Preparation method of chloride ion erosion resistant concrete

Abstract

The invention provides a manufacturing method of chloride ion erosion resistant concrete, which has the core principle that a chloride ion trapping agent is added into the concrete, the trapping agent adopts a chloromethyl styrene-divinyl benzene copolymer, trimethylamine and sodium hydroxide, the mixture is fully stirred and reacted at 50 DEG C, and the reaction endpoint of Merrifield resin and trimethylamine can be accurately judged by utilizing a PH control method, so that the chloride ion erosion resistant concrete can be obtained. And then mixing with zeolite and polyvinyl alcohol (PVA) according to a certain mass ratio, grinding into powder, and uniformly mixing to prepare the concrete additive which can be mixed with concrete for use and is resistant to chloride ion corrosion, so that free chloride ions are effectively captured, the chloride ion corrosion resistance of the concrete is remarkably improved, and the service life of the concrete is prolonged. According to the technical scheme, the resin adsorption capacity can be improved, the capacity of capturing free chloride ions in concrete is enhanced, corrosion of chloride ions to steel bars is remarkably reduced, and the service life of a concrete structure is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to a method for preparing chloride ion corrosion resistant concrete. Background Art

[0002] As a widely used building material, concrete plays an important role in infrastructure such as water conservancy projects, bridges, and seaports. In local saline-alkali areas, concrete structures are exposed to high concentrations of ions for a long time, especially chloride ion environments. Chloride ions will penetrate into the concrete, causing steel bars to rust, which in turn causes the strength of the concrete structure to decrease and shorten its service life. At present, traditional methods of concrete resistance to chloride ion corrosion mainly rely on increasing the density of concrete or using anti-corrosion coatings, but these methods have problems such as high cost, complex construction, and limited effect.

[0003] In the prior art, there are three main low-cost technical means for resisting chloride ion corrosion: one is to add inorganic salts, such as aluminate additives. Aluminate can react with chloride ions to form Friedel salts to fix chloride ions in concrete and prevent them from further penetration. However, some aluminates are not very stable in the natural environment, and will expand inside the concrete after combining with concrete, causing premature cracking of the building body; the second is to add physical adsorption particles, such as zeolite porous materials. This solution is low-cost, but many gaps are invaded by water during concrete processing, resulting in a significant decrease in porosity. In actual use, this solution has not been observed to have any effect on resisting chloride ion corrosion; the third is to add organic scavengers, such as amine organic matter, polymers containing amino groups (such as anionic resins), etc. The former has been verified to be effective in the laboratory, but in actual construction, amine organic matter usually has a disgusting odor. Large-scale use affects the working environment of construction workers and endangers health. The latter is usually limited in application due to two important reasons: insufficient resin exchange capacity and weak exchange capacity. At present, my country's marine construction facilities adopt high-cost anti-corrosion technical solutions, but there is little technical research on low-cost construction solutions in some local high-salt environments inland. Therefore, it is of great significance to develop an environmentally friendly and easy-to-use low-cost chloride ion scavenger for the preparation of concrete formulas that are resistant to chloride ion corrosion and enhance the durability of concrete. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing chloride ion erosion resistant concrete. The core principle is to add a chloride ion scavenger into the concrete. The scavenger can be mixed with the concrete to prepare chloride ion resistant concrete, effectively capture free chloride ions, thereby significantly improving the chloride ion erosion resistance of the concrete and extending the service life of water conservancy project facilities. To achieve the above purpose, the present invention adopts the following technical scheme.

[0005] Step (1) Preparation of capture agent: Purchase chloromethylstyrene-divinylbenzene-styrene copolymer (CAS: 55844-94-5, hereinafter referred to as Merrifield resin), add trimethylamine, sodium hydroxide and Merrifield resin to the aqueous solution, stir well at 50°C for 30 hours, and observe the pH during the period. If the pH is less than 10, it is necessary to supplement the reaction substrate.

[0006] Furthermore, the reaction has the following critical control points: The original reaction ratio of the capture agent is Merrifield resin: trimethylamine: sodium hydroxide: water mass ratio 100: (1-5): (1.5-7.5): 5000. When it is detected that the pH of the reaction system drops below 10, 0.5%-1.5% sodium hydroxide of the mass of the Merrifield resin is added. If the pH continues to drop after waiting for 1 hour, 0.5%-1.5% sodium hydroxide of the mass of the Merrifield resin is added. Otherwise, 1%-3% trimethylamine of the mass of the Merrifield resin is added. If the pH continues to drop after waiting for 1 hour, the above steps are repeated until the pH does not drop after adding sodium hydroxide and trimethylamine, and the reaction reaches the end point.

[0007] Preferably, in the above critical control points, chloromethylstyrene-divinylbenzene-styrene copolymer (Merrifield resin) can be replaced by chloromethylstyrene-divinylbenzene copolymer, and the material ratio after replacement remains unchanged.

[0008] Preferably, in the above critical control points, trimethylamine can be replaced by triethylamine. When triethylamine is used, step (1) and the critical control points are as follows: chloromethylstyrene-divinylbenzene-styrene copolymer (Merrifield resin), triethylamine and ethanol are mixed in a mass ratio of 100:(10-28):500, stirred in a closed container at 50°C for 160 hours, and then sodium hydroxide is added in a mass ratio of 100:(2-8), stirred for 24 hours and filtered.

[0009] The treated Merrifield resin was then repeatedly washed with deionized water to remove unreacted reagents and by-products, and dried in a hot air drying oven at 50° C. for 6 hours.

[0010] Step (2) Preparation of concrete additives: The modified Merrifield resin, zeolite and polyvinyl alcohol (PVA) prepared in step (1) are mixed in a mass ratio of 100:(15-25):(1-3) and ground into powder and mixed evenly.

[0011] Step (3) Preparation of pre-mixed concrete: Cement, purified water, sand and gravel are mixed in a mass ratio of 1:0.5:1.8:3.2, and then the premixed concrete and the concrete additive prepared in step (2) are mixed in a mass ratio of 1000:(1-5) to obtain a final product. The product is taken to the construction site for pouring and has good resistance to chloride ion corrosion after solidification. Beneficial Effects

[0012] The pH control method used in the modified Merrifield resin in the technical solution of the present application can accurately determine the reaction endpoint of the Merrifield resin and trimethylamine, and can reduce the adverse effects of chlorine introduced into the raw materials on the final product.

[0013] In the production of concrete additives, zeolite and polyvinyl alcohol play a good role in water retention, which can improve the efficiency of chloride ion migration and facilitate capture by modified Merrifield resin.

[0014] The entire technical solution of the present application can increase the adsorption capacity of the resin, enhance the ability to capture free chloride ions inside the concrete, significantly reduce the corrosion of chloride ions on steel bars, and extend the service life of the concrete structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a real shot of the standard comparison piece made in Example 2 after being processed under the conditions of Example 4.

[0016] Figure 2 This is a real shot of the comparative piece with additives added made in Example 3 after being processed under the conditions of Example 4. DETAILED DESCRIPTION

[0017] The technical scheme of the present invention is further illustrated by specific examples below. The cement used in all the following examples is purchased from ordinary Portland cement of Huaxin Cement (product implementation standard GB175-2023); other raw and auxiliary materials whose sources are not specifically stated, such as various auxiliaries used in additives, are purchased from third parties through online channels; sand and stone in aggregates are purchased from local building materials markets.

[0018] In the following examples, all test pieces use a uniform specimen shape, and the standard specimen shape is a 150mm×150mm×150mm cube. The specimen processing method is to pour the prepared concrete into the test mold, vibrate and compact it, put a steel bar with a polished surface, a diameter of 10mm, and a length of 150mm in the center area, smooth the surface, and then cure it under standard conditions. The specimen curing conditions are to cure it for 28 days in an environment with a temperature of 20°C and a relative humidity of ≥95%.

[0019] In the following examples, all compressive strength tests were performed using a hydraulic pressure testing machine. The specific method is as follows: place the specimen on the lower pressure plate of the pressure testing machine, ensure that the center of the specimen is aligned with the center of the pressure plate, and apply pressure at a constant rate of 0.1 MPa / s until the specimen is destroyed. Record the maximum pressure value when the specimen is destroyed, and calculate the compressive strength at the time of destruction. Example 1

[0020] Concrete additive production: 100 g of Merrifield resin (chloromethylstyrene-divinylbenzene-styrene copolymer, CAS: 55844-94-5), trimethylamine, sodium hydroxide and water are placed in a stirring reaction vessel at a mass ratio of 100:5:1.5:5000, and a pH meter is connected to the vessel for stirring reaction. When the pH of the reaction system is detected to drop below 10, 1.5 g of sodium hydroxide is added and stirring is continued for 1 hour. When the pH is detected to be lower than 10 again, 1.5 g of sodium hydroxide is added again. At this time, the pH usually stops dropping. Then 3 g of trimethylamine is added. After waiting for 1 hour, the pH continues to drop. The above steps are repeated. When the pH drop rate is observed to slow down, the amount of sodium hydroxide and trimethylamine added is reduced to 0.5 g and 1 g each time, until the pH does not drop after the addition of sodium hydroxide and trimethylamine, and the reaction reaches the end point. The treated Merrifield resin was then repeatedly washed with deionized water to remove unreacted reagents and by-products, and dried in a 50°C hot air drying oven for 6 hours to obtain 102.8 grams of modified Merrifield resin. 100 grams of modified Merrifield resin, zeolite, and polyvinyl alcohol (PVA) were mixed and ground into powders according to a mass ratio of 100:15:2 and mixed evenly to finally obtain 117 grams of concrete additive. Since trimethylamine is a gas at room temperature, the trimethylamine added in this embodiment is converted from a trimethylamine aqueous solution. For example, a 20% mass fraction trimethylamine aqueous solution requires weighing an aqueous solution 5 times the weight of trimethylamine to be added. If anhydrous trimethylamine is added directly, the operation is as follows: weigh trimethylamine at low temperature (below 0°C), and then place it in a gasification container at room temperature. The gasification container conduit is inserted into the reaction system, and the conduit is provided with a one-way valve to allow the trimethylamine to be naturally gasified and absorbed by the solution. Example 2

[0021] Preparation of standard comparison piece: Cement, purified water, sand, and gravel are mixed in a mass ratio of 1:0.5:1.8:3.2, and a steel bar with a diameter of 10 mm and a length of 150 mm is placed vertically in the middle of a cubic test mold with a side length of 150 mm according to the above test piece preparation method, and concrete is poured in, the surface is smoothed, and then cured under standard conditions. This example obtains a standard comparison piece, which is used to compare the corrosion situation with the standard piece with other additives added. Example 3

[0022] Preparation of a comparative piece with additives added: Cement, purified water, sand, and gravel are mixed in a mass ratio of 1:0.5:1.8:3.2 to prepare 13 kg, and then 36 g of concrete additives are added. Referring to the above test piece preparation method, a steel bar with a diameter of 10 mm and a length of 150 mm is vertically placed in the middle of a cubic test mold with a side length of 150 mm, concrete is poured in, the surface is smoothed, and then cured under standard conditions. This example obtains a comparative piece with additives added, which is used to compare the erosion situation with the standard comparative piece. Example 4

[0023] Place 3 of each group of the above-mentioned comparison pieces in a 2mol / L sodium chloride solution and soak for 60 days. Take them out and dry them. Place the specimens on the lower platen of the pressure testing machine to ensure that the center of the specimen is aligned with the center of the platen. Place the steel bars horizontally and apply pressure at a constant rate of 0.1MPa / s until the specimen is destroyed. The recorded compressive strength is as follows:

[0024] For the two broken comparison pieces, the degree of internal steel bar corrosion is shown in the attached Figure 1 , Attachment Figure 2 , with reference to the attached drawings, Figure 1 This is a standard comparison piece made in Example 2. It can be clearly seen that the steel bar has been completely corroded under high concentration of chloride ions, and the internal steel bar structure has been completely broken and disintegrated. Figure 2 It has also been severely corroded, but the main steel structure is basically intact. Example 5

[0025] The standard parts made in Example 1 and Example 3 were soaked in pure water for 60 days, taken out and dried, and the test pieces were placed on the lower platen of the pressure testing machine to ensure that the center of the test piece was aligned with the center of the platen, and the steel bars were placed horizontally. Pressure was applied at a constant rate of 0.1 MPa / s until the test piece was destroyed. The recorded compressive strength was as shown in the following table:

[0026] This example is to verify the effect of adding additives on the original concrete strength. The experimental data show that after adding organic additives, there is no obvious decrease in the compressive strength of concrete.

[0027] It should be pointed out that the chloride ion concentration of the test environment in Example 4 does not exist in the actual engineering environment, and the concrete erosion progress time in the actual environment is measured in years. In order to accelerate the erosion process, the example uses a sodium chloride solution with a higher concentration. Although the test is not rigorous enough, it is sufficient to prove the effectiveness of the technical solution of the present application. Example 5 was originally intended to verify that the addition of organic additives would not have an adverse effect on the strength of concrete. However, compared with Example 4, after soaking in salt solution and water, the compressive strength of the concrete dropped unreasonably. It is speculated that the excessively high salt concentration may have destroyed the structure of the concrete itself, or that the severe corrosion of the steel bars affected the stability of the internal structure of the concrete. This also indirectly verifies the effectiveness of the technical solution of the present application in resisting chloride ion erosion.

[0028] In addition, in the technical solution of the present application, the steel bars are directly inserted into the concrete structure. Theoretically, this practice will not have a substantial impact on the compressive strength of the concrete. However, considering that in actual engineering, the corrosion of steel bars will affect the stability of large-scale building structures, it is reasonable for the present application to infer the effectiveness of the technical solution of the present application by observing the corrosion of steel bars.

[0029] The Merrifield resin used in the above embodiments is one of the common basic carrier resins for making chloride ion scavengers. The use of other chloromethyl-type styrene polymers, or the method of cyclically adding amines and bases in this application to increase the proportion of active group modification, or replacing trimethylamine with other amines that are easily reactive with chloromethyl-type styrene polymers, and adding adsorbents and water-retaining agents to the modified resin are all derivative technical solutions of the present invention. Although not involved in the embodiments of the present application, they should all fall within the scope of protection of the present application.

Claims

1. A method for producing chloride ion erosion resistant concrete, characterized in that: It includes the following steps: Step (1) Preparation of the capture agent: Chloromethylstyrene-divinylbenzene-styrene copolymer (Merrifield resin), trimethylamine, sodium hydroxide and water are mixed in a mass ratio of 100: (1-5): (1.5-7.5): 5000, and stirred for 30 hours. When it is detected that the pH of the reaction system drops below 10, 0.5%-1.5% sodium hydroxide by mass of the Merrifield resin is added. After waiting for 1 hour, if the pH continues to drop, 0.5%-1.5% sodium hydroxide by mass of the Merrifield resin is added. Otherwise, 1%-3% trimethylamine by mass of the Merrifield resin is added. After waiting for 1 hour, if the pH continues to drop, the above steps are repeated until the pH does not drop after adding sodium hydroxide and trimethylamine, and the reaction reaches the end point. The Merrifield resin is then repeatedly washed with deionized water to remove unreacted reagents and by-products, and dried in a hot air drying oven at 50° C. for 6 hours to obtain a modified Merrifield resin. Step (2) Preparation of concrete additive: the modified Merrifield resin, zeolite and polyvinyl alcohol (PVA) prepared in step (1) are mixed in a mass ratio of 100:(15-25):(1-3), ground into powder and mixed evenly; Step (3) Preparation of premixed concrete: Cement, purified water, sand and gravel are mixed in a mass ratio of 1:0.5:1.8:3.2 to obtain premixed concrete, and then the premixed concrete and the concrete additive prepared in step (2) are mixed in a mass ratio of 1000:(1-5) to obtain a final product, which has good resistance to chloride ion corrosion after solidification.

2. The method for producing chloride ion corrosion resistant concrete according to claim 1, characterized in that: In the step (1), chloromethylstyrene-divinylbenzene-styrene copolymer (Merrifield resin) can be replaced by chloromethylstyrene-divinylbenzene copolymer, and the material ratio after replacement remains unchanged.

3. The method for producing chloride ion corrosion resistant concrete according to claim 1, characterized in that: The trimethylamine can be replaced by triethylamine. When triethylamine is used, the step (1) is as follows: chloromethylstyrene-divinylbenzene-styrene copolymer (Merrifield resin), triethylamine and ethanol are mixed in a mass ratio of 100:(10-28):500, stirred at 50 degrees Celsius for 160 hours in a closed container, and then sodium hydroxide is added in a mass ratio of 100:(12-18). After stirring for 24 hours, the mixture is filtered, and the treated Merrifield resin is repeatedly washed with deionized water and dried in a hot air drying oven at 50 degrees Celsius for 6 hours to obtain a modified Merrifield resin.

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