[0008] In one embodiment, the CaO content in the carbide slag is B2, 65%≤B2≤70%; the SiO2 content in the carbide slag is C, 1%≤C≤2%; and the Al2O3 content in the carbide slag is D, 1.5%≤D≤2.5%.

[0009] In one embodiment, the content of SiO2 in the rice husk ash is A2, 90%≤A2≤95%; the content of Fe2O3 in the rice husk ash is E, 0.5%≤E≤1%.

[0010] The present invention also provides a method for preparing a rice husk ash and carbide slag composite curing agent, which is used to prepare the rice husk ash and carbide slag composite curing agent as described above. The method for preparing the rice husk ash and carbide slag composite curing agent comprises:

[0011] obtaining the rice husk ash;

[0012] Obtaining the carbide slag;

[0013] Weigh 10 to 30 parts of the rice husk ash and 5 to 15 parts of the carbide slag by mass and mix them to form a composite curing agent base material;

[0014] Distilled water is added to the composite curing agent base material, adjusted to a preset moisture content and stirred evenly to obtain the rice husk ash and carbide slag composite curing agent.

[0015] In one embodiment, the step of obtaining the rice husk ash comprises:

[0016] Hulling the rice to obtain rice husk;

[0017] The rice husk is calcined at 600° C.±50° C. to obtain the rice husk ash having a SiO 2 content of A1.

[0018] In one embodiment, the step of obtaining the carbide slag comprises:

[0019] The industrial waste carbide slag is ground to a particle size d, d≤100 μm, to obtain the carbide slag with a CaO content of B1.

[0020] In one embodiment, the preset moisture content is W, 8%≤W≤15%.

[0021] The technical solution of the present invention is to combine 10 to 30 parts by mass of rice husk ash with 5 to 15 parts by mass of carbide slag, wherein the SiO2 content A1 of the rice husk ash is ≥85% and the CaO content B1 of the carbide slag is ≥60%, thereby achieving efficient solidification of dredged sludge. The highly active SiO2 of the rice husk ash and the CaO in the carbide slag generate hydrated calcium silicate (CSH gel) in the hydration reaction, forming a continuous cementing network, which significantly improves the early strength of the solidified soil. At the same time, the nanoporous structure of the rice husk ash reduces the porosity of the soil through physical filling, and combined with its water storage properties, continuously releases water to maintain the hydration reaction process, effectively solving the problem of stagnation of the strength of traditional cement-based materials in the later stage. In addition, the ratio range of rice husk ash and carbide slag avoids the accumulation of unreacted particles caused by excessive rice husk ash, or the problem of insufficient cementing products at low dosage by optimizing the balance between active components and porosity. The present invention replaces traditional cement with industrial and agricultural waste, utilizes waste raw materials to improve the strength of the soil after dredged silt solidification, reduces energy consumption and carbon emissions, and is more adaptable to the environmental requirements of complex projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] Figure 1 A schematic flow chart of an embodiment of a method for preparing a rice husk ash and carbide slag composite curing agent provided by the present invention;

[0024] 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;

[0025] 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;

[0026] 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;

[0027] 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;

[0028] 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;

[0029] 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;

[0030] Figure 8 A strength model diagram of rice husk ash calcium carbide slag soil according to the present invention;

[0031] 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;

[0032] 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;

[0033] 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.

[0034] 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

[0035] 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.

[0036] 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.

[0037] 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.

[0038] In dredging projects, silt solidification is a critical step in ensuring project stability and environmental safety. While traditional solidification materials (such as cement and lime) can effectively improve the strength of solidified silt, their production is energy-intensive, resulting in significant carbon emissions. Their long-term use can lead to resource waste and increased environmental burden. Furthermore, cement-based materials have poor compatibility with silt, resulting in low early strength and insufficient durability after solidification.

[0039] In order to solve this technical problem, the present invention provides a rice husk ash and carbide slag composite curing agent and a preparation method thereof.

[0040] In one embodiment of the present invention, the rice husk ash and carbide slag composite curing agent is used for dredging silt, and the rice husk ash and carbide slag composite curing agent includes 10 to 30 parts by mass of rice husk ash and 5 to 15 parts by mass of carbide slag; wherein the SiO2 content in the rice husk ash is A1, A1 ≥ 85%, and the CaO content in the carbide slag is B1, B1 ≥ 60%.

[0041] Specifically, rice husk ash, a waste material used in biomass power generation, was obtained. X-ray fluorescence (XRF) analysis revealed that the calcined rice husk ash had a SiO2 content of 92%, a Fe2O3 content of 0.7%, and an Al2O3 content of 0.25%, meeting the Al2O3 requirement of ≥85%. Furthermore, nitrogen adsorption measurements revealed a specific surface area of 380 m2 / g and a nanoporosity of 32%. Its nanoporous structure effectively absorbs moisture from sludge and provides an active reaction interface.

[0042] Industrial carbide slag waste was ball milled to a particle size of ≤80μm and sieved to obtain a uniform powder. XRF analysis showed that the carbide slag contained 67.8% CaO, 1.6% SiO₂, and 1.9% Al₂O₃, meeting the B1 requirement of ≥60%. The ground carbide slag is highly reactive, with the CaO reacting with the water in the sludge and the SiO₂ in the rice husk ash to form a hydration reaction.

[0043] Weigh 15 parts rice husk ash and 7 parts carbide slag by weight and mix them in a twin-shaft mixer for 20 minutes until uniform, forming a composite curing agent base. Distilled water is then added to the base to adjust the moisture content to 12% (W = 8% to 15%), and stirring is continued for 10 minutes to obtain a paste-like composite curing agent.

[0044] In the technical solution provided by the invention, 10 to 30 parts by mass of rice husk ash and 5 to 15 parts by mass of carbide slag are combined for use, wherein the SiO2 content A1 of the rice husk ash is ≥85% and the CaO content B1 of the carbide slag is ≥60%, thereby achieving efficient solidification of dredged sludge. The highly active SiO2 of the rice husk ash and the CaO in the carbide slag generate hydrated calcium silicate (CSH gel) in the hydration reaction, forming a continuous cementing network, which significantly improves the early strength of the solidified soil. At the same time, the nanoporous structure of the rice husk ash reduces the porosity of the soil through physical filling, and combined with its water storage properties, continuously releases water to maintain the hydration reaction process, effectively solving the problem of stagnation of strength of traditional cement-based materials in the later stage. In addition, the ratio range of rice husk ash and carbide slag avoids the accumulation of unreacted particles caused by excessive rice husk ash, or the problem of insufficient cementing products at low dosages by optimizing the balance between active components and porosity. The present invention replaces traditional cement with industrial and agricultural waste, utilizes waste raw materials to improve the strength of the soil after dredged silt solidification, reduces energy consumption and carbon emissions, and is more adaptable to the environmental requirements of complex projects.

[0045] To validate the rice husk ash and carbide slag composite curing agent, the paste-like composite curing agent obtained in the above example was added to dredged sludge (initial moisture content 54.9%, liquid limit 38.3%) at a rate of 22% by weight of dry soil. The mixture was mechanically stirred until uniform. The mixture was compacted into cylindrical specimens with a diameter of 50 mm and a height of 100 mm. After standing for 24 hours, the specimens were demolded and sealed for curing in an environment with a humidity of >90% at 20°C to obtain the first cured soil.

[0046] After seven days of curing, the unconfined compressive strength (UCS) of the sample reached 508 kPa, a 370% increase compared to unsolidified silt (108 kPa) and a 126% increase compared to soil solidified with carbide slag alone (225 kPa). This effect is attributed to the synergistic reaction between the nano-SiO₂ in rice husk ash and the CaO in carbide slag. The CaO hydrates to form Ca(OH)₂, which reacts with the active SiO₂ in the rice husk ash to form hydrated calcium silicate (CSH gel), forming a dense cementitious network.

[0047] After 28 days of curing, the UCS further increased to 849.6 kPa, a 67.2% increase compared to the 7-day strength. The nanopores in rice husk ash continuously release absorbed water during the later stages of curing, maintaining the hydration reaction and avoiding the strength bottleneck caused by the stagnant reaction in traditional cement-based materials.

[0048] See also Figure 9 , 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.

[0049] Scanning electron microscopy (SEM) showed that CSH gel and needle-shaped ettringite in the composite solidified soil were interwoven into a continuous skeleton, filling the pores and wrapping the soil particles ( Figure 9 cd). Compared with single carbide slag solidified soil ( Figure 9 ab), its porosity is reduced by 42% and its density is significantly improved.

[0050] First, in order to verify the effectiveness of the ratio range of rice husk ash (10-30 parts) and carbide slag (5-15 parts), the following two groups of comparative tests were set up:

[0051] Group 1: 10 parts rice husk ash + 5 parts carbide slag (SiO2 content 89%, CaO content 65%);

[0052] Group 2: 30 parts of rice husk ash + 15 parts of carbide slag (SiO2 content 94%, CaO content 70%).

[0053] Group 1 Effect:

[0054] The UCS at 7 days was 360 kPa, and the UCS at 28 days was 620 kPa. When the rice husk ash content was low, the nanofilling effect was insufficient and the cementation product was less, resulting in a lower strength than the first stabilized soil in the above embodiment.

[0055] Group 2 Effect:

[0056] The UCS was 427 kPa after 7 days and 765 kPa after 28 days. Excessive addition of rice husk ash (30 parts) increased the porosity (SEM showed accumulation of unreacted SiO2 particles), which in turn reduced the strength.

[0057] Therefore, a ratio of 10 to 30 parts rice husk ash to 5 to 15 parts carbide slag ensures efficient CSH gel formation and structural density by balancing active components and porosity. When the mass ratio of rice husk ash to carbide slag is 15:7, the synergistic effect is optimal, reaching peak strength and durability.

[0058] Secondly, in order to verify the lower limit requirements of SiO2 (A1 ≥ 85%) and CaO (B1 ≥ 60%), the following comparison groups were set up:

[0059] Group 3: rice husk ash SiO2 content 83% (A1<85%) + carbide slag CaO content 58% (B1<60%);

[0060] Group 4: Rice husk ash SiO2 content 85% + carbide slag CaO content 60%.

[0061] Group 3 Effects:

[0062] The UCS was only 320 kPa after 28 days. The low activity of SiO2 and CaO resulted in insufficient hydration reaction and scarce cementation products (SEM showed a loose structure).

[0063] Group 4 Effects:

[0064] The 28-day UCS was 650 kPa, an increase of 103% compared with Group 3. When A1 ≥ 85% and B1 ≥ 60% were met, the active components of rice husk ash and carbide slag fully participated in the reaction, verifying the necessity of chemical composition limitation in this example.

[0065] In an embodiment of the present invention, the mass ratio of the rice husk ash to the carbide slag is 15:7.

[0066] Specifically, the mass ratio of the rice husk ash to the calcium carbide slag is 15:7, which ensures the efficient generation of CSH gel and avoids reaction imbalance caused by excess or insufficient amount; at this ratio, the nanopore filling and hydration products are evenly distributed, significantly reducing the porosity (<20%), which can further improve the soil's impermeability and durability; and it can adapt to silts with different moisture contents, and the strength stability of the solidified soil is better than that of traditional cement-based materials (28-day UCS fluctuation range is <10%).

[0067] In an embodiment of the present invention, the porosity of the nanopores of the rice husk ash is

[0068] Specifically, it was measured by thermogravimetric analysis (TGA), The rice husk ash can absorb 23.7% of water by mass at a relative humidity of 95%, and the sustained release rate reaches 82% during the 28-day curing period. The interface binding energy between CSH gel and rice husk ash in the sample is 2.1nN / nm, which is higher than The sample was improved by 160%.

[0069] In an embodiment of the present invention, the specific surface area of the rice husk ash is SSA, 200m 2 / g≤SSA≤500m 2 / g.

[0070] At 7% carbide slag content, when SSA is increased from 150m 2 / g increased to 200m 2 / g, the UCS value jumped from 420kPa to 580kPa in 28 days; when SSA reached 500m 2 / g, the UCS value can reach 820kPa, but it continues to increase to 550m 2 / g, the strength dropped to 780kPa. Scanning electron microscopy showed that SSA = 350m 2 / g sample has a CSH gel filling rate of 82% and a pore tortuosity coefficient of 4.7, which is significantly better than that of samples with low specific surface area. Moreover, after 10 freeze-thaw cycles, SSA = 200m 2 The mass loss rate of the sample is 3.2% and the SSA is 500m 2 / g sample is only 1.8%, showing better structural stability.

[0071] Specifically, in an embodiment of the present invention, the CaO content in the carbide slag is B2, 65%≤B2≤70%; the SiO2 content in the carbide slag is C, 1%≤C≤2%; the Al2O3 content in the carbide slag is D, 1.5%≤D≤2.5%.

[0072] More specifically, in an embodiment of the present invention, the content of SiO2 in the rice husk ash is A2, 90%≤A2≤95%; the content of Fe2O3 in the rice husk ash is E, 0.5%≤E≤1%.

[0073] See also Figure 1 The present invention also provides a method for preparing a rice husk ash and carbide slag composite curing agent, which is used to prepare the rice husk ash and carbide slag composite curing agent as described above. The method for preparing the rice husk ash and carbide slag composite curing agent comprises:

[0074] Step S10, obtaining the rice husk ash;

[0075] Step S20, obtaining the carbide slag;

[0076] Step S30, weighing 10 to 30 parts of the rice husk ash and 5 to 15 parts of the carbide slag by mass, and mixing them to form a composite curing agent base material;

[0077] Step S40, adding distilled water to the composite curing agent base material, adjusting the water content to a preset value and stirring evenly to obtain the rice husk ash and carbide slag composite curing agent.

[0078] Specifically, in step S10, the hulled rice husks are placed in a high-temperature furnace for biomass power generation and incinerated at 600°C under oxygen-limited conditions for at least two hours. After incineration, the husk ash is naturally cooled to room temperature and then ultrafinely ground using a ball mill to a controlled particle size distribution within the range of 1-50 μm. The active SiO2 content must be at least 90%, ensuring that the active ingredients can be effectively released during the subsequent hydration reaction.

[0079] In step S20, the bulk carbide slag is first crushed into particles with a particle size of ≤5mm, and then screened through a 0.075mm standard square mesh sieve to remove unreacted calcium carbide impurities. The pretreated carbide slag should have a CaO content of ≥65% and a free water content of ≤3%. The screened carbide slag powder needs to be sealed and stored in a dry environment to prevent moisture absorption and agglomeration, which may lead to reduced activity.

[0080] In step S30, 10 to 30 parts by mass of rice husk ash and 5 to 15 parts by mass of carbide slag are dry-mixed using a double-screw conical mixer to obtain a composite curing agent base. The mixing parameters are set as follows: a speed of 25 rpm, a mixing time of 15 minutes, and a coefficient of variation (CV) of mixing uniformity of ≤5%.

[0081] In step S40, distilled water is added to the composite curing agent base to adjust the moisture content to a preset moisture content W, within the range of 8% ≤ W ≤ 15%. The mixture is stirred at 120 rpm for 8 minutes, followed by 30 minutes of stabilization to allow for even water penetration. This moisture content range increases the hydration reaction rate by 40% to 55% while preventing excessive moisture from loosening the soil structure.

[0082] In this example, when the composite curing agent base material was incorporated into dredged sludge at a concentration of 22% (based on the dry weight of the sludge), the 7-day unconfined compressive strength reached 508 kPa, a 210% increase compared to cement-cured soil with the same dosage. The 28-day strength reached 849.6 kPa, and the ultimate strain was 4.2%, demonstrating toughness superior to conventional materials. Electron microscopy revealed a CSH gel filling rate of ≥85% within the cured product, and the peak pore diameter distribution decreased from 5-10 μm in untreated soil to 0.1-1 μm. The energy consumption per ton of curing agent produced was only 17% of that of cement, reducing CO2 emissions by 89%.

[0083] It should be understood that the rice husk ash and carbide slag composite curing agent refers to the above embodiments. Since the preparation method of the rice husk ash and carbide slag composite curing agent adopts all the technical solutions of all the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here one by one.

[0084] Specifically, in an embodiment of the present invention, the step of obtaining the rice husk ash includes:

[0085] Step S11, hulling the rice to obtain rice husks;

[0086] Step S12: calcining the rice husk at 600° C.±50° C. to obtain the rice husk ash having a SiO 2 content of A1.

[0087] More specifically, in an embodiment of the present invention, the step of obtaining the carbide slag includes:

[0088] Step S21, grinding the industrial waste carbide slag to a particle size d, d≤100 μm, to obtain the carbide slag with a CaO content of B1.

[0089] The specific surface area of carbide slag with particle size ≤100μm increases significantly (from 0.5m 2 / g increased to 1.2m 2 / g), accelerates the hydration of CaO to generate Ca(OH)2, which reacts with SiO2 in rice husk ash to form CSH gel (see Figure 9 SEM analysis of cd). Ensure that the CaO content is ≥60% to avoid insufficient cementation products due to interference from impurities. Calcium carbide slag and rice husk ash (specific surface area 380m 2 / g) to form a uniform mixed system, the dispersion of the curing agent is improved after being added to the sludge, and the pore filling rate is increased to 82% (compared with 42% of single carbide slag).

[0090] As a specific verification example, silt was obtained from the bottom of a lake. The basic physical indicators of the silt are shown in the following table:

[0091]

[0092] 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:

[0093] 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

[0094] 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 microstructure morphology was observed using scanning electron microscopy.

[0095] (1) Specimen preparation and maintenance:

[0096] 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%.

[0097] (2) Unconfined compressive strength test:

[0098] 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.

[0099] (3) Scanning electron microscope test:

[0100] 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 taken as observation samples.

[0101] Test results and analysis:

[0102] Unconfined compressive strength, unconfined compressive strength of calcium carbide slag:

[0103] 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%.

[0104] Effect of rice husk ash dosage:

[0105] 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.

[0106] 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%.

[0107] Depend on Figure 3It 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 3 The 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.

[0108] 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:

[0109] q u =ax 2 +bx+c

[0110] 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:

[0111] Maintenance 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

[0112] As can be seen from the table above, the fitting effect R 2 better.

[0113] Effect of curing age:

[0114] The influence of curing age on the strength development of solidified soil is as follows: Figure 5 shown.

[0115] 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%.

[0116] 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).

[0117] Ultimate strain of rice husk ash calcium carbide slag:

[0118] 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.

[0119] 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.

[0120] 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.

[0121] Failure morphology analysis:

[0122] 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.

[0123] Intensity regression prediction model

[0124] 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%:

[0125]

[0126] 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:

[0127]

[0128] For this model, the perfect quadratic polynomial can be written as:

[0129] Q=z0+a*x+b*y+c*x 2 +d*y 2 +f*x*y

[0130] Where x is the curing age, days; y is the rice husk ash dosage, %; a, b, c, d, f, z0 are regression coefficients.

[0131] The regression analysis fitting coefficients are shown in the following table:

[0132]

[0133] According to the above table, the regression model of rice husk ash calcium carbide slag soil is:

[0134] Q=-72.8+38.93*T+46.69*a0+(-0.69)*T 2 +(-1.66)*a0 2 +

[0135] 0.08*T*a0

[0136] Where, T is the curing age, days; a0 is the amount of rice husk ash added, %.

[0137] 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 .

[0138] Microscopic characteristics and mechanisms:

[0139] Effect of rice husk ash dosage on the microstructure of stabilized soil:

[0140] 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 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.

[0141] 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.

[0142] 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.

[0143] Changes of microstructure of rice husk ash carbide slag stabilized soil with age:

[0144] 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).

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] Reaction mechanism of rice husk ash and carbide slag solidified soil:

[0150] 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:

[0151] (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.

[0152] (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:

[0153] SiO2+Ca(OH)2+nH2O→CaO·SiO2·(n+1)H2O

[0154] (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.

[0155] Based on the above analysis, a micro-evolution mechanism model of rice husk ash carbide slag solidified silt soil was proposed. Figure 11 shown.

[0156] in conclusion:

[0157] (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.

[0158] (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.

[0159] (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%.

[0160] (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;

[0161] (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.

[0162] 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 rice husk ash carbide slag composite curing agent, characterized in that: Used for dredging silt, the rice husk ash and carbide slag composite curing agent includes 10 to 30 parts by mass of rice husk ash and 5 to 15 parts by mass of carbide slag; wherein the SiO2 content in the rice husk ash is A1, A1≥85%, and the CaO content in the carbide slag is B1, B1≥60%.

2. The rice husk ash carbide slag composite curing agent according to claim 1, characterized in that The mass ratio of the rice husk ash to the carbide slag is 15:

7.

3. The rice husk ash carbide slag composite curing agent according to claim 1, wherein The porosity of the nanopores of the rice husk ash is φ, 20%≤φ≤40%.

4. The rice husk ash carbide slag composite curing agent according to claim 3, characterized in that The specific surface area of the rice husk ash is SSA, 200m 2 / g≤SSA≤500m 2 / g.

5. The rice husk ash carbide slag composite curing agent according to any one of claims 1 to 4, characterized in that The content of CaO in the carbide slag is B2, 65%≤B2≤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%.

6. The rice husk ash carbide slag composite curing agent according to any one of claims 1 to 4, characterized in that The content of SiO2 in the rice husk ash is A2, 90%≤A2≤95%; the content of Fe2O3 in the rice husk ash is E, 0.5%≤E≤1%.

7. A method for preparing a rice husk ash and carbide slag composite curing agent, characterized in that: For preparing the rice husk ash and carbide slag composite curing agent according to any one of claims 1 to 6, the preparation method of the rice husk ash and carbide slag composite curing agent comprises: obtaining the rice husk ash; Obtaining the carbide slag; Weigh 10 to 30 parts of the rice husk ash and 5 to 15 parts of the carbide slag by mass and mix them to form a composite curing agent base material; Distilled water is added to the composite curing agent base material, adjusted to a preset moisture content and stirred evenly to obtain the rice husk ash and carbide slag composite curing agent.

8. The method for preparing a rice husk ash and carbide slag composite curing agent according to claim 7, wherein: The steps of obtaining the rice husk ash include: Hulling the rice to obtain rice husk; The rice husk is calcined at 600° C.±50° C. to obtain the rice husk ash having a SiO 2 content of A1.

9. The method for preparing a rice husk ash and carbide slag composite curing agent according to claim 7, wherein: The steps of obtaining the carbide slag include: The industrial waste carbide slag is ground to a particle size d, d≤100 μm, to obtain the carbide slag with a CaO content of B1.

10. The method for preparing a rice husk ash and carbide slag composite curing agent according to claim 7, wherein: The preset moisture content is W, 8%≤W≤15%.

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