Large-particle-size coarse aggregate-containing 3D printing concrete with low binding material mixing amount

Abstract

The invention belongs to the technical field of building 3D printing concrete, and relates to low-cementing-material-mixing-amount large-particle-size coarse aggregate-containing 3D printing concrete, which is prepared from the following raw materials: a cementing material, a fine aggregate, a coarse aggregate, a flocculating agent, a water reducing agent, an accelerator and water. Compared with the prior art, the preparation of the concrete containing the large-particle-size coarse aggregate (20mm), which is low in cementing material content and can be used for implementing 3D printing construction, is realized through a hydroxypropyl methyl cellulose ether-polycarboxylate superplasticizer-aluminum sulfate accelerator system.

Description

Technical Field

[0001] The present invention belongs to the technical field of 3D printing concrete for construction, and particularly relates to a 3D printing concrete containing large-sized coarse aggregates with a low dosage of cementitious materials. Background Art

[0002] The rapid development of 3D printing technology has attracted wide attention in the fields of architecture and engineering. Through digital design and precise control, 3D printing concrete technology can achieve precise positioning and shaping of concrete materials, thereby improving construction efficiency, reducing costs, and expanding design possibilities. Past research has shown that construction using 3D printing technology can significantly reduce construction waste, labor costs, and production time.

[0003] To further reduce construction costs and enhance the late strength of large-scale structures, 3D printing concrete containing coarse aggregates has been continuously developed. However, since the concrete needs to go through multiple stages such as mixing, pumping, extrusion, and shaping during the 3D printing process, the printed concrete needs to maintain a certain fluidity during the mixing and pumping stages to avoid pump pipe blockage, and rapidly improve its mechanical properties after extrusion to achieve rapid shaping. Therefore, to meet these requirements, the commonly used 3D printing concrete mixture containing coarse aggregates has a high cement content and a small maximum aggregate size to reduce the negative impact of coarse aggregates on printability. However, a high cementitious material content results in a large shrinkage of the formed concrete. Therefore, adding larger-sized coarse aggregates and reducing the cement dosage in 3D printing concrete is an effective strategy to reduce carbon emissions and improve construction quality.

[0004] Generally speaking, from the perspectives of social development and industry technology, there is an urgent need to develop concrete applicable to 3D printing and its preparation method to meet the construction requirements of 3D printing technology and the green development needs of the construction industry, thereby promoting the progress of the construction industry. Currently, most of the 3D printing concrete formulas containing coarse aggregates have a small aggregate size and a cementitious material content much higher than that of ordinary concrete.

[0005] Patent application CN117486555A discloses a two-component 3D printing concrete containing coarse aggregates, its preparation method and device. The two-component 3D printing concrete containing coarse aggregates is formed by mixing component A and component B. Component A consists of cement, admixture, coarse aggregates, fine aggregates and pumping agent; Component B consists of thickening agent, setting regulator and thixotropic agent. The rheological properties and open time of the 3D printing concrete are controllable, and it has good adhesiveness, extrudability and constructability. In the 3D printing concrete formula disclosed in this patent, the mass ratio of aggregates to binder reaches 1.91 at most, which is much smaller than that of ordinary concrete. The aggregate-binder ratio of concrete refers to the ratio of concrete aggregates to binder. Aggregates include coarse aggregates and fine aggregates, while binders include materials with setting effects such as cement, fly ash, slag powder, silica fume, etc. The smaller the aggregate-binder ratio, the easier it is to print, but it may lead to increased costs, increased carbon emissions, and increased risks of shrinkage and cracking of the printed products. Once the aggregate-binder ratio is increased, it is difficult to meet the requirements of the rapid growth of the mechanical properties of 3D printing concrete after the extrusion stage. In addition, the two-component strategy introduces new construction equipment, and precise control of the geometric parameters and performance parameters of this construction equipment is required, and complex multi-parameter debugging work needs to be carried out, which greatly reduces the construction efficiency and increases the construction cost. In view of this, the present invention proposes a 3D printing concrete with simple components, without the need for new mixing equipment, and an aggregate-binder ratio that can reach 5.5, as well as its preparation method, so as to reduce costs and simplify the preparation process. Summary of the Invention

[0006] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a 3D printing concrete containing large-size coarse aggregates with a low binder content, so as to solve the problems of high cost and large carbon emissions caused by the small maximum particle size of coarse aggregates and high binder consumption in current 3D printing concrete.

[0007] The purpose of the present invention can be achieved through the following technical solutions: The present invention provides a 3D printing concrete, and the raw materials of the concrete include binder, fine aggregates, coarse aggregates, flocculant, water reducer, accelerator and water. Among them, the ratio of the sum of the masses of coarse aggregates and fine aggregates to the mass of the binder is 2.5 - 5.5:1; The mass ratio of the binder, fine aggregates, coarse aggregates, flocculant, water reducer, accelerator and water is 100:(150 - 350):(0 - 200):(0.05 - 0.25):(0.5 - 1.5):(2 - 3):(35 - 45); The gel material is portland cement; The flocculant is hydroxypropyl methyl cellulose ether; The water reducer is a polycarboxylate-based water reducer; The accelerator is a liquid alkali-free accelerator.

[0008] Furthermore, the mass ratio of the cementitious material, fine aggregate, coarse aggregate, flocculant, water reducer, accelerating agent and water is 100:(150 - 250):(100 - 200):(0.05 - 0.25):(0.5 - 1.5):(2 - 3):(35 - 45).

[0009] Furthermore, the mass ratio of the cementitious material, fine aggregate, coarse aggregate, flocculant, water reducer, accelerating agent and water is 100:200:150:(0.05 - 0.15):(0.5 - 1.5):(2 - 3):38.

[0010] Furthermore, the cementitious material is selected from any one of Portland cements with grades 425, 525, 625 or 725.

[0011] Furthermore, the particle size range of the fine aggregate is 0 - 5 mm, conforming to continuous grading.

[0012] Furthermore, the particle size range of the coarse aggregate is 5 - 20 mm, conforming to continuous grading.

[0013] Furthermore, the flocculant is a powdery hydroxypropyl methyl cellulose ether with a viscosity of 200,000.

[0014] Furthermore, the water reducer is a high water - reducing liquid polycarboxylate - based water reducer with the main component being isobutenol polyoxyethylene ether.

[0015] Furthermore, the accelerating agent is a liquid alkali - free accelerating agent with the main component being aluminum sulfate.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a 3D printable concrete, which uses coarse aggregates with a maximum particle size of 20 mm, and the bone-cement ratio can reach up to 5.5 at most, significantly reducing the amount of cementitious materials in the 3D printable concrete. To address the reduction in fluidity caused by the coarse aggregates, the slow development rate of mechanical properties resulting in reduced printability of the material, as well as the increased requirements for printability on material properties due to the increase in the height of the single-layer printed concrete and the increase in the density of the concrete, three key admixtures, namely a flocculant, a water reducer, and a quick-setting agent, are adopted. Hydroxypropyl methyl cellulose ether is used as the flocculant, which can increase the viscosity of the concrete by increasing the viscosity of the pore solution, reduce problems such as segregation caused by the addition of large-sized coarse aggregates, and improve the stability during the concrete pumping process. The polycarboxylate-based water reducer can increase the spacing between cement molecules during the fresh stage through two effects, namely electrostatic repulsion and steric hindrance, to increase the fluidity of the concrete, ensure that the concrete has sufficient workability during the mixing, pumping stages, and before extrusion, and make up for the problem of insufficient late mechanical properties caused by the low content of cementitious materials. The liquid alkali-free quick-setting agent has little negative impact on the late mechanical properties. It can accelerate the hydration reaction rate at the early age, improve the slow development of mechanical properties caused by the low content of cementitious materials and the large particle size of the coarse aggregates, and ensure that the concrete can quickly take shape after extrusion.

[0017] The present invention uses a specific dosage ratio of Portland cement, fine aggregates, coarse aggregates, flocculant, water reducer, and quick-setting agent for compounding. The dosage of hydroxypropyl methyl cellulose ether is sufficient to improve the stability during the concrete pumping process while having little impact on the fluidity of the concrete; the dosage of the polycarboxylate water reducer is sufficient to improve the fluidity of the concrete while having little impact on the late mechanical properties and being compatible with the hydroxypropyl methyl cellulose ether at the said dosage; the dosage of the aluminum sulfate quick-setting agent is sufficient to ensure that the concrete can quickly take shape after extrusion while having little impact on the late mechanical properties and not covering the effects of the polycarboxylate water reducer and hydroxypropyl methyl cellulose ether at the said dosage; the hydroxypropyl methyl cellulose ether - polycarboxylate water reducer - aluminum sulfate quick-setting agent system at the said dosage realizes a synergistic effect, can ignore the influence of the coarse aggregate particle size, and can ensure that its fluidity, rheological properties, and mechanical property development rate meet the process requirements of 3D printing while having a low cement dosage, greatly reducing the preparation cost of 3D printable concrete and reducing the carbon emissions during the preparation process of 3D printable concrete.

[0018] (2) The 3D printable concrete provided by the present invention is a single-component mixture, and there is no need to completely manufacture a new set of 3D printing extrusion devices, with low equipment costs. Description of the Drawings

[0019] Figure 1 is the static yield stress of the 3D printable concrete of the present invention; Figure 2 is the printing effect of the 3D printable concrete of the present invention. Detailed Embodiments

[0020] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0021] 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 all commercially available.

[0022] For example, the cement used in the following examples is P·I 42.5R Portland cement, purchased from China National Building Materials Research Institute Co., Ltd., with a fineness of 357 m 2 / kg and a density of 3.11 g / cm 3 . The fine aggregate has a fineness modulus of 3.1, is purchased from China National Building Materials Research Institute Co., Ltd., and has a particle size greater than 0 mm and less than 5 mm. The coarse aggregate is purchased from China National Building Materials Research Institute Co., Ltd., and has a particle size greater than 5 mm and less than 20 mm. The flocculant hydroxypropyl methylcellulose ether is purchased from Jinzhou Baoyi Building Materials Technology Co., Ltd. The liquid polycarboxylate water reducer is purchased from Hunan Zhongyan Building Materials Technology Co., Ltd. The alkali-free liquid accelerator is purchased from Laiyang Keyu Building Admixture Factory, and its main component is aluminum sulfate.

[0023] Example 1 This embodiment provides a 3D printing concrete containing large-size coarse aggregate with a low cementitious material content. The raw materials are Portland cement, fine aggregate, coarse aggregate, flocculant, water reducer, accelerator and water with a mass ratio of 100:200:150:0.1:1:2.5:38.

[0024] Specifically, the masses of the raw materials are: 500 kg of Portland cement, 1000 kg of fine aggregate, 750 kg of coarse aggregate, 0.5 kg of flocculant, 5 kg of water reducer, 12.5 kg of accelerator, and 190 kg of water.

[0025] The preparation process of the 3D printing concrete containing large-size coarse aggregate with a low cementitious material content includes the following steps: First step, put the weighed Portland cement, fine aggregate, coarse aggregate and flocculant into a mixer and start stirring until evenly stirred; Second step, put the water reducer solution pre-mixed with water into the mixer at one time and start stirring until evenly stirred; Step 3: Add the pre-weighed accelerating agent into the mixer. Take samples every 10 minutes during the mixing process. Load the samples into the sample cylinder of the ICAR rheometer, and then insert the vane into the mixture; set the rotational speed of the vane in the rheometer to 0.025 revolutions per second, and the initial torque of the vane shaft to zero; start the test, and when the torque-time curve reaches the maximum value and the torque gradually decreases, end the test and record the maximum value of the torque. Test 1 data point every 10 minutes for a total of 90 minutes. According to the geometric parameters of the rheometer, convert the torque into the static yield stress. The test results are as Figure 1 shown. When the static yield stress of the 3D printed concrete mixture within a certain period of time satisfies the following formula: static yield stress ≥ √3 (self-weight + vertical component of other external loads), it meets the 3D printing requirements. From Figure 1 it can be obtained that during the construction period of the 3D printed concrete mixture in this embodiment, the static yield stress reaches 1.17 kPa within 20 minutes, which is sufficient to bear the self-weight of the 3D printed concrete mixture and external loads, meeting the material bearing capacity requirements for single-layer printing.

[0026] When the static yield stress of the concrete reaches 1.17 kPa, stop mixing and discharge the material for the single-layer printing test. The mixture is conveyed to a circular printing extrusion head with a diameter of 80 mm through a delivery pump and a screw pump. The robotic arm drives the extrusion head to move at a speed of 500 mm / s to print a single-layer printed concrete with a length greater than 1000 mm. The printing results are shown in Figure 2 . Figure 2 It shows that the concrete in this embodiment is successfully pumped and extruded, and there is no obvious shape change after extrusion. The printed strip of the concrete slurry is continuous without breakpoints, and the coarse aggregates are tightly wrapped by the mortar, indicating that the concrete can resist the self-weight of the 3D printed concrete or the combined action of the self-weight and other external loads. Therefore, the concrete in this embodiment has excellent printability.

[0027] Perform performance tests on the 3D printed concrete obtained in this embodiment to measure the comprehensive performance of the 3D printed concrete during the entire 3D printing construction process. The slump measurement is carried out according to the steps in the standard GB / T 50080-2016 "Standard Test Method for Properties of Ordinary Concrete Mixtures". The specific method for slump measurement is as follows: After placing the prepared 3D printed concrete mixture into the slump cone according to the standard GB / T50080-2016 "Standard Test Method for Properties of Ordinary Concrete Mixtures", lift the slump cone vertically and steadily and place it beside the specimen; when the specimen no longer continues to slump or the slump time reaches 30 s, use a steel ruler to measure the height difference between the height of the cone and the highest point of the concrete specimen after slumping as the slump value. The recommended slump value of the concrete provided by the delivery pump manufacturer should be greater than 40 mm and less than 130 mm, and the recommended slump value of the concrete by the mixer is between 50 mm and 200 mm.

[0028] The slump of the 3D printed concrete obtained in this example at the fresh stage is 90 mm, meeting the requirements of the equipment for the fluidity of the material; during the construction period of the 3D printed concrete mixture in this example, the static yield stress reaches 1.17 kPa within 20 minutes, which is sufficient to bear the self-weight of the 3D printed concrete mixture and external loads, fully meeting the requirements of the construction rate of ultra-early-age 3D printed concrete. In addition, for the mechanical properties of the hardened concrete, according to GBT 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the concrete samples with ages of 1 day, 3 days, and 28 days under standard curing conditions are tested by a compression testing machine. The unconfined compressive strengths of the 3D printed concrete obtained in this example at ages of 1 day, 3 days, and 28 days are 15.4 MPa, 22.2 MPa, and 47.5 MPa respectively, meeting the C40 concrete standard.

[0029] The above results show that the 3D printed concrete and its preparation method in this example can not only realize the preparation of 3D printed concrete containing large-size coarse aggregates, but also prepare concrete with target properties by adjusting the material properties at the fresh stage and ultra-early age through the change of the dosage of admixtures (the admixtures include water reducer, accelerator, and flocculant). In fact, the basic idea of the method in this example can also be used in similar work and material preparation in other fields.

[0030] Example 2 The raw materials used are portland cement, fine aggregate, coarse aggregate, flocculant, water reducer, accelerator, and water with a mass ratio of 100:150:100:0.05:0.5:2:35, and the rest is the same as in Example 1.

[0031] The slump of the 3D printed concrete obtained in this example at the fresh stage is 90 mm, meeting the requirements of the equipment for the fluidity of the material; during the construction period of the 3D printed concrete mixture in this example, the static yield stress reaches 1.17 kPa within 20 minutes, which is sufficient to bear the self-weight of the 3D printed concrete mixture and external loads, meeting the material bearing capacity requirements for single-layer printing; the unconfined compressive strengths of the 3D printed concrete obtained in this example at ages of 1 day, 3 days, and 28 days are 16.2 MPa, 21.2 MPa, and 48.3 MPa respectively, meeting the C40 concrete standard.

[0032] Example 3 The raw materials used are portland cement, fine aggregate, coarse aggregate, flocculant, water reducer, accelerator, and water with a mass ratio of 100:250:200:0.25:1.5:3:45, and the rest is the same as in Example 1.

[0033] The slump of the 3D printed concrete obtained in this embodiment is 90 mm in the fresh state, meeting the requirements of the equipment for the fluidity of the material; during the construction period, the static yield stress of the 3D printed concrete mixture in this embodiment reaches 1.17 kPa within 20 minutes, which is sufficient to bear the self-weight of the 3D printed concrete mixture and external loads, meeting the requirements for the material bearing capacity of single-layer printing; the unconfined compressive strengths of the 3D printed concrete obtained in this embodiment at the ages of 1 day, 3 days, and 28 days are 16.0 MPa, 22.2 MPa, and 47.8 MPa respectively, meeting the C40 concrete standard.

[0034] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. 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 efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A 3D printing concrete containing large-size coarse aggregate and low cementitious material content, characterized in that: The raw materials of the concrete include cementitious material, fine aggregate, coarse aggregate, flocculant, water reducing agent, accelerating agent and water, wherein the ratio of the sum of the mass of the coarse aggregate and the fine aggregate to the mass of the cementitious material is 2.5-5.5:1; The mass ratio of cementitious material, fine aggregate, coarse aggregate, flocculant, water reducer, accelerator and water is 100:(150-350):(0-200):(0.05-0.25):(0.5-1.5):(2-3):(35-45); The gel material is silicate cement; The flocculant is hydroxypropyl methyl cellulose ether; The water reducing agent is a polycarboxylic acid water reducing agent; The quick-setting agent is a liquid alkali-free quick-setting agent.

2. The 3D printing concrete containing large-size coarse aggregate and low cementitious material content according to claim 1, characterized in that: The mass ratio of the cementitious material, fine aggregate, coarse aggregate, flocculant, water reducer, accelerator and water is 100:(150-250):(100-200):(0.05-0.25):(0.5-1.5):(2-3): (35-45)。 3. The 3D printing concrete containing large-size coarse aggregate and low cementitious material content according to claim 2, characterized in that: The mass ratio of the cementitious material, fine aggregate, coarse aggregate, flocculant, water reducer, accelerator and water is 100:200:150:(0.05-0.15):(0.5-1.5):(2-3):

38.

4. The 3D printing concrete containing large-size coarse aggregate and low cementitious material content according to claim 1, characterized in that: The cementitious material is selected from any one of the silicate cements with the labels 425, 525, 625 or 725.

5. The 3D printing concrete containing large-size coarse aggregate and low cementitious material content according to claim 1, characterized in that: The particle size of the fine aggregate is in the range of 0-5 mm, which conforms to continuous grading.

6. The 3D printing concrete containing large-size coarse aggregate and low cementitious material content according to claim 1, characterized in that: The particle size of the coarse aggregate is in the range of 5-20 mm, which conforms to the continuous grading.

7. The 3D printing concrete containing large-size coarse aggregate and low cementitious material content according to claim 1, characterized in that: The flocculant is powdered hydroxypropyl methylcellulose ether with a viscosity of 200,000.

8. The 3D printing concrete containing large-size coarse aggregate and low cementitious material content according to claim 1, characterized in that: The water reducing agent is a high water reducing liquid polycarboxylic acid water reducing agent whose main component is isobutylene alcohol polyoxyethylene ether.

9. The 3D printing concrete containing large-size coarse aggregate and low cementitious material content according to claim 1, characterized in that: The quick-setting agent is a liquid alkali-free quick-setting agent whose main component is aluminum sulfate.

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