Self-compacting micro-expansion high bulk density concrete and preparation method thereof

Abstract

This application relates to a self-compacting, micro-expansion, high-density concrete and its preparation method. By weight, it comprises 240-400 parts cement, 80-150 parts fly ash, 30-100 parts silica fume, 20-60 parts rheology modifier, 20-60 parts expansive agent, 50-150 parts internal curing agent, 600-900 parts fine aggregate, 800-1200 parts coarse aggregate, 140-260 parts water, and 5-12 parts admixture. The rheology modifier includes glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 1:(0.1-0.3):(0.001-0.01). The expansive agent includes calcium oxide and active magnesium oxide. The internal curing agent includes natural zeolite and zeolite powder. The fine aggregate includes river sand and iron tailings. The coarse aggregate includes crushed stone and iron tailings. This application can solve the problem of the constraint between the density, volume stability and workability of concrete in related technologies, thereby realizing the self-compacting, micro-expansion and high density functions of concrete.

Description

Technical Field

[0001] This application relates to the field of bridge technology, and in particular to a self-compacting micro-expansion high-density concrete and its preparation method. Background Technology

[0002] The ultra-short side-span concrete composite slab-truss composite beam structure is a novel bridge structural system with advantages such as shorter side spans, convenient construction, and high economic efficiency. However, in order to balance the load of the main beam in the middle span, the chords of the side spans need to be filled with concrete, and the concrete must have a unit weight >2500 kg / m³. 3 It achieves the function of weight-bearing; it has a micro-expansion function to avoid voids and debonding; it meets the self-compacting requirements and is easy to construct.

[0003] Generally, adding heavy aggregates such as iron filings to concrete can meet the density requirements, but it can lead to segregation and affect workability. Adding expansive agents can reduce shrinkage to some extent, but it's difficult to achieve micro-expansion, and it also leads to a decrease in density and workability. Increasing the sand ratio and cementitious material content can improve workability, but it reduces density and increases shrinkage. Therefore, the density, volume stability, and workability of concrete are interdependent and mutually restrictive, and current technologies cannot simultaneously meet the requirements for density, micro-expansion, and self-compacting concrete. Summary of the Invention

[0004] This application provides a self-compacting, micro-expansion, high-density concrete and its preparation method to solve the constraint problem between the density, volume stability, and workability of concrete in related technologies, thereby realizing the self-compacting, micro-expansion, and high-density functions of concrete.

[0005] In the first aspect, a self-compacting, micro-expansion, high-density concrete is provided, which, by weight, comprises: 240-400 parts of cement, 80-150 parts of fly ash, 30-100 parts of silica fume, 20-60 parts of rheology modifier, 20-60 parts of expansion agent, 50-150 parts of internal curing agent, 600-900 parts of fine aggregate, 800-1200 parts of coarse aggregate, 140-260 parts of water, and 5-12 parts of admixture;

[0006] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylic acid ether, wherein the mass ratio of glass microspheres, cellulose ether, and polycarboxylic acid ether is 1:(0.1-0.3):(0.001-0.01).

[0007] The expanding agent includes calcium oxide and active magnesium oxide;

[0008] The internal maintenance agent includes natural zeolite and zeolite powder;

[0009] The fine aggregate includes river sand and iron tailings;

[0010] The coarse aggregate includes crushed stone and iron tailings.

[0011] In some embodiments, the median particle size D50 of the glass microspheres is 5–12 μm, the viscosity of the cellulose ether is 100,000–200,000, and the hydroxyl value of the polycarboxylic acid ether is 20–30 mg KOH / g.

[0012] In some embodiments, the mass ratio of calcium oxide to active magnesium oxide is 1:(0.5-2).

[0013] In some embodiments, the calcium oxide has a purity of 90% or higher and a specific surface area of ​​≥300 m². 2 / kg;

[0014] The active magnesium oxide has a purity of over 95% and a citric acid value of 150–200s.

[0015] In some embodiments, the mass ratio of the natural zeolite to zeolite powder is 1:(1-2).

[0016] In some embodiments, the natural zeolite has a particle size of 0.15–3 mm and a porosity of ≥50%;

[0017] The zeolite powder has a particle size of 150-300 mesh and a porosity of ≥50%.

[0018] In some embodiments, the iron tailings account for 30% to 100% of the mass fraction of the fine aggregate;

[0019] The river sand has a particle size of 0.075–4.75 mm, a fineness modulus of 2.5–2.9, and an apparent density of 2400–2600 kg / m³. 3 ;

[0020] The iron tailings are produced by crushing iron tailings ore, with a particle size of 0.075–4.75 mm and an apparent density of 3200–3300 kg / m³. 3 .

[0021] In some embodiments, the iron tailings account for 40% to 100% of the mass fraction of the coarse aggregate;

[0022] The crushed stone is a continuously graded crushed stone with a diameter of 5-15 mm and an apparent density of 2500-2800 kg / m³. 3 ;

[0023] The iron tailings are produced by crushing iron tailings ore, with a particle size of 5-15 mm and an apparent density of 3300-3500 kg / m³. 3 .

[0024] In some embodiments, the cement is silicate cement or ordinary silicate cement;

[0025] The fly ash is Class I or Class II fly ash of Category F;

[0026] The silica fume is grade 90 silica fume or grade 85 silica fume;

[0027] The admixture is a polycarboxylate superplasticizer with a water reduction rate of ≥25%.

[0028] Secondly, a method for preparing self-compacting micro-expansion high-density concrete as described in any of the above-mentioned methods is provided, comprising:

[0029] Glass microspheres, cellulose ether, and polycarboxylic acid ether are mixed to obtain a rheology-modified material;

[0030] Calcium oxide and active magnesium oxide are mixed to obtain an expanding agent;

[0031] Natural zeolite and zeolite powder are placed in a container, and a certain amount of water is added to pre-wet them to obtain a pre-wetted internal curing agent.

[0032] Cement, fly ash, silica fume, rheology modifier, expansion agent and fine aggregate are mixed to obtain the first mixture;

[0033] Pour the pre-wetted internal curing agent, the remaining water, and the additives into the first mixture and continue stirring to obtain the second mixture;

[0034] Pour the coarse aggregate into the second mixture and continue mixing to obtain fresh concrete;

[0035] Freshly mixed concrete is compacted, molded, and cured to obtain self-compacting, micro-expansion, high-density concrete.

[0036] The beneficial effects of the technical solution provided in this application include:

[0037] This application successfully prepared self-compacting, micro-expansion, high-density concrete by incorporating rheology modifiers, expansive agents, internal curing agents, and iron tailings into the concrete, achieving a coordinated balance between the concrete's workability, volume stability, and density.

[0038] The rheology modifier proposed in this application is composed of glass microspheres, cellulose ether, and polycarboxylate ether. By synergistically combining the ball-bearing lubrication effect of glass microspheres, the thickening effect of cellulose ether, and the water-reducing effect of polycarboxylate ether, it achieves high fluidity, high consistency, high homogeneity, and good stability in fresh concrete, effectively solving the problems of segregation and bleeding in self-compacting concrete.

[0039] The expansive agent proposed in this application is composed of calcium oxide and low-activity active magnesium oxide. The expansion reaction of calcium oxide mainly occurs in the early stage of hydration, while the expansion reaction of low-activity active magnesium oxide mainly occurs in the later stage of hydration. Therefore, the expansive agent can continuously carry out the expansion reaction throughout the entire cycle of concrete hydration, completely compensating for the shrinkage of concrete and achieving a micro-expansion effect.

[0040] The internal curing agent proposed in this application is composed of natural zeolite and zeolite powder. After absorbing water, the natural zeolite and zeolite powder are added to the concrete. As the concrete hydration reaction proceeds, the free water absorbed by the natural zeolite and zeolite powder is gradually released, further promoting cement hydration and the reaction of the expansive agent. Simultaneously, the natural zeolite and zeolite powder have different pore sizes. The natural zeolite mainly provides reaction water for the initial stage of cement hydration and calcium oxide, while the zeolite powder mainly provides reaction water for the later stage of cement hydration and the low-activity active magnesium oxide, thus achieving a gradient internal curing effect and ensuring complete cement hydration and sufficient reaction of the expansive agent.

[0041] This application utilizes iron tailings and iron tailings stones with high apparent density to replace a portion of traditional river sand and gravel, achieving high density in concrete. Furthermore, by processing iron tailings ore into iron tailings and iron tailings stones, not only is the amount of natural sand and gravel used significantly reduced, but the waste iron tailings ore is also utilized efficiently, realizing the high-efficiency value-added utilization of iron tailings resources. This has green and environmentally friendly significance and meets the requirements of sustainable development. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0043] Figure 1 A flowchart illustrating the preparation method of self-compacting micro-expansion high-density concrete provided in this application embodiment. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0045] This application provides a self-compacting, micro-expansion, high-density concrete, which, by weight, comprises: 240-400 parts cement, 80-150 parts fly ash, 30-100 parts silica fume, 20-60 parts rheology modifier, 20-60 parts expansion agent, 50-150 parts internal curing agent, 600-900 parts fine aggregate, 800-1200 parts coarse aggregate, 140-260 parts water, and 5-12 parts admixture.

[0046] Cement, fly ash, silica fume, and admixtures are commonly used materials. For example, the cement can be silicate cement or ordinary silicate cement, the fly ash can be Class I or Class II fly ash, the silica fume can be Grade 90 or Grade 85 silica fume, and the admixture can be polycarboxylate superplasticizer with a water reduction rate of ≥25%.

[0047] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 1:(0.1-0.3):(0.001-0.01). Within this range, the concrete exhibits high fluidity, high homogeneity, and low viscosity, thereby achieving self-compacting properties. Excessive glass microspheres increase the concrete's spread but may lead to segregation and bleeding; insufficient glass microspheres result in excessive viscosity, hindering construction. Excessive cellulose ether makes the concrete too viscous, inconvenient to construct; insufficient cellulose ether leads to poor homogeneity and easy segregation and bleeding. Excessive polycarboxylate ether results in excessive laitance and easy stratification; insufficient polycarboxylate ether leads to poor fluidity and inability to achieve self-compacting properties.

[0048] The applicant's research revealed that if the median particle size D50 of the glass microspheres is too low, the ball-bearing effect is not significant, resulting in minimal improvement in concrete fluidity. Conversely, if the median particle size D50 of the glass microspheres is too high, the internal porosity of the concrete increases, affecting later-stage strength and durability. To achieve self-compacting, micro-expansion, and high-density concrete, the median particle size D50 of the glass microspheres is 5–12 μm.

[0049] The applicant's research revealed that if the viscosity of the cellulose ether is too low, it has little effect on improving the consistency of the slurry; if it is too high, the consistency of the slurry increases significantly, resulting in poor concrete workability. To achieve self-compacting, micro-expansion, and high-density concrete, the viscosity of the cellulose ether is set at 100,000 to 200,000.

[0050] The applicant discovered through research that if the hydroxyl value of the polycarboxylate ether is too low, the intermolecular stability is poor, resulting in a poor water-reducing effect; if it is too high, the synthesis process becomes more difficult and uneconomical. To achieve self-compacting, micro-expansion, and high-density concrete, the hydroxyl value of the polycarboxylate ether is 20–30 mg KOH / g.

[0051] The rheology modifier is composed of glass microspheres, cellulose ether, and polycarboxylate ether. The glass microspheres are smooth spheres that can exert a ball-bearing effect and reduce the frictional resistance between the slurry. The cellulose ether can increase the anti-dispersion ability and homogeneity of the cement paste, improve the stability of concrete, and prevent segregation, bleeding, etc. The surface adsorption and steric hindrance of the polycarboxylate ether can make the cement particles disperse evenly and reduce the amount of water used.

[0052] The expanding agent comprises calcium oxide and activated magnesium oxide; the mass ratio of calcium oxide to activated magnesium oxide is 1:(0.5-2), the purity of the calcium oxide is above 90%, and the specific surface area is ≥300m². 2 / kg; the purity of the active magnesium oxide is above 95%, and the citric acid value is 150-200s.

[0053] The expansion agent is composed of calcium oxide and low-activity active magnesium oxide. Calcium oxide can generate calcium hydroxide in the early stage of cement hydration, and the volume of calcium hydroxide is twice that of calcium oxide, so it can cause volume expansion. The low-activity active magnesium oxide begins to generate magnesium hydroxide in the later stage of cement hydration. As magnesium hydroxide continues to grow, the crystals come into contact with each other and squeeze the pore walls, thus causing volume expansion.

[0054] When calcium oxide and active magnesium oxide are mixed, an expansion agent is formed. Because calcium oxide has high activity, it reacts first. After the calcium oxide reaction is completed, the less active magnesium oxide reacts, thereby achieving long-term expansion of concrete and continuously compensating for the shrinkage caused by hydration.

[0055] High purity of calcium oxide and active magnesium oxide is crucial to ensure good expansion effects in concrete; if the purity is too low, the expansion effect will be insignificant. Specific surface area is essential to ensure high activity of calcium oxide; a purity below 300 m² is desirable. 2 If the citric acid value is less than 150s, the reaction is delayed and the initial expansion is not obvious. The citric acid value ensures the low activity of magnesium oxide. If it is less than 150s, the activity is too high and the expansion is insufficient in the later stage. If it is greater than 200s, the activity is too low and the reaction is too slow. At the same time, there is a possibility of cracking during the later expansion stage.

[0056] The internal curing agent comprises natural zeolite and zeolite powder; the mass ratio of natural zeolite to zeolite powder is 1:(1-2). After the natural zeolite and zeolite powder are mixed and saturated with water, they are added to the concrete in this ratio to achieve gradient water release. That is, the natural zeolite releases water first, followed by the zeolite powder. The entire water release process corresponds to the reaction between cement and the expansion agent, achieving a full-cycle internal curing effect. If the ratio is higher than this, with more natural zeolite, the internal curing agent may release water prematurely, failing to achieve the later internal curing effect, resulting in insufficient cement hydration and active magnesium oxide reaction. If the ratio is lower than this, with more zeolite powder, the internal curing agent will not release enough water in the early stage, resulting in insufficient calcium oxide reaction and insignificant early expansion effect of the concrete.

[0057] The natural zeolite has a particle size of 0.15–3 mm and a porosity of ≥50%; the zeolite powder has a particle size of 150–300 mesh and a porosity of ≥50%.

[0058] Based on preliminary test data, the applicant found that natural zeolite with a particle size in the range of 0.15–0.3 mesh and zeolite powder with a particle size of 150–300 mesh can absorb the most water while having the least impact on the mechanical properties of concrete. If the particle size is too small, the water absorption will be too low; if the particle size is too large, the mechanical properties of the concrete will decrease significantly. A porosity of ≥50% is set to ensure sufficient water absorption and avoid insufficient water absorption.

[0059] The internal curing agent is composed of natural zeolite and zeolite powder. Natural zeolite and zeolite powder have high porosity. By being pre-saturated with water and added to the concrete, they can provide free water for the reaction between cement and the expansion agent. At the same time, natural zeolite has a larger pore size, mainly providing free water in the early stage of hydration; while zeolite powder has a smaller pore size, mainly providing free water in the later stage of hydration.

[0060] The fine aggregate includes river sand and iron tailings; the iron tailings account for 30% to 100% of the mass fraction of the fine aggregate; the river sand has a particle size of 0.075 to 4.75 mm, a fineness modulus of 2.5 to 2.9, and an apparent density of 2400 to 2600 kg / m³. 3 The iron tailings are produced by crushing iron tailings ore, with a particle size of 0.075–4.75 mm and an apparent density of 3200–3300 kg / m³. 3 .

[0061] According to the test results, when the replacement rate of iron tailings is less than 30%, the concrete density cannot meet the requirement of 2500 kg / m³. 3 .

[0062] The coarse aggregate comprises crushed stone and iron tailings. The iron tailings account for 40% to 100% of the mass fraction of the coarse aggregate; the crushed stone is continuously graded crushed stone of 5 to 15 mm with an apparent density of 2500 to 2800 kg / m³.3 The iron tailings are produced by crushing iron tailings ore, with a particle size of 5–15 mm and an apparent density of 3300–3500 kg / m³. 3 .

[0063] According to the test results, when the replacement rate of iron tailings is less than 40%, the concrete density cannot meet the requirement of 2500 kg / m³. 3 .

[0064] To meet the project requirements, the concrete density must be at least 2500 kg / m³. 3 Concrete prepared using only river sand and conventional crushed stone does not meet the required density. Therefore, this application proposes to use iron tailings to replace part or all of the river sand and iron tailings to replace part or all of the crushed stone in the preparation of concrete to achieve the goal of high density. At the same time, it not only provides a new way for the resource utilization of iron tailings, but also reduces the amount of natural sand and gravel used, which is in line with the concept of green environmental protection.

[0065] See Figure 1 As shown in the embodiments of this application, a method for preparing self-compacting micro-expansion high-density concrete is also provided, which includes the following steps:

[0066] 101: Glass microspheres, cellulose ether and polycarboxylic acid ether are mixed to obtain rheology modified material.

[0067] In step 101, during actual mixing, the mixing can be carried out at a speed of 400-500 rpm and a time of 20-24 hours.

[0068] 102: Calcium oxide and active magnesium oxide are mixed to obtain an expanding agent.

[0069] In step 102, during actual mixing, the mixing can be carried out at a speed of 200-300 rpm and a time of 20-24 hours.

[0070] 103: Place natural zeolite and zeolite powder in a container, add a certain amount of water to pre-wet, and obtain a pre-wetted internal curing agent.

[0071] The amount of water added in step 102 can be determined as needed. For example, as an example, the added water accounts for 20% of the 140-260 parts of water. After the water is added, the container is sealed and left to stand for 20-24 hours.

[0072] 104: Cement, fly ash, silica fume, rheology modifier, expansion agent and fine aggregate are mixed to obtain the first mixture.

[0073] The stirring time in step 104 can be set according to actual needs, such as stirring for 60±5 seconds.

[0074] 105: Pour the pre-wetted internal curing agent, the remaining water and additives into the first mixture, and continue stirring to obtain the second mixture.

[0075] The stirring time in step 105 can be set according to actual needs, such as stirring for 60±5 seconds.

[0076] 106: Pour the coarse aggregate into the second mixture and continue mixing to obtain fresh concrete.

[0077] The stirring time in step 106 can be set according to actual needs, such as stirring for 120±5 seconds.

[0078] 107: The freshly mixed concrete is compacted and cured to obtain self-compacting, micro-expansion, high-density concrete.

[0079] The present application will be described below through some embodiments and comparative examples.

[0080] Example 1

[0081] A self-compacting, micro-expansion, high-density concrete, by weight, comprises: 300 parts cement, 100 parts fly ash, 80 parts silica fume, 50 parts rheology modifier, 50 parts expansion agent, 100 parts internal curing agent, 800 parts fine aggregate, 1000 parts coarse aggregate, 200 parts water, and 9 parts admixture.

[0082] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylic acid ether, with a mass ratio of 1:0.2:0.005.

[0083] The expanding agent comprises calcium oxide and active magnesium oxide; the mass ratio of calcium oxide to active magnesium oxide is 1:1.

[0084] The internal curing agent includes natural zeolite and zeolite powder; the mass ratio of natural zeolite to zeolite powder is 1:1.5.

[0085] The cement is P·Ⅱ52.2 silicate cement, the fly ash is Class F Grade I fly ash, and the silica fume is Grade 90 silica fume.

[0086] The median particle size D50 of the glass microspheres is 9.5 μm, the viscosity of the cellulose ether is 180,000, and the hydroxyl value of the polycarboxylic acid ether is 23 mg KOH / g.

[0087] The calcium oxide has a purity of 95% and a specific surface area of ​​360 m². 2 / kg; the purity of the active magnesium oxide is 99%, and the citric acid value is 180s.

[0088] The natural zeolite has a particle size of 0.15–3 mm and a porosity of ≥50%; the zeolite powder has a particle size of 150–300 mesh and a porosity of ≥50%.

[0089] The fine aggregate includes river sand and iron tailings; the iron tailings account for 60% of the mass fraction of the fine aggregate; the river sand has a particle size in the range of 0.075–4.75 mm, a fineness modulus of 2.6, and an apparent density of 2600 kg / m³. 3 The iron tailings are produced by crushing iron tailings ore, with a particle size ranging from 0.075 to 4.75 mm and an apparent density of 3250 kg / m³. 3 .

[0090] The coarse aggregate comprises crushed stone and iron tailings. The iron tailings account for 60% of the mass fraction of the coarse aggregate; the crushed stone is continuously graded crushed stone of 5-15 mm with an apparent density of 2700 kg / m³. 3 The iron tailings are produced by crushing iron tailings ore, with a particle size ranging from 5 to 15 mm and an apparent density of 3400 kg / m³. 3 .

[0091] The admixture is a polycarboxylate superplasticizer with a water reduction rate of 30%.

[0092] Example 2

[0093] The difference from Example 1 is as follows:

[0094] A self-compacting, micro-expansion, high-density concrete, by weight, comprises: 400 parts cement, 150 parts fly ash, 100 parts silica fume, 60 parts rheology modifier, 60 parts expansion agent, 150 parts internal curing agent, 900 parts fine aggregate, 1200 parts coarse aggregate, 260 parts water, and 12 parts admixture.

[0095] Example 3

[0096] The difference from Example 1 is as follows:

[0097] A self-compacting, micro-expansion, high-density concrete, by weight, comprises: 240 parts cement, 80 parts fly ash, 30 parts silica fume, 20 parts rheology modifier, 20 parts expansion agent, 50 parts internal curing agent, 600 parts fine aggregate, 800 parts coarse aggregate, 140 parts water, and 5 parts admixture.

[0098] Example 4

[0099] The difference from Example 1 is as follows:

[0100] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 1:0.1:0.005.

[0101] Example 5

[0102] The difference from Example 1 is as follows:

[0103] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylic acid ether, with a mass ratio of 1:0.3:0.005.

[0104] Example 6

[0105] The difference from Example 1 is as follows:

[0106] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylic acid ether, with a mass ratio of 1:0.2:0.001.

[0107] Example 7

[0108] The difference from Example 1 is as follows:

[0109] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 1:0.2:0.01.

[0110] Example 8

[0111] The difference from Example 1 is as follows:

[0112] The mass ratio of calcium oxide to active magnesium oxide is 1:0.5.

[0113] Example 9

[0114] The difference from Example 1 is as follows:

[0115] The mass ratio of calcium oxide to active magnesium oxide is 1:2.

[0116] Example 10

[0117] The difference from Example 1 is as follows:

[0118] The mass ratio of the natural zeolite to zeolite powder is 1:1.

[0119] Example 11

[0120] The difference from Example 1 is as follows:

[0121] The mass ratio of the natural zeolite to zeolite powder is 1:2.

[0122] Example 12

[0123] The difference from Example 1 is as follows:

[0124] The fine aggregate contains 30% iron tailings by mass; the coarse aggregate contains 40% iron tailings by mass.

[0125] Example 13

[0126] The difference from Example 1 is as follows:

[0127] The fine aggregate contains 100% iron tailings by mass; the coarse aggregate contains 100% iron tailings by mass.

[0128] Comparative Example 1

[0129] The difference from Example 1 is as follows:

[0130] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 2:0.2:0.005.

[0131] Comparative Example 2

[0132] The difference from Example 1 is as follows:

[0133] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 0.5:0.2:0.005.

[0134] Comparative Example 3

[0135] The difference from Example 1 is as follows:

[0136] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 1:0.4:0.005.

[0137] Comparative Example 4

[0138] The difference from Example 1 is as follows:

[0139] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 1:0.05:0.005.

[0140] Comparative Example 5

[0141] The difference from Example 1 is as follows:

[0142] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 1:0.2:0.02.

[0143] Comparative Example 6

[0144] The difference from Example 1 is as follows:

[0145] The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, with a mass ratio of 1:0.2:0.0005.

[0146] Comparative Example 7

[0147] The difference from Example 1 is as follows:

[0148] The mass ratio of calcium oxide to active magnesium oxide is 1:0.2.

[0149] Comparative Example 8

[0150] The difference from Example 1 is as follows:

[0151] The mass ratio of calcium oxide to active magnesium oxide is 1:3.

[0152] Comparative Example 9

[0153] The difference from Example 1 is as follows:

[0154] The mass ratio of the natural zeolite to zeolite powder is 1:0.5.

[0155] Comparative Example 10

[0156] The difference from Example 1 is as follows:

[0157] The mass ratio of the natural zeolite to zeolite powder is 1:3.

[0158] Comparative Example 11

[0159] The difference from Example 1 is as follows:

[0160] The fine aggregate does not contain iron tailings, and the coarse aggregate does not contain iron tailings.

[0161] The above embodiments and comparative examples were tested for expansion, T500, bulk density, compressive strength and expansion performance.

[0162] The expansion degree and T500 adopt the "Technical Specification for Application of Self-Compacting Concrete (JGJT 283-2012)".

[0163] The bulk density is determined according to the "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" (GB / T50080-2016).

[0164] The compressive strength was determined according to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T50081-2019), with an age of 28 days.

[0165] The expansion performance was tested using the self-generated volume deformation test method for concrete in the "Test Procedure for Hydraulic Concrete" (SLT 352-2020).

[0166] The test results are shown in Table 1 below:

[0167] Table 1. Concrete performance test results of the examples and comparative examples.

[0168]

[0169]

[0170] According to the data in Table 1, it can be seen that the freshly mixed concrete in all examples is in good condition, with a spread ≥ 600 mm, T500 ≤ 8 s, and possesses self-compacting function; the expansion value 7d ≥ 75 × 10 -6 28d≥45×10 -6 90d≥20×10 -6 It has a micro-expansion function; its bulk density is >2500kg / m³. 3 It meets the target value for high density. Overall, it achieves the self-compacting, micro-expansion, and high density function of concrete.

[0171] Based on the experimental results of Examples 1, 2, 3, 4, 5, and 6 and Comparative Examples 1, 2, 3, 4, 5, and 6, it can be seen that the concrete of Examples 1, 2, 3, 4, 5, and 6 has low viscosity and high consistency, and possesses good workability such as water retention, cohesiveness, and homogeneity. Furthermore, its spread is ≥605mm, and its T500 is ≤7s, meeting the performance indicators of self-compacting concrete. In contrast, the concrete of Comparative Examples 1, 2, 3, 4, 5, and 6 exhibits segregation and bleeding, poor water retention, poor cohesiveness, and poor homogeneity. Moreover, its spread and T500 indicators do not meet the performance indicators of self-compacting concrete. This indicates that when the mass ratio of glass microspheres, cellulose ether, and polycarboxylate ether in the rheology modifier is not within the range of 1:(0.1~0.3):(0.001~0.01), the workability of the concrete deteriorates, and it cannot achieve the self-compacting function.

[0172] Based on the test results of Examples 1, 8, and 9 and Comparative Examples 7 and 8, it can be seen that the concrete expansion value of Examples 1, 8, and 9 is ≥75×10⁻⁶ days (7d). -6 28d≥46×10 -6 90d≥20×10 -6 It exhibits micro-expansion properties. This indicates that when the mass ratio of calcium oxide to active magnesium oxide in the expansive agent is maintained within the range of 1:(0.5–2), the concrete can maintain good volume stability. In contrast, the calcium oxide content of the expansive agent in Comparative Example 7 is relatively high, and the 7-day expansion value of the concrete reaches 93 × 10⁻⁶. -6 However, its expansion performance was insufficient in the later stages, with the expansion value dropping to 25 × 10⁻⁶ after 28 days. -6The 90-day expansion value was even less than 0, indicating volume shrinkage. In Comparative Example 8, the active magnesium oxide content of the expansive agent was too high, and the 7-day expansion value of the concrete was only 43 × 10⁻⁶. -6 Due to insufficient expansion in the early stages, expansion became difficult in the later stages, resulting in a 90-day expansion value of -18 × 10⁻⁶. -6 It shows a contraction trend.

[0173] Combining the test results of Examples 1, 10, and 11 and Comparative Examples 9 and 10, it can be seen that the concrete of Examples 1, 10, and 11 exhibits good micro-expansion properties, while maintaining a compressive strength >60 MPa. This indicates that when the mass ratio of natural zeolite to zeolite powder in the internal curing agent is maintained within the range of 1:(1-2), the concrete exhibits good volume stability and mechanical properties. In contrast, the internal curing agent in Comparative Example 9 has a higher natural zeolite content, resulting in a 7-day expansion value of 91 × 10⁻⁶ MPa. -6 However, its expansion performance in the later stages is significantly insufficient, with an expansion value of only 13 × 10⁻⁶ at 28 days. -6 Shrinkage was observed after 90 days, and the compressive strength was only 48.6 MPa, indicating a significant decrease in mechanical properties. In Comparative Example 10, the zeolite powder content of the internal curing agent was too high, resulting in insufficient early-stage expansion of the concrete, only 26 × 10⁻⁶ MPa. -6 Later, it also showed a shrinkage trend, and the workability of the concrete was poor.

[0174] Compared to Comparative Example 11, the unit weight of concrete in Examples 1, 12, and 13 is significantly increased. When the content of iron tailings and aggregate is 100%, the unit weight of concrete can reach 2640 kg / m³. 3 Without the addition of iron tailings and gravel, the density of the concrete is only 2410 kg / m³. 3 It does not meet the requirement of a bulk density ≥2500kg / m³ 3 This indicates that increasing the amount of iron tailings and gravel can significantly increase the density of concrete.

[0175] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A self-compacting, micro-expansion, high-density concrete, characterized in that: Based on parts by weight, it comprises: 240-400 parts cement, 80-150 parts fly ash, 30-100 parts silica fume, 20-60 parts rheology modifier, 20-60 parts expansive agent, 50-150 parts internal curing agent, 600-900 parts fine aggregate, 800-1200 parts coarse aggregate, 140-260 parts water, and 5-12 parts admixture, wherein the admixture is a polycarboxylate superplasticizer; The rheology modifier comprises glass microspheres, cellulose ether, and polycarboxylate ether, wherein the mass ratio of glass microspheres, cellulose ether, and polycarboxylate ether is 1:(0.1-0.3):(0.001-0.01). The expanding agent comprises calcium oxide and active magnesium oxide, wherein the mass ratio of calcium oxide to active magnesium oxide is 1:(0.5-2). The internal curing agent includes natural zeolite and zeolite powder, and the mass ratio of natural zeolite to zeolite powder is 1:(1-2). The fine aggregate includes river sand and iron tailings; The coarse aggregate includes crushed stone and iron tailings.

2. The self-compacting, micro-expansion, high-density concrete as described in claim 1, characterized in that: The median particle size D50 of the glass microspheres is 5-12 μm, the viscosity of the cellulose ether is 100,000-200,000, and the hydroxyl value of the polycarboxylic acid ether is 20-30 mgKOH / g.

3. The self-compacting, micro-expansion, high-density concrete as described in claim 1, characterized in that: The calcium oxide has a purity of 90% or higher and a specific surface area of ​​≥300m². 2 / kg; The active magnesium oxide has a purity of over 95% and a citric acid value of 150–200s.

4. The self-compacting, micro-expansion, high-density concrete as described in claim 1, characterized in that: The natural zeolite has a particle size of 0.15–3 mm and a porosity of ≥50%. The zeolite powder has a particle size of 150-300 mesh and a porosity of ≥50%.

5. The self-compacting, micro-expansion, high-density concrete as described in claim 1, characterized in that: The iron tailings account for 30% to 100% of the mass fraction of the fine aggregate; The river sand has a particle size of 0.075–4.75 mm, a fineness modulus of 2.5–2.9, and an apparent density of 2400–2600 kg / m³. 3 ; The iron tailings are produced by crushing iron tailings ore, with a particle size of 0.075–4.75 mm and an apparent density of 3200–3300 kg / m³. 3 .

6. The self-compacting, micro-expansion, high-density concrete as described in claim 1, characterized in that: The iron tailings account for 40% to 100% of the mass fraction of the coarse aggregate; The crushed stone is a continuously graded crushed stone with a diameter of 5-15 mm and an apparent density of 2500-2800 kg / m³. 3 ; The iron tailings are produced by crushing iron tailings ore, with a particle size of 5-15 mm and an apparent density of 3300-3500 kg / m³. 3 .

7. The self-compacting, micro-expansion, high-density concrete as described in claim 1, characterized in that: The cement is silicate cement or ordinary silicate cement; The fly ash is Class I or Class II fly ash of Category F; The silica fume is grade 90 silica fume or grade 85 silica fume; The water reduction rate of the polycarboxylate superplasticizer is ≥25%.

8. A method for preparing self-compacting, micro-expansion, high-density concrete as described in any one of claims 1 to 7, characterized in that, It includes: Glass microspheres, cellulose ether, and polycarboxylic acid ether are mixed to obtain a rheology-modified material; Calcium oxide and active magnesium oxide are mixed to obtain an expanding agent; Natural zeolite and zeolite powder are placed in a container, and a certain amount of water is added to pre-wet them to obtain a pre-wetted internal curing agent. Cement, fly ash, silica fume, rheology modifier, expansion agent and fine aggregate are mixed to obtain the first mixture; Pour the pre-wetted internal curing agent, the remaining water, and the additives into the first mixture and continue stirring to obtain the second mixture; Pour the coarse aggregate into the second mixture and continue mixing to obtain fresh concrete; Freshly mixed concrete is compacted, molded, and cured to obtain self-compacting, micro-expansion, high-density concrete.

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