JP2004068341A - Bridge superstructure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To construct a box girder by using a precast concrete board as a web in bridge superstructure works. <P>SOLUTION: In a bridge superstructure in which the web is installed between a lower floor slab and an upper floor slab and the box girder is constituted, the web is composed of a prestressed concrete board in which a PC steel material is tensioned in the vertical direction, and extremely-stiff strength concrete having 28-day compressive strength in 100 to 180 N/mm<SP>2</SP>is used as the concrete of the prestressed concrete board. Extremely-stiff strength concrete having the self-contraction quantity of 400 μm or less per 1 m in an age of 60 days is used. The PC concrete board is manufactured in a factory or on a site-fabrication yard, the concrete board is carried at a building place and installed at a place correspoding to the web of the box girder and the box girder is constructed by cast-in-placing the lower floor slab and the upper floor slab. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a bridge superstructure for constructing a box girder using a PC concrete plate using ultra-high strength concrete as a web.
[0002]
[Prior art]
In the superstructure of a bridge in which the lower slab and the upper slab are connected by a web and a box girder is used, the web is subjected to a large shearing force. Therefore, when this is constructed of concrete panels, the panels need to be thickened.
[0003]
However, when the lower slab and the upper slab are constructed from cast-in-place concrete, making the concrete panels thinner and lighter is advantageous in terms of both workability and cost. However, in order to make the concrete web of the box girder thin, it must be made of a material that can withstand large shear forces.
[0004]
Conventionally, in the field of architecture, there is an application experience of 100~150N / mm ² class of ultra-high-strength concrete. However, there is no experience in the field of civil engineering, and there are few examples of using ultra-high-strength concrete for webs used as precast members in ordinary bridge superstructures. There is some experience of using a special cement-based composite material that does not contain coarse aggregate and is composed of particles of 2 mm or less and metal fibers or resin fibers. However, this composite material has high strength but high cost. Since compressive strength 100~150N / mm ² level concrete proven in the construction field of the self-shrinkage is large, it is as it is unsuitable for web bridge superstructure.
[0005]
[Problems to be solved by the invention]
When the web of the bridge superstructure is made of concrete, it is possible to increase the reinforcing steel material to compensate for the lack of strength due to concrete, but the web cannot be made too thin because the compressive failure of the concrete precedes. . Therefore, it is basically impossible to construct a web with concrete panels. When a concrete panel having a pretension structure is used, the anchoring of the PC steel depends on the adhesion between the steel and the concrete. However, the length required for anchoring is usually long, which is inefficient.
[0006]
Therefore, an object of the present invention is to solve such a problem and to construct a web for a bridge superstructure by using concrete panels.
[0007]
[Means for Solving the Problems]
The present invention relates to a bridge superstructure in which a web is attached between a lower slab and an upper slab to form a box girder, wherein the web is formed of a prestressed concrete plate in which a PC steel material is tensioned in a vertical direction. wherein the concrete of the concrete plate is a ultra-high strength concrete of 28 days compressive strength 100~180N / mm ^2. The PC concrete plate made by tensioning PC steel is manufactured in a factory or on-site production yard, transported to the erection place, installed at the position corresponding to the web of the box girder, and cast the lower slab and the upper slab in place. By building a box girder.
[0008]
The ultra-high-strength concrete of the PC concrete plate used for the web has a self-shrinkage at a material age of 60 days of 400 μm or less per m. Such ultra-high-strength concrete includes water, cement-containing binders, fine aggregates, coarse aggregates having a maximum dimension of 20 mm or less, water reducing agents in accordance with JIS A 6204 “Chemical admixture for concrete”, AE water reducing agents or high-performance The AE water reducing agent is produced by mixing with a water cement ratio of 15 to 25%, a coarse aggregate amount of 200 to 400 L / m ³ , and an air amount of less than 3%. As a part of the coarse aggregate, an artificial aggregate having a water absorption of 5 to 20%, a crushing load of 1,000 to 2,000 N, and a specific gravity of 1.4 to 2.0 is used. (2) The expanding material is 10 to 30 kg / m ³ , or (3) a shrinkage reducing agent in an amount of 1 to 4% by weight of the binder including cement.
[0009]
Embodiment
FIG. 1 shows an example of a bridge superstructure according to the present invention. As shown in the figure, this superstructure is to construct a box girder by attaching a web 3 to the side between the lower slab 1 and the upper slab 2, and the lower slab 1 and the upper slab 2 are cast in place. The inner cables 4 are buried in the inside of these floor slabs, and the outer cables 5 are routed appropriately by utilizing the cavities inside the box girders.
[0010]
In the present invention, a prestressed concrete plate 7 (referred to as a PC concrete plate) in which a PC steel material 6 is stretched in a vertical direction is used as a material forming the web 3 in such a box girder. As the concrete of the PC concrete plate 7, an ultra-high-strength concrete 8 having a small amount of self-shrinkage is used. The PC concrete plate 7 itself is manufactured in a factory or a production yard. This is carried into the erection place, installed at a predetermined position, and the lower deck 1 and the upper deck 2 are cast in place.
[0011]
Ultrahigh strength concrete 8 for use in the manufacture of PC concrete plate 7 is of a 28 day compressive strength 100~180N / mm ² level, below 400μm per autogenous shrinkage amount 1m at 60 days the age, preferably 300μm or less belongs to.
[0012]
Hereinafter, this ultra-high strength concrete will be described. For self-shrinkage of obtaining an ultra-high strength concrete showing a less and 100~180N / mm ² class compressive strength, in the present invention include water, binder containing cement (Portland cement or pozzolanic admixture Mixed cement, specially treated silica fume, etc.), fine aggregate, coarse aggregate having a maximum dimension of 20 mm or less, water reducing agent according to JIS A 6204 "Chemical admixture for concrete", AE water reducing agent or high-performance AE water reducing agent at least one, water-cement ratio 15-25%, coarse aggregate amount 200~400L / ^{m 3} and air content of less than 3%, for a base of formulation, under this basic formulation, the following means is adopted for I do.
(1) As a part of the coarse aggregate, an artificial aggregate having a water absorption of 5 to 20%, a crushing load of 1,000 to 2,000 N, and a specific gravity of absolutely dry of 1.4 to 2.0 is used.
(2) 10 to ³⁰ kg / m ^{3 of an} expanding material is blended.
(3) The shrinkage reducing agent is blended in an amount of 1 to 4% by weight of the unit cement amount (the binder containing cement).
[0013]
The artificial aggregate having the physical properties as described in the above (1) is made of, for example, coal ash and shale, and a powdered material thereof is weighed at a predetermined ratio, for example, coal ash: shale = 5: 5 to 7: 3. The mixture can be obtained by mixing at a ratio, granulating by adding water or a binder, firing the granulated product at a high temperature (1100 ° C. or higher), and appropriately adjusting the firing conditions and the cooling process from the firing temperature. it can. The obtained fired product can be separated into fine aggregate and coarse aggregate by crushing and classifying it. The coarse aggregate is used as a part of the coarse aggregate for obtaining the ultra-high-strength concrete of the present invention with a maximum particle size of 15 mm or less.
[0014]
The self-shrinkage of concrete is caused by the progress of the hydration reaction of cement inside the concrete, which consumes water in the pores and moves the water surface to the pores with smaller pores, thereby causing capillary tension due to the surface tension of water. Is described as a phenomenon caused by the increase. This is due to the so-called “self-drying”. This is particularly noticeable in high-strength concrete with a low water-cement ratio. When the structure is densified using silica fume or the like, the capillary tension further increases, and the amount of shrinkage also increases. When water-absorbed artificial aggregate having the physical properties as described in (1) is used, the effect of reducing this self-drying is achieved. In other words, the artificial aggregate functions as a “reservoir” in the concrete, compensates for the water consumed by the hydration reaction, and exerts a “self-curing effect” to reduce drying in the pore space, thereby achieving a self-curing effect. Shrinkage and drying shrinkage can be reduced.
[0015]
A typical example of the production of artificial aggregate having the above physical properties (1) is as follows: Coal ash coarse powder (a), which is a by-product of a thermal power plant having the following chemical components, and shale having the following chemical components. The powder (b) is mixed at a weight ratio of (a) :( b) of approximately 6: 4, a binder is added, and the mixture is granulated. The mixture is fired at about 1100 to 1200 ° C. in a rotary kiln. Then, in the cooling process, it is rapidly cooled from approximately 100 to 200 ° C. into water. The obtained fired product can be roughly crushed and classified to be separated into a fine aggregate of 5 mm or less and a coarse aggregate of 5 to 15 mm.
(A) Chemical component value (mass%) of coal ash = SiO ₂ : about 54%, Al ₂ O ₃ : about 29%, Fe ₂ O ₃ + FeO: about 4.5%, CaO: about 3.5%, MgO: about 1.0%, ignition loss: about 4.7%
(B) Chemical component value (mass%) of shale = SiO ₂ : about 70%, Al ₂ O ₃ : about 13%, Fe ₂ O ₃ + FeO: about 4.2%, CaO: about 1.6%, MgO : About 1.6%, ignition loss: about 5.6%
[0016]
The thus obtained coarse aggregate having a size of 5 to 15 mm has an absolute dry specific gravity of 1.52, a hot water absorption of 15%, and a crushing load of 1130 N according to JIS Z8841. Here, the hot water absorption refers to a value obtained by measuring the water absorption in a process of firing the artificial aggregate from 100 to 200 ° C., and then at room temperature and in a surface dry state. In this product, the pore volume is almost uniformly distributed in the pore radius of 50 to 6000 nm, and the cumulative pore volume (total pore volume) reaches about 110 m ³ / g. This contributes to high strength while having a low specific gravity, and effectively acts to enhance water retention performance. According to the same principle, by selecting the raw materials and properly controlling the firing conditions, the crushing load according to JIS Z8841 is in the range of 1000 to 2000 N, the specific gravity in the absolute dryness is in the range of 1.4 to 2.0, and the water absorption is An artificial aggregate in the range of 5 to 20% can be manufactured, and by using this artificial aggregate, an ultra-high-strength concrete with a small amount of self-shrinkage can be manufactured.
[0017]
If the crushing load of the artificial aggregate is less than 1000 N, concrete strength of 100 N / mm ² or more cannot be obtained. Conversely, if the crush load exceeds 2000 N, a sufficient amount of pores cannot be secured, and the water absorption rate decreases. Therefore, it cannot contribute to the reduction of the amount of self-shrinkage. Therefore, the crushing load of the artificial aggregate used in the present invention is 1000 to 2000N, preferably 1200 to 1800N. If the specific gravity of the artificial aggregate is less than 1.4, it is difficult to secure a crushing load of 1000 N or more, and if the specific gravity exceeds 2.0, it becomes difficult to secure a sufficient water absorption. The absolute specific gravity of the artificial aggregate used in the present invention is 1.4 to 2.0, preferably 1.50 to 1.70. If the water absorption is less than 5%, the effect of improving concrete shrinkage and drying shrinkage is not sufficiently exhibited. If it exceeds 20%, it is difficult to secure a crushing strength of 1000N or more at a specific gravity of 2.0 or less. The artificial aggregate used in the present invention preferably has a water absorption of 5 to 20%.
[0018]
Such an artificial aggregate is used as a part of the aggregate for concrete, for example, as 5 to 30% by weight of the total coarse aggregate, the water cement ratio is 15 to 25%, and the total coarse aggregate amount is 200 to 400 L. / M ³ , air content is less than 3%, and concrete is mixed with at least one of a water reducing agent according to JIS A 6204, an AE water reducing agent or a high-performance AE water reducing agent as a chemical admixture. As a result, a low-shrink ultrahigh-strength concrete having a compressive strength of 100 to 150 N / mm ² and a self-shrinkage of 400 μm or less per m can be obtained.
[0019]
Since this concrete has a small amount of self-shrinkage, loss of prestress can be reduced. Therefore, it is possible to obtain a PC concrete plate with extremely high strength and high crack resistance. By constructing the web using this PC concrete plate, it is possible to increase the reinforcing steel material and reduce the web thickness. Thus, a box girder structure that is more excellent in workability and economy than before can be realized.
[0020]
Next, the case where the self-shrinkage rate of the ultra-high-strength concrete is reduced by blending the expanding material of the above (2) will be described.
[0021]
The expansive material reacts with water to form needle-like crystals called ettringite, which form a coarser structure than ordinary cement reaction products. It expands. In the present invention, the expansion effect of the expanding material compensates for the amount of self-shrinkage of the ultra-high-strength concrete, and the basic composition of the ultra-high-strength concrete, that is, the binder containing water and cement (Portland cement or Pozzolan) Mixed cement containing special admixtures, specially treated silica fume, etc.), fine aggregate, coarse aggregate having a maximum dimension of 20 mm or less, water reducing agent according to JIS A 6204 “Chemical admixture for concrete”, AE water reducing agent or When kneading at least one of the high-performance AE water reducing agents with a water-cement ratio of 15 to 25%, a coarse aggregate amount of 200 to 400 L / m ³ , and an air amount of less than 3%, a commercially available expanding agent is used. by adding in an amount of 10 to 30 kg / ^{m 3,} the ultra-high strength concrete 400μm per 1m autogenous shrinkage of less, preferably It was found that it is possible to 50μm or less.
[0022]
Examples of commercially available expanding materials include Power CSA and Power CSA type R (trade names) manufactured by Denka Corporation.
[0023]
The case of reducing the self-shrinkage of ultra-high-strength concrete by blending the shrinkage reducing agent of the above (3) will be described. The shrinkage reducing agent has the effect of reducing the surface tension of water in the pores, which is the cause of shrinkage. The effect of reducing self-shrinkage and drying shrinkage is exhibited by reducing the capillary tension. In the present invention, the basic composition of the above-mentioned ultra-high-strength concrete, that is, a binder containing water and cement (including cement mixed with Portland cement or a pozzolan-based admixture, silica fume specially treated, etc.), fine bone Wood, coarse aggregate having a maximum dimension of 20 mm or less, at least one of a water reducing agent according to JIS A 6204 “Chemical admixture for concrete”, an AE water reducing agent or a high-performance AE water reducing agent, with a water cement ratio of 15 to 25% and coarse bone When kneading under a material volume of 200 to 400 L / m ³ and an air volume of less than 3%, a commercially available shrinkage reducing agent is blended in an amount of 1 to 4% by weight of a cement-containing binder to achieve this ultra high content. It has been found that the amount of self-shrinkage of the high-strength concrete can be reduced to 400 μm or less, preferably 350 μm or less per 1 m.
[0024]
As a commercially available shrinkage reducing agent, for example, Tetra Guard AS21 (trade name, manufactured by Taiheiyo Materials Corporation) can be used.
[0025]
In this manner, by adding an appropriate amount of the expanding material or the shrinkage reducing agent, the self-shrinkage amount is small and the loss of prestress can be reduced as in the case of (1). Therefore, it is possible to obtain a PC concrete plate with extremely high strength and high crack resistance. By constructing a web using this PC concrete plate, it is possible to increase the reinforcing steel material and reduce the web thickness. Thus, a box girder structure that is more excellent in workability and economy than before can be realized.
[0026]
The use of the high-strength artificial aggregate having a water absorption of 5 to 20% and the blending of the expanding agent or the shrinkage reducing agent may be applied alone or in combination.
[0027]
As the binder used for the ultra-high strength concrete of the present invention, besides Portland cement, the following binders such as silica fume, fly ash, coal gasification fly ash, blast furnace slag fine powder and the like can be used.
[0028]
The chemical admixture (at least one of a water reducing agent according to JIS A 6204, an AE water reducing agent or a high-performance AE water reducing agent) used in the ultra-high strength concrete of the present invention includes polycarboxylic acid type, polyether type, naphthalene type and melamine. Sulfonic acids, aminosulfonic acids and the like can be used, but polycarboxylic acids and polyethers are particularly preferred. In addition, an antifoaming agent can be used as an auxiliary.
[0029]
【The invention's effect】
As described above, according to the present invention, since the ultrahigh-strength PC concrete plate is used as the web of the box girder, the construction of the box girder is facilitated and the cost is reduced. Therefore, it is possible to exhibit practical effects that have not been achieved in the past in terms of both workability and economical efficiency of the bridge superstructure.
[Brief description of the drawings]
FIG. 1 is a partially cutaway perspective view showing an example of a box girder of a bridge superstructure according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Lower slab 2 Upper slab 3 Web 4 Inner cable 5 Outer cable 6 PC steel material 7 PC concrete board 8 Ultra high strength concrete

Claims (5)

In a bridge superstructure in which a web is attached between a lower slab and an upper slab to form a box girder, the web is composed of a prestressed concrete plate formed by tensioning a PC steel material in a vertical direction, and the concrete of the prestressed concrete plate is bridge superstructure, characterized in that but an ultra high strength concrete of 28 days compressive strength 100~180N / mm ^2. The bridge superstructure according to claim 1, wherein the ultra-high-strength concrete has a self-shrinkage at a material age of 60 days of 400 µm or less per m. Ultra-high-strength concrete includes water, cement-containing binders, fine aggregates, coarse aggregates having a maximum dimension of 20 mm or less, and water reducing agents in accordance with JIS A 6204 "Chemical admixture for concrete", AE water reducing agents or high-performance AE water reducing agents. At least one of the above is kneaded with a water cement ratio of 15 to 25%, a coarse aggregate amount of 200 to 400 L / m ³ , and an air amount of less than 3%. The bridge upper part according to claim 1 or 2, wherein artificial aggregate having a water absorption of 5 to 20%, a crushing load of 1000 to 2000 N, and a specific gravity of 1.4 to 2.0 is used as a part of the aggregate. Construction. Ultra-high-strength concrete includes water, cement-containing binders, fine aggregates, coarse aggregates having a maximum dimension of 20 mm or less, and water reducing agents in accordance with JIS A 6204 "Chemical admixture for concrete", AE water reducing agents or high-performance AE water reducing agents. At least one of the following is mixed under a water cement ratio of 15 to 25%, a coarse aggregate amount of 200 to 400 L / m ³ , and an air amount of less than 3%. The bridge superstructure according to claim 1 or 2, wherein 10 to ³⁰ kg / m3 is blended. Ultra-high-strength concrete includes water, cement-containing binders, fine aggregates, coarse aggregates having a maximum dimension of 20 mm or less, and water reducing agents in accordance with JIS A 6204 "Chemical admixture for concrete", AE water reducing agents or high-performance AE water reducing agents. At least one of the following is kneaded under a water-cement ratio of 15 to 25%, a coarse aggregate amount of 200 to 400 L / m ³ , and an air amount of less than 3%, thereby further reducing shrinkage. The bridge superstructure according to claim 1 or 2, wherein the agent is mixed with 1 to 4% by weight of the binder including cement.

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