In-situ organic-inorganic polymerization modified cement-based material and preparation method thereof

Abstract

The invention provides an in-situ organic-inorganic polymerization modified cement-based material. The modified cement-based material is prepared from 0.5 to 5 parts of modified cement, 0.5 to 5 parts of a monomer, 0.001 to 1 part of an initiator, 100 parts of a cement-based material, 0.1 to 1 part of a water reducing agent, 200 to 300 parts of aggregate and 20 to 50 parts of water, the modified cement is obtained by modifying cement through polymerizable siloxane; the dosage ratio of the polymerizable siloxane to the cement is (0.05-0.3): 1. The method for in-situ construction of a polymerization system in the cement-based material is different from direct addition of a polymer emulsion, cement hydration products and polymers can be connected through chemical bonds by adding organic polymerization monomers and modified cement into cement, and the breaking strength is improved under the condition that the compressive strength is not reduced or even improved to a certain extent.

Description

Technical Field

[0001] This invention relates to the field of cement-based materials technology, specifically to an in-situ organic-inorganic polymer modified cement-based material and its preparation method. Background Technology

[0002] Cement-based composite materials have become a major building material worldwide due to their abundant raw materials, low cost, high strength, and simple production process, and are widely used in large-scale projects such as civil buildings, roads, bridges, airports, ports, and water conservancy. However, cement-based composite materials are inhomogeneous, porous, and brittle materials. When subjected to external loads, stress initially concentrates at defects. Nanocracks are generated at the loosely accumulated hydration products and gradually propagate into micron-sized cracks. Under continuous load, these micron-sized cracks continue to expand and merge, forming macroscopic cracks, ultimately leading to brittle fracture. The presence of pores and cracks not only reduces strength but also induces problems such as infiltration. Infiltrating harmful ions reduce durability, increase maintenance costs, and shorten service life. Therefore, strengthening cement-based composite materials has become one of the current research hotspots.

[0003] Currently, researchers are attempting to improve the brittle properties of cement-based composites by adding reinforcing materials. Studies have shown that introducing high-toughness materials, among which fibers and polymer emulsions are two of the most studied and widely used, has been effective. However, both materials currently have several problems. Fibers are unevenly dispersed during concrete mixing, easily agglomerating, resulting in poor workability and pumping difficulties. Furthermore, since fiber toughening in concrete mainly relies on the pull-in effect to limit crack propagation, the performance of fiber-modified concrete is closely related to the dispersion and orientation of fibers. Therefore, the stability of fiber-modified concrete is relatively difficult to control, requiring careful attention to various aspects in practical applications. Polymer emulsion-modified concrete first appeared in 1923, when the first patent for this concept was granted to Cresson. This patent concerned paving materials using natural rubber latex. Since then, considerable research and development on polymer modification of cement mortar and concrete has been conducted in various countries for 70 years or more. Polymer-modified mortar and concrete using these materials have become popular building materials due to their good cost and cost balance. Over a long period of time, many effective polymer modification systems for cement mortar and concrete have been developed and are now used in various applications in the construction industry. Polymer-based admixtures can be classified by state into polymer emulsions, redispersible polymer powders, water-soluble polymers, and liquid polymers. Currently, polymer emulsions and redispersible polymer powders are the most widely used methods for improving the flexural strength of cement-based materials. However, this improvement in flexural strength often comes at the cost of sacrificing the compressive strength of the cement-based material. For example, in the 2019 work reported by Farshad Farshchi Tabrizi, SBA-modified concrete showed a 22.6% increase in flexural strength, but a significant decrease in compressive strength.

[0004] This decline is mainly due to the lack of activity in traditional additives such as fibers and polymer emulsions. They neither participate in the hydration reaction nor alter the hydration process; their role in concrete is solely related to their own physical properties. They do not modify the microstructure of concrete. This modification is primarily physical. Therefore, finding a chemically active reinforcing material that can interact more with concrete binders is of great significance for preparing high-strength, high-toughness, and long-life cement-based composite materials.

[0005] Patent 202111276847.9 discloses a fiber- and polymer composite modified cement-based repair mortar and its preparation method. The repair mortar comprises raw materials: cement, fly ash, sand, fiber, polymer emulsion, water-reducing agent, and water. Combining fiber toughening modification with polymer reinforcement modification technology allows for complementary advantages. The addition of fiber enhances the fracture resistance of the polymer-modified repair mortar, while the addition of polymer also improves the interfacial strength of the fiber-modified repair mortar. However, in this patent, the fiber and polymer exert their effects independently, without a synergistic effect.

[0006] Patent 202210889246.3 provides an in-situ organic-inorganic polymer-modified cement-based composite material and its preparation method, relating to the field of cement-based materials technology. This invention combines polymer monomers and inorganic nanomaterials, co-polymerizing them in-situ within a cement matrix. Uniformly distributed inorganic nanomaterials are added to the existing polymer network structure, forming an organic-inorganic composite star-chain network structure. The inorganic nanomaterials fill and promote hydration, while simultaneously strengthening the polymer network. The inorganic nanomaterials, polymer, and hydration products form an organic-inorganic interpenetrating network structure. However, in this network structure, the organic network intersperses within the inorganic network, and the interaction between them is purely physical, thus not fully utilizing the effects of the organic network. Summary of the Invention

[0007] Existing technologies for cement modification, which involve directly adding polymers or fibers to cement, suffer from problems such as decreased strength and poor compatibility between organic and inorganic components. This invention provides an in-situ organic-inorganic polymer-modified cement-based material and its preparation method. By using a silane coupling agent to modify cement particles, the organic polymer network can better crosslink with cement hydration products during the later curing process, maximizing the toughening effect of in-situ polymerization. Furthermore, the preparation method of this application is simple, convenient to construct, and has great application potential.

[0008] An in-situ organic-inorganic polymer modified cement-based material, wherein the modified cement-based material comprises 0.5-5 parts of modified cement, 0.5-5 parts of monomer, 0.001-1 parts of initiator, 100 parts of cement-based material, 0.1-1 parts of water-reducing agent, 340 parts of aggregate, and 20-50 parts of water.

[0009] The modified cement is obtained by modifying cement with polymerizable siloxanes; the cement is a binder component that can participate in the CSH generation process, that is, a cement component containing common mineral clinker components; the selected silane coupling agent modifies the cement particles so that the organic polymer network can better crosslink with the cement hydration products during the later curing process, and exert the toughening effect of in-situ polymerization to a greater extent.

[0010] The ratio of polymerizable siloxane to cement is (0.05-0.3):1.

[0011] The above polymerizable siloxane structure contains at least one vinyl group.

[0012] The polymerizable siloxanes mentioned above are any one or a mixture of two or more of the following: vinyltrimethoxysilane (VTMS), vinyltriethoxysilane (VTES), methacryloyloxypropyltrimethoxysilane (MAPTMS), methacryloyloxypropyltriethoxysilane (MAPTES), methacryloyloxymethyltriethoxysilane (AAPTES), acryloyloxymethyltrimethoxysilane (AAMTMS), and acryloyloxypropyltrimethoxysilane (AAPTMS).

[0013] The amount of modified cement used is 0.5-5% of the amount of binder in cement-based materials.

[0014] The monomers mentioned above are any one or a mixture of two or more of the following general formulas (1)-(4):

[0015] (1)

[0016] (2)

[0017] (3)

[0018] (3)

[0019] Wherein, R1 is H, CH3 or CH3COOH, and R2 is H or an active metal ion;

[0020] R3 is H or CH3, and R4 and R5 are independently H, CH3, CH2CH3, CH2OH, CH2CH2OH, and CH2CHCH3OH, respectively.

[0021] R6, R7, and R8 are each independently H or CH3; R9 is an alkyl group with 4-30 carbon atoms; X1, X2, and X3 are each independently O or NH; and the values ​​of a and b range from 4 to 50.

[0022] The amount of monomer used is 0.5-5% of the amount of binder in cement-based materials. When using monomer, it needs to be prepared into a solution, and the water used should be 70% of the total water mass. The mass fraction of the monomer solution is 1.4-23%.

[0023] The aforementioned initiators are thermal initiators of the medium temperature range (30–100°C) and redox initiation systems.

[0024] The aforementioned thermal initiator is any one or a mixture of two or more of the following in any proportion: azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobisisobutylamidine hydrochloride, ammonium persulfate, azobiscyanopentanoic acid, tetratert-butyl peroxide, benzoyl peroxide, and tert-butyl peroxide; the aforementioned redox system is composed of a persulfate or peroxide as an oxidant and a sulfite or organic amine as a reducing agent.

[0025] The oxidizing agent is at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent is one or more of ferrous sulfate, oxalic acid, glucose, sodium sulfite, sodium bisulfite, sodium metabisulfite, triethanolamine, and triisopropanolamine; the amount of reducing agent used is 50-200% of the oxidizing agent.

[0026] The amount of initiator used is 0.2-10% of the monomer. The initiator needs to be prepared as a solution before application. The mass fraction of the oxidant or thermal initiator solution is 0.00009-0.075%. The reducing agent needs to be dissolved in the monomer solution before application.

[0027] The aforementioned in-situ organic-inorganic polymer-modified cementitious material possesses an organic-inorganic composite star-chain network structure. Unlike other organic-inorganic hybrid modified cementitious materials, the organic polymer network in the in-situ organic-inorganic polymer-modified cementitious material constructed in this invention is chemically bonded to the surface of the inorganic components, greatly enhancing the effect of the polymer network.

[0028] A method for preparing an in-situ organic-inorganic polymer modified cement-based material includes the following steps: (1) modifying cement with polymerizable siloxane to obtain modified cement; (2) preparing monomers and initiators into solutions as mixing liquids; (3) mixing the mixing liquid, water-reducing agent, aggregate, modified cement and cement-based material in step (2), and obtaining the in-situ organic-inorganic polymer modified cement-based material after curing.

[0029] The specific steps of step (1) above are as follows: Under the condition of 60℃, the toluene solution containing polymerizable siloxane and hydrochloric acid are slowly added dropwise or directly added to the toluene containing cement; after the dropwise addition is completed, the reaction is maintained at 60℃ for 1.5h, and then the temperature is raised to 80℃ for 10h; then the mixture is extracted, washed and vacuum dried at 90℃ for 24h; finally, it is ground in a mortar and sieved to ensure that the particle size is <38um, which is the modified cement.

[0030] The mass fraction of toluene solutions containing polymerizable siloxanes is 0.5-2%; the mass fraction of toluene dispersions in cement is 3-30%.

[0031] This application has the following advantages over the prior art:

[0032] (1) This invention utilizes a method to chemically bond hydrated particles and polymer networks in cement-based hybrid materials, thereby constructing an organic-inorganic hybrid network at the microscopic level within cement, combining polymers and hydrated particles to enhance concrete toughness. The organic and inorganic components of the aforementioned organic-inorganic hybrid network particles are interconnected by chemical bonds. The hybridization of the organic and inorganic components is characterized by the inorganic portion being the dominant component, while the organic portion consists of interconnected, non-connected inorganic components forming a network. The organic portion is an organic polymer skeleton formed by the free radical polymerization of polymerizable monomers and modified functional groups on modified cement. This polymerization process occurs after the addition of organically polymerized siloxane-modified cement and monomers to the cement-based hybrid material.

[0033] (2) The modified cement used introduces functional groups with double bonds into the hydrated calcium silicate gel during hydration. Subsequently, the double bonds on the calcium silicate gel undergo free radical polymerization with the added polymerizable monomers to form an organic-inorganic hybrid network. Different calcium silicate gels are connected on the formed hybrid network, which optimizes the defects of short-range order and long-range disorder at the microscale of cement-based materials, thereby achieving the purpose of improving the mechanical properties of cement-based materials.

[0034] (3) The above-mentioned in-situ construction of a polymer system in cement-based materials is different from the direct addition of polymer emulsion. By adding organic polymer monomers and modified cement to cement, cement hydration products and polymers can be connected by chemical bonds, thereby improving flexural strength while ensuring that compressive strength does not decrease or even increases.

[0035] (4) Compared with the traditional method of directly adding polymer emulsions or fibers, this method requires less organic monomer addition and has no negative impact on the workability of cement-based materials; in fact, it may even improve workability under certain conditions. Compared with the traditional method of adding polymer emulsions or in-situ polymerization, this method can more effectively utilize the role of the organic polymer network in cement-based materials, that is, by linking organic and inorganic components through chemical bonds, it can more effectively improve flexural strength. Attached Figure Description

[0036] Figure 1 Comparison of SEM images of Example 2 and the baseline sample at 28 days of age;

[0037] Figure 2 This is a comparison image of the N element distribution in Example 2 and the reference sample after 28 days of SEM-mapping. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] The monomer structures and their corresponding names used in the following embodiments are shown in Table 1 below:

[0040] Table 1

[0041]

[0042]

[0043] Example 1

[0044] (1) Add 10 parts cement and 300 parts toluene to the reactor, stir evenly, and then add 100 parts of a 2wt% AAPTES toluene solution and 0.2 parts hydrochloric acid dropwise at a rate of 3 ml / min at 60℃. After the addition is completed, maintain the temperature at 60℃ for 1.5 h, then raise the temperature to 80℃ and maintain it for 10 h. Wash with Soxhlet extraction of toluene, and finally vacuum dry at 90℃ for 24 h in a vacuum drying oven to obtain the product modified cement particles. The obtained product is ground in a mortar and sieved to ensure that the particle size is <38 μm.

[0045] (2) Mix 0.02 parts of triisopropanolamine, 0.5 parts of polymerizable monomer P1 and 30 parts of water thoroughly to make mixing solution A.

[0046] (3) Mix 0.02 parts of potassium persulfate with 5 parts of water thoroughly to make mixing solution B.

[0047] (4) Mix standard sand, water-reducing agent, cement-based materials, mixing liquid A, mixing liquid B, and modified cement in a ratio of 225:0.3:100:30.5:5:1 using automatic mixing. The mixing process is as follows: low speed mixing for 60 seconds - high speed mixing for 30 seconds - stop mixing for 90 seconds, high speed mixing for 60 seconds, for a total of 4 minutes. Place the resulting cement paste in a 40*40*160mm mold. After hardening, remove the mold and mark the sample obtained after curing to the required age as specimen block AS1. This specimen block is the one with an internal organic-inorganic hybrid network.

[0048] Example 2

[0049] (1) Add 10 parts of Onoda cement and 300 parts of toluene to the reactor. After stirring evenly, add 100 parts of a 1 wt% AAPTES toluene solution and 0.2 parts of hydrochloric acid dropwise at a rate of 3 ml / min at 60°C. After the addition is complete, maintain the temperature at 60°C for 1.5 h, then raise the temperature to 80°C and maintain it for 10 h. Wash with Soxhlet extraction of toluene, and finally vacuum dry at 90°C for 24 h in a vacuum drying oven to obtain the product modified cement particles. The obtained product is ground in a mortar and sieved to ensure that the particle size is <38 μm.

[0050] (2) Mix 0.02 parts of triisopropanolamine, 2.5 parts of polymerizable monomer P4 and 30 parts of water thoroughly to make mixing solution A.

[0051] (3) Mix 0.02 parts of potassium persulfate with 5 parts of water thoroughly to make mixing solution B.

[0052] (4) Mix standard sand, water-reducing agent, cement-based materials, mixing liquid A, mixing liquid B, and modified cement particles in a ratio of 200:0.3:100:32.5:5:1 using automatic mixing. The mixing process is as follows: low speed mixing for 60 seconds - high speed mixing for 30 seconds - stop mixing for 90 seconds, high speed mixing for 60 seconds, for a total of 4 minutes. Place the resulting cement paste in a 40*40*160mm mold. After hardening, remove the mold and cure until the desired curing age. The resulting sample is marked as specimen block AS2. This specimen block is the one with an internal organic-inorganic hybrid network.

[0053] Example 3

[0054] (1) Add 10 parts cement and 300 parts toluene to the reactor, stir evenly, and then add 100 parts of a 1wt% AAPTES toluene solution and 0.2 parts hydrochloric acid dropwise at a rate of 3 ml / min at 60℃. After the addition is completed, maintain the temperature at 60℃ for 1.5 h, then raise the temperature to 80℃ and maintain it for 10 h. Wash with Soxhlet extraction of toluene, and finally vacuum dry at 90℃ for 24 h in a vacuum drying oven to obtain the product modified cement particles. The obtained product is ground in a mortar and sieved to ensure that the particle size is <38 μm.

[0055] (2) Mix 0.02 parts of triisopropanolamine, 5 parts of polymerizable monomer P3 and 30 parts of water thoroughly to make mixing solution A.

[0056] (3) Mix 0.02 parts of potassium persulfate with 5 parts of water thoroughly to make mixing solution B.

[0057] (4) Mix standard sand, water-reducing agent, cement-based materials, mixing liquid A, mixing liquid B, and modified cement particles in a ratio of 300:0.3:100:35:5:1 using automatic mixing. The mixing process is as follows: low speed mixing for 60 seconds - high speed mixing for 30 seconds - stop mixing for 90 seconds, high speed mixing for 60 seconds, for a total of 4 minutes. Place the resulting cement paste in a 40*40*160mm mold. After hardening, remove the mold and mark the sample obtained after curing to the required age as specimen block AS3. This specimen block is the one with an internal organic-inorganic hybrid network.

[0058] Example 4

[0059] (1) Add 10 parts cement and 300 parts toluene to the reactor, stir evenly, and then add 100 parts of a 2wt% AAPTES toluene solution and 0.2 parts hydrochloric acid dropwise at a rate of 3 ml / min at 60℃. After the addition is completed, maintain the temperature at 60℃ for 1.5 h, then raise the temperature to 80℃ and maintain it for 10 h. Wash with Soxhlet extraction of toluene, and finally vacuum dry at 90℃ for 24 h in a vacuum drying oven to obtain the product modified cement particles. The obtained product is ground in a mortar and sieved to ensure that the particle size is <38 μm.

[0060] (2) Mix 0.02 parts of triisopropanolamine, 0.5 parts of polymerizable monomer P4 and 30 parts of water thoroughly to make mixing solution A.

[0061] (3) Mix 0.02 parts of potassium persulfate with 5 parts of water thoroughly to make mixing solution B.

[0062] (4) Mix standard sand, water-reducing agent, cement-based materials, mixing liquid A, mixing liquid B, and modified cement particles in a ratio of 225:0.3:100:30.5:5:1 using automatic mixing. The mixing process is as follows: low speed mixing for 60 seconds - high speed mixing for 30 seconds - stop mixing for 90 seconds, high speed mixing for 60 seconds, for a total of 4 minutes. Place the resulting cement paste in a 40*40*160mm mold. After hardening, remove the mold and cure until the desired curing age. The resulting sample is marked as specimen block AS4. This specimen block is the one with an internal organic-inorganic hybrid network.

[0063] Example 5

[0064] (1) Add 10 parts cement and 300 parts toluene to the reactor, stir evenly, and then add 100 parts of a 1wt% AAPTES toluene solution and 0.2 parts hydrochloric acid dropwise at a rate of 3 ml / min at 60℃. After the addition is completed, maintain the temperature at 60℃ for 1.5 h, then raise the temperature to 80℃ and maintain it for 10 h. Wash with Soxhlet extraction of toluene, and finally vacuum dry at 90℃ for 24 h in a vacuum drying oven to obtain the product modified cement particles. The obtained product is ground in a mortar and sieved to ensure that the particle size is <38 μm.

[0065] (2) Mix 0.02 parts of triisopropanolamine, 0.5 parts of polymerizable monomer P5 and 30 parts of water thoroughly to make mixing solution A.

[0066] (3) Mix 0.02 parts of potassium persulfate with 5 parts of water thoroughly to make mixing solution B.

[0067] (4) Mix standard sand, water-reducing agent, cement-based materials, mixing liquid A, mixing liquid B, and modified cement particles in a ratio of 225:0.3:100:30.5:5:1 using automatic mixing. The mixing process is as follows: low speed mixing for 60 seconds - high speed mixing for 30 seconds - stop mixing for 90 seconds, high speed mixing for 60 seconds, for a total of 4 minutes. Place the resulting cement paste in a 40*40*160mm mold. After hardening, remove the mold and mark the sample obtained after curing to the required age as specimen block AS5. This specimen block is the one with an internal organic-inorganic hybrid network.

[0068] Example 6

[0069] (1) Add 10 parts cement and 300 parts toluene to the reactor, stir evenly, and then add 100 parts of a 2wt% AAPTES toluene solution and 0.2 parts hydrochloric acid dropwise at a rate of 3 ml / min at 60℃. After the addition is completed, maintain the temperature at 60℃ for 1.5 h, then raise the temperature to 80℃ and maintain it for 10 h. Wash with Soxhlet extraction of toluene, and finally vacuum dry at 90℃ for 24 h in a vacuum drying oven to obtain the product modified cement particles. The obtained product is ground in a mortar and sieved to ensure that the particle size is <38 μm.

[0070] (2) Mix 0.5 parts of polymerizable monomer P4 with 30 parts of water thoroughly to make mixing liquid A.

[0071] (3) Mix 0.04 parts of ammonium persulfate with 5 parts of water thoroughly to make mixing solution B.

[0072] (4) Standard sand, water-reducing agent, cement-based materials, mixing liquid A, mixing liquid B, and modified cement particles were mixed in a ratio of 225:0.3:100:30.5:5:1 using automatic mixing. The mixing process was as follows: low speed mixing for 60 seconds - high speed mixing for 30 seconds - stop mixing for 90 seconds, then high speed mixing for 60 seconds, for a total of 4 minutes. The resulting cement paste was placed in a 40*40*160mm mold. After hardening, the mold was removed, and the sample was steam-cured at 60℃ for 48 hours. The sample obtained after curing was marked as specimen block AS5. This specimen block is the one with an internal organic-inorganic hybrid network.

[0073] Comparative Example 1

[0074] (1) Add 10 parts cement and 300 parts toluene to the reactor, stir evenly, and then add 100 parts toluene solution and 0.2 parts hydrochloric acid dropwise at a rate of 3 ml / min at 60℃. After the addition is completed, maintain the temperature at 60℃ for 1.5 h, then raise the temperature to 80℃ and maintain it for 10 h. Wash with toluene using Soxhlet extraction, and finally vacuum dry at 90℃ for 24 h in a vacuum drying oven to obtain product J-cement particles. The obtained product is ground in a mortar and sieved to ensure that the particle size is <38 μm.

[0075] (2) Mix 0.02 parts of triisopropanolamine, 2.5 parts of polymerizable monomer P1 and 30 parts of water thoroughly to make mixing solution A.

[0076] (3) Mix 0.02 parts of potassium persulfate with 5 parts of water thoroughly to make mixing solution B.

[0077] (4) Mix standard sand, water-reducing agent, cement-based materials, mixing liquid A, mixing liquid B, and cement particles J in a ratio of 225:0.3:100:32.5:5:1 using automatic mixing. The mixing process is as follows: low speed mixing for 60 seconds - high speed mixing for 30 seconds - stop mixing for 90 seconds, then high speed mixing for 60 seconds, for a total of 4 minutes. Place the resulting cement paste in a 40*40*160mm mold. After hardening, remove the mold and mark the sample obtained after curing to the required age as specimen block R1.

[0078] Comparative Example 2

[0079] (1) Add 10 parts cement and 300 parts toluene to the reactor, stir evenly, and then add 100 parts of a 2wt% AAPTES toluene solution and 0.2 parts hydrochloric acid dropwise at a rate of 3 ml / min at 60℃. After the addition is completed, maintain the temperature at 60℃ for 1.5 h, then raise the temperature to 80℃ and maintain it for 10 h. Wash with Soxhlet extraction of toluene, and finally vacuum dry at 90℃ for 24 h in a vacuum drying oven to obtain the product modified cement particles. The obtained product is ground in a mortar and sieved to ensure that the particle size is <38 μm.

[0080] (2) Mix 0.02 parts of triisopropanolamine and 30 parts of water thoroughly to make mixing solution A.

[0081] (3) Mix 0.02 parts of potassium persulfate with 5 parts of water thoroughly to make mixing solution B.

[0082] (4) Mix standard sand, water-reducing agent, cement-based materials, mixing liquid A, mixing liquid B, and modified cement in a ratio of 225:0.3:100:30:5:1 using automatic mixing. The mixing process is as follows: low speed mixing for 60 seconds - high speed mixing for 30 seconds - stop mixing for 90 seconds, then high speed mixing for 60 seconds, for a total of 4 minutes. Place the resulting cement paste in a 40*40*160mm mold. After hardening, remove the mold and mark the sample obtained after curing to the required age as specimen block R2.

[0083] Comparative Example 3

[0084] (1) Add 10 parts cement and 300 parts toluene to the reactor, stir evenly, and then add 100 parts toluene solution and 0.2 parts hydrochloric acid dropwise at a rate of 3 ml / min at 60℃. After the addition is completed, maintain the temperature at 60℃ for 1.5 h, then raise the temperature to 80℃ and maintain it for 10 h. Wash with toluene using Soxhlet extraction, and finally vacuum dry at 90℃ for 24 h in a vacuum drying oven to obtain product J-cement particles. The obtained product is ground in a mortar and sieved to ensure that the particle size is <38 μm.

[0085] (2) 0.02 parts of triisopropanolamine, 0.02 parts of potassium persulfate, 0.5 parts of polymerizable monomer P4, 20 parts of 10% AAPTES ethanol solution and 70 parts of water were thoroughly mixed and reacted at 60°C for 5 hours. After the reaction was completed, the solvent small molecules were removed by dialysis to obtain an aqueous solution of sodium polymethacrylate with siloxane.

[0086] (3) Mix standard sand, water-reducing agent, cement-based materials, sodium polymethyl methacrylate aqueous solution, and J-cement particles in a ratio of 225:0.3:100:37.5:1 using an automatic mixing system. The mixing process is as follows: low speed mixing for 60 seconds - high speed mixing for 30 seconds - stop mixing for 90 seconds, then high speed mixing for 60 seconds, for a total of 4 minutes. Place the resulting cement paste in a 40*40*160mm mold. After hardening, remove the mold and mark the resulting sample as specimen block R3 after curing to the designated age.

[0087] Comparative Example 4

[0088] (1) Standard sand, water-reducing agent, cement, water, and polyacrylamide emulsion were mixed in a ratio of 225:0.3:100:32.5:5 using an automatic mixer. The mixing process was as follows: low speed for 60 seconds, high speed for 30 seconds, stop mixing for 90 seconds, and then high speed for 60 seconds, for a total of 4 minutes. The resulting cement paste was placed in a 40*40*160mm mold. After hardening, the mold was removed, and the samples obtained after curing to the designated age were marked as R4 test blocks.

[0089] Comparative Example 5

[0090] Commercially available nano-silica, purchased from Aladdin, with a particle size of 15 nanometers, was used. Standard sand, water-reducing agent, cement, water, and nano-silica were mixed in a ratio of 225:0.3:100:32.5:0.2 using an automatic mixer. The mixing process was as follows: low speed for 60 seconds, high speed for 30 seconds, stop mixing for 90 seconds, then high speed for 60 seconds, for a total of 4 minutes. The resulting cement paste was placed in a 40*40*160mm mold. After hardening, the mold was removed, and the samples obtained after curing to the designated age were marked as R5 test blocks.

[0091] Test Example 1: Mortar Mechanical Property Test

[0092] ISO standard sand was prepared with a sand-to-cement ratio of 3:1 and a water-to-cement ratio of 0.36. Onoda P·11·52.5 cement was used, and the water-reducing agent was PCAR-I, a commercially available polycarboxylate superplasticizer from Subote Corporation. The fluidity of each mortar group was kept consistent by controlling the amount of water-reducing agent used. Specimens prepared in Examples 1-6 and Comparative Examples 1-4 were cured at 25°C and above 95% humidity after molding. As a comparison, a reference sample was prepared with a sand-to-cement ratio of 3:1 and a water-to-cement ratio of 0.36, without the addition of in-situ polymerizable monomers and modified cement, and prepared under the same conditions as Example 1. The test methods are referenced in (Construction and Building Materials, 2013, 49, 121). The test results are shown in Table 2.

[0093] Table 2

[0094]

[0095] As can be seen from the mortar mechanical property data in Table 2, under the same water-cement ratio, the hardened mortar with an internally constructed in-situ polymer network obtained in the embodiments of the present invention has the following advantages: it can significantly improve early mechanical properties. Sample AS1 can improve 7-day flexural strength by 23% and 7-day compressive strength by 30%, and this improvement effect can continue to increase with the increase of admixture dosage. Sample AS3, which has the best improvement effect, can improve 7-day flexural strength by 34% and compressive strength by 28%. However, sample R1, which does not involve modified cement particles, can only improve flexural strength by 10% and compressive strength by 12%. Sample R2, which only involves modified cement particles but does not have polymer monomers and cannot polymerize, shows a 1% decrease in 7-day flexural strength and a 3% decrease in compressive strength. In R3, since the monomer and siloxane are reacted first to obtain a modified polyacrylamide emulsion, the results show that this modified emulsion can improve toughness better than directly adding polymer emulsion (R4), but the improvement effect is far lower than the in-situ polymerization of the embodiments and R1. Sample R4, which directly adds polymer emulsion, can improve early flexural strength by 7% and decrease compressive strength by 7%. Regarding later-stage mechanical properties, Example 1 using the method of this invention can also improve 28-day compressive strength by 11% and flexural strength by 10%. AS3 obtained using Example 3 can improve flexural strength by 24% and compressive strength by 11%. Among these, the sample without modified cement particles only improved flexural strength by 10%, while compressive strength decreased by 7%. Example 6, due to the use of thermal initiation technology and early steam curing, exhibited significantly higher early-stage mechanical properties than other blank samples, with the improvement gradually decreasing in the later stages. Compared to ordinary in-situ polymerization, samples doped with modified cement particles to construct an organic-inorganic hybrid can comprehensively improve the compressive and flexural strength of mortar, demonstrating a clear advantage.

[0096] Test Example 2: Liquidity Test

[0097] The cement paste used was Onoda P11.52.5 cement with a water-cement ratio of 0.3. The admixture dosage was calculated based on the reduced weight of the cementitious material (unit: mass percentage, %bwoc). The water-reducing agent used was PCAR-I, a commercially available polycarboxylate superplasticizer from Subote Company. Specific test methods were performed in accordance with the relevant provisions of GB8077-2000 "Test Method for Homogeneity of Concrete Admixtures". The test results are shown in Table 3 below:

[0098] Table 3

[0099]

[0100] As can be seen from the workability data of the neat cement paste in Table 3, under the same water-cement ratio and the same amount of water-reducing agent, the modified neat cement paste obtained in the embodiments of the present invention can improve the workability (specifically, the fluidity) of the neat cement paste, and the improvement effect is more obvious in some of the embodiments. In Comparative Example 1, the direct addition of unmodified cement particles to the cement-based material is equivalent to a slight reduction in the water-cement ratio of the paste, so the workability is lower than that of Example 2, but because the amount added is too small, it has no significant impact on the workability. In Comparative Example 2, only modified cement particles were added. Due to the modified functional groups on the surface of these modified cement particles, the overall air content increases, which improves the workability of the sample. Comparative Examples 3 and 4 directly added polymer emulsions, which leads to a slight increase in fluidity, but the effect is not as good as that of Comparative Example 1, which directly added monomers. Comparative Example 5 used commercially available nano-silica at a dosage of 0.2%. It can be seen that this common powder material significantly reduces the early fluidity of the paste, affecting the workability of the paste.

[0101] This application compares the SEM images and SEM-mapping N element distribution images of the baseline sample and the sample from Example 2 at 28 days of age, as well as the SEM-mapping images of the N element distribution. Figure 1 and Figure 2 As shown, it can be seen that there is almost no nitrogen element in the reference sample. However, since 2.5% of P4 was added in Example 2 to form a polymer gel network that is uniformly distributed in the cement through in-situ polymerization, the nitrogen element can be seen to be uniformly distributed in the nitrogen element distribution diagram. This indirectly proves that the in-situ organic-inorganic polymer modified cement-based material of this application has an organic-inorganic composite star chain network structure.

[0102] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An in-situ organic-inorganic polymer-modified cementitious material, characterized in that: The modified cement-based material comprises 0.5-5 parts modified cement, 0.5-5 parts monomer, 0.001-1 part initiator, 100 parts cement-based material, 0.1-1 part water-reducing agent, 200-300 parts aggregate, and 20-50 parts water. The modified cement is obtained by modifying cement with polymerizable siloxanes; The monomer structure contains at least one unsaturated double bond, and the amount of monomer used is 0.5-5% of the amount of adhesive in the cement-based material, with a mass fraction of 1.4-23%. The amount of initiator used is 0.2-10% of the monomer, and the mass fraction of the initiator solution is 0.00009-0.075%.

2. The in-situ organic-inorganic polymer modified cementitious material according to claim 1, characterized in that: The polymerizable siloxane structure contains at least one unsaturated double bond, and the ratio of the polymerizable siloxane to cement is (0.05-0.3):

1.

3. The in-situ organic-inorganic polymer modified cementitious material according to claim 2, characterized in that: The polymerizable siloxane is any one or a mixture of two or more of vinyltrimethoxysilane, vinyltriethoxysilane, methacryloyloxypropyltrimethoxysilane, methacryloyloxypropyltriethoxysilane, methacryloyloxymethyltriethoxysilane, acryloyloxymethyltrimethoxysilane, and acryloyloxypropyltrimethoxysilane in any proportion.

4. The in-situ organic-inorganic polymer modified cementitious material according to claim 1, characterized in that: The monomer is any one or a mixture of two or more of the following general formulas (1)-(4): (1) (2) (3) (4) Wherein, R1 is H, CH3 or CH3COOH, and R2 is H or an active metal ion; R3 is H or CH3, and R4 and R5 are independently H, CH3, CH2CH3, CH2OH, CH2CH2OH, and CH2CHCH3OH, respectively. R6, R7, and R8 are each independently H or CH3; R9 is an alkyl group with 4-30 carbon atoms; X1, X2, and X3 are each independently O or NH; and the values ​​of a and b range from 4 to 50.

5. The in-situ organic-inorganic polymer modified cementitious material according to claim 1, characterized in that: The initiator is a medium-temperature (30-100℃) thermal initiator or a redox initiation system.

6. The in-situ organic-inorganic polymer modified cementitious material according to claim 1, characterized in that: The thermal initiator is any one or a mixture of two or more of the following in any proportion: azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobisisobutylamidine hydrochloride, ammonium persulfate, azobiscyanopentanoic acid, tetratert-butyl peroxide, benzoyl peroxide, and tert-butyl peroxide; the redox system consists of a persulfate or peroxide as an oxidant and a sulfite or organic amine as a reducing agent.

7. The in-situ organic-inorganic polymer modified cementitious material according to claim 1, characterized in that: The oxidant is at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent is one or more of ferrous sulfate, oxalic acid, glucose, sodium sulfite, sodium bisulfite, sodium metabisulfite, triethanolamine, and triisopropanolamine; the amount of reducing agent used is 50-200% of the oxidant.

8. A method for preparing an in-situ organic-inorganic polymer-modified cementitious material according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Modified cement is obtained by modifying cement with polymerizable siloxane; (2) Prepare solutions of monomer and initiator separately as mixing liquid; (3) Mix the mixing liquid, water-reducing agent, aggregate, modified cement and cement in step (2), and after solidification, obtain in-situ organic-inorganic polymer modified cement-based material.

9. The method for preparing an in-situ organic-inorganic polymer-modified cementitious material according to claim 8, characterized in that, The specific steps of step (1) are as follows: at 60°C, a toluene solution containing polymerizable siloxane and hydrochloric acid are slowly added dropwise or directly to a toluene solution containing cement; after the addition is completed, the reaction is maintained at 60°C for 1.5 hours, and then the temperature is raised to 80°C for 10 hours; then the mixture is extracted, washed, and vacuum dried at 90°C for 24 hours; finally, it is ground in a mortar and sieved to ensure that the particle size is <38 μm, which is the modified cement.

10. The method for preparing an in-situ organic-inorganic polymer-modified cementitious material according to claim 8, characterized in that: The monomer mass fraction in the monomer solution prepared in step (2) is 1.4-23%; the initiator mass fraction in the initiator solution prepared in step (2) is 0.00009-0.075%.

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