Self-sensing lightweight phosphogypsum aggregate and preparation method thereof

Abstract

This invention provides a self-sensing lightweight phosphogypsum aggregate and its preparation method, belonging to the field of building materials. The self-sensing lightweight phosphogypsum aggregate of this invention comprises a phosphogypsum core and a conductive flexible coating encapsulating the surface of the phosphogypsum core. The raw materials of the phosphogypsum core include phosphogypsum and conductive fibers at a mass percentage of 1% to 5%. The raw materials of the conductive flexible coating include polyurethane elastomer, conductive fillers at a mass percentage of 1% to 10%, and conductive fibers at a mass percentage of 2% to 5%. This invention utilizes the ability of phosphogypsum to react with cement to generate high-sulfur hydrated calcium sulfoaluminate, and incorporates a certain amount of conductive fibers, admixtures, polymers, etc., to prepare lightweight aggregate with internal curing and self-sensing effects, solving the problems of difficult utilization of phosphogypsum and poor sensing accuracy and high cost of self-sensing aggregates.

Description

Technical Field

[0001] This invention belongs to the field of building materials, specifically relating to a self-sensing internal curing lightweight phosphogypsum aggregate and its preparation method. Background Technology

[0002] With the rapid development and widespread adoption of computer technology, information technology has laid the foundation for intelligent building. The construction industry is increasingly applying computer technology to building design, construction management, and operation and maintenance. Simultaneously, big data analytics and cloud computing technologies enable real-time monitoring and optimized management of building operation, playing a crucial role in self-sensing concrete. Self-sensing concrete is applied to various building structures, such as bridges, buildings, tunnels, and critical infrastructure projects. It helps engineers and architects better monitor structural health, promptly identify potential problems, and improve structural safety and reliability. This relies on the development of sensor technology, IoT technology, big data, and cloud computing, as well as the increasing demand for building structural safety and sustainability. Utilizing a built-in sensor network, these sensors can monitor physical parameters of the concrete structure, such as stress, strain, temperature, and humidity. Sensor signals can be transmitted wirelessly or wired to a data acquisition system for real-time monitoring and analysis.

[0003] Despite the immense potential of self-sensing concrete, several challenges remain. First, traditional coarse aggregates are typically non-conductive, creating a barrier to conductive pathways in self-sensing concrete. To overcome this, researchers have attempted to use conductive aggregates, such as iron ore. However, the coarse electrical signals from these aggregates may affect sensing accuracy, as the introduced conductivity may be insufficiently uniform or stable. Second, currently, self-sensing concrete is primarily used to detect crack initiation patterns, a crucial application in structural health monitoring. However, this sensing capability is relatively limited, as it mainly focuses on crack formation and propagation, potentially failing to detect other types of damage, such as corrosion or fatigue. Third, the cost of self-sensing concrete is currently relatively high, mainly due to its specialized materials and manufacturing processes. Furthermore, the production of self-sensing concrete often results in the loss of solid waste, limiting its application in the field of sustainable building materials.

[0004] With the acceleration of modernization and continuous industrial development, the amount of industrial solid waste is increasing year by year. Due to poor management or a lack of effective treatment facilities, industrial solid waste is often directly landfilled or incinerated, which not only wastes resources but also pollutes the environment. Phosphogypsum is a common type of industrial solid waste, which may contain radioactive elements and heavy metals, and improper handling can cause environmental pollution. The proper treatment of phosphogypsum requires advanced technology and equipment, making it difficult to process and resulting in widespread low-value applications. Therefore, this patent utilizes the ability of phosphogypsum to react with cement to generate high-sulfur hydrated calcium sulfoaluminate, and incorporates a certain amount of conductive fibers, additives, polymers, etc., to prepare lightweight aggregates with internal curing and self-sensing effects, solving the problems of difficult utilization of phosphogypsum and poor sensing accuracy and high cost of self-sensing aggregates. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a novel functional self-sensing lightweight aggregate and its preparation method, which addresses the above-mentioned shortcomings. The self-sensing lightweight aggregate of this invention can not only provide basic strength for concrete, but also has multiple functional characteristics such as lightweight, internal curing, and self-sensing. It can sense the formation and expansion of cracks and also has self-sensing performance for other types of damage.

[0006] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0007] In one aspect, the present invention provides a self-sensing lightweight phosphogypsum aggregate, comprising a phosphogypsum core and a conductive flexible coating covering the surface of the phosphogypsum core; the raw materials of the phosphogypsum core include phosphogypsum and conductive fibers with a mass percentage of 1% to 5%, and the raw materials of the conductive flexible coating include polyurethane elastomer, conductive filler with a mass percentage of 1% to 10%, and conductive fibers with a mass percentage of 2% to 5%.

[0008] This invention adds a specific proportion of conductive fibers to both the core and the conductive flexible coating of a self-sensing lightweight phosphogypsum aggregate, along with a specific amount of conductive filler in the conductive flexible coating, to form a special mesh-like conductive pathway structure—a conductive network. This network not only effectively connects the core and the conductive flexible coating, enhancing the interfacial bonding strength and ensuring the basic strength of the concrete, but also further strengthens the conductive pathways of the concrete, improving the sensitivity of electrical signal transmission. This makes it easier to identify and sense the formation and propagation of concrete cracks, and also allows the concrete to sense different levels of external force, deformation, drying, and whether the external concrete is cracked. This enables the concrete to have self-sensing properties for stress, strain, and fatigue damage under different loads.

[0009] Based on the above technical solution, the conductive fibers in the phosphogypsum core are the same type and function as the conductive fibers in the conductive flexible coating.

[0010] Based on the above technical solution, the conductive fiber is one or a combination of stainless steel fiber, conductive aramid fiber, and semi-carbonized polyacrylonitrile fiber, with a resistivity of 10 Ω·cm. -2 ~10 -4 Ω·cm, fiber diameter 0.2~0.6mm, fiber length 2~5mm.

[0011] Based on the above technical solution, the self-sensing lightweight aggregate has a particle size of 10-20 mm, wherein the core particle size of the self-sensing lightweight aggregate is 8-18 mm, and the thickness of the conductive flexible coating of the self-sensing lightweight aggregate is 2-3 mm. The overall bulk density of the self-sensing lightweight aggregate is 800 kg / m³. 3 ~1200kg / m 3 .

[0012] Based on the above technical solution, the raw materials of the phosphogypsum core of the self-sensing lightweight aggregate include phosphogypsum, red mud, fly ash, cement, foaming agent A, and conductive fibers; the raw materials of the conductive flexible coating include polyurethane elastomer, conductive filler, foaming agent B, and conductive fibers.

[0013] Based on the above technical solution, the phosphogypsum is obtained by modifying phosphogypsum powder with quicklime and drying it at 40°C to constant weight. The phosphogypsum, red mud, and fly ash are passed through a 0.15mm square hole sieve.

[0014] Based on the above technical solution, the raw materials of the phosphogypsum core, by weight percentage, include: 50%–55% phosphogypsum, 5%–10% red mud, 5%–10% fly ash, 10%–15% cement, 0.2%–2% foaming agent A, 1%–5% conductive fiber, and 20%–25% water; the raw materials of the conductive flexible coating, by weight percentage, include 86%–93% polyurethane elastomer, 1%–10% conductive filler, 0.2%–1% foaming agent B, and 2%–5% conductive fiber.

[0015] Polyurethane elastomers, as a novel solvent-free and pollution-free green material, possess excellent elasticity, wear resistance, toughness, and corrosion resistance. Compared to elastomers such as polyurea and epoxy resins, polyurethane elastomers, while slightly less hard, exhibit superior elasticity and toughness. Furthermore, the addition of conductive fillers to polyurethane elastomers endows them with a certain degree of conductivity, and the presence of conductive fibers further enhances their ability to conduct electrical signals.

[0016] Based on the above technical solution, the foaming agent A can be a calcium carbonate foaming agent, which can improve its physical properties and reduce density. The main components of calcium carbonate foaming agents are calcium carbonate (CaCO3) and some activators, such as fatty acid salts. In concrete and cement products, calcium carbonate foaming agents reduce the density of materials by releasing gas into the material to form microbubbles and create a closed-cell structure in the product; it can also reduce density, improve thermal insulation performance, improve water absorption performance, improve workability, and has a certain degree of environmental friendliness.

[0017] Based on the above technical solution, the foaming agent B can be dimethyl ether. Dimethyl ether foaming agent is a surfactant-type foaming agent. Dimethyl ether foaming agent can react with polyurethane prepolymer to generate a large amount of gas and cure rapidly.

[0018] Based on the above technical solution, the polyurethane elastomer is formed by spraying an isocyanate component solution (component A) and a hydroxyl compound component solution (component B) using a portable spray gun.

[0019] Based on the above technical solution, the polyurethane elastomer comprises an isocyanate component and a hydroxyl compound component in a weight ratio of 1:(2.5-4). The isocyanate component comprises, by weight percentage: 65%-85% isocyanate and 15%-35% polymer diol. The hydroxyl compound component comprises, by weight percentage: 65%-75% chain extender, 0-5% catalyst, and 20%-30% plasticizer.

[0020] Based on the above technical solution, the isocyanate is one or more combinations of diphenylmethane diisocyanate (MDI), liquefied MDI, toluene diisocyanate (TDI), etc.; the polymer diol is one or more combinations of polyester diol, polycaprolactone diol, etc.; the chain extender is one or more combinations of ethylene glycol, 1,4-butanediol, benzidine, etc.; the catalyst is one or more combinations of triethylamine, triethanolamine, propylenediamine, etc.; and the plasticizer is one or more combinations of dioctyl phthalate, tributyl phosphate, epoxidized polyacrylate, etc.

[0021] Preferably, the conductive filler is one or a combination of carbon black, graphene, and micron-sized indium tin oxide.

[0022] A second aspect of the present invention provides a method for preparing self-sensing lightweight phosphogypsum aggregate, comprising the steps of:

[0023] 1) Mix cement, red mud, phosphogypsum, fly ash, foaming agent A, and conductive fiber according to the specified proportions;

[0024] 2) The mixed powder is fed into a pelletizing machine for water spraying and granulation, then cured and dried to constant weight to produce phosphogypsum cores;

[0025] 3) Place the isocyanate component of the polyurethane elastomer raw material into one cartridge of the spray gun of the spraying machine, and place the conductive filler, foaming agent B, conductive fiber, and the hydroxyl compound component of the polyurethane elastomer raw material into the other cartridge of the spray gun. Then, the air compressor provides power to the spray gun to push the piston forward, pushing the components in the two cartridges into the mixing tube for mixing, and then atomizing and spraying them onto the phosphogypsum core through the nozzle. The process ends when the conductive flexible coating particle size is reached. After water curing, self-sensing lightweight phosphogypsum aggregate is obtained.

[0026] Based on the above technical solution, in step 2), the pelletizing machine is a disc pelletizing machine. The disc pelletizing machine performs water spraying granulation at a speed of 30-45 r / min and an inclination angle of 45-60°. After 3-4 minutes, the pellets are formed to obtain aggregate. Then, the aggregate continues to roll in the pelletizing disc for 5-10 minutes to form the core. The formed aggregate core is placed in a laboratory water tank for curing at a temperature of 20±2℃. After curing for 24 hours, it is dried at 40℃ to constant weight.

[0027] A third aspect of the present invention provides a self-sensing concrete, the raw materials of which include a self-sensing lightweight phosphogypsum aggregate as described in any one of the above claims or a self-sensing lightweight phosphogypsum aggregate prepared by the above method.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] (1) The functional self-sensing lightweight aggregate of the present invention has the characteristics of being lightweight, internally cured, and self-sensing. This is because different foaming agents are added to the core of the aggregate and the conductive flexible coating, which reduces its weight but still maintains a certain strength, thus achieving the effect of being lightweight. At the same time, the aggregate has the characteristics of internal curing and self-sensing, and can sense the level of external force, deformation, drying level, and whether the external concrete is cracked, thereby improving volume stability. Using this aggregate, not only does it have the ability to sense cracking failure, but also, due to the high elasticity of the conductive flexible coating, it enables the concrete to have self-sensing performance in terms of stress, strain, and fatigue damage under compressive (uniaxial, quasi-biaxial, and triaxial, as well as impact, monotonic, and cyclic loading), tensile (uniaxial, splitting tension, monotonic, and cyclic loading), and bending (uniaxial and impact, three-point bending and four-point bending, monotonic, and cyclic loading) loads.

[0030] (2) The addition of conductive fibers to lightweight aggregates can improve the tensile strength of concrete, inhibit crack development, and thus improve load-bearing capacity and ductility. The addition of conductive fibers to aggregates can improve resistivity and bridge cracks internally, thereby improving the brittleness of concrete. The self-sensing lightweight aggregates obtained by the method of this invention have excellent conductivity, heat resistance, and flexibility, and can conduct electrical signals, giving them lightweight and self-sensing characteristics.

[0031] (3) In the core, phosphogypsum will undergo a hydration reaction with cement hydration components to generate high-sulfur hydrated calcium sulfoaluminate, i.e. ettringite, which can provide a certain strength to the aggregate; the pores inside will store a certain amount of water, which is beneficial for providing moisture for the internal curing of the aggregate; the mesh fibers doped in the core overlap with each other, which is beneficial for signal transmission and plays a certain role in dispersing stress, reducing volume deformation, and thus improving the strength and volume stability of the aggregate; the fibers between the core and the conductive flexible coating can play an effective connecting role and enhance the interface connection strength.

[0032] (4) The self-sensing lightweight phosphogypsum aggregate of the present invention contains a special conductive network. Compared with general conductive aggregates, it has better sensitivity in conducting electrical signals. When concrete prepared with it as aggregate is subjected to external stimuli (load and environmental factors), the electrical signals inside it will show a certain regularity. The characteristic electrical signals generated by the deformation of the conductive flexible coating are easier to identify and sense than the electrical signals of general materials. When concrete is subjected to load, the conductive flexible coating of the aggregate will undergo a large deformation. This deformation causes the contact range and contact area of ​​the conductive filler and conductive fiber in the conductive flexible coating to change. The electrical signals presented externally will also change accordingly. For example, when subjected to continuous pressure (without cracks in the concrete), the electrical signal (FCR) shows a slow upward trend. When cracks appear in the concrete, the FCR rises suddenly, and shows different degrees of increase with the increase in the number and width of cracks, until the concrete is destroyed. Thus, the addition of self-sensing lightweight phosphogypsum aggregate enables the concrete to have self-sensing ability.

[0033] (5) For concrete containing the conductive flexible coating phosphogypsum lightweight aggregate of the present invention, it is easier to detect structural changes in concrete, and also enables concrete to be detected and managed more intelligently. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of self-sensing lightweight phosphogypsum aggregate. Detailed Implementation

[0035] The technical solution 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.

[0036] This invention provides a self-sensing lightweight phosphogypsum aggregate, comprising a phosphogypsum core and a conductive flexible coating covering the surface of the phosphogypsum core; the phosphogypsum core is made of phosphogypsum and conductive fibers at a mass percentage of 1% to 5%, and the conductive flexible coating is made of polyurethane elastomer, conductive filler at a mass percentage of 1% to 10%, and conductive fibers at a mass percentage of 2% to 5%.

[0037] In some examples of the present invention, the conductive fiber is one or a combination of stainless steel fiber, conductive aramid fiber, and semi-carbonized polyacrylonitrile fiber, with a resistivity of 10 Ω·cm. -2 ~10 -4 Ω·cm, fiber diameter 0.2~0.6mm, fiber length 2~5mm.

[0038] In some examples of the present invention, the particle size of the self-sensing lightweight aggregate is 10-20 mm, wherein the particle size of the core of the self-sensing lightweight aggregate is 8-18 mm, and the thickness of the conductive flexible coating of the self-sensing lightweight aggregate is 2-3 mm.

[0039] In a specific example of the present invention, the raw materials of the phosphogypsum core, by weight percentage, include: 50%–55% phosphogypsum, 5%–10% red mud, 5%–15% fly ash, 10%–15% cement, 0.2%–2% foaming agent A, 1%–5% conductive fiber, and 20%–25% water; the raw materials of the conductive flexible coating, by weight percentage, include 86%–93% polyurethane elastomer, 1%–10% conductive filler, 0.2%–1% foaming agent B, and 2%–5% conductive fiber.

[0040] In some examples of the present invention, the polyurethane elastomer is formed by spraying an isocyanate component solution (component A) and a hydroxyl compound component solution (component B) using a portable spray gun. The polyurethane elastomer comprises an isocyanate component and a hydroxyl compound component in a weight ratio of 1:(2.5-4). The isocyanate component comprises, by weight percentage: 65%-85% isocyanate and 15%-35% polymer diol. The hydroxyl compound component comprises, by weight percentage: 65%-75% chain extender, 0-5% catalyst, and 20%-30% plasticizer. The isocyanate is one or more of diphenylmethane diisocyanate (MDI), liquefied MDI, toluene diisocyanate (TDI), etc.; the polymer diol is one or more of polyester diol, polycaprolactone diol, etc.; the chain extender is one or more of ethylene glycol, 1,4-butanediol, benzidine, etc.; the catalyst is one or more of triethylamine, triethanolamine, propylenediamine, etc.; the plasticizer is one or more of dioctyl phthalate, tributyl phosphate, epoxidized polyacrylate, etc.

[0041] In some examples of the present invention, the conductive filler is one or more of carbon black, graphene, micron-sized indium tin oxide, etc.

[0042] In some examples of the present invention, the phosphogypsum is obtained by modifying phosphogypsum powder with quicklime and then drying it to constant weight at 40°C.

[0043] This invention also provides a method for preparing self-sensing lightweight phosphogypsum aggregate, comprising the following steps:

[0044] S1. Mix cement, red mud, phosphogypsum, fly ash, foaming agent A, and conductive fiber according to the specified proportions.

[0045] S2. The mixed powder is fed into a pelletizer and water spraying is performed using a disc pelletizer. The rotation speed is 30-45 r / min and the inclination angle is 45-60°. After 3-4 minutes, the pellets are formed to obtain aggregate. Then the aggregate continues to roll in the pelletizing disc for 5-10 minutes to form the core.

[0046] S3. Place the prepared aggregate core in a laboratory water tank for curing at a temperature of 20±2℃. After curing for 24 hours, dry it at 40℃ to constant weight.

[0047] S4. Place the dried aggregate core on a disc-type pelletizer. Then, according to the formula, place polyurethane elastomer component A into one cartridge of the spray gun, and place polyurethane elastomer component B, conductive filler, foaming agent B, and conductive fiber into the other cartridge of the spray gun. Then, the air compressor provides power to the spray gun, pushing the piston forward to push the components in the two cartridges into the mixing tube for mixing. The mixture is then atomized through the atomization switch and sprayed onto the aggregate core through the nozzle. The process ends when the conductive flexible coating particle size is reached.

[0048] S5. The obtained self-sensing lightweight phosphogypsum aggregate is then subjected to water curing as described above.

[0049] Unless otherwise specified, the self-sensing lightweight phosphogypsum aggregates in the following embodiments are all prepared using the above method; in addition, to further illustrate, verify and invent the technical solution, in the following embodiments, the cement type is ordinary Portland cement with a strength grade of 42.5, and the fly ash is grade 1 fly ash; the phosphogypsum is obtained by thoroughly mixing phosphogypsum powder, quicklime and water, allowing it to stand for aging for 24 hours, and then drying it at 40°C to constant weight, wherein the ratio of phosphogypsum powder: quicklime: water = 100:50:1 (mass ratio); the phosphogypsum, red mud and fly ash are passed through a 0.15mm square-hole sieve; the foaming agent A is a calcium salt foaming agent, and the foaming agent... B uses dimethyl ether as a foaming agent; the conductive filler is carbon black; the isocyanate component comprises 75% isocyanate and 25% polymer diol, wherein the isocyanate is diphenylmethane diisocyanate (MDI) and the polymer diol is polyester diol; the hydroxyl compound component comprises 70% chain extender, 5% catalyst, and 25% plasticizer, wherein the chain extender is ethylene glycol; the catalyst is triethylamine; the plasticizer is dioctyl phthalate; the self-sensing lightweight aggregate particle size is 15 mm, wherein the particle size of the self-sensing lightweight aggregate core is 13 mm, and the thickness of the conductive flexible coating of the self-sensing lightweight aggregate is 2 mm. The range of options for the size of the self-sensing lightweight aggregate, the foaming agent, the conductive filler, and the polyurethane elastomer has been listed in the specification, and all self-sensing lightweight phosphogypsum aggregates obtained within the scope of this invention can solve the technical problems of this invention; therefore, the data in the embodiments will not be exhaustive.

[0050] Example 1

[0051] A self-sensing lightweight phosphogypsum aggregate comprises, by weight percentage, the following raw materials for its phosphogypsum core: 52% phosphogypsum, 8% red mud, 5% fly ash, 12% cement, 1% foaming agent A, 2% conductive fiber, and 20% water; the raw materials for the conductive flexible coating comprise, by weight percentage, 90% polyurethane elastomer, 5% conductive filler, 1% foaming agent B, and 4% conductive fiber; the polyurethane elastomer comprises isocyanate and hydroxyl compound components in a weight ratio of 1:3. The conductive fiber is conductive aramid fiber with a resistivity of 10 Ω·cm. -2 Ω·cm, fiber diameter 0.3mm, fiber length 3mm.

[0052] Example 2

[0053] A self-sensing lightweight phosphogypsum aggregate, wherein the raw materials of its phosphogypsum core, by weight percentage, include: 50% phosphogypsum, 5% red mud, 7.5% fly ash, 13% cement, 1.5% foaming agent A, 3% conductive fiber, and 20% water; the raw materials of the conductive flexible coating, by weight percentage, include 86% polyurethane elastomer, 10% conductive filler, 0.2% foaming agent B, and 3.8% conductive fiber; the polyurethane elastomer comprises isocyanate and hydroxyl compound components in a weight ratio of 1:4. The conductive fiber is semi-carbonized polyacrylonitrile fiber with a resistivity of 10 Ω·cm. -2 Ω·cm, fiber diameter 0.2mm, fiber length 4mm.

[0054] Example 3

[0055] A self-sensing lightweight phosphogypsum aggregate, wherein the raw materials of its phosphogypsum core, by weight percentage, comprise: 55% phosphogypsum, 5% red mud, 5% fly ash, 10% cement, 0.2% foaming agent A, 1% conductive fiber, and 23.8% water; the raw materials of the conductive flexible coating, by weight percentage, comprise: 92% polyurethane elastomer, 3% conductive filler, 0.5% foaming agent B, and 4.5% conductive fiber; the polyurethane elastomer comprises isocyanate and hydroxyl compound components in a weight ratio of 1:2.5. The conductive fiber is stainless steel fiber with a resistivity of 10 Ω·cm. -4 Ω·cm, fiber diameter 0.6mm, fiber length 5mm.

[0056] Comparative Example 1

[0057] A self-sensing lightweight phosphogypsum aggregate, which is basically the same as in Example 1, except that the conductive fibers in the core are replaced with an equal amount of conductive filler.

[0058] Comparative Example 2

[0059] A self-sensing lightweight phosphogypsum aggregate, which is basically the same as in Example 1, uses an equal amount of conductive filler to replace the conductive fibers in the core and the conductive flexible coating.

[0060] Comparative Example 3

[0061] A self-sensing lightweight phosphogypsum aggregate, which is basically the same as in Example 1, uses an equal amount of conductive fibers to replace the conductive filler in the conductive flexible coating.

[0062] Comparative Example 4

[0063] A self-sensing lightweight phosphogypsum aggregate, which is basically the same as in Example 1, has all the conductive fibers in the conductive flexible coating added to the core.

[0064] Comparative Example 5

[0065] Commercially available lightweight core-shell phosphogypsum aggregate (without self-sensing properties) has a bulk density of 871 kg / m³. 3 .

[0066] Test case

[0067] Density and compressive strength of the self-sensing lightweight phosphogypsum aggregates in Examples 1-3 and Comparative Examples 1-5 were tested. Density testing followed the bulk density test method in "Lightweight Aggregates and Their Test Methods Part 2: Lightweight Aggregates Test Methods" (GB 17431.2-2010-T). Compressive strength testing followed the cylinder method for determining lightweight coarse aggregate particle size in "Lightweight Aggregates and Their Test Methods Part 2: Lightweight Aggregates Test Methods" (GB17431.2-2010-T). The results are shown in Table 1.

[0068] Table 1. Density and compressive strength tests of self-sensing lightweight phosphogypsum aggregate.

[0069]

[0070] The self-sensing lightweight phosphogypsum aggregate of this invention has a density grade of 800, which is higher than that of lightweight aggregate of the same grade.

[0071] Self-sensing concrete was prepared using self-sensing lightweight phosphogypsum aggregates from Examples 1-3 and Comparative Examples 1-4. The raw materials for the concrete included: 450 kg / m³ of cement. 3 150 kg / m³ of fly ash 3 Silica fume 150kg / m 3 Self-sensing lightweight phosphogypsum aggregate 650kg / m³ 3 Fine aggregate 300kg / m³ 3 Conductive filler 40kg / m 3 Water-reducing agent 30kg / m 3Water 289kg / m 3 The preparation method of the above-mentioned self-sensing lightweight phosphogypsum aggregate concrete includes the following steps:

[0072] (1) Add fine aggregate, cement, silica fume and fly ash to a concrete mixer and premix for 2 minutes;

[0073] (2) Pour in the self-sensing lightweight phosphogypsum aggregate and stir for 2 minutes;

[0074] (3) Pour in water and water-reducing agent and stir for 3 minutes;

[0075] (4) After the mixture in the mixing pot reaches a viscous state, add the conductive filler evenly and continue stirring for 2 minutes;

[0076] (5) After the fresh concrete leaves the mixing pot, it is molded, vibrated and shaped, and the surface is covered with a waterproof film. It is cured under the standard conditions specified in GB / T 50081. After 1 day, the mold is removed and standard curing is carried out.

[0077] Four-point bending test and resistance measurement experiment were performed on the specimen, and the collected data were processed and analyzed.

[0078]

[0079] Where R t Rt is the resistance of the specimen measured at time t0, and R0 is the initial resistance of the concrete beam at time t0 before loading.

[0080]

[0081] in, COD The crack opening displacement change value (mm) is the value of the crack opening displacement. FCR This represents the increment (%) of the corresponding rate of change in resistance.

[0082] The test results are shown in Table 2:

[0083] Table 2 Self-sensing performance test of self-sensing lightweight phosphogypsum aggregate concrete

[0084]

[0085] Compared to the comparative examples, the self-sensing lightweight phosphogypsum aggregate concrete prepared by this invention exhibits more sensitive electrical signals, making it easier to identify and perceive the formation and propagation of concrete cracks. This is mainly because the combined use of conductive filler and conductive fibers in Example 1 improves the internal conductive network of the concrete. Since the conductive filler is sensitive to changes in microstructure, and the conductive fibers resist and conduct macroscopic deformation, their synergy enhances the concrete's sensitivity to stress and strain. Even when the concrete is subjected to small external forces or when its internal structure begins to change, significant changes in electrical signals are generated. Compared to comparative examples 1-4, this allows for earlier detection of internal concrete damage and makes it easier to identify the generation and development of concrete cracks, demonstrating superior crack detection performance.

[0086] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A self-sensing lightweight phosphogypsum aggregate, characterized in that, It includes a phosphogypsum core and a conductive flexible coating wrapped around the surface of the phosphogypsum core; the raw materials of the phosphogypsum core include phosphogypsum, red mud, fly ash, cement, foaming agent A and conductive fibers with a mass percentage of 1% to 5%; the raw materials of the conductive flexible coating include polyurethane elastomer, foaming agent B, conductive filler with a mass percentage of 1% to 10% and conductive fibers with a mass percentage of 2% to 5%.

2. The self-sensing lightweight phosphogypsum aggregate according to claim 1, characterized in that, The conductive fiber is one or a combination of stainless steel fiber, conductive aramid fiber, and semi-carbonized polyacrylonitrile fiber, with a resistivity of 10 Ω·cm. -2 ~10 -4 Ω·cm, fiber diameter 0.2~0.6mm, fiber length 2~5mm.

3. The self-sensing lightweight phosphogypsum aggregate according to claim 1, characterized in that, The self-sensing lightweight phosphogypsum aggregate has a particle size of 10-20 mm, wherein the core particle size of the self-sensing lightweight phosphogypsum aggregate is 8-18 mm, and the thickness of the conductive flexible coating of the self-sensing lightweight phosphogypsum aggregate is 2-3 mm.

4. The self-sensing lightweight phosphogypsum aggregate according to claim 1, characterized in that, The raw materials of the phosphogypsum core, by weight percentage, include: 50%–55% phosphogypsum, 5%–10% red mud, 5%–10% fly ash, 10%–15% cement, 0.2%–2% foaming agent A, 1%–5% conductive fiber, and 20%–25% water; the raw materials of the conductive flexible coating, by weight percentage, include 86%–93% polyurethane elastomer, 1%–10% conductive filler, 0.2%–1% foaming agent B, and 2%–5% conductive fiber.

5. The self-sensing lightweight phosphogypsum aggregate according to claim 1, characterized in that, The polyurethane elastomer comprises an isocyanate component and a hydroxyl compound component in a weight ratio of 1:(2.5-4). The isocyanate component comprises, by weight percentage: 65%-85% isocyanate and 15%-35% polymer diol. The hydroxyl compound component comprises, by weight percentage: 65%-75% chain extender, 0-5% catalyst, and 20%-30% plasticizer.

6. The self-sensing lightweight phosphogypsum aggregate according to claim 5, characterized in that, The isocyanate is one or more of diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI); the polymer diol is a polyester diol; the chain extender is one or more of ethylene glycol, 1,4-butanediol, and benzidine; the catalyst is one or more of triethylamine, triethanolamine, and propylenediamine; and the plasticizer is one or more of dioctyl phthalate, tributyl phosphate, and epoxidized polypropylene ester.

7. The self-sensing lightweight phosphogypsum aggregate according to claim 1, characterized in that, The conductive filler is one or more of carbon black, graphene, and micron-sized indium tin oxide.

8. The self-sensing lightweight phosphogypsum aggregate according to claim 1, characterized in that, The phosphogypsum is obtained by modifying phosphogypsum powder with quicklime and drying it to constant weight. The phosphogypsum, red mud, and fly ash are passed through a 0.15mm square hole sieve.

9. The method for preparing a self-sensing lightweight phosphogypsum aggregate as described in claim 1, characterized in that, Including the following steps: 1) Mix cement, red mud, phosphogypsum, fly ash, foaming agent A, and conductive fiber according to the specified proportions; 2) The mixed powder is fed into a pelletizing machine for water spraying and granulation, then cured and dried to constant weight to produce phosphogypsum cores; 3) The isocyanate component of the polyurethane elastomer is placed in one cartridge of the spray gun of the spraying machine, and the conductive filler, foaming agent B, conductive fiber, and the hydroxyl compound component of the polyurethane elastomer are placed in the other cartridge of the spray gun. Then, the air compressor provides power to the spray gun to push the piston forward, pushing the components in the two cartridges into the mixing tube for mixing, and then atomizing and spraying them onto the phosphogypsum core through the nozzle. The process ends when the conductive flexible coating particle size is reached. After water curing, a self-sensing lightweight phosphogypsum aggregate is obtained. The isocyanate component includes isocyanate and polymer diol, and the hydroxyl compound component includes chain extender, catalyst, and plasticizer.

10. A self-sensing concrete, characterized in that, The raw materials include a self-sensing lightweight phosphogypsum aggregate as described in any one of claims 1-8 or a self-sensing lightweight phosphogypsum aggregate prepared by the method described in claim 9.

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