阅读说明：本技术 一种清水混凝土外加剂 (Fair-faced concrete additive ) 是由 吴鑫 刘华东 向鹏 刘登贤 江晓君 桂根生 关素敏 胡江 张荣华 何东栗 周楷文 于 2019-11-25 设计创作，主要内容包括：本发明公开了一种清水混凝土外加剂,涉及建筑材料领域,其特征在于,按照质量百分比,包括以下原料：聚羧酸减水剂15.0％～20％、纳米硅消泡剂0.1％～0.2％、表面活性剂1.0％～3.0％、改性合成增稠剂1％～2％、水70％～85％。本发明中,通过八甲基环四硅氧烷、四甲基含氢聚硅氧烷和丙烯基聚醚聚合得到的聚醚有机硅中,包括-[Si(CH<Sub>3</Sub>)<Sub>2</Sub>O]-链段、羟基、聚醚基等集团,亲水性和亲油性基团性能和数量均符合消泡剂的要求,进一步的加入纳米二氧化硅,可以进一步提高聚醚有机硅的分散性,并提高聚醚有机硅的疏水性,提高破泡能力,降低混凝土中的气泡,提高混凝土表面光滑度。(The invention discloses an exposed concrete admixture, which relates to the field of building materials and is characterized by comprising the following raw materials in percentage by mass: 15.0-20 percent of polycarboxylic acid water reducing agent, 0.1-0.2 percent of nano silicon defoamer, 1.0-3.0 percent of surfactant, 1-2 percent of modified synthetic thickener and 70-85 percent of water. In the present invention, - [ Si (CH) is included in the polyether silicones obtained by polymerizing octamethylcyclotetrasiloxane, tetramethylhydrogenpolysiloxane and propenyl polyether 3 ) 2 O]The performance and the quantity of the hydrophilic group and the lipophilic group of the groups such as a chain segment, a hydroxyl group, a polyether group and the like meet the requirements of the defoaming agent, and the dispersibility of the polyether organic silicon can be further improved by further adding the nano silicon dioxide,and the hydrophobicity of the polyether organic silicon is improved, the foam breaking capacity is improved, the air bubbles in the concrete are reduced, and the surface smoothness of the concrete is improved.)

1. The fair-faced concrete admixture is characterized by comprising the following raw materials in percentage by mass:

15.0-20 percent of polycarboxylic acid water reducing agent, 0.1-0.2 percent of nano silicon defoamer, 1.0-3.0 percent of surfactant, 1-2 percent of modified synthetic thickener and 70-85 percent of water.

2. The fair-faced concrete admixture of claim 1, wherein the preparation method of the nano silicon defoamer comprises the following steps:

(1) mixing octamethylcyclotetrasiloxane and tetramethyl hydrogen-containing polysiloxane, heating to 40-70 ℃ under the protection of nitrogen, adding chloroplatinic acid, and reacting to obtain end group type hydrogen-containing silicone oil;

(2) adding propenyl polyether into the terminal group type hydrogen-containing silicone oil obtained in the step (1), heating to 90-110 ℃ under the protection of nitrogen, adding chloroplatinic acid, and reacting to obtain polyether organic silicon;

(3) and (3) adding nano silicon dioxide into the polyether organic silicon obtained in the step (2), placing the polyether organic silicon into a high-pressure reaction kettle, and reacting for 2-4 hours at the temperature of 300-450 ℃ to obtain the nano silicon defoaming agent.

3. The bare concrete admixture according to claim 2, wherein the octamethylcyclotetrasiloxane and the tetramethylhydrogenpolysiloxane are mixed in the step (1) in a volume ratio of 1-1.2: 3-4.

4. The bare concrete admixture according to claim 2, wherein the addition amount of the propenyl polyether in the step (2) is 35-50% of the volume of the octamethylcyclotetrasiloxane.

5. The bare concrete admixture according to claim 2, wherein the amount of the nano silica added in the step (3) is 30-50 g/L.

6. The fair-faced concrete admixture of claim 2, wherein the addition amount of the chloroplatinic acid in the step (1) and the step (2) is 0.003-0.005 mL/L and 0.001-0.003 mL/L respectively.

7. The fair-faced concrete admixture of claim 1, wherein the polycarboxylate superplasticizer comprises the following raw materials in parts by mass: 30-35 parts of maleic anhydride, 5-15 parts of methyl allyl polyvinyl ether, 5-8 parts of ammonium persulfate, 20-25 parts of acrylic acid, 18-25 parts of NaOH and 2-4 parts of an initiator.

8. The fair-faced concrete admixture of claim 7, wherein the preparation method of the polycarboxylate water reducer comprises the following steps:

step one, adding maleic anhydride and methyl allyl polyvinyl ether into NaOH aqueous solution, and uniformly mixing for later use;

step two, simultaneously adding an ammonium persulfate aqueous solution into the mixed solution obtained in the step one, and heating the mixed solution for later use;

step three, heating the mixed solution in the step two to 80 ℃, and simultaneously dripping an initiator and acrylic acid into the mixed solution;

and step four, continuously heating the mixed solution obtained in the step three to 90 ℃, and keeping for 1h to obtain the polycarboxylic acid water reducing agent.

9. The bare concrete admixture according to claim 8, wherein the dropping rate of the initiator in the third step is 0.41mL/min, and the dropping acceleration rate of the acrylic acid in the third step is 0.60 mL/min.

10. The bare concrete admixture according to claim 8, wherein the concentration of the NaOH aqueous solution in the first step is 0.15-0.20 g/mL, and the concentration of the ammonium persulfate aqueous solution in the second step is 0.2 g/mL.

Technical Field

The invention relates to the field of building materials, in particular to an admixture for fair-faced concrete.

Background

The concrete admixture is a chemical substance which is added in the process of stirring the concrete, accounts for less than 5 percent of the mass of the cement and can obviously improve the performance of the concrete. The concrete admixture has the characteristics of multiple varieties, small mixing amount, great influence on the performance of concrete, low investment, quick response and obvious technical and economic benefits. With the continuous progress of scientific technology, the additive is increasingly applied.

The bare concrete is also called as decorative concrete, after the bare concrete is poured, no material such as coating, tile sticking, stone sticking and the like exists, the original color of the concrete is directly expressed, the addition of the additive into the bare concrete is a common means for the conventional bare concrete placement, and the performance requirement of the bare concrete is higher than that of the traditional reinforced concrete, so that the types and the addition amount of the additive are main factors directly influencing the performance of the bare concrete except the basic components of the concrete.

The common concrete admixtures mainly comprise a naphthalene-based high-efficiency water reducing agent, a polycarboxylic acid high-performance water reducing agent and an aliphatic high-efficiency water reducing agent, when the concrete admixtures are applied to the fair-faced concrete, the finally obtained fair-faced concrete has the appearance quality problems of more surface bubbles, pitted surface, honeycomb, serious color difference and the like, so the common concrete admixtures cannot be directly applied to the fair-faced concrete, the research specially aiming at the admixtures for the fair-faced concrete is lack of systematic research at present, the existing research mainly focuses on how to optimize the mixing ratio of the fair-faced concrete and the admixtures and how to improve the workability of the fair-faced concrete, the research on how to improve the durability of the fair-faced concrete by the admixtures is lack, and the existing fair-faced concrete buildings in China have the main problems of more microcracks, lower crack resistance grade and poorer durability, therefore, it is required to develop an admixture which can ensure the crack resistance grade and durability of the fair-faced concrete and can be applied to the fair-faced concrete.

As to the influence of the admixture on the fair-faced concrete, the influence of the admixture on the performance of the machine-made sand fair-faced concrete (beam-Yuanbo, Tomling sensitivity and the like, concrete [ J ], No. 4 of 2015) in more detail discusses the influence of the water reducing agent, the air entraining agent, the tackifier and the shrinkage reducing agent on the performance of the fair-faced concrete when the water reducing agent, the air entraining agent, the tackifier and the shrinkage reducing agent are used independently and compounded, and the admixture suitable for the machine-made sand fair-faced concrete (qualified natural sand in southwest area is lack, machine-made sand is generally adopted) is obtained, and the prepared concrete has good cohesiveness and homogeneity, uniform color, excellent apparent quality, compact microstructure, 28d drying shrinkage rate of less than 250 multiplied by 10 < -6 >, early crack resistance level of IV and good durability.

However, in practical applications, the applicant finds that the fair-faced concrete building obtained according to the document can meet the qualified requirements in the initial inspection, but after 3 months, the fair-faced concrete building still has microcracks, and further has the problems of early anti-cracking grade slip and durability slip, so that the embodiment provided by the document is not optimal.

Disclosure of Invention

The invention aims to: aiming at the problems, the bare concrete admixture is provided, and when the admixture is added into bare concrete, the water marks and air bubbles on the surface of the poured bare concrete can be obviously reduced.

The technical scheme adopted by the invention is as follows:

the fair-faced concrete admixture is characterized by comprising the following raw materials in percentage by mass:

15.0-20 percent of polycarboxylic acid water reducing agent, 0.1-0.2 percent of nano silicon defoamer, 1.0-3.0 percent of surfactant, 1-2 percent of modified synthetic thickener and 70-85 percent of water.

Further, the preparation method of the nano silicon defoaming agent comprises the following steps:

(1) mixing octamethylcyclotetrasiloxane and tetramethyl hydrogen-containing polysiloxane, heating to 40-70 ℃ under the protection of nitrogen, adding chloroplatinic acid, and reacting to obtain end group type hydrogen-containing silicone oil;

(2) adding propenyl polyether into the terminal group type hydrogen-containing silicone oil obtained in the step (1), heating to 90-110 ℃ under the protection of nitrogen, adding chloroplatinic acid, and reacting to obtain polyether organic silicon;

(3) and (3) adding nano silicon dioxide into the polyether organic silicon obtained in the step (2), placing the polyether organic silicon into a high-pressure reaction kettle, and reacting for 2-4 hours at the temperature of 300-450 ℃ to obtain the nano silicon defoaming agent.

The material with excellent defoaming performance should have low solubility and high dispersibility in foaming liquid, and the material with high solubility and high dispersibility has strong foam breaking capability and weak foam inhibition. The polyether polysiloxane copolymer for defoaming and foam inhibiting has certain hydrophobicity, while the hydrogen silicone oil has too small relative molecular weight, too large relative molecular weight, large viscosity and poor reaction activity. The invention does not adequately ensure that the copolymer has sufficient lipophilicity. In the present invention, - [ Si (CH) is included among polyether silicones obtained by polymerizing octamethylcyclotetrasiloxane, tetramethylhydrogenpolysiloxane and propenyl polyether ₃) ₂O]Chain segment, hydroxyl group, polyether group and other groups, and the polyether organosilicon has proper chain segment length and hydrophilic and lipophilic groups in proper amount.

Furthermore, the nano silicon dioxide is added in the invention, the silicon dioxide is an inorganic substance, the dispersibility of the polyether organic silicon can be further improved, and meanwhile, the silicon dioxide reacts with the polyether organic silicon at high temperature and high pressure, the hydrophobicity of the polyether organic silicon can be further improved by modifying the silicon dioxide, the foam breaking capacity is improved, the air bubbles in the concrete are reduced, and the surface smoothness of the concrete is improved.

Further, in the step (1), octamethylcyclotetrasiloxane and tetramethyl hydrogen polysiloxane are mixed according to the volume ratio of 1-1.2: 3-4.

Furthermore, the addition amount of the propenyl polyether in the step (2) is 35-50% of the volume of the octamethylcyclotetrasiloxane.

Furthermore, the adding amount of the nano silicon dioxide in the step (3) is 30-50 g/L.

Further, the addition amount of the chloroplatinic acid in the step (1) and the step (2) is 0.003-0.005 mL/L and 0.001-0.003 mL/L respectively.

Further, the polycarboxylate superplasticizer comprises the following raw materials in parts by mass: 30-35 parts of maleic anhydride, 5-15 parts of methyl allyl polyvinyl ether, 5-8 parts of ammonium persulfate, 20-25 parts of acrylic acid, 18-25 parts of NaOH and 2-4 parts of an initiator.

Further, the preparation method of the polycarboxylate superplasticizer comprises the following steps:

step one, adding maleic anhydride and methyl allyl polyvinyl ether into NaOH aqueous solution, and uniformly mixing for later use;

step two, simultaneously adding an ammonium persulfate aqueous solution into the mixed solution obtained in the step one, and heating the mixed solution for later use;

step three, heating the mixed solution in the step two to 80 ℃, and simultaneously dripping an initiator and acrylic acid into the mixed solution;

and step four, continuously heating the mixed solution obtained in the step three to 90 ℃, and keeping for 1h to obtain the polycarboxylic acid water reducing agent.

Further, the dropping rate of the initiator in the third step is 0.41mL/min, and the dropping acceleration rate of the acrylic acid in the third step is 0.60 mL/min.

Further, the concentration of the NaOH aqueous solution in the first step is 0.15-0.20 g/mL, and the concentration of the ammonium persulfate aqueous solution in the second step is 0.2 g/mL.

By adopting the technical scheme, the prepared fair-faced concrete can obviously eliminate water marks and air bubbles, but the poured fair-faced concrete is easy to deposit and precipitate.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

1. in the present invention, - [ Si (CH) is included among polyether silicones obtained by polymerizing octamethylcyclotetrasiloxane, tetramethylhydrogenpolysiloxane and propenyl polyether ₃) ₂O]The performance and the quantity of hydrophilic and lipophilic groups of the groups such as chain segments, hydroxyl groups, polyether groups and the like meet the requirements of the defoaming agent, and the nano silicon dioxide is further added, so that the dispersibility of the polyether organic silicon can be further improved, the hydrophobicity of the polyether organic silicon can be improved, the foam breaking capacity can be improved, the bubbles in the concrete can be reduced, and the surface smoothness of the concrete can be improved.

2. The polycarboxylate superplasticizer adopted by the invention solves the problem that the surface is not smooth due to the fact that silicon dioxide is easily precipitated when the defoaming agent is used. Can obviously improve the workability and plasticity retention of the freshly-mixed fair-faced concrete.

Detailed Description

All of the features disclosed in this specification, or all of the steps in any method or process so disclosed, may be combined in any combination, except combinations of features and/or steps that are mutually exclusive.

Any feature disclosed in this specification (including any accompanying claims, abstract) may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. That is, unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features.