Phosphogypsum-based self-leveling mortar based on recycled concrete and preparation method of phosphogypsum-based self-leveling mortar

Abstract

The invention relates to the technical field of ardealite-based self-leveling mortar, in particular to ardealite-based self-leveling mortar based on recycled concrete and a preparation method of the ardealite-based self-leveling mortar. The phosphogypsum-based self-leveling mortar based on the recycled concrete is prepared from the following raw materials in parts by mass: 41 to 106 parts of II type anhydrous gypsum, 3.3 to 6.6 parts of recycled aggregate, 2.5 to 7.5 parts of cement, 0.5 to 2.5 parts of active filler, 2.5 to 5 parts of fly ash, 0.5 to 5 parts of glass beads, 0.5 to 1.5 parts of hyperbranched polyester, 0.1 to 1 part of graphene oxide, 0.01 to 0.15 part of glutaraldehyde, 0.01 to 0.1 part of lanthanum nitrate, 1 to 2 parts of calcium chloride, 0.5 to 1.5 parts of sodium tripolyphosphate, 1 to 2 parts of dispersing agent, 1 to 2 parts of water-retaining agent and 1 to 2 parts of stabilizer. 1-2 parts of a retarder, 1-2 parts of a defoaming agent, 1-2 parts of a water reducing agent and 0.01-0.1 part of an air entraining agent. The ardealite-based self-leveling mortar takes the II-type anhydrite and the recycled aggregate as main raw materials, and the obtained ardealite-based self-leveling mortar has the advantages of low shrinkage and high strength.

Description

Technical Field

[0001] The present invention relates to the technical field of phosphogypsum-based self-leveling mortar, and particularly relates to a phosphogypsum-based self-leveling mortar based on recycled concrete and a preparation method thereof. Background Art

[0002] Self-leveling mortar is mainly composed of cementitious materials, aggregates and admixtures, etc., and has good fluidity and stability, and the construction speed is fast. It is widely used in floor leveling construction of schools, hospitals, factories, office buildings, etc. At present, self-leveling mortar can be divided into two categories: cement-based and gypsum-based according to different cementitious materials. Among them, gypsum-based self-leveling mortar is considered to be a more promising building material due to its advantages such as light weight, fast setting and hardening, and good stability.

[0003] However, with the expansion of the application fields of gypsum, its resources have also begun to be in short supply. Existing gypsum-based self-leveling mortar mostly uses quartz sand as a filler, and has relatively high quality requirements for quartz sand, increasing the production cost. Recycled aggregate is a new type of environmentally friendly building material that uses waste concrete as raw material and is processed by processes such as crushing, washing and grading, and partially or completely replaces natural aggregate. Its core lies in realizing the resource utilization of construction waste. If recycled aggregate can be used to replace quartz sand in gypsum-based self-leveling mortar, the production cost can be further reduced, and it is more competitive in terms of economy.

[0004] If recycled aggregate is used in gypsum-based self-leveling mortar, although the cost can be reduced, the main problems faced are poor compressive strength, poor freeze-thaw resistance, and easy shrinkage and cracking, which become a major pain point restricting its wide application and an important factor limiting the application of recycled aggregate in gypsum-based self-leveling mortar. Summary of the Invention

[0005] The purpose of the present invention is to solve the disadvantages existing in the prior art, and to provide a phosphogypsum-based self-leveling mortar based on recycled concrete and a preparation method thereof.

[0006] A phosphogypsum-based self-leveling mortar based on recycled concrete, the raw materials of which include, by mass: 41-106 parts of type II anhydrous gypsum, 3.3-6.6 parts of recycled aggregate, 2.5-7.5 parts of cement, 0.5-2.5 parts of active filler, 2.5-5 parts of fly ash, 0.5-5 parts of expanded perlite, 0.5-1.5 parts of hyperbranched polyester, 0.1-1 part of graphene oxide, 0.01-0.15 part of glutaraldehyde, 0.01-0.1 part of lanthanum nitrate, 1-2 parts of calcium chloride, 0.5-1.5 parts of sodium tripolyphosphate, 1-2 parts of dispersant, 1-2 parts of water retention agent, 1-2 parts of stabilizer, 1-2 parts of retarder, 1-2 parts of defoamer, 1-2 parts of water reducing agent, 0.01-0.1 part of air entraining agent.

[0007] Preferably, type II anhydrous gypsum is made from phosphogypsum as raw material.

[0008] Preferably, the cement is ordinary Portland cement with a strength grade of 42.5.

[0009] Preferably, the vitrified microspheres have a particle size of 50 - 70 mesh, a bulk density of 140 - 148 kg / m 3 , a thermal conductivity of 0.06 - 0.07 W / (m·K), and a volume water absorption rate of 24 - 26%.

[0010] Preferably, the dispersant is sodium dodecyl sulfate.

[0011] Preferably, the active filler is activated alumina or / and activated silica, and its particle size is 300 - 400 mesh.

[0012] Preferably, the water retention agent is hydroxypropyl methyl cellulose ether, and its viscosity at 25°C is 5000 - 7000 mPa·s.

[0013] Preferably, the retarder is degraded calcium polyamide.

[0014] Preferably, the water reducer is a polycarboxylate superplasticizer, and the water reduction rate is 28 - 30%.

[0015] Preferably, the defoamer is dimethyl silicone oil and / or polypropylene glycol.

[0016] Preferably, the stabilizer is one of BASF Starvis 3003F, stabilizer TAB - 2, and stabilizer T - 386.

[0017] Preferably, the air - entraining agent is one of Clariant air - entraining agent AE - 80, ZS - 109A concrete air - entraining agent, and air - entraining agent 22076.

[0018] The above - mentioned method for preparing phosphogypsum - based self - leveling mortar based on recycled concrete includes the following steps:

[0019] S1. Add hyperbranched polyester and graphene oxide into N,N - dimethylformamide, stir at 40 - 50°C for 20 - 40 min, add aqueous glutaraldehyde solution thereto, stir at 60 - 80°C for 10 - 30 min, filter, wash, vacuum - dry, and add type II anhydrous gypsum, recycled aggregate, cement, and active filler and stir evenly to obtain a dry - mixed material;

[0020] S2. Add the water retention agent, stabilizer, retarder, defoamer, water reducer, and air - entraining agent into water and mix evenly to obtain a mixed material;

[0021] S3. Add fly ash to water and ultrasonically treat for 20 - 40 min. Add lanthanum nitrate and calcium chloride thereto and continue ultrasonically treating for 1 - 2 h. Add sodium tripolyphosphate and a dispersant thereto, stir at 60 - 80 °C for 5 - 10 h, filter, calcine at 300 - 400 °C for 20 - 30 min, cool to room temperature, pulverize and sieve, and sequentially add a mixture, a dry mix, and vitrified microspheres and stir for 10 - 30 min.

[0022] Preferably, in S3, the ultrasonic frequency is 20 - 30 kHz.

[0023] Beneficial effects:

[0024] The present invention uses dendritic macromolecular hyperbranched polyester to coat graphene oxide, and uses glutaraldehyde to promote the cross-linking reaction between the two, which can not only improve the stability, but also be compounded with type II anhydrous gypsum, recycled aggregate, cement, and active filler, so that the highly branched macromolecular chain segment structure on the surface can be fully dispersed in the system and form a network structure during the gel hardening process, thereby enabling the system to quickly coagulate. The product not only has excellent setting time, but also is not easy to shrink and crack.

[0025] Since the surface of fly ash is negatively charged, the present invention uses it to adsorb lanthanum and calcium ions, and the adsorption strength is relatively high. Under the action of sodium tripolyphosphate, lanthanum and calcium ions form chemical bonds on fly ash, with high bonding strength and uniform loading. After high-temperature calcination, the product is compounded with the dry mix, which can significantly improve the compressive strength of the phosphogypsum-based self-leveling mortar after hydration and hardening, and has excellent freeze-thaw resistance, making it easier for the phosphogypsum-based self-leveling mortar to meet the standard requirements of JC / T 1023 - 2007 "Gypsum-based Self-leveling Mortar".

[0026] The present invention also uses the cooperation of the dry mix and a water retention agent (hydroxypropyl methylcellulose ether). Not only is the water retention of the self-leveling more excellent, but also during water retention and thickening, the physical and chemical co-crosslinking network formed between hydroxypropyl methylcellulose ether and the dry mix improves the construction stability and reduces the cost.

[0027] The present invention uses type II anhydrous gypsum and recycled aggregate as the main raw materials, which not only realizes the recycling of solid waste resources, is beneficial to saving resources and production costs, but also the obtained phosphogypsum-based self-leveling mortar has the advantages of low shrinkage and high strength. Description of the drawings

[0028] Figure 1 It is a comparison chart of the initial setting time and final setting time of the phosphogypsum-based self-leveling mortar obtained in Example 5 and Comparative Examples 1 - 2.

[0029] Figure 2 It is a comparison chart of the 24-hour flexural strength and 24-hour compressive strength of the phosphogypsum-based self-leveling mortar obtained in Example 5 and Comparative Examples 1 - 2.

[0030] Figure 3 The comparison chart of the 28-day absolute dry flexural strength and 28-day absolute dry compressive strength of the phosphogypsum-based self-leveling mortar obtained in Example 5 and Comparative Examples 1-2.

[0031] Figure 4 The comparison chart of the 28-day dried tensile bond strength and dimensional change rate of the phosphogypsum-based self-leveling mortar obtained in Example 5 and Comparative Examples 1-2.

[0032] Figure 5 The comparison chart of the number of freeze-thaw cycles of the phosphogypsum-based self-leveling mortar obtained in Example 5 and Comparative Examples 1-2. Detailed implementation manners

[0033] The following type II anhydrous gypsum used is purchased from Hubei Yifu Jinchu New Materials Co., Ltd. and made from phosphogypsum. The following recycled aggregate used is purchased from Guizhou Panshi Gaoke New Materials Co., Ltd. with a particle size < 4.75 mm. The following hyperbranched polyester used is purchased from Shanghai Huicheng Biotechnology Co., Ltd. with the brand number H40. The following expanded perlite used is purchased from Hebei Jiegui Mineral Products Co., Ltd. with a particle size of 50 mesh and a bulk density of 145 kg / m 3 , a thermal conductivity of 0.06 W / (m·K), and a volume water absorption rate of 25%. The following calcium salt of degraded polyamide used is from Italian company SICIT2000 with the model PLAST RETARD PE. The following polycarboxylate superplasticizer used is purchased from Kunming Shengwei Concrete Admixture Co., Ltd.

[0034] The present invention will be further illustrated below with specific examples.

[0035] Example 1

[0036] A phosphogypsum-based self-leveling mortar based on recycled concrete, the raw materials of which include: 4100 g of type II anhydrous gypsum, 330 g of recycled aggregate, 250 g of P.O. 42.5 ordinary Portland cement, 50 g of 400-mesh activated alumina, 250 g of class II fly ash, 50 g of expanded perlite, 50 g of hyperbranched polyester, 10 g of graphene oxide, 1 g of glutaraldehyde, 1 g of lanthanum nitrate, 100 g of calcium chloride, 50 g of sodium tripolyphosphate, 100 g of sodium dodecyl sulfate, 100 g of hydroxypropyl methyl cellulose ether, 100 g of stabilizer TAB-2, 100 g of calcium salt of degraded polyamide, 100 g of dimethyl silicone oil, 100 g of polycarboxylate superplasticizer, and 1 g of ZS-109A concrete air-entraining agent.

[0037] The preparation method of the above phosphogypsum-based self-leveling mortar based on recycled concrete includes the following steps:

[0038] S1. Add hyperbranched polyester and graphene oxide into 2000 g of N,N-dimethylformamide, stir at 40 °C for 20 min, add an aqueous solution of glutaraldehyde with a mass fraction of 1%, stir at 60 °C for 10 min, filter, wash successively with water and absolute ethanol, dry in vacuum, add type II anhydrous gypsum, recycled aggregate, P.O.42.5 ordinary Portland cement, and activated alumina, and stir evenly to obtain a dry mixture;

[0039] S2. Add hydroxypropyl methyl cellulose ether, stabilizer TAB-2, calcium salt of degraded polyamide, dimethyl silicone oil, polycarboxylate superplasticizer, and ZS-109A concrete air-entraining agent into water and mix evenly to obtain a mixture;

[0040] S3. Add class II fly ash into deionized water and ultrasonically treat for 20 min at an ultrasonic frequency of 20 kHz. Add lanthanum nitrate and calcium chloride and continue to ultrasonically treat for 1 h. Add sodium tripolyphosphate and sodium dodecyl sulfate, stir at 60 °C for 5 h, filter, calcine at 300 °C for 20 min, cool to room temperature, crush and pass through a 100-mesh sieve, and successively add the mixture, the dry mixture, and expanded perlite, and stir at a speed of 20 r / min for 10 min.

[0041] Example 2

[0042] A phosphogypsum-based self-leveling mortar based on recycled concrete, the raw materials of which include: 10600 g of type II anhydrous gypsum, 660 g of recycled aggregate, 750 g of P.O.42.5 ordinary Portland cement, 250 g of 400-mesh activated silica, 500 g of class II fly ash, 500 g of expanded perlite, 150 g of hyperbranched polyester, 100 g of graphene oxide, 15 g of glutaraldehyde, 10 g of lanthanum nitrate, 200 g of calcium chloride, 150 g of sodium tripolyphosphate, 200 g of sodium dodecyl sulfate, 200 g of hydroxypropyl methyl cellulose ether, 200 g of stabilizer T-386, 200 g of calcium salt of degraded polyamide, 200 g of dimethyl silicone oil, 200 g of polycarboxylate superplasticizer, and 10 g of ZS-109A concrete air-entraining agent.

[0043] The preparation method of the above-mentioned phosphogypsum-based self-leveling mortar based on recycled concrete includes the following steps:

[0044] S1. Add hyperbranched polyester and graphene oxide into 4000 g of N,N-dimethylformamide, stir at 50 °C for 40 min, add an aqueous solution of glutaraldehyde with a mass fraction of 3%, stir at 80 °C for 30 min, filter, wash successively with water and absolute ethanol, dry in vacuum, add type II anhydrous gypsum, recycled aggregate, P.O.42.5 ordinary Portland cement, and activated silica, and stir evenly to obtain a dry mixture;

[0045] S2. Add hydroxypropyl methylcellulose ether, stabilizer T-386, calcium salt of degraded polyamide, dimethyl silicone oil, polycarboxylate superplasticizer, and ZS-109A concrete air-entraining agent into water and mix evenly to obtain a mixture.

[0046] S3. Add Class II fly ash into deionized water and perform ultrasonic treatment for 40 min at an ultrasonic frequency of 30 kHz. Add lanthanum nitrate and calcium chloride thereto and continue ultrasonic treatment for 2 h. Add sodium tripolyphosphate and sodium dodecyl sulfate thereto, stir at 80 °C for 10 h, filter, calcine at 400 °C for 30 min, cool to room temperature, pulverize and pass through a 100-mesh sieve, and sequentially add the mixture, dry mixture, and vitrified microspheres, and stir at a speed of 50 r / min for 30 min.

[0047] Example 3

[0048] A phosphogypsum-based self-leveling mortar based on recycled concrete, the raw materials of which include: 7700 g of type II anhydrous gypsum, 580 g of recycled aggregate, 400 g of P.O. 42.5 ordinary Portland cement, 200 g of 400-mesh activated alumina, 350 g of Class II fly ash, 350 g of vitrified microspheres, 75 g of hyperbranched polyester, 70 g of graphene oxide, 50 g of glutaraldehyde, 70 g of lanthanum nitrate, 120 g of calcium chloride, 125 g of sodium tripolyphosphate, 120 g of sodium dodecyl sulfate, 170 g of hydroxypropyl methylcellulose ether, 120 g of BASF Starvis 3003F, 170 g of calcium salt of degraded polyamide, 120 g of polypropylene glycol, 170 g of polycarboxylate superplasticizer, and air-entraining agent 220762 g.

[0049] The preparation method of the above-mentioned phosphogypsum-based self-leveling mortar based on recycled concrete includes the following steps:

[0050] S1. Add hyperbranched polyester and graphene oxide into 3500 g of N,N-dimethylformamide, stir at 42 °C for 35 min, add an aqueous solution of 1% glutaraldehyde thereto, stir at 75 °C for 15 min, filter, wash successively with water and absolute ethanol, dry in vacuum, and add type II anhydrous gypsum, recycled aggregate, P.O. 42.5 ordinary Portland cement, and activated alumina and stir evenly to obtain a dry mixture.

[0051] S2. Add hydroxypropyl methylcellulose ether, BASF Starvis 3003F, calcium salt of degraded polyamide, polypropylene glycol, polycarboxylate superplasticizer, and air-entraining agent XP 22076 into water and mix evenly to obtain a mixture.

[0052] S3. Add Class II fly ash into deionized water and ultrasonically treat it for 35 min at an ultrasonic frequency of 21 kHz. Add lanthanum nitrate and calcium chloride into it and continue ultrasonic treatment for 100 min. Add sodium tripolyphosphate and sodium dodecyl sulfate into it, stir at 65 °C for 9 h, filter, calcine at 330 °C for 28 min, cool to room temperature, crush and sieve through a 100-mesh sieve. Then add the mixture, dry blend, and vitrified microspheres in sequence, and stir at a speed of 30 r / min for 25 min.

[0053] Example 4

[0054] A phosphogypsum-based self-leveling mortar based on recycled concrete, the raw materials of which include: 7200 g of type II anhydrous gypsum, 410 g of recycled aggregate, 600 g of P.O. 42.5 ordinary Portland cement, 100 g of 400-mesh activated silica, 450 g of Class II fly ash, 150 g of vitrified microspheres, 125 g of hyperbranched polyester, 30 g of graphene oxide, 10 g of glutaraldehyde, 3 g of lanthanum nitrate, 180 g of calcium chloride, 75 g of sodium tripolyphosphate, 180 g of sodium dodecyl sulfate, 130 g of hydroxypropyl methylcellulose ether, 180 g of BASF Starvis 3003F, 130 g of calcium salt of degraded polyamide, 180 g of polypropylene glycol, 130 g of polycarboxylate superplasticizer, air-entraining agent 220768 g.

[0055] The preparation method of the above-mentioned phosphogypsum-based self-leveling mortar based on recycled concrete comprises the following steps:

[0056] S1. Add hyperbranched polyester and graphene oxide into 2500 g of N,N-dimethylformamide, stir at 48 °C for 25 min, add an aqueous solution of glutaraldehyde with a mass fraction of 3% into it, stir at 65 °C for 25 min, filter, wash successively with water and absolute ethanol, dry in vacuum, and add type II anhydrous gypsum, recycled aggregate, P.O. 42.5 ordinary Portland cement, and activated silica and stir evenly to obtain a dry blend;

[0057] S2. Mix hydroxypropyl methylcellulose ether, BASF Starvis 3003F, calcium salt of degraded polyamide, polypropylene glycol, polycarboxylate superplasticizer, and air-entraining agent XP 22076 into water and mix evenly to obtain a mixture;

[0058] S3. Add class II fly ash to deionized water and ultrasonically treat it for 25 min at an ultrasonic frequency of 27 kHz. Add lanthanum nitrate and calcium chloride to it and continue ultrasonic treatment for 80 min. Add sodium tripolyphosphate and sodium dodecyl sulfate to it, stir at 75 °C for 7 h, filter, calcine at 370 °C for 22 min, cool to room temperature, crush and sieve through a 100-mesh sieve, and sequentially add the mixture, dry mixture, and vitrified microspheres, and stir at a speed of 40 r / min for 15 min.

[0059] Example 5

[0060] A phosphogypsum-based self-leveling mortar based on recycled concrete, the raw materials of which include: 7200 g of type II anhydrous gypsum, 500 g of recycled aggregate, 500 g of P.O. 42.5 ordinary Portland cement, 150 g of 400-mesh activated alumina, 400 g of class II fly ash, 200 g of vitrified microspheres, 100 g of hyperbranched polyester, 50 g of graphene oxide, 8 g of glutaraldehyde, 5 g of lanthanum nitrate, 150 g of calcium chloride, 100 g of sodium tripolyphosphate, 150 g of sodium dodecyl sulfate, 150 g of hydroxypropyl methyl cellulose ether, 150 g of BASF Starvis 3003F, 150 g of calcium salt of degraded polyamide, 150 g of polypropylene glycol, 150 g of polycarboxylate superplasticizer, and 5 g of Clariant air-entraining agent AE-80.

[0061] The preparation method of the above-mentioned phosphogypsum-based self-leveling mortar based on recycled concrete includes the following steps:

[0062] S1. Add hyperbranched polyester and graphene oxide to 3000 g of N,N-dimethylformamide, stir at 45 °C for 30 min, add an aqueous solution of glutaraldehyde with a mass fraction of 1-3% to it, stir at 70 °C for 20 min, filter, wash successively with water and absolute ethanol, dry in vacuum, and add type II anhydrous gypsum, recycled aggregate, P.O. 42.5 ordinary Portland cement, and activated alumina and stir evenly to obtain a dry mixture;

[0063] S2. Add hydroxypropyl methyl cellulose ether, BASF Starvis 3003F, calcium salt of degraded polyamide, polypropylene glycol, polycarboxylate superplasticizer, and air-entraining agent to water and mix evenly to obtain a mixture;

[0064] S3. Add class II fly ash to deionized water and ultrasonically treat it for 30 min at an ultrasonic frequency of 24 kHz. Add lanthanum nitrate and calcium chloride to it and continue ultrasonic treatment for 90 min. Add sodium tripolyphosphate and sodium dodecyl sulfate to it, stir at 70 °C for 8 h, filter, calcine at 350 °C for 25 min, cool to room temperature, crush and sieve through a 100-mesh sieve, and sequentially add the mixture, dry mixture, and vitrified microspheres, and stir at a speed of 35 r / min for 20 min.

[0065] Comparative Example 1

[0066] A phosphogypsum-based self-leveling mortar based on recycled concrete, the raw materials of which include: 7200 g of type II anhydrous gypsum, 500 g of recycled aggregate, 500 g of P.O. 42.5 ordinary Portland cement, 150 g of 400-mesh activated alumina, 400 g of class II fly ash, 200 g of expanded perlite, 100 g of hyperbranched polyester, 50 g of graphene oxide, 5 g of lanthanum nitrate, 150 g of calcium chloride, 100 g of sodium tripolyphosphate, 150 g of sodium dodecyl sulfate, 150 g of hydroxypropyl methylcellulose ether, 150 g of BASF Starvis 3003F, 150 g of calcium salt of degraded polyamide, 150 g of polypropylene glycol, 150 g of polycarboxylate superplasticizer, and 5 g of Clariant air-entraining agent AE-80.

[0067] The preparation method of the above phosphogypsum-based self-leveling mortar based on recycled concrete comprises the following steps:

[0068] S1. Add hyperbranched polyester and graphene oxide to type II anhydrous gypsum, recycled aggregate, P.O. 42.5 ordinary Portland cement, and activated alumina, and stir evenly to obtain a dry mixture.

[0069] S2. Add hydroxypropyl methylcellulose ether, BASF Starvis 3003F, calcium salt of degraded polyamide, polypropylene glycol, polycarboxylate superplasticizer, and air-entraining agent to water and mix evenly to obtain a mixed material.

[0070] S3. Add class II fly ash to deionized water and ultrasonically treat it for 30 min at an ultrasonic frequency of 24 kHz. Add lanthanum nitrate and calcium chloride thereto and continue ultrasonic treatment for 90 min. Add sodium tripolyphosphate and sodium dodecyl sulfate thereto, stir at 70 °C for 8 h, filter, calcine at 350 °C for 25 min, cool to room temperature, pulverize and pass through a 100-mesh sieve, and successively add the mixed material, the dry mixture, and expanded perlite, and stir at a speed of 35 r / min for 20 min.

[0071] Comparative Example 2

[0072] A phosphogypsum-based self-leveling mortar based on recycled concrete, the raw materials of which include: 7200 g of type II anhydrous gypsum, 500 g of recycled aggregate, 500 g of P.O. 42.5 ordinary Portland cement, 150 g of 400-mesh activated alumina, 400 g of class II fly ash, 200 g of vitrified microspheres, 100 g of hyperbranched polyester, 50 g of graphene oxide, 8 g of glutaraldehyde, 155 g of calcium chloride, 100 g of sodium tripolyphosphate, 150 g of sodium dodecyl sulfate, 150 g of hydroxypropyl methyl cellulose ether, 150 g of BASF Starvis 3003F, 150 g of degraded polyamide calcium salt, 150 g of polypropylene glycol, 150 g of polycarboxylate superplasticizer, and 5 g of Clariant air-entraining agent AE-80.

[0073] The preparation method of the above-mentioned phosphogypsum-based self-leveling mortar based on recycled concrete comprises the following steps:

[0074] S1. Add hyperbranched polyester and graphene oxide into 3000 g of N,N-dimethylformamide, stir at a temperature of 45 °C for 30 min, add an aqueous solution of glutaraldehyde with a mass fraction of 1-3% thereto, stir at a temperature of 70 °C for 20 min, filter, wash successively with water and absolute ethanol, dry in vacuum, and add type II anhydrous gypsum, recycled aggregate, P.O. 42.5 ordinary Portland cement, and activated alumina and stir evenly to obtain a dry mixture;

[0075] S2. Add hydroxypropyl methyl cellulose ether, BASF Starvis 3003F, degraded polyamide calcium salt, polypropylene glycol, polycarboxylate superplasticizer, and air-entraining agent into water and mix evenly to obtain a mixed material;

[0076] S3. Add class II fly ash into deionized water and ultrasonically treat for 30 min, with an ultrasonic frequency of 24 kHz, add calcium chloride thereto and continue ultrasonically treating for 90 min, add sodium tripolyphosphate and sodium dodecyl sulfate thereto, stir at a temperature of 70 °C for 8 h, filter, calcine at a temperature of 350 °C for 25 min, cool to room temperature, crush and pass through a 100-mesh sieve, and successively add the mixed material, the dry mixture, and vitrified microspheres, and stir at a speed of 35 r / min for 20 min.

[0077] Refer to JC / T 1023-2007 "Gypsum-based Self-leveling Mortar" to measure the initial setting time, final setting time, 24-hour flexural strength, 24-hour compressive strength, 28-day absolute dry flexural strength, 28-day absolute dry compressive strength, 28-day dried tensile bond strength, and dimensional change rate of the phosphogypsum-based self-leveling mortar obtained in Example 5 and Comparative Examples 1-2 respectively.

[0078] As Figures 1 to 4As shown, the initial setting time and final setting time of the phosphogypsum-based self-leveling mortar obtained in Example 5 are the shortest, the dimensional change rate is the smallest, while the 24-hour flexural strength, 24-hour compressive strength, 28-day absolute dry flexural strength, 28-day absolute dry compressive strength, and 28-day dried tensile bond strength are the highest, superior to Comparative Examples 1-2 (P < 0.05).

[0079] Refer to the slow freezing method in GB / T 50082-2009 "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete" to conduct the frost resistance test and test the number of freeze-thaw cycles of the phosphogypsum-based self-leveling mortar obtained in Example 5 and Comparative Examples 1-2.

[0080] As Figure 5 shown, the number of freeze-thaw cycles of the phosphogypsum-based self-leveling mortar obtained in Example 5 is the largest and the frost resistance is the best, superior to Comparative Examples 1-2 (P < 0.05).

[0081] The applicant believes that: This is because the present invention uses dendritic macromolecular hyperbranched polyester to coat graphene oxide and uses glutaraldehyde to promote the cross-linking reaction between the two, which can not only improve the stability but also be compounded with type II anhydrous gypsum, recycled aggregate, cement, and active filler, so that the highly branched macromolecular chain segments on the surface can be fully dispersed in the system and form a network structure during the gel hardening process, thereby enabling the system to coagulate rapidly. The product not only has excellent setting time but also is not prone to shrinkage and cracking. At the same time, since fly ash has a negative charge on its surface, the present invention uses it to adsorb lanthanum and calcium ions with a relatively high adsorption strength, and under the action of sodium tripolyphosphate, lanthanum and calcium ions form a chemical bond on fly ash with a high bonding strength and uniform loading. After high-temperature calcination, the product is compounded with the dry-mixed material, which can significantly improve the compressive strength of the phosphogypsum-based self-leveling after hydration and hardening, and has excellent frost resistance and thawing resistance.

[0082] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A phosphogypsum-based self-leveling mortar based on recycled concrete, characterized in that: The raw materials include, by mass, 41-106 parts of type II anhydrous gypsum, 3.3-6.6 parts of recycled aggregate, 2.5-7.5 parts of cement, 0.5-2.5 parts of active filler, 2.5-5 parts of fly ash, 0.5-5 parts of vitrified microspheres, 0.5-1.5 parts of hyperbranched polyester, 0.1-1 parts of graphene oxide, 0.01-0.15 parts of glutaraldehyde, 0.01-0.1 parts of lanthanum nitrate, 1-2 parts of calcium chloride, 0.5-1.5 parts of sodium tripolyphosphate, 1-2 parts of dispersant, 1-2 parts of water retaining agent, 1-2 parts of stabilizer, 1-2 parts of retarder, 1-2 parts of defoaming agent, 1-2 parts of water reducing agent and 0.01-0.1 parts of air entraining agent.

2. The phosphogypsum-based self-leveling mortar based on recycled concrete according to claim 1, characterized in that: The particle size of the vitrified microspheres is 50-70 mesh and the bulk density is 140-148 kg / m 3 , thermal conductivity is 0.06-0.07W / (m·K), and volume water absorption is 24-26%.

3. The phosphogypsum-based self-leveling mortar based on recycled concrete according to claim 1, characterized in that: The dispersant is sodium lauryl sulfate.

4. The phosphogypsum-based self-leveling mortar based on recycled concrete according to claim 1, characterized in that: The active filler is active alumina and / or active silicon oxide, and its particle size is 300-400 meshes.

5. The phosphogypsum-based self-leveling mortar based on recycled concrete according to claim 1, characterized in that: The water retaining agent is hydroxypropyl methylcellulose ether, and its viscosity at 25°C is 5000-7000mPa.s.

6. The phosphogypsum-based self-leveling mortar based on recycled concrete according to claim 1, characterized in that: The retarder is a degraded polyamide calcium salt.

7. The phosphogypsum-based self-leveling mortar based on recycled concrete according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid high performance water reducing agent with a water reducing rate of 28-30%.

8. The phosphogypsum-based self-leveling mortar based on recycled concrete according to claim 1, characterized in that: The defoaming agent is dimethyl silicone oil and / or polypropylene glycol.

9. A method for preparing phosphogypsum-based self-leveling mortar based on recycled concrete according to any one of claims 1 to 8, characterized in that: The steps include: S1. Add hyperbranched polyester and graphene oxide to N,N-dimethylformamide, stir at 40-50° C. for 20-40 min, add glutaraldehyde aqueous solution thereto, stir at 60-80° C. for 10-30 min, filter, wash, vacuum dry, add type II anhydrous gypsum, recycled aggregate, cement, and active filler, and stir evenly to obtain a dry mix; S2, adding a water retaining agent, a stabilizer, a retarder, a defoaming agent, a water reducing agent, and an air entraining agent into water and mixing them evenly to obtain a mixture; S3. Add fly ash into water and ultrasonically treat it for 20-40 minutes, add lanthanum nitrate and calcium chloride thereto and continue ultrasonically treating it for 1-2 hours, add sodium tripolyphosphate and dispersant thereto, stir at 60-80°C for 5-10 hours, filter, calcine at 300-400°C for 20-30 minutes, cool to room temperature, crush and sieve, add mixed material, dry mixed material and vitrified microspheres in turn and stir for 10-30 minutes.

10. The method for preparing phosphogypsum-based self-leveling mortar based on recycled concrete according to claim 9, characterized in that: In S3, the ultrasound frequency is 20-30kHz.

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