Method for regulating and controlling rheological property of 3D printing concrete

Abstract

The invention relates to a method for regulating and controlling the rheological property of 3D printing concrete, which comprises the following steps: pumping a concrete material containing a water reducing agent into a secondary stirring container in front of a 3D printing head, introducing CO2 gas into the secondary stirring container, and meanwhile, carrying out secondary stirring on the concrete material, so that the CO2 gas and the concrete material containing the water reducing agent are subjected to physical and chemical effects; and during secondary stirring, the concrete material subjected to secondary stirring is conveyed to a 3D printing head for printing. After secondary stirring in a CO2 gas environment, the concrete material containing the water reducing agent is accelerated in hardening speed and reduced in fluidity, so that the constructability of the concrete material can be effectively improved, and the mechanical property of the concrete material added with the water reducing agent is also improved. In addition, the fluidity and the hardening speed of the concrete can be regulated and controlled by controlling the doping amount of the water reducing agent. Compared with the prior art, the technical problem that the pumpability and constructability rheology of the 3D printing concrete are difficult to be compatible can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printed concrete, and in particular to a method for regulating the rheological properties of 3D printed concrete. Background Art

[0002] 3D printing concrete technology has gradually become a hot technology for low-carbon digital construction due to its advantages such as high degree of mechanization, fast construction speed, no need for formwork, high degree of freedom in architectural design, and less material waste. However, due to its unique extrusion molding and layer-by-layer construction method, high requirements are placed on the rheological properties of the printing material. On the one hand, the concrete printing material needs to have a certain fluidity to meet the requirements of pumping (pumpability) and continuous and stable extrusion (extrudability). On the other hand, it needs to have a certain plastic strength after extrusion and can harden quickly to withstand the gravity of the upper concrete and the pressure applied to it by the print head (constructibility). However, how to solve the rheological incompatibility problem of pumpability, extrudability and constructability has always been one of the difficult problems that 3D printing concrete technology needs to solve.

[0003] In response to the above-mentioned rheological incompatibility issues of pumpability, extrudability and buildability, the main solution currently adopted by academia and industry is to find a balance point within the range of rheological properties required for pumpability, extrudability and buildability, and prepare 3D printing materials based on this balance point. However, the disadvantage of this method is that it greatly limits the applicable mix ratio of 3D printing materials and increases the amount of cement in the material, thereby increasing the carbon footprint of this technology.

[0004] In addition, in recent years, a concept of "on-demand solidification" 3D printing concrete technology has been proposed. The characteristic of this technology is that the rheological parameters of concrete can be controlled more accurately, and the rheological properties of materials at each stage of printing can be adjusted according to demand. The high-fluidity concrete material is pumped to the print head, and then the accelerator is injected near the nozzle and combined with the concrete, aiming to accelerate the setting time and change the rheological properties of the concrete so that it can have a certain strength after extrusion. The disadvantage of this 3D printing concrete rheology modification technology is that the commonly used accelerators (such as sodium chloride / calcium, sodium nitrate / calcium, sodium silicate and calcium aluminate cement) will reduce the later mechanical properties and durability of concrete. In order to compensate for the negative impact of the accelerator on the performance of concrete, the common practice in engineering is to increase the design grade of concrete strength, but this leads to an increase in the amount of cement, which not only increases the cost of concrete, but also increases the carbon emissions in the production process of its raw materials. Summary of the invention

[0005] The purpose of the present invention is to provide a new method for regulating the rheological properties of 3D printed concrete, so as to solve the technical problem of the rheological incompatibility between the pumpability and constructability of 3D printed concrete.

[0006] The objective of the present invention can be achieved by the following technical scheme: a method for regulating the rheological properties of 3D printed concrete, wherein a concrete material containing a water reducer is pumped into a secondary mixing container in front of a 3D printing head, CO2 gas is introduced into the secondary mixing container, and the concrete material is simultaneously subjected to secondary mixing, so that the CO2 gas and the concrete material containing the water reducer undergo a physical and chemical reaction, and while the secondary mixing is being performed, the secondary mixed concrete material is transported to the 3D printing head for printing.

[0007] Preferably, the water reducer is selected from one or more of polycarboxylate water reducers, lignin sulfonate water reducers, naphthalene-based high-efficiency water reducers, melamine-based high-efficiency water reducers, aminosulfonate-based high-efficiency water reducers, and fatty acid-based high-efficiency water reducers.

[0008] In the present invention, water-reducing agent molecules can be adsorbed on the surface of cement particles, converting the surface charge of cement particles into negative charge. Due to the principle of like repels like, cement particles with the same charge will repel each other, causing cement particles to disperse from each other, disintegrate the flocculation structure, and release the enclosed part of water, thereby effectively increasing the fluidity of the concrete mixture. After CO2 stirring, the carbonized product will cover the water-reducing agent molecules on the surface of cement particles, inhibiting the electrostatic repulsion caused by the water-reducing agent molecules, thereby reducing the efficiency of the water-reducing agent. Therefore, CO2 gas can significantly reduce the fluidity of concrete containing water-reducing agent and shorten the setting time.

[0009] Further preferably, the water reducer is selected from polycarboxylate water reducer.

[0010] Preferably, the water reducing agent contained in the concrete material is 0.01%-1% of the mass of cement.

[0011] Preferably, the concrete material composition includes cement clinker, mineral admixtures, sand, water, water reducing agent and thickener.

[0012] Further preferably, the water-binder ratio of the concrete material is 0.3-0.5, wherein the water-binder ratio refers to the ratio of the mass of water to the total mass of cement clinker and mineral admixtures.

[0013] Further preferably, the mortar-sand ratio of the concrete material is 0.5-1. The mortar-sand ratio refers to the ratio of the total mass of cement clinker and mineral admixture to the mass of sand.

[0014] Further preferably, the cement clinker is selected from one or more of Portland cement and clinker, aluminate cement and clinker, and sulphoaluminate cement and clinker.

[0015] Further preferably, the mineral admixture is selected from one or more of fly ash, silica fume, slag, glass powder, steel slag, waste concrete powder and limestone powder.

[0016] Further preferably, the mineral admixture accounts for 0%-50% of the mass of the whole cementitious material, and the specific amount can be selected according to national standards. Wherein, the cementitious material refers to cement clinker and mineral admixture.

[0017] Further preferably, the thickener is selected from one or more of starch ether, cellulose ether, water-soluble polyacrylamide, casein, and welan gum.

[0018] More preferably, the thickener is selected from cellulose ethers.

[0019] Further preferably, the thickener accounts for 0.01%-0.3% of the mass of the entire gelling material.

[0020] Further preferably, the sand is selected from one or more of river sand, machine-made sand and regenerated sand.

[0021] Further preferably, the water is selected from tap water or purified water.

[0022] Preferably, the concrete material is pre-mixed with a target workability of 200-300 mm, and the pre-mixed concrete material is pumped to a secondary carbonation mixer (i.e., a secondary mixing container) for carbonation mixing (i.e., CO2 gas is introduced during secondary mixing).

[0023] Preferably, during the carbonization stirring process, parameters such as CO2 flow rate, stirring speed, stirring time, etc. are adjusted as needed. In some embodiments, the workability of the concrete printing material after carbonization stirring is 150-200mm, so that it meets the requirements of 3D printing.

[0024] Further preferably, the CO2 flow rate is 1-5 L / min / kg, wherein L / min / kg refers to the corresponding CO2 flow rate per kilogram of concrete printing material, the stirring speed is 160-200 RPM, and the stirring time is 200-280 s.

[0025] Preferably, the CO2 gas is industrial-grade CO2 or industrial tail gas with a high concentration of CO2 gas.

[0026] Further preferably, the CO2 gas is industrial-grade CO2 with a CO2 concentration greater than 99% or industrial tail gas with a CO2 concentration greater than 20%.

[0027] Preferably, the method for regulating the rheological properties of 3D printed concrete comprises the following steps:

[0028] (1) The concrete materials are configured in proportion and a certain amount of water reducing agent is included in the raw materials to obtain a concrete material with higher fluidity and better pumpability;

[0029] (2) pumping the concrete material prepared in step (1) into a secondary mixing container in front of the 3D printing head;

[0030] (3) CO2 gas is introduced into the secondary mixing container, and the concrete material is secondary mixed at the same time, so that the CO2 gas and the concrete material added with the water reducer undergo physical and chemical reactions. After CO2 mixing, the fluidity of the concrete material is reduced and the setting time is shortened, thereby improving the constructability of the concrete material;

[0031] (4) While the secondary mixing is being performed, the secondary mixed concrete material is transported to the 3D printing head for printing.

[0032] The present invention proposes a new method for regulating the rheological properties of 3D printed concrete, which is similar to the "solidification on demand" method. This method can ensure that the 3D printed concrete material has good fluidity during pumping and good buildability after extrusion, thereby solving the rheological incompatibility problem of pumpability and buildability. At the same time, this method can also improve the mechanical properties of 3D printed concrete after hardening, overcoming the problem that commonly used accelerators reduce the later mechanical properties of 3D printed concrete materials.

[0033] The prior art does not consider the joint regulatory effect of water reducer and CO2 gas on the buildability of concrete. The present invention adds water reducer to concrete, which greatly improves the fluidity of concrete and prolongs the setting time. However, CO2 stirring can greatly weaken the effect of water reducer. Therefore, through CO2 stirring, the fluidity of concrete with water reducer added is reduced, and the setting time is shortened, which can further improve the buildability of 3D printed concrete. In addition, the fluidity and hardening speed of concrete can be regulated by controlling the amount of water reducer added.

[0034] The present invention utilizes the inhibitory effect of CO2 on water reducing agent and the promoting effect of CO2 on cement hydration, and regulates the rheological properties and setting time of 3D printed concrete materials by secondary stirring of the concrete materials in an environment where CO2 is introduced, thereby ensuring that the 3D printed concrete materials have good fluidity during pumping and good constructability after extrusion, thereby improving the efficiency of 3D printing.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. Compared with the concrete material before CO2 stirring, the concrete material after CO2 stirring of the present invention has lower fluidity and shorter setting time, thereby improving the constructability of the 3D printed concrete material. In addition, by controlling the amount of water reducer, the adjustment range of fluidity and setting time can be controlled to achieve the required value. Therefore, the present invention can solve the technical problem of rheological incompatibility between pumpability and constructability of 3D printed concrete by controlling CO2 stirring parameters and water reducer amount.

[0037] 2. Although water reducers can increase fluidity, some water reducers have an air entraining effect, which will increase the pores in the concrete, thereby reducing the strength of the concrete. After the present invention uses CO2 stirring, the negative effect of the water reducer on the strength is eliminated or reduced. Therefore, the method of the present invention can effectively enhance the strength of concrete, improve the mechanical properties of 3D printing concrete materials, and facilitate its application in 3D printing buildings.

[0038] 3. During the secondary mixing process of the present invention, the 3D printed concrete reacts with CO2, and the concrete can fix carbon dioxide, providing a path for carbon sequestration.

[0039] 4. The present invention does not need to increase the design grade of concrete strength, and can avoid problems such as increased cement usage, increased concrete costs, and increased carbon emissions during the raw material production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention uses greenhouse gas CO2 as a rheology regulator to change the rheological properties of concrete materials during concrete 3D printing and improve the performance of concrete after printing. DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0042] A method for regulating the rheological properties of 3D printed concrete, such as Figure 1 As shown, the concrete material containing the water reducer (high pumpability printing material) is pumped into the secondary carbonization mixer in front of the 3D printing head, CO2 gas is introduced into the secondary carbonization mixer, and the concrete material is secondary stirred at the same time, so that the CO2 gas and the concrete material containing the water reducer undergo physical and chemical reactions. While the secondary stirring is being performed, the secondary stirred concrete material (high constructionability printing material) is transported to the 3D printing head for printing.

[0043] The following describes it in detail with reference to specific embodiments.

[0044] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0045] Comparative Example 1

[0046] First, the 3D concrete printing material was pre-prepared according to the mix ratio in Table 1 without adding a water reducer. The pre-preparation process includes dry mixing Portland cement, sand, and hydroxypropyl methylcellulose, and then adding water to mix until uniform. After that, the pre-prepared printing material was pumped to a secondary carbonization mixer for carbonization mixing. The parameters used were: CO2 concentration: >99%; mixing rate: 180RPM; CO2 injection rate: 2.5L / min / kg according to the material mass in the carbonization mixer; and carbonization time: 240s. The properties of the 3D printing material before and after carbonization modification are shown in Table 2, where the pumpability is characterized by the fluidity data measured by the table jumping test, the constructability is characterized by the penetration resistance data of a 5mm diameter rod after 2 hours, and the 1-day and 28-day compressive strengths are measured by 40×40×40mm test blocks.

[0047] Example 1

[0048] First, the 3D concrete printing material was pre-prepared according to the mix ratio in Table 1. The water reducer used was a powdered polycarboxylate water reducer, and the amount of the water reducer was 0.1% of the cement mass. The pre-preparation process included dry mixing of Portland cement, sand, water reducer, and hydroxypropyl methylcellulose, and then adding water to mix until uniform. After that, the pre-prepared printing material was pumped to a secondary carbonization mixer for carbonization mixing. The parameters used were: CO2 concentration: >99%; mixing rate: 180RPM; CO2 injection rate: 2.5L / min / kg according to the material mass in the carbonization mixer; and carbonization time: 240s. The properties of the 3D printing material before and after carbonization modification are shown in Table 2, where the pumpability was characterized by the fluidity data measured by the table jumping test, the constructability was characterized by the penetration resistance data of a 5mm diameter rod after 2 hours, and the 1-day and 28-day compressive strengths were measured by 40×40×40mm test blocks.

[0049] Example 2

[0050] First, the 3D concrete printing material was pre-prepared according to the mix ratio in Table 1. The water reducer used was a powdered polycarboxylate water reducer, and the amount of the water reducer was 0.2% of the cement mass. The pre-preparation process included dry mixing of Portland cement, sand, water reducer, and hydroxypropyl methylcellulose, and then adding water to mix until uniform. After that, the pre-prepared printing material was pumped to a secondary carbonization mixer for carbonization mixing. The parameters used were: CO2 concentration: >99%; stirring rate: 180RPM; CO2 injection rate: 2.5L / min / kg according to the material mass in the carbonization mixer; and carbonization time: 240s. The properties of the 3D printing material before and after carbonization modification are shown in Table 2, where the pumpability was characterized by the fluidity data measured by the table jumping test, the constructability was characterized by the penetration resistance data of a 5mm diameter rod after 2 hours, and the 1-day and 28-day compressive strengths were measured by 40×40×40mm test blocks.

[0051] The results show that: (1) For concrete without water reducer, the fluidity is slightly reduced after carbonation mixing, but for concrete with water reducer, the fluidity is significantly reduced after carbonation mixing; (2) The addition of water reducer reduces the penetration resistance of concrete, but after carbonation mixing, the penetration resistance is significantly enhanced; (3) The addition of water reducer reduces the 1-day and 28-day strength of concrete, but after carbonation mixing, the strength of concrete with water reducer is significantly enhanced. It can be seen that the combination of carbonation mixing and water reducer can effectively improve the constructability of concrete, solve the rheological incompatibility problem between pumpability and constructability, and improve mechanical properties.

[0052] Table 1: Mix ratio of 3D printed concrete prepared in Comparative Example 1 and Examples 1-2 (kg / m 3 )

[0053]

[0054] Table 2: Performance indicators of printing materials before and after carbonization modification of Comparative Example 1 and Examples 1-2

[0055]

[0056]

[0057] The present invention regulates the rheological properties and setting time of 3D printed concrete materials by combining carbonization stirring with a water reducer, thereby ensuring that the 3D printed concrete materials have good fluidity during pumping and good buildability after extrusion, solving the rheological incompatibility problem between pumpability and buildability. In addition, the method proposed by the present invention can also improve the strength of 3D printed concrete after hardening, while achieving carbon absorption and helping carbon neutrality.

[0058] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for regulating the rheological properties of 3D printed concrete, characterized in that: The concrete material containing the water reducer is pumped into a secondary mixing container in front of the 3D printing head, CO2 gas is introduced into the secondary mixing container, and the concrete material is secondary mixed at the same time, so that the CO2 gas and the concrete material containing the water reducer undergo physical and chemical reactions. While the secondary mixing is being performed, the secondary mixed concrete material is transported to the 3D printing head for printing.

2. The method for regulating the rheological properties of 3D printed concrete according to claim 1, characterized in that: The water reducer is selected from one or more of polycarboxylate water reducers, lignin sulfonate water reducers, naphthalene-based high-efficiency water reducers, melamine-based high-efficiency water reducers, aminosulfonate-based high-efficiency water reducers, and fatty acid-based high-efficiency water reducers.

3. The method for regulating the rheological properties of 3D printed concrete according to claim 1, characterized in that: The water reducing agent contained in the concrete material is 0.01%-1% of the mass of cement.

4. The method for regulating the rheological properties of 3D printed concrete according to claim 1, characterized in that: The concrete material composition includes cement clinker, mineral admixture, sand, water, water reducing agent and thickener.

5. The method for regulating the rheological properties of 3D printed concrete according to claim 4, characterized in that: The water-cement ratio of the concrete material is 0.3-0.5, and the mortar-sand ratio is 0.5-1.

6. The method for regulating the rheological properties of 3D printed concrete according to claim 4, characterized in that: The cement clinker is selected from one or more of silicate cement and clinker, aluminate cement and clinker, sulphoaluminate cement and clinker.

7. The method for regulating the rheological properties of 3D printed concrete according to claim 4, characterized in that: The mineral admixture is selected from one or more of fly ash, silica fume, slag, glass powder, steel slag, waste concrete powder and limestone powder; The mineral admixture accounts for 0%-50% of the mass of the entire cementitious material.

8. The method for regulating the rheological properties of 3D printed concrete according to claim 4, characterized in that: The thickener is selected from one or more of starch ether, cellulose ether, water-soluble polyacrylamide, casein, and welan gum; The thickener accounts for 0.01%-0.3% of the mass of the entire gelling material.

9. The method for regulating the rheological properties of 3D printed concrete according to claim 1, characterized in that: The target workability of the secondary mixing is 150-200mm.

10. The method for regulating the rheological properties of 3D printed concrete according to any one of claims 1 to 9, characterized in that: The CO2 gas is industrial-grade CO2 or industrial tail gas containing CO2 gas.

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