Three-dimensional printing forming mortar composition

Abstract

To provide a three-dimensional printing forming mortar that has properties suitable for printing and a viscosity that ensures good stability of the mortar extruded from a print head, that has sufficient compressive strength, that has low shrinkage, that has high expansibility, that has low CO2 emission, and that uses a fired clay as a main component.SOLUTION: A three-dimensional printing forming mortar composition according to the present invention comprises: a cement; 10% to 50% of fired clay with respect to the dry weight of a binder; 2% to 5% of an expanding agent containing calcium oxide and calcium sulfate with respect to the dry weight of the mortar; and an additive or a mixture.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] His materials science interests include cement-based materials and 3D printing. [Background technology]

[0002] Portland cement is a widely used building material whose production emits large amounts of CO2. Type I Portland cement, in particular, has a high clinker-to-additive (admixture) ratio (also called the clinker coefficient). Generally, its clinker ratio is higher than 0.92. As a result, mortar or concrete using Portland cement as a binder emits large amounts of CO2. A commonly used method to reduce the clinker ratio in cement is to use various types of auxiliary cementitious materials, such as fly ash, bottom ash, blast furnace slag, or calcined clay. Replacing clinker with a replacement material results in a decrease in early-age compressive strength because the reaction rate of the auxiliary cementitious material is slower than that of the clinker in the initial reaction. Furthermore, most auxiliary cementitious materials require the products of the clinker hydration reaction to trigger the pozzolanic reaction. Therefore, the properties of the replacement material need to be improved to improve the initial reaction. This improvement can be achieved through either chemical or physical treatment. A chemical treatment that can be performed in existing manufacturing processes is to control the auxiliary cementitious material phase by controlling the manufacturing process, or a physical treatment that can be easily performed is to increase the surface area for reaction, for example by grinding the replacement material to achieve a higher fineness.

[0003] However, the composition or phase of the auxiliary cementitious material, which is fly ash, bottom ash, or blast furnace slag, cannot be effectively controlled because they are by-products from other industries, whereas the composition of calcined clay can be effectively controlled because it is a direct production of the auxiliary cementitious material, not a product of other products. Therefore, calcined clay is suitable for use as an auxiliary cementitious material in cement with low CO2 emissions.

[0004] Improving supplemental cementitious materials by grinding them to achieve a higher fineness increases shrinkage, particularly autogenous and drying shrinkage, of cement or mortar and concrete using such cement. Cement replacement materials, particularly replacement materials that are calcined clay (cement blended with calcined clay is referred to herein as LC3), are finely ground to achieve a higher fineness to offset the slower initial reaction rate of the cement caused by replacing clinker with the replacement material. Thus, mixing calcined clay with cement or using LC3-type cement for mortar or concrete work results in higher viscosity, which reduces fluidity or workability and necessitates an increase in the water-to-binder ratio, which reduces compressive strength and increases drying shrinkage. If the water-to-binder ratio needs to be the same as the original ratio, this can be achieved by increasing the amount of agent or plasticizer. Nevertheless, autogenous shrinkage still increases with increasing fineness of the cement composition.

[0005] Increased shrinkage and drying shrinkage due to internal dehydration make mortar and concrete more susceptible to cracking. This cracking can shorten the service life of the workpiece or structure. Reducing shrinkage in mortar or concrete can be achieved by using admixtures that help offset shrinkage, such as expansive agents (expansive additives) or shrinkage-reducing admixtures. Reducing shrinkage with admixtures increases the cost of the mortar or concrete. Similarly, improving the fluidity or workability of mortar or concrete with plasticizers increases the cost.

[0006] In addition to improving materials to reduce CO2 emissions, constructing building components or structures using cementitious materials through 3D printing is another method that helps reduce CO2 emissions compared to conventional building systems. During the manufacturing process, mortar with the appropriate properties is linearly pressed or extruded along the structure or workpiece, layer by layer, until the desired workpiece is obtained.

[0007] Mortar suitable for 3D printing must have the appropriate viscosity to ensure stability when extruded from the print head, but must not be as fluid as typical poured or poured mortar or concrete. Therefore, the results of using highly finely ground calcined clay or LC3 cement are as described above. The following examples are examples of research into the use of calcined clay or LC3 cement in 3D printing of cementitious materials.

[0008] A paper published by Sumaiya Afroz in Construction and Building Materials Journal, Vol. 386, 2023, investigated the use of cement blended with calcined clay and limestone as binders to suppress shrinkage cracking in concrete and mortar. The study found that concrete using blended calcined clay as a binder (replacing 44% of the cement) cracked earlier than control concrete without blended calcined clay as a binder. This is because early autogenous shrinkage is the main factor causing concrete distortion. Experiments compared replacement of cement with calcined clay by 14%, 44%, and 59%. A highly reactive calcined clay was used. The calcined clay selected was calcined kaolin, containing 47.5% kaolinite and 84% amorphous. Experimental results showed that the total shrinkage (μm / day) of concrete and mortar with cement replaced with calcined clay increased. 0.5 ) was found to be higher than the total shrinkage of the control concrete and mortar, especially in the early stages, which resulted in earlier shrinkage cracking than the control concrete. As the study shows, adding highly reactive calcined clay increases shrinkage, making the concrete / mortar more susceptible to cracking than the control concrete or concrete without calcined clay.

[0009] U.S. Patent No. 20220106230A1, titled "3D PRINTABLE PORTLAND LIMESTONE CLAY-BASED MORTAR UTILIZING LOCALLY AVAILABLE MATERIALS," published by Icon Technology Inc. of Austin, Texas, USA, on April 7, 2022, discloses a 3D printing mortar made of calcined clay and reduced-portland cement (OPC). The printing mortar comprises a mixture of type I / II Portland cement, calcined clay, ground calcium carbonate (limestone), and sand as dry ingredients. The calcined clay in U.S. Patent No. 20220106230A1 is made from clay containing more than 60% kaolinite and is calcined at a temperature of 600-800°C, specifically 650-850°C, for 1-2 hours. In a preferred embodiment, the ratio of calcined clay to Portland cement was approximately 0.148, the ratio of calcium carbonate to Portland cement was approximately 0.333, the ratio of sand to Portland cement was approximately 3.0, and the ratio of water to dry mortar was in the range of 0.39 to 0.40. Mortars with these ratios have workability suitable for 3D printing and material compression molding, and can maintain desirable shape, layering, and green strength when injected through a print head. The main factors in the mixture composition were the ratio of calcined clay to Portland cement, the ratio of calcium carbonate to Portland cement, and the ratio of sand to Portland cement. The compressive strength of the resulting mortar mixture was approximately 3,300 psi (approximately 224 ksc) at 7 days. The above invention does not improve the properties of calcined clay to make it suitable for use. Furthermore, the above patent publication does not mention the properties related to shrinkage and cracking, which are problems associated with the use of calcined clay.

[0010] Therefore, in order to obtain a material for 3D printing of buildings or structures that has low CO2 emissions and excellent durability, it is necessary to develop a mortar mixture for 3D printing that contains fired clay and has excellent cracking properties. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 20220106230A1 [Non-patent literature]

[0012] [Non-Patent Document 1] Written by Sumaiya Afroz, “Construction and Building Materials Journal” Vol.386, published 2023 Summary of the Invention

[0013] The present invention provides a mortar for 3D printing that contains calcined clay as a primary component, has properties suitable for printing, a viscosity that ensures good stability of the mortar extruded from the print head, sufficient compressive strength, low shrinkage, high expansion, and low CO2 emissions. The mortar composition for 3D printing according to the present invention contains cement, 10 to 50% calcined clay, 2 to 5% of an expansion agent including calcium oxide and calcium sulfate, and additives or admixtures. [Brief explanation of the drawings]

[0014] [Figure 1] 1 shows the compressive strength of the examples according to the experiment. [Figure 2] The drying shrinkage of Examples A to D is shown. [Figure 3] The drying shrinkage of Examples E to H is shown. DETAILED DESCRIPTION OF THE INVENTION

[0015] The mortar composition for 3D printing molding according to the present invention is a mortar that emits less CO2 than general mortars for 3D printing molding, and is produced by mixing a cement-substitute material, which is calcined clay that emits less CO2 than clinker, with a high proportion of calcined clay.

[0016] In addition, to reduce shrinkage caused by the addition of calcined clay with a high fineness, the mortar composition contains calcium oxide and calcium sulfate as expanding agents. Research has shown that cementitious mortar compositions containing calcined clay and calcium oxide and calcium sulfate as expanding agents exhibit significantly improved expansion. This is because the synergistic effect of the calcined clay and the expanding agent significantly improves the expansion of the mortar, as shown in Experiment 1 below.

[0017] Therefore, based on the above principle, the mortar composition for three-dimensional printing according to the present invention is Cement and 10-50% of the dry weight of the binder is calcined clay; 2-5% of the dry weight of the mortar as an expanding agent; Fine aggregate and an additive or admixture; The calcined clay has an average particle size of 5 to 50 micrometers, the expansion agent contains calcium oxide and calcium sulfate, and the ratio of the calcined clay to the expansion agent is 2:1 to 25:1.

[0018] For purposes of the present invention, the components that function as binders, e.g., cement and calcined clay, are collectively referred to as "binders."

[0019] Cement is a binding agent or binder that gives strength to materials. Cement is a fine powder that can be hardened with water to give strength. The cement includes one or more of Portland cement, hydraulic cement, blended cement, high alumina cement (aluminate cement), calcium sulfoaluminate cement, and alkali activated cement. The Blaine fineness of the cement is 2,700 to 5,600 cm 2 / g. Preferably, the clinker content is 92% or less and the fineness of the cement is 3,500 to 5,000 cm 2 / g of blended cement.

[0020] Calcined clay is a cement-replacement material with a low CO2 emission or carbon footprint. Calcined clay is typically produced by calcining kaolinite-containing soil or clay at temperatures of approximately 600-800°C and pulverizing to a desired size, resulting in a cement-replacement material that can undergo a pozzolanic reaction and solidify to impart strength to the material. The calcined clay used in the research to develop this mortar composition had a kaolinite content of 20-45%, an amorphous phase content of 40-70%, and was pulverized to an average fineness of 5-50 micrometers. The present invention does not limit the calcined clay to having only the properties specified herein.

[0021] The expanding agent according to the present invention contains calcium sulfate and calcium oxide as main components. The expanding agent has an average surface area of ​​4,000 to 7,000 cm. 2 / g, and when used with calcined clay of a specified particle size or fineness, the expansion properties are improved. The expansion agent content is 2-5% by weight, and in the expansion agent containing calcium oxide and calcium sulfate, the calcium oxide content is 50-90% by weight of the expansion agent, and the calcium sulfate content is 10-40% by weight of the expansion agent.

[0022] In addition to the aforementioned cement, calcined clay, and expanding agent, this mortar composition further contains fine aggregate, water, and additives or admixtures that optimize the mortar's properties for three-dimensional printing. The additives include a set retarder, a thickener, and a rheology modifier, which provide pumpability, printability, and buildability suitable for three-dimensional printing. The material extruded from the nozzle has good stability, allowing for fixed-size print lines and achieving workpieces as designed. The additives or admixtures that optimize pumpability, printability, and buildability include one or more of a set retarder, a thickener, a rheology modifier, a redispersible powder, or fibers that may be selected from natural, synthetic, or metal fibers.

[0023] The content of the fine aggregate is 70 to 80% of the dry weight of the mortar. The fine aggregate includes one or more of sand, finely crushed sand, crushed limestone, recycled aggregate, or inert particles inert to the cement, has an average particle size of more than 600 micrometers, contains less than 10%, and has a coarseness ratio of 2.3 to 5.5.

[0024] The set retarder includes one or more of the following functional compounds: sodium silicofluoride, sucrose, or gluconic acid.

[0025] The thickening agent includes one or more of a cellulose or starch ether.

[0026] The rheology modifier includes one or more of naphthalene, melamine, or polycarboxylate.

[0027] The redispersible powder comprises one or more of acetate, acrylic, vinyl acetate, epoxy, or ethylene vinyl acetate in an amount of 0-5% of the dry weight of the mortar.

[0028] The fibers include natural fibers, synthetic fibers, or metal fibers, and the amount of each type of fiber is 0.05-4% of the dry weight of the mortar.

[0029] The water content, or the ratio of water to dry mortar (w / c), is preferably 0.1 to 0.3. When the dry mortar is mixed with a predetermined amount of water, the wet density is 2,300 kg / m 3 and dry density is less than 2,100 kg / m 3 A mortar having a viscosity of less than 1000 MPa is obtained.

[0030] The following examples are examples of the effects on shrinkage of mortars made from calcined clay, on shrinkage of mortars made from calcined clay and an expanding agent, and on compressive strength of mortars containing calcined clay and an expanding agent.

[0031] Experiment 1: Study on the effect of calcined clay and expansive agent on the compressive strength and expansive properties of mortar Examples A, B, C, and D were mortars consisting of 21.6% cement, 2.4% calcined clay, and 73% fine aggregate by weight, with expansion agent contents of 0, 1, 3, and 5%, respectively. Examples E, F, G, and H were mortars consisting of 12% cement, 12% calcined clay, and 73% fine aggregate by weight, with expansion agent contents of 0, 1, 3, and 5%, respectively. The compositions of Examples A-H are summarized in Table 1.

[0032] Table 1 shows the compositions of Examples AH.

[0033] [Table 1]

[0034] Examples A-H were then mixed with water and tested for compressive strength on day 1 according to the ASTM C109 standard, with the results shown in Table 2 and Figure 1. The examples were also tested for expansion on day 3 and shrinkage on day 14 according to the ASTM C596 standard, with the results shown in Table 2 and Figures 2-3.

[0035] Table 2 shows the compressive strength of the mortar on the first day, the expansion on the third day, and the shrinkage on the fourteenth day for Examples A to H.

[0036] [Table 2] Note: Negative expansiveness means that shrinkage has occurred.

[0037] As can be seen from Experiment 1, Examples A and E, which contained different amounts of calcined clay without adding an expanding agent, showed a slight improvement in expansion, while Examples C, D, G, and H, which contained increasing amounts of calcined clay and expanding agent, showed a dramatic improvement in expansion. This suggests that the appropriate calcined clay and expanding agent have a synergistic effect with each other, resulting in better expansion or shrinkage properties. Furthermore, the addition of an expanding agent improves the compressive strength of the mortar, making it advantageous for use as a material for molding building components.

[0038] Best Mode of the Invention The best mode of the present invention is as described in the detailed description of the invention.

Claims

1. Cement and - 10-50% of the dry weight of the binder is calcined clay; - 2-5% of the dry weight of the mortar as an expanding agent; - Fine aggregate, - an additive or admixture, The calcined clay has an average fineness of 5 to 50 micrometers, the expansion agent contains calcium oxide and calcium sulfate, and the ratio of the calcined clay to the expansion agent is 2:1 to 25:

1. A mortar composition for three-dimensional printing molding.

2. The mortar composition for three-dimensional printing according to claim 1, wherein the cement is one or more selected from the group consisting of portland cement, hydraulic cement, blended cement, high alumina cement (aluminate cement), calcium sulfoaluminate cement, and alkali-activated cement.

3. The mortar composition for three-dimensional printing according to claim 1, wherein the calcined clay has a kaolinite content of 20 to 45% and an amorphous content of 40 to 70% by weight of the calcined clay.

4. The mortar composition for three-dimensional printing molding according to claim 1, wherein the ratio of the fired clay to the binder is 10 to 50%.

5. The mortar composition for three-dimensional printing molding according to claim 1, wherein the content of the fine aggregate is 70 to 80% of the dry weight of the mortar.

6. The mortar composition for three-dimensional printing according to claim 1 or 5, wherein the fine aggregate comprises one or more of sand, finely crushed sand, crushed limestone, recycled aggregate, or inert particles that are inert to the cement.

7. The mortar composition for three-dimensional printing according to claim 1 , wherein the admixture comprises a set retarder, a thickener, a rheology modifier, a redispersible powder, or a fiber.

8. The mortar composition for three-dimensional printing according to claim 7, wherein the set retarder is a functional compound of sodium silicofluoride, sucrose, or gluconic acid.

9. The mortar composition for three-dimensional printing according to claim 7 , wherein the thickener is cellulose or starch ether.

10. The mortar composition for three-dimensional printing according to claim 7 , wherein the rheology modifier is naphthalene, melamine, or polycarboxylate.

11. The mortar composition for three-dimensional printing according to claim 7, wherein the redispersible powder is acetate, acrylic, vinyl acetate, epoxy, or ethylene vinyl acetate at 0 to 5% of the dry weight of the mortar.

12. The mortar composition for three-dimensional printing according to claim 7, wherein the fibers include one or more of natural fibers, synthetic fibers, or metal fibers as components, and the amount of each type of fiber is 0.05 to 4% of the dry weight of the mortar.

13. The mortar composition for three-dimensional printing according to claim 1, wherein the ratio of water to dry mortar is 0.1 to 0.3.

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