Integrated construction process of green composite foundation for resource utilization of sludge residue soil

Abstract

The invention relates to the technical field of environmental geotechnical engineering, and discloses a green composite foundation integrated construction process for resource utilization of sludge muck, which comprises the following steps: adding a composite pretreatment agent prepared from an oxidizing agent, a heavy metal stabilizer and an ion exchanger into the sludge muck for first-stage stirring; oxidizing and decomposing organic matters, pre-mineralizing and fixing heavy metals and purifying a chemical environment to obtain pretreated slurry; a composite gelling and exciting system prepared from a gelling material, an exciting agent and a long-acting pH buffering agent is added into the slurry for second-stage stirring, so that efficient gelling and long-acting stabilization of the internal pH value are achieved in the purified environment, and homogeneous slurry is obtained; and finally, the homogeneous slurry is solidified to form the composite foundation. Through chemical regulation and control of time sequence separation, harmful components in the sludge are converted into beneficial structural units of a solidified body, and the formed composite foundation has the beneficial effects of high mechanical strength, high environmental stability and high long-term durability.

Description

Technical Field

[0001] This invention relates to the field of environmental geotechnical engineering technology, specifically to an integrated construction process for green composite foundations that utilizes silt and slag resources. Background Technology

[0002] Silt and slag, as solid wastes with high water content and complex composition, are typically utilized through solidification / stabilization techniques. However, current technologies generally employ cement-based cementitious materials for one-time mixing of the silt. The humic acid and other organic matter commonly found in silt strongly inhibit the hydration reaction of cement, hindering the formation and bonding of hydration products. This results in a loose, porous structure in the solidified body, ultimately failing to meet engineering requirements in terms of mechanical strength.

[0003] For contaminated sludge containing heavy metals, traditional solidification processes mainly rely on the highly alkaline environment generated by cement hydration to convert heavy metal ions into hydroxide precipitates for fixation. However, these hydroxides lack chemical stability under changes in environmental pH or long-term acidic corrosion, posing a risk of secondary leaching of heavy metals and a potential threat to environmental safety.

[0004] In addition, the long-term durability of the solidified body itself is also a key issue. Alkaline substances such as calcium hydroxide generated by cement hydration inside the solidified body will gradually be lost or neutralized under the long-term effects of groundwater or acid rain, leading to structural deterioration and strength reduction of the solidified body, making it difficult to guarantee its long-term service stability as an engineering material. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a green integrated construction process for the resource utilization of silt and slag foundations. This process solves the problems in existing silt solidification technologies, such as low strength due to high organic matter content inhibiting hydration reactions, high leaching toxicity due to unreliable physical encapsulation of heavy metals, and insufficient long-term durability of the solidified body due to internal alkalinity loss.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a green composite foundation integrated construction process for the resource utilization of silt and slag, comprising the following steps: The composite pretreatment agent is added to the sludge and slag for the first stage of mixing to obtain a pretreated slurry. The composite pretreatment agent is made of an oxidant, a heavy metal stabilizer, and an ion exchanger. A composite cementing and activation system is added to the pretreated slurry for the second stage of mixing to obtain a homogeneous slurry for forming a composite foundation. The composite cementing and activation system is made of cementing materials, a sulfate activator, an alkaline activator, and a long-lasting pH buffer. The homogeneous slurry is then solidified to form the composite foundation.

[0007] By adopting the above technical solution, this invention solves the problem of competition and interference between pollutant treatment and cementitious material hydration by utilizing a time-separated chemical reaction pathway. The specific reaction mechanism and technical effects are as follows: First, during the initial mixing stage, chemical environment reconstruction and pre-sealing of contaminants are carried out. Oxidants (such as sodium persulfate) dissolve in water and generate sulfate radicals with high oxidation potential. These radicals preferentially oxidize organic macromolecules such as humic acid and fulvic acid adsorbed on the surface of soil particles, causing them to break down. This reaction destroys the organic matter coating on the soil particles, exposing active sites on the particle surface and eliminating the steric hindrance effect of organic matter on the subsequent formation of cement hydration products. Simultaneously, anions (such as phosphate) dissociated from heavy metal stabilizers react chemically with free heavy metal ions (lead, cadmium, etc.) in the slurry, generating mineral salts with low solubility, achieving chemical mineralization of heavy metals. Ion exchangers adsorb ammonium ions in the slurry through their porous structure. All these processes are completed before the addition of cementitious materials, eliminating the chemical inhibition of the hydration reaction by organic matter and impurity ions.

[0008] Secondly, during the second stage of mixing and solidification, the cementitious framework is constructed and long-term alkalinity is controlled. Upon addition of the composite cementitious and activating system, the alkaline activator rapidly increases the system's pH, disrupting the glassy network structure of the finely ground blast furnace slag powder, causing it to depolymerize and release active calcium, silicon, and aluminum components. The sulfate ions provided by the sulfate activator react with the dissolved aluminum phase and calcium ions, rapidly generating needle-like ettringite crystals. A large number of ettringite crystals act as micro-reinforcing materials, intertwining with the hydrated calcium silicate gel generated by the cementitious material to form a dense solidified framework.

[0009] Third, a long-term pH buffering mechanism is established. Long-term pH buffers (such as lightly calcined magnesium oxide) do not participate in the early rapid hydration of the system, but rather hydrate at a slower rate to form magnesium hydroxide. During the long-term service of the solidified body, when the alkalinity of the internal pore fluid decreases due to external acidic erosion or its own carbonization, the dissolution equilibrium of magnesium hydroxide shifts, continuously releasing hydroxide ions and locking the internal pH value of the solidified body within a moderately alkaline range. This chemical buffering mechanism prevents the acidic decomposition of hydrated calcium silicate gel and heavy metal precipitates, thereby ensuring the long-term mechanical properties and environmental safety of the composite foundation.

[0010] Preferably, the oxidant is sodium persulfate, the heavy metal stabilizer is anhydrous disodium hydrogen phosphate, and the ion exchanger is natural clinoptilolite powder.

[0011] By adopting the above technical solutions, the sulfate radicals provided by sodium persulfate have targeted oxidizing ability against recalcitrant organic matter; the phosphate precipitate formed by anhydrous disodium hydrogen phosphate and heavy metals has extremely high chemical stability over a wide pH range; natural clinoptilolite powder not only plays an ion exchange role, but also serves as a micron-sized active filler to fill the pores of the slurry and improve its density.

[0012] Preferably, the composite pretreatment agent is made from raw materials comprising the following parts by weight: 5-30 parts sodium persulfate; 2-25 parts anhydrous disodium hydrogen phosphate; and 10-50 parts natural clinoptilolite powder.

[0013] By adopting the above technical solution, this formulation range achieves synergistic effects of each component. The amount of sodium persulfate is sufficient to oxidize the organic layer without causing excessive sulfate residue; the proportion of disodium hydrogen phosphate ensures redundancy in capturing heavy metals with fluctuating concentrations; and the amount of zeolite powder balances the adsorption capacity and the rheological properties of the slurry.

[0014] Preferably, the cementing material is a combination of ordinary silicate cement and finely ground blast furnace slag powder, the sulfate activator is desulfurized gypsum, the alkaline activator is calcium hydroxide, and the long-lasting pH buffer is lightly calcined magnesium oxide.

[0015] By adopting the above technical solution, a five-element cementitious system consisting of cement, slag, gypsum, calcium, and magnesium was constructed. Ordinary silicate cement provides basic strength; slag powder provides later-stage strength and reduces heat of hydration under the dual activation of calcium hydroxide and desulfurized gypsum; lightly calcined magnesium oxide independently undertakes the function of maintaining long-term alkalinity. Each component has a clear division of labor and does not interfere with each other.

[0016] Preferably, the composite cementing and activating system is made from raw materials comprising the following parts by weight: 50-150 parts of ordinary silicate cement; 50-150 parts of finely ground blast furnace slag powder; 10-40 parts of desulfurized gypsum; 5-20 parts of calcium hydroxide; and 5-20 parts of lightly calcined magnesium oxide.

[0017] By adopting the above technical solution, the mass ratio is optimized to achieve the desired ratio of ettringite to CSH gel, ensuring the compactness of the solidified structure. In particular, the amount of lightly calcined magnesium oxide is controlled at 5-20 parts, which provides sufficient alkalinity reserve while avoiding the problem of poor volume stability caused by excessive hydration expansion.

[0018] Preferably, the amount of composite pretreatment agent is 1.7-10.5% of the mass of sludge and slag; the amount of composite cementing and activating system is 12.0-38.0% of the mass of sludge and slag.

[0019] By adopting the above technical solution, this process dynamically adjusts the dosage of additives within the above range according to the moisture content and pollution level of sludge and slag, which can control the water-solid ratio of the treated slurry within a suitable range, ensuring that the fluidity of the homogeneous slurry meets the requirements for construction pumping, while ensuring the mechanical strength index after solidification.

[0020] Preferably, the stirring speed in the first stage is 30-60 rpm, and the time is 15-30 minutes.

[0021] By adopting the above technical solution, the stirring parameters provide sufficient shear force to disperse the pretreatment agent into the interior of the sludge micro-agglomerates, and ensure the kinetic time required for the oxidation and precipitation reactions, thus ensuring the complete reaction.

[0022] Preferably, the stirring speed in the second stage is 40-80 rpm, and the time is 20-40 minutes.

[0023] By adopting the above technical solutions, increasing the rotation speed and extending the stirring time helps to fully mix the cementitious material with the pretreated slurry, prevents local enrichment of cementitious material, and ensures the consistency of the curing quality of the homogeneous slurry.

[0024] Preferably, the curing conditions are a temperature of 18-22℃ and a relative humidity of 95-99%.

[0025] By adopting the above technical solutions, the high-humidity curing environment prevents plastic shrinkage cracks caused by excessive evaporation of moisture on the slurry surface, and the suitable temperature conditions promote the healthy growth of ettringite crystals.

[0026] Preferably, the initial moisture content of the silt and slag is 65-85%.

[0027] By adopting the above technical solution, the process is suitable for silt and slag with high fluidity and soft plasticity, and does not require costly mechanical dewatering pretreatment, thus realizing the direct in-situ utilization of waste soil with high moisture content.

[0028] This invention provides a green integrated construction technology for composite foundations that utilizes silt and slag resources. It has the following beneficial effects: 1. This invention employs a time-separation process, utilizing the oxidant in the composite pretreatment agent in the first stage to decompose the organic inhibitors in the sludge, thereby eliminating their negative impact on subsequent hydration reactions and obtaining a more compact solidified body, thus improving the mechanical strength of the composite foundation.

[0029] 2. In the first stage, the heavy metal stabilizer in the composite pretreatment agent reacts with the heavy metal ions in the sludge to pre-convert them into phosphate minerals with high chemical stability. In the second stage, the minerals are physically encapsulated by the hydration products of the cementitious material. This achieves a dual effect of chemical fixation and physical locking of heavy metals, which greatly reduces the risk of long-term leaching of pollutants and improves the environmental safety of the composite foundation.

[0030] 3. This invention adds lightly calcined magnesium oxide as a long-lasting pH buffer to the composite cementing and activation system. By utilizing its slow and continuous hydration reaction, the pH value inside the solidified body is kept stable at a medium-to-strong alkaline platform for a long time. This effectively inhibits the erosion of the cemented structure by external acidic media and maintains an environment that inhibits heavy metal ions, thereby improving the long-term durability and service stability of the composite foundation. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] In the claims and specific embodiments of this invention, "parts by weight" is a unit expressing the relative mass ratio between components. Without departing from the spirit of this invention, parts by weight can correspond to any actual unit of mass, such as grams (g), kilograms (kg), or tons (t). For ease of description, grams (g) are chosen as the unit of mass in the following embodiments of this invention, wherein 1 part by weight corresponds to 1 gram (g), but the scope of protection of this invention is not limited to this specific weight class.

[0033] Preparation Examples 1-6: Preparation Example 1: This preparation example provides a composite pretreatment agent (System I), including the following steps: 5.0g sodium persulfate, 2.0g anhydrous disodium hydrogen phosphate and 10.0g natural clinoptilolite powder were placed in a V-type mixer and mixed at 25 rpm for 15 minutes at 20℃ and 50% relative humidity to obtain a uniform powdered composite pretreatment agent, which was then sealed and stored for later use.

[0034] Preparation Example 2: This preparation example provides a composite pretreatment agent (System I), including the following steps: 17.5g sodium persulfate, 13.5g anhydrous disodium hydrogen phosphate and 30.0g natural clinoptilolite powder were placed in a V-type mixer and mixed at 30 rpm for 20 minutes at 25℃ and 40% relative humidity to obtain a uniform powdered composite pretreatment agent, which was then sealed and stored for later use.

[0035] Preparation Example 3: This preparation example provides a composite pretreatment agent (System I), including the following steps: 30.0g sodium persulfate, 25.0g anhydrous disodium hydrogen phosphate and 50.0g natural clinoptilolite powder were placed in a V-type mixer and mixed at 35 rpm for 25 minutes at 30℃ and 30% relative humidity to obtain a uniform powdered composite pretreatment agent, which was then sealed and stored for later use.

[0036] Preparation Example 4: This preparation example provides a composite gelling and activation system (System II), including the following steps: 50.0g of ordinary silicate cement, 50.0g of finely ground blast furnace slag powder, 10.0g of desulfurized gypsum, 5.0g of calcium hydroxide and 5.0g of lightly calcined magnesium oxide were placed in a V-type mixer and mixed at 25 rpm for 25 minutes at a temperature of 20℃ and a relative humidity of 50% to obtain a uniform powdered composite cementitious and activating system, which was then sealed and stored for later use.

[0037] Preparation Example 5: This preparation example provides a composite gelling and activation system (System II), including the following steps: 100.0g of ordinary silicate cement, 100.0g of finely ground blast furnace slag powder, 25.0g of desulfurized gypsum, 12.5g of calcium hydroxide and 12.5g of lightly calcined magnesium oxide were placed in a V-type mixer and mixed at 30 rpm for 30 minutes at a temperature of 25℃ and a relative humidity of 40% to obtain a uniform powdered composite cementitious and activating system, which was then sealed and stored for later use.

[0038] Preparation Example 6: This preparation example provides a composite gelling and activation system (System II), including the following steps: 150.0g of ordinary silicate cement, 150.0g of finely ground blast furnace slag powder, 40.0g of desulfurized gypsum, 20.0g of calcium hydroxide and 20.0g of lightly calcined magnesium oxide were placed in a V-type mixer and mixed at 35 rpm for 35 minutes at a temperature of 30℃ and a relative humidity of 30% to obtain a uniform powdered composite cementitious and activating system, which was then sealed and stored for later use.

[0039] Examples 1-3: Example 1: This embodiment provides a green composite foundation integrated construction technology for the resource utilization of silt and slag, including the following steps: Take 1000g of silt and slag with an initial moisture content of 65%, place it in a mixing container, add 17.0g of the composite pretreatment agent prepared in Preparation Example 1 at an ambient temperature of 20℃, start the mixing equipment, and carry out the first stage of mixing at a speed of 30rpm for 15 minutes.

[0040] After the first stage of stirring is completed, 120.0 g of the composite gelling and activating system prepared in Preparation Example 4 is immediately added to the container, the stirring speed is increased to 40 rpm, and the second stage of stirring is carried out. Stirring is continued for 20 minutes to obtain a homogeneous slurry for constructing a composite foundation.

[0041] Stop stirring and allow the homogeneous slurry to solidify at a temperature of 18°C ​​and a relative humidity of 95% to form a solidified composite foundation.

[0042] Example 2: This embodiment provides a green composite foundation integrated construction technology for the resource utilization of silt and slag, including the following steps: Take 1000g of silt and slag with an initial moisture content of 75%, place it in a mixing container, add 61.0g of the composite pretreatment agent prepared in Preparation Example 2 at an ambient temperature of 25℃, start the mixing equipment, and carry out the first stage of mixing at a speed of 45rpm for 22 minutes.

[0043] After the first stage of stirring is completed, 250.0 g of the composite gelling and activating system prepared in Preparation Example 5 is immediately added to the container, the stirring speed is increased to 60 rpm, and the second stage of stirring is carried out. Stirring is continued for 30 minutes to obtain a homogeneous slurry for constructing a composite foundation.

[0044] Stop stirring and allow the homogeneous slurry to solidify at a temperature of 20°C and a relative humidity of 98% to form a solidified composite foundation.

[0045] Example 3: This embodiment provides a green composite foundation integrated construction technology for the resource utilization of silt and slag, including the following steps: Take 1000g of silt and slag with an initial moisture content of 85%, place it in a mixing container, add 105.0g of the composite pretreatment agent prepared in Preparation Example 3 at an ambient temperature of 30℃, start the mixing equipment, and carry out the first stage of mixing at a speed of 60rpm for 30 minutes.

[0046] After the first stage of stirring is completed, 380.0 g of the composite gelling and activating system prepared in Preparation Example 6 is immediately added to the container, the stirring speed is increased to 80 rpm, and the second stage of stirring is carried out. Stirring is continued for 40 minutes to obtain a homogeneous slurry for constructing a composite foundation.

[0047] Stop stirring and allow the homogeneous slurry to solidify at a temperature of 22°C and a relative humidity of 99% to form a solidified composite foundation.

[0048] Comparative Examples 1-6: Comparative Example 1: Compared with Example 2, the difference is that: a traditional cement-based curing method is used, the composite pretreatment agent prepared in Example 2 is not added, and the composite cementitious and activating system consists only of 100.0g of ordinary Portland cement and 100.0g of finely ground blast furnace slag powder, and is added and mixed in one go, while the rest are the same.

[0049] Comparative Example 2: Compared with Example 2, the difference is that the time-controlled process of phased feeding is not adopted. Instead, at the beginning of the process, the composite pretreatment agent prepared in Example 2 and the composite cementing and activating system prepared in Example 5 are all added to the sludge and slag at one time and stirred continuously at 60 rpm for 30 minutes. The rest are the same.

[0050] Comparative Example 3: The difference from Example 2 is that the composite pretreatment agent used does not contain sodium persulfate, but all other aspects are the same.

[0051] Comparative Example 4: The difference from Example 2 is that the composite pretreatment agent used does not contain anhydrous disodium hydrogen phosphate, but all other aspects are the same.

[0052] Comparative Example 5: The difference from Example 2 is that the composite pretreatment agent used does not contain natural clinoptilolite powder, but all other aspects are the same.

[0053] Comparative Example 6: Compared with Example 2, the difference is that the composite gelling and activating system used does not contain lightly calcined magnesium oxide, and it is replaced with an equal mass of calcium hydroxide, while the rest are the same.

[0054] Test Example 1-3: Test Example 1: Step-by-Step Verification Test of Core Mechanism This test case is used to verify the effectiveness of the first-stage purification and reconstruction mechanism and the second-stage pH long-term locking mechanism in the time-sequential separation chemical reaction pathway adopted in this scheme.

[0055] Test steps: The slurry obtained after the first stage of stirring according to the process in Example 2, and before the addition of the composite gelling and activation system, was taken as Group A sample. Untreated raw sludge and slag were taken as Group B sample. Group A and Group B samples were placed in centrifuge tubes and centrifuged at 4000 r / min for 15 minutes. The supernatant was collected and filtered using a 0.45 μm filter membrane. The chemical oxygen demand (COD) concentration of the filtrate was determined according to GB11914-89 standard. The concentrations of dissolved lead (Pb) and cadmium (Cd) ions in the filtrate were determined by inductively coupled plasma mass spectrometry (ICP-MS) according to GB / T17138-1997 standard. The concentrations of ammonium ions (as NH4+) in the filtrate were determined according to GB7479-87 standard. + The concentration of (-N).

[0056] In addition, cured bodies prepared according to the processes of Example 2 and Comparative Example 6 were taken and cured under standard conditions for 7 days, 28 days, and 90 days, respectively. The cured bodies at each age were crushed, and particles with a diameter less than 2.5 mm were obtained by sieving. The crushed particles were accurately weighed and added to deionized water at a solid-liquid ratio of 1:10. After sealing, the mixture was shaken at 120 rpm for 18 hours on a horizontal shaker. After shaking, the mixture was allowed to stand for 2 hours to clarify, and the supernatant was collected. The pH value of the supernatant for each group was measured at a constant temperature of 25°C using a three-point calibrated pH meter.

[0057] Test data: Table 1. Verification data of the first phase of purification effect

[0058] Table 2. Verification data on pH long-term lock-in effect Conclusion Analysis: Table 1 shows that, compared with the original sludge, the supernatant of the slurry treated in the first stage of this scheme showed a reduction of 87.1% in chemical oxygen demand, 98.6% in dissolved lead ion concentration, 99.1% in dissolved cadmium ion concentration, and 94.0% in ammonium ion concentration. This data indicates that the addition of the composite pretreatment agent decomposed organic matter in the aqueous phase through oxidation, fixed heavy metal ions through precipitation, and captured ammonium ions through ion exchange, thus purifying the chemical microenvironment of the sludge before the gelation reaction began.

[0059] Table 2 shows that the pH value of the leachate from the cured body of Example 2 was 12.61 at the beginning of curing, decreased with the extension of curing time, and stabilized at 10.82 after 90 days. In Comparative Example 6, which lacked lightly calcined magnesium oxide, the pH value of the leachate from the cured body continuously decreased from 12.73 at the beginning to 9.17 after 90 days. This data comparison indicates that the lightly calcined magnesium oxide in the composite gelling and activating system, acting as a slow-acting alkali source, provides an alkalinity reserve through continuous hydration reaction after the calcium hydroxide is consumed, maintaining the system pH value within the medium-to-strong alkaline range.

[0060] Based on the above data, the time-sequential separation chemical reaction pathway of this scheme is confirmed. The first-stage chemical pretreatment provides reaction conditions with low organic matter, low heavy metal ions, and low interfering ions for the second-stage gelation reaction. On this basis, the composite gelation and activation system in the second stage not only completes hydration gelation, but its component design also regulates the long-term chemical environment of the solidified body.

[0061] Test Example 2: Comprehensive Comparison Test of Key Engineering Performance Test steps: According to GB / T50123 standard, the homogeneous slurries prepared in Examples 1-3 and Comparative Examples 1-6 were made into standard specimens and cured under standard conditions. The unconfined compressive strength (UCS) of the specimens cured for 3 days, 7 days, and 28 days was tested using a universal testing machine. In addition, solidified bodies prepared in Examples 1-3 and Comparative Examples 1, 2, and 4 and cured for 28 days were also taken. The solidified bodies were crushed and passed through a 2.5 mm square-hole sieve. Leaching experiments were performed on the crushed samples according to HJ / T299-2007 standard. The concentrations of lead (Pb) and cadmium (Cd) in the leachate were determined using inductively coupled plasma mass spectrometry.

[0062] Test data: Table 3. Comparison of Unconfined Compressive Strength and Leaching Toxicity

[0063] Conclusion Analysis: Table 3 shows the unconfined compressive strength data, indicating that the cured bodies of Examples 1-3 exhibited higher strength at all ages than all comparative examples. Example 2 showed a 508% increase in 28-day strength compared to Comparative Example 1. Example 2 also showed a 261% increase in 28-day strength compared to Comparative Example 2. This data demonstrates that the phased feeding timing control process improved the final strength of the cured body by avoiding ineffective reactions between components. The strength improvement of Example 2 compared to Comparative Example 3 (without oxidant) and Comparative Example 4 (without phosphate) indicates that the oxidative decomposition of organic matter to relieve hydration inhibition, and the induction of hydrated calcium silicate gel nucleation by phosphate mineral particles, both contribute to improving the mechanical properties of the cured body.

[0064] Leaching toxicity data showed that the heavy metal leaching concentrations of the cured bodies in Examples 1-3 were significantly lower than those in the comparative examples. Compared to Comparative Examples 1 and 4, the lead concentration in the leachate of Example 2 decreased by 99.1% and 98.8%, respectively. Data from Comparative Example 4 indicated that the lack of a pre-mineralization step with disodium hydrogen phosphate meant that even with subsequent cement hydration, effective chemical fixation of heavy metals was impossible. The comparison between Example 2 and Comparative Example 2 also demonstrated that a time-separated reaction pathway plays a crucial role in achieving stable solidification of heavy metals.

[0065] The aforementioned mechanical properties and environmental stability data corroborate each other. The solidified structure formed through chemical pretreatment in this scheme is not only the source of high mechanical strength, but also the basis for physically encapsulating and chemically fixing heavy metals.

[0066] Test Example 3: Comparative Test of Long-Term Durability (Resistance to Chemical Erosion) Test steps: Standard specimens prepared and cured for 28 days were taken from Examples 2, 1, and 6. The initial mass of each group of specimens was measured, and the initial unconfined compressive strength of the un-soaked parallel specimens was tested. The remaining samples were completely immersed in a sulfuric acid solution with a pH of 4.0 for 28 days. After immersion, the samples were removed, rinsed with deionized water, and then dried in an oven at 60°C to constant weight. The final mass was measured. The unconfined compressive strength of the dried samples was then tested. The mass loss rate is calculated as (initial mass - final mass) / initial mass × 100%; the strength retention factor is calculated as follows: calculate.

[0067] Experimental data: Table 4. Long-term durability test data

[0068] Conclusion Analysis: The data in Table 4 show that after being eroded by the acidic solution, the mass loss rate of the cured body in Example 2 was 2.18%, and the strength retention coefficient was 89.4%. The mass loss rate of the cured body in Comparative Example 1 reached 15.72%, and the strength retention coefficient was only 38.6%. The mass loss rate and strength retention coefficient of the cured body in Comparative Example 6 were 9.53% and 61.7%, respectively.

[0069] The low mass loss rate and high strength retention coefficient of the cured body in Example 2 are attributed to the stability of its internal structure and chemical environment. This method utilizes a dense cured body structure formed through chemical pretreatment and induced nucleation, which hinders the intrusion of acidic solutions. Simultaneously, the pH buffering capacity provided by the continuous hydration of lightly calcined magnesium oxide maintains the alkaline microenvironment within the cured body, inhibiting the acidic decomposition of gel phases such as hydrated calcium silicate gel.

[0070] Comparative Example 1, using traditional cement curing, resulted in a high porosity in its cured structure. The internal alkaline substances were easily and rapidly neutralized by acidic solutions, leading to the disintegration of the cementitious structure. While Comparative Example 6 formed a dense cured structure, the lack of a long-lasting alkaline source like lightly calcined magnesium oxide meant its internal alkaline environment could not remain stable under acidic attack, causing continuous decomposition of the cementitious phase and a decline in mechanical properties. This data comparison demonstrates that the dense physical structure and stable internal chemical environment formed by this method together constitute the foundation for the high durability of the cured body.

Claims

1. A green composite foundation integrated construction technology for the resource utilization of silt and slag, characterized in that, Includes the following steps: The composite pretreatment agent is added to the sludge and slag for the first stage of mixing to obtain the pretreated slurry. The composite pretreatment agent is made of an oxidant, a heavy metal stabilizer and an ion exchanger. A composite cementitious and activating system is added to the pretreated slurry, and a second stage of stirring is carried out to obtain a homogeneous slurry for forming a composite foundation. The composite cementitious and activating system is made of cementitious materials, sulfate activators, alkaline activators and long-lasting pH buffers. The homogeneous slurry is solidified to form a composite foundation.

2. The integrated construction technology for green composite foundation utilization of silt and slag as described in claim 1, characterized in that, The oxidant is sodium persulfate, the heavy metal stabilizer is anhydrous disodium hydrogen phosphate, and the ion exchanger is natural clinoptilolite powder.

3. The integrated construction technology for green composite foundation utilization of silt and slag as described in claim 2, characterized in that, The composite pretreatment agent is made from raw materials comprising the following parts by weight: 5-30 parts of sodium persulfate; 2-25 parts of anhydrous disodium hydrogen phosphate; 10-50 parts of natural clinoptilolite powder.

4. The integrated construction technology for green composite foundation utilization of silt and slag as described in claim 1, characterized in that, The cementing material is a combination of ordinary silicate cement and finely ground blast furnace slag powder, the sulfate activator is desulfurized gypsum, the alkaline activator is calcium hydroxide, and the long-lasting pH buffer is lightly calcined magnesium oxide.

5. The integrated construction technology for green composite foundation utilization of silt and slag as described in claim 4, characterized in that, The composite gelling and activating system is made from raw materials comprising the following parts by weight: 50-150 parts of the ordinary silicate cement; 50-150 parts of the finely ground blast furnace slag powder; 10-40 parts of the desulfurized gypsum; 5-20 parts of the calcium hydroxide; The lightly calcined magnesium oxide is 5-20 parts.

6. The integrated construction technology for green composite foundation utilization of silt and slag as described in claim 1, characterized in that, The amount of the composite pretreatment agent is 1.7-10.5% of the mass of the sludge and slag; the amount of the composite cementing and activating system is 12.0-38.0% of the mass of the sludge and slag.

7. The integrated construction technology for green composite foundation utilization of silt and slag as described in claim 1, characterized in that, The stirring speed in the first stage is 30-60 rpm, and the time is 15-30 minutes.

8. The integrated construction technology for green composite foundation utilization of silt and slag as described in claim 1, characterized in that, The stirring speed in the second stage is 40-80 rpm, and the time is 20-40 minutes.

9. The integrated construction technology for green composite foundation utilization of silt and slag as described in claim 1, characterized in that, The curing conditions are a temperature of 18-22℃ and a relative humidity of 95-99%.

10. The integrated construction technology for green composite foundation utilization of silt and slag as described in claim 1, characterized in that, The initial moisture content of the silt and slag is 65-85%.

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