Superfine basalt composite admixture

Abstract

The invention provides a superfine basalt composite admixture, and belongs to the technical field of building materials. The composite material is prepared from superfine basalt powder, active silicon powder and active calcium carbonate according to the mass ratio of (55-65): (25-35): 10. The particle size of the superfine basalt powder is smaller than or equal to 45 microns, and the specific surface area is larger than or equal to 400 m < 2 > / kg; the particle size of the active silicon powder is less than or equal to 0.3 mu m; wherein the content of amorphous SiO2 is greater than or equal to 93%. According to the composite admixture composed of the superfine basalt powder, the active silicon powder and the active calcium carbonate, through a triple synergistic mechanism of physical filling, pozzolanic reaction and crystal nucleus effect, the mechanical strength (the breaking strength is improved by 43.99%, and the compressive strength is improved by 15.85%) and the durability (the chloride ion diffusion coefficient is reduced by 1-2 orders of magnitude) of the concrete are remarkably improved. Meanwhile, by utilizing the characteristics of industrial solid waste, the cement consumption can be reduced by 30-50%, the CO2 emission can be reduced by more than 200kg / m < 3 >, and remarkable environmental protection benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and in particular relates to an ultrafine basalt composite admixture. Background Technology

[0002] Against the backdrop of the global green and low-carbon transformation of the construction industry, the high carbon emissions of traditional cement production are increasingly becoming a key factor restricting sustainable development—approximately 0.8 tons of CO2 are emitted for every ton of cement produced, and the cement industry contributes about 8% of global anthropogenic CO2 emissions. At the same time, the increasing demands on concrete performance from infrastructure construction are driving innovation in mineral admixture technology. In recent years, basalt-based composite admixture systems have received widespread attention from academia and engineering communities due to their dual characteristics of performance enhancement and environmental friendliness.

[0003] Basalt, the most widely distributed igneous rock in the Earth's crust, exhibits unique physicochemical activity after ultrafine processing (600-800 mesh). When combined with active silica powder and calcium carbonate in a 60:30:10 ratio, it can form a multi-scale synergistic enhancement effect. A scientific and technological achievement evaluation published by Beijing Xuanze New Materials Co., Ltd. in April 2025 showed that its basalt composite powder technology has reached the "international leading level" and has been applied on a large scale in high-speed rail and highway tunnel support projects both domestically and internationally. Guangxi Airport Management Group also applied for a basalt-based UHPC patent in 2025, highlighting its value in special engineering projects. This paper, combining the latest research progress and engineering practice, systematically analyzes the technical principles, performance advantages, industrialization status, and development path of this composite admixture, providing theoretical support for the promotion of green high-performance concrete. Summary of the Invention

[0004] The purpose of this invention is to propose an ultrafine basalt composite admixture, which is composed of ultrafine basalt powder, active silica powder, and active calcium carbonate in a mass ratio of 55-65:25-35:10.

[0005] The ultrafine basalt powder has a particle size ≤45μm and a specific surface area ≥400m². 2 / kg;

[0006] The particle size of the active silicon powder is ≤0.3μm; wherein the amorphous SiO 2 Content ≥93%.

[0007] Preferably, the particle size of the ultrafine basalt powder is ≤25μm.

[0008] More preferably, the particle size of the ultrafine basalt powder is ≤19μm.

[0009] Preferably, the specific surface area of ​​the activated calcium carbonate is 600-900 m². 2 / kg.

[0010] Preferably, the proportion of the ultrafine basalt composite admixture in the cementitious material is ≥20%.

[0011] More preferably, the proportion of the ultrafine basalt composite admixture in the cementitious material is ≥35%.

[0012] The three components of this invention play different roles in the hydration and hardening process of concrete, forming a multi-scale reinforcement mechanism:

[0013] Ultrafine basalt powder: The main material has a specific surface area of ​​400-625 m². 2 The powder, weighing approximately 5-30 μm, exhibits a near-spherical morphology, acting as a "micro-bearing" effect in fresh concrete and significantly improving its rheological properties. Experiments show that increasing the fineness of the basalt powder from 325 mesh (corresponding to a particle size of 45 μm) to 800 mesh (corresponding to a particle size of 19 μm) can improve the initial slump of concrete by 15%-20%, while reducing the risk of segregation. During the hardening stage, these ultrafine particles fill the 10-100 nm capillary pores in the cement paste, increasing the proportion of harmless pores (<50 nm in diameter) to over 80%, significantly optimizing the pore structure.

[0014] Activated silica fume: Provides high pozzolanic activity, with an amorphous SiO2 content >93% and an average particle size of 0.1-0.3μm. During the mid-stage of cement hydration (7-28 days), silica fume reacts with Ca(OH)2 to form a low calcium-to-silicon ratio (CSH) gel (C / S≈1.2-1.5), reducing the thickness of the interfacial transition zone (ITZ) by approximately 40% and significantly improving interfacial bond strength.

[0015] Activated calcium carbonate has a dual function: on the one hand, it accelerates the early hydration of C3S through the nucleation effect, shortening the setting time; on the other hand, it reacts with C3A to form aluminocarbonates (such as monoaluminocarbonates), refining the pore structure. Its particle size needs to be controlled within 600-900 μm. 2 / kg, forming a complementary gradation with basalt powder.

[0016] The three components of this invention work synergistically at different hydration stages of concrete to form a triple reinforcement network of "physical-chemical-crystallization":

[0017] Early hydration stage (0-3 days): Activated calcium carbonate provides nucleation sites, accelerates the hydrolysis of tricalcium silicate, and increases the 24-hour strength by 30%-40%, solving the problem of low early strength of admixture concrete;

[0018] Mid-stage hydration (3-28 days): Active silica powder consumes a large amount of Ca(OH)2 to generate highly stable CSH gel. At the same time, aluminosilicates in basalt powder gradually dissociate under alkaline conditions and participate in secondary hydration reactions.

[0019] During long-term service: Unreacted basalt micropowder continues to exert its micro-aggregate effect, inhibiting shrinkage stress concentration and compensating for shrinkage of 300×10. -6 ~600×10 -6 This significantly reduces the risk of cracking.

[0020] The specific functions are shown in Table 1 below:

[0021] Table 1. Mechanism of Action of the Three Components at Each Stage of Concrete Hydration

[0022] Hydration stage Basalt powder dominant role Active silica powder dominant role Active calcium carbonate dominant role Early stage (0-3 days) Physical lubrication, improve workability Surface adsorption water reducing agent Crystal nucleus effect, accelerating C3S hydrolysis Medium term (3-28 days) Micro aggregate filling, reduce porosity C-S-H generated by pozzolanic reaction Carbonate aluminates phase generated Long term (> 28 days) Continuous filling, inhibit shrinkage Gel densification Stability phase formation

[0023] In summary, this invention, a composite admixture composed of ultrafine basalt powder, activated silica powder, and activated calcium carbonate, significantly improves the mechanical strength (flexural strength increased by 43.99%, compressive strength increased by 15.85%) and durability of concrete (chloride ion diffusion coefficient reduced by 1-2 orders of magnitude) through a triple synergistic mechanism of physical filling, pozzolanic reaction, and crystal nucleation effect. Simultaneously, by utilizing the characteristics of industrial solid waste, it can reduce cement usage by 30%-50% and reduce CO2 emissions by 200 kg / m³. 3 All of the above have significant environmental benefits. Detailed Implementation

[0024] To better understand the present invention, the present invention will be further described below with reference to specific serial numbers. The terminology used in the serial numbers is for describing specific embodiments and does not constitute a limitation on the scope of protection of the present invention.

[0025] In the specific implementation methods, unless otherwise specified, the experimental methods used are all conventional methods, and the materials and reagents used are all commercially available unless otherwise specified.

[0026] Unless otherwise specified, percentages, % and so on in the specific implementation are assumed to be mass percentages.

[0027] Example 1: Effect of basalt powder of different fineness on the mechanical properties of concrete

[0028] In C60 concrete, 30% composite admixture was added, and the effect of composite admixtures with different fineness of ultrafine basalt powder on mechanical properties was observed.

[0029] The specific ratio of the composite admixture is basalt powder: silicon powder: calcium carbonate = 60:30:10; wherein the particle size of the active silicon powder is ≤0.3μm; and the amorphous SiO₂... 2Content ≥93%; specific surface area of ​​active calcium carbonate 600-900 m² 2 / kg.

[0030] The results are shown in Table 2 below.

[0031] Table 2. Effects of basalt powder of different fineness on the mechanical properties of concrete (at a dosage of 30%)

[0032] Powder fineness (mesh) Slump (mm) 28d compressive strength (MPa) 28d flexural strength (MPa) Flexural compressive ratio 325 (reference) 190 76.5 8.9 0.116 600 215(+13.2％) 84.2(+10.1％) 11.2(+25.8％) 0.133 800 225(+18.4％) 89.5(+17.0％) 12.8(+43.8％) 0.143

[0033] The test methods for slump, 28-day compressive strength, and 28-day flexural strength in Table 2 are derived from GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" and GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0034] As shown in Table 2, the workability of freshly mixed concrete directly determines the construction quality. The "ball effect" of ultrafine basalt powder (800 mesh) significantly reduces the viscosity of the paste. When the admixture is 30% of the total cementitious material, the concrete slump can reach 220 mm, meeting the requirements for pumping construction. In terms of mechanical properties, the composite admixture shows a significant enhancement in flexural strength. In C60 concrete, when 30% composite admixture is added, the 28-day flexural strength reaches 12.8 MPa, an increase of 43.80% compared to the baseline group; the compressive strength reaches 89.5 MPa, an increase of 17.0%. This difference stems from:

[0035] Mechanism for improving flexural strength: The CSH gel formed by basalt microparticles and silica fume creates a "fiber-gel" interwoven structure, which enhances interfacial toughness;

[0036] Mechanism for improving compressive strength: It mainly benefits from the reduction in porosity. Mercury porosimetry shows that the total porosity decreased from 14.2% to 10.0%, of which the number of harmful pores >100nm was reduced by more than 60%.

[0037] Example 2: Effect of composite admixtures with different mass ratios on the mechanical properties of concrete

[0038] Different proportions of composite admixtures were added to C60 concrete, and the effects of different proportions of composite admixtures on mechanical properties were observed; the results are shown in Table 3 below.

[0039] The specific ratio of the composite admixture is basalt powder: silica powder: calcium carbonate = 60:30:10; wherein the particle size of the basalt powder is ≤19μm and the specific surface area is ≥400m². 2 / kg; the particle size of the active silicon powder is ≤0.3μm, and the amorphous SiO₂ 2 Content ≥93%; specific surface area of ​​active calcium carbonate 600-900 m² 2 / kg.

[0040] Table 3. Effects of different proportions of composite admixtures on the mechanical properties of concrete.

[0041] Mixing ratio (%) Slump (mm) 28d compressive strength (MPa) 28d flexural strength (MPa) Flexural compressive ratio 0 120 52.0 6.2 0.119 10 160 67.5 8.7 0.128 20 185 78.5 10.7 0.136 35 245 97.0 14.0 0.144

[0042] Example 3: Effect of composite admixtures with different proportions on the mechanical properties of concrete

[0043] In C60 concrete, 30% of composite admixtures with different proportions were added, and the effects of different proportions of composite admixtures on mechanical properties were observed; the results are shown in Table 4 below.

[0044] The composite admixture is composed of basalt powder, silica powder, and calcium carbonate; wherein the basalt powder has a particle size ≤19μm and a specific surface area ≥400m². 2 / kg; the particle size of the active silicon powder is ≤0.3μm, and the amorphous SiO₂ 2 Content ≥93%; specific surface area of ​​active calcium carbonate 600-900 m² 2 / kg.

[0045] Table 4. Effects of different proportions of composite admixtures on the mechanical properties of concrete (admixture dosage 30%)

[0046] Mass ratio of basalt powder, silica powder, calcium carbonate Slump (mm) 28d compressive strength (MPa) 28d flexural strength (MPa) Flexural compressive ratio 55：35：10 210 92.0 13.2 0.143 60：30：10 225 89.5 12.8 0.143 65：25：10 245 86.5 12.3 0.142

[0047] Table 4 shows that the specific surface area is very large, resulting in high water demand; as the content increases, the fluidity decreases and the slump declines; the amount of water-reducing agent needs to be increased to compensate for the loss of fluidity. Silica fume and pozzolanic material have high activity, filling micropores and generating more CSH gel, leading to a significant increase in compressive strength. Simultaneously, the interfacial transition zone is strengthened, resulting in a slight increase in flexural strength. While the micro-aggregate effect of basalt powder weakens as the content decreases, its negative impact on strength is offset by the increase in silica fume content.

[0048] On the other hand, as the proportion of silica fume decreases, the water demand decreases, and the viscosity of concrete decreases; the slump increases. The active components of pozzolanic ash decrease, weakening the densification effect; the compressive strength decreases slightly. The interfacial strengthening effect weakens, but the brittleness decreases; at the same time, the filling effect of basalt powder is enhanced, but its activity is lower than that of silica fume, and its contribution to strength is limited, resulting in a slight decrease in flexural strength.

[0049] When pursuing ultra-high strength, a ratio of 55:35:10 is selected, requiring the addition of water-reducing agents and slump retainers to compensate for the loss of fluidity. When prioritizing pumpability or having lower performance requirements, a ratio of 65:25:10 is selected, still exceeding the C60 strength requirement, and construction is smoother.

[0050] This invention improves concrete durability through a three-pronged approach using basalt composite admixture concrete:

[0051] Resistance to chloride ion attack: The densified interface structure effectively inhibits ion migration. Electrical flux tests show that the electrical flux of concrete with composite admixtures is <800C, while traditional concrete often exceeds 2000C. In marine engineering, the chloride ion penetration depth in the tidal zone is <5mm over 5 years, far below the standard limit of 15mm. This is attributed to the active silica powder reducing the directional arrangement of Ca(OH)2, thus lowering the porosity of the ITZ zone to below 0.5%.

[0052] Improved crack resistance: The micro-expansion properties of basalt powder compensate for drying shrinkage. Circular ring tests show a crack reduction coefficient of up to 56.3%, achieving a "crack-free" effect, especially in panel concrete, as seen in the application case of the Kaihua Reservoir project in Zhejiang.

[0053] Freeze-thaw resistance and corrosion resistance: After 300 freeze-thaw cycles, the dynamic modulus retention rate of the admixture concrete is >85%, and the mass loss is <0.8g / m³. 2 When soaked in a 5% sulfate solution for 180 days, the expansion rate is only 1 / 3 that of ordinary concrete.

[0054] Microscopic studies (SEM / XRD) revealed that steam curing at 90℃ further activated the system's activity. High temperature promoted the depolymerization of aluminosilicate glass in basalt, reacting with Ca... 2+ The reaction generates CASH gel, which increases the fiber-matrix interfacial bonding strength by 40%.

[0055] The technology of this invention aligns with the concept of a circular economy, creating dual green benefits:

[0056] Resource recycling: Each cubic meter of concrete consumes 120 kg of waste basalt powder, solving the problem of solid waste accumulation in stone processing;

[0057] Carbon emission reduction: Reduce cement usage by 30%-50%, and reduce CO2 emissions by 200-250 kg / m³. 3 ;

[0058] - Cost advantage: Basalt powder costs only 300-500 yuan / ton, which is 1 / 5 of silica fume, reducing the cost of UHPC materials by 25%-35%.

[0059] Compared with traditional admixtures, basalt composite systems have significant advantages in both performance and environmental friendliness, as shown in Table 5 below.

[0060] Table 5 Comparison of Concrete Performance Indicators

[0061] Performance index Ordinary fly ash concrete Slag powder concrete Basalt composite admixture concrete 28d compressive strength (MPa) 45-55 55-65 75-95 Flexural compressive ratio 0.11-0.13 0.12-0.14 0.14-0.16 Chloride ion diffusion coefficient (×10-12 m2 / s) 8-12 5-8 0.8-1.5 Material cost (Yuan / m 3 )]]> 300-350 350-400 280-330 CO2emissions (kg / m 3 )]]> 350-400 300-350 200-250

[0062] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. An ultrafine basalt composite admixture, characterized in that, It is composed of ultrafine basalt powder, active silica powder, and active calcium carbonate in a mass ratio of 55-65:25-35:10; The ultrafine basalt powder has a particle size ≤45μm and a specific surface area ≥400m². 2 / kg; The particle size of the active silicon powder is ≤0.3μm; wherein the amorphous SiO 2 Content ≥93%.

2. The ultrafine basalt composite admixture according to claim 1, characterized in that, The particle size of the ultrafine basalt powder is ≤25μm.

3. The ultrafine basalt composite admixture according to claim 2, characterized in that, The particle size of the ultrafine basalt powder is ≤19μm.

4. The ultrafine basalt composite admixture according to claim 1, characterized in that, The specific surface area of ​​the active calcium carbonate is 600-900 m². 2 / kg.

5. The ultrafine basalt composite admixture according to claim 1, characterized in that, The proportion of the ultrafine basalt composite admixture in the cementitious material is ≥20%.

6. The ultrafine basalt composite admixture according to claim 5, characterized in that, The proportion of the ultrafine basalt composite admixture in the cementitious material is ≥35%.