Supersulfate cement concrete based on construction waste aggregates and minerals and its preparation method

Abstract

This invention relates to a supersulfate cement concrete based on construction waste aggregate and minerals, and its preparation method. The concrete, by mass, comprises 380-460 parts supersulfate cement; 950-1250 parts modified mixed aggregate; 0-150 parts natural sand; 135-165 parts water; and a water-reducing agent at 0.7-1.2% of the total mass of the cementitious materials. The modified mixed aggregate is obtained by mixing construction waste and calcium vanadium stone enrichment at a mass ratio of (85-92):(8-15), followed by sequential modification with alkali solution, silane coupling agent, and slag. The present invention achieves a construction waste aggregate replacement rate of 70-100%, requires no complex modification equipment or processes, is easy to scale up for industrial production, and is highly practical.

Description

Technical Field

[0001] This invention relates to the field of building materials and comprehensive utilization of solid waste resources, and more specifically, to a supersulfate cement concrete based on construction waste aggregates and minerals and its preparation method. Background Technology

[0002] Supersulfate cement, with granulated blast furnace slag, dihydrate gypsum, and a small amount of silicate cement clinker as its core cementitious components, boasts advantages such as low heat of hydration, excellent resistance to sulfate attack, high solid waste content, and environmental friendliness, making it a promising candidate for applications in underground engineering, corrosion-resistant structures, and construction waste recycling. However, in existing technologies, supersulfate cement concrete exhibits slow early strength development, with a 1-day compressive strength typically below 6 MPa and a 3-day strength less than 20 MPa. This makes it difficult to meet the urgent demands for early load-bearing capacity in projects requiring rapid construction, immediate support, and emergency repairs, thus limiting its industrial-scale promotion.

[0003] To improve early strength, existing technologies typically focus on modifying the cementitious material: First, externally applied strong alkaline activators such as sulfoaluminate clinker, water glass, and calcium nitrate (CN121159177B, CN107827379B) accelerate slag hydration through a strongly alkaline environment. However, this can easily lead to increased system shrinkage, poor volume stability, and increased production costs. Second, external application of synthesized AFt seed crystals, such as CN119263682A and CN112062494A, synthesizes submicron / nano AFt through chemical reactions. Seed crystals, as external additives, do not involve in-situ Aft of construction waste aggregates; third, crystal morphology control, calcination modification, or compounding with early-strength minerals such as calcium fluoroaluminate in gypsum (CN121318223A, CN120518333B) can slightly improve early strength, but the process is complex, costly, and easily results in coarse morphology and loose structure of ettringite; fourth, the use of nanomaterials, fiber reinforcement, and other means (CN116332547A, CN113716898B) has problems such as poor dispersibility, insufficient durability, and difficulty in large-scale application.

[0004] Meanwhile, the resource utilization of construction waste is often limited to simply replacing natural aggregates, involving only basic treatments such as crushing, impurity removal, and washing, without systematic design and precise control of the aggregate's own mineral composition (free CaO, active SiO2 / Al2O3, AFt crystals, etc.). Direct application of such aggregates to supersulfate cement systems can easily lead to problems such as excessively high free CaO causing volume expansion, insufficient free CaO resulting in inadequate activation, or an imbalance in the active SiO2 / Al2O3 ratio causing uneven formation of ettringite. This makes it impossible to simultaneously achieve early strength improvement and volume stability control, hindering the synergistic development of high-value solid waste and high-performance concrete.

[0005] In addition, in existing studies, ettringite (AFt) is mostly passively generated as a hydration product. There is no technology that uses construction waste aggregate as an active carrier for AFt crystals to actively stimulate the early hydration of supersulfate cement through in-situ extraction and directional compounding. This is a gap in the current technology field.

[0006] Therefore, there is an urgent need to provide a supersulfate cement concrete technology that starts from the aggregate of construction waste, extracts AFt crystals in situ for synergistic hydration, has a simple process and controllable cost, and can significantly improve 1-day early strength and ensure later strength stability and volume stability, so as to solve many defects of the existing technology. Summary of the Invention

[0007] Based on the aforementioned technical problems in the existing technology, the present invention provides a supersulfate cement concrete based on construction waste aggregates and minerals. By adding AFt crystals extracted and enriched in situ from construction waste aggregates to the concrete, it serves as the core carrier for early strength and forms a synergistic hydration effect with the supersulfate cement system. Without the need for complex cementitious material modification, it can achieve a leapfrog improvement in early strength in 1 day, while taking into account the later strength development and volume stability, and greatly improve the resource utilization efficiency of construction waste.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A supersulfate cement concrete based on construction waste aggregates and minerals, comprising the following components by weight:

[0010] 380-460 parts of supersulfate cement;

[0011] 950-1250 parts of modified mixed aggregate;

[0012] 0-150 parts of natural sand;

[0013] 135-165 parts water;

[0014] Water-reducing agent, at 0.7-1.2% of the total mass of cementitious materials;

[0015] The modified mixed aggregate is obtained by mixing construction waste and calcium vanadium stone enrichment in a mass ratio of (85-92):(8-15) and then modifying it with alkali solution, silane coupling agent and slag in sequence.

[0016] The content of calcium vanadate crystals in the calcium vanadate enrichment is ≥65%;

[0017] The modified mixed aggregate contains 0.8-1.8% free CaO, 2.2-3.2 active SiO2 / Al2O3, and ≥10% calcium vanadate crystals.

[0018] In some embodiments, the calcium vanadium concentrate is obtained by extracting, washing, and drying waste concrete with ammonium chloride solution; the waste concrete contains 0.5-0.9% free CaO and has an active SiO2 / Al2O3 ratio of 3.2-3.8.

[0019] In some embodiments, the preparation of the perovskite enrichment includes the following steps:

[0020] The waste concrete was crushed to a particle size ≤5mm, and the ammonium chloride solution was added to react. After the reaction was completed, the solid and liquid were separated, the precipitate was collected, washed with deionized water until no ammonium chloride residue remained, and then dried to obtain the calcium vanadium stone enrichment.

[0021] In some embodiments, the mass concentration of the ammonium chloride solution is 5-8%.

[0022] In some embodiments, the solid-liquid ratio of the waste concrete and the ammonium chloride solution is 1g:3-5mL.

[0023] In some embodiments, the preparation of the modified mixed aggregate includes the following steps:

[0024] The construction waste is crushed and graded, then mixed with the calcium vanadium concentrate to obtain mixed aggregate; the alkaline solution is added to the mixed aggregate for activation; after the reaction is complete, a silane coupling agent is added and mixed evenly; finally, an additive with a specific surface area ≥600 m² is added. 2 / kg of slag powder is mixed evenly and then dried to a moisture content of 2-4% to obtain the modified mixed aggregate.

[0025] In some embodiments, the construction waste is crushed and graded to obtain coarse aggregate with a particle size of 5-20 mm and fine aggregate with a particle size of 0.15-4.75 mm. The coarse aggregate, fine aggregate and calcium vanadium stone concentrate are mixed to obtain mixed aggregate.

[0026] In some embodiments, the mass ratio of coarse aggregate to fine aggregate is (5-8):1.

[0027] In some embodiments, the mass concentration of the alkaline solution is 1.2-5%.

[0028] In some embodiments, the amount of alkali solution added is 2-3% of the mass of the mixed aggregate.

[0029] In some embodiments, the amount of silane coupling agent added is 0.3-0.5% of the mass of the mixed aggregate.

[0030] In some embodiments, the amount of slag powder added is 3-5% of the mass of the mixed aggregate.

[0031] In some embodiments, the solute in the alkaline solution includes sodium hydroxide and water glass, wherein the mass ratio of sodium hydroxide to water glass is 1:1.5-4.

[0032] In some embodiments, the construction waste includes at least one of waste ceramics, waste red bricks, and waste concrete.

[0033] In some embodiments, the supersulfate cement comprises slag, gypsum, and clinker; by mass percentage, it comprises:

[0034] Slag content: 76-84%;

[0035] 13-18% plaster;

[0036] Clinker 3-6%.

[0037] In some embodiments, the clinker is silicate cement clinker.

[0038] The present invention also provides a method for preparing supersulfate cement concrete based on construction waste aggregates and minerals according to any of the above embodiments, comprising the following steps:

[0039] S1. Weigh out the supersulfate cement, modified mixed aggregate, natural sand, water and water-reducing agent respectively;

[0040] S2. Mix the modified aggregate and natural sand evenly, then add supersulfate cement and mix evenly to obtain the mixture.

[0041] S3. Mix water and water-reducing agent evenly to obtain a water-reducing agent solution;

[0042] S4. Add the water-reducing agent solution to the mixture and mix evenly to obtain the supersulfate cement concrete.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] The present invention incorporates AFt crystals extracted in situ from construction waste aggregates into the concrete raw materials, providing a large number of active nucleation sites in the early stages of hydration. This breaks through the induction period barrier of traditional supersulfate cement hydration, induces rapid depolymerization of slag glass, and accelerates Ca2+ hydration. 2+ Al 3+ SO4 2- The directional crystallization and growth of plasma enables AFt crystals to rapidly form a densely interwoven network structure within 1 day, directly constructing the early strength framework of concrete. Compared with the passive generation of AFt in existing technologies, the seed-induced effect of this invention can increase the amount of AFt crystals generated within 1 day by 60% to 100%, directly driving a leapfrog improvement in early strength.

[0045] This invention employs a three-component gradient compounding method to strictly control the free CaO and active SiO2 / Al2O3 in the mixed aggregate, forming an ion-synergistic supply system with in-situ extracted AFt crystals. The free CaO slowly releases OH⁻ during the initial hydration stage, creating a mild alkaline environment. This avoids the rapid hydration shrinkage of slag caused by a strongly alkaline environment while providing sufficient Ca for AFt crystal growth. 2+ With OH - The active SiO2 / Al2O3 precisely matches the ion requirements for AFt crystal growth, continuously replenishing Al. 3+ With SiO4 4- This invention ensures that AFt crystals always grow in a short, rod-shaped, highly crystalline morphology, avoiding the structural looseness caused by disordered, coarse, needle-like AFt crystals, and further enhancing the early structural density. Furthermore, the invention modifies the aggregate through composite alkali activation and ultrafine slag coating, forming a highly active transition layer on the surface of the AFt-containing aggregate. Composite alkali activation activates active sites on the aggregate surface, promoting a tight bond between AFt crystals and slag hydration products; high specific surface area slag micro-powder coating fills the interfacial pores between the aggregate and the slurry, reducing the formation of interfacial microcracks. This interfacial strengthening effect ensures that the early strength core units (AFt crystals, aggregate, and slurry) form a tightly bonded whole, avoiding strength loss due to interfacial separation during early hydration, and further consolidating the early strength foundation.

[0046] The solution of this invention achieves a construction waste aggregate replacement rate of 70% to 100%, significantly disposes of solid waste, and reduces overall costs by 15% to 25%. It only uses conventional crushing, screening, AFt extraction, and compounding processes, and gypsum only undergoes grinding. It does not require complex modification equipment and processes, making it easy to scale up industrial production and highly practical. Attached Figure Description

[0047] Figure 1 SEM image of AFt crystals extracted in situ from construction waste aggregate;

[0048] Figure 2 The image shows the morphology of AFt crystals generated during the hydration of ordinary supersulfate cement.

[0049] Figure 3 This is a distribution diagram of early hydration products in concrete according to the present invention;

[0050] Figure 4 This is a distribution diagram of early hydration products in ordinary supersulfate cement concrete.

[0051] Figure 5 The compressive strength is shown in the examples and comparative examples;

[0052] Figure 6 The Aft and free CaO contents are for the examples and comparative examples. Detailed Implementation

[0053] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0054] 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 be limiting of the invention.

[0055] The pretreatment and detection methods for some raw materials in the following examples and comparative examples are as follows:

[0056] 1. Raw materials and testing methods

[0057] Supersulfate cement: made from granulated blast furnace slag (specific surface area 450±20m²) 2 / kg, activity index ≥95%), dihydrate gypsum (purity ≥95%, specific surface area 380±20m²) 2 Mix the silicate cement clinker (strength grade 42.5, conforming to GB / T 200-2017 "Silica Cement") at a mass ratio of 80%:15%:5% evenly and set aside.

[0058] Construction waste aggregate: Select waste red bricks, waste concrete blocks, and waste ceramic fragments generated from building demolition. They should be free from obvious weathering and impurities. Remove surface dust, soil, and large debris in advance, and sort and stack them for later use.

[0059] AFt crystal enrichment: prepared from waste concrete aggregate in situ, quantitative analysis by X-ray diffraction (XRD) showed that the AFt crystal content was ≥65% and the particle size was ≤100μm in the dry state, ready for use;

[0060] Polycarboxylate superplasticizer: solid content 20%, water reduction rate ≥26%, chlorine-free and alkali-free, meeting the requirements of GB / T 8076-2008 "Concrete Admixtures";

[0061] Auxiliary materials: Lightly calcined lime powder (purity ≥90%, fineness ≥300 mesh), metakaolin (specific surface area ≥800 m²) 2 / kg, active Al2O3 content ≥35%), used for mineral parameter control;

[0062] Water: Tap water, pH value 7.0~7.5, free of impurities and corrosive, conforming to GB / T 5749-2022 "Standards for Drinking Water Quality".

[0063] All performance testing methods comply with current national standards.

[0064] Compressive strength: GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete";

[0065] Drying shrinkage rate: GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete";

[0066] Free CaO: Glycerol-ethanol method;

[0067] Activated SiO2 / Al2O3: Alkali dissolution-acid-base titration method;

[0068] AFt crystal content: quantitative analysis by X-ray diffraction (XRD);

[0069] Volume stability: Le Chatelier clamp method;

[0070] Content of needle-shaped and flaky aggregate particles: GB / T 14685-2022 "Construction Pebbles and Crushed Stone".

[0071] 2. Pretreatment processes for some raw materials

[0072] (1) Pretreatment of construction waste aggregate

[0073] Crushing by category: Waste red bricks, waste concrete blocks, and waste ceramic fragments are separately fed into a jaw crusher for coarse crushing, with the particle size of the crushed material controlled at 50~100mm; then the three types of materials after coarse crushing are separately fed into a cone crusher for secondary fine crushing. During the fine crushing process, the discharge port size of the crusher is controlled to ensure that the maximum particle size of the aggregate after fine crushing is ≤20mm and the content of needle-shaped and flaky particles is ≤15%;

[0074] Air separation for impurity removal: The three types of finely crushed aggregates are fed into an air separator, and the air separation pressure is adjusted to 0.4MPa (range 0.3~0.5MPa). Light impurities (such as plastics, wood chips, dust, etc.) in the aggregates are removed by air separation, ensuring that the removal rate of light impurities is ≥98%.

[0075] Magnetic separation for impurity removal: The aggregate after air separation is fed into a magnetic separator (magnetic field strength ≥1200 Gauss). The magnetic field adsorbs and removes magnetic metal impurities (such as steel bar fragments, iron nails, etc.) from the aggregate, ensuring that the content of magnetic impurities is ≤0.1% to avoid impurities interfering with the subsequent AFt extraction and hydration reaction;

[0076] Multi-stage screening: The three types of aggregates after impurity removal are fed into a double-layer linear vibrating screen (screen mesh sizes of 20mm and 0.15mm respectively) to obtain coarse aggregates of 5~20mm and fine aggregates of 0.15~4.75mm. The proportion of stone powder (particle size <0.15mm) under the screen is controlled to ≤8%. The screened coarse and fine aggregates are stacked separately and properly labeled.

[0077] Mineral parameter testing: Samples were taken from the three types of aggregates after grading. The free CaO content was determined by the glycerol-ethanol method, and the active SiO2 and active Al2O3 contents were determined by the alkali-acid-base titration method. A basic mineral database was established, including:

[0078] Red brick: Free CaO 1.8%~2.5%, active SiO2 / Al2O3 1.8~2.2;

[0079] Waste concrete: Free CaO 0.5%~0.9%, Active SiO2 / Al2O3 3.2~3.8;

[0080] Waste ceramics: Free CaO 0.1%~0.3%, active SiO2 / Al2O3 4.0~4.5;

[0081] The test results serve as the basis for subsequent compounding and regulation.

[0082] (2) In-situ extraction of AFt crystals

[0083] Raw material sampling and pretreatment: Samples are taken from the waste concrete coarse aggregate after impurity removal and screening. Aggregates with a particle size of 5-10 mm are preferred. These are then crushed to a particle size ≤ 5 mm, placed in an oven at 60℃ for 2 hours to remove surface moisture, and set aside for later use.

[0084] Preparation of extract: Prepare a 5% (w / w) ammonium chloride aqueous solution using analytical grade ammonium chloride, stir well, and let stand for 30 minutes to ensure that the ammonium chloride is completely dissolved without precipitation or stratification.

[0085] Selective extraction: The pretreated waste concrete aggregate powder and ammonium chloride extract were placed in an ultrasonic reactor at a solid-liquid ratio of 1g:4mL. The reaction temperature was adjusted to 25~35℃, the ultrasonic equipment was turned on, the ultrasonic power was set to 400W, and the ultrasonic time was 30min. During the ultrasonic process, the mixture was stirred once every 10min to ensure that the aggregate powder and the extract were in full contact.

[0086] Centrifugation: After ultrasonication, the mixture in the reactor is sent to a high-speed centrifuge. The speed is set to 4000 r / min and the centrifugation time is 20 min to separate the AFt crystal concentrate from the aggregate residue and extract. The supernatant and the middle coarse particles are removed, and the precipitate at the bottom of the centrifuge tube is collected to obtain crude AFt crystals.

[0087] Washing and purification: Place the obtained crude AFt crystals into a beaker, add deionized water, stir well and let stand for 10 minutes, pour off the supernatant, and repeat the washing 3 to 5 times until the pH value of the washing solution reaches 7.0 to 7.5 and there is no ammonium chloride residue, to ensure the purity of AFt crystals;

[0088] Drying and enrichment: The washed AFt crystals were placed in a vacuum drying oven, the drying temperature was set to 70℃, the drying time was 3 hours, and the crystals were dried to constant weight to obtain AFt crystal concentrates. The SEM morphology of the concentrates is shown in the figure below. Figure 1 As shown. XRD analysis confirmed that the AFt crystal content was ≥65%. The sample was pulverized to a particle size ≤100μm, sealed, and stored for later use.

[0089] (3) Aggregate blending and mineral composition regulation

[0090] Determining the blending ratio: Based on the mineral database of the three types of aggregates and combined with the target parameters (free CaO 0.8%~1.8%, active SiO2 / Al2O3 2.2~3.2, total AFt crystal content ≥10%), the amount of waste ceramics was fixed at 10%. The amount of waste red bricks (45%~60%) and waste concrete blocks (30%~45%) was linearly adjusted, and AFt crystal enrichment (8%~15%) was added at the same time. The blending ratio of each group of aggregates was calculated and determined to ensure that the mineral parameters of the mixed aggregates after blending fall within the target range and that the mass ratio of coarse aggregate to fine aggregate of each type of aggregate after blending is 7:3.

[0091] Free CaO regulation:

[0092] If the free CaO content of the compounded aggregate is >1.8%, the compounded aggregate is placed in an oven at 70℃ (range 60~80℃) and dried for 2 hours. Then, an appropriate amount of deionized water is added for pre-wetting (moisture content controlled at 5%~8%). The aggregate is then placed in a constant temperature and humidity chamber (temperature 20±2℃, relative humidity ≥90%) for aging for 3 hours (range 2~4 hours) to promote the decomposition of free CaO into Ca(OH)2, eliminating potential volume stability issues. After aging, the aggregate is dried to a moisture content of 2%~4%.

[0093] If the free CaO in the blended aggregate is <0.8%, add lightly calcined lime powder (0.5%~1.2%) evenly to the blended aggregate, stir thoroughly to ensure uniform dispersion of the lightly calcined lime powder, replenish the alkalinity of the system, and provide a mild and continuous source of Ca. 2+ source;

[0094] Regulation of active SiO2 / Al2O3:

[0095] If the active SiO2 / Al2O3 ratio of the mixed aggregate after compounding is greater than 3.2, the amount of waste red bricks should be appropriately increased until the target range is reached.

[0096] If the ratio of active SiO2 / Al2O3 in the mixed aggregate after compounding is less than 2.2, add 5%~10% metakaolin to the mixed aggregate, or appropriately increase the amount of waste ceramics, stir evenly, supplement active Al2O3, and finely adjust to the target range to ensure a suitable supply of silicon and aluminum ions for AFt crystal growth.

[0097] Mixing and stirring: The regulated mixed aggregate (containing AFt crystal enrichment) is fed into a forced mixer and stirred for 120 seconds to ensure that the aggregate, AFt crystals, and regulators (lightly calcined lime powder and metakaolin) are mixed evenly without lumps or stratification, thus obtaining the preliminary modified mixed aggregate.

[0098] (4) Aggregate composite modification

[0099] Alkali activation: Prepare a 2% (by mass) composite alkali solution (sodium hydroxide: water glass = 1:2). Feed the pre-modified mixed aggregate into the spraying equipment and spray the composite alkali solution evenly (spraying amount is 2%~3% of the aggregate mass). During the spraying process, continuously stir to ensure that the aggregate surface is evenly covered with alkali solution, activate the active sites on the aggregate surface, and promote the bonding of AFt crystals with subsequent cement paste.

[0100] Silane coupling agent spraying: Cool the aggregate activated by alkali solution to room temperature, and spray the silane coupling agent evenly. The dosage is 0.3%~0.5% of the aggregate mass. Stir for 60 seconds to form a protective film on the surface of the aggregate with the silane coupling agent, reduce the water absorption rate of the aggregate, and improve the interfacial adhesion between the aggregate and the cement paste.

[0101] Ultrafine slag coating: Adding materials with a specific surface area ≥600m² to the sprayed aggregate. 2 The ultrafine slag powder is added at a rate of 3% to 5% of the mass of the mixed aggregate. The mixture is stirred continuously for 90 seconds to ensure that the ultrafine slag powder is evenly coated on the surface of the aggregate, filling the tiny pores on the surface of the aggregate and further optimizing the surface properties of the aggregate.

[0102] Drying control: The composite modified aggregate is sent into an oven and dried at 60℃ for 1 hour. The final moisture content of the aggregate is controlled at 2%~4%, and the water absorption rate is controlled at 5%~7%. Modified construction waste mixed aggregate containing AFt crystals is obtained, sealed and stored for later use.

[0103] 3. Concrete mixing

[0104] Equipment preparation: Use a forced concrete mixer. Clean the inner wall and mixing blades of the mixer in advance to ensure that there are no debris or water accumulation. Adjust the mixer speed to 140 r / min and set it aside.

[0105] Material metering: According to the mix proportions of the examples / comparative examples, accurately meter the supersulfate cement, modified mixed aggregate, natural sand, water, and polycarboxylate superplasticizer, and control the metering error within ±1% to avoid metering deviation from affecting concrete performance;

[0106] Segmented mixing:

[0107] S1: Feed the measured modified aggregate and natural sand (if needed) into the mixer and dry mix for 30 seconds to ensure that the aggregate is mixed evenly;

[0108] S2: Add the measured amount of supersulfate cement and continue dry mixing for 30 seconds to ensure that the cement evenly covers the surface of the aggregate.

[0109] S3: Mix the measured water and polycarboxylate superplasticizer evenly, slowly add it to the mixer, start the mixer, and mix for 90 seconds until the concrete mixture is uniform, fine, without lumps or segregation, and the slump is controlled at 120±10mm.

[0110] Mixture testing: After mixing, take samples immediately to test the slump and spread of the concrete mixture to ensure that it meets the construction requirements. If the slump is insufficient, the amount of water-reducing agent can be increased appropriately. If segregation occurs, the mixing time can be extended by 30 seconds.

[0111] 4. Casting and Standard Curing

[0112] Mold preparation: A 100mm×100mm×100mm cube mold is used for compressive strength testing, and a 100mm×100mm×400mm prism mold is used for drying shrinkage testing.

[0113] Casting and shaping: Slowly pour the well-mixed concrete mixture into the test mold. After pouring 1 / 3 of the test mold height, gently vibrate it with a vibrator for 20 seconds until there are no air bubbles or sinking on the surface of the mixture, ensuring that the concrete is dense. After casting, use a trowel to smooth the surface of the test mold and remove excess mixture.

[0114] Pre-curing: Place the poured test mold into a constant temperature and humidity curing chamber (temperature 20±2℃, relative humidity ≥95%) and pre-cur for 24 hours to ensure the initial setting of concrete and avoid surface cracking.

[0115] Demolding: After 24 hours of pre-curing, gently remove the mold to avoid damaging the surface of the test block. Mark the demolded test block.

[0116] Standard curing: Place the demolded test blocks into a standard curing room (temperature 20±2℃, relative humidity ≥95%) and cure until the specified age.

[0117] Examples and Comparative Examples

[0118] Example 1

[0119] A type of supersulfate cement concrete, the raw materials of which, by weight, include: 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (52% red brick + 38% waste concrete + 10% ceramics + 12% AFt enrichment), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (accounting for 1.0% of the cement mass).

[0120] After the mixed aggregate is compounded, the free CaO is 1.3% and the active SiO2 / Al2O3 ratio is 2.7, requiring no additional adjustment;

[0121] Aggregate modification involves spraying 2% of the mixed aggregate mass of composite alkaline solution (NaOH:water glass = 1:2), 0.4% of silane coupling agent, and 4% of ultrafine slag powder (specific surface area ≥600m²). 2 / kg) coating.

[0122] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0123] Distribution of early hydration products in concrete as follows Figure 3 As shown.

[0124] Example 2

[0125] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (48% red brick + 42% waste concrete + 10% ceramics + 10% AFt enrichment), 150 parts of water, 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass), and 3.3 parts of lightly calcined lime powder (external admixture, 0.3% of mixed aggregate mass).

[0126] After the aggregate is compounded, the initial free CaO is 1.0%, and the amount is adjusted to 1.2% by adding 0.3% lightly calcined lime powder. The active SiO2 / Al2O3 ratio is 2.8, and no additional adjustment is required.

[0127] The modified mixed aggregate is prepared by spraying 2% of the mixed aggregate with composite alkali solution, 0.4% of silane coupling agent, and 4% of ultrafine slag coating.

[0128] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0129] Example 3

[0130] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (58% red brick + 32% waste concrete + 10% ceramics + 15% AFt enrichment), 150 parts of water, 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass), and 88 parts of metakaolin (8% external admixture, accounting for 8% of mixed aggregate mass).

[0131] The initial active SiO2 / Al2O3 ratio after the mixed aggregate was compounded was 2.4. It was adjusted to 2.4 by adding 8% metakaolin. The free CaO was 1.5%, and no additional adjustment was required.

[0132] The modified mixed aggregate is prepared by spraying 2% of the mixed aggregate with composite alkali solution, 0.4% of silane coupling agent, and 4% of ultrafine slag coating.

[0133] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0134] Example 4

[0135] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (45% red brick + 45% waste concrete + 10% ceramics + 8% AFt enrichment), 150 parts of water, 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass), and 13.2 parts of lightly calcined lime powder (1.2% external admixture, accounting for the mass of mixed aggregate);

[0136] After the aggregate is compounded, the initial free CaO is 0.7%, and the amount is adjusted to 0.8% by adding 1.2% lightly calcined lime powder. The active SiO2 / Al2O3 ratio is 2.9, and no additional adjustment is required.

[0137] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0138] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0139] Example 5

[0140] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (60% red brick + 30% waste concrete + 10% ceramics + 12% AFt enrichment), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass).

[0141] After the aggregate is compounded, the free CaO content is 1.8%. It is stabilized by drying at 70℃ for 2 hours and pre-wetting and aging for 4 hours. The active SiO2 / Al2O3 ratio is 2.3, and no additional adjustment is required.

[0142] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0143] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0144] Example 6

[0145] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (55% red brick + 35% waste concrete + 10% ceramics + 12% AFt enrichment), 150 parts of water, 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass), and 55 parts of metakaolin (5% external admixture, accounting for 1.0% of mixed aggregate mass).

[0146] After the aggregate is compounded, the initial active SiO2 / Al2O3 ratio is 2.2, which is adjusted to 2.2 by adding 5% metakaolin. The free CaO is 1.4%, which does not require additional adjustment.

[0147] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0148] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0149] Example 7

[0150] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (46% red brick + 44% waste concrete + 10% ceramics + 12% AFt enrichment), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass).

[0151] After the aggregate is compounded, the free CaO content is 1.2% and the active SiO2 / Al2O3 ratio is 3.2, requiring no additional adjustment;

[0152] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0153] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0154] Example 8

[0155] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (50% red brick + 40% waste concrete + 10% ceramics + 12% AFt enrichment), 150 parts of water, 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass), and 6.6 parts of lightly calcined lime powder (0.6% external admixture, accounting for 0.6% of mixed aggregate mass);

[0156] After the aggregate is compounded, the initial free CaO is 1.0%, and the amount is adjusted to 1.3% by adding 0.6% lightly calcined lime powder. The active SiO2 / Al2O3 ratio is 2.6, and no additional adjustment is required.

[0157] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0158] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0159] Comparative Example 1

[0160] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of natural crushed stone + natural sand (coarse aggregate: fine aggregate = 7:3), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass).

[0161] The concrete is mixed, poured, and cured according to a standardized process without any additional treatment.

[0162] The morphology of Aft crystals generated during the hydration of supersulfate cement in this comparative example is as follows: Figure 2 As shown; the distribution of early hydration products in concrete is as follows Figure 4 As shown.

[0163] Comparative Example 2

[0164] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of mixed aggregate (52% red brick + 38% waste concrete + 10% ceramics), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass).

[0165] Construction waste aggregates undergo only sorting, crushing, air separation, magnetic separation for impurity removal, and screening pretreatment. After blending, the free CaO content is 1.3%, and the active SiO2 / Al2O3 ratio is 2.7.

[0166] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0167] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0168] Comparative Example 3

[0169] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of mixed aggregate (52% red brick + 38% waste concrete + 10% ceramic), 132 parts of commercially available AFt seed crystals (external admixture, accounting for 12% of the mass of mixed aggregate), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (accounting for 1.0% of the cement mass).

[0170] After compounding, the free CaO content is 1.3%, and the active SiO2 / Al2O3 ratio is 2.7.

[0171] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0172] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0173] Comparative Example 4

[0174] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (52% red brick + 38% waste concrete + 10% ceramics + 12% AFt enrichment), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass).

[0175] After the aggregate is compounded, the free CaO content is 2.5%, and the active SiO2 / Al2O3 ratio is 2.6.

[0176] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0177] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0178] Comparative Example 5

[0179] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (52% red brick + 38% waste concrete + 10% ceramics + 4% AFt enrichment), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass).

[0180] After the aggregate is compounded, the free CaO content is 1.3% and the active SiO2 / Al2O3 ratio is 3.2, requiring no additional adjustment;

[0181] The composite modification involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0182] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0183] Comparative Example 6

[0184] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (52% red brick + 38% waste concrete + 10% ceramics + 16% AFt enrichment), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass).

[0185] After the aggregate is compounded, the free CaO content is 1.3% and the active SiO2 / Al2O3 ratio is 2.3, requiring no additional adjustment;

[0186] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0187] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0188] Comparative Example 7

[0189] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of modified mixed aggregate containing AFt crystals (65% red brick + 25% waste concrete + 10% ceramics + 12% AFt enrichment), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass).

[0190] After the aggregate was compounded, the free CaO content was 2.1%, the active SiO2 / Al2O3 ratio was 3.5, and no mineral parameter adjustments were made.

[0191] The composite modification of mixed aggregates involves spraying with 2% composite alkali solution, applying 0.4% silane coupling agent, and coating with 4% ultrafine slag.

[0192] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0193] Comparative Example 8

[0194] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of mixed aggregate containing AFt crystals (52% red brick + 38% waste concrete + 10% ceramics + 12% AFt enrichment), 150 parts of water, and 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass).

[0195] After the aggregate is compounded, the free CaO content is 1.3% and the active SiO2 / Al2O3 ratio is 2.7, requiring no additional adjustment.

[0196] The mixed aggregates are not subject to composite alkali spraying, silane coupling agent spraying, or ultrafine slag coating modification.

[0197] The mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0198] Comparative Example 9

[0199] Mix proportions (parts by weight): 420 parts of supersulfate cement, 1100 parts of natural crushed stone + natural sand (coarse aggregate: fine aggregate = 7:3), 150 parts of water, 4.2 parts of polycarboxylate superplasticizer (1.0% of cement mass), and 6.3 parts of sodium hydroxide (external admixture, 1.5% of cement mass).

[0200] Without mineral regulation and aggregate modification, the mixing, pouring, and curing of concrete shall be carried out in accordance with the above-mentioned unified process.

[0201] The performance test results of the embodiments and comparative examples are as follows: Figures 5-6 And as shown in Table 1.

[0202] Table 1. Data from the Examples and Comparative Examples

[0203]

[0204]

[0205] As shown in Table 1 and Figure 5As shown, the 1-day compressive strength of Examples 1-8 is 18.2-21.5 MPa, which is 136%-202% higher than that of Comparative Example 1 (7.1 MPa) with natural aggregate, and 11%-18% higher than that of the scheme without AFt extraction (Comparative Example 2). This fully demonstrates the core driving role of in-situ extracted AFt crystals and synergistic hydration in early strength. Compared with Comparative Example 3 (external AFt, 1-day strength 17.2 MPa), the 1-day strength of the scheme of the present invention is higher, indicating that the AFt crystals in situ bonded to the aggregate have better compatibility with the supersulfate cement system and a more significant seed induction effect.

[0206] As shown in Table 1 and Figures 5-6 Examples 4 (8% AFt doping, 1-day strength 18.2 MPa) and 3 (15% AFt doping, 1-day strength 19.8 MPa) show that when the AFt crystal doping is controlled between 8% and 15%, the 1-day strength continuously increases. However, the 1-day strength of Comparative Example 5 (AFt doping < 5%) and Comparative Example 6 (AFt doping > 15%) is lower than that of the examples, indicating that the AFt doping range of 8% to 15% is not an obvious optimal range, and deviation from this range will not achieve the best effect of synergistic hydration.

[0207] Examples 1-8 demonstrate that by precisely controlling mineral parameters, free CaO (0.8%-1.8%) and the SiO2 / Al2O3 activity ratio (2.2-3.2) synergistically combine with AFt crystals to achieve both high early strength and satisfactory stability. In contrast, Comparative Example 7 (free CaO 2.1%, SiO2 / Al2O3 = 3.5, no compound control) exhibited a 1-day strength of only 14.2 MPa and poor stability. This demonstrates that the combined control of mineral parameters and AFt crystals is a key innovation and cannot be replaced by a single factor.

[0208] The 90-day drying shrinkage of Examples 1-8 is ≤340×10⁻⁸. -6 Comparison Example 1 (512×10 -6 The strength of the material is reduced by ≥35%, the crack resistance level reaches Grade I, and the strength continues to increase in the later stage without shrinkage. Compared with Comparative Example 9 (external addition of early strength agent, excessive shrinkage), this invention solves the technical contradiction between early strength and shrinkage, demonstrating the technical advantages of AFt synergistic hydration.

[0209] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0210] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A type of supersulfate cement concrete based on construction waste aggregates and minerals, characterized in that, By mass parts, it includes the following components: 380-460 parts of supersulfate cement; 950-1250 parts of modified mixed aggregate; 0-150 parts of natural sand; 135-165 parts water; Water-reducing agent, at 0.7-1.2% of the total mass of cementitious materials; The modified mixed aggregate is obtained by mixing construction waste and calcium vanadium stone enrichment in a mass ratio of (85-92):(8-15) and then modifying it with alkali solution, silane coupling agent and slag in sequence. The content of calcium vanadate crystals in the calcium vanadate enrichment is ≥65%; The modified mixed aggregate contains 0.8-1.8% free CaO, 2.2-3.2 active SiO2 / Al2O3, and ≥10% calcium vanadate crystals.

2. The construction and demolition waste aggregate and mineral based supersulfated cement concrete according to claim 1, characterized in that, The calcium vanadium concentrate was obtained by extracting, washing, and drying waste concrete with ammonium chloride solution; the waste concrete contained 0.5-0.9% free CaO and had an active SiO2 / Al2O3 ratio of 3.2-3.

8.

3. The construction waste aggregate and mineral supersulfate cement concrete according to claim 2, characterized by, The preparation of the calcium vanadate concentrate includes the following steps: The waste concrete was crushed to a particle size ≤5mm, and the ammonium chloride solution was added to react. After the reaction was completed, the solid and liquid were separated, the precipitate was collected, washed with deionized water until no ammonium chloride residue remained, and then dried to obtain the calcium vanadium stone enrichment.

4. The construction and demolition waste aggregate and mineral based ultra-sulphate cement concrete as claimed in claim 2, wherein, The mass concentration of the ammonium chloride solution is 5-8%; and / or the solid-liquid ratio of the waste concrete to the ammonium chloride solution is 1:(3-5).

5. The construction and demolition waste aggregate and mineral based supersulfated cement concrete as claimed in claim 1, wherein, The preparation of the modified mixed aggregate includes the following steps: The construction waste is crushed and graded, then mixed with the calcium vanadium concentrate to obtain mixed aggregate; the alkaline solution is added to the mixed aggregate for activation; after the reaction is complete, a silane coupling agent is added and mixed evenly; finally, an additive with a specific surface area ≥600 m² is added. 2 / kg of slag powder is mixed evenly and then dried to a moisture content of 2-4% to obtain the modified mixed aggregate.

6. The supersulfate cement concrete based on construction waste aggregates and minerals according to claim 5, characterized in that, The mass concentration of the alkali solution is 1.2-5%; and / or, the amount of alkali solution added is 2-3% of the mass of the mixed aggregate; and / or, the amount of silane coupling agent added is 0.3-0.5% of the mass of the mixed aggregate; and / or, the amount of slag powder added is 3-5% of the mass of the mixed aggregate.

7. The supersulfate cement concrete based on construction waste aggregates and minerals according to claim 6, characterized in that, The solute in the alkaline solution includes sodium hydroxide and water glass, and the mass ratio of sodium hydroxide to water glass is 1:1.5-4.

8. The supersulfate cement concrete based on construction waste aggregates and minerals according to any one of claims 1-7, characterized in that, The construction waste includes at least one of waste ceramics, waste red bricks, and waste concrete.

9. The construction and demolition waste aggregate and mineral based supersulfated cement concrete as claimed in claim 1, wherein, The supersulfate cement comprises slag, gypsum, and clinker; by mass percentage, it includes: Slag content: 76-84%; 13-18% plaster; Clinker 3-6%.

10. The method for preparing supersulfate cement concrete based on construction waste aggregates and minerals according to any one of claims 1-9, characterized in that, Includes the following steps: S1. Weigh out the supersulfate cement, modified mixed aggregate, natural sand, water and water-reducing agent respectively; S2. Mix the modified aggregate and natural sand evenly, then add supersulfate cement and mix evenly to obtain the mixture. S3. Mix water and water-reducing agent evenly to obtain a water-reducing agent solution; S4. Add the water-reducing agent solution to the mixture and mix evenly to obtain the supersulfate cement concrete.

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