Phosphogypsum building material and preparation method therefor

Abstract

Disclosed in the present disclosure are a phosphogypsum building material and a preparation method therefor. The phosphogypsum building material comprises an alkaline excitation material, fly ash, and an unsaturated carboxylic acid water reducing agent, wherein the water reducing agent can exert an original water reducing effect of the water reducing agent; furthermore, the water reducing agent facilitates slow release of Ca2+ from phosphogypsum hemihydrate, thereby exerting a retarding effect, and accelerates the dissolution of fly ash glass phases, thereby promoting a hydration process thereof, and a complex formed with an unsaturated carboxylic acid can act as a filler to fill in gaps between crystals of a gel material, thereby enhancing the strength of the material. Compared with an ordinary polycarboxylic acid water reducing agent, the phosphogypsum building material of the present disclosure has a better retarding effect, and a building material test piece obtained thereby has better mechanical properties.

Description

Phosphogypsum building material and preparation method thereof Technical Field

[0001] The present disclosure relates to the technical field of phosphogypsum building materials, and in particular to phosphogypsum building materials and a preparation method thereof. Background Art

[0002] Phosphogypsum is a solid waste residue generated during the wet production of phosphoric acid. It has an extremely low utilization rate and is mostly disposed of by stockpiling. Long-term stockpiling not only occupies a large amount of land resources, but also causes great harm to the environment. The comprehensive development and utilization of phosphogypsum has become a safety and environmental issue that urgently needs to be addressed.

[0003] The semi-hydrated phosphoric acid process has the advantages of low energy consumption and high phosphoric acid concentration. The shift from the dihydrate process to the semi-hydrated process is the future development trend of the phosphorus chemical industry. Semi-hydrated phosphogypsum is a by-product of the semi-hydrated phosphoric acid process. Its main component is CaSO4·1 / 2H2O, which has potential gelling activity. The gelling reaction of semi-hydrated phosphogypsum is as follows: 4CaSO4·1 / 2H2O+2H2O→3CaSO4·2H2O. However, semi-hydrated phosphogypsum has the following disadvantages as a gelling material: (1) the water requirement is much greater than the actual hydration water requirement; (2) the setting time is short. Modifying gypsum by adding admixtures such as water reducers and retarders can effectively solve the above problems of semi-hydrated phosphogypsum gel materials.

[0004] The commonly used system for preparing gypsum-based building materials using hemihydrate gypsum is: hemihydrate gypsum, cement, water reducer, and retarder. In this system, the water reducer reacts with the Ca 2+ It is adsorbed on the surface of gypsum particles, changing the properties of the solid-liquid interface of gypsum particles, thereby improving the dispersibility of gypsum particles, releasing the adsorbed water in phosphogypsum, reducing water demand, and increasing the hydration rate; retarders are usually small molecular organic acids such as citric acid and phosphates, which tend to react with free Ca 2+ Combining into insoluble matter, it reduces the supersaturation of the gypsum liquid phase, especially the early supersaturation, thereby reducing the dissolution of hemihydrate gypsum and the formation of crystal nuclei, and thus slowing down the hydration process. Although this type of retarder has a good retarding effect, due to the early reduction of the supersaturation of the reaction system, the formation of crystal nuclei and crystal growth are restricted, resulting in less overlap between the crystals of the final setting product, a loose structure, and a significant decrease in the mechanical strength of the material. An improvement in the mechanical strength of materials is particularly necessary for advanced building materials.

[0005] In view of this, the present disclosure is proposed.

[0006] Summary of the Invention

[0007] The purpose of the present disclosure is to provide a phosphogypsum building material and a preparation method thereof, so as to improve the mechanical properties of the phosphogypsum building material while ensuring the retarding effect.

[0008] The present disclosure is achieved as follows:

[0009] In a first aspect, the present disclosure provides a phosphogypsum building material having a water content of 50 wt% to 75 wt%, comprising the following components: 100 parts by weight of hemihydrate phosphogypsum, 2 to 8 parts by weight of an alkaline activating material, 5 to 10 parts by weight of fly ash, and 0.8 to 2 parts by weight of an unsaturated polycarboxylic acid water reducer.

[0010] In some embodiments, the unsaturated polycarboxylic acid water-reducing agent is obtained by reacting a polymer containing an amino group or a hydroxyl group with maleic anhydride.

[0011] In some embodiments, the unsaturated polycarboxylic acid water reducer is obtained by reacting branched polyethyleneimine with maleic anhydride.

[0012] In some embodiments, the molar ratio of amino group to maleic anhydride in the branched polyethyleneimine is 1:(1.05-1.1).

[0013] In some embodiments, the reaction temperature is 60° C. to 80° C., and the reaction time is 10 min to 30 min.

[0014] In some embodiments, the number average molecular weight of the branched polyethyleneimine is 10 kDa to 30 kDa.

[0015] In some embodiments, the amine value of the branched polyethyleneimine is 17 mg / g to 19 mg / g calculated on a dry basis.

[0016] In some embodiments, the hemihydrate phosphogypsum is selected from one or both of α-hemihydrate phosphogypsum and β-hemihydrate phosphogypsum.

[0017] In some embodiments, the hemihydrate phosphogypsum has a soluble phosphorus content of ≤0.1 wt %, and a soluble fluorine content of ≤0.03 wt %.

[0018] In some embodiments, the moisture content of the hemihydrate phosphogypsum is ≤5 wt %.

[0019] In some embodiments, the alkaline activating material is quicklime or Portland cement.

[0020] In some embodiments, the mass fraction of calcium oxide in the fly ash is 1.6wt% to 1.7wt%; and / or the mass fraction of aluminum oxide is 25wt% to 35wt%; and / or the mass fraction of iron oxide is 3.0wt% to 3.5wt%.

[0021] In some embodiments, the fly ash is one or more of Class I fly ash, Class II fly ash, and Class III fly ash.

[0022] In some embodiments, the water content is equal to the amount of water used as determined by standard consistency.

[0023] In a second aspect, the present disclosure provides a method for preparing the phosphogypsum building material according to any one of the aforementioned embodiments, comprising mixing hemihydrate phosphogypsum, an alkaline activating material, fly ash, an unsaturated polycarboxylic acid water reducer and water to obtain the phosphogypsum building material.

[0024] In some embodiments, the alkaline activating material, hemihydrate phosphogypsum, fly ash and unsaturated polycarboxylic acid water reducer are poured into a stirring device for premixing, and then water is added and mixed uniformly to obtain the phosphogypsum building material.

[0025] The present disclosure has the following beneficial effects:

[0026] The disclosed phosphogypsum building material comprises alkaline activating material, fly ash and unsaturated carboxylic acid water reducer, which can exert its original water reducing effect and is beneficial to the Ca content in hemihydrate phosphogypsum. 2+ The slow release of the agent slows setting, accelerates the dissociation and hydration of fly ash glass, and the resulting complex of unsaturated carboxylic acid and hydroxybenzoic acid acts as a filler, filling the gaps between gel crystals and reinforcing the material. Compared to conventional polycarboxylate superplasticizers, the phosphogypsum building material disclosed herein exhibits superior slow setting, and the resulting building material specimens exhibit superior mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 is a mixture of PC900 polycarboxylate water reducer and aluminum chloride;

[0029] Figure 2 shows a mixture of unsaturated carboxylic acid water reducer PEIHC-1 and aluminum chloride. DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0031] One embodiment of the present disclosure provides a phosphogypsum building material having a water content of 50 wt% to 75 wt%, and comprising the following components: 100 parts by weight of hemihydrate phosphogypsum, 2 to 8 parts by weight of an alkaline activating material, 5 to 10 parts by weight of fly ash, and 0.8 to 2 parts by weight of an unsaturated polycarboxylic acid water reducer.

[0032] Specifically, in the phosphogypsum building material in this embodiment, for every 100 parts by weight of hemihydrate phosphogypsum, the following can be added: 2, 3, 4, 5, 6, 7, 8 parts by weight of alkaline activating material or any value between 2 and 8 parts by weight; 5, 6, 7, 8, 9, 10 parts by weight of fly ash or any value between 5 and 10 parts by weight; and 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2 parts by weight of unsaturated polycarboxylic acid water reducer or any value between 0.8 and 2 parts by weight.

[0033] Fly ash is one of the most common mineral admixtures and a key component in the development of green and low-carbon building materials. However, due to the dense surface glass (Al-O-Si bonds), its early hydration activity is low. Adding alkalis, such as Ca(OH)2, to fly ash can dissolve the surface glass and significantly increase its hydration activity.

[0034] The present invention provides a building material component with the comprehensive advantages of improving water reduction, slow setting effect, and improving fly ash hydration activity. The principle is as follows: unsaturated polycarboxylic acid water reducer reacts with carboxylate radicals to form Ca 2+ The combination of fly ash and the adsorption of Al on the surface of hemihydrate phosphogypsum particles improves its dispersibility and releases the adsorbed water, which plays a role in reducing water. After adding water, the hydration system becomes alkaline, the glass on the surface of the fly ash begins to disintegrate, and Al is dissolved from the surface. 3+ 、Fe 3+ ; Due to Fe 3+ It is a transition metal ion with an unfilled d orbital that can accept the electron pair of the ligand, so it has a high coordination activity; in addition, due to the 3+ It has strong coordination activity with carboxylic acid. This is because the Al-O bond energy is large, up to 521kJ / mol, and the binding speed is fast. Therefore, when there is Al 3+ 、 Fe 3+ Dissolution, because Ca 2+ The coordination activity of the unsaturated polycarboxylic acid water reducer is not as good as the other two, and the carboxylate in the unsaturated polycarboxylic acid water reducer is more inclined to combine with them; therefore, the effect is: the water reducer exerts its original water-reducing effect; the Ca in hemihydrate phosphogypsum 2+ The slow release has a slow setting effect; it accelerates the dissociation of fly ash glass and speeds up its hydration process; the unsaturated carboxylic acid formed and the complex can be used as a filler to fill the gaps between the gel material crystals and play a reinforcing role on the material.

[0035] In some embodiments, the unsaturated polycarboxylic acid water reducer is obtained by reacting a polymer containing amino or hydroxyl groups with maleic anhydride, wherein the maleic anhydride can provide unsaturated double bonds and carboxyl groups, and the polymer provides amino and hydroxyl groups that can react with carboxyl groups, thereby obtaining an unsaturated polycarboxylic acid water reducer. Compared with saturated polycarboxylic acid water reducers, the unsaturated carboxylic acid double bond can be conjugated with the carboxylate ion, thereby making the negative charge more stable and the acidity enhanced. The stronger acidity makes it have higher coordination activity, and it has better coordination with Al 3+ 、Fe 3+ Can form more stable complexes.

[0036] In some embodiments, the unsaturated polycarboxylic acid water reducer is obtained by reacting branched polyethyleneimine with maleic anhydride.

[0037] In this embodiment, polyethyleneimine is used as the polymer main body. On the one hand, the branching degree and the larger number of fatty chains of branched polyethyleneimine make the steric hindrance effect stronger, which is beneficial to the water reduction effect; on the other hand, it prevents the unsaturated polycarboxylic acid complex from immediately precipitating and adhering to the surface of dihydrate gypsum crystals or fly ash surface to hinder the hydration reaction.

[0038] In some embodiments, the molar ratio of amino group to maleic anhydride in the branched polyethyleneimine is 1:(1.05-1.1), specifically 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.1 or any value between 1:(1.05-1.1).

[0039] In this embodiment, excessive addition of maleic anhydride can enable the amino groups in the esterified polyethyleneimine to react fully, and a large number of carboxyl groups are retained in the water reducer to form a complex.

[0040] In some embodiments, the reaction temperature is 60°C to 80°C, specifically 60°C, 65°C, 60°C, 75°C, 80°C or any value between 60°C and 80°C; at this temperature, a relatively fast reaction efficiency can be maintained, and there are fewer side reactions; the reaction time is 10 min, 15 min, 20 min, 25 min, 30 min, specifically 10 min to 30 min or any value between 10 min and 30 min. Continuing to extend the reaction time does not significantly improve the degree of reaction.

[0041] In some embodiments, the number average molecular weight of the branched polyethyleneimine is 10 kDa to 30 kDa, specifically 10 kDa, 15 kDa, 20 kDa, 25 kDa, 30 kDa or any value between 10 kDa and 30 kDa.

[0042] Taking into account the steric hindrance effect, if the number average molecular weight is too small, the steric hindrance effect is weak and has little impact on the results; if the number average molecular weight is too large, the reaction difficulty will increase.

[0043] In some embodiments, the amine value of the branched polyethyleneimine is 17 mg / g to 19 mg / g calculated on a dry basis, specifically 17 mg / g, 17.5 mg / g, 18 mg / g, 18.5 mg / g, 19 mg / g or any value between 17 mg / g and 19 mg / g.

[0044] In order to ensure the effect of the water reducer, the density of the carboxylate groups in the water reducer needs to reach a certain value. If the density of the carboxylate groups is too low, the number of carboxylate groups participating in the formation of the complex in the water reducer will be too small, and the effect will not be significantly improved. If the density of the carboxylate groups is too high, it may not be able to fully react.

[0045] In some embodiments, the hemihydrated phosphogypsum is selected from one or both of α-type hemihydrated phosphogypsum and β-type hemihydrated phosphogypsum. For example, the hemihydrated phosphogypsum can be α-type hemihydrated phosphogypsum, β-type hemihydrated phosphogypsum, or a mixture of α-type hemihydrated phosphogypsum and β-type hemihydrated phosphogypsum.

[0046] In some embodiments, the soluble phosphorus content of the hemihydrate phosphogypsum is ≤0.1wt%, for example, it can be 0.02wt%, 0.04wt%, 0.06wt%, 0.08wt%, 0.1wt% or any value less than 0.1wt%; the soluble fluorine content is ≤0.03wt%, for example, it can be 0.005wt%, 0.01wt%, 0.015wt%, 0.02wt%, 0.025wt%, 0.03wt% or any value less than 0.03wt%.

[0047] The presence of phosphorus and fluorine will affect the crystallization of materials, and thus affect the strength properties of building materials. Therefore, the content of phosphorus and fluorine needs to be within the allowable range.

[0048] In some embodiments, the moisture content of the hemihydrated phosphogypsum is ≤5wt%, specifically 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, or any value ≤5wt%. In some examples, the hemihydrated phosphogypsum is dried before preparing the building material. This removes the effects of moisture and facilitates control of the amount of hemihydrated phosphogypsum added. It should be noted that the moisture content in this embodiment refers to the free water content and does not include bound water.

[0049] In some embodiments, the alkaline activating material is quicklime or silicate cement, which provides an alkaline environment for the phosphogypsum building material, breaking the Al-O-Si bond to form aluminum colloidal silica.

[0050] In some embodiments, the mass fraction of calcium oxide in the fly ash is 1.6wt% to 1.7wt%, specifically 1.6wt%, 1.62wt%, 1.64wt%, 1.66wt%, 1.68wt%, 1.7wt% or any value between 1.6wt% and 1.7wt%; and / or the mass fraction of aluminum oxide is 25wt% to 35wt%, specifically 25wt%, 27wt%, 29wt%, 31wt%, 33wt%, 35wt% or any value between 25wt% and 35wt%.

[0051] The calcium oxide in fly ash is alkaline, which can reduce the amount of cement and quicklime used. If the aluminum content is too low, it is not conducive to forming a complex with unsaturated carboxylic acid. If the aluminum content is too high, the hydration rate will be too fast, which is not conducive to construction. Therefore, the aluminum content needs to be reasonably selected. In addition, fly ash also contains iron, which can also form a complex with unsaturated carboxylic acid. Therefore, the iron content can also be controlled. For example, fly ash with a mass fraction of ferric oxide of 3.0wt% to 3.5wt% can be selected. Specifically, it can be 3.0wt%, 3.1wt%, 3.2wt%, 3.3wt%, 3.4wt%, 3.5wt% or any value between 3.0wt% and 3.5wt%.

[0052] In some embodiments, the fly ash is one or more of Class I fly ash, Class II fly ash and Class III fly ash, and the content, particle size and activity of calcium oxide, aluminum oxide and iron oxide in Class I fly ash, Class II fly ash and Class III fly ash are different, among which Class I fly ash has a smaller particle size, greater activity and less glassy Al-O-Si content on the surface.

[0053] In some embodiments, the water content is equal to the water content determined according to the standard consistency, thereby obtaining a phosphogypsum building material having a consistency that meets the standard requirements.

[0054] Another embodiment of the present disclosure provides a method for preparing the phosphogypsum building material described in any one of the aforementioned embodiments, comprising mixing hemihydrate phosphogypsum, an alkaline activating material, fly ash, an unsaturated polycarboxylic acid water reducer, and water to obtain the phosphogypsum building material.

[0055] The phosphogypsum building material disclosed herein only requires preparing the raw materials and mixing them according to a preset ratio, which is convenient for preparation and use.

[0056] In some embodiments, the alkaline activating material, hemihydrate phosphogypsum, fly ash and unsaturated polycarboxylic acid water reducer are poured into a stirring device for premixing, and then water is added to mix evenly to obtain the phosphogypsum building material. The other raw materials except water are preliminarily mixed before adding water, which is more conducive to uniform mixing of the raw materials.

[0057] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0058] Some raw material description:

[0059] The chemical composition of cement and fly ash is shown in Table 1:

[0060] Table 1

[0061] The fly ash was taken from a thermal power plant in Wuhan. The specific surface area was 440m 2 / kg, fineness is 5.25%, density is 2.2g / cm 3 .

[0062] The physical properties of α-hemihydrate gypsum and β-hemihydrate gypsum are shown in Table 2:

[0063] Table 2

[0064] β-hemihydrate gypsum comes from Hubei Yihua Group Co., Ltd. It is a gray powdery solid prepared by low-temperature calcination of dihydrate phosphogypsum in a rotary kiln.

[0065] α-hemihydrate gypsum is self-produced and is prepared from dihydrate phosphogypsum using the autoclaved microcrystallization method.

[0066] Example 1

[0067] The structural parameters of the branched polyethyleneimine (purchased from Shanghai Hanluo New Materials Co., Ltd.) used in this example are as follows:

[0068] Table 3

[0069] In this example, an unsaturated polycarboxylic acid water-reducing agent, designated PEIHC-1, was prepared by the following method: 20 g of branched polyethyleneimine was weighed and placed in a reactor. Mechanical stirring was started and the temperature was raised to 60° C. Maleic anhydride was slowly added, with a molar ratio of the amino group to maleic anhydride of 1.05. Stirring was continued for 30 minutes to obtain a light yellow viscous liquid, which was the unsaturated polycarboxylic acid water-reducing agent. The NMR results were as follows:

[0070] 1 H-NMR (CDCl3, 600Hz, ppm): 1.58 (s, NH2), 2.5~2.8 (m, CH2), 3.06~3.30 (m, O=CN-CH2), 6.26~6.55 (d, -CH=CH-).

[0071] Figures 1 and 2 show mixtures of PC900 polycarboxylate superplasticizer (Jiangsu Nigao Technology Co., Ltd.), unsaturated carboxylate superplasticizer PEIHC-1, and aluminum chloride, respectively. The solvent is anhydrous acetonitrile, and the weight ratio of superplasticizer to anhydrous aluminum chloride is 1:0.01. Figure 1 shows that the liquid level remains horizontal after tilting the centrifuge tube, indicating that PC900 polycarboxylate superplasticizer cannot form a solid complex with aluminum ions. However, in Figure 2, the liquid level tilts with the centrifuge tube, indicating that PEIHC-1 can form a solid complex with aluminum ions. This is due to the difference in acidity between the two.

[0072] Example 2

[0073] In this example, an unsaturated polycarboxylic acid water-reducing agent, designated PEIHC-2, was prepared by the following method: 20 g of branched polyethyleneimine was weighed and placed in a reactor. Mechanical stirring was started and the temperature was raised to 80° C. Maleic anhydride was slowly added, with a molar ratio of the amino group to maleic anhydride of 1.2. Stirring was continued for 10 minutes to obtain a light yellow viscous liquid, which was the unsaturated polycarboxylic acid water-reducing agent. The NMR results were as follows:

[0074] 1 H-NMR (CDCl3, 600Hz, ppm): 1.58 (s, NH2), 2.5~2.8 (m, CH2), 3.06~3.30 (m, O=CN-CH2), 6.26~6.55 (d, -CH=CH-).

[0075] Example 3

[0076] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 3 parts of quicklime, 8 parts of fly ash, and 1.2 parts of PEIHC-1. The water amount is determined according to the standard consistency.

[0077] The preparation method is as follows:

[0078] (1) Drying hemihydrate phosphogypsum to a moisture content of ≤5%;

[0079] (2) Weigh each component according to the ratio;

[0080] (3) Pour the alkaline activating material, hemihydrate phosphogypsum, fly ash, and unsaturated polycarboxylic acid water reducer into a mixer in sequence and pre-mix them evenly;

[0081] (4) Add water and stir until the materials are evenly mixed.

[0082] Example 4

[0083] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of beta-hemihydrate phosphogypsum, 3 parts of quicklime, 8 parts of fly ash, and 1.2 parts of PEIHC-1. The water amount is determined according to the standard consistency.

[0084] The preparation method is the same as Example 3.

[0085] Example 5

[0086] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 3 parts of quicklime, 8 parts of fly ash, and 1.2 parts of PEIHC-2. The water amount is determined according to the standard consistency.

[0087] The preparation method is the same as Example 3.

[0088] Example 6

[0089] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 3 parts of quicklime, 5 parts of fly ash, and 1.2 parts of PEIHC-1. The water amount is determined according to the standard consistency.

[0090] The preparation method is the same as Example 3.

[0091] Example 7

[0092] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 3 parts of quicklime, 10 parts of fly ash, and 1.2 parts of PEIHC-1. The water amount is determined according to the standard consistency.

[0093] The preparation method is the same as Example 3.

[0094] Example 8

[0095] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 3 parts of quicklime, 8 parts of fly ash, and 0.8 part of PEIHC-1. The water amount is determined according to the standard consistency.

[0096] The preparation method is the same as Example 3.

[0097] Example 9

[0098] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 3 parts of quicklime, 8 parts of fly ash, and 2 parts of PEIHC-1. The water amount is determined according to the standard consistency.

[0099] The preparation method is the same as Example 3.

[0100] Example 10

[0101] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 8 parts of Portland cement, 8 parts of fly ash, and 1.2 parts of PEIHC-1. The water amount is determined according to the standard consistency.

[0102] The preparation method is the same as Example 3.

[0103] Example 11

[0104] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 2.5 parts of Portland cement, 2 parts of quicklime, 8 parts of fly ash, and 2 parts of PEIHC-1. The water amount is determined according to the standard consistency.

[0105] The preparation method is the same as Example 3.

[0106] Comparative Example 1

[0107] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 3 parts of quicklime, 8 parts of fly ash, and 1.2 parts of PC900 polycarboxylate water reducer (produced by Jiangsu Nigao Technology Co., Ltd.). The water consumption is determined according to the standard consistency.

[0108] The preparation method is the same as Example 3.

[0109] Comparative Example 2

[0110] A phosphogypsum building material comprises the following components, calculated by mass: 100 parts of α-hemihydrate phosphogypsum, 3 parts of quicklime, and 1.2 parts of PEIHC-1. The water amount is determined according to the standard consistency.

[0111] Performance testing:

[0112] The properties of the phosphogypsum building materials obtained in the above examples and comparative examples were tested using the following test methods. The test results are shown in Table 4.

[0113] (1) Determine the water consumption for standard consistency and the initial and final setting times according to GB / T17669.4-1999.

[0114] (2) Determine the absolute dry strength of the specimen according to GB / T17669.3-1999.

[0115] (3) Water content analysis: Computrac MAX5000XL moisture analyzer was used to determine the content of gypsum adhering water and crystallization water.

[0116] (4) Pore structure analysis: The pore structure of the hardened gypsum was determined using a Pore Master-33 mercury intrusion instrument (Quanta, USA) in accordance with GB / T21650.1-2008 / ISO15901-1:205 (Determination of void size distribution and porosity of solid materials by mercury intrusion and gas adsorption method - Part 1: Mercury intrusion method).

[0117] Table 4

[0118] As can be seen from the data in the table, the unsaturated polycarboxylic acid water-reducing agent provided by the present disclosure has the effect of reducing water and retarding setting, and the effects of unsaturated polycarboxylic acid PEIHC-1 (corresponding to Example 3) and PEIHC-2 (corresponding to Example 5) are comparable. From the results, it can be seen that the amount of fly ash added has a significant effect on the setting time and mechanical strength of the material (Examples 3, 6, and 7). The more fly ash added, the longer the setting time of the material, and the strength shows a trend of first increasing and then decreasing. This is because fly ash has hydration reaction activity and can be added to gypsum to increase the strength of the hardened body; however, its activity is released as the surface glass is destroyed as the reaction proceeds. Therefore, if too much is added, the fly ash that has not fully reacted during the material setting will mainly act as filler and microaggregate, resulting in a decrease in compressive strength. The reaction process of fly ash hydration is essentially a gel process. Therefore, when the hydration reaction is more complete, the porosity (specific pore volume) of the material is lower, the pore size is smaller, and the mechanical properties are better. The more water reducer is added (Examples 8, 3, and 9), the more the mechanical strength of the material decreases first and then changes little, and the porosity changes little, while the average pore size increases. The reason is that the more water reducer is added, the stronger the retarding effect on the material, which makes the saturation of liquid calcium ions and sulfate ions insufficient, which is not conducive to the formation of crystal nuclei, thereby causing a decrease in mechanical strength. However, the more water reducer is added, the more complexes of unsaturated carboxylic acids and metal ions are formed, which act as toughening agents to fill the gaps in the material and play a partial reinforcing role, so that the mechanical strength does not decrease with the increase of water reducer. The macropores of the gel material are mainly caused by water evaporation, so the less water is used, the lower the porosity of the material, and the complexes of unsaturated carboxylic acids and metal ions can only fill small pores, so the average pore size will increase with the increase of water reducer. Compared with Comparative Example 1, the water-reducing effect and retarding effect of the unsaturated polycarboxylic acid water-reducing agent in Example 3 are better than those of the PC900 polycarboxylic acid water-reducing agent, and the mechanical properties of the obtained gel material are better. The reason is that the steric hindrance effect of the unsaturated polycarboxylic acid water-reducing agent is greater than that of the ordinary polycarboxylic acid water-reducing agent, so the dispersibility of the gypsum particles is better; since the unsaturated carboxylic acid is more acidic, it has a stronger binding ability with calcium ions, so the initial setting time of Example 2 is longer, but as the fly ash releases aluminum ions and iron ions, calcium ions are released, so the difference in the final setting time between the two is shortened; since the initial supersaturation in Comparative Example 1 is higher, the number of crystal nuclei formed is greater, which is beneficial to improving the mechanical properties, but its water consumption is large, resulting in more voids, and it is impossible to form a complex of unsaturated carboxylic acid and metal as a reinforcing filler. Therefore, under the action of two aspects, its mechanical properties are not much different from those of Example 3. Industrial Applicability

[0119] The disclosed phosphogypsum building material comprises alkaline activating material, fly ash and unsaturated carboxylic acid water reducer, which can exert its original water reducing effect and is beneficial to the Ca content in hemihydrate phosphogypsum. 2+The slow release of the agent slows setting, accelerates the dissociation and hydration of fly ash glass, and the resulting complex of unsaturated carboxylic acid and hydroxybenzoic acid acts as a filler, filling the gaps between gel crystals and reinforcing the material. Compared to conventional polycarboxylate superplasticizers, the phosphogypsum building material disclosed herein exhibits superior slow setting, and the resulting building material specimens exhibit superior mechanical properties.

Claims

1. A phosphogypsum building material, characterized in that, the water content is 50wt% - 75wt%, and it comprises the following components: 100 parts by weight of hemihydrate phosphogypsum, 2 - 8 parts by weight of alkaline activator, 5 - 10 parts by weight of fly ash, and 0.8 - 2 parts by weight of unsaturated polycarboxylate water reducer.

2. The phosphogypsum building material according to claim 1, characterized in that, the unsaturated polycarboxylate water reducer is obtained by reacting a polymer containing amino or hydroxyl group with maleic anhydride.

3. The phosphogypsum building material according to claim 2, characterized in that, the unsaturated polycarboxylate water reducer is obtained by reacting branched polyethyleneimine with maleic anhydride.

4. The phosphogypsum building material according to claim 3, characterized in that, the molar ratio of amino group to maleic anhydride in the branched polyethyleneimine is 1:(1.05 - 1.1).

5. The phosphogypsum building material according to claim 3 or 4, characterized in that, the reaction temperature is 60°C - 80°C, and the reaction time is 10min - 30min.

6. The phosphogypsum building material according to any one of claims 3 - 5, characterized in that, the number average molecular weight of the branched polyethyleneimine is 10 kDa - 30 kDa.

7. The phosphogypsum building material according to any one of claims 3 - 6, characterized in that, the amine value of the branched polyethyleneimine calculated on a dry basis is 17mg / g - 19mg / g.

8. The phosphogypsum building material according to any one of claims 1 - 7, characterized in that, the hemihydrate phosphogypsum is selected from one or both of α - type hemihydrate phosphogypsum and β - type hemihydrate phosphogypsum.

9. The phosphogypsum building material according to any one of claims 1 - 8, characterized in that, the soluble phosphorus content of the hemihydrate phosphogypsum is ≤0.1wt%, and the soluble fluorine content is ≤0.03wt%.

10. The phosphogypsum building material according to any one of claims 1 - 9, characterized in that, the moisture content of the hemihydrate phosphogypsum is ≤5wt%.

11. The phosphogypsum building material according to any one of claims 1 - 10, characterized in that, the alkaline activator is quicklime or portland cement.

12. The phosphogypsum building material according to any one of claims 1 - 11, characterized in that, the mass fraction of calcium oxide in the fly ash is 1.6wt% - 1.7wt%; and / or, the mass fraction of aluminum oxide is 25wt% - 35wt%; and / or, the mass fraction of iron(III) oxide is 3.0wt% - 3.5wt%.

13. The phosphogypsum building material according to claim 12, characterized in that, the fly ash is one or several of Class I fly ash, Class II fly ash and Class III fly ash.

14. The phosphogypsum building material according to any one of claims 1 - 13, characterized in that, the water content is equal to the water consumption determined according to the standard consistency.

15. A preparation method of the phosphogypsum building material according to any one of claims 1 - 14, characterized in that, Mix hemihydrate phosphogypsum, alkaline activator, fly ash, unsaturated polycarboxylate water reducer and water to obtain the phosphogypsum building material.

16. The phosphogypsum building material according to claim 15, characterized in that pour the alkaline activator, hemihydrate phosphogypsum, fly ash and unsaturated polycarboxylate water reducer into a stirring device for premixing, and then add water and mix evenly to obtain the phosphogypsum building material.

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