A vitrified microsphere-aerogel modified cement-based material and a method for preparing the same

Abstract

The application discloses a kind of vitrified microsphere-aerogel modified cement-based materials and preparation method thereof, vitrified microsphere-aerogel modified cement-based materials include cementing material, aggregate system, water reducing agent, defoaming agent;Cementing material includes cement, silica fume;Aggregate system includes fine sand, SiO2 Aerogel particle, vitrified microsphere.A kind of vitrified microsphere-aerogel modified cement-based materials and preparation method thereof provided by the application, by the complex mixing synergistic modification design of aerogel and vitrified microsphere, the optimization promotion of heat insulation performance of cement-based modified cement-based material can be realized with the effective compensation of mechanical property loss caused by single material, and accordingly cement-based modified cement-based material with heat insulation performance and mechanical strength can be successfully prepared.

Description

Technical Field

[0001] This invention relates to a modified cement-based material, and more particularly to a vitrified microsphere-aerogel modified cement-based material and its preparation method. Background Technology

[0002] Against the backdrop of global macro-strategies for addressing climate change and promoting sustainable development, energy conservation and carbon reduction in the construction sector have become crucial for achieving carbon neutrality. Therefore, developing a novel modified cement-based material with synergistically optimized thermal insulation and mechanical properties to meet the integrated needs of strengthening and energy-saving retrofitting existing building structures not only provides new theoretical support and technological pathways for the synergistic regulation of multi-performance building materials but also deeply aligns with urban renewal and dual-carbon development trends.

[0003] Currently, building insulation materials are mainly divided into two categories: organic and inorganic. Organic lightweight insulation materials such as polystyrene foam have the characteristics of being lightweight and having excellent insulation performance, but they also have prominent problems such as flammability, insufficient durability, and environmental pollution. Inorganic insulation materials such as rock wool have the advantages of good fire resistance and high durability, but they generally have the disadvantages of poor insulation efficiency and high water absorption. Neither type of material can fully meet the development needs of my country's building energy conservation field. SiO2 aerogel, as a new type of nanoporous solid material, has an extremely low bulk density, which can be as low as three times the density of air, and a porosity as high as 99.8%, thus constructing a unique three-dimensional nano-network structure with a pore size range of 1-100 nm. This results in an extremely low thermal conductivity (0.013-0.016 W / (m·K)) at room temperature, and its thermal insulation performance is significantly better than that of traditional materials. In addition, this material also has a high specific surface area of ​​up to 1000 m². 2 With properties such as high g / g density, superhydrophobicity, Class A fire resistance, lightweight flexibility, and good chemical stability, it is hailed as one of the most promising new thermal insulation materials. Introducing it into a cement matrix to prepare aerogel-modified cement-based materials provides a novel approach for developing high-performance building materials that combine efficient thermal insulation with reliable structural reinforcement.

[0004] While the incorporation of aerogels can significantly improve the thermal insulation performance of cement-based materials, their low strength and significant brittleness often inevitably lead to a significant deterioration in the mechanical properties of the modified cement-based materials. Research on using aerogel incorporation to improve the thermal insulation performance of cement-based materials has made some progress, but relying solely on controlling the aerogel dosage or intrinsic properties is insufficient to simultaneously achieve excellent thermal insulation and mechanical properties in modified cement-based materials. Therefore, the composite design of multiple functional components is considered a key strategy for achieving synergistic optimization of material properties. Summary of the Invention

[0005] In view of this, the present invention proposes a vitrified microsphere-aerogel modified cement-based material and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A vitrified microsphere-aerogel modified cementitious material, comprising a cementitious material, an aggregate system, a water-reducing agent, and a defoamer; the cementitious material comprises cement and silica fume; the aggregate system comprises fine sand, SiO2 aerogel particles, and vitrified microspheres.

[0008] The mass ratio of the cementitious material to the aggregate system is 1:1; the cement accounts for 78%–85% of the mass of the cementitious material, and the silica fume accounts for 15%–20% of the mass of the cementitious material; the fine sand accounts for 74%–84% of the mass of the aggregate system, the SiO2 aerogel particles account for 6% of the mass of the aggregate system, and the vitrified microspheres account for 10%–20% of the mass of the aggregate system; the water-reducing agent accounts for 0.2%–0.5% of the total mass of the cementitious material, and the defoamer accounts for 0.1%–0.2% of the total mass of the cementitious material.

[0009] Furthermore, the cement used is PO 42.5 grade ordinary Portland cement;

[0010] The density of the cement is 3 g / cm³. 3 The flexural strength of the cement at 3 days is 4.0 MPa, the compressive strength of the cement at 3 days is 20 MPa, the flexural strength of the cement at 28 days is 7.5 MPa, and the compressive strength of the cement at 28 days is 43.0 MPa.

[0011] Furthermore, the SiO2 aerogel particles are hydrophobic SiO2 aerogel particles;

[0012] The packing density of the hydrophobic SiO2 aerogel particles is 0.2 g / cm³. 3 Specific surface area is 500-1000 m² 2 / g, porosity >90%, pore size 1-100nm, thermal conductivity 0.013-0.016W / (m·k).

[0013] Furthermore, the mass percentage of SiO2 in the silica ash is ≥ 92%.

[0014] Furthermore, the particle size range of the quartz fine sand is 0.06–2 mm.

[0015] Furthermore, the vitrified microspheres have a particle size of 2.0 mm, a thermal conductivity of 0.031 W / (m·K), and a bulk density of 120 kg / cm³.3 The compressive strength of the cylinder is 150 kPa.

[0016] Furthermore, the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

[0017] Furthermore, the defoamer is a P803 type powder defoamer.

[0018] This invention also provides a method for preparing a vitrified microsphere-aerogel modified cement-based material, comprising the following steps:

[0019] Step 1: First, dry mix cement, silica fume, fine sand, and SiO2 aerogel particles evenly to obtain a dry mix; at the same time, mix water, water-reducing agent, and defoamer evenly to obtain an admixture mixture; the mass ratio of water to cementitious materials is 1.

[0020] Step 2: Add the dry mix to the additive mixture under stirring, and continue stirring until a uniform fresh slurry is obtained; after the fresh slurry is uniformly mixed, add the vitrified microspheres and stir gently.

[0021] Step 3: Pour the slurry mixed in Step 2 into a mold coated with release agent to obtain a specimen;

[0022] Step 4: Smooth the surface of the specimen and place it in a curing chamber to cure for the specified age to obtain vitrified microsphere-aerogel modified cement-based material.

[0023] Furthermore, in step three, the mold is tamped by hand until the surface is covered with slurry and no large air bubbles overflow.

[0024] In step four, the temperature in the curing chamber is (20±2)℃ and the relative humidity is ≥95%.

[0025] Compared with existing technologies, the beneficial effects of this invention are:

[0026] (1) The present invention provides a vitrified microsphere-aerogel modified cement-based material. The aerogel can significantly improve the thermal insulation performance of the material. Within the dosage range tested in the present invention, when the dosage is 6%, the modified cement-based material has the lowest thermal conductivity. The nanoporous structure effectively increases the thermal resistance.

[0027] (2) The present invention provides a vitrified microsphere-aerogel modified cement-based material. Through the synergistic modification design of 6% aerogel and 15% vitrified microsphere, the thermal insulation performance of the modified cement-based material can be optimized and improved, and the mechanical property loss caused by a single admixture can be effectively compensated. Based on this, a modified cement-based material with both thermal insulation performance and mechanical strength can be successfully prepared, providing a practical material solution for the integration of energy saving and reinforcement of building structures.

[0028] (3) The present invention provides a vitrified microsphere-aerogel modified cement-based material. The microscopic mechanism shows that the aerogel and the vitrified microsphere jointly construct a "nano-micro" multi-level thermal insulation structure. The aerogel provides nanoscale filling, while the vitrified microsphere maintains the structural stability of the material by further reducing the thermal conductivity through the micron-level closed-pore structure and surface nucleation effect. Attached Figure Description

[0029] Figure 1 The graph shows the thermal conductivity of the modified cementitious materials with different aerogel contents according to the present invention.

[0030] Figure 2 The graph shows the thermal conductivity of the modified cement-based materials with different vitrified microsphere dosages according to the present invention.

[0031] Figure 3 This is a bar chart showing the 28-day compressive strength of the modified cementitious materials with different aerogel contents according to the present invention.

[0032] Figure 4 This is a bar chart showing the 28-day compressive strength of the modified cementitious materials with different vitrified microsphere dosages according to the present invention.

[0033] Figure 5 The XRD spectra of the modified cementitious materials with different aerogel contents according to the present invention are shown.

[0034] Figure 6 The XRD spectra of the modified cement-based materials of the present invention with different vitrified microsphere contents are shown.

[0035] Figure 7 Scanning electron microscope images of the modified cement-based materials with different aerogel contents according to the present invention;

[0036] Figure 8 The images show scanning electron microscope (SEM) images of the modified cement-based materials of the present invention with different vitrified microsphere dosages. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0040] Example 1

[0041] A vitrified microsphere-aerogel modified cement-based material, comprising cementitious materials, aggregate system, water-reducing agent, and defoamer; the cementitious materials include cement and silica fume; the aggregate system includes fine sand, SiO2 aerogel particles, and vitrified microspheres.

[0042] The mass ratio of cementitious materials to aggregate system is 1:1; the mass percentage of cement in cementitious materials is 82%, and the mass percentage of silica fume in cementitious materials is 18%; the mass percentage of fine sand in aggregate system is 79%, the mass percentage of SiO2 aerogel particles in aggregate system is 6%, and the mass percentage of vitrified microspheres in aggregate system is 15%; the mass of water-reducing agent is 0.5% of the total mass of cementitious materials, and the mass of defoamer is 0.2% of the total mass of cementitious materials.

[0043] This experiment used aerogel and vitrified microspheres as functional insulation components, and designed the mix proportion using an equal-mass substitution method for fine aggregate (sand). The mass percentage of SiO2 in silica fume was ≥ 92%. The particle size range of the quartz fine sand was 0.06–2 mm. The water-reducing agent was a polycarboxylate-based high-efficiency water-reducing agent. The defoamer was a P803 type powder defoamer.

[0044] The cement used is PO 42.5 grade ordinary Portland cement.

[0045] The SiO2 aerogel particles are hydrophobic SiO2 aerogel particles.

[0046] This invention also provides a method for preparing a vitrified microsphere-aerogel modified cement-based material, comprising the following steps:

[0047] Step 1: Weigh 4920g of cement, 1080g of silica fume, 4740g of fine sand, and 360g of SiO2 aerogel particles. First, put the cement, silica fume, fine sand, and SiO2 aerogel particles into a mixer and dry mix them evenly to obtain a dry mix. At the same time, weigh 30g of water-reducing agent and 12g of defoamer. Mix the water with the water-reducing agent and defoamer evenly to obtain an admixture mixture. The mass ratio of water to cementitious materials is 1.

[0048] Step 2: Add dry mix to the additive mixture under stirring, and continue stirring until a uniform fresh slurry is obtained; weigh 900g of vitrified microspheres, and after the fresh slurry is mixed evenly (for the vitrified microsphere group, the aerogel and slurry must be mixed evenly before adding the vitrified microspheres and stirring lightly), add the vitrified microspheres and stir lightly.

[0049] Step 3: Pour the slurry mixed in Step 2 into a mold coated with release agent to obtain a specimen; to prevent aerogel from floating, use manual tamping to tamp the slurry in the mold until the surface is covered with slurry and no large air bubbles overflow.

[0050] Step 4: Finally, smooth the surface of the specimen and place it in a curing chamber with a temperature of (20±2)℃ and a relative humidity of ≥95% to cure it for the specified age to obtain vitrified microsphere-aerogel modified cement-based material.

[0051] Example 2

[0052] Compared with Example 1, the difference is that the mass of fine sand is 5040g, the mass of SiO2 aerogel particles is 360g, and the mass of vitrified microspheres is 600g, that is, the mass percentage of fine sand in the aggregate system is 84%, the mass percentage of SiO2 aerogel particles in the aggregate system is 6%, and the mass percentage of vitrified microspheres in the aggregate system is 10%.

[0053] Everything else is the same as in Example 1.

[0054] Example 3

[0055] Compared with Example 1, the difference is that the mass of fine sand is 4440g, the mass of SiO2 aerogel particles is 360g, and the mass of vitrified microspheres is 1200g, that is, the mass percentage of fine sand in the aggregate system is 74%, the mass percentage of SiO2 aerogel particles in the aggregate system is 6%, and the mass percentage of vitrified microspheres in the aggregate system is 20%.

[0056] Everything else is the same as in Example 1.

[0057] Comparative Example 1

[0058] A modified cement-based material, comprising cementitious materials, an aggregate system, a water-reducing agent, and a defoamer; the cementitious materials include cement and silica fume; the aggregate system includes fine sand.

[0059] The mass ratio of cementitious materials to aggregate system is 1:1; the mass percentage of cement in cementitious materials is 82%, the mass percentage of silica fume in cementitious materials is 18%; the mass percentage of fine sand in aggregate system is 100%; the mass of water-reducing agent is 0.5% of the total mass of cementitious materials, and the mass of defoamer is 0.2% of the total mass of cementitious materials.

[0060] The silica fume contains ≥ 92% SiO2 by mass. The particle size range of the fine quartz sand is 0.06–2 mm. The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent. The defoamer is a P803 type powder defoamer.

[0061] The cement used is PO 42.5 grade ordinary Portland cement.

[0062] This invention also provides a method for preparing a modified cement-based material, comprising the following steps:

[0063] Step 1: Weigh 4920g of cement, 1080g of silica fume, and 6000g of fine sand. First, put the cement, silica fume, and fine sand into a mixer and dry mix them evenly to obtain a dry mix. At the same time, weigh 30g of water-reducing agent and 12g of defoamer. Mix the water with the water-reducing agent and defoamer evenly to obtain an admixture mixture. The mass ratio of water to cementitious materials is 1.

[0064] Step 2: Add the dry mix to the additive mixture while it is being stirred, and continue stirring until a uniform fresh slurry is obtained;

[0065] Step 3: Pour the slurry mixed in Step 2 into a mold coated with release agent to obtain a specimen; to prevent aerogel from floating, use manual tamping to tamp the slurry in the mold until the surface is covered with slurry and no large air bubbles overflow.

[0066] Step 4: Finally, smooth the surface of the specimen and place it in a curing chamber with a temperature of (20±2)℃ and a relative humidity of ≥95% to cure it for the specified age to obtain vitrified microsphere-aerogel modified cement-based material.

[0067] Comparative Example 2

[0068] An aerogel-modified cementitious material, a vitrified microsphere-aerogel-modified cementitious material, the aerogel-modified cementitious material includes cementitious materials, aggregate system, water-reducing agent, and defoamer; the cementitious materials include cement and silica fume; the aggregate system includes fine sand and SiO2 aerogel particles.

[0069] The mass ratio of cementitious materials to aggregate system is 1:1; the mass percentage of cement in cementitious materials is 82%, and the mass percentage of silica fume in cementitious materials is 18%; the mass percentage of fine sand in aggregate system is 98%, and the mass percentage of SiO2 aerogel particles in aggregate system is 2%; the mass of water-reducing agent is 0.5% of the total mass of cementitious materials, and the mass of defoamer is 0.2% of the total mass of cementitious materials.

[0070] This experiment used aerogel as the functional thermal insulation component. The silica fume contained ≥ 92% SiO2 by mass. The particle size range of the fine quartz sand was 0.06–2 mm. The water-reducing agent was a polycarboxylate-based high-efficiency water-reducing agent. The defoamer was P803 type powder defoamer.

[0071] The cement used is PO 42.5 grade ordinary Portland cement.

[0072] The SiO2 aerogel particles are hydrophobic SiO2 aerogel particles.

[0073] This invention also provides a method for preparing an aerogel-modified cementitious material, comprising the following steps:

[0074] Step 1: Weigh 4920g cement, 1080g silica fume, 5880g fine sand, and 120g SiO2 aerogel particles. First, put the cement, silica fume, fine sand, and SiO2 aerogel particles into a mixer and dry mix them evenly to obtain a dry mix. At the same time, weigh 30g water-reducing agent and 12g defoamer. Mix the water with the water-reducing agent and defoamer evenly to obtain an admixture mixture. The mass ratio of water to cementitious materials is 1.

[0075] Step 2: Add the dry mix to the additive mixture while it is being stirred, and continue stirring until a uniform fresh slurry is obtained;

[0076] Step 3: Pour the slurry mixed in Step 2 into a mold coated with release agent to obtain a specimen; to prevent aerogel from floating, use manual tamping to tamp the slurry in the mold until the surface is covered with slurry and no large air bubbles overflow.

[0077] Step 4: Finally, smooth the surface of the specimen and place it in a curing chamber with a temperature of (20±2)℃ and a relative humidity of ≥95% to cure it for the specified age to obtain vitrified microsphere-aerogel modified cement-based material.

[0078] Comparative Example 3

[0079] Compared with Comparative Example 2, the difference is that the mass of fine sand is 5760g and the mass of SiO2 aerogel particles is 240g, that is, the mass percentage of fine sand in the aggregate system is 96% and the mass percentage of SiO2 aerogel particles in the aggregate system is 4%.

[0080] The rest are the same as in Comparative Example 2.

[0081] Comparative Example 4

[0082] Compared with Comparative Example 2, the difference is that the mass of fine sand is 5640g and the mass of SiO2 aerogel particles is 360g, that is, the mass percentage of fine sand in the aggregate system is 94% and the mass percentage of SiO2 aerogel particles in the aggregate system is 6%.

[0083] The rest are the same as in Comparative Example 2.

[0084] Comparative Example 5

[0085] Compared with Comparative Example 2, the difference is that the mass of fine sand is 5520g and the mass of SiO2 aerogel particles is 480g, that is, the mass percentage of fine sand in the aggregate system is 92% and the mass percentage of SiO2 aerogel particles in the aggregate system is 8%.

[0086] The rest are the same as in Comparative Example 2.

[0087] Figure 1-8 A0, A1, A2, A3, A4, and A5 in the table correspond to Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5, respectively. Figure 1-8 B1, B2, and B3 in the text correspond to Example 1, Example 2, and Example 3, respectively.

[0088] According to the standard GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials", the thermal conductivity of the dried specimens was tested using a PDR-3030B dual-plate thermal conductivity meter. The specimens used in Examples 1-3 and Comparative Examples 1-5 were 300 mm × 300 mm × 30 mm in size and were demolded after 48 hours of hardening. After surface smoothing, they were placed in a curing chamber for 7 days, followed by drying in a 50 ℃ drying oven until the mass remained constant. Three specimens were prepared for each example or comparative example, and the test results were taken as the arithmetic mean.

[0089] The thermal conductivity test results of the modified cementitious materials in Comparative Examples 1-5 with aerogel are as follows: Figure 1 As shown, with the increase of aerogel content, the thermal conductivity of the modified cement-based material exhibits a non-linear change characteristic of first decreasing and then increasing. In Comparative Examples 1-5, when the aerogel content increased from 0% to 6%, the thermal conductivity of the sample decreased from 0.3464 W / (m·K) to 0.2237 W / (m·K), a decrease of 35%, mainly due to the aerogel's nanoporosity > 90%. Its introduction effectively increased the interfacial thermal resistance within the system and prolonged the heat conduction path, thus significantly improving the material's thermal insulation performance. When the aerogel content increased to 8%, the thermal conductivity increased to 0.2353 W / (m·K). This is because excessive aerogel content easily leads to agglomeration, and the agglomerates easily encapsulate excessive mixing water. The synergistic effect of these two factors forms a local thermal bridge effect, weakening the thermal insulation effect of the aerogel itself and reducing the overall thermal insulation effect of the material. At the same time, excessively high content will destroy the dispersion stability of the aerogel in the cement matrix.

[0090] With the aerogel content fixed at 6% (the aerogel content was fixed at 6% in Comparative Example 4 and Examples 1-3), the effect of vitrified microspheres on the thermal conductivity of the modified cement-based material is as follows: Figure 3 As shown in the figure. The results show that after incorporating vitrified microspheres in Examples 1-3, the thermal conductivity of the modified cement-based material was further reduced. As the content of vitrified microspheres increased from 0% to 15%, the thermal conductivity of the modified cement-based material decreased from 0.2237 W / (m·K) to 0.1642 W / (m·K), a decrease of 27%, which is 53% lower than that of the baseline group of Comparative Example 1 without aerogel and vitrified microspheres. This is mainly because vitrified microspheres have a closed-cell hollow structure and their inherent thermal conductivity is much lower than that of fine sand. When replacing fine sand with an equal mass, it can not only increase the overall porosity of the system, but also effectively block the heat flow transfer path by uniformly dispersing it in the matrix, extend the heat conduction distance, and further reduce the thermal conductivity. When the vitrified microsphere content increases to 20%, the thermal conductivity rises slightly. This phenomenon is due to the fact that excessive vitrified microspheres will cause particle accumulation and the internal structure of the material to become loose, which will enhance the connectivity between pores, thereby aggravating the internal heat convection effect and weakening the thermal insulation performance of the material.

[0091] Referring to the "Standard for Test Methods of Basic Performance of Building Mortar" JGJ / T70-2009, the compressive strength of cubic specimens (70.7 mm × 70.7 mm × 70.7 mm) from Examples 1-3 and Comparative Examples 1-5 at 28 days of age was tested. Before loading, the specimens were ensured to be centered and the bearing surface perpendicular to the loading direction. The loading process was kept uniform and continuous, with the loading rate controlled at approximately 0.5 MPa / s, until the specimen failed, and the peak load was recorded. At least three valid specimens were selected for each example or comparative example test, and the arithmetic mean was taken as the final result of the compressive strength of that group.

[0092] The 28-day compressive strength test results of the modified cementitious materials in Comparative Examples 1-5 with aerogel are as follows: Figure 3As shown in the figure, the 28-day compressive strength of the modified cementitious material generally decreases with increasing aerogel content, and exhibits stage-like changes in different content ranges; the fitting curves given in the figure can accurately describe this relationship. Without aerogel, the compressive strength of the modified cementitious material was 57.78 MPa. When the aerogel content was 2%, its slight negative impact on the sample density was offset by the filling effect of silica fume, the reactive effect, and the dispersing effect of the water-reducing agent, resulting in no significant stress concentration. The compressive strength decreased to 56.29 MPa, with no significant change. The slope of the fitted curve in this interval was relatively small, perfectly matching the characteristics of the gradual fluctuation in strength observed in the actual test. When the content increased to 4% or higher, the strength degradation effect became prominent. On the one hand, the aerogel itself has extremely low strength due to its nano-skeleton structure, and it adsorbs a large amount of mixing water during stirring, hindering the normal hydration of cement. On the other hand, the weak interface between the aerogel and the cement matrix formed a large number of interface defects with increasing content, becoming stress concentration points and accelerating failure. This led to a sharp decrease in the overall density of the material, a reduction in the load-bearing area, and a precipitous deterioration in compressive strength from the baseline value. At a content of 4%, the strength dropped to 19.44 MPa, and at contents of 6% and 8%, the strength further declined to 17.96 MPa and 11.61 MPa, respectively. MPa, a decrease of 80% compared to the A0 benchmark group, and the fitted curve shows a rapid downward trend in this range, which is highly consistent with the measured law of the cliff-like deterioration of strength in this stage.

[0093] With a fixed aerogel content of 6% (the aerogel content was fixed at 6% in Comparative Example 4 and Examples 1-3), the effect of co-doped vitrified microspheres on the compressive strength of the modified cementitious material at 28 days of age is as follows: Figure 4As shown in the figure. The results show that after incorporating vitrified microspheres in Examples 1-3, the compressive strength of the modified cementitious materials exhibited a trend of "slow decrease - tending to stabilize - mild decrease" with the increase of vitrified microsphere dosage. This is mainly due to the dynamic evolution of the material properties of vitrified microspheres and the internal structure and density of the modified cementitious materials. When the vitrified microsphere dosage increased from 0% to 10%, the compressive strength decreased from 17.96 MPa to 15.61 MPa, a decrease of about 13%. This is mainly because the vitrified microspheres themselves are lightweight and porous with low compressive strength, which weakens the compressive performance after incorporation. However, a small dosage has little disturbance to the density and slightly fills the voids between the aerogel and the matrix, buffering the deterioration. When the dosage increased to 15%, the compressive strength decreased slightly to 15.34 MPa, without showing a significant decrease. An appropriate amount of vitrified microspheres can fill the voids between the aerogel and the cement matrix, exert the micro-aggregate skeleton effect, optimize the internal stress distribution, and to a certain extent offset the negative impact of its own low strength, making the strength tend to stabilize. When the admixture content increased to 20%, the compressive strength dropped to 13.54 MPa. This was because excessive vitrified microspheres replaced the aggregate, resulting in an excessively low proportion of the cementitious system, a loose internal structure, increased porosity, and failure of the skeletal effect, leading to a further decrease in strength. The exponential fitting curve in the figure better reflects the overall decreasing strength relationship, and the fitting trends at each stage highly match the measured data.

[0094] The phase composition of the samples from Examples 1-3 and Comparative Examples 1-5 was analyzed using X-ray diffraction (XRD). Single-frequency Cu Kα radiation was used, with a working voltage of 40 kV, a working current of 20 mA, a speed of 2° / min, and a scanning range of 10–80°. All samples for microscopic testing were taken from specimens after 7 days of standard curing.

[0095] The XRD patterns of cementitious materials modified with different aerogel contents at 7 days of age in Comparative Examples 1-5 are shown below. Figure 5 As shown, the main hydration products in the early stage of hydration are Ca(OH)2 and SiO2, with Ca(OH)2 originating from the hydration of tricalcium silicate and dicalcium silicate in cement clinker. As the hydration process progresses, the diffraction peak intensities of AFt and CSH significantly increase, indicating that the aerogel incorporation does not change the types of early-stage cement hydration products; it mainly plays a physical filling role and does not participate extensively in the chemical reaction. However, changes in aerogel dosage affect the amount of hydration products generated. In the high dosage range (Comparative Example 4, Comparative Example 5), the CSH diffraction peak intensity significantly decreases. This is because increased aerogel dosage encapsulates a large amount of water, leading to insufficient effective water for cement hydration. Since CSH is a major cement hydration product, water shortage directly reduces its generation. When the aerogel dosage increases to 8%, excessive aerogel aggregation occurs. This physical filling spatially encroaches on the growth space of AFt and slows down the hydration reaction rate, resulting in a failure to reach the normal level.

[0096] Figure 6XRD patterns of modified cementitious materials with vitrified microspheres were obtained by fixing the aerogel content at 6% (the aerogel content was fixed at 6% in Comparative Example 4 and Examples 1-3). As shown in the figure, the addition of vitrified microspheres in Examples 1-3 intensified the hydration product reaction, indicating that the microspheres acted as nucleation sites, accelerating the formation of hydration products. With the incorporation of vitrified microspheres, the CSH diffraction peaks gradually increased, suggesting a possible slow pozzolanic effect on their surface, further consuming Ca(OH)2 to generate additional CSH gel. No significant changes were observed in the diffraction peaks of the later hydration products, indicating that the aerogel and vitrified microspheres sufficiently promoted hydration. With the increase in the vitrified microsphere content, they gradually filled the voids, becoming lightweight aggregates in the cement matrix. The micron-sized porous surface of vitrified microspheres forms an interfacial transition zone with the cement paste. The uneven surface creates a localized low water-cement ratio region around the microspheres, disrupting the preferred orientation of Ca(OH)₂ and CSH gels and forcing them to grow randomly and interwoven, consistent with the microstructure analysis. Simultaneously, the external hydration product network connects with the microspheres, forming a strong mechanical anchoring effect, far exceeding the physical adsorption effect solely based on van der Waals forces. Hydration product analysis indicates that the main function of vitrified microspheres is to improve the spatial distribution of hydration products and optimize the interface, reducing microstructural defects. Aerogels primarily function as physical fillers and reduce thermal conductivity, synergistically working with vitrified microspheres to construct a lightweight, high-strength, and thermally insulating mortar.

[0097] The microstructure of the samples from Examples 1-3 and Comparative Examples 1-5 was observed using a Tescan Mira4 field emission scanning electron microscope (SEM) with accelerating voltages ranging from 3 to 30 kV. Before testing, the samples were dried and vacuum-sprayed with gold to enhance conductivity and reduce charge accumulation.

[0098] Figure 7 The figures show the microstructure of modified cementitious materials with different aerogel contents. In the figures, (a), (b), (c), (d), (e), (f), (g), and (h) correspond to: Comparative Example 1 with 0% aerogel, (a) magnified view, Comparative Example 2 with 2% aerogel, Comparative Example 3 with 4% aerogel, Comparative Example 4 and Examples 1-3 with 6% aerogel, (e) magnified view, Comparative Example 5 with 8% aerogel, and Comparative Example 5 with 8% aerogel, respectively. As the aerogel content increases from 0% to 8%, the microstructure of the material exhibits a regular evolution from a dense to a highly porous system. Figure 7 As shown in (a) and (b), the baseline group has a dense structure, rich in lamellar CH, needle-like AFt, and dense CSH gel, with well-interwoven hydration products; as the doping concentration increases to 2%-4%, as... Figure 7As shown in (c) and (d), the porosity of the material is significantly increased, mainly due to the high specific surface area and nanoporous structure of the aerogel itself, which introduces a large number of isolated and partially interconnected pores. When the doping concentration increases to 6%, as... Figure 7 As shown in (e), the aerogel particles exhibit localized agglomeration, leading to an increase in micron-sized pores inside the matrix and at the aerogel-cement stone interface. These interface defects increase thermal resistance and significantly reduce the thermal conductivity of the material. Figure 7 (f) Further, it is shown that a large amount of CSH gel is attached to the periphery of the aerogel, and some CSH grows in situ within its nanopores. This structure helps to enhance the interfacial transition zone and improve the toughness of the material. When the doping concentration reaches 8%, such as Figure 7 As shown in (g) and (h), excessive aggregation and interconnected pores of the aerogel lead to an increase in unhydrated particles, structural deterioration, and consequently, an increase in thermal conductivity and a further decrease in strength, consistent with the results of macroscopic mechanical properties.

[0099] Figure 8 SEM images of the modified cementitious material with vitrified microspheres were obtained when the aerogel content was fixed at 6% (the aerogel content was fixed at 6% in Comparative Example 4, Example 2, and Example 3). Figures (a), (b), (c), and (d) correspond to the following examples, respectively: Example 4 with 6% aerogel, Example 2 with 6% aerogel + 15% vitrified microspheres, Example 2 with 6% aerogel + 15% vitrified microspheres, and Example 3 with 6% aerogel + 20% vitrified microspheres. Figure 8 (b) It is evident that aerogel and vitrified microspheres coexist in the matrix: the aerogel fills the interfacial region between the vitrified microspheres and the cement matrix, while the vitrified microspheres provide skeletal support for the system, effectively suppressing the tendency of structural loosening caused by aerogel alone. Simultaneously, ettringite is observed to grow along the surface of the vitrified microspheres and further fill the pores, a process that helps mitigate strength loss. The composite system further reduces the thermal conductivity by introducing more interfacial heat flow barriers. Figure 8 (c) This indicates that the vitrified microspheres have a hollow closed-cell structure, making them prone to breakage during stirring. When the vitrified microsphere content increases to 20%, as... Figure 8 (d) Particle accumulation and pore coarsening occur, leading to a weakening of the thermal conductivity optimization effect; simultaneously, the relative content of hydration products decreases, resulting in deterioration of mechanical properties. The results indicate that an appropriate amount of vitrified microspheres and aerogel can form a synergistic effect in the microstructure, jointly optimizing the thermal and mechanical properties of the modified cement-based material.

[0100] It is evident that aerogel can significantly improve the thermal insulation performance of materials. Within the dosage range tested in this invention, 6% is the optimal dosage. When the dosage is 6%, the modified cement-based material has the lowest thermal conductivity of 0.2237 W / (m·K), which is 35% lower than the undoped group. Its nanoporous structure effectively increases thermal resistance, but excessive dosage will lead to pore connectivity and moisture encapsulation, causing the thermal conductivity to rebound and significantly deteriorating the compressive strength.

[0101] By employing a synergistic modification design involving the co-admixture of 6% aerogel and 15% vitrified microspheres, the thermal insulation performance of cement-based modified cementitious materials can be optimized and improved, while effectively compensating for the mechanical property losses caused by single admixtures. Under this co-admixture ratio, the thermal conductivity of the modified cementitious material decreased to 0.1642 W / (m·K), a cumulative reduction of 53% compared to the unadmixed group, while the compressive strength remained at 15.34 MPa, showing no significant difference compared to the sample with 10% vitrified microspheres. This invention successfully prepared a cement-based modified cementitious material possessing both thermal insulation performance and mechanical strength, providing a practical material solution for the integrated energy conservation and reinforcement of building structures.

[0102] Microscopic mechanisms show that aerogel and vitrified microspheres jointly construct a "nano-micro" multi-level thermal insulation structure. Aerogel provides nanoscale filling, while vitrified microspheres maintain the structural stability of the material by further reducing the thermal conductivity through micron-level closed-pore structure and surface nucleation effect.

[0103] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A vitrified microsphere-aerogel modified cement-based material, characterized in that, The vitrified microsphere-aerogel modified cementitious material includes cementitious materials, aggregate system, water-reducing agent, and defoamer; the cementitious materials include cement and silica fume; the aggregate system includes fine sand, SiO2 aerogel particles, and vitrified microspheres. The mass ratio of the cementitious material to the aggregate system is 1:1; the cement accounts for 78%–85% of the mass of the cementitious material, and the silica fume accounts for 15%–20% of the mass of the cementitious material; the fine sand accounts for 74%–84% of the mass of the aggregate system, the SiO2 aerogel particles account for 6% of the mass of the aggregate system, and the vitrified microspheres account for 10%–20% of the mass of the aggregate system; the water-reducing agent accounts for 0.2%–0.5% of the total mass of the cementitious material, and the defoamer accounts for 0.1%–0.2% of the total mass of the cementitious material.

2. The vitrified microsphere-aerogel modified cement-based material according to claim 1, characterized in that, The cement used is PO 42.5 grade ordinary Portland cement; The density of the cement is 3 g / cm³. 3 The flexural strength of the cement at 3 days is 4.0 MPa, the compressive strength of the cement at 3 days is 20 MPa, the flexural strength of the cement at 28 days is 7.5 MPa, and the compressive strength of the cement at 28 days is 43.0 MPa.

3. The vitrified microsphere-aerogel modified cement-based material according to claim 1, characterized in that, The SiO2 aerogel particles are hydrophobic SiO2 aerogel particles. The packing density of the hydrophobic SiO2 aerogel particles is 0.2 g / cm³. 3 Specific surface area is 500-1000 m² 2 / g, porosity >90%, pore size 1-100nm, thermal conductivity 0.013-0.016W / (m·k).

4. The vitrified microsphere-aerogel modified cement-based material according to claim 1, characterized in that, The silica fume contains ≥ 92% SiO2 by mass.

5. The vitrified microsphere-aerogel modified cement-based material according to claim 1, characterized in that, The particle size range of the quartz fine sand is 0.06 to 2 mm.

6. The vitrified microsphere-aerogel modified cement-based material according to claim 1, characterized in that, The vitrified microspheres have a particle size of 2.0 mm, a thermal conductivity of 0.031 W / (m·K), and a bulk density of 120 kg / cm³. 3 The compressive strength of the cylinder is 150 kPa.

7. The vitrified microsphere-aerogel modified cement-based material according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

8. The vitrified microsphere-aerogel modified cement-based material according to claim 1, characterized in that, The defoamer is a P803 type powder defoamer.

9. A method for preparing a vitrified microsphere-aerogel modified cementitious material as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: First, dry mix cement, silica fume, fine sand, and SiO2 aerogel particles evenly to obtain a dry mix; at the same time, mix water, water-reducing agent, and defoamer evenly to obtain an admixture mixture; the mass ratio of water to cementitious materials is 1. Step 2: Add the dry mix to the additive mixture under stirring, and continue stirring until a uniform fresh slurry is obtained; after the fresh slurry is uniformly mixed, add the vitrified microspheres and stir gently. Step 3: Pour the slurry mixed in Step 2 into a mold coated with release agent to obtain a specimen; Step 4: Smooth the surface of the specimen and place it in a curing chamber to cure for the specified age to obtain vitrified microsphere-aerogel modified cement-based material.

10. The method for preparing a vitrified microsphere-aerogel modified cement-based material according to claim 9, characterized in that, In step three, the mold is tamped by manual tamping until the surface is covered with slurry and no large air bubbles overflow. In step four, the temperature in the curing chamber is (20±2)℃ and the relative humidity is ≥95%.

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