Powdered alkali-free quick-setting agent and preparation method thereof

Abstract

The present invention provides a powdered alkali-free quick-setting admixture and a preparation method thereof. The raw materials for preparing the powdered alkali-free quick-setting admixture include, by weight, 62-80 parts of a coagulant, 5-12 parts of modified nano-ettringite, 4-10 parts of a fluoride, 4-8 parts of a complexing agent, 2-3 parts of an early strength agent, 2-3 parts of a pH regulator, 1-2 parts of a stabilizer, 0.5-1 part of a viscosity regulator, and 0.01-0.02 parts of a defoaming agent. The powdered alkali-free quick-setting admixture prepared using the above raw materials can effectively improve the early strength of shotcrete and reduce its rebound rate.

Description

Technical Field

[0001] The present invention relates to the field of concrete building materials, in particular to a powdery alkali-free quick-setting agent. The present invention also relates to a preparation method of the powdery alkali-free quick-setting agent. Background Art

[0002] As an indispensable admixture for shotcrete, accelerators can promote the rapid setting and hardening of cement concrete and are widely used in tunnel construction for railway and highway projects. Liquid accelerators used for wet spraying construction of tunnels are divided into two categories: alkaline accelerators and alkali-free accelerators. Alkaline (low-alkali) liquid accelerators generally have an alkali content greater than 1%. This type of liquid accelerator will more or less have an adverse effect on the mechanical properties and durability of concrete. Liquid alkali-free accelerators have been widely used in recent years due to their low alkali content and low corrosiveness, which do not affect the later strength and durability of concrete. However, the liquid alkali-free accelerators on the market currently have disadvantages such as high dosage, poor stability, low early strength, poor compatibility with cement, and high rebound rate.

[0003] With the development of infrastructure construction in my country, the demand for tunnel shotcrete is enormous, especially in infrastructure projects in the southwest region, where the bridge-tunnel ratio exceeds 70%. The market for alkali-free accelerators used in tunnel shotcrete is enormous, but fierce competition has driven down prices and reduced overall performance. Currently, most commercially available powdered accelerators are alkaline, made from calcined and ground alumina clinker, lime, alkali metal carbonates, and silicates. While generally cheaper than liquid accelerators, they are insoluble in water and can only be used in dry shotcrete construction. This process has been gradually phased out due to drawbacks such as severe dust pollution and high rebound. Water-soluble powdered alkali-free accelerators offer broad market prospects, as they significantly reduce transportation costs, can be mixed on-site with water, are convenient for storage and use, and have minimal negative impact on concrete durability. Summary of the Invention

[0004] The invention provides a powdery alkali-free quick-setting agent to improve the early strength of concrete and reduce the rebound rate.

[0005] A powdery alkali-free quick-setting agent. The raw materials for preparing the powdery alkali-free quick-setting agent include, by weight, 62-80 parts of a coagulant, 5-12 parts of modified nano-ettringite, 4-10 parts of a fluoride, 4-8 parts of a complexing agent, 2-3 parts of an early strength agent, 2-3 parts of a pH regulator, 1-2 parts of a stabilizer, 0.5-1 part of a viscosity regulator, and 0.01-0.02 parts of a defoaming agent.

[0006] Furthermore, the coagulant includes components A and B in a mass ratio of (8.5-9.0): (1.0-1.5), component A includes at least one of industrial-grade aluminum sulfate 18hydrate and polyaluminum sulfate, and component B includes at least one of polyaluminum ferric silicate, polyaluminum ferric phosphate, and polyaluminum magnesium silicate.

[0007] Furthermore, the modified nano-ettringite comprises nano-ettringite powder containing nano-calcium silicate with an average particle size of 20 to 80 nm.

[0008] Furthermore, the fluoride includes at least one of magnesium fluorosilicate, ammonium fluoroaluminate, potassium fluoroaluminate, and sodium fluoride.

[0009] Furthermore, the complexing agent includes organic alcohol amine.

[0010] Furthermore, the early strength agent includes at least one of nano-silica and nano-alumina; and / or the pH regulator includes at least one of glycine, p-toluenesulfonic acid, oxalic acid, and tartaric acid; and / or the stabilizer includes at least one of pseudo-boehmite, lithium magnesium silicate, and hydrated magnesium silicate; and / or the viscosity regulator includes at least one of weinlun gum, xanthan gum, guar gum, hydroxyethyl cellulose, and sodium polyacrylate; and / or the defoamer includes a powdered polyether-modified polysiloxane defoamer.

[0011] The present invention also proposes a method for preparing a powdered alkali-free quick-setting agent, which is characterized in that the method comprises the following steps:

[0012] The coagulant, fluoride and complexing agent are added to a grinder for grinding, and then a pH regulator, a viscosity regulator and a stabilizer are added for grinding. The ground materials and modified nano-ettringite, early strength agent and defoaming agent are added to a mixer for mixing to obtain the powdered alkali-free quick-setting agent.

[0013] Further, the preparation method of the modified nano-ettringite comprises the following steps:

[0014] S1) uniformly mixing water and sulfoaluminate cement, centrifuging, and then filtering to obtain a cement paste supernatant; S2) adding a high molecular polymer dispersion to the cement paste supernatant and stirring uniformly to form a dispersant solution; S3) dropwise adding a calcium salt aqueous solution, a silicon salt aqueous solution, an aluminum salt aqueous solution, and a sulfate aqueous solution to the dispersant solution, wherein the calcium-silicon molar ratio of the four raw materials, the calcium salt, the silicon salt, the aluminum salt, and the sulfate, is 2.5-3.0, the calcium-aluminum molar ratio is 10.0-15.0, and the aluminum-sulfur molar ratio is 0.5-0.8, and stirring is performed using a high-speed shear disperser during the dropwise addition process, and the reaction temperature is 10°C-30°C; S4) adding an organic modifier to adjust the pH to 11.0-12.0, and continuing stirring to obtain a suspension; S5) spray-drying the suspension to obtain a white powder, thereby obtaining the modified nano-ettringite powder.

[0015] Furthermore, the calcium salt aqueous solution includes an aqueous solution of at least one of calcium nitrate, calcium formate, and calcium acetate; and / or the silicon salt aqueous solution includes an aqueous solution of at least one of sodium silicate, potassium silicate, and magnesium fluorosilicate; and / or the aluminum salt aqueous solution includes an aqueous solution of at least one of aluminum nitrate and aluminum dihydrogen phosphate; and / or the sulfate aqueous solution includes an aqueous solution of at least one of magnesium sulfate, manganese sulfate, and lithium sulfate.

[0016] Furthermore, the organic modifier includes at least one of monoethanolamine, diethanolamine, and diethanol monoisopropanolamine.

[0017] The powdered alkali-free quick-setting agent of the present invention has good comprehensive performance, simple preparation process, low transportation cost, convenient storage and use, good water solubility, can be added with water on site for immediate use, has good adaptability to cement, and can be compounded with water in different proportions to form liquid quick-setting agents of different concentrations according to different cement properties. The powdered alkali-free quick-setting agent is alkali-free and chlorine-free, has a low dosage, high early strength, a 1d compressive strength of ≥15 MPa, no loss of late strength, a 28d compressive strength ratio of ≥100%, good stability, a low rebound rate of shotcrete of <6%, and all indicators meet the requirements of GB / T35159-2017 "Accelerators for Shotcrete", and is very suitable for promotion and application. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0019] The experimental methods in the following examples, unless otherwise specified, are conventional methods. The experimental materials used in the following examples, unless otherwise specified, were purchased from conventional biochemical reagent stores. Furthermore, unless otherwise specified in this example, the terms and processes involved in this example should be understood in accordance with general knowledge and conventional methods in the prior art.

[0020] A powdery alkali-free quick-setting agent. The raw materials for preparing the powdery alkali-free quick-setting agent include, by weight, 62-80 parts of a coagulant, 5-12 parts of modified nano-ettringite, 4-10 parts of a fluoride, 4-8 parts of a complexing agent, 2-3 parts of an early strength agent, 2-3 parts of a pH regulator, 1-2 parts of a stabilizer, 0.5-1 part of a viscosity regulator, and 0.01-0.02 parts of a defoaming agent.

[0021] Coagulants typically contain a certain amount of aluminum sulfate. Aluminum sulfate dissociates in water, and the sulfate ions produced by its hydrolysis react with calcium ions generated by cement hydration to form fine secondary gypsum. This is more active than the original gypsum in cement, accelerating its reaction with tricalcium aluminate in the cement, making it easier to form needle-shaped ettringite crystals. Furthermore, aluminum sulfate reacts directly and rapidly with calcium hydroxide in the liquid phase to form ettringite. This ettringite expands and interlocks to form a dense network structure, filling pores and cracks, densifying the slurry and promoting strength development, leading to rapid setting of cement concrete. Furthermore, the reduced concentration of calcium ions in the liquid phase promotes the dissolution of tricalcium aluminate. Aluminum ions also accelerate the formation of CSH (calcium silicate hydrate) gel, shortening the induction period of tricalcium silicate, thereby accelerating further hydration and rapidly setting the cement. The intermixing of silicate and sulfate creates lattice defects in the crystals, enhancing hydration activity.

[0022] The coagulant of the present invention preferably comprises components A and B in a mass ratio of (8.5-9.0):(1.0-1.5), wherein component A comprises at least one of technical-grade aluminum sulfate 18hydrate and polyaluminum sulfate, and component B comprises at least one of polyaluminum ferric silicate, polyaluminum ferric phosphate, and polyaluminum magnesium silicate. Compared with the traditional single aluminum sulfate component (aluminum to sulfate molar ratio of 0.66), the two-component coagulant increases the aluminum content and reduces the sulfate content, thus overcoming the shortcomings of the single aluminum sulfate component, which has a limited accelerating effect and an excessively high sulfate content and easily reduces the durability of concrete.

[0023] The fluoride component can form a stable fluorine-aluminum complex with the aluminum salt in the coagulant, increasing the aluminum ion concentration in the liquid phase and improving the accelerating effect on the setting of the shotcrete. The fluoride includes at least one of magnesium fluorosilicate, ammonium fluoroaluminate, potassium fluoroaluminate, and sodium fluoride.

[0024] The modified nano-ettringite component can promote the hydration of cement minerals and improve the early strength of concrete through the action of nano-crystal nuclei. The modified nano-ettringite of the present application preferably adopts nano-ettringite mixed crystals containing nano-calcium silicate, which can promote the rapid hydration of silicate and aluminate minerals in cement through a stronger nano-crystal nucleus effect, and generate more densely structured CSH (hydrated calcium silicate) and AFt (hydrated calcium sulfoaluminate) hydration products in a short time. CSH and AFt are interwoven together to form a tight network structure, which can greatly accelerate the coagulation and hardening of sprayed concrete. Without affecting the later strength, the ultra-early 3h to 24h mechanical properties of sprayed concrete are improved, and the rebound rate of sprayed concrete is reduced. It synergizes with the defoamer component and the early strength agent component to jointly reduce the porosity of sprayed concrete and greatly improve the durability of sprayed concrete. The average particle size of the more preferred modified nano-ettringite is 20 to 80nm, and its nano-crystal nucleus effect is better.

[0025] The synergistic effect of the coagulant component, the fluoride component and the modified nano-ettringite component enables the powdered alkali-free quick-setting agent of the present invention to be compounded with water into a liquid quick-setting agent, which can meet the rapid setting requirements at a lower dosage and greatly shorten the cement setting time.

[0026] The complexing agent component can effectively improve the complexing ability of aluminum ions, promote the rapid dissolution of aluminum ions in the liquid phase, and increase the dissolution rate of aluminum phase substances in the powdered accelerator in water. It preferably includes solid organic alcoholamines, such as triisopropanolamine.

[0027] The early strength accelerator component can synergistically work with the modified nano-ettringite component in the powdered accelerator of the present invention to reduce the nucleation barrier of cement hydration, provide nucleation growth points for cement hydration products, accelerate the cement hydration process, and compensate for the adverse effects of the fluoride component on early strength. Nano-scale silica and alumina are preferred. Compared with traditional early strength accelerators, nano-silica and nano-alumina can effectively improve the early compressive strength of mortar and concrete mixed with accelerators, while also having a high guaranteed rate of late strength and no adverse effect on late strength.

[0028] The pH adjuster component inhibits the hydrolysis and precipitation of aluminum ions in the formulated liquid accelerator and reduces the viscosity of the liquid accelerator, thereby preventing excessive viscosity after prolonged storage or at low temperatures. The pH adjuster preferably includes at least one of glycine, p-toluenesulfonic acid, oxalic acid, and tartaric acid.

[0029] The stabilizer component can form a three-dimensional network structure in the liquid phase system when the powdered accelerator is compounded with water to form a liquid accelerator, which has a very good suspension and dispersion effect on the supersaturated aluminum phase substance in the accelerator and the nanomaterials (modified nano-ettringite and early strength agent) in the system, and under the synergistic effect of the above-mentioned pH regulator, it avoids crystallization, precipitation and other phenomena, and greatly improves the stability.

[0030] Viscosity modifiers can adjust the viscosity of concrete. By constraining the free water in the cement paste, the gaps between cement particles are preserved, reducing interparticle friction and facilitating deformation of the mixture. Increased viscosity also enhances cohesion, significantly improving the concrete's resistance to segregation. Preferably, the defoamer comprises at least one of: vinasse, xanthan gum, guar gum, hydroxyethyl cellulose, and sodium polyacrylate. Furthermore, the defoamer comprises a powdered polyether-modified polysiloxane defoamer.

[0031] The powdered alkali-free quick-setting agent of the present invention has a fast setting time, high early strength, 1d compressive strength ≥15MPa, no loss of later strength, 28d compressive strength ratio ≥100%, and various indicators meet the requirements of GB / T35159-2017 standard. The powdered alkali-free quick-setting agent of the present invention has good water solubility and is easy to store and use. The dosage is low (5% to 7%), and the liquid quick-setting agent after dissolving in water has good stability, and the stable period is greater than 3 months, which meets the use requirements. It has good adaptability to cement and can be compounded into liquid quick-setting agents of different concentrations with water in different ratios (0.5 to 1.5): 1 according to the characteristics of different cements to adapt to different cements. Using the powdered alkali-free quick-setting agent of the present invention, water is added on site to compound into liquid quick-setting agents of different concentrations for sprayed concrete, and the rebound rate is less than 6%, which greatly saves engineering costs.

[0032] The present invention also provides a method for preparing a powdered alkali-free quick-setting agent, which specifically comprises the following steps:

[0033] The raw materials are weighed according to the ratio, and the coagulant, fluoride, and complexing agent are added to a grinder and ground for 30 to 60 minutes. Then, a pH adjuster, viscosity adjuster, and stabilizer are added and ground for 30 to 60 minutes. The ground materials, modified nano-ettringite, early strength agent, and defoamer are added to a mixer and mixed for 30 to 60 minutes to obtain a uniformly mixed powder material, which is the powdered alkali-free accelerating setting agent. The powdered alkali-free accelerating setting agent prepared by this method has a fineness of 400 to 500 mesh.

[0034] Preferably, the preparation method of modified nano ettringite specifically comprises the following steps:

[0035] S1) Mix water and sulfoaluminate cement in a mass ratio of 1.2 to 1.5:1 and stir with a mechanical stirrer for 5 to 10 minutes to obtain a cement paste suspension. The cement paste suspension is then centrifuged in a centrifuge for 20 to 30 minutes. The centrifuge is then centrifuged once, and the centrifuge is filtered through a 0.45 μm filter membrane to obtain a transparent cement paste supernatant. S2) Add a polymer dispersion having a solids content of 40% to 50% to the cement paste supernatant obtained in S1, with the mass ratio of the cement paste supernatant to the polymer dispersion being 4 to 4.5:1, and stir evenly to obtain a dispersant solution. S3) A calcium salt aqueous solution with a mass percentage concentration of 20% to 25%, a silicon salt aqueous solution with a mass percentage concentration of 15% to 20%, an aluminum salt aqueous solution with a mass percentage concentration of 2% to 5% and a sulfate aqueous solution with a mass percentage concentration of 5% to 10% are simultaneously added dropwise to the dispersant solution prepared in S2, wherein the calcium-silicon molar ratio (Ca / Si) of the four raw materials of calcium salt, silicon salt, aluminum salt and sulfate is 2.5 to 3.0, the calcium-aluminum molar ratio (Ca / Al) is 10.0 to 15.0, the aluminum-sulfur molar ratio (Al / S) is 0.5 to 0.8, the mass ratio of the calcium salt aqueous solution to the dispersant solution is 0.5 to 1.0, and a high-speed shear disperser is used for stirring during the dropwise addition process at a stirring rate of 2000 to 4000 rpm, the reaction temperature is 10°C to 30°C, and the calcium salt, silicon salt, aluminum salt and sulfate aqueous solution are all added dropwise for 2h to 3h. S4) After the dropwise addition is complete, an organic modifier is added to adjust the pH to 11.0-12.0, and stirring is continued for 10-20 minutes to obtain a milky white suspension. S5) The suspension obtained in S4 is spray-dried to obtain a white powder, namely, nano-ettringite powder containing nano-calcium silicate with an average particle size of 20-80 nm.

[0036] Preferably, the above-mentioned high molecular polymer dispersion is an early strength polycarboxylate water reducer with a water reduction rate of ≥27%. It is a copolymer with an ultra-long polyoxyethylene side chain synthesized from raw materials such as a polyether macromonomer with a molecular weight of 4000 to 5000. It can be the GK-3000 polycarboxylate high performance water reducer (early strength type) produced by Shijiazhuang Changan Yucai Building Materials Co., Ltd.

[0037] Preferably, the calcium salt aqueous solution comprises an aqueous solution of at least one of calcium nitrate, calcium formate, and calcium acetate. The silicon salt aqueous solution comprises an aqueous solution of at least one of sodium silicate, potassium silicate, and magnesium fluorosilicate. The aluminum salt aqueous solution comprises an aqueous solution of at least one of aluminum nitrate and aluminum dihydrogen phosphate. The sulfate aqueous solution comprises an aqueous solution of at least one of magnesium sulfate, manganese sulfate, and lithium sulfate. The organic modifier comprises at least one of monoethanolamine, diethanolamine, and diethanol monoisopropanolamine.

[0038] The modified nano-ettringite of the present application, in the preparation process, first adopts the cement paste supernatant of the centrifugal filtration of sulphoaluminate cement hydration suspension to be prepared into a dispersant solution by mixing with a polymer dispersion liquid, the cement paste supernatant itself contains a small amount of hydration product nano-ettringite and calcium silicate components, which are well dispersed under the action of the polymer dispersion liquid, and in the process of adding calcium salt, silicon salt, aluminum salt and sulfate dropwise, the crystal nucleus induction effect can be brought into play, and the attachment point of the reaction product is provided, which promotes the generation of more small nano-ettringite and nano-calcium silicate mixed crystals, effectively shortens the preparation time, and improves the reaction efficiency. The preferred polymer dispersion liquid can prevent the nano-material particle size generated by the reaction from growing further. At the same time, the addition of an organic modifier, by adjusting the system to a specific pH, is conducive to controlling the particle size of the modified nano-ettringite suspension, improving the stability of the modified nano-ettringite suspension, avoiding excessive precipitation of the particle size, and affecting the subsequent production of a fine powder.

[0039] The preparation process of the modified nano-ettringite contained in the powdered alkali-free quick-setting agent of the present invention can simultaneously prepare nano-ettringite mixed crystals containing nano-calcium silicate. During the preparation process, aluminum atoms can enter the calcium silicate structure and silicon atoms can enter the ettringite structure, so that the ettringite contains more lattice defects. The more lattice defects, the higher the hydration activity. When added to cement concrete, the nano-crystal can exert a stronger nano-crystal nucleation effect, greatly accelerate the hydration of silicate and aluminate minerals in the cement, generate more CSH and AFt, and quickly interweave to form a dense spatial network structure, thereby improving the ultra-early strength without affecting the later strength.

[0040] The specific implementation scheme of the present invention is described in detail below.

[0041] Example 1:

[0042] The powdered alkali-free quick-setting agent of this embodiment includes the following raw materials in parts by weight: 65 parts of accelerator, 10 parts of modified nano-ettringite, 10 parts of fluoride, 7.5 parts of complexing agent, 3 parts of early strength agent, 2.5 parts of pH regulator, 1.0 part of stabilizer, 1.0 part of viscosity regulator, and 0.01 part of defoaming agent.

[0043] The modified nano-ettringite is a nano-ettringite powder containing nano-calcium silicate with an average particle size of 50 nm. The preparation method is as follows: S1) water and sulfoaluminate cement are mixed in a mass ratio of 1.3:1 and stirred with a mechanical stirrer for 10 minutes to obtain a cement slurry suspension. The cement slurry suspension is then centrifuged in a centrifuge for 20 minutes. The centrifuge is then centrifuged again once and filtered through a 0.45 μm filter membrane to obtain a transparent cement slurry supernatant. S2) the cement slurry supernatant prepared in S1 is added to a polymer dispersion having a solid content of 40%, with the mass ratio of the cement slurry supernatant to the polymer dispersion being 4.5:1, and the mixture is stirred evenly to obtain a dispersant solution. S3) A 20% by mass calcium salt aqueous solution, a 15% by mass silicon salt aqueous solution, a 2% by mass aluminum salt aqueous solution and a 5% by mass sulfate aqueous solution are simultaneously added dropwise to the dispersant solution prepared in S2, wherein the calcium-silicon molar ratio (Ca / Si) of the four raw materials of calcium salt, silicon salt, aluminum salt and sulfate is 2.5, the calcium-aluminum molar ratio (Ca / Al) is 12.0, the aluminum-sulfur molar ratio (Al / S) is 0.5, and the calcium salt aqueous solution is 100% by mass. The mass ratio of the dispersant solution to the suspension was 0.6, and a high-speed shear disperser was used for stirring during the dropwise addition process at a stirring rate of 2000 rpm, a reaction temperature of 10° C., and a dropwise addition time of 2.5 hours. S4) After the dropwise addition was completed, an organic modifier was added to adjust the pH to 11.2, and stirring was continued for 10 minutes to obtain a milky white suspension. S5) The suspension obtained in S4 was spray-dried to obtain a white powder, i.e., a nano-ettringite powder containing nano-calcium silicate with an average particle size of 50 nm.

[0044] The aforementioned high-molecular polymer dispersion is an early-strength polycarboxylate water-reducing agent with a water-reduction rate of ≥27%. It is a copolymer with ultra-long polyoxyethylene side chains synthesized from polyether macromonomers with a molecular weight of 4,000 to 5,000. It can be the GK-3000 polycarboxylate high-performance water-reducing agent (early-strength type) produced by Shijiazhuang Chang'an Yucai Building Materials Co., Ltd. The aforementioned calcium salt aqueous solution is prepared by dissolving calcium nitrate in water; the silicon salt aqueous solution is prepared by dissolving potassium silicate in water; the aluminum salt aqueous solution is prepared by dissolving aluminum nitrate in water; and the sulfate aqueous solution is prepared by dissolving magnesium sulfate in water. The aforementioned organic modifier is monoethanolamine.

[0045] The coagulant is a powdered mixture of components A and B at a ratio of 8.5:1.5. Component A is industrial-grade aluminum sulfate 18hydrate, and component B is polyaluminum ferric silicate. The fluoride is magnesium fluorosilicate. The complexing agent is a solid alcoholamine, commercially available triisopropanolamine. The early strength agent is hydrophilic nanosilica. The pH adjuster is glycine. The stabilizer is pseudo-boehmite. The viscosity modifier is Wenlun rubber. The defoamer is a powdered polyether-modified polysiloxane defoamer.

[0046] Example 2:

[0047] The powdered alkali-free quick-setting agent of this embodiment includes the following raw materials in parts by weight: 68 parts of coagulant, 12 parts of modified nano-ettringite, 7 parts of fluoride, 5.5 parts of complexing agent, 2.5 parts of early strength agent, 2.5 parts of pH regulator, 1.5 parts of stabilizer, 1.0 part of viscosity regulator, and 0.02 part of defoaming agent.

[0048] The modified nano-ettringite is a nano-ettringite powder containing nano-calcium silicate with an average particle size of 70 nm. The preparation method is as follows: S1) water and sulfoaluminate cement are mixed in a mass ratio of 1.4:1 and stirred with a mechanical stirrer for 5 minutes to obtain a cement slurry suspension. The cement slurry suspension is then centrifuged in a centrifuge for 20 minutes. The centrifuge is then centrifuged once again and filtered through a 0.45 μm filter membrane to obtain a transparent cement slurry supernatant. S2) the cement slurry supernatant prepared in S1 is added to a polymer dispersion having a solid content of 50%, with the mass ratio of the cement slurry supernatant to the polymer dispersion being 4:1, and the mixture is stirred evenly to obtain a dispersant solution. S3) A 23% by mass calcium salt aqueous solution, a 17% by mass silicon salt aqueous solution, a 3% by mass aluminum salt aqueous solution and an 8% by mass sulfate aqueous solution are simultaneously added dropwise to the dispersant solution prepared in S2, wherein the calcium-silicon molar ratio (Ca / Si) of the four raw materials of calcium salt, silicon salt, aluminum salt and sulfate is 2.8, the calcium-aluminum molar ratio (Ca / Al) is 12.5, the aluminum-sulfur molar ratio (Al / S) is 0.6, and the calcium salt aqueous solution is 17% by mass silicon salt, 17% by mass silicon salt, 17% by mass aluminum salt and 17% by mass sulfate aqueous solution. The mass ratio of the dispersant solution is 0.8, and a high-speed shear disperser is used for stirring during the dropwise addition process at a stirring rate of 2500 rpm, a reaction temperature of 20°C to 30°C, and a dropwise addition time of 3 hours. S4) After the dropwise addition is completed, an organic modifier is added to adjust the pH to 11.5, and stirring is continued for 20 minutes to obtain a milky white suspension. S5) The suspension obtained in S4 is spray-dried to obtain a white powder, namely, a nano-ettringite powder containing nano-calcium silicate with an average particle size of 70 nm.

[0049] The aforementioned high-molecular polymer dispersion is an early-strength polycarboxylate water-reducing agent with a water-reduction rate of ≥27%. It is a copolymer with ultra-long polyoxyethylene side chains synthesized from raw materials such as a polyether macromonomer with a molecular weight of 4,000 to 5,000. It can be the GK-3000 polycarboxylate high-performance water-reducing agent (early-strength type) produced by Shijiazhuang Chang'an Yucai Building Materials Co., Ltd. The aforementioned calcium salt aqueous solution is prepared by dissolving calcium nitrate in water; the silicon salt aqueous solution is prepared by dissolving magnesium fluorosilicate in water; the aluminum salt aqueous solution is prepared by dissolving aluminum dihydrogen phosphate in water; and the sulfate aqueous solution is prepared by dissolving manganese sulfate in water. The aforementioned organic modifier is diethanolamine.

[0050] The coagulant is a powdered mixture of components A and B at a ratio of 9:1. Component A is industrial-grade aluminum sulfate 18hydrate, and component B is polymagnesium aluminum silicate. The fluoride is ammonium fluoroaluminate. The complexing agent is a solid alcoholamine, commercially available triisopropanolamine. The early strength agent is hydrophilic nanosilica. The pH adjuster is p-toluenesulfonic acid. The stabilizer is lithium magnesium silicate. The viscosity modifier is guar gum. The defoamer is a powdered polyether-modified polysiloxane defoamer.

[0051] Example 3:

[0052] The powdered alkali-free quick-setting agent of this embodiment includes the following raw materials in parts by weight: 73 parts of coagulant, 8 parts of modified nano-ettringite, 6 parts of fluoride, 6 parts of complexing agent, 2.5 parts of early strength agent, 2 parts of pH regulator, 2 parts of stabilizer, 0.5 parts of viscosity regulator, and 0.02 parts of defoaming agent.

[0053] The modified nano-ettringite is a nano-ettringite powder containing nano-calcium silicate with an average particle size of 60 nm. The preparation method is as follows: S1) water and sulfoaluminate cement are mixed in a mass ratio of 1.5:1 and stirred with a mechanical stirrer for 5 minutes to obtain a cement slurry suspension. The cement slurry suspension is then centrifuged in a centrifuge for 30 minutes. The centrifuge is then centrifuged once again and filtered through a 0.45 μm filter membrane to obtain a transparent cement slurry supernatant. S2) the cement slurry supernatant prepared in S1 is added to a polymer dispersion having a solids content of 50%, with the mass ratio of the cement slurry supernatant to the polymer dispersion being 4:1, and the mixture is stirred evenly to obtain a dispersant solution. S3) adding a 25% by mass calcium salt aqueous solution, an 18.5% by mass silicon salt aqueous solution, a 5% by mass aluminum salt aqueous solution, and a 7% by mass sulfate aqueous solution to the dispersant solution prepared in S2, and simultaneously adding to the above-mentioned dispersant solution, wherein the calcium-silicon molar ratio (Ca / Si) of the four raw materials of calcium salt, silicon salt, aluminum salt and sulfate is 3.0, the calcium-aluminum molar ratio (Ca / Al) is 15.0, and the aluminum-sulfur molar ratio (Al / S) is 1. The mass ratio of the calcium salt aqueous solution to the dispersant solution is 0.5, and the mass ratio of the calcium salt aqueous solution to the dispersant solution is 0.6. During the dropwise addition, a high-speed shear disperser is used for stirring at a stirring rate of 3000 rpm, the reaction temperature is 30° C., and the dropwise addition time is 2 h. S4) After the dropwise addition is completed, an organic modifier is added to adjust the pH to 11.5, and stirring is continued for 20 min to obtain a milky white suspension. S5) The suspension obtained in S4 is spray-dried to obtain a white powder, i.e., a nano-ettringite powder containing nano-calcium silicate with an average particle size of 60 nm.

[0054] The high molecular polymer dispersion is an early-strength polycarboxylate water-reducing agent with a water-reduction rate of ≥27%. It is a copolymer with ultra-long polyoxyethylene side chains synthesized from raw materials such as polyether macromonomers with a molecular weight of 4000-5000. It can be the GK-3000 polycarboxylate high-performance water-reducing agent (early-strength type) produced by Shijiazhuang Changan Yucai Building Materials Co., Ltd. The calcium salt aqueous solution is prepared by dissolving calcium formate in water; the silicon salt aqueous solution is prepared by dissolving magnesium fluorosilicate in water; the aluminum salt aqueous solution is prepared by dissolving aluminum nitrate in water, and the sulfate aqueous solution is prepared by dissolving lithium sulfate in water. The organic modifier is diethanol monoisopropanolamine.

[0055] The coagulant is a powdered mixture of components A and B at a ratio of 8.5:1.5. Component A is polyaluminum sulfate, and component B is polyaluminum ferric silicate. The fluoride is ammonium fluoroaluminate. The complexing agent is a solid alcoholamine, commercially available triisopropanolamine. The early strength agent is nano-alumina. The pH adjuster is oxalic acid. The stabilizer is hydrated magnesium silicate. The viscosity modifier is hydroxyethyl cellulose. The defoamer is a powdered polyether-modified polysiloxane defoamer.

[0056] Example 4:

[0057] The powdered alkali-free quick-setting agent of this embodiment includes the following raw materials in parts by weight: 77.5 parts of accelerator, 5 parts of modified nano-ettringite, 5 parts of fluoride, 5 parts of complexing agent, 2 parts of early strength agent, 3 parts of pH regulator, 2 parts of stabilizer, 0.5 parts of viscosity regulator, and 0.01 parts of defoaming agent.

[0058] The modified nano-ettringite is a nano-ettringite powder containing nano-calcium silicate with an average particle size of 35 nm. The preparation method is as follows: S1) water and sulfoaluminate cement are mixed in a mass ratio of 1.5:1 and stirred with a mechanical stirrer for 10 minutes to obtain a cement slurry suspension. The cement slurry suspension is then centrifuged in a centrifuge for 30 minutes. The centrifuge is then centrifuged again once and filtered through a 0.45 μm filter membrane to obtain a transparent cement slurry supernatant. S2) the cement slurry supernatant prepared in S1 is added to a polymer dispersion having a solid content of 45%, with the mass ratio of the cement slurry supernatant to the polymer dispersion being 4.5:1, and the mixture is stirred evenly to obtain a dispersant solution. S3) A 23% by mass calcium salt aqueous solution, a 15% by mass silicon salt aqueous solution, a 4% by mass aluminum salt aqueous solution and a 6% by mass sulfate aqueous solution are simultaneously added dropwise to the dispersant solution prepared in S2, wherein the calcium-silicon molar ratio (Ca / Si) of the four raw materials of calcium salt, silicon salt, aluminum salt and sulfate is 3.0, the calcium-aluminum molar ratio (Ca / Al) is 13.5, the aluminum-sulfur molar ratio (Al / S) is 0.7, and the calcium salt aqueous solution is 0. The mass ratio of the dispersant solution to the suspension was 0.8, and a high-speed shear disperser was used for stirring during the dropwise addition process at a stirring rate of 3500 rpm, a reaction temperature of 20°C, and a dropwise addition time of 2.5 hours. S4) After the dropwise addition was completed, an organic modifier was added to adjust the pH to 12.0, and stirring was continued for 20 minutes to obtain a milky white suspension. S5) The suspension obtained in S4 was spray-dried to obtain a white powder, namely, a nano-ettringite powder containing nano-calcium silicate with an average particle size of 35 nm.

[0059] The high molecular polymer dispersion is an early-strength polycarboxylate water-reducing agent with a water-reduction rate of ≥27%. It is a copolymer with ultra-long polyoxyethylene side chains synthesized from raw materials such as polyether macromonomers with a molecular weight of 4000 to 5000. It can be the GK-3000 polycarboxylate high-performance water-reducing agent (early-strength type) produced by Shijiazhuang Changan Yucai Building Materials Co., Ltd. The calcium salt aqueous solution is prepared by dissolving calcium acetate in water; the silicon salt aqueous solution is prepared by dissolving magnesium fluorosilicate in water; the aluminum salt aqueous solution is prepared by dissolving aluminum dihydrogen phosphate in water, and the sulfate aqueous solution is prepared by dissolving lithium sulfate in water. The organic modifier is diethanol monoisopropanolamine.

[0060] The coagulant is a powdered mixture of components A and B in a 9:1 ratio. Component A is polyaluminum sulfate, and component B is polyaluminum ferrosilicate. The fluoride is magnesium fluorosilicate and sodium fluoride in a 4:1 mass ratio. The complexing agent is a solid alcoholamine, commercially available triisopropanolamine. The early strength agent is nano-alumina. The pH adjuster is tartaric acid. The stabilizer is pseudo-boehmite. The viscosity modifier is xanthan gum. The defoamer is a powdered polyether-modified polysiloxane defoamer.

[0061] The preparation method of the powdery alkali-free quick-setting agent of Example 1 to Example 4 is as follows:

[0062] According to the raw material ratio, the coagulant, fluoride and complexing agent are weighed and added into the grinder for grinding for 30 to 60 minutes, and then the pH regulator, viscosity regulator and stabilizer are added and ground for 30 to 60 minutes. The ground materials and modified nano-ettringite, early strength agent and defoaming agent are added into the mixer and mixed for 30 to 60 minutes to obtain a uniformly mixed powder material with a fineness of 400 to 500 meshes, which is the powdered alkali-free quick-setting agent.

[0063] Comparative Examples 1 to 7:

[0064] The powdered alkali-free quick-setting agent of Comparative Example 1 is substantially the same as that of Example 1, except that the modified nano-ettringite component is not added to Comparative Example 1;

[0065] The powdered alkali-free accelerator of Comparative Example 2 is basically the same as that of Example 1, except that the cement paste supernatant of the first step S1 is removed in the preparation process of the modified nano-ettringite component of Comparative Example 2, and the cement paste supernatant is replaced by water of equal mass.

[0066] The powdered alkali-free quick-setting agent of Comparative Example 3 is basically the same as that of Example 1, except that the sulphoaluminate cement in the preparation process of the modified nano-ettringite component of Comparative Example 3 is replaced by an equal mass of silicate cement.

[0067] The powdered alkali-free accelerator of Comparative Example 4 is basically the same as that of Example 1, except that the preparation process of the modified nano-ettringite component of Comparative Example 4 is different, comprising the following steps: preparing a modified calcium silicate hydrate nano-crystal core early strength agent according to Example 3 disclosed in patent CN111253107A, preparing a nano-ettringite crystal core early strength agent according to Example 2 disclosed in patent CN113213803A, mixing the two so that the calcium-silicon ratio and aluminum-sulfur ratio of the mixed solution are the same as those of the modified nano-ettringite in Example 1, and then spray drying according to the fifth step S5 in the preparation process of the modified nano-ettringite in Example 1 of the present invention to obtain a white powder, which is the modified nano-ettringite component of Comparative Example 4.

[0068] The powdered alkali-free quick-setting agent of Comparative Example 5 is substantially the same as that of Example 1, except that the coagulant of Comparative Example 5 is the coagulant of Example 4 disclosed in Patent No. CN115784664A.

[0069] The powdered alkali-free quick-setting agent of Comparative Example 6 is substantially the same as that of Example 1, except that no early strength agent component is added to Comparative Example 6.

[0070] The powdery alkali-free quick-setting agent of Comparative Example 7 is a powdery alkali-free quick-setting agent prepared according to Example 1 disclosed in patent CN112142359A.

[0071] The following is the experimental part of the present invention:

[0072] The powdered alkali-free accelerator described in this invention is mixed with water at a ratio of (0.5-1.5):1 to form a liquid accelerator. The recommended dosage in shotcrete is 5%-7% of the total cementitious material. GB / T35159-2017, "Accelerators for Shotcrete," stipulates general requirements for alkali-free accelerators: alkali content ≤ 1.0%, chloride ion content ≤ 0.1%, and pH ≥ 2.0. Testing has shown that the powdered alkali-free accelerators prepared in Examples 1-4, when compounded into liquid alkali-free accelerators, meet these requirements in terms of alkali content, chloride ion content, and pH. The performance requirements for pastes and mortars incorporating liquid alkali-free accelerators are shown in Table 1.

[0073] Table 1 Performance requirements of mortar and paste containing alkali-free accelerator (GB / T35159-2017)

[0074]

[0075] Test Item 1

[0076] The powdered alkali-free quick-setting agents prepared in Examples 1 to 4, as well as the powdered alkali-free quick-setting agents of the comparative examples, were mixed with water at a ratio of 1:1 to prepare liquid alkali-free quick-setting agents. The setting time, compressive strength, and other indicators were tested according to the test methods specified in GB / T35159-2017 "Accelerators for Shotcrete." The test cement was the benchmark cement P.I. 42.5. The test results are shown in Table 2.

[0077] Table 2 Performance of the alkali-free quick-setting agent of the present invention (reference cement)

[0078]

[0079]

[0080] As can be seen from the data in Table 2, the powdered alkali-free accelerator of the present invention exhibits excellent performance. When each embodiment is dissolved in water to form a liquid accelerator, the dosage is relatively low. At a dosage of 6% to 7%, all performance indicators meet the requirements of the GB / T35159-2017 standard when tested using benchmark cement. The 6-hour compressive strength is greater than 1.5 MPa, the 1-day compressive strength is greater than 15.0 MPa, and the high early-stage strength from 6 to 24 hours ensures construction safety and schedule, making it particularly suitable for projects requiring rapid support. Furthermore, the later-stage strength does not shrink, and may even improve, with the 28-day compressive strength ratio exceeding 100%.

[0081] The alkali-free accelerator of Comparative Example 1 is not added with the modified nano-ettringite component in Example 1, so the setting time is slow. At 6% dosage, the final setting is greater than 12min, the early compressive strength is also lower than that of Example 1, the 6h compressive strength is lower than 1MPa, the 1d strength is lower than 15MPa, and the 90d compressive strength ratio is less than 100%. The setting time and 90d compressive strength ratio indicators do not meet the requirements of the GB / T35159-2017 "Accelerator for Shotcrete" standard; the alkali-free accelerator of Comparative Example 2 (compared to the preparation process of the modified nano-ettringite component in Example 1, which does not contain cement slurry supernatant) and the alkali-free accelerator of Comparative Example 3 (compared to Example 1, the preparation process of the modified nano-ettringite component does not contain cement slurry supernatant) are not added. The preparation process of the modified nano-ettringite component uses silicate cement instead of sulphoaluminate cement). Compared with Example 1, the setting time is slower and the compressive strength is reduced, indicating that the preparation process of the modified nano-ettringite in the alkali-free accelerator of Comparative Example 2 does not contain cement slurry supernatant, and the preparation process cannot play a role in inducing crystal nuclei, and the formation of reaction products cannot be accelerated. The preparation process of the modified nano-ettringite in the alkali-free accelerator of Comparative Example 3 uses silicate cement instead of sulphoaluminate cement to prepare cement slurry supernatant. Compared with the sulphoaluminate cement supernatant, the silicate cement slurry supernatant has much less nano-ettringite and calcium silicate content, and cannot play a good role in inducing crystal nuclei. The alkali-free quick-setting agent of Comparative Example 4 has a different preparation process than the modified nano-ettringite component of Example 1. The nano-ettringite and calcium silicate are prepared separately and then mixed and pulverized. The setting time and 6h and 1d compressive strength of the corresponding alkali-free quick-setting agent are lower than those of the quick-setting agent of Example 1. The reason is that the modified nano-ettringite preparation process of Example 1 can simultaneously produce nano-ettringite mixed crystals containing nano-calcium silicate. During the preparation process, aluminum atoms can enter the calcium silicate structure and silicon atoms can enter the ettringite structure, so that it contains a large number of lattice defects. The more lattice defects, the higher the hydration activity. When added to cement concrete, it can exert a stronger nano-crystal nucleation effect, greatly accelerate the hydration of silicate and aluminate minerals in cement, generate more CSH and AFt, and quickly interweave to form a dense spatial network structure, thereby improving the ultra-early strength without affecting the later strength. The alkali-free accelerators of Comparative Examples 5 to 7 are inferior to the powdered alkali-free accelerator of the present invention in terms of setting time, strength and other properties. This shows that the alkali-free accelerator of the present invention has better performance due to the synergistic effect of the components.

[0082] Test Item 2

[0083] The powdered alkali-free quick-setting agent of Example 2 was mixed with water at a ratio of 1.5:1 to prepare a liquid alkali-free quick-setting agent. Huaxin Cement P.O42.5, Lafarge Cement P.O42.5, Yaobai Cement P.O42.5, Conch Cement P.O42.5 and Qilianshan Cement P.O42.5 were used to conduct compatibility tests between the quick-setting agent and cement. The test results are shown in Table 3.

[0084] Table 3 Performance of alkali-free quick-setting agent of the present invention (project cement)

[0085]

[0086]

[0087] As can be seen from the data in Table 3, the powdered alkali-free quick-setting agent of the present invention, after being formulated into a liquid quick-setting agent and using cement for various engineering projects, all performance indicators meet the performance requirements of GB / T35159-2017 for alkali-free quick-setting agents in Table 1, indicating that the quick-setting agent of the present invention has good adaptability to various cements and can largely meet the use requirements of various engineering projects.

[0088] Test Item 3

[0089] The powdered alkali-free accelerators prepared in Examples 1 to 4, as well as the powdered alkali-free accelerators from the comparative examples, were mixed with water at a ratio of 1:1 to prepare liquid alkali-free accelerators. Shotcrete rebound tests were conducted at a liquid accelerator dosage of 6% to 7% according to the method described in Appendix G of JGJ / T372-2016, "Technical Specifications for the Application of Shotcrete." The test results are shown in Table 4. The cement used in the tests was Lafarge PO42.5R cement, and the water reducer was GK-3000 polycarboxylic acid high-performance water reducer produced by Shijiazhuang Chang'an Yucai Building Materials Co., Ltd.

[0090] Table 4 Rebound rate of shotcrete

[0091]

[0092] As can be seen from Table 4, under the same shotcrete mix ratio, the use of the powdered alkali-free accelerator of the present invention to prepare a liquid accelerator at a dosage of 6% to 7% results in a low rebound rate (<6%) of the shotcrete, demonstrating good application results. The alkali-free accelerators of Comparative Examples 1 to 7, even at higher dosages than the various embodiments of the present invention, still achieve high rebound rates (>9%) of the shotcrete.

[0093] In summary, the powdered alkali-free quick-setting agent of the present invention has good comprehensive performance, simple preparation process, low transportation cost, convenient storage and use, good water solubility, can be added with water on site for immediate use, has good adaptability to cement, and can be compounded with water in different proportions to form liquid quick-setting agents of different concentrations according to different cement properties. It is alkali-free and chlorine-free, has a low dosage, high early strength, 1d compressive strength ≥15MPa, no loss of later strength, 28d compressive strength ratio ≥100%, good stability, low rebound rate of shotcrete, rebound rate <6%, and all indicators meet the requirements of GB / T35159-2017 "Accelerator for Shotcrete", and is very suitable for promotion and application.

[0094] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0095] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A powdery alkali-free quick-setting agent, characterized in that: The raw materials for preparing the powdered alkali-free quick-setting agent include, by weight: 62-80 parts of a coagulant, 5-12 parts of a modified nano-ettringite, 4-10 parts of a fluoride, 4-8 parts of a complexing agent, 2-3 parts of an early strength agent, 2-3 parts of a pH regulator, 1-2 parts of a stabilizer, 0.5-1 parts of a viscosity regulator, and 0.01-0.02 parts of a defoaming agent; Wherein, the preparation method of described modified nano ettringite comprises the following steps: S1) mixing water and sulphoaluminate cement uniformly, centrifuging, and then filtering to obtain a cement paste supernatant; S2) adding the polymer dispersion to the cement paste supernatant and stirring uniformly to form a dispersant solution; S3) adding a calcium salt aqueous solution, a silicon salt aqueous solution, an aluminum salt aqueous solution, and a sulfate aqueous solution dropwise to the dispersant solution, wherein the calcium-silicon molar ratio of the four raw materials, the calcium salt, the silicon salt, the aluminum salt, and the sulfate, is 2.5-3.0, the calcium-aluminum molar ratio is 10.0-15.0, and the aluminum-sulfur molar ratio is 0.5-0.8, and stirring is performed using a high-speed shear disperser during the dropwise addition process, and the reaction temperature is 10° C.-30° C.; S4) adding an organic modifier to adjust the pH to 11.0-12.0, and continuing stirring to obtain a suspension; S5) spray-drying the suspension to obtain a white powder, thereby obtaining the modified nano-ettringite; The coagulant includes components A and B in a mass ratio of (8.5-9.0): (1.0-1.5), wherein component A includes at least one of industrial-grade aluminum sulfate 18hydrate and polyaluminum sulfate, and component B includes at least one of polyaluminum ferric silicate, polyaluminum ferric phosphate, and polyaluminum magnesium silicate.

2. The powdery alkali-free quick-setting admixture according to claim 1, characterized in that: The modified nano-ettringite comprises nano-ettringite powder containing nano-calcium silicate and having an average particle size of 20-80 nm.

3. The powdery alkali-free quick-setting admixture according to claim 1, characterized in that: The fluoride includes at least one of magnesium fluorosilicate, ammonium fluoroaluminate, potassium fluoroaluminate and sodium fluoride.

4. The powdery alkali-free quick-setting admixture according to claim 1, characterized in that: The complexing agent includes organic alcohol amine.

5. The powdery alkali-free quick-setting admixture according to any one of claims 1 to 4, characterized in that: The early strength agent includes at least one of nano-silica and nano-alumina; and / or the pH regulator includes at least one of glycine, p-toluenesulfonic acid, oxalic acid, and tartaric acid; and / or the stabilizer includes at least one of pseudo-boehmite, lithium magnesium silicate, and hydrated magnesium silicate; and / or the viscosity regulator includes at least one of weinlun gum, xanthan gum, guar gum, hydroxyethyl cellulose, and sodium polyacrylate; and / or the defoamer includes a powdered polyether-modified polysiloxane defoamer.

6. The method for preparing the powdery alkali-free quick-setting admixture according to claim 1, wherein: The method comprises the following steps: The coagulant, fluoride and complexing agent are added to a grinder for grinding, and then a pH regulator, a viscosity regulator and a stabilizer are added for grinding. The ground materials and modified nano-ettringite, early strength agent and defoaming agent are added to a mixer for mixing to obtain the powdered alkali-free quick-setting agent.

7. The method for preparing the powdery alkali-free quick-setting admixture according to claim 6, wherein: The calcium salt aqueous solution includes an aqueous solution of at least one of calcium nitrate, calcium formate, and calcium acetate; And / or, the silicon salt aqueous solution includes an aqueous solution of at least one of sodium silicate, potassium silicate, and magnesium fluorosilicate; And / or, the aluminum salt aqueous solution includes an aqueous solution of at least one of aluminum nitrate and aluminum dihydrogen phosphate; And / or, the sulfate aqueous solution includes an aqueous solution of at least one of magnesium sulfate, manganese sulfate, and lithium sulfate.

8. The method for preparing the powdery alkali-free quick-setting admixture according to claim 6 or 7, characterized in that: The organic modifier includes at least one of monoethanolamine, diethanolamine, and diethanol monoisopropanolamine.

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