Method for preparing high-performance concrete internal curing agent from rice husks

Abstract

The invention discloses a method for preparing a high-performance concrete internal curing agent from rice husks. According to the method, efficient activation of silicon components in the rice husks is achieved by adjusting the concentration of the alkali liquor, and meanwhile the problem that the hydrophilicity of the rice husks is reduced due to excessive hydrolysis of cellulose in the rice husks is solved. The method can be used for preparing the high-performance concrete internal curing agent by directly utilizing the rice husks, the process is simple, the cost is low, and the high-performance concrete internal curing agent has good compatibility with a cement base material and high water retention rate when being added into concrete as the internal curing agent.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-performance concrete internal curing agent by utilizing rice husks, and belongs to the field of concrete admixtures. Background Art

[0002] Since the 1980s, high-performance concrete has been increasingly widely used in the construction of various large buildings. However, the water-cement ratio of high-performance concrete is relatively low. As hydration proceeds, the water in the tiny pores of the concrete is insufficient for hydration, resulting in self-shrinkage of the concrete and cracks. These cracks seriously affect the strength and durability of high-performance concrete. External curing methods such as sprinkling and covering can only maintain the surface of the concrete, and it is difficult for water to enter the interior of the concrete material. The problem of high-performance concrete being prone to cracking cannot be effectively solved. Therefore, the development of internal curing agents that can slowly release water inside the concrete is an important way to solve the problem of early cracking of high-performance concrete.

[0003] The most commonly used internal curing agent is a highly absorbent resin, but the synthesis process of this type of internal curing agent is complex, the compatibility with cement-based materials is poor, and the price is expensive, making it difficult to promote and apply. Therefore, the development of a low-cost internal curing agent with high compatibility with cement is an urgent problem to be solved in this field. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing a high-performance concrete internal curing agent using rice husks, which is characterized in that the synthesis steps and conditions of the method are as follows, and the parts of the following raw materials are all parts by weight: (1) 1-3 parts of rice husks are crushed into 100-200 meshes by a wall breaking machine, and then dispersed in 10-20 parts of a strong alkaline solution with a mass fraction of 10%-15%, reacted at 50-80°C for 8-16 hours, cooled to 25-35°C after the reaction, and the pH of the solution is adjusted to neutral with an acid; (2) introducing carbon dioxide gas into the solution obtained in parts (1) at a gas flow rate of 3-5 mL / s, reacting for 12-16 hours, filtering out all water with a plate and frame filter press, and drying the obtained filter residue at 120° C.-150° C. to constant weight to obtain a rice husk-based high performance concrete internal curing agent; The strong base in step (1) is one or more of sodium hydroxide, potassium hydroxide and lithium hydroxide.

[0005] The principle of the method involved in the present invention is: First, the discarded rice husks are broken up and soaked in a strong alkaline solution to fully convert the silicon-containing components (silicic acid, silicon dioxide) in the rice husk residue into soluble sodium silicate. Excessive carbon dioxide gas is introduced into the above-mentioned mixed solution to convert the sodium silicate in the solution into silicic acid precipitation, which is filtered again. The filter residue is heated and dried, and the silicic acid precipitation is decomposed and converted into amorphous silicon dioxide and uniformly adsorbed on the surface of the rice husk residue. The rice husk residue obtained in this way has both high water absorption and high cement compatibility.

[0006] The experiment found that when the mass fraction of strong alkali was 10%-15%, the silicon component in the rice husk was fully dissolved, and more than 95% of the silicon dioxide was uniformly adsorbed on the surface of the rice husk residue. When it was added to high-performance concrete as an internal curing agent at a ratio of 5%, the autogenous shrinkage rate could be reduced by 70% and 50% after hydration for 7 days and 14 days, respectively (see Example 1 and Example 2); When the mass fraction of strong alkali is less than 10%, the silica in rice husk cannot be fully dissolved, and most of it is still hidden in the xylem of rice husk. Only more than 60% of the silica is adsorbed on the surface of rice husk residue. When it is added to high-performance concrete at a ratio of 5% as an internal curing agent, the autogenous shrinkage rate can only be reduced by 40% and 20% after hydration for 7d and 14d, respectively (see Comparative Example 1); when the mass fraction of strong alkali is greater than 20%, although the silicon component in rice husk is fully dissolved and converted into silica and adsorbed on the surface of rice husk residue, cellulose also begins to hydrolyze in large quantities, resulting in a significant decrease in the hydrophilicity and water absorption rate of rice husk residue. When it is added to high-performance concrete at a ratio of 5% as an internal curing agent, the autogenous shrinkage rate can only be reduced by 30% and 20% after hydration for 7d and 14d, respectively (see Comparative Example 2). BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The present invention is a process flow diagram. DETAILED DESCRIPTION

[0008] The present invention is specifically described below through embodiments, which are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Technical engineers in this field can make some non-essential improvements and adjustments to the present invention based on the contents of the above invention. Example

[0009] (1) 1 part of rice husk was crushed into 100 meshes by a wall breaking machine and then dispersed in 10 parts of 12% sodium hydroxide solution by mass, reacted at 60°C for 14 hours, cooled to 25°C after the reaction, and the pH of the solution was adjusted to neutral with hydrochloric acid; (2) carbon dioxide gas was introduced into 11 parts of the solution obtained in (1) at a gas flow rate of 3 mL / s. After reacting for 12 hours, all water was filtered out using a plate and frame filter press. After filtering, the filter residue was dried at 130° C. to constant weight to obtain a rice husk-based high performance concrete internal curing agent. X-ray diffraction and SEM element mapping results showed that 95% of the silicon components in rice husks were converted into amorphous silicon dioxide and uniformly adsorbed on the surface of rice husk residue. When it was added to high-performance concrete at a ratio of 5% as an internal curing agent, the autogenous shrinkage rates at 7d and 14d after hydration were reduced by 70% and 50%, respectively. Example

[0010] (1) 3 parts of rice husks were crushed to 200 meshes using a wall breaking machine and then dispersed in 20 parts of 14% sodium hydroxide solution. The mixture was reacted at 80°C for 16 hours. After the reaction, the temperature was lowered to 30°C and the pH of the solution was adjusted to neutral using hydrochloric acid. (2) carbon dioxide gas was introduced into 23 parts of the solution obtained in (1) at a gas flow rate of 5 mL / s. After reacting for 16 hours, all water was filtered out using a plate and frame filter press. After filtering, the filter residue was dried at 140° C. to constant weight to obtain a rice husk-based high performance concrete internal curing agent. X-ray diffraction and SEM element mapping results showed that 96% of the silicon components in rice husks were converted into amorphous silicon dioxide and uniformly adsorbed on the surface of rice husk residue. When it was added to high-performance concrete as an internal curing agent at a ratio of 5%, the autogenous shrinkage rates at 7d and 14d after hydration were reduced by 65% ​​and 48%, respectively.

[0011] (1) 2 parts of rice husks were crushed into 200 meshes by a wall breaking machine and then dispersed in 15 parts of 5% by mass sodium hydroxide solution. The mixture was reacted at 80°C for 16 hours. After the reaction, the temperature was lowered to 30°C and the pH of the solution was adjusted to neutral with hydrochloric acid. (2) carbon dioxide gas was introduced into 17 parts of the solution obtained in (1) at a gas flow rate of 4 mL / s. After reacting for 16 hours, all water was filtered out using a plate and frame filter press. After filtering, the filter residue was dried at 140° C. to constant weight to obtain a rice husk-based high performance concrete internal curing agent. X-ray diffraction and SEM element mapping results showed that only 40% of the silicon components in rice husks were converted into amorphous silica and adsorbed on the surface of rice husk residue. When it was added to high-performance concrete as an internal curing agent at a ratio of 5%, the autogenous shrinkage rates at 7d and 14d after hydration were only reduced by 4% and 20%, respectively.

[0012] (1) 2 parts of rice husks were crushed to 200 meshes using a wall breaking machine and then dispersed in 20 parts of 20% by mass sodium hydroxide solution. The mixture was reacted at 80°C for 16 hours. After the reaction, the temperature was lowered to 35°C and the pH of the solution was adjusted to neutral using hydrochloric acid. (2) carbon dioxide gas was introduced into 23 parts of the solution obtained in (1) at a gas flow rate of 5 mL / s. After reacting for 16 hours, all water was filtered out using a plate and frame filter press. After filtering, the filter residue was dried at 140° C. to constant weight to obtain a rice husk-based high performance concrete internal curing agent. X-ray diffraction and SEM element mapping results showed that more than 98% of the silicon components in rice husks were converted into amorphous silicon dioxide and uniformly adsorbed on the surface of rice husk residue. When it was added into high-performance concrete at a ratio of 5% as an internal curing agent, the autogenous shrinkage rates after hydration for 7d and 14d were reduced by 30% and 20% respectively.

Claims

1. A method for preparing a high-performance concrete internal curing agent using rice husk, characterized in that The synthesis steps and conditions of the method are as follows, and the parts of the following raw materials are all parts by weight: (1) 1-3 parts of rice husks are crushed into 100-200 meshes by a wall breaking machine, and then dispersed in 10-20 parts of a strong alkaline solution with a mass fraction of 10%-15%, reacted at 50-80°C for 8-16 hours, cooled to 25-35°C after the reaction, and the pH of the solution is adjusted to neutral with an acid; (2) introducing carbon dioxide gas into the solution obtained in parts (1) at a gas flow rate of 3-5 mL / s, reacting for 12-16 hours, filtering out all water with a plate and frame filter press, and drying the obtained filter residue at 120° C.-150° C. to constant weight to obtain a rice husk-based high performance concrete internal curing agent; The strong base in step (1) is one or more of sodium hydroxide, potassium hydroxide and lithium hydroxide.

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