CN110590260B - Method for improving performance of recycled concrete by using carbon dioxide - Google Patents

Abstract

The invention aims to provide a method for improving regeneration mixture by using carbon dioxideMethod of performance of a concrete. The method is to add Ca (OH) rich in calcium ₂ The powder is mixed with water to form a calcium hydroxide solution. Then, introducing carbon dioxide gas into the solution until the solution is completely carbonized, then adding cement and the solution produced in the first step, mixing and stirring for 60s, then adding the regenerated coarse aggregate, stirring for 60s, finally pouring sand and natural coarse aggregate, and fully stirring for 120s to obtain the concrete mixture. The compression strength and the breaking strength of the recycled concrete prepared by the method are improved to a certain extent, and the method can fix carbon dioxide in the atmosphere. The process is CO ₂ And the popularization and application of the recycled aggregate provide directions, the application range of the recycled aggregate is expanded, and the recycled aggregate has important theoretical value and obvious economic and environmental benefits and has great significance for the development of concrete.

Description

A method for improving the performance of recycled concrete by using carbon dioxide

technical field

The invention relates to the fields of resource recycling and building materials, in particular to a method for improving the performance of recycled concrete by utilizing carbon dioxide.

Background technique

With the rapid development of China's economy, the shortage of natural resources and the problems of environmental pollution are becoming more and more serious. As a high consumption industry, the construction industry consumes a lot of natural resources every year. According to data, China's current annual consumption of sand and gravel aggregates exceeds 20 billion tons, which is the largest mineral resource currently mined. At the same time, with the continuous advancement of urbanization, the amount of new urban construction, the demolition of old urban areas, and the reconstruction of urban villages are all increasing rapidly, resulting in more and more construction waste. At present, my country produces more than 2 billion tons of construction waste every year, accounting for about 30% to 40% of the total amount of urban waste. The waste is crushed and screened to be recycled into recycled aggregate, which can partially or completely replace natural aggregate, which can not only solve the problem of lack of natural aggregate in many areas, but also reduce environmental pollution and save landfill land for construction waste. Conducive to the sustainable development of the construction industry. However, unlike natural aggregates, there are old mortars on the surface of recycled concrete aggregates, and in the process of crushing, the waste concrete is collided and ground, resulting in many micro-cracks in the recycled aggregates. The microcracks inside the recycled aggregate and the attached old cement mortar lead to an increase in the water absorption, porosity, and crushing value of the recycled aggregate, which makes the performance of recycled concrete significantly worse than that of ordinary concrete, which greatly limits the use of recycled concrete. Therefore, it is necessary to study methods to improve the performance of recycled concrete.

On the other hand, with the development of society, a large amount of carbon dioxide is produced in the process of human production and life, which also indirectly leads to global warming. As the development direction of green building materials, this method is very important to fix the carbon dioxide in the atmosphere. Through theoretical calculation, assuming 100% carbonization, 1 ton of cement can absorb 0.5 ton of carbon dioxide to form 1.5 tons of solid calcium carbonate and silica gel. At present, 9-20% of carbon dioxide has been absorbed by a large amount of cement, and carbon dioxide curing technology has great potential to create high-quality, durable and sustainable cement products.

At present, the method of improving concrete performance through carbon dioxide is mainly to use carbon dioxide to cure concrete. Carbon dioxide can enter concrete and can interact with unhydrated cement particles (mainly tricalcium silicate, dicalcium silicate) and cement hydration products (mainly hydration products). Calcium silicate, calcium hydroxide) react to generate calcium carbonate and silica gel, which fill the pores of concrete, thereby improving the performance of concrete. But the rate of carbonization remains a major hurdle for this technology. This is because the carbonation rate of early concrete depends on the diffusion of carbon dioxide into the concrete matrix, which is very slow. _In addition, the carbonization product CaCO3 particles can fill the pores in the concrete matrix, making the diffusion of _CO2 more difficult.

SUMMARY OF THE INVENTION

The present invention directly passes CO ₂ into the slurry, thus eliminating the slow diffusion process of CO ₂ through the concrete matrix in the carbon dioxide curing concrete technology. This process provides direction for the promotion and application of CO ₂ and recycled aggregates, expands the application scope of recycled concrete, has important theoretical value and significant economic and environmental benefits, and is of great significance to the development of concrete.

In order to achieve the above object, the technical scheme adopted in the present invention is:

In the first step, calcium-rich Ca(OH) ₂ powder is mixed with water to form a calcium hydroxide solution. Then, pass carbon dioxide gas into the solution until the solution is completely carbonized;

The present invention directly feeds _CO2 into the slurry, thus eliminating the slow diffusion process of _CO2 through the concrete matrix in the carbon dioxide curing concrete technology. This process provides direction for the promotion and application of CO ₂ and recycled aggregates, expands the application scope of recycled concrete, has important theoretical value and significant economic and environmental benefits, and is of great significance to the development of concrete.

In order to achieve the above object, the technical scheme adopted in the present invention is:

In the first step, calcium-rich Ca(OH) ₂ powder is mixed with water to form a calcium hydroxide solution. Then, pass carbon dioxide gas into the solution until the solution is completely carbonized;

Step 2, add cement and mix and stir for 60s with the solution produced in the first step;

Step 3, then add recycled coarse aggregate and stir for 60s, then pour in sand and natural coarse aggregate, and fully stir for 120s to obtain a concrete mixture;

In the first step, since _CO2 is in the gas phase in the environment, it cannot be mixed with other components. To do this we first absorb carbon dioxide with a Ca(OH) ₂ solution. The introduced carbon dioxide gas first dissolves in water to form carbonic acid, which is then hydrolyzed to H ⁺ and CO ₃ ²⁻ , which meet the Ca ²⁺ released from the slaked lime to form nano to submicron calcium carbonate precipitates. Continue to feed the carbon dioxide, and some of the calcium carbonate will dissolve to form calcium bicarbonate, which has a higher solubility in water. Therefore, the slaked lime solution after passing through carbon dioxide contains abundant calcium carbonate particles, Ca ²⁺ , HCO ₃ ^- and a small amount of CO ₃ ^2- . After this solution is mixed with Portland cement, Ca(OH) ₂ produced by cement hydration reacts with HCO ₃ ^- to form calcium carbonate precipitation. Nano- to sub-micron calcium carbonate precipitates can fill cracks and pores in recycled aggregates and can also fill pores in concrete matrices, resulting in a denser microstructure. In addition, the pre-carbonization method can produce more ettringite in the sample, resulting in a larger volume of hydration products of the cement. This densifies the microstructure of the hardened cement, thus helping to improve concrete performance.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments.

Example 1

A method for using carbon dioxide to improve the performance of self-compacting recycled concrete specifically includes the following steps: first, mixing Ca(OH) ₂ powder with water to form a calcium hydroxide solution. Then, carbon dioxide was bubbled through the solution to complete carbonation, as measured by a pH meter. The second step is to add cement and mix with the solution produced in the first step for 60s. Then, the recycled coarse aggregate was added and stirred for 60 s, then sand and natural coarse aggregate were poured in, and the concrete mixture was obtained by fully stirring for 120 s.

The 28d compressive strength and flexural strength of the self-compacting concrete made by this example are increased by 13.4% and 14.4%, respectively, and the water absorption and porosity are decreased by 15% and 14%.

Example 2

A method for improving the performance of concrete by using carbon dioxide specifically includes the following steps: firstly, mixing Ca(OH) ₂ powder with water to form a calcium hydroxide solution, and the dosage of Ca(OH) ₂ per liter of water is 10.36g. Then, carbon dioxide was passed into the solution at 2 L/min, and the slurry was stirred at 800 rpm using a magnetic stirrer for about 10 minutes. Then, cement, coarse aggregate, and sand were added, and the mixture was fully stirred for 120 s to obtain a mixture.

The compressive strengths of concretes 7d and 28d made by this example were both increased by 16%, and the flexural strengths of 7d and 28d were increased by 7% and 5%, respectively. This method has little effect on the drying shrinkage of concrete.

Example 3

A method for improving the performance of concrete by using carbon dioxide specifically includes the following steps: firstly, mixing Ca(OH) ₂ powder with water to form a calcium hydroxide solution, and the amount of Ca(OH) ₂ per liter of water is 38.48g. Then, carbon dioxide was passed into the solution at 2 L/min, and the slurry was stirred at 800 rpm using a magnetic stirrer for about 15 minutes. Then, cement, coarse aggregate, and sand were added, and the mixture was fully stirred for 120 s to obtain a mixture.

The compressive strengths of concretes 7d and 28d made by this example were increased by 10% and 13%, respectively, and the flexural strengths of 7d and 28d were increased by 8% and 5%, respectively. This method has little effect on the drying shrinkage of concrete.

Claims (4)

1. a method utilizing carbon dioxide to improve the performance of recycled concrete, is characterized in that, comprises the following steps: In the first step, calcium-rich Ca(OH) ₂ powder is mixed with water to form a calcium hydroxide solution. Then, pass carbon dioxide gas into the solution until the solution is completely carbonized; The solution thus prepared contains abundant calcium carbonate particles, Ca ²⁺ , HCO ₃ ^- and a small amount of CO ₃ ^2- ; Step 2, add cement and mix and stir for 60 s with the solution produced in the first step; Step 3, adding recycled coarse aggregate and stirring for 60 s, then pouring in sand and natural coarse aggregate, and fully stirring for 120 s to obtain a concrete mixture. 2. preparation method according to claim 1 is characterized in that described in step ₁ , Ca(OH) Powder is mixed into calcium hydroxide solution with water, and wherein Ca(OH) in every liter of water _The consumption is 10.36 g or 38.48 g. 3. preparation method according to claim 1 is characterized in that described in step 1, the introduction speed of carbon dioxide is 2 L/min. 4. The preparation method according to claim 1, characterized in that in step 1, a magnetic stirrer stirs the solution at a speed of 800 rpm for 10 minutes or 15 minutes.