METHOD FOR LAYER-BY-LAYER DEPOSITION OF CONCRETE

Abstract

The invention relates to a method for layer-by-layer deposition of concrete by providing extrudable concrete. A first flow comprising a binder material and water and a second flow comprising a carrier material, an additional component and water are mixed in a static mixer to form a third flow of extrudable concrete. The material of the second flow has a shorter initial setting time than the material of the first flow. The first flow has a first viscosity V1 and the second flow has a second viscosity V2 so that the ratio V1/V2 ranges between 1/40 and 40. The third flow has a viscosity larger than the viscosity of the first flow and the second flow and a yield stress larger than the yield stress of the first flow and the second flow. The material of the third flow has an initial setting time shorter than initial setting time of the first flow.

The invention further relates to a system to extrude concrete, in particular for layer-by-layer deposition of concrete.

Claims

1. A method for layer-by-layer deposition of concrete, said method comprising providing extrudable concrete by supplying a first flow and a second flow to a static mixer, said first flow comprising a first material and water, said first material comprising a binder material and having a first initial setting time T1, said first flow having a first viscosity V1 ranging between 0.1 Pa.Math.s and 60 Pa.Math.s and a first yield stress Y1, said second flow comprising a second material and water, said second material comprising a carrier material comprising powdery material and at least one additional compound, said additional compound being a compound, when added to said first material to form a mixture of said first material and said additional compound, being able to reduce the initial setting time of said mixture compared to said first initial setting time T1, said second material having a second initial setting time T2, said second flow having a second viscosity V2 ranging between 0.1 Pa.Math.s and 60 Pa.Math.s and a second yield stress Y2, whereby said first viscosity V1 and said second viscosity V2 define a ratio V1/V2 ranging between 1/40 and 40 and whereby said second initial setting time T2 is equal to or larger than said first initial setting time T1; mixing said first flow and said second flow in said static mixer to obtain a third flow comprising said extrudable concrete, said third flow comprising a mixture of said first material and said second material and optionally comprising water, said mixture of said first material and said second material having a third initial setting time T3, said third flow having a third viscosity V3 and a third yield stress Y3, whereby said third viscosity V3 is larger than said first viscosity V1 and larger than said second viscosity V2, whereby said third yield stress Y3 is larger than said first yield stress Y1 and larger than said second yield stress Y2 and whereby said third initial setting time T3 is shorter than said first initial setting time T1; dispensing said third flow from said static mixer.

2. The method according to claim 1, wherein said first and said second flow are supplied to said static mixer by pumping.

3. The method according to claim 1, wherein said carrier material comprises powdery material having an average particle size lower than 100 μm.

4. The method according to claim 1, wherein said third initial setting time T3 is shorter than half of said first initial setting time T1.

5. The method according to claim 1, wherein said third viscosity V3 is at least 2 times said first viscosity V1 or at least 2 times said second viscosity V2 and/or wherein said third yield stress Y3 is at least 200 times said first yield stress Y1 or at least 200 times said second yield stress Y2.

6. The method according to claim 1, wherein said ratio V1/V2 ranges between 1/20 and 20.

7. The method according to claim 1, wherein said first flow is supplied to said static mixer with a flow rate F1 and said second flow is supplied to said static mixer with a flow rate F2, with said ratio F1/F2 ranging between 1/10 and 10.

8. The method according to claim 1, wherein said first flow is supplied to the static mixer by pumping said material of said first flow by a first pump and said second flow is supplied to the static mixer by pumping said material of said second flow by a second pump.

9. The method according to claim 1, wherein said binder material comprises a cementitious binder material and/or an alkali activated binder material.

10. The method according to claim 1, wherein said second flow is free (or substantially free) of said binder material.

11. The method according to claim 1, wherein said carrier material is selected from the group consisting of limestone filler and mineral powders such as sand or quartz powder.

12. The method according to claim 1, wherein said additional compound comprises a setting and/or hardening accelerator, said setting and/or hardening accelerator comprising an inorganic salt, preferably an inorganic salt of alkali and earth alkali metals, an organic salt or a compound selected from the group consisting of amines and/or organic acids and their salts.

13. The method according to claim 1, wherein said additional compound comprises an alkali activator comprising a metal hydroxide, preferably an alkali hydroxide selected, a non-silicate weak acid salt, a silicate, an aluminate, an aluminosilicate or a non-silicate strong acid salt.

14. A system for layer-by-layer deposition of concrete, said system comprising a static mixer having at least a first inlet for introducing a first flow in said static mixer, at least a second inlet for introducing a second flow in said static mixer and at least one outlet for providing a third flow, whereby said first flow comprises a first material, said first material comprising binder material and water, said first flow having a first viscosity V1 ranging between 0.1 Pa.Math.s and 60 Pa.Math.s and a first yield stress Y1, said first material having a first initial setting time T1, said second flow comprising a second material and water, said second material comprising a carrier material comprising powdery material and at least one additional compound, said additional compound being a compound when added to said first flow of material being able to reduce the first initial setting time T1 of said first flow of material, said second flow having a second viscosity V2 ranging between 0.1 Pa.Math.s and 60 Pa.Math.s and a second yield stress Y2, said second material having an initial setting time T2, whereby said first viscosity V1 and said second viscosity V2 define a ratio V1/V2 ranging between 1/40 and 40 and whereby said second initial setting time T2 is equal to or larger than said first initial setting time T1; said material of said first flow and said material of said second flow being mixed in said static mixer to obtain said third flow comprising said extrudable concrete, said third flow comprising a mixture of said first material, said second material and a water, said mixture of said first material and said second material having a third initial setting time T3. said third flow having a third viscosity V3 and a third yield stress Y3, whereby said third viscosity V3 is larger than said first viscosity V1 and larger than said second viscosity V2, whereby said third yield stress Y3 is larger than said first yield stress Y1 and larger than said second yield stress Y2 and whereby said third initial setting time T3 is shorter than said first initial setting time T1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The present invention will be discussed in more detail below, with reference to the attached drawings, in which:

[0076] FIG. 1 shows a system to extrude concrete according to the present invention;

[0077] FIG. 2 shows some schematic illustrations of static mixers;

[0078] FIG. 3 shows the initial setting time T1 of the first material of the first flow, the initial setting time T2 of the second material of the second flow and the initial setting time T3 of the material of the extrudable concrete.

DESCRIPTION OF EMBODIMENTS

[0079] 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.

[0080] When referring to the endpoints of a range, the endpoint values of the range are included.

[0081] When describing the invention, the terms used are construed in accordance with the following definitions, unless indicated otherwise.

[0082] 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.

[0083] 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.

[0084] The term ‘static mixer’ refers to devices for continuous mixing of fluid materials not using moving parts.

[0085] 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.

[0086] The term ‘retarder’ refers to a chemical additive used to postpone cement hydration and to keep a cementitious material workable.

[0087] The term ‘accelerator’ refers to a chemical additive that contrary to retarders, accelerates the setting time of cementitious materials, in particular the initial setting time of cementitious material.

[0088] FIG. 1 shows a system 100 to extrude concrete according to the present invention. The system 100 comprises a robot having a robotic arm A. A first flow comprising a binder material and water is pumped by means of a first pump B to a static mixer D. A second flow comprising a carrier material and at least one additional compound is pumped by means of a second pump C to the static mixer D. The material of the first flow and the material of the second flow are mixed by the static 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 static 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.

[0089] The first flow comprises for example sand (850 kg/m.sup.3), ordinary Portland cement (850 kg/m.sup.3), tap water (297.5 kg/m.sup.3), and superplasticizer (2.55 kg/m.sup.3). The second flow comprises for example sand (763.7 kg/m.sup.3), limestone powder (742.8 kg/m.sup.3), tap water (267.8 kg/m.sup.3), superplasticizer (3.9 kg/m.sup.3), viscosity modifying admixture (0.9 kg/m.sup.3) and accelerator (120.9 kg/m.sup.3).

[0090] Any type of static mixer known in the art can be considered. Examples comprise plate type static mixers. Alternatively, housed-elements designs mixers comprising a series of baffles can be considered such as static mixers comprising helical mixing elements (right or left hand or alternating right and left hand mixing elements). FIG. 2 shows some schematic illustration of static mixers. FIG. 2(a) shows a Kenics® static mixer with a right twist-left twist and an angle of blade twists of 180°. FIG. 2(b) shows a Ross LPD (Low Pressure Drop) static mixer having semi-elliptical plates with right rotation—left rotation and a crossing angle of 90°. FIG. 2(c) shows a standard Sulzer® SMX static mixer with (n, N.sub.p, N.sub.x)=(number of crosses over the height, number of parallel bars over the length, number of crossing bars over the width)=(2, 3, 8).

[0091] FIG. 2(d) and FIG. 2(e) show two examples of SMX static mixers with (n, N.sub.p, N.sub.x)=(n, 2n−1, 3n). FIG. 2(d) shows a rectangular version with n=1 and FIG. 2e) shows a compact version with n=3. It is clear that other types of static mixers can be considered as well.

[0092] 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.

EXPERIMENTAL RESULTS

Starting Material

[0093] The following starting materials are used: [0094] Binder material: ordinary Portland cement (OPC), [0095] Carrier material: Limestone powder (LP) having a particle size ranging between 0.4 to 40 μm and an average particle size around 3 μm, [0096] Superplasticizer (SP): polycarboxylate ether (MasterGlenium 51 from BASF), [0097] Viscosity modifying admixture (VMA): hydroxypropyl methyl cellulose (MOT 60,000 YP4 from Shin-Etsu) (VMA), [0098] Accelerator (ACC): aluminate salts (49-AF from Sika).

[0099] The chemical composition of OPC and LP are given in Table 1.

TABLE-US-00001 TABLE 1 Wt(%) CaO SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 MgO Na.sub.2O K.sub.2O SO.sub.3 Cl.sup.− LOI OPC 64.3 18.3 5.2 4.0 1.4 0.32 0.43 3.5 0.06 2.7 LP 48.85 8.15 1.28 0.88 1.41 1.25 0.28 0.05 — 37.29 With LOI: Loss on ignition

[0100] The compositions of the first flow and the second flow as shown in Table 2 were prepared according to mixing protocols shown in Table 3 (First flow) and Table 4 (Second flow).

[0101] The first initial setting time T1 of the first material of the first flow and the second initial setting time T2 of the second material of the second flow are shown in FIG. 3. The flow diameters of the first flow, the second flow and the third flow, which are measured by a flow table test, are 289 mm, 300 mm and 136 mm, respectively. It is clear that the first flow and the second flow show a high fluidity while the third flow shows a low fluidity.

[0102] A tubular shaped 3D object having an outer diameter of 40 cm and a wall thickness of 5 cm was 3D printed. A height of the 3D object of 1.7 m was obtained in 5 minutes during a first test. In another test a height of the tubular shaped 3D object of 3 m was obtained in 9 minutes.

TABLE-US-00002 TABLE 2 Compositions (in kg/m.sup.3) Sand OPC LP Water SP VMA ACC First flow 850 850 0 297.5 2.55 0 0 Second flow 863.7 0 742.8 267.8 3.9 0.9 120.9 Note: the volume ratio between the first flow and the second flow is 2.

TABLE-US-00003 TABLE 3 Step Action Duration 1 Add SP into water — 2 Add water into binder (OPC) — 3 Mix with 140 rpm 30 s 4 Add sand and mix with 140 rpm 30 s 5 Mix with 285 rpm 30 s 6 Scrape 30 s 7 Keep rest 60 s 8 Mix with 285 rpm 60 s With rpm being revolutions per minute

TABLE-US-00004 TABLE 4 Step Action Duration 1 Add SP into water — 2 Add water into powders (LP, VMA, and ACC) — 3 Mix with 140 rpm 30 s 4 Add sand and mix with 140 rpm 30 s 5 Mix with 285 rpm 30 s 6 Scrape 30 s 7 Keep rest 60 s 8 Mix with 285 rpm 60 s

[0103] Further examples of composition of the first and second flow are given in Table 5, Table 6 and Table 7.

TABLE-US-00005 TABLE 5 Compositions (in kg/m.sup.3) Sand OPC LP Water SP VMA ACC First flow 712.9 1069.4 0 396.7 5.7 0 0 Second flow 1425.9 0 712.9 204.8 5.7 2.9 149.7

TABLE-US-00006 TABLE 6 Calcium Compositions sulfoaluminate quartz (in kg/m.sup.3) Sand cement powder Water SP VMA Retarder ACC First flow 998.1 1069.4 0 300.9 5.7 0 20 0 Second flow 855.5 0 712.9 417.6 5.7 2.9 0 149.7

TABLE-US-00007 TABLE 7 Bast Sodium Compositions Fly furnace Quartz hydroxide (in kg/m.sup.3) Sand ash slag powder Water SP solution First flow 1140.7 500.4 559.3 0 237.1 5.7 0 Second flow 570.4 0 0 712.9 0 0 673.7