A kind of phosphogypsum-based cementitious material and preparation method thereof

Abstract

The present invention provides a phosphogypsum-based cementitious material and a preparation method thereof. The phosphogypsum-based cementitious material comprises a mixed powder and an admixture, wherein the mixed powder comprises, by mass percentage, 40% to 50% of phosphogypsum, 44% to 52% of solid waste residue, and 6% to 8% of an alkaline activator, which totals 100%; the admixture is a mixture of sodium aluminate, lithium carbonate, and a layered bimetallic composite oxide, and the admixture is 1.03% to 4.05% of the mass of the mixed powder. The phosphogypsum-based cementitious material of the present invention can solve the existing technical problems of long setting time and low early strength.

Description

Technical Field

[0001] The invention belongs to the technical field of new building materials, and particularly relates to a phosphogypsum-based cementitious material and a preparation method thereof. Background Art

[0002] Phosphogypsum is an industrial byproduct of phosphoric acid produced by wet process in phosphorus chemical enterprises. Every ton of phosphoric acid produced will generate about 5 tons of phosphogypsum. Phosphate chemical enterprises in my country discharge tens of millions of tons of phosphogypsum every year, and the accumulated stockpile is very large, which poses a serious threat to the ecological environment and the safety of the dam.

[0003] With phosphogypsum as the main raw material, a hydraulic cementitious material is prepared through modification and component optimization design, which can replace or partially replace ordinary cement. It can not only consume a large amount of phosphogypsum, greatly reduce energy consumption and carbon dioxide emissions, but also the prepared products have wider applicability and higher added value.

[0004] Traditional cementitious materials are mainly cast in a casting process, and their high water-cement ratio results in a long setting time and slow strength development for the persulfate phosphogypsum cementitious system, which is mainly caused by the impurity ions in the phosphogypsum and the slow hydration rate of the early mineral powder.

[0005] The phosphogypsum-based cementitious materials prepared in the prior art have the problems of long setting time and low early strength. The current solution to this problem is mainly to improve it by pretreating the phosphogypsum or adding an early strength agent. The treatment methods for phosphogypsum are currently mainly concentrated on water washing, neutralization, calcination and wet grinding. These methods will make the process complicated and may cause secondary pollution. CN102745924A discloses a phosphogypsum modification method for shortening the setting time of phosphogypsum-based cement concrete, that is, pretreating the phosphogypsum and improving the early performance of the phosphogypsum-based cementitious materials by wet grinding. The main method is to add a small amount of steel slag and mineral powder to the phosphogypsum and mix them with wet grinding. The persulfated phosphogypsum cementitious material prepared by this method still has the problem of long setting time, and the process is relatively complicated and time-consuming. Compared with the method of pretreating raw materials, the method of adding an early strength agent is simpler and will not cause secondary pollution. CN107056115A discloses a coagulant-type early strength agent for phosphogypsum-based cementitious materials and its preparation method. However, the early strength agent used in this process needs to be prepared by calcination and other processes, which has high energy consumption and a complicated process. Summary of the invention

[0006] The present invention provides a phosphogypsum-based cementitious material and a preparation method thereof to solve the above technical problems. The phosphogypsum-based cementitious material can solve the existing technical problems of long setting time and low early strength.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A phosphogypsum-based cementitious material, comprising a mixed powder and an admixture, wherein the mixed powder, calculated by mass percentage, comprises: 40% to 50% phosphogypsum, 44% to 52% solid waste residue, and 6% to 8% alkaline activator, totaling 100%; the admixture is a mixture of sodium aluminate, lithium carbonate, and layered bimetallic composite oxide, and the amount of the admixture is 1.03% to 4.05% of the mass of the mixed powder.

[0009] Preferably, the solid waste residue is one or a mixture of two or more of slag powder, red mud or construction solid waste powder.

[0010] Preferably, the alkaline activator is steel slag and / or ordinary Portland cement.

[0011] Preferably, the dosage of the sodium aluminate, lithium carbonate and layered bimetallic composite oxide is 0.5-2.0%, 0.03-0.05% and 0.5%-2.0% of the mass of the mixed powder.

[0012] The method for preparing the phosphogypsum-based cementitious material comprises the following steps:

[0013] Weigh phosphogypsum, solid waste residue and alkaline activator according to the proportion, put them into a mixer and mix the powders evenly to obtain a mixed powder;

[0014] Weigh the admixture according to the ratio, add it into a predetermined amount of water and stir thoroughly until it is completely dissolved to prepare solution A;

[0015] The mixed powder and solution A are stirred evenly to obtain a semi-dry mixture;

[0016] Weigh an appropriate amount of semi-dry mixture and put it into the mold cavity, and use a press to press the semi-dry mixture into a block;

[0017] The obtained blocks are placed in a natural environment for water spraying and curing.

[0018] Preferably, the predetermined amount of water added is determined according to the water-to-solid ratio selected for the test block, and the water-to-solid ratio ranges from 0.05 to 0.2.

[0019] Preferably, a press is used for pressing. When the press reaches a set pressure value, a pressure holding program needs to be set, and the pressure holding time is set to 1 min to 5 min. At the same time, it is necessary to ensure that the volume of the test block obtained by each pressing is consistent.

[0020] Preferably, the water spraying curing refers to water spraying curing at intervals of 18h to 24h for 3d to 7d in a natural environment.

[0021] Preferably, the phosphogypsum needs to be dried at 30-50° C. and passed through a 0.15 mm sieve.

[0022] The present invention utilizes the synergistic effect of sodium aluminate, lithium carbonate and layered bimetallic composite oxide. When the three are co-doped, sodium aluminate provides sufficient aluminum phase for lithium carbonate, which can promote the growth of calcium vanadium and the effect of lithium carbonate, mainly due to the rapid precipitation of lithium-containing aluminum hydroxide, which can serve as a crystal nucleus to accelerate the growth of amorphous Al(OH) 3 The non-uniform precipitation of AFm phase can accelerate the whole hydration process. At the same time, lithium ions can induce the precipitation of AFm phase in the early stage of hydration, and then transform into mixed AFt phase containing sulfate. The layered bimetallic composite oxide (LDO) itself can directly serve as a nucleating agent, so that the aluminum phase released by the active admixture slag powder in the system can quickly generate calcium vanadium through the LDO nucleating agent. When the three are mixed, the formation of calcium vanadium can be promoted to the greatest extent in the early stage. The two major sources of calcium vanadium formation are: the external aluminum phase promotes the formation of nuclei, and the second is to provide nuclei to promote the hydration of the active admixture slag powder in the system. The addition of sodium aluminate alone only plays the role of providing aluminum phase, which plays a role in promoting the formation of calcium vanadium. Repeated addition of lithium carbonate cannot promote the hydration reaction in this system. Only in an aluminum-rich environment can lithium carbonate promote hydration. When LDO is used alone, it plays the role of providing seeds, but the effect of promoting hydration is not obvious.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The dry hard cementitious material is prepared by low water-cement ratio pressing and molding, which solves the problem of long setting time of traditional casting and molding. The low water-cement ratio dry hard molding test block has a dense initial structure. After being placed in a press and applying pressure, it can be demolded within 1 minute of pressure maintenance. Compared with the traditional high water-cement ratio casting and molding test block, the dry hard system has no setting time problem, does not need to occupy the mold, and is convenient to construct in a specific construction environment, which is conducive to practical engineering applications, especially in road engineering, where the roller can be directly used for flow operation, and a large amount of solid waste such as phosphogypsum, slag, steel slag, red mud, and construction solid waste powder can be consumed, realizing large-scale production. In addition, by adding a small amount of admixtures, aluminum phases and more nucleation sites are provided, and excellent synergistic effects can be achieved when three selected admixtures are added at the same time, promoting the hydration of mineral powder while inducing the rapid generation of early calcium sulfonate and other products, thereby improving the early performance, and absorbing more construction solid waste while maintaining strength.

[0025] The present invention proposes a method for regulating phosphogypsum-based cementitious materials, which promotes hydration reaction and provides nucleation sites by reducing the water-cement ratio and using a pressing molding method and an external modifier. The former can directly solve the problem of long setting time, and the test block can be demoulded after molding and has a certain initial strength. The latter can directly promote the hydration reaction of the system, accelerate the progress of the hydration reaction and improve the density of the test block. The present invention can solve the problems of long setting time and low early strength of phosphogypsum-based cementitious materials while reducing the porosity, and can absorb more construction solid waste while maintaining strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the mold structure for mixed powder compression molding;

[0027] In the figure, 1-briquetting, 2-mould, 3-semi-dry mixture, 4-tabletting. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] This specific embodiment provides a regulated phosphogypsum-based cementitious material, which is obtained by mixing a mixed powder and a solution A to form a semi-dry mixture and then applying pressure through a press; the mixed powder, calculated by mass percentage, includes: phosphogypsum 40% to 50%, solid waste residue 44% to 52%, alkaline activator 6% to 8%, a total of 100%. The solid waste residue is one or a mixture of two or more of slag powder, red mud or construction solid waste powder.

[0030] This specific embodiment provides a method for preparing a phosphogypsum-based cementitious material, comprising the following steps:

[0031] 1) Weigh phosphogypsum, solid waste residue, and alkaline activator according to the proportion, put them into a blender and mix the powders evenly to obtain a mixed powder;

[0032] 2) Weigh the admixture according to the ratio, add it into a predetermined amount of water and stir it thoroughly until it is completely dissolved to prepare solution A;

[0033] 3) The mixed powder and solution A are stirred evenly to obtain a semi-dry mixture;

[0034] 4) Weigh an appropriate amount of semi-dry mixture and put it into the mold cavity, and use a press to press the semi-dry mixture into a block;

[0035] 5) The obtained block is placed in a natural environment for water spraying and curing.

[0036] In a preferred embodiment, in step 1), the phosphogypsum is dried at 40°C and passed through a 0.15 mm sieve.

[0037] In a preferred embodiment, in step 2), the mixed powder is prepared according to a mass ratio of 40% to 50% phosphogypsum, 44% to 52% solid waste residue, and 6% to 8% alkaline activator, and the weighed powder is mixed evenly using a ball mill.

[0038] In a preferred embodiment, in step 3), sodium aluminate, lithium carbonate and layered bimetallic composite oxide are used as external admixtures in the system, and the admixture amount thereof is 0.05% to 2% of the mass of the mixed powder.

[0039] In the preferred embodiment, when preparing solution A, the amount of water used to prepare solution A is determined according to the water-solid ratio selected for the test block. The water-solid ratio of the phosphogypsum-based cementitious material is uniformly selected to be 0.15, that is, the mass of water is 15% of the mass of the mixed powder.

[0040] In a preferred embodiment, in step 4), the mixed powder and solution A are placed in a mixer and stirred thoroughly to make the semi-dry mixture evenly dispersed.

[0041] In the preferred embodiment, in step 5), an appropriate amount of semi-dry mixture is weighed and placed in the mold cavity, and a press is used to press. When the press reaches the set pressure value, the pressure holding program needs to be set again, and the pressure holding time is set to 1 minute. At the same time, the volume of the test block obtained by each pressing must be consistent. Therefore, it is necessary to ensure that the error of the powder weighed each time is less than 0.05g.

[0042] In a preferred embodiment, in step 6), the water spraying curing includes: water spraying curing every 24 hours in a natural environment for up to 7 days.

[0043] The following is a detailed description of the embodiments.

[0044] In the following embodiments, the phosphogypsum is an industrial byproduct of phosphoric acid produced by a phosphorus chemical enterprise through a wet process, and its main chemical components are dihydrate gypsum (CaSO 4 · 2 H 2 O); the physical properties of slag powder meet S95 and above; red mud is industrial solid waste discharged when the aluminum industry extracts alumina, and its main component is SiO 2 、Al 2 O 3 ,CaO,Fe 2 O 3 etc.; the construction solid waste powder is the powder made by separation and grinding of construction solid waste; the alkaline activator is one of steel slag or ordinary Portland cement or a mixture thereof.

[0045] Comparative Example 1

[0046] Material preparation: put the phosphogypsum into a blast drying oven, set the temperature to 40°C, and after blast drying for 10 hours, pass through a 0.15mm sieve;

[0047] Preparation of mixed powder: weigh 40% phosphogypsum, 52% slag powder, 2% steel slag and 6% cement as alkaline activator according to mass ratio, put them into a planetary ball mill and mix for 15 minutes;

[0048] Weigh 100g of mixed powder, set the water-to-solid ratio to 0.15, and weigh 15g of water.

[0049] Add 100g of mixed powder and 15g of aqueous solution into a blender and stir the semi-dry mixture evenly.

[0050] Weigh an appropriate amount of semi-dry mixture and put it into the mold cavity. Gently compact the semi-dry mixture, place the matching pressing block on the upper part of the cavity filled with powder, place the whole in the middle of the press, and set the pressure value of the press to 20MPa. When the press reaches the set pressure value, maintain the pressure for 1 minute, and the error of the powder weighed each time is less than 0.05g.

[0051] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. Stop spraying water after 3 days.

[0052] The phosphogypsum-based cementitious material prepared in this comparative example was tested and found that the 3d compressive strength was 3.12MPa, the 7d compressive strength was 11.41MPa, and the 28d compressive strength was 21.71MPa.

[0053] Comparative Example 2

[0054] Material preparation: put the phosphogypsum into a blast drying oven, set the temperature to 40°C, and after blast drying for 10 hours, pass through a 0.15mm sieve;

[0055] Preparation of mixed powder: weigh 40% phosphogypsum, 52% slag powder, 2% steel slag and 6% cement as alkaline activator according to mass ratio, put them into a planetary ball mill and mix for 15 minutes;

[0056] Weigh 100 g of the mixed powder, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 1.0 g of sodium aluminate and 0.05 g of lithium carbonate, add them to 15 g of water and stir thoroughly until the sodium aluminate and lithium carbonate are completely dissolved to obtain solution A.

[0057] Add 100 g of the mixed powder and the prepared solution A into a blender, and stir the semi-dry mixture evenly.

[0058] Weigh an appropriate amount of semi-dry mixture and put it into the mold cavity, compact the semi-dry mixture lightly, place the matching pressing block on the upper part of the cavity filled with powder, place the whole in the middle of the press, and set the pressure value of the press to 20MPa. When the press reaches the set pressure value, the pressure is maintained for 5 minutes, and the error of the powder weighed each time is less than 0.05g.

[0059] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0060] The phosphogypsum-based cementitious material prepared in this comparative example was tested and found that the 3d compressive strength was 5.07MPa, the 7d compressive strength was 16.21MPa, and the 28d compressive strength was 28.51MPa.

[0061] Comparative Example 3

[0062] Material preparation is the same as that of Comparative Example 1. Preparation of mixed powder is the same as that of Comparative Example 1.

[0063] Weigh 100 g of the mixed powder for use, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 1.0 g of sodium aluminate and 2.0 g of LDO, add them to 15 g of water and stir thoroughly until the sodium aluminate and LDO are completely dissolved to obtain solution A.

[0064] Add 100 g of the mixed powder and the prepared solution A into a blender, and stir the semi-dry mixture evenly.

[0065] The pressing steps are the same as in Example 1.

[0066] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0067] The phosphogypsum-based cementitious material prepared in this example was tested and found to have a 3d compressive strength of 4.59 MPa, a 7d compressive strength of 15.42 MPa, and a 28d compressive strength of 26.61 MPa.

[0068] Comparative Example 4

[0069] Material preparation is the same as that of Comparative Example 1.

[0070] The mixed powder was prepared in the same manner as in Comparative Example 1.

[0071] Weigh 100 g of the mixed powder for use, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 0.05 g of lithium carbonate and 2.0 g of LDO, add them to 15 g of water and stir thoroughly until the lithium carbonate and LDO are completely dissolved to obtain solution A.

[0072] Add 100 g of the mixed powder and the prepared solution A into a blender, and stir the semi-dry mixture evenly.

[0073] The compression molding steps are the same as those of Comparative Example 1.

[0074] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0075] The phosphogypsum-based cementitious material prepared in this example was tested and found to have a 3d compressive strength of 3.94 MPa, a 7d compressive strength of 12.11 MPa, and a 28d compressive strength of 22.89 MPa.

[0076] Example 1

[0077] Material preparation is the same as that of Comparative Example 1.

[0078] The mixed powder was prepared in the same manner as in Comparative Example 1.

[0079] Weigh 100 g of the mixed powder for use, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 0.5 g of sodium aluminate, 0.03 g of lithium carbonate, and 0.5 g of LDO, add them to 15 g of water and stir thoroughly until the sodium aluminate, lithium carbonate and LDO are completely dissolved to obtain solution A.

[0080] Add 100 g of the mixed powder and the prepared solution A into a blender, and stir the semi-dry mixture evenly.

[0081] The compression molding steps are the same as those of Comparative Example 1.

[0082] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0083] The phosphogypsum-based cementitious material prepared in this example was tested and found to have a 3d compressive strength of 9.04 MPa, a 7d compressive strength of 21.32 MPa, and a 28d compressive strength of 30.02 MPa.

[0084] Example 2

[0085] Material preparation is the same as that of Comparative Example 1.

[0086] The mixed powder was prepared in the same manner as in Comparative Example 1.

[0087] Weigh 100 g of the mixed powder for use, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 2.0 g of sodium aluminate, 0.04 g of lithium carbonate, and 1.0 g of LDO, add them to 15 g of water and stir thoroughly until the sodium aluminate, lithium carbonate and LDO are completely dissolved to obtain solution A.

[0088] Add 100 g of the mixed powder and the prepared solution A into a blender, and stir the semi-dry mixture evenly.

[0089] The compression molding steps are the same as those of Comparative Example 1.

[0090] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0091] The phosphogypsum-based cementitious material prepared in this example was tested and found to have a 3d compressive strength of 9.99 MPa, a 7d compressive strength of 23.22 MPa, and a 28d compressive strength of 29.39 MPa.

[0092] Example 3

[0093] Material preparation is the same as that of Comparative Example 1.

[0094] The mixed powder was prepared in the same manner as in Comparative Example 1.

[0095] Weigh 100 g of mixed powder for use, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 1.0 g of sodium aluminate, 0.05 g of lithium carbonate, and 2.0 g of LDO, add them into 15 g of water and stir thoroughly until the sodium aluminate, lithium carbonate and LDO are completely dissolved to obtain solution A.

[0096] Add 100 g of the mixed powder and the prepared solution A into a blender, and stir the semi-dry mixture evenly.

[0097] The compression molding steps are the same as those of Comparative Example 1.

[0098] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0099] The phosphogypsum-based cementitious material prepared in this example was tested and found to have a 3d compressive strength of 12.42 MPa, a 7d compressive strength of 27.12 MPa, and a 28d compressive strength of 32.19 MPa.

[0100] Example 4

[0101] Material preparation is the same as that of Comparative Example 1.

[0102] Mixed powder preparation: weigh 50% phosphogypsum, 44% slag powder, 2% steel slag and 4% cement as alkaline activator according to mass ratio, put them into a planetary ball mill and mix for 15 minutes.

[0103] Weigh 100 g of the mixed powder for use, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 1.0 g of sodium aluminate, 0.05 g of lithium carbonate, and 2.0 g of LDO, add them into 15 g of water and stir thoroughly until the sodium aluminate, lithium carbonate and LDO are completely dissolved to obtain solution A.

[0104] Add 100 g of the mixed powder and the prepared solution A into a blender, and stir the semi-dry mixture evenly.

[0105] The compression molding steps are the same as those of Comparative Example 1.

[0106] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0107] The phosphogypsum-based cementitious material prepared in this example was tested and found to have a 3d compressive strength of 10.52 MPa, a 7d compressive strength of 25.32 MPa, and a 28d compressive strength of 30.01 MPa.

[0108] Example 5

[0109] Material preparation is the same as that of Comparative Example 1.

[0110] Mixed powder was prepared by weighing 50% phosphogypsum, 30% slag powder, 14% red mud, 2% steel slag and 4% cement as alkaline activator according to the mass ratio, putting them into a planetary ball mill and mixing for 15 minutes.

[0111] Weigh 100 g of the mixed powder for use, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 1.0 g of sodium aluminate, 0.05 g of lithium carbonate, and 2.0 g of LDO, add them into 15 g of water and stir thoroughly until the sodium aluminate, lithium carbonate and LDO are completely dissolved to obtain solution A.

[0112] Add 100 g of the mixed powder and the prepared solution A into a blender, and stir the semi-dry mixture evenly.

[0113] The compression molding steps are the same as those of Comparative Example 1.

[0114] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0115] The phosphogypsum-based cementitious material prepared in this example was tested and found to have a 3d compressive strength of 8.02 MPa, a 7d compressive strength of 19.23 MPa, and a 28d compressive strength of 24.33 MPa.

[0116] Example 6

[0117] Material preparation is the same as that of Comparative Example 1.

[0118] For the preparation of mixed powder, 50% of phosphogypsum, 30% of slag powder, 14% of construction solid waste powder, 2% of steel slag and 4% of cement as alkaline activator are weighed according to the mass ratio, put into a planetary ball mill and mix for 15 minutes.

[0119] Weigh 100 g of the mixed powder for use, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 1.0 g of sodium aluminate, 0.05 g of lithium carbonate, and 2.0 g of LDO, add them into 15 g of water and stir thoroughly until the sodium aluminate, lithium carbonate and LDO are completely dissolved to obtain solution A.

[0120] Add 100g of the mixed powder and aqueous solution into a blender and stir the semi-dry mixture evenly.

[0121] The compression molding steps are the same as those of Comparative Example 1.

[0122] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0123] The phosphogypsum-based cementitious material prepared in this example was tested and found to have a 3d compressive strength of 8.85 MPa, a 7d compressive strength of 19.95 MPa, and a 28d compressive strength of 28.01 MPa.

[0124] Example 7

[0125] Material preparation is the same as that of Comparative Example 1.

[0126] Mixed powder preparation: weigh 50% phosphogypsum, 30% slag powder, 7% red mud, 7% construction solid waste powder, 2% steel slag and 4% cement as alkaline activator according to mass ratio, put them into a planetary ball mill and mix for 15 minutes.

[0127] Weigh 100 g of the mixed powder for use, set the water-to-solid ratio to 0.15, weigh 15 g of water, weigh 1.0 g of sodium aluminate, 0.05 g of lithium carbonate, and 2.0 g of LDO, add them to 15 g of water and stir thoroughly until the lithium carbonate and LDO are completely dissolved to obtain solution A.

[0128] Add 100 g of the mixed powder and the prepared solution A into a blender, and stir the semi-dry mixture evenly.

[0129] The compression molding steps are the same as those of Comparative Example 1.

[0130] After the pressed test block is demoulded, its surface is sprayed wet with a spray bottle and placed in a natural environment. During this period, water is sprayed once every 24 hours to moisten the surface of the test block. The spraying of water is stopped after 7 days.

[0131] The phosphogypsum-based cementitious material prepared in this example was tested and found to have a 3d compressive strength of 8.00 MPa, a 7d compressive strength of 18.92 MPa, and a 28d compressive strength of 27.69 MPa.

[0132] From the strength data obtained from the above comparative examples and embodiments, it can be seen that the strength improvement effect of the composite addition of sodium aluminate, lithium carbonate and layered bimetallic composite oxide is much higher than that of the composite addition of any two of the external admixtures. The main reason is that when only sodium aluminate and lithium carbonate are added, what mainly happens is that lithium carbonate uses the externally added aluminum phase as a rapid precipitation of lithium-containing aluminum hydroxide to form calcium sulfonate, and has a weak effect on the hydration of the slag powder itself; when lithium carbonate and layered bimetallic composite oxide are added, due to the small amount of aluminum phase in the system, lithium carbonate has almost no effect and cannot promote hydration and increase The amount of calcium vanadate, layered bimetallic composite oxides can provide more nucleation sites for the hydration of slag powder to generate calcium vanadate, but from the strength data, the effect of strength improvement is not obvious, mainly because it is difficult to excite the slag powder in the early stage, and it still needs external admixtures to provide more hydration products in the early stage; when sodium aluminate, lithium carbonate and layered bimetallic composite oxides are added, sodium aluminate provides sufficient aluminum phase for lithium carbonate, which can promote the growth of calcium vanadate and the role of lithium carbonate, mainly due to the rapid precipitation of lithium-containing aluminum hydroxide, which can serve as a crystal nucleus to accelerate the amorphous Al(OH) 3 The non-uniform precipitation of the hydration reaction system accelerates the entire hydration process. The layered bimetallic oxide (LDO) itself can directly serve as a nucleating agent, so that the aluminum phase released by the active admixture slag powder in the system can quickly generate ettringite through the LDO nucleating agent. When the three are mixed together, the formation of ettringite can be promoted at the earliest stage to the greatest extent.

[0133] The above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here, so the obvious changes or modifications derived are still within the protection scope of the invention.

Claims

1. A phosphogypsum-based cementitious material, It is characterized in that The phosphogypsum-based cementitious material includes a mixed powder and an admixture. The mixed powder, calculated by mass percentage, includes: 40% to 50% phosphogypsum, 44% to 52% solid waste slag, and 6% to 8% alkaline activator, totaling 100%; the admixture is a mixture of sodium aluminate, lithium carbonate, and layered bimetallic composite oxides, and the amount of the admixture is 1.03% to 4.05% of the mass of the mixed powder; the solid waste slag is a mixture of one or more of slag powder, red mud, or construction solid waste fine powder, and the amounts of sodium aluminate, lithium carbonate, and layered bimetallic composite oxides are 0.5% to 2.0%, 0.03% to 0.05%, and 0.5% to 2.0% of the mass of the mixed powder.

2. The phosphogypsum-based cementitious material according to claim 1, It is characterized in that The alkaline activator is steel slag and / or ordinary Portland cement.

3. The method for preparing the phosphogypsum-based cementitious material according to claim 1, It is characterized in that The steps include: Weigh phosphogypsum, solid waste residue and alkaline activator according to the proportion, put them into a mixer and mix the powders evenly to obtain a mixed powder; Weigh the admixture according to the ratio, add it into a predetermined amount of water and stir thoroughly until it is completely dissolved to prepare solution A; The mixed powder and solution A are stirred evenly to obtain a semi-dry mixture; Weigh an appropriate amount of semi-dry mixture and put it into the mold cavity, and use a press to press the semi-dry mixture into a block; The obtained blocks are placed in a natural environment for water spraying and curing.

4. The preparation method according to claim 3, It is characterized in that The predetermined amount of water added is determined according to the water-to-solid ratio selected for the test block, and the water-to-solid ratio ranges from 0.05 to 0.

2.

5. The preparation method according to claim 3, It is characterized in that When using a press to press, when the press reaches the set pressure value, it is necessary to set the pressure holding program and set the pressure holding time to 1min~5min. At the same time, it is necessary to ensure that the volume of the test block obtained each time is consistent.

6. The preparation method according to claim 3, It is characterized in that The water spraying curing refers to water spraying curing at intervals of 18h~24h for 3d~7d in a natural environment.

7. The preparation method according to claim 3, It is characterized in that The phosphogypsum needs to be dried at 30-50°C and passed through a 0.15 mm sieve.

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