Enhanced recycled aggregate concrete and method of making the same

Abstract

The present application relates to cement-based building material technical field, especially to a kind of enhanced recycled aggregate concrete and preparation method thereof, the raw material of SAP particle is adjusted from the synthesis angle first in the present application, the surface group and pore structure of SAP particle are regulated, then the loading of nanometer silicon dioxide is carried out, and the enhanced SAP is prepared after silane coupling agent treatment, which has internal curing and hydration enhancement effect, and can be targeted to reinforce recycled aggregate concrete.

Description

Technical Field

[0001] This invention relates to the field of cement-based building materials technology, and in particular to an enhanced recycled aggregate concrete and its preparation method. Background Technology

[0002] Recycled aggregate solid waste-based concrete can both dispose of solid waste and save natural aggregates, and its performance optimization has always been a research hotspot. Traditional methods for reinforcing recycled aggregate solid waste-based concrete have certain limitations, such as limited strength improvement and poor environmental adaptability. Therefore, developing a new type of reinforcing material for recycled aggregate solid waste-based concrete has significant practical application value. SAP is a cross-linked polymer compound containing hydrophilic functional groups such as carboxyl, sulfonic acid, hydroxyl, and amide groups on its molecular chain, capable of absorbing water equivalent to tens to thousands of times its own weight. Upon contact with water or aqueous solutions, SAP begins to swell and form a hydrogel, exhibiting excellent water retention. Incorporating SAP into recycled aggregate solid waste-based concrete can form a micro-"reservoir" within the concrete. When the internal slurry of the recycled aggregate solid waste-based concrete experiences "water shortage" due to cement hydration, SAP can release the absorbed water, compensating for the humidity in the cement slurry, promoting continued cement hydration, and thus effectively reducing the autogenous shrinkage and cracking of the recycled aggregate solid waste-based concrete.

[0003] Reference 1 (Wang Yifan, He Yingzhuo, Lin Yuchen, Effect of Crystallizing Admixtures on Self-Healing of Concrete Cracks [J], Shanxi Architecture, 2021(6): 109-110) studied concrete mixtures incorporating penetrating crystalline materials. The influence of crystalline admixtures on the mechanical properties and crack width of the modified concrete was analyzed by measuring the strength and crack width. The results showed that penetrating crystalline materials are beneficial for improving the compressive strength and self-healing width of concrete cracks, thus enhancing the structural integrity of the concrete.

[0004] Reference 2 (Xie Peng, Lan Tangwei, Research on the Influence of SAP Internal Curing Agent on Concrete Performance [J], Concrete World, 2021(5):68-72) published the use of high water absorption resin SAP as an internal curing agent for concrete, applied to C40 and C60 concrete, and studied the effects of internal curing agent dosage and pre-absorption rate on concrete workability, compressive strength and autogenous shrinkage properties. The results showed that the water absorption ratio of SAP can reach up to 150 times; the incorporation of pre-absorbent SAP can improve the workability of concrete and reduce time loss; the incorporation of SAP can reduce the early compressive strength of concrete, but the appropriate dosage can improve the later compressive strength of concrete; due to the gradual release of water in pre-absorbent SAP, SAP can reduce part of the autogenous shrinkage deformation of concrete to a certain extent.

[0005] Reference 3 (Zhang Min, Mechanism Analysis and Engineering Application of Polycarboxylate High-Performance Water-Reducing Agent [J], 2020(09):113-114) studied the advantages of polycarboxylate high-efficiency water-reducing agents compared with other water-reducing agents, and explained the high water reduction rate of polycarboxylate water-reducing agents and the problems existing in engineering applications.

[0006] The shortcomings of the above technologies are:

[0007] (1) Reference 1 uses penetrating crystallizing materials. These materials achieve waterproofing by penetrating into the interior of recycled aggregate solid waste-based concrete and crystallizing. However, their ability to repair larger cracks or crack propagation is limited. If the recycled aggregate solid waste-based concrete structure has cracks, and the width or depth of the cracks exceeds the material's penetration and repair capabilities, then this microcrystalline penetration alone cannot completely repair them. In particular, for cracks that may develop later due to settlement, shrinkage, or other reasons, the lack of elastic compensation may lead to a decrease in waterproofing effectiveness.

[0008] (2) Reference 2 only uses SAP. When SAP is introduced into recycled aggregate solid waste-based concrete, SAP releases some water, which leads to a decrease in the strength of the surrounding recycled aggregate solid waste-based concrete. When the SAP dosage is large, SAP will release water after absorbing water, but its particles may leave pores after releasing water. These pores will reduce the density of the recycled aggregate solid waste-based concrete, which may lead to a decrease in the strength of the recycled aggregate solid waste-based concrete. This effect is more obvious when the SAP dosage is high.

[0009] (3) Reference 3 uses polycarboxylate superplasticizer. However, under high-temperature conditions, polycarboxylate superplasticizer may not effectively maintain the slump of recycled aggregate solid waste-based concrete, affecting construction. Carboxylate superplasticizers are quite sensitive to temperature changes, and the slump retention of recycled aggregate solid waste-based concrete may vary significantly depending on the season. Currently, there are relatively few functional polycarboxylate superplasticizer products on the market, which may be insufficient to meet special construction requirements, and the raw material cost of polycarboxylate superplasticizers is relatively high.

[0010] Studies have shown that nanomaterials have a reinforcing effect on concrete. Highly active nano-silica can fill the small pores in recycled aggregate solid waste-based concrete and undergo a secondary hydration reaction with cement hydration products. However, this invention shows that directly adding nano-silica has a limited reinforcing effect on recycled aggregate concrete with added SAP. This may be because directly adding nano-silica cannot change the performance difference between the SAP-affected zone and the matrix. Existing technology CN118373644A discloses an in-situ generated organic-inorganic core-shell structure internal curing cement-based material. During the cement hydration and hardening process, the surface nano-silica shell reacts with the cement hydration products hydrogen and oxygen... The calcium leaching reaction forms a hard CSH gel shell, thereby creating an organic-inorganic core-shell structure in situ within the hardened cementitious material. This helps compensate for the decrease in strength of the hardened cementitious material caused by the collapse and pore formation during the hydration and hardening process of the introduced superabsorbent resin. However, the present invention found that the modified SAP has a limited reinforcing effect on recycled aggregates. This may be because the surface of the recycled aggregates is rough, angular, and has defects such as microcracks. The CSH gel shell formed on the surface of the modified SAP does not further reinforce the interface with the recycled aggregates. Furthermore, the CSH gel shell may affect the release of moisture, thus affecting the internal curing effect. Summary of the Invention

[0011] To address the problems existing in the prior art, this invention provides an enhanced recycled aggregate concrete. First, the raw materials of SAP particles are adjusted from a synthetic perspective to regulate the surface groups and pore structure of the SAP particles. Then, after loading nano-silica, the particles are treated with a silane coupling agent to prepare the enhanced SAP, which has both internal curing and hydration enhancement effects, and can provide targeted reinforcement for recycled aggregate concrete.

[0012] Specifically, the reinforced recycled aggregate concrete of the present invention is characterized by comprising the following raw materials in parts by weight: 300-350 parts cement, 80-100 parts fly ash, 20-50 parts mineral powder, 800-900 parts recycled fine aggregate, 1000-1100 parts recycled coarse aggregate, 3-5 parts reinforced SAP particles, 6-10 parts water-reducing agent, 1-3 parts retarder, and 150-160 parts water.

[0013] The enhanced SAP particles are prepared by crosslinking and polymerization of 100 parts acrylic acid, 3-5 parts trimethylsilyl methacrylate, and 1-3 parts 4-phenyl-1-butene with 1-2 parts crosslinking agent. Then, 2-4 parts nano-silica are loaded into the pores of the SAP particles, followed by soaking in silane coupling agent, filtration, and drying to obtain the final product.

[0014] This invention loads nano-silica into the pores of SAP particles. The reinforced SAP particles can release highly active nano-silica during the water release process, which can fill the fine pores of recycled aggregate concrete and undergo a secondary hydration reaction with the cement hydration process, thereby increasing the proportion of gel pores, reducing the most probable pore size, optimizing the pore structure of recycled aggregate solid waste-based concrete, improving the interface structure with recycled aggregate, and thus improving the performance of the SAP-affected zone.

[0015] Preferably, the cement is at least one of silicate cement and ordinary silicate cement. More preferably, the cement strength grade is ≥42.5.

[0016] Preferably, the recycled fine aggregate and recycled coarse aggregate are obtained by crushing and screening construction waste.

[0017] Preferably, the fineness modulus of the recycled fine aggregate is 2.0-2.6.

[0018] Preferably, the recycled coarse aggregate has a particle size of 5-20 mm.

[0019] Preferably, the enhanced SAP manufacturing process is as follows:

[0020] 1) Mix 100 parts acrylic acid, 3-5 parts trimethylsilyl methacrylate, 1-3 parts 4-phenyl-1-butene, and 280-320 parts water until homogeneous. Adjust the pH to 6-7, add 1-2 parts crosslinking agent, stir until homogeneous, add 0.5-1.5 parts pore-forming agent, 0.4-0.6 parts initiator, and 1-2 parts reducing agent to carry out polymerization reaction to obtain gel. Cut the gel into small pieces, dry, and pulverize to obtain SAP particles.

[0021] 2) Ultrasonically mix SAP particles with a suspension containing 2-4 parts of nano-silica to load the nano-silica into the pores of the SAP particles. Add silane coupling agent for soaking, filter, and dry to obtain the final product.

[0022] In the preparation of reinforced SAP particles, this invention first optimizes the molecular structure by adding trimethyl methacrylate and 4-phenyl-1-butene to introduce silicic acid groups and phenyl groups. Experiments show that the prepared SAP particles can effectively load nano-silica particles. After water absorption and expansion, the pore size of the SAP particles is between 0.1-1 mm. The water absorption and release characteristics are more suitable for curing recycled aggregate concrete. Subsequent treatment with a silane coupling agent is beneficial to the dispersion of reinforced SAP particles in concrete paste and their bonding with the material interface, enhancing their compatibility with recycled aggregate concrete and preventing premature escape of nano-silica, which would reduce the reinforcing effect.

[0023] Preferably, the crosslinking agent in step 1) is N,N'-methylenebisacrylamide.

[0024] Preferably, the pore-forming agent is a mixture of methanol, ethanol, and sodium bicarbonate in a mass ratio of (5-7):(0.5-1.5):(2-4). The addition of this pore-forming agent can further improve the water absorption and exchange capacity of SAP.

[0025] Preferably, the initiator is ammonium persulfate.

[0026] Preferably, the reducing agent is sodium sulfite.

[0027] Preferably, the initiator and reducing agent can be added dropwise to the reaction system as needed, or added in other ways.

[0028] Preferably, in step 1), the stirring is done with magnetic stirring at a speed of 280-350 r / min, and the pulverizing is done with a universal pulverizer at a speed of 4000-5000 rpm.

[0029] Preferably, in step 1), the SAP particle size is 0.05-0.5 mm.

[0030] Preferably, in step 2), the ultrasonic power is 500-600W, the ultrasonic frequency is 18-22kHz, and the ultrasonic time is 0.5-1h. This invention uses ultrasonic dispersion to load nano-silica into SAP particles.

[0031] Preferably, the coupling agent in step 2) is at least one of KH550 and KH560. The amount of coupling agent added is sufficient to submerge the water-absorbing resin particles.

[0032] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent.

[0033] Preferably, the retarder is at least one of tartaric acid, sodium gluconate, and boric acid.

[0034] This invention also relates to a method for preparing the aforementioned reinforced recycled aggregate concrete, specifically comprising the following steps: weighing each raw material according to its weight proportions, and mixing the raw materials evenly to obtain the final product. This invention does not limit the mixing order of the raw materials; commonly used step-by-step concrete mixing processes in the art are all within the scope of protection of this invention's preparation method, as long as the raw materials can be mixed evenly and the concrete has good workability.

[0035] This invention has the following technical advantages:

[0036] 1. The enhanced SAP particles of this invention are designed from a molecular structure perspective, exhibiting excellent internal curing effects, reducing shrinkage in recycled aggregate concrete, and improving concrete durability.

[0037] 2. The enhanced SAP particles of this invention are loaded with nano-silica and protected by a silane coupling agent, exhibiting good dispersibility and adaptability. During internal curing, the nano-silica particles can fill fine pores, and the hydration products can optimize the pore structure of recycled aggregate concrete, enhance the interfacial transition zone, and improve the mechanical properties of recycled aggregate concrete.

[0038] 3. The method of this invention is simple. The raw materials, experimental instruments, and experimental environment required in the preparation process are all relatively common, which is conducive to further promotion and has good application prospects. Detailed Implementation

[0039] To characterize the technical effects of this invention, recycled aggregate concrete was prepared and its performance was tested. During the experiment, P·O42.5 cement, Grade II fly ash, and Grade S95 mineral powder were used. The fineness modulus of the recycled fine aggregate was 2.3, and the particle size of the recycled coarse aggregate was a continuous gradation of 5-20 mm. Polycarboxylate superplasticizer was used as the water-reducing agent, and sodium gluconate was used as the retarder. In the preparation of the reinforced SAP, N,N'-methylenebisacrylamide was used as the crosslinking agent, a mixture of methanol, ethanol, and sodium bicarbonate in a mass ratio of 6:1:3 was used as the pore-forming agent, ammonium persulfate was used as the initiator, sodium sulfite was used as the reducing agent, and KH550 was used as the coupling agent.

[0040] Example 1

[0041] Recycled aggregate concrete, characterized in that it is composed of the following raw materials in parts by weight: 330 parts cement, 100 parts fly ash, 50 parts mineral powder, 880 parts recycled fine aggregate, 1050 parts recycled coarse aggregate, 4 parts reinforced SAP particles, 9 parts water-reducing agent, 2 parts retarder, and 155 parts water.

[0042] The enhanced SAP manufacturing process is as follows:

[0043] 1) Mix 100 parts acrylic acid, 5 parts trimethylsilyl methacrylate, 2 parts 4-phenyl-1-butene, and 300 parts water evenly, adjust the pH to 7, add 2 parts crosslinking agent, stir evenly, add 1 part pore-forming agent, 0.5 parts initiator, and 1 part reducing agent to carry out polymerization reaction to obtain gel. Cut the gel into small pieces, dry, and pulverize to obtain SAP particles.

[0044] 2) Ultrasonically mix SAP particles with a suspension containing 4 parts of nano-silica to load the nano-silica into the pores of the SAP particles. Add silane coupling agent for soaking, filter, and dry to obtain the final product.

[0045] The concrete was tested and found to have a 28-day compressive strength of 53.8 MPa, a 28-day tensile strength of 4.2 MPa, a 28-day shrinkage rate of 0.016%, and a mass loss rate of 0.6% after 300 freeze-thaw cycles.

[0046] Example 2

[0047] Recycled aggregate concrete, characterized in that it is composed of the following raw materials in parts by weight: 340 parts cement, 100 parts fly ash, 30 parts mineral powder, 880 parts recycled fine aggregate, 1050 parts recycled coarse aggregate, 3 parts reinforced SAP particles, 8 parts water-reducing agent, 2 parts retarder, and 155 parts water.

[0048] The enhanced SAP manufacturing process is as follows:

[0049] 1) Mix 100 parts acrylic acid, 4 parts trimethylsilyl methacrylate, 2 parts 4-phenyl-1-butene, and 300 parts water until homogeneous. Adjust the pH to 7, add 1.8 parts crosslinking agent, stir until homogeneous, add 1 part pore-forming agent, 0.5 parts initiator, and 1 part reducing agent to carry out polymerization reaction to obtain gel. Cut the gel into small pieces, dry, and pulverize to obtain SAP particles.

[0050] 2) Ultrasonically mix SAP particles with a suspension containing 3 parts of nano-silica to load the nano-silica into the pores of the SAP particles. Add silane coupling agent for soaking, filter, and dry to obtain the final product.

[0051] The concrete was tested and found to have a 28-day compressive strength of 52.5 MPa, a 28-day tensile strength of 4.1 MPa, a 28-day shrinkage rate of 0.019%, and a mass loss rate of 0.8% after 300 freeze-thaw cycles.

[0052] Comparative Example 1

[0053] Recycled aggregate concrete is characterized by being composed of the following raw materials in parts by weight: 330 parts cement, 100 parts fly ash, 50 parts mineral powder, 880 parts recycled fine aggregate, 1050 parts recycled coarse aggregate, 9 parts water-reducing agent, 2 parts retarder, and 155 parts water.

[0054] This comparative example is a blank example without SAP. The concrete was tested and found to have a 28-day compressive strength of 42.7 MPa, a 28-day tensile strength of 2.9 MPa, a 28-day shrinkage rate of 0.036%, and a mass loss rate of 6.6% after 300 freeze-thaw cycles.

[0055] Comparative Example 2

[0056] Recycled aggregate concrete is characterized by being composed of the following raw materials in parts by weight: 330 parts cement, 100 parts fly ash, 50 parts mineral powder, 880 parts recycled fine aggregate, 1050 parts recycled coarse aggregate, 4 parts acrylamide-type SAP particles, 9 parts water-reducing agent, 2 parts retarder, and 155 parts water.

[0057] The concrete was tested and found to have a 28-day compressive strength of 40.9 MPa, a 28-day tensile strength of 2.6 MPa, a 28-day shrinkage rate of 0.021%, and a mass loss rate of 1.8% after 300 freeze-thaw cycles.

[0058] Comparative Example 3

[0059] Recycled aggregate concrete, characterized in that it is composed of the following raw materials in parts by weight: 330 parts cement, 100 parts fly ash, 50 parts mineral powder, 880 parts recycled fine aggregate, 1050 parts recycled coarse aggregate, 4 parts reinforced SAP particles, 9 parts water-reducing agent, 2 parts retarder, and 155 parts water.

[0060] The enhanced SAP was prepared by the process described in Example 16 of the prior art CN118373644A, and its SAP was enhanced by two layers of silica sol and admixture.

[0061] The concrete was tested and found to have a 28-day compressive strength of 43.1 MPa, a 28-day tensile strength of 3.0 MPa, a 28-day shrinkage rate of 0.022%, and a mass loss rate of 1.4% after 300 freeze-thaw cycles.

[0062] Comparative Example 4

[0063] Recycled aggregate concrete, characterized in that it is composed of the following raw materials in parts by weight: 330 parts cement, 100 parts fly ash, 50 parts mineral powder, 880 parts recycled fine aggregate, 1050 parts recycled coarse aggregate, 4 parts reinforced SAP particles, 9 parts water-reducing agent, 2 parts retarder, and 155 parts water.

[0064] The enhanced SAP manufacturing process is as follows:

[0065] 1) Mix 100 parts acrylic acid, 7 parts acrylamide, and 300 parts water evenly, adjust the pH to 7, add 2 parts crosslinking agent, stir evenly, add 1 part pore-forming agent, 0.5 parts initiator, and 1 part reducing agent to carry out polymerization reaction to obtain gel. Cut the gel into small pieces, dry, and pulverize to obtain SAP particles.

[0066] 2) Ultrasonically mix SAP particles with a suspension containing 4 parts of nano-silica to load the nano-silica into the pores of the SAP particles. Add silane coupling agent for soaking, filter, and dry to obtain the final product.

[0067] The concrete was tested and found to have a 28-day compressive strength of 46.6 MPa, a 28-day tensile strength of 3.4 MPa, a 28-day shrinkage rate of 0.029%, and a mass loss rate of 1.6% after 300 freeze-thaw cycles.

[0068] Comparative Example 5

[0069] Recycled aggregate concrete, characterized in that it is composed of the following raw materials in parts by weight: 330 parts cement, 100 parts fly ash, 50 parts mineral powder, 880 parts recycled fine aggregate, 1050 parts recycled coarse aggregate, 4 parts reinforced SAP particles, 9 parts water-reducing agent, 2 parts retarder, and 155 parts water.

[0070] The enhanced SAP manufacturing process is as follows:

[0071] 1) Mix 100 parts acrylic acid, 5 parts trimethylsilyl methacrylate, 2 parts 4-phenyl-1-butene, and 300 parts water evenly, adjust the pH to 7, add 2 parts crosslinking agent, stir evenly, add 1 part pore-forming agent, 0.5 parts initiator, and 1 part reducing agent to carry out polymerization reaction to obtain gel. Cut the gel into small pieces, dry, and pulverize to obtain SAP particles.

[0072] 2) Soak SAP particles in silane coupling agent, filter, and dry to obtain the final product.

[0073] The concrete was tested and found to have a 28-day compressive strength of 45.0 MPa, a 28-day tensile strength of 3.2 MPa, a 28-day shrinkage rate of 0.025%, and a mass loss rate of 1.7% after 300 freeze-thaw cycles.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. 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. Such 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.

Claims

1. An enhanced recycled aggregate concrete, characterized by, The cement is at least one of Portland cement and ordinary Portland cement. The preparation process of the enhanced SAP particles is as follows: 1) uniformly mix 100 parts of acrylic acid, 3-5 parts of trimethylsilyl methacrylate, 1-3 parts of 4-phenyl-1-butene, and 280-320 parts of water, adjust the pH value to 6-7, add 1-2 parts of a crosslinking agent, uniformly stir, add 0.5-1.5 parts of a pore-forming agent, 0.4-0.6 parts of an initiator, and 1-2 parts of a reducing agent for polymerization, obtain a gel, cut the gel into small pieces, dry, crush, and obtain SAP particles, 2) ultrasonically mix the SAP particles with a 2-4 part nano-silica suspension to load the nano-silica into the pores of the SAP particles, add a silane coupling agent for soaking, filter, and dry to obtain the enhanced SAP particles.

2. The enhanced recycled aggregate concrete according to claim 1, wherein, The cement is at least one of Portland cement and ordinary Portland cement.

3. The enhanced recycled aggregate concrete according to claim 1, wherein The recycled fine aggregate and the recycled coarse aggregate are obtained by crushing and screening construction waste.

4. The enhanced recycled aggregate concrete according to claim 1, wherein The fineness modulus of the recycled fine aggregate is 2.0-2.6, and the particle size of the recycled coarse aggregate is 5-20 mm.

5. The enhanced recycled aggregate concrete according to claim 4, wherein In step 1), the crosslinking agent is N,N'-methylenebisacrylamide, the pore-forming agent is a mixture of methanol, ethanol, and sodium bicarbonate in a mass ratio of (5-7):(0.5-1.5):(2-4), the initiator is ammonium persulfate, and the reducing agent is sodium sulfite.

6. The enhanced recycled aggregate concrete according to claim 5, wherein In step 1), the particle size of the SAP particles is 0.05-0.5 mm.

7. The enhanced recycled aggregate concrete according to claim 6, wherein In step 2), the ultrasonic power is 500-600 W, the ultrasonic frequency is 18-22 kHz, and the ultrasonic time is 0.5-1 h.

8. The enhanced recycled aggregate concrete according to claim 1, wherein The water-reducing agent is polycarboxylic acid water-reducing agent, and the retarder is at least one of tartaric acid, sodium gluconate, and boric acid.

9. The method of producing enhanced recycled aggregate concrete according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: weighing each raw material according to the weight parts, and uniformly mixing each raw material to obtain the cement-based composite material.