Phosphogypsum-based frost-resistant mortar

Abstract

The application relates to the field of mortar, and discloses a phosphogypsum-based anti-freezing mortar, which comprises the following components in parts by weight: cement 100 parts; water 45-55 parts; silica ash 4-5 parts; slag 40-50 parts; gypsum retarder 0.8-1.2 parts; and nano-montmorillonite powder coated modified phosphogypsum powder, the mass ratio of the nano-montmorillonite powder to the modified phosphogypsum powder to the cement being (1.2-1.5):1. The silica ash and the slag supplement the strength of the mortar, and the nano-montmorillonite powder can fill the gaps in the mortar, improve the connection tightness of the cement and the modified phosphogypsum, so that a large amount of phosphogypsum can be mixed under the condition of ensuring a certain strength, the phosphogypsum can be consumed quickly, and the storage cost and environmental pollution of the phosphogypsum can be reduced.

Description

Technical Field

[0001] This application relates to the field of mortars, and more particularly to a phosphogypsum-based antifreeze mortar. Background Technology

[0002] Phosphogypsum is a byproduct of the phosphate fertilizer industry. Producing one ton of phosphoric acid generates approximately five tons of waste residue. If phosphogypsum is stockpiled, it can easily pollute the environment due to its content of soluble phosphorus, fluorine, free acids, and other impurities. Therefore, phosphate fertilizer production companies need to establish dedicated stockpiles, which not only occupy land but also incur high costs and may damage the environment.

[0003] Currently, cement-based concrete remains the main building material for various engineering projects such as housing, municipal works, transportation, and water conservancy. However, the production of cement not only emits a large amount of CO2, but also consumes a large amount of non-renewable energy sources such as clay and coal.

[0004] The main component of undiluted phosphogypsum is CaSO2·2H2O, which does not have gelling properties. However, by calcining it at high temperature, 1.5 molecules of water of crystallization can be removed, forming hemihydrate phosphogypsum, which has certain gelling properties and solidifies rapidly upon contact with water.

[0005] The invention patent with patent number CN107686255B discloses a modified phosphogypsum and a rigid waterproof phosphogypsum mortar and its preparation method. It reduces the amount of cement by adding modified phosphogypsum as a raw material to the mortar. However, the amount of phosphogypsum added is only 1-5 wt% of the cement, which makes it impossible to efficiently utilize phosphogypsum and also makes it impossible to significantly reduce the amount of cement. Summary of the Invention

[0006] In order to improve the problem of weak bonding between mortar and aerated concrete blocks, this application provides a phosphogypsum-based antifreeze mortar.

[0007] This application provides a phosphogypsum-based antifreeze mortar, which adopts the following technical solution:

[0008] The phosphogypsum-based antifreeze mortar comprises the following components in parts by weight:

[0009] 100 parts cement;

[0010] 45-55 parts water;

[0011] 4-5 parts silica fume;

[0012] 40-50 parts of slag;

[0013] 0.8-1.2 parts of gypsum retarder;

[0014] Modified phosphogypsum powder coated with nano-montmorillonite powder, wherein the mass ratio of nano-montmorillonite powder modified phosphogypsum powder to cement is (1.2-1.5):1.

[0015] By adopting the above technical solution, cement and modified phosphogypsum are used as the main gelling materials, and silica fume improves the compressive strength of the mortar. Slag powder has potential activity under alkaline conditions, and the hydration of cement generates a certain amount of Ca(OH)2, which then generates CSH gel, optimizing the internal structure of the mortar and improving its density, which in turn helps to improve the strength of the modified phosphogypsum mortar.

[0016] Nano-montmorillonite powder has high water absorption capacity, expands after absorbing water and has a certain water retention capacity, and recovers its volume after dehydration. By coating nano-montmorillonite powder with nano-montmorillonite powder, the volume of montmorillonite expands after absorbing water, improving the density of the coating on modified phosphogypsum. Furthermore, the water retention capacity of montmorillonite reduces the contact rate between gypsum powder and water, thus providing a certain retarding effect. This reduces the amount of gypsum retarder needed, saving costs.

[0017] The small particles of montmorillonite powder can fill pores and defects in concrete, increasing its density and strength. Furthermore, montmorillonite has good dispersing properties, promoting a tight bond between cement and modified gypsum, thus improving the concrete's crack resistance and freeze-thaw resistance. This allows the mortar to maintain good strength even when large amounts of phosphogypsum are incorporated, leading to rapid consumption of the phosphogypsum and reducing storage costs and environmental pollution.

[0018] Optionally, the modified phosphogypsum powder coated with nano-montmorillonite powder is prepared as follows: 20 parts by weight of nano-montmorillonite powder are sprayed with 2-2.5 parts of a 3-4 wt% coupling agent aqueous solution under stirring conditions. After mixing evenly, undisturbed phosphogypsum powder is added and heated to 50-60℃ and stirred evenly. The mass ratio of nano-montmorillonite powder to undisturbed phosphogypsum powder is 1:(6-6.5). Then, it is calcined until dry to obtain the modified phosphogypsum powder coated with nano-montmorillonite powder.

[0019] By adopting the above technical solution, the coupling agent modifies the nano-montmorillonite powder, and then loads the nano-montmorillonite onto the original phosphogypsum powder. Then, calcination is carried out to remove 1.5 water of crystallization from the original phosphogypsum, while the nano-montmorillonite powder is loaded onto the modified gypsum powder more stably, and finally modified phosphogypsum powder coated with nano-montmorillonite powder is obtained.

[0020] Before the dehydration treatment of the original phosphogypsum powder, nano-montmorillonite is loaded with a coupling agent, which utilizes the original calcination process of the original phosphogypsum powder, simplifies the process of nano-montmorillonite coating and modification, and makes the modification convenient.

[0021] Optionally, the coupling agent is a silane coupling agent.

[0022] By employing the above technical solution, the silane coupling agent enables the nano-montmorillonite powder to be firmly coated onto the modified phosphogypsum powder, resulting in uniform coating, improved retarding effect, reduced dosage of gypsum retarder, and lower costs. Simultaneously, the modified phosphogypsum powder coated with nano-montmorillonite powder prepared using the silane coupling agent exhibits good compatibility with mortar, ensuring uniform dispersion and thus improving mortar strength.

[0023] Optionally, the calcination temperature is 160-167℃ and the calcination time is 6-12h.

[0024] By adopting the above technical solution, the low-temperature calcination method at 160-167℃ makes it difficult to decompose or passivate impurities such as phosphorus, fluorine, and organic matter in phosphogypsum, so that impurities such as phosphorus, fluorine, and organic matter are less likely to overflow and cause pollution during calcination.

[0025] Optionally, the undisturbed phosphogypsum powder is passed through a 200-mesh sieve.

[0026] By adopting the above technical solution, the particle size of the original phosphogypsum powder should not be too large or too small. If it is too large, it will easily lead to different local strengths of the mortar, resulting in a decrease in mortar strength. If it is too small, it will easily affect the coating effect of the nano montmorillonite powder.

[0027] In summary, this application includes at least one of the following beneficial technical effects:

[0028] 1. The strength of mortar is supplemented by silica fume and slag, and nano montmorillonite powder can fill the gaps in the mortar, improve the bonding tightness between cement and modified phosphogypsum, so that a large amount of phosphogypsum can be added under the condition of ensuring a certain strength, thereby quickly consuming phosphogypsum and reducing the storage cost and environmental pollution of phosphogypsum.

[0029] 2. After nano-montmorillonite is coated on the surface of modified phosphogypsum, it slows down the efficiency of the modified phosphogypsum in contact with water, thereby slowing down the setting of the modified phosphogypsum, making it easier to construct, and preventing the mortar from setting too quickly during construction, which would cause delamination when applying two layers of mortar.

[0030] 3. Before the dehydration treatment of the original phosphogypsum powder, nano-montmorillonite is loaded with a coupling agent, which utilizes the original calcination process of the original phosphogypsum powder, simplifies the process of nano-montmorillonite coating and modification, makes modification convenient, and reduces the cost of the modification process.

[0031] 4. The silane coupling agent more firmly coats the nano-montmorillonite powder onto the modified phosphogypsum powder, thus improving the retarding effect. The modified phosphogypsum powder coated with nano-montmorillonite powder prepared by the silane coupling agent has good compatibility with the mortar, resulting in uniform dispersion and thus improving the strength of the mortar. Detailed Implementation

[0032] The present application will be further described in detail below with reference to Examples 1-7 and Comparative Examples 1-5.

[0033] Raw material name

[0034] The cement is PO42.5 silicate cement; the slag is S95 grade granulated blast furnace slag powder; the silica fume is microsilica powder sold by Gongyi Aochuang Building Materials Co., Ltd., with a silicon content greater than or equal to 97%; the nano montmorillonite powder is Mengchuang Jiamu brand, model MCJM-01; the gypsum retarder is sold by Jinan Binhai Trading Co., Ltd., model sghnj; the undisturbed phosphogypsum powder passes through a 200-mesh sieve. The silane coupling agents are KH-550 and KH-560, and the titanate coupling agent is NXH-401.

[0035] Example

[0036] Example 1

[0037] The phosphogypsum-based antifreeze mortar comprises the following components by weight:

[0038] 100kg of cement;

[0039] Water 45kg;

[0040] 4 kg of silica fume;

[0041] 40kg of slag;

[0042] 0.8 kg of gypsum retarder;

[0043] Modified phosphogypsum powder coated with nano-montmorillonite powder, wherein the mass ratio of nano-montmorillonite powder modified phosphogypsum powder to cement is 1.2:1.

[0044] The modified phosphogypsum powder coated with nano-montmorillonite powder was prepared by the following method: 20 kg of nano-montmorillonite powder was sprayed with 2 kg of 3wt% KH-550 aqueous solution under stirring conditions, and after being stirred and mixed evenly, 120 kg of undisturbed phosphogypsum powder was added, heated to 60℃ and stirred evenly. The mass ratio of nano-montmorillonite powder to undisturbed phosphogypsum powder was 1:6. Then, it was calcined at 160℃ for 12 h to completely dry, thus obtaining the modified phosphogypsum powder coated with nano-montmorillonite powder.

[0045] The phosphogypsum-based antifreeze mortar is prepared by the following method: cement is added to a mixer according to the required mass, then water is added and mixed evenly. Slag and gypsum retarder are added and mixed evenly. Finally, modified phosphogypsum powder coated with nano-montmorillonite powder is added and mixed evenly to prepare the phosphogypsum-based antifreeze mortar.

[0046] Example 2

[0047] The phosphogypsum-based antifreeze mortar comprises the following components by weight:

[0048] 100kg of cement;

[0049] Water 55kg;

[0050] 5 kg of silica fume;

[0051] 50kg of slag;

[0052] 1.2 kg of gypsum retarder;

[0053] The modified phosphogypsum powder coated with nano-montmorillonite powder has a mass ratio of nano-montmorillonite powder modified phosphogypsum powder to cement of 1.5:1.

[0054] The modified phosphogypsum powder coated with nano-montmorillonite powder was prepared by the following method: 20 kg of nano-montmorillonite powder was sprayed with 2.5 kg of 4 wt% KH-550 aqueous solution under stirring conditions. After stirring and mixing evenly, 130 kg of undisturbed phosphogypsum powder was added and heated to 60°C and stirred evenly. The mass ratio of nano-montmorillonite powder to undisturbed phosphogypsum powder was 1:6.5. Then, it was calcined at 167°C for 6 hours to completely dry, thus obtaining the modified phosphogypsum powder coated with nano-montmorillonite powder.

[0055] The phosphogypsum-based antifreeze mortar is prepared by the following method: cement is added to a mixer according to the required mass, then water is added and mixed evenly. Slag and gypsum retarder are added and mixed evenly. Finally, modified phosphogypsum powder coated with nano-montmorillonite powder is added and mixed evenly to prepare the phosphogypsum-based antifreeze mortar.

[0056] Example 3

[0057] The phosphogypsum-based antifreeze mortar comprises the following components by weight:

[0058] 100kg of cement;

[0059] 50kg of water;

[0060] 4.6 kg of silica fume;

[0061] 43 kg of slag;

[0062] 1 kg of gypsum retarder;

[0063] Modified phosphogypsum powder coated with nano-montmorillonite powder, wherein the mass ratio of nano-montmorillonite powder modified phosphogypsum powder to cement is 1.4:1.

[0064] The modified phosphogypsum powder coated with nano-montmorillonite powder was prepared by the following method: 20 kg of nano-montmorillonite powder was sprayed with 2.2 kg of 3.7 wt% KH-550 aqueous solution under stirring conditions. After stirring and mixing evenly, 126 kg of undisturbed phosphogypsum powder was added and heated to 56°C and stirred evenly. The mass ratio of nano-montmorillonite powder to undisturbed phosphogypsum powder was 1:6.3. Then, it was calcined at 164°C for 10 h to completely dry, thus obtaining the modified phosphogypsum powder coated with nano-montmorillonite powder.

[0065] The phosphogypsum-based antifreeze mortar is prepared by the following method: cement is added to a mixer according to the required mass, then water is added and mixed evenly. Slag and gypsum retarder are added and mixed evenly. Finally, modified phosphogypsum powder coated with nano-montmorillonite powder is added and mixed evenly to prepare the phosphogypsum-based antifreeze mortar.

[0066] Example 4,

[0067] The difference from Example 3 is that KH-550 is replaced with an equal amount of KH-560.

[0068] Example 5

[0069] The difference from Example 3 is that KH-560 is replaced with an equal amount of NXH-401.

[0070] Example 6

[0071] The difference from Example 3 is that the mass ratio of nano-montmorillonite powder to undisturbed phosphogypsum powder is 1:8.

[0072] Example 7

[0073] The difference from Example 3 is that the mass ratio of nano-montmorillonite powder to undisturbed phosphogypsum powder is 1:3.

[0074] Comparative Example

[0075] Comparative Example 1

[0076] The difference from Example 3 is that no slag is added.

[0077] Comparative Example 2

[0078] The difference from Example 3 is that the amount of slag added is 60 kg.

[0079] Comparative Example 3

[0080] The difference from Example 3 is that no silica fume is added.

[0081] Comparative Example 4

[0082] The difference from Example 3 is that the nano-montmorillonite powder does not coat the modified phosphogypsum powder. The original phosphogypsum powder is directly calcined at 165°C for 8 hours to obtain modified phosphogypsum powder. Then, equal masses of nano-montmorillonite powder and modified phosphogypsum powder are directly added to the mortar and stirred until uniform.

[0083] Comparative Example 5

[0084] The difference from Comparative Example 4 is that no nano-montmorillonite powder was added.

[0085] Performance testing

[0086] Mortar setting time determination: According to the construction industry standard "Standard for Test Methods of Basic Performance of Building Mortar" (JGJ / T70—2009), the initial setting time and final setting time of cement mortar were determined respectively, and the results are recorded in Table 1.

[0087] Compressive strength test: The compressive strength was tested using a 40mm×40mm×40mm test block and a pressure testing machine. The results are recorded in Table 1.

[0088] For the frost resistance test, the test block cured for 28 days was frozen at -20℃ for 24 hours, then placed at room temperature, and the compressive strength was tested. The change rate of compressive strength after freezing was calculated using the following formula: Change rate of compressive strength after freezing = (28-day room temperature compressive strength - frozen temperature compressive strength) / 28-day room temperature compressive strength * 100%. The results are recorded in Table 1.

[0089] Table 1

[0090]

[0091] As can be seen from Examples 1-3 and Table 1, the modified phosphogypsum is incorporated in a large amount in this application. The mortar is reinforced by silica fume, slag and nano montmorillonite powder, resulting in good strength. This facilitates the consumption of a large amount of modified phosphogypsum, reducing the storage cost and environmental pollution of phosphogypsum.

[0092] As can be seen from Examples 3, 4, and 5 and Table 1, compared with NXH-401, KH-550 and KH-560 are better able to firmly bond nano-montmorillonite powder to the surface of modified phosphogypsum powder, and make the modified phosphogypsum powder compatible with mortar, which makes it easier for the mortar to maintain good strength and frost resistance.

[0093] Based on Examples 3 and 6-7 and Table 1, it can be seen that when the mass ratio of nano-montmorillonite powder to undisturbed phosphogypsum powder is 1:6.3, the amount of nano-montmorillonite powder is reasonable and does not easily affect the strength of the mortar. At the same time, the nano-montmorillonite powder is evenly coated on the surface of the modified phosphogypsum powder, which has a good retarding effect.

[0094] As can be seen from Example 3 and Comparative Examples 1-2 and Table 1, the addition of slag can effectively improve the strength of mortar. However, when too much slag is added, it will actually damage the strength of the mortar.

[0095] Combining Example 3 and Comparative Example 3 with Table 1, it can be seen that the silica fume material has fine particles, a large specific surface area, and contains a large amount of SiO2. During the hydration process, it reacts preferentially to generate additional CSH gel, which facilitates the improvement of the compressive strength of the mortar matrix.

[0096] As can be seen from Example 3 and Comparative Example 4, and Table 1, directly adding nano-montmorillonite powder to mortar cannot retard the setting of modified phosphogypsum, and at the same time reduces the strength of the mortar. This is mainly because after nano-montmorillonite is coated on the surface of modified phosphogypsum, it slows down the efficiency of the modified phosphogypsum in contact with water, thereby slowing down the setting of modified phosphogypsum. At the same time, the modified phosphogypsum powder coated with nano-montmorillonite powder prepared by silane coupling agent has good compatibility with mortar, making it evenly dispersed, thereby improving the strength of mortar.

[0097] Based on Comparative Examples 4-5 and Table 1, it can be seen that the addition of nano-montmorillonite powder alone does not significantly improve the setting effect of modified phosphogypsum, but it can improve the strength and freeze-thaw resistance of mortar to a certain extent.

[0098] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A phosphogypsum-based antifreeze mortar, characterized in that, Includes the following components in parts by weight: 100 parts cement; 45-55 parts water; 4-5 parts silica fume; 40-50 parts of slag powder; 0.8-1.2 parts of gypsum retarder; Modified phosphogypsum powder coated with nano-montmorillonite powder, wherein the mass ratio of nano-montmorillonite powder modified phosphogypsum powder to cement is (1.2-1.5):1; The preparation method of the modified phosphogypsum powder coated with nano-montmorillonite powder is as follows: 20 parts by weight of nano-montmorillonite powder are sprayed with 2-2.5 parts of 3-4wt% coupling agent aqueous solution under stirring conditions. After stirring and mixing evenly, the original phosphogypsum powder is added and heated to 50-60℃ and stirred evenly. The mass ratio of nano-montmorillonite powder to original phosphogypsum powder is 1:(6-6.5). Then, it is calcined to dryness to obtain the modified phosphogypsum powder coated with nano-montmorillonite powder. The coupling agent is a silane coupling agent; The calcination temperature is 160-167℃, and the calcination time is 6-12h; the raw phosphogypsum powder passes through a 200-mesh sieve.

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