A waste construction waste non-fired brick and a preparation method thereof

Abstract

The application discloses a kind of waste engineering spoil non-fired brick and preparation method thereof, first join phosphogypsum and Portland cement to solidify engineering spoil, then utilize soybean urease to catalyze urea hydrolysis, to induce calcium carbonate deposition in mixture material to further improve. Both reduce the pollution of phosphating byproduct to environment, and improve the mechanical properties and pore structure of engineering spoil, effectively reduce its compressibility, and utilize solidified engineering spoil on-site compression forming non-fired brick, realize the recycling of two kinds of waste.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a non-fired brick made from waste construction waste and its preparation method. Background Technology

[0002] During earthwork excavation, construction sites generate a large amount of waste soil. Statistics show that approximately 2 billion tons of construction waste are generated annually in my country, and this waste is typically disposed of through landfill. Due to the nature of construction machinery, the excavated soil is often in lumps. These lumps are generally not compacted during landfilling, remaining mostly as small blocks or clumps ranging from a few millimeters to tens of centimeters in size. Therefore, they possess a highly uneven, doubly porous structure, resulting in high permeability, high compressibility, low strength, and poor overall stability. Direct landfill disposal not only occupies land resources but may also trigger geological disasters such as mudslides and ground deformation, threatening human safety and causing property damage. To address this issue, based on a thorough understanding of the properties of this waste construction soil, on-site improvement and solidification are performed to construct temporary construction roads, allowing for the full utilization of the waste soil, which has significant engineering and environmental implications.

[0003] Meanwhile, phosphogypsum is an industrial byproduct of the wet process production of phosphoric acid in phosphate chemical enterprises. my country's phosphate chemical industry discharges over 50 million tons of phosphogypsum annually, and this figure is growing at a rate of 15% per year. Domestically, the main method for treating phosphogypsum is stockpiling, with a comprehensive utilization rate of only about 10%. As a solid waste, stockpiling phosphogypsum not only wastes land resources but also easily causes environmental pollution due to its content of phosphorus and other harmful substances. The phosphogypsum problem has become a global challenge related to the sustainable development of the phosphate chemical industry and environmental protection. Therefore, researching phosphogypsum waste recycling technology is crucial for phosphate chemical enterprises to achieve sustainable development.

[0004] In summary, if some connection can be established between waste construction waste and phosphogypsum, and the solidified waste can be treated with phosphogypsum and then used for construction, the recycling of both types of waste can be achieved, reducing overall costs and meeting the requirements of green environmental protection and sustainable development. Therefore, using phosphogypsum to improve waste construction waste has significant environmental and economic implications. Summary of the Invention

[0005] This invention provides a method for preparing non-fired bricks from waste construction waste. The bricks are prepared by solidifying waste construction waste using a combination of biomineralization and cement-phosphogypsum composite cementitious materials. This method reduces the environmental pollution caused by phosphating byproducts, improves the mechanical properties and pore structure of the construction waste, effectively reduces its compressibility, and utilizes the solidified construction waste to form non-fired bricks on-site, thus achieving the recycling of both types of waste materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing non-fired bricks from waste construction waste specifically includes the following steps:

[0008] Step S1: Select waste construction soil from the site, screen it, and test its moisture content;

[0009] Step S2: Select waste phosphogypsum, dry it at low temperature, crush it, and sieve it to obtain phosphogypsum particles within a predetermined particle size range.

[0010] Step S3: Select waste soybean meal and mix it evenly with water, let it stand and filter out the soybean residue to obtain soybean urease solution;

[0011] Step S4: Grind the urea granules into powder and dissolve them in water to obtain a urea solution;

[0012] Step S5: Mix the phosphogypsum particles obtained in step S2 with silicate cement to obtain mixture A. Add the engineering waste to mixture A and continue to mix to obtain mixture B. Add water to mixture B to obtain mixture C.

[0013] Step S6: Spray the soybean urease solution from step S3 onto the surface of mixture C to obtain mixture D. Let it stand for 5-10 hours. Then spray the urea solution obtained in step S4 onto the surface of mixture D and let it stand for 24-30 hours to obtain solidified engineering slag.

[0014] Step S7: Press the solidified engineering waste obtained in step S6 into shape using a brick press to obtain non-fired bricks.

[0015] Preferably, in step S1, the test ensures that the moisture content of the engineering waste soil is 20%-40%.

[0016] Preferably, in step S2, the waste phosphogypsum is dried at 60-65°C for 72 hours; after crushing, phosphogypsum particles with an average particle size of 0.05mm-0.15mm are sieved out.

[0017] Preferably, in step S3, the waste soybean meal selected is waste yellow soybean meal, the mass ratio of soybean meal to water is 1:10-1:80, and the standing time is 5-10 hours.

[0018] Preferably, in step S4, the mass ratio of urea to water is 1:5 to 1:20.

[0019] Preferably, in step S5, the mass ratio of the added phosphogypsum particles, silicate cement, engineering waste soil and water is 2-8:10-20:110-130:20-40.

[0020] Preferably, in step S5, the silicate cement used is silicate cement with the grade PO 42.5; the moisture content of the solidified engineering slag is between 40% and 60%; and the moisture content of mixture C is between 40% and 60%.

[0021] Preferably, in step S6, the mass ratio of soybean urease solution, urea solution and engineering waste soil in step S5 is 10-20:20-60:110-130.

[0022] Preferably, in step S7, the pressing pressure is 10-20 MPa.

[0023] The beneficial effects of this invention are:

[0024] 1. The method for preparing non-fired bricks from waste engineering slag provided by the present invention involves first thoroughly mixing phosphogypsum and ordinary silicate cement, then adding them to the slag for solidification treatment, and then using soybean urease to catalyze the hydrolysis of urea to induce calcium carbonate deposition to further improve the slag. The full utilization of the two waste materials can increase the yield stress of the material by 70-80% and the unconfined compressive strength by 40-50%. The solidified engineering slag can be used to press and form non-fired bricks on site, which can greatly reduce construction and transportation costs compared with traditional preparation methods.

[0025] 2. The present invention uses a spraying method to add soybean urease solution and urea solution, which will not disturb the structure of the solidified soil. Spraying allows the solution to slowly penetrate without causing significant disturbance, while filling the pore structure and making the strengthening effect more obvious.

[0026] 3. The waste engineering slag non-fired brick and its preparation method provided by the present invention utilize phosphogypsum as a solidification modifier for waste engineering slag, transforming harmful substances such as phosphorus in phosphogypsum into harmless products, reducing the environmental pollution of phosphating by-products, improving the mechanical properties and pore structure of the slag, effectively reducing its compressibility, reducing the overall cost, and meeting the requirements of green environmental protection and sustainable development. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0028] Figure 1 The microstructure of solidified engineering waste soil prepared in Comparative Example 1 provided by this invention;

[0029] Figure 2The microstructure of solidified engineering waste soil prepared according to Example 1 of this invention;

[0030] Figure 3 The microstructure of solidified engineering waste soil prepared according to Example 2 of this invention;

[0031] Figure 4 The microstructure of solidified engineering waste soil prepared according to Example 3 of the present invention is shown. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] A large amount of waste soil is generated during civil engineering construction. Its internal multi-pore structure results in high permeability, high compressibility, low strength and poor overall stability. Therefore, it needs to be pretreated if it is to be used to make non-fired bricks. Combined with the characteristics of phosphogypsum, which is also a waste product, phosphogypsum can be used to prepare high-strength cementitious materials. Therefore, phosphogypsum can be used as a modifier for solidifying waste soil.

[0034] To better utilize waste construction waste and phosphogypsum, this application provides a method for preparing non-fired bricks made from waste construction waste using a microbial mineralization combined with cement-phosphogypsum composite cementitious material. The method involves mixing phosphogypsum and ordinary silicate cement in water, resulting in a series of physicochemical reactions. The products fill the pores between the waste particles, achieving a solidification effect. Ordinary silicate cement undergoes hydration in the mixture, producing cementitious substances such as hydrated calcium silicate and hydrated calcium aluminate. Calcium silicate hydrate coats the surface of soil particles, making the soil material structure denser and improving stability. Calcium aluminate reacts with phosphogypsum to form ettringite, which fills the pores between soil particles, making the material more compact and contributing to stress, strengthening the skeletal structure and enhancing stability. Furthermore, soybean urease catalyzes the hydrolysis of urea, reacting with calcium salts in the mixture to induce calcium carbonate precipitation, which fills the pores in the waste soil for further modification.

[0035] Specifically, the following steps are included:

[0036] Step S1: Select waste construction soil from the site, sieve it, and test its moisture content. Testing the moisture content ensures that the appropriate amount of water can be added according to the mixing ratio in subsequent methods. Generally, during testing, we need to ensure that the moisture content of the waste soil is between 20% and 40%.

[0037] Step S2: Select waste phosphogypsum. The chemical composition of phosphogypsum includes CaO and SO3, and the main mineral component is gypsum (CaSO4·2(H2O)). Dry the phosphogypsum at a low temperature of 60-65℃ for 72 hours to ensure that the moisture attached to the slag is fully evaporated. Then crush it by grinding equipment and screen it with a sieve to screen it with a particle size of 1mm-0.01mm. The average particle size of the screened particles is 0.05mm-0.15mm. Phosphogypsum particles in this range can undergo sufficient hydration reaction in the subsequent mixing process.

[0038] Step S3: Select waste soybean paste, add water at a mass ratio of 1:10-1:80, stir well, and let stand for 5 hours to obtain soybean urease solution.

[0039] Step S4: Weigh an appropriate amount of urea granules, grind them into powder using a grinding device, and dissolve them in water at a mass ratio of 1:5 to 1:20 to obtain a urea solution.

[0040] Step S5: Mix 2-8 parts by weight of phosphogypsum granules obtained in step S2 with 10-20 parts by weight of silicate cement. After mixing evenly, mixture A is obtained. The silicate cement used is silicate cement with grade P.O42.5. Add 110-130 parts by weight of slag to mixture A and continue to mix evenly to obtain mixture B. Add 20-40 parts by weight of water to mixture B to obtain mixture C. The moisture content of mixture C is between 40% and 60%.

[0041] Step S6: Take 10-20 parts by mass of the soybean urease solution from step S3 and spray it onto the surface of mixture C to obtain mixture D. Let it stand for 8-10 hours to ensure that the urease solution penetrates into the pores of the slag. Then, spray 20-60 parts by mass of the urea solution obtained in step S4 onto the surface of mixture D and let it stand for 24-30 hours to obtain solidified engineering slag.

[0042] Step S7: Press the solidified engineering waste obtained in step S6 into shape using a brick press to obtain non-fired bricks.

[0043] To further verify the superior strength of the waste construction waste non-fired bricks provided in this application, several specific embodiments are given. In these embodiments, the waste construction waste used has a particle size of 3-7 mm and its main chemical components are SiO2, Al2O3, etc. The legume used is soybean meal. The phosphogypsum used is taken from the gypsum stockpile of a phosphate fertilizer plant; it is gray in appearance, has a pH value of 3.2, and its main chemical components are gypsum (CaSO4·2(H2O)), etc. The ordinary Portland cement used is grade PO 42.5, and its main chemical components are CaO, SiO2, etc. The chemical composition (parts by mass) of the above raw materials is shown in Table 1.

[0044] Table 1:

[0045]

[0046] Comparative Example 1:

[0047] The selected materials, in parts by weight, include: 120 parts of slag, 0 parts of phosphogypsum, 15 parts of silicate cement, 30 parts of water, 10 parts of soybean urease solution, and 50 parts of urea solution. The waste construction slag is then improved and solidified according to the following steps:

[0048] Step S1: The construction waste soil is sieved through a screen and the moisture content is measured to be 20%;

[0049] Step S2: Select waste soybean paste, add water at a mass ratio of 1:10, stir well, and let stand for 10 hours to obtain soybean urease solution;

[0050] Step S3: Weigh an appropriate amount of urea granules, grind them into powder of 0.05-0.07mm using a grinding device, and dissolve them in water at a mass ratio of 1:10 to obtain a urea solution.

[0051] Step S4: After mixing the slag and silicate cement, add 30 parts of water and continue mixing.

[0052] Step S5: Take 10 parts by mass of the soybean urease solution from step S2 and spray it onto the surface of the slag, let it stand for 10 hours, then spray 50 parts by mass of the urea solution obtained in step S3 onto the surface of the slag, let it stand for 24 hours, and obtain solidified engineering slag.

[0053] Step S6: Press the solidified engineering waste obtained in step S5 into bricks using a brick press to obtain non-fired bricks at a molding pressure of 20 MPa.

[0054] Following the above method, the solidified engineering slag obtained in Comparative Example 1 was subjected to uniaxial compression test and unconfined compressive strength test according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Its yield stress reached 186 kPa and its unconfined compressive strength reached 255 kPa.

[0055] Example 1:

[0056] The selected materials, in parts by weight, include: 120 parts of slag, 2 parts of phosphogypsum, 15 parts of silicate cement, 30 parts of water, 10 parts of soybean urease solution, and 50 parts of urea solution. The waste construction slag is then improved and solidified according to the following steps:

[0057] Step S1: The slag is sieved through a screen and the moisture content is measured to be 20%.

[0058] Step S2: Select waste phosphogypsum, dry the phosphogypsum at low temperature, crush it through a grinding device, and sieve the crushed phosphogypsum to obtain phosphogypsum particles in the range of 0.01-1mm particle size.

[0059] Step S3: Select waste soybean paste, add water at a mass ratio of 1:10, stir well, and let stand for 10 hours to obtain soybean urease solution;

[0060] Step S4: Weigh an appropriate amount of urea granules, grind them into powder of 0.05-0.07mm using a grinding device, and dissolve them in water at a mass ratio of 1:10 to obtain a urea solution.

[0061] Step S5: After mixing the slag and silicate cement, add 30 parts of water and continue mixing.

[0062] Step S6: Take 10 parts by mass of the soybean urease solution from step S3 and spray it onto the surface of the slag, let it stand for 10 hours, then spray 50 parts by mass of the urea solution obtained in step S4 onto the surface of the slag, let it stand for 24 hours, and obtain solidified engineering slag.

[0063] Step S7: Press the solidified engineering waste obtained in step S6 into bricks using a brick press to obtain non-fired bricks at a molding pressure of 20 MPa.

[0064] Following the above method, the solidified engineering slag obtained in Example 1 was subjected to uniaxial compression test and unconfined compressive strength test according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Its yield stress reached 312 kPa and its unconfined compressive strength reached 273 kPa.

[0065] Example 2:

[0066] The selected materials, in parts by weight, include: 120 parts of slag, 5 parts of phosphogypsum, 15 parts of silicate cement, 30 parts of water, 10 parts of soybean urease solution, and 50 parts of urea solution. The waste construction slag is then improved and solidified according to the following steps:

[0067] Step S1: The slag is sieved through a screen and the moisture content is measured to be 20%.

[0068] Step S2: Select waste phosphogypsum, dry the phosphogypsum at low temperature, crush it through a grinding device, and sieve the crushed phosphogypsum to obtain phosphogypsum particles in the range of 0.01-1mm particle size.

[0069] Step S3: Select waste soybean paste, add water at a mass ratio of 1:10, stir well, and let stand for 10 hours to obtain soybean urease solution;

[0070] Step S4: Weigh an appropriate amount of urea granules, grind them into powder of 0.05-0.07mm using a grinding device, and dissolve them in water at a mass ratio of 1:10 to obtain a urea solution.

[0071] Step S5: After mixing the slag and silicate cement, add 30 parts of water and continue mixing.

[0072] Step S6: Take 10 parts by mass of the soybean urease solution from step S3 and spray it onto the surface of the slag, let it stand for 10 hours, then spray 50 parts by mass of the urea solution obtained in step S4 onto the surface of the slag, let it stand for 24 hours, and obtain solidified engineering slag.

[0073] Step S7: Press the solidified engineering waste obtained in step S6 into bricks using a brick press to obtain non-fired bricks at a molding pressure of 20 MPa.

[0074] Following the above method, the solidified engineering slag obtained in Example 2 was subjected to uniaxial compression test and unconfined compressive strength test according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Its yield stress reached 392 kPa and its unconfined compressive strength reached 376 kPa.

[0075] Example 3:

[0076] The selected materials, in parts by weight, include: 120 parts of slag, 8 parts of phosphogypsum, 15 parts of silicate cement, 30 parts of water, 10 parts of soybean urease solution, and 50 parts of urea solution. The waste construction slag is then improved and solidified according to the following steps:

[0077] Step S1: The slag is sieved through a screen and the moisture content is measured to be 20%.

[0078] Step S2: Select waste phosphogypsum, dry the phosphogypsum at low temperature, crush it through a grinding device, and sieve the crushed phosphogypsum to obtain phosphogypsum particles in the range of 0.01-1mm particle size.

[0079] Step S3: Select waste soybean paste, add water at a mass ratio of 1:10, stir well, and let stand for 10 hours to obtain soybean urease solution;

[0080] Step S4: Weigh an appropriate amount of urea granules, grind them into powder of 0.05-0.07mm using a grinding device, and dissolve them in water at a mass ratio of 1:10 to obtain a urea solution.

[0081] Step S5: After mixing the slag and silicate cement, add 30 parts of water and continue mixing.

[0082] Step S6: Take 10 parts by mass of the soybean urease solution from step S3 and spray it onto the surface of the slag, let it stand for 10 hours, then spray 50 parts by mass of the urea solution obtained in step S4 onto the surface of the slag, let it stand for 24 hours, and obtain solidified engineering slag.

[0083] Step S7: Press the solidified engineering waste obtained in step S6 into bricks using a brick press to obtain non-fired bricks at a molding pressure of 20 MPa.

[0084] Following the above method, the solidified engineering slag obtained in Example 3 was subjected to uniaxial compression test and unconfined compressive strength test according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Its yield stress reached 327 kPa and its unconfined compressive strength reached 281 kPa.

[0085] Microscopic scanning studies will be conducted on the solidified engineering waste soil structures prepared in Comparative Example 1 and Examples 1-3. For example... Figure 1 The image shown is a microscopic SEM scan of the solidified slag material in Comparative Example 1. When no phosphogypsum was added to the material, only calcium carbonate and hydrated calcium silicate (CSH) products were observed. Figure 2 The image shown is a microscopic SEM scan of the solidified slag material from Example 1. With the addition of phosphogypsum, needle-like ettringite crystals were generated in the sample. However, the low amount of phosphogypsum resulted in very little ettringite formation, and the crystal growth was insufficient. Figure 3 The image shown is a microscopic SEM scan of the solidified slag material from Example 2. The phosphogypsum content increased to 30%, accelerating the formation of ettringite crystals and filling the pores. Simultaneously, the hydrated calcium silicate adhering to the soil particle surface combined with the needle-like ettringite crystals, resulting in a more compact microstructure. Figure 4As shown, the solidified slag material of Example 3 is a microscopic SEM scan image. As the amount of phosphogypsum continues to increase, a large number of generated ettringite crystals fully fill the pores. However, some ettringite crystals are squeezed out of the pores, indicating that there is no space for the crystals to continue growing. Furthermore, the excessive amount of ettringite crystals compresses the soil particles, leading to the destruction of the material structure and a decrease in strength.

[0086] In summary, by utilizing soybean urease and cement-phosphogypsum composite cementitious materials, and by controlling the dosage of phosphogypsum, a denser and more stable microstructure can be formed in solidified engineering waste materials. The optimal dosage of phosphogypsum is approximately 30% of the cement mass. Compared to traditional methods, this can increase the yield stress by 70-80% and the unconfined compressive strength by 40-50%. Therefore, the method provided in this application for improving and solidifying waste engineering waste can significantly improve its compressibility and stability. Using the obtained solidified material in the construction of temporary access roads at engineering sites increases waste utilization, reduces processing costs, and the process is simple, resulting in significant environmental and socio-economic benefits.

[0087] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0088] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing non-fired bricks from waste construction waste, characterized in that: Specifically, the following steps are included: Step S1: Select waste construction soil from the site, screen it, and test its moisture content; Step S2: Select waste phosphogypsum, dry it at low temperature, crush it, and sieve it to obtain phosphogypsum particles within a predetermined particle size range. Step S3: Select waste soybean meal and mix it evenly with water, let it stand and filter out the soybean residue to obtain soybean urease solution; Step S4: Grind the urea granules into powder and dissolve them in water to obtain a urea solution; Step S5: Mix the phosphogypsum particles obtained in step S2 with silicate cement to obtain mixture A. Add the engineering waste to mixture A and continue to mix to obtain mixture B. Add water to mixture B to obtain mixture C. The mass ratio of the added phosphogypsum particles, silicate cement, engineering waste and water is 5:15:120:

30. Step S6: Spray the soybean urease solution from step S3 onto the surface of mixture C to obtain mixture D, let it stand for 5-10 hours, then spray the urea solution obtained in step S4 onto the surface of mixture D, let it stand for 24-30 hours to obtain solidified engineering waste soil; the mass ratio of soybean urease solution, urea solution and engineering waste soil in step S5 is 10:50:

120. Step S7: Press the solidified engineering waste obtained in step S6 into shape using a brick press to obtain non-fired bricks.

2. The method for preparing non-fired bricks from waste engineering slag according to claim 1, characterized in that: In step S1, the test ensures that the moisture content of the construction waste soil is 20%-40%.

3. The method for preparing non-fired bricks from waste engineering slag according to claim 1, characterized in that: In step S2, the waste phosphogypsum is dried at 60-65℃ for 72 hours; after crushing, phosphogypsum particles with an average particle size of 0.05 mm-0.15 mm are sieved out.

4. The method for preparing non-fired bricks from waste engineering slag according to claim 1, characterized in that: In step S3, the waste soybean meal selected is waste yellow soybean meal, the mass ratio of soybean meal to water is 1:10-1:80, and the standing time is 5-10 hours.

5. The method for preparing non-fired bricks from waste engineering slag according to claim 1, characterized in that: In step S4, the mass ratio of urea to water is 1:5 to 1:

20.

6. The method for preparing non-fired bricks from waste engineering slag according to claim 1, characterized in that: In step S5, the selected silicate cement is silicate cement with the grade PO 42.5; the moisture content of the solidified engineering slag is between 40% and 60%; and the moisture content of mixture C is between 40% and 60%.

7. The method for preparing non-fired bricks from waste engineering slag according to claim 1, characterized in that: In step S7, the compression molding pressure is 10-20 MPa.

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