CN103613308B - Water-reducing polycarboxylate concrete slump-retaining agent and preparation method thereof - Google Patents

Abstract

The invention relates to a water-reducing polycarboxylate concrete slump-retaining agent and a preparation method thereof. Its molecular weight is 18,000 to 48,000, and its general structural formula is as follows: Formula I: In the formula: m=1 to 10, n=5 to 20, p= 4~10, q=1~7, k=1~10. Compared with the existing slump-retaining agents, the present invention has the advantages that: the carboxylic acid group can act as retarder and slump-retainer, and the alcoholic hydroxyl group can act as retarder; the itaconic acid introduced in the molecular structure has Two -COOH can complex Ca ²⁺ , which can effectively delay cement hydration; the sulfonic acid group introduced in the molecular structure can preferentially disperse cement particles and delay cement hydration; the benzene ring in the molecular structure is easy to produce steric hindrance effect, enhance the dispersion stability of the water reducing agent; the slump-preserving effect is obvious, less affected by the climate, and the compatibility is good when used in conjunction with other admixtures; the amount of slump-retaining agent can be obtained in a very low range. Effect.

Description

Water-reducing polycarboxylate concrete slump-retaining agent and preparation method thereof

technical field

The invention belongs to the research field of concrete admixtures in building materials, and in particular relates to a water-reducing polycarboxylate concrete slump-retaining agent and a preparation method thereof.

Background technique

With the development of construction industries such as transportation, hydropower and real estate, people's requirements for the construction performance, strength index and durability of concrete materials are constantly increasing. Adding admixtures to concrete is a necessary means to meet people's requirements, especially the water reducing agent has become an indispensable part.

In the 1930s, the first generation of water reducers represented by lignin sulfonate began to be used in the field of building materials. Subsequently, since the 1960s, naphthalene-based water reducers, benzenesulfonate formaldehyde condensates and melamine sulfonate formaldehyde condensates have appeared in foreign markets, thus achieving rapid research and application of water reducers. develop. In the early 1990s, the research on polycarboxylate high-efficiency water-reducers achieved rapid development and became the main development direction of high-efficiency water-reducers in the 21st century.

With the continuous emergence of high-rise buildings and the improvement of construction requirements for building materials, almost all concrete is required to be pumpable, and high-efficiency water reducers are an essential part of pumping, and polycarboxylate water reducers become an important part of it. However, the pumped concrete produced from the concrete mixing plant often needs to be transported over a long distance, and the construction environment (higher temperature, etc.) is different, which will inevitably lead to the loss of slump of the concrete, thereby affecting the construction of the concrete.

At present, the methods mainly used to reduce the slump of concrete mixed with water reducer mainly include repeated addition of water reducer, post-mixing of water reducer, composite retarder and slow release method, etc. However, the effects achieved by these methods are not very obvious, are not environmentally friendly, or are costly.

Patent CN102093521A reports a preparation method of polycarboxylic acid high slump retention agent: adopt maleic anhydride and polyethylene glycol diesterization method to prepare crosslinking monomer, and copolymerize with macromolecular unsaturated polyether in redox system to produce Partially cross-linked. However, the esterification rate of this invention is not high, and the preparation process is not environmentally friendly, which is not conducive to large-scale production and application.

Patent CN102390950 reports a slow-release polycarboxylic acid-based slump-retaining agent and its preparation method: using unsaturated carboxylic acid polyethylene glycol monoester, unsaturated polyoxyalkylene ether monoester, unsaturated monocarboxylic acid and its Derivative monomer and unsaturated ethylenic sulfonic acid and its sodium salt are copolymerized and mixed. This solution can effectively solve the compatibility problem between sand and gravel materials with large mud content and water reducer, but its effectiveness is greatly affected by temperature and pH, and cannot fundamentally solve the concrete slump under different conditions loss problem.

Patent CN102558454A reports a preparation method of polycarboxylic acid slump-retaining agent; it is formed by copolymerization of acrolein-producing tail liquid, unsaturated polyether and acrylic acid derivatives. Although the slump-retaining agent prepared by this method can reduce the production cost of the slump-retaining agent, it cannot prevent the adsorption of the layered porous internal structure of the clay material, and the slump-retaining effect is not ideal when the mud content of the sandstone is high.

Contents of the invention

The technical problem to be solved by the present invention is to provide a water-reducing polycarboxylate concrete slump-retaining agent with simple production process, good compatibility with cement, low dosage, and high slump-retaining agent for the above-mentioned prior art and its preparation method.

The technical solution adopted by the present invention to solve the above-mentioned technical problems is: water-reducing polycarboxylate concrete slump-retaining agent, its molecular weight is 18000～48000, and the general structural formula is as follows:

In the formula: m=1~10, n=5~20, p=4~10, q=1~7, k=1~10.

The preparation method of water-reducing polycarboxylate concrete slump-retaining agent is characterized in that comprising the following steps: simultaneously dropping TPEG, styrene, sodium methacrylic acid sulfonate and itaconic acid into a reactor, adding water, wherein water and The mass ratio of TPEG is 0.6, stir and heat to 60°C, keep warm, and at the same time dropwise add 20% mass fraction of hydroxyethyl acrylate solution, 1.5h to drop completely; 5% mass fraction of initiator solution, 3h to drop completely; The molecular weight regulator solution with a mass fraction of 5% was added dropwise completely in 3.5 hours. After the material was added dropwise, it was kept for 1.5 hours, and sodium hydroxide was added to adjust the pH=6.5 to obtain a water-reducing polycarboxylate concrete slump retaining agent.

According to the above scheme, TPEG: styrene: sodium methacrylate sulfonate: itaconic acid: hydroxyethyl acrylate: initiator: the mass ratio of regulator is 35: (0.5～1.5): (0.5～1.5): (2.0 ~5.0): (0.5~1.5): (0.1~0.3): (0.05~0.15).

According to the above scheme, the initiator is a mixture of ammonium persulfate and potassium persulfate, and its mass ratio is 1:1-7.

According to the above scheme, the molecular weight regulator is a mixture of mercaptoacetic acid and β-mercaptopropionic acid, the mass ratio of which is 1:1-5.

The loss of slump depends mainly on the rate at which the dispersibility of the superplasticizer decreases. The instability of cement paste is that they have a large interface energy. In order to reduce the interface, the particles will coalesce with each other. After the high-efficiency superplasticizer is added, the hydrophobic groups of the superplasticizer are directional adsorbed on the surface of the cement particles, forming an adsorption layer with a strong electric field, which disperses the cement particles, thereby hindering or destroying the formation of cement flocs. In addition, the high-efficiency superplasticizer molecules contain more branched chains. After the superplasticizer is adsorbed on the surface of cement particles, it will generate steric hindrance, which will inhibit the adsorption of cement on the high-efficiency water-reducer, so that the dispersion ability will not decrease rapidly. It has been found through experiments that if groups that preferentially adsorb cement particles (such as sulfonic acid groups) are introduced into the carboxylic acid copolymer, these groups will preferentially form insoluble complexes with calcium ions in the cement, resulting in cement The adsorption amount of the particles to the water reducing agent is reduced. This preferential adsorption makes the residual water reducing amount or concentration in the liquid phase higher, which helps to reduce the slump loss. In addition, if polyether-type long side chains are introduced into the copolymer molecule, these side chains have good affinity for water, and the oxygen ions in the ether group form hydrogen bonds with water molecules, forming a stable hydrophilic stereo Protective layer, thereby delaying the aggregation of cement particles. In addition, the introduction of a molecular structure that can be hydrolyzed into carboxylic acid or alcohol in the cement alkaline medium in the copolymer will also reduce the slump loss of fresh concrete.

The synthesis reaction equation of the present invention is as follows:

Compared with existing slump retaining agents, the present invention has the advantages of:

a. The hydroxyethyl acrylate introduced in the molecular structure is hydrolyzed into carboxylic acid and alcohol in the alkaline environment of cement slurry, in which the carboxylic acid group can act as a retarding and slump-preserving effect, and the alcoholic hydroxyl group can act as a retarding effect;

b. The itaconic acid introduced into the molecular structure has two -COOH in its molecule, which can complex Ca ²⁺ and effectively delay the hydration of cement;

c. The sulfonic acid group introduced in the molecular structure can preferentially disperse cement particles and delay cement hydration;

d. The benzene ring in the molecular structure is easy to produce steric hindrance effect, which enhances the dispersion stability of the water reducing agent;

e. The slump-preserving effect is obvious, less affected by the climate, and has good compatibility when used in conjunction with other admixtures;

f. The high-efficiency slump-retaining effect can be obtained in a very low range of slump-retaining agent content, generally mixed with 0.01-0.06% of the cement dosage.

The slump of freshly mixed concrete is basically not lost, and even the slump of 1 hour is improved.

Detailed ways

In order to further illustrate the content of the present invention, the following examples are particularly listed to further describe the present invention. The protection scope of the present invention shall be determined by the description of the claims. The present invention evaluates by comparing the commercially available products and the products prepared in each embodiment by testing indicators such as the setting time of the cement paste and the viscosity of the paste.

The water-reducing polycarboxylate concrete slump-retaining agent has a molecular weight of 18,000 to 48,000, and its general structure is as follows:

In the formula: m=1~10, n=5~20, p=4~10, q=1~7, k=1~10.

Examples 1-10:

Put TPEG, styrene (ST), sodium methacrylate sulfonate (MAS) and itaconic acid (IA) into the reactor at the same time, add water, wherein the mass ratio of water to TPEG is 0.6, stir and heat to 60°C, Insulation, then dropwise add 20% mass fraction of hydroxyethyl acrylate (HEA) solution, 1.5h drop completely; at the same time dropwise add 5% mass fraction initiator (ACT) solution, 3h drop completely; 5% molecular weight regulator (LZ) solution, 3.5h drop completely. After the material is added dropwise, keep it warm for 1.5 hours, add sodium hydroxide to adjust the pH=6.5, and obtain the water-reducing polycarboxylate concrete slump retaining agent.

Table 1 embodiment table (mass ratio)

For the above 10 examples, according to the above-mentioned experimental method and material ratio, the slump-retaining agent was synthesized, and related evaluation was carried out. According to the water-cement ratio of 0.29, the solid content of polycarboxylate superplasticizer is 0.1%, and the fluidity and setting time of cement slurry are tested. The results are shown in Table 2.

Table 1 Clean slurry coagulation time experiment

Note: The polycarboxylate superplasticizer is KH-5 polycarboxylate superplasticizer produced by Wuhan Huaxuan High-tech Co., Ltd.

Table 1 shows the effect of slump-retaining agent on the fluidity and setting time of cement slurry. As can be seen from the data in Table 1, there is an obvious fluidity loss in SO, and the fluidity of 2h is only 120mm; and after adding the water-reducing polycarboxylate slump-retaining agent synthesized by the present invention, the initial fluidity is significantly improved, and 1h , 2h fluidity is significantly improved, so the slump retention agent synthesized by the invention has good dispersion and dispersion retention, which can effectively improve the fluidity and flow retention of the slurry. From the point of view of setting time, after adding slump-retaining agent, the setting time of cement slurry basically does not change. Except that the final setting time in group No. 7 was 34 minutes longer than that of the blank sample, the changes of initial setting and final setting times in other groups were all within 20 minutes. Therefore, the incorporation of the concrete slump-retaining agent prepared in the embodiment basically has no effect on the setting time of the cement paste, and will not affect the original working performance of the concrete.

Claims (4)

1. the preparation method of water reducing type polycarboxylic acid concrete slump retaining agent, its molecular weight is 18000 ~ 48000, general structure as shown in the formula:

In formula: m=1 ~ 10, n=5 ~ 20, p=4 ~ 10, q=1 ~ 7, k=1 ~ 10, it is characterized in that including following steps: TPEG, vinylbenzene, methylpropene sodium sulfonate and methylene-succinic acid are dropped in reactor simultaneously, add water, wherein the mass ratio of water and TPEG is 0.6, stir and be heated to 60 DEG C, insulation, drips the Hydroxyethyl Acrylate solution of massfraction 20% simultaneously, and 1.5h drips completely; The initiator solution of massfraction 5%, 3h drips completely; The molecular-weight adjusting agent solution of massfraction 5%, 3.5h drips completely, and material dropping is complete, and insulation 1.5h, hydro-oxidation sodium regulates pH=6.5, obtains water reducing type polycarboxylic acid concrete slump retaining agent.

2. the preparation method of water reducing type polycarboxylic acid concrete slump retaining agent according to claim 1, is characterized in that TPEG: vinylbenzene: methylpropene sodium sulfonate: methylene-succinic acid: Hydroxyethyl Acrylate: initiator: the mass ratio of conditioning agent is 35:(0.5 ~ 1.5): (0.5 ~ 1.5): (2.0 ~ 5.0): (0.5 ~ 1.5): (0.1 ~ 0.3): (0.05 ~ 0.15).

3. the preparation method of water reducing type polycarboxylic acid concrete slump retaining agent according to claim 1 and 2, it is characterized in that described initiator is the mixture of ammonium persulphate and Potassium Persulphate, its mass ratio is 1:1 ~ 7.

4. the preparation method of water reducing type polycarboxylic acid concrete slump retaining agent according to claim 1 and 2, it is characterized in that molecular weight regulator is the mixture of Thiovanic acid and β-mercaptopropionic acid, its mass ratio is 1:1 ~ 5.