JPH0336085B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of constructing a concrete structure, and more particularly to a method of applying compressive stress to a concrete wall or the like in advance to prevent cracks. Generally, in a structure made of reinforced concrete, after the concrete hardens, tensile stress is generated at various locations due to drying shrinkage, and cracks occur over time due to this tensile stress. These cracks not only damage the appearance of the structure but also accelerate the deterioration of the structure.
FIG. 1 shows a wall 2 of reinforced concrete structure provided with an opening 1. In such a case,
Cracks tend to form at the corners of the opening. Therefore, conventionally,
When constructing such a wall body 2, reinforcing bars 3 other than wall reinforcements were arranged around one opening of the wall body 2 to disperse shrinkage strain and prevent the occurrence of cracks. However, this conventional method is not sufficiently effective.
As a result, cracks often occur at the corners of the opening, and some kind of improvement has been desired. The present invention provides an unbonded steel material equipped with a bearing plate in a bottomed cylinder filled with an expanding agent, which is placed in a concrete pouring space, and while concrete is poured in the concrete pouring space, the expanding agent is removed. This method solves the above-mentioned conventional problems by elongating the unbonded steel material by expansion and creating compressive stress in the poured concrete due to the reaction force.
The object of the present invention is to provide a method for constructing a concrete structure that can prevent such cracks. Hereinafter, the method of the present invention will be explained in detail based on the drawings. Figures 2 and 3 show an example of a concrete structure constructed using the method of the present invention.
A wall 12 with an opening 11 is constructed.
When constructing such a wall 12, a formwork is constructed according to the position and shape of the wall 12 to be constructed to form a concrete pouring space S, and the space S
Concrete is poured with predetermined wall reinforcements arranged inside the wall. In the method of the present invention, when placing wall reinforcements, a pair of bottomed cylinders 14 equipped with unbonded steel members 13 are placed inside the concrete. is arranged at the corner of the opening 11 of the casting space S, with the cylinder body 14 filled with an expanding agent 15 and a bearing plate 16 for sealing the expanding agent 15 attached to the unbonded steel material 13. do. Here, the pair of bottomed cylinders 14 are formed into a cylindrical shape that is slightly tapered as it approaches the bottom, and a through hole h of a required diameter is formed approximately in the center of the bottom. They are perforated and arranged so that their bottoms face each other with an appropriate distance between them. The expansion agent 15 is made of a chemical substance that expands in volume due to hydration reaction, such as calcium oxide or magnesium oxide, and is mixed into sand containing an appropriate amount of water in order to control the amount of expansion and replenish moisture. At least it is used. As the above-mentioned swelling agent 15, the following chemical substances are well known and are in practical use. Calcium sulfoaluminate clinker In this chemical substance, watertight ettringite is produced by the hydration reaction of the following formula. 9CaO・3Al ₂ O ₃・CaSO ₄ +8CaSO ₄ +96H ₂ O → 3 (3CaO・Al ₂ O ₃・3CaSO ₄・32H ₂ O) (ettringite) This ettringite expands due to a hydration reaction. Mixture of calcium oxide and alumina white This chemical substance also produces watertight ettringite through the hydration reaction of the following formula. 6CaO+Al ₂ O ₃ +3SO ₃ +32H ₂ O →3CaO・Al ₂ O ₃・3CaSO ₄・32H ₂ O (ettringite) Similarly to the above, this ettringite expands due to the hydration reaction. Calcium oxide Calcium oxide is produced by the following hydration reaction:
Watertight calcium hydroxide is produced. CaO + _{H 2} O → Ca (CH) Calcium dioxide undergoes a rapid hydration reaction and simultaneously generates strong heat, so usually magnesium oxide (MgO) is mixed with calcium oxide to delay the reaction. . In this chemical substance as well, the calcium hydroxide expands due to the hydration reaction, as described above and in the same manner as above. Here, the amount of expansion can be optimally set by adjusting the mixing ratio of the above-mentioned chemical substances and the sand or the water content of the sand. The mixing amount of the above chemical substances is 20 to 40 kg/m ³ of sand, depending on the packing density.
is a reasonable amount. In addition, as in the case of calcium oxide described above, when calcium oxide is used in combination with multiple chemicals with different hydration reaction rates, such as magnesium oxide, the optimum mixing ratio of each chemical can be adjusted. The expansion rate can be adjusted. Furthermore, the bearing pressure plate 16 is arranged so that each bottomed cylinder 1
The expansion agent 15 is attached to the upper side of each of the cylinders 14 to seal the expansion agent 15 in the bottomed cylinder 14, and they are connected to each other by an unbonded steel material 13 inserted into the through hole h of the bottomed cylinder 14. A backup material 17 is provided. When concrete is placed in the concrete placement space S, the placed concrete begins to harden, but at this time, the expansion agent 15 expands at a predetermined rate due to the chemical substance therein causing a hydration reaction. do. Due to this expansion, the bearing plates 16 move away from each other and the unbonded steel material 13 expands, while the unbonded steel material 13
6, a reaction force is generated at the bottom of the cylinder 14, a compressive stress σc is generated in the hardened poured concrete, and cracks around the opening 11 are prevented. This compressive stress σc has an average cross-sectional area of the wall 12.
Ac, the Young's modulus of the wall 12 is Ec, the cross-sectional area of the unbonded steel material 13 is As, the Young's modulus of the unbonded steel material 13 is Es, the length of the unbonded steel material 13 is l,
Furthermore, when the sum of the shrinkage of the wall body 12 and the elongation of the unbonded steel material 13 is Δl, it is expressed by the following equation. σc=Δl/l・1/(1/AcEc+1/AsEs)Ac Also, here Ad=450cm ² , l=50cm, Δl=0.1
cm, and using steel rods of three different diameters as the unbonded steel material 13, the compressive stress σc is calculated for each case as shown in the following table.

[Table] Next, the results of an analysis conducted by the present inventors in order to demonstrate the safety of a concrete wall mixed with expansion agent 15 will be explained. Here, the unbonded steel material 13 and the bottomed cylinder 1
4, an expanding agent 15, and a bearing pressure plate 16 were analyzed assuming that the device C was disposed at a corner of the opening 11 of the casting space S. Concrete compressive strength is allowed to be 1/3 of the fracture strength under long-term loads. From this, if the concrete fracture strength is set as Fc = 210Kg/cm ² , the concrete compressive strength will be fc = 70Kg/cm ² . The cross section of concrete compressed by device C is
Assuming that Ac=12×12=144cm ² , the amount of shrinkage of concrete is Δlc, the Young's modulus of concrete is Ec, and the length of device C is lcm, then due to the relationship σc=Ec×Δlc/lc, Δlc=σc/Ecl= 70/2.1×10 ⁵ l = 3.3×10 ^-4 ×l. When the diameter of the unbonded steel material 13 is 22 mm, the cross-sectional area of the unbonded steel material 13 is As = 3.8 cm, and the Young's modulus is Es, so the compressive stress σs of the unbonded steel material 13 is σs = Ac・fc/As = 144× 70/3.8 = 2653Kg/cm. Therefore, the amount of elongation Δls of the unbonded steel material 13 is as follows: Δls=σs/Esl=2653/2.1×10 ⁶ l=12.6×10 ⁻⁴ ×l. From this, the maximum value of the total amount of elongation Δle of the expansion agent 15 at both ends can be determined by the following equation. Δle=Δls+Δls=(3.3+12.6)10 ^-4 l =15.9×10 ^-4 l Therefore, the total amount of elongation Δle of the expanding agent 15 at both ends should be Δle≦Δlc+Δls=15.9×10 ^-4 l By determining each condition, the concrete wall mixed with the expansion agent 15 can apply compressive stress to the poured concrete without destroying the concrete wall. By the way, in the above, unbonded steel material 13
is constructed so that its both ends are pulled by the expansion of the expansion agent 15, but the same effect can be achieved by fixing one end of the unbonded steel material 13 to a required fixed part and pulling only the other end. . In addition, unbonded steel 13, expansion agent 15, etc. were placed before concrete was poured, but unbonded steel 13, expansion agent 15, etc. were placed in one piece before concrete was poured and the concrete had not hardened. It is also possible to push in the set item later. As described above, according to the method of the present invention, the unbonded steel material is elongated as the poured concrete hardens, and as a result, compressive stress can be applied to the poured concrete in advance, so that the concrete does not shrink during drying. It is also possible to construct concrete structures that do not cause cracks. In addition, since the expansion amount and expansion speed of the expansion agent can be easily adjusted, it is possible to apply compressive stress of the optimum strength to the concrete structure, and it also eliminates the troublesome arrangement of reinforcing bars as in the past. Saves work.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing a conventional reinforcement method around openings in concrete walls, Figures 2 and 3 are for explaining the method of the present invention; A schematic diagram of the constructed wall, and FIG. 3 is an enlarged view of the main part of FIG. 2. 13... Unbonded steel material, 14... Bottomed cylinder,
15... Expansion agent, 16... Bearing plate, σc... Compressive stress.

Claims (1)

[Claims] 1. A bottomed cylindrical body filled with an expanding agent is placed in a concrete casting space, a bearing plate is attached to the bottomed cylindrical body to seal the expanding agent, and an unbonded steel material is provided on the bearing plate, and the concrete is placed in the concrete. Construction of a concrete structure characterized by pouring concrete into a pouring space, and expanding an expanding agent as the poured concrete hardens to elongate unbonded steel and generate compressive stress in the poured concrete. Method.