Preparation of steel slag-slag cement concrete spiral cast-in-place pile

Abstract

The application discloses a kind of steel slag-slag cement concrete spiral cast-in-place pile preparation, it is related to building material and carbon neutralization technical field, the composition of this concrete includes: slag powder, gypsum, limestone powder, steel slag powder, clinker, water, fine stone, sand, water reducing agent.The application takes steel slag, slag and other industrial solid waste as main body cementitious material, substantially reduces the amount of clinker, reduces carbon emissions by 160-250 kg per cubic meter of concrete, reduces material cost by 10-30 yuan, realizes solid waste resource utilization.The concrete has the characteristics of long setting time, strong erosion resistance, good fluidity, excellent anti-segregation, especially suitable for the construction of super-long spiral cast-in-place pile with a length of more than 40 meters and other pile bodies or underground engineering structures with high requirements for workability and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of building materials and carbon neutrality technology, and in particular to the preparation of a steel slag-slag cement concrete spiral cast-in-place pile. Background Technology

[0002] With the continuous advancement of infrastructure construction in my country, especially the rapid development of ports, cross-sea channels, land reclamation, and coastal industrial zones in coastal areas, ultra-long spiral cast-in-place piles, as a highly efficient, low-noise, and adaptable pile foundation construction technology, are widely used in large bridges, high-rise buildings, coastal protection, and temporary support structures. These piles are typically designed to exceed 40 meters in length and require multiple processes during construction, including hole drilling, concrete pumping, and reinforcement cage insertion. The construction cycle for a single pile generally exceeds 12 hours. Meanwhile, the steel industry is a pillar industry of my country's national economy, accounting for more than 50% of global steel production annually. The resulting large amounts of solid waste, such as blast furnace slag and converter slag, have long faced problems such as land occupation due to stockpiling, low resource utilization rates, and significant environmental pressure. The building materials industry, as a major carbon emitter, emits approximately 825 kg CO2 per ton of cement clinker during its traditional production process. Under the "dual carbon" target (carbon reduction and emission reduction), there is an urgent need to find alternative material systems that are low-carbon and highly efficient in utilizing solid waste.

[0003] Existing concrete systems based on silicate cement present numerous problems when applied to ultra-long spiral cast-in-place piles. Firstly, there is a fundamental mismatch between the material's temporal properties and the construction sequence. Ultra-long pile construction requires the concrete to maintain plasticity throughout the entire process of pouring, vibration, and reinforcement cage insertion, with an operational window lasting at least 12 hours. However, the initial setting time of ordinary silicate cement concrete is generally 4-8 hours, and the final setting time does not exceed 12 hours. If there are delays in the process or equipment failures, blockages due to initial setting, pile breakage, or the inability to insert the reinforcement cage to the design elevation are highly likely, leading to engineering quality accidents. Secondly, there is a contradiction between the material's spatial properties and the structural stability of the pile. Ultra-long pile concrete needs to be pumped over long distances and dropped vertically. Due to the density difference between aggregate and cement paste, segregation is prone to occur. In ordinary concrete, the density difference between coarse aggregate and cement paste is approximately 300-500 kg / m³. 3In piles exceeding 40 meters in height, the risk of segregation is significantly amplified, leading to decreased pile uniformity, insufficient local strength, and affecting the overall bearing capacity of the pile. Secondly, there is a long-term conflict between the chemical properties of materials and the corrosiveness of the service environment. Groundwater and soil in coastal or reclaimed areas are rich in high concentrations of chloride ions (≥5000 mg / L) and sulfate ions (≥2000 mg / L). Ordinary silicate cement hydration products contain large amounts of calcium hydroxide and high-calcium silicate hydrates, which easily react with corrosive media, leading to volume expansion, strength reduction, and steel corrosion, making it difficult to guarantee the design life of the pile foundation. Furthermore, there is a significant gap between resource and environmental attributes and the requirements of green and low-carbon development. Traditional concrete uses a large amount of clinker, resulting in high carbon emission intensity, which cannot meet the urgent need for low-carbon materials in engineering construction.

[0004] To address the aforementioned issues, existing technologies have attempted improvements from different angles, but none have systematically resolved the requirements for the synergistic application of multiple properties of concrete materials in ultra-long spiral cast-in-place piles. Some projects have delayed setting time by adding retarders (such as sodium gluconate and sucrose) to ordinary concrete; however, retarders are temperature-sensitive, their effectiveness diminishes significantly under high-temperature conditions, and they fail to improve the concrete's resistance to segregation and erosion, while also causing delayed early strength development and impacting construction efficiency. In coastal projects, sulfate-resistant silicate cement or the addition of rust inhibitors and mineral admixtures are commonly used to improve durability; however, these solutions still rely primarily on clinker as the main cementitious component, failing to effectively reduce carbon emissions, and their setting time remains within the conventional range, unable to meet the time window requirements for ultra-long pile construction. Increasing the content of slag powder or fly ash can reduce the heat of hydration and improve later-stage durability to some extent; however, limited by the setting characteristics of ordinary cement systems, excessively high dosages can lead to low early strength, unstable setting time, and limited adaptability to complex solid waste compositions such as steel slag, making it difficult to achieve a high proportion of solid waste utilization. A few studies have used steel slag as an aggregate or micro powder to partially replace cement, but these studies are mostly focused on ordinary concrete or non-critical structures. There is a lack of systematic design and verification for the construction of ultra-long cast-in-place piles and coastal erosion environments. Issues such as the free calcium oxide content, volume stability, and activity fluctuation of steel slag have not yet been effectively controlled at the engineering level. Summary of the Invention

[0005] This application provides a method for preparing steel slag-mineral slag cement concrete spiral cast-in-place piles, which solves the problems in the prior art. Using industrial solid wastes such as steel slag and mineral slag as the main cementitious components, and through gypsum activation and activity regulation, a fine stone concrete system suitable for ultra-long spiral cast-in-place piles is constructed, achieving synergistic optimization of material time properties, spatial properties, chemical properties and resource and environmental properties.

[0006] This application provides a method for preparing a steel slag-blast cement concrete spiral cast-in-place pile. The preparation process is as follows: solid materials are added to a mixer and stirred evenly. Then, water-reducing agent is dissolved in water and added to the mixer for wet mixing until the mixture is uniform.

[0007] Solid materials include cementitious materials and aggregates;

[0008] Cementitious materials include waste residue powder and cementitious base materials. Waste residue powder includes slag powder and steel slag powder; cementitious base materials include gypsum, limestone powder and clinker. Aggregates include: fine stone and sand; The raw materials, by weight, include: slag powder: 130-180 parts; gypsum: 28-38 parts; limestone powder: 5-20 parts; steel slag powder: 140-180 parts; clinker: 10-20 parts; water: 170-190 parts; fine stone: 1060-1160 parts; sand: 680-900 parts; and water-reducing agent: 1-3 parts.

[0009] Furthermore, the slag powder is S95 or S105 slag powder with a specific surface area of ​​not less than 360 m². 2 / kg.

[0010] Furthermore, the gypsum is any one of natural anhydrite powder, fluorogypsum, titanium gypsum, desulfurized gypsum, natural dihydrate gypsum, and phosphogypsum, with an SO3 content of not less than 35%.

[0011] Furthermore, the specific surface area of ​​the limestone powder is not less than 320 m². 2 / kg.

[0012] Furthermore, the specific surface area of ​​the steel slag powder is not less than 300 m². 2 / kg.

[0013] Furthermore, the clinker is silicate cement clinker.

[0014] Furthermore, the fine stone particle size is 4.75-13.2 mm, and the fine stone is crushed stone, pebbles or steel slag.

[0015] Furthermore, the sand is river sand, manufactured sand, or steel slag.

[0016] Furthermore, the water-reducing agent is any one or a combination of several of the first-generation, second-generation, and third-generation water-reducing agents.

[0017] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: The root of the existing technical problems lies in the fundamental contradiction between the material properties of traditional silicate cement concrete and the engineering requirements of ultra-long spiral cast-in-place piles. From a materials science perspective, the core of the hydration reaction of silicate cement is the reaction of tricalcium silicate and dicalcium silicate with water to form hydrated calcium silicate gel and calcium hydroxide. This reaction is relatively rapid at room temperature, allowing the cement paste to complete its initial setting within a few hours. This is an advantage in ordinary building structures, ensuring construction progress and early strength. However, when applied to ultra-long cast-in-place piles, it leads to numerous problems. The density of coarse aggregate in ordinary concrete (typically 2600–2800 kg / m³) 3 ) and the density of cement paste (approximately 1800–2000 kg / m³) 3 Significant differences exist between the density and slurry levels in ultra-long piles. During the vertical pumping and descent of ultra-long piles, the gravitational differentiation effect caused by density differences is amplified, leading to the sinking of coarse aggregate and the floating of slurry, resulting in unevenness in the pile body. Furthermore, the presence of calcium hydroxide in the hydration products of silicate cement makes the hardened slurry prone to ettringite-gypsum expansion reactions in sulfate environments, while in chloride environments, the high porosity leads to rapid chloride ion penetration, accelerating steel corrosion. Therefore, the three core parameters of traditional concrete—setting kinetics, density matching, and the stability of hydration products—are all systematically incompatible with the construction of ultra-long piles and their service in coastal environments.

[0018] This application uses steel slag powder and blast furnace slag powder as the main cementing materials (total dosage 280–360 kg / m³). 3 The addition of gypsum as a sulfate activator reduces the amount of silicate cement clinker to 0–5% of the total cementitious materials. Under the activation of sulfate ions provided by gypsum, the active alumina and silica in the slag powder undergo a pozzolanic reaction to generate ettringite and hydrated calcium silicate. The steel slag powder provides an alkaline environment to promote slag hydration, and its own active mineral phases also participate in the reaction. The hydration rate is controlled by the dissolution rate of gypsum and the release rate of sulfate ions, rather than by the rapid hydration of tricalcium silicate. Therefore, the setting time is significantly extended to over 14 hours, providing a sufficient safety window for ultra-long pile construction. Simultaneously, the steel slag powder has a high density (approximately 3100–3300 kg / m³). 3 This increases the density of the mortar, significantly reducing the density difference between the paste and the aggregate, and fundamentally suppressing segregation caused by gravity differentiation. The hydration products of this system contain almost no free calcium hydroxide, but are mainly low-alkalinity hydrated calcium silicate, ettringite, and hydrated calcium aluminate. They exhibit high chemical stability, are not prone to corrosive swelling reactions in sulfate and chloride environments, and have a significant filling effect, forming a dense microstructure that greatly reduces the penetration channels of harmful ions.

[0019] This application reduces carbon emissions by 160–250 kg per cubic meter of concrete, disposes of 280–360 kg of industrial solid waste, and lowers material costs by 10–30 yuan, achieving the triple goals of low carbon, low cost, and high solid waste utilization. Detailed Implementation

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] Example 1: This example aims to provide a concrete mix proportion calculated accurately using the volumetric method to ensure the compactness and homogeneity of the material system. Based on the component range provided in the invention, volumetric calculations and mix proportion optimization are performed using the measured density of each material, ultimately determining the following mix proportion (per cubic meter of concrete): Blast furnace slag powder: 164 kg. S95 grade blast furnace slag powder is used, with a density of 2900 kg / m³. 3 Specific surface area 360 m² 2 / kg, 7d activity index ≥95%.

[0022] Gypsum: 33 kg. Desulfurized gypsum was used, with a density of 2340 kg / m³. 3 The SO3 content is 38%.

[0023] Limestone powder: 10 kg. Density 2700 kg / m³ 3 Specific surface area ≥350 m² 2 / kg, CaCO3 content ≥90%.

[0024] Steel slag powder: 164 kg. Converter steel slag powder with a density of 3300 kg / m³ is used. 3 Specific surface area ≥300 m² 2 / kg, f-CaO content ≤2.5%.

[0025] Silicate cement clinker: 10 kg. Density 3150 kg / m³ 3 Strength level 52.5.

[0026] Fine aggregate: 1128 kg. Made of 5-10mm continuously graded limestone crushed stone, with a density of 2700 kg / m³. 3 Crushing index ≤12%.

[0027] Sand: 738 kg. Medium sand (river sand) from Zone II, density 2650 kg / m³.3 Fineness modulus 2.6, mud content ≤2.0%.

[0028] Water: 172 kg. Drinking water quality in accordance with JGJ 63-2006 "Standard for Water Used in Concrete".

[0029] Water-reducing agent: 2 kg. Polycarboxylate-based high-performance water-reducing agent (40% solids content), density 1080 kg / m³. 3 .

[0030] After calculation, the sum of the absolute volumes of all components is 998.5 L. Considering an air content of approximately 1% (10 L), the total volume is 999.5 L, which is equivalent to 1 m³. 3 The theoretical error for (1000 L) is 0.05%, which meets the engineering mix proportion accuracy requirements. This calculation ensures that the slurry fully coats the aggregate, forming a dense structure.

[0031] Preparation and standard curing process: A forced twin-shaft mixer (capacity 500L) is used. The feeding sequence is as follows: first, add all the powders (slag powder, steel slag powder, gypsum, limestone powder, and clinker) and dry mix for 90 seconds; then add sand and fine stone and continue dry mixing for 60 seconds; dissolve the water-reducing agent in the mixing water and pour it evenly over 60 seconds, followed by wet mixing for 180 seconds until the mixture is uniform and there is no visible bleeding or segregation.

[0032] Immediately after discharge, the workability of the fresh concrete was tested according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The concrete was poured into molds with dimensions of 100mm×100mm×100mm and 150mm×150mm×150mm, compacted and smoothed on a vibrating table. The molded specimens were left to stand for (24±2) hours in an environment with a temperature of (20±2)℃ and relative humidity >95%. After demolding, the specimens were immediately transferred to a standard curing room (temperature (20±2)℃, relative humidity ≥95%) and cured for the specified age. Performance was tested at 3d, 7d, 28d, and 56d.

[0033] The cementitious material-based concrete provided in Example 1 of this invention underwent comprehensive performance testing according to relevant national standards, and its performance characteristics are as follows: Regarding the performance of fresh concrete, according to GB / T 50080-2016, its slump / spread is (245±10) mm / 650 mm, indicating good fluidity and filling properties. The slump retention value after 2 hours reaches 230 mm, demonstrating excellent slump retention performance. The initial setting time is (8.5±0.5) h, and the final setting time is (12.0±0.5) h. This extended setting time perfectly matches the entire process cycle of ultra-long spiral cast-in-place piles, from hole formation, concrete pumping, pouring to reinforcement cage insertion. Even if there are delays in the process or equipment failures, problems such as pipe blockage, pile breakage, or inability to insert the reinforcement cage to the design elevation due to initial concrete setting can be avoided. The unit weight is 2408 kg / m³, and the pressure bleeding rate is only 35 mL, far lower than that of ordinary pumped concrete (usually 60~100 mL). (mL), with excellent anti-segregation and stability, it can effectively suppress aggregate sinking and slurry floating caused by gravity separation during the vertical drop of ultra-long piles, and is suitable for ultra-deep pile pumping scenarios.

[0034] The mechanical properties of the hardened concrete were tested according to GB / T 50081-2019. The strength development was stable and the later growth was significant: the 3-day compressive strength was 18.5 MPa, 7 days reached 28.8 MPa, 28 days increased to 39.2 MPa, and 56 days further increased to 46.5 MPa; the 28-day splitting tensile strength was 3.8 MPa, indicating that the hydration reaction of the cementitious system is sustainable, has good crack resistance, and can adapt to the deformation requirements of the pile under load.

[0035] In terms of durability, according to GB / T 50082-2009, after 28 days of standard curing, the impermeability pressure is greater than 1.5 MPa, reaching the P15 impermeability grade; the chloride ion diffusion coefficient measured by the RCM method after 28 days is 2.05 × 10⁻⁶. -12 m 2 / s, belonging to the "low" permeability level II, indicates that the concrete has good resistance to chloride ion erosion and is suitable for coastal high chloride salt environments; after soaking in 5% Na2SO4 solution for 150 days, the compressive strength corrosion resistance coefficient is 0.97, corresponding to the KS150 sulfate erosion resistance level; the 28-day and 90-day drying shrinkage values ​​are 285×10 -6 375×10 -6 It has a lower shrinkage value than ordinary Portland cement concrete of the same strength grade (typically about 350×10⁻⁶ after 28 days). -6 90 days, approximately 450 x 10 -6 It has good volume stability, reducing the risk of pile cracking.

[0036] The heat of hydration performance was tested using the heat of solution method according to GB / T 12959-2008. The heat of hydration at 3 days was 165 kJ / kg, and at 7 days it was 210 kJ / kg, which is significantly lower than that of ordinary Portland cement (the heat of hydration at 3 days is usually 250~300 kJ / kg, and the heat of hydration at 7 days is 300~350 kJ / kg). The low heat of hydration characteristic is beneficial to reducing the internal temperature rise of large-volume concrete and reducing the risk of cracking caused by temperature stress. It has important engineering significance for large-section structures such as ultra-long cast-in-place piles.

[0037] Example 2: This example focuses on an optimized design for a coastal environment characterized by high salinity, high humidity, and strong sulfate attack. By increasing the dosage of gypsum and active admixtures, and optimizing the hydration products of the cementitious system, high density and chemical stability are achieved. Precise calculations are performed using the volumetric method, with the following mix proportions (per cubic meter of concrete): Slag powder (S95 grade): 180 kg, density 2850 kg / m³ 3 Specific surface area ≥ 420 m² 2 / kg.

[0038] Gypsum (natural anhydrite): 38 kg, density 2340 kg / m³ 3 SO3 content ≥40%.

[0039] Limestone powder: 20 kg, density 2700 kg / m³ 3 Specific surface area ≥350 m² 2 / kg.

[0040] Steel slag powder: 140 kg, density 3300 kg / m³ 3 Specific surface area ≥320 m² 2 / kg.

[0041] Silicate cement clinker: 20 kg, density 3050 kg / m³ 3 Strength level 52.5.

[0042] Fine stone (5-13.2mm granite crushed stone): 1120 kg, density 2640 kg / m³ 3 .

[0043] Sand (manufactured sand, limestone): 750 kg, density 3000 kg / m³ 3 Fineness modulus 2.8, stone powder content 8%.

[0044] Water (drinking water): 190 kg.

[0045] Water-reducing agent (aliphatic high-efficiency water-reducing agent): 3 kg, density 1000 kg / m³ 3 .

[0046] The sum of the absolute volumes of all components is 1003.03 L. After considering the gas content of 1.0% (10 L), the total volume of the mixture is 1013.03 L. The relative error between this and the theoretical value of 1000 L is +1.30%, which is within the allowable range for engineering applications, proving that the proportioning is reasonable and feasible.

[0047] Preparation and standard curing process: A twin-shaft forced mixer with a rated capacity of 0.5 m³ is used. 3 Feeding sequence: First, add all powder materials (slag powder, steel slag powder, gypsum, limestone powder, clinker) and dry mix at 30 rpm for 90 seconds; add sand and fine stone and continue dry mixing for 60 seconds; completely dissolve the water-reducing agent in the mixing water and add it uniformly over 60 seconds while stirring, then increase the speed to 45 rpm and wet mix for 180 seconds until the mixture is uniform.

[0048] Immediately after discharge, the workability was tested according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The concrete was poured to a depth of 100 mm. 3 150 mm 3 Compressive strength test molds, as well as special test molds for impermeability, sulfate resistance, and shrinkage, are vibrated and smoothed on a vibrating table. The molded specimens are then left to stand for 48±2 hours at a temperature of (20±2)℃ and relative humidity >90% (due to the long retardation time) before demolding. After demolding, the specimens are immediately transferred to a standard curing room (temperature (20±2)℃, relative humidity ≥95%) for curing until the specified age.

[0049] Systematic testing of concrete was conducted according to national standards: Regarding the performance of the freshly mixed concrete, tested according to GB / T 50080-2016, its slump / spread is 255mm / 690mm, and its fluidity is further improved compared to Example 1, making it suitable for ultra-long pile construction scenarios with longer pumping distances and more complex pipeline layouts; the initial setting time is 21.2h and the final setting time is 29.8h, and the ultra-long setting time provides sufficient safe operating window for the construction process under complex working conditions; the apparent density is 2520kg / m³. 3 With a pressure bleeding rate of only 32mL, it exhibits excellent anti-segregation properties and pumping stability. The slurry has a stronger ability to coat the aggregate, making it particularly suitable for anti-segregation control during the vertical drop of ultra-long piles.

[0050] The mechanical properties of the hardened concrete were tested according to GB / T 50081-2019. The strength development was stable and the later growth was significant: the 3-day compressive strength was 17.2 MPa, 7 days reached 31.8 MPa, 28 days increased to 44.5 MPa, 60 days further increased to 63.6 MPa, and 90 days reached 57.0 MPa; the 28-day splitting tensile strength was 3.5 MPa, indicating that the product has good crack resistance. The strength development showed a continuous and stable growth trend, and the later strength growth was significant, indicating that the hydration reaction of the cementitious system has a long duration, which is conducive to the long-term bearing capacity of the pile. Its axial compressive strength and elastic modulus both meet the C40 design grade requirements, and some indicators reach the C50 level.

[0051] In terms of durability, according to GB / T 50082-2009 testing: after 28 days of standard curing, the impermeability grade is >P16 (water penetration height <30mm), indicating excellent water penetration resistance; the chloride ion diffusion coefficient measured by the RCM method after 28 days is 1.85×10⁻⁶. -12 m 2 / s, and the electrical flux measured by the electrical flux method was 860 coulombs at 28 days and 510 coulombs at 56 days, both belonging to the "very low" permeability level; after immersion in 5% Na2SO4 solution for 150 days, the compressive strength corrosion resistance coefficient was 1.05, the mass change rate was +0.18%, and the sulfate resistance grade reached KS180; after carbonization under standard conditions for 28 days, the carbonization depth was 0 mm, and after rapid carbonization for 28 days, the carbonization depth was only 1.5 mm, showing outstanding carbonization resistance; the early crack resistance performance (plate method) showed that the total crack area per unit area was <45 mm. 2 / m 2 The crack resistance level is Grade 1.

[0052] Example 3: This example aims to provide a concrete mix design that optimizes early strength development while maintaining good durability. By appropriately reducing the water-cement ratio and adjusting the proportion of gypsum and limestone powder, the early hydration of the cementitious system is accelerated while ensuring workability and setting time, meeting the requirements of certain engineering scenarios with strict requirements on demolding time or load-bearing time. The mix design is calculated precisely using the volumetric method, and is as follows (per cubic meter of concrete): Slag powder (S105 grade): 170 kg, density 2850 kg / m³ 3 Specific surface area 456 m² 3 / kg, with high activity in the early stages.

[0053] Gypsum (desulfurized gypsum): 28 kg, density 2340 kg / m³ 3 SO3 content ≥36%.

[0054] Limestone powder: 5 kg, density 2700 kg / m³ 3 Specific surface area ≥320 m² 2 / kg, mainly used as a micro-aggregate filler.

[0055] Steel slag powder: 150 kg, density 3300 kg / m³ 3 Specific surface area ≥320 m² 2 / kg.

[0056] Silicate cement clinker: 10 kg, density 3050 kg / m³ 3 .

[0057] Fine stone (5-10mm basalt gravel): 1130 kg, density 2640 kg / m³ 3 It has a low crushing value, which is conducive to strength development.

[0058] Sand (river sand, medium sand): 780 kg, density 3000 kg / m³ 3 Fineness modulus 2.7.

[0059] Water (drinking water): 170 kg.

[0060] Water-reducing agent (polycarboxylate-based high-performance water-reducing agent): 2 kg, density 1000 kg / m³ 3 Water reduction rate ≥25%.

[0061] Volume calculation: The absolute volume of each component is 982.23 L. After considering the introduction of 1.0% gas content (about 10 L), the total volume of the mixture is 992.23 L. The relative error between the mixture and the theoretical value of 1000 L is -0.78%. The mixture is dense and has good volume stability.

[0062] Preparation and standard curing process: A forced planetary mixer was used. The feeding sequence was as follows: first, fine stone, sand, and about half of the cementitious materials (slag powder, steel slag powder) were added and dry-mixed for 60 seconds for pre-mixing; then, the remaining cementitious materials (gypsum, limestone powder, clinker) and water-reducing agent powder (if in powder form) were added and dry-mixed for 60 seconds; finally, all water was added at once and wet-mixed for 180 seconds. The total mixing time was controlled within 5 minutes. Workability was tested immediately after discharge according to GB / T 50080-2016. After molding, the specimens were left to stand in an environment of (20±2)℃ and >90% humidity for (36±2) hours before demolding, and then moved to a standard curing room. To simulate the actual working conditions of the pile body, an additional set of specimens was set up, and after demolding, they were placed in an outdoor damp pit at (15±5)℃ and covered for curing to compare strength development.

[0063] Performance testing methods and results: Systematic testing was conducted according to national standards, and the performance results are as follows: Regarding the performance of the freshly mixed concrete, tested according to GB / T 50080-2016, its slump / spread is 235mm / 620mm, and its workability meets the requirements for pumping construction; the initial setting time is (14.5±0.5)h and the final setting time is (21.0±1.0)h. This setting time is still much longer than that of ordinary concrete, but shorter than that of Examples 1-2, which can accelerate the project progress while ensuring construction safety; the unit weight is 2480kg / m³. 3 The water exudation rate was only 1.2% after 3 hours, exhibiting extremely low water exudation characteristics.

[0064] The mechanical properties of the hardened concrete were tested according to GB / T50081-2019, showing excellent strength development: under standard curing conditions, the 1-day compressive strength was 10.5 MPa (significantly higher than that of the pure slag / steel slag system), reaching 22.8 MPa at 3 days, increasing to 35.6 MPa at 7 days, 52.1 MPa at 28 days, and further increasing to 58.3 MPa at 56 days; under the same curing conditions (simulating pile working conditions), the 3-day strength was 20.5 MPa, and the 28-day strength was 49.8 MPa, indicating good strength development in the field; the 28-day splitting tensile strength was 3.9 MPa; referring to GB / T50152-2012, the bond strength corresponding to the pull-out force at 28 days was 4.8 MPa, meeting the design requirements for rebar anchorage.

[0065] In terms of durability: tested according to GB / T 50082-2009, the 28-day impermeability pressure is >1.4MPa (corresponding to impermeability grade >P14); the 28-day chloride ion diffusion coefficient D was measured using the RCM method. RCM 2.25×10 -12 m 2 / s; Resistance to sulfate attack was tested using the wet-dry cycle method, and the strength corrosion resistance coefficient K after 120 cycles was determined. f The strength is 0.93, and the sulfate resistance grade reaches KS120, which can meet the requirements of general corrosive environments. The early crack resistance performance was tested by the circular restraint method. The cracking time was later than 24 hours and the final crack width was less than 0.1 mm, indicating excellent early crack resistance.

[0066] Example 4: This example pertains to a temporary support project (backfilling to be completed within 60 days of construction completion). Therefore, a mixture of natural sand and steel slag sand was used for the fine aggregate portion. Based on the component range provided in the invention description, volume calculations and mix proportion optimization were performed using the measured density of each material, ultimately determining the following mix proportion (per cubic meter of concrete): Blast furnace slag powder: 172 kg. S105 grade blast furnace slag powder is used, with a density of 2850 kg / m³. 3 Specific surface area 460 m² 2 / kg, 7d activity index ≥105%.

[0067] Gypsum: 33 kg. Desulfurized gypsum was used, with a density of 2340 kg / m³. 3 The SO3 content is 38%.

[0068] Limestone powder: 15 kg. Density 2700 kg / m³ 3 Specific surface area 370 m² 2 / kg, CaCO3 content ≥90%.

[0069] Steel slag powder: 140 kg. Converter steel slag powder with a density of 3300 kg / m³ is used. 3 Specific surface area 360 m² 2 / kg, f-CaO content ≤2.5%.

[0070] Silicate cement clinker: 20 kg. Density 3150 kg / m³ 3 Strength level 52.5.

[0071] Fine aggregate: 1108 kg. 5-10mm continuously graded limestone crushed stone, density 2700 kg / m³. 3 Crushing index ≤12%.

[0072] Sand: 400 kg. Medium sand (river sand) from Zone II, density 2650 kg / m³. 3 Fineness modulus 2.6, mud content ≤2.0%.

[0073] Steel slag sand: 450 kg, using steel slag sand with a particle size of less than 10 mm, with a 4.75 mm passing rate of 95%. Density: 3250 kg / m³ 3 , .

[0074] Water: 172 kg. Drinking water quality in accordance with JGJ 63-2006 "Standard for Water Used in Concrete".

[0075] Water-reducing agent: 2 kg. Polycarboxylate-based high-performance water-reducing agent (40% solids content), density 1080 kg / m³. 3 .

[0076] After calculation, the sum of the absolute volumes of all components is 999.5 L. Considering an air content of approximately 1% (10 L), the total volume is 1000.5 L, which is equivalent to 1 m³. 3The theoretical error for (1000 L) is 0.05%, which meets the engineering mix proportion accuracy requirements. This calculation ensures that the slurry fully coats the aggregate, forming a dense structure.

[0077] Preparation and standard curing process: A forced twin-shaft mixer (capacity 500L) is used. The feeding sequence is as follows: first, add all the powders (slag powder, steel slag powder, gypsum, limestone powder, and clinker) and dry mix for 60 seconds; then add sand and fine stone and continue dry mixing for 60 seconds; dissolve the water-reducing agent in the mixing water and pour it evenly over 30 seconds, followed by wet mixing for 180 seconds until the mixture is uniform and there is no visible bleeding or segregation.

[0078] Immediately after discharge, the workability of the fresh concrete was tested according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The concrete was poured into molds with dimensions of 100mm×100mm×100mm and 150mm×150mm×150mm, compacted and smoothed on a vibrating table. The molded specimens were left to stand for (24±2) hours in an environment with a temperature of (20±2)℃ and relative humidity >95%. After demolding, the specimens were immediately transferred to a standard curing room (temperature (20±2)℃, relative humidity ≥95%) and cured for the specified age. Performance was tested at 3d, 7d, 28d, and 56d.

[0079] The cementitious material-based concrete provided in Example 4 of this invention underwent comprehensive performance testing according to relevant national standards, and its performance characteristics are as follows: Regarding the performance of fresh concrete, according to GB / T 50080-2016, its slump / spread is (245±10) mm / 650 mm, indicating good fluidity and filling properties. The slump retention value after 2 hours reaches 230 mm, demonstrating excellent slump retention performance. The initial setting time is (8.5±0.5) h, and the final setting time is (10.0±0.5) h. This extended setting time perfectly matches the entire process cycle of ultra-long spiral cast-in-place piles, from hole formation, concrete pumping, pouring to reinforcement cage insertion. Even if there are delays in the process or equipment failures, problems such as pipe blockage, pile breakage, or inability to insert the reinforcement cage to the design elevation due to initial concrete setting can be avoided. The unit weight is 2509 kg / m³, and the pressure bleeding rate is only 30 mL, far lower than that of ordinary pumped concrete (typically 60~100 mL). (mL), with excellent anti-segregation and stability, it can effectively suppress aggregate sinking and slurry floating caused by gravity separation during the vertical drop of ultra-long piles, and is suitable for ultra-deep pile pumping scenarios.

[0080] The mechanical properties of the hardened concrete were tested according to GB / T 50081-2019. The strength development was stable with significant increases in later stages: the 3-day compressive strength was 19.6 MPa, reaching 30.7 MPa at 7 days, increasing to 41.6 MPa at 28 days, and further increasing to 46.2 MPa at 56 days; the 28-day splitting tensile strength was 3.9 MPa. This indicates that the hydration reaction of the cementitious system is sustainable, possessing good crack resistance and able to adapt to the deformation requirements of the pile under load. The steel slag sand remained stable within 56 days, without any strength reduction. In terms of durability, according to GB / T 50082-2009, after 28 days of standard curing, the impermeability pressure is greater than 1.5 MPa, reaching the P15 impermeability grade; the chloride ion diffusion coefficient measured by the RCM method after 28 days is 1.98 × 10⁻⁶. -12 m 2 / s, belonging to the "low" permeability level II, indicates that the concrete has good resistance to chloride ion erosion and is suitable for coastal high chloride salt environments; after soaking in 5% Na2SO4 solution for 150 days, the compressive strength corrosion resistance coefficient is 0.85, corresponding to the KS150 sulfate erosion resistance level; the 28-day and 90-day drying shrinkage values ​​are 265×10 -6 354×10 -6 It has a lower shrinkage value than ordinary Portland cement concrete of the same strength grade (typically about 350×10⁻⁶ after 28 days). -6 90 days, approximately 450 x 10 -6 It has good volume stability, reducing the risk of pile cracking.

[0081] The heat of hydration performance was tested using the heat of solution method according to GB / T 12959-2008. The heat of hydration at 3 days was 178 kJ / kg, and at 7 days it was 230 kJ / kg, which is significantly lower than that of ordinary Portland cement (the heat of hydration at 3 days is usually 250~300 kJ / kg, and the heat of hydration at 7 days is 300~350 kJ / kg). The low heat of hydration characteristic is beneficial to reducing the internal temperature rise of large-volume concrete and reducing the risk of cracking caused by temperature stress. It has important engineering significance for large-section structures such as ultra-long cast-in-place piles.

[0082] Example 5: This example pertains to a temporary support project (backfilling to be completed within 60 days of construction completion), requiring only C25 concrete. Therefore, steel slag sand was used in the fine aggregate portion, with a small amount of admixtures. Based on the component range provided in the invention description, volume calculations and mix proportion optimization were performed using the measured density of each material, ultimately determining the following mix proportion (per cubic meter of concrete): Blast furnace slag powder: 130 kg. S95 grade blast furnace slag powder is used, with a density of 2830 kg / m³. 3 Specific surface area 360 m² 2 / kg, 7d activity index ≥95%.

[0083] Gypsum: 30 kg. Phosphogypsum is used, density 2340 kg / m³. 3 The SO3 content is 39%.

[0084] Limestone powder: 15 kg. Density 2700 kg / m³ 3 Specific surface area 370 m² 2 / kg, CaCO3 content ≥90%.

[0085] Steel slag powder: 170 kg. Converter steel slag powder with a density of 3300 kg / m³ is used. 3 Specific surface area 360 m² 2 / kg, f-CaO content ≤2.5%.

[0086] Silicate cement clinker: 10 kg. Density 3150 kg / m³ 3 Strength level 52.5.

[0087] Fine aggregate: 1120 kg. Made of 5-10mm continuously graded limestone crushed stone, with a density of 2700 kg / m³. 3 Crushing index ≤12%.

[0088] Steel slag sand: 900 kg, using steel slag sand with a particle size of less than 10 mm, with a 4.75 mm passing rate of 95%. Density: 3250 kg / m³ 3 , .

[0089] Water: 172 kg. Drinking water quality in accordance with JGJ 63-2006 "Standard for Water Used in Concrete".

[0090] Water-reducing agent: 1 kg. Polycarboxylate-based high-performance water-reducing agent (32% solids content), density 1080 kg / m³. 3 .

[0091] After calculation, the sum of the absolute volumes of all components is 999.9 L. Considering an air content of approximately 1% (10 L), the total volume is 1000.9 L, which is equivalent to 1 m³. 3 The theoretical error for (1000 L) is 0.09%, which meets the engineering mix proportion accuracy requirements. This calculation ensures that the slurry fully coats the aggregate, forming a dense structure.

[0092] Preparation and standard curing process: A forced twin-shaft mixer (capacity 500L) is used. The feeding sequence is as follows: first, add all the powders (slag powder, steel slag powder, gypsum, limestone powder, and clinker) and dry mix for 60 seconds; then add sand and fine stone and continue dry mixing for 60 seconds; dissolve the water-reducing agent in the mixing water and pour it evenly over 30 seconds, followed by wet mixing for 180 seconds until the mixture is uniform and there is no visible bleeding or segregation.

[0093] Immediately after discharge, the workability of the fresh concrete was tested according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The concrete was poured into molds with dimensions of 100mm×100mm×100mm and 150mm×150mm×150mm, compacted and smoothed on a vibrating table. The molded specimens were left to stand for (24±2) hours in an environment with a temperature of (20±2)℃ and relative humidity >95%. After demolding, the specimens were immediately transferred to a standard curing room (temperature (20±2)℃, relative humidity ≥95%) and cured for the specified age. Performance was tested at 3d, 7d, 28d, and 56d.

[0094] The cementitious material-based concrete provided in Example 5 of this invention underwent comprehensive performance testing according to relevant national standards, and its performance characteristics are as follows: Regarding the performance of fresh concrete, according to GB / T 50080-2016, its slump / spread is (245±10) mm / 650 mm, indicating good fluidity and filling properties. The slump retention value after 2 hours reaches 230 mm, demonstrating excellent slump retention performance. The initial setting time is (10.5±0.5) h, and the final setting time is (13.0±0.5) h. This extended setting time perfectly matches the entire process cycle of ultra-long spiral cast-in-place piles, from hole formation, concrete pumping, pouring to reinforcement cage insertion. Even if there are delays in the process or equipment failures, problems such as pipe blockage, pile breakage, or inability to insert the reinforcement cage to the design elevation due to initial concrete setting can be avoided. The unit weight is 2588 kg / m³, and the pressure bleeding rate is only 38 mL, far lower than that of ordinary pumped concrete (typically 60~100 mL). (mL), with excellent anti-segregation and stability, it can effectively suppress aggregate sinking and slurry floating caused by gravity separation during the vertical drop of ultra-long piles, and is suitable for ultra-deep pile pumping scenarios.

[0095] The mechanical properties of the hardened concrete were tested according to GB / T 50081-2019. The strength development was stable with significant increases in later stages: the 3-day compressive strength was 15.6 MPa, reaching 21.5 MPa at 7 days, increasing to 35.6 MPa at 28 days, and further increasing to 38.2 MPa at 56 days; the 28-day splitting tensile strength was 2.8 MPa. This indicates that the hydration reaction of the cementitious system is sustainable, possessing good crack resistance and able to adapt to the deformation requirements of the pile under load. The steel slag sand remained stable within 56 days, without any strength reduction. In terms of durability, according to GB / T 50082-2009, after 28 days of standard curing, the seepage resistance pressure is greater than 1.2 MPa, reaching the P15 seepage resistance grade; the chloride ion diffusion coefficient measured by the RCM method after 28 days is 2.58 × 10⁻⁶. -12 m 2 / s, belonging to the "low" permeability level II, indicates that the concrete has good resistance to chloride ion erosion and is suitable for coastal high chloride salt environments; after soaking in 5% Na2SO4 solution for 150 days, the compressive strength corrosion resistance coefficient is 1.15, corresponding to the KS150 sulfate erosion resistance level; the 28-day and 90-day drying shrinkage values ​​are 269×10 -6 371×10 -6 It has a lower shrinkage value than ordinary Portland cement concrete of the same strength grade (typically about 350×10⁻⁶ after 28 days). -6 90 days, approximately 450 x 10 -6 It has good volume stability, reducing the risk of pile cracking.

[0096] The heat of hydration performance was tested using the heat of solution method according to GB / T 12959-2008. The heat of hydration at 3 days was 152 kJ / kg, and at 7 days it was 210 kJ / kg, which is significantly lower than that of ordinary Portland cement (the heat of hydration at 3 days is usually 250~300 kJ / kg, and the heat of hydration at 7 days is 300~350 kJ / kg). The low heat of hydration characteristic is beneficial to reducing the internal temperature rise of large-volume concrete and reducing the risk of cracking caused by temperature stress. It has important engineering significance for large-section structures such as ultra-long cast-in-place piles.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a steel slag-blast furnace cement concrete spiral cast-in-place pile, characterized in that, The preparation process is as follows: add solid materials to a mixer and stir evenly, then dissolve the water-reducing agent in water and add it to the mixer for wet mixing until the mixture is uniform; Solid materials include cementitious materials and aggregates; Cementitious materials include waste residue powder and cement-based materials. Waste residue powder includes slag powder and steel slag powder. Cement base materials include gypsum, limestone powder, and clinker; Aggregates include: fine stone and sand; The raw materials, by weight, include: slag powder: 130-180 parts; gypsum: 28-38 parts; limestone powder: 5-20 parts; steel slag powder: 140-180 parts; clinker: 10-20 parts; water: 170-190 parts; fine stone: 1060-1160 parts; sand: 680-900 parts; and water-reducing agent: 1-3 parts.

2. The preparation of a steel slag-blast cement concrete spiral cast-in-place pile as described in claim 1, characterized in that, The slag powder mentioned is S95 or S105 slag powder, with a specific surface area of ​​not less than 360m². 2 / kg.

3. The preparation of a steel slag-blast cement concrete spiral cast-in-place pile as described in claim 1, characterized in that, The gypsum is any one of natural anhydrite powder, fluorogypsum, titanium gypsum, desulfurized gypsum, natural dihydrate gypsum, and phosphogypsum, with an SO3 content of not less than 35%.

4. The preparation of a steel slag-blast cement concrete spiral cast-in-place pile as described in claim 1, characterized in that, The limestone powder has a specific surface area of ​​not less than 320 m². 2 / kg.

5. The preparation of a steel slag-blast cement concrete spiral cast-in-place pile as described in claim 1, characterized in that, The specific surface area of ​​the steel slag powder is not less than 300m². 2 / kg.

6. The preparation of a steel slag-blast cement concrete spiral cast-in-place pile as described in claim 1, characterized in that, The clinker mentioned is silicate cement clinker.

7. The preparation of a steel slag-blast cement concrete spiral cast-in-place pile as described in claim 1, characterized in that, The fine stone has a particle size of 4.75-13.2 mm and can be crushed stone, pebbles, or steel slag.

8. The preparation of a steel slag-blast cement concrete spiral cast-in-place pile as described in claim 1, characterized in that, The sand mentioned is river sand, manufactured sand, or steel slag.

9. The preparation of a steel slag-blast cement concrete spiral cast-in-place pile as described in claim 1, characterized in that, The water-reducing agent is any one or a combination of several of the first-generation, second-generation, and third-generation water-reducing agents.