A polyvinyl alcohol fiber reinforced concrete and its manufacturing method

Abstract

The present invention relates to the technical field of concrete, and specifically to a polyvinyl alcohol fiber-reinforced concrete and a manufacturing method thereof. The present invention overcomes the problem of poor durability of the concrete after construction. The synthetic raw materials of the present invention include composite cement, composite aggregate, polyvinyl alcohol fiber, modified water reducer, modified strengthening agent, self-healing capsule and deionized water. The present invention first combines the composite cement and the composite aggregate and controls the stirring time to improve the compressive strength of the concrete; then adds the prepared modified water reducer and modified strengthening agent to improve the flexural strength of the concrete; then prepares the self-healing capsule and makes it synergistically act with the modified strengthening agent to improve the density and compressive strength of the concrete; finally, introduces the polyvinyl alcohol fiber to synergistically act with the composite cement to improve the splitting tensile strength of the concrete, so as to improve the durability of the concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and specifically to a polyvinyl alcohol fiber reinforced concrete and a manufacturing method thereof. Background Art

[0002] Concrete is the most commonly used raw material in the fields of construction, municipal engineering, etc. With the development of construction projects and infrastructure, people have begun to have higher requirements for the performance of traditional concrete. Although ordinary concrete has the advantage of high compressive strength, its disadvantages such as low tensile strength and easy cracking have gradually emerged. Under some complex stress and harsh environmental conditions, its durability and safety are also challenged; although reinforced concrete can avoid the increase in brittleness of ordinary concrete and effectively improve the problem of poor toughness of ordinary concrete, the cracking strength has not been improved. After the concrete cracks, the steel bars lose protection and corrode, seriously affecting the durability of the reinforced concrete structure.

[0003] In order to conform to the development of the industry, people have begun to try to add various materials to concrete to improve the safety, durability and seismic resistance of the structure. In this process, fiber materials have begun to be introduced. In the early 20th century, some researchers tried to add steel fibers to concrete, which was an early exploration of fiber reinforced concrete. The addition of steel fibers improved the tensile strength and crack resistance of concrete to a certain extent, but due to the limited understanding of material properties and processing technology at that time, the effect was not very ideal. The workability and construction performance of the concrete after adding steel fibers became worse instead, and the steel fibers were prone to agglomeration, affecting the uniformity of the concrete.

[0004] With the continuous emergence of various new fiber materials, in addition to steel fibers, materials such as glass fibers and polypropylene fibers have begun to appear, and the performance characteristics and application scopes of different fiber materials have been further explored. Among them, polyvinyl alcohol fiber reinforced concrete has also been developed. Polyvinyl alcohol fibers have good adhesion and crack resistance, and show good application prospects in some structures that require high crack resistance and toughness, but at the same time, problems such as low compressive strength and poor toughness have also emerged.

[0005] Therefore, the current concrete still has the disadvantages of poor toughness, low compressive strength and easy cracking, resulting in poor durability of the constructed concrete, which limits its industrial use.

[0006] For this reason, a polyvinyl alcohol fiber reinforced concrete and a manufacturing method thereof are proposed. Summary of the Invention

[0007] The object of the present invention is to design a polyvinyl alcohol fiber reinforced concrete and its manufacturing method. The synthetic raw materials of the present invention include composite cement, composite aggregate, polyvinyl alcohol fiber, modified water reducer, modified strengthening agent, self-healing capsule and deionized water. The present invention first combines the composite cement and the composite aggregate and controls the stirring time to improve the compressive strength of the concrete; then adds the prepared modified water reducer and modified strengthening agent to improve the flexural strength of the concrete; then prepares the self-healing capsule and makes it act synergistically with the modified strengthening agent to improve the density and compressive strength of the concrete; finally, introduces the polyvinyl alcohol fiber to act synergistically with the composite cement to improve the splitting tensile strength of the concrete, so as to improve the durability of the concrete.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] On the one hand, the present invention provides a polyvinyl alcohol fiber reinforced concrete. In terms of parts by weight, the polyvinyl alcohol fiber reinforced concrete includes the following components:

[0010] Composite cement: 600 - 700 parts; deionized water: 200 parts; composite aggregate: 150 - 190 parts; polyvinyl alcohol fiber: 46 - 50 parts; modified water reducer: 11 - 15 parts; modified strengthening agent: 5 - 7 parts; self-healing capsule: 3 - 7 parts;

[0011] The composite cement includes portland cement, sand, silica fume and fly ash;

[0012] The polyvinyl alcohol fiber includes polyvinyl alcohol chips and diatomite;

[0013] The modified water reducer includes calcium lignosulfonate and styrene;

[0014] The modified strengthening agent includes nano calcium carbonate and γ-glycidoxypropyltrimethoxysilane;

[0015] The self-healing capsule includes methyl methacrylate and sodium alginate.

[0016] Preferably, the composite aggregate is composed of a mixture of limestone particles and basalt particles. The weight ratio of the limestone particles to the basalt particles is 3:2. The particle size of the limestone particles is 15 mm - 19 mm, and the particle size of the basalt particles is 6 mm - 8 mm.

[0017] On the other hand, the present invention provides a manufacturing method of the polyvinyl alcohol fiber reinforced concrete. The manufacturing method is as follows:

[0018] S1 Mix 600 - 700 parts of composite cement, 150 - 190 parts of composite aggregate and 150 parts of deionized water, with a stirring speed of 800 rpm and a stirring time of 50 min - 70 min to obtain a cement slurry;

[0019] S2 puts the cement slurry, 11 - 15 parts of modified water reducer, 5 - 7 parts of modified strengthening agent, 3 - 7 parts of self - healing capsules and 50 parts of deionized water into a blender and stirs at a speed of 1100 rpm for 70 min - 90 min to obtain a mixed slurry;

[0020] S3 puts 46 - 50 parts of polyvinyl alcohol fibers into the mixed slurry and continues to stir at a speed of 900 rpm for 50 min - 90 min to obtain a concrete slurry;

[0021] S4 pours the concrete slurry into a mold, and after molding, sprays water for curing under the conditions of a temperature of 24°C and a humidity of 60%. After 7 days, polyvinyl alcohol fiber - reinforced concrete is obtained.

[0022] Preferably, the preparation method of the composite cement in S1 is: putting Portland cement, sand, silica fume and fly ash into a grinder according to the weight ratio, using deionized water as the medium, grinding for 2 h - 4 h, and drying to obtain the composite cement; the weight ratio is 6 - 10:6:2:1.

[0023] Preferably, the preparation method of the modified water reducer in S2 is: putting 5 - 9 parts of calcium lignosulfonate and 20 parts of deionized water into a three - necked flask, stirring at 80°C for 30 min to form solution A; dissolving 1 part of styrene in 5 parts of acetone to form solution B; dissolving 1 part of potassium persulfate in 5 parts of deionized water to form solution C; adding solution B dropwise to solution A during heating and stirring, and the dropping time is 20 min to obtain solution D; then adding solution C dropwise to solution D, the dropping time is 60 min - 80 min, and continuing to react for 6 h to obtain solution E; centrifuging, washing and drying solution E to obtain the modified water reducer.

[0024] Preferably, the preparation method of the modified strengthening agent in S2 is: mixing 6 - 8 parts of nano - calcium carbonate and 6 parts of nano - titanium dioxide to obtain mixture A; putting mixture A into an oven and drying at 60°C for 6 h to obtain mixture B; dissolving 1 part of γ - glycidoxypropyltrimethoxysilane in 6 parts of ethanol to obtain mixture C; slowly adding mixture B to mixture C and stirring at 60°C - 80°C for 90 min to obtain mixture D; centrifuging and washing mixture D, and then vacuum - drying for 12 h to obtain the modified strengthening agent.

[0025] Preferably, the preparation method of the self-healing capsules in S2 is as follows: Dissolve 0.6 parts of sodium alginate in 10 parts of deionized water to obtain an aqueous sodium alginate solution; dissolve 1 part of calcium chloride in 15 parts of deionized water to obtain an aqueous calcium chloride solution; slowly add 3 - 5 parts of methyl methacrylate to the aqueous sodium alginate solution under stirring conditions, with the stirring speed being 500 rpm, and then continue stirring for 10 min - 20 min to obtain a homogeneous emulsion; use a syringe to dropwise add the homogeneous emulsion into the aqueous calcium chloride solution, and then soak it in the aqueous calcium chloride solution for 2 h to obtain microcapsule precursors; wash the microcapsule precursors with deionized water, collect the microcapsules by centrifugation, and obtain self-healing capsules after drying.

[0026] Preferably, the preparation method of the polyvinyl alcohol fibers in S3 is as follows: Dissolve 0.5 parts of tetraethyl orthosilicate in 5 parts of ethanol to obtain a diluted solution; disperse 8 - 10 parts of ground diatomite in 10 parts of ethanol, add the diluted solution, and stir at 450 rpm for 50 min to obtain a precursor solution; centrifuge, wash, and dry the precursor solution to obtain substance A; dissolve 6 - 8 parts of polyvinyl alcohol chips in 40 parts of deionized water, and stir at 95 °C for 3 h to obtain a polyvinyl alcohol solution; cool the polyvinyl alcohol solution to 60 °C, add 0.5 parts of sodium dodecyl sulfate, 0.5 parts of zinc dialkyldithiocarbamate, and substance A, and continue stirring for 90 min to obtain a spinning solution; filter and dry the spinning solution and then spin it into fibers, with the spinning speed being 30 m / min and the fiber diameter being 10 μm - 20 μm; perform a primary drawing on the fibers, with the temperature of the primary drawing being 150 °C and the magnification of the primary drawing being 4 times, then perform a secondary drawing, with the temperature of the secondary drawing being 100 °C and the magnification of the secondary drawing being 2 times, and obtain polyvinyl alcohol fibers after cutting.

[0027] Preferably, the molecular weight of the polyvinyl alcohol chips is 30000.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. First, the present invention combines composite cement and composite aggregate and controls the mixing time to improve the compressive strength of concrete. Portland cement, sand, silica fume, and fly ash are mixed according to the weight ratio. Portland cement, as the main cementitious material, provides a basic strength foundation. Sand, as fine aggregate, plays a role in skeleton filling. Silica fume and fly ash act together with Portland cement to form a more compact particle packing system, thus improving the compressive strength. After the large particles of limestone and small particles of basalt are mixed to form composite aggregate, there are certain voids between the large particles of limestone, and the small particles of basalt can fill these voids, making the aggregate packing more compact; limestone, as the main skeleton material, provides the overall structural support, while the small particles of basalt are like "reinforcement points", and they work together to improve the compressive strength of concrete. Composite cement can also fill the small voids between composite aggregates, making the internal structure of concrete more dense and improving the compressive strength.

[0030] 2. Then, the present invention adds the prepared modified water reducer and modified enhancer to improve the flexural strength of concrete. The modified water reducer prepared by graft modification has better dispersion performance. It can make the composite cement and composite aggregate disperse more evenly, reducing the agglomeration phenomenon. During the modification process, ammonium persulfate thermally decomposes to generate sulfate radicals, which attack the β-O-4 aryl ether bond or the ortho-carbon atom of the phenolic hydroxyl group in the lignosulfonate molecule, extract hydrogen atoms to generate lignin macromolecular radicals, and styrene containing vinyl double bonds combines with the lignin macromolecular radicals to grow polystyrene side chains on the lignin skeleton. The rigid benzene ring structure of the polystyrene side chains forms an adsorption layer with a thickness ≥ 3nm on the surface of cement particles, preventing particles from approaching through the steric repulsion effect. This adsorption layer can also effectively transmit stress and improve the flexural strength. The coupling agent modified enhancer can improve the compatibility between the enhancer and the concrete matrix. The coupling agent can act as a "bridge" between the enhancer and the concrete matrix. One end binds to the active groups on the surface of the enhancer, and the other end binds to the surface of the concrete matrix, effectively sharing stress, thus improving the flexural strength. The modified water reducer and modified enhancer can work together to optimize the interfacial stress transfer inside the concrete. The modified water reducer makes each component disperse evenly and improves the state of the composite cement - composite aggregate interface, providing a good foundation for stress transfer. After the modified enhancer is evenly distributed in the concrete and well bonded to the matrix, it can better share and transmit stress when the concrete is subjected to bending stress.

[0031] 3. The present invention improves the density and compressive strength of concrete by preparing self - healing capsules and having a synergistic effect with modified reinforcing agents. During the concrete mixing process, the self - healing capsules synthesized from methyl methacrylate can adapt to the extrusion of surrounding particles without breaking and maintain their function of filling voids. When acting synergistically with modified reinforcing agents, the self - healing capsules can form a more compact filling system together with the modified reinforcing agents. When the concrete generates cracks under external pressure, the self - healing capsules break, releasing the internal repair agent. The repair agent can fill the cracks, undergo a curing reaction at the crack, and reconnect the concrete parts on both sides of the crack, which is equivalent to reconstructing a compressive structure inside the concrete. When acting synergistically with modified reinforcing agents, this repair effect is more significant.

[0032] 4. Finally, the present invention introduces polyvinyl alcohol fibers to have a synergistic effect with composite cement to improve the splitting tensile strength of concrete. Polyvinyl alcohol fibers have a high tensile strength. When micro - cracks appear, the polyvinyl alcohol fibers can span the cracks and play a role in bridging the cracks. The hydration products generated by the components (such as silica fume and fly ash) in the composite cement during the hydration process can fill the voids between the polyvinyl alcohol fibers and the concrete matrix, enhancing the bond between the polyvinyl alcohol fibers and the matrix. The polyvinyl alcohol fibers can effectively disperse stress in the concrete. When the concrete is subjected to splitting tensile force, the stress will be transmitted between the fibers and the matrix, and the polyvinyl alcohol fibers will not break immediately but can continue to bear a certain amount of tensile force, giving the concrete a certain ductility during the failure process. The composite cement makes the concrete matrix more dense, reducing its internal porosity, which is beneficial to the transmission of stress inside the matrix. At the same time, the components in the composite cement interact with the polyvinyl alcohol fibers, further optimizing the stress transmission path, thereby improving the splitting tensile strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the compressive strength diagram of Example 34 and Comparative Examples 10 - 12 in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0035] Specifically refer to Figure 1 , the present invention provides a polyvinyl alcohol fiber - reinforced concrete and its manufacturing method, and the technical solutions are as follows:

[0036] Example 1

[0037] Preparation of composite cement:

[0038] Put Portland cement, sand, silica fume and fly ash into a grinder according to the weight ratio, using deionized water as the medium, grind for 2 h, and obtain composite cement after drying; the weight ratio is 6:6:2:1.

[0039] The composite aggregate is composed of limestone particles and basalt particles mixed together, and the weight ratio of limestone particles to basalt particles is 3:2. The particle size of limestone particles is 15 mm, and the particle size of basalt particles is 6 mm.

[0040] Preparation of modified water reducer:

[0041] Put 5 parts of calcium lignosulfonate and 20 parts of deionized water into a three-necked flask, stir at 80 °C for 30 min to form solution A; dissolve 1 part of styrene in 5 parts of acetone to form solution B; dissolve 1 part of potassium persulfate in 5 parts of deionized water to form solution C; add solution B dropwise to solution A during heating and stirring, and the dropping time is 20 min to obtain solution D; then add solution C dropwise to solution D, the dropping time is 60 min, and continue to react for 6 h to obtain solution E; centrifuge, wash and dry solution E to obtain the modified water reducer.

[0042] Preparation of modified strengthening agent:

[0043] Mix 6 parts of nano calcium carbonate and 6 parts of nano titanium dioxide to obtain mixture A; put mixture A into an oven and dry at 60 °C for 6 h to obtain mixture B; dissolve 1 part of γ-glycidoxypropyltrimethoxysilane in 6 parts of ethanol to obtain mixture C; slowly add mixture B to mixture C and stir at 60 °C for 90 min to obtain mixture D; centrifuge and wash mixture D, and then dry it under vacuum for 12 h to obtain the modified strengthening agent.

[0044] Preparation of self-healing capsules:

[0045] Dissolve 0.6 part of sodium alginate in 10 parts of deionized water to obtain an aqueous sodium alginate solution; dissolve 1 part of calcium chloride in 15 parts of deionized water to obtain an aqueous calcium chloride solution; slowly add 3 parts of methyl methacrylate to the aqueous sodium alginate solution under stirring conditions, and the stirring speed is 500 rpm, then continue to stir for 10 min to obtain a homogeneous emulsion; use a syringe to add the homogeneous emulsion dropwise into the aqueous calcium chloride solution, and then soak it in the aqueous calcium chloride solution for 2 h to obtain the microcapsule precursor; wash the microcapsule precursor with deionized water, collect the microcapsules by centrifugation, and dry to obtain the self-healing capsules.

[0046] Preparation of polyvinyl alcohol fiber:

[0047] Dissolve 0.5 parts of tetraethyl orthosilicate in 5 parts of ethanol to obtain a diluted solution; disperse 8 parts of ground diatomite in 10 parts of ethanol, add the diluted solution, and stir at 450 rpm for 50 min to obtain a precursor solution; after centrifuging, washing, and drying the precursor solution, obtain substance A; dissolve 6 parts of polyvinyl alcohol slices in 40 parts of deionized water, and stir at 95 °C for 3 h to obtain a polyvinyl alcohol solution; cool the polyvinyl alcohol solution to 60 °C, add 0.5 parts of sodium dodecyl sulfate, 0.5 parts of zinc dialkyldithiocarbamate, and substance A, and continue stirring for 90 min to obtain a spinning solution; filter and dry the spinning solution and then spin it into fibers at a spinning speed of 30 m / min and a fiber diameter of 10 μm; perform a primary drawing on the fibers at a temperature of 150 °C and a draw ratio of 4 times, then perform a secondary drawing at a temperature of 100 °C and a draw ratio of 2 times, and cut to obtain polyvinyl alcohol fibers.

[0048] Fabricate polyvinyl alcohol fiber-reinforced concrete:

[0049] S1 Stir and mix 600 parts of composite cement, 150 parts of composite aggregate, and 150 parts of deionized water at a stirring speed of 800 rpm for 50 min to obtain a cement slurry;

[0050] S2 Put the cement slurry, 11 parts of modified water reducer, 5 parts of modified strengthening agent, 3 parts of self-healing capsules, and 50 parts of deionized water into a mixer and stir at a speed of 1100 rpm for 70 min to obtain a mixed slurry;

[0051] S3 Put 46 parts of polyvinyl alcohol fibers into the mixed slurry and continue to stir at a speed of 900 rpm for 50 min to obtain a concrete slurry;

[0052] S4 Pour the concrete slurry into a mold, and after molding, perform water spraying and curing under the conditions of a temperature of 24 °C and a humidity of 60%. After 7 days, obtain polyvinyl alcohol fiber-reinforced concrete.

[0053] Example 2 - 11 Refer to the parameter conditions in Example 1, and the specific differences are shown in Table 1.

[0054] Table 1 Parameter conditions of Examples 1 - 11

[0055]

[0056] Comparative Example 1 Refer to the parameter conditions in Example 1, the difference is that the composite cement is not ground.

[0057] Comparative Example 2 Refer to the parameter conditions in Example 1, the difference is that only portland cement is used as the matrix cement.

[0058] Comparative Example 3 Referring to the parameter conditions in Example 1, the difference is that the weight ratio of portland cement, sand, silica fume and fly ash is 1:1:1:1.

[0059] Comparative Example 4 Referring to the parameter conditions in Example 1, the difference is that the particle size of basalt particles in the composite aggregate is 17 mm.

[0060] Comparative Example 5 Referring to the parameter conditions in Example 1, the difference is that the particle size of limestone particles in the composite aggregate is 7 mm.

[0061] Example 12 Compressive strength test

[0062] The compressive strengths of Examples 1-11 and Comparative Examples 1-5 were detected in accordance with GB / T50081-2002 Standard Test Method for Mechanical Properties of Ordinary Concrete. The results are shown in Table 2.

[0063] Table 2 Compressive strength test of Examples 1-11 and Comparative Examples 1-5

[0064]

[0065] It can be found from Table 2 that in Examples 1-5 and Comparative Examples 1-3, the compressive strength of the comparative examples is relatively low. When the mixture is not ground, the particle sizes of various components are different, and it is difficult to mix these materials of different particle sizes evenly. During the preparation of concrete, this will lead to uneven internal structure of the concrete, thus affecting the compressive strength of the concrete; when only portland cement is used as the matrix cement, the structure formed after hardening is relatively single, lacking filling and skeleton auxiliary materials such as sand, silica fume and fly ash, and the compressive strength will be significantly reduced; when the weight ratio of portland cement, sand, silica fume and fly ash is 1:1:1:1, due to the large specific surface area and high activity of silica fume, more water will be consumed during the hardening process of the concrete, and the hydration reaction inside the concrete is relatively intense. After the water is lost, the shrinkage stress generated is likely to cause cracks on the surface of the concrete; in the examples, portland cement is used as the main cementitious material, providing a basic strength foundation. Sand, as fine aggregate, plays a role in skeleton filling. Silica fume and fly ash act together with portland cement to form a more compact particle packing system. This synergistic effect enables the porosity of the concrete to continuously decrease during the entire hardening process, thus effectively improving the compressive strength of the concrete. The compressive strength of Example 4 at 28 days is 54.5 MPa. In Examples 6-11 and Comparative Examples 4-5, when all large particle aggregates are used, due to the increase in porosity and loose particle packing, the compressive strength of the concrete will decrease significantly. When bearing pressure, the stress is mainly transmitted through the contact points between the aggregates. When only large particle aggregates are used, the contact points are relatively few and there are more pores, and the stress concentration phenomenon will be more serious; when all small particle aggregates are used, because there is no stable skeleton formed by large particles, when bearing pressure, the small particles are prone to move and rearrange, thus reducing the compressive strength; in the examples, after the large particle limestone and small particle basalt are mixed to form a composite aggregate, the coarse and fine particles can fill the voids with each other. There are certain voids between the large particles of limestone, and the small particle basalt can fill these voids, making the aggregate packing more compact. This compact packing state reduces the total volume of pores inside the concrete, thus improving the density of the concrete and increasing the compressive strength; by controlling the mixing time, the composite cement and the composite aggregate are mixed more evenly. The composite cement can fill the small voids between the composite aggregates, making the internal structure of the concrete more dense. The two can have a synergistic effect and jointly improve the compressive strength. The compressive strength of Example 10 at 28 days is 59.1 MPa.

[0066] Examples 13-24 Refer to the parameter conditions in Example 10, the difference is that the preparation parameters of the modified water reducer and the modified strength enhancer and the dosage of the composite aggregate are changed. The specific differences are shown in Table 3.

[0067] Table 3 Parameter conditions of Example 10 and Examples 13-24

[0068]

[0069] Comparative Example 6 Refer to the parameter conditions in Example 10, with the difference that calcium lignosulfonate is not graft-modified.

[0070] Comparative Example 7 Refer to the parameter conditions in Example 10, with the difference that the modified water reducer is not added.

[0071] Comparative Example 8 Refer to the parameter conditions in Example 10, with the difference that nano-calcium carbonate is not modified with a coupling agent.

[0072] Comparative Example 9 Refer to the parameter conditions in Example 10, with the difference that the composite aggregate is not added.

[0073] Example 25 Flexural Strength Test

[0074] The flexural strength of Examples 10, 13 - 24 and Comparative Examples 6 - 9 was detected in accordance with GB / T50081 - 2002 Standard Test Method for Mechanical Properties of Ordinary Concrete, and the results are shown in Table 4.

[0075] Table 4 Flexural Strength Test of Examples 10, 13 - 24 and Comparative Examples 6 - 9

[0076]

[0077] It can be found from Table 4 that in Examples 10, 13 - 18 and Comparative Examples 6 - 7, when calcium lignosulfonate is not graft - modified, the flexural strength of the concrete is relatively low, indicating that a single water - reducing agent cannot significantly improve the flexural strength of the concrete; when the modified water - reducing agent is not added, the flexural strength decreases, indicating that the modified water - reducing agent is an indispensable part of the concrete; in the examples, the graft - modified water - reducing agent has better dispersion performance. It can make each component disperse more evenly in the concrete, reduce the agglomeration phenomenon, and can be adsorbed on the surface of the composite cement and composite aggregate, improving the bonding performance of the composite cement - composite aggregate interface. The active groups in the molecular structure of the graft - modified water - reducing agent can chemically react with the surfaces of cement and aggregate to form a stronger interface layer, thereby increasing the flexural strength and enhancing the durability of the concrete. In Examples 19 - 22 and Comparative Example 8, when nano - calcium carbonate is not modified with a coupling agent, the flexural strength of Comparative Example 8 is relatively low, and the durability of the concrete cannot be guaranteed; in the examples, the coupling - agent - modified enhancer can improve the compatibility between the modified enhancer and the composite aggregate. The coupling agent in the modified enhancer can play a "bridge" role between the enhancer and the composite aggregate. One end of it binds to the active groups on the surface of the enhancer, and the other end binds to the surface of the composite aggregate, making the combination between the two closer, thereby increasing the flexural strength. In Examples 23 - 24 and Comparative Example 9, when the composite aggregate is not added, the flexural capacity of the concrete is limited. When subjected to bending force, cracks are likely to appear and the concrete will be quickly damaged, resulting in a significant reduction in the durability of the concrete; in the examples, by controlling the dosage of the composite aggregate, it can have a synergistic effect with the modified water - reducing agent and the modified enhancer. The combined action of the modified water - reducing agent and the modified enhancer can optimize the interfacial stress transfer inside the concrete. The modified water - reducing agent makes the composite aggregate particles disperse evenly and improves the interfacial state, providing a good foundation for stress transfer. After the modified enhancer is evenly distributed in the concrete and well - bonded with the composite aggregate, it can better share and transfer stress when the concrete is subjected to bending stress.

[0078] Examples 26 - 35 Refer to the parameter conditions in Example 23, except that the dosages of the modified enhancer and the self - healing capsule, the preparation parameters of the self - healing capsule, and the stirring time in S2 are changed. The specific differences are shown in Table 5.

[0079] Table 5 Parameter Conditions of Example 23 and Examples 26 - 35

[0080]

[0081] Comparative Example 10 Refer to the parameter conditions in Example 23, except that the modified enhancer is not added.

[0082] Comparative Example 11 Refer to the parameter conditions in Example 23, except that only methyl methacrylate is added as the repair agent.

[0083] Comparative Example 12 Refer to the parameter conditions in Example 23, with the difference that the self-healing capsules are not added.

[0084] Example 36 Density and compressive strength test

[0085] The densities of Examples 23, 26 - 35 and Comparative Examples 10 - 12 were detected in accordance with GB / T50080 - 2016 Standard Test Methods for Properties of Ordinary Concrete Mixtures, and the compressive strengths of Examples 23, 26 - 35 and Comparative Examples 10 - 12 were detected in accordance with GB / T50081 - 2002 Standard Test Methods for Mechanical Properties of Ordinary Concrete. The compressive strengths of Example 34 and Comparative Examples 10 - 12 are as Figure 1 shown, and the 28-day compressive strength was detected again 24 hours after the detection. The obtained results are shown in Table 6.

[0086] Table 6 Density and compressive strength tests of Examples 23, 26 - 35 and Comparative Examples 10 - 12

[0087]

[0088] From Table 6 and Figure 1It can be found that in Examples 23, 26 - 27 and Comparative Example 10, when the modified reinforcing agent is not added, there may be more defects and pores in the internal structure of the concrete, and a tight compressive skeleton cannot be formed, resulting in a decrease in both density and compressive strength; in the examples, the modified reinforcing agent itself can improve the particle packing state inside the concrete. It can adsorb on the surface of the composite cement, making the arrangement between particles more compact, thereby increasing the density and compressive strength of the concrete. In Examples 28 - 33 and Comparative Examples 11 - 12, when only methyl methacrylate is added, although it can increase the density and compressive strength of the concrete to a certain extent, the self - repair function is lacking; when the self - repair capsules are not added, the density and compressive strength of the concrete decrease, indicating that the self - repair capsules also have the function of filling voids; in the examples, when the self - repair capsules are evenly dispersed in the concrete, they can fill some voids like fine aggregates, thus increasing the density of the concrete. Moreover, the shell of the self - repair capsules has certain elasticity and toughness. During the concrete mixing process, the capsules can adapt to the extrusion of surrounding particles without breaking and maintain their function of filling voids. When the concrete is subjected to external pressure, the self - repair capsules break, releasing the internal repair agent. The repair agent can fill the cracks and undergo a curing reaction at the crack to reconnect the concrete parts on both sides of the crack; when acting synergistically with the modified reinforcing agent, the capsules and the modified reinforcing agent can form a more compact filling system, thereby increasing the density and compressive strength of the concrete and improving its durability. In Examples 34 - 35, the mixing time is controlled to make the mixing of the cement slurry with the modified water - reducing agent, modified reinforcing agent, and self - repair capsules more uniform, enabling each component to fully exert its synergistic effect. The modified reinforcing agent itself can strengthen the internal structure of the concrete, effectively disperse stress, and prevent stress concentration. When acting synergistically with the self - repair capsules, the self - repair capsules increase the compactness of the concrete, providing a good matrix environment for the better performance of the modified reinforcing agent and improving the durability of the concrete. When the concrete undergoes the first compressive test and there are gaps or cracks inside, the internal self - repair capsules play a role. They release the internal repair agent, filling the gaps or cracks that appear and reconnecting the concrete on both sides of the crack. It can be found from Table 6 that the compressive strength of the examples does not decrease significantly. In Comparative Example 10, due to the absence of the modified reinforcing agent, when cracks appear in the concrete, the compressive strength decreases significantly; in Comparative Examples 11 - 12, neither the single repair agent nor the absence of self - repair capsules can keep the cracked concrete at its original compressive strength, and the compressive strength decreases significantly. This shows that the self - repair capsules play an important role in repairing cracks, enabling the concrete to still maintain a relatively high compressive strength after self - repairing cracks and improving the durability of the concrete.

[0089] Examples 37 - 48 Referring to the parameter conditions in Example 34, the difference lies in changing the dosages of composite cement and polyvinyl alcohol fibers, the preparation parameters of polyvinyl alcohol fibers, and the stirring time in S3. The specific differences are shown in Table 7.

[0090] Table 7 Parameter Conditions of Example 34 and Examples 37 - 48

[0091]

[0092] Comparative Example 13 Referring to the parameter conditions in Example 34, the difference lies in not adding diatomaceous earth during the synthesis of polyvinyl alcohol fibers.

[0093] Comparative Example 14 Referring to the parameter conditions in Example 34, the difference lies in that the fiber diameter is 50 μm.

[0094] Comparative Example 15 Referring to the parameter conditions in Example 34, the difference lies in not adding polyvinyl alcohol fibers.

[0095] Example 49 Splitting Tensile Strength Test

[0096] The splitting tensile strength of Example 34, Examples 37 - 48 and Comparative Examples 13 - 15 was detected in accordance with GB / T50081 - 2002 Standard Test Method for Mechanical Properties of Ordinary Concrete. The results are shown in Table 8.

[0097] Table 8 Splitting Tensile Strength Test of Example 34, Examples 37 - 48 and Comparative Examples 13 - 15

[0098]

[0099] It can be found from Table 8 that in Examples 34 and 37-38, when controlling the dosage of composite cement, the materials in the composite cement can fill the pores between various components during the hydration process, refine the pore size, reduce the porosity of the concrete, and improve the splitting tensile strength. In Examples 39-46 and Comparative Examples 13-15, when diatomaceous earth is not added during the synthesis of polyvinyl alcohol fibers, since diatomaceous earth has a high specific surface area and a special porous structure, after adding, it can interact with the polyvinyl alcohol molecular chain, play the role of physical cross-linking points, and enhance the force between molecular chains. Without adding diatomaceous earth, the properties such as the tensile strength and elongation at break of the fibers may decrease, and the fibers are prone to breakage; when the fiber diameter is relatively large, 50 μm, the larger the fiber diameter, the relatively poorer its flexibility, and brittle fracture is likely to occur; when polyvinyl alcohol fibers are not added, the splitting tensile strength of the concrete decreases significantly, which indicates that polyvinyl alcohol fibers are a necessary component in the concrete; in the examples, when microcracks appear, the polyvinyl alcohol fibers can span the cracks, play the role of bridging the cracks, prevent the further expansion of the cracks, and can effectively disperse the stress, dispersing the concentrated stress into the surrounding concrete matrix. In Examples 47-48, by controlling the mixing time, all components are stirred and mixed evenly to play their roles together. The hydration products generated by the components in the composite cement (such as silica fume and fly ash) during the hydration process can fill the voids between the polyvinyl alcohol fibers and the concrete matrix, enhancing the bond between the polyvinyl alcohol fibers and the matrix. This synergistic effect enables the internal structure of the concrete to maintain better integrity when subjected to tensile force, thereby improving the splitting tensile strength. The presence of the composite cement provides a good foundation for the effective transmission of stress. At the same time, the components in the composite cement can interact with the polyvinyl alcohol fibers, further optimizing the stress transmission path. This synergistic effect enables the concrete to better resist deformation during the splitting tensile process, thereby improving the splitting tensile strength and ultimately enhancing the durability.

[0100] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyvinyl alcohol fiber reinforced concrete, characterized in that: The polyvinyl alcohol fiber reinforced concrete comprises the following components in parts by weight: Composite cement: 600-700 parts; Deionized water: 200 parts; Composite aggregate: 150-190 parts; Polyvinyl alcohol Fiber: 46-50 parts; modified water reducing agent: 11-15 parts; modified reinforcing agent: 5-7 parts; Self-repair capsules: 3-7 servings; The composite cement comprises silicate cement, sand, silica fume and fly ash; the preparation method of the composite cement comprises: putting the silicate cement, the sand, the silica fume and the fly ash into a grinder according to the weight ratio, using deionized water as a medium, grinding for 2h-4h, and drying to obtain the composite cement; the weight ratio is 6-10:6:2:1; The polyvinyl alcohol fiber comprises polyvinyl alcohol slices and diatomaceous earth; The modified water reducing agent includes calcium lignin sulfonate and styrene; The modified reinforcing agent includes nano calcium carbonate and γ-glycidyloxypropyltrimethoxysilane; The self-repairing capsule comprises methyl methacrylate and sodium alginate.

2. The polyvinyl alcohol fiber reinforced concrete according to claim 1, characterized in that: The composite aggregate is a mixture of limestone particles and basalt particles, the weight ratio of the limestone particles to the basalt particles is 3:2, the particle size of the limestone particles is 15mm-19mm, and the particle size of the basalt particles is 6mm-8mm.

3. A method for preparing polyvinyl alcohol fiber reinforced concrete, characterized in that: The polyvinyl alcohol fiber reinforced concrete according to claim 1 is prepared by: S1: 600-700 parts of composite cement, 150-190 parts of composite aggregate and 150 parts of deionized water are stirred and mixed at a stirring speed of 800 rpm for a stirring time of 50 min-70 min to obtain cement slurry; S2: putting the cement slurry, 11-15 parts of modified water reducing agent, 5-7 parts of modified reinforcing agent, 3-7 parts of self-repairing capsules and 50 parts of deionized water into a mixer, stirring at a speed of 1100 rpm for 70 min-90 min to obtain a mixed slurry; S3: adding 46-50 parts of polyvinyl alcohol fibers into the mixed slurry, and continuing to stir at a speed of 900 rpm for 50 min-90 min to obtain concrete slurry; S4 pours the concrete slurry into a mold, and after molding, sprays water for curing at a temperature of 24° C. and a humidity of 60%, and obtains the polyvinyl alcohol fiber reinforced concrete after 7 days.

4. The method for preparing polyvinyl alcohol fiber reinforced concrete according to claim 3, characterized in that: The preparation method of the modified water reducing agent in S2 is as follows: 5-9 parts of calcium lignin sulfonate and 20 parts of deionized water are placed in a three-necked flask, and stirred at 80° C. for 30 minutes to form a solution A; 1 part of styrene is dissolved in 5 parts of acetone to form a solution B; 1 part of potassium persulfate is dissolved in 5 parts of deionized water to form a solution C; The solution B is added dropwise to the solution A during heating and stirring, and the dropping time is 20 minutes to obtain a solution D; then the solution C is added dropwise to the solution D, and the dropping time is 60 minutes to 80 minutes, and the reaction is continued for 6 hours to obtain a solution E; the solution E is centrifuged, washed and dried to obtain the modified water reducing agent.

5. The method for preparing polyvinyl alcohol fiber reinforced concrete according to claim 3, characterized in that: The preparation method of the modified enhancer described in S2 is as follows: 6-8 parts of nano-calcium carbonate and 6 parts of nano-titanium dioxide are mixed to obtain a mixture A; the mixture A is placed in an oven and dried at 60°C for 6 hours to obtain a mixture B; 1 part of γ-glycidyloxypropyltrimethoxysilane is dissolved in 6 parts of ethanol to obtain a mixture C; the mixture B is slowly added to the mixture C, and stirred at 60°C-80°C for 90 minutes to obtain a mixture D; the mixture D is centrifugally washed and vacuum dried for 12 hours to obtain the modified enhancer.

6. The method for preparing polyvinyl alcohol fiber reinforced concrete according to claim 3, characterized in that: The preparation method of the self-repairing capsule described in S2 is: dissolve 0.6 parts of sodium alginate in 10 parts of deionized water to obtain a sodium alginate aqueous solution; dissolve 1 part of calcium chloride in 15 parts of deionized water to obtain a calcium chloride aqueous solution; slowly add 3-5 parts of methyl methacrylate to the sodium alginate aqueous solution under stirring conditions, the stirring speed is 500rpm, and then continue stirring for 10min-20min to obtain a uniform emulsion; use a syringe to add the uniform emulsion dropwise to the calcium chloride aqueous solution, and then soak it in the calcium chloride aqueous solution for 2h to obtain a microcapsule precursor; wash the microcapsule precursor with deionized water, collect the microcapsules by centrifugation, and obtain the self-repairing capsule after drying.

7. The method for preparing polyvinyl alcohol fiber reinforced concrete according to claim 3, characterized in that: The preparation method of the polyvinyl alcohol fiber in S3 is as follows: dissolving 0.5 parts of tetraethyl orthosilicate in 5 parts of ethanol to obtain a diluted solution; dispersing 8-10 parts of ground diatomaceous earth in 10 parts of ethanol, adding the diluted solution, and stirring at 450 rpm for 50 minutes to obtain a precursor solution; centrifuging the precursor solution, washing, and drying to obtain substance A; dissolving 6-8 parts of polyvinyl alcohol slices in 40 parts of deionized water, stirring at 95°C for 3 hours to obtain a polyvinyl alcohol solution; cooling the polyvinyl alcohol solution to 60°C, adding 0.5 parts of dodecane, and stirring at 95°C for 3 hours to obtain a polyvinyl alcohol solution. Sodium alkyl sulfate, 0.5 parts of zinc dialkyl dithiocarbamate and the substance A, continue stirring for 90 minutes to obtain a spinning solution; the spinning solution is filtered and dried, and then spun to form fibers, the spinning speed is 30m / min, and the fiber diameter is 10μm-20μm; the fiber is stretched once, the temperature of the first stretching is 150℃, the multiple of the first stretching is 4 times, and then stretched twice, the temperature of the second stretching is 100℃, the multiple of the second stretching is 2 times, and the polyvinyl alcohol fiber is obtained after cutting.

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