CN108793819B - A kind of composite concrete anti-cracking agent and preparation method thereof - Google Patents

Abstract

The invention provides a composite concrete anti-cracking agent, which belongs to the technical field of building materials. The anti-cracking agent comprises the following components in mass percentage: 3-7% of polypropylene glycol, 7-10% of polyvinyl alcohol, 1-3% of VAE emulsion, 0.01% of defoamer, 10-15% of nano-zinc oxide, Sodium methyl silicate 3 to 5%, the rest is water. The preparation method of the anti-cracking agent of the present invention: 1) adding polyvinyl alcohol to the cold water until the volatile substances overflow, then heating in a water bath to accelerate the dissolution, and maintaining the temperature until the solution no longer contains tiny particles, and then filtered and lowered to room temperature for use; 2 ) with polypropylene glycol, VAE emulsion, water, stirring to obtain mixed solution A; 3) polyvinyl alcohol solution, mixed solution A are placed in a stirrer, add nano-zinc oxide, sodium methyl silicate, defoamer, and Mix well to make concrete anti-cracking agent. The composite concrete anti-cracking agent of the invention can obviously inhibit the evaporation of water on the concrete surface, reduce the plastic shrinkage of the concrete, inhibit the cracking of the concrete surface, and improve the durability of the concrete.

Description

A kind of composite concrete anti-cracking agent and preparation method thereof

technical field

The invention belongs to the technical field of building materials, in particular to a composite concrete anti-cracking agent and a preparation method thereof.

Background technique

Concrete is the most widely used and important basic material in current construction projects; its advantages of high compressive strength, simple construction, wide material sources, and low prices make it an irreplaceable position; however, it also has plastic shrinkage. It is easy to crack at times, resulting in defects such as insufficient water seepage resistance, resulting in insufficient durability of concrete, which directly affects the service life of concrete buildings. It is almost impossible to completely avoid cracks in engineering. Although the shrinkage of concrete is not large, cracks will accelerate the carbonization rate of concrete, and also provide channels for air and water penetration, resulting in a series of concrete frost heave and steel corrosion. Durability issues. The early cracks of concrete also directly affect the bearing capacity and stiffness of concrete components in the later stage, making them unable to be used normally, and repairing cracks in the later stage requires a lot of manpower, material resources and financial resources, so it is of great significance to control the defects of concrete structures and reduce the shrinkage cracks of concrete. .

In the process of concrete use, adding additives or spraying concrete curing agent before the initial setting of concrete is a more effective way to control the plastic shrinkage and cracks of concrete. The surface curing agent is sprayed on the concrete surface to form a film to prevent the evaporation of water on the concrete surface. In the plastic stage of concrete, the plastic shrinkage of concrete is suppressed by spraying concrete surface curing agent, which can reduce the occurrence of plastic cracks. However, in a harsh climate environment, the curing agent sprayed on the concrete surface will be damaged, the film-forming effect is poor, and the expected effect cannot be achieved, and manual spraying is required, which is time-consuming and labor-intensive.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a kind of internal mixing in the concrete in view of the above-mentioned deficiencies in the prior art. During the solidification and hardening of the concrete, a layer of dense film is formed on its surface, which hinders the evaporation of water, and inhibits the plastic shrinkage of the concrete to generate cracks. Special admixture for concrete crack resistance and preparation method. The composite concrete anti-cracking agent of the invention can obviously inhibit the evaporation of water on the concrete surface, reduce the plastic shrinkage of the concrete, and inhibit the cracking of the concrete surface, thereby improving the durability of the concrete.

The object of the present invention is achieved through the following technical solutions:

A composite concrete anti-cracking agent, comprising the following components by mass percentage: 3-7% of polypropylene glycol, 7-10% of polyvinyl alcohol, 1-3% of VAE emulsion, 0.01% of defoamer, and 10% of nano-zinc oxide. ~ 15%, sodium methyl silicate 3 ~ 5%, and the rest is water.

The composite concrete anti-cracking agent of the present invention has the functions of increasing the compactness of concrete, reducing the evaporation rate of water on the concrete surface, etc. The main technical principles are as follows:

1. The concrete anti-cracking agent is uniformly dispersed in the concrete by stirring. After the concrete is in the form, a dense polymer film is formed on its surface, which can effectively reduce the evaporation of water on the concrete surface and reduce the moisture content of the concrete surface. Evaporation is too fast, creating the risk of plastic shrinkage cracking of the concrete.

2. The sodium methyl silicate component in the composite concrete anti-cracking agent has good penetrating crystallinity; the silanol group in its molecular structure reacts with the silanol group in the silicate material for dehydration and cross-linking, so as to achieve " "Anti-capillary effect" forms an excellent hydrophobic layer, which effectively reduces the evaporation of water on the concrete surface and reduces the possibility of plastic shrinkage and cracking of the concrete due to the rapid evaporation of water on the concrete surface.

3. Under the condition of strong alkalinity inside the concrete, the nano-zinc oxide in the composite concrete anti-cracking agent will react with the Ca(OH) ₂ in the system to form soluble zincate, and the resultant is wrapped on the surface of the cement particles. It hinders the hydration of cement to a certain extent. With the continuous progress of cement hydration reaction, the generated zincate gradually dissolves. This process refines the crystal morphology of cement hydration products and increases the overall compaction performance of concrete.

4. The reaction products of the components and some components of the composite concrete anti-cracking agent, such as nano-zinc oxide and soluble zincate, can fill the capillary channels between the cement particles to form a dense interpenetrating network structure, which can make the cement stone The internal structure is denser and has a micro-expansion effect, which greatly enhances the crack resistance of concrete.

As a specific embodiment of the composite concrete anti-cracking agent of the present invention, the molecular weight of the polypropylene glycol is 400-600.

As a specific embodiment of the composite concrete anti-cracking agent of the present invention, the polyvinyl alcohol adopts polyvinyl alcohol 1788 type, the degree of polymerization is 1700, and the degree of alcoholysis is 88%.

As a specific embodiment of the composite concrete anti-cracking agent of the present invention, the VAE emulsion is an emulsion obtained by copolymerization of vinyl acetate-ethylene, wherein the content of vinyl acetate is 70% to 95%.

As a specific embodiment of the composite concrete anti-cracking agent of the present invention, the defoaming agent is polydimethylsiloxane.

As a specific embodiment of the composite concrete anti-cracking agent of the present invention, the purity of the nano-zinc oxide is ≥99.5%, the average particle size is 30 nm, and the density is 5.6 kg/m ³ .

As a specific embodiment of the composite concrete anti-cracking agent of the present invention, the solid content of the sodium methyl silicate is ≥30%.

A preparation method of a composite concrete anti-cracking agent, comprising the following steps:

1) Weigh each raw material by weight percentage;

2) Slowly add polyvinyl alcohol into cold water while stirring, fully swell, disperse and wait for volatile substances to overflow, then heat up in a water bath to accelerate dissolution, and keep warm until the solution no longer contains tiny particles, filter and cool down to room temperature for later use;

3) The polypropylene glycol, VAE emulsion and water taken by weighing are uniformly stirred at normal temperature to obtain mixed solution A;

4) Put the polyvinyl alcohol solution and the mixed solution A in the mixer, add nano-zinc oxide, sodium methyl silicate and defoamer while stirring under normal temperature conditions, and stir evenly to make a composite concrete anti-cracking agent.

As a specific embodiment of the method for preparing a composite concrete cracking inhibitor according to the present invention, in step 2), the temperature of the cold water is 20-30° C.; the stirring speed is 70-100 r/min; The temperature is raised to 95°C; the holding time is 2-2.5 hours; the filtration adopts a 28-30 mesh stainless steel mesh to filter impurities.

As a specific embodiment of the method for preparing a composite concrete cracking inhibitor according to the present invention, in step 3), the stirring speed is 150-200 r/min; in step 4), the stirring speed is 200-200 r/min 250r/min.

Compared with the prior art, the present invention has the following beneficial effects:

1. The anti-cracking agent of the present invention can effectively inhibit the evaporation of concrete moisture, reduce the cracks caused by plastic shrinkage, and improve the crack resistance of concrete by being incorporated into concrete and forming a dense polymer film on the concrete surface during the concrete setting and hardening process. , which is beneficial to the improvement of concrete durability.

2. The anti-cracking agent of the present invention adopts the method of internal mixing, which is convenient to use, does not increase the subsequent operation, and does not bring adverse effects on the construction performance of concrete.

Description of drawings

Figure 1 shows the concrete compressive strength of Examples 1-5.

Figure 2 shows the compressive strength of concrete in Comparative Examples 1-4.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention.

In the following examples, three kinds of concrete with different strength grades are used, and their mixing ratios are shown in Table 1.

Table 1 Concrete mix ratio

In the following examples, the anti-cracking performance of concrete is measured and characterized with reference to the test method for early plastic cracking of concrete slab restraint in "Guidelines for Durability Design and Construction of Concrete Structures"; Methods The compressive strength of concrete was measured and characterized.

In the following examples, the molecular weight of the polypropylene glycol used is 400; the polyvinyl alcohol adopts the polyvinyl alcohol 1788 type, and the alcoholysis degree is 88%; the vinyl acetate-ethylene copolymer emulsion, the vinyl acetate content is 70% to 95%; The average particle size of zinc is 30nm, the density is 5.6kg/m ³ ; the solid content of sodium methyl silicate is ≥30%.

Examples 1 to 5

For the composite concrete anti-cracking agents described in Examples 1-5, the raw material ratios are shown in Table 1, and the test results are shown in Table 4 and Figure 1. The preparation method includes the following steps:

1) weigh each raw material according to the raw material ratio in Table 1;

2) Slowly add the weighed polyvinyl alcohol to the cold water of about 20°C while stirring, fully swell, disperse and wait for the overflow of volatile substances, wherein the stirring speed is 70-100r/min, and then the temperature is heated to 95°C by heating in a water bath. Accelerate the dissolution at about ℃, and keep the temperature for 2 to 2.5 hours until the solution no longer contains tiny particles. After filtering impurities through a 28-mesh stainless steel mesh, it is cooled to room temperature for use.

3) The weighed polypropylene glycol, VAE emulsion, and water are stirred evenly at room temperature under the condition of 150-200 r/min to obtain mixed solution A for use.

4) Place the prepared polyvinyl alcohol solution and mixed solution A in a stirrer, and at a rate of 200-250 r/min under normal temperature conditions, add nano-zinc oxide, sodium methyl silicate, polydimethylsiloxane while stirring. Methyl siloxane, and stir to make a composite concrete anti-cracking agent.

Table 2 The proportion of raw material components/% of concrete anti-cracking agents in Examples 1-5

Comparative Examples 1 to 4

The following comparative examples are used to further highlight and illustrate the creative contribution of the present invention. The raw material ratios of the concrete anti-cracking agents described in Comparative Examples 1 to 4 are shown in Table 3, and the test results are shown in Table 5 and Figure 2. The preparation method and implementation Examples 1 to 5 are the same.

Table 3 The ratio of raw material components of the concrete anti-cracking agent in Comparative Examples 1 to 4/%

Table 4 Examples 1-5 concrete cracking area

Table 5 Comparative Examples 1-4 Concrete cracking area

In Table 4 and Table 5, the reference group indicates that no anti-cracking agent is added.

The results of above-mentioned table 4, table 5 and Fig. 1 and Fig. 2 show that: after the ordinary concrete mixture is mixed with the concrete anti-cracking agent of the present invention, the cracks generated in the concrete plastic stage can be obviously reduced, and the concrete strength of each strength grade will not be. A decrease will result in a slight increase. Under different strength grades, the anti-cracking effect of the present invention is better, among which the anti-cracking agents prepared in Example 1, Example 3 and Example 4 with the best effect are applied under the C30 strength level, and the concrete cracking area is higher than that of the benchmark group. It is reduced by 91%, and the cracked area of C40 concrete is reduced by 92.1% compared with the benchmark group. C60 has no cracks, and the effect is the best. In the comparative example, the crack resistance of the concrete is poor, and the effect on the strength of the concrete is not obvious.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (8)

1. The composite concrete crack resistance agent is characterized by comprising the following components in percentage by mass: 3-7% of polypropylene glycol, 7-10% of polyvinyl alcohol, 1-3% of VAE emulsion, 0.01% of defoaming agent, 10-15% of nano zinc oxide, 3-5% of sodium methylsilicate and the balance of water; the VAE emulsion is emulsion obtained by vinyl acetate-ethylene copolymerization, wherein the content of vinyl acetate is 70-95%; the purity of the nano zinc oxide is more than or equal to 99.5 percent, the average grain diameter is 30nm, and the density is 5.6kg/m³。

2. The composite concrete crack resistance agent as claimed in claim 1, wherein the molecular weight of the polypropylene glycol is 400-600.

3. The compound concrete crack resistance agent as claimed in claim 1, wherein the polyvinyl alcohol is 1788 type polyvinyl alcohol, the polymerization degree is 1700, and the alcoholysis degree is 88%.

4. The compound concrete crack resistance agent as claimed in claim 1, wherein the defoaming agent is polydimethylsiloxane.

5. The compound concrete crack resistance agent as claimed in claim 1, wherein the solid content of the sodium methyl silicate is not less than 30%.

6. The preparation method of the compound concrete crack resistance agent as claimed in any one of claims 1 to 5, characterized by comprising the following steps:

1) weighing the raw materials according to the weight percentage;

2) slowly adding polyvinyl alcohol into cold water while stirring for fully swelling and dispersing until volatile substances overflow, heating in a water bath for accelerating dissolution, keeping the temperature until the solution does not contain micro particles, filtering, and cooling to room temperature for later use;

3) uniformly stirring the weighed polypropylene glycol, VAE emulsion and water at normal temperature to obtain a mixed solution A;

4) and (3) placing the polyvinyl alcohol solution and the mixed solution A into a stirrer, adding the nano zinc oxide, the sodium methyl silicate and the defoaming agent while stirring at normal temperature, and uniformly stirring to prepare the composite concrete anti-cracking agent.

7. The preparation method of the composite concrete anti-cracking agent according to claim 6, wherein in the step 2), the temperature of the cold water is 20-30 ℃; the stirring speed is 70-100 r/min; heating in water bath to 95 deg.C; the heat preservation time is 2-2.5 hours; and the filtering adopts a 28-30 mesh stainless steel net to filter impurities.

8. The preparation method of the composite concrete anti-cracking agent according to claim 6, wherein in the step 3), the stirring speed is 150-200 r/min; in the step 4), the stirring speed is 200-250 r/min.

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