Foam concrete doped with coal gasification slag and preparation method thereof

Abstract

The invention relates to the field of concrete materials, and particularly discloses coal gasification slag doped foam concrete and a preparation method thereof, the foam concrete comprises the following raw materials: 400-500 parts of cement, 150-250 parts of coal gasification slag, 225-300 parts of water, 1.9-2.4 parts of a foaming agent, 0.8-1.6 parts of a water reducing agent, 2.5-6.5 parts of an alkali activator, 0.2-0.4 part of cellulose, and 5-15 parts of a waterproof agent. Carrying out ball milling on the coal gasification slag, sieving, uniformly mixing and stirring with cement, an alkali activator and a waterproof agent, uniformly mixing water and a water reducing agent, adding the mixture, and uniformly stirring to obtain slurry; and adding water to dilute a foaming agent, adding cellulose, mixing, uniformly stirring to prepare foam, adding the slurry, uniformly mixing, pouring, curing, and molding. The foam concrete doped with the coal gasification slag prepared by the invention is fine and dense in foam pores, uniform in pore diameter, high in strength and good in thermal insulation performance, solves the problem of resource utilization of the coal gasification slag, reduces the use amount of cement, is outstanding in comprehensive performance, and can be popularized and used in a large range.

Description

Technical Field

[0001] This invention belongs to the field of building concrete materials, specifically a foamed concrete with coal gasification slag and its preparation method. Background Technology

[0002] The output of industrial solid waste is increasing year by year, but the effective utilization rate is not high. Large accumulations of solid waste not only cause environmental pollution but can also affect human health. my country's energy structure is dominated by coal, and coal gasification, as a core technology for the clean and efficient utilization of coal, has led to the generation of large amounts of coal gasification slag due to its large-scale application. Currently, the main methods for treating coal gasification slag are stockpiling and landfilling, causing serious environmental pollution and the occupation of land resources.

[0003] Foamed concrete is a new type of lightweight building material that can effectively reduce energy consumption. Traditional foamed concrete uses cement as the main binder, supplemented with admixtures such as fly ash or silica fume, with foam introduced externally and mixed with water. However, in recent years, the large-scale use of fly ash and silica fume has led to a supply shortage, and the cost of producing foamed concrete has also begun to increase. Therefore, finding alternative solid waste materials is currently a key focus in the construction concrete materials industry.

[0004] Coal gasification slag is obtained directly from the coarse separation process after the coal gasification reaction. The residue carried by the high-temperature coal gas is processed through separators and gravity settling chambers to separate particles with a diameter ≥0.1mm. No complex pretreatment is required; only crushing and screening to adjust the particle size distribution are needed. Coal gasification slag is mainly composed of SiO2, Al2O3, CaO, and Fe2O3, with high contents of SiO2 and Al2O3, exhibiting potential reactivity. Furthermore, coal gasification slag is lightweight and porous, theoretically suitable as a filler in lightweight building materials to improve their thermal insulation properties. Therefore, using coal gasification slag as an admixture in lightweight foamed concrete is an efficient and feasible approach for the resource utilization of solid waste.

[0005] Foamed concrete consists of foam and slurry. The lower the density of foamed concrete, the higher the foam content in the matrix. When coal gasification slag is used as an admixture, its lightweight, porous nature and strong water absorption will intensify gas-liquid exchange at the foam interface in the slurry, causing foam dehydration and breakage. This results in larger pores within the matrix, increasing structural inhomogeneity, which not only affects the thermal insulation performance of the foamed concrete but also hinders strength development. Therefore, directly using coal gasification slag as an admixture to prepare foamed concrete presents certain challenges. Summary of the Invention

[0006] To address the shortcomings of the existing technology, this invention provides a foamed concrete incorporating coal gasification slag and its preparation method. The coal gasification slag is ball-milled to a certain fineness, and then an alkali activator is used to enhance its activity. A waterproofing agent and cellulose are used to modify its surface, inhibiting its water absorption while stabilizing the foam. This allows the coal gasification slag to be incorporated into the foamed concrete at a relatively high dosage. This not only solves the resource utilization problem of coal gasification slag and reduces cement usage, but also produces foamed concrete with excellent mechanical properties and good thermal insulation performance.

[0007] This invention provides a foamed concrete with coal gasification slag, which is prepared from the following raw materials in parts by weight: 400-500 parts cement, 150-250 parts coal gasification slag, 225-300 parts water, 1.9-2.4 parts foaming agent, 0.8-1.6 parts water-reducing agent, 2.5-6.5 parts alkali activator, 0.2-0.4 parts cellulose, and 5-15 parts waterproofing agent.

[0008] Preferably, the cement is ordinary Portland cement with a strength grade ≥ P·O 42.5.

[0009] Preferably, the coal gasification slag is coarse coal gasification slag with a SiO2 content of not less than 30% and an Al2O3 content of not less than 10%.

[0010] Preferably, the foaming agent is one of the following: tea saponin plant protein foaming agent, saponin plant protein foaming agent, aluminum powder foaming agent, or synthetic surfactant foaming agent, with a foaming ratio of 18 to 22 times. The synthetic surfactant foaming agent can be sodium dodecyl sulfate foaming agent or alkyl sulfate foaming agent between C12 and C22.

[0011] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent, which is one or more of methacrylic acid-maleic anhydride copolymer, acrylic acid-polyoxyethylene ether monomethyl ether copolymer, and maleic anhydride-polyoxyethylene ether allyl ester copolymer.

[0012] Preferably, the alkaline activator is calcium hydroxide powder.

[0013] Preferably, the cellulose is hydroxypropyl methylcellulose (HPMC).

[0014] Preferably, the waterproofing agent is an organosilicon nano-waterproofing agent. This organosilicon nano-waterproofing agent is one or more of a silane coupling agent, nano-silicone resin, and sodium methylsilicate.

[0015] Another object of the present invention is to provide a method for preparing the above-mentioned foamed concrete with added coal gasification slag, wherein the specific preparation steps are as follows: (1) Grind the coal gasification slag into balls and then pass it through a 100-mesh sieve; (2) Mix the sieved coal gasification slag with cement, alkali activator and waterproofing agent until uniform to obtain a mixture; (3) After mixing water and water-reducing agent evenly, add the mixture and stir until uniform to obtain a slurry; (4) Then dilute the foaming agent with water, add cellulose and mix, stir evenly to make foaming liquid, and add the foaming liquid to the foaming machine to make foam; (5) Add the foam to the slurry, mix and stir evenly, pour into the mold, and cure for 28 days at 25℃ and RH90%.

[0016] In the technical solution of this invention, the coal gasification slag is ball-milled and then passed through a 100-mesh sieve. Through ball milling, the specific surface area of ​​the material increases and the particle size decreases, enabling it to effectively fill the pores of foamed concrete, preventing the agglomeration of cement particles and achieving a micro-aggregate filling effect. After ball milling, the glassy structure of the coal gasification slag particles is destroyed, releasing glass microspheres with pozzolanic activity. Furthermore, the sharp edges are softened, making the surface smoother, which helps reduce internal friction in the slurry, improves the slurry structure, and increases its strength. On the other hand, ball milling better releases the silicon and aluminum oxides in the coal gasification slag, increasing its activity, and the alkali activator—calcium hydroxide—dissociates to release Ca. 2+ and OH - OH - The increased concentration of these elements accelerates the dissolution of silicon and aluminum components in the coal gasification slag. The dissolved silicon and aluminum phase components in the system more readily combine with metal cations, such as Ca. 2+ It combines with the dissolved silicon-aluminum phase components, thereby quickly reaching saturation and forming CSH gel. This promotes the secondary hydration reaction of coal gasification slag and cement hydration products, generating more hydration products, accelerating the hydration reaction rate, and making the structure of the hydration products more compact, which is more conducive to strength development.

[0017] The active ingredients, such as silanes, in the organosilicon nano-waterproofing agent can chemically react with hydroxyl (-OH) groups on the surface of coal gasification slag. In the slurry, the alkoxy groups in the silanes hydrolyze to form silanols, which then undergo a condensation reaction to form a waterproof organosilicon resin film on the surface of the coal gasification slag particles. This film is tightly bonded to the coal gasification slag surface through chemical bonds, exhibiting strong adhesion. It forms a barrier between particles and air bubbles, effectively inhibiting gas-liquid exchange caused by the high water absorption of the coal gasification slag, thus improving structural stability.

[0018] When HPMC is incorporated into the slurry, the hydroxyl groups (-OH) in the HPMC molecular structure can interact with the hydroxyl groups (-OH) on the surface of the gasification slag to form hydrogen bonds, enhancing the adhesion between the two. HPMC adheres to the surface of the gasification slag particles, forming a thin film that isolates the slag from the foam. This effectively reduces foam dehydration and breakage caused by the high water absorption of the gasification slag, and inhibits uneven pore size development. Furthermore, the uniformly distributed HPMC particles adsorb at the gas-liquid interface of the foam wall, balancing the interfacial tension and forming a solid-liquid-gas three-phase foam. This hinders drainage between the gas and liquid phases, prevents gas phase transfer, and significantly reduces the connectivity between the internal pores of the foamed concrete, resulting in finer pores and a more uniform pore size distribution. This improves thermal insulation performance and is beneficial for strength development.

[0019] Compared with the prior art, the beneficial effects of the present invention are: The foamed concrete prepared by this invention can contain more than 30% coal gasification slag. It has fine and uniform pores, high strength, and good thermal insulation performance. It solves the problem of resource utilization of coal gasification slag, reduces the amount of cement used, and its strength is far higher than the requirements of the current foamed concrete industry standard. It also has excellent thermal insulation performance and outstanding comprehensive performance, which can be widely promoted and used. Attached Figure Description

[0020] Figure 1 These are sample images of concrete foam prepared in Example 3 and Comparative Examples 7-8.

[0021] Figure 1 (a) is a sample of the concrete foam prepared in Example 3. Figure 1 (b) is a concrete foam sample prepared in Comparative Example 7. Figure 1 (c) shows the concrete foam sample prepared in Comparative Example 8. As can be seen from the figure, the concrete foam prepared in Example 3 of this invention is small and uniform, with a high material density. In contrast, the comparative example, lacking key components, has a high foam porosity, is non-uniform, and has a hollow structure, resulting in low compressive strength and low specific strength.

[0022] Figure 2 These are sample images and electron microscope photographs of the foamed concrete prepared in Example 1.

[0023] Figure 2 (a) is a sample of foamed concrete prepared in Example 1. Figure 2 (b) is an electron microscope image of the foamed concrete prepared in Example 1. Figure 3 These are sample images and electron microscope photographs of the foamed concrete prepared in Example 3.

[0024] Figure 3 (a) is a sample of foamed concrete prepared in Example 3. Figure 3(b) is an electron microscope image of the foamed concrete prepared in Example 3. The image shows that the concrete foam prepared in Example 1 of this invention is small and uniform, with a high material density. Compared to Example 1, the foamed concrete in Example 3 has more and finer bubbles, resulting in a higher dry density.

[0025] Figure 4 These are sample images and electron microscope photographs of the foamed concrete prepared in Comparative Example 4.

[0026] Figure 4 (a) is a sample of foamed concrete prepared in Comparative Example 4. Figure 3 (b) is an electron microscope image of the foamed concrete prepared in Comparative Example 4. The image shows that the foamed concrete in Comparative Example 4 has more foam and the material is not uniform. Detailed Implementation

[0027] The technical solution of the present invention will be further analyzed and explained through specific embodiments below.

[0028] The raw materials used in the embodiments of this invention, including cement, calcium hydroxide powder, organosilicon nano waterproofing agent, polycarboxylate superplasticizer, foaming agent and cellulose, are all commercially available molded products.

[0029] Example 1 Preparation of foamed concrete with coal gasification slag: Step 1: Grind the coal gasification slag into balls and then pass it through a 100-mesh sieve; Step 2: By weight, mix 400 parts of cement, 150 parts of coal gasification slag (after sieving), 2.5 parts of calcium hydroxide powder, and 5 parts of organosilicon nano waterproofing agent (silane coupling agent), and stir until uniform to obtain a mixture. Step 3: By weight, add 250 parts of water and 0.8 parts of polycarboxylate superplasticizer (methacrylic acid-maleic anhydride copolymer) to the mixture and stir until uniform to obtain a slurry; Step 4: By weight, mix 1.9 parts of foaming agent (aluminum powder foaming agent) and 0.2 parts of cellulose (hydroxypropyl methylcellulose), dilute with water, stir evenly with a magnetic stirrer to form a foaming liquid, and add the foaming liquid to the foaming machine to make foam; Step 5: Mix the slurry prepared in Step 3 and the foam prepared in Step 4 together until uniform, then pour into a mold and cure for 28 days at 25°C and 90% RH.

[0030] Example 2 The difference between Embodiment 2 and Embodiment 1 of the present invention is that the raw materials used are: 450 parts cement, 200 parts coal gasification slag (after sieving), 4 parts calcium hydroxide powder, 9 parts organosilicon nano waterproofing agent, 275 parts water, 1.1 parts polycarboxylate superplasticizer, 2.1 parts foaming agent, and 0.3 parts cellulose.

[0031] The concrete preparation process in Example 2 is the same as that in Example 1.

[0032] Example 3 The difference between Embodiment 3 and Embodiment 1 of the present invention is that the raw materials used are: 500 parts cement, 150 parts coal gasification slag (after sieving), 4.5 parts calcium hydroxide powder, 12 parts organosilicon nano waterproofing agent; 300 parts water, 1.2 parts polycarboxylate superplasticizer; 2.2 parts foaming agent, and 0.4 parts cellulose.

[0033] The concrete preparation process in Example 3 is the same as that in Example 1.

[0034] Example 4 The difference between Example 4 and Example 1 of this invention is that the raw materials used are: 450 parts cement, 250 parts coal gasification slag (after sieving), 6.5 parts calcium hydroxide powder, 15 parts organosilicon nano waterproofing agent, 275 parts water, 1.6 parts polycarboxylate superplasticizer, 2.4 parts foaming agent, and 0.3 parts cellulose.

[0035] The concrete preparation process in Example 4 is the same as that in Example 1.

[0036] Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that no treatment is performed on the coal gasification slag during the preparation process. It is used directly as an admixture without the addition of alkali activator, organosilicon nano-waterproofing agent, and cellulose. The preparation process is as follows: Step 1: By weight, mix 500 parts of cement and 150 parts of coal gasification slag until uniform to obtain a mixture; Step 2: By weight, add 300 parts water and 1.2 parts polycarboxylate superplasticizer to the mixture and stir until uniform to obtain a slurry; Step 3: Dilute 2.2 parts of foaming agent with water by weight, stir evenly to form a foaming liquid, and add the foaming liquid to the foaming machine to make foam; Step 4: Mix the slurry prepared in Step 2 and the foam prepared in Step 3 together until uniform, then pour into a mold and cure for 28 days at 25°C and 90% RH.

[0037] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that no organosilicon nano-waterproofing agent and cellulose were used in the preparation process.

[0038] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that the coal gasification slag was not ball-milled and sieved during the preparation process.

[0039] Comparative Example 4 The difference between Comparative Example 4 and Example 3 is that the coal gasification slag was not ball-milled and sieved during the preparation process, and no alkali activator was used.

[0040] Comparative Example 5 The difference between Comparative Example 5 and Example 3 is that no organosilicon nano-waterproofing agent was used in the preparation process.

[0041] Comparative Example 6 The difference between Comparative Example 6 and Example 3 is that cellulose was not used in the preparation process.

[0042] Comparative Example 7 The difference between Comparative Example 7 and Example 3 is that no alkali activator and organosilicon nano-waterproofing agent were used in the preparation process.

[0043] Comparative Example 8 The difference between Comparative Example 8 and Example 3 is that no alkali activator and cellulose were used in the preparation process.

[0044] The concrete prepared in Examples 1-4 and Comparative Examples 1-8 were tested using the following methods: 1. The 28-day cubic compressive strength of the concrete prepared in Examples 1-4 and Comparative Examples 1-8 was tested according to the "Test Procedures for Cement and Cement Concrete in Highway Engineering" (JTG3420-2020). The specific measurement process is as follows. When measuring compressive strength, the loading rate is 6.75 kN / s, and the loading is continuous. There are 3 concrete test samples, and the error control range is ±10%. Calculate the average value.

[0045] 2. The slump of the concrete prepared in Examples 1-4 and Comparative Examples 1-8 was tested using a slump meter in accordance with the "Test Procedures for Cement and Cement Concrete in Highway Engineering" (JTG3420-2020).

[0046] 3. Measurement method of thermal conductivity: The thermal conductivity of the specimen shall be tested in accordance with the provisions of GB / T10294. The specimen size is 300×300×30 mm. The foamed concrete specimen shall be placed vertically between the cooling unit and the heating unit of the thermal conductivity tester. Input the basic information such as specimen thickness, specimen density, and specimen area, set the hot plate temperature and cold plate temperature, set the temperature control time and stabilization calculation time, record the test data, and calculate the thermal conductivity.

[0047] 4. Specific strength is measured and calculated according to the formula compressive strength / density.

[0048] The performance of the samples obtained in Examples 1-4 and Comparative Examples 1-8 was tested, and the results are as follows:

[0049] The data in Table 1 are compared and analyzed in conjunction with Examples 1-4 and Comparative Examples 1-8.

[0050] In Examples 1-4 of this invention, without changing the type of raw materials, only by appropriately adjusting the amount of materials within the scope defined by this invention, some fluctuations in the performance of the specimens may occur, which is normal. The performance of each group of specimens exceeds the requirements of the current industry standard for foamed concrete, with the result of Example 3 being the best.

[0051] Comparative Examples 1-8 modified the technical methods and raw material components based on Example 3. In Comparative Example 1, no treatment was performed on the gasification slag; it was used directly as an admixture, and no alkali activator, organosilicon nano-waterproofing agent, or cellulose was added to the raw materials. The specimens collapsed and were difficult to mold. In Comparative Example 2, no surface modification and foam stabilization treatment was performed on the gasification slag using organosilicon nano-waterproofing agent and cellulose. The specimens still collapsed, indicating that organosilicon nano-waterproofing agent and cellulose can inhibit defoaming of the gasification slag and improve the stability of the slurry. In Comparative Examples 6 and 8, specimens without cellulose collapsed, showing that cellulose is the main factor maintaining the stability of the foamed concrete slurry. In Comparative Example 5, no organosilicon nano-waterproofing agent was used; the specimens could be molded, but the density increased, and the strength and thermal insulation performance decreased. This indicates that organosilicon nano-waterproofing agent can inhibit defoaming of the gasification slag and also improves the stability of the slurry to some extent. Comparative Example 7 further eliminated the use of the alkali activator compared to Comparative Example 5, and the specimen strength further decreased, indicating that the alkali activator is an important factor affecting strength.

[0052] In Comparative Example 3, the coal gasification slag was not ball-milled and sieved, resulting in increased specimen density, decreased strength, and reduced thermal insulation. In Comparative Example 4, the coal gasification slag was not ball-milled and sieved, and no alkali activator was used. As a result, the performance of the specimen was further reduced compared to Comparative Example 3. This indicates that ball milling and sieving to a certain fineness can effectively improve the activity of coal gasification slag, allowing the surface modifiers, organosilicon nano-waterproofing agent and cellulose, to play a better role.

[0053] The above results demonstrate the necessity of the technical means of this invention.

Claims

1. A foamed concrete incorporating coal gasification slag, characterised in that, It is prepared from the following raw materials in parts by mass: Cement 400-500 parts, coal gasification slag 150-250 parts, water 225-300 parts, foaming agent 1.9-2.4 parts, water reducing agent 0.8-1.6 parts, alkali activator 2.5-6.5 parts, cellulose 0.2-0.4 parts, waterproof agent 5-15 parts.

2. The foamed concrete according to claim 1, wherein, The cement is ordinary Portland cement, and the strength grade is ≥P·O 42.

5.

3. The foamed concrete coal gasification slag according to claim 1, characterized in that, The coal gasification slag is coal gasification coarse slag, and the SiO2 content is not less than 30%, and the Al2O3 content is not less than 10%.

4. The foamed concrete according to claim 1, wherein, The foaming agent is a plant protein type foaming agent, and the foaming ratio is 18-22 times.

5. The foamed concrete according to claim 1, wherein, The water reducing agent is a polycarboxylic acid water reducing agent.

6. The foamed concrete coal gasification slag according to claim 1, characterized in that, The alkali activator is calcium hydroxide powder.

7. The foamed concrete according to claim 1, wherein, The cellulose is hydroxypropyl methyl cellulose.

8. The foamed concrete coal gasification slag according to claim 1, characterized in that, The waterproof agent is a silicone nano waterproof agent.

9. The method of claim 1-8, wherein the foamed concrete is prepared by mixing coal gasification slag with cement, water, and a foaming agent, and then foaming the mixture. The specific preparation steps are as follows: (1) The coal gasification slag is ball milled and then passed through a 100-mesh sieve; (2) The sieved coal gasification slag is mixed with cement, alkali activator and waterproof agent and stirred until uniform to obtain a mixture; (3) The water and water reducing agent are mixed and then added to the mixture and stirred until uniform to obtain a slurry; (4) Then the foaming agent is diluted with water, mixed with cellulose, stirred until uniform to obtain a foaming liquid, and the foaming liquid is added to a foaming machine to form a foam; (5) The foam is added to the slurry, mixed and stirred until uniform, poured into a mold, and cured at 25℃ and RH 90% for 28 days.

Images