Geopolymer-oriented delayed coagulation and viscosity reduction type phosphate group micromolecular water reducing agent and preparation method thereof

Abstract

The preparation method comprises the following steps: carrying out free radical addition polymerization on a phosphoric acid small monomer consisting of ethylene phosphoric acid, vinyl phosphate and cis-propenyl phosphoric acid and unsaturated polyoxyethylene ether under the action of a chain transfer agent and an initiator under inert shielding gas to obtain the geopolymer-oriented delayed coagulation and viscosity reduction type phosphoric acid small molecular water reducing agent, wherein the free radical addition polymerization is carried out on the phosphoric acid small monomer consisting of ethylene phosphoric acid, vinyl phosphate and cis-propenyl phosphoric acid and the unsaturated polyoxyethylene ether, so as to obtain the geopolymer-oriented delayed coagulation and viscosity reduction type phosphoric acid small molecular water reducing agent. And adjusting the pH value to 6.0-7.0 by using an alkali solution to obtain the retarding and viscosity reducing type phosphate group small molecule water reducing agent. According to the present invention, the water reducing agent has strong adsorption performance and strong retarding and viscosity reducing performance in the geopolymer system, the unsaturated polyoxyethylene ether is adopted as the macromonomer of the water reducing agent, the side chain can provide the steric hindrance effect after the polymerization so as to achieve the dispersion effect, and the synergistic effect of the unsaturated polyoxyethylene ether and the water reducing agent achieves the retarding and viscosity reducing purposes in the geopolymer.

Description

Technical Field

[0001] The invention relates to the technical field of high-efficiency water reducing agents for green building materials, and specifically to a slow-setting and viscosity-reducing phosphate-based small-molecule water reducing agent for geopolymers and a preparation method thereof, which has the effects of water reduction, slow setting, and viscosity reduction, and can be used in a multi-component geopolymer system. Background Art

[0002] Geopolymer is a three-dimensional mesh cementitious material generated by the reaction of aluminosilicate precursors and alkali activators. It has the characteristics of high strength, good durability, fire resistance and high temperature resistance, and the utilization of industrial solid waste. It is considered to be an ideal substitute for cement. However, the high viscosity of geopolymer leads to its poor fluidity and too fast setting time. These performance problems limit its wide application. High-efficiency water reducer is known as the fifth component of concrete and is often used to improve the working performance and mechanical properties of cement concrete. However, high-efficiency water reducer performs poorly in geopolymer, mainly because the high alkalinity of the alkali activator affects the structural stability and adsorption capacity of the water reducer. At present, no effective water reducer suitable for geopolymer has been developed.

[0003] Some water reducers in the prior art have slow setting or viscosity reducing effects. Patent CN 109053974 B discloses a method for preparing a viscosity reducing polycarboxylic acid water reducer, which is obtained by copolymerizing a dibasic acid monomer, a polyether macromonomer, and a viscosity reducing aid. Patent CN 112940198 B discloses a method for preparing a slow setting polycarboxylic acid water reducer, which is obtained by phosphorylating and unsaturating monosaccharides and copolymerizing them with polyether macromonomers.

[0004] However, the method of introducing viscosity reducing and slow setting groups in the above invention is relatively complicated, and its product also performs poorly in the high alkaline environment of geopolymer. The molecular weight of the common water reducer on the market is more than 20,000, which either does not work on geopolymer or sometimes even causes its viscosity to increase. In order to solve the performance problem of geopolymer caused by high viscosity, the present invention synthesizes a small molecule water reducer by adding unsaturated phosphoric acid and unsaturated polyether, and utilizes the joint action of mercaptopropionic (ethyl) acid, phosphoric acid compound and vitamin E chain transfer effect. The synthesized small molecule water reducer can play the effect of water reduction, slow setting and viscosity reduction in geopolymer. In addition, the synthesis method of the present invention is environmentally friendly, convenient, suitable for industrial production, and has excellent applicability in geopolymer, filling the gap in geopolymer water reducer. Summary of the invention

[0005] In view of the situation that the existing geopolymer materials are affected by poor working performance and the poor adaptability of the existing high-efficiency water reducers to geopolymers and the complicated preparation process, the technical problem to be solved by the present invention is to provide a slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers and a preparation method, which uses phosphate groups as adsorption groups to provide extremely strong adsorption and slow-setting effects. The combined effect of the chain transfer effect of mercaptopropionic (ethyl) acid, phosphate compounds and vitamin E can control the reaction to generate a small molecule water reducer, and the molecular weight of the final product is controlled within 11,000, especially around 5,000. The smaller molecular weight makes the water reducer more flexible and stable in high-viscosity and high-alkalinity geopolymers without crosslinking or entanglement, and the structure is stable, the effect is excellent, and the working performance of multi-element geopolymers is greatly improved, especially, and the market prospect is broad.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] A method for preparing a slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers, the method comprising the following steps: subjecting a small phosphate monomer consisting of vinyl phosphate, vinyl phosphate ester and cis-allyl phosphate to free radical addition polymerization with an unsaturated polyoxyethylene ether under the action of a chain transfer agent and an initiator under an inert protective gas, and then adjusting the pH to 6.0-7.0 with an alkaline solution to obtain a slow-setting and viscosity-reducing phosphate-based small molecule water reducer.

[0008] In the above preparation method, a preservative may be added at the end.

[0009] Furthermore, the specific steps of the preparation method are:

[0010] (1) introducing an inert protective gas into a reaction container to exhaust the air in the reaction container, adding unsaturated polyoxyethylene ether and water into the reaction container, and stirring until the unsaturated polyoxyethylene ether is completely dissolved;

[0011] (2) If the initiator is only peroxide, the dissolved unsaturated polyoxyethylene ether is heated to 60-80°C; the phosphoric acid small monomer, chain transfer agent and chain transfer auxiliary agent are dissolved in water as solution A, and are added dropwise to the reaction container in batches using a constant flow pump, and each addition time is 30-50 minutes; at the same time, the initiator is dissolved in water as solution B and is added dropwise to the reaction container in batches using a constant flow pump, and the addition time is 40-60 minutes; after each batch of addition is completed, the reaction is continued at 60-80°C for 30-60 minutes of heat preservation and stirring;

[0012] If the initiator is composed of a peroxide and a reducing substance, then solution A and solution B are added dropwise at room temperature, that is, the phosphoric acid small monomer, the chain transfer agent, and the chain transfer auxiliary agent are dissolved in water as solution A, and a constant flow pump is used to dropwise add the solution to the reaction container in batches, and each dropwise addition time is 30 to 50 minutes; at the same time, the initiator is dissolved in water as solution B, and a constant flow pump is used to dropwise add the solution to the reaction container in batches, and the dropwise addition time is 40 to 60 minutes; after each batch of dropwise addition is completed, the reaction is continued to be stirred for 30 to 60 minutes;

[0013] (3) Add dropwise and stir the mixture until the reaction is complete, stop heating, cool to room temperature, stop introducing the inert protective gas, adjust the pH value to 6.0-7.0 with an alkaline solution, and then add a preservative to obtain a slow-setting and viscosity-reducing phosphate-based small molecule water reducer.

[0014] Furthermore, the chain transfer agent is at least one of thioglycolic acid, mercaptopropionic acid, and the like.

[0015] The chain transfer aid is vitamin E; the preservative is at least one of potassium sorbate, calcium propionate, parabens, sodium diacetate, etc.

[0016] The peroxide is at least one of persulfate, hydrogen peroxide, etc.;

[0017] The reducing substance is at least one of sodium bisulfite, L-ascorbic acid, and the like.

[0018] The present invention also protects the slow-setting and viscosity-reducing phosphate-based small-molecule water-reducing agent for geopolymers obtained by the preparation method.

[0019] Furthermore, the water reducing agent is composed of the following in terms of the amount of substance:

[0020] Component A: 25-50 parts of vinyl phosphoric acid, 25 parts of vinyl phosphate, 25 parts of cis-allyl phosphoric acid;

[0021] Component B: 25-50 parts of unsaturated polyoxyethylene ether;

[0022] Component C: 8-10 parts of chain transfer agent, 1-2 parts of chain transfer aid vitamin E;

[0023] Component D: 4-10 parts of initiator;

[0024] Component E: alkaline solution, adjust the system pH to 6.0-7.0;

[0025] Component F: 0.8-1.2 parts of preservative.

[0026] Furthermore, the molecular weight of the slow-setting and viscosity-reducing phosphate-based small molecule water reducer is 4000-11000, and the solid content of the water reducer is 20%-30%; preferably, the molecular weight distribution PDI is 1.4-1.6.

[0027] The invention protects a geopolymer mortar, wherein the geopolymer mortar adopts the slow-setting and viscosity-reducing phosphate-based small molecule water reducer, and the addition amount of the slow-setting and viscosity-reducing phosphate-based small molecule water reducer is 1-3% of the mass of the cementitious material in the geopolymer mortar; the cementitious material is the sum of fly ash, slag and steel slag.

[0028] Furthermore, the fluidity of the geopolymer mortar is increased by more than 55%, the final setting time is extended by more than 140%, and the viscosity is reduced by more than 30%.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The molecular weight of the slow-setting and viscosity-reducing phosphate-based small molecule water reducer of the present invention is controlled within 11,000, preferably about 5,000 (4,000-6,000), and is prepared by the addition polymerization of unsaturated phosphate small monomers such as vinyl phosphate, vinyl phosphate ester, and cis-allyl phosphate with unsaturated polyether macromonomers. The special type of phosphate small monomer serves as an adsorption group, which can provide stronger adsorption performance and slow-setting and viscosity-reducing performance in the geopolymer system. The unsaturated polyoxyethylene ether serves as a macromonomer of the water reducer, and its side chain can provide steric hindrance after polymerization to achieve a dispersion effect. The synergistic effect of the two achieves the purpose of slow-setting and viscosity-reducing in the geopolymer.

[0031] (2) In the formula of the present invention, under the synergistic chain transfer effect of multiple phosphoric acid compounds, mercaptopropionic (ethyl) acid and vitamin E, and prepared by batch dropwise addition, the molecular weight of the water reducer can be controlled to be 4000-6000, and the molecular weight distribution is narrow (PDI is 1.4-1.6). The water reducer has a stable structure and strong adsorption. The adsorption amount in geopolymer is about twice that of the existing phosphoric acid-based water reducer. The higher adsorption amount brings better dispersion effect and water reduction effect. At the same time, a large amount of small phosphoric acid monomers makes the water reducer have excellent retarding effect.

[0032] (3) The present invention has strong stability and its structure does not change in the sodium silicate solution. The solid content of the water reducer of the present invention is 20%-30%. When the dosage is 2%, the water reduction rate is 15%-25%.

[0033] (4) The high-efficiency water-reducing agent prepared in Example 1, at a dosage of 2%, increases the fluidity of fly ash-slag-steel slag multi-element geopolymer mortar by more than 80%, prolongs the final setting time by more than 250%, reduces the viscosity by more than 40%, and improves the 7d and 28d compressive strength of the geopolymer to a certain extent. This proves that the water-reducing agent of the present invention is a rare water-reducing agent suitable for geopolymer systems, which can effectively improve the working performance of geopolymers without reducing the compressive strength, solves the construction pain points of fast setting and poor fluidity of geopolymers, and has broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a comparison chart of the test results of the adsorption amount of the water reducing agent prepared in Examples 1-2 and Comparative Examples 1-4 in geopolymer.

[0035] Figure 2 The infrared spectrum stability test diagrams of Example 1 and Comparative Example 1 in a high alkaline environment, wherein (a) is the infrared spectrum diagram of the water reducer of Example 1; and (b) is the infrared spectrum diagram of the water reducer of Comparative Example 1. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below in conjunction with the embodiments and drawings, but this is not intended to limit the scope of protection of the present application. The contents presented are only some embodiments of the present invention, not all embodiments.

[0037] The mechanism of action of the water reducer of the present invention is as follows: the phosphoric acid monomer composed of vinyl phosphoric acid, vinyl phosphate ester and cis-allyl phosphoric acid has a high charge density, and its adsorption effect with the cations on the surface of the geopolymer precursor particles is stronger and more reliable, thus solving the problem of low adsorption of the traditional water reducer and the geopolymer precursor material. The phosphoric acid group has extremely strong hydrophilicity and can increase the hydrophilic-lipophilic balance value of the water reducer, thereby improving the viscosity reduction effect of the water reducer. In addition, the phosphoric acid compound can be adsorbed on the surface of the precursor material particles to form a layer of insoluble film, which prevents further reaction of the particles and slows down the reaction speed, thereby achieving an excellent retarding effect. More importantly, the phosphate compound has a certain chain transfer property. Under the joint action of mercaptopropionic acid and vitamin E, the reaction can be controlled to generate a small molecule water reducer. The molecular weight of the product is around 11,000. The molecular weight can be further controlled to be around 4,000-6,000. The smaller molecular weight makes the water reducer more flexible and stable in high-viscosity, high-alkalinity geopolymers without cross-linking or entanglement. The synergistic effect with vitamin E significantly improves the stability of the water reducer.

[0038] The slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers of the present invention comprises the following components in terms of molar mass:

[0039] Component A: 25-50 parts of vinyl phosphoric acid, 25 parts of vinyl phosphate, 25 parts of cis-allyl phosphoric acid;

[0040] Component B: 25-50 parts of unsaturated polyoxyethylene ether;

[0041] Component C: 8-10 parts of chain transfer agent, 1-2 parts of chain transfer aid vitamin E;

[0042] Component D: 4-10 parts of initiator, at least one of peroxides such as ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, etc., can be used, and reducing substances can also be added thereto, such as a redox system composed of hydrogen peroxide and L-ascorbic acid, or a redox system composed of ammonium persulfate and sodium bisulfite as the initiator, and heating and heat preservation treatment is not required at this time;

[0043] Component E: alkaline solution, adjust the system pH to 6.0-7.0;

[0044] Component F: 0.8-1.2 parts of preservative.

[0045] The unsaturated polyoxyethylene ether may be selected from at least one of APEG, HPEG, VPEG, TPEG, etc., and the molecular weight may be selected from 2000 to 3200.

[0046] The chain transfer agent can be at least one of mercaptoacetic acid, mercaptopropionic acid, etc. The chain transfer synergistic effect of the phosphoric acid monomer, mercaptopropionic (ethyl) acid, and vitamin E can control the requirement of small molecular weight and improve the stability and antioxidant properties of the polymer.

[0047] The alkaline solution can be a strong alkaline solution such as sodium hydroxide or potassium hydroxide;

[0048] The preservative is at least one of potassium sorbate, calcium propionate, parabens, sodium diacetate and the like.

[0049] The specific steps of the preparation method of the above-mentioned water reducing agent are:

[0050] (1) introducing an inert protective gas into a reaction container to exhaust the air in the reaction container, adding unsaturated polyoxyethylene ether and water into the reaction container, and stirring until the unsaturated polyoxyethylene ether is completely dissolved;

[0051] (2) If the initiator is only peroxide, the dissolved unsaturated polyoxyethylene ether is heated to 60-80°C; the phosphoric acid small monomer, chain transfer agent and chain transfer auxiliary agent are dissolved in water as solution A, and are added dropwise to the reaction container in batches using a constant flow pump, and each addition time is 30-50 minutes; at the same time, the initiator is dissolved in water as solution B and is added dropwise to the reaction container in batches using a constant flow pump, and the addition time is 40-60 minutes; after each batch of addition is completed, the reaction is continued at 60-80°C for 30-60 minutes of heat preservation and stirring;

[0052] If the initiator is composed of a peroxide and a reducing substance, then solution A and solution B are added dropwise at room temperature, that is, the phosphoric acid small monomer, the chain transfer agent, and the chain transfer auxiliary agent are dissolved in water as solution A, and a constant flow pump is used to dropwise add the solution to the reaction container in batches, and each dropwise addition time is 30 to 50 minutes; at the same time, the initiator is dissolved in water as solution B, and a constant flow pump is used to dropwise add the solution to the reaction container in batches, and the dropwise addition time is 40 to 60 minutes; after each batch of dropwise addition is completed, the reaction is continued to be stirred for 30 to 60 minutes;

[0053] (3) Add dropwise and stir the mixture until the reaction is complete, stop heating, cool to room temperature, stop introducing the inert protective gas, adjust the pH value to 6.0-7.0 with an alkaline solution, and then add a preservative to obtain a slow-setting and viscosity-reducing phosphate-based small molecule water reducer.

[0054] In the preparation method of the present invention, it is preferred to drip solution A and solution B in batches at the same time, and the dripping time of solution B is longer, and the batches of the two are the same, which is conducive to the reaction to generate a water reducer with a smaller molecular weight and a narrower molecular weight distribution (i.e., the size of each molecule is similar). When other chain transfer aids (such as potassium sulfite and isopropanol) are used in the present invention, the treatment effect on the geopolymer is poor.

[0055] Example 1

[0056] The slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers in this embodiment has the following amounts of raw materials:

[0057] Component A: 50 parts of ethylene phosphoric acid, 25 parts of vinyl phosphate, and 25 parts of cis-allyl phosphoric acid.

[0058] Component B: 50 parts of APEG with a molecular weight of 2400.

[0059] Component C: 8 parts of mercaptopropionic acid, 2 parts of vitamin E.

[0060] Component D: 4 parts each of hydrogen peroxide and L-ascorbic acid.

[0061] Component E: 1M sodium hydroxide solution.

[0062] Component F: 1 part of potassium sorbate.

[0063] The preparation process is: nitrogen is introduced into a three-necked flask, APEG and water are added after 15 minutes, and stirred at room temperature until completely dissolved. Three small phosphoric acid monomers, mercaptopropionic acid, and vitamin E are dissolved in water as solution A, and a constant flow pump is used to drop them into the reaction container 4 times, and each drop time is 50 minutes; at the same time, hydrogen peroxide and L-ascorbic acid are dissolved in water as solution B, and are dropped into the reaction container 4 times, and each drop time is 60 minutes; each time solution A and solution B are dropped at the same time, and the drop time of solution B is longer. After each drop is completed, stir the reaction for 30 minutes. After all the drops are completed and the stirring reaction is completed, stop stirring, stop ventilation, neutralize with 1M sodium hydroxide solution until the pH value is 6.5-7.0, and then add 1 part of potassium sorbate to obtain the water reducer.

[0064] Example 2

[0065] The slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers in this embodiment has the following amounts of raw materials:

[0066] Component A: 50 parts of ethylene phosphoric acid, 25 parts of vinyl phosphate, and 25 parts of cis-allyl phosphoric acid.

[0067] Component B: 33 parts of APEG with a molecular weight of 2400.

[0068] Component C: 8 parts of mercaptopropionic acid, 2 parts of vitamin E.

[0069] Component D: 4 parts of ammonium persulfate.

[0070] Component E: sodium hydroxide solution.

[0071] Component F: 1 part of potassium sorbate.

[0072] The preparation process is as follows: nitrogen is introduced into a three-necked flask, and APEG and water are added after 15 minutes, heated to 80°C, and stirred until completely dissolved; maintaining this temperature, three small phosphate monomers, mercaptopropionic acid, and vitamin E are dissolved in water as solution A, and a constant flow pump is used to drop them into the reaction vessel 4 times, each time for 50 minutes; at the same time, ammonium persulfate is dissolved in water as solution B, and is added to the reaction vessel 4 times, each time for 60 minutes. After each drop is completed, keep warm and stir to react for 30 minutes. After all the drops are added and the reaction is completed by keeping warm and stirring, stop heating and stirring, and stop ventilation; neutralize with 1M sodium hydroxide solution until the pH value is 6.5-7.0, and then add 1 part of potassium sorbate.

[0073] Example 3

[0074] The raw material composition and preparation process of the slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers in this embodiment are the same as those in Example 2, except that in this embodiment, component B uses 25 parts of APEG with a molecular weight of 2800, and each drop is added with insulation and stirring for 60 minutes.

[0075] Example 4

[0076] The raw material composition and preparation process of the slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers in this embodiment are the same as those in Example 3, except that in this embodiment, 8 parts of thioglycolic acid are used as the chain transfer agent, and 4 parts of potassium persulfate are used as the D component. Each drop is added with insulation and stirring for 45 minutes.

[0077] Example 5

[0078] The raw material composition and preparation process of the slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers in this embodiment are the same as those in Example 1, except that in this embodiment, the chain transfer agent is 8 parts of thioglycolic acid, and the B component is 25 parts of TPEG with a molecular weight of 2400, and each addition is carried out dropwise and stirred for 30 minutes.

[0079] Example 6

[0080] The raw material composition and preparation process of the slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers in this embodiment are the same as those in Example 4, except that, in this embodiment, the chain transfer agent is 10 parts of mercaptopropionic acid and 1 part of vitamin E, the B component is 30 parts of VPEG with a molecular weight of 2800 and 4 parts of ammonium persulfate, the insulation temperature is 70° C., and the mixture is added dropwise in two batches, and each batch is kept warm and stirred for reaction for 30 minutes.

[0081] Example 7

[0082] The raw material composition and preparation process of the slow-setting and viscosity-reducing phosphate-based small molecule water reducer in this embodiment are the same as those in Example 1, except that component A is 30 parts of vinyl phosphoric acid, 25 parts of vinyl phosphate, and 25 parts of cis-allyl phosphoric acid. In this embodiment, 4 parts of ammonium persulfate and 4 parts of sodium bisulfite are used as initiators, and the dropping process is also completed at room temperature.

[0083] Comparative Example 1

[0084] This comparative example synthesizes a phosphate-based water reducer, and the preparation process is the same as in Example 1. The amount of each material is as follows:

[0085] Component A: 50 parts of acrylic acid; 50 parts of diethyl vinyl phosphate.

[0086] Component B: 30 parts of APEG with a molecular weight of 2400.

[0087] Component C: 8 parts of mercaptopropionic acid and 2 parts of vitamin E.

[0088] Component D: 4 parts each of hydrogen peroxide and L-ascorbic acid.

[0089] Component E: 1M sodium hydroxide solution.

[0090] Compared with Example 1, this comparative example selects different types of small phosphoric acid monomers (vinyl diethyl phosphate) and acrylic acid for use together, and its water reducing agent performance is poor.

[0091] Comparative Example 2

[0092] This comparative example synthesizes a phosphate-based water reducer, and the preparation process is the same as in Example 1. The amount of each material is as follows:

[0093] Component A: 50 parts of ethylene phosphoric acid, 25 parts of vinyl phosphate, and 25 parts of cis-allyl phosphoric acid.

[0094] Component B: 50 parts of APEG with a molecular weight of 2400.

[0095] Component C: 8 parts of mercaptopropionic acid.

[0096] Component D: 4 parts each of hydrogen peroxide and L-ascorbic acid.

[0097] Component E: 1M sodium hydroxide solution.

[0098] Component F: 1 part of potassium sorbate.

[0099] In this comparative example, vitamin E is not added relative to Example 1.

[0100] Comparative Example 3

[0101] This comparative example synthesizes a phosphate-based water reducer, and the preparation process is the same as in Example 1. The amount of each material is as follows:

[0102] Component A: 50 parts of ethylene phosphoric acid, 25 parts of vinyl phosphate, and 25 parts of cis-allyl phosphoric acid.

[0103] Component B: 50 parts of APEG with a molecular weight of 2400.

[0104] Component C: 8 parts of benzoyl peroxide, 2 parts of vitamin E.

[0105] Component D: 4 parts each of hydrogen peroxide and L-ascorbic acid.

[0106] Component E: 1M sodium hydroxide solution.

[0107] Component F: 1 part of potassium sorbate.

[0108] In this comparative example, when benzoyl peroxide is selected as the chain transfer agent, the performance is significantly reduced relative to that of Example 1.

[0109] Comparative Example 4

[0110] The formula of the water reducer in this comparative example is the same as that in Example 1, except that the preparation process is as follows: nitrogen is introduced into a three-necked flask, and APEG and water are added after 15 minutes, and stirred until completely dissolved; three small phosphate monomers, mercaptopropionic acid, and vitamin E are dissolved in water as solution A, and a constant flow pump is used to drop them into the reaction vessel for 2 hours; at the same time, hydrogen peroxide and L-ascorbic acid are dissolved in water as solution B, and are added dropwise to the reaction vessel for 2.5 hours. After the addition is complete, stirring is continued for 2 hours. After the reaction is completed, stirring and ventilation are stopped; the obtained water reducer is neutralized with 1M sodium hydroxide solution until the pH value is 6.5-7.0, and then 1 part of potassium sorbate is added.

[0111] This comparative example adopts a one-time feeding method relative to Example 1, and the effect of the batch addition process relative to Example 1 is poor.

[0112] In the present invention, the synthesized water reducer is directly added to the stirred geopolymer slurry, or it can be dissolved in water first and added together with water. The water reducer of the present invention has excellent effect on the geopolymer system. The molecular weight of the embodiment measured by gel permeation chromatography is around 5000. It has excellent retarding effect and good fluidity improvement effect on the gelling material. At the same time, it significantly reduces the plastic viscosity and yield stress of the geopolymer, and has almost no adverse effect on the compressive strength. In order to verify the effect of the water reducer in the geopolymer, the following experiment was carried out.

[0113] The water reducing agent prepared in the above embodiment was added into geopolymer to test its effect, which is as follows:

[0114] (1) 30 parts (by weight) of fly ash, 50 parts of slag, 20 parts of steel slag, 4 parts of quartz powder, 36 parts of quartz sand, and 8 parts of anhydrous sodium silicate were added to a cement mortar mixer and mixed thoroughly by slow stirring for 2 minutes to obtain a dry material.

[0115] (2) Dissolve 2 parts of water reducer in 32 parts of water, add to dry materials, and stir slowly for 2 minutes. Pause for 15 seconds, scrape the remaining material on the pot wall with a scraper, and stir quickly for 2 minutes. After stirring, use a jumping table to measure the fluidity and a Vicat instrument to measure the setting time. Put the geopolymer mortar into a 50*50*50mm cubic mold, vibrate and compact it, and cure it in an environment of 20℃ for 3 days, 7 days, and 28 days. Use a compression machine to measure its unconfined compressive strength. The specific data are as follows:

[0116] Table 1 Effect of water reducer on geopolymer performance

[0117]

[0118]

[0119] From the above data, it can be seen that when the water reducer of the present invention is applied to geopolymer, it has excellent slow setting and viscosity reduction effects, and greatly improves the setting time of geopolymer mortar. In Example 1, a 2% water reducer can increase the fluidity of the geopolymer by 80%, delay the final setting time by more than 250%, reduce the viscosity by more than 40%, and improve the 7d and 28d compressive strength of the geopolymer by 1.4% and 2.0%, respectively. The fluidity of the geopolymer in the embodiment is above 230mm, preferably 240-270mm; the final setting time is above 220min, preferably 240-320min; the viscosity is controlled below 2.0Pa·s, preferably below 1.8Pa·s; and the 28d compressive strength is maintained at about 90MPa.

[0120] Compared with the four groups of comparative examples, the present invention performs well in terms of improved working performance, reduced viscosity, and improved compressive strength. The comparison results show that the small molecule water reducer synthesized by the chain transfer synergistic effect of phosphoric acid small monomer, mercaptopropionic (ethyl) acid, and vitamin E in the present invention has an excellent effect in geopolymers. At the same time, the batch dropwise addition process adopted by the present invention also significantly improves the effect of the water reducer in geopolymers under the same conditions.

[0121] Table 2 compares the size and distribution of the molecular weight of each group. It can be seen that the molecular weight of the water reducer synthesized in the embodiment of the present invention is around 5000 and the molecular weight distribution is narrow, which is one of the reasons why the present invention has excellent effect.

[0122] Table 2 Molecular weight and distribution of some groups

[0123] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 <![CDATA[M W (g / mol)]]> 5106 4988 39100 15695 20840 10170 PDI 1.41 1.48 1.95 1.72 1.85 2.21

[0124] Weigh 10g of fly ash-slag-steel slag geopolymer, 0.8g of anhydrous sodium silicate, and 1g of high-efficiency water reducer into a volumetric flask and add deionized water. Stir the slurry with a magnetic stirrer for 5min, 10min, 15min, and 30min, then filter (using a 0.45μm filter membrane), and use a total organic carbon analyzer (TOC) to determine the organic carbon content of the filtrate. The adsorption amount of the water reducer can be calculated by the concentration difference before and after adsorption. The results are as follows: Figure 1 As shown. The adsorption amount of Example 1 of the present invention in 30 minutes is 21.3 mg / g, which is the highest among all groups. However, the adsorption amount of Comparative Example 1 in geopolymer is only 11.2 mg / g, which is about half of that of the embodiment. The adsorption amounts of the remaining comparative examples are also significantly lower than those of the embodiment. The excellent adsorption amount ensures the excellent effect of the water reducer of the present invention in geopolymer.

[0125] The stability of the water reducer of the present invention in a highly alkaline environment was analyzed by infrared spectroscopy. Taking Example 1 and Comparative Example 1 as examples, the water reducer was placed in a 20wt% sodium silicate solution for 2h and then compared with the water reducer structure not placed in the alkaline solution. The results are as follows: Figure 2 . Figure 2 (a) is the infrared spectrum of Example 1. The infrared characteristic peak of the P=O bond is 1140-1300cm -1 , compared with before and after being placed in the alkaline solution, this part of the characteristic peaks has almost no change, indicating that the water reducer of Example 1 has good stability. Figure 2 (b) is the infrared spectrum of comparative example 1, 1597cm -1 It is the infrared characteristic peak of carboxylate. After being placed in alkaline solution, the characteristic peak shifts significantly, indicating that the structure of the water reducer has changed and its alkaline stability is poor.

[0126] The present invention describes some embodiments. Any deformation and modification of these embodiments without departing from the principle of the present invention are equivalent to the present invention and are included in the protection scope of the present invention.

[0127] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for preparing a slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers, characterized in that: The preparation method comprises the following contents: Under inert protective gas, free radical addition polymerization is carried out on phosphoric acid monomers composed of vinyl phosphoric acid, vinyl phosphate ester and cis-allyl phosphoric acid and unsaturated polyoxyethylene ether under the action of chain transfer agent and initiator, and then the pH is adjusted to 6.0-7.0 with alkaline solution to obtain a slow-setting and viscosity-reducing phosphoric acid-based small molecule water reducer.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the vinyl phosphoric acid, vinyl phosphate and cis-allyl phosphoric acid is 1-2:1:

1.

3. The preparation method according to claim 1, characterized in that: The molar number of the unsaturated polyoxyethylene ether is 1 / 4 to 1 / 2 of the total molar number of the phosphoric acid small monomer; the unsaturated polyoxyethylene ether is at least one of APEG, HPEG, VPEG or TPEG, and the preferred molecular weight is 2000 to 3200; the alkaline solution is at least one of sodium hydroxide and potassium hydroxide.

4. The preparation method according to claim 1, characterized in that: The specific steps of the preparation method are: (1) introducing an inert protective gas into a reaction container to exhaust the air in the reaction container, adding unsaturated polyoxyethylene ether and water into the reaction container, and stirring until the unsaturated polyoxyethylene ether is completely dissolved; (2) If the initiator is only peroxide, the dissolved unsaturated polyoxyethylene ether is heated to 60-80°C; the phosphoric acid small monomer, chain transfer agent and chain transfer auxiliary agent are dissolved in water as solution A, and are added dropwise to the reaction container in batches using a constant flow pump, and each addition time is 30-50 minutes; at the same time, the initiator is dissolved in water as solution B and is added dropwise to the reaction container in batches using a constant flow pump, and the addition time is 40-60 minutes; after each batch of addition is completed, the reaction is continued at 60-80°C for 30-60 minutes of heat preservation and stirring; If the initiator is composed of a peroxide and a reducing substance, then solution A and solution B are added dropwise at room temperature, that is, the phosphoric acid small monomer, the chain transfer agent, and the chain transfer auxiliary agent are dissolved in water as solution A, and a constant flow pump is used to dropwise add the solution to the reaction container in batches, and each dropwise addition time is 30 to 50 minutes; at the same time, the initiator is dissolved in water as solution B, and a constant flow pump is used to dropwise add the solution to the reaction container in batches, and the dropwise addition time is 40 to 60 minutes; after each batch of dropwise addition is completed, the reaction is continued to be stirred for 30 to 60 minutes; (3) Add dropwise and stir the mixture until the reaction is complete, stop heating, cool to room temperature, stop introducing the inert protective gas, adjust the pH value to 6.0-7.0 with an alkaline solution, and then add a preservative to obtain a slow-setting and viscosity-reducing phosphate-based small molecule water reducer.

5. The preparation method according to claim 4, characterized in that: The chain transfer agent is at least one of thioglycolic acid and mercaptopropionic acid, and the chain transfer aid is vitamin E; the preservative is at least one of potassium sorbate, calcium propionate, parabens, and sodium diacetate; The peroxide is at least one of persulfate and hydrogen peroxide; The reducing substance is at least one of sodium bisulfite and L-ascorbic acid.

6. A slow-setting and viscosity-reducing phosphate-based small molecule water reducer for geopolymers obtained by the preparation method according to any one of claims 1 to 5.

7. The slow-setting and viscosity-reducing phosphate-based small molecule water reducer according to claim 6, characterized in that: The composition of the water reducing agent is calculated by the amount of substance: Component A: 25-50 parts of vinyl phosphoric acid, 25 parts of vinyl phosphate, 25 parts of cis-allyl phosphoric acid; Component B: 25-50 parts of unsaturated polyoxyethylene ether; Component C: 8-10 parts of chain transfer agent, 1-2 parts of chain transfer aid vitamin E; Component D: 4-10 parts of initiator; Component E: alkaline solution, adjust the system pH to 6.0-7.0; Component F: 0.8-1.2 parts of preservative.

8. The slow-setting and viscosity-reducing phosphate-based small molecule water reducer according to claim 6, characterized in that: The molecular weight of the slow-setting and viscosity-reducing phosphate-based small-molecule water reducer is 4000-11000, and the solid content of the water reducer is 20%-30%; the preferred molecular weight distribution PDI is 1.4-1.

6.

9. A geopolymer mortar, characterized in that: The geopolymer mortar adopts the slow-setting and viscosity-reducing phosphate-based small molecule water reducer as described in any one of claims 6-8, and the addition amount of the slow-setting and viscosity-reducing phosphate-based small molecule water reducer is 1-3% of the mass of the cementitious material in the geopolymer mortar; the cementitious material is the sum of fly ash, slag and steel slag.

10. The mortar according to claim 9, characterized in that The fluidity of the geopolymer mortar is increased by more than 55%, the final setting time is extended by more than 140%, and the viscosity is reduced by more than 30%.

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