Gypsum-based self-leveling mortar with high softening coefficient and low water absorption rate and preparation method thereof

Abstract

The invention discloses gypsum-based self-leveling mortar with a high softening coefficient and a low water absorption rate and a preparation method of the gypsum-based self-leveling mortar, and belongs to the technical field of building materials. The mortar is prepared from the following raw materials in parts by weight: 550 to 700 parts of high-quality desulfurized gypsum, 50 to 150 parts of high belite Portland cement, 50 to 150 parts of pretreated reinforced recycled aggregate, 100 to 200 parts of high-water-resistance filler, 0.3 to 0.8 part of suspension stabilizer, 2 to 5 parts of water reducing agent, 0.5 to 2 parts of defoaming agent, 1 to 3 parts of retarder, 10 to 20 parts of bonding reinforcing component and 400 to 450 parts of water. The invention also discloses a preparation method of the mortar. Through the continuous hydration and self-repairing of the high belite cement, the densification modification of the recycled aggregate, the hydrophobic treatment of the high-water-resistance filler and the synergistic effect of the hydrophobic latex powder, the water resistance of the mortar is remarkably improved, so that the mortar has the advantages of high softening coefficient, low water absorption rate and excellent construction performance and mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to gypsum-based self-leveling mortar with high softening coefficient and low water absorption rate and its preparation method. Background Technology

[0002] Desulfurized gypsum is an industrial byproduct generated during the flue gas desulfurization process in coal-fired power plants. Its annual production is enormous, and its resource utilization is of great significance for environmental protection and sustainable development. In recent years, with the rapid development of underfloor heating systems and the renovation market for old houses, gypsum-based self-leveling materials have been widely used due to their advantages such as convenient construction, good flatness, and crack resistance. However, traditional gypsum-based materials generally suffer from poor water resistance, low softening coefficient, and high water absorption, which severely restricts their application in humid environments or in situations requiring high water resistance.

[0003] Currently, the industry typically improves the water resistance of gypsum materials by adding cement, organic adhesive powder, and water-repellent agents, but it remains difficult to achieve a good balance between cost control, environmental friendliness, and performance improvement. Therefore, developing a gypsum-based self-leveling mortar that combines high water resistance, good mechanical properties, low cost, and environmental friendliness has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] The primary objective of this invention is to provide a gypsum-based self-leveling mortar with a high softening coefficient and low water absorption rate to solve the problem of insufficient water resistance of existing gypsum-based materials.

[0005] Another objective of this invention is to provide a method for preparing the above-mentioned gypsum-based self-leveling mortar, which is simple in process, cost-controllable, and suitable for industrial production.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Firstly, a gypsum-based self-leveling mortar with a high softening coefficient and low water absorption rate is provided, comprising the following raw materials in parts by weight: 550-700 parts of high-quality desulfurized gypsum; 50-150 parts of high-belite silicate cement; 50-150 parts of pretreated reinforced recycled aggregate; 100-200 parts of high water-resistant filler; Suspension stabilizer 0.3–0.8 parts; 2-5 parts water-reducing agent; Defoamer 0.5-2 parts; 1-3 parts of retarder; 10-20 parts of adhesive reinforcing component; 400-450 parts water.

[0007] Furthermore, the high-quality desulfurized gypsum has a hemihydrate content >92% and an average particle size D. 50 It is 20–25 μm.

[0008] Furthermore, the high-belite silicate cement has a C2S content ≥40%, a C3A content ≤6%, and a specific surface area of ​​300–350 m². 2 / kg.

[0009] Furthermore, the pretreated reinforced recycled aggregate is prepared through the following steps: Waste concrete is crushed, screened, washed, and dried to obtain recycled aggregate; The recycled aggregate was placed in a 0.03 mol / L N,N-dimethylethanolamine solution, and 2 mol / L carbon dioxide gas was introduced at a flow rate of 16 L / h. The reaction was carried out at 25 °C for 5–7 h, and the aggregate was obtained by vacuum drying. The aggregate is soaked in a 1-3% (w / w) solution of diethylenetriaminepentimidephosphonic acid for 1-2 hours, then removed and dried to obtain the pretreated reinforced recycled aggregate.

[0010] Furthermore, the highly water-resistant filler is prepared through the following steps: Weigh 1.0 kg of municipal solid waste incineration residue and 3.0~5.0 kg of spodumene tailings powder, mix and dry to obtain mixed dry powder; add 35~50 g of vinyltris(β-methoxyethoxy)silane, 2000 ml of isopropanol and 500 ml of distilled water to the mixed dry powder, stir for more than 6 hours at a speed of ≥300 r / min, and then dry at 80℃ to constant weight to obtain the high water-resistant filler.

[0011] Furthermore, the suspension stabilizer is hydroxypropyl methylcellulose with a viscosity of 400 mPa·s.

[0012] Furthermore, the water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate >30%, the defoamer is an alkali-resistant silicone defoamer, and the retarder is an alkali-resistant protein retarder.

[0013] Furthermore, the adhesive reinforcing component is a hydrophobic redispersible latex powder.

[0014] Furthermore, the hydrophobic redispersible latex powder is a copolymer of vinyl acetate and ethylene.

[0015] Secondly, a method for preparing the above-mentioned gypsum-based self-leveling mortar is provided, comprising the following steps: S1. Weigh each raw material according to the proportions; S2. Mix all raw materials except water evenly to obtain dry powder; S3. Add water to the dry powder and stir evenly to obtain the gypsum-based self-leveling mortar.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses industrial solid waste such as desulfurized gypsum, recycled aggregate, and municipal solid waste incineration residue as the main raw materials, which greatly reduces the consumption of natural resources and production costs.

[0017] 2. This invention fundamentally improves the water resistance of gypsum matrix through the synergistic effect of high-belite cement, pretreated recycled aggregate, highly water-resistant filler, and water-repellent latex powder. Specifically, the high C2S mineral content in high-belite cement undergoes continuous hydration in the later stages, constantly generating hydration products that densify the matrix and can repair damage to a certain extent when exposed to water; after amine-catalyzed carbon dioxide strengthening treatment and organophosphoric acid soaking, the active substances such as calcium hydroxide attached to the inside and surface of the recycled aggregate react with carbon dioxide to generate hydration products such as calcium carbonate and calcium silicate. These products effectively seal the surface and internal pores of the aggregate, thereby densifying the aggregate structure, significantly reducing its own water absorption rate, and fundamentally improving its water resistance; after the municipal solid waste incineration slag and spodumene tailings powder are modified with silane coupling agent (vinyltris(β-methoxyethoxy)silane), the surface changes from hydrophilic to hydrophobic, effectively blocking water penetration; after the hydrophobic redispersible latex powder forms a film, it forms a hydrophobic polymer network inside the mortar, further hindering the migration of water molecules.

[0018] 3. Under the above-mentioned synergistic modification, the product of the present invention achieves a high softening coefficient and low water absorption rate while maintaining excellent flowability, mechanical strength and dimensional stability. Its comprehensive performance meets and exceeds the relevant standard requirements. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] In this embodiment of the invention, the high-quality desulfurized gypsum has a hemihydrate content >92% and an average particle size D. 50 It is 20–25 μm.

[0021] In this embodiment of the invention, the high-belite silicate cement has a C2S content ≥40%, a C3A content ≤6%, and a specific surface area of ​​300–350 m². 2 / kg.

[0022] In this embodiment of the invention, the preparation process of pretreated reinforced recycled aggregate is as follows: Waste concrete is initially crushed to a particle size of <100mm, then further crushed to below 20mm using a cone crusher. After vibrating screening, aggregate with a particle size range of 0.15~0.425mm is obtained. To remove some surface impurities, the screened aggregate is washed using a stone washing machine and dried at 60℃ for later use. The dried recycled aggregate was placed in a stainless steel container, and a 0.03 mol / L N,N-dimethylethanolamine solution was injected into the container to ensure that the recycled aggregate was completely submerged in the N,N-dimethylethanolamine solution. At the same time, 2 mol / L carbon dioxide gas was injected into the device at a flow rate of 16 L / h. The reaction temperature was controlled at about 25°C, and the reaction time was 5-7 h. After the reaction was completed, the aggregate was dried under vacuum to constant weight to obtain recycled aggregate. Recycled aggregates were soaked in a 1-3% (w / w) solution of diethylenetriaminepentimidephosphonic acid for 1-2 hours, ensuring that the solution completely submerged the aggregates. After soaking, the aggregates were removed and dried to obtain pretreated reinforced recycled aggregates.

[0023] In this embodiment of the invention, the preparation process of the highly water-resistant filler is as follows: Weigh 1 kg of municipal solid waste incineration residue and 3.0~5.0 kg of spodumene tailings powder, mix them and dry them. Then add 35~50 g of vinyltris(β-methoxyethoxy)silane, 2000 ml of isopropanol and 500 ml of distilled water, and stir with a stirrer for more than 6 hours, maintaining a speed of ≥300 r / min. Then dry at 80℃ to constant weight to obtain a high water-resistant filler.

[0024] In this embodiment of the invention, the suspension stabilizer is low-viscosity hydroxypropyl methylcellulose with a viscosity of 400 mPa·s.

[0025] In this embodiment of the invention, the water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate > 30%.

[0026] In this embodiment of the invention, the defoamer is an alkali-resistant silicone defoamer, which can effectively defoam in a highly alkaline environment and is compatible with a variety of surfactants.

[0027] In this embodiment of the invention, the retarder is an alkali-resistant protein retarder, specifically a gypsum retarder.

[0028] In this embodiment of the invention, the adhesive reinforcing component is a hydrophobic redispersible latex powder, specifically a copolymer of vinyl acetate and ethylene, which has extremely low water absorption and good air permeability.

[0029] In this embodiment of the invention, the preparation method of gypsum-based self-leveling mortar includes the following steps: S1. Weigh each raw material according to the proportions; S2. Mix all raw materials except water evenly to obtain dry powder; S3. Add water to the dry powder and stir evenly to obtain the gypsum-based self-leveling mortar.

[0030] Example 1, as a preferred embodiment of the present invention, is a gypsum-based self-leveling mortar with a high softening coefficient and low water absorption rate. The raw material composition is shown in Table 1 below.

[0031] Table 1. Raw material composition of gypsum-based self-leveling mortar in Example 1

[0032] Example 2, as a preferred embodiment of the present invention, is a gypsum-based self-leveling mortar with a high softening coefficient and low water absorption rate. The raw material composition is shown in Table 2 below.

[0033] Table 2 Raw material composition of gypsum-based self-leveling mortar in Example 2

[0034] Example 3, as a preferred embodiment of the present invention, is a gypsum-based self-leveling mortar with a high softening coefficient and low water absorption rate. The raw material composition is shown in Table 3 below.

[0035] Table 3 Raw material composition of gypsum-based self-leveling mortar in Example 3

[0036] Example 4, as a preferred embodiment of the present invention, is a gypsum-based self-leveling mortar with a high softening coefficient and low water absorption rate. The raw material composition is shown in Table 4 below.

[0037] Table 4. Raw material composition of gypsum-based self-leveling mortar in Example 4

[0038] Comparative Example 1: Compared with Example 2, the mortar in this comparative example only replaced the high belite silicate cement with ordinary 425 silicate cement, while the other conditions remained unchanged.

[0039] Comparative Example 2, compared with Example 2, only the pretreated reinforced recycled aggregate was replaced with quartz sand with a similar particle size distribution, while the other conditions remained unchanged.

[0040] Comparative Example 3, compared with Example 2, only the high water-resistant filler was replaced with limestone powder with a similar particle size distribution, while the other conditions remained unchanged.

[0041] Comparative Example 4, compared with Example 2, replaced the pretreated reinforced recycled aggregate and the high water-resistant filler with quartz sand and limestone powder with similar particle size distribution, respectively, while keeping the other conditions unchanged.

[0042] Test case Performance tests were conducted on the gypsum-based self-leveling mortars of Examples 1-4 and Comparative Examples 1-4. Conventional performance tests were strictly performed in accordance with standard JC / T 1023-2021 "Gypsum-based Self-leveling Mortar". The softening coefficient K = f / F, where f is the compressive strength of the specimen in the saturated state and F is the compressive strength of the specimen in the oven-dry state. For the water absorption test, the specimen was dried to constant weight and the mass was recorded as M0. Then, it was immersed in water for 6 hours, the surface water was wiped off with a damp towel, and the weight was recorded as M1. The water absorption rate P = (M1-M0) / M0×100%. Specimens cured for 28 days were used for both the softening coefficient and water absorption tests. The relevant results are shown in Table 5.

[0043] Table 5 Performance Test Results

[0044] As can be seen from the performance test results in Table 5, the physical and mechanical properties and water resistance of each embodiment (1-4) of the present invention all meet the requirements of the building materials industry standard JC / T 1023-2021. The requirements of "Gypsum-based Self-leveling Mortar" were met. Comparative analysis revealed that the sample using high-belite silicate cement, pretreated reinforced recycled aggregate, and high-water-resistant filler, while maintaining good workability (flowability > 140 mm) and mechanical properties (28-day compressive strength ≥ 26.0 MPa), exhibited significantly better water resistance than the comparative example. Specifically, the water absorption rate of the sample (8.2%~9.3%) was significantly lower than that of the comparative example (generally > 9.7%, with comparative example 4 reaching 12.9%), and the softening coefficient of the sample (0.77~0.88) was significantly higher than that of the comparative example (all < 0.71, with comparative example 4 only 0.59). This confirms that the present invention systematically improves the water resistance of gypsum-based self-leveling mortar through the continuous hydration and self-healing of high-belite cement, the densification modification of recycled aggregate, the hydrophobic treatment of high-water-resistant filler, and the synergistic water-blocking effect of hydrophobic latex powder, while also ensuring excellent workability and mechanical properties.

[0045] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A gypsum-based self-leveling mortar with a high softening coefficient and low water absorption rate, characterized in that... Including the following parts by weight of raw materials: 550-700 parts of high-quality desulfurized gypsum; 50-150 parts of high-belite silicate cement; 50-150 parts of pretreated reinforced recycled aggregate; 100-200 parts of high water-resistant filler; Suspension stabilizer 0.3–0.8 parts; 2-5 parts of water-reducing agent; Defoamer 0.5-2 parts; 1-3 parts of retarder; 10-20 parts of adhesive reinforcing component; 400-450 parts water.

2. The gypsum-based self-leveling mortar according to claim 1, characterized in that, The high-quality desulfurized gypsum has a hemihydrate content >92% and an average particle size D. 50 It is 20–25 μm.

3. The gypsum-based self-leveling mortar according to claim 1, characterized in that, The high-belite silicate cement has a C2S content ≥40%, a C3A content ≤6%, and a specific surface area of ​​300–350 m². 2 / kg.

4. The gypsum-based self-leveling mortar according to claim 1, characterized in that, The pretreated and reinforced recycled aggregate is prepared through the following steps: Waste concrete is crushed, screened, washed, and dried to obtain recycled aggregate; The recycled aggregate was placed in a 0.03 mol / L N,N-dimethylethanolamine solution, and 2 mol / L carbon dioxide gas was introduced at a flow rate of 16 L / h. The reaction was carried out at 25 °C for 5–7 h, and the aggregate was obtained by vacuum drying. The aggregate is soaked in a 1-3% (w / w) solution of diethylenetriaminepentimidephosphonic acid for 1-2 hours, then removed and dried to obtain the pretreated reinforced recycled aggregate.

5. The gypsum-based self-leveling mortar according to claim 1, characterized in that, The highly water-resistant filler is prepared through the following steps: Weigh 1.0 kg of municipal solid waste incineration residue and 3.0~5.0 kg of spodumene tailings powder, mix and dry to obtain mixed dry powder; add 35~50 g of vinyltris(β-methoxyethoxy)silane, 2000 ml of isopropanol and 500 ml of distilled water to the mixed dry powder, stir for more than 6 hours at a speed of ≥300 r / min, and then dry at 80℃ to constant weight to obtain the high water-resistant filler.

6. The gypsum-based self-leveling mortar according to claim 1, characterized in that, The suspension stabilizer is hydroxypropyl methylcellulose with a viscosity of 400 mPa·s.

7. The gypsum-based self-leveling mortar according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate >30%, the defoamer is an alkali-resistant silicone defoamer, and the retarder is an alkali-resistant protein retarder.

8. The gypsum-based self-leveling mortar according to claim 1, characterized in that, The adhesive reinforcing component is a hydrophobic redispersible latex powder.

9. The gypsum-based self-leveling mortar according to claim 8, characterized in that, The hydrophobic redispersible latex powder is a copolymer of vinyl acetate and ethylene.

10. A method for preparing gypsum-based self-leveling mortar as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Weigh each raw material according to the proportions; S2. Mix all raw materials except water evenly to obtain dry powder; S3. Add water to the dry powder and stir evenly to obtain the gypsum-based self-leveling mortar.

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