Modified styrene-butadiene emulsion and fiber reinforced mortar and preparation method thereof

Abstract

The invention relates to a modified styrene-butadiene emulsion and fiber reinforced mortar and a preparation method thereof. The preparation method comprises the following steps: firstly, modifying a conventional styrene-butadiene emulsion, designing a core layer to be bisphenol A epoxy resin and a shell layer to be butadiene, styrene, alkyl (meth) acrylate and hydroxyl (meth) acrylate, and then modifying an inorganic nano material by using an amino-containing silane coupling agent to obtain a modified inorganic nano material; an introduced amino group and epoxy resin in a butylbenzene emulsion core layer are subjected to a curing reaction, so that a multi-phase interpenetrating network structure is formed, the crosslinking density of the polymer emulsion after curing and film forming is increased, the compatibility of an inorganic material and an organic polymer film is improved, and the mechanical property and the water resistance of the fiber-reinforced mortar are further remarkably improved; the prepared fiber reinforced mortar is suitable for being used as a tunnel or slope support material.

Description

Technical Field

[0001] The present invention belongs to the field of building materials, and particularly relates to a modified styrene-butadiene emulsion and fiber-reinforced mortar and a preparation method thereof. Background Art

[0002] In recent decades, steel fibers, polymer fibers, plant fibers, etc. have been widely used in cement-based composite mortars. The presence of fibers can block the expansion of cracks in the mortar, reduce the stress concentration of initial defects in the mortar, produce a toughening effect, improve tensile, flexural and impact strengths, improve energy absorption and strain capacity, resist cracking caused by drying shrinkage, reduce permeability, and improve freeze-thaw resistance. To further improve the toughness of fiber cement composite mortar and the bond between the mortar and steel bars or substrates, a certain amount of polymer is incorporated into the mortar to prepare polymer-fiber cement mortar. The polymer can improve the flexural strength and flexural-compressive ratio of the mortar, reduce the elastic modulus and stiffness, improve flexibility and deformation ability, improve bonding strength, wear resistance and durability, and can cooperate with the fibers to enhance the toughness and waterproof effect of the composite mortar. For example, styrene-butadiene emulsion (SB) has a good improvement effect on the tensile properties of PVA fiber cement mortar. As the amount of polymer increases, the failure mode of the mortar gradually changes from interfacial failure to overall failure and internal failure of the mortar. However, although the incorporation of the polymer increases the toughness of the mortar, it significantly reduces the compressive strength, early hydration and other properties of the mortar.

[0003] To improve the adverse effects of polymer emulsions on mortar, adding inorganic nanoparticles is a feasible solution. Inorganic nanoparticles can promote the early hydration process of cement, reduce the porosity in the mortar through physical filling, increase the density of the mortar, thereby improving the air-entraining property brought by polymer emulsions such as styrene-butadiene emulsion, and further improving the mechanical properties of the mortar.

[0004] Recent studies have shown that nano-SiO2 can regulate the setting and hardening of polymer-cement composite mortar, optimize the pore structure of the modified mortar, and improve its compressive strength. However, in the actual application process, due to the small particle size and high surface activity of nano-SiO2, it is easy to agglomerate to form larger aggregates, and its compatibility with organic polymer emulsions is poor, thus affecting the strengthening of the mechanical properties of the mortar by nano-SiO2. Therefore, there is still room for optimizing the mechanical properties of the composite mortar. In addition, for cold-region highway tunnels under low-temperature and high-humidity conditions, higher requirements are placed on the anti-seepage and waterproof properties of the composite mortar, and it is necessary to specifically improve the waterproof properties of the composite mortar to adapt to the application scenarios with high humidity and easy water seepage. Summary of the Invention

[0005] Aiming at the defects of the prior art, the core layer of the present invention is bisphenol A epoxy resin, and the shell layer is butadiene, styrene, alkyl (meth)acrylate and hydroxyalkyl (meth)acrylate. By improving the polymerization monomers and the special core-shell structure, the interaction between the styrene-butadiene emulsion and the amino-modified nano-SiO2 is increased, thereby improving the mechanical properties of the fiber-reinforced mortar.

[0006] To achieve the above technical objectives, the technical solution adopted by the present invention is as follows: First aspect, a modified styrene-butadiene emulsion, which comprises the following raw materials in weight percentages: deionized water 35-55%, polyvinyl alcohol 1-10%, epoxy resin 17-23%, styrene or methylstyrene 9-12%, butadiene 13-18%, alkyl (meth)acrylate 0.5-5%, hydroxyalkyl (meth)acrylate 0.5-2.5%, polymerizable emulsifier 0.1-1.5%, initiator 0.05-1%; Among them, the epoxy resin is bisphenol A epoxy resin, and its structural general formula is: , where n is a positive integer greater than or equal to 1.

[0007] The alkyl (meth)acrylate is selected from: alkyl (meth)acrylates with 1-4 carbon atoms in the alkyl group; Preferably, the alkyl (meth)acrylate is selected from any one or more of: methyl (meth)acrylate, ethyl (meth)acrylate and butyl (meth)acrylate; The hydroxyalkyl (meth)acrylate is selected from any one or more of: 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate; The polymerizable emulsifier is selected from: anionic polymerizable emulsifiers, nonionic polymerizable emulsifiers or anionic-nonionic composite polymerizable emulsifiers. Preferably, the polymerizable emulsifier is selected from ammonium 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether sulfate (ANPS).

[0008] The initiator is selected from a redox initiator system, which contains at least two initiators, one of which is an oxidant and one is a reductant; Preferably, the oxidant in the initiator is selected from at least one or more of: ammonium persulfate, potassium persulfate, benzoyl peroxide, tert-butyl hydroperoxide, hydrogen peroxide and diisopropylbenzene peroxide, and the reductant in the initiator is selected from at least one or more of: sodium bisulfite, ascorbic acid, sodium formaldehyde sulfoxylate, dimethylaniline and alkyl mercaptan; More preferably, the initiator is selected from sodium formaldehyde sulfoxylate and tert-butyl hydroperoxide.

[0009] Second aspect, the preparation method of the above-mentioned modified styrene-butadiene emulsion includes: S1. Mix epoxy resin and polyvinyl alcohol evenly, and then add partial deionized water for mechanical dispersion to obtain an epoxy resin aqueous dispersion. S2. Pre-emulsify styrene or methylstyrene, butadiene, (meth)acrylic acid alkyl ester, (meth)acrylic acid hydroxy ester, (meth)acrylic acid, polymerizable emulsifier and partial deionized water to make them disperse to form a pre-emulsion; dissolve the initiator in partial deionized water to obtain an initiator solution. S3. Drop the pre-emulsion and the initiator solution into the epoxy resin aqueous dispersion, and carry out a heat preservation reaction after the dropping is completed.

[0010] Preferably, in step S1, the epoxy resin and polyvinyl alcohol are mixed evenly at 80-100 °C. In step S1, after the epoxy resin and polyvinyl alcohol are mixed evenly, add partial deionized water and carry out mechanical dispersion at 80-100 °C. In step S3, drop the pre-emulsion and the initiator solution into the epoxy resin aqueous dispersion at 50-80 °C. In step S3, carry out a heat preservation reaction at 50-80 °C after the dropping is completed.

[0011] In the third aspect, the application of the above-mentioned modified styrene-butadiene emulsion in cement-based composite mortar.

[0012] In the fourth aspect, a fiber-reinforced mortar, comprising: cement, fiber, fine aggregate, amino-modified inorganic nanomaterial, the above-mentioned modified styrene-butadiene emulsion, water reducer and defoamer. Among them, the cement is portland cement, and preferably, the cement is early-strength portland cement. The fiber is selected from any one of polypropylene fiber, polyvinyl alcohol fiber or plant fiber, and preferably, the fiber is selected from polyvinyl alcohol fiber. Preferably, the length of the fiber is not less than 10 mm, the elongation at break ≥5%, and the Young's modulus ≥35 GPa. The fine aggregate is selected from river sand or machine-made sand, and its particle size range is 8-100 mesh. Preferably, the fine aggregate is selected from river sand, and more preferably, the fine aggregate is 20-40 mesh river sand. The amino-modified inorganic nanomaterial is selected from amino-modified nano-silica. Preferably, the amino-modified nano-silica is obtained by modifying the surface of nano-silica with a silane coupling agent containing amino groups.

[0013] Preferably, the amino-containing silane coupling agent includes any one or more of 3-aminopropyltrimethoxysilane (coupling agent KH540), 3-aminopropyltriethoxysilane (coupling agent KH550), 3-aminopropylmethyldiethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (silane coupling agent KH792), or N-aminoethyl-3-aminopropylmethyldimethoxysilane; The water reducing agent is selected from polycarboxylate water reducing agents or naphthalene-based water reducing agents. Preferably, the water reducing agent is selected from naphthalene-based water reducing agents.

[0014] The defoaming agent is selected from non-ionic dry powder defoaming agents.

[0015] Furthermore, based on the weight of cement, fine aggregate is 200 - 300%, modified styrene-butadiene emulsion is 5 - 25%, fiber is 0.5 - 2.5%, amino-modified inorganic nanomaterial is 1 - 5%, water reducing agent is 0.5 - 2.5%, defoaming agent is 0.5 - 2.5%, and water is 25 - 50%.

[0016] Fifthly, the preparation method of the above-mentioned fiber-reinforced mortar includes: mixing fiber, fine aggregate, defoaming agent and cement to obtain dry material, mixing water reducing agent, modified styrene-butadiene emulsion, amino-modified inorganic nanomaterial and water to obtain wet material, and mixing the dry material and the wet material evenly to obtain fiber-reinforced mortar.

[0017] Sixthly, the application of the above-mentioned fiber-reinforced mortar in the field of tunnel and slope support materials.

[0018] The beneficial effects of the present invention are as follows: Firstly, the conventional styrene-butadiene emulsion is modified. The core layer is designed as bisphenol A epoxy resin, and the shell layer is butadiene, styrene, alkyl (meth)acrylate and hydroxyl (meth)acrylate. Secondly, the inorganic nanomaterial is modified with an amino-containing silane coupling agent. The introduced amino group undergoes a curing reaction with the epoxy resin in the core layer of the styrene-butadiene emulsion. That is, the amino-modified inorganic nanomaterial acts as an epoxy curing agent, thereby forming a multi-interpenetrating network structure, increasing the crosslinking density after the polymer emulsion cures into a film and the compatibility between the inorganic material and the organic polymer film, and then significantly improving the mechanical properties and water immersion resistance of the fiber-reinforced mortar. Therefore, the prepared fiber-reinforced mortar is suitable for use as a tunnel or slope support material, especially having better durability in the special application environment of cold region highway tunnels with high humidity and easy water seepage. Description of the Drawings

[0019] Figure 1 It is the infrared spectrogram of the film-forming substance of the modified styrene-butadiene emulsion prepared in Examples 1 - 3. Among them, the blue line is the film-forming substance of the modified styrene-butadiene emulsion in Example 1, the red line is the film-forming substance of the modified styrene-butadiene emulsion in Example 2, and the green line is the film-forming substance of the modified styrene-butadiene emulsion in Example 3.

[0020] Figure 2 Transmission electron microscopy (TEM) observation diagram of latex particles in the modified styrene-butadiene emulsion prepared in Example 1. Detailed implementation manners

[0021] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0022] It should be noted that the terms used here are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] If the specific experimental conditions are not specified in the examples, they are usually in accordance with the conventional conditions in the art or in accordance with the conditions recommended by the reagent company; the materials, reagents, etc. used in the examples, unless otherwise specified, can be obtained through commercial channels.

[0024] Preparation of amino-modified hydrophilic nano-silica aqueous solution: Add 100 g of nano-silica hydrosol (Nissan Chemical, solid content 30%, particle size 20 nm) and 0.9 g of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (silane coupling agent KH792) to the flask in sequence, heat to 60 °C under stirring, adjust the pH of the aqueous solution to 3.5 - 4.5 using formic acid, and keep the reaction at 60 °C for 2 h to obtain the amino-modified hydrophilic nano-silica aqueous solution. Example 1

[0025] Preparation of the modified styrene-butadiene emulsion. First, add 200 g of liquid epoxy resin WSR6101 (E-44, Nantong Xingchen) and 20 g of polyvinyl alcohol to a stainless-steel Parr reactor equipped with a dispersion disk. Preheat the reactor to 85 °C and stir the mixture at a speed of 2000 rpm for 15 min to fully mix the epoxy phase and the polyvinyl alcohol phase.

[0026] Add 330 mL of deionized water to the above mixture at a speed of 10 mL / min using a peristaltic pump. After the addition is completed, stir at a speed of 500 rpm for 30 min, cool the Parr reactor to a 50 °C water bath, filter, and collect the filtered epoxy resin aqueous dispersion.

[0027] 94 g of a diluted epoxy resin aqueous dispersion (40% solids content) was charged into a three-necked flask equipped with a condenser and a mechanical stirrer. The flask was immersed in a water bath at 65 °C, the mechanical stirring rate was set at 200 rpm, nitrogen was slowly purged through the flask, and cooling water was turned on to flow through the condenser. 19.4 g of deionized water and 1.4 g of a reactive emulsifier, ammonium 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether sulfate (ANPS), were stirred in a glass wide-mouth bottle for 10 min. Subsequently, 18 g of styrene, 30 g of butadiene, 4.2 g of butyl acrylate, 2.2 g of 2-hydroxyethyl acrylate, and 0.8 g of methyl acrylate were added to the wide-mouth bottle, and stirring was continued for 20 min to form an emulsion. The mixture was then fed into the three-necked flask at a stable rate over 90 min through an injection pump. 0.56 g of sodium formaldehyde sulfoxylate and 0.28 g of tert-butyl hydroperoxide were separately dissolved in 5 g of deionized water and then fed into the three-necked flask at the same rate within 60 min through two separate injection pumps. After the feeding was completed, the three-necked flask was immersed in a water bath at 65 °C for heat-retaining reaction for 1 h. After the reaction was completed, the modified styrene-butadiene emulsion was collected by filtration. Example 2

[0028] The preparation method of the epoxy resin aqueous dispersion was the same as that in Example 1.

[0029] 94 g of a diluted epoxy resin aqueous dispersion was charged into a three-necked flask equipped with a condenser and a mechanical stirrer. The flask was immersed in a water bath at 65 °C, the mechanical stirring rate was set at 200 rpm, nitrogen was slowly purged through the flask, and cooling water was turned on to flow through the condenser. 19.4 g of deionized water and 1.4 g of a reactive emulsifier, ammonium 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether sulfate (ANPS), were stirred in a glass wide-mouth bottle for 10 min. Subsequently, 18 g of styrene, 30 g of butadiene, 4.4 g of butyl acrylate, 1.8 g of 2-hydroxypropyl acrylate, and 1.0 g of ethyl acrylate were added to the wide-mouth bottle, and stirring was continued for 20 min to form an emulsion. The mixture was then fed into the three-necked flask at a stable rate over 90 min through an injection pump. 0.56 g of sodium formaldehyde sulfoxylate and 0.28 g of tert-butyl hydroperoxide were separately dissolved in 5 g of deionized water and then fed into the three-necked flask at the same rate within 60 min through two separate injection pumps. After the feeding was completed, the three-necked flask was immersed in a water bath at 65 °C for heat-retaining reaction for 1 h. After the reaction was completed, the modified styrene-butadiene emulsion was collected by filtration. Example 3

[0030] The preparation method of the epoxy resin aqueous dispersion was the same as that in Example 1.

[0031] 94 g of the diluted epoxy resin aqueous dispersion was charged into a three-necked flask equipped with a condenser and a mechanical stirrer. The flask was immersed in a water bath at 65 °C, the mechanical stirring rate was set at 200 rpm, nitrogen was slowly purged through the flask, and the cooling water was turned on to flow through the condenser. 19.4 g of deionized water and 1.4 g of the reactive emulsifier 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate (ANPS) were stirred in a glass wide-mouth bottle for 10 min. Subsequently, 18 g of styrene, 30 g of butadiene, 2.4 g of ethyl acrylate, 2 g of hydroxyethyl methacrylate, and 2.8 g of butyl acrylate were added to the wide-mouth bottle, and stirring was continued for 20 min to form an emulsion. The mixture was fed into the three-necked flask through an injection pump at a stable rate over 90 min. 0.56 g of sodium formaldehyde sulfoxylate and 0.28 g of tert-butyl hydroperoxide were dissolved separately in 5 g of deionized water, and then fed into the three-necked flask through two separate injection pumps at the same rate over 60 min. After the feeding was completed, the three-necked flask was immersed in a water bath at 65 °C for heat-retaining reaction for 1 h. After the reaction was completed, the modified styrene-butadiene emulsion was collected by filtration.

[0032] Preparation of fiber-reinforced mortar: P·Ⅱ 52.5R type portland cement was selected as the cement; amino-modified hydrophilic nano-silica aqueous solution was selected as the inorganic nano-material; the polymer emulsions of Examples 4-6 were the modified styrene-butadiene emulsions prepared in Examples 1-3, and the polymer emulsion of the comparative example was Styrofan ECO 7623 styrene-butadiene emulsion (BASF). Polyvinyl alcohol fiber was a new synthetic fiber (PVA) made by solvent wet cooling gel spinning. The length of the PVA fiber was 12 mm, the fiber diameter was 40 μm, the elongation at break was 6%, the Young's modulus was ≥35 GPa, and the tensile strength was 1600 MPa. Naphthalene-based water reducer (PA) was selected as the water reducer, with a water reduction rate of 20%, and Axilat DF 770 DD (AT) was selected as the defoamer.

[0033] The PVA fibers were incorporated into the fiber-reinforced mortar at a volume fraction, fixed at 1.0% of the cement. The amino-modified hydrophilic nano-silica aqueous solution was incorporated into the fiber-reinforced mortar at a mass fraction, fixed at 2.5% of the cement (based on the solid content relative to the cement). Three dosages of styrene-butadiene emulsion, 0%, 10%, and 20% (based on the solid content relative to the cement), were used. The water-cement ratio of the fiber-reinforced mortar depended on the dosage of the styrene-butadiene emulsion. The water-cement ratio was 0.48 when the dosage of the styrene-butadiene emulsion was 0%, 0.39 when the dosage was 10%, and 0.30 when the dosage was 20%. The water-cement ratio was adjusted at different dosages of the styrene-butadiene emulsion to keep the fluidity consistent. The cement-sand ratio was 1:3 by mass, the mass fraction of the naphthalene-based water reducer relative to the cement was 1.0%, and the mass fraction of the defoamer relative to the cement was 0.2%. Example 4

[0034] Based on P·Ⅱ 52.5R type Portland cement, 260% of 20 - 40 mesh river sand, 10% of the styrene - butadiene emulsion prepared in Example 1, 1.0% of PVA fiber, 2.5% of amino - modified hydrophilic nano - silica, 1.0% of naphthalene - based water - reducing agent, 0.2% of defoamer, and 39% of water. Example 5

[0035] Based on P·Ⅱ 52.5R type Portland cement, 260% of 20 - 40 mesh river sand, 20% of the styrene - butadiene emulsion prepared in Example 1, 1.0% of PVA fiber, 2.5% of amino - modified hydrophilic nano - silica, 1.0% of naphthalene - based water - reducing agent, 0.2% of defoamer, and 30% of water. Example 6

[0036] Based on P·Ⅱ 52.5R type Portland cement, 260% of 20 - 40 mesh river sand, 10% of the styrene - butadiene emulsion prepared in Example 2, 1.0% of PVA fiber, 2.5% of amino - modified hydrophilic nano - silica, 1.0% of naphthalene - based water - reducing agent, 0.2% of defoamer, and 39% of water. Example 7

[0037] Based on P·Ⅱ 52.5R type Portland cement, 260% of 20 - 40 mesh river sand, 20% of the styrene - butadiene emulsion prepared in Example 2, 1.0% of PVA fiber, 2.5% of amino - modified hydrophilic nano - silica, 1.0% of naphthalene - based water - reducing agent, 0.2% of defoamer, and 30% of water. Example 8

[0038] Based on P·Ⅱ 52.5R type Portland cement, 260% of 20 - 40 mesh river sand, 10% of the styrene - butadiene emulsion prepared in Example 3, 1.0% of PVA fiber, 2.5% of amino - modified hydrophilic nano - silica, 1.0% of naphthalene - based water - reducing agent, 0.2% of defoamer, and 39% of water. Example 9

[0039] Based on P·Ⅱ 52.5R type Portland cement, 260% of 20 - 40 mesh river sand, 20% of the styrene - butadiene emulsion prepared in Example 3, 1.0% of PVA fiber, 2.5% of amino - modified hydrophilic nano - silica, 1.0% of naphthalene - based water - reducing agent, 0.2% of defoamer, and 30% of water.

[0040] Comparative Example 1 Based on P·Ⅱ 52.5R type Portland cement, without adding styrene - butadiene emulsion, 260% of 20 - 40 mesh river sand, 1.0% of PVA fiber, 2.5% of amino - modified hydrophilic nano - silica, 1.0% of naphthalene - based water - reducing agent, 0.2% of defoamer, and 48% of water.

[0041] Comparative Example 2 Based on P·Ⅱ 52.5R Portland cement, 260% of 20-40 mesh river sand, 10% of Styrofan ECO 7623 styrene-butadiene emulsion, 1.0% of PVA fiber, 2.5% of amino-modified hydrophilic nano-silica, 1.0% of naphthalene-based water reducer, 0.2% of defoamer, and 39% of water.

[0042] Comparative Example 3 Based on P·Ⅱ 52.5R Portland cement, 260% of 20-40 mesh river sand, 20% of Styrofan ECO 7623 styrene-butadiene emulsion, 1.0% of PVA fiber, 2.5% of amino-modified hydrophilic nano-silica, 1.0% of naphthalene-based water reducer, 0.2% of defoamer, and 30% of water.

[0043] Comparative Example 4 Based on P·Ⅱ 52.5R Portland cement, 260% of 20-40 mesh river sand, 20% of the styrene-butadiene emulsion prepared in Example 1, 1.0% of PVA fiber, 2.5% of unmodified hydrophilic fumed nano-silica (purity 99.9%, specific surface area greater than or equal to 120 g / m 2 )2.5%, 1.0% of naphthalene-based water reducer, 0.2% of defoamer, and 30% of water.

[0044] Testing Method The film-forming substances after drying of the modified styrene-butadiene emulsions prepared in Examples 1, 2, and 3 were characterized by infrared spectroscopy (attenuated total reflection method), and the test results are as Figure 1 shown. At the same time, the epoxy-modified styrene-butadiene emulsion of Example 1 was characterized by transmission electron microscopy for its appearance morphology. The emulsion was diluted in deionized water, and then 5 μL of the diluted emulsion was dropped onto a TEM test grid. The appearance morphology of the latex particles of the modified styrene-butadiene emulsion was observed using a JEM-1230 TEM at a voltage of 120 kV and listed in Table 2. It can be seen from Table 2 that the epoxy-modified styrene-butadiene emulsion prepared in Example 1 has a core-shell structure, and the epoxy resin serves as the core layer and together with the shell layer of butadiene, styrene, and acrylate monomers forms the latex particles of the epoxy-modified styrene-butadiene emulsion.

[0045] For the mortar mixing process of Examples 4-9 and Comparative Examples 1-4, refer to the standard of GB / T 17671-2021. The PVA fiber, 20-40 mesh river sand, and defoamer were premixed evenly with Portland cement before being added to the mixing pan. Then, the water reducer, amino-modified hydrophilic fumed nano-silica (or hydrophilic fumed nano-silica) and epoxy-modified styrene-butadiene emulsion (or styrene-butadiene emulsion) and water were mixed evenly. Finally, the two were mixed according to the standard to obtain the corresponding fiber-reinforced mortar.

[0046] The mortar was molded in a triple mold, demolded after being cured for 24 h with plastic wrap covering, and then cured in a curing room at a temperature of (20±1) °C and a relative humidity of (60±5) % until the specified age (7 d or 28 d).

[0047] The flexural and compressive strength tests referred to GB / T 17671-2021 "Methods for Testing the Strength of Cement Mortar". The loading rate for the flexural strength test was 50 N / s, and the loading rate for the compressive strength test was 2.4 kN / s. Through the flexural strength test, the flexural strength and compressive strength at 7 d and 28 d were obtained, and the compressive-to-flexural ratio was obtained by processing the flexural and compressive strength at 28 d.

[0048] The tensile bond strength test referred to JGJ / T70-2009 "Standard Test Methods for Basic Properties of Building Mortars", and the tensile bond strength of the specimens after 28 d of curing was tested.

[0049] Water immersion treatment: The specimens to be tested were placed in a water bath box for a water bath for 48 h, the water bath temperature was set at 60±2 °C. After that, the water on the surface of the specimens was blotted dry with absorbent paper and left at room temperature for 2 h, and then the tensile bond strength was tested according to the above method.

[0050] The test results of Examples 4-9 and Comparative Examples 1-4 are listed in Table 1.

[0051]

[0052] Through the data analysis of Table 1, it can be seen that the fiber-reinforced mortar prepared in Examples 4-9 has higher flexural strength, compressive strength, compressive-to-flexural ratio and tensile bond strength under the same dosage of polymer emulsion. According to the difference in the dosage of epoxy-modified styrene-butadiene emulsion, the flexural strength of the fiber-reinforced mortar prepared in Examples 4-9 can be controlled within the range of 12~16 MPa, the compressive strength can be controlled within the range of 42~54 MPa, and the tensile bond strength can be controlled within the range of 4.5~7.5 MPa.

[0053] No polymer emulsion was used in the fiber-reinforced mortar in Comparative Example 1, and it was difficult to form a polymer curing film in the mortar, so it could not improve the flexural strength of the mortar. Therefore, the flexural strength of the fiber-reinforced mortar in Comparative Example 1 decreased significantly compared with that in Examples 4-9, and at the same time, the tensile bond strength was very low, because the fiber-reinforced mortar lacked polymer components that could be cured into a film.

[0054] In Comparative Examples 2 and 3, epoxy-modified styrene-butadiene latex was not used, and conventional styrene-butadiene latex was used. There were no functional groups for reaction with amino-modified hydrophilic nano-silica, and the crosslinking density of the polymer cured film was not high. Therefore, under the same dosage of styrene-butadiene latex, the flexural strength, compressive strength, tensile adhesion strength, and tensile adhesion strength after immersion treatment of Comparative Examples 2 and 3 were lower than those of Examples 4-9. In Comparative Example 4, epoxy-modified styrene-butadiene latex and conventional hydrophilic nano-silica were used. Similarly, due to insufficient crosslinking sites between the two, the crosslinking density of the polymer cured film was relatively low, resulting in lower flexural strength, compressive strength, tensile adhesion strength, and tensile adhesion strength after immersion treatment of Comparative Example 4 than those of Examples 4-9 under the same dosage of styrene-butadiene latex. This was particularly evident from the comparison of the strength test results after 28 days of curing.

[0055] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of them. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention. Although the specific implementation manners of the present invention have been described above, it does not limit the protection scope of the present invention. Those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made without creative labor by those skilled in the art are still within the protection scope of the present invention.

Claims

1. A modified styrene-butadiene emulsion, characterized in that, It comprises raw materials in the following weight percentages: deionized water 35 - 55%, polyvinyl alcohol 1 - 10%, epoxy resin 17 - 23%, styrene or methylstyrene 9 - 12%, butadiene 13 - 18%, (meth)acrylic acid alkyl ester 0.5 - 5%, (meth)acrylic acid hydroxy ester 0.5 - 2.5%, polymerizable emulsifier 0.1 - 1.5%, initiator 0.05 - 1%; Among them, the epoxy resin is bisphenol A epoxy resin, and its structural general formula is: , where n is a positive integer greater than or equal to 1; (Meth)acrylic acid alkyl ester is selected from: (meth)acrylic acid alkyl esters with 1 - 4 carbon atoms in the alkyl group; (Meth)acrylic acid hydroxy ester is selected from: any one or more of hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate; The polymerizable emulsifier is selected from: anionic polymerizable emulsifier, non - ionic polymerizable emulsifier or anionic - non - ionic composite polymerizable emulsifier; The initiator is selected from redox initiator systems, including at least two initiators, one being an oxidant and one being a reductant.

2. The modified styrene-butadiene emulsion according to claim 1, wherein, The said (meth)acrylic acid alkyl ester is selected from: any one or more of methyl (meth)acrylate, ethyl (meth)acrylate and butyl (meth)acrylate.

3. The modified styrene-butadiene emulsion according to claim 1, wherein The oxidant in the initiator is selected from: at least one or more of ammonium persulfate, potassium persulfate, benzoyl peroxide, tert - butyl hydroperoxide, hydrogen peroxide and dicumyl peroxide; the reductant in the initiator is selected from: at least one or more of sodium bisulfite, ascorbic acid, sodium formaldehyde sulfoxylate, dimethylaniline and alkyl mercaptan.

4. The preparation method of the modified styrene-butadiene emulsion according to any one of claims 1-3, characterized in that, The preparation method includes: S1. Mix epoxy resin and polyvinyl alcohol evenly, and then add part of deionized water for mechanical dispersion to obtain an epoxy resin aqueous dispersion; S2. Pre - emulsify styrene or methylstyrene, butadiene, (meth)acrylic acid alkyl ester, (meth)acrylic acid hydroxy ester, (meth)acrylic acid, polymerizable emulsifier and part of deionized water to make them disperse to form a pre - emulsion; dissolve the initiator in part of deionized water to obtain an initiator solution; S3. Drop the pre - emulsion and the initiator solution into the epoxy resin aqueous dispersion, and carry out a heat - preservation reaction after dropping is completed.

5. The preparation method of the modified styrene-butadiene emulsion according to claim 4, characterized in that, In step S1, epoxy resin and polyvinyl alcohol are mixed evenly at 80 - 100°C; And / or, in step S1, after epoxy resin and polyvinyl alcohol are mixed evenly, add part of deionized water and carry out mechanical dispersion at 80 - 100°C; And / or, in step S3, drop the pre - emulsion and the initiator solution into the epoxy resin aqueous dispersion at 50 - 80°C; And / or, in step S3, carry out a heat - preservation reaction at 50 - 80°C after dropping is completed.

6. Application of the modified styrene - butadiene emulsion according to any one of claims 1 - 3 in cement - based composite mortar.

7. A fiber-reinforced mortar, characterized in that, The fiber - reinforced mortar includes: cement, fiber, fine aggregate, amino - modified inorganic nanomaterial, the modified styrene - butadiene emulsion according to any one of claims 1 - 3, water - reducing agent and defoaming agent; Wherein, the cement is Portland cement; The fiber is selected from any one of polypropylene fiber, polyvinyl alcohol fiber or plant fiber; The fine aggregate is selected from river sand or manufactured sand, and its particle size range is 8 - 100 mesh; The amino - modified inorganic nanomaterial is selected from amino - modified nano - silica; The water reducing agent is selected from polycarboxylate water reducing agents or naphthalene series water reducing agents; The defoaming agent is selected from non-ionic dry powder defoaming agents.

8. The fiber-reinforced mortar according to claim 7, characterized in that, Based on the weight of cement, fine aggregate is 200-300%, the modified styrene-butadiene emulsion according to any one of claims 1-3 is 5-25%, fiber is 0.5-2.5%, amino-modified inorganic nanomaterial is 1-5%, water reducing agent is 0.5-2.5%, defoaming agent is 0.5-2.5%, and water is 25-50%.

9. The preparation method of the fiber-reinforced mortar according to any one of claims 7-8, comprising: Mix the fiber, fine aggregate, defoaming agent and cement to obtain dry material, mix the water reducing agent, modified styrene-butadiene emulsion, amino-modified inorganic nanomaterial and water to obtain wet material, and mix the dry material and wet material evenly to obtain fiber-reinforced mortar.

10. Application of the fiber-reinforced mortar according to any one of claims 7-8 in the field of tunnel and slope support materials.

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