Coal-fired slag modification method and application thereof
By modifying coal-fired slag with fly ash-cement mixture, the problem of poor workability of coal-fired slag in mortar and concrete has been solved, enabling the application of high-strength and environmentally friendly building materials and solving the problems of resource waste and environmental pollution.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHIHEZI UNIVERSITY
- Filing Date
- 2026-03-10
- Publication Date
- 2026-05-05
AI Technical Summary
The porous structure of coal-fired furnace slag results in poor workability, low strength, and poor stability when used in the production of mortar and concrete. Furthermore, its extensive landfill disposal causes environmental pollution and resource waste, making it difficult to widely apply in the building materials industry.
Modified coal slag is prepared by adding fly ash-cement mixture and water to the crushed and screened coal slag, and then using a horizontal slow mixing method to fill and coat the slag pores, improve fluidity, and provide the water required for hydration.
It significantly improves the compressive strength and fluidity of modified coal slag, achieving 100% replacement of natural sand, and has both environmental and economic benefits. It is suitable for the production of high-strength mortar and concrete.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to the field of mortar and concrete preparation technology, specifically to a method for modifying coal-fired furnace slag and its application. Background Technology
[0002] Coal-fired furnace slag is the grayish-black ash discharged from the bottom of the furnace after coal combustion, also known as furnace slag, with an annual national output of approximately 200 million tons. Depending on the furnace type and discharge method, the particle size of the slag varies, ranging from over 30 cm to only tens of micrometers. The chemical composition of the slag is basically the same as that of fly ash, mainly consisting of SiO2, Al2O3, FeO, CaO, MgO, and small amounts of R2O, S, and P. The mineral composition of the slag is glassy, exhibiting stable properties. Its significant structural characteristic is its porous and brittle nature, with a porosity reaching up to 90%. Depending on the porosity, the compressive strength of the slag ranges from tens of MPa to a few tenths of an MPa. The porosity results in a high water absorption rate, leading to poor workability, low strength, poor stability, and inadequate frost resistance when used in mortar and concrete production. In particular, when slag replaces natural sand in mortar and concrete production, the compressive strength of the mortar and concrete decreases by up to 50%, severely restricting its widespread application.
[0003] Currently, apart from a small portion being used for building material production, most of the slag is disposed of through landfill, resulting in significant land occupation, environmental pollution, and resource waste. There is an urgent need for safe disposal and recycling of slag.
[0004] Mortar and concrete production requires a large amount of sand and gravel. In 2023, my country's demand for concrete sand and gravel exceeded 15 billion tons, of which sand accounted for 6 billion tons. With the strengthening of national environmental protection efforts, my country is facing a severe "sand shortage." Therefore, the rational utilization of solid waste, including coal-fired furnace slag, to replace or partially replace natural sand in the production of mortar and concrete has become an inevitable choice for solid waste management, environmental protection, and the sustainable development of the building materials industry.
[0005] Based on this, the present invention provides a method for modifying coal-fired furnace slag and its application in the production of high-strength mortar or concrete, aiming to improve the mechanical properties of slag, enhance the workability of mortar and concrete, and provide technical support for solid waste treatment and the production of high-strength mortar and concrete. Summary of the Invention
[0006] The purpose of this invention is to provide a method for modifying coal-fired boiler slag and the modified coal-fired boiler slag prepared by the method of this invention.
[0007] Another object of the present invention is to provide the method for modifying coal slag described herein or the application of modified coal slag in the production of high-strength mortar or concrete.
[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The method for modifying coal-fired furnace slag according to the present invention includes the following steps: S1. After crushing and screening the coal-fired furnace slag, dry it until the moisture content is below 5%; S2. Add 5%-15% of the mass of fly ash-cement mixture to the coal slag, and stir horizontally at a slow speed to ensure that the pores of the slag are filled with the mixed powder; wherein, the mass ratio of fly ash to cement in the fly ash-cement mixture is 90:10. S3. Add water equal to 10%-18% of the mass of coal slag, stir slowly, and it's ready.
[0009] Preferably, in the coal-fired furnace slag modification method of the present invention, the screening in step S1 specifically involves passing the material through a 4.75mm sieve.
[0010] Preferably, in the coal-fired slag modification method of the present invention, the step S1 involves drying the slag until the moisture content is less than 3%.
[0011] Preferably, in the coal slag modification method of the present invention, the amount of fly ash-cement mixture added in step S2 is 10%-15% of the mass of the coal slag.
[0012] In a further preferred embodiment, in the coal slag modification method of the present invention, the amount of fly ash-cement mixture added in step S2 is 15% of the mass of the coal slag.
[0013] Preferably, in the coal slag modification method of the present invention, the amount of water added in step S3 is 15%-18% of the mass of the coal slag.
[0014] In a further preferred embodiment, in the coal slag modification method of the present invention, the amount of water added in step S3 is 18% of the mass of the coal slag.
[0015] Preferably, in the coal slag modification method of the present invention, the stirring time in step S2 or step S3 is 3-5 min.
[0016] The modified coal slag described in this invention is prepared using the method described above.
[0017] The present invention relates to the method for modifying coal slag or the application of modified coal slag in the production of high-strength mortar or concrete.
[0018] The beneficial effects of this invention are: 1. This invention provides a method for modifying coal-fired furnace slag. By filling and coating the pores of the slag with fly ash-cement mixture, the porosity of the slag is reduced and the fluidity of the slag is improved. At the same time, the pre-added water is adsorbed in the slag, providing moisture for the hydration of cement in mortar or concrete, which can significantly improve the compressive strength of mortar and concrete.
[0019] 2. In the coal-fired slag modification method provided by the present invention, the mixing method when dry mixing slag and fly ash-cement is horizontal slow mixing, which can effectively prevent fly ash-cement from settling to the bottom and slag from floating on the fly ash-cement, ensuring that fly ash-cement fills the slag pores to the maximum extent.
[0020] 3. The modified slag provided by this invention can replace natural sand in the production of mortar and concrete, achieving 100% replacement of natural sand with slag. Its raw materials are derived from industrial solid waste, are inexpensive and readily available, and the process is simple and easy to implement. This invention has significant environmental and economic benefits. Attached Figure Description
[0021] Figure 1 The slag remains as it was. Figure 2 The slag is modified by filling with fly ash-cement mixture containing 10% slag mass and wetting with water. Detailed Implementation
[0022] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The following embodiments are for explanation and illustration only, and do not constitute a limitation on the technical solution of the present invention.
[0023] Example 1 Slag modification methods and their application in the production of high-strength mortar.
[0024] The slag is crushed, sieved through a 4.75 mm sieve, and dried until the moisture content is below 3.0%. Mortar is produced according to a cement:slag mass ratio of 1:3. First, room temperature slag is weighed and added to a mortar mixing pot, along with 5% of the slag mass of fly ash-cement mixture (fly ash to cement mass ratio of 90:10). The slag and mixture are stirred for 3-5 minutes, simulating a horizontal mixing method, by slowly turning the mixture from the bottom of the pot upwards to ensure thorough mixing with the slag and filling the pores of the slag with the mixture. Then, the mixture is placed in a mortar mixer, and 10% of the slag mass of water is added. The mixer is started and stirred slowly for 3-5 minutes. Finally, a measured amount of cement is added, and the water amount is adjusted to ensure the mortar consistency is 40±10 mm.
[0025] Example 2 Slag modification methods and their application in the production of high-strength mortar.
[0026] The slag is crushed, sieved through a 4.75 mm sieve, and dried until the moisture content is below 3.0%. Mortar is produced according to a cement:slag mass ratio of 1:3. First, room temperature slag is weighed and added to a mortar mixing pot, along with 10% of the slag mass of fly ash-cement mixture (fly ash to cement mass ratio of 90:10). The slag and mixture are stirred for 3-5 minutes, simulating a horizontal mixing method, by slowly turning the mixture at the bottom of the pot upwards to ensure thorough mixing with the slag and filling the pores of the slag with the mixture. Then, the mixture is placed in a mortar mixer, and 15% of the slag mass of water is added. The mixer is started and stirred slowly for 3-5 minutes. Finally, a measured amount of cement is added, and the water amount is adjusted to ensure the mortar consistency is 40±10 mm.
[0027] Example 3 Slag modification methods and their application in the production of high-strength mortar.
[0028] The slag is crushed, sieved through a 4.75 mm sieve, and dried until the moisture content is below 3.0%. Mortar is produced according to a cement:slag mass ratio of 1:3. First, room temperature slag is weighed and added to a mortar mixing pot, along with 15% of the slag mass of fly ash-cement mixture (fly ash to cement mass ratio of 90:10). The slag and mixture are stirred for 3-5 minutes, simulating a horizontal mixing method, by slowly turning the mixture from the bottom of the pot upwards to ensure thorough mixing with the slag and filling the pores of the slag with the mixture. Then, the mixture is placed in a mortar mixer, and 18% of the slag mass of water is added. The mixer is started and stirred slowly for 3-5 minutes. Finally, a measured amount of cement is added, and the water amount is adjusted to ensure the mortar consistency is 40±10 mm.
[0029] Example 4 Slag modification methods and their application in the production of high-strength mortar.
[0030] The slag is crushed, sieved through a 4.75 mm sieve, and dried until the moisture content is below 3.0%. Mortar is produced according to a cement:slag mass ratio of 1:2. First, room temperature slag is weighed and added to a mortar mixing pot, along with 10% of the slag mass of fly ash-cement mixture (fly ash to cement mass ratio of 90:10). The slag and mixture are stirred for 3-5 minutes, simulating a horizontal mixing method, by slowly turning the mixture from the bottom of the pot upwards to ensure thorough mixing with the slag and filling the pores of the slag with the mixture. Then, the mixture is placed in a mortar mixer, and 15% of the slag mass of water is added. The mixer is started and stirred slowly for 3-5 minutes. Finally, a measured amount of cement is added, and the water amount is adjusted to ensure the mortar consistency is 40±10 mm.
[0031] Example 5 Slag modification methods and their application in the production of high-strength mortar.
[0032] The slag is crushed, sieved through a 4.75 mm sieve, and dried to a moisture content of 10%. Mortar is produced according to a cement:slag mass ratio of 1:3. First, room temperature slag is weighed and added to a mortar mixing pot, along with 10% of the slag mass of fly ash-cement mixture (fly ash to cement mass ratio of 90:10). The slag and mixture are stirred for 3-5 minutes, simulating a horizontal mixing method, by slowly turning the mixture from the bottom of the pot upwards to ensure thorough mixing with the slag and filling the pores of the slag with the mixture. Then, the mixture is placed in a mortar mixer, and 8% of the slag mass of water is added. The mixer is started and stirred slowly for 3-5 minutes. Finally, a measured amount of cement is added, and the water amount is adjusted to ensure the mortar consistency is 40±10 mm.
[0033] Example 6 Slag modification methods and their application in the production of high-strength concrete.
[0034] The slag is crushed, sieved through a 4.75 mm sieve, and then dried until the moisture content is below 3.0%. Concrete is produced according to the C30 concrete mix ratio of cement:slag:aggregate = 1:1.92:3.41. First, weigh the room-temperature slag and add it to a horizontal concrete mixer. Add 5% of the slag's mass of fly ash-cement mixture (fly ash to cement mass ratio of 90:10). Start the horizontal mixer and slowly mix the slag and mixture for 3-5 minutes to ensure the pores of the slag are filled with the mixture. Then, add 10% of the slag's mass of water and slowly mix for 3-5 minutes. Finally, add the measured amounts of cement and aggregate, adjusting the water amount according to a concrete slump of 150±30 mm.
[0035] Example 7 Slag modification methods and their application in the production of high-strength concrete.
[0036] The slag is crushed, sieved through a 4.75 mm sieve, and then dried until the moisture content is below 3.0%. Concrete is produced according to the C30 concrete mix ratio of cement:slag:aggregate = 1:1.92:3.41. First, weigh the room-temperature slag and add it to a horizontal concrete mixer. Add 10% of the slag's mass of fly ash-cement mixture (fly ash to cement mass ratio of 90:10). Start the horizontal mixer and slowly mix the slag and mixture for 3-5 minutes to ensure the pores of the slag are filled with the mixture. Then, add 15% of the slag's mass of water and slowly mix for 3-5 minutes. Finally, add the measured amounts of cement and aggregate, adjusting the water amount according to a concrete slump of 150±30 mm.
[0037] Example 8 Slag modification methods and their application in the production of high-strength concrete.
[0038] The slag is crushed, sieved through a 4.75 mm sieve, and then dried until the moisture content is below 3.0%. Concrete is produced according to the C30 concrete mix ratio of cement:slag:aggregate = 1:1.92:3.41. First, weigh the room-temperature slag and add it to a horizontal concrete mixer. Add 15% of the slag's mass of fly ash-cement mixture (fly ash to cement mass ratio of 90:10). Start the horizontal mixer and slowly mix the slag and mixture for 3-5 minutes to ensure the pores of the slag are filled with the mixture. Then, add 18% of the slag's mass of water and slowly mix for 3-5 minutes. Finally, add the measured amounts of cement and aggregate, adjusting the water amount according to a concrete slump of 150±30 mm.
[0039] Example 9 Slag modification methods and their application in the production of high-strength concrete.
[0040] The slag is crushed, sieved through a 4.75 mm sieve, and then dried until the moisture content is below 3.0%. Concrete is produced according to the C40 concrete mix ratio of cement:slag:aggregate = 1:1.2:2.3. First, weigh the room-temperature slag and add it to a horizontal concrete mixer. Add 10% of the slag's mass of fly ash-cement mixture (fly ash to cement mass ratio of 90:10). Start the horizontal mixer and slowly mix the slag and mixture for 3-5 minutes to ensure the pores of the slag are filled with the mixture. Then, add 15% of the slag's mass of water and slowly mix for 3-5 minutes. Finally, add the measured amounts of cement and aggregate, adjusting the water amount according to a concrete slump of 150±30 mm.
[0041] To further verify the reliability of the present invention and select the optimal solution, the inventors conducted a series of comparative experiments, as follows: 1. Reference test of slag mortar (1) Reference 1 Weigh 42.5 silicate cement and river sand into a mortar mixing pot according to a mortar-to-mortar ratio of 1:3, and adjust the amount of water added according to a mortar consistency of 40±10 mm.
[0042] (2) Reference ratio 2 After crushing the slag, sieve it through a 4.75 mm sieve, and dry it until the moisture content is less than 5%. Weigh the slag at room temperature and 42.5 silicate cement into a mortar mixing pot according to the cement:slag mass ratio of 1:3. Adjust the amount of water added according to the mortar consistency of 40±10 mm.
[0043] (3) Reference ratio 3 After crushing the slag, sieve it through a 4.75 mm sieve and dry it until the moisture content is less than 5%. Weigh out the slag and 42.5 silicate cement at room temperature into a mortar mixing pot according to the cement:slag mass ratio of 1:3. Then add 10% of the slag mass of fly ash-cement mixture and adjust the amount of water added according to the mortar consistency of 40±10 mm.
[0044] Mortar was produced according to the methods of Examples 1-5 and Reference Examples 1-3. The water-to-material ratio was recorded during the experiment. The mortar was mixed, molded, vibrated, shaped, cured, demolded, and further cured and tested according to the Cement Mortar Strength Test Method (ISO Method) (GB / T17671-2021). The average compressive strength of the mortar after 28 days of standard curing was tested, and the results are shown in Table 1.
[0045] ; As shown in Table 1, compared with the river sand mortar of Reference 1, the slag mortar of Reference 2 without fly ash-cement mixture modification had a 25.9% decrease in compressive strength and an 18.7% increase in water absorption. The slag mortar (Reference 3) prepared by directly adding 10% fly ash-cement mixture had an 8.8% increase in compressive strength and a 25.0% increase in water absorption compared with Reference 1, which is related to the increase in fly ash-cement. The slag mortars (Examples 1-3) prepared by adding 5%, 10%, and 15% fly ash-cement mixture, respectively, had compressive strengths increased by 48.2%, 70.8%, and 75.5%, respectively, and water absorptions increased by 25.0%, 25.0%, and 31.2%, respectively, compared with Reference 1. As can be seen from the above, the compressive strength of slag mortar produced using fly ash-cement mixture modified slag significantly exceeds that of cement-river sand mortar, and the compressive strength of slag mortar increases with the increase of fly ash-cement mixture content. Due to the porosity of slag, the water-to-material ratio of slag mortar in Examples 1-5 is increased, with a maximum increase of 43.8% compared to Reference Example 1.
[0046] In Example 4, the mortar-to-cement ratio was 1:2, and the compressive strength reached 56.6 MPa. This mortar strength is significantly higher than the crushing strength of the slag, indicating the feasibility of using slag to produce high-strength mortar. The high water-to-material ratio in Example 4 is related to the high water requirement of the cement. In Example 5, the slag moisture content was 10%. The mortar produced according to the method in Example 5 showed a 14.8% increase in compressive strength compared to the reference example 3, indicating that filling slag with fly ash-cement mixture at a 10% moisture content is beneficial for improving the compressive strength of the slag mortar. However, compared to Example 2, the compressive strength decreased by 26.9%, indicating that when the slag moisture content is high, the amount of fly ash-cement mixture entering the slag pores is limited, and the filling effect is somewhat affected.
[0047] 2. Reference test of slag concrete (1) Reference ratio 4 According to the mass ratio of C30 concrete, cement: river sand: gravel = 1:1.92:3.41, weigh out the gravel, river sand and 42.5 silicate cement and add them to the horizontal concrete mixer. Adjust the amount of water according to the concrete slump of 150±30 mm.
[0048] (2) Reference ratio 5 After crushing the slag, sieve it through a 4.75 mm sieve and dry it until the moisture content is below 5%. According to the mass ratio of C30 concrete, cement:slag:aggregate = 1:1.92:3.41, weigh the aggregate, slag and 42.5 silicate cement into a horizontal concrete mixer, and adjust the amount of water added according to the concrete slump of 150±30 mm.
[0049] (3) Reference ratio 6 After crushing the slag, sieve it through a 4.75 mm sieve and dry it until the moisture content is below 5%. According to the mass ratio of cement:slag:aggregate = 1:1.2:2.3 for C40 concrete, weigh out the aggregate, slag and 42.5 silicate cement into a horizontal concrete mixer, and adjust the amount of water added according to the concrete slump of 150±30 mm.
[0050] Concrete was produced according to the methods of Examples 6-9 and Reference Examples 4-6. The water-to-material ratio was recorded during the experiment. The mixing, molding, compaction, molding, curing, demolding, continued curing and strength testing were carried out according to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T50081-2019). The average compressive strength of the concrete after 28 days of standard curing was tested, and the results are shown in Table 2.
[0051] ; As shown in Table 2, compared with the C30 river sand concrete in Reference Example 4, the slag concrete prepared by replacing river sand with slag (Reference Example 5) had a 17.9% decrease in compressive strength and a 22.2% increase in water absorption. Compared with Reference Example 4, the slag concrete prepared by adding 5%, 10%, and 15% fly ash-cement mixture (Examples 6-8) had a -2.8%, 16.0%, and 21.7% increase in compressive strength, and a 33.3%, 33.3%, and 44.4% increase in water absorption, respectively. Compared with the slag concrete prepared in Reference Example 5, the slag concrete prepared by adding 5%, 10%, and 15% fly ash-cement mixture (Examples 6-8) had a 18.4%, 41.4%, and 48.3% increase in compressive strength, respectively.
[0052] Reference Example 6 is C40 slag concrete, and Example 9 is a C40 example in which fly ash-cement mixture fills and encapsulates slag to replace river sand. Compared with Reference Example 6, the compressive strength of the slag concrete in Example 9 is increased by 7.8%. It can be seen that using fly ash-cement mixture to modify slag to produce slag concrete can significantly improve its compressive strength.
[0053] Figure 1 The slag remains as it was. Figure 2 The slag is modified by filling with a fly ash-cement mixture containing 10% slag by weight and then wetting it with water. Figure 1 , Figure 2 It can be seen that the original slag is porous and has sharp edges. After being filled with fly ash-cement mixture and modified by adding water, the pores of the slag are filled and blocked, a large amount of mixture adheres to the surface, and the shape is rounded.
[0054] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.
Claims
1. A method for modifying coal-fired furnace slag, characterized in that, Includes the following steps: S1. After crushing and screening the coal-fired furnace slag, dry it until the moisture content is below 5%; S2. Add 5%-15% of the mass of fly ash-cement mixture to the coal slag, and stir horizontally at a slow speed to ensure that the pores of the slag are filled with the mixed powder; wherein, the mass ratio of fly ash to cement in the fly ash-cement mixture is 90:
10. S3. Add water equal to 10%-18% of the mass of coal slag, stir slowly, and it's ready.
2. The method for modifying coal-fired boiler slag according to claim 1, characterized in that, The sieving process described in step S1 specifically involves passing the material through a 4.75 mm sieve.
3. The method for modifying coal-fired boiler slag according to claim 1, characterized in that, In step S1, the product is dried until the moisture content is below 3%.
4. The method for modifying coal-fired boiler slag according to claim 1, characterized in that, The amount of fly ash-cement mixture added in step S2 is 10%-15% of the mass of coal-fired slag.
5. The method for modifying coal-fired boiler slag according to claim 4, characterized in that, The amount of fly ash-cement mixture added in step S2 is 15% of the mass of coal-fired slag.
6. The method for modifying coal-fired boiler slag according to claim 1, characterized in that, The amount of water added in step S3 is 15%-18% of the mass of coal-fired slag.
7. The method for modifying coal-fired boiler slag according to claim 6, characterized in that, The amount of water added in step S3 is 18% of the mass of the coal-fired slag.
8. The method for modifying coal-fired boiler slag according to claim 1, characterized in that, The stirring time in step S2 or step S3 is 3-5 min.
9. A modified coal slag prepared by the coal slag modification method according to claim 1.
10. The method for modifying coal slag as described in claim 1 or the application of the modified coal slag as described in claim 9 in the production of high-strength mortar or concrete.