Concrete containing solid waste and preparation process thereof

Abstract

The invention relates to the technical field of cement preparation, and provides concrete containing solid waste and a preparation technology thereof.The preparation technology of the concrete containing the solid waste comprises the following steps that cement and waste concrete powder are put into a stirring machine, dry mixing is conducted for 1-2 min till the mixture is uniform, then river sand, natural gravel and construction waste gravel are added, dry mixing continues for 3-4 min, and the mixture is stirred to be uniform; and slowly adding a polycarboxylic acid water reducing agent and deionized water, carrying out wet mixing for 1-2 min, adding the composite fibers into the mixer in batches, continuing to carry out mixing for 3-5 min, and carrying out curing so as to obtain the concrete. Chitosan fibers are subjected to chemical modification treatment and compounded with steel fibers according to a specific proportion, and the compound is used as a reinforcing component to be introduced into a concrete system; the microstructure of the concrete is effectively optimized, the mechanical property and crack resistance of the material are remarkably improved, and meanwhile resource utilization of solid waste is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of cement preparation, and in particular to concrete containing solid waste and a preparation process thereof. Background Art

[0002] In the field of traditional concrete preparation, the recycling and utilization of solid waste has always been an important research direction. Solid waste such as construction waste and waste concrete are usually simply crushed and used as aggregate to partially replace natural sand and gravel. However, due to the old cement paste attached to their surface, high porosity and uneven strength, direct use will lead to a decrease in the mechanical properties of concrete and insufficient durability. In the existing technology, mechanical activation or chemical excitation are often used to improve the activity of waste concrete powder, but it is still difficult to completely compensate for its negative impact on concrete performance when used alone. In addition, ordinary fiber-reinforced concrete mostly uses a single type of fiber (such as steel fiber or synthetic fiber). Although it can improve crack resistance, steel fiber is easy to corrode and has high cost, and the interfacial bonding between organic fiber and cement matrix is ​​weak, making it difficult to achieve multi-scale synergistic reinforcement effects. Especially in the interface transition zone, traditional fibers are difficult to effectively inhibit the propagation of microcracks, resulting in an increased risk of early cracking of concrete.

[0003] Therefore, in order to solve the above problems, the present invention provides a concrete containing solid waste and a preparation process thereof. Summary of the Invention

[0004] The present invention provides a concrete containing solid waste and a preparation process thereof, which solves the defects in the related art.

[0005] The technical solutions of the present invention are as follows: A process for preparing concrete containing solid waste comprises the following steps: adding cement and waste concrete powder into a mixer, dry-mixing for 1-2 minutes until uniform, then adding river sand, natural gravel, and construction waste gravel, and continuing dry-mixing for 3-4 minutes, then slowly adding a polycarboxylate water reducer and deionized water, wet-mixing for 1-2 minutes, then adding composite fibers into the mixer in batches, continuing mixing for 3-5 minutes, and curing to obtain concrete.

[0006] More optimally, the concrete includes the following components: 90-100 parts of cement, 120-150 parts of river sand, 150-200 parts of natural crushed stone, 80-100 parts of construction waste crushed stone, 30-50 parts of waste concrete powder, 45-50 parts of deionized water, 0.8-1 part of polycarboxylate water reducer, and 12-15 parts of composite fiber.

[0007] More optimally, the composite fiber comprises modified chitosan fiber and steel fiber in a mass ratio of 1:1-2.

[0008] More optimally, the preparation process of the modified chitosan fiber is: S1: chitosan is added to an acetic acid solution and stirred until completely dissolved, then slowly added to a sodium hydroxide solution, soaked for 10-12 hours, washed, dried, and then transferred to an epichlorohydrin solution, adjusted to pH 12, and reacted at 40-50°C for 3-5 hours. After the reaction is complete, the chitosan fiber is washed to obtain a cross-linked chitosan fiber; S2: Dissolve thiourea and glutaraldehyde in deionized water, adjust the pH to 4.5-5, and react at 40-50°C with stirring for 3-5 hours. After the reaction is completed, cool to room temperature, adjust the pH to 3-4, and filter and purify to obtain a thiourea intermediate solution; S3: Add cross-linked chitosan fiber to the thiourea intermediate solution, increase the temperature to 70-80°C, react for 6-8 hours, transfer to glutaraldehyde solution after the reaction, adjust the pH to 4.5-5, cross-link at 40-50°C for 3-4 hours, wash, and dry to obtain modified chitosan fiber.

[0009] In the scheme, the structure of the modified chitosan fiber is shown below:

[0010] More optimally, the cross-linked chitosan fiber raw material includes the following components: by weight, 1-2 parts of chitosan, 15-20 parts of acetic acid solution, 300-400 parts of sodium hydroxide solution, and 0.2-0.3 parts of epichlorohydrin solution.

[0011] More optimally, the concentration of the acetic acid solution is 3 vol%-5 vol%; the concentration of the sodium hydroxide solution is 1-2 mol / L; and the concentration of the epichlorohydrin solution is 0.25 vol%-0.3 vol%.

[0012] More optimally, the thiourea intermediate solution raw materials include the following components: 4-5 parts of thiourea, 15-20 parts of glutaraldehyde, and 150-200 parts of deionized water, by weight.

[0013] More optimally, the modified chitosan fiber raw material comprises the following components: by weight, 1-2 parts of cross-linked chitosan fiber, 150-200 parts of thiourea intermediate solution, and 15-20 parts of glutaraldehyde.

[0014] Compared with the prior art, the present invention has the following advantages: The present invention chemically modifies chitosan fibers, compounds them with steel fibers in a specific ratio, and introduces them into the concrete system as a reinforcing component. This effectively optimizes the concrete's microstructure, significantly improves the material's mechanical properties and crack resistance, and simultaneously realizes resource utilization of solid waste. The details are as follows: First, while chitosan itself possesses excellent fiber-forming properties and biocompatibility, the limited activity of its surface functional groups (such as hydroxyl and amino groups) makes it difficult to form strong interactions with the cement matrix. The introduction of thiourea groups effectively increases the polarity and reactivity of the chitosan fiber surface, promoting hydrogen or chemical bonding with cement hydration products, thereby improving fiber-matrix interfacial adhesion and enhancing stress transfer efficiency.

[0015] Secondly, chitosan fibers, due to their small size and flexibility, mainly act on the microscopic scale of concrete, filling capillary pores, optimizing pore structure, and inhibiting early plastic shrinkage cracks; steel fibers, with their high strength and rigidity, mainly play a reinforcing role at the macroscopic scale, effectively improving the tensile strength, impact resistance and toughness of concrete; after the two are combined, they can jointly play a role in crack prevention, toughening and crack resistance at different scales, realizing multi-level reinforcement from nano to macro levels.

[0016] Third, chitosan fibers, due to their excellent interfacial bonding ability, preferentially work in the weak interface transition zone between cement paste and aggregate, reducing the formation of microcracks. Steel fibers, on the other hand, can span potential crack areas over a wider range, providing additional load-bearing capacity and ductile support. The synergistic effect of these two significantly improves the overall density and structural stability of concrete. DETAILED DESCRIPTION

[0017] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0018] In the following examples and comparative examples, Cement is commercially available ordinary Portland cement with a PO42.5 Waste concrete powder is made from waste concrete with calcium carbonate as aggregate, and the particles are smaller than 15μm; The fineness modulus of river sand is 2.79; The particle size of natural crushed stone is 5-20mm with continuous gradation; The particle size of the construction waste gravel is 5-20mm with continuous gradation; The steel fiber has a length of 30 mm and a diameter of 0.5 mm.

[0019] Example 1 A process for preparing concrete containing solid waste comprises the following steps: adding 90 parts of cement and 30 parts of waste concrete powder into a mixer, dry-mixing for 1 minute until uniform, then adding 120 parts of river sand, 150 parts of natural crushed stone, and 80 parts of construction waste crushed stone, and continuing dry-mixing for 3 minutes, then slowly adding 0.8 parts of a polycarboxylate water reducer and 45 parts of deionized water, wet-mixing for 1 minute, then adding 12 parts of composite fiber (comprising modified chitosan fiber and steel fiber in a mass ratio of 1:1) into the mixer in portions, continuing mixing for 3 minutes, and curing to obtain concrete; Wherein, the preparation process of modified chitosan fiber is: S1: Add 1 part of chitosan to 15 parts of acetic acid solution, stir until completely dissolved, then slowly add it to 300 parts of sodium hydroxide solution, soak for 10 hours, wash, dry, and then transfer to 0.2 parts of epichlorohydrin solution, adjust the pH to 12, react at 40°C for 3 hours, and after the reaction is completed, wash to obtain cross-linked chitosan fiber; the concentration of the acetic acid solution is 3 vol%; the concentration of the sodium hydroxide solution is 1 mol / L; the concentration of the epichlorohydrin solution is 0.25 vol%; S2: Dissolve 4 parts of thiourea and 15 parts of glutaraldehyde in 150 parts of deionized water, adjust the pH to 4.5, and react at 40°C with stirring for 3 hours. After the reaction, cool to room temperature, adjust the pH to 3, and filter and purify to obtain a thiourea intermediate solution; S3: Add 1 part of cross-linked chitosan fiber to 150 parts of thiourea intermediate solution, increase the temperature to 70°C, react for 6 hours, and after the reaction is completed, transfer to 15 parts of glutaraldehyde, adjust the pH to 4.5, cross-link at 40°C for 3 hours, wash, and dry to obtain modified chitosan fiber.

[0020] Example 2 A process for preparing concrete containing solid waste comprises the following steps: adding 100 parts of cement and 50 parts of waste concrete powder into a mixer, dry-mixing for 2 minutes until uniform, then adding 150 parts of river sand, 200 parts of natural crushed stone, and 100 parts of construction waste crushed stone, and continuing dry-mixing for 4 minutes, then slowly adding 1 part of a polycarboxylate water reducer and 50 parts of deionized water, wet-mixing for 2 minutes, then adding 15 parts of composite fiber (comprising modified chitosan fiber and steel fiber in a mass ratio of 1:2) into the mixer in portions, continuing mixing for 5 minutes, and curing to obtain concrete; Wherein, the preparation process of modified chitosan fiber is: S1: 2 parts of chitosan were added to 20 parts of acetic acid solution, stirred until completely dissolved, then slowly added to 400 parts of sodium hydroxide solution, soaked for 12 hours, washed, dried, and then transferred to 0.3 parts of epichlorohydrin solution, adjusted to pH 12, reacted at 50°C for 5 hours, and washed after the reaction to obtain cross-linked chitosan fiber; the concentration of the acetic acid solution was 5 vol%; the concentration of the sodium hydroxide solution was 2 mol / L; the concentration of the epichlorohydrin solution was 0.3 vol%; S2: Dissolve 5 parts of thiourea and 20 parts of glutaraldehyde in 200 parts of deionized water, adjust the pH to 5, and react at 50°C with stirring for 5 hours. After the reaction is completed, cool to room temperature, adjust the pH to 4, and filter and purify to obtain a thiourea intermediate solution; S3: Add 2 parts of cross-linked chitosan fiber to 200 parts of thiourea intermediate solution, increase the temperature to 80°C, react for 8 hours, transfer to 20 parts of glutaraldehyde after the reaction, adjust the pH to 5, cross-link at 50°C for 4 hours, wash, and dry to obtain modified chitosan fiber.

[0021] Example 3 A process for preparing concrete containing solid waste comprises the following steps: adding 95 parts of cement and 40 parts of waste concrete powder into a mixer, dry-mixing for 1.5 minutes until uniform, then adding 130 parts of river sand, 180 parts of natural crushed stone, and 90 parts of construction waste crushed stone, and continuing dry-mixing for 3.5 minutes, then slowly adding 0.9 parts of a polycarboxylate water reducer and 48 parts of deionized water, and wet-mixing for 1.5 minutes, then adding 13 parts of composite fiber (comprising modified chitosan fiber and steel fiber in a mass ratio of 1:1.5) in portions into the mixer, continuing mixing for 4 minutes, and curing to obtain concrete; Wherein, the preparation process of modified chitosan fiber is: S1: 1.5 parts of chitosan were added to 17.5 parts of acetic acid solution, stirred until completely dissolved, then slowly added to 350 parts of sodium hydroxide solution, soaked for 11 hours, washed, dried, and then transferred to 0.25 parts of epichlorohydrin solution, adjusted to pH 12, reacted at 45°C for 4 hours, and washed after the reaction to obtain cross-linked chitosan fiber; the concentration of the acetic acid solution was 4 vol%; the concentration of the sodium hydroxide solution was 1.5 mol / L; the concentration of the epichlorohydrin solution was 0.275 vol%; S2: Dissolve 4.5 parts of thiourea and 17.5 parts of glutaraldehyde in 175 parts of deionized water, adjust the pH to 4.75, and stir the mixture at 45°C for 4 hours. After the reaction, cool to room temperature, adjust the pH to 3.5, and filter and purify to obtain a thiourea intermediate solution; S3: Add 1.5 parts of cross-linked chitosan fiber to 175 parts of thiourea intermediate solution, increase the temperature to 75°C, and react for 7 hours. After the reaction is completed, transfer to 17.5 parts of glutaraldehyde, adjust the pH to 4.75, cross-link at 45°C for 3.5 hours, wash, and dry to obtain modified chitosan fiber.

[0022] Comparative Example 1 This comparative example does not add modified chitosan fiber, and the rest is the same as Example 3, specifically as follows: A process for preparing concrete containing solid waste comprises the following steps: adding 95 parts of cement and 40 parts of waste concrete powder into a mixer, dry-mixing for 1.5 minutes until uniform, then adding 130 parts of river sand, 180 parts of natural gravel, and 90 parts of construction waste gravel, and continuing dry-mixing for 3.5 minutes, then slowly adding 0.9 parts of polycarboxylate water reducer and 48 parts of deionized water, wet-mixing for 1.5 minutes, then adding 13 parts of steel fiber into the mixer in portions, continuing mixing for 4 minutes, and curing to obtain concrete.

[0023] Comparative Example 2 This comparative example does not modify the chitosan fiber, and the rest is the same as Example 3, specifically as follows: A process for preparing concrete containing solid waste comprises the following steps: adding 95 parts of cement and 40 parts of waste concrete powder into a mixer, dry-mixing for 1.5 minutes until uniform, then adding 130 parts of river sand, 180 parts of natural crushed stone, and 90 parts of construction waste crushed stone, and continuing dry-mixing for 3.5 minutes, then slowly adding 0.9 parts of polycarboxylate water reducer and 48 parts of deionized water, and wet-mixing for 1.5 minutes, and then adding 13 parts of composite fiber (comprising chitosan fiber and steel fiber in a mass ratio of 1:1) into the mixer in portions, continuing mixing for 4 minutes, and curing to obtain concrete.

[0024] Comparative Example 3 This comparative example does not add steel fiber, and the rest is the same as Example 3, specifically as follows: A process for preparing concrete containing solid waste comprises the following steps: adding 95 parts of cement and 40 parts of waste concrete powder into a mixer, dry-mixing for 1.5 minutes until uniform, then adding 130 parts of river sand, 180 parts of natural gravel, and 90 parts of construction waste gravel, and continuing dry-mixing for 3.5 minutes, then slowly adding 0.9 parts of polycarboxylate water reducer and 48 parts of deionized water, wet-mixing for 1.5 minutes, then adding 13 parts of modified chitosan fiber into the mixer in portions, continuing mixing for 4 minutes, and curing to obtain concrete.

[0025] Detection experiment: The anti-cracking cement prepared in the examples and comparative examples was cured according to the curing method of the test specimens in GB / T 50081-2019. The curing period was 28 days, and the following performance tests were performed on the cured samples: (1) Conduct mechanical property tests in accordance with GB / T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete"; (2) The above samples were tested for crack resistance. The dimensions of all specimens were 600mm×600mm×50mm. The test temperature was controlled at 25°C. During the test, each specimen with a mold was placed in a wind-blown environment. The cracking condition of each concrete specimen was observed for 24 hours using a feeler gauge specially designed to measure crack width. The obtained data are shown in Table 1 below: Table 1

[0026] Conclusion: The present invention successfully prepared a high performance concrete containing solid waste by compounding chemically modified chitosan fibers and steel fibers in a specific ratio as reinforcement components.

[0027] The experimental results show that the concrete has significantly improved mechanical properties and crack resistance. The compressive strengths of Examples 1-3 reached 61.8 MPa, 62.1 MPa, and 62.9 MPa, respectively, and the flexural strengths were 8.2 MPa, 8.3 MPa, and 8.5 MPa, respectively. None of the concretes showed any cracking, demonstrating excellent overall performance. In comparison, although the compressive strength of comparative example 1 (without modified chitosan fiber) is slightly higher (66.1 MPa), the flexural strength is reduced (7.1 MPa) and cracks appear (maximum crack width 0.35 mm), indicating that a single steel fiber cannot effectively inhibit cracking; the compressive strength and flexural strength of comparative example 2 (unmodified chitosan fiber) are significantly reduced (55.8 MPa and 6.2 MPa), and multiple cracks appear, indicating that fiber modification is crucial to interface bonding and performance improvement; the performance of comparative example 3 (without steel fiber) is the worst (compressive strength 45.1 MPa, flexural strength 5.6 MPa, and 5 cracks), further verifying the synergistic reinforcement effect of the composite fiber.

[0028] In summary, the present invention not only realizes the resource utilization of solid waste by optimizing the fiber composite system, but also significantly improves the mechanical properties and crack resistance of concrete, and has important practical application value.

[0029] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A concrete containing solid waste, characterized in that: The invention comprises the following components in parts by weight: 90-100 parts of cement, 120-150 parts of river sand, 150-200 parts of natural crushed stone, 80-100 parts of construction waste crushed stone, 30-50 parts of waste concrete powder, 45-50 parts of deionized water, 0.8-1 part of polycarboxylate water reducer, and 12-15 parts of composite fiber; the composite fiber comprises modified chitosan fiber and steel fiber in a mass ratio of 1:1-2.

2. The concrete containing solid waste according to claim 1, characterized in that: The preparation process of the modified chitosan fiber is as follows: S1: chitosan is added to an acetic acid solution and stirred until completely dissolved, then slowly added to a sodium hydroxide solution, soaked for 10-12 hours, washed, dried, and then transferred to an epichlorohydrin solution, adjusted to a pH of 12, reacted, and washed after the reaction is complete to obtain cross-linked chitosan fibers; S2: Dissolve thiourea and glutaraldehyde in deionized water, adjust the pH to 4.5-5, and stir to react. After the reaction is completed, cool to room temperature, adjust the pH to 3-4, and filter and purify to obtain a thiourea intermediate solution; S3: adding cross-linked chitosan fiber to the thiourea intermediate solution, reacting, and transferring to glutaraldehyde solution after the reaction is completed, adjusting the pH to 4.5-5, cross-linking at 40-50°C for 3-4 hours, washing, and drying to obtain modified chitosan fiber.

3. The concrete containing solid waste according to claim 1, characterized in that: In step S1, the reaction temperature is 40-50° C. and the reaction time is 3-5 h.

4. The concrete containing solid waste according to claim 1, characterized in that: In step S2, the stirring reaction temperature is 40-50° C. and the time is 3-5 hours.

5. The concrete containing solid waste according to claim 1, characterized in that: In step S3, the reaction temperature is 70-80° C. and the reaction time is 6-8 h.

6. The concrete containing solid waste according to claim 2, characterized in that: The cross-linked chitosan fiber raw material comprises the following components: by weight, 1-2 parts of chitosan, 15-20 parts of acetic acid solution, 300-400 parts of sodium hydroxide solution, and 0.2-0.3 parts of epichlorohydrin solution.

7. The concrete containing solid waste according to claim 2, characterized in that: The concentration of the acetic acid solution is 3 vol%-5 vol%; the concentration of the sodium hydroxide solution is 1-2 mol / L; and the concentration of the epichlorohydrin solution is 0.25 vol%-0.3 vol%.

8. The concrete containing solid waste according to claim 2, characterized in that: The thiourea intermediate solution raw materials include the following components: 4-5 parts of thiourea, 15-20 parts of glutaraldehyde, and 150-200 parts of deionized water in parts by weight.

9. The concrete containing solid waste according to claim 2, characterized in that: The modified chitosan fiber raw material comprises the following components: by weight, 1-2 parts of cross-linked chitosan fiber, 150-200 parts of thiourea intermediate solution, and 15-20 parts of glutaraldehyde.

10. The process for preparing concrete containing solid waste according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: putting cement and waste concrete powder into a mixer, dry-mixing for 1-2 minutes until uniform, then adding river sand, natural gravel, and construction waste gravel, continuing dry-mixing for 3-4 minutes, then slowly adding polycarboxylate water reducer and deionized water, wet-mixing for 1-2 minutes, then adding composite fibers into the mixer in batches, continuing mixing for 3-5 minutes, and curing to obtain concrete.

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