Solid waste-based cementing material with high solid waste mixing amount and low alkali excitation as well as preparation method and application of solid waste-based cementing material

Abstract

The invention discloses a preparation method and application of a solid waste-based cementing material with high solid waste mixing amount and low alkali excitation, and belongs to the field of building materials and resource utilization. The cementing material comprises the following components in parts by mass: 30-55 parts of construction waste regenerated micro powder, 20-40 parts of fly ash, 10-25 parts of steel slag micro powder, 5-15 parts of desulfurized gypsum, 5-12 parts of a composite alkali activator and 0-3 parts of an optional additive, wherein the composite alkali activator consists of 50-80% of sodium carbonate, 10-30% of sodium sulfate and 5-20% of sodium metaaluminate; the preparation method comprises the steps of solid waste pretreatment, matrix mixing, exciting agent preparation, dry mixing and the like. The industrial solid waste is used as the main raw material, the solid waste mixing amount is high, low alkali and safety are achieved, the early strength development speed is high, the 28-day compressive strength is about 50 MPa, the 42.5-grade cement standard is met, the process is simple, the method is suitable for an existing production line, and the method can be used for preparing building mortar and concrete.

Description

Technical Field

[0001] This invention relates to the field of building materials and resource utilization technology, and in particular to a method for preparing a solid waste-based cementitious material using a variety of industrial solid wastes as the main raw materials and employing a low-alkali composite activation system, and its application in mortar and concrete. Background Technology

[0002] Traditional cementitious materials, represented by ordinary silicate cement, consume large amounts of natural resources such as limestone and clay during their production and emit massive amounts of carbon dioxide (CO2), making them a major source of carbon emissions in the building materials industry. Meanwhile, industries such as steel, power, and demolition generate large quantities of solid waste, such as steel slag, fly ash, recycled construction waste powder, and desulfurized gypsum. The accumulation of these solid wastes not only occupies land but also poses environmental risks such as heavy metal leaching and dust pollution. Therefore, utilizing solid waste to prepare new cementitious materials is a key path to achieving a green and low-carbon transformation in the building materials industry.

[0003] Currently, most common solid waste-based cementitious materials utilize alkali-activated geopolymer technology. However, this technology faces several bottlenecks in practical application: First, to achieve sufficient early strength, a high proportion of cement clinker or highly active slag powder is often required, limiting the actual utilization rate of solid waste and diminishing its carbon reduction effect. Second, activators commonly employ strong alkaline substances such as sodium hydroxide (NaOH) and liquid sodium silicate (water glass), whose high corrosiveness poses a threat to the safety of production and construction, and may also create a potential alkali-aggregate reaction risk to the reinforcing steel in concrete. Furthermore, high solid waste content systems generally suffer from slow early hydration reactions and delayed strength development, easily leading to early shrinkage and cracking of the products, affecting project quality and construction progress.

[0004] Therefore, developing a solid waste-based cementitious material with high solid waste content, low activator alkalinity and good safety, rapid early strength development, and good compatibility with existing production processes has become a technical challenge to be solved in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a solid waste-based cementitious material with high solid waste content and low alkali activation, as well as its preparation method and application, which can realize the efficient resource utilization of solid waste without the use of cement clinker, and at the same time has excellent mechanical properties, construction safety and process adaptability.

[0006] The technical solution adopted by this invention to solve its technical problem is: a solid waste-based cementitious material with high solid waste content and low alkali activation, comprising, by mass parts: 30-55 parts of recycled construction waste powder, 20-40 parts of fly ash, 10-25 parts of steel slag powder, 5-15 parts of desulfurized gypsum, 5-12 parts of composite alkali activator, and 0-3 parts of optional admixture; the composite alkali activator is composed of the following components by mass percentage: 50-80% sodium carbonate, 10-30% sodium sulfate, and 5-20% sodium aluminate; the admixture includes one or more of water-reducing agents, defoamers, air-entraining agents, or shrinkage compensators.

[0007] Furthermore, the specific surface area of ​​the recycled construction waste powder described in this invention is 300-450 m² / kg. It is prepared by crushing, removing impurities, drying, and grinding construction waste. Its main component is silicate minerals, which have potential gelling activity.

[0008] Furthermore, the fly ash described in this invention is Grade II or Grade I fly ash, with a 45μm sieve residue of ≤20%, and is rich in active SiO2 and Al2O3, which can react with activators to generate hydration products with gelling properties.

[0009] Furthermore, the steel slag powder of the present invention has a specific surface area of ​​400-500 m² / kg and a free CaO mass fraction of ≤2.5%, which can effectively reduce the volume stability problem caused by the hydration expansion of free CaO. At the same time, the CaO, SiO2 and other components contained therein can participate in the hydration reaction to improve the strength.

[0010] Furthermore, the desulfurized gypsum of the present invention contains ≥80% CaSO4•2H2O by mass, which, as a sulfate component, can promote the formation of ettringite (AFt), optimize the structure of hydration products, and improve the early strength and volume stability of the material.

[0011] Meanwhile, the present invention also provides a method for preparing a solid waste-based cementitious material, comprising the following steps:

[0012] (1) Solid waste pretreatment: Construction waste is crushed, cleaned, dried and then ground to a specific surface area of ​​300-450 m² / kg to obtain construction waste recycled powder; steel slag is magnetically separated to remove iron, dried and then ground to a specific surface area of ​​400-500 m² / kg to obtain steel slag powder; desulfurized gypsum is dried and then ground to a particle size of ≤80 μm for later use;

[0013] (2) Preparation of cementitious matrix: Mix construction waste recycled powder, fly ash, steel slag powder and desulfurized gypsum in proportion, stir for 3-5 minutes to obtain cementitious matrix;

[0014] (3) Preparation of composite alkali activator: Sodium carbonate, sodium sulfate and sodium aluminate are mixed in proportion to obtain composite alkali activator;

[0015] (4) Preparation of finished product: Mix the gel matrix and the composite alkali activator at a mass ratio of 100:(5-12) and stir for 2-4 minutes. If an admixture is added, continue stirring for 1-2 minutes after adding it to obtain solid waste-based gel material.

[0016] The present invention also provides the application of the above-mentioned solid waste-based cementitious material in the preparation of building mortar, wherein the water-cement ratio of the mortar is 0.25 to 0.35, the sand-cement ratio is 1.5 to 2.5, and the sand is building sand conforming to GB / T 14684.

[0017] The present invention also provides the application of the above-mentioned solid waste-based cementitious material in the preparation of concrete, wherein the solid waste-based cementitious material completely or partially replaces ordinary Portland cement, with a replacement rate of 30-100 wt%, and the mix proportion of the concrete can be conventionally adjusted according to the design strength grade.

[0018] The beneficial effect of this invention is that it solves the defects existing in the prior art.

[0019] 1. High solid waste content and significant environmental benefits: The cementitious matrix of this invention is composed entirely of four types of industrial solid waste: recycled construction waste powder, fly ash, steel slag powder, and desulfurized gypsum. It does not contain cement clinker, and the total solid waste content is ≥90wt% (excluding admixtures and water). This significantly improves the resource utilization rate of industrial solid waste, significantly reduces the consumption of natural mineral resources and carbon dioxide emissions. For every ton of cementitious material produced by this invention, approximately 0.8 tons of carbon dioxide emissions can be reduced. At the same time, it solves the environmental problems caused by solid waste stockpiling.

[0020] 2. Low-alkali activation, excellent safety and durability: The solid composite alkali activation system composed of sodium carbonate, sodium sulfate and sodium aluminate is adopted, which abandons the traditional strong alkali solution. The pH value of the slurry is controlled between 10 and 12, which is relatively mild. It does not cause strong irritation to construction personnel during operation and will not corrode steel bars, effectively improving the durability and safety of building structures.

[0021] 3. Excellent mechanical properties and rapid early strength development: Through the synergistic effect of each component in the composite alkali activator, sodium carbonate provides a weakly alkaline environment to initiate the hydration reaction of active components in solid waste, sodium sulfate accelerates the formation of ettringite (AFt) to improve early strength, and sodium aluminate optimizes the structure of hydration products (C-(A)-SH gel coexists with AFt / AFm), so that the material has a 3d compressive strength ≥25MPa, a 7d compressive strength ≥37MPa, and a 28d compressive strength of 49-51MPa, which fully meets or even exceeds the mechanical performance requirements of 42.5 grade ordinary Portland cement, while effectively reducing the risk of drying shrinkage cracking;

[0022] 4. Simple process and strong adaptability: All raw materials are in dry powder state, and the preparation process does not require a complicated solution preparation and storage system. It can be produced directly on existing cement or dry mortar production lines. The mixing and blending processes are compatible with existing production lines and do not require additional equipment modification, which reduces the cost and difficulty of industrialization.

[0023] 5. Wide range of applications and strong practicality: It can be widely used in the preparation of building mortar (such as masonry mortar and plastering mortar) and concrete engineering (such as cast-in-place concrete and precast concrete components). When replacing 30-100wt% of ordinary Portland cement, it can still ensure the mechanical properties and durability of mortar and concrete, and meet the needs of different engineering scenarios. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the embodiments.

[0025] Example 1

[0026] 1. Cementitious matrix composition (parts by weight): 40 parts recycled construction waste powder, 30 parts fly ash, 20 parts steel slag powder, and 10 parts desulfurized gypsum; wherein, the recycled construction waste powder has a specific surface area of ​​380 m² / kg, the fly ash is Grade I fly ash with 12% residue on a 45μm sieve, the steel slag powder has a specific surface area of ​​450 m² / kg and a free CaO mass fraction of 1.8%, and the desulfurized gypsum contains 85% CaSO₄•2H₂O mass fraction.

[0027] 2. Compound alkali activator formulation (mass percentage): Sodium carbonate 70%, sodium sulfate 15%, sodium aluminate 15%;

[0028] 3. Preparation of cementitious materials: Mix 100 parts of cementitious matrix, 8 parts of composite alkali activator and 0.5 parts of high-efficiency water-reducing agent, stir for 3 minutes to obtain solid waste-based cementitious materials;

[0029] 4. Preparation of building mortar: 450 kg / m³ of cementitious material, 900 kg / m³ of ISO standard sand (sand-cement ratio 2.0), and 135 kg / m³ of water (water-cement ratio 0.30) are mixed evenly to obtain building mortar;

[0030] 5. Mechanical property testing: Tests were conducted according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar", and the results are shown in the table below:

[0031] Age Flexural strength / MPa Compressive strength / MPa 3d 5.7 26.6 7d 7.2 39.5 28d 8.8 51.2

[0032] The above results show that the 28-day compressive strength of the solid waste-based cementitious material in this embodiment can reach about 50 MPa, which meets or even exceeds the performance requirements of grade 42.5 ordinary Portland cement.

[0033] Example 2

[0034] 1. Cementitious matrix composition (parts by weight): 50 parts recycled construction waste powder, 25 parts fly ash, 15 parts steel slag powder, and 10 parts desulfurized gypsum; wherein, the recycled construction waste powder has a specific surface area of ​​350 m² / kg, the fly ash is Class II fly ash with 18% residue on a 45μm sieve, the steel slag powder has a specific surface area of ​​420 m² / kg and a free CaO mass fraction of 2.2%, and the desulfurized gypsum contains 82% CaSO₄•2H₂O mass fraction.

[0035] 2. Compound alkali activator formulation (mass percentage): Sodium carbonate 60%, sodium sulfate 25%, sodium aluminate 15%;

[0036] 3. Preparation of cementitious materials: Mix 100 parts of cementitious matrix and 10 parts of composite alkali activator, stir for 4 minutes to obtain solid waste-based cementitious materials;

[0037] 4. Preparation of building mortar: 450 kg / m³ of cementitious material, 900 kg / m³ of ISO standard sand (sand-cement ratio 2.0), and 144 kg / m³ of water (water-cement ratio 0.32) are mixed evenly to obtain building mortar;

[0038] 5. Mechanical property testing: Tests were conducted according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar", and the results are shown in the table below:

[0039] Age Flexural strength / MPa Compressive strength / MPa 3d 5.2 25.3 7d 6.7 37.7 28d 8.5 49.0

[0040] This embodiment maintains a high strength level while increasing the amount of recycled construction waste powder, further verifying the feasibility of the high solid waste content of the present invention.

[0041] Comparative example (ordinary silicate cement mortar)

[0042] 1. Cementitious material: P.O42.5 ordinary Portland cement;

[0043] 2. Standard mortar mix proportion: cement 450kg / m³, ISO standard sand 900kg / m³ (sand-binder ratio 2.0), water 225kg / m³ (water-binder ratio 0.50);

[0044] 3. Mechanical property testing: Tests were conducted according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar", and the results are shown in the table below:

[0045] Age Flexural strength / MPa Compressive strength / MPa 3d 4.8 22.5 7d 6.3 33.3 28d 8.2 46.7

[0046] As can be seen from the test results of Examples 1 and 2 and the comparative examples above, the mortar prepared by the solid waste-based cementitious material of the present invention has flexural strength and compressive strength at 3d, 7d and 28d ages that are superior to or equivalent to P.O42.5 ordinary Portland cement mortar. Among them, the 28-day compressive strength can reach 49-51MPa, exceeding the performance requirements of 42.5 grade ordinary Portland cement. At the same time, the solid waste content of the present invention is ≥90wt%, which is significantly better than existing solid waste-based cementitious materials. Moreover, the low-alkali composite activation system is adopted, which is safer and simpler in process, and has significant technical advantages and promotion value.

[0047] The above description is only a specific embodiment of the present invention. Various examples and illustrations do not constitute a limitation on the substantive content of the present invention. Those skilled in the art can make modifications or variations to the above-described specific embodiments after reading the specification without departing from the substance and scope of the invention.

Claims

1. A solid waste-based cementitious material with high solid waste content and low alkali activation, characterized in that: By weight, it includes: 30-55 parts of recycled construction waste powder, 20-40 parts of fly ash, 10-25 parts of steel slag powder, 5-15 parts of desulfurized gypsum, 5-12 parts of composite alkali activator, and 0-3 parts of optional admixtures; the composite alkali activator is composed of the following components by weight percentage: 50-80% sodium carbonate, 10-30% sodium sulfate, and 5-20% sodium aluminate; the admixtures include one or more of water-reducing agents, defoamers, air-entraining agents, or shrinkage compensators.

2. The solid waste-based cementitious material with high solid waste content and low alkali activation as described in claim 1, characterized in that: The specific surface area of ​​the recycled construction waste powder is 300-450 m² / kg.

3. The solid waste-based cementitious material with high solid waste content and low alkali activation as described in claim 1, characterized in that: The fly ash is Grade II or Grade I fly ash, with a 45μm sieve residue of ≤20%.

4. The solid waste-based cementitious material with high solid waste content and low alkali activation as described in claim 1, characterized in that: The steel slag powder has a specific surface area of ​​400-500 m² / kg and a free CaO mass fraction of ≤2.5%.

5. The solid waste-based cementitious material with high solid waste content and low alkali activation as described in claim 1, characterized in that: The desulfurized gypsum contains ≥80% CaSO4•2H2O by mass.

6. A method for preparing a solid waste-based cementitious material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Solid waste pretreatment: Construction waste is crushed, cleaned, dried and then ground to a specific surface area of ​​300-450 m² / kg to obtain construction waste recycled powder; steel slag is magnetically separated to remove iron, dried and then ground to a specific surface area of ​​400-500 m² / kg to obtain steel slag powder; desulfurized gypsum is dried and then ground to a particle size of ≤80 μm for later use; (2) Preparation of cementitious matrix: Mix construction waste recycled powder, fly ash, steel slag powder and desulfurized gypsum in proportion, stir for 3-5 minutes to obtain cementitious matrix; (3) Preparation of composite alkali activator: Sodium carbonate, sodium sulfate and sodium aluminate are mixed in proportion to obtain composite alkali activator; (4) Preparation of finished product: Mix the gel matrix and the composite alkali activator at a mass ratio of 100:(5-12) and stir for 2-4 minutes. If an admixture is added, continue stirring for 1-2 minutes after adding it to obtain solid waste-based gel material.

7. The application of the solid waste-based cementitious material as described in any one of claims 1 to 5 in the preparation of building mortar, characterized in that, The water-cement ratio of the mortar is 0.25 to 0.35, and the sand-cement ratio is 1.5 to 2.

5.

8. The application of the solid waste-based cementitious material as described in any one of claims 1 to 5 in the preparation of concrete, characterized in that, The solid waste-based cementitious material can completely or partially replace ordinary Portland cement, with a replacement rate of 30-100 wt%.