A cement admixture and a method for preparing the same

Abstract

The scheme discloses the technical field of cement admixture preparation, and relates to a cement admixture which comprises ethylenediaminetetraacetic acid solution and polyamide solution, wherein the polyamide solution is a solution state of amino groups of polyamide combined with carbonate and bicarbonate. During preparation, the ethylenediaminetetraacetic acid solution is mixed with the polyamide solution to obtain the cement admixture. The admixture can significantly improve the carbonation speed of cement and the compressive strength of cement after carbonation.

Description

Technical Field

[0001] This invention belongs to the field of cement admixture preparation technology, and specifically relates to a cement admixture and its preparation method. Background Technology

[0002] Carbonation of concrete primarily occurs because CO2 gas from the air permeates through the fine pores of hardened concrete, reacting chemically with alkaline substances (Ca(OH)2) to form carbonates (CaCO3) and water, thus reducing the alkalinity of the concrete. During cement hydration, a large amount of calcium hydroxide is generated, filling the concrete pores with a saturated calcium hydroxide solution. This alkaline medium provides good protection for the reinforcing steel, causing the formation of insoluble Fe2O3 and Fe3O4 on the steel surface, known as a passivation film. Carbonation lowers the alkalinity of the concrete. When carbonation exceeds the concrete's protective layer, in the presence of water and air, the concrete loses its protective effect on the reinforcing steel, causing it to rust. However, for pure concrete, carbonation can actually help improve its strength.

[0003] For example, patent CN113979660B discloses a low-calcium cement admixture and its preparation and application methods. This admixture uses ethylenediaminetetraacetic acid (EDTA) solution and sodium chloride solution as raw materials. EDTA acts as a chelating agent, binding with divalent metal ions such as magnesium, manganese, ferrous, and calcium ions, thereby improving the compressive strength and durability of the carbonized product. Sodium chloride solution, as a carbonization catalyst, can promote the carbonization of the EDTA-calcium silicate mineral complex by breaking the silica gel layer and can also alter the internal structure of the low-calcium cement, making it easier for carbon dioxide to enter the sample and increasing the carbonization rate. This admixture improves the compressive strength of the carbonized product to some extent, but the carbonization efficiency and the compressive strength of the carbonized product need further improvement. Summary of the Invention

[0004] The present invention aims to provide a cement admixture to accelerate the carbonation rate of cement and improve the compressive strength of cement after carbonation.

[0005] One type of cement admixture in this scheme includes an ethylenediaminetetraacetic acid solution and a polyamide solution, wherein the polyamide solution is a solution of amino groups combined with carbonate and bicarbonate groups of polyamide.

[0006] The working principle and beneficial effects of this scheme are as follows: This scheme uses ethylenediaminetetraacetic acid (EDTA) and polyamide solution as raw materials. When applied to calcium-containing cement, the carbonate and bicarbonate ions in the polyamide solution can quickly combine with calcium ions to form calcium carbonate, accelerating the cement carbonation rate. EDTA, acting as a chelating agent, can combine with divalent metal ions such as calcium, magnesium, manganese, and ferrous ions, thus improving the compressive strength and durability of the carbonated product. Furthermore, when the carbonate and bicarbonate ions in the polyamide solution detach, modified polyamide fibers are formed. These fibers can form a network structure in the concrete, increasing the cement's toughness and ductility, effectively preventing cracking and crack propagation after carbonation, and improving the crack resistance and tensile strength of the carbonated cement. Additionally, polyamide fibers can effectively control micro-cracks in concrete, increasing the tensile strength of the cement, thereby further improving the compressive strength of the concrete.

[0007] Furthermore, the preparation process of the polyamide solution is as follows: Polyamide is fully dissolved in 1-3% acetic acid, then an aqueous solution of ammonium bicarbonate is added and allowed to react fully. Non-amino-containing polyamide components are removed by extraction with solvents of different concentrations (containing water or a mixture with water). Finally, excess carbon dioxide is bubbled into the solution containing amino-containing polyamide and solvent to obtain the polyamide solution. After dissolving the polyamide in acetic acid, the ammonium ions of ammonium bicarbonate displace the acetic acid bound to the polyamide. The acetic acid and the ammonium ions of ammonium bicarbonate combine to form ammonium acetate impurities. After extraction and purification, a solution containing only polyamide and water is obtained. Excess carbon dioxide is then bubbled into this solution to obtain a polyamide solution in which carbonate and bicarbonate ions are bound to the amino groups of the polyamide and remain in a liquid state.

[0008] Furthermore, the volume ratio of the ethylenediaminetetraacetic acid (EDTA) solution to the polyamide solution is 6–10:1; the concentration of EDTA in the EDTA solution is 3–8%. Cement admixtures within this ratio range exhibit better performance.

[0009] Furthermore, the concentration of ethylenediaminetetraacetic acid in the ethylenediaminetetraacetic acid solution is 5%.

[0010] Based on the above-mentioned cement admixture, this application also provides a method for preparing the cement admixture, comprising the following steps: mixing an ethylenediaminetetraacetic acid solution with a polyamide solution to obtain the cement admixture.

[0011] Based on the above-mentioned cement admixture, this application also provides a method for improving the compressive strength of cement after carbonation, comprising the following steps: mixing the cement admixture with cement in a uniform mixture to obtain a cement mixture of 10-15 wt%.

[0012] Furthermore, this application also provides another method for improving the compressive strength of cement after carbonation, comprising the following steps: mixing polyamide solution with cement evenly and letting it stand for 0.5 to 1 hour, turning it over every 20 minutes during the standing period; then adding ethylenediaminetetraacetic acid solution and mixing evenly to obtain a cement mixture of 10 to 15 wt%, wherein the volume ratio of ethylenediaminetetraacetic acid solution to polyamide solution is 6 to 10:1.

[0013] Furthermore, a method for improving the compressive strength of concrete after carbonation includes the following steps: mixing aggregates, cement admixtures and cement evenly to obtain a cement mixture with a water-cement ratio of 0.4 to 0.55, wherein the weight ratio of aggregates to cement is 2 to 4:1.

[0014] Furthermore, a method for improving the compressive strength of concrete after carbonation includes the following steps: mixing aggregates, polyamide solution, and cement evenly and letting stand for 0.5 to 1 hour, turning the mixture every 20 minutes during the standing period; then adding ethylenediaminetetraacetic acid solution and mixing evenly to obtain a cement mixture with a water-cement ratio of 0.4 to 0.55, wherein the volume ratio of ethylenediaminetetraacetic acid solution to polyamide solution is 6 to 10:1, and the weight ratio of aggregates to cement is 2 to 4:1. Detailed Implementation

[0015] The following detailed description illustrates the specific implementation method:

[0016] Preparation of polyamide solution: Polyamide is fully dissolved in 2% acetic acid, and then ammonium bicarbonate aqueous solution is added to react fully at a reaction temperature of 20-30℃, 25℃ is selected in the example; non-amino polyamide components are then removed by extraction or dialysis, and finally excess carbon dioxide is introduced into the solution containing amino polyamide and solvent to obtain polyamide solution; the amounts of polyamide, acetic acid and ammonium bicarbonate can be added according to the normal reaction ratio, which will not be elaborated here.

[0017] The concentration of ethylenediaminetetraacetic acid is 5%.

[0018] The volume ratio of ethylenediaminetetraacetic acid solution to polyamide solution is 7:1.

[0019] Cement: White silicate cement from Sichuan Zongsheng Special Cement Co., Ltd., cement type: PW-152.5.

[0020] Aggregate: Chinese ISO standard sand.

[0021] Example 1: A method for improving the compressive strength of concrete after carbonation, comprising the following steps:

[0022] Step 1: Mix the gravel, ethylenediaminetetraacetic acid solution, and polyamide solution evenly to obtain the cement admixture;

[0023] Step 2: Mix the cement admixture with the cement paste evenly to obtain a cement mixture with a water-cement ratio of 0.5.

[0024] Example 2: A method for improving the compressive strength of concrete after carbonation, comprising the following steps: mixing gravel, polyamide solution and cement evenly and letting stand for 1.5 hours, turning over every 20 minutes during the standing period; then adding ethylenediaminetetraacetic acid solution and mixing evenly to obtain a cement mixture with a water-cement ratio of 0.5.

[0025] Comparative Example 1: A method for improving the compressive strength of concrete after carbonation, comprising the following steps:

[0026] Step 1: Mix 4 wt% ethylenediaminetetraacetic acid solution and 2 wt% sodium chloride solution at a mass ratio of 1:1 to prepare a mixed solution. After standing and aging for 5 hours, the low-calcium cement admixture is obtained.

[0027] Step 2: Mix the gravel, low-calcium cement, cement admixture and cement to obtain a cement mixture with a water-cement ratio of 0.5.

[0028] Comparative Example 2: A method for improving the compressive strength of concrete after carbonation, comprising the following steps: mixing gravel, water and cement to obtain a cement mixture with a water-cement ratio of 0.5.

[0029] In Examples 1-2 and Comparative Examples 1-2, the weight ratio of cement to gravel was 1:3.

[0030] According to the standard GB / T 17671-2021, the cement mixtures of Examples 1-2 and Comparative Examples 1-2 were prepared into prisms of 40mm*40mm*160mm. Three prism samples were selected from each example, and their compressive strength and flexural strength were tested. The test results are shown in the table below:

[0031]

[0032] The test data shows that the cement admixture prepared in this application can significantly improve the flexural strength and compressive strength of concrete. It can also achieve good results when the ethylenediaminetetraacetic acid solution in the cement admixture is mixed with the polyamide solution or stored separately and then used together.

[0033] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A cement admixture characterized by: The cement additive comprises ethylenediamine tetraacetic acid solution and polyamide solution, the volume ratio of the ethylenediamine tetraacetic acid solution to the polyamide solution is 6-10:1; the concentration of ethylenediamine tetraacetic acid in the ethylenediamine tetraacetic acid solution is 3-8%; the polyamide solution is a solution state of amino combined with carbonate and bicarbonate of polyamide; the polyamide is dissolved by 1-3% acetic acid, then the bicarbonate ammonium aqueous solution is added for reaction, then the non-amino-containing polyamide components are removed by adding different gradient concentrations of solvent extraction, finally the polyamide solution is obtained by introducing excess carbon dioxide into the solution of the amino-containing polyamide and the solvent; the solvent contains water or is mixed with water.

2. The cement admixture according to claim 1, characterized in that: The concentration of ethylenediamine tetraacetic acid in the ethylenediamine tetraacetic acid solution is 5%.

3. A method of preparing a cement admixture according to any one of claims 1 to 2, characterized in that: The cement additive is obtained by mixing the ethylenediamine tetraacetic acid solution and the polyamide solution.

4. A method of increasing the compressive strength of carbonated concrete, characterized by: The cement mixture with a water-cement ratio of 0.4-0.55 is obtained by uniformly mixing the cement additive of any one of claims 1-2 with aggregate and cement, and the weight ratio of the aggregate to the cement is 2-4:

1.

5. A method of increasing the compressive strength of carbonated concrete, characterized by: The cement mixture with a water-cement ratio of 0.4-0.55 is obtained by uniformly mixing the polyamide solution in the cement additive of any one of claims 1-2 with aggregate and cement, and placing for 0.5-1 h, and the aggregate and cement are stirred every 20 min during the placing; then the ethylenediamine tetraacetic acid solution is added and uniformly mixed, wherein the volume ratio of the ethylenediamine tetraacetic acid solution to the polyamide solution is 6-10:1, and the weight ratio of the aggregate to the cement is 2-4:1.

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