A pozzolan-like cementitious material - slag geopolymer cement and a method of making the same

Abstract

The application discloses a kind of volcano ash-like cementitious material-geopolymer cement and a preparation method thereof, the geopolymer cement includes geopolymer cementitious material, alkali activator, sand and water, the geopolymer cementitious material is composed of 50wt%~90wt% granulated blast furnace slag and 10wt%~50wt% volcano ash-like cementitious material, and the mass ratio of geopolymer cementitious material and sand is 1:3.The application solves the problems of poor flowability, large shrinkage and other problems of alkali-activated slag geopolymer, greatly improves the flexural strength, effectively improves the compressive strength, and increases the application range of geopolymer cementitious material;It disposes mine stripping waste soil and abandoned low-grade limestone, reduces the impact of solid waste on land occupation and environmental pollution, and saves cost.

Description

Technical Field

[0001] This invention relates to the field of cement materials technology, specifically to a pozzolanic cementitious material—slag geopolymer cement—and its preparation method. Background Technology

[0002] Under the global circular economy policy, the production of traditional building materials such as silicate cement is accompanied by high carbon emissions, exacerbating global climate change. Finding reasonable and effective measures to reduce carbon emissions is now urgent. Efficiently utilizing low-CO2 emission resources to achieve economic growth has been prioritized. Among these measures, maximizing the utilization of bulk industrial solid waste is a powerful tool for promoting green, sustainable, and low-carbon development and building a resource-saving and environmentally friendly society.

[0003] The disposal of large quantities of solid waste is quite difficult today, mainly relying on passive stockpiling. Some hazardous solid waste is disposed of through methods such as landfill, incineration, chemical conversion, and microbial treatment, while some is dumped into the ocean. The accumulation of solid waste not only occupies a large amount of land and wastes human and material resources, but also pollutes soil, air, and water bodies, and even endangers human health.

[0004] Granulated blast furnace slag (GGBS) and metakaolin (MK) are common industrial solid wastes that generally contain large amounts of silicon (Si) and aluminum (Al), which constitute the main components of geopolymer precursors. However, these high-quality composite materials face challenges such as rising transportation costs, declining grades, insufficient supply, and increased costs. Developing new green cementitious materials is an inevitable trend.

[0005] The utilization rate of stripped waste soil and low-grade limestone from mining operations is low, less than 5% in China. Studies have shown that calcined clay-limestone to prepare LC3 cementitious materials, when added to cement as admixtures, can achieve good physicochemical properties. However, this requires high-quality clay, generally demanding a high proportion of kaolin content. Since most mining stripped waste soil contains little or no kaolin, how to utilize these low-grade solid waste soil and limestone has become an urgent technical problem to be solved. Summary of the Invention

[0006] To overcome the aforementioned technical difficulties, this invention provides a pozzolanic cementitious material—slag geopolymer cement—and its preparation method. The pozzolanic cementitious material, obtained by lightly burning waste soil and low-grade waste limestone from mining operations, is used to replace part of the slag in the preparation of geopolymer cementitious materials. Compared with adding it as an admixture to ordinary cement, the oligopolymer cementitious material has better overall performance, which can not only reduce the environmental impact of solid waste storage, but also greatly reduce the cost of geopolymer cementitious materials.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] On one hand, the present invention provides a pozzolanic cementitious material-slag geopolymer cement, comprising geopolymer cementitious material, alkali activator, sand and water. The geopolymer cementitious material is composed of granulated blast furnace slag with a mass ratio of 50wt% to 90wt% and pozzolanic cementitious material with a mass ratio of 10wt% to 50wt%. The mass ratio of geopolymer cementitious material to sand is 1:3. The mass of the activator is calculated based on an alkali equivalent of 4wt%, and the mass of water is calculated based on a water-cement ratio of 0.5.

[0009] Furthermore, the chemical composition of granulated blast furnace slag includes 38.6 wt% CaO, 33.5 wt% SiO2 and 12.87 wt% Al2O3.

[0010] Furthermore, the pozzolanic cementitious material is produced by lightly calcining mine stripping waste soil and waste low-grade limestone at 800℃. The specific surface area of ​​the pozzolanic cementitious material is 420 m². 2 / kg.

[0011] Furthermore, the ratio of mine stripping waste soil to waste low-grade limestone is the mass ratio when the CaO / SiO2 molar ratio in the pozzolanic cementitious material is 0.9, determined by the chemical composition of the two materials.

[0012] Furthermore, the chemical composition of the mine stripping waste soil includes 42.5 wt% to 45.1 wt% SiO2, 12.4 wt% to 14.2 wt% Al2O3 and 1.8 wt% to 2.0 wt% CaO.

[0013] Furthermore, the chemical composition of the waste low-grade limestone includes 5.8 wt% to 6.2 wt% SiO2, 1.5 wt% to 2.0 wt% Al2O3 and 46.1 wt% to 47.5 wt% CaO.

[0014] Furthermore, the activator is water glass with a modulus of 1.2 and a solid content of 25 wt%.

[0015] When the activator is water glass, the mass of water is calculated with a water-cement ratio of 0.5, including the water content in the water glass and the additional mixing water.

[0016] Furthermore, the water glass is sodium water glass.

[0017] Furthermore, the sand is manufactured sand.

[0018] This invention utilizes the CaO / SiO2 molar ratio to control the proportion of mine stripping waste soil and waste low-grade limestone, as well as the light-burning temperature, to prepare a pozzolanic cementitious material. Under the action of an alkali activator, the pozzolanic cementitious material and granulated blast furnace slag ultimately form a new type of geopolymer cement with excellent performance, low cost, and green low carbon emissions. It has good comprehensive performance, which can not only reduce the environmental impact of solid waste storage, but also greatly reduce costs.

[0019] On the other hand, the present invention provides a method for preparing a pozzolanic cementitious material—slag geopolymer cement—comprising the following steps:

[0020] S1. Mix the alkaline activator with water until homogeneous to obtain a mixture;

[0021] S2. Add the geopolymer cementitious material to the mixture, stir, then add sand and mix evenly to obtain a pozzolanic cementitious material - slag geopolymer cement.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention solves the problems of poor flowability and large shrinkage of geopolymers in alkali slag bases, while greatly improving flexural strength and compressive strength, thus expanding the application range of geopolymer cementitious materials. In terms of environmental benefits, it disposes of mine stripping waste and waste low-grade limestone, reducing the impact of solid waste on land occupation and environmental pollution, and saving costs.

[0024] 2. The raw materials of this invention are simple, easy to obtain and make full use of solid waste that is difficult to treat. It has low requirements for mine stripping waste soil and limestone, and uses sand as fine aggregate, which is green and low-carbon.

[0025] 3. The raw materials for the pozzolanic cementitious material prepared by this invention have wide applicability. Since mine overburden and waste low-grade limestone are large quantities of solid waste that are difficult to utilize, and because most mine overburden contains little or no high-purity components, they are unsuitable as raw materials for calcining LC3 cementitious materials. This invention obtains a pozzolanic cementitious material by controlling the CaO / SiO2 ratio of mine overburden and waste low-grade limestone during light calcination. While ensuring the same CaO / SiO2 ratio, activity tests were conducted using different types of mine overburden and low-grade limestone, and the strength fluctuations were minimal. The pozzolanic cementitious material, when combined with slag under the action of an alkali activator, yields geopolymer cement, which also exhibits good comprehensive performance.

[0026] 4. Compared with alkali slag cement without volcanic ash-like binders, the geopolymer cement of this invention can achieve better fluidity, increase setting time, facilitate construction operations, and improve early flexural strength, making it more suitable for engineering fields with high requirements for early flexural strength, such as airport pavement and ordinary road construction. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] In this embodiment of the invention, the chemical composition of the granulated blast furnace slag includes 38.6 wt% CaO, 33.5 wt% SiO2 and 12.87 wt% Al2O3.

[0029] In this embodiment of the invention, the pozzolanic cementitious material is prepared by lightly calcining mine stripping waste soil and waste low-grade limestone at 800°C, and the specific surface area of ​​the pozzolanic cementitious material is 420 m². 2 / kg. The ratio of mine stripping waste soil to waste low-grade limestone is the mass ratio when the CaO / SiO2 molar ratio in the pozzolanic cementitious material is 0.9, determined by the chemical composition of the two materials.

[0030] In this embodiment of the invention, the chemical composition of the mine stripping waste soil includes 42.5wt% to 45.1wt% of SiO2, 12.4wt% to 14.2wt% of Al2O3 and 1.8wt% to 2.0wt% of CaO.

[0031] In this embodiment of the invention, the chemical composition of the waste low-grade limestone includes 5.8wt% to 6.2wt% SiO2, 1.5wt% to 2.0wt% Al2O3 and 46.1wt% to 47.5wt% CaO.

[0032] In this embodiment of the invention, the activator is water glass with a modulus of 1.2 and a solid content of 25 wt%.

[0033] In this embodiment of the invention, the sand is manufactured sand.

[0034] In this embodiment of the invention, the preparation method of pozzolanic cementitious material-slag geopolymer cement includes the following steps:

[0035] S1. Mix the alkaline activator with water until homogeneous to obtain a mixture;

[0036] S2. Add the geopolymer cementitious material to the mixture, stir, then add sand and mix evenly to obtain a pozzolanic cementitious material - slag geopolymer cement.

[0037] Example 1

[0038] As a preferred embodiment of the present invention, the pozzolanic cementitious material-slag geopolymer cement of this embodiment comprises (by mass parts) 100 parts of geopolymer cementitious material, 300 parts of sand, the mass of activator is calculated based on an alkali equivalent of 4 wt%, and the mass of water is calculated based on a water-cement ratio of 0.5. The geopolymer cementitious material is composed of 90 parts of granulated blast furnace slag and 10 parts of pozzolanic cementitious material.

[0039] Example 2

[0040] As a preferred embodiment of the present invention, the pozzolanic cementitious material-slag geopolymer cement of this embodiment comprises (by weight parts) 100 parts of geopolymer cementitious material, 300 parts of sand, the mass of the activator is calculated based on an alkali equivalent of 4 wt%, and the mass of water is calculated based on a water-cement ratio of 0.5. The geopolymer cementitious material is composed of 80 parts of granulated blast furnace slag and 20 parts of pozzolanic cementitious material.

[0041] Example 3

[0042] As a preferred embodiment of the present invention, the pozzolanic cementitious material-slag geopolymer cement of this embodiment comprises (by mass parts) 100 parts of geopolymer cementitious material, 300 parts of sand, the mass of activator calculated as 4 wt% alkali equivalent, and the mass of water calculated as a water-cement ratio of 0.5. The geopolymer cementitious material is composed of 70 parts of granulated blast furnace slag and 30 parts of pozzolanic cementitious material.

[0043] Example 4

[0044] As a preferred embodiment of the present invention, the pozzolanic cementitious material-slag geopolymer cement of this embodiment comprises (by weight parts) 100 parts of geopolymer cementitious material, 300 parts of sand, the mass of the activator is calculated based on an alkali equivalent of 4 wt%, and the mass of water is calculated based on a water-cement ratio of 0.5. The geopolymer cementitious material is composed of 60 parts of granulated blast furnace slag and 40 parts of pozzolanic cementitious material.

[0045] Example 5

[0046] As a preferred embodiment of the present invention, the pozzolanic cementitious material-slag geopolymer cement of this embodiment comprises (by mass parts) 100 parts of geopolymer cementitious material, 300 parts of sand, the mass of the activator is calculated based on an alkali equivalent of 4 wt%, and the mass of water is calculated based on a water-cement ratio of 0.5. The geopolymer cementitious material is composed of 50 parts of granulated blast furnace slag and 50 parts of pozzolanic cementitious material.

[0047] Comparative Example 1

[0048] The cement composition in this comparative example is the same as that in Example 2, except that the geopolymer cementitious material is replaced with granulated blast furnace slag.

[0049] Comparative Example 2

[0050] The cement composition of this comparative example is the same as that of Example 2, except that the geopolymer cementitious material is replaced with P·O 42.5 cement and no alkali activator is added.

[0051] Comparative Example 3

[0052] The cement composition of this comparative example is the same as that of Example 2, except that the pozzolanic cementitious material is replaced with P·O 42.5 cement.

[0053] Test case

[0054] The cement from the examples and comparative examples was poured into 40mm*40mm*160mm molds, placed on a vibrating table for vibration and smoothing, and then cured with a film for 24 hours before demolding. Tests were conducted after curing in a water tank at 20±1℃ for 3 days, 7 days, and 28 days. The test results are shown in Tables 1 and 2.

[0055] Table 1. Flowability, setting time, and autogenous shrinkage of cement paste

[0056]

[0057] The data in Table 1 show that the fluidity, initial setting time, final setting time, and 7-day autogenous shrinkage of the geopolymer cements in Examples 1 to 5 all meet the standards. Furthermore, with the increase in the amount of pozzolanic cementitious material, i.e., from Example 1 to Example 5, the fluidity of the geopolymer cement first increases and then decreases, while the setting time gradually increases and the autogenous shrinkage gradually decreases. The maximum fluidity is achieved when the amount of pozzolanic cementitious material is 20 wt%.

[0058] Table 2 Mechanical Strength of Cement

[0059]

[0060] The data in Table 2 show that the flexural strength and compressive strength of the geopolymer cement in Examples 1 to 5 all meet the standards. Furthermore, as the amount of pozzolanic cementitious material increases, i.e. from Example 1 to Example 5, the flexural strength and compressive strength of the geopolymer cement first increase and then decrease, reaching their maximum when the amount of pozzolanic cementitious material is 20wt%.

[0061] Compared to Comparative Example 1, where the content of the volcanic ash-like cementitious material was 0, Example 2 showed an increase of 211.4% in 3-day flexural strength, 62.9% in 3-day compressive strength, 64.5% in 28-day flexural strength, and 41.8% in 28-day compressive strength. Compared to Comparative Example 2, which used P·O 42.5 grade cement, Example 2 showed an increase of 70.3% in 3-day flexural strength, 36.1% in 3-day compressive strength, 40.4% in 28-day flexural strength, and 13.8% in 28-day compressive strength. Compared to Comparative Example 3, which replaced the volcanic material with P·O 42.5 grade cement, Example 2 showed an increase of 3.8% in 3-day flexural strength, 4.7% in 3-day compressive strength, 6.8% in 28-day flexural strength, and 7.5% in 28-day compressive strength.

[0062] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A type of pozzolanic cementitious material—slag geopolymer cement, characterized in that, It includes geopolymer cementitious material, alkali activator, sand and water. The geopolymer cementitious material is composed of granulated blast furnace slag with a mass ratio of 50wt% to 90wt% and pozzolanic cementitious material with a mass ratio of 10wt% to 50wt%. The mass ratio of geopolymer cementitious material to sand is 1:

3. The mass of alkali activator is calculated based on an alkali equivalent of 4wt%. The mass of water is calculated based on a water-cement ratio of 0.

5. Pozzolanic cementitious material is produced by lightly calcining mine stripping waste soil and waste low-grade limestone at 800℃. The specific surface area of ​​the pozzolanic cementitious material is 420 m². 2 / kg; The ratio of mine stripping waste soil to waste low-grade limestone is the mass ratio when the CaO / SiO2 molar ratio in the pozzolanic cementitious material is 0.9, determined by the chemical composition of the two materials. The alkali activator is water glass with a modulus of 1.2 and a solid content of 25 wt%.

2. The pozzolanic cementitious material-slag geopolymer cement according to claim 1, characterized in that, The chemical composition of granulated blast furnace slag includes 38.6 wt% CaO, 33.5 wt% SiO2 and 12.87 wt% Al2O3.

3. The pozzolanic cementitious material-slag geopolymer cement according to claim 1, characterized in that, The chemical composition of the mine overburden includes 42.5wt%~45.1wt% SiO2, 12.4wt%~14.2wt% Al2O3 and 1.8wt%~2.0wt% CaO.

4. The pozzolanic cementitious material-slag geopolymer cement according to claim 1, characterized in that, The chemical composition of waste low-grade limestone includes 5.8wt%~6.2wt% SiO2, 1.5wt%~2.0wt% Al2O3 and 46.1wt%~47.5wt% CaO.

5. The pozzolanic cementitious material-slag geopolymer cement according to claim 1, characterized in that, The water glass is sodium silicate.

6. The pozzolanic cementitious material-slag geopolymer cement according to claim 1, characterized in that, The sand is manufactured sand.

7. The method for preparing a pozzolanic cementitious material-slag geopolymer cement according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Mix the alkaline activator with water until homogeneous to obtain a mixture; S2. Add the geopolymer cementitious material to the mixture, stir, then add sand and mix evenly to obtain a pozzolanic cementitious material - slag geopolymer cement.

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