Production method of concrete member and concrete member

Abstract

To provide a production method capable of preventing cracking at a side edge with a thin part even when steam curing is applied.SOLUTION: Provided is a production method of a concrete member, the concrete member formed at a side edge in a width direction of a thin thickness part thinner than an adjacent body part. The production method includes: a step (step S1) of forming a plate-like concrete part through installing concrete in a mold; steps (steps S2, S3) of carrying out steam-curing at 45°C or lower by placing a curing sheet so as to cover the concrete part; steps (step S4, S5) of removing the curing sheet when temperature difference between an outside and an inner side of the curing sheet is equal to or less than a specific value after feeding steam is stopped; steps (step S6, S8) of installing heat insulation material on the thin thickness part; and a step (step S9) of removing the heat insulation material after completion of cooling the concrete part.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a concrete member in which a thin-walled portion that is thinner than an adjacent main body portion is formed at a widthwise side edge, and to the concrete member. [Background technology]

[0002] In the manufacturing process of producing precast concrete components by pouring concrete into reinforced formwork in a factory or work yard, accelerated curing such as steam curing is carried out as a means of facilitating form removal and increasing productivity (see Patent Documents 1 and 2).

[0003] In steam curing, the precast concrete components before being stripped of their forms are placed inside a simple curing enclosure made of a curing sheet and a lightweight steel pipe frame, and steam generated using a boiler is pumped into the enclosure to raise the temperature to a high temperature of around 60°C at normal pressure.

[0004] After the set high temperature is reached, the high temperature is maintained for about 2 to 4 hours, and after the supply of steam is stopped and the material is left to cool naturally, the simple curing cover is removed and curing is completed by leaving the material in air. The formwork is removed during this cooling period and reused for the next production cycle.

[0005] Patent documents 1 and 2 focus on the problem that when precast concrete components such as box culverts, concrete slabs of a certain thickness, and shield segments are manufactured by steam curing, the temperature of the peripheral edges, which have good heat dissipation properties, drops earlier than the temperature of the center during the slow cooling period, making cracks more likely to occur at the edges and corners.

[0006] In order to prevent cracks from occurring at the edges and corners of the precast concrete components after steam curing, insulation is placed at the edges and corners to keep them warm during air curing, preventing the temperature difference with the center from becoming too large. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2000-290087 A [Patent Document 2] JP 2011-57533 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, for concrete components such as half precast slabs (see Figure 2), which have thin-walled sections at their widthwise side edges that are thinner than the adjacent main body section, simply placing insulation material at the side edges during air curing can be difficult to suppress temperature differences, and there is a risk that the occurrence of cracks cannot be reliably prevented.

[0009] Therefore, an object of the present invention is to provide a method for manufacturing a concrete member and a concrete member that do not cause cracks to occur at the side edges, which become thin-walled portions, even when steam curing is performed. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the manufacturing method of the concrete member of the present invention is a manufacturing method of a concrete member in which a thin-walled portion that is thinner than an adjacent main body portion is formed at a widthwise side edge, and is characterized by comprising the steps of: forming a plate-shaped concrete portion by pouring concrete into a formwork; installing a curing sheet so that the concrete portion is covered and performing steam curing at 45°C or less; removing the curing sheet after stopping the supply of water vapor and when the temperature difference between the inside and outside of the curing sheet becomes equal to or less than a predetermined value; installing insulation material for the thin-walled portion; and removing the insulation material after the concrete portion is slowly cooled.

[0011] Here, it is preferable that the formwork surface forming the surface of the thin wall portion is formed of a material with high thermal insulation properties. Furthermore, when prestressing is introduced by the PC steel bars arranged in the depth direction perpendicular to the width direction after the curing sheet is removed, the PC steel bars can be arranged in the thin wall portion or the closest position thereto within a range where a predetermined cover can be secured. In this case, the cross-sectional area of ​​the PC steel bars determined at the time of design can be divided into two pieces, and one PC steel bar with a smaller cross-sectional area can be arranged in the thin wall portion or the closest position thereto within a range where a predetermined cover can be secured. Furthermore, the thermal insulation material is removed from the thin wall portion after the final curing is completed.

[0012] The invention of a concrete member is characterized in that it comprises a concrete portion in which a thin portion thinner than an adjacent main portion is formed at a side edge in the width direction, the thin portion and the main portion being made of concrete, main reinforcing bars arranged in the main portion toward a depth direction perpendicular to the width direction, prestressing steel members arranged in the thin portion and the main portion toward the depth direction, and reinforcing bars arranged in the width direction so as to sandwich at least the prestressing steel members of the thin portion from above and below. Here, a plurality of reinforcing bars sandwiching the prestressing steel members of the thin portion from above and below are arranged at intervals in the depth direction. Effect of the Invention

[0013] In the method for manufacturing a concrete member of the present invention thus configured, the maximum temperature of the steam curing is set to 45°C or less, and the temperature difference between the inside and outside is checked when removing the curing sheet. Furthermore, heat insulation is installed in the thin-walled portion until the concrete portion has finished cooling.

[0014] In this way, by not only installing insulation in the thin-walled areas but also by paying attention to the timing of removing the curing sheet and suppressing the temperature rise caused by steam curing, it is possible to prevent cracks from occurring in the side edges that become the thin-walled areas even when steam curing is performed.

[0015] In addition, in the concrete member of the invention, prestressing steel bars are placed in the thin walled sections, and the top and bottom of the prestressing steel bars are sandwiched between reinforcing bars. This configuration makes it possible to introduce prestress uniformly throughout the entire concrete member without causing cracks in the thin walled sections. [Brief description of the drawings]

[0016] [Figure 1] 2 is a flowchart illustrating the steps of a method for manufacturing a concrete member according to the present embodiment. [Diagram 2] FIG. 2 is an explanatory diagram illustrating a half precast slab as a concrete member of this embodiment. [Diagram 3] FIG. 1 is an explanatory diagram showing a schematic diagram of the principle by which cracks occur in a thin-walled portion due to a temperature difference. [Figure 4] FIG. 2 is an explanatory diagram showing the steam curing process. [Diagram 5] FIG. 13 is an explanatory diagram showing the configuration of a formwork around a thin-walled portion. [Figure 6] FIG. 2 is an explanatory diagram showing each process after steam curing. [Figure 7] FIG. 2 is an explanatory diagram of the final curing process. [Figure 8] FIG. 2 is an explanatory diagram showing an example of the arrangement of PC steel members in Example 1. [Figure 9] FIG. 4 is an explanatory diagram showing another example of arrangement of PC steel members in Example 1. [Figure 10] FIG. 2 is an explanatory diagram illustrating the arrangement relationship between PC steel members and reinforcing bars in the first embodiment. [Figure 11] FIG. 1 is an explanatory diagram of three test specimens described in Example 2. [Figure 12] FIG. 1 is an explanatory diagram of the experimental results using three test specimens. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a method for manufacturing a concrete member and a concrete member according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a flow chart for explaining the steps of the method for manufacturing a concrete member according to the present embodiment. Fig. 2 is an explanatory diagram illustrating a half precast slab 1 as the concrete member according to the present embodiment.

[0018] First, we will explain the half precast slab 1, which is an example of a concrete member. The half precast slab 1 is a plate-shaped reinforced concrete member, as shown in Figure 2. The half precast slab 1 manufactured in a factory or the like is transported to the site and installed in a predetermined position, and the slab with the completed cross section is constructed by integrating it with cast-in-place concrete poured from above.

[0019] The half precast slab 1 illustrated in Fig. 2 comprises a main body portion in which convex portions 22 and concave portions 23 are alternately formed, and thin-walled portions 21 formed on the side edges of the main body portion. Here, the thin-walled portions 21 are provided on both sides of the width direction X of the half precast slab 1. The direction perpendicular to the width direction X will be described as the depth direction Y, but either the width direction X or the depth direction Y may be longer.

[0020] The protruding portions 22 constituting the main body extend in the depth direction Y. The protruding portions 22 are the thickest parts of the half precast slab 1. The thin-walled portions 21 are adjacent to the protruding portions 22 located on both sides of the multiple parallel protruding portions 22 provided on the main body.

[0021] That is, the thin-walled portion 21 is thinner than the adjacent protruding portion 22, and is formed in a tapered shape in which the thickness gradually decreases toward the side edge in the width direction X (see the enlarged view in FIG. 5). On the other hand, the recessed portion 23, which becomes the main body portion, is also formed to be thinner than the protruding portion 22.

[0022] The thin-walled portion 21 and the main body portion (the convex portion 22, the concave portion 23) are formed by poured concrete into an integral concrete portion 2. Inside this concrete portion 2, as shown in Fig. 2, main reinforcing bars 3 are arranged in the depth direction Y, and PC steel members 4 are also arranged in the depth direction Y.

[0023] Furthermore, joint reinforcing bars 31 are provided on at least both side edges of the half precast slab 1 so as to protrude from the protrusions 22 in the width direction X. In Fig. 2, a plurality of loop reinforcing bars, each having a loop-shaped end, are arranged as joint reinforcing bars 31 at intervals in the depth direction Y.

[0024] In the manufacture of such half precast slabs 1, steam curing is generally used to increase productivity. However, the temperature drop during slow cooling after steam curing is greater in the thin-walled portion 21 with a small cross section than in the protruding portion 22. Figure 3 is an explanatory diagram that shows a schematic diagram of the principle by which cracks occur in the thin-walled portion 21 due to a temperature difference.

[0025] 3, the temperature drop is slow in the protruding portion 22 with a large cross section, whereas the temperature drop is fast in the thin-walled portion 21 with a small cross section and an open edge to the outside. The recessed portion 23 has a small cross section like the thin-walled portion 21, but since it is surrounded by the protruding portion 22, the temperature drop is not as fast.

[0026] If the rate of temperature drop differs between the thin-walled portion 21 and the protruding portion 22 in this way, a difference occurs in the amount of partial shrinkage due to the temperature drop, and it is believed that thermal cracks will occur in the thin-walled portion 21 that is restrained by the protruding portion 22 with a large cross section. In particular, if steam curing is performed at a high temperature of 50°C to 80°C, a sudden temperature drop is likely to occur during gradual cooling.

[0027] Therefore, in the manufacturing method of the concrete member of this embodiment, a manufacturing process is adopted that prevents thermal cracks from occurring in the side edges that become the thin-walled portions 21 even when steam curing is performed. Below, the steps of the manufacturing method of the concrete member of this embodiment will be described with reference to Fig. 1 and Figs. 4 to 7.

[0028] First, in step S1, concrete is poured into the formwork. For example, as shown in Fig. 4, the formwork (53, 54, 541, 542) is assembled to the bottom plate 51 having a flat upper surface.

[0029] As shown in Fig. 4, the recess 23 of the half precast slab 1 is formed by an intermediate formwork 53. A balance frame 52 is installed to fix this intermediate formwork 53 in a floating state. The side formwork 54 that forms the side surface of the protrusion 22 is also supported by the balance frame 52.

[0030] 5 is an explanatory diagram showing the configuration of the formwork around the thin-walled portion 21. A rubber formwork 542 and a vertical surface side formwork 541 are arranged below the side formwork 54, and the vertical surface side formwork 541 is fixed to the bottom plate 51 by fixing bolts 55. The rubber formwork 542 is made of a heat insulating material such as chloroprene rubber, and can be arranged along the tapered portion of the upper surface of the thin-walled portion 21. This rubber formwork 542 is made of a material that does not deform even when lateral pressure from concrete acts on it.

[0031] The vertical surface side formwork 541 is arranged to form a vertical surface which will become the side end surface of the thin-walled portion 21. A polystyrene foam board 543 which will serve as a heat insulating material is arranged at a location which will become the formwork surface which will form the lower surface and the side end surface of the thin-walled portion 21.

[0032] By doing this, immediately after pouring the concrete, the underside and the vicinity of the side end faces of the surface side of the thin-walled portion 21 are covered with insulating material called polystyrene foam plate 543, and the vicinity of the upper surface is also covered with insulating material called rubber formwork 542 to keep the surface warm. Concrete is poured into the inside of the formwork (53, 54, 541, 542) installed on the bottom plate 51 in the above manner.

[0033] In step S2, as shown in Fig. 4, steam pipes 57 are arranged around the bottom plate 51, and a curing sheet 56 is installed. The steam pipes 57 have holes at regular intervals for discharging steam, and are installed along both sides of the poured concrete portion 2, facing the depth direction Y (see Fig. 2).

[0034] The curing sheet 56 is placed so as to cover the poured concrete portion 2 and the steam pipe 57. When preparations for steam curing are complete, steam curing (preliminary curing) begins in step S3. First, high-temperature steam is supplied to the steam pipe 57 to raise the temperature inside the curing sheet 56 to 20°C, and the state is maintained for three hours.

[0035] Next, the amount of steam supply is increased, and the temperature inside the curing sheet 56 is gradually raised over a period of two hours until it reaches 45°C. Once the temperature inside the curing sheet 56 reaches 45°C, that temperature is maintained for six hours. The reason why the maximum temperature for steam curing is set to 45°C or less is to prevent a sudden drop in temperature of the concrete part 2 during gradual cooling after the supply of steam is stopped, and steam curing is carried out at a relatively low temperature of 45°C, which has as little temperature difference as possible with the outside air temperature.

[0036] After the six-hour steam curing is completed, the supply of steam is stopped. After the supply of steam is stopped, the curing sheet 56 is left covering the curing sheet 56 in order to prevent a sudden drop in temperature. The temperature inside the curing sheet 56 gradually drops, and slow cooling is continued until the temperature difference between the inside and outside of the curing sheet 56 becomes 13.5°C or less (step S4).

[0037] After the slow cooling is completed, the curing sheet 56 is removed to release the restraint on the concrete part 2 (step S5). Figure 6 is an explanatory diagram showing each process after the steam curing. First, as shown in Figure 6(a), the balance frame 52 and the intermediate formwork 53 that was fixed by the balance frame 52 are removed.

[0038] 6(b), the fixing bolts 55 that fixed the vertical surface side formwork 541 to the bottom plate 51 are removed to prevent movement restraint during the introduction of prestress and the occurrence of cracks due to external restraint. At this stage, in order to suppress the temperature drop in the thin-walled portion 21 and to lower the temperature of the protruding portion 22 of the main body first, a protective cloth 61 acting as a heat insulating material is installed to cover the thin-walled portion 21 (step S6).

[0039] Then, in step S7, prestress is applied to the concrete portion 2. As shown in FIG. 2 (see FIG. 8 and FIG. 9), the PC steel member 4 tensioned by a set tension is embedded in the protruding portion 22 of the concrete portion 2. Then, when the concrete strength of the concrete portion 2 is 36 N / mm 2 After the above-mentioned phenomena have occurred, prestress is introduced by releasing the tension in the steel members at both ends of the PC steel member 4 to which tensile force had been applied.

[0040] 6(c), the protective cloth 61 is removed once, the side formwork 54 is removed, and the removed protective cloth 61 is reinstalled to continue the thermal curing of the thin-walled portion 21. Then, the thin-walled portion 21 is left covered with the protective cloth 61 for about three hours, and the internal temperature of the entire concrete portion 2 is lowered to about the outside air temperature.

[0041] Fig. 7 is an explanatory diagram of the final curing process. To move to the final curing, in step S8, plate-shaped heat-insulating material 62 is installed. Specifically, the vertical surface side formwork 541 and the rubber formwork 542 that were installed for insulation around the thin-walled portion 21 are removed, and in place of them, plate-shaped heat-insulating material 62 is installed on the thin-walled portion 21 of the half precast slab 1 installed on the mat 63 as shown in Fig. 7(a).

[0042] Plate-shaped heat-insulating material 62 is a heat insulating material made of urethane foam, and is attached to the outer circumferential surface of thin-walled portion 21 using a holding clip 621. Clip 621 may be any type capable of clamping plate-shaped heat-insulating material 62 together with thin-walled portion 21, and for example, a reinforcing bar protective cover having a width of about 100 mm and a depth of about 1000 mm may be used.

[0043] For the concrete portion 2, roughening is performed as necessary on the upper surface, which will be the pouring surface for the in-situ poured concrete. At this time, for waterproofing and heat retention, the plate-shaped heat-retaining material 62 is left attached to the thin-walled portion 21, and the pouring surface is roughened by high-pressure washing. In other words, the thin-walled portion 21 is not roughened in order to continue the heat retention by the plate-shaped heat-retaining material 62.

[0044] Fig. 7(b) shows the state of final curing in step S9. The half precast slab 1 placed on the stand 58 after the roughening process is entirely covered with a curing sheet 59 with the plate-shaped heat-insulating material 62 attached to the thin-walled portion 21, and is left to cool (cool) for 12 hours or more. Then, after the final curing is completed, the sheet 59 and the plate-shaped heat-insulating material 62 are removed.

[0045] Next, the operation of the method for manufacturing a concrete member according to this embodiment will be described. In the method for manufacturing a concrete member configured as described above, the maximum temperature of the steam curing is set to 45°C or less, and the difference between the inside and outside temperatures is also checked when removing the curing sheet 56. Then, for the thin-walled portion 21, a plate-shaped heat-retaining material 62 that acts as a heat insulator is placed until the gradual cooling of the concrete portion 2 is completed.

[0046] Specifically, prestress is introduced by curing the thin-walled portion 21 while leaving the formwork (542, 543) having a heat-retaining effect in place. Furthermore, during static curing after the introduction of prestress, a plate-shaped heat-retaining material 62 is attached to the thin-walled portion 21.

[0047] In this way, by not only installing insulation material in the thin-walled portion 21 but also limiting the temperature rise caused by steam curing to less than that of general high-temperature steam curing and paying attention to the timing of removing the curing sheet 56, it is possible to prevent cracks from occurring on the side edges that will become the thin-walled portion 21 even when steam curing is performed.

[0048] That is, by carrying out steam curing at a relatively low temperature of 45°C, it is possible to prevent a sudden drop in temperature during slow cooling. Furthermore, by locally insulating the thin-walled portion 21, where a temperature drop is likely to occur, with formwork (542, 543) using insulating material, protective cloth 61, or plate-shaped heat-insulating material 62, it is possible to reduce the temperature difference due to differences in material thickness.

[0049] If it is possible to prevent cracks from occurring on the side edges that form the thin-walled portions 21 in this way, there will be no need to revise the mix design in order to increase the concrete strength, and material costs can be reduced. In addition, since the temperature around the concrete during steam curing can be lowered compared to conventional techniques, the amount of LPG and heavy oil used as fuel for steam curing can be reduced. EXAMPLES

[0050] In the above embodiment, a method for manufacturing a concrete member has been described, but in this Example 1, an embodiment of a concrete member will be described with reference to Figures 8 to 10. Note that the same terms or the same reference numerals will be used to describe the same or equivalent parts as those described in the above embodiment.

[0051] In the half precast slabs 1A and 1B of Example 1, which serve as concrete members, the PC steel members 4 are arranged in a depth direction Y (see FIG. 1) perpendicular to the width direction X. In the half precast slab 1A shown in FIG. 8, the PC steel members 4 are arranged in each of the protruding portions 22 in the longitudinal direction (depth direction Y) of the protruding portions 22.

[0052] Here, when prestressing is applied using the PC steel 4, it is desirable to apply prestress uniformly not only over the entire length of the concrete section 2 in the longitudinal direction (depth direction Y), but also over the entire width in the width direction X (see Figure 1).

[0053] On the other hand, the prestressing steel members 4 are not usually placed in thin areas such as the thin-walled portion 21. This is because in thin areas, the required cover may not be secured and there is a risk of cracks occurring due to the introduction of prestress.

[0054] Here, in the pretensioning method, prestress is introduced by the adhesion effect between the PC steel 4 and the concrete, so prestress is difficult to introduce near the end of the PC steel 4 and in places away from the PC steel 4 in the width direction X. If sufficient prestress is not introduced, tensile stress will occur due to temperature stress during manufacturing and load during construction, which may cause cracks.

[0055] Therefore, in the half precast slab 1A shown in Fig. 8, the bottom PC steel member 4 is moved in the width direction X to a position closest to the thin-walled portion 21 or to the thin-walled portion 21 within a range where a predetermined cover can be ensured. This makes it possible to introduce prestress uniformly around the end of the thin-walled portion 21 in the depth direction Y.

[0056] 9 is an explanatory diagram showing another example of the arrangement of the PC steel members 4 in Example 1. Since the PC steel members 4 only need to be arranged in a required cross-sectional area within the cross section of the concrete portion 2, when they are arranged in a thin location, they can be arranged as PC steel members 4A and 4B obtained by dividing the cross-sectional area of ​​a normal PC steel member 4 determined at the time of design into two.

[0057] Specifically, one of the divided PC steel members 4B is left in its original position at the convex portion 22, and the other PC steel member 4A with a smaller cross-sectional area is placed in a position closest to the thin-walled portion 21 or in the thin-walled portion 21, within the range where the specified cover can be secured.

[0058] Furthermore, in order to prevent cracks from occurring even when the PC steel members 4, 4A are placed in areas where the concrete is thin, the PC steel members 4, 4A can be sandwiched above and below by reinforcing bars arranged in the width direction X.

[0059] 10 is an explanatory diagram illustrating the arrangement relationship between the PC steel members (4, 4A) and the reinforcing bars in Example 1. As shown in this figure, the PC steel member arranged in the thin-walled portion 21 or in its vicinity is interposed between the loop joint reinforcing bar (A) that becomes the joint reinforcing bar 31 and the lower edge side reinforcing bar (B).

[0060] The loop joint reinforcing bars (A) are arranged in the width direction X and in multiple pieces at intervals of 250 mm in the depth direction Y. On the other hand, the lower edge reinforcing bars (B) are arranged in the width direction X and in multiple pieces at intervals of 125 mm in the depth direction Y.

[0061] In this way, if rebars oriented in a direction perpendicular to the extension direction of the PC steel members are arranged above and below the PC steel members (4, 4A), even if the PC steel members (4, 4A) are arranged in a thin location such as the thin-walled portion 21, cracks will not occur and prestress can be uniformly introduced over the entire length and width of the concrete portion 2. Furthermore, a sufficient prestress effect can be introduced even in the thin-walled portion 21 away from the convex portion 22, and the tensile stress of the thin-walled portion 21 can be reduced.

[0062] Other configurations and effects are substantially the same as those of the above-described embodiment or other examples, and therefore description thereof will be omitted. EXAMPLES

[0063] Hereinafter, the results of an experiment conducted to confirm the effects of the above-described embodiment and Example 1 will be described with reference to Fig. 11 and Fig. 12. Note that the same terms or the same reference numerals will be used to describe the same or equivalent parts as those described in the above-described embodiment or Example 1.

[0064] In the experiment of Example 2, the heat retention effect on the thin-walled portion 21 and the effect of introducing prestress were confirmed. Fig. 11 is an explanatory diagram of three test specimens described in Example 2. "Test specimen No. 1" is a test specimen for which no countermeasures were taken, that is, neither the manufacturing method for the concrete member described in the above embodiment nor the appropriate arrangement of the PC steel members described in Example 1 was carried out.

[0065] In contrast, "No. 2 test specimen" is a test specimen for verifying the effectiveness of heat retention measures, in which prestress is introduced while the thin-walled portion 21 is kept warm using the rubber formwork 542, polystyrene foam board 543, and protective cloth 61 described in the above embodiment.

[0066] Furthermore, "Test Specimen No. 3" is a test specimen in which the same heat retention measures as those in "Test Specimen No. 2" were applied, with the PC steel 4 moved to the thin-walled section 21, in order to verify the effectiveness of the heat retention measures and proper placement of the PC steel.

[0067] The measurement items for each test specimen were as follows: strain gauges were installed in the thin-walled portion 21 and the convex portion 22 at distances of 350 mm (350 cross section), 700 mm, 1400 mm, and 3425 mm from the end of the depth direction Y of the test specimen with a total length of 6,850 mm, and the changes in strain and temperature during annealing were measured.

[0068] Figure 12 is an explanatory diagram of the experimental results for the three specimens. In detail, the measurement results are shown for the thin-walled part of the 350 cross section (350F), the bottom of the convex part (350BL), and the center of the slab member (350CL). First, the effect of the insulation measures is considered by comparing the temperature and strain of the No. 1 specimen (without measures) and the No. 2 specimen (with insulation measures).

[0069] Comparing the two test results in terms of the temperature difference Δt1 (temperature drop) in the thin-walled portion (350F) between the temperature when the curing sheet 56 was removed and the temperature before prestressing was introduced, the temperature drop (temperature difference Δt1) of the thin-walled portion (350F) of specimen No. 2 was smaller than that of specimen No. 1, which means that it can be said that the temperature drop in the thin-walled portion 21 was suppressed. As a result, the temperature difference Δt2 and strain difference Δμ0 between the thin-walled portion (350F) and the convex portion (350F) before prestressing were suppressed, and it is considered that the occurrence of thermal cracks due to the temperature difference between the thin-walled portion 21 and the convex portion 22 can be suppressed.

[0070] Next, by comparing the temperature and strain of test specimen No. 2 (insulation measures) and test specimen No. 3 (insulation measures + proper placement of PC steel), the effect of reducing tensile stress in thin-walled section 21 by proper placement of PC steel is considered.

[0071] Comparing the two test results in terms of the strain difference Δμ1 in the thin-walled portion (350F) before and after the introduction of prestress, it was found that the No. 3 specimen had a greater introduced compressive strain difference Δμ1 than the No. 2 specimen, and that the appropriate placement of the PC steel 4 had made it possible to reduce the tensile stress in the thin-walled portion 21. In addition, the strain difference Δμ2 between the thin-walled portion (350F) and the convex portion (350BL) after the introduction of prestress decreased in the No. 3 specimen, which suggests that a relatively uniform prestress had been introduced to the cross section.

[0072] Other configurations and effects are substantially the same as those of the above-described embodiment or other examples, and therefore description thereof will be omitted.

[0073] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments and examples, and design changes that do not deviate from the gist of the present invention are included in the present invention.

[0074] For example, in the above embodiment and Examples 1 and 2, half precast slabs 1, 1A, 1B having a main body portion in which a plurality of convex portions 22 and concave portions 23 are alternately formed have been described as examples, but the present invention is not limited to this, and can be applied to any concrete member in which the main body portion adjacent to the thin-walled portion 21 is formed thicker than the thin-walled portion 21. Furthermore, the thin-walled portion 21 may be formed only on one side edge in the width direction X of the concrete member. [Explanation of symbols]

[0075] 1, 1A, 1B: Half precast slab (concrete member) 2: Concrete section 21: Thin section 22: Protruding part (main body) 3: Main rebar 31: Reinforced concrete joint (reinforced concrete) 4,4A,4B:PC steel material 542: Rubber formwork (highly insulating material) 543: Styrofoam board (highly insulating material) 61: Protective cloth (insulation material) 62: Plate-shaped heat-insulating material (thermal insulation material) X: Width direction Y: Depth direction

Claims

1. A method for manufacturing a concrete member, comprising forming a thin-walled portion on a widthwise side edge of the concrete member, the thin-walled portion being thinner than an adjacent main body portion, the method comprising the steps of: A step of forming a plate-shaped concrete portion by pouring concrete into the formwork; A step of placing a curing sheet so as to cover the concrete portion and performing steam curing at 45°C or less; After stopping the supply of water vapor, removing the curing sheet when the temperature difference between the inside and outside of the curing sheet becomes equal to or less than a predetermined value; providing a heat insulating material to the thin wall portion; and removing the insulation material after the concrete portion has been slowly cooled.

2. The method for manufacturing a concrete member according to claim 1, wherein a form surface forming a surface of the thin-walled portion is made of a material having high thermal insulation properties.

3. A method for manufacturing a concrete member as described in claim 1 or 2, characterized in that after removing the curing sheet, when prestress is introduced by PC steel members arranged in the depth direction perpendicular to the width direction, the PC steel members are arranged in the thin-walled portion or a position closest to it to the extent that a predetermined cover can be secured.

4. A method for manufacturing a concrete member as described in claim 3, characterized in that in order to position the PC steel member at the thin-walled portion or the closest position thereto within a range where a specified cover can be secured, the cross-sectional area of ​​the PC steel member determined at the time of design is divided into two, and one PC steel member with the smaller cross-sectional area is positioned at the thin-walled portion or the closest position thereto within a range where a specified cover can be secured.

5. 3. The method for manufacturing a concrete member according to claim 1, wherein the insulating material is removed from the thin-walled portion after final curing is completed.

6. A concrete member having a thin-walled portion formed on a widthwise side edge thereof, the thin-walled portion being thinner than an adjacent main body portion, a concrete portion in which the thin-walled portion and the main body portion are formed of concrete; A main reinforcing bar arranged in the main body portion in a depth direction perpendicular to the width direction; PC steel members arranged in the thin-walled portion and the main body portion toward the depth direction; A concrete member characterized by comprising reinforcing bars arranged in the width direction so as to sandwich at least the PC steel material of the thin-walled portion from above and below.

7. The concrete member according to claim 6, characterized in that the reinforcing bars sandwiching the PC steel material of the thin-walled portion from above and below are arranged at intervals in the depth direction.

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