METHOD FOR LAYER-BY-LAYER DEPOSITION OF CONCRETE USING RAPIDLY HYDRATING CEMENTITIOUS MATERIAL AND BICOMPONENT CEMENTITIOUS BINDER COMPOSITION THEREFOR

Abstract

The invention relates to a method for layer-by-layer deposition of concrete, in particular of concrete using a rapidly hydrating cementitious binder.

A first flow and a second flow are supplied to a mixer to obtain extrudable concrete. The pH of the second flow is larger than the pH of the first flow. The first flow comprises a retarded cementitious binder obtainable by mixing a cementitious binder with a retarder comprising boron and sodium. The retarder allows to increase the setting time of the cementitious binder and allows to influence the pH of the first flow in such a way that the pH of the first flow is lower than the pH of a flow equal to the first flow but comprising the cementitious binder instead of the retarded cementitious binder. The second flow comprises a carrier material. The volume fraction of the carrier material is at least 20 vol % of the second flow.

The present invention also relates to a bicomponent cementitious binder composition comprising a first component comprising rapidly hydrating cementitious material.

Claims

1. A method for layer-by-layer deposition of concrete, the method comprising providing extrudable concrete by supplying a first flow and a second flow to a mixer, the first flow having a first pH (pH1) and comprising a first material and optionally water, the first material comprising a retarded cementitious binder obtainable by mixing a cementitious binder with a retarder, the cementitious binder having an initial setting time Tcem and the retarded cementitious binder having an initial setting time Tret cem, with the cementitious binder being selected from the group consisting of calcium sulfoaluminate and calcium aluminate, with the retarder comprising a compound when mixed with the cementitious binder to provide the retarded cementitious binder being able to influence the initial setting time so that the initial setting time of the retarded cementitious binder Tret cem is higher than the initial setting time of the cementitious binder Tcem and with the retarder being able to influence the pH of the first flow in such a way that the first pH (pH1) of the first flow is lower than the pH of a flow equal to the first flow but comprising the cementitious binder instead of the retarded cementitious binder and not comprising the retarder, the retarder comprising a compound comprising boron and sodium; the second flow having a second pH (pH2) and comprising a second material and optionally water, the second material having a second initial setting time (T2), with the second pH (pH2) being larger than the first pH (pH1) and with the difference between the first pH (pH1) and the second pH (pH2) being at least 2, the second material comprising a carrier material and optionally a pH modifier, with the volume fraction of the carrier material being at least 20 vol % of the second flow; mixing the first flow and the second flow in the mixer to obtain a third flow comprising extrudable concrete, the third flow comprising a mixture of the first material, the second material and optionally water, with the mixture of the first material, the second material having an initial setting time T3, whereby the initial setting time T3 is smaller than the initial setting time of the retarded cementitious binder Tret cem.

2. The method according to claim 1, wherein the second material comprises a cementitious binder and a pH modifier and optionally a binder material and/or aggregate material and/or supplementary cementitious material and/or one or more additional compound.

3. The method according to claim 1, wherein the initial setting time T3 is smaller than the initial setting time of the cementitious binder Tcem.

4. The method according to claim 1, wherein the first pH (pH1) ranges between 7 and 10 and the second pH (pH2) ranges between 10 and 14.

5. The method according to claim 1, wherein the retarder comprises di-sodium tetraborate decahydrate.

6. The method according to claim 1, wherein the volume fraction of the carrier material is at least 20 vol % of the second material.

7. The method according to claim 1, wherein the second material comprises at least 20 vol % of a powdery carrier material having an average particle size lower than 100 m.

8. The method according to claim 7, wherein said powdery carrier material comprises limestone powder, a mineral powder or combinations thereof.

9. The method according to claim 1, wherein the pH modifier comprises a hydroxide.

10. The method according to claim 1, wherein the binder material comprises a cementitious binder material, an alkali activated binder material or a combination of a cementitious binder material and an alkali activated binder material and/or wherein the at least one additional compound comprises a plasticizer or superplasticizer.

11. The method according to claim 1, wherein both the first and the second flow are free from carbonates and sulfates.

12. A bicomponent cementitious binder composition comprising a first component and a second component, wherein the first component comprises a retarded cementitious binder obtainable by mixing at least 30 wt % of a first cementitious binder, between 0.1 and 5 wt % of a retarder, the first cementitious binder being selected from the group consisting of sulfoaluminate cement, aluminate cement and combinations thereof, the retarder comprising a compound comprising boron and sodium, and wherein the second component comprises a carrier material and optionally a pH modifier with the volume fraction of the carrier material being at least 20 vol % of the second component.

13. The bicomponent cementitious binder composition according to claim 14, wherein the second component further comprises a pH modifier, the pH modifier being present in an amount ranging between 0 and 6 wt % of retarded cementitious binder of the first component.

14. The bicomponent cementitious binder composition according to claim 12, wherein the pH modifier comprises a hydroxide.

15. The bicomponent cementitious binder composition according to claim 12, the second component further comprises a binder material and/or aggregate material and/or supplementary cementitious material and/or one or more additional compound.

16. The bicomponent cementitious binder composition according to claim 12, wherein the binder material of the second component comprises a cementitious binder material and the second component comprises at least one pH modifier wherein the binder material of the second component comprises an alkali activated binder material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0165] The present invention will be discussed in more detail below, with reference to the attached drawings, in which:

[0166] FIG. 1 shows a system to extrude concrete according to the present invention;

[0167] FIG. 2 shows a schematic representation of the mixing process of the present invention;

[0168] FIG. 3 shows the stress-strain graph of example 1 compared to a conventional 3D printable concrete mixture;

[0169] FIG. 4 shows the penetration resistance of the mixtures of an example according to the present invention compared to comparative examples.

DESCRIPTION OF EMBODIMENTS

[0170] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings are only schematic and are non-limiting. The size of some of the elements in the drawing may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0171] When referring to the endpoints of a range, the endpoint values of the range are included.

[0172] When describing the invention, the terms used are construed in accordance with the following definitions, unless indicated otherwise.

[0173] The term and/or when listing two or more items, means that any one of the listed items can by employed by itself or that any combination of two or more of the listed items can be employed.

[0174] The terms first, second and the like used in the description as well as in the claims, are used to distinguish between similar elements and not necessarily describe a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances.

[0175] The term static mixer refers to devices for continuous mixing of fluid materials not using moving parts.

[0176] The term dynamic mixer refers to devices for continuous mixing of fluid materials using moving parts.

[0177] The term plasticizer and the term superplasticizer refer to a chemical additive in concrete used to (1) reduce the water/cement ratio and/or (2) prevent particle agglomeration of cement particles.

[0178] The term retarder refers to a chemical additive used to delay cement hydration and to keep a cementitious material workable. The term retarder thus refers to a chemical additive that is slowing down the setting of cementitious material and increases the initial setting time of the cementitious material.

[0179] The term accelerator refers to a chemical additive that contrary to retarders, accelerates the hydration reaction of the cementitious materials and thereby shortening the setting time of cementitious materials, in particular the initial setting time of cementitious material.

[0180] FIG. 1 shows a system to extrude concrete according to the present invention. The system comprises a six-axis industrial robot having an articulated arm A. A first flow comprising a retarded cementitious binder and water is pumped by means of a first pump B to a mixer D, for example a static or dynamic mixer. A second flow comprising a carrier material and water and having a pH higher than the pH of the first flow is pumped by means of a second pump C to the mixer D. The material of the first flow and the material of the second flow are mixed by the mixer D and the mixture is extruded from the nozzle of the deposition head of the 3D printer to form the 3D printed object F. The first pump B, the second pump C and the extruder are controlled by the controller E. The concrete is placed by robot arm A. Movements of the robot arm are controlled by controller E. Once mixed by the mixer the mixture should be sufficiently fluid to allow conveying and extrusion. On the other hand, the mixture should provide the required mechanical stability of the 3D printed object F.

[0181] Any type of mixer known in the art suitable to mix the first flow and the second flow can be considered. Both static mixers as well as dynamic mixers can be considered.

[0182] Any type of pump known in the art that is able to pump the first and/or the second flow can be considered. The pumps are preferably able to deliver high viscosity fluids with a steady flow rate. Alternatively, positive displacement pumps can be considered. In positive displacement pumps a fluid is moved by trapping a fixed amount and forcing that trapped volume into the discharge pipe. Examples of such pumps comprise progressive cavity pumps, peristaltic pumps, impulse pumps with several cavities, gear pumps, and screw pump. It is clear that other types of pumps can be considered as well.

[0183] FIG. 2 shows the mixing process of the method according to the present invention.

EXPERIMENTAL RESULTS

Example 1

[0184] In a first example a first flow (mixture A) and a second flow (mixture B) are prepared using the following starting materials: [0185] Binder material: CSA cement. The specific gravity of the CSA cement is 3.15 The chemical composition of the CSA cement is given in Table 1; [0186] Borax (di-sodium tetraborate decahydrate, Na.sub.2B.sub.4O.sub.7.Math.10H.sub.2O); [0187] Calcium hydroxide (CH) powder, analytical grade having a purity of more than 96% from Carl Roth chemicals; [0188] Limestone powder; [0189] Fine aggregates having a nominal maximum size of 2 mm, fineness modulus of 2.4 and a specific gravity of 2.65.

[0190] The compositions of the first flow (Mixture A) and of the second flow (Mixture B) are shown in Table 2. Mixture A and mixture B were prepared according to the mixing protocols shown in respectively Table 3 and Table 4.

TABLE-US-00001 TABLE 1 Chemical and mineralogical composition of CSA cement Composition Quantity (% by mass) Oxide CaO 41.50 SiO.sub.2 8.14 Al.sub.2O.sub.3 23.20 Fe.sub.2O.sub.3 1.05 (Na.sub.2O).sub.e 0.86 MgO 3.22 SO.sub.3 18.36 Loss on ignition 1.45 Phase Ye'elimite 54.64 Belite 18.97 Anhydrite 23.70 Bassanite 0.27 Periclase 2.40

TABLE-US-00002 TABLE 2 Mix proportions of Mixture A (CSA cement-based mixture) and limestone-based mixtures (Mixture B) (kg/m.sup.3) of example 1 CSA Limestone Mixture Sand cement powder Water Borax Ca(OH).sub.2 A 1076.0 896.7 0 313.8 17.9 0 B 1066.8 0 847.5 313.8 0 41.5

TABLE-US-00003 TABLE 3 Mixing procedure for Mixture A of example 1 Step Process Duration (s) 1 Add retarder to the CSA cement 2 Add the CSA cement + retarder to the aggregate 3 Dry mix at 140 rpm 30 4 Add water into the CSA cement + retarder + aggregate 5 Mix at 140 rpm 30 6 Mix at 285 rpm 60 7 Scrape the bottom of the mixer 8 Continue mixing at 285 rpm 60 rpmrotations per minute

TABLE-US-00004 TABLE 4 Mixing procedure for mixture B of example 1 Step Process Duration (s) 1 Add pH modifier to the powder material 2 Add pH modifier + powder material to the aggregate 3 Dry mix at 140 rpm 30 4 Add water into the pH modifier + powder material 5 Mix at 140 rpm 30 6 Mix at 285 rpm 60 7 Scrape the bottom of the mixer 8 Continue mixing at 285 rpm 60 rpmrotations per minute

[0191] FIG. 3 shows the stress-strain graph of concrete deposited according to the method of the present invention using mixture A and mixture B as specified in example 1 compared to concrete deposited using a conventional mixture for 3D printing. The conventional mixture for 3D printing is a one component mixture not comprising an accelerator. A conventional 3D printable mixture typically has an initial setting time in the range of 60 to 90 minutes.

[0192] From FIG. 3, it is clear that the elastic modulus (slope of the stress-strain graph) and compressive strength (maximum stress from the stress-strain graph) are significantly higher for the 3D printable mixture according to the present invention as compared to a typical conventional 3D printable concrete mixture.

Examples 2, 3 and 4

[0193] Examples 2, 3 and 4 comprising a first flow (mixture A) and a second flow (mixture B) are specified below using the following start materials: [0194] Binder material (CSA cement), borax, calcium hydroxide (CH) powder, limestone powder, fine aggregates as specified in Example 1; [0195] Portland cement; [0196] Sodium gluconate; [0197] Aluminum sulfate; [0198] Superplasticizer (SP) polycarboxylate ether (MasterGlenium 51 from BASF); [0199] Alkali activated mixture (AAM) precursor comprising for example fly ash, blast furnace slag, metakaolin, steel slag, or copper slag. Also blends or mixtures of these materials can be considered; [0200] Alkali activated mixture (AAM) activator comprise for example sodium hydroxide, sodium silicate or sodium sulfate. Also blends or mixtures of these materials can be considered.

[0201] The compositions of the first flow (Mixture A) and of the second flow (Mixture B) of example 2, 3 and 4 are given in Table 5 (Example 2), Table 6 (Example 3) and Table 7 (Example 4).

TABLE-US-00005 TABLE 5 Mix proportions of Mixture A (CSA cement-based mixture) and Mixture B (Portland cement-based mixture) (kg/m3) of example 2. CSA Portland Superplas- Mixture Sand cement cement Water Borax ticizer A 1076.0 896.7 0 313.8 17.9 0 B 1076.0 0 896.7 313.8 0 5.4

TABLE-US-00006 TABLE 6 Mix proportions of Mixture A (CSA cement-based mixture) and Mixture B (Portland cement-based mixture with calcium hydroxide) (kg/m3) of example 3 CSA Portland Mixture Sand cement cement Water Borax Ca(OH).sub.2 Superplasticizer A 1076.0 896.7 0 313.8 17.9 0 0 B 1076.0 0 842.9 313.8 0 53.8 5.4

TABLE-US-00007 TABLE 7 Mix proportions of Mixture A (CSA cement-based mixture) and Mixture B (Alkali-activated mixture) (kg/m.sup.3) of a fourth embodiment of the present invention CSA AAM AAM Mixture Sand cement precursor activator Water Borax A 1076.0 896.7 0 0 313.8 17.9 B 1076.0 0 842.9 208.6 140.3 0 AAMAlkali activated material

Examples 5, 6, 7 and 8

[0202] The setting time of concrete obtained according to the present invention was compared with comparative examples.

[0203] In examples 5 to 8 two different mixtures (mixture A1 and mixture A2) were used as first flow and two different mixture (mixture B1 and mixture B2) were used as second flow. The mixtures were combined as shown in Table 9. The compositions of the mixtures A1, A2, B1 and B2 are shown in Table 10. The pH of the mixtures B1 and B2 is given in Table 10.

[0204] In example 5 to 8 the volume ratio of the first flow (mixture A1 or A2) to the second flow (mixture B1 or 2) is 70:30.

TABLE-US-00008 TABLE 9 combinations of mixtures A and B First flow Second flow Example 5 A1 B1 (comparative pH 10 example) Example 6 A2 B1 (according to pH 10 invention) Example 7 A1 B2 (comparative pH 2.46 example) Example 8 A2 B2 (comparative pH 2.46 example)

TABLE-US-00009 TABLE 10 Mix proportions of mixture A1, A2, B1 and B2 Quantity (kg/m.sup.3) Material A1 A2 B1 B2 CSA cement 896.7 896.7 Limestone powder 857.0 857.0 Aggregate 1076.0 1076.0 1028.5 1028.5 Borax 4.48 Sodium gluconate 4.48 Calcium hydroxide 35.9 Aluminum sulfate 35.9 Water 313.8 313.8 300.0 300.0

[0205] The initial setting time and final setting time of the mixtures given in example 5 to 8 were measured using a penetration test whereby the initial and final setting times are determined as the times when the penetration resistance equals 3.5 MPa and 27.6 MPa. FIG. 4 shows the penetration resistance of the mixtures of example 5, 6, 7 and 8, whereby Mixture 1 represents example 5, Mixture 2 represents example 6, Mixture 3 represents example 7 and Mixture 4 represents example 8.

[0206] FIG. 4 clearly shows the surprising effect when A2 (first flow) and mixture B1 (second flow) (denoted as mixture 2 in FIG. 4) are combined. This combined mixture exhibits a very low initial setting time, compared to other combinations shown in FIG. 4. The initial setting time T3 of the combined mixture of mixture A2 and mixture B1 is less than 5 minutes.