Coarse slag composite machine-made sand concrete and preparation method thereof

Abstract

The invention discloses coarse slag composite machine-made sand concrete and a preparation method thereof, and belongs to the technical field of concrete preparation. The coarse slag composite machine-made sand concrete is prepared from the following raw materials in parts by weight: 320-430 parts of a cementing material, 800-1000 parts of fine aggregate, 740-1100 parts of gravel, 8-15 parts of a compound additive and 130-170 parts of water, the fine aggregate is formed by compounding coarse tailing machine-made sand and desert sand, wherein the coarse tailing machine-made sand accounts for 30-85% of the total mass of the fine aggregate. The decarburized coarse tailing machine-made sand and the desert sand are compounded to serve as fine aggregate, the cementing material, the broken stone and the compound additive in a specific proportion are combined, a synergistic effect is formed by utilizing the volcanic ash activity of the coal gasification coarse tailings and the grading advantage of the desert sand, the workability, the mechanical property and the durability of the concrete are improved, and meanwhile the concrete quality is improved. Resource utilization of the coarse tailing solid waste and replacement of natural sand are achieved, the problem that natural sand resources are deficient is solved, and the requirement for green and low-carbon development is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of concrete preparation, and particularly relates to a coarse residue composite machine-made sand concrete and a preparation method thereof. BACKGROUND

[0002] With the rapid development of infrastructure construction, high-quality natural sand resources for concrete are increasingly scarce, and the exploitation of natural sand is strictly limited by environmental protection policies, so finding a substitute for natural sand has become an important development direction of the concrete industry. Machine-made sand gradually becomes an ideal substitute for natural sand due to the advantages of abundant raw materials, adjustable performance and low cost.

[0003] Coal gasification process is an important technical means for clean utilization of coal, but a large amount of coal gasification residue is produced in the process, of which coarse residue accounts for 60%-80% of the total residue. The main components of coal gasification coarse residue are Al2O3, SiO2, CaO, Fe2O3 and residual carbon, which belongs to the general solid waste of fired clay. If not reasonably utilized, it will not only occupy a large amount of land resources, but also may cause environmental pollution, so realizing its resource utilization is an inevitable demand for sustainable development of the industry.

[0004] In the prior art, the application of coal gasification residue in the building material field has been concerned, such as for producing cement, concrete aggregate, wall materials and the like. However, the high content of residual carbon in the coal gasification residue will adversely affect the performance of concrete. As a porous inert substance, residual carbon will increase the water demand of fresh concrete, resulting in increased bleeding of concrete, larger drying shrinkage, and reduced strength and durability of concrete; at the same time, the hydrophobic film formed on the surface of residual carbon particles will hinder the growth and mutual connection of hydrate crystals and cementitious bodies, and destroy the internal structure of concrete.

[0005] After decarburization, the mineral composition of coal gasification residue is mainly amorphous substance, containing C3S and C2S minerals with high crystallinity, which has pozzolanic activity. When applied in concrete, it can improve the bonding strength between the surface of coarse residue and cement hydration products through secondary hydration reaction with cement hydration products; and the activity of coarse residue powder is much higher than that of stone powder in ordinary machine-made sand, which can play an active filling role in the hydration process of concrete, making the structure of cement hydration products more dense, which is beneficial to improving the durability of concrete.

[0006] Based on the above status, it is necessary to develop a kind of concrete taking decarburized coal gasification coarse residue and desert sand as composite fine aggregate and a preparation method thereof. SUMMARY

[0007] To solve the above problems, the purpose of the present application is to provide a coarse slag composite machine-made sand concrete and a preparation method thereof, by compounding the coal gasification coarse tailing machine-made sand after decarburization with desert sand as fine aggregate, combining cementing materials, gravel and compounded additives in a specific proportion, utilizing the synergistic effect of the pozzolanic activity of the coal gasification coarse tailing and the grading advantage of the desert sand, improving the workability, mechanical properties and durability of the concrete, realizing the resource utilization of the coal gasification slag solid waste and the replacement of natural sand, relieving the problem of shortage of natural sand resources, and meeting the demand of green and low-carbon development.

[0008] To achieve the above purpose, the technical scheme of the present application is as follows: a coarse slag composite machine-made sand concrete and a preparation method thereof, which are made of the following raw materials by weight:

[0009] cementing materials 320-430 parts, fine aggregate 800-1000 parts, gravel 740-1100 parts, compounded additives 8-15 parts and water 130-170 parts;

[0010] The cementing materials are composed of cement and fly ash, wherein the cement accounts for 72%-75% of the total mass of the cementing materials;

[0011] The fine aggregate is composed of coarse tailing machine-made sand and desert sand, wherein the coarse tailing machine-made sand accounts for 30%-85% of the total mass of the fine aggregate, and the coarse tailing machine-made sand is a particle after decarburization and screening pretreatment, and the fineness modulus is controlled at 3.0-3.7;

[0012] The compounded additives are composed of polycarboxylic acid water reducer and cellulose ether, wherein the cellulose ether accounts for 0.05%-0.15% of the total mass of the cementing materials.

[0013] Further, the solid content of the polycarboxylic acid water reducer is 35-40%.

[0014] Further, the cellulose ether is hydroxypropyl methyl cellulose ether.

[0015] The principle of the basic scheme is that the coal gasification slag is pretreated by decarburization and screening, with a fineness modulus of 3.0-3.7, and has pozzolanic activity, and the amorphous SiO2 and Al2O3 can have a secondary hydration reaction with the cement hydration product (such as Ca (OH)2), thereby improving the interfacial bonding strength; the desert sand particles are small, which can fill the gaps between the coarse tailing machine-made sand, optimize the grading of the fine aggregate, and reduce the porosity of the concrete. The two are compounded in a proportion of 30%-85%, which can not only utilize the activity effect of the coarse tailing, but also utilize the filling effect of the desert sand, thereby improving the workability and compactness of the concrete.

[0016] Cement accounts for 72%-75% of cementitious materials, providing the basis for early strength; fly ash as an auxiliary cementitious material can reduce hydration heat, and its glass bead shape helps to improve the fluidity of concrete, complementing the pozzolanic activity of coarse slag machine-made sand to jointly improve the late strength.

[0017] Polycarboxylic acid water reducing agent (solid content 35-40%) can effectively disperse cementitious material particles and reduce water consumption; hydroxypropyl methylcellulose ether can improve the water retention of concrete and inhibit bleeding, and cooperates with composite fine aggregate to ensure the workability of fresh concrete.

[0018] The beneficial effects of the basic scheme are: 1. Coal gasification slag is converted into high-performance machine-made sand, which is used to replace natural sand in cooperation with desert sand, to alleviate the shortage of natural sand resources and reduce solid waste storage pollution, in line with the "double carbon" and circular economy concepts.

[0019] 2. The grading of the composite fine aggregate is reasonable, and it is matched with specific cementitious materials and admixtures to make the concrete have good workability (fluidity, water retention) and mechanical properties (compressive and flexural strength), and the secondary hydration reaction can improve the density of the concrete and enhance the durability of the concrete, such as impermeability and carbonization resistance.

[0020] 3. The raw material ratio range is wide, which can be adjusted according to the actual resource situation; the preparation process is simple (dry mixing and then adding water and stirring), which is suitable for industrial production and easy to popularize and apply.

[0021] 4. The cost of obtaining coal gasification slag and desert sand is low, which can replace natural sand and part of cement to reduce the production cost of concrete, and has economic and environmental benefits.

[0022] A preparation method of coarse slag machine-made sand concrete, comprising the following steps:

[0023] S1, coal gasification slag pretreatment: using a coal gasification slag pretreatment device to treat the coal gasification slag mixed slurry to reduce the carbon content, and then screen to remove particles larger than 4.75 mm, to obtain coarse tail slag machine-made sand with a fineness modulus of 3.0-3.7;

[0024] S2, batching: weighing cement, fly ash, coarse tail slag machine-made sand prepared in step S1, desert sand, gravel, polycarboxylic acid water reducing agent, cellulose ether and water according to the ratio;

[0025] S3, stirring: put all the dry materials weighed in step S2 into a mixer, dry mix for 30-60 seconds to make them evenly mixed, then add water and stir for 90-120 seconds, and the coarse slag composite machine-made sand concrete is obtained.

[0026] Further, the carbon removal treatment in step S1 is to calcine the coal gasification slag at 600-800℃ for 1-2 hours.

[0027] Further, the decarburization treatment is carried out in an inert atmosphere or air.

[0028] Further, after the screening treatment in step S1, a step of mechanically activating the obtained manufactured sand is further included.

[0029] The beneficial effects of the basic scheme are: 1. The decarburization is achieved by calcining at 600-800℃ for 1-2 hours, which can effectively reduce the residual carbon content of the coarse slag and avoid the adverse effects of residual carbon on the water demand, strength and durability of concrete; the subsequent screening removes particles larger than 4.75mm, and the fineness modulus of the manufactured sand is accurately controlled at 3.0-3.7, laying a foundation for the optimization of the grading of composite fine aggregate. The decarburization treatment can be carried out in an inert atmosphere or air, which is suitable for different production conditions and enhances the process flexibility.

[0030] 2. The optional mechanical activation step can further refine the manufactured sand particles, increase the specific surface area, stimulate the pozzolanic activity, promote the secondary reaction with the cement hydration products, and improve the interfacial bonding strength and overall mechanical properties of concrete.

[0031] 3. In the batching link, each component is accurately weighed in proportion, and the dry mixing + water mixing combined stirring process is adopted, which not only ensures uniform mixing of dry materials, but also enables the materials to be fully hydrated, ensuring the workability of the concrete mixture and the stability of the finished product performance, which is suitable for continuous industrial production and easy for large-scale promotion.

[0032] Further, the coal gasification slag pretreatment device in step S1 includes a calcining assembly, the calcining assembly is connected with a gas circulation assembly, the calcining assembly is connected with a screening assembly, the screening assembly is connected with an activation assembly, a controller is fixedly connected to the activation assembly, and the calcining assembly, the gas circulation assembly, the screening assembly and the activation assembly are signal connected with the controller.

[0033] The calcining assembly is used for heating and calcining the coal gasification slag to remove residual carbon.

[0034] The gas circulation assembly is used for supplying an inert atmosphere for the calcining assembly and recovering the inert gas to remove waste gas.

[0035] The screening assembly is used for classifying and screening the decarburized coarse slag, removing particles larger than 4.75mm, and sending 2.36-4.75mm particles to the activation assembly.

[0036] The activation assembly is used for refining the 2.36-4.75mm decarburized coarse slag and activating the pozzolanic activity of the decarburized coarse slag.

[0037] Further, the calcination assembly comprises a calcination furnace in an inclined manner, a lining furnace is coaxially sleeved in the calcination furnace, a feeding port is formed at the top end of the lining furnace, a waste pipe is communicated with the bottom end of the lining furnace, an electric control valve is further arranged between the lining furnace and the waste pipe, an electric heating wire is arranged in the side wall of the calcination furnace, a temperature sensor is arranged in the calcination furnace, a driving motor is fixedly connected in parallel with the side wall at the top end of the calcination furnace, a driving gear is coaxially fixedly connected with the output shaft of the driving motor, a driven gear ring is fixedly connected with the outer periphery of the top end of the lining furnace, the driven gear ring is engaged with the driving gear, and the electric control valve, the electric heating wire, the temperature sensor and the driving motor are signal connected with the controller.

[0038] Further, the gas circulation assembly comprises a gas storage tank, inert gas is stored in the gas storage tank, a recovery pipe is communicated with the top end of the gas storage tank, the recovery pipe is communicated with the side wall at the top end of the calcination furnace, a gas filling pipe is communicated with the side wall at the bottom of the gas storage tank, the gas filling pipe is communicated with the side wall at the middle of the calcination furnace, a gas pump with a barometer is arranged in the recovery pipe and the gas filling pipe, carbon dioxide adsorption material is filled in the recovery pipe, and the barometer and the gas pump are signal connected with the controller.

[0039] Further, the screening assembly comprises a storage bin, the storage bin is communicated with the bottom end of the calcination furnace, the storage bin is rotatably connected with the waste pipe, the bottom of the storage bin is provided with a discharging port, a plurality of first screening holes are formed in the side wall of the lining furnace, an annular screening net is slidably sleeved on the outer periphery of the waste pipe, the outer periphery of the annular screening net is fixedly connected with the inner wall of the storage bin, an arc-shaped push block is fixedly connected with the outer side wall at the bottom end of the lining furnace, the arc-shaped push block is slidably matched with the annular screening net, a plurality of top beads are fixedly connected on the bottom wall of the arc-shaped push block, the size of the top beads is the same as the aperture of the annular screening net, the position where the gas filling pipe is connected with the calcination furnace corresponds to the bottom end of the movement track of the arc-shaped push block, and the top end of the annular screening net is provided with a pushing port.

[0040] Further, the activation assembly comprises a grinding bowl, the grinding bowl is rotatably connected with the top wall of the storage bin, a plurality of grinding balls are arranged in the grinding bowl, a plurality of second screening holes with the same aperture as the annular screening net are formed in the side wall of the grinding bowl, the aperture of the second screening holes is smaller than that of the first screening holes, a sealing cover is rotatably connected on the grinding bowl, an activation pipe is communicated with one side wall of the sealing cover, the activation pipe is communicated with the pushing port, a driving shaft is fixedly connected with the bottom wall of the grinding bowl, an activation bevel gear is fixedly connected with the bottom end of the driving shaft, a driving bevel gear is fixedly sleeved on the outer periphery of the waste pipe, and the driving bevel gear is engaged with the activation bevel gear.

[0041] Further, the feeding port, the bottom end of the waste pipe and the discharging port are all hingedly connected with sealing covers.

[0042] The beneficial effects of the basic scheme are: 1. The device integrates the functions of calcination, gas circulation, screening and activation, and realizes the continuous processing of coal gasification slag from decarburization to activation by controlling the linkage of each component, reduces the intermediate transfer link, greatly improves the pretreatment efficiency, and is suitable for industrial batch production.

[0043] 2. The calcination assembly uses electric heating wires in conjunction with temperature sensors, and the temperature is controlled in real time (600-800℃) by the controller. Combined with the rotation of the inner lining furnace, the coal gasification slag is heated evenly, ensuring that residual carbon is fully removed. The inclined calcination furnace design, combined with the inner lining furnace push, avoids material accumulation and further ensures the stability of the decarbonization effect.

[0044] 3. The gas circulation component recovers the inert gas after calcination through the recovery pipe, and after being treated by carbon dioxide adsorption material, it is reintroduced into the calcination furnace to realize the recycling of inert gas and reduce gas source consumption; the gas pump and pressure gauge linkage controller accurately control the gas pressure in the furnace, which not only ensures the stability of the inert atmosphere, but also reduces waste gas emissions, meeting the requirements of green production.

[0045] 4. In the screening component, the first screening hole of the inner lining furnace performs initial classification, and the annular screening screen further screens the particles; when the arc-shaped pusher rotates with the inner lining furnace, its bottom top bead can clean the screen aperture, effectively preventing blockage and ensuring screening efficiency; the push port accurately delivers 2.36-4.75mm particles into the activation component, achieving precise classification processing.

[0046] 5. The grinding bowl of the activation component is linked to the waste discharge pipe through a drive bevel gear, which does not require an additional power source and saves energy. The grinding balls refine the 2.36-4.75mm particles, and the second screening hole controls the discharge particle size, effectively activating the pozzolanic activity of the coarse slag and laying the foundation for the subsequent improvement of concrete performance. Attached Figure Description

[0047] Figure 1 The results are from XRD analysis of the coarse tailings from coal gasification.

[0048] Figure 2 The results are from SEM analysis of the coarse tailings from coal gasification.

[0049] Figure 3 This is a line graph showing the compressive strength of coarse slag composite concrete at different ages.

[0050] Figure 4 This is a SEM image of sample 1 after 28 days of standard curing.

[0051] Figure 5 The image shows the SEM image of the interface between the hydration products and the coarse tailings of Sample 2 after 28 days of standard curing.

[0052] Figure 6 The image shows the microstructure of the hydration products of sample 2 after 28 days of standard curing.

[0053] Figure 7 Carbonation depth of composite manufactured sand concrete with different proportions of coarse slag.

[0054] Figure 8 This is an isometric view of the coal gasification slag pretreatment device in an embodiment of the present invention.

[0055] Figure 9 This is a side sectional view of the coal gasification slag pretreatment device in an embodiment of the present invention.

[0056] The reference numerals in the accompanying drawings of the instruction manual include: 1. Calcination furnace; 2. Gas filling pipe; 3. Drive motor; 4. Drive gear; 5. Driven gear ring; 6. Lined furnace; 7. Recovery pipe; 8. Storage silo; 9. Sealing cover; 10. Discharge port; 11. First screening hole; 12. Arc-shaped pusher block; 13. Electrically controlled valve; 14. Activation pipe; 15. Second screening hole; 16. Grinding bowl; 17. Activation bevel gear; 18. Drive bevel gear; 19. Waste discharge pipe; 20. Annular screening screen. Detailed Implementation

[0057] The following detailed description illustrates the specific implementation method:

[0058] Example 1

[0059] The basics are as follows: Figures 1 to 7 As shown: A coarse slag composite manufactured sand concrete, made from the following raw materials in parts by weight:

[0060] 320-430 parts cementitious material, 800-1000 parts fine aggregate, 740-1100 parts crushed stone, 8-15 parts compound admixture and 130-170 parts water;

[0061] The cementitious material is composed of cement and fly ash, with cement accounting for 72%-75% of the total mass of the cementitious material;

[0062] The fine aggregate is composed of coarse tailings manufactured sand and desert sand, wherein the coarse tailings manufactured sand accounts for 30%-85% of the total mass of the fine aggregate, and the coarse tailings manufactured sand is a particle that has undergone decarburization and screening pretreatment, with a fineness modulus controlled at 3.0-3.7.

[0063] The compound admixture is composed of polycarboxylate superplasticizer and cellulose ether, wherein the cellulose ether accounts for 0.05%-0.15% of the total mass of the cementitious material, the cellulose ether is hydroxypropyl methylcellulose ether, and the solid content of the polycarboxylate superplasticizer is 35-40%.

[0064] The specific implementation process is as follows: Due to the characteristics of the production process, the mineral composition of the coarse tailings consists of glassy substances with pozzolanic activity. It can undergo a secondary hydration reaction with cement hydration products, enhance the interfacial strength between cement stone and fine aggregate, make the final cement hydration product structure more compact, and improve the durability of concrete.

[0065] Specific R&D process: I. Experimental materials

[0066] 1. Cementing materials

[0067] (1) Cement

[0068] The cement used in this study was Yatai P·O 42.5 grade ordinary Portland cement, and its basic performance indicators are shown in Table 1.

[0069] Table 1. Main properties of cement

[0070]

[0071] (2) Fly ash

[0072] The fly ash (FA) used in this study came from Jilin Dafang Commercial Concrete Company. It was grade II fly ash with an apparent density of 1970 kg / m³. 3 Specific surface area 399m² 2 / kg, chemical composition is shown in Table 2.

[0073] Table 2. Chemical composition of fly ash (%)

[0074]

[0075] 2. Natural aggregates

[0076] The fine aggregate used in this study was natural sand with a bulk density of 1465 kg / m³. 3 Apparent density 2570 kg / m³ 3 Particle size 0.35-0.50, fineness modulus Mx=2.40.

[0077] The weathered sand (desert sand) excavated at the Ordos plant site has a bulk density of 1465 kg / m³. 3 Apparent density 2570 kg / m³ 3 The particle size is 1.18-0.075 mm, the moisture content is 4%, the mud content is 6.65%, and the fineness modulus Mx is 1.16.

[0078] 3. Coal gasification tailings manufactured sand

[0079] (1) Basic physical properties and fineness modulus of manufactured sand from coal gasification coarse tailings

[0080] Manufactured sand is the original solid waste from coal gasification slag, with a bulk density of 1350 kg / m³. 3 Apparent density 2370 kg / m³ 3 The number of particles larger than 4.75mm was relatively large, accounting for 9.3%. After communicating with the supplier, the manufacturer controlled the particle size of the coarse slag during the supply process and screened out large particles larger than 4.75mm. The screening results of the coarse tailings manufactured sand after controlling the particle size are shown in Table 3.

[0081] Table 3. Screening results of manufactured sand from coarse coal gasification slag

[0082]

[0083] The fineness modulus Mx of the coal gasification tailings after particle size control, calculated by sieving test, is 3.41, which is relatively reasonable and conforms to the fineness modulus of common manufactured sand in my country, making it suitable for use in concrete.

[0084] (2) Crushing index of coarse tailings slag manufactured sand

[0085] The crushing index of coarse tailings manufactured sand was tested according to GB / T 14684-2022 "Sand for Construction". The test results are shown in Table 4.

[0086] Table 4. Test results of crushing index of coarse tailings manufactured sand

[0087]

[0088] The single-stage crushing value is less than 25%, which meets the Class II requirements for manufactured sand crushing index.

[0089] (3) Chemical and mineral composition of coarse tailings manufactured sand

[0090] Table 5 shows the XRF test results of the chemical composition of the coarse tailings from coal gasification. The results show that the oxide content in the coarse tailings, from high to low, is silicon dioxide, aluminum oxide, calcium oxide, and iron oxide. It belongs to the calcined clay aluminosilicate minerals and has stable chemical properties when used as fine aggregate in concrete.

[0091] Table 5. Percentage of oxides in manufactured sand from coal gasification coarse tailings

[0092]

[0093] Figure 1 The XRD test results for the coarse tailings show that amorphous phases are present in the coal gasification coarse tailings. Overall, amorphous phases are the main component. Combined with Table 5, it can be determined that the amorphous phases are mainly aluminosilicate glass and amorphous carbon. The crystalline phase is a small amount of quartz. Based on the source of the coarse tailings, the quartz phase is mainly formed by the crystallization of the glass phase during the cooling process.

[0094] The active silica and alumina on the surface of the coarse tailings manufactured sand react with calcium hydroxide in the cement paste to form hydrated calcium silicate and hydrated calcium aluminate. This reduces the risk of calcium hydroxide leaching, improves the durability of concrete, and improves the microstructure of cement hydration products, increasing the density of the concrete. Furthermore, the coarse tailings powder, a common component of manufactured sand, possesses pozzolanic activity that inevitably enhances the secondary hydration reaction.

[0095] (4) Microscopic morphology analysis of coarse tailings manufactured sand

[0096] The microstructure of coarse tailings consists of Figure 2 As shown in the figure, a large number of irregular glassy bodies are formed on the surface of the coarse slag, and there is a certain slag formation phenomenon. This is because Al2O3, SiO2 and alkaline components such as MgO and CaO in the slag are prone to form a eutectic under high temperature conditions. After rapid cooling, the eutectic forms fine slag particles.

[0097] 4. Coarse aggregate

[0098] The coarse aggregate is crushed stone with a maximum particle size of 31.5mm, sourced from Jilin Dafang Commercial Concrete Company.

[0099] 5. Admixtures

[0100] Polycarboxylate superplasticizer: The polycarboxylate superplasticizer used in the experiment was a high-performance polycarboxylate superplasticizer (liquid) produced by Tianjin Weihe Technology Development Co., Ltd., with a solid content of 38wt%.

[0101] Cellulose ether: Hydroxypropyl methylcellulose ether produced by Shandong Yiteng New Material Co., Ltd.

[0102] 6. Water

[0103] All water used in the experiment was domestic water.

[0104] II. Preliminary Mix Proportion Study of Coarse Tailings Slag Manufactured Sand Concrete

[0105] In this study, the mix design of coarse tailings manufactured sand concrete adopted the empirical method. The following two factors need to be considered in the mix design process: 1. The mix proportion of C30 concrete commonly used by local commercial concrete enterprises; 2. The workability requirements of pumped C30 concrete in the local area; 3. Durability requirements.

[0106] 1. Coal gasification tailings partially replace natural sand

[0107] The mix design of C30 concrete with partial replacement of river sand by coarse tailings from coal gasification is shown in Table 6. 100mm×100mm×100mm cubic specimens were prepared according to the standard requirements of GB / T50081 "Test Methods for Mechanical Properties of Ordinary Concrete", and their slump was tested.

[0108] Table 6. Mix proportions and mechanical properties of concrete with partial replacement of river sand with coarse slag

[0109]

[0110] 1-2: Fine ash did not significantly improve the workability of fresh concrete. Compared with 1-1, obvious bleeding occurred. The fine ash particles did not effectively improve the workability of the concrete. Due to the large specific surface area of ​​the fine ash, its addition to the concrete increased the water demand. In addition, due to the high carbon content of the coal gasification slag, it did not form a viscous paste with the cement paste. Visually, the amount of concrete paste was too small to be usable. After standard curing for 1 day, the molded concrete specimens were quickly cured for 24 hours. After removing them and wiping off the surface moisture, mechanical property tests were conducted. Replacing part of the river sand with coarse tailings is equivalent to increasing the fineness modulus of the fine aggregate. Therefore, it is necessary to reduce the amount of gravel to control the workability of the concrete. The strength of sample 1-5 after 24 hours of quick curing is higher than that of C30 concrete commonly used in Ordos commercial concrete plants.

[0111] 2. Coal gasification coarse tailings + water-washed desert weathered sand system

[0112] Considering the high fineness modulus and large water demand of coal gasification tailings, and from a practical application perspective, a composite fine aggregate system of coal gasification tailings and desert sand was adopted for concrete mix design. This solves the problems of segregation and bleeding that occur when using coarse tailings alone in concrete, and also effectively utilizes the large reserves of local desert sand, despite its limited application. To ensure the comparability of the experimental process, the Inner Mongolian desert sand was washed, dried, and used for later use. The specific concrete experimental mix proportions are shown in Table 7.

[0113] After adopting the coarse tailings + desert sand composite fine aggregate system, the workability of concrete was significantly improved. When the slump was 240mm, the samples all had good cohesiveness and water retention. This is mainly because the fineness modulus of desert sand is too small and the specific surface area is large. After the two fine aggregates are compounded, the specific surface area and porosity of the aggregate are both small. On the one hand, the amount of cementitious materials can be reduced, and on the other hand, the concrete can have good mechanical properties.

[0114] Table 7. Mix proportions and mechanical properties of C30 concrete made from coarse slag and clean desert sand

[0115]

[0116] The mechanical property test results show that the strength of samples 2-3 and 2-4 both exceed that of the blank sample. This demonstrates their practical application value.

[0117] 3. Coal gasification coarse tailings + desert sand system

[0118] For practical application requirements, this study explored the mix proportions and mechanical properties of a composite concrete system of coarse tailings and unwashed desert sand. Two groups with better workability and mechanical properties in Table 6 were selected as the basic mix proportions for design. In addition, considering the high mud content (6.65%) of desert sand, the flowability of concrete was adjusted by adjusting the amount of admixtures. The specific mix proportions are shown in Table 8.

[0119] Table 8. Mix proportions and mechanical properties of C30 concrete made from coarse slag and desert sand

[0120]

[0121] After adjustment, the coarse tailings + desert sand composite fine aggregate system concrete exhibited good workability, with no segregation or bleeding observed at a slump of 240mm. Sample 3-2 achieved a 7-day strength of 24 MPa, reaching 80% of its later-stage strength, fully meeting the actual construction requirements.

[0122] III. Laboratory Mix Proportioning and Performance Study of Coarse Tailings Slag-Made Sand Concrete

[0123] 1. Mix proportions and mechanical properties of coarse tailings composite concrete system

[0124] Based on the preliminary mix proportion study, the research team conducted a systematic laboratory mix proportion test of coarse tailings concrete from an economic perspective. The specific mix proportions and mechanical properties are shown in Table 9. Line graphs were plotted using the 3-day, 7-day, and 28-day compressive strength data of the coarse tailings composite concrete system from Table 9. See [link to table]. Figure 3 .

[0125] Table 9. Mix proportions and mechanical properties of coarse tailings and desert sand composite fine aggregate concrete (based on 1m³) 3 count)

[0126]

[0127] As shown in the figure, when the content of coarse tailings from coal gasification is 50 wt%, the highest 3-day compressive strength of the specimen reaches 22.6 MPa. When the content of coarse tailings from coal gasification is 90 wt%, the 3-day compressive strength is only 7.73 MPa. Furthermore, the highest 7-day compressive strength of the specimen is 25.3 MPa. With continued standard curing, the strength of the specimen continues to increase after 28 days. However, when the content of coarse tailings from coal gasification exceeds 50 wt%, the strength gradually decreases. It is noteworthy that specimen 2 (20 wt% coarse coal gasification tailings + 80 wt% desert sand) exhibits the highest 28-day compressive strength of 47.4 MPa. When the content of coarse coal gasification tailings is 90wt%, the mechanical properties of the concrete specimens can reach 30MPa, reflecting a relatively stable early-stage strength development rate and a faster later-stage strength development. With a fixed content of coarse coal gasification tailings, the 3-day, 7-day, and 28-day compressive strengths of the samples all increased to varying degrees with the increase of cementitious materials, indicating that increasing the content of cementitious materials is beneficial to the development of the mechanical properties of the concrete specimens. From a long-term perspective, incorporating an appropriate amount of coarse coal gasification tailings contributes to the development of concrete strength.

[0128] 2. Microscopic Morphology Analysis of Coarse Slag Composite System Concrete

[0129] Based on the mechanical test results, Sample 1 and Sample 2 were selected for SEM analysis. The fragments of the samples after mechanical testing were placed in anhydrous ethanol and left to stand for 2 hours to terminate the hydration reaction. After drying, the samples were sprayed with gold for microscopic morphology analysis.

[0130] The microstructure and hydration degree analysis of sample 1 are shown in the figure. Figure 4 The microstructure and hydration degree analysis of sample 2 are shown in [reference needed]. Figure 5 and Figure 6 .

[0131] As can be seen from the figure, after 28 days of standard curing, the concrete of sample 1 showed good hydration effect, and the cement hydration products and aggregate interface showed good adhesion. The hydration product system was mainly composed of an amorphous gel structure, which encapsulated the generated crystal structure. Figure 4 The upper left corner shows the interface between hydration products and fly ash. Microscopic analysis clearly shows that fly ash underwent a very obvious secondary hydration reaction with the primary hydration products of cement at 28 days. A sufficient number of gel products were generated on the surface of fly ash particles and showed obvious cross-linking with the primary hydration products of cement. Figure 4 The remaining areas represent the interface between cement hydration products and coarse tailings from coal gasification. As can be seen from the three figures, the cement hydration products and coarse tailings exhibit good bonding at the interface. The hydration products in the interface region have a dense gel structure. Judging from the microscopic morphology, the product should be CSH gel, which differs from the interface region of concrete with river sand as fine aggregate, which has poor crystallinity and is loose crystalline. Therefore, it has better compressive strength.

[0132] When the desert sand content is increased to 20% of the fine aggregate content (sample 2), from Figure 5 It can be seen that with the increase of desert sand content, the micro-interface of coarse tailings composite concrete is greatly improved, and the adhesion between concrete hydration products and the surface of coarse tailings is significantly enhanced. This is because the increase in desert sand content reduces the unit water consumption of concrete, which is equivalent to reducing the water-cement ratio of concrete, increasing the degree of hydration of concrete, and improving the adhesion between the gel and the coarse tailings interface. In addition, because coarse tailings contain a large number of glassy structures, they can undergo a secondary hydration reaction similar to that of active admixtures under the alkaline conditions inside the concrete. As shown in the four figures, after 28 days of hydration, the coarse tailings show the formation of a large number of three-dimensional network-like hydration products, which greatly enhances the adhesion between aggregates and cement paste. As is well known, in concrete below C60 grade, the interface between cement paste and aggregate is the weakest stress zone when it fails under compressive stress. This is because the aggregate is an inert system, and a certain amount of water film is adsorbed on its surface during concrete forming, resulting in an excessively high water-cement ratio in the interface area. This affects the density of the interfacial products, which are mainly composed of poorly crystallized crystalline structures. Therefore, these products fail first under stress, generating continuous micro-cracks and ultimately leading to concrete failure. In contrast, the surface structure of coarse tailings exhibits a high degree of amorphousness. Therefore, during concrete hydration, it can significantly improve the structure and types of products at the interface, greatly increasing the density of the interface and thus improving the compressive strength of the concrete. This is consistent with the results of concrete mechanical property tests. This study shows that C40 strength grade concrete can be prepared using a C30 concrete mix proportion.

[0133] Figure 6 The image shows the microstructure of the hydration products of sample 2. As can be seen from the image, the hydration products of sample 2 have a higher density and are mainly composed of amorphous gels. In addition, the secondary hydration reaction of fly ash is significantly effective, resulting in a significant increase in the later strength of the concrete.

[0134] 3. Study on the freeze-thaw resistance of coarse slag composite concrete system

[0135] According to GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" and GB / T50081 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", test specimens for the long-term performance and durability of concrete were prepared. The concrete specimens were prism specimens with dimensions of 100mm×100mm×400mm. The specimens were cured for 28 days under standard conditions and then tested by the rapid freezing method.

[0136] The freeze-thaw cycle test should be stopped if any of the following conditions occur:

[0137] (1) Reach the specified number of freeze-thaw cycles;

[0138] (2) The relative dynamic modulus of elasticity of the specimen decreased to 60%;

[0139] (3) The mass loss rate of the specimen reached 5%.

[0140] The relative modulus of elasticity is calculated using the following formula:

[0141] ×100

[0142] In the formula: —The relative dynamic modulus of elasticity (%) of the i-th concrete specimen after N freeze-thaw cycles, accurate to 0.1; —The transverse fundamental frequency (Hz) of the i-th concrete specimen after N freeze-thaw cycles; —The initial transverse fundamental frequency (Hz) of the i-th concrete specimen after N freeze-thaw cycles.

[0143]

[0144] —The relative dynamic modulus of elasticity (%) of a set of concrete specimens after N freeze-thaw cycles, accurate to 0.1. The relative dynamic modulus of elasticity P should be the arithmetic mean of the test results of three specimens. When the difference between the maximum or minimum value and the median value exceeds 15% of the average value, this value should be discarded, and the median value should be taken as the measured value.

[0145] The test results show that after 280 freeze-thaw cycles, the relative dynamic modulus of elasticity of one specimen of sample 2 is close to 0.6, which meets the failure requirement. However, the mass loss and relative freeze-thaw modulus of elasticity of the other two specimens still meet the standard requirements. For safety reasons, this study sets the freeze-thaw resistance grade of coarse slag composite manufactured sand concrete to F280, which meets the freeze-thaw resistance requirements of conventional commercial concrete.

[0146] 4. Study on the carbonation resistance of coarse slag composite concrete system

[0147] Samples 1-4 of the coarse slag composite manufactured sand concrete were cured to the specified age and then placed in a carbonation test chamber with a CO2 concentration of 20%, a temperature of 20℃, and a relative humidity of 90%. The carbonation depth of the concrete sections at 60d, 90d, and 120d was measured using the phenolphthalein colorimetric method.

[0148] Carbonation depth of coarse slag composite manufactured sand concrete with different mix proportions is shown in [reference needed]. Figure 7As the carbonation age increased, the carbonation depth of coarse slag composite manufactured sand concrete also increased. Increasing the desert sand content could reduce the carbonation depth. When the desert sand content was 30wt% (sample 3), the carbonation value of the concrete was the lowest. The carbonation pattern of coarse slag composite manufactured sand concrete also conforms to the current carbonation development pattern of commercial concrete.

[0149] Example 2

[0150] The difference from the above embodiments is that, as Figure 8 and Figure 9 The method for preparing coarse slag manufactured sand concrete includes the following steps:

[0151] S1. Pretreatment of coal gasification slag: The coal gasification slag mixture is decarbonized using a coal gasification slag pretreatment device to reduce the residual carbon content. Then, it is screened to remove particles larger than 4.75mm, resulting in coal gasification coarse tailings manufactured sand with a fineness modulus of 3.0-3.7. The decarbonization process involves calcining the coal gasification slag at 600-800℃ for 1-2 hours in an inert atmosphere or air. The process also includes a step of mechanically activating the resulting manufactured sand.

[0152] S2. Ingredients: Weigh cement, fly ash, coarse tailings manufactured sand obtained in step S1, desert sand, crushed stone, polycarboxylate superplasticizer, cellulose ether and water according to the proportion.

[0153] S3. Mixing: Put all the dry materials weighed in step S2 into the mixer and dry mix for 30-60 seconds to make them evenly mixed. Then add water and mix for 90-120 seconds. The coarse slag composite manufactured sand concrete is then discharged.

[0154] The coal gasification slag pretreatment device in step S1 includes a calcination component, a gas circulation component connected to the calcination component, a screening component connected to the calcination component, an activation component connected to the screening component, and a controller attached to the activation component. The calcination component, gas circulation component, screening component, and activation component are all connected to the controller via signal.

[0155] The calcination assembly is used to heat and calcine coal gasification slag to remove residual carbon. The calcination assembly includes an inclined calcination furnace 1, with an inner lining furnace 6 coaxially rotatably fitted inside the calcination furnace 1. The top of the inner lining furnace 6 has a feed port, and the bottom of the inner lining furnace 6 is connected to a waste discharge pipe 19. An electric control valve 13 is also installed between the inner lining furnace 6 and the waste discharge pipe 19. Electric heating wires are laid inside the side wall of the calcination furnace 1. A temperature sensor is installed inside the calcination furnace 1. A drive motor 3 is welded parallel to the top side wall of the calcination furnace 1. A drive gear 4 is coaxially welded to the output shaft of the drive motor 3. A driven gear ring 5 is welded to the outer periphery of the top of the inner lining furnace 6. The driven gear ring 5 meshes with the drive gear 4. The electric control valve 13, electric heating wires, temperature sensor, and drive motor 3 are all connected to the controller signal.

[0156] A gas circulation assembly is used to supply an inert atmosphere to the calcination assembly and to recover inert gas to remove waste gas. The gas circulation assembly includes a gas storage tank containing inert gas. The top of the gas storage tank is connected to a recovery pipe 7, which is connected to the top side wall of the calcination furnace 1. The bottom side wall of the gas storage tank is connected to an inflation pipe 2, which is connected to the middle side wall of the calcination furnace 1. Both the recovery pipe 7 and the inflation pipe 2 are equipped with air pumps with barometers. The recovery pipe 7 is also filled with carbon dioxide adsorption material. Both the barometer and the air pump are connected to the controller signal.

[0157] The screening component is used for grading and screening the coarse slag from decarbonization, removing particles larger than 4.75mm, and feeding particles of 2.36-4.75mm into the activation component. The screening component includes a storage bin 8, which is connected to the bottom of the calcining furnace 1 and is rotatably connected to the waste discharge pipe 19. The bottom of the storage bin 8 has a discharge port 10. The side wall of the inner lining furnace 6 has several first screening holes 11. The outer periphery of the waste discharge pipe 19 is slidably fitted with an annular screening mesh 20. The outer periphery of the annular screening mesh 20 is welded to the inner wall of the storage bin 8. An arc-shaped pusher block 12 is welded to the outer wall of the bottom of the inner lining furnace 6. The arc-shaped pusher block 12 is slidably fitted with the annular screening mesh 20. Several top beads are welded on the bottom wall of the arc-shaped pusher block 12. The size of the top beads is the same as the aperture of the annular screening mesh 20. The connection between the gas filling pipe 2 and the calcining furnace 1 corresponds to the bottom end of the movement trajectory of the arc-shaped pusher block 12. The top of the annular screening mesh has a push port.

[0158] An activation component is used to refine 2.36-4.75mm decarbonization coarse slag and activate the pozzolanic activity of the decarbonization coarse slag. The activation component includes a grinding bowl 16, which is rotatably connected to the top wall of the storage bin 8. Several grinding balls are placed inside the grinding bowl 16. Several second screening holes 15 with the same aperture as the annular screen are opened on the side wall of the grinding bowl 16. The aperture of the second screening holes 15 is smaller than that of the first screening holes 11. A sealing cover 9 is rotatably connected to the grinding bowl 16. An activation tube 14 is connected to one side wall of the sealing cover 9. The activation tube 14 is connected to the push port. A drive shaft is welded to the bottom wall of the grinding bowl 16. An activation bevel gear 17 is welded to the bottom end of the drive shaft. A drive bevel gear 18 is welded to the outer periphery of the waste discharge pipe 19. The drive bevel gear 18 meshes with the activation bevel gear 17.

[0159] The feed inlet, the bottom of the waste discharge pipe 19, and the discharge outlet 10 are all hinged with sealing caps.

[0160] The specific implementation process is as follows: Coal gasification slag includes coal gasification fine slag and coal gasification coarse slag. The decarbonization pretreatment of the coal gasification fine slag and coal gasification coarse slurry is called coal gasification coarse tailings.

[0161] The preparation of manufactured sand concrete from coal gasification coarse slag begins with the pretreatment of the coal gasification coarse slag. The entire process relies on an integrated pretreatment device for efficient and coordinated operation. First, the controller of the coal gasification coarse slag pretreatment device is activated, putting the calcination component, gas circulation component, screening component, and activation component into their preset working states. For the calcination component, the operator feeds the coal gasification slag mixture slurry into the inclined lining furnace 6 through the feed inlet, and closes the sealing cover of the feed inlet to ensure the furnace's airtightness. The controller drives the drive motor 3 at the top of the calcination furnace 1, and the driving gear 4 drives the driven gear ring 5 on the outer periphery of the lining furnace 6 to rotate, causing the lining furnace 6 to rotate coaxially with the calcination furnace 1. Simultaneously, the electric heating wires on the side wall of the calcination furnace 1 are activated, and the heating power is adjusted in real time by the temperature sensor inside the furnace to stabilize the furnace temperature at 600-800℃. During this process, the rotation of the inner lining furnace 6 causes the gasification slag to be continuously turned and pushed in the inclined furnace body, avoiding local accumulation and ensuring that each piece of gasification slag is heated evenly. After 1-2 hours of calcination, the residual carbon in the gasification slag is fully decomposed, achieving decarbonization treatment and effectively reducing the adverse effects of residual carbon on the subsequent concrete performance.

[0162] Combination Figure 9 As shown, the gas circulation component works synchronously with the calcination component. Inert gas (such as nitrogen) in the gas storage tank is transported to the middle of the calcination furnace 1 through the gas filling pipe 2. The gas pump and pressure gauge maintain a stable inert atmosphere in the furnace under the control of the controller, preventing unnecessary oxidation reactions of the coal gasification slag at high temperatures. The carbon-containing waste gas (such as carbon dioxide) generated during the calcination process is discharged from the top of the calcination furnace 1 along with the inert gas through the recovery pipe 7. The carbon dioxide adsorption material (such as alkaline adsorbent) in the recovery pipe 7 adsorbs and removes the carbon dioxide from the waste gas. The purified inert gas is returned to the gas storage tank for recycling, which reduces the consumption of inert gas and the emission of waste gas, achieving energy saving and environmental protection. If decarbonization is carried out in the air, the gas circulation component can be shut down by the controller, and the calcination can be completed directly using the air atmosphere, enhancing the flexibility of the process.

[0163] The coarse tailings after decarbonization are pushed to the bottom as the inner lining furnace 6 rotates. They are initially classified and screened through the first screening hole 11 with a diameter of 4.75mm. Smaller particles fall onto the annular screening mesh 20 for a second classification and screening. Coarse tailings particles with a particle size smaller than 2.36mm fall directly into the storage bin 8 as part of the manufactured sand. As the inner lining furnace 6 rotates, the arc-shaped pusher block 12 on the outer wall of the bottom end of the inner lining furnace 6 will form a sliding fit with the annular screening mesh 20, pushing the coarse tailings with a particle size of 2.36mm-4.75mm to tumble and screen. The top bead on the bottom wall of the arc-shaped pusher block 12 will repeatedly strike the screen mesh as it rotates, effectively vibrating and preventing screen blockage, thus ensuring screening efficiency. Meanwhile, the gas introduced through the air inlet pipe 2 forms an airflow impact at the bottom of the arc-shaped pusher block 12's movement trajectory, further assisting in the screening of coarse tailings; while particles of 2.36-4.75mm are pushed into the activation component by the arc-shaped pusher block 12 through the push port at the top of the annular screening mesh, achieving precise particle grading.

[0164] In the activation component, particles from the push port enter the grinding bowl 16 through the activation pipe 14. The grinding bowl 16 meshes with the drive bevel gear 18 on the outer periphery of the waste discharge pipe 19 via the activation bevel gear 17 at the bottom of the drive shaft, achieving synchronous rotation with the power of the rotating inner furnace 6, eliminating the need for an additional power source and saving energy. The grinding balls inside the grinding bowl 16 impact and grind the 2.36-4.75mm particles as the bowl rotates, refining the particles and activating their pozzolanic activity. The sealing cover 9 prevents dust leakage during the grinding process. The ground particles are screened through the second screening hole 15 on the side wall of the grinding bowl 16 to obtain composite standard activated coarse tailings particles with a particle size smaller than 2.36mm. These particles, together with the fine particles in the storage bin 8, form coal gasification coarse tailings manufactured sand with a fineness modulus of 3.0-3.7, completing the pretreatment process.

[0165] After pretreatment, the material is batched. Cement, fly ash, the aforementioned coal gasification coarse tailings manufactured sand, desert sand, crushed stone, polycarboxylate superplasticizer, cellulose ether, and water are precisely weighed according to the specified proportions to ensure accurate ratios and guarantee concrete performance. Next, the mixing stage begins. All dry materials are added to the mixer and dry-mixed for 30-60 seconds to ensure uniform mixing. Water is then added and mixed for 90-120 seconds to fully hydrate and disperse the materials, ultimately yielding coal gasification coarse tailings manufactured sand concrete.

[0166] Throughout the process, the components of the pretreatment unit operate collaboratively through a controller, achieving continuous processing of decarbonization, screening, and activation, thus ensuring the quality stability of the manufactured sand. The preparation method is simple and the steps are closely linked, realizing the resource utilization of coal gasification slag and alleviating resource shortages by replacing natural sand through blending with desert sand. The final concrete, due to the pozzolanic activity of the manufactured sand, the reasonable gradation of the composite fine aggregate, and the regulating effect of admixtures, possesses excellent workability, mechanical properties, and durability, comprehensively achieving a balance between environmental benefits, economic benefits, and technical performance.

[0167] Example 3

[0168] The difference from the above embodiments is that a coarse slag composite manufactured sand concrete is made from raw materials in the following proportions:

[0169] 280 kg of cement; 110 kg of fly ash; 830 kg of sand (415 kg of coarse slag and 415 kg of desert sand); 1000 kg of gravel; 12.6 kg of composite admixture; 135 kg of water (2% moisture content for manufactured sand and desert sand).

[0170] Table 10. Compressive Strength Test Data 1

[0171]

[0172] Example 4

[0173] The difference from the above embodiments is that a coarse slag composite manufactured sand concrete is made from raw materials in the following proportions:

[0174] 260 kg of cement; 110 kg of fly ash; 850 kg of sand (425 kg of coarse slag and 425 kg of desert sand); 1000 kg of gravel; 11.9 kg of composite admixture; 139.5 kg of water (2% moisture content in coarse slag and desert sand).

[0175] Table 11. Compressive Strength Test Data 2

[0176]

[0177] Example 5

[0178] The difference from the above embodiments is that a coarse slag composite manufactured sand concrete is made from raw materials in the following proportions:

[0179] 270 kg of cement; 110 kg of fly ash; 840 kg of sand (420 kg of coarse slag and 420 kg of desert sand); 1000 kg of gravel; 12.3 kg of composite admixture; 135 kg of water (2% moisture content of coarse slag and desert sand).

[0180] Table 12. Compressive Strength Test Data 3

[0181]

[0182] Example 6

[0183] The difference from the above embodiments is that a coarse slag composite manufactured sand concrete is made from raw materials in the following proportions:

[0184] 250 kg of cement; 110 kg of fly ash; 860 kg of sand (345 kg of coarse slag and 515 kg of desert sand); 1000 kg of gravel; 11.6 kg of composite admixture; 140 kg of water (2% moisture content of coarse slag and desert sand).

[0185] Table 13. Compressive strength test data 4

[0186]

[0187] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0188] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A coarse slag composite manufactured sand concrete, characterized in that: Made from the following parts by weight of raw materials: 320-430 parts cementitious material, 800-1000 parts fine aggregate, 740-1100 parts crushed stone, 8-15 parts compound admixture and 130-170 parts water; The cementitious material is composed of cement and fly ash, with cement accounting for 72%-75% of the total mass of the cementitious material; The fine aggregate is composed of coarse tailings manufactured sand and desert sand, wherein the coarse tailings manufactured sand accounts for 30%-85% of the total mass of the fine aggregate, and the coarse tailings manufactured sand is a particle that has undergone decarburization and screening pretreatment, with a fineness modulus controlled at 3.0-3.

7. The compound admixture is composed of polycarboxylate superplasticizer and cellulose ether, wherein the cellulose ether accounts for 0.05%-0.15% of the total mass of the cementitious material.

2. The coarse slag composite manufactured sand concrete according to claim 1, characterized in that: The solid content of polycarboxylate superplasticizer is 35-40%.

3. The coarse slag composite manufactured sand concrete according to claim 2, characterized in that: The cellulose ether is hydroxypropyl methylcellulose ether.

4. A method for preparing coarse slag manufactured sand concrete, based on the coarse slag composite manufactured sand concrete according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Pretreatment of coal gasification slag: The coal gasification slag mixture is decarbonized using a coal gasification slag pretreatment device to reduce the residual carbon content. Then, it is screened to remove particles larger than 4.75mm, resulting in coarse tailings manufactured sand with a fineness modulus of 3.0-3.

7. S2. Ingredients: Weigh cement, fly ash, coarse tailings manufactured sand obtained in step S1, desert sand, crushed stone, polycarboxylate superplasticizer, cellulose ether and water according to the proportion. S3. Mixing: Put all the dry materials weighed in step S2 into the mixer and dry mix for 30-60 seconds to make them evenly mixed. Then add water and mix for 90-120 seconds. The coarse slag composite manufactured sand concrete is then discharged.

5. The method for preparing coarse slag manufactured sand concrete according to claim 4, characterized in that: The decarbonization process in step S1 involves calcining the coal gasification slag at 600-800℃ for 1-2 hours.

6. The method for preparing coarse slag manufactured sand concrete according to claim 5, characterized in that: The decarbonization process is carried out in an inert atmosphere or in air.

7. The method for preparing coarse slag manufactured sand concrete according to claim 4, characterized in that: After the screening process in step S1, the process also includes a step of mechanically activating the obtained manufactured sand.

8. The method for preparing coarse slag manufactured sand concrete according to claim 4, characterized in that: The coal gasification slag pretreatment device in step S1 includes a calcination component, a gas circulation component connected to the calcination component, a screening component connected to the calcination component, an activation component connected to the screening component, and a controller fixedly connected to the activation component. The calcination component, the gas circulation component, the screening component, and the activation component are all connected to the controller via signal. Calcination assembly, used to heat and calcine coal gasification slag to remove residual carbon; A gas circulation assembly is used to supply an inert atmosphere to the calcination assembly and to recover inert gas to remove waste gas. The screening component is used to classify and screen the coarse slag from the decarbonization process, remove particles larger than 4.75mm, and send particles of 2.36-4.75mm to the activation component. The activation component is used to refine the 2.36-4.75mm decarburized coarse slag and activate the pozzolanic activity of the decarburized coarse slag.

9. The method for preparing coarse slag manufactured sand concrete according to claim 8, characterized in that: The calcination assembly includes an inclined calcination furnace (1), a lining furnace (6) is coaxially rotatably connected inside the calcination furnace (1), a feed port is opened at the top of the lining furnace (6), a waste discharge pipe (19) is connected to the bottom of the lining furnace (6), an electric control valve (13) is also provided between the lining furnace (6) and the waste discharge pipe (19), an electric heating wire is laid inside the side wall of the calcination furnace (1), a temperature sensor is provided inside the calcination furnace (1), a drive motor (3) is fixedly connected parallel to the top side wall of the calcination furnace (1), a drive gear (4) is fixedly connected coaxially to the output shaft of the drive motor (3), a driven gear ring (5) is fixedly connected to the outer periphery of the top of the lining furnace (6), the driven gear ring (5) meshes with the drive gear (4), and the electric control valve (13), electric heating wire, temperature sensor and drive motor (3) are all connected to the controller signal.

10. The method for preparing coarse slag manufactured sand concrete according to claim 8, characterized in that: The gas circulation assembly includes a gas storage tank containing inert gas. The top of the gas storage tank is connected to a recovery pipe (7), which is connected to the top side wall of the furnace (1). The bottom side wall of the gas storage tank is connected to an inflation pipe (2), which is connected to the middle side wall of the furnace (1). Both the recovery pipe (7) and the inflation pipe (2) are equipped with air pumps with barometers. The recovery pipe (7) is also filled with carbon dioxide adsorption material. Both the barometer and the air pump are connected to the controller signal.

11. The method for preparing coarse slag manufactured sand concrete according to claim 8, characterized in that: The screening assembly includes a storage bin (8), which is connected to the bottom of the furnace (1). The storage bin (8) is rotatably connected to the waste discharge pipe (19). The bottom of the storage bin (8) has a discharge port (10). The side wall of the inner lining furnace (6) has several first screening holes (11). The outer periphery of the waste discharge pipe (19) is slidably fitted with an annular screening mesh (20). The outer periphery of the annular screening mesh (20) is fixedly connected to the inner wall of the storage bin (8). The outer side wall of the bottom of the inner lining furnace (6) is fixedly connected with an arc-shaped push block (12). The arc-shaped push block (12) is slidably fitted with the annular screening mesh (20). Several top beads are fixedly connected to the bottom wall of the arc-shaped push block (12). The size of the top beads is the same as the aperture of the annular screening mesh (20). The connection between the gas filling pipe (2) and the furnace (1) corresponds to the bottom of the movement trajectory of the arc-shaped push block (12). The top of the annular screening mesh has a push port.

12. The method for preparing coarse slag manufactured sand concrete according to claim 8, characterized in that: The activation component includes a grinding bowl (16), which is rotatably connected to the top wall of the storage bin (8). Several grinding balls are placed inside the grinding bowl (16). Several second screening holes (15) with the same aperture as the annular screen are opened on the side wall of the grinding bowl (16). The aperture of the second screening holes (15) is smaller than that of the first screening holes (11). A sealing cover (9) is rotatably connected to the grinding bowl (16). An activation tube (14) is connected to one side wall of the sealing cover (9). The activation tube (14) is connected to the push port. A drive shaft is fixedly connected to the bottom wall of the grinding bowl (16). An activation bevel gear (17) is fixedly connected to the bottom end of the drive shaft. A drive bevel gear (18) is fixedly sleeved on the outer periphery of the waste discharge pipe (19). The drive bevel gear (18) meshes with the activation bevel gear (17).

13. The method for preparing coarse slag manufactured sand concrete according to claim 8, characterized in that: The inlet, the bottom of the waste pipe (19), and the outlet (10) are all hinged with sealing caps.

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