OA21333A - 3D concrete printing with ductile 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) reinforcing at least one of the layers (102, 106). The elongated steel element (104) has an elastic and plastic elongation at break that exceeds 4 %. The high elongation of the elongated steel element gives an increased ductility to the concrete structure (100).

Description

Title: 3D CONCRETE PRINTING WITH DUCTILE 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 pump 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 rébar 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 mây 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 i

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 lot of advantages such as lightweight, high tensile strength and flexibility, their reinforcement effect was not adéquate to provide the required ductility and impact résistance. Hence, 3D printed concrète structures hâve not been frequently used for load bearing situations.

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 hâve improved ductility.

It is a fiirther object of the invention to provide for 3D concrète printed constructions that are more résistant to impact.

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 reinforcing at least one of the two or.more layers, and preferably ail of these layers. The elongated Steel element has a carbon content ranging from 0.60 % to 1.20 %. The elongated Steel element has been patented followed by cold working, e.g. by rolling or drawing, until a tensile strength exceeding 2500 MPa, e.g. exceeding 2750 MPa.

The elongated Steel element can be a Steel wire or a steel cord.

In case of a steel cord, the steel côrd has steel filaments or steel strands having steel filaments. 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 cord, 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 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.

The elongated Steel element has an elastic and plastic élongation at break that exceeds 4%, preferably exceeds 4.5%, e.g. 5% or 6% or more. As will be explained hereinafter, the so-called structural élongation of the elongated Steel element is not included in this value of élongation.

The tenus ‘cementitious material’ refer to concrète, mortar, cernent, ...

Common Steel cords comprising high-carbon patented and drawn Steel filaments hâve an elastic and plastic élongation at break of maximum 2%. Steel cords used in the présent invention hâve an elastic and plastic élongation at break of more than double this value.

Steel cords hâve an undulated radially extemal surface due to their twisted nature. The protruding parts form possible anchorage points in the cementitious matrix when the structure is subjected to tensile loads or bending loads. The Steel cord part between the two anchorage points bridges an originated crack. The more this steel cord part can elongate the more ductile the concrète structure. So the steel cords used in the présent invention elongate much more and provide much more ductility to the 3D printed structure. The thus reinforced structure shall hâve more impact résistance and may hâve better chances to function as load bearing structure.

The elongated steel element used in the présent invention is preferably in a stress-relieved State.

In general, ail types of steel wires or steel cord that are flexible enough to travel with and through the printer head are appropriate. The steel cord may be a single strand steel cord or a multi-strand steel cord.

The elongated steel éléments may be provided with a corrosion résistant coating. The corrosion résistant coating may be a metallic coating such as zinc, a zinc alloy or brass. The corrosion résistant coating may be also a polymeric coating.

In case of a zinc or zinc alloy coating or in the absence of any coating, it is préférable to coat the elongated steel éléments with benzimidazole, e.g. by spraying or dipping.

According to a particular aspect of the présent invention, there is also provided a process of manufacturing a concrète construction by way of 3D printing as described above. The 3 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 schematically shows the way of making a construction made by 3D concrète printing.

FIGURE 2 shows load élongation curves of two types of steel cord.

Mode(s) for Carrying Ont 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 slurry 112 and the steel cord 108. The printer head 110 is moving in the direction of the arrow 114.

As the printer head 110 feeds both the concrète slurry 112 and the steel cord 108, the steel cord is following the same path as the concrète layer 106. As the path may be curved and may comprise bends, the steel cord 108 must be flexible enough. This means that the steel filaments hâve a filament diameter d ranging ffôm 0.03 mm to 0.65 mm, e.g. from 0.10 mm to 0.40 mm. In case of 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 2 shows a load-elongation curve 20 of a common available steel cord and a load-elongation curve 22 of a steel cord to be used in the présent invention. The abscissa is the élongation A in percentage and the ordinate is the tensile strength R expressed in MPa. This load-elongation curve is obtained in a tensile test carried out according to norms ISO 6892 and DIN 51210.

The élongation curves 20 and 22 may or may not hâve a first relatively large élongation at small loads. This élongation is called the structural élongation A_s and is a conséquence of the twisted nature of the steel cords. By exercising a small load, the steel filaments or strands inside the

Steel cord shift somewhat and contact one another more firmly until the Steel cord starts to behave as a whole. This structural élongation A_s may be small or large, or even be absent, dépendent upon the type of Steel cord construction.

The following phase of élongation is the elastic élongation according to Hooke’s law. The Steel cord behaves as a whole and elongates linearly according to the applied load over an elastic élongation A_e.

The final phase of élongation is the plastic élongation. After the elastic élongation A_e, the steel filaments start to flow plastically until final fracture of the Steel cord.

The degree of plastic élongation A_p is the basic différence between common steel cords and Steel cords to be used for the présent invention. For steel cords to be used for the présent invention, this degree of plastic élongation is much larger. The sum of A_e and A_p is more than 4%, i.e. more than 4.5%, e.g. more than 5%, more than 6%.

Steel cords to be used in the présent invention can be made as follows.

Starting Steel Composition

Starting material is a steel rod with Steel composition along following Unes:

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%;

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%;

aphosphorus 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%.

After some preceding wire drawing operations and receiving a final patenting treatment, the steel cords may preferably be provided with a metallic coating in order to increase the corrosion résistance.

Type of Metallic Coating

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 then the eutectoid composition with about 5% of aluminium.

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.

The thus coated steel wires are then subjected to a final diameter réduction e.g. by wet wire drawing until the final filament diameter is obtained. The final diameter ranges between 0.10 mm and 0.80 mm, e.g. between 0.15 mm and 0.60 mm, e.g. between 0.20 mm and 0.40 mm.

Thereafter the steel filaments are twisted into a steel cord.

The thus twisted cord is subjected to a stress-relieving treatment, e.g. by passing the cord through a high-frequency or mid-frequency induction coil of a length that is adapted to the speed of the cord; indeed it is observed that a thermal treatment at a specified température of about 300 °C and for a certain period of time brings about a réduction of tensile strength of about 10% without any increase in plastic élongation at break; by slightly increasing the température, however, to more than 400 °C, a fùrther decrease of the tensile strength is observed and at the same time an increase in the plastic élongation at break; in this way the plastic élongation can be increased to more than 6%, while the tensile strength decreases with about 10% to 15%.

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.

Reference Numbers

100 construction made by 3D concrète printing

102 first layer

104 steel cord

106 second layer

108 steel cord

110 printer head or ilozzle

112 concrète slurry

114 direction of movement

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 reinforcing at least one of said two or more layers, said elongated steel element having a carbon content ranging from 0.60% to 1.20%, said elongated steel element being cold worked to hâve a tensile strength exceeding 2500 MP a, CHARACTERIZED IN THAT said elongated steel element has an elastic and plastic élongation at break that exceeds 4 %.

2. The construction according to claim 1, wherein said elongated steel element is in a stress-relieved State.

3. The construction according to claim 1 or claim 2, wherein said elongated steel element is a steel wire.

4. The construction according to claim 1 or claim 2, wherein said elongated steel element is a steel cord.

5. The construction according to claim 4, wherein said steel cord comprises two or more steel strands.

6. The construction according to claim 4, wherein said steel cord is a single strand cord. .

7. The construction according to any one of the preceding claims, wherein said elongated element is provided with a corrosion résistant coating.

8. The construction according to claim 7, wherein said corrosion résistant coating is a zinc alloy coating.

9. The construction according to any one of the preceding claims, wherein said elongated element is provided with benzimidazole.

10. A process of manufacturing a concrète construction according to any one of the preceding

5 claims 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.