High-strength dry-mixed mortar for tailings sand resource utilization and preparation method thereof

Abstract

The application relates to the technical field of building materials, and discloses a tailing sand resource utilization type high-strength dry-mixed mortar and a preparation method thereof, which comprises the following components by weight: tailing sand 50-70 parts, cementing material 18-28 parts, mineral admixture 5-10 parts, re-dispersible latex powder 1-2 parts, defoaming agent 0.1-0.3 parts, polycarboxylic acid type high-performance water reducing agent 0.1-0.35 parts, hydroxypropyl methyl cellulose ether 0.05-0.2 parts, organic silicon water repellent 0.05-0.15 parts, wood fiber 0.1-0.4 parts, polypropylene short fiber 0.05-0.15 parts, air entraining agent 0.005-0.02 parts and auxiliary aggregate 1-5 parts. The dry-mixed mortar is prepared by using industrial solid wastes such as iron tailing sand, copper tailing sand and molybdenum tailing sand as main fine aggregate, tailing sand is realized in bulk absorption and high-value utilization, and the dry-mixed mortar has excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and more specifically, to a high-strength dry-mixed mortar for the resource utilization of tailings sand and its preparation method. Background Technology

[0002] With the continuous advancement of infrastructure construction and the expansion of mining scale in my country, the annual discharge of tailings of metals such as iron, copper, and molybdenum has been steadily increasing. The long-term stockpiling of large quantities of tailings not only occupies significant land resources but also easily leads to environmental and safety hazards such as dust pollution, water seepage, and slope instability. The large-scale, high-value resource utilization of tailings has become a critical issue that the industry urgently needs to address. At the same time, the demand for dry-mixed mortar in the construction engineering sector is rising year by year. Traditional dry-mixed mortar mainly uses natural river sand as fine aggregate. Long-term large-scale mining has led to the depletion of river sand resources, supply shortages, and significant price fluctuations. Furthermore, the poor gradation stability of natural sand directly affects the construction performance and mechanical properties of the mortar, which is incompatible with the current development concepts of green, low-carbon, ecological, environmentally friendly, and sustainable resource utilization.

[0003] Although some studies have attempted to use tailings sand as aggregate in the preparation of building mortar, existing technologies generally suffer from insufficient applicability and poor overall performance. Tailings sand particles are typically irregular in morphology, have high surface roughness, unreasonable primary gradation, and high mud and impurity content. Direct use in mortar easily leads to poor workability, easy bleeding and segregation, and low density, making it difficult to meet the performance requirements of high-strength mortar. Relying solely on cement as a single cementitious component not only results in high cement consumption, high heat of hydration, and high carbon emissions, but also easily leads to high shrinkage during the mortar hardening process, slow early strength gain, and problems such as shrinkage cracking and insufficient bonding strength in the later stages. At the same time, existing admixture systems are mostly single-function additives, and their functions such as water retention, thickening, water reduction, water repellency, and crack resistance are difficult to work synergistically. They are not well matched with tailings sand-based cementitious systems, easily causing phenomena such as segregation, hollowing, poor water resistance, and unstable strength. In addition, traditional dry-mixed mortar preparation processes are mostly simple physical blending processes, resulting in uneven dispersion of various admixtures, easy agglomeration, difficulty in ensuring product uniformity, and insufficient construction performance and quality stability, which cannot meet the needs of continuous and stable industrial production.

[0004] Constrained by the above factors, current tailings sand-based mortars generally suffer from low mechanical strength, poor volume stability, insufficient impermeability, frost resistance, and durability. This makes it difficult to meet the comprehensive requirements for high strength, low shrinkage, high bonding, crack resistance, and long service life in scenarios such as building masonry, interior and exterior wall plastering, wear-resistant flooring, and structural repair. This greatly limits the large-scale and high-value application of tailings sand in high-quality dry-mixed mortars.

[0005] Based on this, a green high-strength dry-mixed mortar that can achieve large-scale tailings disposal, replace natural sand and gravel, has excellent comprehensive performance, and has a simple and stable preparation process is provided. This is of great practical significance for promoting the resource utilization of solid waste, reducing resource consumption and carbon emissions in the building materials industry, and improving the quality of construction projects. Summary of the Invention

[0006] In view of this, the present invention proposes a high-strength dry-mixed mortar for the resource utilization of tailings sand and its preparation method, aiming to solve at least one of the current background technical problems.

[0007] This invention proposes a high-strength dry-mixed mortar for the resource utilization of tailings sand, comprising the following components in parts by weight: Tailings sand 50-70 parts, cementitious material 18-28 parts, mineral admixture 5-10 parts, redispersible latex powder 1-2 parts, defoamer 0.1-0.3 parts, polycarboxylate-based high-performance water-reducing agent 0.1-0.35 parts, hydroxypropyl methylcellulose ether 0.05-0.2 parts, organosilicon water-repellent agent 0.05-0.15 parts, wood fiber 0.1-0.4 parts, polypropylene short fiber 0.05-0.15 parts, air-entraining agent 0.005-0.02 parts, auxiliary aggregate 1-5 parts.

[0008] Preferably, the tailings sand is one or a mixture of iron tailings sand, copper tailings sand, and molybdenum tailings sand; The tailings sand is composed of different particle size ranges, specifically: tailings sand <0.075mm accounts for 8%-12%, tailings sand 0.075-0.150mm accounts for 8%-12%, tailings sand 0.150-0.300mm accounts for 45%-55%, and tailings sand 0.300-0.600mm accounts for 25%-35%.

[0009] Preferably, the cementitious material is at least one of ordinary Portland cement with a strength grade of 42.5, ordinary Portland cement with a strength grade of 52.5, or slag Portland cement.

[0010] Preferably, the mineral admixture is one or more of fly ash, slag powder, and silica fume; the auxiliary aggregate is one or more of manufactured sand, slag, and lightweight aggregate, with a particle size range of 0.6-2.36 mm.

[0011] Preferably, the redispersible latex powder is an ethylene-vinyl acetate copolymer latex powder; the organosilicon hydrophobic agent is sodium methylsilicate or potassium methylsilicate, with a solid content ≥30%.

[0012] Preferably, the wood fibers have a length of 0.5-3 mm and an ash content of ≤10%; the polypropylene short fibers have a diameter of 10-20 μm and a length of 6-12 mm.

[0013] Preferably, the air-entraining agent is a triterpenoid saponin air-entraining agent, a rosin thermal polymer air-entraining agent, or an alkylbenzene sulfonate air-entraining agent, and the defoamer is an organosilicon defoamer or a polyether defoamer.

[0014] This invention also provides a method for preparing high-strength dry-mixed mortar for the resource utilization of tailings sand as described in the above technical solution, comprising the following steps: (1) The tailings sand is dried and screened to remove impurities, and then compounded according to the preset particle size distribution to obtain pretreated tailings sand; (2) The cementitious materials, mineral admixtures, redispersible latex powder, wood fiber, and polypropylene short fiber are mixed in the first step to obtain a premixed base material; (3) The polycarboxylate superplasticizer, hydroxypropyl methylcellulose ether, organosilicon water-repellent agent, defoamer, air-entraining agent and 1-2 parts of auxiliary aggregate are mixed for a second time to obtain an admixture predispersion; (4) The pretreated tailings sand, the remaining auxiliary aggregate, and the premixed base material obtained in step (1) are mixed for the third time. After the mixture is evenly mixed, the additive predispersant obtained in step (3) is added and the mixture is stirred for 3-5 minutes to obtain the mixture. (5) Place the mixture at a temperature of 15-30℃ and a relative humidity of ≤40% and let it stand for 12-24 hours to age; (6) The aged material obtained in step (5) is passed through a vibrating screen to remove agglomerates, and the tailings sand resource utilization type high-strength dry-mixed mortar is obtained.

[0015] Preferably, the conditions for the first mixing are: using a double cone premixer or a V-type mixer, a mixing speed of 15-30 r / min, a mixing time of 3-8 minutes, and a mixing temperature controlled at 25-40℃; The conditions for the second mixing are: using a high-speed disperser, a dispersion speed of 800-1200 r / min, a dispersion time of 2-4 minutes, and a dispersion temperature of 20-35℃; The conditions for the third mixing are as follows: a planetary forced mixer or a twin-shaft paddle mixer is used, the stirring linear speed is 2-5 m / s, the mixing time is 4-6 minutes, the material temperature is 30-50℃ during the mixing process, and the material is dry-mixed for 2-3 minutes before the mixing begins, and then the additive pre-dispersion is added and the mixing continues.

[0016] The present invention also provides an application of the tailings sand resource utilization type high-strength dry-mixed mortar described in the above technical solution, specifically its application in building masonry mortar, plastering mortar, floor mortar or repair mortar.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses industrial solid waste such as iron tailings sand, copper tailings sand, and molybdenum tailings sand as the main fine aggregates, realizing the large-scale disposal and high-value utilization of tailings sand, significantly reducing the dependence on the mining of natural river sand, which is conducive to alleviating the problems of land occupation, environmental pollution and ecological damage caused by tailings stockpiling, and is in line with the green, low-carbon and sustainable development building materials industry policy.

[0018] (2) The present invention achieves excellent mechanical properties by using precise gradation and compounding of tailings sand, synergistic optimization of cementitious materials and mineral admixtures, and water-reducing and enhancing effects of polycarboxylate high-performance water-reducing agent. This can meet the engineering requirements of high strength and high bonding performance in masonry, plastering, flooring and repair scenarios.

[0019] (3) This invention significantly improves the water retention and workability of mortar by compounding functional components such as hydroxypropyl methylcellulose ether, wood fiber, polypropylene short fiber and air-entraining agent. At the same time, the three-dimensional network reinforcement structure formed by wood fiber and polypropylene short fiber can effectively inhibit plastic shrinkage and drying shrinkage, effectively reducing the risk of mortar cracking and hollowing.

[0020] (4) The present invention incorporates organosilicon hydrophobic agent and air-entraining agent, which makes the mortar form a uniform and stable closed microporous structure and hydrophobic film layer, eliminating the risk of steel reinforcement corrosion. At the same time, it has good freeze-thaw resistance and water resistance, extending the service life of building structures. It is especially suitable for humid environments, coastal projects and parts with high requirements for waterproofing and seepage prevention. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0022] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0024] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0025] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0026] This invention provides a high-strength dry-mixed mortar for the resource utilization of tailings sand, preferably comprising the following components in parts by weight: Tailings sand 50-70 parts, cementitious material 18-28 parts, mineral admixture 5-10 parts, redispersible latex powder 1-2 parts, defoamer 0.1-0.3 parts, polycarboxylate-based high-performance water-reducing agent 0.1-0.35 parts, hydroxypropyl methylcellulose ether 0.05-0.2 parts, organosilicon water-repellent agent 0.05-0.15 parts, wood fiber 0.1-0.4 parts, polypropylene short fiber 0.05-0.15 parts, air-entraining agent 0.005-0.02 parts, auxiliary aggregate 1-5 parts.

[0027] In this invention, the tailings sand is preferably one or a mixture of iron tailings sand, copper tailings sand, and molybdenum tailings sand; The tailings sand is preferably composed of different particle size ranges, specifically: tailings sand <0.075mm accounts for 8%-12%, tailings sand 0.075-0.150mm accounts for 8%-12%, tailings sand 0.150-0.300mm accounts for 45%-55%, and tailings sand 0.300-0.600mm accounts for 25%-35%.

[0028] Tailings sand, as a major fine aggregate in mortar, can be used to dispose of large quantities of industrial solid waste such as iron, copper, and molybdenum, replacing natural river sand and reducing resource consumption and material costs. After screening, impurity removal, and gradation optimization, tailings sand can form a continuous and dense particle skeleton, effectively improving the volume stability, mechanical strength, and wear resistance of mortar. At the same time, the rough surface of its particles can enhance the interfacial bonding with the cementitious paste, improving the overall density and bonding performance of the structure, and providing a stable supporting skeleton and high-strength foundation for the mortar.

[0029] In this invention, the cementitious material is preferably at least one of ordinary Portland cement with a strength grade of 42.5, ordinary Portland cement with a strength grade of 52.5, or slag Portland cement.

[0030] The cementitious material of this invention is the core of the mortar system's strength. It is mainly composed of 42.5 or 52.5 grade silicate cement and slag silicate cement. Through hydration reaction, it generates a large amount of hydrated calcium silicate and ettringite, firmly binding the aggregates into a whole, ensuring rapid early strength development and continuous strength growth in the later stages of the mortar. A reasonable amount of cementitious material can give the mortar sufficient compressive, flexural, and bond strength, meeting the high strength and high stability requirements of masonry, plastering, and flooring projects. Simultaneously, it is compatible with the characteristics of tailings sand aggregate, improving the density of the interface transition zone.

[0031] In this invention, the mineral admixture is preferably one or more of fly ash, slag powder, and silica fume; the auxiliary aggregate is preferably one or more of manufactured sand, slag, and lightweight aggregate, with a particle size range of 0.6-2.36 mm.

[0032] The mineral admixtures of this invention include fly ash, slag powder, silica fume, etc., and possess excellent activity effects, micro-aggregate filling effects, and morphology effects. They can partially replace cement and optimize the gradation of the cementitious system. Their fine particles can fill the pores between cement paste and aggregates, increasing mortar density and reducing the risk of shrinkage and cracking. The active components can undergo secondary hydration reactions with cement hydration products, improving later-stage strength and durability, while reducing heat of hydration, minimizing internal defects, and significantly improving the mortar's impermeability, freeze-thaw resistance, and corrosion resistance.

[0033] The auxiliary aggregates of this invention include manufactured sand, lightweight aggregates, etc., used to further optimize the overall particle size distribution of mortar, adjust bulk density and workability, and compensate for local gradation deficiencies in tailings sand. It can improve mortar density, strength, and abrasion resistance, enhance workability, and adapt to the diverse requirements of different projects for fluidity, strength, and abrasion resistance, making the mortar suitable for various applications such as masonry, plastering, flooring, and repair.

[0034] In this invention, the redispersible latex powder is preferably ethylene-vinyl acetate copolymer latex powder; the organosilicon hydrophobic agent is preferably sodium methylsilicate or potassium methylsilicate, with a solid content ≥30%.

[0035] The redispersible latex powder of this invention is mainly composed of ethylene-vinyl acetate copolymer. After mortar is mixed with water, it can be redispersed into an emulsion. During the hardening process, it forms a film that penetrates the cement stone structure, creating a flexible network structure. This component can significantly improve the bonding strength, flexibility, and impact resistance of mortar, improve the bond between mortar and the wall substrate, reduce brittle cracking of the hardened body, and at the same time improve the water resistance, alkali resistance, and workability of mortar. It is especially suitable for exterior wall plastering and engineering scenarios with high adhesion requirements.

[0036] The organosilicon hydrophobic agent of this invention is mainly composed of sodium methylsilicate and potassium methylsilicate. After incorporation, it forms a hydrophobic film on the pore walls inside the mortar, reducing the surface tension of the system and significantly decreasing water absorption and moisture absorption. It effectively prevents moisture intrusion, improves the mortar's impermeability, water resistance, and freeze-thaw resistance, reduces salt precipitation, efflorescence, and frost heave damage, extends the service life of the mortar in humid, freeze-thaw, and coastal high-salt and high-humidity environments, and enhances its durability and stability.

[0037] In this invention, the length of the wood fiber is preferably 0.5-3 mm and the ash content is ≤10%; the diameter of the polypropylene short fiber is preferably 10-20 μm and the length is preferably 6-12 mm.

[0038] The wood fibers of this invention possess high dispersibility and a network structure, enabling them to form a spatial network in mortar. This enhances water retention, resistance to wall adhesion, and resistance to plastic cracking, while inhibiting shrinkage cracks in the mortar during the plasticization and drying stages. Simultaneously, it improves workability, reduces bleeding and segregation, and increases the uniformity and stability of the mixture, significantly improving the workability and appearance quality of plastering mortar.

[0039] The polypropylene short fibers of this invention are uniformly distributed in a randomized manner in the mortar, forming a three-dimensional micro-reinforcement system. This system effectively disperses stress, prevents the initiation and propagation of microcracks, and significantly improves the crack resistance, impact resistance, and toughness of the mortar. It can reduce drying shrinkage and autogenous shrinkage, reduce the risk of cracking in the hardened body, and improve volume stability. It is especially suitable for applications such as flooring, repairs, and exterior walls where crack resistance and impact resistance are required.

[0040] In this invention, the air-entraining agent is preferably a triterpenoid saponin air-entraining agent, a rosin thermal polymer air-entraining agent, or an alkylbenzene sulfonate air-entraining agent, and the defoamer is preferably an organosilicon defoamer or a polyether defoamer.

[0041] The air-entraining agent of this invention can introduce a large number of uniform, stable, and closed microbubbles, improving the workability and fluidity of mortar, reducing frictional resistance between aggregates, and lowering the risks of bleeding, segregation, and caking. The microbubbles can release frost heave pressure, improving the mortar's frost resistance and impermeability, while also improving its adaptability to low-temperature construction, ensuring good workability and durability even under complex climatic conditions.

[0042] The defoamer of this invention is mainly composed of organosilicon or polyether, which can effectively suppress and eliminate large and harmful air bubbles generated during mortar mixing and construction, avoiding internal defects such as pores, voids, and pitting. By reducing interconnected pores and large-diameter pores, the density, mechanical strength, and surface smoothness of the mortar can be significantly improved, while reducing the risk of bleeding and segregation, ensuring that the admixtures play their full role, and making the internal structure of the mortar uniform and stable, which is beneficial to improving strength, impermeability, and durability.

[0043] The present invention also provides a method for preparing high-strength dry-mixed mortar for the resource utilization of tailings sand as described in the above technical solution, preferably comprising the following steps: (1) The tailings sand is dried and screened to remove impurities, and then compounded according to the preset particle size distribution to obtain pretreated tailings sand; The preferred specific step is as follows: Iron tailings, copper tailings, or molybdenum tailings are fed into a drum dryer and dried at 105℃-115℃ until the moisture content is ≤1.0%. The dried tailings are then sieved through a multi-stage vibrating screen to separate four particle sizes: <0.075mm, 0.075-0.150mm, 0.150-0.300mm, and 0.300-0.600mm, while removing impurities such as stones, grass roots, and soil clumps. The tailings are then precisely blended according to the following mass ratios: <0.075mm accounts for 8%-12%, 0.075-0.150mm accounts for 8%-12%, 0.150-0.300mm accounts for 45%-55%, and 0.300-0.600mm accounts for 25%-35%. After thorough mixing, a pre-treated tailings with stable gradation and continuous particle size is obtained for later use.

[0044] (2) The cementitious materials, mineral admixtures, redispersible latex powder, wood fiber, and polypropylene short fiber are mixed in the first step to obtain a premixed base material; The preferred step is to weigh the cementitious material, mineral admixture, redispersible latex powder, wood fiber, and polypropylene short fiber according to the mass fractions, and put them into a double cone premixer or V-type mixer for low-speed mixing; control the mixing speed at 15-30 r / min, the mixing temperature at 25-40℃, and the mixing time at 3-8 minutes to ensure that the powder and fiber components are initially and evenly dispersed, avoid agglomeration, and obtain a well-dispersible premixed base material for later use.

[0045] (3) The polycarboxylate superplasticizer, hydroxypropyl methylcellulose ether, organosilicon water-repellent agent, defoamer, air-entraining agent and 1-2 parts of auxiliary aggregate are mixed for a second time to obtain an admixture predispersion; The preferred specific step is as follows: Weigh out polycarboxylate-based high-performance water-reducing agent, hydroxypropyl methylcellulose ether, organosilicon water-repellent agent, defoamer, and air-entraining agent according to the specified mass fractions, and add 1-2 parts of auxiliary aggregate as a dispersion carrier. Put them into a high-speed disperser together; set the dispersion speed to 800-1200 r / min, the dispersion temperature to 20-35℃, and the dispersion time to 2-4 minutes. Utilize the carrier effect of the auxiliary aggregate to fully disperse and uniformly load the various trace additives, avoiding uneven dispersion and local agglomeration of the additives due to excessively low dosage, and obtain a stable and uniform pre-dispersion of the additives for later use.

[0046] (4) The pretreated tailings sand, the remaining auxiliary aggregate, and the premixed base material obtained in step (1) are mixed for the third time. After the mixture is evenly mixed, the additive predispersant obtained in step (3) is added and the mixture is stirred for 3-5 minutes to obtain the mixture. The preferred specific step is as follows: the pretreated tailings sand, the remaining auxiliary aggregates, and the premixed base material are added together to a planetary forced mixer or a twin-shaft paddle mixer. Initial dry mixing is performed for 2-3 minutes to allow the aggregates and base material to be initially mixed. Then, the pre-dispersion of the additives is added, and the stirring linear speed is controlled at 2-5 m / s and the material temperature at 30-50°C. Stirring continues for 4-6 minutes, and finally, low-speed homogenization is performed for 1 minute to ensure that all components are completely and evenly mixed in the dry powder state, without segregation, agglomeration, or stratification, resulting in a homogeneous mixture.

[0047] (5) Place the mixture at a temperature of 15-30℃ and a relative humidity of ≤40% and let it stand for 12-24 hours to age; The preferred specific step is to transfer the mixture into a sealed aging chamber, control the temperature inside the chamber to 15-30℃ and the relative humidity to ≤40%, and let it stand for aging for 12-24 hours. The aging process allows the additive components to be further adsorbed and balanced on the powder surface, eliminates the internal stress generated during the mixing process, improves the storage stability of the dry powder and the uniformity after mixing with water, and avoids problems such as rapid thickening, water seepage, and fluctuations in workability during use.

[0048] (6) The aged material obtained in step (5) is passed through a vibrating screen to remove agglomerates, and the tailings sand resource utilization type high-strength dry-mixed mortar is obtained.

[0049] The preferred specific step is as follows: after aging, the material is screened through a 2.36mm standard vibrating screen to remove any possible powder agglomerates and hard particles; the undersize material is the finished high-strength dry-mixed mortar for tailings sand resource utilization; the finished product is then metered, packaged, and sealed for storage to ensure it is kept in a dry environment and to prevent it from getting damp and clumping.

[0050] In this invention, the preferred conditions for the first mixing are: using a double-cone premixer or a V-type mixer, a mixing speed of 15-30 r / min, a mixing time of 3-8 minutes, and a mixing temperature controlled at 25-40℃; The preferred conditions for the second mixing are: using a high-speed disperser, a dispersion speed of 800-1200 r / min, a dispersion time of 2-4 minutes, and a dispersion temperature of 20-35℃; The preferred conditions for the third mixing are: using a planetary forced mixer or a twin-shaft paddle mixer, with a stirring linear velocity of 2-5 m / s, a mixing time of 4-6 minutes, a material temperature of 30-50℃ during the mixing process, and dry mixing for 2-3 minutes before adding the pre-dispersion of the additive and continuing to stir.

[0051] The present invention also provides an application of the tailings sand resource utilization type high-strength dry-mixed mortar described in the above technical solution, specifically its application in building masonry mortar, plastering mortar, floor mortar or repair mortar.

[0052] Example 1 (1) 50 parts of iron tailings sand were fed into a drum dryer and dried at 110°C until the moisture content was ≤1.0%. Then, the sand was screened through a multi-stage vibrating screen to separate four particle sizes: <0.075mm, 0.075–0.150mm, 0.150–0.300mm, and 0.300–0.600mm, to remove impurities such as stones and mud clumps. The sand was then graded and mixed in the following proportions: <0.075mm accounted for 8%, 0.075–0.150mm accounted for 8%, 0.150–0.300mm accounted for 45%, and 0.300–0.600mm accounted for 35%. The mixture was stirred evenly to obtain pretreated tailings sand for later use.

[0053] (2) Mix 18 parts of 42.5 grade ordinary Portland cement, 5 parts of fly ash, and 1 part of ethylene. Vinyl acetate copolymer latex powder, 0.1 parts of wood fiber with a length of 0.5 mm and an ash content of 10%, and 0.05 parts of polypropylene short fiber with a diameter of 10 μm and a length of 6 mm are put into a double cone premixer and mixed for 3 minutes at a speed of 15 r / min and a temperature of 25℃ to fully disperse the powder and fiber without agglomeration, so as to obtain a premixed base material for later use.

[0054] (3) Mix 0.1 parts of polycarboxylate-based high-performance water-reducing agent, 0.05 parts of hydroxypropyl methylcellulose ether, 0.05 parts of sodium methylsilicate water-repellent agent with a solid content of 30%, 0.1 parts of organosilicon defoamer, 0.005 parts of triterpenoid saponin air-entraining agent and 1 part of manufactured sand with a particle size of 0.6 mm and add it to a high-speed disperser. Disperse it for 2 minutes at a speed of 800 r / min and a temperature of 20℃ to make the trace amount of additives uniformly loaded on the surface of the aggregate, and obtain the additive pre-dispersion for later use.

[0055] (4) The pretreated tailings sand and premixed base material are put into a planetary forced mixer and dry-mixed for 2 minutes for preliminary homogenization. Then, the additive predispersant is added and stirred for 4 minutes at a stirring linear speed of 2 m / s and a material temperature of 30°C. Finally, it is homogenized at low speed for 1 minute to make all components completely and uniformly mixed to obtain the mixture.

[0056] (5) Low temperature and low humidity aging: The mixture is transferred into a sealed aging chamber and aged for 12 hours at a temperature of 15℃ and relative humidity of ≤40% to allow the components to fully adsorb and balance, thereby improving the stability of the dry powder and the uniformity of mixing.

[0057] (6) After the screening and aging process is completed, the material is passed through a 2.36mm standard vibrating screen to remove agglomerates and large particles. The material under the screen is the finished product of high-strength dry-mixed mortar for the resource utilization of tailings sand.

[0058] Example 2 (1) 70 parts of copper tailings sand were fed into a drum dryer and dried at 110°C until the moisture content was ≤1.0%. After being classified by a multi-stage vibrating screen, impurities were removed. The tailings sand was precisely compounded according to the following proportions: <0.075mm accounted for 12%, 0.075–0.150mm accounted for 12%, 0.150–0.300mm accounted for 55%, and 0.300–0.600mm accounted for 25%. The mixture was stirred evenly to obtain pretreated tailings sand for later use.

[0059] (2) Mix 28 parts of 52.5 grade ordinary Portland cement, 10 parts of slag powder, and 2 parts of ethylene. Vinyl acetate copolymer latex powder, 0.4 parts of wood fiber with a length of 3 mm and an ash content of 10%, and 0.15 parts of polypropylene short fiber with a diameter of 20 μm and a length of 12 mm are put into a V-type mixer and mixed for 8 minutes at a speed of 30 r / min and a temperature of 40℃ to fully disperse the components and obtain a premixed base material for later use.

[0060] (3) Mix 0.35 parts of polycarboxylate-based high-performance water-reducing agent, 0.2 parts of hydroxypropyl methylcellulose ether, 0.15 parts of potassium methylsilicate water-repellent agent with a solid content of 30%, 0.3 parts of polyether defoamer, 0.02 parts of rosin thermal polymer air-entraining agent and 2 parts of lightweight aggregate with a particle size of 2.36 mm and add them to a high-speed disperser. Disperse the mixture for 4 minutes at a speed of 1200 r / min and a temperature of 35℃ to make the admixture highly dispersed and obtain the admixture pre-dispersion for later use.

[0061] (4) Add the pretreated tailings sand, the remaining 3 parts of lightweight aggregate and premixed base material to a twin-shaft paddle mixer and dry mix for 3 minutes. Then add the pre-dispersion additive and continue mixing for 6 minutes at a stirring linear speed of 5 m / s and a material temperature of 50°C to ensure that the system is free from stratification and agglomeration, and obtain the mixture.

[0062] (5) Low temperature and low humidity aging: The mixture is placed in a sealed aging chamber and aged for 24 hours at a temperature of 30℃ and relative humidity of ≤40% to eliminate internal stress and stabilize the activity of additives.

[0063] (6) After the material is screened and aged, it is screened by a 2.36mm standard vibrating screen to remove agglomerates and obtain the finished product of high-strength dry-mixed mortar for the resource utilization of tailings sand.

[0064] Performance testing The dry-mixed mortar samples prepared in Examples 1 and 2 were mixed with clean tap water at a water-to-material ratio of 0.14, stirred for 180 seconds using a mortar mixer, allowed to stand for 30 seconds, and then stirred for another 60 seconds to form a homogeneous mortar mixture. Subsequently, various performance tests were conducted, and the specific standards and operating procedures are as follows: (1) Consistency test According to JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar", a mortar consistency tester was used. The mixture was loaded into the cone of the consistency tester in one go, the surface was smoothed, and the depth of the cone sinking into the mortar was measured. The test was repeated twice and the average value was taken.

[0065] (2) Water retention rate test According to GB / T 25181-2019 "Premixed Mortar", a water retention rate test device was used to determine the water retention capacity of the mortar under specified negative pressure conditions and calculate the water retention rate.

[0066] (3) Condensation time test According to JGJ / T 70-2009, a mortar penetration resistance meter was used to record the time corresponding to the penetration resistance reaching 3.5MPa and 28MPa, which were the initial setting time and the final setting time, respectively.

[0067] (4) Compressive strength and flexural strength tests According to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", the mortar mixture was placed into a 40mm×40mm×160mm mold, vibrated and cured for 3 days and 28 days, and the flexural strength and compressive strength were tested respectively.

[0068] (5) Tensile bond strength test According to JGJ / T 70-2009, cement mortar blocks were used as the base layer to form bonded specimens. After standard curing for 28 days, the tensile bond strength was tested using a universal testing machine.

[0069] (6) Drying shrinkage value test According to GB / T 17671-2021, a 40mm×40mm×160mm mold was used to measure the length change after molding and after 28 days of curing, and the drying shrinkage value was calculated.

[0070] (7) Permeability resistance test According to JGJ / T 70-2009, a mortar impermeability tester was used to apply pressure step by step, and the impermeability grade was determined by the maximum pressure when there was no water seepage at the end face of the specimen.

[0071] (8) Chloride ion content test According to the relevant methods in GB / T 14684-2022 "Sand for Construction", the chloride ion content in mortar was determined by potentiometric titration.

[0072] The test results are shown in Table 1. Table 1 Test Results As shown in Table 1, the high-strength dry-mixed mortar for tailings sand resource utilization prepared by this invention has excellent comprehensive performance. Its 28-day compressive strength can reach up to 42.0 MPa, meeting the requirements for high-strength masonry, plastering, and flooring projects. The mortar has high water retention, moderate setting time, and excellent workability. It also boasts high tensile bond strength and low drying shrinkage, effectively inhibiting cracking and hollowing. Its impermeability grade reaches P10, demonstrating outstanding durability. Furthermore, its low chloride ion content eliminates the risk of steel reinforcement corrosion, making it widely applicable to various construction projects. Simultaneously, the product uses bulk industrial tailings sand as the main raw material, realizing the resource utilization of solid waste and achieving economic, social, and environmental benefits.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A high-strength dry-mixed mortar for the resource utilization of tailings sand, characterized in that, The components include the following parts by mass: Tailings sand 50-70 parts, cementitious material 18-28 parts, mineral admixture 5-10 parts, redispersible latex powder 1-2 parts, defoamer 0.1-0.3 parts, polycarboxylate-based high-performance water-reducing agent 0.1-0.35 parts, hydroxypropyl methylcellulose ether 0.05-0.2 parts, organosilicon water-repellent agent 0.05-0.15 parts, wood fiber 0.1-0.4 parts, polypropylene short fiber 0.05-0.15 parts, air-entraining agent 0.005-0.02 parts, auxiliary aggregate 1-5 parts.

2. The high-strength dry-mixed mortar for tailings sand resource utilization according to claim 1, characterized in that, The tailings sand is one or more of iron tailings sand, copper tailings sand, and molybdenum tailings sand; The tailings sand is composed of different particle size ranges, specifically: tailings sand <0.075mm accounts for 8%-12%, tailings sand 0.075-0.150mm accounts for 8%-12%, tailings sand 0.150-0.300mm accounts for 45%-55%, and tailings sand 0.300-0.600mm accounts for 25%-35%.

3. The high-strength dry-mixed mortar for tailings sand resource utilization according to claim 1, characterized in that, The cementing material is at least one of ordinary Portland cement with a strength grade of 42.5, ordinary Portland cement with a strength grade of 52.5, or slag Portland cement.

4. The high-strength dry-mixed mortar for tailings sand resource utilization according to claim 1, characterized in that, The mineral admixture is one or more of fly ash, slag powder, and silica fume; the auxiliary aggregate is one or more of manufactured sand, slag, and lightweight aggregate, with a particle size range of 0.6-2.36 mm.

5. The high-strength dry-mixed mortar for tailings sand resource utilization according to claim 1, characterized in that, The redispersible latex powder is an ethylene-vinyl acetate copolymer latex powder; the organosilicon hydrophobic agent is sodium methylsilicate or potassium methylsilicate, with a solid content ≥30%.

6. The high-strength dry-mixed mortar for tailings sand resource utilization according to claim 1, characterized in that, The wood fibers have a length of 0.5-3 mm and an ash content of ≤10%; the polypropylene short fibers have a diameter of 10-20 μm and a length of 6-12 mm.

7. The high-strength dry-mixed mortar for tailings sand resource utilization according to claim 1, characterized in that, The air-entraining agent is a triterpenoid saponin air-entraining agent, a rosin thermal polymer air-entraining agent, or an alkylbenzene sulfonate air-entraining agent, and the defoamer is an organosilicon defoamer or a polyether defoamer.

8. A method for preparing high-strength dry-mixed mortar for the resource utilization of tailings sand as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) The tailings sand is dried and screened to remove impurities, and then compounded according to the preset particle size distribution to obtain pretreated tailings sand. (2) The cementitious material, mineral admixture, redispersible latex powder, wood fiber and polypropylene short fiber are mixed in the first mixing to obtain a premixed base material; (3) The polycarboxylate superplasticizer, hydroxypropyl methylcellulose ether, organosilicon water-repellent agent, defoamer, air-entraining agent and 1-2 parts of auxiliary aggregate are mixed for a second time to obtain an admixture predispersion; (4) The pretreated tailings sand, the remaining auxiliary aggregate, and the premixed base material obtained in step (1) are mixed for the third time. After the mixture is evenly mixed, the additive predispersant obtained in step (3) is added and the mixture is stirred for 3-5 minutes to obtain the mixture. (5) Place the mixture at a temperature of 15-30℃ and a relative humidity of ≤40% and let it stand for 12-24 hours to age; (6) The aged material obtained in step (5) is passed through a vibrating screen to remove agglomerates, and the tailings sand resource utilization type high-strength dry-mixed mortar is obtained.

9. The method for preparing high-strength dry-mixed mortar for tailings sand resource utilization according to claim 8, characterized in that, The conditions for the first mixing are: using a double cone premixer or a V-type mixer, a mixing speed of 15-30 r / min, a mixing time of 3-8 minutes, and a mixing temperature controlled at 25-40℃; The conditions for the second mixing are: using a high-speed disperser, a dispersion speed of 800-1200 r / min, a dispersion time of 2-4 minutes, and a dispersion temperature of 20-35℃; The conditions for the third mixing are as follows: a planetary forced mixer or a twin-shaft paddle mixer is used, the stirring linear speed is 2-5 m / s, the mixing time is 4-6 minutes, the material temperature is 30-50℃ during the mixing process, and the material is dry-mixed for 2-3 minutes before the mixing begins, and then the additive pre-dispersion is added and the mixing continues.

10. An application of the high-strength dry-mixed mortar for the resource utilization of tailings sand as described in any one of claims 1-8, characterized in that, The application specifically refers to its use in building masonry mortar, plastering mortar, flooring mortar, or repair mortar.

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