Modified wheat straw fiber reinforced foam concrete backfill material and methods of making and using

Abstract

The application discloses a modified wheat straw fiber reinforced foam concrete backfill material and a preparation and use method, and belongs to the field of civil engineering foundation filling construction. The backfill material is composed of concrete dry powder, a composite foaming agent and modified wheat straw fiber. The modified wheat straw fiber is obtained by corroding wheat straw segments with alkali solution, and then immersing the alkali-corroded wheat straw segments into a fiber surface coating film glue solution or directly spraying a layer of fiber surface coating film glue solution on the surface of the alkali-corroded wheat straw segments, so that a layer of fiber surface coating film is attached to the surface of the wheat straw segments. In use, the concrete dry powder, the composite foaming agent and the modified wheat straw fiber are mixed into a slurry according to a proportion and filled into a fat groove. The modified wheat straw fiber is added into the foamed concrete, so that the defects of poor shearing resistance and weak impact resistance of traditional foam concrete filling materials are overcome, and the added industrial value of the wheat straw is improved.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering foundation filling construction, specifically relating to a reinforced foamed concrete backfill material for backfilling trenches of buildings or structures, and its preparation and application methods. Background Technology

[0002] Currently, backfilling trenches for buildings or structures typically uses solid materials such as backfill soil and sand. Due to site limitations, the trench between the basement structure and the foundation pit is often narrow after the exterior walls are constructed, especially in narrow and deep trenches. This makes it difficult to compact materials like backfill soil and sand, failing to achieve the designed effect. If the trench backfill is not compacted, the backfill material is prone to settling and sinking, leading to drainage collapse and even cracking and subsidence of the entrance hall. This subsidence causes endless settlement repairs and may even increase the infiltration of surface water and groundwater into the foundation, increasing water pressure and potentially causing the foundation to float, further increasing water and soil pressure on the exterior walls. Furthermore, the subsidence of the backfill soil can exert a downward pull on the external waterproofing, potentially damaging the structural waterproofing layer and causing leaks in the basement and exterior walls. Furthermore, as the country gradually raises its standards for building quality, higher requirements are being placed on backfill materials for trenches. These requirements are no longer limited to preventing settlement, but also include providing support and protection for buildings or structures, and enhancing their resistance to external factors such as storms and earthquakes. Therefore, it is necessary to find a backfill material that can both reduce settlement of trench filling and improve the resilience of buildings or structures.

[0003] The main reason for the subsidence and settlement of backfill material in trenches is that traditional backfill materials such as soil and sand are highly permeable and not dense. After absorbing water, their weight increases, making them prone to settling under the increased weight of the backfill. Furthermore, these materials have poor cohesion and low resistance to shear deformation, making them more susceptible to settlement under external disturbances. To reduce the weight of the backfill, some projects have begun using foamed soil or foamed concrete for trench backfilling. Foamed soil is readily available and easy to construct, but it has low strength and is suitable for general trench backfilling. For trench backfilling with higher quality requirements, foamed concrete is often chosen. Foamed concrete is a lightweight, porous concrete material made by introducing foam into a slurry composed of cement, aggregates, admixtures, and water, followed by pouring, molding, and curing. Foamed concrete has advantages such as low density, high specific strength, and good thermal insulation performance, and is widely used in insulation materials, base pads, and foundation pit filling. For example, Chinese patent application publication number CN116003062A discloses a foamed concrete and its preparation method for backfilling gas pipelines in tunnels. Its technical solution involves precisely controlling the dosage and setting time of raw materials such as fly ash, cement, and foaming agent. However, this type of foamed concrete has a drawback: low flexural strength, resulting in poor shear resistance, weak impact resistance, and poor support and protection for buildings or structures.

[0004] To address the shortcomings of poor impact resistance and shear strength in backfill materials for slag heaps, researchers have attempted to improve the mechanical properties of foamed concrete by adding fibers. Adding soft, short-cut fibers such as PP (polypropylene) fibers and PVAL (polyvinyl alcohol) fibers to foamed concrete generally does not affect the stability of the foam. However, these fibers are expensive. For example, a lightweight, high-strength foamed concrete disclosed in Chinese patent application publication number CN116332599A uses cement and fly ash as binders, aluminum powder as a foaming agent, and PP fibers as reinforcement. Since PP fibers are synthetic materials, using such synthetic materials as filler is a waste of their potential.

[0005] In an effort to reduce the cost of fiber-reinforced foamed concrete, some have attempted to add cheaper glass fibers or straw fibers. However, these fibers are relatively hard or have sharp tips. If added to foamed concrete, they can easily scratch the foam as the material flows, causing it to rupture, affecting its stability, and making it impossible to produce reliable foamed concrete.

[0006] my country has abundant wheat straw fiber reserves, but the recycling rate has always been very low. Apart from a portion being used for papermaking, the remainder is often burned or buried, causing environmental pollution and resource waste. Due to the low strength and easy rot of wheat straw fiber, its application in building materials is also limited. If wheat straw is modified and a reasonable foaming method is adopted, its use in foamed concrete will greatly increase the added value of wheat straw. Summary of the Invention

[0007] In order to overcome the shortcomings of traditional foamed concrete filling materials, such as poor shear resistance and weak impact resistance, and at the same time increase the added value of wheat straw, this invention provides a modified wheat straw fiber reinforced foamed concrete backfill material.

[0008] This invention also provides a method for preparing and using the modified straw fiber reinforced foamed concrete backfill material.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A modified wheat straw fiber reinforced foamed concrete backfill material is composed of three parts: concrete dry powder, composite foaming agent and modified wheat straw fiber. The modified wheat straw fiber is characterized by the following preparation method: first, wheat straw fragments are corroded with alkaline solution, and then the alkaline-corroded wheat straw fragments are immersed in fiber surface coating film adhesive liquid, or a layer of fiber surface coating film adhesive liquid is directly sprayed on the surface of the alkaline-corroded wheat straw fragments, so that a layer of fiber surface coating film is attached to the surface of the wheat straw fragments.

[0011] The fiber surface coating film adhesive is made by mixing water, polyvinyl alcohol, gum arabic powder and fatty alcohol polyoxyethylene ether in a mass ratio of 100:(1-3):(3-6):(5-7);

[0012] The polyvinyl alcohol mentioned is a polyvinyl alcohol with a degree of alcoholysis of 88% that is soluble in cold water.

[0013] This invention provides a method for preparing modified wheat straw fiber reinforced foamed concrete backfill material, characterized in that the preparation method comprises three parts: preparation of modified wheat straw fiber, preparation of concrete dry powder, and preparation of composite foaming agent, wherein:

[0014] First: Preparation of modified wheat straw fiber

[0015] 1.1: Dry the wheat straw in the sun, cut it into pieces with a length of 10-20mm, corrode it with compound alkaline solution for 24-36 hours, take it out and let it air dry;

[0016] The composite alkaline solution is prepared by adding 3-6 parts by weight of sodium hydroxide and 2-5 parts by weight of calcium hydroxide to 100 parts by weight of water;

[0017] 1.2: Soak the wheat straw fragments obtained in step 1.1 in the fiber surface coating film solution for 1-2 hours, or spray the fiber surface coating film solution directly onto the surface of the wheat straw fragments, so that the surface of the wheat straw is moistened but not dripping. After taking them out, let them dry to obtain modified wheat straw fiber.

[0018] The fiber surface coating film adhesive is made by mixing water, polyvinyl alcohol, gum arabic powder and fatty alcohol polyoxyethylene ether in a mass ratio of 100:(1-3):(3-6):(5-7);

[0019] The polyvinyl alcohol mentioned is a polyvinyl alcohol with a degree of alcoholysis of 88% that is soluble in cold water.

[0020] Second: Preparation of dry concrete powder

[0021] Mix 100-200 parts by weight of cement, 200-300 parts by weight of fly ash, 5-50 parts by weight of ceramic sand, 6-10 parts by weight of water-reducing agent, and 1-2 parts by weight of hydroxypropyl methylcellulose ether in a dry powder mixer until homogeneous, then bag it to obtain concrete dry powder.

[0022] The water-reducing agent is a solid polycarboxylate water-reducing agent, and the ceramic sand is a lightweight fine aggregate with a particle size between 1.15 and 5 mm.

[0023] Third: Preparation of composite foaming agents

[0024] Sodium dodecylbenzenesulfonate, animal protein foaming agent, and sodium lignin sulfonate are mixed evenly in a mass ratio of 1:(0.3-0.6):(0.1-0.3), and then bagged to obtain a composite foaming agent. The animal protein foaming agent is an animal hoof and horn foaming agent.

[0025] The method of using the modified wheat straw fiber reinforced foamed concrete backfill material of this invention is as follows:

[0026] Step 1: Add modified wheat straw fiber and concrete dry powder to water in a mixer at a mass ratio of 1:(80~100):(35~45) and mix evenly to obtain a backfill slurry component with a fluidity between 160~230mm.

[0027] Step 2: Add the composite foaming agent and water together in a foaming machine at a mass ratio of 1:(4~6) to foam and obtain the backfill foam component;

[0028] Step 3: Mix the backfill slurry components and backfill foam components at a volume ratio of 1:(2.5~5.5) evenly (the higher the required density of the backfill material, the less foam component is needed) to obtain the modified straw fiber reinforced foam concrete backfill material slurry; then pour the slurry in layers into the cleaned trench, requiring each layer to be 0.3~0.8m thick. After the lower layer has set, the upper layer should be filled. The curing time should not be less than 3 days, and the minimum ambient temperature during construction should be above 5℃.

[0029] The positive significance of this invention is:

[0030] (1) This invention utilizes a composite alkaline solution to corrode and destroy wheat straw, decomposing substances such as wax, pectin, and lignin that affect cement hydration. This forms a large number of tiny pores on the surface of the wheat straw fibers, which not only effectively improves the mechanical bonding force between the wheat straw fibers and the concrete matrix and enhances the mechanical properties, but also facilitates the subsequent fiber surface coating adhesive to penetrate into the pores, strengthen the wheat straw, and enhance the strength of the wheat straw fibers.

[0031] (2) In addition to polyvinyl alcohol polymer cementitious material, the fiber surface coating film of the present invention also contains gum arabic and fatty alcohol polyoxyethylene ether. Gum arabic is a polar molecule, and the polar groups in its molecule can be firmly adsorbed on the surface of wheat straw fiber. Fatty acid polyoxyethylene ether is a nonionic surfactant with good diffusion and penetration. Together with gum arabic, it is uniformly diffused in polyvinyl alcohol to form a colloid that adheres to the surface of wheat straw fiber, which increases the affinity between wheat straw fiber and air bubbles and has a certain stabilizing effect on foam. In particular, it weakens the sharpness of the wheat straw fiber tip and eliminates the disadvantage of affecting the foaming effect when making foamed concrete in the future.

[0032] (3) After wheat straw fibers are corroded by alkaline solution, some alkaline solution will remain in them. Alkaline solution is not conducive to the hydration of concrete. Conventional practice requires the alkaline-containing fibers to be dealkalized before being added to concrete. Dealkalization is an environmentally polluting process. This invention attaches a fiber surface coating film to the wheat straw fibers after alkaline corrosion, which eliminates the dealkalization process and is beneficial to the environment.

[0033] (4) The main materials of this invention can all be processed in the production workshop, and the production process can be accurately controlled, resulting in stable and reliable product quality. During backfilling, it is only necessary to mix the modified wheat straw fiber, concrete dry powder and composite foaming agent with water until they are evenly mixed. The operation is simple, the construction is convenient and quick, and it is suitable for high-quality projects. Detailed Implementation

[0034] The specific embodiments of the present invention will be described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more explicit definition of the scope of protection of the present invention.

[0035] Example 1: The preparation method of the modified wheat straw fiber reinforced foamed concrete backfill material of the present invention mainly includes three parts: 1. Preparation of modified wheat straw fiber, 2. Preparation of concrete dry powder, and 3. Preparation of composite foaming agent. The specific preparation method is as follows:

[0036] Part 1: Preparation of Modified Wheat Straw Fiber

[0037] 1.1: Dry the wheat straw in the sun and cut it into pieces with a length of 10-20mm;

[0038] 1.2: Add 5 parts by weight of sodium hydroxide and 3 parts by weight of calcium hydroxide to 100 parts by weight of clean tap water to prepare a compound alkaline solution. Put the wheat straw fragments obtained in step 1.1 into the compound alkaline solution to corrode for 24-36 hours, take them out and dry them.

[0039] 1.3: Add 2 parts by weight of polyvinyl alcohol, 5 parts by weight of gum arabic and 6 parts by weight of fatty alcohol polyoxyethylene ether to 100 parts by weight of water to prepare a fiber surface coating film solution. Put the wheat straw obtained in step 1.2 into the fiber surface coating film solution, soak for 1-2 hours, take it out, dry it, and obtain modified wheat straw fiber for later use.

[0040] Part Two: Preparation of Concrete Dry Powder

[0041] 150 parts by weight of cement, 250 parts by weight of fly ash, 25 parts by weight of ceramic sand, 8 parts by weight of water-reducing agent, and 1.5 parts by weight of hydroxypropyl methylcellulose ether are put into a dry powder mixer and mixed evenly to obtain concrete dry powder.

[0042] Part Three: Preparation of Composite Foaming Agent

[0043] Sodium dodecylbenzenesulfonate, animal protein foaming agent, and sodium lignosulfonate were mixed evenly in a mass ratio of 1:0.5:0.2 to obtain a composite foaming agent.

[0044] The method of use in Example 1 is as follows: When backfilling is required, at the construction site, the modified wheat straw fiber and concrete dry powder are mixed with water to prepare the backfill slurry component, and the composite foaming agent is mixed with water to prepare the backfill foam component. Then, the slurry component and the foam component are mixed in proportion for backfilling construction. The specific usage method is as follows:

[0045] Modified wheat straw fiber, concrete dry powder and water were added into a mixer at a mass ratio of 1:90:40 and mixed evenly to obtain the backfill slurry component.

[0046] The composite foaming agent and water are added together in a foaming machine at a ratio of 1:5 to produce the backfill foam component.

[0047] The modified straw fiber reinforced foam concrete backfill material slurry is prepared by mixing the backfill slurry component and the backfill foam component at a volume ratio of 1:4. The prepared modified straw fiber reinforced foam concrete backfill material slurry is then pumped into a cleaned fertilizer tank and poured in layers. The thickness of each layer is controlled between 0.3 and 0.8 m. The next layer is poured after the first layer has set. The curing time is generally 3 days. The minimum ambient temperature during construction must be above 5℃.

[0048] Example 2: The preparation method of Example 2 is the same as that of Example 1, but the usage method is different. That is, when using it in the field, the backfill slurry component and the backfill foam component are mixed at a volume ratio of 1:5.

[0049] Example 3: The preparation method of Example 3 is the same as that of Example 1, but the usage method is different. That is, when using it in the field, the backfill slurry component and the backfill foam component are mixed at a volume ratio of 1:3.

[0050] Example 4: The preparation method of Example 4 is the same as that of Example 1, but the usage method is different. Specifically, the ratio of modified wheat straw fiber, concrete dry powder and water in the backfill slurry is 1:100:45 by mass.

[0051] Example 5: Example 5 is basically the same as Example 1, except that the ratio of modified wheat straw fiber, concrete dry powder and water in the backfill slurry is 1:80:35 by mass.

[0052] To verify the effect of modified wheat straw fiber on the mechanical properties of backfill materials in this invention, two comparative experiments are presented below.

[0053] Control Experiment 1: The method of use in Control Experiment 1 is the same as that in Example 1, but the preparation method is different. Specifically, step 1.3 is not included in the preparation method. That is to say, the coating film adhesive of the present invention is not attached to the surface of the wheat straw. In addition, the wheat straw fibers corroded by alkaline solution are rinsed with water until the pH is <7.5.

[0054] Control Experiment 2: The method used in Control Experiment 2 is the same as that in Example 1, except that steps 1.2 and 1.3 are not included in the preparation method. In other words, the surface of the wheat straw is not treated in any way.

[0055] In accordance with the requirements of the construction industry standard JG / T266-2011, the dry density, 28-day compressive strength and 28-day flexural strength of the backfill materials in the examples and comparative tests were tested, and the test results are shown in Table 1.

[0056] Table 1. Test results of different foamed concrete properties

[0057]

[0058] Comparing the test results of Example 1 and the two comparative test groups, it was found that after adding wheat straw fibers with the fiber surface coating of the present invention to foamed concrete, the 28-day flexural strength was significantly better than that of wheat straw fibers without the fiber surface coating. This shows that the wheat straw fibers modified by the coating of the present invention can indeed improve the flexural performance of foamed concrete.

[0059] Comparing the experimental results of Examples 1 to 3, it was found that when the proportions of the slurry and the composite foaming agent are the same, the dry density and compressive strength of the filling material will decrease when the amount of foam component in the final slurry is increased. Ideally, foamed concrete should have low density and high strength, which is a contradiction. Therefore, in actual construction, the proportion of slurry and composite foaming agent should be determined according to the density requirements of the filling material to achieve a balance between density and strength.

[0060] Comparing the experimental results of Examples 1, 4 and 5, it was also found that increasing the amount of wheat straw fiber incorporated into the slurry is beneficial to improving the flexural strength of the filler material.

[0061] To further verify that the wheat straw fiber modified by this invention is beneficial to foam stability, the following four sets of experiments were conducted to test the effect of different wheat straw fibers on foam stability.

[0062] Cut the wheat straw fiber into 10-20mm segments and divide them into three equal parts. One part is modified using the method of this invention (the wheat straw fiber is soaked in an alkaline solution and then coated with a coating film on the fiber surface). The second part of wheat straw fiber is only soaked in an alkaline solution without coating the fiber surface with a coating film, and the wheat straw fiber is rinsed with water until the pH is <7.5. The third part of wheat straw fiber is not treated in any way.

[0063] 100g of each of the three types of wheat straw fiber were weighed and put into a foam quality tester containing foam. At the same time, a set of control foam samples without fiber were tested. The settling distance and water exudation of the foam were recorded over 1 hour. The test results are shown in Table 2.

[0064] Table 2. Effects of different wheat straw fibers on foam settling distance and water exudation.

[0065] Serial Number Fiber condition description 1h settlement distance / mm 1h per mL 1 Modified wheat straw fiber 9 48 2 Wheat straw fiber soaked only in alkali solution 13 80 3 Untreated wheat straw fiber 14 89 4 No fiber 6 31

[0066] Comparing the settlement distance and bleeding volume of the four test groups in Table 2, it was found that the modified wheat straw fiber of this invention significantly improved foam stability compared to the unmodified wheat straw fiber. However, it was also found that adding wheat straw fiber, regardless of modification, was detrimental to foam stability. This indicates that wheat straw fiber easily scratches the foam, causing it to rupture and affecting its stability. Therefore, in practical engineering applications, it is crucial to strictly control the amount of modified wheat straw fiber added to minimize its impact on foam stability while utilizing wheat straw fiber to improve the mechanical properties of foamed concrete.

[0067] The above examples are merely specific embodiments of the present invention and should not be construed as limiting the present invention. For instance, the components of the concrete dry powder and the composite foaming agent in the five embodiments and the two control test groups are the same. This is only for the purpose of facilitating the comparison of test data. Therefore, the scope of protection should be determined by the scope of the claims.

Claims

1. A method for preparing a modified wheat straw fiber reinforced foam concrete backfill material, characterized in that the modified wheat straw fiber reinforced foam concrete backfill material is composed of three parts of concrete dry powder, composite foaming agent and modified wheat straw fiber, and the detailed preparation method is as follows: First: preparation of modified wheat straw fiber 1.1: Dry the wheat straw, cut into 10-20mm length, use the compound lye to erode 24-36h, take out, dry; The compound lye is prepared by adding 3-6 parts by weight of sodium hydroxide and 2-5 parts by weight of calcium hydroxide in 100 parts by weight of water; 1.2: Put the wheat straw pieces prepared in step 1.1 into the fiber surface coating film glue solution for 1-2h, or directly spray the fiber surface coating film glue solution on the surface of the wheat straw pieces, the surface of the wheat straw is wet but not flowing, dry after taking out, modified wheat straw fiber can be prepared; The fiber surface coating film glue solution is mixed by water, polyvinyl alcohol, gum arabic powder and fatty alcohol polyoxyethylene ether in a mass ratio of 100:(1-3):(3-6):(5-7); The polyvinyl alcohol is a cold water soluble polyvinyl alcohol with an alcoholysis degree of 88%; Second: preparation of concrete dry powder Put cement 100-200 parts by weight, fly ash 200-300 parts by weight, ceramic sand 5-50 parts by weight, water reducing agent 6-10 parts by weight, hydroxypropyl methyl cellulose ether 1-2 parts by weight into the dry powder mixer and stir evenly, then pack to prepare the concrete dry powder; The water reducing agent is a solid polycarboxylic acid type water reducing agent, and the ceramic sand is a lightweight fine aggregate with a particle size of 1.15-5mm; Third: preparation of composite foaming agent Mix sodium dodecyl benzene sulfonate, animal protein foaming agent and sodium lignosulfonate in a mass ratio of 1:(0.3-0.6):(0.1-0.3) to prepare a composite foaming agent, and the animal protein foaming agent is an animal hoof foaming agent.

2. A use method of the modified wheat straw fiber reinforced foam concrete backfill material prepared by the preparation method of claim 1, characterized in that, First step: put the modified wheat straw fiber and the concrete dry powder into the mixer with water in a mass ratio of 1:(80-100):(35-45), stir evenly to prepare a backfill material slurry component with a flow degree of 160-230mm; Second step: add the composite foaming agent and water into the foaming machine in a mass ratio of 1:(4-6) to prepare a backfill material foam component; Third step: mix the backfill material slurry component and the backfill material foam component in a volume ratio of 1:(2.5-5.5), to prepare a modified wheat straw fiber reinforced foam concrete backfill material slurry; then pour the slurry into the cleaned trench in layers, the thickness of each layer is controlled to be 0.3-0.8m, and the upper filling layer is filled after the lower filling layer is cured, the curing time is not less than 3d, and the minimum temperature of the environment during construction is above 5℃.

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