WO2017171668A1

WO2017171668A1 - Macro synthetic concrete reinforcement material and production method thereof

Info

Publication number: WO2017171668A1
Application number: PCT/TR2016/050087
Authority: WO
Inventors: Erhan KOP; Emine GÜVEN; Nurcin Javaherian; Gökce DEMIRCIOGLU
Original assignee: Kordsa Teknik Tekstil Anonim Sirketi
Priority date: 2016-03-29
Filing date: 2016-03-29
Publication date: 2017-10-05

Abstract

The present invention proposes a macro synthetic fiber based based reinforcement material for concrete, which is a cord (10) in form of twisted yarn(s) comprising a twisted fiber (1) comprising polyamide 6 or polyamide 6,6. The present invention further proposes a method for obtention of such reinforcement material.

Description

MACRO SYNTHETIC CONCRETE REINFORCEMENT MATERIAL AND

PRODUCTION METHOD THEREOF Technical Field of the Invention

The present invention relates to a macro synthetic concrete reinforcement material and production method thereof. Background of the Invention

Concrete is generally known as a brittle material with low tensile strength values, several reinforcement materials in fibrous form are employed and to overcome this issue, along with enhancing its strength after an initial crack and improving its ductility. To overcome this, and provide fracture toughness and ductility, fiber-based reinforcement materials are introduced to cement mixtures.

Polymeric macro synthetic reinforcement materials are known to be used to increase load bearing capacity of concrete matrices for e.g. at ground or floor applications, prefabricated structures such as concrete pipes, tunnels and retaining walls, further including blast resistant and impact resistant panel structures. Such reinforcement materials are named structural reinforcement materials targeting provision of load bearing ability to concrete upon first crack (i.e. secondary reinforcement). When concrete cracks, fibers start fuctioning, arrest crack formation and propagation. By this way, fibers increase strength and ductility.

Polyolephinic fibers including polypropylene, polyethylene, polypropylene/ propylene copolymer, and polyvinyl alcohol are known to be used in macro synthetic concrete reinforcement materials. Carbon and basalt based fibers are also used in some applications. Macro synthetic fiber based reinforcement materials in market of in ground applications are usually in form of monofilaments or fibrillated fibers twisted from strips. Polyester fibers are known to have low alkaline resistance. Polypropylene and polyethylene fiber based reinforcement materials as described in WO 2012 / 174414 A2 are widely used in cement preparation. Yet, these materials float in cement mixtures and thus may not get homogeneously distributed in concrete matrix. Additionally, chemical and mechanical adhesion abilities, stiffness and tensile strength of these materials are generally unfavorable.

EP 0 179 551, US 2001/051 266 Al, US 2002/0 182 406 Al and US 2002/0 182 406 Al describe efforts for improving dispersion ability and compatibility of fiber-based reinforcement materials in matrices.

Main problems in fiber-based macro synthetic reinforcement materials for cement mixtures include lack of stiffness, balling in cement mixture due to poor dispersion, inadequate compatibility with concrete matrix such as lack of physical and chemical adhesion resulting in low pullout strength, low tensile strength in reinforcement material, causing low load-carrying ability upon crack formation in concrete; stripping out from the concrete matrix in case of crack formation.

Objects of the Invention Primary object of the present invention is to eliminate the above-mentioned shortcomings in the prior art.

A further object of the present invention is to provide a macro synthetic fiber based reinforcement material for concrete, which has favorable mixing behavior when introduced into cement, and favorable reinforcing behavior in concrete matrix.

A further object of the present invention is to provide a method for obtention of such reinforcement material. Brief Description of the Invention

The present invention proposes a macro synthetic fiber based reinforcement material for concrete, which is a cord in form of twisted yarn(s) comprising a twisted fiber comprising polyamide 6 or polyamide 6,6. The present invention further proposes a method for obtention of such reinforcement material.

Brief Explanation of the Figures

The figures brief explanation of which are herewith provided is solely intended for providing a better understanding of the present invention and are as such not intended to define the scope of protection or the context in which said scope is to be interpreted in the absence of the description.

Figure 1 represents an exemplary twisted yarn embodiment according to the present invention.

Figure 2 shows 4-point flexural strength test result of concrete reinforced with Polyamid 6,6 macro synthetic fiber according to the present invention, compared with concrete reinforced with polypropylene fiber.

Figure 3 schematically depict fiber twisting at formation of two embodiments, namely (a) one-ply cord and (b) two-ply cord according to the present invention, respectively.

Figure 4 depicts an assembly comprising film-wrapped bundles of macro synthetic fiber reinforcement material according to the present invention. Detailed Description of the Invention

The present invention proposes a macro synthetic fiber based concrete reinforcement material, and a method for obtention thereof. The reinforcement material is a cord (10) preferably in form of twisted yarn(s), said twisted yarn(s) comprise one fiber comprising polyamide 6 or polyamide 6,6. Preferably, the reinforcement material according to the present invention comprises two fibers (1), wherein both of said fibers comprise polyamide 6 or polyamide 6,6, more preferably both of the fibers comprise polyamide 6,6. In a preferred embodiment according to the present invention, the fiber based reinforcement material comprises high-strength polyamide 6,6, i.e. polyamide 6,6 based fiber(s) with tensile strength ranging between 900 MPa and 1040 MPa. In an embodiment and relevant method described below, the reinforcement material is made by twisting one fiber (1), and preferably all of the fibers (1) comprise polyamide 6 or polyamide 6,6.

The cord (10) according to the present invention is provided with a high surface compatibility and adhesion ability with a concrete matrix by having polyamide based fiber(s), and by being preferably suitably coated as described below. In accordance with reinforcement material density and surface compatibility/adhesion with concrete, the number of the polyamide based fibers (1) in the twisted yarn of the reinforcement material can be determined. For instance, in an exemplary case where the twisted yarn includes PP and PA fibers, the higher number of PA fibers correspond to a higher reinforcement material density, and a higher pullout strength which is attributed to higher surface polarity and adhesion ability between the reinforcement material and concrete. In another exemplary case where all of the fibers (1) in the twisted yarn are polyamide based, the density of the reinforcement material preferably ranges between 1.12 g/cm³ and 1.16 g/cm³, and the reinforcement material has a high compatibility when mixed with concrete. Presence of lower density fibers in the twisted yarn, results in lower reinforcement material density values. Thus, density of the reinforcement material can be determined by arranging the number of polyamide based fibers and the number of other polymeric fibers with known densities.

Preferably, the linear density of the fibers (1) ranges between 1400 dtex and 4200 dtex, wherein the unit dtex is an abbreviation for decitex, which is the mass of filaments in grams per 10,000 meters.

The present invention further proposes a method for obtention of twisted macro synthetic fiber-based concrete reinforcement material (cord). Here, twisting steps for obtaining two different embodiments are explained: Example 1: Obtaining a cord comprising one fiber (one-ply)

- An individual polyamide based fiber is twisted in a z-direction or s-direction, at a twisting density ranging between 30 tpm and 300 tpm (wherein 'tpm' corresponds to abbreviation of 'twists per meter'). One individually twisted yarn is thus obtained.

Example-2: Obtaining a reinforcement material comprising two fibers (two-ply cord), at least one of the fibers, preferably both of the fibers comprising polyamide 6 or polyamide 6,6:

a. an individual fiber is twisted in a z-direction at a twisting density ranging between 50 tpm and 400 tpm, thus obtention of an individually twisted yarn; b. another individual fiber is twisted in an s-direction at a twisting density ranging between 50 tpm and 300 tpm, thus another individually twisted yarn is obtained;

c. said two twisted yarns are twisted together in an s-direction at a twisting density ranging between 50 tpm and 400 tpm, thus a cord comprising two fibers is obtained;

or, alternatively, said method comprises the following sequential steps:

i. an individual fiber is twisted in an s-direction at a twisting density ranging between 50 tpm and 400 tpm, thus obtention of an individually twisted yarn is thus obtained;

ii. another individual fiber is twisted in a z-direction at a twisting density ranging between 50 tpm and 300 tpm, thus another individually twisted yarn is obtained;

iii. said two twisted yarns are twisted together in a z-direction at a twisting density ranging between 50 tpm and 400 tpm, thus a cord comprising two fibers is obtained. The twisted reinforcement material can be considered and named as a cord.

Cord obtained according to the above method preferably has:

- length (L) ranging between 30 mm and 100 mm,

- diameter (D) ranging between 0.30 mm and 1 mm, and aspect (L/D) ratio lower than a value ranging between 50 and 100.

Greater aspect ratios increase the tendency of balling in cement mixtures and hairy appearance at concrete surface, especially with lower stiffness reinforcement materials in the prior art.

The cord is then preferably subjected to thermal treatment preferably including coating, drying, and orientation. The coating step is performed by dipping the cord into an aqueous dip solution preferably comprising suitable reactives known to skilled person in the art for obtention of a coating layer comprising one or more material selected from a list consisting of polyurethane-, epoxy-, polyacrylate-, silane-, polyamide-, resorcinol-, and formaldehyde-based materials. Thus, reinforcing material (cord) obtained by said method is coated with a coating layer comprising one or more material selected from a list consisting of polyurethane-, epoxy-, polyacrylate-, silane-, polyamide-, resorcinol-, and formaldehyde-based substances.

The thermal treatment (i.e. heat setting to obtain favorable values for modulus, elongation and thermal shrinkage) is performed at a temperature ranging between 150°C and 250°C, more preferably between 210°C and 245°C, along with application of repetitive tension and relaxation onto the cord, to provide favorable orientation and stiffness thereto. The above-mentioned temperature ranges give best results in case where all the fibers comprise polyamide 6,6.

Highest value of the tension applied onto the cord is preferably within a range between 0.1 g/dtex and 1.5 g/dtex, and more preferably between 0.4 g/dtex and 1.2 g/dtex. Suitable exposure time in thermal treatment depends on an oven length used in finishing, linear velocity of the reinforcement material at passing through the oven, and number of oven passings. Optimal exposure time (i.e. total duration of thermal treatment) is within a range between 10 seconds and 120 seconds. The above-mentioned exposure time range give highly favorable results in case where all of the fibers comprise polyamide 6,6.

Average linear density of filaments used in the cord according to the present invention preferably ranges between 4 den and 15 den (abbreviation for 'denier⁷). The cord disperses well in concrete, within a range between 2100 dtex and 8400 dtex.

The coating provides minimized lump formation tendency in the reinforced concrete and furthermore, high chemical adhesion between the cord and concrete, due to polarity compatibility and/or covalent bonding between coating and concrete. Pullout strength of the cord from concrete is thus maximized.

The cord according to the present invention is preferably bundled and wrapped with water soluble polyvinyl acetate (PVA) sheathes (20) to obtain an assembly as illustrated in Fig.4, for facilitated introduction in form of dissolvable packs into cement mixtures. The PVA sheath, which is preferably of a thickness within the range between 20 micrometers and 35 micrometers, is easily dissolvable in the cement mixture, and thus a uniform distribution of concrete cord can be obtained.

In use, such PVA-wrapped reinforcing material bundles are introduced into cement mixtures in transmixers, in paper-based packagings (e.g. paper bags). The paper packaging disintegrates and then the water-soluble PVA wrapping dissolves in aqueous cement mixture, thus the cord gets in direct contact with the cement mixture, and disperses homogeneously therein.

Polyamide 6,6 (PA 66) and polyamide 6 (PA 6) have density values between 1.13- 1.16 g/cm³ and 1.12-1.15 g/cm³, respectively, which are higher than the most widely used synthetic concrete reinforcement material polypropylene (PP, density: 0.90- 0.91 g/cm³). Thus when used in same weight percentages, polyamide-based (PA- based) concrete reinforcement fibers occupy lower volume (corresponding to a lower volumetric ratio and regarding this, a decreased aggregation) in concrete, with respect to polypropylene-based (PP-based) fibers. This allows introduction of higher weight ratios of reinforcement material in case of poliamide-based fibers, in comparison with the case where the fibers mainly consist of PP. Additionally, PA fibers do not float in aqueous media, thanks to the higher density thereof. These facts correspond to an easier application of the fibers according to the present invention, into concrete mixtures. In case where the reinforcement material comprises two fibers, a hybrid cord can be obtained according to the present invention, with one of the fibers being a non- polyamide-based material, e.g. polypropylene. Such embodiment can be considered as useful for tailoring physical properties in accordance with mixture or matrix where the cord is to be included. For instance, the density of the reinforcement material can be tuned by selection of the fiber material for one of the fibers other than polyamide 6 or 6,6 as a value between 0,90 and 1,16 g/cm³.

Additionally PA-based fibers provide enhanced fracture toughness to concrete, in comparison with the above mentioned polyolephinic alternatives widely used in the market. As shown in the Fig.2, the load carried by the concrete reinforced by PA- based fiber according to the present invention increases with increasing crack opening, in a 4-point bending test performed in accordance with ASTM C 1609. PA- based fibers according to the present invention which are exemplified over PA 6,6 in Fig.2, fulfill this performance criterion better than polyolephinic fibers in general, which are exemplified with PP in Fig.2; since tensile strength of e.g. PA 6,6-based fibers is within the range of 700-950 MPa, corresponding to higher values in comparison with that of PP-based fibers, ranging between 500 and 700 MPa. Post-crack strength of concrete matrix depends to the type of reinforcing (fiber) material, its elastic modulus, aspect ratio, tensile strength, fiber surface properties, amount of fiber, fiber orientation and aggregate size. The cord according to the present invention provides a favourable post-crack load carrying capacity to the concrete. Upon formation of crack, the load is transferred onto the fibers of the cord, and the fibers stretch in accordance with increasing crack opening (distance between two sides of crack). Since the surface compatibility of the cord with concrete is high, due to its shape with increased surface area with indentations obtained by twisting, and surface coating providing strong adhesion to concrete, the cord is not easily pulled out from concrete matrix, which corresponds to favorable pullout strength. Thus, the cord successfully shows increasing resistance against widening of crack opening. This phenomenon is visualized by load/deflection test results (according to ASTM C 1609) provided in Fig.2, comparatively against the behavior of PP-based cords used in the market. Hence, reinforced concrete with higher ductility and toughness becomes available with the cord according to the present invention. The cord according to the present invention has a higher toughness when compared to commercial polymer-based macro synthetic reinforcement materials on the market, by having a tensile strength ranging between 900 and 1040 MPa. It has denier per filament (dpf) value within a range between 4 dpf to 15 dpf. Moisture holding capacity of the cord according to the present invention ranges between 3% and 4% (w/w), which corresponds to easy and favorable interface formation in concrete mixtures at curing thereof. Thus, the below objects are achieved by the composite structure according to the present invention and the proposed method for obtention thereof:

- the above-mentioned shortcomings in the prior art are eliminated,

- a macro synthetic fiber based reinforcement material for concrete, which has favorable mixing behavior when introduced into cement, and favorable reinforcing behavior in concrete matrix, is provided,

- a method for obtention of such reinforcement material is provided.

Claims

1. A macro synthetic fiber based reinforcement material for concrete, which is a cord (10) in form of twisted yarn(s) comprising a twisted fiber (1) comprising polyamide 6 or polyamide 6,6.

2. Reinforcement material according to the Claim 1, comprising two twisted fibers (1), wherein both of said fibers comprise polyamide 6 or polyamide 6,6, preferably both of the fibers comprise polyamide 6,6.

3. Reinforcement material according to any of the Claims 1 or 2, coated with a coating layer comprising one or more material selected from a list consisting of polyurethane-, epoxy-, polyacrylate-, silane-, polyamide-, resorcinol-, and formaldehyde-based substances.

4. Reinforcement material according to any of the Claims 1 to 3, wherein the linear density of the fibers range between 1400 dtex and 4200 dtex.

5. Reinforcement material according to any of the Claims 1 to 4, having a length ranging between 30 mm and 100 mm, a diameter ranging between 0.30 mm and 1 mm, and an aspect ratio ranging between 50 and 100.

6. Reinforcement material according to any of the Claims 1 to 5, having a tensile strength ranging between 900 M Pa and 1040 MPa.

7. Reinforcement material according to any of the Claims 1 to 6, wrapped with a water soluble polyvinyl acetate (PVA) sheath for facilitated introduction in form of dissolvable packs into cement mixtures; the sheath preferably having a thickness within the range between 20 micrometers and 35 micrometers.

8. Reinforcement material according to the Claim 7, bundled and then packaged with paper-based material, preferably with a paper bag.

9. A method for obtention of macro synthetic fiber based reinforcement material for concrete, said method comprises the following sequential steps: twisting a fiber comprising polyamide 6 or polyamide 6,6, in a z-direction or s-direction, at a twisting density ranging between 30 tpm and 300 tpm.

10. A method for obtention of macro synthetic fiber based reinforcement material for concrete, the reinforcement material comprising two fibers, at least one thereof comprising polyamide 6 or polyamide 6,6, wherein said method comprises the following sequential steps: - twisting an individual fiber in a z-direction at a twisting density ranging between 50 tpm and 400 tpm;

- twisting another individual fiber in an s-direction at a twisting density ranging between 50 tpm and 300 tpm;

- twisting said two twisted yarns together in an s-direction at a twisting density ranging between 50 tpm and 400 tpm, thus obtention of a cord comprising two fibers;

or, alternatively, said method comprises the following sequential steps:

- twisting an individual fiber in an s-direction at a twisting density ranging between 50 tpm and 400 tpm;

- twisting another individual fiber in a z-direction at a twisting density ranging between 50 tpm and 300 tpm;

- twisting said two twisted yarns together in a z-direction at a twisting density ranging between 50 tpm and 400 tpm, thus obtention of a cord comprising two fibers.

11. Method according to the Claim 10, wherein both of the fibers comprise polyamide 6 or polyamide 6,6, and preferably both of the fibers comprise polyamide 6,6.

12. Method according to any of the Claims 9 to 11, further comprising thermal treatment at a temperature within the range between 150°C and 250°C, preferably between 210°C and 245°C.

13. Method according to the Claim 12, wherein the thermal treatment has a total duration time within a range between 10 seconds and 120 seconds, and the thermal treatment includes: - dipping the cord into an aqueous dip solution suitable for obtention of a coating layer comprising one or more material selected from a list consisting of polyurethane-, epoxy-, polyacrylate-, silane-, polyamide-, resorcinol-, and formaldehyde-based materials;

- application of repetitive tension and relaxation onto the cord, with a maximum value of tension applied onto the cord ranging between 0.1 g/dtex and 1.5 g/dtex, and more preferably between 0.4 g/dtex and 1.2 g/dtex.

14. Method according to any of the claims 9 to 13, followed by wrapping the cord(s) with a water soluble polyvinyl acetate (PVA) sheath (20) for facilitated introduction in form of dissolvable packs into cement mixtures; the sheath preferably having a thickness within the range between 20 micrometers and 35 micrometers.

15. Method according to the claim 14, further comprising bundling and packaging with paper-based material, preferably with a paper bag.