Environment-friendly dry-mixed mortar and preparation method thereof

Abstract

The invention relates to the technical field of building engineering materials, in particular to environment-friendly dry-mixed mortar and a preparation method thereof. The environment-friendly dry-mixed mortar is prepared from the following raw materials in parts by mass: 130 to 150 parts of cement, 60 to 80 parts of fly ash, 750 to 800 parts of fine sand, 20 to 25 parts of modified expanded and vitrified small balls, 7 to 9 parts of modified polycarboxylic acid water reducing agent, 3 to 5 parts of water-retaining agent, 1 to 2 parts of hydroxypropyl methyl cellulose and 3 to 4 parts of polypropylene fiber. The prepared environment-friendly dry-mixed mortar has the advantages of being easy to manufacture, low in cost, environmentally friendly and the like, and meanwhile has the good heat preservation performance, the excellent fluidity, the excellent mechanical performance and the excellent water retention performance. In addition, the invention also provides a preparation method of the dry-mixed mortar which is environment-friendly, low in cost and excellent in performance, and the dry-mixed mortar has important significance for improving the environment-friendly performance and economic benefits of building materials.

Description

Technical Field

[0001] The present application relates to the technical field of building engineering materials, and in particular to an environmentally friendly dry mortar and a preparation method thereof. Background Art

[0002] Dry mortar refers to a granular or powdered material that is physically mixed in a certain proportion of dried and sieved aggregates (such as quartz sand), inorganic cementitious materials (such as cement) and additives (such as polymers). It is transported to the construction site in bags or bulk and can be used directly after adding water and mixing. It is also called dry mortar, dry mixed mortar, dry mixing powder, and some construction adhesives also belong to this category. Dry mortar plays a bonding, cushioning, protective and decorative role in the construction industry in a thin layer state, and is widely used in construction and decoration projects.

[0003] Dry-mix mortar can solve the problem of quality problems caused by the difficulty in grasping the proportion of mortar prepared by traditional technology, and its quality is reliable. Because in traditional technology, mortars for different purposes have different requirements for the material's anti-shrinkage, anti-cracking, thermal insulation, moisture resistance and other properties, and the construction requirements also have different workability, water retention and solidification time, and these properties can only be achieved by strictly preparing according to scientific formulas. Only the production process of dry-mix mortar can meet this requirement: because of accurate measurement and quality assurance, the quality of projects after using dry-mix mortar is significantly improved, the construction period is significantly shortened, and the labor is reduced. In addition, it is easy to use and can be used at any time.

[0004] The environmentally friendly dry-mixed mortar currently available on the market still has problems such as poor fluidity and mechanical properties, limited thermal insulation performance, poor water retention, poor durability, and environmental pollution. Therefore, the development of environmentally friendly dry-mixed mortar with excellent performance in all aspects is of great and practical significance to improving the construction quality of the construction industry. Summary of the invention

[0005] The purpose of this application is to provide an environmentally friendly dry-mix mortar and a preparation method thereof in response to the deficiencies of current technology. The environmentally friendly dry-mix mortar prepared in this application has the advantages of simple preparation, low cost, and green environmental protection. It also has good thermal insulation performance, excellent fluidity, mechanical properties and water retention properties.

[0006] In the first aspect, the present application provides an environmentally friendly dry-mix mortar, which adopts the following technical solution: An environmentally friendly dry-mix mortar comprises the following raw materials, measured by weight: 130-150 parts of cement, 60-80 parts of fly ash, 750-800 parts of fine sand, 20-25 parts of modified expanded glass microspheres, 7-9 parts of modified polycarboxylic acid water-reducing agent, 3-5 parts of water-retaining agent, 1-2 parts of hydroxypropyl methylcellulose, and 3-4 parts of polypropylene fiber.

[0007] By adopting the above technical scheme, cement is used as the main binder to provide the basic strength and structural stability of the mortar. Fly ash: As an auxiliary binder, fly ash can improve the workability of the mortar, reduce the amount of cement, and improve the impermeability and durability. Fine sand: Provides fine aggregate for the mortar and increases the density and strength of the mortar. Modified expanded vitrified microspheres: As lightweight aggregates, modified expanded vitrified microspheres not only improve the thermal insulation performance of the mortar, but also enhance the mechanical properties and durability of the mortar. At the same time, by attaching silica aerogel, the modified expanded vitrified microspheres also solve the problems of instability and high cost of aerogel in the mortar. Modified polycarboxylic acid water reducer: By improving the fluidity of the mortar, improving the pore structure and improving the mechanical properties, the modified polycarboxylic acid water reducer significantly improves the overall performance of the mortar. At the same time, the ester group generated by it plays a role in the cement hardening process, further improving the performance of the mortar. Water retaining agent improves the water retention and fluidity of mortar by improving the viscosity of wet mortar and controlling the particle settling rate, and also helps to prevent cracking and hollowing. Hydroxypropyl methylcellulose: As a thickener, hydroxypropyl methylcellulose helps to improve the workability of mortar. Polypropylene fiber, as a reinforcing material, can improve the crack resistance and toughness of mortar. The synergistic effect of these components in mortar is reflected in: the combination of modified expanded glass microspheres and silica aerogel improves the thermal insulation and mechanical properties; modified polycarboxylic acid water reducer improves the fluidity and mechanical properties of mortar; water retaining agent and hydroxypropyl methylcellulose improve the water retention and workability of mortar; polypropylene fiber enhances the crack resistance and toughness of mortar. The interaction and synergistic effect of these components make environmentally friendly dry-mixed mortar have good comprehensive performance and meet the various needs of building materials.

[0008] Preferably, the cement is ordinary Portland cement of P·O42.5 grade; the fly ash is grade II ash; and the particle size of the fine sand is 20-40 mesh.

[0009] Preferably, the method for preparing the modified expanded vitrified microspheres comprises the following steps: S31, heating 200 parts of expanded vitrified microspheres with a particle size of 0.5 mm-1 mm to 300° C.-350° C. for heat treatment for 5-6 hours to obtain pretreated expanded vitrified microspheres; S32, dispersing 100 parts of tetraethyl orthosilicate and 35 parts of isotridecyl alcohol in 400 parts of 85% ethanol aqueous solution by weight, adjusting the pH to 2-3, adding 2 parts of gel accelerator, and standing at 80°C-90°C for 24 hours to obtain a mixed wet gel; S33, adding 400 parts of the mixed wet gel to 500 parts of the organic solution containing silane according to the mass fraction, soaking for 24h-28h, washing, and vacuum drying to obtain isomeric tridecanol modified silica aerogel powder; S34. Disperse 80 parts of isotridecyl alcohol modified silica aerogel powder in 300 parts of ethanol according to mass fractions, add 200 parts of pretreated expanded vitrified microspheres, mix well, filter and dry to obtain modified expanded vitrified microspheres.

[0010] By adopting the above technical scheme, step S31 (pretreatment): heat treatment of expanded vitrified microspheres at 300-350°C is performed to remove surface impurities and enhance the structural stability of the microspheres, providing a clean surface for subsequent aerogel attachment. Step S32 (aerogel synthesis): using tetraethyl orthosilicate as a silicon source, hydrolysis and condensation are performed under acidic conditions to generate wet silica gel. Adding isomeric tridecanol as a surfactant can regulate the pore structure of the aerogel, and its hydrophobic segments can reduce the water absorption of the aerogel. Step S33 (hydrophobic modification): soaking the wet gel in an organic solution containing silane (such as vinyl triethoxysilane), hydrophobically modifying the surface of the aerogel through a silane coupling agent, and reducing the subsequent interfacial pores with cement hydration products. Step S34 (composite modification): mixing the modified aerogel powder with the pretreated microspheres in ethanol, and filling the open pores on the surface of the microspheres with the high specific surface area of ​​the aerogel to form a "microsphere-aerogel" composite structure. The prepared modified expanded vitrified microspheres, by attaching silica aerogel to expanded vitrified microspheres with a porous structure, not only fill the open pores on the surface of the expanded vitrified microspheres and repair their surface defects, but also enhance the surface strength of the expanded vitrified microspheres to a certain extent. More importantly, the modified expanded vitrified microspheres not only greatly reduce the thermal conductivity of the expanded vitrified microspheres and thus improve the thermal insulation properties of the mortar material, but also effectively solve the problem that aerogel is unstable in mortar and the high cost caused by high dosage, thereby significantly improving the thermal insulation properties, mechanical properties and durability of the environmentally friendly dry-mixed mortar.

[0011] Preferably, in step S33, the silane-containing organic solution is a solution composed of vinyltriethoxysilane and ethanol mixed in a mass ratio of 1:30.

[0012] Preferably, in step S32, the gel accelerator is methyl ethylene oxide.

[0013] Preferably, the preparation method of the modified polycarboxylate water-reducing agent comprises the following steps: S61, adding 18-19 parts of carboxylic acid monomer and 1-1.2 parts of siloxane monomer to 280-300 parts of water according to molar fractions, stirring evenly to obtain a mixed solution A; S62, adding 0.3-0.4 parts of initiator and 0.8-0.9 parts of chain transfer agent to 100 parts of water according to molar fractions, stirring evenly to obtain a mixed solution B; S63. According to the molar fraction, add 8-9 parts of polyether monomer to 120 parts of water and stir, then add 1 part of hydrogen peroxide, stir and heat to 47-50°C, and then drop the mixed solution A and mixed solution B at the same time. After 3 hours of dropwise addition, continue stirring and reacting for 3-4 hours, and then add a 10% mass concentration of NaOH aqueous solution to adjust the pH value to 6.8-7.2 to obtain a modified polycarboxylic acid water reducer.

[0014] By adopting the above technical scheme, carboxylic acid monomers, siloxane monomers with specific structures, polyether monomers, initiators and chain transfer agents are used as raw materials, and the reaction conditions are precisely controlled to prepare the obtained product; on the one hand, the siloxane monomers with specific structures have high stability, so that the alkoxy groups of the siloxane monomers react with polycarboxylic acid to generate ester groups, so that the siloxane molecular chains are effectively grafted onto the side chains of the polycarboxylic acid water reducer without being converted into SiO, thereby significantly improving the steric hindrance effect of the polycarboxylic acid water reducer, and effectively improving the fluidity of the cement mortar when adsorbed on the surface of the recycled dry-mix mortar particles; on the other hand, the generated ester-based cement undergoes a hydrolysis reaction during the mixing and hardening process, so that the siloxane molecular chains fall off from the polycarboxylic acid water reducer, and the siloxane monomers have good dispersibility, and the alkoxy groups and hydroxyl groups contained therein can effectively improve the cross-linking effect between the recycled dry-mix mortar particles, and effectively improve the pore structure of the concrete through its steric hindrance effect and dispersibility. Key control of reaction conditions: 47-50℃ reaction temperature: balance the decomposition rate of initiator (such as ammonium persulfate) and the polymerization activity of monomers to avoid violent polymerization or incomplete reaction. Hydrogen peroxide addition: as an oxidant to assist in initiating free radical polymerization, while avoiding the introduction of metal ions (such as Fe 3+ ), reducing interference with cement hydration. Adjusting pH to 6.8-7.2: neutralizing excess carboxylic acid, preventing hydrolysis or precipitation of the water reducer during storage, and ensuring long-term stability. In short, the synergy of adsorption-dispersion of carboxylic acid monomers, dynamic grafting-hydrolysis of siloxanes, and steric hindrance of polyether monomers can significantly improve the fluidity and mechanical properties of cement mortar.

[0015] Preferably, in step S61, the carboxylic acid monomer is composed of acrylic acid and (E)-3-(naphthalen-1-yl)acrylic acid in a molar ratio of 1:1.

[0016] By adopting the above technical solutions, acrylic acid: provides a strong hydrophilic carboxylic acid group (-COOH), enhances the adsorption capacity of the water reducer on cement particles, reduces the electrostatic repulsion between particles in the initial hydration period, and improves dispersibility. (E)-3-(Naphthalene-1-yl) acrylic acid: The rigid structure of the naphthalene ring increases the steric hindrance effect of the molecular chain, reduces the secondary agglomeration of cement particles, and the hydrophobic naphthalene ring can adjust the hydrophilic-hydrophobic balance of the water reducer and optimize the thickness of the adsorption layer. 1:1 molar ratio: balances hydrophilicity and hydrophobicity to ensure that the water reducer forms a stable adsorption layer on the surface of cement particles, while avoiding excessive dispersion leading to slurry exudation.

[0017] Preferably, in step S61, the siloxane monomer is composed of γ-mercaptopropyltriethoxysilane and vinyltrimethoxysilane in a molar ratio of 2:1.

[0018] By adopting the above technical solution, the alkoxy group of siloxane (such as -OCH 3 ) undergoes an esterification reaction with the hydroxyl groups of the polycarboxylic acid main chain to form a grafted structure, which enhances the steric hindrance effect of the water reducer and improves fluidity. During the cement hardening stage, the ester group hydrolyzes to release the siloxane chain, and its alkoxy and hydroxyl groups react with the cement hydration products (such as CSH gel) to form a cross-linked network, fill the pores, and improve density and compressive strength. Specifically, γ-mercaptopropyltriethoxysilane: Mercapto (-SH) activity: The mercapto group has high reactivity and can undergo a thiol-ene click reaction with the double bonds in carboxylic acid monomers (such as acrylic acid), promoting the grafting of the siloxane molecular chain to the polycarboxylic acid main chain and enhancing the stability of the molecular structure. Ethoxy hydrolysis: The ethoxy (-OC 2 H 5 ) is hydrolyzed under alkaline or acidic conditions to generate silanol (Si-OH), which forms a chemical bond with the surface of cement particles, improving the adsorption capacity of the water reducer on cement particles and enhancing the dispersion effect. Vinyl trimethoxysilane: Vinyl (-CH=CH 2 )Copolymerization ability: Vinyl can react with carboxylic acid monomers (such as acrylic acid) through free radical copolymerization to directly introduce the siloxane structure into the polycarboxylic acid main chain, ensuring the stable grafting of the siloxane molecular chain. 3 ) Rapid hydrolysis: The hydrolysis rate of methoxy is faster than that of ethoxy, and silanol can be generated in the early stage of the reaction, which promotes the esterification reaction between the siloxane molecular chain and the polycarboxylic acid side chain and enhances the steric hindrance effect of the water reducer. The introduction of vinyl can increase the rigidity of the polycarboxylic acid molecular chain and improve the adsorption stability of the water reducer on the surface of cement particles. The synergistic mechanism of the two: (1) Grafting efficiency and stability: The thiol and vinyl complement each other: The thiol group of γ-mercaptopropyltriethoxysilane is rapidly grafted via thiol-ene reaction, while vinyltrimethoxysilane is stably grafted via copolymerization. The combination of the two ensures that the siloxane molecular chain is efficiently and evenly grafted onto the polycarboxylic acid side chain, preventing the siloxane from falling off or converting into SiO2 Hydrolysis rate gradient: methoxy (vinyl trimethoxy silane) hydrolyzes quickly to provide early crosslinking points, while ethoxy (γ-mercaptopropyl triethoxy silane) hydrolyzes slowly to extend the reaction time, forming a gradient crosslinking network and optimizing the dispersibility and collapse retention of the water reducer. (2) Steric hindrance and dispersibility: The alkoxy groups (-OCH 3 / -OC 2 H 5 ) forms a dense siloxane layer on the polycarboxylic acid side chain, which prevents cement particles from agglomerating through steric hindrance and significantly improves the fluidity of the mortar. The rigid structure of vinyl trimethoxysilane combines with the flexible chain segment of γ-mercaptopropyl triethoxysilane to enhance the ability of the water reducer to wrap particles. (3) Dynamic hydrolysis and cross-linking: During the cement hardening process, the grafted siloxane ester group (generated by dealcoholization reaction) gradually hydrolyzes to release silanol (Si-OH), forming chemical bonds with cement hydration products (such as CSH gel) to enhance the density of the mortar. The mercapto group of γ-mercaptopropyl triethoxysilane can also react with metal ions (such as Ca2+) in cement. 2 +) coordination to further strengthen the interface bonding. In summary, by compounding γ-mercaptopropyltriethoxysilane and vinyltrimethoxysilane in a 2:1 molar ratio: combining thiol-ene reaction and free radical copolymerization, the stable grafting of siloxane molecular chains is achieved. The difference in the hydrolysis rate of methoxy and ethoxy groups forms a dynamic cross-linking network, which optimizes the dispersibility and collapse retention of the water reducer. The chemical bonding of siloxane hydrolysis products and cement hydration products significantly improves the density and compressive strength of the mortar.

[0019] Preferably, in step S62, the initiator is ammonium persulfate; and the chain transfer agent is 3-mercaptopropionic acid.

[0020] Preferably, in step S63, the polyether monomer is composed of isobutylene polyethylene glycol ether and isopentanol polyoxyethylene ether in a molar ratio of 1:7.

[0021] By adopting the above technical solutions, isobutylene polyethylene glycol ether (HPEG): the long side chain provides strong steric hindrance, inhibits the aggregation of cement particles, and reduces the viscosity of the slurry. Isopentenol polyoxyethylene ether (TPEG): the highly reactive ether bond promotes copolymerization with carboxylic acid monomers, optimizes the molecular weight distribution, and enhances the encapsulation effect of the water reducer on the particles. 1:7 molar ratio: mainly TPEG, to ensure the flexibility of the water reducer molecular chain, adapt to the surface morphology of cement particles, and improve adsorption stability.

[0022] Preferably, the water retaining agent is composed of sodium salt of styrene sulfonic acid-acrylic acid copolymer and sodium isopropylnaphthalene sulfonate in a mass ratio of 5:2.

[0023] By adopting the above technical scheme, the role of the water retaining agent in the dry mortar is mainly to maintain the moisture of the mortar and prevent the moisture from evaporating or losing too early, thereby ensuring the adhesion and strength of the mortar. As components of the water retaining agent, sodium salt of styrene sulfonic acid-acrylic acid copolymer and sodium isopropyl naphthalene sulfonate can work together to significantly improve the water retention performance of the mortar. Specifically, sodium salt of styrene sulfonic acid-acrylic acid copolymer has good water retention performance and high stability, and can effectively absorb and retain moisture; while sodium isopropyl naphthalene sulfonate has strong hydrophilicity and dispersibility, and can form a stable water film in the mortar to prevent the loss of moisture too quickly. The two are mixed in a certain proportion to form a synergistic effect and improve the overall performance of the water retaining agent. In short, through the combined effect of the two, the uniform dispersion of solid matter in dry mortar can be promoted, the viscosity of wet mortar can be improved, the wet mortar can have better fluidity, and the settling rate of particles in wet mortar can be controlled, so that the final solidified mortar has a higher density, fundamentally eliminating the occurrence of cracks, hollows and other gap defects, and improving the fluidity, mechanical properties and water retention properties of the mortar.

[0024] In the second aspect, the present application provides a method for preparing an environmentally friendly dry-mix mortar, which adopts the following technical solution: As a general technical concept, the present application also provides a method for preparing the above-mentioned environmentally friendly dry-mixed mortar, comprising the following steps: first, according to the mass fractions, mix cement, modified expanded glass microspheres, modified polycarboxylic acid water-reducing agent, water-retaining agent, hydroxypropyl methylcellulose and polypropylene fiber evenly, then add fine sand and fly ash in sequence, stir evenly, and obtain environmentally friendly dry-mixed mortar.

[0025] In summary, the beneficial technical effects of this application are: 1. Environmental protection and cost-effectiveness: By using common building materials such as cement, fly ash, fine sand as the main raw materials, and using additives such as modified expanded vitrified microspheres and modified polycarboxylate water reducers, the production cost is reduced. At the same time, the production process of this environmentally friendly dry mortar is simple, which helps to reduce environmental pollution.

[0026] 2. Excellent physical properties: The use of modified expanded vitrified microspheres not only improves the thermal insulation performance of the mortar, but also enhances the mechanical properties and durability of the mortar. At the same time, the use of modified polycarboxylate water reducer improves the fluidity and mechanical properties of the mortar.

[0027] 3. Improve pore structure: Through the steric hindrance effect and dispersion performance of modified polycarboxylic acid water-reducing agent, the pore structure of concrete is effectively improved, thereby improving the overall performance of mortar.

[0028] 4. Reduce defects: The use of water-retaining agent helps to control the settling rate of particles in wet mortar, thereby increasing the density of the solidified material and reducing the occurrence of cracks, hollows and other defects.

[0029] 5. Improve construction efficiency: Due to the use of modified expanded vitrified microspheres and modified polycarboxylic acid water reducer, the fluidity of the mortar has been significantly improved, the construction process has been reduced, and the construction quality has become more stable. DETAILED DESCRIPTION

[0030] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0031] In the following Examples, Preparation Examples and Comparative Preparation Examples, 1 part by mass means 1 kg; 1 part by mole means 1 mol.

[0032] Preparation Example 1 Preparation of modified expanded glass microspheres The preparation method of modified expanded vitrified microspheres comprises the following steps: S31, heating 200 parts of expanded vitrified microspheres with a particle size of 0.5 mm to 1 mm to 320° C. for heat treatment for 5.6 hours to obtain pretreated expanded vitrified microspheres; S32, dispersing 100 parts of tetraethyl orthosilicate and 35 parts of isotridecyl alcohol in 400 parts of 85% ethanol aqueous solution by weight, adjusting the pH to 2.5, adding 2 parts of gel accelerator methyl ethylene oxide, and aging at 85° C. for 24 hours to obtain a mixed wet gel; S33, adding 400 parts of the mixed wet gel to 500 parts of an organic solution containing silane (a solution composed of vinyltriethoxysilane and ethanol mixed in a mass ratio of 1:30) by weight, soaking for 26 hours, washing, and vacuum drying to obtain isomeric tridecanol modified silica aerogel powder; S34. Disperse 80 parts of isotridecyl alcohol modified silica aerogel powder in 300 parts of ethanol according to mass fractions, add 200 parts of pretreated expanded vitrified microspheres, mix well, filter and dry to obtain modified expanded vitrified microspheres.

[0033] Preparation Example 2 Preparation of modified polycarboxylate water reducer The preparation method of the modified polycarboxylate water-reducing agent comprises the following steps: S61. Add 18.5 parts of carboxylic acid monomer and 1.1 parts of siloxane monomer to 290 parts of water in molar proportions, and stir evenly to obtain a mixed solution A; the carboxylic acid monomer is composed of acrylic acid and (E)-3-(naphthalene-1-yl)acrylic acid in a molar proportion of 1:1; the siloxane monomer is composed of γ-mercaptopropyltriethoxysilane and vinyltrimethoxysilane in a molar proportion of 2:1; S62, adding 0.35 parts of ammonium persulfate and 0.86 parts of chain transfer agent 3-mercaptopropionic acid to 100 parts of water according to molar fractions, stirring evenly to obtain a mixed solution B; S63. According to the molar fraction, add 8.8 parts of polyether monomer (composed of isobutylene polyethylene glycol ether and isopentanol polyoxyethylene ether in a molar fraction of 1:7) to 120 parts of water and stir, then add 1 part of hydrogen peroxide, stir and heat to 48°C, then add mixed solution A and mixed solution B dropwise at the same time. After the addition is completed for 3 hours, continue to stir and react for 3.5 hours, then add a 10% NaOH aqueous solution to adjust the pH value to 7, and obtain a modified polycarboxylic acid water reducer.

[0034] Preparation of Comparative Example 1 Preparation of Modified Polycarboxylate Water-Reducing Agent The same as Preparation Example 2, except that the carboxylic acid monomer is acrylic acid.

[0035] Preparation of Comparative Example 2 Preparation of Modified Polycarboxylate Water-Reducing Agent The same as Preparation Example 2, except that the carboxylic acid monomer is (E)-3-(naphthalene-1-yl)acrylic acid.

[0036] Preparation of Comparative Example 3 Preparation of Modified Polycarboxylate Water-Reducing Agent The same as Preparation Example 2, except that the siloxane monomer is γ-mercaptopropyltriethoxysilane.

[0037] Preparation of Comparative Example 4 Preparation of Modified Polycarboxylate Water-Reducing Agent The same as Preparation Example 2, except that the siloxane monomer is vinyltrimethoxysilane.

[0038] Example 1 An environmentally friendly dry-mix mortar comprises the following raw materials by weight: 130 parts of cement, 60 parts of fly ash, 750 parts of fine sand, 20 parts of modified expanded vitrified microspheres, 7 parts of modified polycarboxylate water-reducing agent, 3 parts of water-retaining agent, 1 part of hydroxypropyl methylcellulose, and 3 parts of polypropylene fiber, wherein the cement is ordinary Portland cement of P·O42.5 grade; the fly ash is grade II ash; the particle size of the fine sand is 20-40 mesh; the modified polycarboxylate water-reducing agent is prepared in Preparation Example 2, and the water-retaining agent is composed of sodium salt of styrene sulfonic acid-acrylic acid copolymer and sodium isopropyl naphthalene sulfonate in a weight ratio of 5:2; The preparation method of the above-mentioned environmentally friendly dry-mixed mortar includes the following steps: first, according to the mass proportions, cement, modified expanded glass microspheres, modified polycarboxylic acid water-reducing agent, water-retaining agent, hydroxypropyl methylcellulose and polypropylene fiber are evenly mixed, and then fine sand and fly ash are added in sequence, and stirred evenly to obtain environmentally friendly dry-mixed mortar.

[0039] Example 2 An environmentally friendly dry-mix mortar comprises the following raw materials by weight: 150 parts of cement, 80 parts of fly ash, 800 parts of fine sand, 25 parts of modified expanded vitrified microspheres, 9 parts of modified polycarboxylate water-reducing agent, 5 parts of water-retaining agent, 2 parts of hydroxypropyl methylcellulose, and 4 parts of polypropylene fiber, wherein the cement is ordinary Portland cement of grade P·O42.5; the fly ash is grade II ash; the particle size of the fine sand is 20-40 mesh; the modified polycarboxylate water-reducing agent is prepared in Preparation Example 2, and the water-retaining agent is composed of sodium salt of styrene sulfonic acid-acrylic acid copolymer and sodium isopropyl naphthalene sulfonate in a weight ratio of 5:2; The preparation method of the above-mentioned environmentally friendly dry-mixed mortar includes the following steps: first, according to the mass proportions, cement, modified expanded glass microspheres, modified polycarboxylic acid water-reducing agent, water-retaining agent, hydroxypropyl methylcellulose and polypropylene fiber are evenly mixed, and then fine sand and fly ash are added in sequence, and stirred evenly to obtain environmentally friendly dry-mixed mortar.

[0040] Example 3 An environmentally friendly dry-mix mortar comprises the following raw materials by weight: 140 parts of cement, 70 parts of fly ash, 780 parts of fine sand, 23 parts of modified expanded vitrified microspheres, 8 parts of modified polycarboxylate water-reducing agent, 4 parts of water-retaining agent, 1.2 parts of hydroxypropyl methylcellulose, and 3.5 parts of polypropylene fiber, wherein the cement is ordinary Portland cement of grade P·O42.5; the fly ash is grade II ash; the particle size of the fine sand is 20-40 mesh; the modified polycarboxylate water-reducing agent is prepared in Preparation Example 2, and the water-retaining agent is composed of sodium salt of styrene sulfonic acid-acrylic acid copolymer and sodium isopropyl naphthalene sulfonate in a weight ratio of 5:2; The preparation method of the above-mentioned environmentally friendly dry-mixed mortar includes the following steps: first, according to the mass proportions, cement, modified expanded glass microspheres, modified polycarboxylic acid water-reducing agent, water-retaining agent, hydroxypropyl methylcellulose and polypropylene fiber are evenly mixed, and then fine sand and fly ash are added in sequence, and stirred evenly to obtain environmentally friendly dry-mixed mortar.

[0041] Comparative Example 1 The same as Example 3, except that the modified polycarboxylic acid water-reducing agent is prepared according to Comparative Example 1.

[0042] Comparative Example 2 The same as Example 3, except that the modified polycarboxylic acid water-reducing agent is prepared according to Comparative Example 2.

[0043] Comparative Example 3 The same as Example 3, except that the modified polycarboxylic acid water-reducing agent is prepared according to Comparative Example 3.

[0044] Comparative Example 4 The same as Example 3, except that the modified polycarboxylic acid water-reducing agent is prepared according to Comparative Example 4.

[0045] Comparative Example 5 The same as Example 3, except that an equal amount of unmodified expanded vitrified microspheres are used instead of modified expanded vitrified microspheres.

[0046] Comparative Example 6 The same as Example 3, except that the water retaining agent is styrene sulfonic acid-acrylic acid copolymer sodium salt.

[0047] Comparative Example 7 The same as Example 3, except that the water retaining agent is sodium isopropylnaphthalenesulfonate.

[0048] Performance Testing 100 kg of the environmentally friendly dry mortar prepared in Examples 1 to 3 and Comparative Examples 1 to 7 were taken respectively, and 14 kg of tap water was added and stirred evenly to form water mortar. The following tests were performed. Each group was tested three times in parallel, and the results were averaged. The test results are shown in Table 1.

[0049] The 28d compressive strength is tested according to the national standard GB / T17671-2021; Thermal conductivity: The thermal conductivity is measured using a JW-Ⅲ heat flow meter thermal conductivity meter and a device for measuring thermal conductivity using a heat pulse method; the water retention rate and consistency are tested in accordance with the JGJ / T70-2009 standard for basic properties test methods for building mortar.

[0050] Table 1 Performance test Analyzing the data in Table 1, we can see that: 1) The environmentally friendly dry-mix mortar prepared in Examples 1 to 3 has good thermal insulation performance, excellent fluidity, mechanical properties and water retention properties.

[0051] 2) The performance comparison analysis of the environmentally friendly dry-mixed mortar prepared in combination with Example 3 and Comparative Examples 1-4 shows that the modified polycarboxylic acid water-reducing agent prepared in the present application is prepared by precisely controlling the reaction conditions using carboxylic acid monomers, siloxane monomers of specific structures, polyether monomers, initiators and chain transfer agents as raw materials; on the one hand, the siloxane monomers of specific structures have high stability, so that the alkoxy groups of the siloxane monomers react with the polycarboxylic acid to generate ester groups, so that the siloxane molecular chains are effectively grafted onto the side chains of the polycarboxylic acid water-reducing agent without being converted into SiO, and the siloxane monomers of specific structures have high stability, so that ... However, the steric hindrance effect of the polycarboxylic acid water-reducing agent is significantly improved, and the fluidity of the cement mortar is effectively improved when it is adsorbed on the surface of the recycled dry-mix mortar particles; on the other hand, a hydrolysis reaction will occur during the mixing and hardening process of the generated ester-based cement, so that the siloxane molecular chain will fall off from the polycarboxylic acid water-reducing agent, and the siloxane monomer has good dispersibility. The alkoxy and hydroxyl groups contained therein can effectively improve the cross-linking effect between the recycled dry-mix mortar particles, and through its steric hindrance effect and dispersibility, the pore structure of the concrete is effectively improved, and the fluidity and mechanical properties of the cement mortar can be significantly improved. In particular, when the carboxylic acid monomer is composed of acrylic acid and (E)-3-(naphthalene-1-yl) acrylic acid in a molar fraction of 1:1 and the siloxane monomer is composed of γ-mercaptopropyltriethoxysilane and vinyltrimethoxysilane in a molar fraction of 2:1, the performance of the modified polycarboxylic acid water-reducing agent prepared is more ideal.

[0052] 3) A comparative analysis of the performance of the environmentally friendly dry-mixed mortars prepared in Example 3 and Comparative Example 5 shows that the modified expanded vitrified microspheres prepared in the present application, by attaching silica aerogel to expanded vitrified microspheres with a porous structure, not only fill the open pores on the surface of the expanded vitrified microspheres and repair their surface defects, but also enhance the surface strength of the expanded vitrified microspheres to a certain extent. More importantly, the modified expanded vitrified microspheres not only greatly reduce the thermal conductivity of the expanded vitrified microspheres, thereby improving the thermal insulation properties of the mortar material, but also effectively solve the problem that the aerogel is unstable in the mortar and the high cost caused by the high dosage, thereby significantly improving the thermal insulation properties, mechanical properties and durability of the environmentally friendly dry-mixed mortar.

[0053] 4) The performance comparison analysis of the environmentally friendly dry-mixed mortar prepared in combination with Example 3 and Comparative Examples 6-7 shows that the water retaining agent is composed of sodium salt of styrene sulfonic acid-acrylic acid copolymer and sodium isopropyl naphthalene sulfonate in a mass ratio of 5:2. The sodium salt of styrene sulfonic acid-acrylic acid copolymer fixes free water by electrostatic adsorption, and sodium isopropyl naphthalene sulfonate delays water evaporation by forming a water film, and the two synergistically improve the water retention rate. At the same time, the synergistic effect between them can promote the uniformity of the dispersion of solid matter in the dry-mixed mortar, improve the viscosity of the wet mortar, make the wet mortar have better fluidity, control the sedimentation rate of particles in the wet mortar, so that the final solidified mortar has a higher density, fundamentally eliminate the generation of cracks, hollows and other gap defects, and improve the fluidity, mechanical properties and water retention of the mortar.

[0054] The above embodiments are only used to explain the technical solutions of the present application rather than to limit them. Although the above embodiments provide a specific description of the present application, relevant technical personnel should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the scope of protection of the present application.

Claims

1. An environmentally friendly dry mortar, characterized in that: The preparation raw materials include the following by weight: 130-150 parts of cement, 60-80 parts of fly ash, 750-800 parts of fine sand, 20-25 parts of modified expanded glass microspheres, 7-9 parts of modified polycarboxylic acid water reducer, 3-5 parts of water retaining agent, 1-2 parts of hydroxypropyl methylcellulose and 3-4 parts of polypropylene fiber.

2. The environmentally friendly dry mortar according to claim 1, characterized in that: The cement is ordinary Portland cement of P·O42.5 grade; the fly ash is grade II ash; and the particle size of the fine sand is 20-40 meshes.

3. The environmentally friendly dry mortar according to claim 1, characterized in that: The preparation method of the modified expanded vitrified microspheres comprises the following steps: S31, heating 200 parts of expanded vitrified microspheres with a particle size of 0.5 mm-1 mm to 300° C.-350° C. for heat treatment for 5-6 hours to obtain pretreated expanded vitrified microspheres; S32, dispersing 100 parts of tetraethyl orthosilicate and 35 parts of isotridecyl alcohol in 400 parts of 85% ethanol aqueous solution by weight, adjusting the pH to 2-3, adding 2 parts of gel accelerator, and standing and aging at 80° C.-90° C. for 24 hours to obtain a mixed wet gel; S33, adding 400 parts of the mixed wet gel to 500 parts of the organic solution containing silane according to the mass fraction, soaking for 24h-28h, washing, and vacuum drying to obtain isomeric tridecanol modified silica aerogel powder; S34. Disperse 80 parts of isotridecyl alcohol modified silica aerogel powder in 300 parts of ethanol according to mass fractions, add 200 parts of pretreated expanded vitrified microspheres, mix well, filter and dry to obtain modified expanded vitrified microspheres.

4. The environmentally friendly dry mortar according to claim 3, characterized in that: In step S33, the silane-containing organic solution is a solution composed of vinyltriethoxysilane and ethanol mixed in a mass ratio of 1:

30.

5. The environmentally friendly dry mortar according to claim 3, characterized in that: In step S32, the gel accelerator is methyl ethylene oxide.

6. The environmentally friendly dry mortar according to claim 1, characterized in that: The preparation method of the modified polycarboxylate water-reducing agent comprises the following steps: S61, adding 18-19 parts of carboxylic acid monomer and 1-1.2 parts of siloxane monomer to 280-300 parts of water according to molar fractions, stirring evenly to obtain a mixed solution A; S62, adding 0.3-0.4 parts of initiator and 0.8-0.9 parts of chain transfer agent to 100 parts of water according to molar fractions, stirring evenly to obtain a mixed solution B; S63. According to the molar fraction, add 8-9 parts of polyether monomer to 120 parts of water and stir, then add 1 part of hydrogen peroxide, stir and heat to 47-50°C, and then drop mixed solution A and mixed solution B at the same time. After 3 hours of dropwise addition, continue stirring and reacting for 3-4 hours, and then add 10% mass concentration of NaOH aqueous solution to adjust the pH value to 6.8-7.2 to obtain modified polycarboxylic acid water reducer.

7. The environmentally friendly dry mortar according to claim 6, characterized in that: In step S61, the carboxylic acid monomer is composed of acrylic acid and (E)-3-(naphthalen-1-yl)acrylic acid in a molar ratio of 1:

1.

8. The environmentally friendly dry mortar according to claim 6, characterized in that: In step S61, the siloxane monomer is composed of γ-mercaptopropyltriethoxysilane and vinyltrimethoxysilane in a molar ratio of 2:

1.

9. The environmentally friendly dry mortar according to claim 6, characterized in that: In step S62, the initiator is ammonium persulfate; the chain transfer agent is 3-mercaptopropionic acid.

10. The environmentally friendly dry mortar according to claim 6, characterized in that: In step S63, the polyether monomer is composed of isobutylene polyethylene glycol ether and isopentanol polyoxyethylene ether in a molar ratio of 1:

7.

11. The environmentally friendly dry mortar according to claim 1, characterized in that: The water retaining agent is composed of sodium salt of styrene sulfonic acid-acrylic acid copolymer and sodium isopropyl naphthalene sulfonate in a mass ratio of 5:

2.

12. A method for preparing the environmentally friendly dry-mix mortar according to any one of claims 1 to 11, characterized in that: The following steps are involved: According to the mass proportions, cement, modified expanded glass microspheres, modified polycarboxylic acid water-reducing agent, water-retaining agent, hydroxypropyl methylcellulose and polypropylene fiber are first mixed evenly, and then fine sand and fly ash are added in sequence and stirred evenly to obtain environmentally friendly dry-mix mortar.

Images