High-temperature-resistant dry-mixed fireproof mortar and preparation process thereof

Abstract

The invention relates to the technical field of building fireproof materials, and discloses high-temperature-resistant dry-mixed fireproof mortar and a preparation process thereof, and the high-temperature-resistant dry-mixed fireproof mortar comprises refractory grade mullite sand, anhydrous sodium hexametaphosphate powder, nano calcium carbonate, 3.5 hydrate zinc borate, aluminate cement, calcined kaolin, closed-cell expanded perlite and redispersible latex powder. Through a step-by-step variable-energy-level mixing technology, functional raw materials are physically anchored on the surface of mullite sand through mechanical friction high shear force to form an active pre-coating layer with the surface loaded with functional powder, then matrix filling is conducted at a medium speed, and finally closed-cell expanded perlite is added in a low-speed flexible mixing mode. The problem of retardation of phosphate to cement hydration is solved through a solid slow release mechanism, the construction operation performance is ensured, the boron-zinc modified melt is used for capturing gas released by nano calcium carbonate to construct a microporous toughening system, and the medium-temperature strength and thermal shock resistance stability of the mortar are improved.

Description

Technical Field

[0001] This invention relates to the field of building fireproof materials technology, specifically to a high-temperature resistant dry-mix fireproof mortar and its preparation process. Background Technology

[0002] Aluminate cement is used as a binder for high-temperature fireproof mortars due to its rapid hardening, early strength, and high-temperature resistance. However, the hydration products of aluminate cement undergo dehydration and decomposition in the temperature range of 400℃ to 800℃. At this temperature, the high-temperature ceramic sintering reaction has not yet started, leading to the breakage of internal chemical bonds and a decrease in strength. To compensate for this lack of mid-temperature strength, existing technologies introduce phosphates as auxiliary binders. However, phosphates have a strong retarding or even inhibiting effect on aluminate cement. Directly increasing the amount of phosphate will seriously interfere with the normal hydration process of cement, resulting in excessively long mortar setting time or insufficient early strength, which cannot meet the construction schedule requirements of actual projects.

[0003] On the other hand, the bound phase formed solely by phosphate is prone to large liquid phase shrinkage at high temperatures and lacks sufficient toughness, which makes the mortar layer prone to cracking or peeling when subjected to alternating hot and cold thermal shock environments. Although the volume stability can be improved by adding fillers, in the traditional dry-mix mortar preparation system, trace amounts of functional powders are difficult to disperse evenly on the aggregate surface to play a role. If the mixing strength is increased in order to pursue dispersion uniformity, the voids of the closed-cell expanded perlite lightweight aggregate added to the formula are easily destroyed, resulting in a decrease in the thermal insulation performance of the finished mortar. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-temperature resistant dry-mix fireproof mortar and its preparation process, which solves the problems of severe strength reduction in traditional aluminate cement-based refractory materials in the medium-temperature range due to the dehydration and decomposition of hydration products, and poor thermal shock resistance due to the mismatch of thermal expansion coefficients between the matrix and aggregate.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a high-temperature resistant dry-mix fireproof mortar, which is made from raw materials comprising the following parts by weight: Refractory grade mullite sand: 25-35 parts; Anhydrous sodium hexametaphosphate powder: 3-5 parts; Nano calcium carbonate: 2-4 parts; Zinc borate 3.5 aqueous solution: 1.5-2.5 parts; Aluminate cement: 35-45 parts; Calcinated kaolin: 5-8 parts; Closed-cell expanded perlite: 10-15 parts; Redispersible latex powder: 1-2 parts.

[0006] By adopting the above technical solution and utilizing a multi-component synergistic reaction mechanism, a new ceramic bonding phase was constructed in the mid-temperature region of aluminate cement failure. The specific mechanism is as follows: Phosphate bonding compensation mechanism: Anhydrous sodium hexametaphosphate undergoes melt polymerization in the intermediate temperature range (400℃-600℃) to form a phosphate network system, which fills the voids left by the dehydration of aluminate cement hydration products and provides the main source of intermediate temperature strength.

[0007] The rheological modification mechanism of boron-zinc melt: Zinc borate 3,5-hydrate decomposes upon heating to produce boron oxide and zinc oxide. These two oxides enter the phosphate melt, changing the viscosity and surface tension of the melt. The modified high-viscosity melt can stably adhere to the surface of mullite aggregate particles, preventing the melt from being lost or excessively penetrating due to gravity, and forming a continuous and thick bonding layer between the aggregates.

[0008] In-situ microporous toughening mechanism: Nano-calcium carbonate decomposes in-situ at high temperature, releasing carbon dioxide gas. Due to the high viscosity of the liquid melt after boron-zinc modification, the released carbon dioxide gas is captured by the melt, forming uniform closed micropores inside the binder layer. This micro-foaming can buffer the thermal expansion mismatch stress between the aggregate and the matrix, and the resulting micro-volume expansion offsets the sintering shrinkage of the matrix, thus improving the thermal shock resistance of the material.

[0009] Preferably, the active pre-coated aggregate is composed of refractory mullite sand, anhydrous sodium hexametaphosphate powder, nano-calcium carbonate and zinc borate 3,5-hydrate forming a surface-loaded functional raw material.

[0010] By adopting the above technical solution, anhydrous sodium hexametaphosphate powder is physically anchored on the surface of mullite sand using mechanochemical action. This pre-coating creates a slow-release dissolution effect, which limits the dissolution rate of phosphate ions in the initial stage of water mixing. This avoids the rapid complexation of high-concentration phosphate ions with calcium ions generated during cement hydration, ensuring that aluminate cement can undergo normal hydration reaction and ensuring that the mortar's setting time and early construction strength meet the project requirements.

[0011] Preferably, aluminate cement and calcined kaolin form a matrix filler mixture, while closed-cell expanded perlite and redispersible latex powder are flexible mixing additives.

[0012] By adopting the above technical solution, calcined kaolin is used as an active filler. It reacts with the decomposition products of aluminate cement at high temperature to generate calcium feldspar phase, which further enhances the strength of the high-temperature matrix. The subsequent addition of closed-cell expanded perlite and redispersible latex powder ensures the integrity of the lightweight aggregate and gives the mortar good thermal insulation performance and workability.

[0013] Secondly, the present invention provides a preparation process for high-temperature resistant dry-mixed fireproof mortar, comprising the following steps: S1. Weigh out refractory mullite sand, anhydrous sodium hexametaphosphate powder, nano calcium carbonate and zinc borate 3.5 water, and put them into a high-speed plow mixer with flying knives for mechanical friction shear mixing to obtain active pre-coated aggregate with surface-loaded functional materials. S2. Weigh aluminate cement and calcined kaolin, add them to the active pre-coated aggregate obtained in S1, adjust the spindle speed of the high-speed plow mixer, and disperse and fill the mixture to obtain the matrix-filled mixture. S3. Weigh closed-cell expanded perlite and redispersible latex powder, add them to the matrix filling mixture obtained in S2, adjust the spindle speed of the high-speed plow mixer, and turn off the fly knife to perform flexible mixing, and obtain the finished high-temperature resistant dry-mixed fireproof mortar.

[0014] By adopting the above technical solution, this invention establishes a stepwise variable energy level mixing process, which achieves the dual construction of raw materials and functions through precise control of the mechanical shear force field: High-shear solid coating: Utilizing the strong mechanical frictional shear force generated by high-speed flying knives and plow blades, anhydrous sodium hexametaphosphate, nano-calcium carbonate, and zinc borate 3.5 water fine powders are forced to undergo plastic deformation and embedding on the surface of mullite sand, forming a firm pre-coating layer. This is a key step in solving the problem of phosphate coagulation inhibition and achieving spatial positioning of high-temperature in-situ reaction.

[0015] Medium-speed dispersion filling: Under medium-speed conditions, the cementitious material is uniformly filled into the aggregate voids to build a dense packing system, while avoiding damage to the pre-coated layer.

[0016] Low-speed flexible composite: The low-speed, bladeless mixing mode protects the vitrified shell of the closed-cell expanded perlite from breakage, ensuring that the dry apparent density and thermal conductivity of the finished mortar remain within the design range.

[0017] Preferably, in step S1, the spindle speed of the high-speed plow mixer is set to 1100-1600 rpm, and the duration of mechanical friction shear mixing is 3-6 minutes.

[0018] By adopting the above technical solution, the rotation speed range and time range ensure sufficient mechanical energy input, enabling the functional raw materials to overcome the surface energy barrier and be uniformly and firmly adsorbed onto the aggregate surface, while avoiding the crushing of the aggregate itself due to excessive friction.

[0019] Preferably, in step S2, the spindle speed of the high-speed plow mixer is adjusted to 300-500 rpm, and the dispersion and filling mixing time is 3-4 minutes.

[0020] By adopting the above technical solution, the macroscopic uniformity of the cementitious material and the pre-coated aggregate is ensured, forming a stable suspension support.

[0021] Preferably, in step S3, the spindle speed of the high-speed plow mixer is adjusted to 60-100 rpm, and the duration of flexible mixing is 1-2 minutes.

[0022] By adopting the above technical solutions, the damage caused by mechanical force to lightweight porous materials is reduced, and the volume stability of the finished fireproof mortar is guaranteed.

[0023] This invention provides a high-temperature resistant dry-mix fireproof mortar and its preparation process. It has the following beneficial effects: 1. This invention improves the mid-temperature mechanical properties and thermal shock resistance of materials by introducing a synergistic modification system of zinc borate 3,5-hydrate and nano-calcium carbonate. The thermal decomposition products of zinc borate 3,5-hydrate optimize the rheological properties of the liquid melt and can effectively capture carbon dioxide gas released by nano-calcium carbonate, forming an in-situ micro-foamed bonding layer at the aggregate interface. This closed-cell micro-foam not only alleviates the stress caused by thermal expansion mismatch, but also compensates for the sintering shrinkage of the matrix through volume micro-expansion, solving the problem of strength reduction and easy cracking of traditional aluminate cement-based materials in the range of 400℃ to 800℃.

[0024] 2. This invention solves the problem of poor hydration compatibility between high-content phosphate and aluminate cement by employing a high-speed mechanical friction shearing process. Through physical strong anchoring, anhydrous sodium hexametaphosphate powder is pre-coated onto the surface of refractory mullite sand, constructing a solid slow-release system. This limits the dissolution rate of phosphate ions in the early stage of mixing, avoids blocking the cement hydration process, and ensures that the high-temperature dry-mix fireproof mortar has normal setting time and excellent early strength at room temperature, achieving a balance between workability and high-temperature functionality.

[0025] 3. This invention achieves the maximization of the integrity and function of different raw materials by establishing a graded variable speed preparation system. Based on the use of high shear force to complete the coating of functional raw materials, the subsequent steps adopt a low-speed flexible mixing method to add closed-cell expanded perlite. This step-by-step energy consumption control strategy avoids the breakage of brittle lightweight aggregates during the mixing process, ensures that the dry apparent density of the finished mortar is maintained at a low level, and guarantees the thermal insulation performance and volume stability of the material. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to embodiments, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Examples 1-5 Example

[0028] This embodiment provides a preparation process for high-temperature resistant dry-mix fireproof mortar, including the following steps: S1. Weigh 30 parts by weight of refractory mullite sand, 4 parts by weight of anhydrous sodium hexametaphosphate powder, 3 parts by weight of nano calcium carbonate, and 2 parts by weight of zinc borate 3.5 hydrate; put the refractory mullite sand, anhydrous sodium hexametaphosphate powder, nano calcium carbonate, and zinc borate 3.5 hydrate into a high-speed plow mixer equipped with a flying knife; start the high-speed plow mixer, set the spindle speed to 1400 rpm, and perform mechanical friction shear mixing for 4 minutes to obtain active pre-coated aggregate with surface-loaded functional raw materials; S2. Weigh 40 parts by weight of aluminate cement and 6.5 parts by weight of calcined kaolin; add the aluminate cement and calcined kaolin to the active pre-coated aggregate obtained in S1; adjust the spindle speed of the high-speed plow mixer to 400 rpm, disperse and fill the mixture for 3.5 minutes to obtain the matrix-filled mixture; S3. Weigh 12 parts by weight of closed-cell expanded perlite and 1.5 parts by weight of redispersible latex powder; add the closed-cell expanded perlite and redispersible latex powder to the matrix filling mixture obtained in S2; adjust the spindle speed of the high-speed plow mixer to 80 rpm and turn off the fly knife, perform flexible mixing, and mix for 1.5 minutes to obtain the finished high-temperature resistant dry-mixed fireproof mortar. Example

[0029] This embodiment provides a preparation process for high-temperature resistant dry-mix fireproof mortar, including the following steps: S1. Weigh 35 parts by weight of refractory mullite sand, 3 parts by weight of anhydrous sodium hexametaphosphate powder, 2 parts by weight of nano calcium carbonate, and 1.5 parts by weight of zinc borate 3.5 water; put the refractory mullite sand, anhydrous sodium hexametaphosphate powder, nano calcium carbonate, and zinc borate 3.5 water into a high-speed plow mixer equipped with a flying knife; start the high-speed plow mixer, set the spindle speed to 1400 rpm, and perform mechanical friction shear mixing for 4 minutes to obtain active pre-coated aggregate with surface-loaded functional raw materials; S2. Weigh 35 parts by weight of aluminate cement and 5 parts by weight of calcined kaolin; add the aluminate cement and calcined kaolin to the active pre-coated aggregate obtained in S1; adjust the spindle speed of the high-speed plow mixer to 300 rpm, and carry out dispersion filling and mixing for 4 minutes to obtain the matrix-filled mixture; S3. Weigh 10 parts by weight of closed-cell expanded perlite and 1 part by weight of redispersible latex powder; add the closed-cell expanded perlite and redispersible latex powder to the matrix filling mixture obtained in S2; adjust the spindle speed of the high-speed plow mixer to 60 rpm and turn off the fly knife, perform flexible mixing, and mix for 2 minutes to obtain the finished high-temperature resistant dry-mixed fireproof mortar. Example

[0030] This embodiment provides a preparation process for high-temperature resistant dry-mix fireproof mortar, including the following steps: S1. Weigh 25 parts by weight of refractory mullite sand, 5 parts by weight of anhydrous sodium hexametaphosphate powder, 4 parts by weight of nano calcium carbonate, and 2.5 parts by weight of zinc borate 3.5 water; put the refractory mullite sand, anhydrous sodium hexametaphosphate powder, nano calcium carbonate, and zinc borate 3.5 water into a high-speed plow mixer equipped with flying knives; start the high-speed plow mixer, set the spindle speed to 1400 rpm, and perform mechanical friction shear mixing for 4 minutes to obtain active pre-coated aggregate with surface-loaded functional raw materials; S2. Weigh 45 parts by weight of aluminate cement and 8 parts by weight of calcined kaolin. Add the aluminate cement and calcined kaolin to the active pre-coated aggregate obtained in S1. Adjust the spindle speed of the high-speed plow mixer to 500 rpm and perform dispersion filling and mixing for 3 minutes to obtain the matrix-filled mixture. S3. Weigh 15 parts by weight of closed-cell expanded perlite and 2 parts by weight of redispersible latex powder; add the closed-cell expanded perlite and redispersible latex powder to the matrix filling mixture obtained in S2; adjust the spindle speed of the high-speed plow mixer to 100 rpm and turn off the fly knife, perform flexible mixing, and mix for 1 minute to obtain the finished high-temperature resistant dry-mixed fireproof mortar. Example

[0031] This embodiment provides a preparation process for high-temperature resistant dry-mix fireproof mortar. The raw material mass ratio is consistent with that in Example 1, but the shear parameters in the preparation process are different. The process includes the following steps: S1. Weigh 30 parts by weight of refractory-grade mullite sand, 4 parts by weight of anhydrous sodium hexametaphosphate powder, 3 parts by weight of nano-calcium carbonate, and 2 parts by weight of zinc borate 3.5 hydrate; put the refractory-grade mullite sand, anhydrous sodium hexametaphosphate powder, nano-calcium carbonate, and zinc borate 3.5 hydrate into a high-speed plow mixer equipped with a flying knife; start the high-speed plow mixer, set the spindle speed to 1600 rpm, and perform mechanical friction shear mixing for 3 minutes to obtain active pre-coated aggregate with surface-loaded functional raw materials; S2. Weigh 40 parts by weight of aluminate cement and 6.5 parts by weight of calcined kaolin; add the aluminate cement and calcined kaolin to the active pre-coated aggregate obtained in S1; adjust the spindle speed of the high-speed plow mixer to 350 rpm, disperse and fill the mixture for 3.5 minutes to obtain the matrix-filled mixture; S3. Weigh 12 parts by weight of closed-cell expanded perlite and 1.5 parts by weight of redispersible latex powder; add the closed-cell expanded perlite and redispersible latex powder to the matrix filling mixture obtained in S2; adjust the spindle speed of the high-speed plow mixer to 90 rpm and turn off the fly knife to perform flexible mixing for 1.2 minutes to obtain the finished high-temperature resistant dry-mixed fireproof mortar. Example

[0032] This embodiment provides a preparation process for high-temperature resistant dry-mix fireproof mortar. The raw material mass ratio is consistent with that in Example 1, but the shear parameters in the preparation process are different. The process includes the following steps: S1. Weigh 30 parts by weight of refractory mullite sand, 4 parts by weight of anhydrous sodium hexametaphosphate powder, 3 parts by weight of nano calcium carbonate, and 2 parts by weight of zinc borate 3.5 hydrate; put the refractory mullite sand, anhydrous sodium hexametaphosphate powder, nano calcium carbonate, and zinc borate 3.5 hydrate into a high-speed plow mixer equipped with a flying knife; start the high-speed plow mixer, set the spindle speed to 1100 rpm, and perform mechanical friction shear mixing for 6 minutes to obtain active pre-coated aggregate with surface-loaded functional raw materials; S2. Weigh 40 parts by weight of aluminate cement and 6.5 parts by weight of calcined kaolin. Add the aluminate cement and calcined kaolin to the active pre-coated aggregate obtained in S1. Adjust the spindle speed of the high-speed plow mixer to 450 rpm and perform dispersion filling and mixing for 3 minutes to obtain the matrix-filled mixture. S3. Weigh 12 parts by weight of closed-cell expanded perlite and 1.5 parts by weight of redispersible latex powder; add the closed-cell expanded perlite and redispersible latex powder to the matrix filling mixture obtained in S2; adjust the spindle speed of the high-speed plow mixer to 70 rpm and turn off the fly knife to perform flexible mixing for 1.8 minutes to obtain the finished high-temperature resistant dry-mixed fireproof mortar.

[0033] Comparative Examples 1-6 Comparative Example 1: Compared with Example 1, the difference is that anhydrous sodium hexametaphosphate powder, nano calcium carbonate and zinc borate 3,5-hydrate were not added in step S1, and refractory mullite sand was mechanically frictionally sheared and mixed separately in a high-speed plow mixer, while the rest were the same.

[0034] Comparative Example 2: The difference from Example 1 is that zinc borate 3,5-hydrate was not added in step S1, but all other steps are the same.

[0035] Comparative Example 3: The difference from Example 1 is that nano-calcium carbonate was not added in step S1, but all other steps are the same.

[0036] Comparative Example 4: The difference from Example 1 is that anhydrous sodium hexametaphosphate powder was not added in step S1, but all other steps are the same.

[0037] Comparative Example 5: Compared with Example 1, the difference is that in step S1, 3 parts by mass of nano calcium carbonate is replaced with 3 parts by mass of ordinary heavy calcium carbonate, and the rest are the same.

[0038] Comparative Example 6: Compared with Example 1, the difference is that the stepwise mixing process of S1, S2 and S3 is adjusted to a one-step overall mixing process. Specifically, all the raw materials in Example 1 are put into the high-speed plow mixer at one time, the spindle speed is set to 300 rpm, and the mixing time is 10 minutes to obtain the high-temperature resistant dry-mixed fireproof mortar. The types and amounts of other raw materials are the same.

[0039] Test Example 1-2: Test Example 1: This test case aims to verify the construction performance and basic physical properties of the high-temperature dry-mixed fireproof mortar prepared in Examples 1 to 5 under normal conditions, in order to confirm whether the introduction of the high-content phosphate and zinc borate system will have an inhibitory effect on the hydration process of aluminate cement.

[0040] According to GB / T1346 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement", a certain volume of water was measured and added to a mixing pot, along with the high-temperature resistant dry-mixed fireproof mortar powder prepared in Examples 1 to 5, and stirred evenly. By adjusting the amount of water added, the high-temperature resistant dry-mixed fireproof mortar was stirred until it reached the standard consistency (the test rod sank 6mm ± 1mm ​​from the bottom plate), and the percentage of water added to the mass of the dry powder was recorded at this point.

[0041] At standard consistency, the mixed high-temperature dry-mix fireproof mortar was poured into a round mold and placed in a curing chamber at a temperature of 20℃±2℃ and a relative humidity greater than 50%. The initial setting time (the needle sinks to 4mm±1mm from the bottom plate) and the final setting time (the needle sinks to 0.5mm) were determined using a Vicat apparatus, and the units were recorded in minutes.

[0042] Referring to the JC / T984 standard "Polymer Cement Waterproof Mortar", high-temperature resistant dry-mixed fireproof mortar of standard consistency was poured into triple molds of 40mm×40mm×160mm and vibrated to form the mortar. After curing under standard conditions for 24 hours, the mortar was demolded and continued to be cured in water for 28 days. The compressive strength of the specimens was then tested using a universal testing machine with a loading rate controlled at 2.4kN / s. The failure load was recorded and the compressive strength was calculated.

[0043] After 28 days of curing, the test blocks were placed in an electric heating drying oven and dried at 105℃ until constant weight. After being removed and cooled to room temperature, the geometric dimensions of the test blocks were measured and the volume was calculated. The mass of the test blocks was weighed, and the mass per unit volume was calculated.

[0044] The experimental results are as follows: The specific data obtained from the test are recorded in Table 1.

[0045] Table 1. Test data on the foundation construction performance and physical properties of Examples 1-5 Test Project Example 1 Example 2 Example 3 Example 4 Example 5 Standard consistency water requirement (%) 24.3 23.8 25.4 24.6 24.1 Initial setting time (minutes) 68 52 94 73 61 Final setting time (minutes) 415 368 522 430 455 28-day room temperature compressive strength (MPa) 46.2 42.8 47.9 46.5 44.1 Dry apparent density (kg / m³) 1582 1545 1612 1595 1568 The results and conclusions are as follows: Table 1 shows that sodium hexametaphosphate, when used as a strong retarder or even an inhibitor in conventional aluminate cement systems, generally results in prolonged non-setting when its addition exceeds 1% of the cement mass. In Examples 1 to 5, the proportion of sodium hexametaphosphate added to the aluminate cement mass far exceeds the conventional amount (up to 5 parts by mass in Example 3, approximately 11% of the cement). However, test data shows that the initial setting time of all examples was controlled between 50 and 95 minutes, and the final setting time was between 6 and 9 hours. This result proves that the friction dispersion pre-coating process in step S1 played a crucial role. Through high-intensity mechanical shearing, anhydrous sodium hexametaphosphate powder was physically anchored on the surface of mullite aggregate and did not directly dissolve completely in the mixing water. This solid-state anchoring effect forms a slow-release mechanism, limiting the complexation rate of phosphate ions with calcium ions generated during cement hydration, thereby ensuring that the aluminate cement can undergo normal hydration reactions and meet the construction requirements for operating time.

[0046] The 28-day compressive strength at room temperature for Examples 1 to 5 remained above 42 MPa. Example 3, with the addition of a higher content of anhydrous sodium hexametaphosphate and nano-calcium carbonate, showed a slight increase in compressive strength (47.9 MPa). This indicates that, under the formulation system of this invention, the functional filler did not disrupt the early skeleton construction of the cement matrix. Compared to Examples 1 and 4, Example 5, due to the use of a lower shear speed (1100 rpm) during preparation, resulted in a slightly shorter initial setting time (61 minutes) and a slightly lower strength (44.1 MPa). This, in turn, confirms the importance of the degree of pre-coating dispersion: the more uniform the dispersion, the less local interference of sodium hexametaphosphate on cement hydration, and the more stable the overall mechanical properties.

[0047] The data from Test Example 1 directly confirms that the high-temperature resistant dry-mix fireproof mortar proposed in this invention is entirely feasible under conventional room temperature construction conditions. By resolving the compatibility issues between chemical raw materials (especially high-phosphate content) and cement hydration through technological means, the prepared mortar has a moderate water requirement, a setting time that meets engineering requirements, and excellent room-temperature mechanical strength, laying a solid matrix foundation for subsequent performance transformation at high temperatures.

[0048] Test Example 2: This test aims to investigate the evolution of mechanical properties, thermal shock resistance, and high-temperature volume stability of the high-temperature resistant dry-mix fireproof mortars prepared in Example 1 and Comparative Examples 1 to 6 under different temperature gradients. By comparing data, the compensating effects of the zinc borate-induced liquid-phase rheological modification mechanism and the in-situ micro-foaming mechanism of nano-calcium carbonate on the performance in the mid-temperature range are verified.

[0049] The freshly prepared high-temperature resistant dry-mixed fireproof mortars of Example 1 and Comparative Examples 1 to 6 were poured into prism-shaped steel molds measuring 40mm × 40mm × 160mm and compacted by vibration. After curing for 24 hours at 20℃ ± 2℃ and relative humidity greater than 90%, the molded specimens were demolded. The demolded specimens were then cured in water for 28 days, and subsequently dried in an oven at 105℃ to constant weight, serving as test samples.

[0050] After drying, the samples were placed in a high-temperature box-type resistance furnace. The heating rate was set to 5℃ / min, and the samples were heated to four target temperatures: 400℃, 600℃, 800℃, and 1100℃. After reaching the target temperature, the samples were held at that temperature for 2 hours, and then allowed to cool naturally to room temperature. The compressive strength of the samples after each temperature treatment was tested using a universal testing machine, and the data were recorded. Three parallel samples were tested at each temperature point, and the average value was taken.

[0051] The test was conducted according to YB / T2206.2, "Test Method for Thermal Shock Resistance of Refractory Materials". The dried sample was placed in a preheated furnace to 800℃ and held for 30 minutes. The sample was then immediately immersed in flowing tap water (15℃~25℃) for rapid cooling for 3 minutes, followed by air drying for 5 minutes. This process was recorded as one thermal shock cycle. The heating, rapid cooling, and drying cycles were repeated until the sample broke in two or the mass loss exceeded 20%. The maximum number of cycles the sample could withstand while remaining intact was recorded.

[0052] The length (L0) of the dried sample before heating was accurately measured using vernier calipers. The sample was then placed in a high-temperature furnace and heated to 800°C at a rate of 5°C / min. After holding at this temperature for 2 hours, the sample was cooled to room temperature with the furnace, and the length (L1) was measured again. The calculation formula is: linear change rate = [(L1-L0) / L0] × 100%. A positive value indicates expansion, and a negative value indicates contraction.

[0053] The experimental results are as follows: The specific test data for each group of samples are recorded in Table 2.

[0054] Table 2. Summary of high-temperature performance test data of Example 1 and Comparative Examples 1-6 Test Project Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Residual compressive strength at 400℃ (MPa) 51.3 32.4 45.2 48.6 30.5 42.1 43.5 Residual compressive strength at 600℃ (MPa) 58.7 12.8 36.5 45.2 8.4 31.8 35.6 Residual compressive strength at 800℃ (MPa) 65.2 10.5 28.3 41.9 11.2 26.4 38.2 Residual compressive strength at 1100℃ (MPa) 72.8 48.6 55.4 68.3 52.1 60.5 62.4 Number of thermal shock cycles (times) 28 3 7 5 2 9 12 Linear change rate at 800℃ (%) +0.32 -1.45 -0.92 -1.21 -1.15 -0.45 -0.68 The results and conclusions are as follows: Table 2 shows that the data from Comparative Example 1 reflects the shortcomings of traditional aluminate cement-based materials: at 600℃ and 800℃, due to the dehydration and decomposition of hydration products and the fact that ceramic sintering has not yet begun, the strength drops sharply to around 10-13 MPa, exhibiting a strength trough. Conversely, Example 1 shows residual strengths of 58.7 MPa and 65.2 MPa at 600℃ and 800℃, respectively, without any strength reduction, and continues to increase with rising temperature. This confirms that the system composed of anhydrous sodium hexametaphosphate, nano-calcium carbonate, and zinc borate successfully constructs a new chemical bonding network in the cement failure temperature range (400-800℃). Comparative Example 4 shows low strength at all high-temperature stages, demonstrating that anhydrous sodium hexametaphosphate, as the main liquid matrix and binder in the mid-temperature range, is the foundation for strength maintenance. Without a phosphate matrix, cement alone cannot maintain stability in the mid-temperature range.

[0055] Compared to Example 1, Comparative Example 2 showed lower strength at 600°C and 800°C than Example 1, and its thermal shock resistance was only 7 cycles. Comparative Example 2 lacked zinc borate 3,5-hydrate, resulting in insufficient boron and zinc oxide produced by its decomposition, leading to excessively low viscosity and insufficient surface tension in the phosphate melt. At high temperatures, the low-viscosity phosphate melt is easily lost due to gravity or excessively penetrates into the porous aggregate, resulting in discontinuous cementitious layers between particles and the inability to form a continuous glassy phase network. The high strength of Example 1 demonstrates that zinc borate 3,5-hydrate modulates the melt rheology, enabling it to stably remain at the aggregate particle contact points and exert a binding effect.

[0056] Example 1 exhibited 28 thermal shock cycles and a linear shrinkage rate of +0.32% at 800℃. In contrast, Comparative Example 3, while possessing acceptable strength (41.9 MPa), only underwent 5 thermal shock cycles and showed shrinkage (-1.21%). This difference validates the existence and function of in-situ micropores. Comparative Example 3, lacking nano-calcium carbonate and a gas source, failed to alleviate the thermal expansion mismatch stress between the mullite aggregate and the matrix, leading to cracking during rapid cooling. In Example 1, the carbon dioxide released from the decomposition of nano-calcium carbonate was captured by the boron-modified high-viscosity melt, forming a closed-cell micro-foamed ceramic glaze. These micropores acted as stress buffers, and the resulting micro-expansion offset the matrix sintering shrinkage, thus improving thermal shock resistance. Comparative Example 5 used ordinary heavy calcium carbonate, whose strength and thermal shock resistance were not as good as those of Example 1. This indicates that large-particle calcium carbonate has low reactivity and the released gas is too concentrated, which easily forms large defect pores instead of uniform micropores, thus disrupting the continuity of the raw materials.

[0057] Compared with Comparative Example 6, the performance indicators of Example 1 are superior to those of Comparative Example 6 in all aspects. In particular, the strength at 800℃ and the thermal shock resistance show greater fluctuations and decreases in Comparative Example 6. This indicates that without pre-coating, trace amounts of functional additives randomly dispersed in the mortar matrix are unlikely to form high-concentration reaction micro-regions on the aggregate surface. Only through the forced friction coating in step S1 can the three raw materials be ensured to be in close contact and positioned at the aggregate interface, thereby allowing hydrothermal activation, melt modification, and gas capture reactions to occur in a predetermined sequence during the heating process.

[0058] In summary, the test results demonstrate that the present invention achieves a strength compensation and toughening system for high-temperature resistant mortar in the medium-temperature range through the synergistic effect between raw materials and the combination of specific processes.

Claims

1. A high-temperature resistant dry-mix fireproof mortar, characterized in that, Made from raw materials comprising the following parts by weight: Refractory grade mullite sand: 25-35 parts; Anhydrous sodium hexametaphosphate powder: 3-5 parts; Nano calcium carbonate: 2-4 parts; Zinc borate 3.5 aqueous solution: 1.5-2.5 parts; Aluminate cement: 35-45 parts; Calcinated kaolin: 5-8 parts; Closed-cell expanded perlite: 10-15 parts; Redispersible latex powder: 1-2 parts.

2. The high-temperature resistant dry-mix fireproof mortar according to claim 1, characterized in that, The refractory-grade mullite sand, the anhydrous sodium hexametaphosphate powder, the nano-calcium carbonate, and the zinc borate 3,5-hydrate form an active pre-coated aggregate with surface-loaded functional materials.

3. The high-temperature resistant dry-mix fireproof mortar according to claim 1, characterized in that, The aluminate cement and the calcined kaolin form a matrix-filled mixture, and the closed-cell expanded perlite and the redispersible latex powder are flexible mixing additives.

4. A preparation process for a high-temperature resistant dry-mix fireproof mortar, characterized in that, The preparation of the high-temperature resistant dry-mix fireproof mortar according to any one of claims 1-3 includes the following steps: S1. Weigh the refractory mullite sand, the anhydrous sodium hexametaphosphate powder, the nano calcium carbonate and the zinc borate 3,5-hydrate, and put them into a high-speed plow mixer with flying knives for mechanical friction shear mixing to obtain active pre-coated aggregate with surface-loaded functional raw materials. S2. Weigh the aluminate cement and the calcined kaolin, add them to the active pre-coated aggregate obtained in S1, adjust the spindle speed of the high-speed plow mixer, and disperse and fill the mixture to obtain the matrix-filled mixture. S3. Weigh the closed-cell expanded perlite and the redispersible latex powder, add them to the matrix filling mixture obtained in S2, adjust the spindle speed of the high-speed plow mixer, and turn off the fly knife to perform flexible mixing, and obtain the finished high-temperature resistant dry-mixed fireproof mortar.

5. The preparation process of a high-temperature resistant dry-mixed fireproof mortar according to claim 4, characterized in that, In step S1, the spindle speed of the high-speed plow mixer is set to 1100-1600 rpm.

6. The preparation process of a high-temperature resistant dry-mixed fireproof mortar according to claim 5, characterized in that, In step S1, the duration of the mechanical friction shear mixing is 3-6 minutes.

7. The preparation process of a high-temperature resistant dry-mixed fireproof mortar according to claim 4, characterized in that, In step S2, the spindle speed of the high-speed plow mixer is adjusted to 300-500 rpm.

8. The preparation process of a high-temperature resistant dry-mixed fireproof mortar according to claim 7, characterized in that, In step S2, the duration of the dispersion filling and mixing is 3-4 minutes.

9. The preparation process of a high-temperature resistant dry-mixed fireproof mortar according to claim 4, characterized in that, In step S3, the spindle speed of the high-speed plow mixer is adjusted to 60-100 rpm.

10. The preparation process of a high-temperature resistant dry-mixed fireproof mortar according to claim 9, characterized in that, In step S3, the duration of the flexible mixing is 1-2 minutes.