Multi-element solid waste negative carbon cement-based material and preparation method thereof

Abstract

The invention belongs to the technical field of negative carbon building materials, and particularly relates to a multi-element solid waste negative carbon cement-based material and a preparation method thereof. The material is prepared from the following components in parts by weight: 10 to 320 parts of carbonized carbide slag, 0 to 240 parts of uncarbonized carbide slag, 25 to 640 parts of calcined coal gangue, 25 to 800 parts of Portland cement, 6 to 320 parts of silica fume and other pozzolanic mineral admixtures and 30 to 800 parts of mixing water. The preparation method comprises the following steps: carbonizing the carbide slag until the content of calcium carbonate is more than or equal to 90%, and calcining and activating the coal gangue at 700-800 DEG C; all the powder raw materials are subjected to dry mixing, water is added for segmented stirring, and standard curing is performed after pouring forming. The carbonized carbide slag is used for replacing limestone to achieve carbon sequestration, the calcined coal gangue is used for replacing calcined clay, natural resources are prevented from being exploited, the cement clinker replacement rate of 70% is achieved through the synergistic effect of multi-element solid waste in a low clinker system, the material has excellent mechanical and durability, and carbon emission and resource consumption are remarkably reduced.

Description

Technical Field

[0001] This invention belongs to the field of negative carbon building materials and solid waste resource utilization technology, and specifically relates to a multi-element solid waste negative carbon cement-based material and its preparation method based on carbide slag carbon capture, carbon utilization and carbon sequestration technology and coal gangue calcination resource utilization technology. Background Technology

[0002] With the booming development of my country's industry and agriculture, as well as its coal, chemical, and metallurgical sectors, a large amount of industrial solid waste is generated annually. Its accumulation not only occupies land but also poses a serious threat to the ecological environment. Therefore, the diversified utilization of solid waste resources will undoubtedly be key to promoting sustainable development of building materials and achieving efficient carbon reduction. Coal gangue, rich in SiO2 (40%–60%) and Al2O3 (15%–30%), has the potential to replace cement due to its cementitious activity, and is therefore often used in the preparation of cement mineral admixtures and geopolymers. Calcium carbide slag, the waste residue after acetylene is obtained from the hydrolysis of calcium carbide, has an annual output of 120 million tons, with a comprehensive utilization rate of less than 70%. Long-term storage easily leads to alkaline pollution. However, its main component, Ca(OH)2, can react with CO2 to generate CaCO3, making it a key raw material for carbon capture in CCUS technology, with huge carbon sequestration potential. Calcium carbide slag, coal gangue, silica fume, and solid wastes such as fly ash, slag, and volcanic ash, which have pozzolanic properties, together constitute a secondary resource pool that urgently needs to be developed.

[0003] The current building materials industry suffers from high carbon emissions and high energy consumption, with 0.87t CO2 / t cement clinker, 70-90 kWh / t cement, and 110-140 kg coal / t cement. Therefore, developing low-carbon, zero-carbon, and negative-carbon building materials has become an essential path for the industry to achieve green transformation and reach its dual-carbon goals. Currently, domestic and international scholars have achieved certain research results in the field of low-carbon building materials, which can be mainly divided into alkali-activated cementitious material systems, magnesium-based cementitious material systems, and low-carbon solid waste-based silicate cementitious systems. However, alkali-activated cementitious material systems require alkali activators with a high carbon footprint and high cost. Furthermore, this cementitious system typically suffers from problems such as rapid setting, flash setting, poor workability, complex compounding and preparation processes, alkali-aggregate reaction, poor acid corrosion resistance, large shrinkage, and difficulty in regeneration and recycling. Compared to low-carbon solid waste-based silicate cementitious systems, magnesium-based cementitious materials typically suffer from high cost, poor water resistance, and poor volume stability. In comparison, solid waste-based silicate cementitious materials have lower costs, better volume stability than the former two, and durability comparable to or even better than ordinary silicate cementitious materials due to their low alkalinity and resistance to acid and alkali corrosion. Therefore, they have a broader prospect in engineering applications. However, most current research focuses on single solid waste-based silicate cement systems, with cementitious materials heavily reliant on a single solid waste. The material performance is limited by the quality of that single solid waste, and the hydration product system is relatively simple. This invention, however, focuses on multiple solid wastes, maximizing the resource utilization of various solid wastes and leveraging the synergistic effects between the properties of different solid wastes. This results in more efficient carbon reduction, control of mechanical properties, and durability.

[0004] Limestone-calcined clay cement (LC) was proposed by Scrivener in 2008. 3 This system has become a research hotspot for new low-carbon building materials. Through the synergistic effect of calcined clay and limestone powder, it can replace 40%–55% of cement clinker. However, the strength decreases significantly when the replacement rate exceeds 55%. Compared to traditional silicate cement, it can reduce carbon emissions by 30%–40%. It has been included in EN197 and ASTMC 618, but there are currently no relevant standards published in my country. However, LC… 3 The cementing system heavily relies on the mining of limestone and high-quality clay. However, the extraction of these non-renewable natural resources typically leads to varying degrees of environmental damage and is highly sensitive to clay calcination processes. When the calcination temperature exceeds 850℃, the mineral activity begins to decrease. This calcination temperature is 50℃–100℃ higher than that of coal gangue, yet carbon emissions remain relatively high. Therefore, replacing non-renewable limestone and clay with other sustainable and recyclable materials is crucial for reconstructing cemented clay systems. 3 Cementitious materials, achieving a cement substitution rate of over 60%, and realizing the resource utilization of solid waste and developing low-carbon, zero-carbon, and negative-carbon sustainable building materials have become current research hotspots in related fields. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-element solid waste negative carbon cement-based material and its preparation method, which is based on carbon-mineralized carbide slag and calcined coal gangue, along with a small amount of uncarbonized carbide slag and pozzolanic mineral admixtures such as silica fume. The aim is to solve the environmental damage caused by the long-term stockpiling of large quantities of carbide slag, coal gangue, and pozzolanic solid waste such as silica fume, and to address the problems of soil and water geological damage and natural resource scarcity caused by the mining of non-renewable natural resources such as limestone and clay. This significantly reduces cement clinker usage to approximately 30%, while simultaneously improving the carbon sequestration capacity of cement-based materials through carbon capture, utilization, and storage technologies. Ultimately, this results in a green, environmentally friendly, highly efficient carbon sequestration, and high cement substitution rate multi-element solid waste negative carbon cement-based cementitious material.

[0006] The technical solution of the present invention is the multi-element solid waste negative carbon cement-based material, which is characterized in that the cement-based material is composed of the following components by weight: 10–320 parts of carbide slag; 0–240 parts of uncarbide slag; 25–640 parts of calcined coal gangue; 25-800 parts of silicate cement; 6-320 parts of silica fume and other pozzolanic mineral admixtures; 30-800 parts of mixing water; Preferably, the silicate cement is P·Ⅰ42.5 or P·Ⅱ42.5 grade silicate cement; The carbide slag has a density of 1750 kg / m³. 3 Fineness 340m 2 / kg, calcium hydroxide content 90%–95%, silicon dioxide content 1%–3%; aluminum oxide content 0.5%–2%; calcium carbonate content ≥90% after carbonation; The calcined coal gangue has the following chemical composition: SiO2 45%–55%, Al2O3 40%–50%, calcination temperature 700–850℃, and fineness ≥325 mesh. The silica fume is characterized in that: in its chemical composition, the weight percentage content of SiO2 is 90% to 98%, the alkali content (calculated as Na2O equivalent) does not exceed 0.75%, the chloride ion content does not exceed 0.3%, and the loss on ignition does not exceed 6%; and its physical properties meet the following requirements: specific surface area is 15 to 22 m² / g, and the activity index after 28 days is greater than 85%. Mixing water: Ordinary tap water.

[0007] As a preferred embodiment, the permissible quality tolerances for the cement-based materials are: ±0.5% for cement; ±0.2% for carbide slag; ±0.2% for carbide slag; ±0.5% for calcined coal gangue; ±0.2% for silica fume; ±0.2% for other pozzolanic mineral admixtures; and ±0.5% for mixing water.

[0008] Preferably, the calcium hydroxide content of the carbide slag before carbonization is ≥94%, and the amount of uncarbonized carbide slag in the powder is 0-10%; the calcium carbonate content of the carbide slag after carbonization is ≥90%, and the amount of carbonized carbide slag in the powder is 10%-20%; the amount of calcined coal gangue is 25%-40%; and the amount of silica fume in the cementitious powder material is 5%-10%.

[0009] As a preferred embodiment, the mass ratio of the volcanic ash mineral admixture (excluding solid waste) to cement is 1:5.

[0010] Another technical solution of the present invention is the aforementioned method for preparing multi-element solid waste negative carbon cement-based materials, which is characterized by including the following steps: (1) Carbonize carbide slag to prepare calcium carbonate. Expose fine carbide slag powder to air or in a carbonation box until the calcium carbonate content is ≥90% to reduce the alkalinity of carbide slag. (2) Calcine the coal gangue at 700-800℃ and then grind it into fine powder to improve the activity of the calcined coal gangue; (3) Accurately weigh the mixing water according to the water requirement of the cementitious material and pour it into the mixing pot. Accurately weigh various raw materials according to the components. Dry mix cement, carbide slag, calcined coal gangue, silica fume and other pozzolanic mineral admixtures. Pour the evenly mixed cementitious material into the mixing water and stir slowly for 90-120 seconds. Then add the remaining mixing water and stir quickly for 90-180 seconds. Pour the mixed slurry into the mold and vibrate and compact it into shape. (4) After curing the mold under standard curing conditions for 2 days, the mold was removed. The sample was then cured until the corresponding age before mechanical property testing was performed. The curing temperature was 20±2℃ and the relative humidity was ≥95%.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Compared with non-renewable natural resources like limestone, this invention utilizes calcium carbide slag, a waste residue mainly composed of calcium hydroxide after the hydrolysis of calcium carbide to obtain acetylene gas. This slag is lower in cost, rich in calcium resources (calcium hydroxide content exceeding 90%), and exhibits good particle dispersibility and significant carbon sequestration potential. Each ton of calcium carbide slag can solidify approximately 0.3 tons of carbon dioxide to generate calcium carbonate. Uncarbonized calcium carbide slag can also provide calcium hydroxide to activate the pozzolanic properties of mineral admixtures, promote secondary hydration of the mineral admixtures, thereby optimizing the hydration process of low-alkalinity cementitious materials and improving matrix density.

[0012] (2) Compared with non-renewable natural resources such as clay, especially limestone calcined clay cement, which relies on high-quality clay, the main chemical components of coal gangue are alumina and silicon dioxide. The mineral components contained are similar to those of clay, such as kaolinite, illite, and quartz. After calcination, its main component is highly active metakaolinite. Therefore, it can generate a large amount of hydrated calcium aluminosilicate under the stimulation of highly alkaline calcium hydroxide and silicate cement, thereby improving the density of cement-based matrix materials. Furthermore, coal gangue, a rock formed during coal formation by the co-deposition of organic and inorganic compounds with coal, has a stockpile exceeding 1 billion tons, with annual emissions reaching 100 million tons. Its cost is far lower than mined clay, and its long-term stockpiling occupies vast amounts of land. There is a risk of water and soil environmental damage and radiation pollution due to the leaching of heavy metals and other harmful substances, as well as the risk of air pollution from spontaneous combustion releasing harmful gases such as SO2, CO, H2S, and NOx. Large-scale coal gangue stockpiles can also trigger geological disasters such as explosions, landslides, and mudslides. Therefore, developing the high-value utilization of coal gangue has become a hot topic and a challenge in developing "zero-waste cities" and a circular economy. Replacing calcined clay with calcined coal gangue offers several advantages. Calcined coal gangue has a more complex composition than calcined clay, and the unburned carbon within it may exist as porous carbon after calcination. This porous carbon can store a certain amount of water in low-alkalinity cement paste, providing internal curing moisture for the later hydration of the carbon-negative cementitious material and ensuring its continuous strength growth. Furthermore, the small amount of unreacted microcrystalline quartz and other minerals in calcined coal gangue can serve as nucleation sites for hydration products, accelerating the hydration of the cement matrix and improving its microporous structure.

[0013] (3) The multi-element solid waste negative carbon cement-based material of the present invention completely replaces limestone with carbide slag and completely replaces calcined clay with calcined coal gangue. 0-10% of uncarbide carbide slag is used to supplement calcium hydroxide used to activate calcined clay and other pozzolanic mineral admixtures such as silica fume. With a reduction in silicate cement content to 30%, the 7-day compressive strength of this negative carbon cement-based composite material can reach 35 MPa, and the 28-day compressive strength can reach 50 MPa, with a flexural-compression ratio of 15%-20%. This is comparable to the mechanical properties of pure silicate cement-based materials under the same conditions, and its carbon emissions are reduced by 68%. Before service, its carbon dioxide fixation rate can be as low as 6%. If carbonization curing or other methods are used, its carbon fixation rate is expected to exceed 20%, which is 45%-55% higher than that of traditional limestone-calcined clay cement.

[0014] (4) The multi-element solid waste negative carbon cementitious material prepared by this invention possesses both excellent mechanical properties and carbon sequestration potential. It not only provides new ideas and application channels for the high-value resource utilization of carbide slag and coal gangue, avoiding the exploitation of natural non-renewable resources, but also significantly increases the silicate cement replacement rate to 70% through the efficient disposal of these two types of solid waste, in conjunction with other pozzolanic mineral admixtures. This avoids a series of environmental problems caused by solid waste stockpiling and also significantly reduces building material costs and production energy consumption. This invention achieves the goals of low cost, low energy consumption, ultra-low carbon emissions, and high carbon sequestration by utilizing solid waste resources. It provides a new approach to developing new technologies for building materials with negative carbon content and carbon sequestration and waste treatment for building waste-free cities, demonstrating significant innovative significance and promising engineering applications.

[0015] (5) The preparation method of this invention uses carbide slag to replace limestone to provide calcium carbonate, calcined coal gangue to replace calcined clay to provide highly active alumina and silica, and pozzolanic mineral admixtures such as silica fume, fly ash, and slag to regulate workability and the richness of hydration products. The synergistic hydration of multiple wastes can significantly increase the cement substitution rate to approximately 70%, thereby deeply reducing carbon emissions, realizing high-value resource utilization of solid waste, reducing pollution from solid waste stockpiling, and avoiding the extraction of natural resources such as limestone and clay. Because calcined coal gangue highly consumes the hydration product calcium hydroxide of cement clinker, the calcium hydroxide content remains at a low level, thus improving resistance to chemical erosion.

[0016] (6) The synergistic hydration and carbonization reactions of the multi-component solid waste in silicate cement described in this invention enhance the strength, durability, and carbon sequestration capacity of cement-based materials. The ingenious combination of various solid wastes provides a new approach of "using waste to sequestrate carbon and using carbon to stabilize" for the high-value-added resource utilization of multi-component solid wastes and the construction of negative carbon cementitious systems, demonstrating significant innovative value and broad engineering application prospects. Attached Figure Description

[0017] Figure 1 These are thermogravimetric analysis diagrams of the carbide slag before and after carbonation according to the present invention. Figure 2 These are the X-ray diffraction patterns of the carbide slag before and after carbonization according to the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to embodiments: Example 1

[0019] The properties of multi-element solid waste negative carbon cement-based materials are as follows: P·Ⅰ42.5 silicate cement, produced by Conch Cement Plant, has a 28-day compressive strength of 49.8 MPa.

[0020] The flexural strength is 7.6 MPa.

[0021] Untreated carbide slag: Ca(OH)₂≥90%, chemical composition as shown in Table 1 below, specific surface area: 340 m² 2 / kg.

[0022] Table 1 shows the chemical composition of uncarbonized carbide slag.

[0023] Carbonized carbide slag: chemical composition CaCO3≥90%, particle size≤75μm.

[0024] Please see Figure 1 , Figure 2 As shown, Figure 1 The thermogravimetric analysis results are shown before and after carbonation of carbide slag. Figure 2 The results are obtained from X-ray diffraction analysis of carbide slag before and after carbonation using the Rietveld method.

[0025] Calcined coal gangue: calcination temperature 750~800℃, chemical composition by weight percentage is as follows: SiO2 53.5%, Al2O3 42.55%, Fe2O3 3.8%, calcium oxide: 0.15%, fineness 325 mesh, sieve residue 2%.

[0026] Silica fume: Its chemical composition by weight percentage consists of the following components: SiO2 98.1%, loss on ignition 1.9%, and fineness 22.1 μm. 2 / g, 28-day activity index 105%.

[0027] Mixing water: tap water.

[0028] Mineral admixture: a mixture of granulated blast furnace slag and fly ash, with an apparent density of 2.9 g / cm³. 3 Specific surface area 420m² 2 / kg, 28d activity index ≥95%.

[0029] Based on its experimental performance indicators, the weight parts of each component of the raw material are as follows: 45 parts of uncarbonized calcium carbide slag; 90 parts of carbide slag; 135 parts of calcined coal gangue; 135 parts of silicate cement; 22.5 parts of silica fume; a total of 22.5 parts of slag and fly ash and other pozzolanic mineral admixtures; 225 parts of mixing water; ISO standard sand: produced according to GB / T17671, fineness modulus 2.5~2.6, 1350 parts.

[0030] A method for preparing multi-element solid waste negative carbon cement-based materials includes the following steps: (1) Place the uncarbonized carbide slag in a carbonization box or expose it to the atmosphere to allow it to carbonize fully. Periodically crush and sieve the carbide slag that clumps during the carbonization process, and carbonize it again until all the carbide slag has a carbonization degree of up to 95%, and the fineness after drying and sieving is ≤75μm and the calcium carbonate content is over 90%. (2) Weigh out the uncarbonized carbide slag, carbide slag, calcined coal gangue, silicate cement, silica fume and mineral admixtures according to the mass ratio, and then pour them into the mixing bucket and mix evenly. (3) Add the dry-mixed powder to the mixing water, and mix the mortar according to GB / T17671-1999 Cement Mortar Strength Test Method. Pour the mixed mortar into a 40mm×40mm×160mm prism mold and vibrate and compact it. (4) After the mold is placed under standard curing conditions and cured for 2 days, it is removed. The sample is then cured for 28 days before the compressive strength and flexural strength of the cementitious material are determined. The curing temperature is 20±2℃ and the relative humidity is ≥95%.

[0031] Comparative Example 1

[0032] Unlike Example 1, this example used 100% P·I 42.5 cement powder to prepare 40mm×40mm×160mm prismatic cement mortar specimens with a water-cement ratio of 0.5 and a binder-mortar ratio of 1:3. The cast specimens were cured under standard curing conditions: temperature 20±1°C and relative humidity 95% for 24 hours. After demolding, they were further cured in a standard curing chamber for 28 days. The mechanical properties of the cement in both examples and comparative examples were then tested. Table 2 shows the test results. Table 3 shows the results of the carbon dioxide curing capacity evaluation for Example 1 and Comparative Example 1.

[0033] Carbon fixation rate calculation method:

[0034] Here This refers to the carbon emissions of cementitious materials. The calcium hydroxide content after complete hydration of silicate cement is approximately 15 wt% to 20 wt% of its mass. For the negative carbon cementitious material of this invention, the calcium hydroxide content is mainly the sum of the calcium hydroxide content in carbonized and uncarbonized carbide slag and the calcium hydroxide content after hydration of silicate cement. The value is the molar mass of CaCO3 (100 g / mol). The molar mass of Ca(OH)2 is 74 g / mol.

[0035] Table 2: Flexural strength and compressive strength of Example 1 and Comparative Example 1.

[0036]

[0037] Table 3 shows the results of the carbon dioxide curing capacity evaluation for Example 1 and Comparative Example 1.

[0038]

[0039] The above description is only a preferred embodiment of the present invention. All variations and modifications made within the scope of the claims of the present invention should be covered by the claims of the present invention.

Claims

1. A multi-element solid waste negative carbon cement-based material, characterized in that, The cement-based material is composed of the following components by weight: 10-320 parts of carbide slag; 0-240 parts of uncarbide slag; 25-640 parts of calcined coal gangue; 25-800 parts of silicate cement; 6-320 parts of silica fume and other pozzolanic mineral admixtures; and 30-800 parts of mixing water.

2. The multi-element solid waste negative carbon cement-based material according to claim 1, characterized in that, The silicate cement is P·Ⅰ42.5 or P·Ⅱ42.5 grade silicate cement; The carbide slag has a density of 1750 kg / m³. 3 Fineness 340m 2 / kg, calcium hydroxide content 90%–95%, silicon dioxide content 1%–3%, aluminum oxide content 0.5%–2%; after carbonation, calcium carbonate content ≥90%; The calcined coal gangue has the following chemical composition: SiO2 45%–55%, Al2O3 40%–50%, calcination temperature 700–850℃, and fineness ≥325 mesh. The uncarbonized carbide slag has a calcium hydroxide content of ≥90% and its dosage accounts for 0-10% of the mass of the carbide slag. The silica fume is characterized in that: in its chemical composition, the weight percentage content of SiO2 is 90% to 98%, the alkali content (calculated as Na2O equivalent) does not exceed 0.75%, the chloride ion content does not exceed 0.3%, and the loss on ignition does not exceed 6%; and its physical properties meet the following requirements: specific surface area is 15 to 22 m² / g, and the activity index after 28 days is greater than 85%. The mixing water is ordinary tap water.

3. The multi-element solid waste negative carbon cement-based material according to claim 1, characterized in that, The permissible quality tolerances for the cement-based materials are as follows: cement ±0.5%; carbide slag ±0.2%; carbide slag ±0.2%; calcined coal gangue ±0.5%; silica fume ±0.2%; and other pozzolanic mineral admixtures ±0.2%; mixing water ±0.5%.

4. The multi-element solid waste negative carbon cement-based material according to claim 1, characterized in that, The calcium hydroxide content of the carbide slag before carbonization is ≥94%, and the amount of uncarbonized carbide slag in the powder is 0-10%; the calcium carbonate content of the multi-element solid waste after carbonization is ≥90%, and the amount of carbonized carbide slag in the powder is 10%-20%; the amount of calcined coal gangue is 25%-40%; and the amount of silica fume in the cementitious powder material is 5%-10%.

5. The multi-element solid waste negative carbon cement-based material according to claims 1 to 3, characterized in that, The mass ratio of the volcanic ash mineral admixture (excluding solid waste) to cement is 1:

5.

6. A method for preparing a multi-element solid waste negative carbon cement-based material according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Carbonize carbide slag to prepare calcium carbonate. Expose fine carbide slag powder to air or in a carbonation box until the calcium carbonate content is ≥90% to reduce the alkalinity of carbide slag. (2) Calcine the coal gangue at 700-800℃ and then grind it into fine powder to improve the activity of the calcined coal gangue; (3) Accurately weigh the mixing water according to the water requirement of the cementitious material and pour it into the mixing pot. Accurately weigh various raw materials according to the components. Dry mix cement, carbide slag, calcined coal gangue, silica fume and other pozzolanic mineral admixtures. Pour the evenly mixed cementitious material into the mixing water and stir slowly for 90-120 seconds. Then add the remaining mixing water and stir quickly for 90-180 seconds. Pour the mixed slurry into the mold and compact it into shape. (4) After curing the mold under standard curing conditions for 2 days, the mold was removed. The sample was then cured until the corresponding age before mechanical property testing was performed. The curing temperature was 20±2℃ and the relative humidity was ≥95%.

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