A polycarboxylate superplasticizer for machine-made sand concrete and a preparation method thereof

Abstract

The application belongs to the field of admixtures for building materials, and particularly relates to a polycarboxylic acid water reducing agent suitable for machine-made sand concrete and a preparation method thereof. The polycarboxylic acid water reducing agent is compounded by a C6 polycarboxylic acid water reducing agent mother liquor with a solid content of 40%, a dispersing component and a viscosity-reducing water-retaining component. The preparation method comprises the following steps: (1) the C6 polycarboxylic acid water reducing agent mother liquor with a solid content of 40% is prepared through a free radical polymerization reaction; and (2) the polycarboxylic acid mother liquor prepared in the step (1) is mixed with the dispersing component, the viscosity-reducing water-retaining component and water, and then stirred uniformly to obtain the product. When the polycarboxylic acid water reducing agent is applied to machine-made sand concrete, the polycarboxylic acid water reducing agent has the advantages of strong initial dispersing capacity, good workability and strong slump retaining capacity, and can improve the mechanical properties of the machine-made sand concrete. The polycarboxylic acid water reducing agent can solve the problems of residual flocculants of machine-made sand and compatibility of the residual flocculants with the polycarboxylic acid high-performance water reducing agent, and has the advantages of short reaction time and low energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of building material admixtures, and particularly relates to a polycarboxylate superplasticizer suitable for manufactured sand concrete and its preparation method. Background Technology

[0002] Polycarboxylate superplasticizers, as third-generation superplasticizers, possess excellent performance, significantly improving the slump of concrete, preventing slump loss, increasing strength, and significantly reducing shrinkage. Furthermore, the product is free of formaldehyde and other harmful substances, making it a green and environmentally friendly product. It is currently widely used in concrete engineering projects such as building construction, highways, bridges, and tunnels. Currently, polycarboxylate superplasticizers are mainly produced by free radical polymerization of isobutylene alcohol polyoxyethylene ether (HPEG, C4) and isopentenyl alcohol polyoxyethylene ether (TPEG, C5) macromonomers and unsaturated carboxylic acid monomers. Room temperature polymerization has been achieved, but the reaction time reaches 5-7 hours, resulting in a long production cycle and high energy consumption.

[0003] In recent years, with the massive investment in construction projects, the demand for concrete and cement products has also increased significantly. As one of the main aggregates in concrete and cement products, the consumption of sand and gravel has risen sharply, with an average of over 5 tons of sand and gravel aggregate required for every ton of cement. Decades of civil engineering construction and extremely rapid consumption have led to increasingly scarce natural sand resources. Natural sand is a local resource and is non-renewable in the short term. The gradual shortage of natural sand resources in many areas has resulted in increasingly higher prices. Driven by economic interests, indiscriminate mining and excavation of natural sand in many places has caused serious environmental pollution. To protect the ecological environment and reduce the production cost of concrete, there is a clear trend towards using manufactured sand to partially or completely replace natural sand as fine aggregate.

[0004] Manufactured sand is produced by crushing and screening natural rocks after removing topsoil, interlayer soil, and weathered surface layers. The resulting sand has a particle size of less than 4.75mm. However, manufactured sand often contains a large amount of impurities and is not highly pure, failing to meet the standards for construction sand. A more economical and convenient treatment method is washing. To implement ecological environmental protection goals and tasks, it is clearly required that sand and gravel production enterprises not discharge wastewater. Therefore, many sand and gravel production enterprises, in order to improve sand and gravel quality, wash sand and use flocculants in their wastewater treatment processes to accelerate the sedimentation of impurities in the wastewater, so as to quickly and effectively purify the washing water for recycling. During this process, after the manufactured sand is washed with the recycled washing water, residual flocculants will adsorb onto the surface of the sand, and the amount of flocculants is uncertain. These residual flocculants enter the mixed concrete along with the manufactured sand, and the high molecular weight of the flocculants will cause poor dispersion performance of the concrete mixture. In addition, compared with natural sand, manufactured sand has a coarse particle shape, sharp edges and corners, poor gradation, and high porosity. When used with HPEG and TPEG to synthesize polycarboxylate superplasticizers, it has always had problems such as excessively rapid slump loss and poor adaptability of concrete mixtures.

[0005] The above problems are often solved by adjusting the dosage of polycarboxylate superplasticizer. However, increasing the dosage can only improve the initial workability of concrete to a certain extent. At the same time, it leads to new problems such as poor control of concrete setting time and segregation, thereby affecting the mechanical properties and durability of concrete. Summary of the Invention

[0006] This invention addresses the problems of residual flocculants in manufactured sand and their compatibility with polycarboxylate superplasticizers by preparing a polycarboxylate superplasticizer suitable for manufactured sand concrete. The aim is to obtain freshly mixed concrete with good workability and ease of construction, while also improving the mechanical properties of the concrete. Simultaneously, it provides a method for preparing a polycarboxylate superplasticizer with short reaction time, low energy consumption, and good adaptability to manufactured sand concrete.

[0007] This invention is implemented as follows:

[0008] A polycarboxylate superplasticizer suitable for manufactured sand concrete is formulated from a C6 polycarboxylate superplasticizer mother liquor with a solid content of 40%, a dispersing component, and a viscosity-reducing and water-retaining component, with the following mass percentages:

[0009]

[0010] Furthermore, the dispersed component is one of hexadecyltrimethylammonium chloride and hexadecyltrimethylammonium bromide.

[0011] Furthermore, the viscosity-reducing and water-retaining component is one of polyethylene glycol and polypropylene glycol with a molecular weight of 800-3000.

[0012] The present invention also provides a method for preparing the polycarboxylate superplasticizer suitable for manufactured sand concrete, comprising the following steps:

[0013] (1) A C6 polycarboxylate superplasticizer mother liquor with a solid content of 40% was prepared by the following free radical polymerization reaction:

[0014] Monomer A and water are added to a reaction vessel and stirred to dissolve them in the water. After the base material is dissolved, oxidant and catalyst are added. Then, a mixed aqueous solution of monomers B and C, an aqueous solution of monomer D, and a mixed aqueous solution of reducing agent and chain transfer agent are added dropwise simultaneously. The first two mixed aqueous solutions are added dropwise over 0.5-1.5 hours, and the third mixed aqueous solution is added dropwise over 0.6-1.6 hours. After all the mixtures have been added dropwise, stirring is continued at room temperature for 0.5-1 hour. After the reaction, liquid alkali is added to neutralize to a pH of 6-8.

[0015] in:

[0016] The molar ratio of monomer A: monomer B: monomer C: monomer D is 1:(1-6):(0.1-3):(0.1-3);

[0017] Monomer A is one of ethylene glycol monovinyl polyethylene glycol ether and hydroxybutyl vinyl polyethylene glycol ether;

[0018] Monomer B is acrylic acid or methacrylic acid;

[0019] Monomer C is one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate;

[0020] Monomer D is 2-hydroxyethyl methacrylate phosphate.

[0021] (2) Take the polycarboxylic acid mother liquor prepared above, mix it with the dispersing component, the viscosity reducing and water retaining component, and water, and stir evenly to obtain the product.

[0022] Furthermore:

[0023] The oxidant is one of hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate, and the oxidant accounts for 0.1% to 6.5% of the total mass of the added monomers.

[0024] The reducing agent is at least one selected from sodium bisulfite, ferrous sulfate, ascorbic acid, and sodium formaldehyde sulfoxylate, and the reducing agent accounts for 0.1% to 3.0% of the total mass of the added monomers.

[0025] The chain transfer agent is one of mercaptopropionic acid, mercaptoacetic acid, and mercaptoethanol, and accounts for 0.1% to 1.5% of the total mass of the added monomers.

[0026] The catalyst is ferrous sulfate heptahydrate, and its mass is 0.001% to 0.10% of the total mass of the added monomers.

[0027] The present invention has the following advantages:

[0028] (1) When the polycarboxylate superplasticizer of the present invention is applied to manufactured sand concrete, it has the advantages of strong initial dispersion ability, good workability and strong slump retention ability, and can improve the mechanical properties of manufactured sand concrete.

[0029] (2) The polycarboxylate high-performance water-reducing agent of the present invention can fully dissolve among its components, and the concentration of the solution is uniform throughout, without stratification, and has good long-term stability during storage.

[0030] (3) This invention provides a polycarboxylate superplasticizer with short reaction time, low energy consumption, and good adaptability to manufactured sand concrete. Compared with the reaction time of 5-7 hours for ordinary polycarboxylate superplasticizer mother liquor, the reaction time of the polycarboxylate mother liquor of this invention is shortened to 1.6-3.6 hours, which greatly reduces the reaction time. At the same time, the reaction is carried out at room temperature without heating, saving energy, reducing consumption, and improving production efficiency. Detailed Implementation

[0031] Example 1:

[0032] 300g of ethylene glycol monovinyl polyethylene glycol ether (molecular weight 3000) was added to a reactor, followed by 364g of water. The mixture was stirred at room temperature until the base material was completely dissolved. After the base material was dissolved, 5.0g of 30% hydrogen peroxide and 0.020g of ferrous sulfate heptahydrate were added. Simultaneously, an aqueous solution prepared from 14.41g of acrylic acid, 17.42g of hydroxyethyl acrylate, and 30g of water, and an aqueous solution prepared from 4.56g of 2-hydroxyethyl methacrylate phosphate and 60g of water were added dropwise, completing the addition within 1.0h. At the same time, an aqueous solution prepared from 1.0g of vitamin C, 1.68g of mercaptoacetic acid, and 62g of water was added dropwise, completing the addition within 1.1h. After all the mixtures were added, the mixture was stirred at room temperature for another 1h. Liquid alkali was added to neutralize the solution to a pH of 6-8, yielding a polycarboxylate mother liquor with a solid content of 40%. Then, take 100g of the above polycarboxylic acid mother liquor, 1.5g of hexadecyltrimethylammonium chloride, and 0.25g of polyethylene glycol (molecular weight 1000), dissolve them in 398.25g of water, and stir to mix evenly to obtain the product.

[0033] Example 2:

[0034] 300g of ethylene glycol monovinyl polyethylene glycol ether (molecular weight 3000) was added to a reactor, followed by 363g of water. The mixture was stirred at room temperature until the base material was completely dissolved. After the base material was dissolved, 5.44g of 30% hydrogen peroxide and 0.017g of ferrous sulfate heptahydrate were added. Simultaneously, an aqueous solution prepared from 17.22g of methacrylic acid, 17.42g of hydroxyethyl acrylate, and 30g of water, and an aqueous solution prepared from 5.70g of 2-hydroxyethyl methacrylate phosphate and 65g of water were added dropwise over 0.6 hours. At the same time, an aqueous solution prepared from 1.19g of vitamin C, 1.77g of mercaptopropionic acid, and 65g of water was added dropwise over 0.7 hours. After all the mixtures were added, the mixture was stirred at room temperature for another 1 hour. Liquid alkali was added to neutralize the solution to a pH of 6-8, yielding a polycarboxylic acid mother liquor with a solid content of 40%. Then, take 125g of the above polycarboxylic acid mother liquor, 1.75g ​​of hexadecyltrimethylammonium bromide, and 0.28g of polyethylene glycol (molecular weight 1000), dissolve them in 372.97g of water, and stir to mix evenly to obtain the product.

[0035] Example 3:

[0036] 300g of hydroxybutylvinyl polyethylene glycol ether (molecular weight 3000) was added to a reactor, followed by 368g of water. The mixture was stirred at room temperature until the base material was completely dissolved. After the base material was dissolved, 5.77g of 30% hydrogen peroxide and 0.025g of ferrous sulfate heptahydrate were added. Simultaneously, an aqueous solution prepared from 21.62g of acrylic acid, 21.63g of hydroxypropyl methacrylate, and 30g of water, and an aqueous solution prepared from 6.84g of 2-hydroxyethyl methacrylate phosphate and 70g of water were added dropwise over 0.5 hours. At the same time, an aqueous solution prepared from 1.05g of vitamin C, 1.75g ​​of mercaptopropionic acid, and 70g of water was added dropwise over 0.6 hours. After all the mixtures were added, the mixture was stirred at room temperature for another 0.8 hours. Liquid alkali was added to neutralize the solution to a pH of 6-8, yielding a polycarboxylate mother liquor with a solid content of 40%. Then, take 75g of the above polycarboxylic acid mother liquor, 2g of hexadecyltrimethylammonium chloride, and 0.3g of polypropylene glycol (molecular weight 1000), dissolve them in 422.7g of water, and stir to mix evenly to obtain the product.

[0037] Example 4:

[0038] 300g of hydroxybutylvinyl polyethylene glycol ether (molecular weight 3000) was added to a reactor, followed by 366g of water. The mixture was stirred at room temperature until the base material was completely dissolved. After the base material was dissolved, 5.24g of 30% hydrogen peroxide and 0.031g of ferrous sulfate heptahydrate were added. Simultaneously, an aqueous solution prepared from 21.52g of methacrylic acid, 19.52g of hydroxypropyl acrylate and 30g of water, and an aqueous solution prepared from 7.98g of 2-hydroxyethyl methacrylate phosphate and 70g of water were added dropwise over 1.4 hours. At the same time, an aqueous solution prepared from 1.22g of vitamin C, 1.81g of mercaptoethanol and 70g of water was added dropwise over 1.5 hours. After all the mixtures were added, the mixture was stirred at room temperature for another 0.8 hours. Liquid alkali was added to neutralize the solution to a pH of 6-8, yielding a polycarboxylic acid mother liquor with a solid content of 40%. Then, take 140g of the above polycarboxylic acid mother liquor, 1.9g of hexadecyltrimethylammonium bromide, and 0.28g of polypropylene glycol (molecular weight 1000), dissolve them in 357.83g of water, and stir to mix evenly to obtain the product.

[0039] Comparative Example 1:

[0040] Take 250g of ordinary polycarboxylate superplasticizer (40% solid content) produced by Fujian Construction Engineering Building Materials Technology Development Co., Ltd., dissolve it in 250g of water, and stir to mix evenly.

[0041] Comparative Example 2:

[0042] Take 100g of the mother liquor from Comparative Example 1, 1.5g of hexadecyltrimethylammonium chloride, and 0.25g of polyethylene glycol (molecular weight 1000), dissolve them in 398.25g of water, and stir to mix evenly.

[0043] Comparison of Application Effects: The polycarboxylate superplasticizer suitable for manufactured sand prepared according to this invention was tested for concrete water reduction rate, air content, slump / spread, and compressive strength at different ages. The concrete water reduction rate and air content test methods were performed according to the relevant provisions of GB 8076-2008 "Concrete Admixtures"; slump / spread was performed according to GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures"; and concrete compressive strength was performed according to the relevant provisions of GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The test cement was P.O42.5 cement, the fineness modulus of manufactured sand was 2.9, and the aggregate was crushed stone with a continuous gradation of 5-20mm. The concrete mix ratio was C:S:G = 360:780:1080. The water content was adjusted to make the initial slump of the fresh concrete (210±10)mm. The solid dosage of the polycarboxylate superplasticizer was 0.18% of the cement weight. The experimental results are shown in Table 1 below.

[0044] Table 1

[0045]

[0046]

[0047] As shown in Table 1, the polycarboxylate high-performance water-reducing agent of the present invention, applicable to manufactured sand, features high water reduction rate and low air content in concrete. Compared with the blank, Comparative Example 1, and Comparative Example 2, the concrete incorporating the present invention exhibits better workability, less slump / spread loss over time, and higher compressive strength at all ages of hardened concrete.

[0048] In the synthesis of polycarboxylate mother liquor in this invention, the C6 polyether macromonomer used has higher double bond activity and less steric hindrance compared to C4 and C5 monomers. This allows for greater freedom of movement of the polyether side chains, thereby improving their encapsulation of cement and resulting in a more adaptable polycarboxylate mother liquor. The special functional group ester group on the polycarboxylate superplasticizer molecule hydrolyzes under conditions of increased alkalinity during cement hydration, releasing carboxyl groups that continuously adsorb onto the cement surface, thus exerting a water-reducing and dispersing effect.

[0049] The phosphate esters introduced into the polycarboxylate superplasticizer molecule hydrolyze under alkaline conditions, preferentially adsorbing soil from manufactured sand, thus reducing the soil's adsorption of the superplasticizer and free water. The dispersing component disperses soil in the concrete aggregate, enhancing the adsorption of soil by the phosphate groups, while also preventing soil aggregation that leads to reduced strength in hardened concrete. The viscosity-reducing and water-retaining components address the problem of increased concrete viscosity and poor dispersibility caused by residual flocculants (with excessively high molecular weight) introduced during manufactured sand washing. These various effects work synergistically, resulting in the polycarboxylate superplasticizer of this invention exhibiting strong initial dispersion, good workability, and strong slump retention when applied to manufactured sand concrete, while also improving the mechanical properties of the concrete.

[0050] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a polycarboxylate superplasticizer suitable for manufactured sand concrete, characterized in that: Includes the following steps: (1) A C6 polycarboxylate superplasticizer mother liquor with a solid content of 40% was prepared by the following free radical polymerization reaction: Monomer A and water were added to a reaction vessel and stirred to dissolve them in the water. After the base material dissolved, oxidant and catalyst were added. Then, a mixed aqueous solution of monomers B and C, an aqueous solution of monomer D, and a mixed aqueous solution of reducing agent and chain transfer agent were added dropwise simultaneously. The first two mixed aqueous solutions were added dropwise over 0.5-1.5 hours, and the third mixed aqueous solution was added dropwise over 0.6-1.6 hours. After all the mixtures were added dropwise, the mixture was stirred at room temperature for another 0.5-1 hour. After the reaction, liquid alkali was added to neutralize the pH to 6-8. in: The molar ratio of monomer A: monomer B: monomer C: monomer D is 1:(1-6):(0.1-3):(0.1-3). Monomer A is one of ethylene glycol monovinyl polyethylene glycol ether and hydroxybutyl vinyl polyethylene glycol ether; Monomer B is acrylic acid or methacrylic acid; Monomer C is one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate; Monomer D is 2-hydroxyethyl methacrylate phosphate; (2) Take the C6 polycarboxylate superplasticizer mother liquor with a solid content of 40% prepared above and mix it with the dispersion component, viscosity reducing and water retaining component, and water according to the following mass percentages. C6 polycarboxylate superplasticizer mother liquor with a solid content of 40% (12%-30%) Dispersed component 0.08%-0.5% Viscosity-reducing and water-retaining components: 0.01%-0.07% Water balance; Stir well to obtain the product.

2. The method for preparing a polycarboxylate superplasticizer suitable for manufactured sand concrete according to claim 1, characterized in that: The dispersed component is one of hexadecyltrimethylammonium chloride and hexadecyltrimethylammonium bromide.

3. The method for preparing a polycarboxylate superplasticizer suitable for manufactured sand concrete according to claim 1, characterized in that: The viscosity-reducing and water-retaining component is one of polyethylene glycol and polypropylene glycol with a molecular weight of 800-3000.

4. The method for preparing a polycarboxylate superplasticizer suitable for manufactured sand concrete according to claim 1, characterized in that: The oxidant is one of hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate, and the oxidant accounts for 0.1% to 6.5% of the total mass of the added monomers.

5. The method for preparing a polycarboxylate superplasticizer suitable for manufactured sand concrete according to claim 1, characterized in that: The reducing agent is at least one of sodium bisulfite, ferrous sulfate, ascorbic acid, and sodium formaldehyde sulfoxylate, and the reducing agent accounts for 0.1% to 3.0% of the total mass of the added monomers.

6. The method for preparing a polycarboxylate superplasticizer suitable for manufactured sand concrete according to claim 1, characterized in that: The chain transfer agent is one of mercaptopropionic acid, mercaptoacetic acid, and mercaptoethanol, and the chain transfer agent accounts for 0.1% to 1.5% of the total mass of the added monomers.

7. The method for preparing a polycarboxylate superplasticizer suitable for manufactured sand concrete according to claim 1, characterized in that: The catalyst is ferrous sulfate heptahydrate, and its mass is 0.001% to 0.10% of the total mass of the added monomers.

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