阅读说明：本技术 一种二氧化碳预拌水泥基复合材料的制备方法 (Preparation method of carbon dioxide premixed cement-based composite material ) 是由 林忠财 汪珉璐 罗双 于 2021-09-24 设计创作，主要内容包括：本发明公开了一种二氧化碳预拌水泥基复合材料的制备方法。包括以下步骤：步骤一：往密闭状态下正搅拌的水泥浆体中通入含二氧化碳的气体30s～240s；步骤二：当水泥浆体流动度明显降低时,向其中加入水泥质量1％～3％的水以恢复其原先的流动度。本发明具有提高材料强度,减少水泥用量,缓解温室效应和经济效益高的特点。(The invention discloses a preparation method of a carbon dioxide pre-mixed cement-based composite material. The method comprises the following steps: the method comprises the following steps: introducing gas containing carbon dioxide into the cement slurry which is stirred in a closed state for 30-240 s; step two: when the fluidity of the cement paste is obviously reduced, water with the mass of 1-3% of the cement is added to restore the original fluidity. The invention has the characteristics of improving the material strength, reducing the cement consumption, relieving the greenhouse effect and having high economic benefit.)

1. The preparation method of the carbon dioxide premixed cement-based composite material is characterized by comprising the following steps of:

the method comprises the following steps: introducing gas containing carbon dioxide into the cement slurry which is stirred in a closed state for 30-240 s;

step two: when the fluidity of the cement paste is obviously reduced, water with the mass of 1-3% of the cement is added to restore the original fluidity.

2. The method for preparing the carbon dioxide ready-mixed cement-based composite material as claimed in claim 1, wherein in the first step, the gas is: liquefied and purified carbon dioxide gas with the purity of 99.99 percent;

or the following steps: the liquefied and purified carbon dioxide gas with the purity of 99.99 percent is mixed with air prepared in industry to obtain mixed gas, wherein the concentration of the carbon dioxide is more than 10 percent;

or the following steps: flue gas recovered from cement plants and/or iron and steel plants, wherein the concentration of carbon dioxide is more than 10%.

3. The method for preparing the carbon dioxide ready-mixed cement-based composite material as claimed in claim 1, wherein in the first step, the cement paste is a composite material with cement as a main cementing material, and comprises cement paste, cement mortar or concrete; the water cement ratio of the cement paste is 0.3-0.6.

4. The method for preparing a carbon dioxide ready-mixed cement-based composite material according to claim 1, wherein in the first step, the cement in the cement paste is ordinary portland cement with a strength grade of 42.5, 42.5R, 52.5 or 52.5R.

5. The preparation method of the carbon dioxide ready-mixed cement-based composite material as claimed in claim 1, wherein in the first step, the stirring speed is 60-300 r/min during the gas introduction.

6. The method for preparing the carbon dioxide pre-mixed cement-based composite material as claimed in claim 1, wherein in the first step, the cement paste is pre-mixed for 30-120 s before the gas is introduced.

7. The method for preparing the carbon dioxide ready-mixed cement-based composite material as claimed in claim 1, wherein after the second step is completed, sand, stones and additives are added into the cement paste, and after the mixture is uniformly mixed, the cement paste is poured.

Technical Field

The invention relates to the technical field of building materials, in particular to a preparation method of a carbon dioxide premixed cement-based composite material.

Background

With the continuous development of industrialization, more and more steel plants and manufacturing plants are built, and the exploitation and combustion of fossil energy and the large amount of carbon dioxide contained in the smoke tail gas emitted by the plants are important sources causing greenhouse effect. Currently, carbon abatement is a major issue facing the world, and "carbon peak-to-peak", "carbon neutralization" has been proposed. For the cement and building materials industry, where carbon emissions are extremely alarming, a very effective solution is to achieve the absorption and fixation of carbon dioxide by the building materials.

The carbonization curing method has been studied for the past century, and achieves the purpose of early strength by performing carbon dioxide curing with a certain concentration in the early stage of hydration of the cement-based material, and simultaneously fixing a certain amount of carbon dioxide. However, three limiting factors exist in the application of the method: firstly, when the method is applied to industrial production, a relatively complex process flow is often needed, pretreatment, pre-curing and the like in the early stage of carbonization and curing are involved, and products need to be transferred and treated for many times. Secondly, due to the restriction of the diffusion efficiency of carbon dioxide, the carbonization realized by the carbon dioxide curing method only stays on the surface layer of the component, and uniform carbonization cannot be realized. And thirdly, the maintenance method can only be applied to maintenance of the prefabricated parts, but 70 percent of the concrete consumption is in site pouring. Therefore, it is important to develop a novel method for absorbing and fixing carbon dioxide.

Disclosure of Invention

The invention aims to provide a preparation method of a carbon dioxide premixed cement-based composite material. The invention has the characteristics of improving the material strength, reducing the cement consumption, relieving the greenhouse effect and having high economic benefit.

The technical scheme of the invention is as follows: a preparation method of a carbon dioxide premixed cement-based composite material comprises the following steps:

the method comprises the following steps: introducing gas containing carbon dioxide into the cement slurry which is stirred in a closed state for 30-240 s;

step two: when the fluidity of the cement paste is obviously reduced, water with the mass of 1-3% of the cement is added to restore the original fluidity.

In the first step of the preparation method of the carbon dioxide premixed cement-based composite material, the gas is: liquefied and purified carbon dioxide gas with the purity of 99.99 percent;

or the following steps: the liquefied and purified carbon dioxide gas with the purity of 99.99 percent is mixed with air prepared in industry to obtain mixed gas, wherein the concentration of the carbon dioxide is more than 10 percent;

or the following steps: flue gas recovered from cement plants and/or iron and steel plants, wherein the concentration of carbon dioxide is more than 10%.

In the first step of the preparation method of the carbon dioxide premixed cement-based composite material, the cement paste is a composite material with cement as a main cementing material, and comprises cement paste, cement mortar or concrete; the water cement ratio of the cement paste is 0.3-0.6.

In the first step of the preparation method of the carbon dioxide premixed cement-based composite material, the cement in the cement paste is ordinary portland cement, and the strength grade of the cement paste is 42.5, 42.5R, 52.5 or 52.5R.

In the first step of the preparation method of the carbon dioxide pre-mixed cement-based composite material, the stirring speed is 60-300 r/min in the gas introduction process.

In the first step of the preparation method of the carbon dioxide pre-mixed cement-based composite material, the cement paste is pre-mixed for 30-120 s before the gas is introduced.

In the preparation method of the carbon dioxide pre-mixed cement-based composite material, after the second step is completed, sand, stones and additives are added into the cement paste, and the mixture is continuously stirred uniformly for pouring.

Has the advantages that: compared with the prior art, the invention can effectively and permanently seal carbon dioxide gas in the cement-based composite material; meanwhile, the carbon dioxide gas injected through the first step of the invention can improve the strength of the cement-based material and correspondingly can reduce the consumption of cement.

Compared with carbonization curing, the early carbonization of the premixed concrete has two advantages:

first, uniform carbonization is achieved. Carbonization maintenance is usually only performed on the surface layer because the diffusion of carbon dioxide is hindered; in the invention, carbon dioxide is contacted with the cement paste during premixing, and the carbon dioxide is diffused more uniformly and fully, so that the carbonization is promoted to be uniform.

Secondly, compared with the carbonization maintenance of building blocks or prefabricated parts, the early carbonization of the ready-mixed concrete can be applied to the cast-in-place, so that the ready-mixed concrete has wider application market.

Therefore, aiming at the defects that the carbonization curing process of the cement-based material is complex, the diffusion rate of carbon dioxide is limited, and uniform carbonization cannot be realized, the invention provides the preparation method which injects carbon dioxide in the stirring process to realize early uniform carbonization and generates nano calcium carbonate in situ as a nucleation site, thereby promoting hydration, accelerating coagulation and improving strength.

The preparation method of the invention can promote the hydration of cement and improve the strength of cement-based materials. Carbon dioxide injected in the stirring process can react with part of cement clinker and cement hydration products, and nano calcium carbonate is generated in situ to be used as a nucleation site, so that the cement hydration is promoted, a more compact structure and better pore distribution are formed, and the strength is increased. The verification proves that the preparation method can realize 10-30% strength improvement, and the corresponding concrete strength can be improved by one grade (5MPa), so that considerable economic benefit can be brought.

The preparation method can permanently seal carbon dioxide, can reduce the cement consumption by 5-10% while keeping the strength of the cement-based composite material unchanged, and can also reduce the carbon emission generated in the production process of the cement-based composite material. The verification proves that the absorption efficiency of the carbon dioxide in the preparation method is more than 80 percent, and the calcium carbonate generated by the reaction is very stable and can be decomposed only at the high temperature of more than 600 ℃, so that the permanent carbon fixation can be realized, and the greenhouse effect can be relieved to a certain extent.

The preparation method of the invention has industrial feasibility. In actual engineering, the invention can be applied to a concrete mixing plant, and concrete subjected to pre-carbonization is filled into a concrete tank truck for on-site pouring; the method can also be applied to concrete mixer trucks for carbonization in the transportation process. Therefore, the carbonization technology of the invention is applied to the production of the ready-mixed commercial concrete, which is beneficial to developing a new market and generating great economic benefit.

In conclusion, the invention has the characteristics of improving the material strength, reducing the cement consumption, relieving the greenhouse effect and having high economic benefit.

Drawings

FIG. 1 is a flow chart of the operation of the present invention;

FIG. 2 shows the results of hydration heat of cement paste.

Detailed Description

The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention.

Example 1. A preparation method of a carbon dioxide premixed cement-based composite material is shown as an operation method in figure 1, and comprises the following specific implementation steps: the materials are accurately weighed according to the water cement ratio of 0.5, water and cement are stirred uniformly, then mixed gas with the carbon dioxide concentration of 20% is continuously introduced into a closed stirrer, the injection time is 2min, the gas flow rate is 100L/min, and the stirring speed is 60-80 r/min. After the aeration was completed, water in an amount of 1% by mass of the cement was added to the stirred tank to compensate for the lost fluidity. Placing the stirred slurry in a steel mould with the thickness of 20 multiplied by 20mm, vibrating for 30s, sealing by using a black plastic film, naturally curing for 24h, and then demoulding; and placing the test block into a standard curing box with the temperature of 20 ℃ and the relative humidity of 95% for curing to the age of 28 days.

The cement is ordinary Portland cement 42.5.

The mixed gas with the carbon dioxide concentration of 20% is prepared by mixing liquefied and purified carbon dioxide with the purity of 99.99% and industrially configured compressed air according to the ratio of 1: volume ratio of 4 was mixed using a gas proportioner.

In order to verify the technical effect of the invention, a control group and an experimental group are set, and strength and microscopic tests are carried out at 1d, 3d, 7d and 28 d. The control group was unvented, and example 1 was the experimental group. The control group and the experimental group were operated under the same conditions and in the same steps except for the aeration and the water replenishment to compensate for the fluidity. The results of the experiment are shown in table 1: for a cement paste with a water cement ratio of 0.5, example 1 can achieve a 26% improvement in 1d strength, a 10% improvement in 3d strength, a 21% improvement in 7d strength, and an 8% improvement in 28d strength. Meanwhile, the absorption efficiency of the carbon dioxide can be obtained according to the content of calcium carbonate in the cement-based composite material calculated according to the thermogravimetric analysis result, wherein the absorption efficiency of the carbon dioxide is more than 80%.

TABLE 1W/C-0.5 Cement Net Strength development

Relative compression strength (%). test group compression strength/control group compression strength at the same age

Example 2. A preparation method of a carbon dioxide premixed cement-based composite material is shown as an operation method in figure 1, and comprises the following specific implementation steps: the materials are accurately weighed according to the water cement ratio of 0.4, water and cement are stirred uniformly, then mixed gas with the carbon dioxide concentration of 20% is continuously introduced into a closed stirrer, the injection time is 2min, the gas flow rate is 100L/min, and the stirring speed is 60-80 r/min. After the aeration was completed, water in an amount of 1% by mass of the cement was added to the stirred tank to compensate for the lost fluidity. Placing the stirred slurry in a steel film with the thickness of 20 multiplied by 20mm, vibrating for 30s, sealing by using a black plastic film, naturally curing for 24h, and then demoulding; and placing the test block into a standard curing box with the temperature of 20 ℃ and the relative humidity of 95% for curing to the age of 28 days.

The cement is ordinary Portland cement 42.5.

The mixed gas with the carbon dioxide concentration of 20% is prepared by mixing liquefied and purified carbon dioxide with the purity of 99.99% and industrially configured compressed air according to the ratio of 1: volume ratio of 4 was mixed using a gas proportioner.

The control group and the experimental group were also set for strength and microscopic tests. The results of the experiments are shown in table 2, example 2 can achieve 18% improvement in 7d strength and 16% improvement in 28d strength for a cement paste with a water cement ratio of 0.4. Meanwhile, the absorption efficiency of the carbon dioxide can be obtained according to the content of calcium carbonate in the cement-based composite material calculated according to the thermogravimetric analysis result, wherein the absorption efficiency of the carbon dioxide is more than 80%.

TABLE 2W/C-0.4 Cement Net Strength development

Relative compression strength (%). test group compression strength/control group compression strength at the same age

Example 3. A preparation method of a carbon dioxide premixed cement-based composite material is shown in an operation method of figure 1 and comprises the following steps:

the method comprises the following steps: introducing gas containing carbon dioxide into the cement slurry which is stirred in a closed state for 30-240 s;

step two: when the fluidity of the cement paste is obviously reduced, adding water with the mass of 1-3% of the cement into the cement paste to restore the original fluidity of the cement paste; the carbonation reaction of ready mixed concrete consumes a certain amount of water, resulting in a reduction in the fluidity of cement and concrete materials. This reduction can be compensated by secondary water replenishment at the later stage of the stirring, and a certain amount of strength gain can be achieved. Through subsequent natural curing, the cement paste and the concrete material are continuously hydrated until the cement paste and the concrete material can be put into use;

step three: and after the second step is finished, adding sand, stones and additives into the cement paste, and continuously stirring uniformly for pouring.

In the first step, the gas is: liquefying and purifying the carbon dioxide gas with the purity of 99.99%;

or the following steps: mixing the liquefied and purified carbon dioxide gas with the purity of 99.99% with industrially configured air to obtain a mixed gas, wherein the concentration of the carbon dioxide is more than 10%;

or the following steps: flue gas recovered by cement plants and/or iron and steel plants can carry certain waste heat, wherein the concentration of carbon dioxide is more than 10%.

In the first step, the cement paste is a composite material with cement as a main cementing material, and comprises cement paste, cement mortar or concrete; the water cement ratio of the cement paste is 0.3-0.6;

under the condition of higher water-cement ratio, the strength of the cement-based composite material is improved by adjusting the dosage of carbon dioxide and secondary water supplement, the optimal early carbonization effect is achieved, carbon dioxide is sealed and stored permanently, and the strength gain effect can be brought.

In the first step, the cement in the cement paste is ordinary portland cement with the strength grade of 42.5, 42.5R, 52.5 or 52.5R.

In the first step, during the carbon dioxide injection process, a faster stirring speed is adopted to promote the absorption reaction of the carbon dioxide, so that a stirring speed of 60-300 r/min (preferably 120-300 r/min) can be selected.

In the first step, the cement paste is premixed for 30-120 s before the gas is introduced.

The principle of the invention is as follows: in the case of premixing concrete, carbon dioxide and tricalcium silicate (3 CaO. SiO) in the cement clinker₂) Dicalcium silicate (2 CaO. SiO)₂) Etc. while reacting with early hydration products of cement such as Ca (OH)₂And calcium silicate hydrate (C-S-H), and the like are subjected to carbonization reaction, and the reaction equation is as follows:

3(3CaO·SiO₂)+(3-x)CO₂+yH₂O→xCaO·SiO₂·yH₂O+(3-x)CaCO₃ (1)

2(2CaO·SiO₂)+(2-x)CO₂+yH₂O→xCaO·SiO₂·yH₂O+(2-x)CaCO₃ (2)

Ca(OH)₂+CO₂→CaCO₃+H₂O (3)

C-S-H+CO₂→CaCO₃+SiO₂+H₂O (4)

as can be seen, the above reactions all produced calcium carbonate (CaCO)₃) The scale of the generated calcium carbonate is nano-scale through microscopic experimental characterization, and the nano-scale calcium carbonate can be used as a nucleation site to promote the generation of cement hydration products, thereby shortening the cement setting time and improving the early strength. The preparation method can realize 10-30% strength improvement, and the cement-based composite material of the same grade can reduce 5-10% cement consumption.

On the one hand, the preparation method can absorb a certain amount of carbon dioxide and permanently seal the carbon dioxide in the cement-based material; on the other hand, the improvement of the strength can correspondingly reduce the consumption of the cement, namely, the carbon emission in the cement production process can be reduced. In conclusion, the material is a green low-carbon material and a preparation method thereof.

The early strength of the sample prepared by the method can be improved by 10-30%, and the carbon dioxide absorption efficiency calculated by a Thermogravimetric Analysis test result is higher than 80%. The results of the heat of hydration showed that the cement samples treated with carbon dioxide had tricalcium silicate (C) as compared to the untreated control₃S) was advanced about 1 to 2 hours and the total hump area was increased, the results are shown in fig. 2.

The invention is not to be considered as limited to the particular embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed.