A large amount of solid waste-based autoclaved aerated concrete block and a preparation method thereof

Abstract

The application belongs to the technical field of building materials, and discloses a large-mixing-amount solid waste based autoclaved aerated concrete block and a preparation method thereof.The autoclaved aerated concrete block comprises the following main materials in terms of mass percentage: activated subway sand 40-50%, blast furnace slag 10-30%, activated steel slag 3-10%, cement 5-15%, quicklime 5-15%, and gypsum 1.5-3%.The autoclaved aerated concrete block further comprises additives, and the mixing amount of each additive is 0.05-0.15% of the foaming agent, 0.03-0.05% of the foam stabilizer, 0.25-0.75% of the alkali activator, and 0.10-0.20% of the water reducing agent, based on the total mass of the main materials.The application uses subway sand, blast furnace slag and steel slag as the main raw materials, solves the problems of resource utilization of subway sand, blast furnace slag and steel slag, and low compressive strength of the autoclaved aerated concrete block prepared from large-mixing-amount subway sand, uneven foaming and corner fracture of the block, realizes the collaborative comprehensive utilization of subway sand and steel metallurgical slag, reduces the production cost of the aerated concrete block, and has significant economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a high-volume solid waste-based autoclaved aerated concrete block and its preparation method. Background Technology

[0002] Subway sand generally refers to the excavated soil generated during the construction of urban subways, mainly including the excavated soil from shield tunneling and the residual sand from track construction. With the rapid development of urban underground space and rail transit engineering, subway sand has become one of the main sources of urban solid waste. However, the resource utilization rate of subway sand in my country is low. The vast majority of subway sand is still disposed of through open-air stockpiling or landfill. Untreated subway sand not only occupies land resources but also reduces soil fertility and ecological quality. At the same time, after being washed away by rainwater, subway sand produces leachate, in which residual heavy metals and salts migrate and cause potential cumulative pollution to the surrounding soil, leading to increasingly prominent environmental problems. In addition, steel slag and blast furnace slag, as industrial waste generated during the iron and steel metallurgy process, also face environmental pollution and resource waste problems. Their resource utilization has become a technical problem that enterprises urgently need to solve.

[0003] Autoclaved aerated concrete (AAC) is an inorganic building material typically made from fly ash, river sand, shale, cement, lime, and other main raw materials, with the addition of appropriate foaming agents and modifiers. The process involves batching, mixing, pouring, pre-curing under static heat, cutting, demolding, and high-pressure autoclaving. AAC has a density only one-fifth that of ordinary concrete, significantly reducing the building's weight when used as a wall material. Furthermore, the numerous pores and micropores within AAC result in a low thermal conductivity, giving it excellent thermal insulation properties. It is currently one of the most promising lightweight, energy-saving, and heat-insulating building materials. Currently, there are few reports on the use of subway sand to prepare autoclaved aerated concrete (AAC). This is mainly because subway sand, as a type of mixed slag, usually suffers from problems such as insufficient effective silicon source, low reactivity, complex mineral composition, and high mud content. In addition, the system contains a lot of impurities such as Al, Fe, Ca, K, and Na. While inhibiting the formation of tobermorite, it also disrupts the gas generation rhythm of aluminum paste. As a result, when subway sand is used directly as a siliceous material in AAC, it will lead to insufficient Si release, accumulation of unreacted particles, incomplete hydrothermal reaction, increased water demand, uneven distribution of internal pores, and density stratification of aerated blocks. Ultimately, this leads to a decrease in the performance of AAC blocks and corner cracking, and these problems are more pronounced at high admixture levels.

[0004] Blast furnace slag is typically rich in Ca, Si, and Al, and has a high glass phase content. Under alkaline and hydrothermal conditions, it rapidly releases active Si, Al, and Ca components, exhibiting high reactivity and making it suitable as a cement admixture to replace part of the cement. In autoclaved aerated concrete (AAC) systems, steel slag can not only serve as a calcium-based raw material to replace traditional lime but also participate in hydrothermal reactions due to its high alkalinity and calcium content. However, because steel slag forms at excessively high temperatures, the mineral crystals within it become too large, with Ca, Fe, Mg, and Al ions dissolving into the mineral lattice, resulting in lower reactivity. If the two are mixed, the significant difference in hydration reaction rates leads to rapid reactions and consumption of large amounts of water and quicklime by blast furnace slag during the thermal shutdown and autoclaving stages. Meanwhile, insufficient hydration space and activators in the later stages prevent the effective activation of steel slag's reactivity, resulting in a porous, weakly connected interfacial structure that reduces the mechanical properties of the AAC.

[0005] Therefore, there is currently a lack of effective and industrializable technical solutions for how to synergistically utilize subway sand, steel slag, and blast furnace slag to prepare autoclaved aerated concrete with a large amount of solid waste. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a high-volume solid waste-based autoclaved aerated concrete block and its preparation method. This not only realizes the resource utilization of a large amount of subway sand, but also achieves the goal of using iron and steel metallurgical waste slag to replace part of the cement and lime to reduce production costs, thus achieving a win-win situation for the environment and the economy.

[0007] To address the technical problems proposed in this invention, this invention provides a high-volume solid waste-based autoclaved aerated concrete block, comprising the following main materials by mass percentage: activated iron sand 40%~50%, blast furnace slag 10%~30%, activated steel slag 3%~10%, cement 5%~15%, quicklime 5%~15%, and gypsum 1.5%~3%; and admixtures, the dosage of each admixture being based on the total mass of the main materials, with the following mass percentages: foaming agent 0.05%~0.15%, foam stabilizer 0.03%~0.05%, alkali activator 0.25%~0.75%, and water-reducing agent 0.10%~0.20%.

[0008] In the above scheme, the water-to-material ratio of the autoclaved aerated concrete blocks during the preparation process is 0.45~0.55. The water-to-material ratio is the mass ratio of mixing water to main material, excluding admixtures.

[0009] In the above scheme, the activated subway sand is obtained by sequentially subjecting subway sand to thermal activation treatment, mechanical ball milling treatment and chemical soaking treatment.

[0010] Furthermore, the subway sand has a SiO2 content of 55wt%~65wt%, a CaO content of 1wt%~8wt%, an Al2O3 content of 14wt%~20wt%, and a particle size of 0.1~0.5mm.

[0011] Furthermore, the temperature of the thermal activation treatment is 750~900℃, and the holding time is 2~4h. Even further, the heating rate during the thermal activation treatment is controlled at 5~15℃ / min.

[0012] Furthermore, the ball milling speed for the mechanical ball milling process is 500-600 rpm, and the milling time is 20-30 min. In the mechanically ball-milled iron sand, particles with a diameter less than 0.074 mm account for more than 80%.

[0013] Further, the chemical soaking treatment involves soaking the mechanically ball-milled iron sand in a NaOH solution at a constant temperature with stirring, then collecting the insoluble matter and drying it to obtain activated iron sand. Even further, the solid-liquid ratio of the chemical soaking treatment is 1:4 to 1:6, the concentration of the NaOH solution is 1 to 5 mol / L, the soaking temperature is 60 to 80°C, and the soaking time is 1 to 4 hours.

[0014] In the above scheme, the SiO2 content of the blast furnace slag is 30wt%~40wt%, the CaO content is 35wt%~45wt%, the Al2O3 content is 15wt%~20wt%, and the proportion of particles with a particle size of less than 0.074mm is more than 80%.

[0015] In the above scheme, the activated steel slag is obtained by aging and drying a mixed slurry made of steel slag, quicklime, gypsum and water.

[0016] Furthermore, the steel slag has a SiO2 content of 10wt%~20wt%, a CaO content of 40wt%~55wt%, an Al2O3 content of 1wt%~5wt%, and a particle size of less than 0.074mm accounts for more than 80%.

[0017] Furthermore, the amount of quicklime used is 3% to 5% of the mass of steel slag, the amount of gypsum used is 1% to 2% of the mass of steel slag, and the amount of water used is 35% to 45% of the total mass of steel slag, quicklime, and gypsum.

[0018] Furthermore, the aging temperature is 25~30℃, and the aging time is 4~6h.

[0019] In the above scheme, the cement is one of P·O 52.5 cement and P·O 42.5 cement.

[0020] In the above scheme, the effective calcium oxide content in the quicklime is >70%.

[0021] In the above scheme, the mass fraction of calcium sulfate dihydrate in the gypsum is above 85%.

[0022] In the above scheme, the foaming agent is aluminum paste. Further, the solid content of the aluminum paste is 65%~75%, the mass fraction of active aluminum in its solid components is greater than 85%, and the particle size of the solid components is 0.015~0.035 mm.

[0023] In the above scheme, the foam stabilizer is hydroxypropyl methylcellulose, which can increase the viscosity and water retention of the slurry, inhibit the coalescence and rupture of bubbles, thereby improving the uniformity of foaming.

[0024] In the above scheme, the alkaline activator is liquid sodium silicate. Further, the modulus of the liquid sodium silicate is 2.6~2.9, and the mass fraction of sodium silicate is 34%~36%.

[0025] In the above scheme, the water-reducing agent is a polyether-type polycarboxylate water-reducing agent, which can significantly reduce the mixing water while maintaining the required fluidity, thereby improving the strength of the blocks.

[0026] This invention also provides a method for preparing autoclaved aerated concrete blocks with a large amount of solid waste, comprising the following steps: S1. Mix activated subway sand, blast furnace slag, activated steel slag, gypsum and water evenly to obtain solid waste slurry; S2. Add alkali activator to solid waste slurry and stir for 15-30 seconds. Then add cement, quicklime, water-reducing agent and foam stabilizer and stir for 30-40 seconds. Finally, add foaming agent and stir for 20-40 seconds to obtain mixed slurry. S3. Pour the mixed slurry into the mold, and after hot static gas curing, cut and demold to obtain the green body; S4. The green body is subjected to autoclaving to obtain autoclaved aerated concrete blocks.

[0027] In the above scheme, the temperature for the hot static gas shutdown curing is 55~65℃, and the time is 3~6 h.

[0028] In the above scheme, the curing pressure of autoclaving is 1.1~1.5 MPa, the curing temperature is 187~203℃, and the curing time is 6~10 h.

[0029] In the above scheme, the dry density of the autoclaved aerated concrete blocks is ≤650 kg / m³. 3 The compressive strength is ≥3.5MPa, meeting the A3.5 B06 grade standard of "Autoclaved Aerated Concrete Blocks" (GB / T 11968-2020).

[0030] The technical concept and technical principle of this invention are as follows: This invention addresses the technical problems of subway sand, including insufficient effective silicon source, low reactivity, complex mineral composition, and high mud content, which prevent its large-scale application in autoclaved aerated concrete. On one hand, it employs a triple activation pretreatment process on the subway sand: calcination activation, mechanical ball milling activation, and chemical alkali soaking. This enhances the subway sand's ability to participate in hydrothermal reactions and improves the performance of the blocks. First, through thermal activation (high-temperature calcination), the crystal structure of inert minerals in the subway sand is disrupted, transforming it into amorphous or metastable phases with higher reactivity. The thermally activated subway sand then undergoes mechanical activation (ball milling), where intense grinding not only refines the sintered particles but also creates numerous lattice defects and broken bonds in the mineral crystals, increasing the specific surface area and reaction sites, thereby improving its reactivity. Finally, the calcined and milled subway sand undergoes further chemical activation (alkali soaking), where the OH- in the alkali solution... - Ions actively attack the Si-O-Si and Si-O-Al chemical bonds on the particle surface, causing them to break. Some silicate and aluminate ions are pre-dissociated, providing a large number of reactive sites for subsequent participation in the formation of tobermorite. On the other hand, the introduction of steel slag and blast furnace slag can release active components such as Si, Al, and Ca under alkaline and hydrothermal conditions. Both can provide a reaction basis for the formation of hydration products such as tobermorite, thereby alleviating the problem of reduced activity in autoclaved aerated concrete systems caused by large amounts of iron sand. However, it is necessary to address the difference in hydration reaction rates between steel slag and blast furnace slag.

[0031] To address the issue of a discontinuity in the reaction rate between steel slag and blast furnace slag due to its low reactivity, a combined alkali-sulfate chemical activation treatment was applied to the steel slag. In the lime-gypsum mixed slurry system, the large amount of OH- produced by lime hydrolysis... - Ions rapidly increase the alkalinity of the medium, disrupting the network lattice structure on the surface of steel slag particles, allowing a large amount of Ca to escape. 2+ AlO2 - and SiO4 4- As the gypsum dissolves and enters the system, SO4 is released during the dissociation of the gypsum. 2- Rapidly reacting with the free Ca 2+ and AlO2 - The reaction combines to form ettringite crystals. This reaction not only consumes some of the free calcium in the system, but also provides a network framework structure for the early billet. It also helps to improve the hydration reaction rate of steel slag during the pre-curing and steam curing stages, thereby achieving the effect of synchronizing the hydration reaction rate with that of blast furnace slag and activated iron sand.

[0032] Furthermore, adding liquid sodium silicate as an alkali activator to the mixed slurry provides a gentle secondary activation of the pre-activated subway sand and steel slag, while simultaneously increasing the alkalinity of the system and accelerating the dissolution of SiO2, Al2O3, CaO, etc., in the subway sand and steel slag, thus fully activating their activity. Adding hydroxypropyl methylcellulose as a foam stabilizer increases the slurry viscosity and water retention, inhibiting bubble coalescence and breakage, thereby improving the uniformity of foaming. Adding polyether-type polycarboxylate superplasticizer significantly reduces the amount of mixing water while maintaining the required fluidity, thereby reducing large pores caused by excessive water evaporation and improving its strength. In summary, through secondary activation and the action of admixtures, the performance of aerated concrete is further improved.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention uses subway sand, blast furnace slag, and steel slag as main raw materials to prepare autoclaved aerated concrete (AAC). A triple activation method combining thermal activation, mechanical activation, and chemical activation is used to improve the hydrothermal reactivity of the subway sand. An alkali-sulfate composite chemical activation method is used to enhance the activity of the steel slag, thereby increasing its hydration reaction rate. Appropriate admixtures are added to address the problems of low compressive strength, uneven foaming, and corner breakage in AAC blocks prepared with large amounts of subway sand in conjunction with blast furnace slag and steel slag. The resulting AAC meets the requirements of the A3.5 B06 grade standard of "Autoclaved Aerated Concrete Blocks" (GB / T11968-2020).

[0034] This invention not only realizes the synergistic resource utilization of subway sand, steel slag, and blast furnace slag, alleviating a series of social and environmental problems caused by the large accumulation of waste slag and reducing the burden on enterprises, but also achieves the goal of turning waste into treasure. The preparation of thermal insulation and energy-saving aerated concrete building materials with a large amount of waste slag not only reduces production costs, but also conforms to the national energy conservation and emission reduction industrial policy and improves resource utilization efficiency. Detailed Implementation

[0035] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0036] In the following examples, the raw materials used include: blast furnace sand, with a SiO2 content of 62.55 wt%, a CaO content of 2.96 wt%, an Al2O3 content of 19.52%, and a particle size of 0.1~0.5 mm; blast furnace slag, with a SiO2 content of 33.42 wt%, a CaO content of 39.42 wt%, an Al2O3 content of 16.06 wt%, and a particle size of less than 0.074 mm accounting for more than 80%; and steel slag, with a SiO2 content of 13.60 wt% and a CaO content of 4%. 5.90wt%, Al2O3 content is 1.40wt%, and particle size less than 0.074mm accounts for more than 80%; cement is commercially available P·O42.5 cement; quicklime, effective calcium oxide content is 72%; gypsum, calcium sulfate dihydrate content is 89%; aluminum paste, solid content is 75%, active aluminum content in solids is 89%, particle size is 0.015~0.035mm; liquid sodium silicate, modulus 2.6, liquid sodium silicate mass fraction is 36%; hydroxypropyl methylcellulose and polyether type polycarboxylate superplasticizer are both industrial grade.

[0037] Example 1 A high-volume solid waste-based autoclaved aerated concrete block comprises the following main materials by mass percentage: 50% activated iron sand, 10% blast furnace slag, 7% activated steel slag, 15% cement, 15% quicklime, and 3% gypsum; it also includes admixtures, the dosage of which is based on the total mass of the main materials, with the following mass percentages: 0.09% aluminum paste, 0.04% hydroxypropyl methylcellulose, 0.5% liquid sodium silicate, and 0.10% polyether-type polycarboxylate superplasticizer. The designed water-to-material ratio is 0.54.

[0038] The preparation method of activated iron sand is as follows: 1) Heat the subway sand to 800℃ at a rate of 10℃ / min and keep it at that temperature for 2 hours; 2) The calcined iron sand was ball-milled at a speed of 600 rpm for 30 minutes to obtain ball-milled iron sand with a particle size of less than 0.074 mm accounting for more than 80%. 3) The ball-milled iron sand was placed in a 3mol / L NaOH aqueous solution at a solid-liquid ratio of 1:6, stirred and soaked at a constant temperature of 70℃ for 4 hours, and then the insoluble matter was collected and dried to obtain activated iron sand.

[0039] The method for preparing activated steel slag is as follows: 1) Weigh a certain amount of steel slag, as well as quicklime and gypsum accounting for 5% of the mass of steel slag and 2% of the mass of gypsum, and add water accounting for 40% of the total mass of dry materials (steel slag, quicklime and gypsum). Mix thoroughly to obtain a mixed slurry. 2) The mixed slurry was sealed and aged at 25°C for 6 hours, and then dried at 105°C to constant weight to obtain activated steel slag.

[0040] In this embodiment, the high-volume solid waste-based autoclaved aerated concrete blocks are obtained through the following steps: (1) Mix activated subway sand, blast furnace slag, activated steel slag, gypsum and water evenly to obtain solid waste slurry; (2) Add liquid sodium silicate to the solid waste slurry and stir for 15 s; (3) Then add cement, quicklime, foam stabilizer and water-reducing agent in sequence, and stir for 40 seconds; (4) Finally, add the foaming agent aluminum paste and stir for 30 seconds to obtain the pre-foamed slurry; (5) Pour the pre-foamed slurry into a steel mold, let it vent at 65°C and cure for 3.5 h, then cut and demold to obtain the blank; (6) The blank is sent into an autoclave for autoclaving, and the curing pressure is controlled at 1.2 MPa, the temperature at 192℃ and the curing time at 8 h. After natural cooling, autoclaved aerated concrete blocks are obtained.

[0041] Example 2 A high-volume solid waste-based autoclaved aerated concrete block comprises the following main materials by mass percentage: 50% activated iron sand, 10% blast furnace slag, 7% activated steel slag, 15% cement, 15% quicklime, and 3% gypsum. It also includes admixtures, the dosage of which is based on the total mass of the main materials, with the following mass percentages: 0.08% aluminum paste, 0.05% hydroxypropyl methylcellulose, 0.4% liquid sodium silicate, and 0.10% polyether-type polycarboxylate superplasticizer. The designed water-to-material mass ratio is 0.50.

[0042] The preparation method of activated iron sand is as follows: 1) Heat the subway sand to 750℃ at a rate of 10℃ / min and keep it at that temperature for 4 hours; 2) The calcined iron sand was ball-milled at a speed of 600 rpm for 25 minutes to obtain ball-milled iron sand with a particle size of less than 0.074 mm accounting for more than 80%. 3) After ball milling, the iron sand was placed in a 4 mol / L NaOH aqueous solution at a solid-liquid ratio of 1:6, stirred and soaked at a constant temperature of 70℃ for 4 hours, and then the insoluble matter was collected and dried to obtain activated iron sand.

[0043] The method for preparing activated steel slag is as follows: 1) Weigh a certain amount of steel slag, as well as quicklime and gypsum accounting for 5% of the mass of steel slag and 2% of the mass of gypsum, and add water accounting for 40% of the total mass of dry materials (steel slag, quicklime and gypsum). Mix thoroughly to obtain a mixed slurry. 2) The mixed slurry was sealed and aged at 25°C for 6 hours, and then dried at 105°C to constant weight to obtain activated steel slag.

[0044] In this embodiment, the high-volume solid waste-based autoclaved aerated concrete blocks are obtained through the following steps: (1) Activated subway sand, blast furnace slag, activated steel slag, gypsum and water are mixed and stirred evenly to obtain solid waste slurry; (2) Add liquid sodium silicate to the slurry and stir for 20 s; (3) Then add cement, quicklime, foam stabilizer and water-reducing agent in sequence, and stir for 35 seconds; (4) Finally, add the foaming agent aluminum paste and stir for 30 seconds to obtain the pre-foamed slurry; (5) Pour the pre-foamed slurry into a steel mold, let it vent at 65°C and cure for 4 hours. After molding, cut and demold to obtain the blank. (6) The blank is sent into an autoclave for autoclaving, and the curing pressure is controlled at 1.1 MPa, the temperature at 187℃ and the curing time at 8 h. After natural cooling, autoclaved aerated concrete blocks are obtained.

[0045] Example 3 A high-volume solid waste-based autoclaved aerated concrete block comprises the following main materials by mass percentage: 45% activated iron sand, 20% blast furnace slag, 10% activated steel slag, 10% cement, 12% quicklime, and 3% gypsum. It also includes admixtures, the dosage of which is based on the total mass of the main materials, with the following mass percentages: 0.12% aluminum paste, 0.04% hydroxypropyl methylcellulose, 0.5% liquid sodium silicate, and 0.15% polyether-type polycarboxylate superplasticizer. The designed water-to-material mass ratio is 0.53.

[0046] The preparation method of activated iron sand is as follows: 1) Heat the subway sand to 850℃ at a rate of 10℃ / min and keep it at that temperature for 2.5 h; 2) The calcined iron sand was ball-milled at a speed of 600 rpm for 25 minutes to obtain ball-milled iron sand with a particle size of less than 0.074 mm accounting for more than 80%. 3) After ball milling, the iron sand was placed in a 5 mol / L NaOH aqueous solution at a solid-liquid ratio of 1:6, stirred and soaked at a constant temperature of 60℃ for 3 hours, and then the insoluble matter was collected and dried to obtain activated iron sand.

[0047] The method for preparing activated steel slag is as follows: 1) Weigh a certain amount of steel slag, and 5% quicklime and 2% gypsum by mass of steel slag, and add water at 45% of the total mass of dry materials (steel slag, quicklime and gypsum) and mix thoroughly to obtain a mixed slurry. 2) The mixed slurry was sealed and aged at 25°C for 5 hours, and then dried at 105°C to constant weight to obtain activated steel slag.

[0048] In this embodiment, the autoclaved aerated concrete blocks with a high content of subway sand and iron and steel metallurgical waste slag are obtained through the following steps: (1) Mix the activated iron sand, blast furnace slag, activated steel slag, gypsum and water in the above fixed mass ratio until uniform to obtain solid waste slurry; (2) Add liquid sodium silicate to the slurry and stir for 25 s; (3) Then add cement, quicklime, foam stabilizer and water-reducing agent in sequence, and stir for 40 seconds; (4) Finally, add the foaming agent aluminum paste and stir for 40 seconds to obtain the pre-foamed slurry; (5) Pour the pre-foamed slurry into a steel mold, let it vent at 60°C and stand for 5 hours. After molding, cut and demold to obtain the blank. (6) The blank is sent into an autoclave for autoclaving, and the curing pressure is controlled at 1.5 MPa, the temperature at 203℃ and the curing time at 3 h. After natural cooling, autoclaved aerated concrete blocks are obtained.

[0049] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the activated subway sand was replaced with unactivated subway sand, which underwent simple crushing and screening, and the proportion of particles with a diameter of less than 0.074 mm was more than 80%.

[0050] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that calcination is not performed when preparing activated iron sand.

[0051] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that, in the preparation of activated iron sand, soaking in sodium hydroxide aqueous solution is not performed.

[0052] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that calcination was not performed during the preparation of activated iron sand, and liquid sodium silicate, hydroxypropyl methylcellulose, and polyether-type polycarboxylate superplasticizer were not added.

[0053] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that the steel slag was not activated.

[0054] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that the steel slag was not activated and no liquid sodium silicate, hydroxypropyl methylcellulose and polyether polycarboxylate superplasticizer were added.

[0055] Comparative Example 7 The only difference between Comparative Example 7 and Example 1 is that quicklime is not added during the activation of steel slag.

[0056] Comparative Example 8 The only difference between Comparative Example 8 and Example 1 is that no gypsum is added during the activation of the steel slag.

[0057] Table 1. Performance of autoclaved aerated concrete blocks prepared in each embodiment and comparative example.

[0058] As can be seen from Table 1, the dry density of the autoclaved aerated concrete blocks prepared in the examples is ≤650 kg / m³. 3 The compressive strength is ≥3.5MPa, meeting the A3.5 B06 grade standard of "Autoclaved Aerated Concrete Blocks" (GB / T 11968-2020). However, the autoclaved aerated concrete blocks prepared in the comparative example have higher dry density and lower strength than the example, and neither meets the A3.5 B06 grade standard of "Autoclaved Aerated Concrete Blocks" (GB / T 11968-2020).

[0059] In Comparative Example 1, because the subway sand was not activated, its low-activity components could not fully participate in the hydrothermal reaction to generate tobermorite-like hydration products, resulting in an increase in unreacted particles in the system, thus significantly reducing its strength. The impurities it contained also affected the gas generation rhythm of the aluminum paste, thus increasing its density.

[0060] In Comparative Example 2, because the subway sand did not undergo calcination and thermal activation treatment, it could not remove hydroxyl groups and transform into active components such as metakaolin, activated silica, and alumina. Instead, it existed in the system as a large number of inert, water-absorbing, and swellable harmful impurities, which hindered the formation of hydrated calcium silicate and high-strength tobermorite, thus reducing its strength.

[0061] In Comparative Example 3, the strength of the test block decreased because the subway sand was not subjected to alkaline soaking and activation treatment. This is because the OH- in the alkaline solution... - Ions attack the Si-O-Si and Si-O-Al chemical bonds on the surface of subway sand particles, causing them to break. Some silicate and aluminate ions are pre-dissociated, providing a large number of reactive sites for subsequent participation in the formation of tobermorite, thus promoting the formation of tobermorite. Without this step, subway sand particles mainly undergo slow surface dissolution during the autoclaving stage, resulting in insufficient active sites and a low nucleation density of tobermorite, which reduces the compressive strength of the blocks.

[0062] In Comparative Example 5, since the steel slag was not activated, the active components in the steel slag could not dissolve quickly during the hydrothermal process of rapid reaction between the activated iron tailings and blast furnace slag, thus reducing the degree of reaction and ultimately leading to a decrease in compressive strength.

[0063] Comparative Example 4 omitted the thermal activation of subway sand, and Comparative Example 6 omitted the activation of steel slag. Furthermore, neither comparative example added any of the three admixtures: alkali activator, foam stabilizer, and water-reducing agent. This resulted in a decrease in compressive strength and an increase in dry density, failing to meet the A3.5 B06 grade standard of "Autoclaved Aerated Concrete Blocks" (GB / T 11968-2020). Specifically, the absence of an alkali activator led to a reduction in soluble silica sources and an imbalance in the calcium-silicon ratio. The absence of a foam stabilizer reduced the water retention capacity of the slurry, decreased the plasticity of the slurry around air bubbles, and caused the generated air bubbles to easily merge into large pores, leading to the collapse of the block. The absence of a water-reducing agent increased the water requirement for the slurry to achieve the same fluidity. While the excess water increased the fluidity of the slurry, it also reduced the viscosity, making it easier for air bubbles to rise and escape. Additionally, the large amount of free water evaporated during hardening, leaving behind larger pores. Therefore, the absence of the three admixtures not only leads to uneven air bubbles in the green body and mold collapse, resulting in an increase in the dry density of the blocks, but is also one of the reasons for the decrease in the compressive strength of the blocks.

[0064] Comparative Example 7 lacked the large amount of OH- produced by the hydrolysis of quicklime because quicklime was not added during the activation of the steel slag. - Ions rapidly increase the alkalinity of the medium, disrupting the network lattice structure on the surface of steel slag particles, allowing a large amount of Ca to escape. 2+ AlO2 - and SiO4 4- The components dissolve into the system, thus failing to effectively activate the low-activity components in the steel slag, leading to a decrease in the strength of the blocks.

[0065] Comparative Example 8, due to the lack of gypsum added during the activation of steel slag, resulted in a decrease in the compressive strength of the blocks and a slight increase in their dry density. It failed to meet the A3.5 B06 grade standard of "Autoclaved Aerated Concrete Blocks" (GB / T 11968-2020). This was because SO4 dissolved from the gypsum... 2- It will react with the Ca dissolved from the steel slag by lime. 2+ and AlO2 - The reaction generates an ettringite system, which provides a network skeleton structure for the early green body and is also conducive to improving the hydration reaction rate of steel slag during the pre-curing and steam curing stages. However, if gypsum is not added during the activation of steel slag, the steel slag is difficult to dissolve continuously. At the same time, without the generated ettringite skeleton, it is difficult to support the porous structure formed by the gas generation of aluminum powder, which ultimately leads to a decrease in the compressive strength and an increase in the dry density of the blocks.

[0066] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A high-volume solid waste-based autoclaved aerated concrete block, characterized in that, The main ingredients include the following components by mass percentage: 40%~50% activated iron sand, 10%~30% blast furnace slag, 3%~10% activated steel slag, 5%~15% cement, 5%~15% quicklime, and 1.5%~3% gypsum; it also includes admixtures, the dosage of each admixture is based on the total mass of the main ingredients, and the mass percentages are as follows: foaming agent 0.05%~0.15%, foam stabilizer 0.03%~0.05%, alkali activator 0.25%~0.75%, and water-reducing agent 0.10%~0.20%; the activated iron sand is obtained by sequentially subjecting iron sand to thermal activation treatment, mechanical ball milling treatment, and chemical soaking treatment; the activated steel slag is obtained by aging and drying a mixed slurry made of steel slag, quicklime, gypsum, and water.

2. The high-volume solid waste-based autoclaved aerated concrete block according to claim 1, characterized in that, The temperature of the thermal activation treatment is 750~900℃, and the holding time is 2~4h; the ball milling speed of the mechanical ball milling treatment is 500~600 rpm, and the ball milling time is 20~30min; the chemical soaking treatment is to soak the mechanically ball-milled iron sand in NaOH solution, and then collect the insoluble matter and dry it to obtain activated iron sand.

3. The autoclaved aerated concrete block with high solid waste admixture content according to claim 2, characterized in that, The heating rate during the thermal activation treatment is controlled at 5~15℃ / min; in the iron sand after mechanical ball milling, the proportion of particles with a diameter less than 0.074mm is more than 80%; the solid-liquid ratio of the chemical soaking treatment is 1:4~1:6, the concentration of NaOH solution is 1~5mol / L, the soaking temperature is 60~80℃, and the soaking time is 1~4h.

4. The autoclaved aerated concrete block with high solid waste content according to claim 1, characterized in that, The steel slag has a SiO2 content of 10wt%~20wt%, a CaO content of 40wt%~55wt%, an Al2O3 content of 1wt%~5wt%, and a particle size of less than 0.074mm accounts for more than 80% of the total. The amount of quicklime used is 3%~5% of the mass of the steel slag, the amount of gypsum used is 1%~2% of the mass of the steel slag, and the amount of water used is 35%~45% of the total mass of the steel slag, quicklime, and gypsum. The aging temperature is 25~30℃, and the aging time is 4~6h.

5. The autoclaved aerated concrete block with high solid waste content according to claim 1, characterized in that, The subway sand has a SiO2 content of 55wt%~65wt%, a CaO content of 1wt%~8wt%, an Al2O3 content of 14wt%~20wt%, and a particle size of 0.1~0.5mm; the blast furnace slag has a SiO2 content of 30wt%~40wt%, a CaO content of 35wt%~45wt%, an Al2O3 content of 15wt%~20wt%, and a particle size of less than 0.074mm accounts for more than 80%.

6. The autoclaved aerated concrete block with high solid waste content according to claim 1, characterized in that, The foaming agent is aluminum paste, the solid content of which is 65% to 75%, the mass fraction of active aluminum in the solid component is greater than 85%, and the particle size of the solid component is 0.015 to 0.035 mm; the alkali activator is liquid sodium silicate, the modulus of which is 2.6 to 2.9, and the mass fraction of sodium silicate is 34% to 36%.

7. The high-volume solid waste-based autoclaved aerated concrete block according to claim 1, characterized in that, The cement is one of P·O 52.5 cement and P·O 42.5 cement; the effective calcium oxide content in the quicklime is >70%; the mass fraction of calcium sulfate dihydrate in the gypsum is above 85%; the foam stabilizer is hydroxypropyl methylcellulose; and the water-reducing agent is a polyether-type polycarboxylate water-reducing agent.

8. The high-volume solid waste-based autoclaved aerated concrete block according to claim 1, characterized in that, The autoclaved aerated concrete (AAC) blocks are prepared with a water-to-material ratio of 0.45 to 0.55; the dry density of the AAC blocks is ≤650 kg / m³. 3 Compressive strength ≥ 3.5 MPa.

9. A method for preparing high-volume solid waste-based autoclaved aerated concrete blocks as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Mix and stir activated subway sand, blast furnace slag, activated steel slag, gypsum and water evenly to obtain solid waste slurry; S2. Add alkali activator to solid waste slurry and stir for 15-30 seconds. Then add cement, quicklime, water-reducing agent and foam stabilizer and stir for 30-40 seconds. Finally, add foaming agent and stir for 20-40 seconds to obtain mixed slurry. S3. Pour the mixed slurry into the mold, and after hot static gas curing, cut and demold to obtain the green body; S4. The green body is subjected to autoclaving to obtain autoclaved aerated concrete blocks.

10. The method for preparing high-volume solid waste-based autoclaved aerated concrete blocks according to claim 9, characterized in that, The temperature for the hot static gas curing is 55~65℃, and the time is 3~6 h; the curing pressure for the autoclaving is 1.1~1.5 MPa, the curing temperature is 187~203℃, and the curing time is 6~10 h.

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