Low-carbon high-impedance cement-based material for subway and preparation method of low-carbon high-impedance cement-based material

Abstract

The invention relates to the technical field of cement-based materials, in particular to a low-carbon high-impedance cement-based material for subways and a preparation method thereof.The low-carbon high-impedance cement-based material comprises 350-450 kg / m < 3 > of limestone calcined clay cement and 75-85 kg / m < 3 > of silica fume; 155-165 kg / m < 3 > of mineral powder; and carbide slag is 55-65 kg / m < 3 >. The silica fume, the mineral powder, the limestone calcined clay cement and the carbide slag are used for replacing part of cement, on one hand, the admixture and a cement hydration product are subjected to secondary hydration, OH <-> of a pore solution is solidified, and the conductivity of the solution is reduced; and on the other hand, the impedance of the cement-based material is improved by reducing the porosity of the material, so that the high-impedance cement-based material prepared after optimization of the mix proportion not only can effectively prevent the harm of stray current, but also further improves the durability of the cement-based material.

Description

Technical Field

[0001] The invention relates to the technical field of cement-based materials, and in particular to a low-carbon high-impedance cement-based material for subways and a preparation method thereof. Background Art

[0002] As an important part of urban rail transit, subways have the advantages of high speed, comfort and convenience, but the DC traction power supply system causes some current leakage in the subway, generating stray current. In addition, the underground where the subway is located faces a complex environment such as abundant groundwater and harmful ion erosion, which puts higher requirements on the durability of cement-based materials. Therefore, the development of high-impedance cement-based materials that meet the two major performance indicators of compressive strength and resistivity can not only effectively protect against the hazards of stray currents, but also improve the bearing capacity of building structures and the durability of cement-based materials, and promote the sustainable development of green building materials.

[0003] Factors that affect the conductivity of concrete include cement type, water-cement ratio, admixtures, curing methods, additives, etc. For example, the early hydration reaction rate of high-alumina cement is relatively fast, which makes the resistivity increase rapidly. Some studies have also found that a small amount of silica fume can significantly increase the resistivity of concrete. However, the high consumption of cement in the construction of infrastructure projects releases a large amount of carbon dioxide. An important challenge facing sustainable development in the next few decades is to develop cement-based materials that use less clinker to replace traditional concrete. This not only reduces carbon emissions, but also makes the performance and durability of concrete superior. However, concrete for subways not only requires high performance, but also has extremely high requirements for the impedance of the material. Existing technologies focus more on improving the mechanical properties of concrete, and there are few studies on high-impedance cement-based materials that meet the two major performance indicators of compressive strength and resistivity. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a low-carbon high-impedance cement-based material for subway and a preparation method thereof.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] On the one hand, a low-carbon high-impedance cement-based material for subway is provided, the components of which include: limestone calcined clay cement 350-450kg / m 3 , silica fume 75-85kg / m 3 ; Mineral powder 155-165kg / m 3 ; Carbide slag 55-65kg / m 3 .

[0007] Furthermore, its components also include: ordinary Portland cement 450-550kg / m 3 ; Water reducing agent 6-7kg / m 3; Fine quartz sand 170-190kg / m 3 ; Coarse quartz sand 680-700kg / m 3 ; Steel fiber 70-80kg / m 3 ; PVA powder 5-10kg / m 3 ; Water 180-200kg / m 3 .

[0008] Furthermore, the silica fume is 970U microsilica powder, the mineral powder is S95 mineral powder, the water reducer is PC-200 polycarboxylic acid water reducer, and the aggregate is well-graded quartz sand.

[0009] Furthermore, limestone calcined clay cement is composed of 30% calcined clay, 15% limestone, 50% clinker and 5% gypsum.

[0010] On the other hand, a method for preparing the above-mentioned low-carbon high-impedance cement-based material for subway is provided, which comprises the following steps:

[0011] Step 1: Calculate and weigh the raw materials of each component according to the mix ratio of the experimental design;

[0012] Step 2: Mix water and water reducer in a glass, then pour it into the blender;

[0013] Step 3: Add cement and admixtures into a mixer and stir for 2 to 4 minutes, then add quartz sand and stir for 2 to 4 minutes;

[0014] Step 4: Slowly add the steel fiber into the mixer to disperse it evenly and stir for 3 to 5 minutes;

[0015] Step 5: Place the mold into the mold and cover the molded specimen with plastic wrap;

[0016] Step 6: After the specimen is placed in air at 20±1℃ and relative humidity of 45±5% for 24 hours, it is demoulded and placed in saturated lime water for curing to the specified age.

[0017] Further, the treatment method of carbide slag is specifically as follows:

[0018] The carbide slag produced in the production process of calcium carbide is graded by screening equipment, and the usable particles are further washed with water to remove soluble salts and impurities in the carbide slag. The slag is then precipitated and the liquid is separated to obtain relatively pure solid carbide slag, which is then hot-air dried and stored in a dry and ventilated environment.

[0019] The beneficial effects of the present invention are:

[0020] Subway concrete not only requires high performance, but also has extremely high requirements for the impedance of the material. Among the mineral admixtures, silica fume, mineral powder and calcium carbide slag are highly active and can undergo secondary hydration reaction with cement hydration product Ca(OH)2 to generate hydrated calcium silicate, which improves the quality of cementitious materials in cement and the interface structure between cement and aggregate, which is not only conducive to the improvement of strength, but also conducive to the improvement of resistivity. In addition, the particles of silica fume and mineral powder are small, which can fill the gaps between cement particles, improve the pore structure of concrete, reduce porosity and reduce pore size, thereby improving the electrical conductivity of cement-based materials. In addition, limestone calcined clay cement (LC3) reduces the use of cement clinker and produces less carbon dioxide emissions during the production process, which helps to alleviate the harm caused by excessive development and construction to the ecological environment. And the high-impedance cement-based material obtained after the mix ratio is optimized has good compressive strength and high resistivity, which effectively reduces the damage of stray current to the structure of cement-based materials, improves the durability of materials, and promotes the development of building materials in the direction of green sustainability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 28d compressive strength of specimens with different mix ratios prepared in the examples;

[0022] Figure 2 28d resistivity of specimens with different mix ratios prepared in the examples. DETAILED DESCRIPTION

[0023] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0024] Example

[0025] A low-carbon high-impedance cement-based material for subways is prepared by mixing ordinary Portland cement, limestone calcined clay cement (LC3), silica fume, mineral powder, carbide slag, water reducer, water, fine quartz sand, coarse quartz sand, fiber and PVA glue powder in a certain proportion. In this embodiment, the silica fume is 970U microsilica powder, the mineral powder is S95 mineral powder, the water reducer is PC-200 polycarboxylate water reducer, and the aggregate is well-graded quartz sand. The preparation method thereof includes:

[0026] (1) Treatment of carbide slag: The carbide slag produced during the production of carbide is graded using screening equipment. The usable particles with a particle size of less than 1 mm are then further washed with water to remove soluble salts and impurities in the carbide slag. The slag is then precipitated and the liquid is separated to obtain relatively pure solid carbide slag, which is then dried with hot air and stored in a dry, ventilated environment.

[0027] (2) Limestone calcined clay cement: It is made of 30% calcined clay (CC), 15% limestone, 50% clinker and 5% gypsum.

[0028] (3) Calculate and weigh the raw materials of each component according to the mix ratio of the experimental design;

[0029] (4) Mix water and water reducing agent in a glass and pour it into a blender;

[0030] (5) Add cement and admixtures into a mixer and stir for 2 to 4 minutes, then add quartz sand and stir for 2 to 4 minutes;

[0031] (6) Slowly add the steel fiber into the mixer to disperse it evenly and stir for 3 to 5 minutes;

[0032] (7) Place the mold into the mold and cover the molded specimen with plastic wrap;

[0033] (8) The specimens are placed in air at 20±1℃ and relative humidity of 45±5% for 24 hours, then demoulded and placed in saturated lime water for curing to the specified age.

[0034] Table 1 is the chemical composition of carbide slag

[0035]

[0036]

[0037] Table 2 shows the performance index of water reducing agent

[0038]

[0039] Table 3 is PVA latex powder

[0040]

[0041] Table 4 shows the mix ratio of low-carbon high-impedance cement-based materials for subways

[0042]

[0043] The present invention is mainly aimed at optimizing the mix ratio of cement-based materials, by adding mineral powder, silica fume, limestone calcined clay cement (LC 3), carbide slag partially replaces cement and adjusts the appropriate dosage between the components. 3 As a good way to develop low-carbon cementitious systems, its application effectively reduces greenhouse gas (CO2) emissions with a ratio of 30% calcined clay (CC), 15% limestone, 50% clinker and 5% gypsum. Metakaolin (calcined clay) will react with Ca(OH)2(CH) generated by clinker hydration to produce aluminum-containing phase products such as CASH gel, and calcium carbonate (Cc) will react with C3A in clinker to produce semi-carbon type hydrated calcium aluminate, etc., thereby inhibiting the decomposition of ettringite (AFt) into monosulfide type hydrated calcium sulfoaluminate (AFm). These effects lead to a higher clinker replacement rate and a finer and denser microstructure, which reduces the porosity of cement-based materials while solidifying the conductive ions in the pore solution of cement-based materials, and improves the strength and durability of the material itself while increasing the resistivity of the material.

[0044] As the terminal product of acetylene gas, carbide slag (CCR) has a high pH value, which increases the alkalinity of the environment when it is landfilled. As a calcium accelerator, CCR partially replaces cement to a small extent. In the presence of SiO2 and Al2O3 in cement or other volcanic ash materials, it produces excessive Ca(OH)2, which reacts synergistically with kaolin to promote the formation of compounds such as CSH and CASH, thereby improving the strength and density of the cement matrix to a certain extent. At the same time, Ca(OH)2 can synthesize stable calcium carbonate by reacting with CO2, thereby realizing the effective reuse of waste resources and providing a new way to prepare low-carbon cement-based materials.

[0045] Under the same experimental conditions, the electrical and mechanical properties of the test pieces obtained with different mix ratios in this embodiment were tested respectively.

[0046] The compressive strength test results are shown in Table 5. The addition of silica fume, mineral powder, carbide slag and other admixtures can not only reduce the production cost of cement-based materials, but also improve their mechanical properties and compactness. It can be seen from the test results that the addition of steel fiber and PVA latex powder can also improve the compressive strength of high-impedance cement-based materials to a certain extent.

[0047] Table 5 shows the compressive strength test results of specimens obtained with different mix ratios

[0048]

[0049] The resistivity test results obtained from the electrical performance test are shown in Table 6 below. Silica fume, mineral powder and other admixtures not only undergo secondary hydration reaction with cement hydration products to improve the interface structure between cement and aggregate, but also fill the gaps between cement particles due to their small particle size, reduce porosity, and thus further increase the resistivity of the material. It can be seen from the test results that the addition of steel fiber will significantly reduce the resistivity of cement-based materials, while the addition of PVA latex powder can significantly increase the resistivity of cement-based materials, because the polymer will be gradually confined in the pores as the cement is hydrated, and the polymer particles will flocculate together to gradually form a film on the surface of the cement particles, thereby reducing the pore connectivity of the cement-based materials.

[0050] Table 6 shows the electrical properties test results of the specimens obtained with different mix ratios

[0051]

[0052]

[0053] In summary, the present invention partially replaces cement by adding mineral powder, silica fume, limestone calcined clay cement (LC3), and carbide slag and adjusts the appropriate dosage of each component, thereby reducing the use of cement clinker and improving material performance, thereby reducing carbon emissions and resource consumption, which is conducive to sustainable development. In addition, carbide slag reacts with volcanic ash materials to generate excessive Ca(OH)2, and can also react with CO2 to generate calcium carbonate, while metakaolin reacts with cement hydration product Ca(OH)2 to generate hydration products such as CSH and CASH, refine the pore structure, and improve the quality of cementitious substances and interface structure in cement stone, thereby improving the strength and resistivity of the material.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0055] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A low-carbon high-impedance cement-based material for subway, characterized in that: Its components include: limestone calcined clay cement 350-450kg / m 3 , silica fume 75-85kg / m 3 ; Mineral powder 155-165kg / m 3 ; Carbide slag 55-65kg / m 3 .

2. The low-carbon high-impedance cement-based material for subway according to claim 1, characterized in that: Its components also include: ordinary Portland cement 450-550kg / m 3 ; Water reducing agent 6-7kg / m 3 ; Fine quartz sand 170-190kg / m 3 ; Coarse quartz sand 680-700kg / m 3 ; Steel fiber 70-80kg / m 3 ; PVA powder 5-10kg / m 3 ; Water 180-200kg / m 3 .

3. The low-carbon high-impedance cement-based material for subway according to claim 1, characterized in that: The silica fume is 970U microsilica powder, the mineral powder is S95 mineral powder, the water reducer is PC-200 polycarboxylic acid water reducer, and the aggregate is well-graded quartz sand.

4. The low-carbon high-impedance cement-based material for subway according to claim 1, characterized in that: Limestone calcined clay cement is made of 30% calcined clay, 15% limestone, 50% clinker and 5% gypsum.

5. The method for preparing the low-carbon high-impedance cement-based material for subway according to any one of claims 2 to 4, characterized in that: The following steps are involved: Step 1: Calculate and weigh the raw materials of each component according to the mix ratio of the experimental design; Step 2: Mix water and water reducer in a glass, then pour it into the blender; Step 3: Add cement and admixtures into a mixer and stir for 2 to 4 minutes, then add quartz sand and stir for 2 to 4 minutes; Step 4: Slowly add the steel fiber into the mixer to disperse it evenly and stir for 3 to 5 minutes; Step 5: Place the mold into the mold and cover the molded specimen with plastic wrap; Step 6: After the specimen is placed in air at 20±1℃ and relative humidity of 45±5% for 24 hours, it is demoulded and placed in saturated lime water for curing to the specified age.

6. The method for preparing low-carbon high-impedance cement-based materials for subway according to claim 5, characterized in that: The specific treatment method of carbide slag is: The carbide slag produced in the production process of calcium carbide is graded by screening equipment, and the usable particles are further washed with water to remove soluble salts and impurities in the carbide slag. The slag is then precipitated and the liquid is separated to obtain relatively pure solid carbide slag, which is then hot-air dried and stored in a dry and ventilated environment.

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