Alkali-activated rice hull ash, slag and tire fragment combined improved expansive soil and preparation method thereof

Abstract

The invention discloses alkali-activated rice hull ash, slag and tire fragment combined improved expansive soil and a preparation method thereof.The improvement method of the expansive soil comprises the steps that alkali-activated rice hull ash and blast furnace slag are used for generating a green low-carbon cementing material to serve as a curing agent, the cementing effect between soil bodies is enhanced, and therefore the mechanical strength of the improved soil is improved; the expansion performance of the solidified soil is reduced. The tire fragments serve as buffering and reinforcing materials, expansion and shrinkage of the expansive soil are weakened or even eliminated, and the shear strength of the soil body is improved. The mass percentages of the alkali-activated rice hull ash, the slag curing agent and the tire fragments are respectively 10%-20% and 1%-3% of the mass percentage of the expansive soil. According to the method, industrial waste is utilized, the stability problem of expansive soil is solved, the influence of waste plastic products on the environment is solved, and the requirement for green and sustainable development is met.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering, and specifically to an alkali-activated rice husk ash, slag and tire fragments combined to improve expansive soil and its preparation method. Background Art

[0002] Expansive soil is a kind of clay formed under natural geological action. Because it contains hydrophilic clay minerals such as montmorillonite and illite, it will cause strong swelling and shrinkage deformation of the soil under hydraulic action, causing serious damage to shallow slopes and road structures.

[0003] In recent years, research has begun on various types of solid waste as modifiers for expansive soil, but the improvement of the swelling and shrinkage and shear strength of the improved soil is not significant, and the performance of the obtained improved soil needs to be further improved.

[0004] The information disclosed in this background art section is only intended to increase the understanding of the overall background of the present invention, and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art already known to those of ordinary skill in the art. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above technical defects, and provide an alkali-activated rice husk ash, slag and tire fragments combined to improve expansive soil and its preparation method. The present invention uses alkali-activated rice husk ash and slag to form a green and low-carbon cementitious material, and tire fragments as a buffer and reinforcement material, and dry-mixes and mixes them to form a mixture and adds it to the expansive soil. This method uses industrial waste, improves the mechanical strength of the improved soil, and reduces the swelling performance of the improved soil. Solve the stability problem of expansive soil, solve the impact of waste plastic products on the environment, and meet the requirements of green and sustainable development.

[0006] To solve the above problems, the technical solution of the present invention is an alkali-activated rice husk ash, slag and tire fragments combined to improve expansive soil: the improved soil is formed by uniformly stirring expansive soil, alkali-activated rice husk ash and slag cementitious material, and tire fragments in proportion.

[0007] Furthermore, the alkali-activated rice husk ash and blast furnace slag green and low-carbon cementitious material is characterized in that it includes rice husk ash, blast furnace slag, sodium hydroxide, and water glass. The addition of water can promote the formation of aggregates, amorphous hydration products, and ettringite (AFt), which are distributed on the soil surface and fill the pores. At the same time, it reduces the hydrophilic mineral components of montmorillonite and illite in the soil, enhancing the cementation between particles. The products of the water glass-activated slag system tend to form in the solution with a relatively fast reaction rate, so the hardened body has a dense structure and small pore size. The reaction products of the sodium hydroxide system tend to form on the surface and inside of the slag particles with a relatively slow reaction rate, so the hardened body has a higher porosity and larger pore size. Using a mixed solution of sodium hydroxide and water glass can react more fully with the slag, balancing the tetracoordinated Al charge with Na and the reaction products in the hydration product system. The products include C-S-H, N-A-S-H, C-A-S-H, etc. Si in the water glass thins the protective film of the silica oxygen network structure on the surface of the slag by bonding dissolved Ca, Mg, and Al, promoting the dissolution of the slag. The incorporation of rice husk ash can form more three-dimensional N-A-S-H gels, which can inhibit the autogenous shrinkage and drying shrinkage during the formation of C-A-S-H, and also make the products dense and the microstructure uniform. Among them, rice husk ash increases the Si / Al of the gel, and the mixed solution of sodium hydroxide and water glass can stimulate the alkali resistance of the hydration products (alkali efflorescence will not only cause the hydration products to lose Na, Al, and polymerize and shrink, but also destroy the uniformity of the distribution of the hydration products. The crystallization growth of alkali efflorescence and the shrinkage of the hydration products will lead to cracking). Thereby improving the mechanical strength of the subgrade soil and reducing the swelling performance of the solidified soil. The mass of the mixture of rice husk ash and slag is 10%-20% of the mass of the expansive soil.

[0008] Furthermore, the tire fragments: are small particles formed after being crushed by special equipment, and are composed of rubber, steel wires, fibers, etc. As buffer and reinforcing materials, the particle size is 1-5 mm, and the mass is 1%-3% of the mass of the expansive soil. (Adding tire fragments can not only be used as aggregate, but also effectively inhibit the alkali efflorescence and drying shrinkage of the alkali-activated cementitious material, and also help improve the soil strength. The alkali solution can remove zinc stearate on the surface of the rubber fragments (resulting in poor adhesion to the gel material matrix), increase the surface hydrophilicity and roughness, and also improve the water permeability, prevent water accumulation, and promote the uniform distribution of soil moisture, avoiding the swelling of the expansive soil due to water accumulation and uneven distribution, reducing the influence of water on the expansive soil, reducing the foundation load, and improving the mechanical properties of the improved soil.

[0009] Furthermore, a preparation method for improving expansive soil by combining alkali-activated rice husk ash, slag, and tire fragments is characterized by including the following steps: Step 1: Mix and dry-mix the rice husk ash and blast furnace slag; Step 2: Obtain an alkali activator by using sodium hydroxide, water glass and water; Step 3: Add the alkali activator to rice husk ash, slag dry material and expansive soil. After stirring evenly, obtain improved soil; Step 4: Pour the mixture into a mold. The prepared specimen is demolded with a jack and sealed with plastic wrap, and cured in a standard curing box until the specified age. The curing temperature is (23±1) °C and the relative humidity is 98%, thus obtaining the improved soil.

[0010] 5. A preparation method for improving expansive soil by combining alkali-activated rice husk ash, slag and tire fragments according to claim 4, wherein: the size of the mold is a 50mm×100mm cylindrical sample, and the number of layers is 3 layers.

[0011] The advantages of the present invention compared with the existing technology are as follows: 1. The present invention has low cost and is easy to manufacture: Rice husk ash and slag are materials with low cost or industrial waste generated by industry, with rich sources and low cost; and the improved soil can be obtained by mixing expansive soil, rice husk ash, slag, sodium hydroxide, water glass and tire fragments evenly according to the proportion.

[0012] 2. The present invention has good mechanical properties: The active components in alkali-activated rice husk ash and slag form geopolymers and other new cementitious materials with cementing ability. The hydration products wrap the soil particles and jointly form a spatial network structure, enhancing the cementing and biting effects between soil particles. Rice husk ash can improve the microstructure of slag-based hydration products by filling pores and microcracks, making its microstructure uniform and dense, with few pores and cracks. The incorporation of rice husk ash can form more three-dimensional N-A-S-H gels, which can inhibit the autogenous shrinkage and drying shrinkage during the formation of C-A-S-H. The contained SiO2 forms silicon-oxygen bridge (Si-O-Si) chains, reducing the gaps in the C-S-H gel and firmly binding the particles together, making the product dense and the microstructure uniform. Among them, rice husk ash increases the Si / Al of the gel, and the mixed solution of sodium hydroxide and water glass can stimulate the anti-efflorescence alkalinity of the hydration products. Further reduce the swelling and shrinkage properties of expansive soil, and both the compressive strength and direct shear strength are improved. Adding tire fragments can not only act as aggregates, but also effectively inhibit the efflorescence and drying shrinkage of alkali-activated cementitious materials, and also help to improve the soil strength. The alkali solution can remove zinc stearate (resulting in poor adhesion to the gel material matrix) on the surface of rubber fragments, increase the surface hydrophilicity and roughness, and can also improve the water permeability, prevent water accumulation and promote the uniform distribution of soil moisture, avoid the expansion of expansive soil due to water accumulation and uneven distribution, reduce the influence of water on expansive soil, reduce the foundation load and improve the mechanical properties of the improved soil.

[0013] 3. The present invention is green and environment-friendly: applying industrial solid waste to the field of expansive soil treatment can reduce carbon emissions, treat waste with waste, and improve the soil properties. Specific Embodiments

[0014] In order to make the content of the present invention easier to be clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0015] An alkali-activated rice husk ash, slag and tire shreds combined to improve expansive soil and its preparation method Implementation cases:

[0016] The above table shows the basic physical index data of the expansive soil.

[0017]

[0018] The above table shows the main chemical components of rice husk ash and blast furnace slag.

[0019] The proportion of the mixture of rice husk ash and slag to the quality of the expansive soil is set at 10%, 15%, and 20%.

[0020] The proportion of tire shreds to the quality of the expansive soil is set at 1%, 2%, and 3%.

[0021] NaOH and Na2SiO3·9H2O (sodium silicate) are prepared into an alkali activator according to a ratio of 1:9. The optimal water content under various ratios is obtained through a compaction test, and the water consumption is added according to the optimal water content. The ratio of the alkali activator to rice husk ash and slag is 1:9.

[0022]

[0023] The above table is the mixing ratio table of the alkali-activated cementitious material.

[0024] First, according to the mixture of rice husk ash and slag being 15% of the quality of the expansive soil and tire shreds being 2% of the quality of the expansive soil, make specimens to determine the best mixing ratio of the alkali-activated cementitious material. Take the naturally air-dried expansive soil, crush it and pass it through a 2 mm sieve, place it in an oven at 105 °C to dry, weigh the curing agent and the expansive soil according to the designed mixing ratio and mix them evenly with a mixer, spray water on the mixed soil sample to the optimal water content, put it into a sealed bag and let it stand for 12 h to ensure the uniformity of the moisture of the test soil sample. The size of the mold is a 50mm×100mm cylindrical sample, with 3 layers, and a light compaction test is carried out, and cured for 7 and 14 days respectively.

[0025]

[0026] The optimal mixing ratio of the alkali-activated cementitious material is: rice husk ash: slag = 6:4.

[0027] The test samples were prepared with the ratio of alkali-activated rice husk ash to slag being 6:4. The experimental results with different material dosages are as follows:

[0028] With the increase of curing time, the properties of the improved soil will be enhanced. The experimental results show that the optimal mass dosage of the cementitious materials in the alkali-activated rice husk ash:slag and tire chips improved expansive soil is about 10%, and the dosage of tire chips is 2%. At this time, the properties of the improved soil reach the best.

[0029] It can be seen from the experimental results that when the geopolymer formed by rice husk ash, slag, tire chips, sodium hydroxide, sodium silicate and water is added to the expansive soil as a mixed admixture, the soil properties are significantly better than those of the specimens prepared from the expansive soil. This is because rice husk ash, slag, sodium hydroxide, sodium silicate and water can promote the formation of geopolymer and amorphous hydrated products, including cementitious materials such as C-A-H, C-S-H, N-A-S-H, C-A-S-H, etc., which are distributed on the soil surface and fill the pores, enhancing the cementation between particles. At the same time, tire chips, as buffer and reinforcement materials, weaken or even eliminate the swelling and shrinkage of the expansive soil. This method effectively improves the strength of the improved soil and reduces the swelling performance of the expansive soil. After being alkali-treated, the tire chips increase the hydrophilicity and roughness of the surface, and can also improve the water permeability, prevent water accumulation and promote the uniform distribution of soil moisture, avoid the swelling of the expansive soil due to water accumulation and uneven distribution, reduce the influence of water on the expansive soil, reduce the foundation load and improve the mechanical properties of the improved soil.

[0030] The above describes the present invention and its implementation manners, and such description is not restrictive. Generally speaking, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural modes and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. An alkali-activated rice husk ash, slag and tire fragments combined to improve expansive soil, characterized in that: The improved soil is formed by uniformly mixing expansive soil, alkali-activated rice husk ash, slag cementitious material and tire fragments in proportion.

2. The alkali-activated rice husk ash, slag and tire fragments combined to improve expansive soil according to claim 1, characterized in that: The alkali-activated blast furnace slag green low-carbon cementitious material comprises rice husk ash and slag, sodium hydroxide, water glass and water to react to generate a green low-carbon cementitious material with good mechanical properties, durability and environmental protection. The mixture of rice husk ash and slag is 10%-30% of the mass of expansive soil.

3. The alkali-activated rice husk ash, slag and tire fragments combined to improve expansive soil according to claim 1, characterized in that: The tire fragments are small particles formed after being crushed by special equipment. They are composed of rubber, steel wire, and fiber. They are used as buffer and reinforcement materials. The particle size is 1-5mm and the mass is 1%-3% of the mass of expansive soil.

4. The method for preparing an alkali-activated rice husk ash, slag and tire fragments combined to improve expansive soil according to claims 1-3, characterized in that: The following steps are involved: Step 1, dry-mixing rice husk ash and blast furnace slag; Step 2, preparing an alkaline activator by mixing sodium hydroxide, water glass and water; Step 3, adding an alkali activator to rice husk ash, dry slag material and expanded soil, and stirring evenly to obtain improved soil; Step 4: Pour the mixture into a mold, demould the prepared sample with a jack and seal it with plastic wrap, and cure it in a standard curing box to the specified age. The curing temperature is (23±1) ℃ and the relative humidity is 98%, and improved soil is obtained.

5. The method for preparing an alkali-activated rice husk ash, slag and tire fragments combined to improve expansive soil according to claim 4, characterized in that: The mold size is 50mm×100mm cylindrical sample, and the number of layers is 3.

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