Multi-element industrial solid waste low-carbon cementing material and preparation method thereof

Abstract

The invention discloses a multi-element industrial solid waste low-carbon cementing material and a preparation method thereof, and belongs to the technical field of building materials. The cementing material comprises the following components in parts by weight: 10-25 parts of phosphorus slag, 30-50 parts of mineral slag, 8-20 parts of gypsum, 15-30 parts of steel slag, 5-15 parts of fly ash, 2-6 parts of a composite activator and 0.5-3 parts of an early strength agent. The composite activator is a solid alkali activator compounded by sodium hydroxide and sodium silicate nonahydrate according to a mass ratio of 1: 3; the early strength agent is a solid early strength agent compounded by calcium chloride and sodium aluminate in a mass ratio of 1: 5. The low-temperature preparation of all solid wastes is realized through chemical component synergy and physical grading optimization of multi-element solid wastes and in combination with a composite excitation system. The 28-day compressive strength of the obtained material is stabilized at 40 MPa or above, the performance of the material is comparable with that of P.O 42.5 cement, and the material has the characteristics of low carbon, environmental protection, low cost and excellent performance, and can be used in the engineering fields of concrete preparation, soil solidification and the like.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a low-carbon cementitious material derived from multi-element industrial solid waste and its preparation method. Background Technology

[0002] The production process of traditional silicate cement is energy-intensive and generates large amounts of carbon emissions. Meanwhile, my country produces massive amounts of industrial solid waste annually, including phosphorus slag, steel slag, fly ash, and phosphogypsum. The accumulation of these wastes not only occupies land but also poses potential environmental pollution. How to efficiently and effectively utilize these solid wastes to prepare cementitious materials with performance comparable to cement is crucial for the building materials industry to achieve a green and low-carbon transformation.

[0003] In existing technologies, some studies have attempted to prepare cementitious materials using single or several types of solid waste. For example, some studies have used industrial solid wastes such as slag, fly ash, steel slag, and desulfurized gypsum, grinding them and then compounding them with a small amount of cement to produce low-carbon, low-clinker cement. However, such materials often suffer from problems such as low early strength, difficulty in controlling setting time, and large performance fluctuations, making it difficult to consistently meet the performance requirements of general-purpose Portland cement. Although the addition of activators can improve performance, different activators have significantly different effects on setting time and strength at different ages, making it difficult for a single activator system to synergistically optimize early and long-term performance. Other patents disclose composite alkali-activated cementitious materials containing components such as steel slag, slag, fly ash, and phosphogypsum, or enhance performance by introducing sulfoaluminate cement and nano-silica. These solutions improve material performance to some extent, but have the following shortcomings: the raw material system is complex, possibly containing cement clinker or requiring high-temperature activation pretreatment, failing to achieve true all-solid-waste and low-temperature preparation; and there is insufficient systematic consideration of the synergistic effects of chemical components and particle size distribution optimization among multiple solid wastes, affecting the stability and optimization of material performance. The current activation system is relatively simple, making it difficult to simultaneously achieve excellent early strength performance and long-term strength development and durability. Therefore, developing a low-carbon cementitious material made entirely from solid waste, with a simple preparation process, stable performance, and comparable to traditional cement has significant environmental and economic value. Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing technologies and provide a low-carbon cementitious material prepared by synergistic processing of multiple industrial solid wastes, along with its preparation method. This material exhibits high solid waste content, excellent performance, and low energy consumption during preparation, and can be widely applied in engineering fields such as construction, transportation, and water conservancy.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a low-carbon cementitious material for multi-component industrial solid waste, comprising the following components by weight: 10-25 parts of phosphorus slag, 30-50 parts of blast furnace slag, 8-20 parts of gypsum, 15-30 parts of steel slag, 5-15 parts of fly ash, 2-6 parts of composite activator, and 0.5-3 parts of early strength agent.

[0007] Furthermore, the gypsum is one or a mixture of two of phosphogypsum and desulfurized gypsum, and its chemical composition contains ≥90% CaSO4·2H2O.

[0008] Furthermore, the slag is granulated blast furnace slag powder with a specific surface area controlled at 400-500 m². 2 / kg; the steel slag is converter steel slag powder with a specific surface area greater than 450m². 2 / kg; the fly ash is Grade I or Grade II fly ash with a specific surface area greater than 350m². 2 / kg.

[0009] Furthermore, the composite activator is a solid alkali activator, composed of sodium hydroxide (NaOH) and sodium silicate nonahydrate (Na2SiO4·9H2O) in a mass ratio of 1:3. Furthermore, the early strength agent is a composite of two of the following: calcium chloride (CaCl2) and sodium aluminate (NaAlO2), in a mass ratio of 1:5.

[0010] A method for preparing a low-carbon cementitious material from multi-element industrial solid waste includes the following steps:

[0011] S1 Raw Material Pretreatment and Grinding: Phosphorus slag, slag, steel slag, and fly ash are dried separately until the moisture content is below 0.5%. Then, according to the grindability of each material, a separate grinding process is adopted: materials with higher hardness, such as steel slag and phosphorus slag, are first ground to a specific surface area ≥ 580 m². 2 / kg; then grind the slag, fly ash, etc. to the specified fineness, with a slag specific surface area of ​​500-560m². 2 / kg, fly ash specific surface area 350-400m² 2 / kg, gypsum dried to a moisture content of less than 0.5%;

[0012] S2 Optimized Grading and Mixing: Based on Fuller's closest packing curve theory, particle gradation design is carried out for powders of different fineness after grinding. The ground phosphorus slag powder, slag powder, steel slag powder, fly ash powder and gypsum powder are put into a high-efficiency mixer according to the design ratio and premixed for 60-300 seconds to form homogeneous solid waste-based dry powder.

[0013] S3 Activator Compounding and Final Mixing: Weigh the compound activator and early strength agent according to the ratio, add them to the solid waste-based dry powder obtained in step S2, and continue mixing for 80-100 seconds until the whole mixture is uniform, thus obtaining the finished low-carbon cementitious material.

[0014] Technical principles and beneficial effects of the present invention:

[0015] Synergistic and Chemical Matching of Multi-Source Solid Waste: This invention selects five bulk industrial solid wastes whose chemical components have inherent complementarity. Slag and fly ash provide abundant aluminosilicate active components; steel slag provides an alkaline environment (such as CaO, MgO, etc.) and iron phase components, whose alkalinity can activate the activity of slag and fly ash; phosphogypsum provides the necessary sulfates (SO4). 2- The phosphorus slag reacts with active Al2O3 and CaO to form ettringite (AFt), which is one of the main sources of early strength. The addition of phosphorus slag can adjust the silica-calcium ratio of the system and promote the formation of more hydrated calcium silicate (CSH) gel. This design achieves the goal of "treating waste with waste and synergistic efficiency".

[0016] Composite activation system: A composite activation system consisting of a solid alkali activator, sulfate activator, and early-strength agent is employed. The solid alkali activator (NaOH + Na₂SiO₃) rapidly provides OH⁻. - And soluble silicate ions, strongly stimulating the activity of all silica-alumina-rich components. Gypsum provides SO4. 2- The reaction with aluminum and calcium ions in the system generates expandable ettringite, which contributes to early strength development and microstructure density. The addition of a specific early-strength agent accelerates the nucleation and growth of hydration products, significantly improving early (3-day) strength and solving the problem of slow early strength development commonly found in alkali-activated materials. Low-carbon, environmentally friendly, and economically beneficial: Over 90% of the raw materials used in this invention are industrial solid waste, with no or only minimal use of cement clinker, significantly reducing carbon emissions and energy consumption at the source. Simultaneously, this invention provides a high-value-added, large-scale utilization channel for large-scale stockpiled industrial solid waste, aligning with the national green development strategy and yielding significant economic, social, and environmental benefits.

[0017] Through the aforementioned component design and process innovation, the cementitious material prepared by this invention exhibits superior performance. Tests show that its 28-day compressive strength can stably reach over 40 MPa, its softening coefficient is higher than 0.90, and it demonstrates excellent workability and long-term durability. Its performance indicators are comparable to P·O 42.5 grade ordinary Portland cement. It can be widely used in various fields such as concrete preparation, soil solidification, roadbed backfilling, and precast components. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto.

[0019] In the following embodiments, all raw materials used are commercially available or industrial by-products, and their basic properties meet the requirements of the aforementioned invention. The preparation method follows the aforementioned three-step process of "separate grinding - gradation design - mixing and activation".

[0020] Weigh each component (unit: parts by weight) according to the proportions shown in Table 1, and prepare the cementitious material according to the aforementioned preparation method. Then, test its standard consistency water requirement, setting time, and compressive strength at various ages according to the "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T 17671-2021). Comparative Example 1 is a formulation without the addition of an early-strength agent (a composite of two of calcium chloride (CaCl2) and sodium aluminate (NaAlO2) in a mass ratio of 1:5), and the rest is the same as in Example 2.

[0021] Table 1: Raw material ratios and performance test results of Examples 1-3 and Comparative Examples 1-6

[0022] Components (parts) Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Phosphate slag 15 20 25 20 0 20 20 20 20 slag 45 40 35 40 40 0 40 40 40 plaster 15 12 10 12 12 12 0 12 12 steel slag 20 22 25 22 22 22 22 0 22 fly ash 10 8 5 8 8 8 8 8 8 Composite activator 4.5 5.0 4.0 5.0 5.0 5.0 5.0 5.0 0 Early strength agent 1.5 2.0 1.0 0 2.0 2.0 2.0 2.0 2.0 Standard consistency water consumption (%) 26.6 25.7 27.2 26.4 25.8 26.2 26.5 26.3 26.3 Initial setting time (min) 145 125 165 210 80 185 100 130 180 Final setting time (min) 210 185 240 310 160 275 145 200 265 Strength (MPa) - 3 days 17.8 21.2 22.7 16.8 13.4 9.8 16.3 16.0 15.5 Strength (MPa) - 7 days 29.4 33.6 36.8 31.1 23.1 16.5 24.6 25.7 26.6 Strength (MPa) - 28 days 45.6 47.5 48.9 44.2 37.5 29.7 38.5 39.5 36.3

[0023] Results analysis:

[0024] As can be seen from Examples 1-3, the cementitious materials prepared by the present invention have excellent performance indicators. The 28-day compressive strength all exceed 40 MPa, with the highest reaching 48.9 MPa (Example 2), which fully meets the strength grade requirements of P·O 42.5 cement.

[0025] The key role of early strength agents: Comparing Example 2 and Comparative Example 1, it is clear that adding 2 parts of early strength agent to the composite activating system can significantly shorten the setting time and greatly improve the 3-day early strength, from 16.8 MPa to 21.2 MPa. This proves that early strength agents in composite activating systems are indispensable for meeting the requirements of rapid construction and early load-bearing capacity in actual engineering projects.

[0026] Formula optimization: Example 2 exhibits the best overall performance, with its formula reflecting a good balance of multiple solid wastes. An appropriate amount of steel slag (22 parts) provides a sufficient alkaline activation environment; phosphogypsum (12 parts) and the composite alkaline activator (5 parts) form a sulfate-alkali composite activation; the early strength agent (2 parts) precisely enhances early strength performance. The addition of phosphate slag and fly ash further optimizes particle size distribution and long-term hydration reaction.

[0027] In summary, the low-carbon cementitious material and its preparation method provided by this invention have successfully achieved efficient resource utilization of various industrial solid wastes. The product has excellent performance, the process route is green and low-carbon, and it has the prospect of large-scale industrial application.

Claims

1. A low-carbon cementitious material for multi-element industrial solid waste, characterized in that, By weight, it includes the following components: 10-25 parts phosphorus slag, 30-50 parts blast furnace slag, 8-20 parts gypsum, 15-30 parts steel slag, 5-15 parts fly ash, 2-6 parts composite activator, and 0.5-3 parts early strength agent.

2. The low-carbon cementitious material for multi-element industrial solid waste according to claim 1, characterized in that, The gypsum is one or a mixture of two of phosphogypsum and desulfurized gypsum, and its chemical composition contains ≥90% CaSO4·2H2O.

3. The low-carbon cementitious material for multi-element industrial solid waste according to claim 1, characterized in that, The slag is granulated blast furnace slag powder with a specific surface area controlled at 400-500 m² / kg; the steel slag is converter steel slag powder with a specific surface area greater than 450 m² / kg. 2 / kg; the fly ash is Grade I or Grade II fly ash with a specific surface area greater than 350m². 2 / kg.

4. The low-carbon cementitious material for multi-element industrial solid waste according to claim 1, characterized in that, The composite activator is a solid alkali activator, which is composed of sodium hydroxide (NaOH) and sodium silicate nonahydrate (Na2SiO4·9H2O) in a mass ratio of 1:

3.

5. The low-carbon cementitious material for multi-element industrial solid waste according to claim 1, characterized in that, The early strength agent is a composite of two of calcium chloride (CaCl2) and sodium aluminate (NaAlO2) in a mass ratio of 1:

5.

6. A method for preparing a low-carbon cementitious material from multi-element industrial solid waste according to any one of claims 1-5, characterized in that, Includes the following steps: S1 Raw Material Pretreatment and Grinding: Phosphorus slag, slag, steel slag, and fly ash are dried separately until the moisture content is below 0.5%. Then, according to the grindability of each material, a separate grinding process is adopted: materials with higher hardness, such as steel slag and phosphorus slag, are first ground to a specific surface area ≥ 580 m². 2 / kg; then grind the slag, fly ash, etc. to the specified fineness, with a slag specific surface area of ​​500-560m². 2 / kg, fly ash specific surface area 350-400m² 2 / kg, gypsum dried to a moisture content of less than 0.5%; S2 Optimized Grading and Mixing: Based on Fuller's closest packing curve theory, particle gradation design is carried out for powders of different fineness after grinding. The ground phosphorus slag powder, slag powder, steel slag powder, fly ash powder and gypsum powder are put into a high-efficiency mixer according to the design ratio and premixed for 60-300 seconds to form homogeneous solid waste-based dry powder. S3 Activator Compounding and Final Mixing: Weigh the compound activator and early strength agent according to the ratio, add them to the solid waste-based dry powder obtained in step S2, and continue mixing for 80-100 seconds until the whole mixture is uniform, thus obtaining the finished low-carbon cementitious material.