Inorganic cementitious material, foamed concrete and method for producing the same

Abstract

The application discloses an inorganic cementing material, which comprises the following components in percentage by mass: calcined coal gangue 40-50%, silicate cement clinker 40-45%, gypsum 5-10%, and aluminum sulfate salt 1-5%. In the cementing material, the content of the coal gangue powder can reach 50% at most, and meanwhile, the 3d strength can be ensured to be not lower than 25MPa. The cementing material can greatly increase the use amount of the coal gangue powder, effectively consume the coal gangue powder, make the prepared cementing material have higher early strength, and meet the requirements of fast hardening and early strength of the foam concrete.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to an inorganic cementitious material, foamed concrete, and its preparation method. Background Technology

[0002] Foamed concrete is widely used in construction projects due to its excellent thermal insulation, lightweight shock resistance, fire resistance, and waterproof properties. Currently, foamed concrete is mainly prepared using ordinary Portland cement or aluminum sulfate cement. However, on the one hand, due to its long setting time, low early strength, and large drying shrinkage, ordinary Portland cement often suffers from poor foam stability, long curing periods, and easy cracking when producing foamed concrete. On the other hand, silicate clinker is the main component of ordinary Portland cement, generally accounting for more than 80% of the total amount. During the firing process, the high firing temperature (above 1450℃) leads to a sharp increase in coal consumption, CO2, and nitrogen oxide emissions. Therefore, the use of ordinary Portland cement to prepare foamed concrete faces considerable constraints in terms of technology, economic cost, and environmental impact.

[0003] Due to its rich aluminum content, high pozzolanic activity index, and certain calorific value, calcined coal gangue is often used as an active mineral admixture in conjunction with ordinary silicate cement to prepare rapid-hardening, early-strength cementitious materials. Existing technologies have conducted extensive research on the activation of coal gangue activity and the hydration mechanism and mechanical properties of cementitious materials after incorporating activated coal gangue. For example, studies have found that after mechanical activation, the microstructure of coal gangue gradually becomes looser and more porous, and the particle size becomes more regular, with a specific surface area reaching 438.28 m² / kg, meeting the fineness requirements for cement in GB / T 175-2007. The larger specific surface area of ​​mechanically activated coal gangue allows for sufficient contact with the solution, improving reaction efficiency, and it can be used as a mineral admixture in cement. However, when the amount of mechanically activated coal gangue reaches 30% of the total cementitious material, the compressive strength of the prepared cementitious material at all ages is low, far lower than that of rapid-hardening aluminum sulfate cement at the corresponding ages. Other studies have found that when coal gangue is calcined at 650℃ for 2 hours and then added to cement in a certain proportion to prepare mortar blocks, the compressive strength of the cement mortar blocks decreases by 9.76%-14.9% when the coal gangue content is 20%, and by 4.7%-8.3% when the calcined coal gangue content is 10%. Further research, through mechanical strength testing of cement mortar, investigated the effects of coal gangue fineness and calcination temperature on its pozzolanic activity. The results showed a positive correlation between the pozzolanic activity and fineness of coal gangue, with the optimal calcination temperature being 800℃. After calcination, kaolinite in the coal gangue transforms into metakaolinite. When ordinary Portland cement is replaced by coal gangue at a ratio of 10%, the compressive and flexural strength of the prepared cementitious material can be improved. However, the amount of coal gangue used in these existing technologies is relatively low, which is not conducive to the consumption and treatment of large quantities of coal gangue. Existing technologies that treat coal gangue using high-temperature activation technology have found that kaolinite in the coal gangue loses its hydroxyl groups during calcination to form metakaolinite. After replacing part of the cement with thermally activated coal gangue, it was found that the early strength of the prepared cementitious material decreased significantly with the increase in the replacement rate of coal gangue during calcination. This is mainly due to the lower degree of early hydration reaction participation of calcined coal gangue. To study the feasibility of preparing low-carbon cement using thermally activated coal gangue, cement was prepared using a 20% admixture. The results showed that a 20% admixture could produce a cementitious material with mechanical properties comparable to ordinary Portland cement. However, the addition of coal gangue increases the water demand of the entire system.

[0004] Therefore, these studies still have problems. When using calcined coal gangue powder to prepare inorganic cementitious materials, the amount of calcined coal gangue is less than 20%. Furthermore, as the amount of calcined coal gangue powder increases, the early mechanical properties of the prepared cementitious materials will decrease significantly, which is not conducive to the application and promotion of coal gangue. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide an inorganic cementitious material, foamed concrete and its preparation method, so as to solve the problems of long setting time, low early strength, large drying shrinkage of foamed concrete, high firing temperature of silicate clinker used, and sharp increase in energy consumption and emissions in the existing technology; at the same time, the amount of calcined coal gangue added during the preparation of inorganic cementitious materials is small, and the increase of the amount of coal gangue will lead to a significant decrease in the early mechanical properties of the cementitious material, which is not conducive to the application and promotion of coal gangue.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] An inorganic cementitious material, calculated by mass percentage, comprises the following components:

[0008] Calcined coal gangue accounts for 40%~50%, silicate cement clinker accounts for 40%~45%, gypsum accounts for 5%~10%, and aluminum sulfate accounts for 1%~5%.

[0009] Preferably, the calcined coal gangue is obtained by the following method:

[0010] After crushing the coal gangue, it is calcined at 960℃~1050℃ for 10~20 minutes and then cooled to obtain the calcined coal gangue.

[0011] Preferably, the heating rate is 6~10℃ / min.

[0012] Preferably, the gypsum is anhydrous calcium sulfate, and the mass fraction of anhydrous calcium sulfate in the gypsum is 98% or more, calculated by mass percentage.

[0013] Preferably, the aluminum sulfate includes one or more of anhydrous Al2(SO4)3, KAl(SO4)2·12H2O, and NaAl(SO4)2. The aluminum sulfate is a white powder of one or more of anhydrous Al2(SO4)3, KAl(SO4)2·12H2O, and NaAl(SO4)2, and is a powder with a fineness of 200 mesh, which dissolves rapidly in water.

[0014] This invention provides a method for preparing an inorganic cementitious material. The specific steps for preparing the above-mentioned inorganic cementitious material are as follows:

[0015] Step 1: Mix calcined coal gangue, silicate cement clinker, gypsum, and aluminum sulfate evenly to obtain a mixture; wherein, calculated by mass percentage, the amount of calcined coal gangue is 40%~50%, the amount of silicate cement clinker is 40%~45%, the amount of gypsum is 5%~10%, and the amount of aluminum sulfate is 1%~5%;

[0016] Step 2: Ball mill the mixture obtained in Step 1, and then sieve it after ball milling to ensure that the specific surface area of ​​the obtained material is not less than 500 m². 2 / kg, to obtain the inorganic cementitious material.

[0017] The present invention provides a foamed concrete, which includes the above-mentioned inorganic cementitious material, foaming agent and water; wherein the foaming agent is a sulfonate foaming agent and the mass ratio of foaming agent to water is 1:(15~30).

[0018] Preferably, the foamed concrete is prepared by the following method:

[0019] (1) Mix water and foaming agent to make foaming slurry, and inject the foaming slurry into the foaming machine to make foam for later use; wherein, the mass ratio of foaming agent to water is 1: (15~30).

[0020] (2) Using the above-mentioned inorganic cementitious material or the inorganic cementitious material prepared by the above-mentioned preparation method as raw material, then mixing it with water, and controlling the water-to-material ratio to be 0.5~0.6, a mixed material slurry is obtained;

[0021] (3) Mix the foam prepared in step (1) with the slurry prepared in step (2) to obtain the foamed concrete.

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

[0023] 1. The cementitious material described in this invention significantly increases the amount of calcined coal gangue used, mainly because calcined coal gangue powder itself is a silica-alumina material. When a large amount of calcined coal gangue cementitious material reacts with water, it can dissolve more Al than in ordinary silicate cement systems. 3+ At this point, further supplementation with aluminum sulfate can further increase the Al content. 3+ The content of Al: On the one hand, with Al 3+ As the concentration increases, aluminum sulfate reacts with calcium hydroxide formed during the hydration of cement clinker to form polyaluminum sulfate. Due to the further increase in the molecular weight of polyaluminum sulfate, its charge also increases. When adsorbed onto the surface of cement particles, it neutralizes the charge on the surface of the cement clinker particles, reducing the zeta potential of the electric double layer on the cement particle surface. This rapidly reduces the repulsive force between cement clinker particles, leading to the rapid aggregation of silicate cement clinker particles and hydrated calcium silicate gel particles formed during hydration. On the other hand, in the highly alkaline environment formed during the hydration of cement clinker, aluminum sulfate salts undergo hydrolysis to form colloidal precipitates of aluminum hydroxide, which can rapidly adsorb free water in the slurry, thereby reducing the fluidity and increasing the viscosity of the slurry system. Ultimately, these two factors result in the cementitious material of this invention exhibiting rapid hardening and early strength characteristics on a macroscopic scale.

[0024] 2. This invention prepares a foamed concrete using the aforementioned cementitious material as the main raw material. The amount of calcined coal gangue powder in the prepared foamed concrete can reach 50%, while the amount of cement clinker can be reduced to 40%. Due to the large-scale application of calcined coal gangue and the significant reduction in the amount of silicate cement clinker in the cementitious material prepared by this invention, the alkalinity (pH) of the prepared cementitious material can be reduced to 10.5. The reduction in alkalinity can effectively reduce the erosion of fibers in the foamed concrete by the cementitious material.

[0025] 3. This invention uses water-soluble aluminum sulfate as a modifier, which enables the prepared cementitious material to have a faster setting time, shortening the initial setting time and final setting time to 8-25 min and 20-50 min, respectively. This not only increases the amount of calcined coal gangue but also shortens the setting time, resulting in significant rapid hardening characteristics. At the same time, the prepared cementitious material has high early strength, with a 3-day strength of over 25 MPa, showing a significant early strength effect compared to ordinary Portland cement. Attached Figure Description

[0026] Figure 1 The graph shows the changes in compressive strength of Examples 4-8 and Comparative Example 1. Detailed Implementation

[0027] This invention will be described clearly and completely with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on this invention are within the scope of protection of this invention.

[0028] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0029] I. An inorganic cementing material

[0030] This invention, after in-depth research on foamed concrete, found that ordinary Portland cement and aluminum sulfate cement are currently widely used cementing materials in foamed concrete production. However, considering the following drawbacks: First, ordinary Portland cement suffers from high energy consumption, resource consumption, large carbon emissions, and severe environmental pollution during production. Second, because aluminum sulfate cement is made by high-temperature calcination of high-quality bauxite and natural gypsum, the concentrated distribution of raw materials leads to highly concentrated production areas, increasing transportation costs and severely limiting its application. Furthermore, the tendency for aluminum sulfate cement to experience strength reduction in the later stages poses a significant challenge to the production of foamed concrete products. Third, while calcined coal gangue is widely used in the production of cementitious materials, this invention further reveals that using coal gangue in the preparation of cementitious materials results in problems such as low admixture dosage and low early strength. In particular, when the admixture dosage of calcined coal gangue exceeds 20%, the reduction in early strength becomes more pronounced. Therefore, this invention attempts to increase the admixture dosage of calcined coal gangue, but it is necessary to address the problem of reduced early strength caused by increasing the admixture dosage. Fourth, the present invention also found that, due to the excessive amount of ordinary silicate cement in the cementitious materials of foamed concrete prepared by the prior art, the alkalinity often reaches 12 to 13 during the hydration process. Under such high alkalinity conditions, the erosion of crack-resistant fibers in foamed concrete will be aggravated. Therefore, in addition to solving the above-mentioned technical problems, the present invention also needs to solve this technical problem.

[0031] This invention adjusts the calcination temperature of coal gangue, raising it to the range of 960-1050℃. At this temperature, the kaolinite in the calcined coal gangue undergoes dehydration and dehydroxylation reactions, resulting in changes in its crystal phase and structural disruption, thereby enhancing the activity of the calcined coal gangue. Unexpectedly, while increasing the amount of calcined coal gangue and reducing the amount of cement clinker, this invention discovered that adding an appropriate amount of aluminum sulfate could solve the aforementioned technical problems. Further investigation into the effects of adding aluminum sulfate under the premise of high-volume calcined coal gangue and low cement clinker content revealed that, because calcined coal gangue powder itself is a silica-alumina material, when the cementitious material prepared from high-volume calcined coal gangue reacts with water, it can dissolve more Al than in ordinary silicate cement systems. 3+ At this point, further supplementation of aluminum sulfate can further increase the Al content in the system. 3+ The content of Al. On the one hand, with Al 3+As the concentration increases, aluminum sulfate reacts with calcium hydroxide formed during the hydration of cement clinker to generate polyaluminum sulfate. Due to the further increase in the molecular weight of polyaluminum sulfate, its charge also increases. When adsorbed onto the surface of cement particles, it neutralizes the charge on the surface of the cement clinker particles, reducing the zeta potential of the double layer on the cement particle surface. This rapidly reduces the repulsive force between cement clinker particles, allowing the silicate cement clinker particles and the hydrated calcium silicate gel particles formed during hydration to quickly aggregate. This significantly shortens the initial and final setting times of the cementitious material described in this invention. It is precisely because of this significant reduction in initial and final setting times that foamed concrete prepared using the inorganic cementitious material of this invention can also significantly shorten the high-temperature curing time and improve mold turnover efficiency and productivity. On the other hand, in the highly alkaline environment formed during the hydration of cement clinker, aluminum sulfate can undergo a hydrolysis reaction to form a colloidal precipitate of aluminum hydroxide, which can quickly adsorb free water in the slurry, thereby reducing the fluidity and increasing the viscosity of the slurry system. Both of these factors contribute to the rapid hardening and early strength characteristics of the inorganic cementitious material described in this invention. Moreover, since the amount of high-energy-consuming cement clinker used in this invention is further reduced, the coal consumption, CO2 and nitrogen oxide emissions of the inorganic cementitious material described in this invention can be significantly reduced, thereby reducing production costs. At the same time, the significant reduction in the amount of silicate cement clinker can lower the pH value of the foamed concrete prepared therefrom to 10.5, which can effectively reduce the erosion of crack-resistant fibers in the foamed concrete.

[0032] The inorganic cementitious material of the present invention comprises the following components by weight percentage:

[0033] Calcined coal gangue accounts for 40%~50%, silicate cement clinker accounts for 40%~45%, gypsum accounts for 5%~10%, and aluminum sulfate accounts for 1%~5%.

[0034] In some embodiments, the amount of calcined coal gangue used is 40% to 50% by mass percentage. Too low a content of calcined coal gangue will lead to the leaching of Al in the system. 3+ Si 4+ Decreasing the concentration leads to an increase in the amount of soluble aluminum sulfate or a decrease in the setting rate of the gel material, which in turn increases the amount of cement clinker used in the gel material, increasing the resource and environmental burden and raising costs; while excessive dosage will lead to an increase in Si in the system. 4+ Al 3+Excessive concentration can lead to excessively rapid setting, making construction impossible. Furthermore, excessive dosage may result in insufficient reaction, causing a decrease in early strength and negatively impacting later strength development. Therefore, the dosage of calcined coal gangue can be 40%, 45%, 50%, or any range and sub-range between these values. Silicate cement clinker is obtained by high-temperature calcination of silicate cement (calcination temperature 1400~1500℃). The silicate cement mainly consists of C3S, C2S, and a small amount of fluxing minerals, and its properties meet the technical requirements of GB / T21372-2024 Silicate Cement Clinker. This invention appropriately controls the amount of silicate cement clinker used. Too little silicate cement clinker leads to insufficient clinker particles and reduced early strength; while too much results in excessively alkaline clinker hydration, severely eroding the glass fibers in foamed concrete. It also increases energy and resource consumption, carbon emissions, and production costs. Therefore, the amount of silicate cement clinker can be 41%, 42%, 43%, 44%, 45%, etc., and all ranges and subranges between these values. The gypsum is anhydrous calcium sulfate, with a mass fraction of anhydrous calcium sulfate exceeding 98%. Excessive gypsum leads to flash setting and poor volume stability in the prepared cementitious material, while too little leads to a retarding effect and reduced strength. Therefore, the amount of gypsum can be 5%, 6%, 7%, 8%, 9%, 10%, etc., and all ranges and subranges between these values. The aluminum sulfate salt includes one or more of anhydrous Al2(SO4)3, KAl(SO4)2·12H2O, and NaAl(SO4)2. Other types of aluminum sulfate salts have low solubility, preventing them from rapidly dissolving the Al required for the reaction system. 3+ Therefore, it fails to promote coagulation and improve early strength. Thus, one or more of anhydrous Al2(SO4)3, KAl(SO4)2·12H2O, and NaAl(SO4)2 are selected. The aluminum sulfate is a powder with a fineness of 200 mesh, which dissolves rapidly in water. Insufficient aluminum sulfate dosage will lead to the leaching of soluble Al in the gelation system. 3+ If the concentration is too low, it will not promote setting and improve early strength, while if the dosage is too high, it will cause "flash setting" of the cementitious material, resulting in reduced fluidity and decreased workability. Therefore, the dosage of aluminum sulfate can be 1%, 2%, 3%, 4%, 5%, etc., as well as all ranges and sub-ranges between these values. It should be understood that in the implementation plan, any of the above ranges can be combined with any other range, as long as the dosage of each component after combination is 100%.

[0035] In some embodiments, the calcined coal gangue is obtained by the following method:

[0036] After crushing coal gangue, it is calcined at 960℃~1050℃ for 10~20 minutes and then cooled to obtain calcined coal gangue. The heating rate is 6~10℃ / min. The original lumpy coal gangue is crushed into particles with a diameter of less than 6mm using a crusher. An appropriate amount of the crushed coal gangue powder is placed in a ceramic crucible and then placed in a box-type resistance furnace. The temperature is raised to 960~1050℃ at a heating rate of 6~10℃ / min and then calcined at a constant temperature for 10~20 minutes. After removal, it is rapidly cooled using a blower to increase the cooling rate, thus obtaining calcined coal gangue. High-temperature calcination causes dehydration and dehydroxylation reactions in the kaolinite in the coal gangue, resulting in changes in the crystal phase, structural destruction, and enhanced activity. If the calcination temperature is too low, the amount of kaolinite in the coal gangue will be insufficient, resulting in insufficient activity of the coal gangue after calcination and failing to achieve the technical effect described in this invention. Conversely, if the calcination temperature is too high, a sintering reaction will occur between the silicon and aluminum components in the coal gangue, leading to the formation of a large amount of low-activity mullite crystals. Therefore, the calcination temperature of coal gangue can be 960℃, 980℃, 1000℃, 1030℃, 1050℃, etc., as well as all ranges and sub-ranges between these values. If the calcination time is too short, the degree of activation of the coal gangue will be insufficient. If the calcination time is too long, a sintering reaction will occur between the silicon and aluminum components in the coal gangue, leading to the formation of a large amount of low-activity mullite crystals; this will also increase the energy consumption of calcination. Therefore, the calcination time of coal gangue can be 10 min, 15 min, 20 min, etc., as well as all ranges and sub-ranges between these values.

[0037] II. A method for preparing an inorganic cementitious material

[0038] Step 1: Mix calcined coal gangue, silicate cement clinker, gypsum, and aluminum sulfate evenly to obtain a mixture. The mass percentages are as follows: calcined coal gangue 40%–50%, silicate cement clinker 40%–45%, gypsum 5%–10%, and aluminum sulfate 1%–5%. A composite mixer is used for mixing. This mixer combines mechanical stirring and pneumatic homogenization. After the mixed materials are fed into the mixer, air is introduced through the porous filter cloth at the bottom of the mixer to fluidize the materials, thus achieving homogenization. Simultaneously, a multi-stage blade agitator is installed inside the mixer to further stir and activate the fluidized materials, reducing stratification caused by differences in material density.

[0039] Step 2: Ball mill the mixture obtained in Step 1 for 25-60 minutes. After ball milling, sieve the mixture to ensure that the specific surface area of ​​the obtained material is not less than 500 m². 2 / kg, to obtain the inorganic cementitious material.

[0040] The inorganic cementitious material of the present invention can be tested according to the fixed method in the "Specifications for Standard Consistency Water Requirement, Setting Time and Soundness Test Methods for Cement" (GB / T1346-2001) to obtain the standard consistency water requirement of the cementitious material prepared by the present invention.

[0041] III. A type of foamed concrete

[0042] The foamed concrete comprises the aforementioned inorganic cementitious material, foaming agent, and water; wherein the foaming agent is a sulfonate foaming agent, and the mass ratio of the foaming agent to water is 1:(15~30).

[0043] The foamed concrete is prepared by the following method:

[0044] (1) Mix water and foaming agent to make foaming slurry, and inject the foaming slurry into the foaming machine to make foam for later use; wherein, the mass ratio of foaming agent to water is 1: (15~30).

[0045] (2) Using the above-mentioned inorganic cementitious material or the inorganic cementitious material prepared by the above-mentioned preparation method as raw material, then mixing it with water, and controlling the water-to-material ratio to be 0.5~0.6, a mixed material slurry is obtained;

[0046] (3) Mix the foam prepared in step (1) with the slurry prepared in step (2) to obtain the foamed concrete.

[0047] IV. Examples and Comparative Examples

[0048] Example 1

[0049] The coal gangue was crushed into particles with a diameter of less than 6 mm, then heated to 1000℃ and calcined for 15 minutes before being taken out and cooled for later use.

[0050] Step 1: Mix calcined coal gangue, silicate cement clinker, gypsum, and aluminum sulfate evenly to obtain a mixture; wherein, calculated by mass percentage, the amount of calcined coal gangue is 40%, the amount of silicate cement clinker is 45%, the amount of gypsum is 10%, and the amount of aluminum sulfate is 5%.

[0051] Step 2: Ball mill the mixture obtained in Step 1, and then sieve it after ball milling to ensure that the specific surface area of ​​the obtained material is not less than 500 m². 2 / kg, to obtain the inorganic cementitious material.

[0052] Example 2

[0053] The method is based on Example 1, but with the following adjustment: the amount of calcined coal gangue is 50%, the amount of silicate cement clinker is 40%, the amount of gypsum is 5%, and the amount of aluminum sulfate is 5% by mass percentage.

[0054] Example 3

[0055] The method is based on Example 1, but with the following adjustment: the amount of calcined coal gangue is 45%, the amount of silicate cement clinker is 43%, the amount of gypsum is 8%, and the amount of aluminum sulfate is 4% by mass percentage.

[0056] The inorganic gel materials prepared in Examples 1-3 were tested for their standard consistency water requirement according to the fixed method in "Specifications for Testing Standard Consistency Water Requirement, Setting Time and Soundness of Cement" (GB / T1346-2001). Based on this, the setting time and soundness of the cementitious materials were also tested. The test results showed that the initial setting time of the inorganic cementitious materials prepared in Examples 1-3 was 8-25 min, and the final setting time was 20-50 min. It is evident that the cementitious material of this invention shortens the setting time while achieving a large amount of calcined coal gangue. Simultaneously, strength tests were conducted according to the method specified in "Test Method for Strength of Cement Mortar (ISO)" (GB / T 17671-2021). The test results showed that the 3-day compressive strength of the prepared cementitious material was 25-27 MPa, exhibiting significant rapid hardening characteristics and early strength effect compared to ordinary Portland cement.

[0057] This invention further investigated the effects of different amounts of aluminum sulfate on the setting time and strength of the inorganic cementitious material. The amounts of other components of the inorganic cementitious material were kept constant, and only the amount of aluminum sulfate was varied. The water-cement ratio was 0.5 in all groups during the experiment. The specific amounts of each component are shown in Table 1. The preparation method was exactly the same as in Example 1. Based on this, the amount of aluminum sulfate was adjusted.

[0058] Table 1 (Unit: copies)

[0059]

[0060] The inorganic gel materials prepared in Examples 4-8 and the comparative example were tested for their standard consistency water requirement according to the fixed method in "Specifications for Test Methods of Standard Consistency Water Requirement, Setting Time and Soundness of Cement" (GB / T1346-2001). Based on this, the setting time and soundness of the gel materials were tested. The test results are shown in Table 2.

[0061] Table 2

[0062]

[0063] Simultaneously, strength tests were conducted on Examples 4-8 and the comparative example according to the methods specified in the "Test Method for Strength of Cement Mortar (ISO)" (GB / T 17671-2021). The test results are as follows: Figure 1 As shown.

[0064] From Table 2 and Figure 1 Combining these observations, we can see that:

[0065] (1) With the increase of aluminum sulfate dosage, the initial setting time and final setting time of the inorganic cementitious material are significantly shortened. However, excessive dosage will lead to a short setting time, i.e. flash setting, which will make construction impossible. Therefore, in actual construction, the dosage of aluminum sulfate can be adjusted according to the construction needs so that the inorganic cementitious material can meet different construction requirements.

[0066] (2) With the increase of aluminum sulfate dosage, the compressive strength of the inorganic cementitious material was significantly improved. Whether in the early, middle or late stage, its compressive strength was significantly improved, especially the early strength was the most significant. This also proves that the inorganic cementitious material of the present invention has excellent early fast hardening properties. However, due to the excessively fast setting speed of Comparative Example 2, even if its strength is good enough, the cementitious material quickly solidifies after water is added, and it is even impossible to pour it into the mold.

[0067] Example 9

[0068] (1) Mix water and foaming agent to make foaming slurry, and inject the foaming slurry into a foaming machine to make foam for later use; wherein the mass ratio of foaming agent to water is 1:15;

[0069] (2) The inorganic cementitious material prepared in Example 1 was used as raw material, and then mixed with water, and the water-to-material ratio was controlled to be 0.5 to obtain a mixed material slurry;

[0070] (3) Mix the foam prepared in step (1) with the slurry prepared in step (2) to obtain the foamed concrete. Use a 5 L iron bucket as a container, pour the above-mixed slurry and air bubbles into the mixing bucket at the same time, and adjust the amount of foam and slurry to obtain three foamed concrete slurries with dry bulk densities of 800 kg / m³, 900 kg / m³ and 1000 kg / m³ respectively. Pour the mixed foamed concrete slurries with different proportions into the mold (a triple mold of 70.7 mm × 70.7 mm × 70.7 mm), vibrate and scrape it flat, and after the surface has slightly solidified, cover it with plastic wrap to keep it moist and carry out curing in the mold. The curing method is to fill the foamed concrete into the mold, vibrate and level it, place it in a constant temperature curing chamber at 30~60℃ for 6~8 hours, then place it in a standard curing chamber for 24 hours before demolding. After demolding, continue to place it in the standard curing chamber for curing until the specified age, and then take it out and conduct compressive strength testing according to the method specified in "Foamed Concrete" (JG / T266-2011).

[0071] Test results show that the 3-day compressive strengths of the prepared foamed concrete with dry bulk densities of 800 kg / m³, 900 kg / m³, and 1000 kg / m³ are 3.5 MPa, 5.6 MPa, and 7.4 MPa, respectively; the 7-day compressive strengths are 5.4 MPa, 7.3 MPa, and 9.8 MPa, respectively; and the 28-day compressive strengths are 8.6 MPa, 10.1 MPa, and 13.2 MPa, respectively. The prepared concrete meets the strength requirements of the corresponding strength grades of foamed concrete in "Foamed Concrete JG / T266-2011".

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. An inorganic cementitious material, characterized in that, The inorganic cementitious material is composed of the following components, calculated by weight percentage: The amount of calcined coal gangue is 40%~50%, the amount of silicate cement clinker is 40%~45%, the amount of gypsum is 5%~10%, and the amount of aluminum sulfate is 1%~5%. The calcined coal gangue is obtained by the following method: The coal gangue is crushed into particles with a diameter of less than 6 mm, and the temperature is raised to 960-1050℃ at a heating rate of 6-10℃ / min. After being kept at a constant temperature for 10-20 min, it is taken out and rapidly cooled by air cooling to obtain calcined coal gangue. The specific surface area of ​​the inorganic cementitious material is not less than 500 m². 2 / kg.

2. The inorganic cementitious material according to claim 1, characterized in that, The gypsum is anhydrous calcium sulfate, and the mass fraction of anhydrous calcium sulfate in the gypsum is more than 98% by mass percentage.

3. The inorganic cementitious material according to claim 1, characterized in that, The aluminum sulfate salt includes one or more of anhydrous Al2(SO4)3, KAl(SO4)2·12H2O, and NaAl(SO4)2.

4. A method for preparing an inorganic cementitious material, characterized in that, The specific steps for preparing the inorganic cementitious material according to any one of claims 1 to 3 are as follows: Step 1: Mix calcined coal gangue, silicate cement clinker, gypsum, and aluminum sulfate evenly to obtain a mixture; wherein, calculated by mass percentage, the amount of calcined coal gangue is 40%~50%, the amount of silicate cement clinker is 40%~45%, the amount of gypsum is 5%~10%, and the amount of aluminum sulfate is 1%~5%; Step 2: Ball mill the mixture obtained in Step 1, and then sieve it after ball milling to ensure that the specific surface area of ​​the obtained material is not less than 500 m². 2 / kg, to obtain the inorganic cementitious material.

5. A type of foamed concrete, characterized in that, The foamed concrete includes the inorganic cementitious material according to any one of claims 1 to 3 or the inorganic cementitious material prepared by the preparation method according to claim 4, and further includes a foaming agent and water; wherein the foaming agent is a sulfonate foaming agent, and the mass ratio of the foaming agent to water is 1:(15~30).

6. The foamed concrete according to claim 5, characterized in that, The foamed concrete is prepared by the following method: (1) Mix water and foaming agent to make foaming slurry, and inject the foaming slurry into the foaming machine to make foam for later use; wherein, the mass ratio of foaming agent to water is 1: (15~30). (2) Using the inorganic cementitious material described in any one of claims 1 to 3 or the inorganic cementitious material prepared by the preparation method described in claim 4 as raw material, then mixing it with water, and controlling the water-to-material ratio to be 0.5 to 0.6 to obtain a mixed material slurry; (3) Mix the foam prepared in step (1) with the slurry prepared in step (2) to obtain the foamed concrete.

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