Lightweight high-strength concrete and mix proportion design method thereof

Abstract

The invention discloses lightweight high-strength concrete and a mix proportion design method thereof, belongs to the technical field of building materials, and aims to solve the technical problems that in the related technology, compound aggregate is prone to segregation due to density difference, interface bonding is weak, and strength development is restricted. The lightweight high-strength concrete is prepared from the following raw materials in per cubic meter of concrete: 380 to 600 kg / m < 3 > of a cementing material, 3.5 to 18 kg / m < 3 > of a nano reinforced phase, 700 to 1100 kg / m < 3 > of a compound aggregate and 0.8 to 2.0 kg / m < 3 > of an inorganic fiber reinforcement, the nano reinforcing phase is selected from nano silicon dioxide and / or nano aluminum oxide, the specific surface area of the nano reinforcing phase is larger than or equal to 200 m < 2 > / g, and the particle size of the nano reinforcing phase is 5-50 nm. Through the design of low water-binder ratio and the introduction of the nano reinforced phase, a concrete compact matrix is constructed; by adding the water reducing agent and a proper amount of fiber, the standing segregation rate of the freshly mixed concrete is effectively reduced under the condition that the viscosity of the concrete is not obviously increased.

Description

A lightweight high-strength concrete and its mix design method Technical Field

[0001] This application relates to the field of building materials technology, and in particular to a lightweight high-strength concrete and its mix design method. Background Technology

[0002] With the increasing number of building stories and the ever-expanding span of structures, there is a growing demand for high-strength, low-density concrete. However, ordinary concrete is heavy and accounts for a large proportion of the total building load, making it even more important to reduce its self-weight. Traditional ordinary concrete has a high density (typically ≥2400 kg / m³). 3 Traditional concrete, characterized by its high brittleness and limited functionality, is no longer sufficient to meet the diverse needs of modern engineering. Lightweight high-strength concrete, on the other hand, utilizes artificial or natural lightweight aggregates instead of ordinary high-density aggregates. Compared to ordinary concrete, it boasts advantages such as lighter weight, higher strength, better seismic performance, better fire resistance, better durability, and superior thermal insulation. Furthermore, the production of lightweight aggregates and the preparation of lightweight aggregate concrete utilize large quantities of industrial solid waste such as fly ash and silica fume, thus reducing environmental pollution.

[0003] In lightweight high-strength concrete, lightweight aggregates such as shale ceramsite and clay ceramsite sand can effectively reduce the apparent density of concrete to 1400-1950 kg / m³. 3 However, its low strength and high water absorption limit the overall mechanical properties of concrete, especially its 28-day compressive strength, which is generally below 40 MPa, making it difficult to meet the "high-strength" standard (high-strength concrete in GB / T 17671-2021 generally refers to ≥50 MPa). High-titanium heavy slag is a large byproduct generated during the smelting of vanadium-titanium magnetite, with annual emissions exceeding ten million tons. Traditional disposal methods mainly involve stockpiling, which not only occupies land but also poses a risk of heavy metal leakage. Appropriately treated high-titanium heavy slag has high hardness and potential cementitious activity, and can be used as coarse aggregate in concrete. However, its density is relatively high (>2800 kg / m³). 3 When used alone, it cannot achieve the goal of "lightweight". If it is simply compounded with lightweight aggregate, it is prone to segregation due to density difference, and the interfacial bonding is weak, which restricts the development of strength.

[0004] Therefore, there is an urgent need to develop a lightweight, high-strength concrete that can reduce the density of concrete while ensuring high aggregate strength by using high-titanium heavy slag composite lightweight aggregate. Summary of the Invention

[0005] This application discloses a lightweight high-strength concrete and its mix design method to solve the technical problem in related technologies where high-titanium heavy slag compounded with lightweight aggregate has weak interfacial bonding, which restricts the development of strength.

[0006] To solve the above problems, this application adopts the following technical solution:

[0007] In the first aspect, this application proposes a lightweight, high-strength concrete comprising the following raw materials per cubic meter of concrete: 380-600 kg / m³ 3 Cementitious materials, 3.5-18 kg / m 3 Nano-reinforced phase, 700-1100 kg / m 3 The compound aggregate and 0.8-2.0 kg / m 3 Inorganic fiber reinforcement.

[0008] Furthermore, it also includes water-reducing agents and mixing water; the water-reducing agent content is 0.8-1.5% of the total mass of the cementitious material; the mixing water controls the water-cement ratio at 0.28-0.32:1.

[0009] Furthermore, the compound aggregate is composed of coarse aggregate and fine aggregate, and the mass ratio of coarse aggregate to fine aggregate is 0.4-1.2:1.

[0010] Furthermore, the nano-reinforcing phase is selected from nano-silica and / or nano-alumina, and its specific surface area is ≥200 m². 2 / g, with a particle size of 5-50 nm.

[0011] Furthermore, per cubic meter of concrete, it also includes 0-30 kg / m³. 3 The phase change material is a microcapsule with paraffin as the core material and silica as the shell material, and its particle size is 10-50 μm.

[0012] Furthermore, the concrete also contains an air-entraining agent, with the air-entraining agent content being 0.02-0.05% of the total mass of the cementitious materials.

[0013] Furthermore, the inorganic fiber reinforcement is basalt fiber, alkali-resistant glass fiber and / or steel fiber, and its length is 6-18 mm, tensile strength ≥3000 MPa, and elastic modulus ≥90 GPa.

[0014] Furthermore, the coarse aggregate is at least one of high-titanium heavy slag, steel slag and copper slag, and it is a particle with a particle size in the range of 5-20 mm.

[0015] Furthermore, the fine aggregate is at least one of shale, clay and fly ash ceramsite, and it is a particle with a particle size in the range of 0.16-5.0 mm.

[0016] Furthermore, the cementitious material includes cement and mineral admixtures, wherein cement accounts for 60-90% of the total mass of the cementitious material, and mineral admixtures account for 10-40% of the total mass of the cementitious material. The mineral admixtures are at least one of fly ash, mineral powder, and silica fume.

[0017] Furthermore, the water-reducing agent is a modified polycarboxylate-based water-reducing agent.

[0018] Secondly, this application also proposes a mix design method for lightweight high-strength concrete as described in the first aspect, comprising the following steps:

[0019] Step 1: Based on the structural and functional requirements corresponding to the engineering application scenario, divide the target project into one of the following three scenarios:

[0020] A. Lightweight load-bearing components, with an apparent density ≤1850 kg / m³ 3 And the 28-day compressive strength is ≥60 MPa;

[0021] B. Structures designed for cold or large temperature difference environments must have phase change temperature regulation function, freeze resistance rating ≥ F300, and thermal conductivity ≤ 0.8 W / (m·K);

[0022] C. High-toughness and impact-resistant structure, requiring 1-day compressive strength ≥25 MPa and impact toughness ≥30% higher than ordinary concrete;

[0023] Step 2: Set the total amount of cementitious material to 380-600 kg / m³ 3 It includes cement and mineral admixtures. The cement ratio is adjusted according to the scenario. Specifically, in scenario A, the cement ratio is 60-75%, in scenario B, the cement ratio is 65-80%, and in scenario C, the cement ratio is 75-90%.

[0024] Based on per cubic meter of concrete, the dosage of inorganic fiber reinforcement in scenario A is 0.8-1.2 kg / m³. 3 In scenario B, the value is 1.0-1.8 kg / m³. 3 In scenario C, the concentration is 1.5-2 kg / m³. 3 ;

[0025] The water-reducing agent dosage is 0.8-1.5% of the total mass of cementitious materials, so that the slump of fresh concrete is in the range of 180-220 mm;

[0026] Step 3: The amount of compound aggregate should be 700-1100 kg / m³ of concrete. 3 Based on the scenario type in step 1, determine the mass ratio of coarse aggregate to fine aggregate in the composite aggregate:

[0027] For scenario A, the mass ratio of coarse aggregate to fine aggregate is set to 0.4-0.7:1;

[0028] For scenario B, set the mass ratio of coarse aggregate to fine aggregate to 0.7-1.0:1, and add phase change material;

[0029] For scenario C, the mass ratio of coarse aggregate to fine aggregate is set to 0.9-1.2:1;

[0030] Step 4: Phase change materials and air-entraining agents are only introduced in scenario B. The dosage of phase change materials is 15-40 kg / m³ of concrete. 3 The air-entraining agent content is 0.02-0.05% of the total mass of the cementitious material;

[0031] Step 5: In scenario A, the doping concentration of the nano-reinforcing phase is 3.5-12 kg / m³. 3 In scenario C, the doping concentration of the nano-reinforcing phase is 16-18 kg / m³. 3 In scenario B, the doping amount of the nano-reinforced phase is taken as M. min -18 kg / m 3 ;in,

[0032]

[0033] M 相变 The amount of phase change material in each cubic meter of concrete;

[0034] Step 6: Prepare test samples and measure the 28-day compressive strength, dry apparent density and impact energy of the samples; if any index deviates from the target threshold by more than ±10%, return to Step 2, Step 3, Step 4 and / or Step 5, and adjust the allocation ratio of each group until the performance requirements of the scenario are met.

[0035] Furthermore, step 2 also includes the following steps: based on the total mass of the cementitious material, controlling the water-cement ratio to be between 0.25 and 0.32:1, and determining the amount of mixing water.

[0036] Furthermore, in step 2, when the amount of inorganic fiber reinforcement is ≥1.5 kg / m 3 Or the amount of phase change material is ≥20 kg / m 3 When the water-reducing agent is added, the dosage is ≥1.2%, and the stirring time of the water-reducing agent is ≥180 s.

[0037] Furthermore, in step 3, the selection of coarse and fine aggregates ensures that the aggregate stability index is ≤62; the aggregate density-particle size matching index is calculated using the following formula:

[0038]

[0039] in:

[0040] ASI: Aggregate Stability Index;

[0041] ρ cApparent density of coarse aggregate, in kg / m³ 3 ;

[0042] ρ f Bulk density of fine aggregate, in kg / m³ 3 ;

[0043] d c : Maximum coarse aggregate size, in meters;

[0044] d p Water-reducing agent dosage, in percentages.

[0045] Furthermore, if the aggregate stability index is >62, the dosage of water-reducing agent can be increased, and ρ can be replaced. f Larger fine aggregates and / or reduced maximum particle size of coarse aggregates.

[0046] The technical solution adopted in this application can achieve the following beneficial effects:

[0047] This application constructs a dense concrete matrix through a low water-cement ratio design and the introduction of nano-reinforcing phases, achieving a 28-day compressive strength of 55-75 MPa. Simultaneously, by using a high proportion of lightweight fine aggregates in the composite aggregate, the apparent density of the concrete is reduced to 1600-1950 kg / m³, meeting the requirements for lightweighting. By adding water-reducing agents and appropriate amounts of fibers, a dual stabilization mechanism of "high yield stress + spatial barrier" is formed without significantly increasing the concrete viscosity, effectively reducing the segregation rate of fresh concrete after standing. This application realizes the resource utilization of industrial waste coarse aggregate, possessing both environmental and economic value. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 is a flowchart illustrating the mix design method for lightweight high-strength concrete in some embodiments of this application. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0051] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0052] In existing technologies, lightweight aggregates such as shale ceramsite and clay ceramsite sand can effectively reduce the apparent density of concrete. However, their low strength and high water absorption limit the overall mechanical properties of concrete, especially the 28-day compressive strength, which is generally below 40 MPa, making it difficult to achieve the "high strength" standard. Appropriately treated high-titanium heavy slag has high hardness and potential cementitious activity, making it suitable as coarse aggregate in concrete. However, its high density means that using it alone cannot achieve the "lightweight" goal. Simple blending with lightweight aggregates easily leads to segregation due to density differences, and weak interfacial bonding restricts strength development.

[0053] This application constructs a dense concrete matrix through a low water-cement ratio design and the introduction of nano-reinforcing phases, achieving a 28-day compressive strength of 55-75 MPa. Simultaneously, by using a high proportion of lightweight and fine aggregates in the composite aggregate, the apparent density of the concrete is reduced to 1600-1950 kg / m³. 3 This invention meets the requirements for lightweighting; by adding water-reducing agents and appropriate amounts of fibers, a dual stabilization mechanism of "high yield stress + spatial isolation" is formed without significantly increasing the viscosity of concrete, effectively reducing the segregation rate of fresh concrete after static setting; this application realizes the resource utilization of industrial waste coarse aggregate, which has both environmental and economic value.

[0054] The following description, in conjunction with Figure 1, details a lightweight high-strength concrete and its mix design method provided in this application through specific embodiments and application scenarios.

[0055] In the first aspect, this application proposes a lightweight, high-strength concrete comprising the following raw materials per cubic meter of concrete: 380-600 kg / m³ 3 Cementitious materials, 3.5-18 kg / m 3 Nano-reinforced phase, 700-1100 kg / m 3 The compound aggregate and 0.8-2.0 kg / m 3The inorganic fiber reinforcement also includes a water-reducing agent and mixing water; the water-reducing agent content is 0.8-1.5% of the total mass of the cementitious material; the mixing water controls the water-cement ratio at 0.28-0.32:1.

[0056] Specifically, the cementitious material is a composite system of silicate cement and mineral admixtures, wherein the mineral admixtures include at least one of fly ash, mineral powder or silica fume, and the admixture accounts for 10-40% of the total amount of cementitious material;

[0057] The nano-reinforcing phases are nano-silica (SiO2) and / or nano-alumina (Al2O3), which are used to fill micropores, strengthen the interfacial transition zone (ITZ) and improve the early strength development rate.

[0058] Compound aggregates have an apparent density of 2800-3200 kg / m³ 3 Industrial waste coarse aggregate (such as high-titanium heavy slag, steel slag, or iron tailings crushed stone) with a bulk density of 600-900 kg / m³ 3 Lightweight fine aggregates (such as shale ceramsite, fly ash ceramsite, or expanded perlite sand) are compounded at a mass ratio of 0.4-1.2:1, and the maximum particle size of coarse aggregates does not exceed 20 mm.

[0059] Inorganic fiber reinforcements are basalt fibers, alkali-resistant glass fibers, or steel fibers, with a length of 6-18 mm, used to suppress plastic shrinkage cracking and improve impact toughness;

[0060] The water-reducing agent is a modified polycarboxylate-based high-performance water-reducing agent, with a dosage of 0.8-1.5% of the total mass of cementitious materials. It has a retarding-slump-preserving molecular structure, which can effectively maintain the fluidity loss rate of fresh concrete within 90 minutes at less than 15%.

[0061] The amount of mixing water is controlled to maintain the water-cement ratio (the mass ratio of water to cementitious materials) within the range of 0.28-0.32:1, ensuring that the slurry has high yield stress (≥35 Pa) and moderate plastic viscosity (0.25–0.40 Pa·s), thereby effectively suppressing the segregation tendency of high density differential aggregate systems.

[0062] This application constructs a dense concrete matrix through a low water-cement ratio design and the introduction of nano-reinforcing phases, achieving a 28-day compressive strength of 55-75 MPa. Simultaneously, by using a high proportion of lightweight and fine aggregates in the composite aggregate, the apparent density of the concrete is reduced to 1600-1950 kg / m³. 3 This invention meets the requirements for lightweighting; by adding water-reducing agents and appropriate amounts of fibers, a dual stabilization mechanism of "high yield stress + spatial isolation" is formed without significantly increasing the viscosity of concrete, effectively reducing the segregation rate of fresh concrete after static setting; this application realizes the resource utilization of industrial waste coarse aggregate, which has both environmental and economic value.

[0063] In some embodiments, the nano-reinforcing phase selected is nano-silica and / or nano-alumina, with a specific surface area ≥200 m². 2 / g, with a particle size of 5-50 nm. These nanoparticles have high reactivity and strong filling effect, and can effectively participate in the hydration reaction of cementitious materials to generate additional CSH gel or calcium aluminum feldspar products, thereby significantly refining the pore structure, strengthening the aggregate-paste interface transition zone (ITZ), and improving the early and late mechanical properties of concrete.

[0064] For example, when the nano-silica doping concentration is 8 kg / m 3 (Contains approximately 1.5%–2.0% of the cementitious material), with a specific surface area of ​​220 m². 2 When the average particle size is 15 nm, compared with the control group without nanoparticles, the 28-day compressive strength is increased by 12%–18%, and the drying shrinkage is reduced by about 20%; when combined with 5 kg / m 3 Nano-alumina (specific surface area 210 m²) 2 When the concrete has a particle size of 20 nm (g), it can maintain high strength (≥65 MPa) while increasing its sulfate resistance coefficient to over 0.92, making it suitable for engineering projects in harsh environments.

[0065] In some embodiments, the nano-reinforcing phase is added during the mixing process by high-speed shear dispersion or by pre-ultrasonic premixing with a portion of the mixing water to avoid agglomeration, ensure its uniform distribution in the slurry, and fully utilize the nanoscale effect.

[0066] In some embodiments, 0-30 kg / m³ of concrete is also included. 3 The phase change material is a microcapsule with paraffin as the core and silica as the shell, with a particle size of 10-50 μm and a phase change temperature range of 18-28℃, suitable for passive temperature regulation requirements in building envelopes. This microcapsule phase change material is prepared via sol-gel or interfacial polymerization, exhibiting a dense shell with good thermal stability and tolerance to alkaline environments. It effectively prevents paraffin leakage within a cement matrix and maintains a latent heat loss rate of less than 10% after multiple thermal cycles (≥500 cycles).

[0067] For example, when 20 kg / m 3When phase change material microcapsules (average particle size 30 μm, latent heat of phase change ≥180J / g) are used, the equivalent heat capacity of concrete increases by about 35%, and the surface temperature fluctuation range is reduced by 4-6℃ in simulated diurnal temperature difference environment, significantly improving indoor thermal comfort. At the same time, since the microcapsules are spherical and the particle size is much smaller than that of fine aggregates, the impact on workability is controllable. Under the condition that the water-reducing agent dosage is increased to 1.2-1.4%, the slump spread of concrete can still be maintained at 550-650mm, and the loss after 1 hour is ≤30mm.

[0068] Although the incorporation of phase change material microcapsules slightly reduces compressive strength (approximately 3-8%), the nano-reinforcing phase (e.g., 10 kg / m³) can mitigate this. 3 The interfacial strengthening effect of nano-SiO2 can control the strength reduction within an acceptable range, and the final 28-day compressive strength can still reach 53-60 MPa, which meets the load-bearing requirements of multi-layer prefabricated exterior wall panels or cold-region structural components.

[0069] In some embodiments, the concrete further comprises an air-entraining agent, the content of which is 0.02-0.05% of the total mass of the cementitious materials. For example, the air-entraining agent is a high-performance air-entraining agent of rosin soap, alkyl sulfonate, or polyether-modified triterpenoid saponin, capable of introducing a large number of uniform, stable, and closed microbubbles during mixing, with an average pore size of 50-200 μm and an air content controlled within the range of 2.0-4.5%.

[0070] In the low water-cement ratio (0.28–0.32:1) and high powder content system of this invention, appropriate air entrainment can significantly improve the workability and segregation resistance of fresh concrete. On the one hand, microbubbles enhance the fluidity of the paste; on the other hand, the bubble network can buffer the aggregate settling path, especially playing a positive role in inhibiting the rapid settling of high-density coarse aggregates. Simultaneously, after hardening, these closed micropores can effectively improve the concrete's resistance to freeze-thaw cycles and salt erosion without significantly sacrificing strength (the compensating effect of nano-reinforcement on matrix densification).

[0071] In addition, the dosage of the air-entraining agent needs to be strictly controlled. When the dosage is below 0.02%, the number of bubbles is insufficient, and the improvement effect is limited; when it exceeds 0.05%, the risk of bubble coalescence increases, which may lead to a significant decrease in strength or surface powdering. Therefore, this application limits the air-entraining agent to the range of 0.02-0.05% to achieve a balance between workability, stability and durability.

[0072] In some embodiments, the inorganic fiber reinforcement is basalt fiber, alkali-resistant glass fiber, and / or steel fiber, with a length of 6-18 mm, tensile strength ≥3000 MPa, and elastic modulus ≥90 GPa. These fibers possess high strength, high modulus, alkali resistance, and good dispersibility, enabling them to form a three-dimensional, randomly distributed micro-reinforced network in the concrete matrix. This effectively inhibits settlement cracks during the plastic stage and the propagation of microcracks after hardening, while simultaneously improving impact toughness and flexural performance. In the dense matrix of this application with a low water-cement ratio (0.28-0.32:1) and high powder content, these high-performance inorganic fibers not only bridge microcracks but also significantly improve the suspension stability of high-density differential aggregates through physical barrier effects, reducing the risk of segregation during static settling.

[0073] For example, when using short-cut basalt fibers with a length of 12 mm, a tensile strength of 3200 MPa, and an elastic modulus of 105 GPa, the dosage is 1.2 kg / m 3 At that time, the initial impact cracking count of the concrete increased from 28 to 57 without fiber reinforcement, and the final impact cracking count increased from 45 to 89, indicating a nearly doubling of impact toughness. Simultaneously, after 1 hour of settling, the coarse aggregate enrichment at the bottom decreased from 8.7% to 4.1%, meeting the stringent homogeneity requirements for pumping and precast components. Furthermore, the 28-day compressive strength remained at 64 MPa, and the apparent density was 1780 kg / m³. 3 It combines lightweight, high strength and high toughness.

[0074] When the fiber length is less than 6 mm, the bridging effect is insufficient; when it exceeds 18 mm, it is prone to clumping during stirring, affecting the uniformity of dispersion. Therefore, this application limits the fiber length to 6-18 mm and combines it with a high-efficiency water-reducing agent and optimized sand ratio to ensure that it is fully dispersed in high-viscosity slurry and fully exerts its reinforcing and toughening performance.

[0075] In some embodiments, the coarse aggregate is at least one of high-titanium heavy slag, steel slag, and copper slag, and is obtained by crushing and screening, with a particle size in the range of 5-20 mm and an apparent density of 2800-3200 kg / m³. 3 The aforementioned industrial waste coarse aggregate possesses high hardness, high density, and good chemical stability, which can effectively improve the volume stability and compressive strength of concrete. Simultaneously, its porous or microcrystalline surface structure facilitates mechanical bonding with cement paste, enhancing interfacial adhesion. By blending it with lightweight fine aggregate, the apparent density of concrete can be significantly reduced while maintaining strength.

[0076] For example, when using particles with a diameter of 5-20 mm and an apparent density of 3050 kg / m³ 3 High-titanium heavy slag was used as coarse aggregate (accounting for 45% of the total amount of composite aggregate), with a bulk density of 780 kg / m³.3 When shale clay sand (55%) is used as a blend, the prepared concrete has a 28-day compressive strength of 68 MPa and an apparent density of 1820 kg / m³. 3 After standing for 1 hour, the segregation rate was only 3.8%.

[0077] Furthermore, when the coarse aggregate particle size is less than 5 mm, it tends to resemble fine aggregate, disrupting the continuity of gradation; when it is greater than 20 mm, it significantly increases the risk of sedimentation and segregation. Therefore, this application strictly limits the coarse aggregate particle size to 5-20 mm to balance strength contribution and stability.

[0078] In some embodiments, the fine aggregate is at least one of shale, clay, and fly ash ceramsite sand, which consists of particles with a particle size in the range of 0.16-5.0 mm formed after high-temperature sintering and expansion, and a bulk density of 600-900 kg / m³. 3 The cylinder compressive strength is ≥3.0 MPa, and the water absorption rate (24 h) is 8-18%.

[0079] The aforementioned lightweight ceramic sand possesses a porous structure, low density, and good thermal stability, which can effectively reduce the apparent density of concrete and improve its thermal insulation performance. Simultaneously, its rough surface and moderately angular shape facilitate mechanical anchoring with cement paste, compensating for potential interfacial weakening issues caused by its low density. Through blending with high-density industrial waste coarse aggregate, a gradient stable structure with a heavier inner core and lighter outer core can be achieved without significantly sacrificing strength, suppressing segregation and improving homogeneity.

[0080] Furthermore, when the particle size of fine aggregate is less than 0.16 mm, it tends to resemble mineral admixtures, which can easily lead to a surge in water demand; when it is greater than 5.0 mm, the boundary with coarse aggregate becomes blurred, disrupting the continuity of gradation and exacerbating the risk of segregation. Therefore, this application strictly limits the particle size of fine aggregate to 0.16-5.0 mm to ensure good filling properties and volume stability.

[0081] Furthermore, the water-reducing agent is a modified polycarboxylate-based water-reducing agent, with retarding functional groups (such as phosphate groups and carboxylic acid ester groups) and / or slump-retaining side chains (such as polyoxyethylene-polyoxypropylene block copolymers) grafted onto its molecular backbone. It exhibits high dispersibility, excellent slump retention, and good adaptability to systems with high powder content. This application utilizes a low water-to-binder ratio (0.28-0.32:1) and a high binder content (380-600 kg / m³). 3 In complex multiphase systems containing nanoparticles, mineral admixtures, and lightweight aggregates, conventional polycarboxylate superplasticizers are prone to rapid loss of fluidity due to adsorption competition or rapid formation of slurry structure. Modified polycarboxylate superplasticizers, by regulating molecular configuration and adsorption kinetics, can effectively delay early hydration and flocculation of cement, maintaining a stable rheological state of the slurry within 60-90 minutes, thus ensuring the requirements for pumping, casting, and homogenization.

[0082] For example, when a phosphate-modified polycarboxylate superplasticizer (40% solids content, ≥30% water reduction rate) is used at a dosage of 1.2% of the total mass of cementitious materials, the initial slump spread of the concrete reaches 620 mm, and remains at 570 mm after 1 hour, with a time loss rate of only 8%. The V-shaped funnel outflow time decreases from 11.3 s in the unmodified PCE system to 8.5 s, indicating a significant improvement in slurry fluidity and stability. Under these conditions, the segregation rate of the compound aggregate (high-titanium slag + shale ceramsite sand) after 1 hour of standing is only 3.9%, far lower than the 7.2% of the ordinary PCE system.

[0083] Furthermore, the dosage of modified polycarboxylate superplasticizer needs to be controlled within the range of 0.8-1.5%. Below 0.8%, insufficient dispersion and slump retention can easily lead to segregation; above 1.5%, it may cause excessive retardation or air entrainment side effects, affecting early strength development. Therefore, this application achieves synergistic optimization of high strength, lightweight, and high stability by limiting the type and dosage range of superplasticizer.

[0084] Secondly, this application also proposes a mix design method for lightweight high-strength concrete as described in the first aspect, comprising the following steps:

[0085] Step 1: Based on the structural and functional requirements corresponding to the engineering application scenario, divide the target project into one of the following three scenarios:

[0086] Scenario A. Lightweight load-bearing components, with an apparent density ≤1850 kg / m³ 3 Furthermore, its 28-day compressive strength is ≥60 MPa, making it suitable for load-bearing components that are sensitive to self-weight, such as prefabricated exterior wall panels and floor slabs in high-rise buildings.

[0087] Scenario B. Structures in cold or large temperature difference environments, requiring phase change temperature regulation function, freeze resistance rating ≥ F300, and thermal conductivity ≤ 0.8 W / (m·K), suitable for cold region building envelopes, high-altitude or desert buildings;

[0088] Scenario C. High-toughness impact-resistant structure, requiring 1-day compressive strength ≥25 MPa (to meet the requirements of rapid demolding or early strength), and impact toughness is ≥30% higher than that of ordinary concrete, suitable for industrial plant floors, military bunkers or key earthquake-resistant components.

[0089] Step 2: Set the total amount of cementitious material to 380-600 kg / m³ 3 It includes cement and mineral admixtures. The cement ratio is adjusted according to the scenario. In scenario A, the cement ratio is 60-75%, which takes into account early strength and economy; in scenario B, the cement ratio is 65-80%, which balances heat of hydration and later strength development; and in scenario C, the cement ratio is 75-90%, which ensures high early strength and high matrix stiffness.

[0090] Based on per cubic meter of concrete, the dosage of inorganic fiber reinforcement in scenario A is 0.8-1.2 kg / m³. 3 Primarily composed of basalt fiber, emphasizing homogeneity and lightweight; in scenario B, the weight is 1.0-1.8 kg / m³. 3 It may contain alkali-resistant glass fiber to enhance its ability to inhibit microcracks caused by freezing; in scenario C, the concentration is 1.5-2 kg / m³. 3 Choose end hook steel fiber or high modulus basalt fiber to maximize toughness.

[0091] The water-reducing agent dosage is 0.8-1.5% of the total mass of cementitious materials, ensuring the slump of fresh concrete is within the range of 180-220 mm, guaranteeing pumpability and compaction. When the inorganic fiber reinforcement dosage is ≥1.5 kg / m³... 3 Or the amount of phase change material is ≥20 kg / m 3 When the water-reducing agent is added, the dosage is ≥1.2%, and the stirring time of the water-reducing agent is ≥180 s.

[0092] Based on the total mass of the cementitious materials, control the water-cement ratio between 0.25 and 0.32:1, and determine the amount of mixing water.

[0093] Step 3: The amount of compound aggregate should be 700-1100 kg / m³ of concrete. 3 Based on the scenario type in step 1, determine the mass ratio of coarse aggregate to fine aggregate in the composite aggregate:

[0094] If it is scenario A, set the mass ratio of coarse aggregate to fine aggregate to 0.4-0.7:1, and increase the proportion of lightweight ceramic sand to reduce density;

[0095] For scenario B, set the mass ratio of coarse aggregate to fine aggregate to 0.7-1.0:1, appropriately increase the amount of coarse aggregate to improve the strength of the skeleton, and add phase change materials;

[0096] For scenario C, the mass ratio of coarse aggregate to fine aggregate is set to 0.9-1.2:1 to enhance the skeleton effect of coarse aggregate and ensure high strength and high toughness.

[0097] The selection of coarse and fine aggregates ensures that the aggregate stability index is ≤62; the aggregate density-particle size matching index is calculated using the following formula:

[0098]

[0099] in:

[0100] ASI: Aggregate Stability Index;

[0101] ρ cApparent density of coarse aggregate, in kg / m³ 3 ;

[0102] ρ f Bulk density of fine aggregate, in kg / m³ 3 ;

[0103] d c : Maximum coarse aggregate size, in meters;

[0104] d p Water-reducing agent dosage, in percentages.

[0105] For example, when using high-titanium heavy slag (ρ c =3000 kg / m 3 ), shale ceramic sand (ρ f =750 kg / m 3 ), Maximum particle size of coarse aggregate d c =20 mm, when the water-reducing agent dosage dp=1.0%, ASI≈53.8≤62, which meets the stability requirements.

[0106] If ASI > 62, it needs to be adjusted by at least one of the following methods: increase the dosage of water-reducing agent d. p Reduce the maximum particle size d of coarse aggregate c ; Select fine aggregates with higher bulk density. The above methods can effectively reduce the particle size difference between coarse and fine aggregates, thereby reducing the segregation rate of fresh concrete after standing and ensuring the strength of the concrete.

[0107] In some embodiments, if the aggregate stability index is >62, the water-reducing agent dosage can be increased, or p-type water-reducing agent can be used. f Larger fine aggregates and / or reduced maximum particle size of coarse aggregates.

[0108] Step 4: Phase change materials and air-entraining agents are only introduced in scenario B. The dosage of phase change materials is 15-40 kg / m³ of concrete. 3 The air-entraining agent content is 0.02-0.05% of the total mass of the cementitious material, used to introduce 2-4.5% of closed microbubbles to improve freeze resistance.

[0109] Step 5: In scenario A, the doping concentration of the nano-reinforcing phase is 3.5-12 kg / m³. 3 In scenario C, the doping concentration of the nano-reinforcing phase is 16-18 kg / m³. 3 In scenario B, the doping amount of the nano-reinforced phase is taken as M. min -18 kg / m 3 ;in,

[0110] (1)

[0111] M 相变 The amount of phase change material in each cubic meter of concrete;

[0112] Nano-SiO2 requires hydration to generate CSH-encapsulated phase change material microcapsules to enhance adhesion. When the phase change material uses paraffin as the core material and silica as the shell material in microcapsules, its addition leads to competitive adsorption between the shell (SiO2) and nano-SiO2 particles, resulting in insufficient reinforcement of the aggregate-slurry interface transition zone (ITZ). Therefore, in scenario B of this application, when adding phase change material, we designed a minimum lower limit for the amount of nano-reinforcing phase doping based on the amount of phase change material added, and eliminated the competitive influence of phase change material on nano-SiO2 through empirical formula (1).

[0113] Step 6: Prepare test samples and measure the 28-day compressive strength, dry apparent density, and impact energy (or initial crack / failure impact count). If any indicator deviates from the target threshold by more than ±10%, return to steps 2, 3, 4, and / or 5 to adjust the proportion of adhesive material, fiber content, aggregate ratio, nanophase, and / or functional components until the performance requirements of the scenario are met.

[0114] Example 1

[0115] Lightweight high-strength concrete with the following components is prepared per cubic meter of concrete:

[0116] The total amount of cementitious materials is 520 kg, including 390 kg of cement (P·O42.5 grade) (accounting for 75%), 80 kg of Grade I fly ash, 50 kg of silica fume, and 10 kg of nano-silica (specific surface area 220 m²). 2 / g, average particle size 15 nm); 980 kg of compound aggregate, including 400 kg of high-titanium heavy slag (particle size 5-20 mm) and shale ceramic sand (particle size 0.16-5.0 mm, bulk density 780 kg / m³). 3 580 kg; 1.0 kg of basalt fiber (length 12 mm, tensile strength 3200 MPa, elastic modulus 105 GPa); 6.24 kg of modified polycarboxylate superplasticizer (phosphate type, solid content 40%) (accounting for 1.2% of the mass of cementitious materials); 156 kg of mixing water (water-cement ratio 0.30).

[0117] The above materials were mixed and molded using conventional processes, and then cured to the specified age before performance testing. The results showed that the dry apparent density of the concrete was 1790 kg / m³. 3 The 28-day compressive strength is 66 MPa, the slump is 205 mm, the 1-hour segregation rate is 3.8%, and the thermal conductivity is 0.91 W / (m·K). All indicators meet the usage requirements of Scenario A.

[0118] Example 2

[0119] Lightweight high-strength concrete with the following components is prepared per cubic meter of concrete:

[0120] The total amount of cementitious materials is 550 kg, including 412 kg of cement (75%), 138 kg of S95 grade mineral powder, 28 kg of phase change microcapsules (paraffin as core material, silica as shell material, particle size 30 μm), 0.11 kg of air-entraining agent (triterpenoid saponins) (0.02% of the cementitious materials), and 12 kg of nano-silica (from the formula...). Calculations show that M min =12); 920 kg of compound aggregate, including 450 kg of high-titanium slag (particle size 10-20 mm) and fly ash ceramsite (bulk density 720 kg / m³). 3 470 kg; 1.5 kg (13 mm in length) of basalt fiber; 7.15 kg (1.3%) of modified polycarboxylate superplasticizer (slump-resistant type); 154 kg of mixing water (water-binder ratio 0.28).

[0121] Tests showed that the concrete has a thermal conductivity of 0.76 W / (m·K), a freeze-thaw resistance grade of F350, a 28-day compressive strength of 62 MPa, a latent heat of phase change of 178 J / g, and a surface temperature fluctuation reduction of 5.2℃ in a simulated diurnal temperature range environment. It fully meets the technical requirements of Scenario B.

[0122] Example 3

[0123] Lightweight high-strength concrete with the following components is prepared per cubic meter of concrete:

[0124] The total amount of cementitious materials is 580 kg, including 522 kg of cement (90%), 58 kg of silica fume; 17 kg of nano-reinforcing phase (containing 10 kg of nano-Al2O3 and 7 kg of nano-SiO2, both with a particle size of 15-20 nm); 1050 kg of compound aggregate, including 550 kg of high-titanium slag (particle size 5–16 mm) and 500 kg of clay ceramsite sand (bulk density 850 kg / m³); 1.8 kg of basalt fiber (length 13 mm, diameter 0.15 mm); 8.12 kg (1.4%) of modified polycarboxylate superplasticizer (early strength type); and 162 kg of mixing water (water-cement ratio 0.28).

[0125] Tests showed that the concrete had a 1-day compressive strength of 28 MPa and a 28-day compressive strength of 71 MPa; the initial cracking impact test count was 62, and the destructive impact test count was 98, representing increases of 107% and 104% respectively compared to ordinary concrete of the same strength (30 initial cracking impacts and 48 destructive impacts). This meets the technical requirements of Scenario C.

[0126] Example 4

[0127] Based on Example 1, the amount of nano-silica was increased from 10 kg to 12 kg, while the other components remained unchanged.

[0128] Tests showed that the concrete had a 28-day compressive strength of 68 MPa and a 1-hour segregation rate of 3.7%. All indicators met the requirements for use in scenario A. Furthermore, this demonstrates that in lightweight, high-strength concrete, the nano-reinforcing phase can effectively fill micropores, strengthen the interfacial transition zone (ITZ), reduce segregation between coarse and fine aggregates, and improve the bond strength of the concrete.

[0129] Example 5

[0130] Based on Example 1, the dosage of the modified polycarboxylate superplasticizer was increased from 1.2% to 1.5% (7.8 kg / m³). 3 ), the remaining components remain unchanged.

[0131] Tests showed that the concrete slump increased to 225 mm, the 1-hour segregation rate further decreased to 2.9%, and the 28-day strength was 65 MPa (slightly lower due to minor adjustments in water usage). This indicates that in high-density differential systems, appropriately increasing the dosage of water-reducing agent can significantly improve homogeneity, making it suitable for projects with pumping heights >50 m.

[0132] Example 6

[0133] Based on Example 2, the phase change material dosage was increased from 28 kg / m³. 3 Reduced to 18 kg / m 3 Therefore, the minimum doping amount of nano-SiO2 is adjusted to 9.5 kg, and the actual doping amount is 10 kg / m³. 3 .

[0134] Testing showed that the concrete's 8-day strength increased to 65 MPa, and its thermal conductivity was 0.79 W / (m·K), still meeting the requirement of ≤0.8; its freeze-thaw resistance grade was F320. This indicates that there is a dynamic compensation relationship between the phase change material and the nanophase, which can be flexibly adjusted using the empirical compensation formula proposed in this application.

[0135] Example 7

[0136] Based on Example 3, the ratio of coarse aggregate to fine aggregate was adjusted from 1.1:1 to 0.9:1 (490 kg of coarse aggregate and 560 kg of fine aggregate), while the rest remained unchanged.

[0137] Tests showed that the time for the fresh concrete mix to flow out of the V-shaped funnel decreased from 9.3 s to 7.8 s, significantly reducing pumping resistance; the 28-day strength was 69 MPa (slightly lower), and the number of impacts still reached 58 initial cracks and 92 failures, meeting toughness requirements and exhibiting better workability, making it suitable for complex reinforced components.

[0138] Comparative Example 1

[0139] Except for replacing the water-reducing agent with a common polycarboxylate-based water-reducing agent (1.0% dosage), the other components were the same as in Example 1. Tests showed that the initial slump of the concrete was 210 mm, which decreased to 140 mm after 1 hour; the segregation rate reached 8.5% after 1 hour; although the 28-day compressive strength was 61 MPa, the coarse aggregate at the bottom of the specimen was significantly enriched, and the strength dispersion coefficient was as high as 12%, indicating that the homogeneity did not meet the engineering requirements.

[0140] Comparative Example 2

[0141] Except for the amount of nano-silica used (0 kg), the other components were the same as in Example 1. Testing showed that the 28-day compressive strength of this concrete was only 54 MPa, lower than the design threshold of 60 MPa; the drying shrinkage rate increased by 25%, and the porosity of the interface transition zone significantly increased, making it unsuitable for load-bearing structures.

[0142] Comparative Example 3

[0143] The formulation of Example 1 was used, but the maximum particle size of the coarse aggregate was 25 mm (exceeding the 5-20 mm range of this application).

[0144] Testing revealed that the segregation rate of the concrete spiked to 9.6% within 1 hour, with "stone pockets" appearing at the bottom of the specimen; the 28-day strength dispersion coefficient reached 15%, with some areas exhibiting a strength of only 52 MPa. This demonstrates that controlling the coarse aggregate size is a crucial prerequisite for suppressing settlement.

[0145] Comparative Example 4

[0146] The formulation of Example 2 was used, but without the addition of an air-entraining agent. Testing revealed that the concrete had an air content of only 1.2%, and after 200 freeze-thaw cycles, the relative dynamic modulus of elasticity retention rate was only 84% (<90%), with a mass loss of 1.8%. Its freeze-thaw resistance grade was only F250, failing to meet the F300 requirement. This demonstrates that air entrainment is a necessary measure to ensure durability in cold-region applications.

[0147] Comparative Example 5

[0148] The formulation of Example 3 was used, but the steel fiber length was changed to 4 mm (lower than the 6-18 mm lower limit of this application). Testing showed that the concrete underwent only 35 initial cracking impacts and 52 failures, with a toughness improvement of less than 30%. The fibers were easily pulled out of the matrix, resulting in a weak bridging effect. This demonstrates that the fiber length needs to be sufficient to form an effective three-dimensional network.

[0149] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0150] Furthermore, it should be noted that the scope of the methods and apparatus in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0151] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A lightweight, high-strength concrete, characterized in that, Including the following raw materials per cubic meter of concrete: 380-600 kg / m³ 3 Cementitious materials, 3.5-18 kg / m 3 Nano-reinforced phase, 700-1100 kg / m 3 The compound aggregate and 0.8-2.0 kg / m 3 The material comprises an inorganic fiber reinforcement; a water-reducing agent and mixing water; the water-reducing agent content is 0.8-1.5% of the total mass of the cementitious material; the mixing water controls the water-cement ratio at 0.28-0.32:1; wherein the composite aggregate is composed of coarse and fine aggregates, and the mass ratio of coarse to fine aggregates is 0.4-1.2:1; the nano-reinforcing phase is selected from nano-silica and / or nano-alumina, and its specific surface area is ≥200 m². 2 / g, with a particle size of 5-50 nm.

2. The lightweight high-strength concrete according to claim 1, characterized in that, Based on per cubic meter of concrete, it also includes 0-30 kg / m³ 3 The phase change material is a microcapsule with paraffin as the core material and silica as the shell material, and its particle size is 10-50 μm; and / or, the concrete further contains an air-entraining agent, the content of which is 0.02-0.05% of the total mass of the cementitious material.

3. The lightweight high-strength concrete according to claim 1, characterized in that, The inorganic fiber reinforcement is basalt fiber, alkali-resistant glass fiber and / or steel fiber, and its length is 6-18 mm, tensile strength ≥3000 MPa, and elastic modulus ≥90 GPa.

4. The lightweight high-strength concrete according to claim 1, characterized in that, The coarse aggregate is at least one of high-titanium heavy slag, steel slag, and copper slag, and is particles with a particle size in the range of 5-20 mm; the fine aggregate is at least one of shale, clay, and fly ash ceramsite, and is particles with a particle size in the range of 0.16-5.0 mm.

5. The lightweight high-strength concrete according to claim 1, characterized in that, The cementitious material includes cement and mineral admixtures, wherein the cement accounts for 60-90% of the total mass of the cementitious material, and the mineral admixtures account for 10-40% of the total mass of the cementitious material, wherein the mineral admixtures are at least one of fly ash, mineral powder and silica fume; and / or, the water-reducing agent is a modified polycarboxylate water-reducing agent.

6. A mix design method for lightweight high-strength concrete according to any one of claims 1-5, characterized in that, The steps include: Step 1: Based on the structural and functional requirements corresponding to the engineering application scenario, the target project is divided into one of the following three scenarios: A. Lightweight load-bearing components, with a required apparent density ≤1850 kg / m³ 3 A. For structures in cold or high-temperature environments, the 28-day compressive strength must be ≥60 MPa; B. For structures in cold or high-temperature environments, the structure must have phase change temperature regulation function, freeze-thaw resistance grade ≥F300, and thermal conductivity ≤0.8 W / (m·K); C. For high-toughness and impact-resistant structures, the 1-day compressive strength must be ≥25 MPa and the impact toughness must be ≥30% higher than that of ordinary concrete; Step 2: The total amount of the cementitious material is set at 380-600 kg / m³. 3 The mixture includes cement and mineral admixtures. The cement percentage is adjusted according to the scenario: 60-75% in scenario A, 65-80% in scenario B, and 75-90% in scenario C. The inorganic fiber reinforcement content is 0.8-1.2 kg / m³ in scenario A. 3 In scenario B, the value is 1.0-1.8 kg / m³. 3 In scenario C, the concentration is 1.5-2 kg / m³. 3 The water-reducing agent is added at a dosage of 0.8-1.5% of the total mass of the cementitious materials, so that the slump of the fresh concrete is within the range of 180-220 mm; Step 3: The compound aggregate dosage is 700-1100 kg / m³ of concrete. 3 Based on the scenario type in step 1, determine the mass ratio of coarse aggregate to fine aggregate in the composite aggregate: for scenario A, set the mass ratio of coarse aggregate to fine aggregate to be 0.4-0.7:1; for scenario B, set the mass ratio of coarse aggregate to fine aggregate to be 0.7-1.0:1, and add phase change material; for scenario C, set the mass ratio of coarse aggregate to fine aggregate to be 0.9-1.2:1; Step 4: Phase change material and air-entraining agent are only introduced in scenario B, and the dosage of phase change material is 15-40 kg / m³ per cubic meter of concrete. 3 The air-entraining agent content is 0.02-0.05% of the total mass of the cementitious material; Step 5: In scenario A, the dosage of the nano-reinforcing phase is 3.5-12 kg / m³. 3 In scenario C, the doping concentration of the nano-reinforcing phase is 16-18 kg / m³. 3 In scenario B, the doping amount of the nano-reinforcing phase is M. min -18 kg / m 3 ;in, M 相变 Step 6: Prepare test samples and measure the 28-day compressive strength, dry apparent density and impact energy of the samples; If any index deviates from the target threshold by more than ±10%, return to Step 2, Step 3, Step 4 and / or Step 5, and adjust the distribution ratio of each group until the performance requirements of the scenario are met.

7. The lightweight high-strength concrete mix design method according to claim 6, characterized in that, Step 2 further includes the following step: determining the amount of mixing water by controlling the water-cement ratio to be between 0.25 and 0.32:1 based on the total mass of the cementitious material.

8. The lightweight high-strength concrete mix design method according to claim 6, characterized in that, In step 2, when the content of the inorganic fiber reinforcement is ≥1.5 kg / m 3 Or the amount of phase change material is ≥20 kg / m 3 When the water-reducing agent is added, the dosage is ≥1.2%, and the stirring time of the water-reducing agent is ≥180 s.

9. The lightweight high-strength concrete mix design method according to claim 6, characterized in that, In step 3, the selection of coarse and fine aggregates ensures that the aggregate stability index is ≤62; the aggregate density-particle size matching index is calculated using the following formula: Where: ASI: Aggregate Stability Index; ρ c Apparent density of coarse aggregate, in kg / m³ 3 ;ρ f Bulk density of fine aggregate, in kg / m³ 3 ;d c d: Maximum coarse aggregate size, in meters (m); p Water-reducing agent dosage, in percentages.

10. The lightweight high-strength concrete mix design method according to claim 9, characterized in that, If the aggregate stability index is >62, the dosage of the water-reducing agent can be increased, or ρ can be replaced. f Larger fine aggregates and / or reduced maximum particle size of the coarse aggregates.

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