CN115724610A

CN115724610A - Thixotropic agent and preparation method and application thereof

Info

Publication number: CN115724610A
Application number: CN202211456393.8A
Authority: CN
Inventors: 蒋亚清; 王玉; 殷康蜓
Original assignee: Hohai University HHU
Current assignee: Hohai University HHU
Priority date: 2022-11-21
Filing date: 2022-11-21
Publication date: 2023-03-03

Abstract

The invention relates to the technical field of building additives, in particular to a thixotropic agent and a preparation method and application thereof, wherein the thixotropic agent is prepared by fully mixing 5-7 parts of montmorillonite, 3-4 parts of an intercalating agent, 0-0.5 part of a modifier, 2-2.5 parts of ethylene diamine tetraacetic acid and 85-90 parts of water, and then adding 0.8-1 part of a dispersant. When the self-compacting cement-based material is used, the solid components accounting for 0.5-0.8% of the mass of the cementing material are doped into a 3D printing cement-based material, self-compacting concrete and a product, the thixotropy of slurry and the yield stress time-varying rate are increased, the 3D printing material is promoted to instantly have high building property after being extruded, the surface humidity of a printing layer is improved through the water retention effect, and the cement-based material 3D printing component is endowed with excellent interlayer bonding performance; meanwhile, the slump expansion degree and the segregation resistance of the self-compacting concrete can be improved.

Description

Thixotropic agent and preparation method and application thereof

Technical Field

The invention relates to the technical field of building additives, in particular to a thixotropic agent and a preparation method thereof.

Background

Montmorillonite is a 2: the layered aluminosilicate clay mineral of type 1 has a basic structural unit comprising a layer of alumino-octahedra sandwiched between two layers of silica tetrahedra, and has a layered structure formed by sharing oxygen atoms. Silicon in silicon-oxygen tetrahedron in the montmorillonite wafer layer can be replaced by aluminum, and aluminum in aluminum-oxygen octahedron can be replaced by magnesium iron easily. Due to the unique layered structure, the montmorillonite has excellent performances of water swelling, high dispersibility, adsorbability and the like, and can effectively improve the thickening and water retention of cement mortar and reduce the creep resistance and the anti-settling capacity in concrete application. However, as an indispensable additive in concrete, when montmorillonite is doped in concrete, polyethylene glycol side chains of polycarboxylate superplasticizer (PCE) molecules are connected to silanol groups on the surface of an aluminum silicon layer in interlayer channels of montmorillonite through multiple hydrogen bonds, resulting in a large amount of PCE molecules being trapped in interlayer regions of a clay structure, and less PCE molecules being available for cement dispersion. The amount of PCE water reducer adsorbed by montmorillonite is reported to be about 100 times higher than cement. Therefore, the sensitivity of the PCE to the montmorillonite greatly weakens the water reducing efficiency of the PCE in the slurry, reduces the working performance of the concrete in the construction process and limits the application of the montmorillonite in the construction industry.

In the 3D printing process of the cement-based material or the pouring process of the self-compacting concrete, the printing and pouring materials need to keep good flowing performance so that slurry can have good transportation and pumping performance, and need to have good thixotropic performance when being extruded or poured to a designed position so as to keep the extruded stack or pouring shape, and when the printing materials on the second layer are extruded and stacked, the lower layer can have enough static yield stress, the rate of change maintains the weight of the dead weight and the subsequent layer without obvious deformation. This constructability requires the thixotropic properties of the paste to be controlled. Thixotropy refers to the ability of a material to flow at high shear rates but increase in strength at low shear rates or at rest. The thixotropic property of the freshly mixed cement paste mainly comes from the initial structure of colloidal bonding and CSH bridges in the paste, is caused by intermolecular force and early hydration, and determines the early flocculation state of the paste. The dispersed montmorillonite can fill gaps between cement particles and/or flocculating constituents and enhance the connection among the particles, and the montmorillonite can also form an interconnection structure under high electrolyte concentration, so that the size distribution of colloid in slurry can not be changed by the montmorillonite, but the combination of particles or aggregates can be increased, the thixotropic stacking rate of the material in the printing or pouring process is enhanced, the rapid increase of the static yield stress of the extruded slurry is realized, the template pressure of self-compacting concrete is reduced, and the constructability of 3D printed cement-based materials is improved. Therefore, the preparation and application of the thixotropic agent based on montmorillonite intercalation modification and suitable for cement-based material 3D printing or self-compacting concrete are necessary to be researched, so as to increase the thixotropy and static yield stress time-varying rate of fresh slurry, improve the construction performance and interlayer bonding performance of a 3D printing member, and improve the slump expansion degree and segregation resistance of self-compacting concrete.

In order to improve the thixotropic properties of 3D printing cement-based materials and self-compacting concrete, the conventional thixotropic agents mainly comprise cellulose ether, polyacrylamide, methyl cellulose ether and the like, and although the thixotropic properties of the materials can be improved, the problems of high mixing amount, poor compatibility with a water reducing agent, high fluidity loss and the like exist.

CN113402904A discloses a preparation method of a low-viscosity composite clay thixotropic agent, which comprises dispersing purified calcium-based bentonite mineral powder, refined sepiolite or refined attapulgite in medium water to prepare suspension slurry, sequentially adding a viscosity reducer, a modifier and an organic acid for modification treatment to obtain modified slurry, and then performing spray drying and airflow pulverization to obtain a finished product.

CN111718149A discloses an oil well cement low-viscosity thixotropic agent and a preparation method thereof, wherein the preparation method comprises the step of effectively combining fly ash and a synthetic polymer thixotropic agent to enable the fly ash to adsorb the polymer thixotropic agent. The invention utilizes the ball effect of the fly ash, the cement paste is low in viscosity in the pump injection process, and the polymer quickly forms a grid structure when the cement paste is static, so that the thixotropic function is achieved. However, the thixotropic agent does not indicate the proper mixing amount in the cement paste, the polymer thixotropic agent mainly comprises a polyacrylamide polymer, polyacrylamide is used as a foam stabilizer, the thixotropic effect can be achieved within a reasonable mixing amount range, and the pumping extrusion performance of the 3D printing material is greatly influenced by too high mixing amount which causes the loss of the fluidity of the paste.

CN109455973.B discloses a thixotropic agent suitable for 3D printing sulphoaluminate cement-based materials, which is prepared by mixing 18 parts of papermaking sludge ash, 12 parts of polyvinyl alcohol, 15 parts of diatomite, 15 parts of metakaolin and 12 parts of sodium polyacrylate. The thixotropic agent can prolong the 3D printing time to 30-60 min and stabilize the slurry structure of the 3D printing sulphoaluminate cement-based material. However, the method mainly utilizes clay substances and slow-setting components to regulate and control the setting and hardening rate of printing paste, is a special thixotropic agent for a sulphoaluminate system, and cannot flexibly regulate and control the rheological properties of all types of cement paste.

Although the thixotropic property of the cement-based material can be improved to a certain extent by the above prior art scheme, the setting time of the slurry is mostly regulated and controlled, and the influence of the static yield stress time-varying rate after the material is extruded or poured on the constructability of the slurry is not considered.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a thixotropic agent and a preparation method and application thereof, and the thixotropic agent has the advantages of simple process and low mixing amount, can effectively increase the thixotropy and the static yield stress time-rate change of a concrete material, and realizes excellent building performance and interlayer bonding performance of a component material.

In order to achieve the purpose, the invention provides the following technical scheme:

a thixotropic agent characterized by: the raw materials comprise, by weight, 5-7 parts of montmorillonite, 3-4 parts of intercalating agent, 0-0.5 part of modifier, 2-2.5 parts of ethylene diamine tetraacetic acid, 85-90 parts of water and 0.8-1 part of dispersant; the montmorillonite is at least one of calcium-based montmorillonite or sodium-based montmorillonite with the particle size of 0.1-1 mu m; the intercalation agent is a maleic acid-acrylic acid block copolymerization polycarboxylic acid water reducing agent with the water reducing rate of 25-30%.

Further, the modifier is at least one of a sodium bicarbonate solution or a sodium acetate solution with the mass concentration of 5%.

Further, the dispersing agent is a viscosity-reducing type polycarboxylate water reducer, namely the polycarboxylate water reducer which enables slurry to have high fluidity and low viscosity and slump-retaining performance at the same time.

The preparation method of the thixotropic agent comprises the following steps:

(1) Adding montmorillonite in parts by weight into a reaction kettle, adding accurately metered water, stirring at the rotating speed of 350-550 r/min for 1.5-2 h, and standing for 24 h;

(2) Sequentially adding the measured intercalator, the modifier, the ethylene diamine tetraacetic acid and the water into a reaction kettle, and stirring and dissolving;

(3) Heating to 60 ℃, keeping the temperature, stirring the montmorillonite solution, slowly dripping the intercalation agent solution, finishing dripping within 30min, and keeping the temperature for reaction for 6 hours;

(4) Adding the weighed dispersant, stirring for 30min at 60 ℃, cooling to 30 ℃, stopping stirring, and pumping the prepared suspension to a storage tank.

The thixotropic agent can be used for 3D printing of cement-based materials, self-compacting concrete and products. When in use, the dosage of the thixotropic agent is 0.5 to 0.8 percent of the mass of the gelled material according to the solid component in the thixotropic agent.

The thixotropic agent promotes the 3D printing material to instantly have high constructability after being extruded by increasing the thixotropy of slurry and the time-varying rate of yield stress, improves the surface humidity of the printing layer by the water retention effect, and endows the cement-based material 3D printing member with excellent interlayer bonding performance; meanwhile, the slump expansion degree and the segregation resistance of the self-compacting concrete can be improved.

Compared with the prior art, the invention has the beneficial effects that:

(1) The preparation method has mild and simple conditions, the used raw materials are nontoxic and harmless and are easy to prepare, and the synthesized thixotropic agent is stored in a suspension dispersion system and is beneficial to mixing or injecting when the material is used.

(2) The thixotropic agent can also obviously improve the thixotropic property (the area of a thixotropic ring is improved by about 2 times) and the time-varying rate of static yield stress of the cement-based material under the condition of lower mixing amount, regulate and control the rheological property and the printable time of the slurry, and produce printable slurry and self-compacting concrete with good extrudability and excellent constructability.

(3) Due to the internal curing and water-retaining effects of the montmorillonite, the water loss on the surface of the printing layer or the pouring layer can be reduced, the shrinkage of the surface of the printing layer or the pouring layer is reduced, and the microstructure of the bonding area of the printing part interface is improved, so that the effect of improving the bonding strength between component layers is achieved.

Drawings

FIG. 1 is a graph showing the area of a thixotropic ring with and without a thixotropic agent.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

Example 1

A preparation method of a thixotropic agent comprises the following steps:

(1) Adding montmorillonite in parts by weight into a reaction kettle, adding accurately metered water, magnetically stirring at a rotating speed of 350-550 r/min for 1.5-2 h, and standing for 24 h;

(4) Adding a metered dispersant, stirring for 30min at 60 ℃, cooling to 30 ℃, stopping stirring, and pumping the prepared suspension to a storage tank.

Example 2

According to the weight portion, 5 portions of sodium-based montmorillonite with the grain diameter of 0.1-1 mu m, 4 portions of intercalation agent, 2.2 portions of ethylene diamine tetraacetic acid, 88 portions of water and 0.8 portion of dispersing agent are stirred in a reaction kettle according to the preparation steps of the embodiment 1 to prepare thixotropic agent suspension liquid T1.

Example 3

According to the parts by weight, 6 parts of sodium montmorillonite with the particle size of 0.1-1 mu m, 3.5 parts of intercalation agent, 2.5 parts of ethylene diamine tetraacetic acid, 87 parts of water and 1 part of dispersing agent are stirred in a reaction kettle according to the preparation steps of the embodiment 1 to prepare thixotropic agent suspension liquid T2.

Example 4

According to the weight portion, 7 portions of calcium-based montmorillonite with the grain diameter of 0.1-1 mu m, 3.5 portions of intercalation agent, 0.25 portion of sodium bicarbonate solution with the mass concentration of 0.5 percent, 2.3 portions of ethylene diamine tetraacetic acid, 86 portions of water and 0.95 portion of dispersing agent are stirred in a reaction kettle according to the preparation steps of the embodiment 1 to prepare thixotropic agent suspension T3.

Example 5

According to the weight portion, 5 portions of calcium-based montmorillonite with the grain diameter of 0.1-1 mu m, 3 portions of intercalation agent, 0.5 portion of sodium bicarbonate solution with the mass concentration of 0.5 percent, 2.5 portions of ethylene diamine tetraacetic acid, 88 portions of water and 1 portion of dispersing agent are stirred in a reaction kettle according to the preparation steps of the embodiment 1 to prepare thixotropic agent suspension T4.

Example 6

According to the weight portion, 6 portions of calcium-based montmorillonite with the grain diameter of 0.1 to 1 mu m, 3.6 portions of intercalation agent, 0.5 portion of sodium sulfate solution with the mass concentration of 0.5 percent, 2 portions of ethylene diamine tetraacetic acid, 87 portions of water and 0.9 portion of dispersing agent are stirred in a reaction kettle according to the preparation steps of the embodiment 1 to prepare thixotropic agent suspension T5.

Example 7

According to the weight portion, 7 portions of sodium-based montmorillonite with the grain diameter of 0.1 to 1 mu m, 3 portions of intercalation agent, 2.5 portions of ethylene diamine tetraacetic acid, 86.6 portions of water and 0.9 portion of dispersing agent are stirred in a reaction kettle according to the preparation steps of the embodiment 1 to prepare thixotropic agent suspension liquid T6.

Application example 1

The thixotropic agent T1, the thixotropic agent T2, and the thixotropic agent T3 prepared in examples 2 to 4 were applied to self-compacting concrete in such a manner that solid components account for 0.8% of the mass of the cementitious material, C30 self-compacting concrete was configured according to the specifications of GB/T50080-2002 standard for testing the performance of general concrete mixtures and JGJ/T283-2012 specification for application of self-compacting concrete, compared to a reference concrete group not doped with the thixotropic agent, and the slump expansion and segregation rate of the self-compacting concrete were measured as shown in table 1 by performing a filling test and a segregation resistance test on fresh concrete.

TABLE 1 working Properties of freshly mixed self-compacting concrete

As can be seen from the above table, the reference concrete group 1 has lower slump expansion and segregation resistance than the thixotropic agent-doped self-compacting concretes T1, T2 and T3 even under the same formulation and construction conditions because no thixotropic agent is added. The T1, T2 and T3 groups of self-compacting concrete doped with the thixotropic agent are different in raw material composition, so that the performance of fresh concrete is different, and the self-compacting concrete containing the modified intercalated sodium-based montmorillonite thixotropic agent has more excellent slump expansion and segregation resistance than the self-compacting concrete containing the modified intercalated calcium-based montmorillonite thixotropic agent.

Application example 2

The thixotropic agents T1, T2 and T3 prepared in the examples 2 to 4 are applied to 3D printing cement-based materials in a manner that solid components account for 0.7% of the mass of the gelled materials, compared with a reference group 3D printing cement-based material not doped with the thixotropic agents, in the experiment, a fresh 3D printing mortar with a water cement ratio of 0.32, a sand-to-cement ratio of 1.5 and a gelled material of PII 42.5-grade portland cement is prepared, and the rheological properties of the slurry are tested and shown in Table 2:

table 2 rheological properties of freshly mixed 3D printing mortar

Contrast 3D and print T1, 3D prints T2, 3D prints the mortar rheology parameter that T3 and 3D printed benchmark group 1 prepared, the group of doping thixotropic agent no matter is initial yield stress or static yield stress's time-varying rate all improves a lot than the benchmark group that does not mix, and as shown in figure 1, 3D prints T2 group thixotropic ring area and has promoted nearly 2 times than 3D and prints benchmark group thixotropic ring area, show that the adding of thixotropic agent can effectively regulate and control 3D and print the rheology of cement-based material, be 3D print the material extrude the back instantaneous higher effective technological way of building performance.

Application example 3

The thixotropic agents T4, T5 and T6 prepared in the examples 5 to 7 are applied to 3D printing cement-based materials in a manner that solid components account for 0.6 percent of the mass of the gelled materials, compared with a reference group 3D printing cement-based material not doped with the thixotropic agents, the experiment prepares fresh 3D printing mortar which has a water cement ratio of 0.32, a sand-cement ratio of 1.2 and a gelled material of PII 42.5-grade portland cement, and the rheological property of the slurry and the interlayer bonding force of a 28D printing piece are tested and shown in Table 3:

table 3 rheological properties of freshly mixed 3D printing mortar

The rheological property parameters of the mortar prepared by comparing the 3D printing T4, the 3D printing T5 and the 3D printing reference group 2 and the interlayer splitting tensile strength are compared, no matter the time-varying rate of the initial yield stress or the static yield stress, the reference group not doped with the thixotropic agent has more difference than the group doped with the thixotropic agent, the thixotropic agent is shown to have high constructability after the 3D printing material is extruded by increasing the thixotropy of slurry and the time-varying rate of the yield stress, the surface humidity of the printing layer is improved by the water retention effect, and the cement-based material 3D printing component is endowed with excellent interlayer bonding performance.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. A thixotropic agent characterized by: the raw materials comprise, by weight, 5-7 parts of montmorillonite, 3-4 parts of intercalating agent, 0-0.5 part of modifier, 2-2.5 parts of ethylene diamine tetraacetic acid, 85-90 parts of water and 0.8-1 part of dispersant; the montmorillonite is at least one of calcium-based montmorillonite or sodium-based montmorillonite with the particle size of 0.1-1 mu m; the intercalation agent is a maleic acid-acrylic acid block copolymerization polycarboxylic acid water reducing agent with the water reducing rate of 25-30%.

2. A thixotropic agent as claimed in claim 1, characterised in that: the modifier is at least one of a sodium bicarbonate solution or a sodium acetate solution with the mass concentration of 5%.

3. A thixotropic agent according to claim 2, characterised in that: the dispersing agent is a viscosity-reducing polycarboxylate superplasticizer.

4. A method of making a thixotropic agent according to any one of claims 1 to 3, comprising the steps of:

5. Use of the thixotropic agent of any one of claims 1 to 3 for 3D printing cementitious materials, self-compacting concretes and articles.

6. Use of the thixotropic agent according to claim 5 in 3D printing cement-based materials, self-compacting concretes and articles, characterized in that: when in use, the thixotropic agent is mixed according to the proportion that the solid component in the thixotropic agent accounts for 0.5-0.8 percent of the mass of the gelled material.