阅读说明：本技术 一种具有减水及防腐功能的混凝土外加剂及其制备方法 (Concrete admixture with water reducing and corrosion preventing functions and preparation method thereof ) 是由 冯鹏 王赢 陈春超 李明远 范舟 刘寅莹 宋倩 于 2021-09-28 设计创作，主要内容包括：本发明提供一种具有减水及防腐功能的混凝土外加剂及其制备方法,该混凝土外加剂包括以下组分及各组分的质量份为：减水剂50～70份、阻锈剂30～50份。本发明主要应用于沿海建筑工程钢筋混凝土中,其质量稳定,性能优良,与各种水泥相容性较好,2h坍落度基本无损失,采用本品配制的混凝土表面无泌水,色差小、无大气泡,外观质量好；采用本品浇筑的腐蚀环境下钢筋混凝土,其能显著缓解氯离子对钢筋钝化膜的破坏,提高抗氯离子侵蚀能力,提升沿海腐蚀环境钢筋混凝土的耐久性。(The invention provides a concrete admixture with water reducing and corrosion preventing functions and a preparation method thereof, wherein the concrete admixture comprises the following components in parts by mass: 50-70 parts of water reducing agent and 30-50 parts of rust inhibitor. The invention is mainly applied to coastal building engineering reinforced concrete, has stable quality, excellent performance, better compatibility with various cements, basically no loss of slump in 2h, no bleeding on the surface of the concrete prepared by the product, small color difference, no large bubbles and good appearance quality; the reinforced concrete poured by the product in the corrosive environment can remarkably relieve the damage of chloride ions to a reinforcing steel bar passive film, improve the resistance to chloride ion corrosion and improve the durability of the reinforced concrete in the coastal corrosive environment.)

1. The concrete admixture with the water reducing and corrosion preventing functions is characterized by comprising the following components in parts by mass: 50-70 parts of water reducing agent and 30-50 parts of rust inhibitor.

2. The concrete admixture with the water reducing and corrosion preventing functions of claim 1, wherein the water reducing agent comprises the following components in parts by mass: 35-40 parts of water, 2-6 parts of sodium methallylsulfonate, 15-20 parts of polyoxyethylene monomethyl ether methacrylate, 8-12 parts of acrylic acid, 2-6 parts of hydroxypropyl acrylate, 0.1-0.3 part of 2-mercaptopropionic acid, 0.2-0.5 part of mercaptoethanol, 5-10 parts of ammonium persulfate solution with the mass fraction of 5%, and 6-25 parts of sodium hydroxide solution with the mass fraction of 30%.

3. The concrete admixture with the water reducing and corrosion preventing functions as claimed in claim 2, wherein the water reducing agent comprises the following components in parts by mass: 38-40 parts of water, 4-5 parts of sodium methallylsulfonate, 16-20 parts of polyoxyethylene monomethyl ether methacrylate, 10-11 parts of acrylic acid, 3-5 parts of hydroxypropyl acrylate, 0.1-0.2 part of 2-mercaptopropionic acid, 0.2-0.4 part of mercaptoethanol, 6-9 parts of ammonium persulfate solution with the mass fraction of 5% and 10-20 parts of sodium hydroxide solution with the mass fraction of 30%.

4. The concrete admixture with the water reducing and corrosion preventing functions as claimed in claim 2, wherein the water reducing agent is prepared by the following method:

1) installing a stirrer, a thermometer, an air duct and a reaction kettle;

2) adding water and sodium methallyl sulfonate into a reaction kettle, and heating to 60 ℃ under the conditions of stirring and nitrogen filling;

3) after the temperature is constant, continuously stirring, and sequentially adding polyoxyethylene monomethyl ether methacrylate, acrylic acid, hydroxypropyl acrylate, 2-mercaptopropionic acid, mercaptoethanol and an ammonium persulfate solution with the mass fraction of 5%;

4) keeping the temperature at the constant temperature of 60 ℃ for 4-6h to ensure that the reaction is complete, and standing and cooling after the reaction is finished;

5) and (3) after the solution is cooled, adding a sodium hydroxide solution with the mass fraction of 30%, and adjusting the pH value to 7.0 to obtain the water reducing agent.

5. The concrete admixture with the water reducing and corrosion preventing functions as claimed in claim 1, wherein the rust inhibitor comprises the following components in parts by mass: 75-85 parts of water, 1-5 parts of sodium molybdate, 3-6 parts of diethylenetriamine, 0.5-1 part of propenyl thiourea, 1-3 parts of 1, 4-butynediol, 3-8 parts of sodium monofluorophosphate and 1-20 parts of sodium hydroxide solution with the mass fraction of 30%.

6. The concrete admixture with the water reducing and corrosion preventing functions as claimed in claim 5, wherein the rust inhibitor comprises the following components in parts by mass: the optimized scheme of the rust inhibitor comprises the following components in parts by mass: 78-82 parts of water, 3-4 parts of sodium molybdate, 4-5 parts of diethylenetriamine, 0.5-0.8 part of propenyl thiourea, 1.5-2.5 parts of 1, 4-butynediol, 4-6 parts of sodium monofluorophosphate and 1-10 parts of sodium hydroxide solution with the mass fraction of 30%.

7. The concrete admixture with water-reducing and corrosion-preventing functions of claim 5, wherein the corrosion inhibitor is prepared by the following method:

1) adding water into a reaction kettle, heating to 40 ℃, adding sodium molybdate, diethylenetriamine and propenyl thiourea, continuously stirring, heating to 70 ℃, and keeping the temperature constant for 2 hours;

2) adding 1, 4-butynediol and sodium monofluorophosphate, continuously stirring, and keeping the temperature at 70 ℃ for 1.5-3 h;

3) and adjusting the pH value to 7.0-8.0 by using 30% by mass of sodium hydroxide, and cooling to normal temperature to obtain the rust inhibitor.

8. The method for preparing a concrete admixture with water-reducing and corrosion-preventing functions of any one of claims 1 to 7, comprising: and (3) putting 50-70 parts of water reducing agent and 30-50 parts of rust inhibitor into a reaction kettle, continuously stirring for 0.5-1 h, and standing for 3h to obtain the concrete admixture.

Technical Field

The invention relates to an engineering material and a preparation method thereof, in particular to a concrete admixture with water reducing and corrosion preventing functions and a preparation method thereof.

Background

The topography of coastal areas is complicated, and the temperature difference and humidity change range is large. The coastal beach area is large, and the coastal beach area comprises high saline-alkali water areas such as a solarization pool and a seawater culture pool; the method also comprises low saline-alkali soil and water areas such as farmlands, freshwater culture ponds and the like. According to the environmental action grade division method in the concrete structure durability design specification (GB/T50476-. The problem of reinforcement rust expansion damage caused by corrosion of reinforced concrete by chloride ions in seawater is the key of the durability design of the ocean engineering structure.

The early-stage engineering in coastal areas generally causes severe damage phenomena such as concrete expansion crack, falling off, reinforcement corrosion and even rust break in a service period, and mainly causes the failure of chloride ion protection in reinforced concrete. Recent investigation shows that the concrete cracks along the reinforcement of the reinforced concrete structure of the coastal sluice in Jiangsu extremely seriously. The key to sustainable development of coastal reinforced concrete buildings is to improve the quality of coastal buildings, prolong the service life of projects and reduce the maintenance and reconstruction cost. Most of the additives used in reinforced concrete poured in coastal areas at the present stage are single concrete water reducing agents only having a water reducing function, and the performance of the reinforced concrete water reducing agents is insufficient in the aspect of preventing reinforcing steel bar corrosion, so that the additives are required to be made in the aspect of improving the quality of coastal reinforced concrete in order to solve the problems that the consumption of the reinforced concrete is increased and the corrosion of reinforced concrete buildings is still caused at present in the large development on coastal areas and the defects of measures for solving the problems.

Disclosure of Invention

Aiming at the current coastal area environment mainly suffering from chloride corrosion, the reinforced concrete is easy to be damaged due to saline-alkali corrosion, and meanwhile, the water reducing agent for the concrete at the present stage has single function and no anti-corrosion performance, the invention aims to provide the concrete admixture with the water reducing and anti-corrosion functions and the preparation method thereof.

In order to achieve the aim, the invention provides a concrete admixture with water reducing and corrosion preventing functions, which comprises the following components in parts by mass: 50-70 parts of water reducing agent and 30-50 parts of rust inhibitor.

Preferably, the water reducing agent comprises the following components in parts by mass: 35-40 parts of water, 2-6 parts of sodium methallylsulfonate, 15-20 parts of polyoxyethylene monomethyl ether methacrylate, 8-12 parts of acrylic acid, 2-6 parts of hydroxypropyl acrylate, 0.1-0.3 part of 2-mercaptopropionic acid, 0.2-0.5 part of mercaptoethanol, 5-10 parts of ammonium persulfate solution with the mass fraction of 5%, and 6-25 parts of sodium hydroxide solution with the mass fraction of 30%.

Preferably, the water reducing agent comprises the following components in parts by mass: 38-40 parts of water, 4-5 parts of sodium methallylsulfonate, 16-20 parts of polyoxyethylene monomethyl ether methacrylate, 10-11 parts of acrylic acid, 3-5 parts of hydroxypropyl acrylate, 0.1-0.2 part of 2-mercaptopropionic acid, 0.2-0.4 part of mercaptoethanol, 6-9 parts of ammonium persulfate solution with the mass fraction of 5% and 10-20 parts of sodium hydroxide solution with the mass fraction of 30%.

Preferably, the water reducing agent is prepared by the following method:

1) installing a stirrer, a thermometer, an air duct and a reaction kettle;

2) adding water and sodium methallyl sulfonate into a reaction kettle, and heating to 60 ℃ under the conditions of stirring and nitrogen filling;

3) after the temperature is constant, continuously stirring, and sequentially adding polyoxyethylene monomethyl ether methacrylate, acrylic acid, hydroxypropyl acrylate, 2-mercaptopropionic acid, mercaptoethanol and an ammonium persulfate solution with the mass fraction of 5%;

4) keeping the temperature at the constant temperature of 60 ℃ for 4-6h to ensure that the reaction is complete, and standing and cooling after the reaction is finished;

5) and (3) after the solution is cooled, adding a sodium hydroxide solution with the mass fraction of 30%, and adjusting the pH value to 7.0 to obtain the water reducing agent.

Preferably, the rust inhibitor comprises the following components in parts by mass: 75-85 parts of water, 1-5 parts of sodium molybdate, 3-6 parts of diethylenetriamine, 0.5-1 part of propenyl thiourea, 1-3 parts of 1, 4-butynediol, 3-8 parts of sodium monofluorophosphate and 1-20 parts of sodium hydroxide solution with the mass fraction of 30%.

Preferably, the rust inhibitor comprises the following components in parts by mass: the optimized scheme of the rust inhibitor comprises the following components in parts by mass: 78-82 parts of water, 3-4 parts of sodium molybdate, 4-5 parts of diethylenetriamine, 0.5-0.8 part of propenyl thiourea, 1.5-2.5 parts of 1, 4-butynediol, 4-6 parts of sodium monofluorophosphate and 1-10 parts of sodium hydroxide solution with the mass fraction of 30%.

Preferably, the rust inhibitor is prepared by the following method:

1) adding water into a reaction kettle, heating to 40 ℃, adding sodium molybdate, diethylenetriamine and propenyl thiourea, continuously stirring, heating to 70 ℃, and keeping the temperature constant for 2 hours;

2) adding 1, 4-butynediol and sodium monofluorophosphate, continuously stirring, and keeping the temperature at 70 ℃ for 1.5-3 h;

3) and adjusting the pH value to 7.0-8.0 by using 30% by mass of sodium hydroxide, and cooling to normal temperature to obtain the rust inhibitor.

The invention also provides a preparation method of the concrete admixture with the water reducing and corrosion preventing functions, which comprises the following steps: and (3) putting 50-70 parts of water reducing agent and 30-50 parts of rust inhibitor into a reaction kettle, continuously stirring for 0.5-1 h, and standing for 3h to obtain the concrete admixture.

Compared with the prior art, the invention provides a composite concrete admixture, which has the dual functions of water reduction and corrosion prevention and has the following beneficial effects:

1. the steel bar reinforced concrete building block is mainly applied to coastal reinforced concrete buildings, and has stable quality and excellent performance;

2. the water reducing agent has good compatibility with various cements, and molecules of the water reducing agent are comb-shaped polymers, so that more stable steric hindrance is formed among cement particles, the fluidity retentivity of the water reducing agent is improved, and the slump constant of the water reducing agent is basically free of loss after 2 hours;

3. the concrete prepared by the product has no bleeding on the surface, small color difference, no large bubbles and good appearance quality;

4. the reinforced concrete poured by the product in a corrosive environment can remarkably relieve the damage of chloride ions to a reinforcing steel bar passive film and improve the resistance to chloride ion corrosion.

Detailed Description

The present invention will be further described with reference to the following examples. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

Example 1

1. Preparation of water reducing agent

1) 38 parts of water, 5 parts of sodium methallylsulfonate, 16 parts of polyoxyethylene monomethyl ether methacrylate, 10 parts of acrylic acid, 6 parts of hydroxypropyl acrylate, 0.2 part of 2-mercaptopropionic acid, 0.4 part of mercaptoethanol, 9 parts of an ammonium persulfate solution with the mass fraction of 5 percent and 15.4 parts of a sodium hydroxide solution with the mass fraction of 30 percent are weighed.

2) Adding weighed water and sodium methallyl sulfonate into a reaction kettle, and slowly heating to 60 ℃ under the conditions of stirring and nitrogen filling;

3) after the temperature is constant, continuously stirring, and sequentially adding weighed polyoxyethylene monomethyl ether methacrylate, acrylic acid, hydroxypropyl acrylate, 2-mercaptopropionic acid, mercaptoethanol and an ammonium persulfate solution with the mass fraction of 5%;

4) keeping the temperature at the constant temperature of 60 ℃ for 4.5 hours to ensure that the reaction is complete, and standing and cooling after the reaction is finished;

5) and (3) after the solution is cooled, adding a sodium hydroxide solution with the mass fraction of 30%, and adjusting the pH value to 8.0 to obtain the water reducing agent.

2. Preparation of rust inhibitor

1) Weighing 78 parts of water, 4 parts of sodium molybdate, 4 parts of diethylenetriamine, 0.6 part of propenyl thiourea, 2 parts of 1, 4-butynediol, 5 parts of sodium monofluorophosphate and 6.4 parts of sodium hydroxide solution with the mass fraction of 30%.

2) Adding water into a reaction kettle, heating to 40 ℃, slowly adding weighed sodium molybdate, diethylenetriamine and propenyl thiourea, continuously stirring, heating to 70 ℃, and keeping the temperature for 2 hours;

3) adding weighed 1, 4-butynediol and sodium monofluorophosphate, continuously stirring, and keeping the temperature at 70 ℃ for 2 hours;

4) and adjusting the pH value to 8.0 by using 30 mass percent of sodium hydroxide, and cooling to normal temperature to obtain the rust inhibitor.

3. Preparation of anti-corrosion functional water reducing agent

And weighing 65 parts of the water reducing agent and 35 parts of the rust inhibitor, placing the materials in a reaction kettle, continuously stirring for 1 hour, and standing for 3 hours to obtain the material.

4. Test Performance

(1) The performance of the admixture of the present invention was tested according to the concrete admixture (GB8076-2008) and the test protocol for hydraulic concrete (SL/T352-2020), and the test results are shown in the following table:

TABLE 1 concrete Admixture Performance test results

Example 2

1. Preparation of water reducing agent

1) Weighing 40 parts of water, 4 parts of sodium methallylsulfonate, 18 parts of polyoxyethylene monomethyl ether methacrylate, 10 parts of acrylic acid, 5 parts of hydroxypropyl acrylate, 0.1 part of 2-mercaptopropionic acid, 0.4 part of mercaptoethanol, 8 parts of an ammonium persulfate solution with the mass fraction of 5 percent and 14.5 parts of a sodium hydroxide solution with the mass fraction of 30 percent.

2) Adding weighed water and sodium methallyl sulfonate into a reaction kettle, and slowly heating to 60 ℃ under the conditions of stirring and nitrogen filling;

3) after the temperature is constant, continuously stirring, and sequentially adding weighed polyoxyethylene monomethyl ether methacrylate, acrylic acid, hydroxypropyl acrylate, 2-mercaptopropionic acid, mercaptoethanol and an ammonium persulfate solution with the mass fraction of 5%;

4) keeping the temperature at the constant temperature of 60 ℃ for 5.5 hours to ensure that the reaction is complete, and standing and cooling after the reaction is finished;

5) and (3) after the solution is cooled, adding a sodium hydroxide solution with the mass fraction of 30%, and adjusting the pH value to about 7.0 to obtain the water reducing agent.

2. Preparation of rust inhibitor

1) Weighing 80 parts of water, 3 parts of sodium molybdate, 4 parts of diethylenetriamine, 0.6 part of propenyl thiourea, 2 parts of 1, 4-butynediol, 5 parts of sodium monofluorophosphate and 5.4 parts of sodium hydroxide solution with the mass fraction of 30%.

2) Adding water into a reaction kettle, heating to 40 ℃, slowly adding weighed sodium molybdate, diethylenetriamine and propenyl thiourea, continuously stirring, heating to 70 ℃, and keeping the temperature for 2 hours;

3) adding weighed 1, 4-butynediol and sodium monofluorophosphate, continuously stirring, and keeping the temperature at 70 ℃ for 3 hours;

4) and adjusting the pH value to 7.0-8.0 by using 30% by mass of sodium hydroxide, and cooling to normal temperature to obtain the rust inhibitor.

3. Preparation of anti-corrosion functional water reducing agent

60 parts of the water reducing agent and 40 parts of the rust inhibitor are weighed and placed in a reaction kettle, and the materials are continuously stirred for 1 hour and kept stand for 3 hours to obtain the invention material.

4. Test Performance

(1) The performance of the admixture of the present invention was tested according to the concrete admixture (GB8076-2008) and the test protocol for hydraulic concrete (SL/T352-2020), and the test results are shown in the following table:

TABLE 2 concrete Admixture Performance test results

Example 3

1. Preparation of water reducing agent

1) Weighing 36 parts of water, 4 parts of sodium methallylsulfonate, 20 parts of polyoxyethylene monomethyl ether methacrylate, 12 parts of acrylic acid, 5 parts of hydroxypropyl acrylate, 0.1 part of 2-mercaptopropionic acid, 0.4 part of mercaptoethanol, 7 parts of 5 mass percent ammonium persulfate solution and 15.5 parts of 30 mass percent sodium hydroxide solution.

2) Adding weighed water and sodium methallyl sulfonate into a reaction kettle, and slowly heating to 60 ℃ under the conditions of stirring and nitrogen filling;

3) after the temperature is constant, continuously stirring, and sequentially adding weighed polyoxyethylene monomethyl ether methacrylate, acrylic acid, hydroxypropyl acrylate, 2-mercaptopropionic acid, mercaptoethanol and an ammonium persulfate solution with the mass fraction of 5%;

4) keeping the temperature at the constant temperature of 60 ℃ for 5.5 hours to ensure that the reaction is complete, and standing and cooling after the reaction is finished;

5) and (3) after the solution is cooled, adding a sodium hydroxide solution with the mass fraction of 30%, and adjusting the pH value to about 7.0 to obtain the water reducing agent.

2. Preparation of rust inhibitor

1) 76 parts of water, 5 parts of sodium molybdate, 4 parts of diethylenetriamine, 0.6 part of propenyl thiourea, 2 parts of 1, 4-butynediol, 5 parts of sodium monofluorophosphate and 7.4 parts of 30% sodium hydroxide solution.

2) Adding water into a reaction kettle, heating to 40 ℃, slowly adding weighed sodium molybdate, diethylenetriamine and propenyl thiourea, continuously stirring, heating to 70 ℃, and keeping the temperature for 2 hours;

3) adding weighed 1, 4-butynediol and sodium monofluorophosphate, continuously stirring, and keeping the temperature at 70 ℃ for 3 hours;

4) and adjusting the pH value to 7.0-8.0 by using 30% by mass of sodium hydroxide, and cooling to normal temperature to obtain the rust inhibitor.

3. Preparation of anti-corrosion functional water reducing agent

And weighing 50 parts of the water reducing agent and 50 parts of the rust inhibitor, placing the materials in a reaction kettle, continuously stirring for 1 hour, and standing for 3 hours to obtain the material.

4. Test Performance

(1) The performance of the admixture of the present invention was tested according to the concrete admixture (GB8076-2008) and the test protocol for hydraulic concrete (SL/T352-2020), and the test results are shown in the following table:

TABLE 3 concrete Admixture Performance test results

Example 4

1. Preparation of water reducing agent

1) 39 parts of water, 5 parts of sodium methallylsulfonate, 16 parts of polyoxyethylene monomethyl ether methacrylate, 12 parts of acrylic acid, 5 parts of hydroxypropyl acrylate, 0.1 part of 2-mercaptopropionic acid, 0.4 part of mercaptoethanol, 6.5 parts of an ammonium persulfate solution with the mass fraction of 5 percent and 16 parts of a sodium hydroxide solution with the mass fraction of 30 percent are weighed.

2) Adding weighed water and sodium methallyl sulfonate into a reaction kettle, and slowly heating to 60 ℃ under the conditions of stirring and nitrogen filling;

3) after the temperature is constant, continuously stirring, and sequentially adding weighed polyoxyethylene monomethyl ether methacrylate, acrylic acid, hydroxypropyl acrylate, 2-mercaptopropionic acid, mercaptoethanol and an ammonium persulfate solution with the mass fraction of 5%;

4) keeping the temperature at the constant temperature of 60 ℃ for 5.5 hours to ensure that the reaction is complete, and standing and cooling after the reaction is finished;

5) and (3) after the solution is cooled, adding a sodium hydroxide solution with the mass fraction of 30%, and adjusting the pH value to 7.0 to obtain the water reducing agent.

2. Preparation of rust inhibitor

1) Weighing 78 parts of water, 4 parts of sodium molybdate, 6 parts of diethylenetriamine, 0.6 part of propenyl thiourea, 2 parts of 1, 4-butynediol, 6 parts of sodium monofluorophosphate and 7.4 parts of sodium hydroxide solution with the mass fraction of 30%.

2) Adding water into a reaction kettle, heating to 40 ℃, slowly adding weighed sodium molybdate, diethylenetriamine and propenyl thiourea, continuously stirring, heating to 70 ℃, and keeping the temperature for 2 hours;

3) adding weighed 1, 4-butynediol and sodium monofluorophosphate, continuously stirring, and keeping the temperature at 70 ℃ for 3 hours;

4) and adjusting the pH value to 7.0-8.0 by using 30% by mass of sodium hydroxide, and cooling to normal temperature to obtain the rust inhibitor.

3. Preparation of anti-corrosion functional water reducing agent

55 parts of the water reducing agent and 45 parts of the rust inhibitor are weighed and placed in a reaction kettle, and the materials are continuously stirred for 1 hour and kept stand for 3 hours to obtain the invention material.

4. Test Performance

(1) The performance of the admixture of the present invention was tested according to the concrete admixture (GB8076-2008) and the test protocol for hydraulic concrete (SL/T352-2020), and the test results are shown in the following table:

TABLE 4 concrete Admixture Performance test results

And (3) data analysis: tables 1 to 4 show the results of the mixing performance, mechanical properties and corrosion resistance of concrete obtained by mixing concrete with different amounts of concrete admixture. Wherein the 1 st row of each table is the different properties of the concrete at an admixture loading of 0, i.e. the reference group.

When the admixture addition is zero, the water reducing rate and the compressive strength ratio of the concrete are comparison data, when the admixture addition is increased to about 1.0%, the water reducing rate of the concrete is increased to between 15% and 20%, the slump loss is also obviously reduced within 2 hours, and the compressive strength ratio is increased by about 1.4 times.

When the addition amount of the admixture is increased to more than 1.5%, the water reducing rate of the concrete is increased to about 25%, the slump loss in 2 hours is 0, the mixing performance of the concrete is obviously improved, and the compressive strength ratio is improved by about 1.6 times.

According to a concrete reinforcement corrosion rapid test method in the specification of Hydraulic concrete test (SL/T352-2020), the corrosion resistance of the concrete doped with the additive is tested, and test results show that the doping amount of the additive in a reference group is 0, the steel bar of the reinforced concrete is corroded after two dry and wet cycles, and after the additive is doped into the concrete, the steel bar of the concrete is not corroded after 10 dry and wet cycles, which shows that the corrosion-resistant component in the additive has obvious effect, and the corrosion risk of the steel bar can be obviously reduced when the additive is used in saline-alkali areas.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.