High-performance light soil using finely ground coral sand and method for preparing same
By synergistically reacting finely ground coral sand with seawater to generate reinforcing phases such as hydrated calcium silicate, the problems of bubble stability and mechanical properties of coral sand in the preparation of lightweight soil were solved, realizing the preparation of high-performance lightweight soil suitable for island and reef engineering.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SOUTHEAST UNIV
- Filing Date
- 2026-04-30
- Publication Date
- 2026-06-09
AI Technical Summary
Existing lightweight soil technology relies on imported siliceous sand materials, which is uneconomical and difficult to supply continuously. During the mixing process, the original coral sand is prone to puncturing air bubbles, resulting in a decrease in porosity and making it difficult to prepare lightweight soil with uniform pores and controllable density.
Finely ground coral sand is produced by grinding it to the micron level using methods such as ball milling. Combined with seawater and additives, it forms reinforcing phases such as hydrated calcium silicate, generating a composite structure of "pores-cement shell-micro aggregates". The calcium and magnesium components of the coral sand react synergistically with cement hydration products to form a chemically bonded reinforcing layer.
It has achieved high-performance lightweight soil with good fluidity and strong self-compacting properties, which reduces engineering costs and improves the mechanical properties and durability of lightweight soil. It is suitable for soft soil treatment and load reduction backfilling in island and reef engineering.
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Figure CN122167108A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of marine infrastructure engineering materials technology, and in particular to a high-performance lightweight soil with good fluidity, strong self-compacting properties, and resistance to cracking, made from finely ground coral sand, and its preparation method. Background Technology
[0002] The construction of deep-sea island and reef projects has long faced the dilemma of scarce soil and rock materials and high transportation costs. In projects such as soft soil foundation treatment, pipeline backfilling, and bridge abutment load reduction, lightweight soil is often required as backfill material to reduce the risk of settlement or even instability of soft soil foundations. Existing lightweight soil technologies mostly use ordinary silicate cement, siliceous fine sand, and foaming agents to introduce air through physical means to form uniform pores, thereby reducing density. However, this type of technology relies on siliceous sand as aggregate, which needs to be transported from the mainland over long distances, making it uneconomical and difficult to supply continuously, and failing to meet the fundamental requirement of local material sourcing for island and reef projects.
[0003] Coral sand, the most abundant native resource on islands and reefs, is primarily composed of calcium carbonate. It possesses natural high calcium and magnesium content and high reactivity, is widely available, and has low extraction costs, making it theoretically an ideal alternative material. Its porous structure allows for the continuous release of calcium and magnesium ions, meaning that coral sand itself is a potential reactive substance, not merely a filler to replace river sand. However, when virgin coral sand is used directly as aggregate, its porous surface and sharp edges easily puncture air bubbles during mixing, leading to a significant decrease in porosity. Simultaneously, its high water absorption rate disturbs foam stability, making it difficult to prepare lightweight soil with uniform pores and controllable density. Furthermore, crushing index tests show that the crushing index of virgin coral sand is much higher than that of standard sand. If used directly in lightweight soil, the fine particles after crushing will further alter the rheological properties of the slurry, exacerbating bubble coalescence or escape. Therefore, overcoming the inherent mechanical defects of coral sand and utilizing its chemical composition advantages has become a key technical challenge in the preparation of locally produced lightweight soil for islands and reefs. Summary of the Invention
[0004] Purpose of the invention: The purpose of this invention is to provide a high-performance lightweight soil with good fluidity, strong self-compacting properties, and resistance to cracking, which is made from finely ground coral sand, and its preparation method.
[0005] Technical solution: The high-performance lightweight soil using finely ground coral sand described in this invention comprises the following components in parts by weight: 100-400 parts finely ground coral sand, 10-50 parts cement, 20-100 parts seawater, and 0-5 parts additives.
[0006] The finely ground coral sand is a micron-sized powder obtained by crushing and grinding coral sand, with a particle size distribution of 10-300μm and a specific surface area of 400-600 m² / kg.
[0007] The cement content is calculated as 10%-20% of the mass of finely ground coral sand;
[0008] The admixtures include a water-reducing agent and a stabilizer. The water-reducing agent is one or more of a polycarboxylate-based high-performance water-reducing agent or a naphthalene-based water-reducing agent, with a water reduction rate of not less than 25%. The stabilizer is one or more of hydroxypropyl methylcellulose ether or modified starch ether.
[0009] Furthermore, the cement is ordinary Portland cement.
[0010] Furthermore, the seawater is either natural seawater or artificially prepared seawater, with a salinity range of 3.0%-3.5%; the seawater contains... , , , , It participates in the cement hydration reaction, promoting the dissolution of calcium and magnesium components on the surface of coral sand particles and the generation of secondary hydration products.
[0011] Furthermore, the coral sand possesses natural alkalinity and continuous calcium and magnesium release properties; the coral sand utilizes the generated hydrated calcium silicate (CSH) gel to adsorb and fix chloride ions.
[0012] Furthermore, when using seawater for mixing, an organic retarder accounting for 0.5%-1.5% of the total mass of the cementitious material is added to control the setting time.
[0013] The method for preparing high-performance lightweight soil using finely ground coral sand according to the present invention includes the following steps:
[0014] S1. Coral sand grinding: Coral sand is ground to the micron level using ball milling, electromagnetic vibration, and microphase reconstruction methods. By precisely controlling the grinding fineness, the synergistic regulation of particle breakage and bubble stability is achieved.
[0015] S2. Raw material preparation and pretreatment: Weigh out 100-400 parts of finely ground coral sand, 10-50 parts of cement, 20-100 parts of seawater and 0-5 parts of additives by weight for later use.
[0016] S3. Dry material premixing and activation: Add finely ground coral sand and cement into the mixing device, first mix at a low speed of 60-100 r / min for 1-2 min, then increase the speed to 150-200 r / min and mix for 30-60 s to fully mix the powder and produce a mechanical activation effect, thus obtaining mixed dry material;
[0017] S4. Preparation of air bubble clusters: Air is used for foaming, and the CaO component in the coral sand generates a calcium carbonate reinforcing phase during the curing process;
[0018] S5. Mixing and Stirring: First Stage: Add 40%-60% of the total seawater to the dry mixture, and add 2-45 parts of air bubble clusters to the slurry and stir at 80-120 r / min for 1-2 minutes to initially wet the powder surface and form a dust-free wet mixture; Second Stage: Add the remaining seawater and additives after pre-mixing them evenly, and simultaneously increase the stirring speed to 200-300 r / min and continue stirring for 2-3 minutes. Utilize the polyvalent cations in the seawater to undergo ion exchange reactions with the surface of the coral sand particles to form a highly fluid, sediment-free, uniform slurry; Third Stage: Reduce the speed to 50-80 r / min and stir for 30-60 seconds to remove large air bubbles from the slurry and test the fluidity. The initial fluidity is controlled at 180-220 mm; The density and strength of the lightweight soil are independently controlled by adjusting the cement dosage, the fineness of the ground coral sand, and the amount of air bubbles.
[0019] S6. Casting and Curing: Cast into the mold, cover the surface with plastic film after molding to prevent moisture evaporation, and place in a standard curing room for curing. The curing temperature is 20±2℃, the relative humidity is ≥95%, and the curing time is 7-28 days; or natural curing can be adopted according to the project conditions. During the curing period, seawater or fresh water is sprayed regularly to keep the soil moist. The total curing time is not less than 28 days.
[0020] Furthermore, in step S1, the coral sand is ground to 10-300 μm.
[0021] Further, step S4 specifically includes: diluting the foaming agent by a dilution ratio of 10-30 times, adding a foam stabilizer and a thickener, and mixing them evenly to obtain a foaming liquid; drawing the foaming liquid into the liquid pipeline of the foaming machine, while simultaneously starting the air compressor, adjusting the air inlet valve to stabilize the compressed air pressure at 200-600 kPa, adjusting the water pump speed ratio of the foaming machine to 20-100, corresponding to a foaming liquid flow rate of 1.0 L / min-5 L / min, controlling the gas-liquid ratio to approximately 1:10 to 1:30, and after the pressure of the foaming device stabilizes and the foaming rate becomes uniform, opening the foam outlet valve to release fine and stable air foam, which is then collected in a container for later use.
[0022] Furthermore, when using seawater for curing in step S5, seawater is sprayed once every 3 days, and the curing temperature is not lower than 10℃.
[0023] Furthermore, in step S6, during the maintenance process, active ions in seawater continuously participate in the formation of the composite cementitious phase of hydrated calcium silicate (CSH), hydrated calcium aluminate (CAH), and chloroaluminate. Chloride ions are adsorbed by the CSH gel or fixed by the formation of Friedel salt, forming a dense microstructure, ultimately resulting in coral sand-based high-performance lightweight soil.
[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:
[0025] (1) In view of the problem that traditional cement lightweight soil has slow early strength development under standard curing conditions, this invention combines the chemical composition characteristics of coral sand with a CaO content of up to 84% or more. By grinding the coral sand, the specific surface area is increased and the surface activity of the particles is stimulated, so that it can react more fully with the cement hydration products during the standard curing process to generate reinforcing phases such as hydrated calcium silicate. Furthermore, these reinforcing phases can directionally wrap the bubble walls to form a chemically bonded reinforcing shell. At the same time, by optimizing the cement content, water-cement ratio and bubble content, the synergistic enhancement of hydration reaction and micro-filling is achieved on the basis of ensuring good fluidity of the slurry, effectively improving the mechanical properties and durability of lightweight soil, and promoting the transformation of island and reef engineering construction towards green environmental protection and resource utilization.
[0026] (2) This invention uses finely ground coral sand to replace the soil material transported from outside the traditional lightweight soil. At the same time, it uses the rich calcium and magnesium components in the coral sand as the active source of the hydration reaction, realizing the use of local materials and the resource utilization of waste, reducing the energy consumption of mining and transportation of soil materials and lowering the engineering cost. In the preparation and curing process of lightweight soil, standard curing process is adopted to make the cement hydration products react with the calcium and magnesium components in the finely ground coral sand to generate reinforcing phases such as hydrated calcium silicate. This not only realizes the resource utilization of coral sand, but also provides a new way to reduce engineering costs.
[0027] (3) The finely ground coral sand used in this invention has a significantly increased specific surface area after mechanical grinding, and the surface activity of the particles is activated. The CaO it contains (content can reach more than 84%) reacts fully with cement hydration products during standard curing to generate cementitious substances such as hydrated calcium silicate. These cementitious substances preferentially accumulate at the bubble wall interface and undergo chemical bonding to form a composite wall structure of "pore-cement shell-micro aggregate". Compared with traditional lightweight soil that relies on the physical wrapping of bubbles by a single cement hydration product, it has higher bubble wall strength and smaller volume shrinkage, which reduces the cracking risk of lightweight soil and improves the long-term stability of engineering structures.
[0028] (4) The lightweight soil prepared by this invention has good fluidity and strong self-compacting properties. The cement content, water-cement ratio and air bubble content can be adjusted according to the engineering needs to achieve flexible control of density (0.6-1.2 g / cm³) and strength (0.8-2.5 MPa). It is especially suitable for projects that need to reduce additional load, such as soft soil replacement on islands and reefs, pipeline backfilling, and bridge abutment backfilling. It reduces additional stress and improves engineering safety and construction efficiency. By utilizing the natural alkalinity and continuous calcium and magnesium release characteristics of coral sand, a unique chemical buffer system is provided for the preparation of lightweight soil in the seawater environment. It realizes the complete replacement of freshwater mixing with seawater. It is entirely sourced from local island and reef resources and does not rely on externally transported materials. It has irreplaceable advantages in deep-sea engineering. Attached Figure Description
[0029] Figure 1 This is a flowchart illustrating the preparation process of the high-performance lightweight soil described in this invention. Detailed Implementation
[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings.
[0031] The high-performance lightweight soil of this invention uses coral sand as the main raw material and cement as the cementing material. By controlling the cement content, water-cement ratio, and foaming agent content, air is introduced physically to form uniform air bubbles. A standard curing process is then introduced while ensuring good fluidity of the slurry. During curing, cement hydration products react synergistically with the calcium and magnesium components in the finely ground coral sand to generate reinforcing phases such as hydrated calcium silicate. These cementing substances can tightly encapsulate the bubble walls, forming a stable "pore-cement shell-microaggregate" composite structure. The finely ground coral sand releases... , Ions chemically bond with CSH at the bubble wall interface, forming a stronger reinforcing layer than traditional physical encapsulation, significantly improving the mechanical stability of the bubble wall. This structure differs from the dense filling structure of traditional solidified soil; by optimizing the matching of porosity and wall strength, it achieves a synergy of low density and high strength, thus significantly reducing material density while ensuring sufficient mechanical properties and durability of the lightweight soil. Simultaneously, this invention precisely controls the fineness of the coral sand (e.g., specific surface area 400-600 m² / kg), transforming its particle strength from "fragile" to "stable micro-aggregate," eliminating the puncturing effect on bubbles and instead utilizing its surface activity to stabilize them. Furthermore, this invention, through optimized mix design, solves the problems of excessively high slurry viscosity, difficulty in uniform bubble dispersion, and casting difficulties under high cement content, achieving performance improvement of lightweight soil under standard curing conditions. It can be applied to engineering fields requiring reduced additional loads, such as soft soil replacement, pipeline backfilling, bridge abutment and abutment backfilling.
[0032] The high-performance lightweight soil using finely ground coral sand described in this invention comprises, by weight, 100-400 parts finely ground coral sand, 10-50 parts cement, 20-100 parts seawater, and 0-5 parts additives.
[0033] The finely ground coral sand is a micron-sized powder obtained by crushing and grinding coral sand, with a particle size distribution of 10-300μm and a specific surface area of 400-600m² / kg. Increased particle surface roughness enhances the exposure of active silicon and aluminum components. This fineness range ensures that the individual particle strength of the coral sand is sufficient to resist mechanical stress during stirring and maintenance, while the significantly increased specific surface area leads to a marked improvement in the dissolution rate of Ca²⁺ and Mg²⁺. This transforms the inherent weakness of raw coral sand—its fragility and ability to destroy air bubbles—into the advantage of stabilizing air bubbles and participating in hydration.
[0034] The cement is ordinary silicate cement, and the cement content is calculated as 10%-20% of the mass of finely ground coral sand.
[0035] The seawater is either natural seawater or artificially prepared seawater, with a salinity range of 3.0%-3.5%; the seawater contains... , , , , Plasma can participate in the cement hydration reaction, promoting the dissolution of calcium and magnesium components on the surface of coral sand particles and the generation of secondary hydration products. Simultaneously, the natural alkalinity (pH 7.0-8.5) and continuous calcium and magnesium release characteristics of coral sand provide a unique chemical buffer system for the preparation of lightweight soil in marine environments. This system can effectively suppress the interference of chloride ions on the stability of the foaming agent and utilize the generated CSH gel to adsorb and fix chloride ions, reducing their migration risk.
[0036] The admixtures include water-reducing agents and stabilizers; the water-reducing agent is one or more of polycarboxylate-based high-performance water-reducing agents or naphthalene-based water-reducing agents, with a water reduction rate of not less than 25%; the stabilizer is one or more of hydroxypropyl methylcellulose ether or modified starch ether, used to adjust the fluidity and anti-segregation properties of the slurry and ensure uniform distribution of air bubbles; when seawater is used for mixing, an organic retarder accounting for 0.5%-1.5% of the total mass of the cementitious material can also be added according to engineering needs to control the setting time, as well as an anti-chloride ion erosion agent to improve the durability of the solidified body.
[0037] like Figure 1 As shown, the present invention provides a method for preparing the aforementioned coral sand-based high-performance lightweight soil, comprising the following steps:
[0038] S1. Coral Sand Grinding: Coral sand is ground to the micron level (10-300μm) using methods such as ball milling, electromagnetic vibration, and microphase reconstruction. By precisely controlling the grinding fineness (e.g., specific surface area of 400-600 m² / kg, specific particle size distribution), the coral sand particles are transformed from "bubble killers" into "bubble stabilizers," achieving synergistic regulation of particle breakage and bubble stability.
[0039] S2. Raw material preparation and pretreatment: Weigh 100-400 parts of finely ground coral sand, 10-50 parts of cement, 20-100 parts of seawater and 0-5 parts of additives according to weight and set aside. Existing lightweight soil technology clearly states that "seawater is not suitable". However, this invention utilizes the natural alkalinity (pH 7.0-8.5) and continuous calcium and magnesium release characteristics of coral sand to provide a unique chemical buffer system for the preparation of lightweight soil in a seawater environment, realizing the complete replacement of freshwater mixing with seawater.
[0040] S3. Dry material premixing and activation: Add finely ground coral sand and cement into the mixing device, first mix at a low speed of 60-100 r / min for 1-2 min, then increase the speed to 150-200 r / min and mix for 30-60 s to fully mix the powder and produce a mechanical activation effect, thus obtaining mixed dry material;
[0041] S4. Preparation of Air Bubble Clusters: Air is used for foaming. The CaO component in the coral sand can generate a calcium carbonate reinforcing phase during the curing process. This "passive carbonization" effect is unique to coral sand and is not present in ordinary lightweight soil. Dilute the foaming agent 10-30 times, add the foam stabilizer and thickener, and mix evenly to obtain the foaming liquid. Draw the foaming liquid into the liquid pipeline of the foaming machine, and simultaneously start the air compressor. Adjust the air inlet valve to stabilize the compressed air pressure at 200-600 kPa, adjust the water pump speed ratio of the foaming machine to 20-100, corresponding to a foaming liquid flow rate of 1.0 L / min-5 L / min, and control the air-liquid ratio to approximately 1:10 to 1:30. After the pressure of the foaming device stabilizes and the foaming rate is uniform, open the foam outlet valve to release fine and stable air foam, collect it in a container, and set it aside for later use.
[0042] S5. Mixing and Stirring: First Stage: Add 40%-60% of the total seawater volume to the dry mixture, and add 2-45 parts of air bubble clusters to the slurry. Stir at 80-120 rpm for 1-2 minutes to initially wet the powder surface, forming a dust-free wet mixture. Second Stage: Add the remaining seawater and additives after pre-mixing them evenly. Simultaneously, increase the stirring speed to 200-300 rpm and continue stirring for 2-3 minutes. Utilize the polyvalent cations in the seawater to undergo ion exchange reactions with the coral sand particles, forming a highly fluid, sediment-free, uniform slurry. Third Stage: Reduce the stirring speed to 50-80 rpm and stir for 30-60 seconds to remove large air bubbles from the slurry. Check the fluidity, ensuring the initial fluidity is controlled at 180-220 mm (according to GB / T). (2419 test); When using seawater curing, spray seawater once every 3 days, and the curing temperature is not lower than 10℃, which can further improve the surface density and chloride ion penetration resistance of the solidified soil. By adjusting the cement content, the fineness of the ground coral sand and the amount of air bubbles, the density and strength of lightweight soil can be independently controlled, breaking the strong correlation constraint of "the lower the density, the lower the strength" in traditional lightweight soil.
[0043] S6. Casting and Curing: The material is cast into molds, and after molding, the surface is covered with a plastic film to prevent moisture evaporation. It is then placed in a standard curing room for curing at a temperature of 20±2℃ and a relative humidity of ≥95% for 7-28 days. Alternatively, natural curing can be used depending on the project conditions, with regular spraying of seawater or freshwater to maintain moisture during the curing period. The total curing time should not be less than 28 days. During the curing process, active ions in the seawater continuously participate in the formation of composite cementitious phases such as hydrated calcium silicate (CSH), hydrated calcium aluminate (CAH), and chloroaluminate. Chloride ions are adsorbed by the CSH gel or fixed by the formation of Friedel salt, significantly reducing chloride ion migration and forming a dense microstructure, ultimately resulting in coral sand-based high-performance lightweight soil.
[0044] This invention utilizes local island and reef materials (coral sand and seawater) in a fully resource-efficient manner, achieving on-site material sourcing and waste resource utilization, reducing energy consumption and carbon emissions from external transportation; it synergistically utilizes the calcium and magnesium components of coral sand to react with cement hydration products, introducing a "pore-cement shell-micro-aggregate" composite structure on the basis of traditional cement hydration, achieving chemical anchoring and reinforcement of the bubble walls; and by controlling the synergistic effect of finely ground coral sand and cement, it achieves high strength performance of lightweight soil at low density.
[0045] Example 1:
[0046] This embodiment uses the following steps:
[0047] S1: Raw material pretreatment: Natural coral sand is crushed and ground, with the particle size distribution controlled at 10-300μm, to obtain finely ground coral sand with a specific surface area of 450 m² / kg; PO 42.5 ordinary silicate cement is selected; natural seawater is coarsely filtered through a 300-mesh filter and left to stand for 24 hours for later use, with a salinity of 3.2%.
[0048] S2: Dry material premixing: Weigh out 200 parts by weight of finely ground coral sand and 30 parts by weight of cement. Put the finely ground coral sand and cement into the mixing device, first mix at a low speed of 80 r / min for 1.5 min, then increase to 180 r / min and mix for 45 s to complete the dry material premixing activation.
[0049] S3: Bubble Cluster Preparation: Dilute the foaming agent 20 times, add the foam stabilizer (hydroxypropyl methylcellulose ether), and mix thoroughly to obtain the foaming liquid. Use air foaming, adjust the air compressor pressure to 400 kPa, the water pump speed ratio to 50, and the air-liquid ratio to 1:20 to release fine and stable air foam, which is then collected in a container for later use.
[0050] S4: Stepwise addition of liquid and mixing:
[0051] First stage: Add 50% aged seawater (25 parts) to the mixed dry material and stir at 100 r / min for 1.5 min to form a wet mixture;
[0052] Second stage: Add the remaining seawater (25 parts), water-reducing agent (polycarboxylate, water reduction rate 28%, accounting for 0.8% of the total mass of cementitious materials), stabilizer (hydroxypropyl methylcellulose ether, accounting for 0.3% of the total mass of cementitious materials), and at the same time add 30 parts (volume parts) of air bubble group, and increase the speed to 250 r / min and stir for 2.5 min;
[0053] Third stage: Reduce the speed to 60 r / min and stir for 45 s to remove large air bubbles. The initial flowability was measured to be 200 mm.
[0054] S5: Pouring and curing: After pouring into the mold, cover with a film and place in a standard curing room at 20±2℃ and relative humidity ≥95% for 28 days to obtain finely ground coral sand-based high-performance lightweight soil.
[0055] Example 2:
[0056] This embodiment uses the following steps:
[0057] S1: Raw material pretreatment: Natural coral sand is crushed and ground, with the particle size distribution controlled at 10-300μm to obtain finely ground coral sand with a specific surface area of 500 m² / kg; PO 42.5 ordinary silicate cement is selected; seawater with a salinity of 3.5% is artificially prepared, coarsely filtered through a 300-mesh filter, and left to stand for 18 hours for later use.
[0058] S2: Dry material premixing: Weigh out 250 parts by weight of finely ground coral sand and 40 parts by weight of cement. Put the finely ground coral sand and cement into the mixing device, first mix at a low speed of 90 r / min for 2 minutes, then increase to 200 r / min and mix for 60 seconds to complete the dry material premixing activation.
[0059] S3: Bubble Cluster Preparation: Dilute the foaming agent 25 times, add the foam stabilizer (modified starch ether), and mix thoroughly to obtain the foaming liquid. Use air foaming, adjust the air compressor pressure to 450 kPa, the water pump speed ratio to 60, and the air-liquid ratio to 1:22 to release fine and stable air foam, which is then collected in a container for later use.
[0060] S4: Stepwise addition of liquid and mixing:
[0061] First stage: Add 50% aged seawater (32.5 parts) to the mixed dry material and stir at 110 r / min for 2 min to form a wet mixture;
[0062] Second stage: Add the remaining seawater (32.5 parts), water-reducing agent (naphthalene-based water-reducing agent, water reduction rate 26%, accounting for 1.0% of the total mass of cementitious materials), stabilizer (modified starch ether, accounting for 0.4% of the total mass of cementitious materials), and at the same time add 38 parts of air bubble group, and increase the speed to 280r / min and stir for 3min.
[0063] Third stage: Reduce the speed to 70 r / min and stir for 50 s to remove large air bubbles. The initial flowability was measured to be 210 mm.
[0064] S5: Pouring and curing: After pouring into the mold, cover with a film and place in a standard curing room at 20±2℃ and relative humidity ≥95% for 28 days to obtain finely ground coral sand-based high-performance lightweight soil.
[0065] Example 3:
[0066] This embodiment uses the following steps:
[0067] S1: Raw material pretreatment: Natural coral sand is crushed and ground, with the particle size distribution controlled at 10-300μm, to obtain finely ground coral sand with a specific surface area of 550 m² / kg; PO 52.5 ordinary silicate cement is selected; natural seawater is coarsely filtered through a 300-mesh filter, left to stand and age for 24 hours, and preheated to 25℃ when the ambient temperature is below 15℃ for use.
[0068] S2: Dry material premixing: Weigh out 300 parts by weight of finely ground coral sand and 50 parts by weight of cement. Put the finely ground coral sand and cement into the mixing device, first mix at a low speed of 100 r / min for 2 minutes, then increase to 200 r / min and mix for 60 seconds to complete the dry material premixing activation.
[0069] S3: Bubble Cluster Preparation: Dilute the foaming agent 30 times, add the foam stabilizer (hydroxypropyl methylcellulose ether and modified starch ether in a 1:1 ratio), and mix thoroughly to obtain the foaming liquid. Use air foaming, adjust the gas cylinder pressure to 400 kPa, the water pump speed ratio to 70, and the gas-liquid ratio to 1:25 to release fine and stable air foam, which is then collected in a container for later use.
[0070] S4: Stepwise addition of liquid and mixing:
[0071] First stage: Add 60% aged seawater (48 parts) to the mixed dry material and stir at 120 r / min for 2 min to form a wet mixture;
[0072] Second stage: Add the remaining seawater (32 parts), water-reducing agent (polycarboxylate, water reduction rate 30%, accounting for 1.2% of the total mass of cementitious materials), stabilizer (compound type, accounting for 0.5% of the total mass of cementitious materials), and at the same time add 45 parts of air bubble group, and stir at 300 r / min for 3 min.
[0073] Third stage: Reduce the speed to 80 r / min and stir for 60 s to remove large air bubbles. The initial flowability was measured to be 220 mm.
[0074] S5: Pouring and curing: After pouring into the mold, cover with a film and place in a standard curing room at 20±2℃ and relative humidity ≥95% for 28 days. During the curing period, spray seawater to keep it moist every 3 days to obtain finely ground coral sand-based high-performance lightweight soil.
Claims
1. A high-performance lightweight soil using finely ground coral sand, characterized in that, It includes the following components in parts by weight: 100-400 parts finely ground coral sand, 10-50 parts cement, 20-100 parts seawater, and 0-5 parts additives; The finely ground coral sand is a micron-sized powder obtained by crushing and grinding coral sand, with a particle size distribution of 10-300μm and a specific surface area of 400-600 m² / kg. The cement content is calculated as 10%-20% of the mass of finely ground coral sand; The admixtures include a water-reducing agent and a stabilizer. The water-reducing agent is one or more of a polycarboxylate-based high-performance water-reducing agent or a naphthalene-based water-reducing agent, with a water reduction rate of not less than 25%. The stabilizer is one or more of hydroxypropyl methylcellulose ether or modified starch ether.
2. The high-performance lightweight soil using finely ground coral sand according to claim 1, characterized in that, The cement is ordinary Portland cement.
3. The high-performance lightweight soil using finely ground coral sand according to claim 1, characterized in that, The seawater is either natural seawater or artificially prepared seawater, with a salinity range of 3.0%-3.5%; the seawater contains... , , , , It participates in the cement hydration reaction, promoting the dissolution of calcium and magnesium components on the surface of coral sand particles and the generation of secondary hydration products.
4. The high-performance lightweight soil using finely ground coral sand according to claim 1, characterized in that, The coral sand has natural alkalinity and continuous calcium and magnesium release properties; the coral sand utilizes the generated hydrated calcium silicate CSH gel to adsorb and fix chloride ions.
5. The high-performance lightweight soil using finely ground coral sand according to claim 1, characterized in that, When using seawater for mixing, add 0.5%-1.5% organic retarder by weight of the total cementitious material to control the setting time.
6. A method for preparing high-performance lightweight soil using finely ground coral sand, characterized in that, Includes the following steps: S1. Coral sand grinding: Coral sand is ground to the micron level using ball milling, electromagnetic vibration, and microphase reconstruction methods. By precisely controlling the grinding fineness, the synergistic regulation of particle breakage and bubble stability is achieved. S2. Raw material preparation and pretreatment: Weigh out 100-400 parts of finely ground coral sand, 10-50 parts of cement, 20-100 parts of seawater and 0-5 parts of additives by weight for later use. S3. Dry material premixing and activation: Add finely ground coral sand and cement into the mixing device, first mix at a low speed of 60-100 r / min for 1-2 min, then increase the speed to 150-200 r / min and mix for 30-60 s to fully mix the powder and produce a mechanical activation effect, thus obtaining mixed dry material; S4. Preparation of air bubble clusters: Air is used for foaming, and the CaO component in the coral sand generates a calcium carbonate reinforcing phase during the curing process; S5. Mixing and stirring: First stage: Add 40%-60% of the total seawater to the mixed dry material, add 2-45 parts of air bubble group to the slurry and stir at 80-120r / min for 1-2min to initially wet the powder surface and form a dust-free wet mixture. Second stage: Add the remaining seawater and additives after they are mixed evenly in advance, and at the same time increase the stirring speed to 200-300 r / min and continue stirring for 2-3 min. The polyvalent cations in the seawater will undergo ion exchange reaction with the surface of the coral sand particles to form a uniform slurry with high fluidity and no sedimentation. The third stage: reduce the rotation speed to 50-80 r / min, stir for 30-60s to remove large air bubbles in the slurry, and test the fluidity. The initial fluidity is controlled at 180-220 mm. The density and strength of the lightweight soil are independently controlled by adjusting the cement content, the fineness of the ground coral sand, and the amount of air bubbles. S6. Casting and Curing: Cast into the mold, cover the surface with plastic film after molding to prevent moisture evaporation, and place in a standard curing room for curing. The curing temperature is 20±2℃, the relative humidity is ≥95%, and the curing time is 7-28 days; or natural curing can be adopted according to the project conditions. During the curing period, seawater or fresh water is sprayed regularly to keep the soil moist. The total curing time is not less than 28 days.
7. The method for preparing high-performance lightweight soil using finely ground coral sand according to claim 6, characterized in that, In step S1, the coral sand is ground to 10-300μm.
8. The method for preparing high-performance lightweight soil using finely ground coral sand according to claim 6, characterized in that, Step S4 specifically includes: Dilute the foaming agent 10-30 times, add the foam stabilizer and thickener, and mix well to obtain the foaming liquid. Draw the foaming liquid into the liquid pipeline of the foaming machine, and simultaneously start the air compressor. Adjust the air inlet valve to stabilize the compressed air pressure at 200-600 kPa. Adjust the water pump speed ratio of the foaming machine to 20-100, corresponding to a foaming liquid flow rate of 1.0 L / min-5 L / min. Control the air-liquid ratio to approximately 1:10 to 1:
30. After the pressure of the foaming device stabilizes and the foaming rate becomes uniform, open the foam outlet valve to release fine, stable air foam, collect it in a container, and set it aside for later use.
9. The method for preparing high-performance lightweight soil using finely ground coral sand according to claim 6, characterized in that, When using seawater for curing in step S5, seawater is sprayed once every 3 days, and the curing temperature is not lower than 10℃.
10. The method for preparing high-performance lightweight soil using finely ground coral sand according to claim 6, characterized in that, In step S6, during the maintenance process, active ions in seawater continuously participate in the formation of the composite cementitious phase of hydrated calcium silicate (CSH), hydrated calcium aluminate (CAH), and chloroaluminate. Chloride ions are adsorbed by CSH gel or fixed by Friedel salt to form a dense microstructure, ultimately resulting in coral sand-based high-performance lightweight soil.