Special polycarboxylic acid water reducing agent for desert sand concrete and preparation method of special polycarboxylic acid water reducing agent

Abstract

The invention relates to the technical field of concrete admixtures, in particular to a special polycarboxylic acid water reducing agent for desert sand concrete and a preparation method of the special polycarboxylic acid water reducing agent. The special polycarboxylic acid water reducing agent for the desert sand concrete comprises the following components: a high-performance polycarboxylic acid water reducing agent and modified paper pulp black liquor, the high-performance polycarboxylate superplasticizer is prepared through a polymerization reaction of a vinyl polyether macromonomer, unsaturated carboxylic acid and a functional monomer under the action of an initiator and a chain transfer agent. According to the special polycarboxylic acid water reducing agent for the desert sand concrete, the high-performance polycarboxylic acid water reducing agent and the modified paper pulp black liquor are compounded and applied to the desert sand concrete, the initial fluidity of the concrete is good, the slump retaining property is good, the water retention property, the wrapping property and the cohesiveness of the concrete are good, and segregation and bleeding phenomena do not exist; the problems that the slump loss of a desert sand concrete mixture is fast and the desert sand concrete mixture is prone to bleeding and segregation due to the fact that the desert sand is large in fine powder amount and poor in gradation are solved.

Description

Technical Field

[0001] The present application relates to the technical field of concrete admixtures, and in particular to a polycarboxylate water reducer specially used for desert sand concrete and a preparation method thereof. Background Art

[0002] With the development of the times, the infrastructure construction at home and abroad has gradually increased, the amount of engineering projects has continued to expand, and the demand for various raw materials used in engineering projects has also continued to increase. In the context of sustainable development, cement concrete, as an essential material for infrastructure projects, is also developing in the direction of greening and durability.

[0003] Aggregate sand accounts for a large proportion of concrete, up to 70%, but the distribution of aggregate sand resources is uneven, and the characteristics of sand and gravel in different regions are different, making it difficult to unify and the transportation cost is high. For example, there is a shortage of engineering sand in Northwest my country, while Northwest China has abundant desert sand resources, and the desert sand reserves in Northwest my country are large and sufficient.

[0004] Desert sand is widely distributed around the world. How to rationally utilize desert sand resources as fine aggregate for concrete in engineering construction to replace existing commonly used concrete sand (such as engineering sand, etc.) is an effective way to solve the shortage of sand resources.

[0005] However, the application of desert sand in concrete mainly has the following problems. Due to the characteristics of desert sand, such as small particles, large amount of fine powder, low particle grading, high mud content (high clay content), severe weathering, difficult adsorption and high water demand, the slump of desert sand concrete mixture is lost quickly, and it is easy to bleed and segregate.

[0006] The existing traditional polycarboxylate water reducer is not very effective in desert sand concrete. It cannot effectively solve the problems of rapid slump loss, easy bleeding and segregation of desert sand concrete mixtures, or the dosage of polycarboxylate water reducer required in desert sand concrete is high, which makes the manufacturing cost high. Summary of the invention

[0007] In order to solve the problems of the prior art mentioned in the above background technology, the present application provides a polycarboxylate water reducer specially used for desert sand concrete, and its technical solution is as follows: The polycarboxylate water-reducing agent for desert sand concrete provided in the present application comprises a high-performance polycarboxylate water-reducing agent and modified pulp black liquor; the high-performance polycarboxylate water-reducing agent is prepared by polymerization reaction of vinyl polyether macromonomer, unsaturated carboxylic acid and functional monomer under the action of initiator and chain transfer agent; the functional monomer is 3-[tri(1-methylethoxy)silyl]propyl methacrylate or a hydrophobic monomer, and the hydrophobic monomer has the following structural formula:

[0008] Wherein, a value is 1 or 2, b value is an integer from 1 to 7, R1 is H or CH3, and R2 is H or F.

[0009] In some embodiments, the weight ratio of the high performance polycarboxylate water reducer to the modified pulp black liquor is (70-80): (15-30).

[0010] In some embodiments, the preparation process of the modified pulp black liquor is as follows: adjusting the pH value of the papermaking black liquor to 10-12 with an acid or a first type of alkali; heating to 60-90°C, adding a first type of oxidant and a catalyst to react at 60-90°C for 1-5 hours, and then neutralizing the reaction liquid with an acid or a first type of alkali to a pH of 7-9 to obtain the modified pulp black liquor; wherein the weight ratio of the papermaking black liquor, the first type of oxidant and the catalyst is 100: (3-8): (0.1-0.5).

[0011] In some embodiments, the pulp black liquor is one or a combination of bamboo pulp papermaking black liquor and wood pulp papermaking black liquor; the lignin content in the papermaking black liquor is 30% to 40%; the first type of oxidant is one or a combination of potassium dichromate and hydrogen peroxide; the catalyst is manganese dioxide; the acid is one or more combinations of salicylic acid, citric acid, and malic acid; the first type of alkali is one or a combination of sodium hydroxide and potassium hydroxide.

[0012] In some embodiments, under the action of an initiator and a chain transfer agent, the vinyl polyether macromonomer, unsaturated carboxylic acid, and functional monomer are polymerized to produce a high-performance polycarboxylic acid water-reducing agent; wherein the polymerization reaction temperature is 40 to 45° C.; and the weight ratio of the vinyl polyether macromonomer, unsaturated carboxylic acid, and functional monomer is (80 to 100): (10 to 15): (10 to 20).

[0013] In some embodiments, the initiator is composed of a reducing agent and a second type of oxidant; the polymerization reaction process is: by weight, 10 to 20 parts of functional monomers, 80 to 100 parts of vinyl polyether macromonomers, 1 to 1.5 parts of the second type of oxidant and 50 to 80 parts of water are added to the reactor; the temperature of the reaction system is controlled at 40 to 45°C, and then 30.5 to 30.8 parts of a reducing agent aqueous solution, 40 to 45 parts of an unsaturated carboxylic acid aqueous solution and 30.4 to 30.9 parts of a chain transfer agent aqueous solution are added respectively, and the addition time is 3 to 4 hours; the reducing agent aqueous solution, the unsaturated carboxylic acid aqueous solution and the chain transfer agent aqueous solution are added. After the addition of the acid aqueous solution and the chain transfer agent aqueous solution is completed, the mixture is kept warm at 40-45° C. for 1-5 hours, and a suitable amount of water is added to adjust the concentration of the reaction product to 40-50%. The pH of the reaction product is adjusted to 6.0-7.0 with the second type of alkali to obtain a high-performance polycarboxylate water-reducing agent. The unsaturated carboxylic acid aqueous solution is formed by dissolving 10-15 parts of unsaturated carboxylic acid in 30 parts of water. The reducing agent aqueous solution is formed by dissolving 0.5-0.8 parts of reducing agent in 30 parts of water. The chain transfer agent aqueous solution is formed by dissolving 0.4-0.9 parts of chain transfer agent in 30 parts of water.

[0014] In some embodiments, the reducing agent aqueous solution, the unsaturated carboxylic acid aqueous solution and the chain transfer agent aqueous solution are added dropwise.

[0015] In some embodiments, the molecular weight of the vinyl polyether macromonomer is 2400-5000; and the unsaturated carboxylic acid is acrylic acid.

[0016] In some embodiments, the reducing agent is one or more combinations of bisulfite, sulfite, bleaching powder, and vitamin C; the second type of oxidant is hydrogen peroxide; the chain transfer agent is one or more combinations of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, n-dodecyl mercaptan, secondary dodecyl mercaptan, and tert-dodecyl mercaptan; the second type of base is sodium hydroxide.

[0017] The present application also provides a method for preparing the polycarboxylate water reducer for desert sand concrete as described above, which comprises the following preparation steps: mixing a high-performance polycarboxylate water reducer and modified paper pulp black liquor to obtain the polycarboxylate water reducer for desert sand concrete.

[0018] The polycarboxylate water-reducing agent for desert sand concrete provided in this application has the following beneficial effects compared with the existing technology: The polycarboxylate water-reducing agent specially used for desert sand concrete provided in the present application adopts a high-performance polycarboxylate water-reducing agent and a modified pulp black liquor composite, and the composite is applied to desert sand concrete. The concrete has good initial fluidity and good slump retention performance, and the concrete has good water retention, encapsulation and cohesion, and has no segregation and bleeding phenomenon, thus overcoming the problems of fast slump loss of desert sand concrete mixture caused by the large amount of fine powder and poor grading of desert sand, and easy bleeding and segregation. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0020] The present application provides an operation example of the preparation process of a polycarboxylate water reducer for desert sand concrete as follows: The preparation process comprises the following steps: mixing a high-performance polycarboxylate water-reducing agent and modified paper pulp black liquor to obtain the polycarboxylate water-reducing agent for desert sand concrete, wherein the weight ratio of the high-performance polycarboxylate water-reducing agent to the modified paper pulp black liquor is (70-80): (15-30).

[0021] 1. The preparation process of high performance polycarboxylate water reducer is: (1) Add 10 to 20 parts of functional monomer, 80 to 100 parts of vinyl polyether macromonomer, 1 to 1.5 parts of the second type oxidant and 50 to 80 parts of water into a reactor; (2) Control the temperature of the reaction system to 40-45°C, then dropwise add 30.5-30.8 parts of a reducing agent aqueous solution, 40-45 parts of an unsaturated carboxylic acid aqueous solution, and 30.4-30.9 parts of a chain transfer agent aqueous solution, respectively, for 3-4 hours; (3) After the addition of the reducing agent aqueous solution, the unsaturated carboxylic acid aqueous solution and the chain transfer agent aqueous solution, the mixture is kept at 40 to 45°C for 1 to 5 hours, and a suitable amount of water is added to obtain a reaction product with a concentration of 40 to 50%; (4) The pH of the reaction product is adjusted to 6.0-7.0 with a second type of alkali to obtain a high-performance polycarboxylate water-reducing agent; The unsaturated carboxylic acid aqueous solution is formed by dissolving 10 to 15 parts of unsaturated carboxylic acid in 30 parts of water; the reducing agent aqueous solution is formed by dissolving 0.5 to 0.8 parts of reducing agent in 30 parts of water; and the chain transfer agent aqueous solution is formed by dissolving 0.4 to 0.9 parts of chain transfer agent in 30 parts of water.

[0022] The functional monomer used is 3-[tri(1-methylethoxy)silyl]propyl methacrylate or a hydrophobic monomer, and the hydrophobic monomer has the following structural formula:

[0023] Wherein, a value is 1 or 2, b value is an integer from 1 to 7, R1 is H or CH3, and R2 is H or F.

[0024] The molecular weight of the vinyl polyether macromonomer used is 2400-5000; the unsaturated carboxylic acid used is acrylic acid; the reducing agent used is one or more combinations of bisulfite, sulfite, bleaching agent, and vitamin C; the second type of oxidant used is hydrogen peroxide; the chain transfer agent used is one or more combinations of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, n-dodecyl mercaptan, secondary dodecyl mercaptan, and tert-dodecyl mercaptan; the second type of alkali used is sodium hydroxide.

[0025] 2. The preparation process of modified pulp black liquor is: The pH value of papermaking black liquor is adjusted to 10-12 with acid or first-class alkali; the temperature is raised to 60-90° C., and the first-class oxidant and catalyst are added to react at 60-90° C. for 1-5 hours, and then the reaction liquid is neutralized with acid or first-class alkali to a pH of 7-9, thereby obtaining the modified paper pulp black liquor; The weight ratio of papermaking black liquor, the first type oxidant and the catalyst is 100: (3-8): (0.1-0.5).

[0026] The pulp black liquor used is one or a combination of bamboo pulp papermaking black liquor and wood pulp papermaking black liquor, and the lignin content in the papermaking black liquor is 30% to 40%. The first type of oxidant used is one or a combination of potassium dichromate and hydrogen peroxide; the catalyst used is manganese dioxide; the acid used is one or a combination of salicylic acid, citric acid, and malic acid; the first type of alkali used is one or a combination of sodium hydroxide and potassium hydroxide.

[0027] The present application also provides the following embodiments and comparative examples: Example 1 1. The preparation process of high performance polycarboxylate water reducer is: 20 g of 2,2,3,3-tetrafluoropropyl methacrylate, 80 g of ethylene glycol monovinyl polyglycol ether, 1.5 g of hydrogen peroxide, and 70 g of water were added to a reaction kettle; The temperature was controlled at 40°C, and then 30.5 g of vitamin C aqueous solution, 43 g of acrylic acid aqueous solution and 30.4 g of thioglycolic acid aqueous solution were added dropwise at a uniform rate for 3 hours. After the addition was completed, the mixture was kept at 40°C for 1 hour, and a suitable amount of water was added to adjust the concentration of the reaction product to 50%. The pH of the reaction product is adjusted to 6.0-7.0 with sodium hydroxide to obtain a high-performance polycarboxylate water-reducing agent; Among them, the acrylic acid aqueous solution is 13g acrylic acid solution dissolved in 30g water; the vitamin C aqueous solution is 0.5g vitamin C dissolved in 30g water, the thioglycolic acid aqueous solution is 0.4g thioglycolic acid dissolved in 30g water, and the molecular weight of ethylene glycol monovinyl polyethylene glycol ether is 3000.

[0028] 2. The preparation process of modified pulp black liquor is: Salicylic acid was added to 100g of bamboo pulp papermaking black liquor to adjust the pH value to 11, the temperature was raised to 70°C, 4g of hydrogen peroxide and 0.2g of manganese dioxide were added, the mixture was reacted at 70°C for 3h, and then neutralized with citric acid to a pH of 7 to obtain modified pulp black liquor. The lignin content in the papermaking black liquor was 30%.

[0029] 3. The preparation process of polycarboxylate water reducer for desert sand concrete is: 80 g of high-performance polycarboxylate water reducer was blended with 20 g of modified pulp black liquor to obtain a polycarboxylate water reducer specifically for desert sand concrete.

[0030] Example 2 1. The preparation process of high performance polycarboxylate water reducer is: 15 g of 1H,1H,2H,2H-perfluorodecyl acrylate, 85 g of butanediol monovinyl polyethylene glycol ether, 1.0 g of hydrogen peroxide, and 50 g of water were added to a reaction kettle; The temperature was controlled at 45°C, and then 30.6g of a bleaching powder aqueous solution, 42g of an acrylic acid aqueous solution and 30.5g of a mercaptopropionic acid aqueous solution were added dropwise at a uniform rate for 3 hours. After the addition was completed, the mixture was kept at 45°C for 1 hour, and a suitable amount of water was added to adjust the concentration of the reaction product to 50%. The pH of the reaction product is adjusted to 6.0-7.0 with sodium hydroxide to obtain a high-performance polycarboxylate water-reducing agent; The acrylic acid aqueous solution is 12g acrylic acid solution dissolved in 30g water, the bleaching powder aqueous solution is 0.6g bleaching powder dissolved in 30g water, the mercaptopropionic acid aqueous solution is 0.5g mercaptopropionic acid dissolved in 30g water, and the molecular weight of butanediol monovinyl polyethylene glycol ether is 2400.

[0031] 2. The preparation process of modified pulp black liquor is: Sodium hydroxide was added to 100g of wood pulp papermaking black liquor to adjust the pH value to 12, the temperature was raised to 80°C, 5g of hydrogen peroxide and 0.4g of manganese dioxide were added, the mixture was reacted at 80°C for 4h, and then neutralized with malic acid to a pH of 7.5 to obtain modified pulp black liquor. The lignin content in the papermaking black liquor was 40%.

[0032] 3. The preparation process of polycarboxylate water reducer for desert sand concrete is: 75g of high-performance polycarboxylate water-reducing agent was mixed with 25g of modified pulp black liquor to obtain a polycarboxylate water-reducing agent specifically for desert sand concrete.

[0033] Example 3 1. The preparation process of high performance polycarboxylate water reducer is: 20 g of 3-[tri(1-methylethoxy)silyl]propyl methacrylate, 80 g of ethylene glycol monovinyl polyglycol ether, 1.5 g of hydrogen peroxide and 80 g of water were added to a reaction kettle; The temperature was controlled at 40°C, and then 30.5 g of vitamin C aqueous solution, 43 g of acrylic acid aqueous solution and 30.4 g of thioglycolic acid aqueous solution were added dropwise at a uniform rate for 3 hours. After the addition was completed, the mixture was kept at 40°C for 1 hour, and a suitable amount of water was added to adjust the concentration of the reaction product to 50%. The pH of the reaction product is adjusted to 6.0-7.0 with sodium hydroxide to obtain a high-performance polycarboxylate water-reducing agent; The acrylic acid aqueous solution is 13 g of acrylic acid solution dissolved in 30 g of water, the vitamin C aqueous solution is 0.5 g of vitamin C dissolved in 30 g of water, the thioglycolic acid aqueous solution is 0.4 g of thioglycolic acid dissolved in 30 g of water, and the molecular weight of ethylene glycol monovinyl polyethylene glycol ether is 3,000.

[0034] 2. The preparation process of modified pulp black liquor is: Salicylic acid was added to 100g of bamboo pulp papermaking black liquor to adjust the pH value to 11, the temperature was raised to 70°C, 4g of hydrogen peroxide and 0.2g of manganese dioxide were added, the reaction was carried out at 70°C for 3h, and then citric acid was used to neutralize the pH to 7 to obtain modified pulp black liquor. Among them, the lignin content in the papermaking black liquor was 35%.

[0035] 3. The preparation process of polycarboxylate water reducer for desert sand concrete is: 80g of high-performance polycarboxylate water-reducing agent was mixed with 20g of modified pulp black liquor to obtain a polycarboxylate water-reducing agent specially used for desert sand concrete.

[0036] Comparative Example 1 (Compared with Example 1, the preparation process of the high-performance polycarboxylate water-reducing agent lacks the addition of hydrophobic monomer) 1. The preparation process of high performance polycarboxylate water reducer is: 80 g of ethylene glycol monovinyl polyglycol ether was added into a reaction kettle together with 1.5 g of hydrogen peroxide and 70 g of water; The temperature was controlled at 40°C, and then 30.5 g of vitamin C aqueous solution, 43 g of acrylic acid aqueous solution and 30.4 g of thioglycolic acid aqueous solution were added dropwise at a uniform rate for 3 hours. After the addition was completed, the mixture was kept at 40°C for 1 hour, and a suitable amount of water was added to adjust the concentration of the reaction product to 50%. The pH of the reaction product is adjusted to 6.0-7.0 with sodium hydroxide to obtain a high-performance polycarboxylate water-reducing agent; Among them, the acrylic acid aqueous solution is 13g acrylic acid solution dissolved in 30g water; the vitamin C aqueous solution is 0.5g vitamin C dissolved in 30g water, the thioglycolic acid aqueous solution is 0.4g thioglycolic acid dissolved in 30g water, and the molecular weight of ethylene glycol monovinyl polyethylene glycol ether is 3000.

[0037] 2. The preparation process of modified pulp black liquor is: Salicylic acid was added to 100g of bamboo pulp papermaking black liquor to adjust the pH value to 11, the temperature was raised to 70°C, 4g of hydrogen peroxide and 0.2g of manganese dioxide were added, the mixture was reacted at 70°C for 3h, and then neutralized with citric acid to a pH of 7 to obtain modified pulp black liquor. The lignin content in the papermaking black liquor was 30%.

[0038] 3. The preparation process of polycarboxylate water reducer for desert sand concrete is: 80 g of high-performance polycarboxylate water reducer was blended with 20 g of modified pulp black liquor to obtain a polycarboxylate water reducer specifically for desert sand concrete.

[0039] Comparative Example 2 (Compared with Example 1, no modified pulp black liquor was added) The difference between this comparative example and Example 1 is that the prepared water reducer contains only high-performance polycarboxylic acid water reducer, and no modified pulp black liquor is added.

[0040] The specific preparation process of high performance polycarboxylate water reducer is: 20 g of 2,2,3,3-tetrafluoropropyl methacrylate, 80 g of ethylene glycol monovinyl polyglycol ether, 1.5 g of hydrogen peroxide, and 70 g of water were added to a reaction kettle; The temperature was controlled at 40°C, and then 30.5 g of vitamin C aqueous solution, 43 g of acrylic acid aqueous solution and 30.4 g of thioglycolic acid aqueous solution were added dropwise at a uniform rate for 3 hours. After the addition was completed, the mixture was kept at 40°C for 1 hour, and a suitable amount of water was added to adjust the concentration of the reaction product to 50%. The pH of the reaction product is adjusted to 6.0-7.0 with sodium hydroxide to obtain a high-performance polycarboxylate water-reducing agent; Among them, the acrylic acid aqueous solution is 13g acrylic acid solution dissolved in 30g water; the vitamin C aqueous solution is 0.5g vitamin C dissolved in 30g water, the thioglycolic acid aqueous solution is 0.4g thioglycolic acid dissolved in 30g water, and the molecular weight of ethylene glycol monovinyl polyethylene glycol ether is 3000.

[0041] Comparative Example 3 (Existing water reducing agent) Kezhijie New Materials Group Co., Ltd. produces PS polycarboxylate water reducer.

[0042] Comparative Example 4 (the polymerizable monomer used is different from the hydrophobic monomer selected in the embodiment) The only difference from Example 1 is that the hydrophobic monomer allyl chloroformate is used in place of the hydrophobic monomer 2,2,3,3-tetrafluoropropyl methacrylate, and the other preparation processes and conditions are the same as those of Example 1.

[0043] Comparative Example 5 (the ratio of high performance polycarboxylate water reducer to modified pulp black liquor is different from that in the example) The only difference from Example 1 is that 90 g of high-performance polycarboxylate water-reducing agent is blended with 10 g of modified pulp black liquor, and the other preparation processes and conditions are consistent with those of Example 1.

[0044] Performance tests of embodiments and comparative examples: The concrete mixture performance test was carried out in accordance with GB / T 50080-2016 "Standard for Test Methods for Performance of Ordinary Concrete Mixtures". The concrete mix ratio is: cement 360kg / m 3 、Mechanical sand 395kg / m 3 , Desert sand 395kg / m 3 、Stone 1060kg / m 3 、Water 162kg / m 3 .

[0045] The performance of the polycarboxylate water-reducing agent prepared in the specific embodiments and comparative examples when applied to desert sand concrete is shown in Table 1 below: Table 1 sample Polycarboxylate water reducer dosage / % Initial slump / mm 2h slump / mm Water seepage rate / % Workability Example 1 0.2 220 205 0 Concrete has good cohesiveness and wrapping properties Example 2 0.2 225 210 0 Concrete has good cohesiveness and wrapping properties Example 3 0.2 220 210 0 Concrete has good cohesiveness and wrapping properties Comparative Example 1 0.2 210 150 3.1 Concrete has poor cohesion and wrapping properties Comparative Example 2 0.2 180 150 1.2 Concrete has good cohesiveness and wrapping properties Comparative Example 3 0.2 180 130 10.2 Concrete has poor cohesion and encapsulation, and severe concrete segregation and bleeding Comparative Example 4 0.2 200 145 5.3 Concrete has poor cohesion and wrapping properties Comparative Example 5 0.2 170 150 4.8 Concrete has poor cohesion and wrapping properties Analysis of the above comparative examples and embodiment data shows that: Compared with Comparative Example 1 (compared with the example, the preparation process of the high-performance polycarboxylate water-reducing agent lacks the addition of hydrophobic monomers), the polycarboxylate water-reducing agent for desert sand concrete prepared in Examples 1-3 has good slump retention performance, no segregation and bleeding, and good concrete cohesion and wrapping properties. The main reasons for this are: Since the high-performance polycarboxylate water-reducing agent in the embodiment has water-retaining and micro-air-entraining effects, a large number of fluorine groups and other groups on its molecular chain form hydrogen bonds with water molecules, forming a three-dimensional network structure inside the cement paste, which increases the viscosity of the mixture and reduces the free water. As the hydrogen bond binding force weakens, a large amount of free water is gradually released, so that the concrete mixture maintains good plasticity and improves the slump retention performance of the concrete. The micro-air-entraining effect of the high-performance polycarboxylate water-reducing agent improves the encapsulation of the concrete and reduces the water bleeding rate.

[0046] Compared with Comparative Example 2 (without the addition of modified pulp black liquor), the polycarboxylate water-reducing agent for desert sand concrete prepared in Examples 1-3 has good initial dispersibility. The main reason for this is that the modified pulp black liquor in the examples contains alkali lignin, which has a three-dimensional network structure and is more likely to occupy most of the active sites of the fine powder in the desert sand concrete, so that the polycarboxylate water-reducing agent is preferentially adsorbed on the surface of cement particles, thereby improving the initial dispersibility of the desert sand concrete.

[0047] Compared with Comparative Example 3 (existing water reducer), the polycarboxylate water reducer for desert sand concrete prepared in Examples 1-3 has better initial dispersion performance and collapse retention performance, better concrete encapsulation and cohesion, and a relatively low concrete water bleeding rate.

[0048] Compared with Comparative Example 4 (the polymerized monomer used is different from the hydrophobic monomer selected in the embodiment), the polycarboxylate water-reducing agent for desert sand concrete prepared in Examples 1-3 has better slump retention performance, better concrete encapsulation and cohesion, and a relatively low concrete water bleeding rate.

[0049] In addition, in addition to the polymerized monomer allyl chloroformate used in Comparative Example 4, if methyl 2-bromoprop-2-enoate or methyl methacrylate is used to replace the hydrophobic monomer specifically selected in the present application, the obtained water reducer is used in desert sand concrete, and the concrete has poor slump retention performance, poor workability, and high water seepage rate.

[0050] Compared with Comparative Example 5 (the ratio of high-performance polycarboxylate water-reducing agent to modified pulp black liquor is different from that in the embodiment), the polycarboxylate water-reducing agent for desert sand concrete prepared in Examples 1-3 has better initial dispersion performance and slump retention performance, and the concrete has better encapsulation and cohesion, and the concrete water bleeding rate is relatively low.

[0051] Therefore, in the embodiment of the present application, a high-performance polycarboxylate water-reducing agent is compounded with modified pulp black liquor to prepare a polycarboxylate water-reducing agent specifically for desert sand concrete, which is applied to desert sand concrete. The concrete has good initial fluidity, good slump retention performance, and good water retention, encapsulation and cohesion, without segregation and water bleeding. The problem of fast slump loss, easy water bleeding and segregation of desert sand concrete caused by the large amount of fine powder and poor grading of desert sand is overcome.

[0052] In summary, the polycarboxylate water-reducing agent for desert sand concrete provided in this application has at least the following design concepts and beneficial effects: (1) High-performance polycarboxylate water-reducing agent has water-retaining and micro-air-entraining effects. A large number of fluorine and other groups on its molecular chain form hydrogen bonds with water molecules, forming a three-dimensional network structure inside the cement paste, which increases the viscosity of the mixture and reduces the free water. As the hydrogen bond binding force weakens, a large amount of free water is gradually released, allowing the concrete mixture to maintain good plasticity and improve the concrete's slump-retaining performance. The micro-air-entraining effect of high-performance polycarboxylate water-reducing agent improves the encapsulation of concrete and reduces the water bleeding rate.

[0053] (2) The modified pulp black liquor contains alkali lignin, which has a three-dimensional network structure and is more likely to occupy most of the active sites of fine powder in desert sand concrete, so that the polycarboxylate water reducer is preferentially adsorbed on the surface of cement particles, thereby improving the initial dispersion performance of desert sand concrete.

[0054] (3) The high-performance polycarboxylate water-reducing agent and modified paper pulp black liquor are compounded to prepare a polycarboxylate water-reducing agent for desert sand concrete. The concrete has good initial fluidity and good slump retention performance. The concrete has good water retention, encapsulation and cohesion, and no segregation and bleeding. If the high-performance polycarboxylate water-reducing agent is used alone in desert sand concrete, the initial dispersion performance of the concrete is poor, resulting in an increase in the amount of water-reducing agent, which greatly increases the production cost of desert sand concrete. If the modified paper pulp black liquor is used alone in desert sand concrete, the concrete workability and slump retention performance are poor, and the concrete is prone to bleeding. It is impossible to overcome the problem that the desert sand concrete mixture loses slump quickly due to the large amount of fine powder and poor grading of desert sand, and is prone to bleeding and segregation. In summary, the present application is compounded by a specific ratio of high-performance polycarboxylic acid water-reducing agent and modified pulp black liquor. The composite water-reducing agent is applied to desert sand concrete. The concrete has good initial fluidity and good slump retention performance. The concrete has good water retention, encapsulation and cohesion, and there is no segregation and water bleeding. It overcomes the problems of fast slump loss, easy water bleeding and segregation of desert sand concrete mixtures caused by the large amount of fine powder and poor grading of desert sand.

[0055] It should be noted that: In this article, “~” is used to indicate a numerical range, and the range indicated by this expression includes two endpoint values.

[0056] In addition to the actual selections embodied in the above specific embodiments, the above formulation ranges may be used in the specific implementation of the present application, including but not limited to the above embodiment schemes.

[0057] The specific parameters or some commonly used reagents or raw materials in the above embodiments are specific embodiments or preferred embodiments of the present application, but are not intended to limit the present application. Those skilled in the art may make adaptive adjustments within the scope of the present application.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A polycarboxylate water reducer specially used for desert sand concrete, characterized by: Its components include high-performance polycarboxylate water-reducing agent and modified pulp black liquor; The high-performance polycarboxylate water-reducing agent is prepared by polymerization reaction of vinyl polyether macromonomer, unsaturated carboxylic acid and functional monomer under the action of initiator and chain transfer agent; The functional monomer is 3-[tri(1-methylethoxy)silyl]propyl methacrylate or a hydrophobic monomer, and the hydrophobic monomer has the following structural formula: Wherein, a value is 1 or 2, b value is an integer from 1 to 7, R1 is H or CH3, and R2 is H or F.

2. The polycarboxylate water reducer for desert sand concrete according to claim 1, characterized in that: The weight ratio of the high-performance polycarboxylate water-reducing agent to the modified pulp black liquor is (70-80): (15-30).

3. The polycarboxylate water reducer for desert sand concrete according to claim 1, characterized in that: The preparation process of the modified pulp black liquor is as follows: adjusting the pH value of papermaking black liquor to 10-12 with acid or first-class alkali; heating to 60-90° C., adding first-class oxidant and catalyst to react at 60-90° C. for 1-5 hours, and then neutralizing the reaction liquid with acid or first-class alkali to pH 7-9, thereby obtaining the modified pulp black liquor; Wherein, the weight ratio of the papermaking black liquor, the first type of oxidant and the catalyst is 100: (3-8): (0.1-0.5).

4. The polycarboxylate water reducer for desert sand concrete according to claim 3, characterized in that: The pulp black liquor is one or a combination of bamboo pulp papermaking black liquor and wood pulp papermaking black liquor; the lignin content in the papermaking black liquor is 30% to 40%; The first type of oxidant is one or a combination of potassium dichromate and hydrogen peroxide; The catalyst is manganese dioxide; The acid is one or more of salicylic acid, citric acid, and malic acid; The first type of alkali is one or a combination of sodium hydroxide and potassium hydroxide.

5. The polycarboxylate water reducer for desert sand concrete according to claim 1, characterized in that: Under the action of an initiator and a chain transfer agent, the vinyl polyether macromonomer, unsaturated carboxylic acid and functional monomer are polymerized to obtain a high-performance polycarboxylic acid water reducer; Wherein, the polymerization reaction temperature is 40-45°C; The weight ratio of the vinyl polyether macromonomer, the unsaturated carboxylic acid and the functional monomer is (80-100): (10-15): (10-20).

6. The polycarboxylate water reducer for desert sand concrete according to claim 1, characterized in that: The initiator is composed of a reducing agent and a second type of oxidizing agent; The polymerization process is: By weight, 10 to 20 parts of functional monomer, 80 to 100 parts of vinyl polyether macromonomer, 1 to 1.5 parts of the second type oxidant and 50 to 80 parts of water are added into a reactor; The temperature of the reaction system is controlled at 40-45°C, and then 30.5-30.8 parts of reducing agent aqueous solution, 40-45 parts of unsaturated carboxylic acid aqueous solution and 30.4-30.9 parts of chain transfer agent aqueous solution are added respectively for 3-4 hours; After the reducing agent aqueous solution, the unsaturated carboxylic acid aqueous solution and the chain transfer agent aqueous solution are added, the mixture is kept at 40 to 45° C. for 1 to 5 hours, and a suitable amount of water is added to adjust the concentration of the reaction product to 40 to 50%; The reaction product is adjusted to pH 6.0-7.0 with a second type of alkali to obtain a high-performance polycarboxylate water-reducing agent; The unsaturated carboxylic acid aqueous solution is formed by dissolving 10 to 15 parts of unsaturated carboxylic acid in 30 parts of water; the reducing agent aqueous solution is formed by dissolving 0.5 to 0.8 parts of reducing agent in 30 parts of water; and the chain transfer agent aqueous solution is formed by dissolving 0.4 to 0.9 parts of chain transfer agent in 30 parts of water.

7. The polycarboxylate water reducer for desert sand concrete according to claim 6, characterized in that: The reducing agent aqueous solution, the unsaturated carboxylic acid aqueous solution and the chain transfer agent aqueous solution are added dropwise.

8. The polycarboxylate water reducer for desert sand concrete according to claim 1, characterized in that: The molecular weight of the vinyl polyether macromonomer is 2400 to 5000; The unsaturated carboxylic acid is acrylic acid.

9. The polycarboxylate water reducer for desert sand concrete according to claim 6, characterized in that: The reducing agent is one or more combinations of bisulfite, sulfite, bleaching agent, and vitamin C; The second type of oxidant is hydrogen peroxide; The chain transfer agent is one or more combinations of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, n-dodecyl mercaptan, secondary dodecyl mercaptan, and tert-dodecyl mercaptan; The second type of base is sodium hydroxide.

10. A method for preparing a polycarboxylate water reducer for desert sand concrete according to any one of claims 1 to 9, characterized in that: The method comprises the following preparation steps: The high-performance polycarboxylate water reducer and the modified paper pulp black liquor are mixed to obtain the polycarboxylate water reducer specially used for desert sand concrete.

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