Lightweight high-toughness all-solid-waste-based 3D printing regenerated mortar and preparation method thereof

Abstract

The invention relates to the technical field of building materials, and particularly discloses lightweight high-toughness all-solid-waste-based 3D printing recycled mortar and a preparation method thereof.The mortar is prepared from solid waste such as recycled powder, fly ash, slag and rubber as main raw materials, and all solid waste of a cementing material and aggregate is achieved; by adding an alkali activator, basalt fiber, polypropylene fiber, a foaming agent, a foam stabilizer, an accelerator, a water-retaining agent, a water reducing agent and water, the lightweight high-toughness all-solid waste-based mortar which is low in density, high in toughness, good in fluidity and suitable for 3D printing is prepared. The preparation method has the beneficial effects that efficient reutilization of multi-source solid wastes is realized, pollution of construction wastes to the environment is reduced, the toughness and light weight of the mortar are remarkably improved through fiber reinforcement and foaming technologies, cracks and cracking in the printing process are reduced, the preparation process is simple, the cost is low, and the prepared mortar has excellent flowability and constructability.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and in particular to a lightweight and high-toughness all-solid waste-based 3D printing recycled mortar and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of the global construction industry, concrete, as one of the most important building materials, has consumed vast quantities of natural resources and energy during its production and use, generating significant amounts of carbon dioxide emissions. According to relevant statistics, approximately 8% of global carbon dioxide emissions come from cement production. As the core raw material of concrete, the high energy consumption and carbon emissions during its production have become a significant obstacle to sustainable development. At the same time, the amount of construction waste generated has also increased year by year. According to relevant research data, the global annual amount of construction waste reaches approximately 2 billion tons. If not properly handled, it will pose a serious threat to the ecological environment.

[0003] The production of traditional concrete materials requires large amounts of cement, consumes high amounts of energy, emits significant carbon emissions, and has low resource utilization, making it difficult to meet modern society's demands for environmental protection, energy conservation, and sustainable development. In recent years, while researchers have begun to focus on the research and application of recycled concrete mortars, existing recycled concrete mortars still lack mechanical properties, lightweighting, high toughness, and printability due to limitations in raw material properties and preparation processes.

[0004] Specifically, traditional recycled concrete mortars typically use recycled aggregates from crushed waste concrete as a partial replacement. However, since the cement mortar attached to the surface of the recycled aggregate is difficult to completely remove and its surface roughness is relatively high, the interfacial bonding between it and the base material is poor, thus affecting the overall mechanical properties. Furthermore, to achieve lightweighting, some research has introduced materials such as foaming agents. However, the foam easily breaks during the foaming process, resulting in a decrease in the material's density and strength, making it difficult to meet the requirements of engineering applications.

[0005] The rapid development of 3D printing technology in the construction industry has placed higher demands on concrete mortar materials used in 3D printing. Such mortars must possess excellent fluidity and printability, while also possessing high strength, high toughness, lightweight properties, and environmental friendliness. However, current 3D printing mortar materials struggle to achieve an effective balance between fluidity, printability, and mechanical properties. This is especially true when using solid waste as a primary raw material. How to ensure both material performance and lightweight properties while maintaining high toughness remains a key challenge.

[0006] Therefore, developing a recycled concrete mortar with solid waste (such as recycled powder, fly ash, mineral powder, rubber, etc.) as the main raw material, which is lightweight, highly tough and has excellent printability, can not only effectively solve the problem of resource utilization of construction waste, but also effectively solve the cracking and shrinkage of materials during 3D printing, and has important environmental and economic value. Summary of the Invention

[0007] In order to solve the above problems, the present invention proposes a lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar and its preparation method. The mortar uses recycled powder, fly ash, slag, rubber and other multi-source solid waste as the main raw materials, realizing that the cementitious material and aggregate are all solid waste. It has the characteristics of low density, high toughness, good fluidity and excellent printability. At the same time, the preparation process is green and low-carbon, low-cost, and has both environmental benefits and economic advantages.

[0008] The technical solution of the present invention is achieved as follows:

[0009] A lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar, comprising the following components:

[0010] Recycled powder, fly ash, mineral powder, regenerated sand, rubber particles, alkali activator, basalt fiber, polypropylene fiber, foaming agent, foam stabilizer, accelerator, water retention agent, water reducing agent and water.

[0011] Preferably, the following components are included by weight: 20-30 parts of recycled powder, 40-120 parts of fly ash, 320-450 parts of mineral powder, 800-1100 parts of regenerated sand, 20-30 parts of rubber particles, 100-150 parts of alkali activator, 3-5 parts of basalt fiber, 3-5 parts of polypropylene fiber, 12-18 parts of foaming agent, 4-6 parts of foam stabilizer, 20-30 parts of accelerator, 2-3 parts of water retaining agent, 12-18 parts of water reducing agent, and 150-210 parts of water.

[0012] Preferably, the recycled powder is recycled powder obtained by crushing, grinding and magnetic separation of waste concrete, with a particle size of ≤0.15 mm and a specific surface area of ​​470-650 m2 / kg.

[0013] Preferably, the fly ash is Class I fly ash, with a specific surface area of ​​450-600 m2 / kg, a fineness of 45 μm sieve residue ≤10%, a calcined amount ≤3%, active components SiO2+Al2O3+Fe2O3≥75%, and a CaO content of 3-5%.

[0014] Preferably, the mineral powder is S95 grade blast furnace slag powder, with a specific surface area of ​​450-550 m2 / kg, a SiO2 content of 32-38%, an Al2O3 content of 11-13%, a CaO content of 38-43%, and a MgO content of 6-10%.

[0015] Preferably, the regenerated sand is regenerated sand obtained by a vibrating screen and a magnetic separator, with a fineness modulus of 2.7-2.9, a particle size range of 0.15-4.75 mm, a bulk density of 1350-1450 kg / m³, and a moisture content of less than 0.2%.

[0016] Preferably, the rubber particles are rubber particles obtained by crushing waste oil tires at room temperature, with a particle size range of ≥0.18 mm and an apparent density of 1000-1200 kg / m³.

[0017] Preferably, the alkaline activator is a mixture of water glass and sodium hydroxide, has a storage time of 24 hours, a modulus of 1.0-1.2, a Na2O content of ≥22%, and a solids content of 38-44%. Water glass with a modulus of 3.2 has a sodium oxide content of ≥8.2% and a silicon oxide content of ≥26%. 1000g of water glass with a modulus of 3.2 can be adjusted to a modulus of 1.0-1.2 by adding 177-245g of 96% sodium hydroxide by mass. To adjust 1000g of water glass with a modulus of 3.2 to a modulus of 1.0, 245g of 96% sodium hydroxide by mass must be added. To adjust 1000g of water glass with a modulus of 3.2 to a modulus of 1.2, 177g of 96% sodium hydroxide must be added.

[0018] Preferably, the basalt fiber is chopped basalt fiber with a fiber length of 6 mm, a diameter range of 7-25 μm, an elastic modulus greater than 35 GPa, a tensile strength greater than 1050 MPa, and an alkali resistance greater than 95%.

[0019] Preferably, the polypropylene fiber is a high-strength polypropylene fiber with a fiber length of 9 mm, a diameter range of 18-25 μm, an elastic modulus greater than 5 GPa, a tensile strength greater than 450 MPa, and an alkali resistance greater than 90%.

[0020] Preferably, the foaming agent is H2O2 solution with a mass fraction of 35%.

[0021] Preferably, the foam stabilizer is cetyltrimethylammonium bromide, analytically pure. Analytically pure is a purity specification for chemical reagents. Analytically pure refers to reagents used for analytical determinations, with very few impurities that do not interfere with the analysis and determination. Analytically pure in this application refers to a purity of 99.7% or higher.

[0022] Preferably, the quick-setting agent is SBT-N (II) liquid alkali-free quick-setting agent, and the 28-day compressive strength retention rate is ≥90%.

[0023] Preferably, the water-retaining agent is hydroxypropyl methylcellulose water-retaining agent with a fineness range of 80-100 mesh and a viscosity of ≥100000 mPa·s.

[0024] Preferably, the water reducer is a polycarboxylic acid high-performance water reducer with a water reduction rate of not less than 30%.

[0025] Preferably, the water is tap water.

[0026] The present invention also provides a method for preparing a lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar, comprising the following steps:

[0027] S1. Weigh the regenerated powder, fly ash, slag and regenerated sand according to the predetermined proportion, put them into a blender, and mix them for 1 minute until they are evenly mixed;

[0028] S2. Add basalt fiber, polypropylene fiber, water retaining agent, foam stabilizer and early strength agent to the dry mix in the mixer, and continue stirring for 1-2 minutes until the fiber and other materials are evenly dispersed;

[0029] S3. Add alkali activator, water and water reducer to the mixer, wherein the alkali activator needs to be prepared in advance by water glass and NaOH and stored for 24 hours, and continue stirring for 1-2 minutes;

[0030] S4. Finally, slowly add the foaming agent into the mixer and stir for 2 minutes to make the mortar foam evenly and fully to obtain a lightweight and high-toughness all-solid waste-based 3D printing recycled mortar.

[0031] By adopting the above technical solution, the beneficial effects of the present invention are:

[0032] (1) The present invention uses solid wastes such as recycled bone meal, fly ash, slag, and rubber as the main raw materials, which are four types of solid waste: finely ground products of building demolition waste, by-products of coal-fired power plants, metallurgical industrial waste slag, and waste tires, respectively, to construct a multi-source solid waste collaborative utilization system. Fly ash and slag generate CSH gel through alkaline excitation, forming a stable matrix structure, realizing the full component utilization of multi-source solid waste. Compared with traditional landfill treatment, it can effectively reduce the land occupation rate of solid waste, while avoiding the problem of groundwater pollution caused by heavy metal ion penetration, and reducing the pollution of construction waste to the environment.

[0033] (2) The present invention constructs a three-dimensional synergistic reinforcement system by adding basalt fiber and polypropylene fiber. Basalt fiber bears the main stress due to its high tensile strength, while polypropylene fiber disperses local stress concentration and blocks the formation of macro cracks through its ultra-high ductility and hydrophobicity. Under the composite action of the two fibers, the mortar's flexural strength and crack resistance are significantly improved, while it also exhibits excellent impact resistance and environmental adaptability, significantly improving the mechanical properties and toughness of the mortar. The low density of polypropylene fiber improves the uniformity of fiber dispersion, and its acid and alkali corrosion resistance further enhances the durability of the mortar in harsh working conditions such as moisture and saline-alkali.

[0034] (3) The present invention uses 35% industrial-grade hydrogen peroxide as a foaming agent. The raw material production technology is mature, the cost is low, the operation is simple, and the reaction is well controlled. In an alkaline environment, hydrogen peroxide is catalytically decomposed to release oxygen, which is safe and environmentally friendly. Hexadecyltrimethylammonium bromide (CTAB) is selected as a foam stabilizer. Its long-chain alkyl groups are oriented at the bubble interface through hydrophobic action, forming a positively charged double-layer structure, which significantly reduces the liquid phase surface tension and inhibits the merging and rupture of bubbles. At the same time, CTAB has good stability and can still maintain good foam stabilization performance during the exothermic process of hydrogen peroxide. Through the synergistic effect of the foaming agent and the foam stabilizer, the mortar is lightweight and the material density is reduced.

[0035] (4) The lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar prepared by the present invention achieves a highly efficient synergy between lightweight properties and excellent printability through particle grading optimization and rheological properties coordinated control technology. Hydroxypropyl methylcellulose is used as a water-retaining agent to improve the rheological properties of the mortar while effectively suppressing the strength attenuation problem caused by early water loss. In addition, by introducing an alkali-activated material system, the printed mortar has the advantages of rapid early strength development and significantly improves the thermal stability and long-term durability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 It is a schematic diagram of the preparation process of the present invention;

[0038] Figure 2 This is the printability test chart of the present invention. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0040] Example 1:

[0041] A lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar includes the following components by weight: 20 parts of recycled powder, 40 parts of fly ash, 320 parts of mineral powder, 800 parts of regenerated sand, 20 parts of rubber particles, 100 parts of alkali activator, 3 parts of basalt fiber, 3 parts of polypropylene fiber, 12 parts of foaming agent, 4 parts of foam stabilizer, 25 parts of accelerator, 2 parts of water retaining agent, 12 parts of water reducing agent, and 150 parts of water.

[0042] Example 2:

[0043] A lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar includes the following components by weight: 25 parts of recycled powder, 60 parts of fly ash, 380 parts of mineral powder, 900 parts of recycled sand, 25 parts of rubber particles, 120 parts of alkali activator, 5 parts of basalt fiber, 5 parts of polypropylene fiber, 15 parts of foaming agent, 5 parts of foam stabilizer, 25 parts of accelerator, 2 parts of water retention agent, 18 parts of water reducer, and 180 parts of water.

[0044] Example 3:

[0045] A lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar includes the following components by weight: 30 parts of recycled powder, 90 parts of fly ash, 450 parts of mineral powder, 1000 parts of recycled sand, 30 parts of rubber particles, 150 parts of alkali activator, 4 parts of basalt fiber, 4 parts of polypropylene fiber, 18 parts of foaming agent, 6 parts of foam stabilizer, 25 parts of accelerator, 3 parts of water retention agent, 12 parts of water reducer, and 210 parts of water.

[0046] Example 4:

[0047] A lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar includes the following components by weight: 20 parts of recycled powder, 120 parts of fly ash, 320 parts of mineral powder, 1100 parts of recycled sand, 30 parts of rubber particles, 100 parts of alkali activator, 3 parts of basalt fiber, 3 parts of polypropylene fiber, 12 parts of foaming agent, 4 parts of foam stabilizer, 25 parts of accelerator, 2 parts of water retention agent, 15 parts of water reducer, and 200 parts of water.

[0048] like Figure 1 As shown, the preparation method of a lightweight and high-toughness all-solid waste-based 3D printing recycled mortar described in Examples 1-4 includes the following steps:

[0049] S1. Weigh the regenerated powder, fly ash, slag and regenerated sand according to the predetermined proportion, put them into a blender, and mix them for 1 minute until they are evenly mixed;

[0050] S2. Add basalt fiber, polypropylene fiber, water retaining agent, foam stabilizer and early strength agent to the dry mix in the mixer, and continue stirring for 1-2 minutes until the fiber and other materials are evenly dispersed;

[0051] S3. Add alkali activator, water and water reducer to the mixer, wherein the alkali activator needs to be prepared in advance by water glass and NaOH and stored for 24 hours, and continue stirring for 1-2 minutes;

[0052] S4. Finally, slowly add the foaming agent into the mixer and stir for 2 minutes to make the mortar foam evenly and fully to obtain a lightweight and high-toughness all-solid waste-based 3D printing recycled mortar.

[0053] Comparative Example 1:

[0054] Comparative Example 1 is compared with Example 1, except that the alkaline activator used in Comparative Example 1 has a modulus of 1.0, 1000g of water glass with a modulus of 3.2 is adjusted to a modulus of 1.0, and 245g of 96% by mass sodium hydroxide needs to be added. The preparation method is the same as that of Example 1.

[0055] Comparative Example 2:

[0056] Compared with Example 2, Comparative Example 2 differs in that Comparative Example 2 does not contain basalt fiber and polypropylene fiber, and its preparation method is the same as that of Example 2.

[0057] Comparative Example 3:

[0058] Compared with Example 3, Comparative Example 3 differs in that Comparative Example 3 contains 6 parts of foaming agent and 2 parts of foam stabilizer, and its preparation method is the same as that of Example 3.

[0059] Comparative Example 4:

[0060] Compared with Example 4, Comparative Example 4 is different in that Comparative Example 4 does not contain rubber particles, and its preparation method is the same as that of Example 4.

[0061] For the lightweight, high-toughness, all-solid waste-based 3D printing mortars prepared in Examples 1-4 and Comparative Examples 1-4 above, some performance parameters were measured before printing. The fluidity of the mortar was tested with reference to GB / T 2419-2005 "Test method for fluidity of cement mortar"; the setting time of the mortar was tested with reference to GB / T 50080-2016 "Standard for test methods for performance of ordinary concrete mixtures".

[0062] The prepared mortar was 3D printed, and the printed test blocks were placed in a standard curing room for curing. After 28 days of curing, the test blocks were cut and polished, and the weight of the test samples was recorded, and the density of the mortar after curing was calculated. The compressive strength and flexural strength of the cured mortar were tested with reference to GB / T50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete".

[0063] The test results are shown in Table 1.

[0064] Table 1 Performance test of lightweight and high-toughness all-solid waste-based 3D printed recycled mortar

[0065] Specimen type Fluidity mm Coagulation time min Density kg / m³ 28d compressive strength MPa 28d flexural strength MPa Example 1 211 117 1151 13.7 4.4 Example 2 218 133 1119 13.4 3.9 Example 3 236 154 984 9.3 2.8 Example 4 184 124 1498 21.4 5.6 Comparative Example 1 226 143 1204 11.3 3.7 Comparative Example 2 219 128 1163 11.7 3.4 Comparative Example 3 214 112 1644 13.1 3.6 Comparative Example 4 196 121 1531 18.4 5.2

[0066] From the test results in Table 1 we can see that:

[0067] The lightweight, high-toughness, all-solid waste-based 3D printing mortar of this invention exhibits excellent fluidity, meeting the extrudability and constructability requirements of 3D printing. Furthermore, the mortar's setting time determines the open time for 3D printing. Sufficient open time significantly reduces hardening during mortar printing and reduces nozzle clogging during pumping, meeting on-site construction requirements.

[0068] From the data of the lightweight, high-toughness, all-solid waste-based 3D printing mortar prepared in Example 1 and Comparative Example 1, it can be concluded that different alkali-activated moduli have a great influence on the performance of the mortar. When the alkali-activated modulus is too low, the mortar fluidity will increase, the setting time will increase, and the compressive and flexural strength of the mortar will be reduced. From the data of the lightweight, high-toughness, all-solid waste-based 3D printing mortar prepared in Example 2 and Comparative Example 2, it can be concluded that the addition of basalt fiber and polypropylene fiber will improve the compressive and flexural strength of the mortar, and have an impact on other mortar properties. Smaller; From the data of the lightweight and high-tough all-solid waste-based 3D printing mortar prepared in Example 3 and Comparative Example 3, it can be concluded that the foaming agent and the foam stabilizer have a greater influence on the performance of the mortar. With the reduction of the foaming agent and the foam stabilizer, the fluidity and setting time of the mortar decrease, and the density, compressive and flexural strength increase; From the data of the lightweight and high-tough all-solid waste-based 3D printing mortar prepared in Example 4 and Comparative Example 4, it can be concluded that the addition of rubber has a greater influence on the compressive and flexural strength of the mortar, and appropriate addition can improve the compressive and flexural strength of the mortar.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar, characterized by: The following components are included by weight: 20-30 parts of recycled powder, 40-120 parts of fly ash, 320-450 parts of mineral powder, 800-1100 parts of regenerated sand, 20-30 parts of rubber particles, 100-150 parts of alkali activator, 3-5 parts of basalt fiber, 3-5 parts of polypropylene fiber, 12-18 parts of foaming agent, 4-6 parts of foam stabilizer, 20-30 parts of accelerator, 2-3 parts of water retaining agent, 12-18 parts of water reducing agent, and 150-210 parts of water.

2. The lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar according to claim 1, characterized in that: The alkaline activator is a mixture of water glass and sodium hydroxide.

3. The lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar according to claim 1, characterized in that: The mass fraction of the foaming agent is 35% H2O2 solution.

4. The lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar according to claim 1, characterized in that: The foam stabilizer is cetyltrimethylammonium bromide.

5. The lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar according to claim 1, characterized in that: The water reducer is a polycarboxylic acid high performance water reducer.

6. A method for preparing a lightweight, high-toughness, all-solid waste-based 3D printing recycled mortar according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Weigh the regenerated powder, fly ash, slag and regenerated sand according to the predetermined proportion, put them into a blender, and mix them for 1 minute until they are evenly mixed; S2. Add basalt fiber, polypropylene fiber, water retaining agent, foam stabilizer and early strength agent to the dry mix in the mixer, and continue stirring for 1-2 minutes until the fiber and other materials are evenly dispersed; S3. Add alkali activator, water and water reducer to the mixer, wherein the alkali activator needs to be prepared in advance by water glass and NaOH and stored for 24 hours, and continue stirring for 1-2 minutes; S4. Finally, slowly add the foaming agent into the mixer and stir for 2 minutes to make the mortar foam evenly and fully to obtain a lightweight and high-toughness all-solid waste-based 3D printing recycled mortar.

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