Self-repairing steel slag-based solid waste cementitious material based on microbial mineralization and preparation method thereof

Abstract

This invention relates to a self-healing steel slag-based solid waste cementitious material based on microbial mineralization and its preparation method, belonging to the field of building materials technology. The material, by mass parts, comprises: 100-150 parts steel slag powder, 50-100 parts blast furnace slag powder, 8-23 parts alkaline activator, 10-20 parts porous steel slag carrier loaded with urea-decomposing bacteria, 200-300 parts aggregate, and 50-70 parts mixing water. The porous steel slag carrier has a porosity of 35%-50% and an average pore size of 10-50 μm, effectively isolating the highly alkaline environment inside the cementitious material from microbial damage. When cracks appear in the material, the invading water activates dormant microorganisms within the carrier, inducing the formation of calcium carbonate precipitate to automatically fill the cracks. This invention not only achieves the resource utilization of industrial solid waste such as steel slag but also possesses continuous self-healing capabilities, with a strength recovery rate of over 90% after 28 days, a significantly reduced chloride ion diffusion coefficient, and significantly improved durability.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a steel slag-based cementitious material with self-healing crack function based on microbial-induced calcium carbonate precipitation technology and its preparation method. Background Technology

[0002] The steel industry generates a large amount of steel slag annually, with my country's annual output exceeding 100 million tons. However, its comprehensive utilization rate has long remained low. The accumulation of large quantities of steel slag not only occupies land but also, under the influence of rainwater leaching, leads to the diffusion of heavy metal ions and the generation of high-pH leachate, posing a potential threat to surrounding soil, water bodies, and ecosystems. Promoting the large-scale, high-value-added utilization of steel slag has become an important issue for achieving resource recycling and building "zero-waste cities."

[0003] Using steel slag in conjunction with other industrial solid wastes to prepare cementitious materials, partially or completely replacing traditional cement, can not only dispose of large quantities of solid waste but also significantly reduce carbon emissions during cement production, aligning with the strategic direction of the building materials industry's green and low-carbon transformation. However, steel slag itself has low reactivity, and cementitious materials prepared primarily from it are often brittle, prone to developing microcracks during hardening or service. These microcracks become rapid channels for the intrusion of moisture and corrosive ions (such as chloride and sulfate ions), accelerating material performance degradation and reducing structural durability and safety. This, to some extent, restricts the widespread application of steel slag-based cementitious materials.

[0004] To address the problem of microcracks in materials, researchers have proposed various self-healing technologies, such as pre-embedding repair agent capsules in materials, constructing microvascular network repair systems, or incorporating shape memory alloys. However, these methods generally suffer from limitations such as complex preparation processes, high costs, difficulty in controlling the uniformity of repair agent distribution, and most can only achieve single-stage repair. Microbial-induced calcium carbonate precipitation technology offers a new possibility for materials to achieve autonomous and continuous self-healing. This technology utilizes the metabolic activities of certain microorganisms to induce the formation of calcium carbonate precipitates at the crack site, thereby sealing the crack. However, the interior of concrete is usually a highly alkaline environment with a pH value higher than 12. This extreme condition will cause ordinary microorganisms directly incorporated into the material to quickly become inactive, preventing the repair mechanism from starting and severely hindering the application of this technology in practical engineering. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a self-healing steel slag-based solid waste cementitious material based on microbial mineralization and its preparation method. The material protects microorganisms from damage by a high-alkali environment through a porous steel slag carrier, realizes autonomous and continuous repair of cracks, and at the same time efficiently disposes of steel slag solid waste and reduces carbon emissions.

[0006] The technical solution adopted by this invention to solve its technical problem is: a self-healing steel slag-based solid waste cementitious material based on microbial mineralization, comprising, by mass parts: 100-150 parts of steel slag powder, 50-100 parts of slag powder, 8-23 parts of alkaline activator, 10-20 parts of microbial composite material, 200-300 parts of aggregate, and 50-70 parts of mixing water.

[0007] The microbial composite material was prepared by loading urea-decomposing bacteria onto a porous steel slag carrier. The porous steel slag carrier had a particle size of 1-3 mm, a porosity of 35%-50%, and an average pore size of 10-50 μm, and was obtained from converter steel slag or electric furnace steel slag through crushing, screening, and pore-forming treatment. The urea-decomposing bacteria were *Bacillus pasteurellii* or *Bacillus licheniformis*, with a loading of 10... 6 -10 8 CFU / g.

[0008] The alkaline activator is a composite activator of water glass and solid sodium hydroxide. The amount of water glass is 5-15 parts, and the modulus is 2.0-3.5; the amount of solid sodium hydroxide is 3-8 parts.

[0009] The specific surface area of ​​both the steel slag powder and the blast furnace slag powder is not less than 400 m² / kg. The aggregate is one or more combinations of standard sand, natural river sand, or recycled aggregate.

[0010] Meanwhile, the present invention also provides a method for preparing the cementitious material, comprising the following steps: (a) Preparation of the microbial composite material: A porous steel slag carrier was immersed in a culture medium rich in urea-decomposing bacteria and cultured with shaking at 25-30℃ for 24-48 hours. After removal, it was air-dried under ventilation at 25-30℃ for 20-28 hours to obtain a composite material loaded with dormant microorganisms. The concentration of the culture medium components was 15-25 g / L yeast extract, 5-15 g / L peptone, and 15-25 g / L urea, and the pH was adjusted to 8.5-9.5.

[0011] (b) Dry mixing: Steel slag powder, slag powder, alkaline activator and microbial composite material are put into a forced mixer and dry mixed for no less than 2 minutes to obtain a uniform dry mixture.

[0012] (c) Mixing and molding: Add mixing water and aggregate to the dry mixture, wet mix for no less than 3 minutes to form a uniform slurry, and then pour it into the mold to form the slurry.

[0013] (d) Curing: Place the molded specimens under standard curing conditions for curing.

[0014] Furthermore, the present invention also provides the application of this cementitious material in road base courses, precast components, mine filling, or structural repair projects.

[0015] The beneficial effect of this invention is that it solves the defects existing in the prior art. 1. It solves the problem of microbial inactivation in the highly alkaline environment of cementitious materials. The porous steel slag carrier provides a protective microenvironment for microorganisms, isolates them from high-alkaline corrosion, and ensures that microorganisms are activated by moisture when cracks occur, achieving long-term self-repair.

[0016] 2. Improved mechanical properties and durability of steel slag-based cementitious materials. The material achieved a 28-day compressive strength of 45.8 MPa, a strength recovery rate of over 92% after pre-cracking, a significantly reduced chloride ion diffusion coefficient, and superior carbonation depth, sulfate resistance, and freeze-thaw resistance compared to traditional steel slag-based cementitious materials.

[0017] 3. It realizes the high-value utilization of steel slag. Using steel slag as the main base material to prepare cementitious materials significantly reduces industrial solid waste, lowers cement usage, and reduces carbon emissions in the building materials production process, which meets the needs of green and low-carbon development.

[0018] 4. The preparation process is simple and controllable, the cost is low, the repair process is autonomous and continuous, no human intervention is required, it is applicable to a variety of engineering fields, and has broad application prospects. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Example

[0020] A self-healing steel slag-based solid waste cementitious material based on microbial mineralization, comprising the following components by mass parts: 120 parts of steel slag powder (specific surface area 450 m² / kg), 80 parts of blast furnace slag powder (specific surface area 450 m² / kg), 10 parts of water glass (modulus 3.3), 5 parts of solid sodium hydroxide, and porous steel slag carrier loaded with Bacillus pasteurellii (loading capacity 5 × 10⁻⁶). 7 15 parts (CFU / g), 250 parts standard sand, and 60 parts distilled water.

[0021] Its preparation method includes the following steps: 1. Preparation of microbial composite material: Prepare a culture medium with the following components: yeast extract 20 g / L, peptone 10 g / L, and urea 20 g / L. Adjust the pH to 9.0 with sodium hydroxide solution. Immerse a converter porous steel slag carrier with a particle size of 2 mm, a porosity of 40%, and an average pore size of 30 μm into the culture medium and culture at 28 °C with shaking for 36 hours. After removal, air dry at 28 °C under ventilation for 24 hours to obtain the microbial composite material.

[0022] 2. Dry mixing: Put steel slag powder, blast furnace slag powder, water glass, solid sodium hydroxide and microbial composite material into a forced mixer and dry mix for 3 minutes to obtain a uniform dry mixture.

[0023] 3. Mixing and molding: Add standard sand and distilled water to the dry mixture, wet mix for 4 minutes to form a uniform slurry, and pour it into a cubic mold to form the slurry.

[0024] 4. Curing: Place the molded specimens in a standard curing room with a temperature of 20±2℃ and a relative humidity of 95% or higher for 28 days.

[0025] Comparative Example 1 Without adding microbial composite materials, the remaining components and preparation methods are the same as in Example 1.

[0026] Comparative Example 2 Ordinary steel slag particles (without pore-forming treatment) were used to replace the porous steel slag carrier for loading microorganisms. The remaining components and preparation methods were the same as in Example 1.

[0027] Comparative Example 3 A porous steel slag carrier without microorganisms was used, and the remaining components and preparation methods were the same as in Example 1.

[0028] The mechanical properties, durability, and self-healing properties of the cementitious materials of Example 1 and Comparative Examples 1-3 were tested, and the results are as follows: Table 1: Mechanical Performance Test Results Test Project 28d flexural strength compressive strength Strength recovery rate after pre-cracking Chloride ion diffusion coefficient Example 1 8.2MPa 45.8MPa 93.1% 3.25*10¹²m² / s Comparative Example 1 8.3MPa 46.2MPa 75.5% 6.84*10¹²m² / s Comparative Example 2 8.1MPa 45.7MPa 68.5% 7.58*10¹²m² / s Comparative Example 3 7.8MPa 43.9MPa 61.3% 9.02*10¹²m² / s Table 2: Durability Test Results Test Project 28d carbonization depth Sulfate erosion resistance coefficient Mass loss rate after 100 freeze-thaw cycles Example 1 2.1mm 0.92K 1.4% Comparative Example 1 3.8mm 0.83K 3.5% Comparative Example 2 4.1mm 0.76K 4.2% Comparative Example 3 4.7mm 0.68K 4.6% Table 3: Strength recovery rate at different repair times Repair time (days) Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 7 47.1% 32.5% 28.4% 25.6% 14 68.7% 48.3% 42.6% 38.2% 28 93.1% 75.5% 68.5% 61.3% 56 97.7% 78.9% 72.3% 66.4% Results analysis: 1. As can be seen from the comparison between Example 1 and Comparative Example 1, when no microbial composite material was added, the material still had a certain degree of strength recovery (mainly due to the inherent characteristics such as the subsequent hydration of unhydrated particles), but its recovery rate (75.5%) was much lower than that of Example 1 (93.1%), and its chloride ion permeability was significantly higher. This proves that the microorganisms loaded in the porous carrier played a dominant role in crack repair.

[0029] 2. A comparison between Example 1 and Comparative Example 2 shows that when ordinary steel slag particles are used as a carrier, although microorganisms are also loaded, the lack of a porous structure leads to a significant inactivation of the microorganisms in the highly alkaline environment, resulting in a repair effect (68.5%) that is even lower than that of Comparative Example 1 without added microorganisms. This strongly demonstrates that a porous carrier structure is crucial for protecting microbial activity and is the key to achieving the self-repair function of this invention.

[0030] 3. A comparison between Example 1 and Comparative Example 3 shows that even with a porous carrier, the self-repairing ability is very limited (61.3%) without active microorganisms, relying solely on the carrier itself or other substances in the environment. This clarifies that the catalytic effect of microorganisms is a necessary condition for the formation of reparative calcium carbonate precipitates.

[0031] 4. In terms of durability indicators, Example 1 is superior to all comparative examples in terms of resistance to carbonization, sulfate attack and freeze-thaw cycles. This indicates that microbial-induced crack self-healing not only restores mechanical strength, but more importantly, it significantly improves the material's ability to resist external corrosive media by blocking the penetration path.

[0032] 5. Table 3 shows that Example 1 repaired faster and was basically completed after 28 days, and reached near-complete recovery after 56 days, demonstrating continuous and efficient repair capabilities.

[0033] 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 self-healing steel slag-based solid waste cementitious material based on microbial mineralization, characterized in that, By weight, it includes the following components: 100-150 parts steel slag powder, 50-100 parts blast furnace slag powder, 8-23 parts alkaline activator, 10-20 parts microbial composite material, 200-300 parts aggregate, and 50-70 parts mixing water; The microbial composite material is prepared by loading urea-decomposing bacteria onto a porous steel slag carrier; the porous steel slag carrier has a particle size of 1-3 mm, a porosity of 35%-50%, and an average pore size of 10-50 μm, and is prepared from converter steel slag or electric furnace steel slag through crushing, screening, and pore-forming treatment; the loading amount of urea-decomposing bacteria on the porous steel slag carrier is 10. 6 -10 8 CFU / g.

2. The self-healing steel slag-based solid waste cementitious material based on microbial mineralization according to claim 1, characterized in that, The urea-decomposing bacteria are *Bacillus pasteurellus* or *Bacillus licheniformis*.

3. The self-healing steel slag-based solid waste cementitious material based on microbial mineralization according to claim 1, characterized in that, The alkaline activator is a composite activator of water glass and solid sodium hydroxide; wherein the amount of water glass is 5-15 parts and the modulus is 2.0-3.5; and the amount of solid sodium hydroxide is 3-8 parts.

4. The self-healing steel slag-based solid waste cementitious material based on microbial mineralization according to claim 1, characterized in that, The specific surface area of ​​both the steel slag powder and the slag powder is not less than 400 m² / kg.

5. The self-healing steel slag-based solid waste cementitious material based on microbial mineralization according to claim 1, characterized in that, The aggregate is one or more of standard sand, natural river sand, or recycled aggregate.

6. A method for preparing a self-healing steel slag-based solid waste cementitious material based on microbial mineralization as described in any one of claims 1-5, characterized in that, Includes the following steps: (a) Preparation of microbial composite material: The porous steel slag carrier was immersed in a culture medium rich in urea-decomposing bacteria and cultured with shaking at 25-30℃ for 24-48 hours. After being taken out, it was air-dried at low temperature to obtain a composite material loaded with dormant microorganisms. (b) Dry mixing: Steel slag powder, slag powder, alkaline activator and microbial composite material prepared in step (a) are put into a mixer and thoroughly dry mixed to obtain a uniform dry mixture; (c) Mixing and molding: Add mixing water and aggregate to the dry mixture from step (b), mix to form a uniform slurry, and pour into a mold to form the slurry; (d) Curing: Place the molded specimens under standard curing conditions for curing.

7. The preparation method according to claim 6, characterized in that, The concentrations of the components in the culture medium in step (a) are: yeast extract 15-25 g / L, peptone 5-15 g / L, and urea 15-25 g / L; the pH of the culture medium is adjusted to 8.5-9.5 using sodium hydroxide solution.

8. The preparation method according to claim 6, characterized in that, The conditions for low-temperature air drying in step (a) are: temperature 25-30℃, air drying for 20-28 hours under ventilated conditions.

9. The preparation method according to claim 6, characterized in that, The mixing in step (c) shall be carried out using a forced mixer; the dry mixing time shall be no less than 2 minutes, and the wet mixing time after adding the mixing water and aggregate shall be no less than 3 minutes.

10. The self-healing steel slag-based solid waste cementitious material according to any one of claims 1-5, characterized in that, Applications in road base courses, precast components, mine filling, or structural repair projects.