CN117417164A - Polymer in-situ modification-based 3D printing concrete and preparation method thereof - Google Patents

Abstract

The invention provides a polymer in-situ modified 3D printing concrete and a preparation method thereof, and relates to the technical field of 3D printing materials. Comprises the following components in percentage by weight: 35-40% of Portland cement; 0.2 to 0.5 percent of polypropylene fiber; 0.2 to 0.4 percent of polycarboxylate water reducer; cement hydration speed regulator 0.1-0.2%; 13.5 to 14 percent of water; 2-5% of an in-situ polymer modifier; the rest is fine sand. The 3D printing concrete has excellent pumpability, extrudability and constructability, can be continuously printed, and has good appearance quality.

Description

Polymer in-situ modification-based 3D printing concrete and preparation method thereof

Technical Field

The invention relates to the technical field of 3D printing materials, in particular to a polymer in-situ modified 3D printing concrete and a preparation method thereof.

Background

The concept of 3D printing technology was proposed in the last 70 th century, a rapid prototyping technology commonly referred to as additive manufacturing (additive manufacturing). The basic principle of the method is that a target object is presented by a 3D model on a computer, then the model is segmented and layered, printers are used for printing in a layered manner, and the layers are overlapped to form a complete object. With the rapid development of 3D printing technology, people begin to research the application of the technology in the field of construction, compared with the traditional construction mode, the concrete 3D printing is environment-friendly, energy-saving and safe, and if the large-scale application is realized, great convenience is brought to human beings.

The 3D printing technology provides the following special performance requirements for concrete materials: (1) Pumpability, 3D printed concrete typically delivers material to the printhead by pumping, requiring the printed material to have good flowability, i.e., a certain pumpability; (2) The extrudability, the printed concrete should be able to maintain good uniformity when extruded through the print head under pressure; (3) The constructability, the material must remain in a certain shape after extrusion to the design location, and the first layer of material should have a certain load-bearing capacity without significant deformation before the second layer of material is laminated. Shape retention depends on the one hand on the thixotropic and setting speed of the slurry and on the other hand on the print layer thickness and the speed of printing. If the material does not have good shape retention, it is difficult to print out the design shape.

The 3D printing step is generally that the prepared 3D concrete material is pumped into a printing nozzle of a 3D printer, a pre-designed and sliced model is opened on an operation platform of the 3D printer, and printing is started by clicking. The printing parameters of the printer nozzle diameter, the single-layer printing height, the walking speed, the layer-to-layer interval and the like are preset by software.

The existing preparation method of 3D printing concrete generally adopts two technical routes: (1) The rapid hardening materials such as sulphoaluminate cement, geopolymer cement, accelerator, coagulant and the like are adopted to accelerate the setting and hardening of concrete, and the ideal state is that the rapid hardening materials have certain extrudability before printing and have certain shape retention capability and constructability after printing. But the pumpability of 3D printed concrete is continuously reduced with time, and the shape retention and constructability are continuously enhanced, which is a gradual process. The 3D printed concrete at different time points has large difference in performance, which may cause difference in quality of the printed concrete at different time points, and the workable time of the printing operation is insufficient. If printed too late, blockage of the pumping line and the extrusion head may occur, resulting in poor extrudability; if the printing is performed too early, the shape retention capability of the concrete is insufficient and the constructability is poor. (2) A certain amount of thixotropic agent, air entraining agent and other materials are mixed into the concrete, so that the concrete has certain thixotropic property, good pumpability and extrudability, but the concrete has low setting and hardening speed, and the shape retaining capability provided by the thixotropic agent is insufficient, so that the constructability and printing quality are poor.

At present, most cement-based thixotropic agents are suitable for prestressed grouting, self-leveling concrete and self-compacting concrete, for example, the application number is 201410283518.0, namely the thixotropic agent for a cement-based system and a preparation method thereof are mainly suitable for a high-fluidity system, and mainly solve the problem of workability of concrete. The application number 201310459296.9 is "a ready-mixed mortar water-retention thixotropic agent and a preparation method thereof", and more is to improve the water retention and cohesiveness of the mortar. The application number 201611221165.7 is that the liquid thixotropic agent prepared by the thixotropic agent preparation method for cement-based systems is not beneficial to the industrial production of 3D printing building dry powder. The application number 201610894393.4 is that the white carbon black mainly plays a thixotropic role through water absorption in the thixotropic agent for the polycarboxylate water reducer, the thixotropic polycarboxylate water reducer and application thereof, and the polycarboxylate water reducer releases water among particles through steric hindrance or electrostatic effect, so that the water consumption of fresh concrete is reduced, and the water consumption and durability are enhanced. The application number 201710566069.6 discloses that sodium dodecyl sulfate serving as a foaming agent cannot play a flocculation role, is not in the category of inorganic salts, and meanwhile, polyacrylamide serving as one of foam stabilizers does not have a thixotropic early strength effect, the polyacrylamide can play a thixotropic early strength effect within a reasonable mixing amount range, the mixing amount is low, the thickening or thixotropic effect is only achieved, the mixing amount is high, the thixotropic and thickening effects are too high, a material needs a strong shearing force to destroy a flocculation structure, and pumping and extrusion are difficult to realize.

As can be seen, the above-mentioned technologies have various problems, and cannot meet the performance requirements of pumpability, shape-retaining ability and constructability of the 3D printed concrete, so that it is difficult to promote the large-scale popularization and application of the 3D printed concrete technology in the building industry.

Disclosure of Invention

(one) solving the technical problems

Aiming at the defects of the prior art, the invention provides a polymer in-situ modified 3D printing concrete and a preparation method thereof.

(II) technical scheme

In order to achieve the above purpose, the invention is realized by the following technical scheme:

the polymer in-situ modified 3D printing concrete comprises the following components in percentage by weight:

the rest is fine sand.

Preferably, the in-situ polymer modifier comprises an alkali-resistant polymer monomer, an initiator and a cross-linking agent, wherein the weight ratio of the alkali-resistant polymer monomer to the initiator to the cross-linking agent is 5:1:1-8:1:1.

Preferably, the alkali-resistant polymer monomer is acrylamide.

Preferably, the initiator is selected from any one of azobisisobutyronitrile, azobis dimethyl valeronitrile and sodium azobiscyano valerate.

Preferably, the crosslinking agent is N, N' -methylenebisacrylamide.

Preferably, the cement hydration speed regulator is a mixture of lithium carbonate and sodium gluconate, and the mass ratio of the lithium carbonate to the sodium gluconate is 1:1-2:1.

In another aspect, a method for preparing a polymer in situ modified 3D printed concrete, comprising the steps of:

s1, weighing silicate cement, fine sand, polypropylene fiber, a polycarboxylate water reducer, water, an alkali-resistant polymer monomer, an initiator, a cross-linking agent and a cement hydration speed regulator according to the proportion;

s2, uniformly stirring an alkali-resistant polymer monomer and 50% of water to form a solution A;

uniformly stirring an initiator, a crosslinking agent, a polycarboxylate superplasticizer and the rest 50% of water to form a solution B;

mixing silicate cement, fine sand, polypropylene fiber and cement hydration speed regulator to form dry powder C;

and S3, adding the solution A and the solution B while stirring the dry powder C, and fully and uniformly mixing to obtain the 3D printing concrete.

(III) beneficial effects

The invention provides a polymer in-situ modified 3D printing concrete. Compared with the prior art, the method has the following beneficial effects:

1. the acrylamide is an organic small molecular polymer with hydrophilic groups, and can improve the fluidity of the freshly mixed 3D printed concrete, thereby improving the pumpability and extrudability of the 3D printed concrete. After the 3D printing concrete is extruded from the printing head, acrylamide and a cross-linking agent are rapidly subjected to in-situ polymerization under the catalysis of an initiator, a reaction formula is shown as formula 1, a large amount of flocculent polymer gel is rapidly formed, a fixed shape is formed, and the bearing capacity and the deformation resistance are rapidly improved, so that the shape retaining capacity and the constructability of the 3D printing concrete are improved, the 3D printing concrete can be continuously printed, and the physical appearance quality is good.

2. The acrylamide is an organic small molecular polymer with hydrophilic groups, can partially replace the water reducing effect of the water reducer, and is beneficial to the uniform dispersion of each component.

3. Due to the excellent characteristic of in-situ polymerization modification, acrylamide is polymerized in situ in a cement matrix to form a complete and uniformly distributed three-dimensional polymer network, and the acrylamide is interpenetrated with a network structure formed by cement hydration to form a composite network structure, so that the network structure is more compact than a network structure formed by simply adding polyacrylamide, the network structure strength of 3D printed concrete is improved greatly, and the shape retention capacity and the constructability are obviously enhanced, so that continuous printing can be realized.

4. The acrylamide reacts with calcium ions, aluminum ions and silicate in the silicate cement to promote the formation of dicalcium silicate and tricalcium silicate, and the calcium silicate and tricalcium silicate are hydrolyzed and filled into micro pores of the cement stone at the same time to play a role in filling. The in-situ polymerization of the acrylamide forms a space reticular structure, plays a bridging role, reduces the porosity, improves the compressive strength of the concrete and improves the durability of the concrete.

5. The 3D printing concrete has certain hydration heat when hydrated, for example, a peroxide initiator commonly used in polyacrylamide is selected to be easily decomposed and lose efficacy in water, and an azo compound initiator selected from azodiisobutyronitrile, azodi-dimethyl valeronitrile, azodi-cyano sodium valerate and the like is not easily hydrolyzed in water by heat.

6. The acrylamide can be subjected to polymerization reaction under the catalysis of the initiator, and the cross-linking agent N, N' -methylene bisacrylamide is added into the acrylamide to form polyacrylamide gel, so that the flocculation structure strength is higher than that of the polyacrylamide, and the constructability and the printing quality of the 3D printing concrete can be improved.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1, 3D printer used in example 1;

FIG. 2 is a photograph of the molding state of concrete in the 3D printing process of the printed concrete prepared in example 1;

FIG. 3 is a photograph of a 3D printed concrete prepared in example 1 after being printed and molded;

fig. 4 is a partial enlarged view of a portion of the 3D printing concrete prepared in example 1 after being printed and molded;

fig. 5 is a photograph of a 3D printed concrete prepared in example 2 after being printed and molded;

fig. 6, photographs of concrete molding state during the printing process of the 3D printing concrete prepared in comparative example 1.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

According to the embodiment of the application, the 3D printing concrete based on polymer in-situ modification and the preparation method thereof are provided, so that the problem that the existing 3D printing concrete cannot meet the performances of pumpability, shape retaining capacity and constructability is solved, and the effects of continuous printing and good appearance quality of a printed object are achieved.

The technical scheme in the embodiment of the application aims to solve the technical problems, and the overall thought is as follows:

the in-situ polymerization reaction of acrylamide and the cross-linking agent under the catalysis of the initiator has the characteristic of mutation, namely, the polymerization reaction degree is low before a certain time point, and the polymerization reaction rapidly occurs when the certain time point is reached. Compared with the gradual change effect of the rapid setting and rapid hardening material on the performance of the 3D printing concrete, the 3D printing concrete based on the polymer in-situ modification has small influence on pumpability and extrudability of the concrete before printing, and can rapidly improve the constructability after printing, so that the printing quality and efficiency are greatly improved. Therefore, the 3D printing concrete has excellent pumpability, extrudability and constructability, can be continuously printed, and has good appearance quality.

In order to better understand the above technical solutions, the following detailed description will refer to the accompanying drawings and specific embodiments.

Example 1:

the embodiment provides a polymer in-situ modified 3D printing concrete which comprises the following raw materials in percentage by weight:

35.0% of Portland cement;

0.2% of polycarboxylate water reducer;

cement hydration speed regulator 0.1%;

13.5% of water;

2% of in-situ polymer modifier.

The in-situ polymer modifier consists of alkali-resistant polymer monomer, initiator and cross-linking agent in the ratio of 5 to 1.

The alkali-resistant polymer monomer is acrylamide.

The initiator is perazo diisobutyronitrile.

The cross-linking agent is N, N' -methylene bisacrylamide.

The cement hydration speed regulator is a mixture of lithium carbonate and sodium gluconate, and the mass ratio of the lithium carbonate to the sodium gluconate is 1:1.

The preparation method of the polymer in-situ modified 3D printing concrete comprises the following steps:

s1, respectively weighing silicate cement, fine sand, polypropylene fiber, a polycarboxylate water reducer, water, alkali-resistant polymer monomer, an initiator, a cross-linking agent and a cement hydration speed regulator according to the proportion;

s2, uniformly stirring an alkali-resistant polymer monomer and 50% of water to form a solution A; uniformly stirring an initiator, a crosslinking agent, a polycarboxylate superplasticizer and the rest 50% of water to form a solution B; mixing silicate cement, fine sand, polypropylene fiber and cement hydration speed regulator to form dry powder C;

and S3, adding the solution A and the solution B while stirring the dry powder C, and fully and uniformly mixing to obtain the polymer in-situ modified 3D printing concrete.

As shown in fig. 1 and 2, the prepared 3D printing based on polymer in-situ modification is pumped into a printing nozzle of a 3D printer, a pre-designed and sliced model is opened on an operating platform of the 3D printer, and printing is started by clicking. Wherein the diameter of the printer nozzle is 20mm, the single-layer printing height is 13mm, the walking speed is 6cm/s, and the interval between layers is 40s. After the 3D printing concrete is extruded from the printing head, the 3D printing concrete can be rapidly formed into a fixed shape and has excellent shape retention capability, so that the 3D printing concrete can be continuously printed, and the 3D printing concrete has good appearance quality in a printing and forming real object as shown in fig. 3 and 4.

Example 2

The embodiment provides a polymer in-situ modified 3D printing concrete, wherein the 3D printing concrete comprises the following raw materials in percentage by weight:

the in-situ polymer modifier consists of alkali-resistant polymer monomer, initiator and cross-linking agent in the ratio of 8 to 1.

The alkali-resistant polymer monomer is acrylamide.

The initiator is azo-bis-dimethyl valeronitrile.

The cross-linking agent is N, N' -methylene bisacrylamide.

The cement hydration speed regulator is a mixture of lithium carbonate and sodium gluconate, and the mass ratio of the lithium carbonate to the sodium gluconate is 2:1.

The preparation method of the polymer in-situ modified 3D printing concrete and the method for printing the real object are the same as in example 1. The photo of the cured object after printing, forming and curing is shown in figure 5. As shown in fig. 5, the 3D printed concrete has good physical appearance quality.

Comparative example 1:

this comparative example differs from example 1 in that an alkali-free aluminum sulfate accelerator was used instead of the in-situ polymer modifier, as in example 1. The concrete is formed during printing as shown in fig. 6.

As shown in fig. 6, after the 3D printing concrete prepared using the alkali-free aluminum sulfate accelerator is extruded from the printing head, a fixed shape cannot be rapidly formed, the shape-retaining ability is poor, the deformation is large, and even collapse is generated, so that the 3D printing concrete cannot be continuously printed, the printable effect is far less than that of examples 1 and 2, and the advantage of the in-situ polymerization method is seen.

It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.

The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (7)

1. The polymer in-situ modified 3D printing concrete is characterized by comprising the following components in percentage by weight:

the rest is fine sand.

2. The polymer in situ modified 3D printed concrete of claim 1, wherein the in situ polymer modifier comprises an alkali-resistant polymer monomer, an initiator, and a cross-linking agent, wherein the weight ratio of the alkali-resistant polymer monomer, the initiator, and the cross-linking agent is 5:1:1 to 8:1:1.

3. The polymer in situ modified 3D printed concrete of claim 1, wherein the alkali resistant polymer monomer is acrylamide.

4. The polymer-based in-situ modified 3D printed concrete of claim 1, wherein the initiator is selected from any one of azobisisobutyronitrile, azobis-dimethyl valeronitrile, sodium azobiscyano valerate.

5. The polymer-based in-situ modified 3D printed concrete of claim 1, wherein the cross-linking agent is N, N' -methylenebisacrylamide.

6. The polymer in situ modified 3D printed concrete of claim 1, wherein the cement hydration rate regulator is a mixture of lithium carbonate and sodium gluconate, and the mass ratio of the lithium carbonate to the sodium gluconate is 1:1-2:1.

7. A method for preparing a polymer-based in-situ modified 3D printed concrete as claimed in any one of claims 1 to 6, comprising the steps of:

s1, weighing silicate cement, fine sand, polypropylene fiber, a polycarboxylate water reducer, water, an alkali-resistant polymer monomer, an initiator, a cross-linking agent and a cement hydration speed regulator according to the proportion;

s2, uniformly stirring an alkali-resistant polymer monomer and 50% of water to form a solution A;

uniformly stirring an initiator, a crosslinking agent, a polycarboxylate superplasticizer and the rest 50% of water to form a solution B;

mixing silicate cement, fine sand, polypropylene fiber and cement hydration speed regulator to form dry powder C;

and S3, adding the solution A and the solution B into the dry powder material C under the stirring condition, and fully and uniformly mixing to obtain the polymer in-situ modified 3D printing concrete.