OA21332A - 3D concrete printing with well anchoring cords. - Google Patents

Abstract

A concrete construction (100) made by 3D concrete printing comprises : - two or more layers (102, 106) of cementitious material extruded one above the other, and - at least one elongated steel element (104, 108) reinforcing at least one of the two or more layers. The elongated steel element (104, 108) is provided with a first crimp. Due to the crimp, a good anchorage in concrete is obtained and the anchorage force is predictable, since the standard deviation of the anchorage force is very small. The elongated steel element can be a single steel wire with a diameter D. the amplitude of the crimp ranges from 1.05xD to 5.0xD. The elongated steel element can also be a steel with steel filaments having a maximum diameter d. The amplitude of the crimp ranges from 1.05xd to 5.0xd.

Description

Title: 3D CONCRETE PRINTING WITH WELL ANCHORING CORDS

Description

Technical Field

The invention relates to a concrète construction that has been made by 3D concrète printing.

Background Art

Additive manufacturing of concrète or cementitious materials, herein referred to as ‘3D concrète printing’, has been expanding rapidly over the past years. According to the technique of 3D concrète printing, a purnp feeds a cementitious slurry via a hose to a printing nozzle that extrades the slurry layer by layer. A gantry robot guides and moves the whole, i.e. the hose and the printing nozzle.

Structures of a cementitious matrix in general, and concrète structures in particular, are known to be brittle and to hâve a poor résistance to tensile or bending stresses. Adding reinforcement to these structures has given these structures more ductility.

The brittle nature is also a problem for structures made by 3D concrète printing.

Traditional reinforcement such as a rebar can be inserted in the printed layers of concrète while the concrète is still uncured. This solution, however, has serions drawbacks. It is labour intensive, error-prone and the adhesion between the rebar and the concrète will be inadéquate. In addition, this solution is against the final goal of 3D concrète printing, namely to minimize manual work.

Reinforcement fibres may be added to the cementitious slurry. But expérience has shown that a mix of cementitious slurry and concrète is difficult to feed through the hose and printing nozzle.

Another way of solving the problem of reinforcement, is to install a reinforcement lattice or net in advance and to extrade the cementitious slurry around it. Here again, the advance installation of the reinforcement demands labour that one wishes to avoid. Moreover, the presence of the reinforcement complicates the extrusion and the working of the printing head.

The Technical University of Eindhoven in coopération with Bekaert has corne up with an élégant solution that allows depositing simultaneously both the concrète and the reinforcement. A reinforcement entraining device having a spool with a flexible Steel cord was added to the printer head. This entraining device travels together with the gantry robot, unwinds the flexible Steel cord from the spool and introduces this flexible steel cord inside the deposited concrète layer. In this way simultaneous déposition of both concrète and reinforcement was obtained.

While the used steel cords hâve a lot of advantages such as light weight, high tensile strength and flexibility, their reinforcement effect was not adéquate and predictable to qualify for reinforcement of load bearing structures.

Disclosure of Invention

It is a general object of the invention to mitigate the drawbacks of the prior art.

It is a more particular object of the invention provide for a reinforcement for 3D concrète printed constructions that is more predictable.

It is a further object of the invention to provide for a reinforcement for 3D concrète printed constructions that is more adéquate.

According to the invention, there is provided a concrète construction made by 3D concrète printing. The construction comprises two or more layers of cementitious material extruded one above the other. The construction further comprises at least one elongated steel element being positioned inside the two or more layers and reinforcing the two or more layers. The elongated steel element may be a steel wire or a steel cord. The steel cord may be a single strand steel cord and comprises twisted steel filaments or may be a multi-strand steel cord that comprises twisted steel strands where each of the strands has twisted steel filaments.

The first crimp has a first amplitude along following Unes:

- in case of a single steel wire with diameter D, the first amplitude ranges from 1.05xD to 5xD;

- in case of a single strand steel cord where the filaments hâve a maximum diameter d, the first amplitude ranges from 1.05xd to 5.0xd;

- in case of a multi-strand steel cord where the steel strands hâve a maximum diameter d’, the first amplitude ranges from 1.05xd’ to 5.0xd’.

Below 1.05 times the relevant diameter (D, d or d’), the effect of improved anchorage in concrète and decreased standard déviation is less pronounced. Above 5 times the relevant diameter (D, d or d’), handling of the elongated steel element becomes more difficult and, in case of a Steel cord, its construction becomes less stable.

The steel wire or the steel cord may be provided with a second crimp different from the first crimp. The second crimp has a second amplitude that lies in the same ranges as the first crimp.

The ternis ‘cementitious material’ refer to concrète, mortar, cernent, or similar material.

The terni ‘crimp’ refers to a plastic deformation in the form of an undulation of the steel filament or steel strand. This undulation results in latéral protrusions of the steel filament or steel strand. These protrusions along the length of the steel cord resuit in an improved anchorage of the steel cord in the concrète once cured. In addition, the degree of anchorage of the steel cord in the concrète shows less déviations from what is expected, so the anchorage behaviour is more predictable. Hence, over-design or too high security factors can be avoided.

In case of a multi-strand steel cord comprising three or more steel strands, some of these steel strands are exposed to the radially extemal side of the steel cord and are referred to as extemal layer strands. Some of these extemal layer strands and preferably ail of these extemal layer strands are provided with a first crimp.

In case of a single strand steel cord having varions steel filaments twisted with each other, some of these steel filaments are exposed to the radially extemal side of the steel cord and are referred to as extemal layer filaments. Some of these extemal layer filaments and preferably ail of these extemal layer filaments are provided with a first crimp.

As mentioned, in a highly préférable embodiment of the invention, a second crimp may be provided to the steel filaments or the steel strands.

Typical features of a crimp are its amplitude and its pitch.

Typical dimensions of the pitch range from 5 times the relevant diameter (wire diameter D, filament diameter d or strand diameter d’) to 50 times the relevant diameter of the elongated steel element. Preferably, in case of a steel cord, the pitch of the crimp is smaller than the prevailing lay length of the steel cord. The ternis ‘prevailing lay length’ of a steel cord are to be understood as the lay length of the radially extemal filaments in case of a single strand steel cord or the lay length of the radially extemal strands in case of a multi-strand Steel cord.

Preferably, the first crimp has a first amplitude that is different from the second amplitude of the second crimp.

Preferably, the first crimp has a first pitch that is different from the second pitch of the second crimp.

A way of giving a crimp to a Steel wire or a steel filament or Steel strand is driving the elongated steel element between a pair of toothed wheels. This pair of toothed wheels may lie in one plane and this plane can be called the plane of the crimp.

The first crimp may hâve a first plane and the second crimp may hâve a second crimp. Preferably, the first plane of the first crimp is different from the second plane of the second crimp.

The elongated steel element may be provided with a corrosion résistant coating. This coating may be metallic or polymeric. In case of zinc or a zinc alloy layer as metallic coating, the elongated element is preferably treated with benzimidazole.

According to an alternative aspect of the invention, there is provided a process of manufacturing a concrète construction as mentioned hereabove. The elongated steel element is fed simultaneously together with the cementitious material through a same printer head or nozzle.

Brief Description of Figures in the Drawings

FIGURE 1 illustrâtes how a continuous reinforcement is added in 3D concrète printing;

FIGURE 2, FIGURE.3 and FIGURE 4 show cross-sections of steel cords;

FIGURE 5 illustrâtes how a double crimp is given to a steel filament;

FIGURE 6 illustrâtes amplitude and pitch of a first crimp;

FIGURE 7 illustrâtes amplitude and pitch of a second crimp.

Mode(s) for Carrying Out the Invention

FIGURE 1 illustrâtes how a construction 100 with reinforcement is made by 3D concrète printing. The construction 100 has a first layer 102 that is reinforced by a steel cord 104. The construction 100 also has a second layer 106 that is reinforced by a steel cord 108, that may be the same steel cord as the steel cord 104 of the first layer. The second layer 106 is in the process of being extruded above the first layer 102. This extrusion is done by means of a printer head or nozzle 110 that is feeding the concrète 112 and the steel cord 108 simultaneously. The printer head 110 is moving in the direction of the arrow 114.

FIGURE 2 shows a cross-section of a single strand steel cord 200 that is suitable to be used in the présent invention. The steel cord 200 has five individual steel filaments 202, 204. One steel filament 202 has two crimps, each crimp lying in another plane. This is symbolically shown by the arrows 206, 208. The other filaments 204 are not provided with crimps.

FIGURE 3 shows a cross-section of another single strand steel cord 300 that is suitable to be used in the présent invention. The steel cord 300 has five filaments 302. Ail steel filaments 302 hâve two crimps, each crimp lying in another plane. This is symbolically shown by the arrows 304, 306.

An examplé of such a steel cord is 5x0.35 (steel filament diameter 0.35 mm) or 5x0.38 (steel filament diameter 0.38 mm).

FIGURE 4 shows a cross-section of a multi-strand steel cord 400. The steel cord 400 has several steel strands 402, 404. Each of the steel strands 402, 404 comprises several steel filaments 406 that are twisted with each other. At least one steel strand 404 has been provided with a crimp, here represented by arrows 408.

In general the steel filaments may hâve a filament diameter d ranging from 0.03 mm to 0.65 mm, e.g. from 0.10 mm to 0.40 mm.

In case of a single steel wire, the wire diameter D ranges from 0.20 mm to 2.0 mm, e.g. from 0.35 mm to 1.50 mm.

In case of a steel strand in a multi-strand steel cord, the diameter d’of the steel strand may range from 0.25 mm to 0.75 mm, e.g. from 0.30 mm to 0.75 mm.

FIGURE 5 schemâtically illustrâtes how a first crimp and a second crimp are provided to a steel filament 500.

The steel filament 500 is moved downstream towards a first pair of toothed wheels 502. The axes of rotation of toothed wheels 502 lie parallel to the y-axis, and the first crimp given is a planar crimp lying in plane xz.

The thus crimped filament 500 is further moved to a second pair of toothed wheels 506. The axes of rotation of toothed wheels 506 lie parallel with the x-axis. The second crimp given by toothed wheels 506 is also a planar crimp and lies in plane yz.

Obviously the resulting wave given to the Steel filament 10 is no longer planar but spatial.

Neither the first pair of toothed wheels 502 nor the second pair of toothed wheels 506 need to be driven by extemal means. They are both driven and rotated by the passing steel filament 500.

It is important that the second pair of toothed wheels 506 is positioned as close as possible to the first pair of toothed wheels 502 in order to prevent the first crimp from tilting or rotating from plane xz to plane yz under influence of the second crimp.

From a more general point of view and in order to control the two crimps given to the filaments, the bending moment, i.e. the moment necessary to give the two crimps, must be kept as small as possible. This can be done, e.g. by appying first the crimp with the smaller amplitude and only thereafter the crimp with the greater amplitude.

Still from a more general point of view, the torsion moment, i.e. the moment necessary to rotate the filament, should be kept as high as possible, since the rotating of the filament must be prevented during or between the two crimping operations. One way to keep the torsion moment as high as possible is the above-mentioned minimum distance between the two pairs of crimping wheels.

A third and following pairs of toothed wheels may be provided in other planes or in the same planes. In this way the spatial structure obtained by the subséquent crimping operations may be optimised or varied to a further degree.

FIGURE 6 shows the first crimp lying in plane xz and FIGURE 7 shows the second crimp lying in plane yz.

The first crimp has a first crimp amplitude Al, which is measured from top to top, with inclusion of filament diameter d. The first crimp has a first crimp pitch Pci, which is equal to the distance between two minima of the first crimp.

The second crimp has a second crimp amplitude A2, which is measured from top to top, with inclusion of filament diameter d. The second crimp has a second crimp pitch Pc2, which is equal to the distance between two minima of the second crimp.

The spots 506 where the second crimp reaches its maxima are hatched in parallel with the axis of the steel filament 500, and the spots 508 where the second crimp reaches its minima are hatched vertically in FIGURE 6.

The spots 510 where the first crimp reaches its maxima are hatched in parallel with the axis of the Steel filament 500, and the spots 512 where the first crimp reaches its minima are hatched vertically in FIGURE 7.

Both the first crimp amplitude Al and the second crimp amplitude A2 may be varied independently of each other. So Al may be equal to A2 or may be different from A2. Both amplitudes may vary between a minimum value which is slightly above value of the filament diameter (e.g. 1,05xd, which means almost no crimp), and a maximum value of about four to five times the filament diameter (4~5xd). This maximum value is dictated for reason of constructional stability.

Both the first crimp pitch Pci and the second crimp pitch Pc2 may be varied ' independently of each other. So Pci may be equal to Pc2 or may be different from Pc2. The more Pci differs from Pc2, the more easy it is to prevent the first crimp from tilting. Both pitches may vary between a minimum value which is about five times the filament diameter d (5xd), and a maximum value of about fifty times the filament diameter d (50xd). It is, however, to be preferred, that in twisted structures at least one, and most preferably both, of the crimp pitches is smaller than the twist pitch of the steel filament in the twisted structure.

Having regard to the above parameters which may be chosen quite freely, i.e. independent of each other, a large variety of wave forms can be obtained.

A first example is that by choosing Al equal to A2 and Pci equal to Pc2 and by shifting the second crimp with a quarter of a pitch in respect of the first crimp, a spatial hélix form can be obtained or at least be approximated without the need for driven rotatory preforming pins.

A second example is that by choosing Al substantially greatér than A2 an oval or elliptical transversal cross-section is obtained.

Steel Composition

The steel filaments may hâve a steel composition along following lines: A plain carbon composition is along following lines (ail percentages being percentages by weight):

a carbon content (% C) ranging from 0.60% to 1.20%, e.g. 0.80% to 1.1%;

a manganèse content (% Mn) ranging from 0.10% to 1.0%, e.g. from 0.20% to 0.80%;

J a Silicon content (% Si) ranging from 0.10% to 1.50%, e.g. from 0.15% to 0.70%;

a sulphur content (% S) below 0.03%, e.g. below 0.01%; aphosporus content (% P) below 0.03%, e.g. below 0.01%.

Altematively, Following éléments may be added to the composition: chromium (%Cr): in amounts ranging from 0.10% to 1.0%, e.g. from 0.10 to 0.50%; nickel (%Ni): in amounts ranging from 0.05% to 2.0%, e.g. from 0.10% to 0.60%; cobalt (%Co): in amounts ranging from 0.05% to 3.0%; e.g. from 0.10% to 0.60%; vanadium (%V): in amounts ranging from 0.05% to 1.0%, e.g. from 0.05% to 0.30%; molybdenum (%Mo): in amounts ranging from 0.05% to 0.60%, e.g. from 0.10% to 0.30%; copper (%Cu): in amounts ranging from 0.10% to 0.40%, e.g. from 0.15% to 0.30%; boron (%B): in amounts ranging from 0.001% to 0.010%, e.g. from 0.002% to 0.006%; niobium (%Nb): in amounts ranging from 0.001% to 0.50%, e.g. from 0.02% to 0.05%; titanium (%Ti): in amounts ranging from 0.001% to 0.50%, e.g. from 0.001% to 0.010%; antimony (%Sb): in amounts ranging from 0.0005% to 0.08%, e.g. from 0.0005% to 0.05%; calcium (%Ca): in amounts ranging from 0.001% to 0.05%, e.g. from 0.0001% to 0.01%; tungsten (%W): e.g. in an amount of about 0.20%; zirconium (%Zr): e.g. in an amount ranging from 0.01% to 0.10%;

aluminium (%A1): preferably in amounts lower than 0.035%, e.g. lower than 0.015%, e.g. lower than 0.005%;

nitrogen (%N): in amounts less than 0.005%;

rare earth metals (%REM): in amounts ranging from 0.010% to 0.050%.

Metallic coating

The Steel filaments of the Steel cord are preferably provided with a metallic coating in order to increase the corrosion résistance.

The metallic coating is preferably a zinc coating or a zinc alloy coating.

A zinc alloy coating may be a zinc aluminium coating that has an aluminium content ranging from 2 per cent by weight to 12 per cent by weight, e.g. ranging from 3 % to 11%. A préférable composition lies around the eutectoid position: Al about. 5 per cent. The zinc alloy coating may further hâve a wetting agent such as lanthanum or cérium in an amount less than 0.1 per cent of the zinc alloy. The remainder of the coating is zinc and unavoidable impurities. Another préférable composition contains about 10% aluminium. This increased amount of aluminium provides a better corrosion protection than the eutectoid composition with about 5% of aluminium.

' _____' I

Other éléments such as Silicon (Si) and magnésium (Mg) may be added to the zinc aluminium coating. With a view to optimizing the corrosion résistance, a particular good alloy comprises 2 % to 10 % aluminium and 0.2 % to 3.0 % magnésium, the remainder being zinc.

An example is 5% Al, 0.5 % Mg and the rest being Zn.

A zinc or zinc alloy coating is preferably applied to the steel wire by means of a hot dip operation. The average thickness of the métal coating is preferably limited to 4 micrometer, e.g. to 3 micrometer.

With a view of inhibiting hydrogen gas évolution during the hardening of concrète reinforced with zinc coated métal éléments, the steel cords may be treated with benzimidazole, e.g. by spraying or by dipping.

The metallic coating may also be a copper alloy such as brass. In comparison with zinc alloy coatings, brass coatings facilitate the diameter réduction by drawing. In an alkaline environment as concrète, brass may be sufficient to provide the required corrosion protection.

Table: Standard Déviation of Pull-out Tests

Cord construction	Standard déviation on 6
	samples
5x0.35 with crimped filaments - invention	6%
3+5x7x0.12 -reference	51%
3x3x0,15 - reference	32%
19+9x7xl ,2 - reference	47%
3x3x0,2 - reference	21%
3+2x0,225 - reference	26%
7+4x0,12 - reference	66%
3x0,3 -reference	94%

Reference Numbers

100 construction made by 3D concrète printing

102 firstlayer

104 steel cord

106 second layer

108 Steel cord

110 printer head or nozzle

112 concrète

114 direction of movement

200 Steel cord

202 Steel filament

204 Steel filament

206 first crimp

208 second crimp

300 steel cord

302 steel filament

304 first crimp

306 second crimp

400 steel cord

402 steel strand

404 steel strand

406 steel filament

408 first crimp

500 steel filament

502 first pair of toothed wheels

504 second pair of toothed wheels

506 position of maximum of second crimp

508 position of minimum of second crimp

510 position of maximum of first crimp

512 position of minimum of first crimp

Claims (10)

1. A concrète construction made by 3D concrète printing said construction comprising:

- two or more layers of cementitious material extruded one above the other, and

- at least one elongated Steel element positioned inside said two or more layers along the length of said two or more layers and reinforcing said two or more layers, said elongated Steel element being:

- either a single Steel wire having a wire diameter D, D ranging from 0.20 mm to 2.0 mm, said single Steel wire being provided with a first crimp, said crimp having a first amplitude ranging from 1.05xD to 5.00xD,

- or a Steel cord comprising Steel filaments, said steel filaments having a maximum filament diameter d, d ranging from 0.03 mm to 0.65 mm, at least one of said filaments being provided with a first crimp, said first crimp having a first amplitude ranging from 1.05xd to 5.00xd.

2. The construction according to claim 1, said steel wire or at least of said filaments of said steel cord being provided with a second crimp different from said first crimp, said second crimp:

- either having a second amplitude ranging from 1,05xD to 5.00xD in case of a single steel wire as reinforcement element,

- or having a second amplitude ranging from 1.05xd to 5.00xd in case of a steel cord as reinforcement element.

3. The construction according to claim 2, wherein said first amplitude differs from said second amplitude.

4. The construction according to claim 2 or claim 3, wherein said first crimp has a first pitçh, wherein said second crimp has a second pitch, said first pitch differing from said second pitch.

5. The construction according to any one of claims 2 to 4, wherein the first crimp lies in a first plane, n

. . ...___:_____________________________________________________________J wherein the second crimp lies in a second plane, the first plane being different from the second plane.

6. The construction according to any one of the preceding daims, said elongated Steel element being a steel cord, ail of the steel filaments of said steel cord being provided with a first crimp.

7. The construction according to daim 6, said elongated steel element being a steel cord, ail of the steel filaments of said steel cord being provided with a second crimp.

8. The construction according to any one of the preceding daims, wherein said elongated steel element is provided with a zinc or zinc alloy coating and where said elongated steel éléments has been treated with benzimidazole.

9. A concrète construction made by 3D concrète printing said construction comprising:

- two or more layers of cementitious material extruded one above the other, and

- at least one elongated steel element positioned inside said two or more layers along the length of said two or more layers and reinforcing said two or more layers, said elongated steel element being a steel cord comprising steel strands, said steel strands comprising steel filaments, said steel strands having a maximum filament diameter d’, d’ ranging from 0.25 mm to 0.75 mm, at least ône of said filaments being provided with a first crimp, said first crimp having a first amplitude ranging from 1.05xd’ to 5.00xd’.

10. A process of manufacturing a concrète construction according to any one of the preceding daims by way of 3D printing, wherein said elongated steel element is fed simultaneously together with the cementitious material through a same printer head or nozzle.