Pregrouted PC steel material and method for hardening pregrout layer thereof

Abstract

Provided is a pregrouted PC steel material comprising a PC steel stranded wire composed of a plurality of steel wires, a pregrout layer disposed on the outer periphery of the PC steel stranded wire so as to accommodate the PC steel stranded wire, a sheath covering the outer periphery of the pregrout layer, and a capsule including a pregrout-hardening agent and a film with which the agent is covered, the capsule being interposed among the steel wires constituting the PC steel stranded wire. The capsule has a strength such that the capsule is not broken before tensioning the PC steel stranded wire but is broken by a tensile force during the tensioning. Also provided is a method for hardening the pregrout layer.

Claims

1. A pregrouted PC steel material comprising: a PC steel stranded wire composed of a plurality of steel wires; a pregrout layer disposed on an outer periphery of said PC steel stranded wire so as to accommodate said PC steel stranded wire; a sheath covering an outer periphery of said pregrout layer; and a capsule including a pregrout-hardening agent and a film with which said pregrout-hardening agent is covered, said capsule being interposed among said steel wires constituting said PC steel stranded wire, said capsule having a strength such that said capsule is not broken before tensioning said PC steel stranded wire but is broken by compressive and shearing forces exerted on the capsule present in a gap among said steel wires with a narrowing of the gap during the tensioning, wherein said capsule and a binder are interposed among said steel wires constituting said PC steel stranded wire, and said binder includes a hardenable resin.

2. The pregrouted PC steel material according to claim 1, wherein said binder includes an epoxy resin.

3. A method for hardening the pregrout layer of the pregrouted PC steel material as defined in claim 1, comprising the steps of: embedding said pregrouted PC steel material in concrete; and tensioning said PC steel stranded wire to provide said concrete with compressive stress and breaking said film of said capsule by a tensile force during the tensioning to allow said pregrout-hardening agent to flow out to said pregrout layer.

4. The pregrouted PC steel material according to claim 1, wherein a compressive breaking strength of said capsule is more than or equal to 3N and less than or equal to 300N.

5. The pregrouted PC steel material according to claim 1, wherein a heat-resistant temperature of said film of said capsule is more than or equal to 50 C.

6. The pregrouted PC steel material according to claim 1, wherein a material of said film of said capsule is gelatin or urethane acrylate.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a cross sectional view showing an embodiment of a pregrouted PC steel material according to the present invention.

(2) FIG. 2 is an enlarged cross sectional view showing a capsule contained in the pregrouted PC steel material shown in FIG. 1.

(3) FIG. 3 is a cross sectional view showing the step of threading a stranded wire composed of a core wire and lateral wires of an inner layer through an opening of a die.

(4) FIG. 4 is a cross sectional view showing another embodiment of the pregrouted PC steel material according to the present invention.

DESCRIPTION OF EMBODIMENTS

(5) FIG. 1 is a cross-sectional view (a cross-sectional view in a direction perpendicular to the longitudinal direction) showing an embodiment of a pregrouted PC steel material in accordance with the present invention. As with conventionally known pregrouted PC steel materials, a pregrouted PC steel material 10 shown in FIG. 1 includes a PC steel stranded wire 1 with a multi-layered structure in which a plurality of steel wires 1a, 1b, 1c, and 1d composed of a piano wire or the like are stranded together, a pregrout layer 2 composed of an epoxy resin (a pregrout material) and disposed on the outer periphery of PC steel stranded wire 1 so as to accommodate PC steel stranded wire 1, and a sheath 3 composed of polyethylene and covering the outer periphery of pregrout layer 2. In the present embodiment, the diameter of each of steel wires 1a, 1b and 1c is set at 6.1 to 6.7 mm, the diameter of steel wire 1d is set at approximately 5 mm, the diameter of PC steel stranded wire 1 is set at 28.6 mm, and the thickness of sheath 3 is set at approximately 1.5 mm. PC steel stranded wire 1 is composed of a total of 19 steel wires 1a, 1b, 1c, and d.

(6) A capsule 4 as shown in FIG. 2 is interposed among the steel wires constituting PC steel stranded wire 1. Capsule 4 has a structure in which a hardening agent 4a is covered with a film 4b. Capsule 4 is a capsule in which hardening agent 4a including an aliphatic polyamine and an imidazole is covered with film 4b composed of gelatin/a urethane acrylate. In the present embodiment, an average particle diameter T of capsule 4 is set at 1.5 mm, and an average thickness t of film 4b is set at 65 m.

(7) Pregrouted PC steel material 10 can be manufactured by the following method. First, 6 lateral wires (inner layer steel wires) 1b as an inner layer are stranded on the periphery of core wire (steel wire) 1a, and 6 lateral wires (outer layer steel wires) 1c and 6 lateral wires (outer layer steel wires) 1d as an outer layer are stranded on the periphery of the inner layer to obtain a stranded wire. After or at the same time when the stranded wire is subjected to a stretching treatment, it is subjected to a bluing treatment to stabilize the stranded state.

(8) Then, while the strand of the our layer (lateral wires 1c and 1d) of the stranded wire is partially and sequentially loosened to open, a stranded wire composed of core wire 1a and the inner layer (lateral wires 1b) is passed through a reservoir accommodating a kneaded material of capsule 4 and a hinder 5 composed of an epoxy resin or the like.

(9) The periphery of the inner layer (lateral wires 1b) is covered with the kneaded material of capsule 4 and binder 5 (capsule 4-containing binder 5) by the passage through the reservoir accommodating the kneaded material.

(10) Thereafter, as depicted in FIG. 3, the stranded wire composed of core wire 1a and the inner layer (lateral wires 1b) is threaded through a prescribed shaped opening of a die 6 so as to remove the kneaded material of capsule 4 and binder 5 that has existed on a part of the outer periphery of the inner layer (lateral wires 1b) and to have the kneaded material of capsule 4 and binder 5 interposed among respective lateral wires 1b of the inner layer. This allows capsule 4 to be disposed among respective lateral wires 1b, which provides an advantage that capsule 4 will not be crushed when lateral wires le and id of the our layer are re-stranded.

(11) The inner peripheral surface of the opening of die 6 has such a shape that circular arc-shaped surfaces 6a for guiding lateral wires 1b and circular arc-shaped surfaces 6b for guiding the kneaded material of capsule 4 and binder 5 to gaps among respective lateral wires 1b at the outer periphery of the inner layer are alternately arranged. Thus, threading the stranded wire through the opening allows the kneaded material of capsule 4 and binder 5 to be smoothly disposed among respective lateral wires 1b. Circular arc-shaped surfaces 6b have a smaller curvature radius than circular arc-shaped surfaces 6a. For instance, the curvature radius of circular arc-shaped surfaces 6b may be approximately half of that of circular arc-shaped surfaces 6a (for instance, the curvature radii of circular arc-shaped surfaces 6a and 6b may be 3.08 mm and 1.5 mm, respectively).

(12) The number of capsules 4 to be interposed among lateral wires 1b suitably set, based on the number such that breaking of capsule 4 does not occur in a subsequent step, namely when lateral wires 1c and 1d of the our layer are re-stranded, which can be identified by experiments in advance. The setting of the number of capsules 4 is performed by adjustment of the size of capsule 4, the concentration of capsules 4 in binder 5 or so on.

(13) After disposing the kneaded material of capsule 4 and binder 5 on a part of the outer periphery of the inner layer (lateral wires 1b) as described above, loosening of the above-described outer layer (lateral wires 1c and 1d) is stopped, and the outer layer (lateral wires 1c and 1d) is re-stranded around the inner layer (lateral wires 1b). By this re-stranding, part of the kneaded material placed on the outer periphery of the inner layer (lateral wires 1b) is usually moved to the gaps among lateral wires 1c and 1d of the outer layer. Therefore, capsule 4 is usually interposed also among lateral wires 1c and 1d of the outer layer. Means (untwisting means) as described above for partially and sequentially loosening the strand of the outer layer of the stranded wire to open while covering the stranded wire composed of core wire 1a and lateral wires 1b with resin is well known itself (e.g., Japanese Patent Laying-Open No. 05-200825, paragraphs 0012 to 0034, and FIGS. 1 to 10).

(14) Finally, pregrout layer 2 is disposed by a conventionally known method on the outer periphery of PC steel stranded wire 1 with the kneaded material of capsule 4 and binder 5 interposed between the inner and outer layers (lateral wires 1b, 1c and 1d), and sheath 3 is formed therearound by extrusion molding to obtain pregrouted PC steel material 10 shown in FIG. 1.

(15) Pregrouted PC steel material 10 can be used in post-tensioning construction in a similar manner to conventional pregrouted PC steel materials. If PC steel stranded wire 1 of pregrouted PC steel material 10 is tensioned and fixed after placing and hardening concrete, compressive stress can be provided for the concrete by a reaction force of the tensile force.

(16) When a tensile force of 500 to 700 kN was applied to PC steel stranded wire 1 of pregrouted PC steel material 10 of the present embodiment, film 4b of capsule 4 was broken, and hardening agent 4a therein flowed out to pregrout layer 2 (hardening agent 4a was added to pregrout layer 2). With such outflow of hardening agent 4a, complete hardening of pregrout layer 2 could be achieved in about a half period as compared with the conventional method for flowing hardening agent 4a by breaking film 4b by dissolution with water or the like.

(17) When pregrouted PC steel material 10 was subjected to a bending test (with a radius of curvature of 1.0 m and held for 30 seconds) assuming the state of pregrouted PC steel material 10 wound around a drum, breakage of capsule 4 was not recognized.

(18) In the present invention, capsule 4 and binder 5 can also be interposed between core wire 1a and lateral wires 1b of the inner layer as in the embodiment shown in FIG. 4, for example. In this case, during manufacturing thereof, lateral wires (inner layer) 1b will also be untwisted. In the case where capsule 4 and binder 5 are also to be interposed between core wire 1a and lateral wires 1b of the inner layer in the embodiment shown in FIG. 1, capsule 4 and binder 5 may or may not be interposed between the inner layer (lateral wires 1b) and the outer layer (lateral wires 1c).

(19) It is needless to say that the present invention is also applicable to a 7-strand pregrouted PC steel material 10 in which six lateral wires 1b are stranded together around core wire 1a as shown in FIG. 4. It is also needless to say that capsule 4 may also be added to pregrout layer 2 in the embodiments shown in FIGS. 4 and 1.

(20) In the case where capsule 4 is added to pregrout layer 2, needle-like fillers (fibers) can be added to pregrout layer 2 for the purpose of promoting breakage of film 4b to achieve more smooth breakage of film 4b. The needle-like tillers can also be present in binder 5 among core wire 1a and lateral wires 1b and among lateral wires 1b, 1c and 1d.

(21) Although the amount of the kneaded material of capsule 4 and binder 5 interposed between lateral wires 1b and 1b is controlled by die 6 in the above-described embodiment, capsule 4 and the like can cover (can be interposed among) lateral wires 1b and the like merely by passage through the reservoir accommodating the kneaded material, namely, merely by dipping, as long as breakage of capsule 4 is permitted.

(22) The present invention does not eliminate an embodiment in which a conventional hardening agent has been blended in pregrout layer 2. It is needless to say that, when PC steel stranded wire 1 is tensioned, when a certain degree of viscosity is required of pregrout layer 2, and the like, it is necessary to suitably blend a hardening agent not covered with a film or an encapsulated hardening agent covered with a film but the film is dissolved with water or the like to obtain the hardening effect. It is needless to say that, in such cases, a required amount of the hardening agent should be blended in pregrout layer 2 beforehand. That is, the present invention is intended to promote hardening of pregrout layer 2 by breaking the capsules by a tensile force during the tensioning of PC steel stranded wire 1, as described above.

(23) It is needless to say that conventionally well-known materials other than an epoxy resin can be employed suitably for the pregrout material and binder 5, and that hardening agent 4a in accordance with the pregrout material is employed.

(24) It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the claims not by the description above, and is intended to include any modification within the meaning and scope equivalent to the terms of the claims.

REFERENCE SIGNS LIST

(25) 1 PC steel stranded wire; 1a core wire (steel wire); 1b lateral wire of inner layer (steel wire); 1c lateral wire (steel wire) of outer layer; 2 pregrout layer; 3 sheath; 4 capsule; 4a hardening agent (pregrout-hardening agent); 4b film; 5 binder (epoxy resin); 6 die; 6a, 6b circular arc-shaped surface; 10, 10 pregrouted PC steel material.