CEMENTITIOUS MIXTURE FOR A 3D PRINTER, WITH IMPROVED PERFORMANCE, AND RELATIVE USE IN SAID PRINTER

Abstract

A cementitious mixture for a 3D printer, with improved performance, is described, and its relative use, more specifically for the production of finished products having a complex geometry using a 3D printing apparatus.

Claims

1. A cementitious mixture for a 3D printer which comprises a) a cement or hydraulic binder, b) a latent hydraulic addition, c) a filler, d) one or more aggregates, e) one or more additives, f) water, wherein the filler of component c) is selected from the group consisting of calcareous, silica or silico-calcareous fillers, and mixtures thereof, having a particle size which is such that 90% by weight of the filler passes through an 0.063 mm sieve; component d) is present in a quantity ranging from 10% to 80% by weight, with respect to the total weight of the cementitious mixture, and comprises calcareous, silica or silico-calcareous aggregates, and mixtures thereof, having a particle size with a maximum diameter less than or equal to 2 mm, said component d) comprising one or more fractions having a particle size with a diameter greater than 0.2 mm, and a fraction having a particle size with a diameter less than or equal to 0.2 mm and such that less than 2% by weight of said component d) passes through an 0.063 mm sieve; component e) comprises a superplasticizer, at least two rheology modifiers, a shrinkage reducing agent, a hydrophobic agent and mixtures thereof, said cementitious mixture being characterized by a torque value ranging from 1,000 N.Math.mm to 2,100 N.Math.mm, measured at a rotation rate of 5 rpm and at a temperature of 20° C.

2. The cementitious mixture according to claim 1, wherein the ratio between the superplasticizer and the at least two rheology modifiers, when simultaneously present, ranges between 0.6 and 2.3.

3. The cementitious mixture according to claim 1, comprising: a) from 10% to 70% by weight of hydraulic binder or cement; b) from 0.0% to 25% by weight of a natural or artificial hydraulic addition having a specific surface ranging from 3,500 cm2/g to 6,500 cm2/g, determined according to the Blaine method according to EN 196-6:2010; c) from 10% to 50% by weight of a filler, selected from the group consisting of calcareous, silica or silico-calcareous fillers and mixtures thereof, having a particle size such that 90% by weight of the filler passes through an 0.063 mm sieve; d) from 10% to 80% by weight of calcareous, silica or silico-calcareous aggregates and mixtures thereof, having a particle size with a maximum diameter less than or equal to 2 mm, said component d) being composed of one or more fractions having a particle size greater than 0.2 mm, and a fraction having a particle size with a diameter less than or equal to 0.2 mm and such that less than 2% by weight passes through an 0.063 mm sieve; e) from 0.01% to 1.5% by weight of a superplasticizer selected from the group consisting of acrylic-based polycarboxylates, lignosulfonates, naphthalene sulfonates, melamine or vinyl compounds, and mixtures thereof; from 0.009% to 0.5% by weight of a rheology modifying agent which is a polyamide having a MW ranging from 2×106Da to 2×107Da; from 0.005% to 1.0% by weight of a rheology modifying agent selected from the group consisting of cellulose or its derivatives; from 0.0% to 1.0% by weight of a shrinkage reducing agent; from 0.0% to 0.5% of a hydrophobic additive selected from silicone or silane derivatives and/or mixtures thereof, wherein the binder/aggregate weight ratio ranges from 0.4 to 2.0 the binder being composed of components a) and b) of the cementitious mixture, wherein the ratio between the superplasticizer and the two rheology modifiers, when simultaneously present, ranges between 0.6 and 2.3; and said mixture has a torque value ranging from 1,000 N.Math.mm to 2,100 N.Math.mm, measured at a rotation rate of 5 rpm and at a temperature of 20° C.

4. The cementitious mixture according to claim 1, wherein the water/binder weight ratio ranges from 0.25 to 0.8, the binder comprising components a) and b) of the cementitious mixture.

5. The cementitious mixture according to claim 1, wherein the weight ratio water/total cementitious mixture in powder form is within the range of 15% to 21%.

6. The cementitious mixture according to claim 1, wherein component a) of the mixture is selected from the group consisting of CEM I 52.5 R, or CEM I 52.5 N, sulfoaluminate cement, and mixtures mixtures thereof.

7. The cementitious mixture according to claim 1, wherein component b) of the mixture is granulated blast-furnace slag, having a specific surface ranging from 3,500 cm2/g to 6,500 cm2/g, determined according to the Blaine method according to EN 196-6:2010.

8. The cementitious mixture according to any of the previous claims, comprising: a) from 10% to 70% by weight of hydraulic binder or cement, selected from the group consisting of CEM I 52.5 or CEM I 52.5 N, sulfoaluminate cement, and mixtures thereof; b) from 0.5% to 20% by weight of granulated blast-furnace slag, having a specific surface ranging from 4,000 cm2/g to 5,000 cm2/g, determined according to the Blaine method according to EN 196-6:2010; c) from 15% to 40% by weight of a calcareous filler having a particles size which is such that 90% by weight of the filler passes through an 0.063 mm sieve; d) from 25% to 50% by weight of calcareous, silica or silico-calcareous aggregates, and mixtures thereof, having a particle size with a maximum diameter less than or equal to 2 mm, said component d) being composed of one or more fractions having a particle size greater than 0.2 mm and a fraction having a particle size with a diameter less than or equal to 0.2 mm and which is such that less than 2% by weight passes through an 0.063 mm sieve; e) from 0.05% to 0.8% by weight of a superplasticizer based on polycarboxylic ether; from 0.01% to 0.3% by weight of a rheology modifying agent which is a polyamide with the amide nitrogen substituted and having a MW ranging from 2×106Da to 5×106Da; from 0.008% to 0.50% by weight of a rheology modifying agent which is hydroxymethylethyl cellulose; from 0.3% to 0.6% by weight of a shrinkage reducing agent; from 0.10% to 0.30% of a hydrophobic additive selected from silicone or silane derivatives and/or mixtures thereof, wherein the binder/aggregate weight ratio ranges from 0.55 to 1.4, the binder comprising components a) and b) of the cementitious mixture, wherein the ratio between the superplasticizer and the at least two rheology modifiers, when simultaneously present, ranges between 0.7 and 1.2; and said mixture has a torque value ranging from 1,000 N.Math.mm to 2,100 N.Math.mm, measured at a rotation rate of 5 rpm and at a temperature of 20° C.

9. Use of a cementitious mixture according to claim 1, as extrusion material in a 3D printer, comprising printing a 3D item.

10. A 3D printing process comprising the following steps: preparing a cementitious mixture according to claim 1; feeding the cementitious mixture to a 3D printer; extruding of the cementitious mixture from the 3D printer with an extruder suitable for extruding the mixture; printing the 3D item by depositing consecutive layers of the cementitious mixture.

11. An apparatus for printing a 3D object fed with a cementitious mixture according to claim 1, said apparatus comprising a feeder, an extruder, a flexible pipe which connects the feeder to the extruder comprising a nozzle.

12. A finished product having a complex geometry obtained by 3D printing with a 3D printer fed with a cementitious mixture according to claim 1.

13. The cementitious mixture according to claim 1, wherein component d) is present in a quantity ranging from 25% to 50% by weight, with respect to the total weight of the cementitious mixture.

14. The cementitious mixture according to claim 1, wherein component d) comprises one or more fractions having a particle size with a diameter greater than 0.6 mm, and a fraction having a particle size with a diameter less than or equal to 0.2 mm and such that less than 2% by weight of said component d) passes through an 0.063 mm sieve.

15. The cementitious mixture according to claim 1, wherein the ratio between the superplasticizer and the at least two rheology modifiers, when simultaneously present, ranges between 0.7 and 1.2.

16. The cementitious mixture according to claim 3, wherein the hydraulic binder or cement is selected from the group consisting of Portland cement, sulfoaluminate cement and/or aluminous cement and/or quick-setting natural cement, and mixtures thereof.

17. The cementitious mixture according to claim 3, wherein the natural or artificial hydraulic addition is a granulated blast-furnace slag.

18. The cementitious mixture according to claim 3, wherein the natural or artificial hydraulic addition has a specific surface ranging from 4,000 cm2/g to 5,000 cm2/g, determined according to the Blaine method according to EN 196-6:2010.

19. The cementitious mixture according to claim 3, wherein the filler comprises from 15% to 40% by weight.

20. The cementitious mixture according to claim 3, wherein the binder/aggregate weight ratio ranges from 0.55 to 1.4.

Description

[0112] As previously indicated, the main components of the apparatus for implementing the 3D printing process, to which the cementitious mixture according to the present invention is fed, to be subsequently extruded and deposited, are the following:

[0113] 1) Pumping system;

[0114] 2) Flexible pipe connecting the pump to the extruder;

[0115] 3) Extruder;

[0116] 4) Circular or rectangular outlet nozzle.

[0117] The extrusion device can be mounted on any type of machine or robot that can receive it, so as to combine the extrusion process with the specific advantages relating to the kinematics of the machine/robot.

[0118] More specifically:

[0119] FIG. 6 shows the feeding pump (1) which, in this case is a peristaltic pump. The flexible plastic pipe (2) that connects the feeding pump (1) to the extruder (3) is characterized by a circular section, with an internal diameter of 20 mm and a length ranging from 1.5 to 3 cm. The extruder (3) has been optimized for application with the cementitious mixture according to the present invention and is schematically shown in FIG. 1.

[0120] This extruder is provided with an interchangeable outlet nozzle (4) having a circular or rectangular geometry. With respect to the first geometry, the diameter of the nozzle ranges from 4 mm to 20 mm, whereas in the case of a rectangular geometry, the short side measures from 2 to 8 mm and the long side from 6 to 24 mm.

[0121] All the parts of the extruder are made of ABS (acrylonitrile-butadiene-styrene) and are in turn printed using a 3D printer capable of processing polymeric materials.

[0122] The printing parameters can be controlled with various types of software. This software allows the object designed to be divided into sections governed by the printing resolution to be obtained. In particular, the object to be printed is designed by creating a 3D digital model using a CAD application, and is then divided into layers using the above-mentioned software, subsequently providing the machine with instructions and establishing the path (layer by layer) that the nozzle must follow in order to build the object. The software for dividing the object into layers has generally been created to manage materials such as plastic or metal and therefore it does not allow some important parameters, such as for example the flow-rate of the outgoing material, to be controlled directly.

[0123] In order to control the flow-rate of the extruded material, an approach has been followed similar to the control model of the extrusion of plastic material. The first step is to calculate the flow-rate required for printing the object. This is given by the diameter of the nozzle, the height of the layer, and the speed of the print head. Therefore, once the flow-rate value is known, the pump settings can be established, so that it can correctly supply the extruder:

[0124] The examples provided hereunder aim at demonstrating the efficiency of cementitious compositions according to the present invention, when processed by means of a 3D printing apparatus.

EXAMPLE 1

[0125] A formulation of a cementitious mixture having the composition shown in the following Table 1 was prepared using a Hobart mixer, according to the following procedure: [0126] the solid components were mixed for 10 seconds at a rate of 140 rpm; [0127] water was then added and all the components were mixed for 2 minutes and 30 seconds at a rate of 140 rpm; [0128] the mixing was interrupted for 45 seconds to collect any material possibly remaining on the walls of the container; [0129] all the components were then mixed for 2 minutes at a rate of 140 rpm.

TABLE-US-00001 TABLE 1 Formulation extruded according to Example 1. Composition Component (weight %) Cement I 52.5 R 18.13% GGBS 17.50% Calcareous Filler 20.54% Silico-calcareous sand (0.00-0.200 mm)  9.40% Silico-calcareous sand (0.600-1.000 mm) 23.00% Silico-calcareous sand (1.000-1.500 mm) 10.64% Superplasticizer  0.13% Rheology modifier 1  0.01% Rheology modifier 2  0.06% Superplasticizer/(Rheology modifier 1 +  1.86 Rheology modifier 2) Shrinkage reducing agent  0.44% Hydrophobic agent  0.15% Water/binder  0.47 Water/Total powder cementitious mixture 16.50% Binder/aggregate  0.83

[0130] The cement is a cement of the type I 52.5 R coming from the Rezzato plant. The GGBS included in the formulation constitutes the latent hydraulic addition and is a granular blast furnace slag (GGBS: “ground grain ground slag”) compliant with EN 15167-1:2006, having a specific surface equal to 4,450 cm.sup.2/g (determined according to the Blaine method according to the standard EN 196-6: 2010), supplied by the company Ecocem with the trade-name of “Loppa di altoforno granulata macinata” (Ground granular blast furnace slag).

[0131] The calcareous filler is a high-purity filler, marketed by Omya Spa with the trade-name of Omyacarb 2-AV. The silico-calcareous aggregates were added in three fractions, a first fraction with a particle-size distribution ranging from 0.00 to 0.200 mm, a second fraction with a particle-size distribution ranging from 0.600 to 1.000 mm and a third fraction with a particle-size distribution ranging from 1.000 to 1.500 mm.

[0132] The superplasticizer is based on polycarboxylic ether, called Melflux 2641 F, and marketed by BASF. The rheology modifier 1 is a hydroxymethylethylcellulose called “Tylose MH 60004 P6” marketed by ShinEtsu. The rheology modifier 2 is a high-molecular-weight synthetic polymer, more specifically a polyamide with the amide nitrogen substituted with a molecular weight approximately equal to 2×10.sup.6Da, called Starvis 3040F marketed by BASF.

[0133] The shrinkage reducing agent (SRA), called SRA04, is marketed by Neuvendis; this is a mixture of glycols and special surfactants. The hydrophobic agent is a silane-based additive, more specifically an alkyl-oxysilane, called SEAL 200, marketed by Elotex.

[0134] These five additives are in solid form.

[0135] The ratio between the superplasticizer and the sum of the two rheology modifiers is equal to 1.86.

[0136] The water/binder ratio is equal to 0.47, the percentage referring to the weight ratio water/total cementitious mixture in powder form is 16.50%, whereas the binder/aggregate ratio is equal to 0.83 (wherein the binder is composed of cement and the latent hydraulic addition GGBS).

[0137] At the end of the mixing, the cementitious mixture having the composition indicated in Table 1, was characterized by means of a rotational viscometer with a controlled rotation rate, model Schleibinger Viskomat XL, at a temperature of 20° C. The test allowed the torque of the material to be characterized within a rotation-rate range varying from a minimum value of 5 rpm to a maximum value of 60 rpm, by means of a step method. Each velocity value was maintained for 1 minute and the total duration of the test was 15 minutes. The torque value, obtained at a rotation rate of 5 rpm, proved to be equal to 1342 N.Math.mm.

[0138] At the end of the mixing, the cementitious mixture was inserted into the hopper of the peristaltic pump model Umiblok Magic Plus P100 (as shown in FIG. 6), with the help of a steel pestle to facilitate the flow of the cementitious mixture towards the feeding hole, then proceeding for pumping. This latter operation was carried out by setting the speed regulator of the pump at the minimum scale value.

[0139] The mixture prepared as previously indicated was extruded using a triple-layered tapered-spiral printing path. The geometry of the 3D model in question derives from a triangle with rounded corners. The model was successfully printed (as shown in FIG. 2) in a single printing session, applying the following printing parameters:

[0140] Height of layer: 12.0 mm;

[0141] Printing speed: 36 mm/s;

[0142] Extrusion flow-rate: 51 Kg/h;

[0143] Nozzle geometry: 15 mm diameter.

[0144] The mechanical resistance to compression value at 24 hours was equal to 12.9 MPa, according to the loading ramp as described in EN 196-1:2016.

EXAMPLE 2

[0145] A formulation of a cementitious mixture having the composition shown in the following Table 2 was prepared using a Hobart mixer, according to the following procedure: [0146] the solid components were mixed for 10 seconds at a rate of 140 rpm; [0147] water was then added and all the components were mixed for 2 minutes and 30 seconds at a rate of 140 rpm; [0148] the mixing was interrupted for 45 seconds to collect any material possibly remaining on the walls of the container; [0149] all the components were then mixed for 2 minutes at a rate of 140 rpm.

TABLE-US-00002 TABLE 2 Formulation extruded according to Example 2. Composition Component (weight %) Cement I 52.5 R 17.22% Sulfoaluminate cement  4.99% GGBS 16.63% Calcareous Filler 19.50% Silico-calcareous sand (0.00-0.200 mm)  9.83% Silico-calcareous sand (0.600-1.000 mm) 21.85% Silico-calcareous sand (1.000-1.500 mm)  9.22% Superplasticizer  0.13% Rheology modifier 1  0.01% Rheology modifier 2  0.06% Superplasticizer/(Rheology modifier  1.86 1 + Rheology modifier 2) Shrinkage reducing agent  0.42% Hydrophobic agent  0.14% Water/binder  0.44 Water/Total powder cementitious mixture  16.8% Binder/aggregate  0.94

[0150] The cement is a cement of the type I 52.5 R coming from the Rezzato plant. The sulfoaluminate cement comes from the Guardiaregia plant. The GGBS included in the formulation constitutes the latent hydraulic addition and is a granular blast furnace slag (GGBS: “ground grain ground slag”) compliant with EN 15167-1:2006, having a specific surface equal to 4,450 cm.sup.2/g (determined according to the Blaine method according to the standard EN 196-6: 2010), supplied by the company Ecocem with the trade-name of “Loppa di altoforno granulata macinata” (Ground granular blast furnace slag).

[0151] The calcareous filler is a high-purity filler, marketed by Omya Spa under the trade-name of Omyacarb 2-AV. The silico-calcareous aggregates were added in three fractions, a first fraction with a particle-size distribution ranging from 0.00 to 0.200 mm, a second fraction with a particle-size distribution ranging from 0.600 to 1.000 mm and a third fraction with a particle-size distribution ranging from 1.000 to 1.500 mm.

[0152] The superplasticizer is based on polycarboxylic ether, called Melflux 2641 F, and marketed by BASF.

[0153] The rheology modifier 1 is a hydroxymethylethylcellulose called “Tylose MH 60004 P6” marketed by ShinEtsu. The rheology modifier 2 is a high-molecular-weight synthetic polymer, more specifically a polyamide with the amide nitrogen substituted with a molecular weight approximately equal to 2×10.sup.6Da, called Starvis 3040F marketed by BASF.

[0154] The shrinkage reducing agent (SRA), called SRA04, is marketed by Neuvendis; this is a mixture of glycols and special surfactants. The hydrophobic agent is a silane-based additive, more specifically an alkyl-oxysilane, called SEAL 200, marketed by Elotex.

[0155] These five additives are in solid form.

[0156] The ratio between the superplasticizer and the sum of the two rheology modifiers is equal to 1.86.

[0157] The water/binder ratio is equal to 0.44, the percentage referring to the weight ratio water/total cementitious mixture in powder form is 16.80%, whereas the binder/aggregate ratio is equal to 0.94 (wherein the binder is composed of cement type I 52.5 R, sulfoaluminate cement and the latent hydraulic addition GGBS).

[0158] At the end of the mixing, the cementitious mixture having the composition indicated in Table 2, was characterized by means of a rotational viscometer with a controlled rotation rate, model Schleibinger Viskomat XL, at a temperature of 20° C. The test allowed the torque of the material to be characterized within a rotation-rate range varying from a minimum value of 5 rpm to a maximum value of 60 rpm, by means of a step method. Each velocity value was maintained for 1 minute and the total duration of the test was 15 minutes. The torque value, obtained at a rotation rate of 5 rpm, proved to be equal to 1191 N.Math.mm.

[0159] At the end of the mixing, the cementitious mixture was inserted into the hopper of the peristaltic pump model Umiblok Magic Plus P100 (as shown in FIG. 6), with the help of a steel pestle to facilitate the flow of the cementitious mixture towards the feeding hole, then proceeding for pumping. This latter operation was carried out by setting the speed regulator of the pump at the minimum scale value.

[0160] The mixture prepared as previously indicated was extruded using a conical triple-layered printing path. The model was successfully printed (as shown in FIG. 3) in a single printing session, applying the following printing parameters:

[0161] Height of layer: 12.0 mm;

[0162] Printing speed: 36 mm/s;

[0163] Extrusion flow-rate: 51 Kg/h;

[0164] Nozzle geometry: 15 mm diameter.

[0165] The mechanical resistance to compression value at 7 hours proved to be equal to 7.8 MPa, whereas that at 24 hours was equal to 17.5 MPa, according to the loading ramp as described in EN 196-1:2016.

EXAMPLE 3

[0166] A formulation of a cementitious mixture having the composition shown in the following Table 3 was prepared using a Hobart mixer, according to the procedure: [0167] the solid components were mixed for 10 seconds at a rate of 140 rpm; [0168] water was then added and all the components were mixed for 2 minutes and 30 seconds ata rate of 140 rpm; [0169] all the components were then further mixed for 2 minutes and 30 seconds at a rate of 240 rpm; [0170] the mixing was interrupted for 45 seconds to collect any material possibly remaining on the walls of the container; [0171] all the components were then mixed for 2 minutes at a rate of 140 rpm.

TABLE-US-00003 TABLE 3 Formulation extruded according to Example 3. Composition Component (weight %) Cement I 52.5 R 18.13% GGBS 17.50% Calcareous Filler 33.56% Silico-calcareous sand (0.00-0.200 mm) 20.00% Silico-calcareous sand (0.600-1.000 mm) 10.00% Superplasticizer  0.15% Rheology modifier 1  0.01% Rheology modifier 2  0.06% Superplasticizer/(Rheology modifier 1 +  2.14 Rheology modifier 2) Shrinkage reducing agent  0.44% Hydrophobic agent  0.15% Water/binder  0.51 Water/Total powder cementitious mixture 17.85% Binder/aggregate  1.19

[0172] The cement is a cement of the type I 52.5 R coming from the Rezzato plant. The GGBS included in the formulation constitutes the latent hydraulic addition and is a granular blast furnace slag (GGBS: “ground grain ground slag”) compliant with EN 15167-1:2006, having a specific surface equal to 4,450 cm.sup.2/g (determined according to the Blaine method according to the standard EN 196-6: 2010), supplied by the company Ecocem with the trade-name of “Loppa di altoforno granulata macinata” (Ground granular blast furnace slag).

[0173] The calcareous filler is a high-purity filler, marketed by Omya Spa under the trade-name of Omyacarb 2-AV. The silico-calcareous aggregates were added in two fractions, a first fraction with a particle-size distribution ranging from 0.00 to 0.200 mm and a second fraction with a particle-size distribution ranging from 0.600 to 1.000 mm.

[0174] The superplasticizer is based on polycarboxylic ether, called Melflux 2641 F, and marketed by BASF. The rheology modifier 1 is a hydroxymethylethylcellulose called “Tylose MH 60004 P6” marketed by ShinEtsu. The rheology modifier 2 is a high-molecular-weight synthetic polymer, more specifically a polyamide with the amide nitrogen substituted with a molecular weight approximately equal to 2×10.sup.6Da, called Starvis 3040F marketed by BASF.

[0175] The shrinkage reducing agent (SRA), called SRA04, is marketed by Neuvendis: it is a mixture of glycols and special surfactants. The hydrophobic agent is a silane-based additive, more specifically an alkyl-oxysilane, called SEAL 200, marketed by Elotex.

[0176] These five additives are in solid form.

[0177] The ratio between the superplasticizer and the sum of the two rheology modifiers is equal to 2.14.

[0178] The water/binder ratio is equal to 0.51, the percentage referring to the weight ratio water/total cementitious mixture ratio in powder form is 17.85%, whereas the binder/aggregate ratio is equal to 1.19 (wherein the binder is composed of cement and the latent hydraulic addition GGBS).

[0179] At the end of the mixing, the cementitious mixture having the composition indicated in Table 3, was characterized by means of a rotational viscometer with a controlled rotation rate, model Schleibinger Viskomat XL, at a temperature of 20° C. The test allowed the torque of the material to be characterized within a rotation-rate range varying from a minimum value of 5 rpm to a maximum value of 60 rpm, by means of a step method. Each velocity value was maintained for 1 minute and the total duration of the test was 15 minutes. The torque value, obtained at a rotation rate of 5 rpm, proved to be equal to 1410 N.Math.mm.

[0180] At the end of the mixing, the cementitious mixture was inserted into the hopper of the peristaltic pump model Umiblok Magic Plus P100 (as shown in FIG. 6), with the help of a steel pestle to facilitate the flow of the cementitious mixture towards the feeding hole, then proceeding for pumping. This latter operation was carried out by setting the speed regulator of the pump at the minimum scale value.

[0181] The mixture prepared as previously indicated was extruded using a triple-layered spiral printing path, having a geometry deriving from an octagon. The geometry of the 3D model in question derives from a triangle with rounded corners. The model was successfully printed (as shown in FIG. 4) in a single printing session, applying the following printing parameters:

[0182] Height of layer: 12.0 mm;

[0183] Printing speed: 36 mm/s;

[0184] Extrusion flow-rate: 51 Kg/h;

[0185] Nozzle geometry: 15 mm diameter.

[0186] The mechanical resistance to compression value at 24 hours proved to be equal to 17.5 MPa, according to the loading ramp as described in EN 196-1:2016.

EXAMPLE 4

[0187] A formulation of a cementitious mixture having the composition shown in the following Table 4 was prepared using a Hobart mixer, according to the procedure: [0188] the solid components were mixed for 10 seconds at a rate of 140 rpm; [0189] water was then added and all the components were mixed for 2 minutes and 30 seconds at a rate of 140 rpm; [0190] all the components were then further mixed for 2 minutes and 30 seconds at a rate of 240 rpm; [0191] the mixing was interrupted for 45 seconds to collect any material possibly remaining on the walls of the container; [0192] all the components were then mixed for 2 minutes at a rate of 140 rpm.

TABLE-US-00004 TABLE 4 Formulation extruded according to Example 4. Composition Component (weight %) Cement I 52.5 R 17.22% Sulfoaluminate cement  5.00% GGBS 16.60% Calcareous Filler 31.90% Silico-calcareous sand (0.00-0.200 mm) 19.00% Silico-calcareous sand (0.600-1.000 mm)  9.50% Superplasticizer  0.15% Rheology modifier 1  0.01% Rheology modifier 2  0.06% Superplasticizer/(Rheology modifier  2.14 1 + Rheology modifier 2) Shrinkage reducing agent  0.42% Hydrophobic agent  0.14% Water/binder  0.50 Water/Total powder cementitious mixture 19.00% Binder/aggregate  1.36

[0193] The cement is a cement of the type I 52.5 R coming from the Rezzato plant. The sulfoaluminate cement comes from the Guardiaregia plant. The GGBS included in the formulation constitutes the latent hydraulic addition and is a granular blast furnace slag (GGBS: “ground grain ground slag”) compliant with EN 15167-1:2006, having a specific surface equal to 4,450 cm.sup.2/g (determined according to the Blaine method according to the standard EN 196-6: 2010), supplied by the company Ecocem with the trade-name of “Loppa di altoforno granulata macinata” (Ground granular blast furnace slag).

[0194] The calcareous filler is a high-purity filler, marketed by Omya Spa under the trade-name of Omyacarb 2-AV. The silico-calcareous aggregates were added in two fractions, a first fraction with a particle-size distribution ranging from 0.00 to 0.200 mm and a second fraction with a particle-size distribution ranging from 0.600 to 1,000 mm.

[0195] The superplasticizer is based on polycarboxylic ether, called Melflux 2641 F, and marketed by BASF. The rheology modifier 1 is a hydroxymethylethylcellulose called “Tylose MH 60004 P6” marketed by ShinEtsu. The rheology modifier 2 is a high-molecular-weight synthetic polymer, more specifically a polyamide with the amide nitrogen substituted with a molecular weight approximately equal to 2×10.sup.6Da, called Starvis 3040F marketed by BASF.

[0196] The shrinkage reducing agent (SRA), called SRA04, is marketed by Neuvendis: it is a mixture of glycols and special surfactants. The hydrophobic agent is a silane-based additive, more specifically an alkyl-oxysilane, called SEAL 200, marketed by Elotex.

[0197] These five additives are in solid form.

[0198] The ratio between the superplasticizer and the sum of the two rheology modifiers is equal to 2.14.

[0199] The water/binder ratio is equal to 0.50, the percentage referring to the weight ratio water/total cementitious mixture ratio in powder form is 19.00%, whereas the binder/aggregate ratio is equal to 1.36 (wherein the binder consists of I 52.5 R-type cement, sulfoaluminate cement and the latent hydraulic addition GGBS).

[0200] At the end of the mixing, the cementitious mixture having the composition indicated in Table 4, was characterized by means of a rotational viscometer with a controlled rotation rate, model Schleibinger Viskomat XL, at a temperature of 20° C. The test allowed the torque of the material to be characterized within a rotation-rate range varying from a minimum value of 5 rpm to a maximum value of 60 rpm, by means of a step method. Each velocity value was maintained for 1 minute and the total duration of the test was 15 minutes. The torque value, obtained at a rotation rate of 5 rpm, proved to be equal to 1250 N.Math.mm.

[0201] At the end of the mixing, the cementitious mixture was inserted into the hopper of the peristaltic pump model Umiblok Magic Plus P100 (as shown in FIG. 6), with the help of a steel pestle to facilitate the flow of the cementitious mixture towards the feeding hole, then proceeding for pumping. This latter operation was carried out by setting the speed regulator of the pump at the minimum scale value.

[0202] The mixture prepared as previously indicated was extruded using a straight double-layered printing path, having a length of 20 cm for each layer. The model was successfully printed (as shown in FIG. 5) in a single printing session, applying the following printing parameters:

[0203] Height of layer: 12.0 mm;

[0204] Printing speed: 36 mm/s;

[0205] Extrusion flow-rate: 51 Kg/h;

[0206] Nozzle geometry: 15 mm diameter.

[0207] The mechanical resistance to compression value at 8 hours proved to be equal to 7.6 MPa, whereas that at 24 hours was equal to 17.9 MPa, according to the loading ramp as described in EN 196-1:2016.

EXAMPLE 5 (Comparative)

[0208] A formulation of a cementitious mixture having the composition shown in the following Table 5 was prepared using a Hobart mixer, according to the following procedure: [0209] the solid components were mixed for 10 seconds at a rate of 140 rpm; [0210] water was then added and all the components were mixed for 2 minutes and 30 seconds at a rate of 140 rpm; [0211] the mixing was interrupted for 45 seconds to collect any material possibly remaining on the walls of the container; [0212] all the components were then mixed for 2 minutes at a rate of 140 rpm.

TABLE-US-00005 TABLE 5 Formulation extruded according to Example 5. Composition Component (weight %) Cement I 52.5 R 18.13% GGBS 17.50% Calcareous Filler 33.40% Silico-calcareous sand (0.00-0.200 mm) 20.00% Silico-calcareous sand (0.600-1.000 mm) 10.00% Superplasticizer  0.13% Rheology modifier 2  0.25% Superplasticizer/(Rheology modifier — 1 + Rheology modifier 2) Shrinkage reducing agent  0.44% Hydrophobic agent  0.15% Water/binder  0.52 Water/Total powder cementitious mixture  18.5% Binder/aggregate  1.19

[0213] The cement is a cement of the type I 52.5 R coming from the Rezzato plant. The GGBS included in the formulation constitutes the latent hydraulic addition and is a granular blast furnace slag (GGBS: “ground grain ground slag”) compliant with EN 15167-1:2006, having a specific surface equal to 4,450 cm.sup.2/g (determined according to the Blaine method according to the standard EN 196-6: 2010), supplied by the company Ecocem with the trade-name of “Loppa di altoforno granulata macinata” (Ground granular blast furnace slag).

[0214] The calcareous filler is a high-purity filler, marketed by Omya Spa under the trade-name of Omyacarb 2-AV. The silico-calcareous aggregates were added in two fractions, a first fraction with a particle-size distribution ranging from 0.00 to 0.200 mm and a second fraction with a particle-size distribution ranging from 0.600 to 1.000 mm.

[0215] The superplasticizer is based on polycarboxylic ether, called Melflux 2641 F, and marketed by BASF. The rheology modifier 2 is a high-molecular-weight synthetic polymer, more specifically a polyamide with the amide nitrogen substituted with a molecular weight approximately equal to 2×10.sup.6Da, called Starvis 3040F marketed by BASF.

[0216] The shrinkage reducing agent (SRA), called SRA04, is marketed by Neuvendis: it is a mixture of glycols and special surfactants. The hydrophobic agent is a silane-based additive, more specifically an alkyloxysilane, called SEAL 200, marketed by Elotex.

[0217] These four additives are in solid form.

[0218] The ratio between the superplasticizer and the sum of the two rheology modifiers was not calculated because the rheology modifier 1 is not present in the formula.

[0219] The water/binder ratio is equal to 0.52, the percentage referring to the weight ratio water/total cementitious mixture ratio in powder form is 18.50%, whereas the binder/aggregate ratio is equal to 1.19 (wherein the binder consists of cement and the latent hydraulic addition GGBS). At the end of mixing, the cementitious mixture proved to be extremely fluid, therefore not characterized by rheological behaviour suitable for being printed (the rheological test was not significant for the characterization of this formulation).

[0220] With the same maximum size of the aggregate (see examples 3 and 4), the greater fluidity of the cementitious mixture of Example 5 derives from the fact that only rheology modifier 2 is present, i.e. the high-molecular-weight polyamide (Starvis), without cellulose. It is thanks to the system of rheology modifiers according to the present invention, in fact, that the cementitious mixture has the necessary rheological properties.

EXAMPLE 6 (Comparative)

[0221] A formulation of a cementitious mixture having the composition shown in the following Table 6 was prepared using a Hobart mixer, according to the following procedure: [0222] the solid components were mixed for 10 seconds at a rate of 140 rpm; [0223] water was then added and all the components were mixed for 2 minutes and 30 seconds at a rate of 140 rpm; [0224] the mixing was interrupted for 45 seconds to collect any material possibly remaining on the walls of the container; [0225] all the components were then mixed for 2 minutes at a rate of 140 rpm.

TABLE-US-00006 TABLE 6 Formulation extruded according to Example 6. Composition Component (weight %) Cement I 52.5 R 18.13% GGBS 17.50% Calcareous Filler 33.55% Silico-calcareous sand (0.00-0.200 mm) 20.00% Silico-calcareous sand (0.600-1.000 mm) 10.00% Superplasticizer  0.13% Rheology modifier 1  0.1% Superplasticizer/(Rheology modifier 1 + — Rheology modifier 2) Shrinkage reducing agent  0.44% Hydrophobic agent  0.15% Water/binder  0.52 Water/Total powder cementitious mixture  18.5% Binder/aggregate  1.19

[0226] The cement is a cement of the type I 52.5 R coming from the Rezzato plant. The GGBS included in the formulation constitutes the latent hydraulic addition and is a granular blast furnace slag (GGBS: “ground grain ground slag”) compliant with EN 15167-1:2006, having a specific surface equal to 4,450 cm.sup.2/g (determined according to the Blaine method according to the standard EN 196-6: 2010), supplied by the company Ecocem with the trade-name of “Loppa di altoforno granulata macinata” (Ground granular blast furnace slag).

[0227] The calcareous filler is a high-purity filler, marketed by Omya Spa under the trade-name of

[0228] Omyacarb 2-AV. The silico-calcareous aggregates were added in two fractions, a first fraction with a particle-size distribution ranging from 0.00 to 0.200 mm and a second fraction with a particle-size distribution ranging from 0.600 to 1.000 mm.

[0229] The superplasticizer is based on polycarboxylic ether, called Melflux 2641 F, and marketed by BASF. The rheology modifier 1 is a hydroxymethylethylcellulose called “Tylose MH 60004 P6” marketed by ShinEtsu.

[0230] The shrinkage reducing agent (SRA), called SRA04, is marketed by Neuvendis: it is a mixture of glycols and special surfactants. The hydrophobic agent is a silane-based additive, more specifically an alkyloxysilane, called SEAL 200, marketed by Elotex.

[0231] These four additives are in solid form. The ratio between the superplasticizer and the sum of the two rheology modifiers was not calculated because the rheology modifier 2 is not present in the formula.

[0232] The water/binder ratio is equal to 0.52, the percentage referring to the weight ratio water/total cementitious mixture ratio in powder form is 18.50%, whereas the binder/aggregate ratio is equal to 1.19 (wherein the binder consists of cement and the latent hydraulic addition GGBS). At the end of mixing, the material resulted stiff and rubbery. For this reason, it was not possible to perform the rheological tests because the limit torque value of the equipment (3000 N.Math.mm) was exceeded by the initial torque of the material. Therefore, the material presented a higher torque with respect to the one characterizing the material in order to be processed according to the present invention.

EXAMPLE 7

[0233] A formulation of a cementitious mixture having the composition shown in the following Table 7 was prepared using a Hobart mixer, according to the following procedure: [0234] the solid components were mixed for 10 seconds at a rate of 140 rpm; [0235] water was then added and all the components were mixed for 2 minutes and 30 seconds at a rate of 140 rpm; [0236] the mixing was interrupted for 45 seconds to collect any material possibly remaining on the walls of the container; [0237] all the components were then mixed for 2 minutes at a rate of 140 rpm.

TABLE-US-00007 TABLE 7 Formulation extruded according to Example 7. Composition Component (weight %) Cement I 52.5 R 17.50% GGBS 17.50% Calcareous Filler 22.20% Silico-calcareous sand (0.00-0.200 mm)  9.40% Silico-calcareous sand (0.600-1.000 mm) 23.00% Silico-calcareous sand (1.000-1.500 mm)  9.70% Superplasticizer  0.06% Rheology modifier 1  0.01% Rheology modifier 2  0.06% Superplasticizer/(Rheology modifier 1 +  0.86 Rheology modifier 2) Shrinkage reducing agent  0.44% Hydrophobic agent  0.15% Water/binder  0.47 Water/Total powder cementitious mixture 16.50% Binder/aggregate  0.85

[0238] The cement is a cement of the type I 52.5 R coming from the Rezzato plant. The GGBS included in the formulation constitutes the latent hydraulic addition and is a granular blast furnace slag (GGBS: “ground grain ground slag”) compliant with EN 15167-1:2006, having a specific surface equal to 4,450 cm.sup.2/g (determined according to the Blaine method according to the standard EN 196-6: 2010), supplied by the company Ecocem with the trade-name of “Loppa di altoforno granulata macinata” (Ground granular blast furnace slag).

[0239] The calcareous filler is a high-purity filler, marketed by Omya Spa with the trade-name of Omyacarb 2-AV. The silico-calcareous aggregates were added in three fractions, a first fraction with a particle-size distribution ranging from 0.00 to 0.200 mm, a second fraction with a particle-size distribution ranging from 0.600 to 1.000 mm and a third fraction with a particle-size distribution ranging from 1.000 to 1.500 mm.

[0240] The superplasticizer is based on polycarboxylic ether, called Melflux 2641 F, and marketed by BASF. The rheology modifier 1 is a hydroxymethylethylcellulose called “Tylose MH 60004 P6” marketed by ShinEtsu. The rheology modifier 2 is a high-molecular-weight synthetic polymer, more specifically a polyamide with the amide nitrogen substituted with a molecular weight approximately equal to 2×10.sup.6Da, called Starvis 3040F marketed by BASF.

[0241] The shrinkage reducing agent (SRA), called SRA04, is marketed by Neuvendis; this is a mixture of glycols and special surfactants. The hydrophobic agent is a silane-based additive, more specifically an alkyl-oxysilane, called SEAL 200, marketed by Elotex.

[0242] These five additives are in solid form. The ratio between the superplasticizer and the sum of the two rheology modifiers is equal to 0.86

[0243] The water/binder ratio is equal to 0.47, the percentage referring to the weight ratio water/total cementitious mixture in powder form is 16.50%, whereas the binder/aggregate ratio is equal to 0.85 (wherein the binder is composed of cement and the latent hydraulic addition GGBS).

[0244] At the end of the mixing, the cementitious mixture having the composition indicated in Table 7, was characterized by means of a rotational viscometer with a controlled rotation rate, model Schleibinger Viskomat XL, at a temperature of 20° C. The test allowed the torque of the material to be characterized within a rotation-rate range varying from a minimum value of 5 rpm to a maximum value of 60 rpm, by means of a step method. Each velocity value was maintained for 1 minute and the total duration of the test was 15 minutes. The torque value, obtained at a rotation rate of 5 rpm, proved to be equal to 1344 N.Math.mm, thus resulting compliant with the torque range expected by the present invention.

[0245] At the end of the mixing, the cementitious mixture was inserted into a cylindrical gas-pressurized supply tank with the help of a spatula and arranged so as to completely fill the container reducing the air trapped in the material as much as possible. The cylindrical gas-pressurized supply tank contains a piston which pushes the fluid, i.e. the cementitious mixture; the pressure is supplied by pressurized air, directly connected to the tank and regulated by a pressure gauge. The cylindrical gas-pressurized supply tank was thus prepared for being connected to the extruder mounted on the printing machine, using a flexible plastic tube. This tube connects the pump-tank system to the extruder and it is characterized by a circular section, with an internal diameter of 20 mm and a length ranging from 1.5 to 3 m. The tank pressure was set at 6.0 bars.

[0246] The mixture prepared as previously indicated was extruded using a triple-layered spiral printing path, having a geometry deriving from a cylinder. The model was successfully printed in a single printing session, applying the following printing parameters:

[0247] Height of layer: 8.0 mm;

[0248] Printing speed: 25 mm/s;

[0249] Nozzle geometry: 10 mm diameter.

[0250] The mechanical resistance to compression value at 24 hours proved to be equal to 17.0 MPa, according to the loading ramp as described in EN 196-1:2016.

BIBLIOGRAPHY

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