JP2000053476A - Production of chemical prestress member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a member into which large chemical prestress is introduced with little loss in the chemical prestress by kneading a cement compsn. containing a cement and an expanding material to prepare a concrete, forming the obtd. concrete and ageing it in hot water at a specified temp. SOLUTION: A cement compsn. containing a cement preferably of 100 pts.wt. and an expanding material (e.g. hauyne-base, calcium oxide-base material) preferably of 2 to 16 pts.wt. is kneaded to prepare a concrete, which is formed and aged in a hot water at >100 deg.C, preferably at 120 to 200 deg.C, preferably in a vertical pressure chamber. As a result, large expansion strain and compression strength can be obtd. at a lower temp. and in a shorter retention time compared to the process of autoclave ageing. Since hardening of the cement is significantly accelerated, specified compression strength can be obtd. in a short time. Further, specified chemical prestress can be introduced so that the use amt. of the expanding material can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a chemical prestressing member used in the field of civil engineering and construction, and more particularly, to a method of introducing a large amount of chemical prestress,
The present invention relates to a method for manufacturing a high-strength chemical prestress member having a small loss of chemical prestress.

[0002]

2. Description of the Related Art At present, chemical prestress is introduced into members used for fume pipes, box culverts, and the like by incorporating an expandable material in order to improve the bending strength (No. 7). Proceedings of the Annual Conference of Concrete Engineering, 33-36, 1985). However, there was a problem that such chemical prestress was lost due to creep, drying shrinkage, relaxation of reinforcing steel, etc., which occurred in the members with the passage of age (supervised by Shigeyoshi Nagataki, high-performance concrete, published by Gihodo) , 43-46
P. 1997).

[0003] On the other hand, as a method for increasing the initial strength of concrete, autoclave curing (high-temperature, high-pressure steam curing) which is currently used industrially, reduces drying shrinkage after curing is completed, and also reduces creep after curing is completed. Because of the reduction, it was effective for the loss of chemical prestress after curing. However, there has been a problem that most of the chemical pre-stress is lost due to remarkable shrinkage strain of the member during curing and the relaxation of the reinforcing bar at high temperatures (atsushi Nakamura, recent cement and concrete products). , Industry and Products, No. 53, pp. 42-53).

The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems, and as a result, by curing the members by a specific method,
The present invention has been completed by obtaining the knowledge that the above-mentioned problem can be solved and chemical prestress can be introduced.

[0005]

That is, the present invention provides a chemical preform which comprises molding a concrete kneaded with a cement composition containing cement and an expanding material, and curing the mixture in high-temperature water exceeding 100 ° C. This is a method for manufacturing a stress member.

Hereinafter, the present invention will be described in more detail.

In the chemical prestressing member according to the present invention, during curing, the entire member is always in contact with high-temperature water exceeding 100 ° C., and the atmosphere is kept at high temperature and high pressure.

[0008] Here, the high-temperature water is water having a temperature exceeding 100 ° C, preferably from 120 to 200 ° C, more preferably from 140 to 180 ° C. If the temperature is lower than 100 ° C., it may not be possible to obtain a chemical prestressed member with a small loss of chemical prestress.

The high-temperature water used in the present invention can be prepared by placing the water under a high temperature and a high pressure. When a chemical prestress member is manufactured by using the high temperature water, an airtight pressure vessel is required. The material is not particularly limited as long as it is a pressure-resistant container having airtightness, and a pressure cooker or the like used as a conventional autoclave device can also be used.
However, since the pressure vessel such as a pressure cooker that has been usually used as the autoclave device is of a horizontal type,
It is conceivable that high-temperature water flows out when the hatch is opened after curing is completed. For example, it is preferable to fill a vertical pressure vessel with high-temperature water and cure the member in a state where the member is submerged therein.

[0010] The cement composition used in the present invention contains cement and an expanding material. here,
As the cement, various portland cements such as ordinary, low heat, high strength, and super high strength, and various mixed cements obtained by mixing silica, blast furnace slag, or fly ash with these portland cements can be used. It is also possible to use a mixture of Portland cement with silica, blast furnace slag, or fly ash exceeding a mixing ratio determined by JIS or the like.Activated silica such as silica fume or clay mineral such as metakaolin can be used. It is also possible to use a cement mixed with a material or an unfired material.

As the expanding material used in the present invention, an expanding material such as an autoin type or a calcium oxide type can be used. The use amount of the expanding material is preferably 2 to 16 parts by weight, more preferably 4 to 12 parts by weight, based on 100 parts by weight of cement. If the amount is less than 2 parts by weight, the effects of the present invention may not be obtained,
Exceeding 16 parts by weight may cause excessive expansion, leading to expansion failure.

The type and amount of the aggregate used in the present invention are not particularly limited, and those which are generally used in the concrete field can be used. In addition, water is not particularly limited, and water that is generally used in the concrete field can be used.

[0013] These materials are kneaded by a usual method, put into a mold and molded. There is no particular limitation on the pre-setting time (pre-setting time) after the molding of the member until the curing according to the present invention is performed, as long as the chemical pre-stress member can be removed from the mold after the material age. The heating time for heating to high-temperature water is not particularly limited, but is preferably about 1 to 5 hours, more preferably about 3 hours. The time for holding the temperature after reaching the maximum temperature (holding time) is not particularly limited, but is preferably 1 to 8 hours, and 2 to 5 hours.
Time is more preferable. Further, the time for cooling to the room temperature thereafter (cooling time) is not particularly limited as long as the time is sufficient for the chemical prestress member to be cooled to the room temperature.

[0014]

Hereinafter, the present invention will be described in detail with reference to experimental examples.

Experimental Example 1 Water / (cement + expanding material) ratio (W / B) 35%, fine aggregate ratio (S / a) 42%,
Fine aggregate 684kg / m ^3, coarse aggregate 946kg / m ^3, water 173 kg / m ^3, and with a concrete mix of water reducing agent 6.38kg / m ^3, a concrete was prepared, after demolding at 1 day age of The cured product was cured in high-temperature water at 180 ° C. and 10 atm for 5 hours, the length change of the cured product in a restrained state was measured, the chemical prestress was calculated, and the flexural strength and compressive strength were measured. The results are also shown in Table 1.
For comparison, after demolding at a material age of 1 day, autoclave curing at 180 ° C. and 10 atm for 5 hours and after demolding at a material age of 1 day,
Curing was carried out for 48 hours at room temperature in water at 1 ° C. and 1 atm.

<Materials used> Cement: ordinary Portland cement, specific gravity 3.16, Blaine value 3,220 cm ² / g Expanding material a: Calcium oxide type, commercial product, Blaine value 3,
100cm ² / g Expanding material b: Awyn type expanding material, commercial product, Blaine value 2,
950cm ² / g Expanding material c: Awyn-based expanding material, first-class reagent CaCO ₃ , Al ₂
O ₃ , and CaSO ₄ at a CaO / Al ₂ O ₃ molar ratio of 6.5 to 18, CaSO ₄ / Al
_The 2O ₃ molar ratio was blended to be 1.5 to 4 and calcined in an electric furnace at 1,350 ° C. for 1 hour.
Adjusted to 0 ± 200cm ² / g Fine aggregate: weathered granite mountain sand, specific gravity 2.56, water absorption 1.8
7. Coarse grain ratio 2.45 Coarse aggregate: Rhyolite crushed stone, specific gravity 2.67, water absorption 1.20, coarse particle ratio 7.19, maximum aggregate size 20mm Water reducing agent: Polycarboxylic acid polymer surfactant, commercially available

<Measurement method> Length change rate: JIS A 6202-1980 "Concrete expansion material"
In accordance with Reference 1 “Test method for restraining expansion and shrinkage of expansive concrete, Method B”
The length is measured immediately before curing (one day of age) and immediately after the cooling time ends (three days of age), and the difference is defined as the length change, and the length change is measured at the measurement distance of 385 mm. The value obtained by the division was defined as the length change rate. Chemical prestress: σ = εEs (As / Ac) (where σ is the chemical prestress, ε is the strain of the concrete member measured by the length change rate measuring method (= length change rate), and Es is the elastic modulus of the steel material 2.06 × 10 ⁵ N / mm ² , A
s is the cross-sectional area of steel material 1.1 × 10 ² mm ² , and Ac is the cross-sectional area of concrete member 99 × 10 ² mm ² ) Bending strength: JIS A 6202-1980 “Concrete expansion material”
Reference 1 Specimens were prepared in accordance with “Method B for restraint expansion and shrinkage test of expanded concrete”, demolded at the age of 1 day, and then cured, and JIS A 1106 “Bending strength test of concrete” Method, and measure the bending strength at the age of 3 days, and after each curing, cure at a temperature of 20 ° C and a humidity of 50% RH, and measure the bending strength at the age of 28 days. Compressive strength: In accordance with JIS A 1108 "Test Method for Compressive Strength of Concrete"

[0018]

[Table 1]

From the table, it is clear that the use of the method of the present invention introduces a large amount of chemical prestress, improves the bending strength, and expresses the compressive strength in the initial stage.

Experimental Example 2 After completion of the curing shown in Table 2, curing was carried out under the conditions of a temperature of 20 ° C. and a humidity of 50% RH, and the rate of change in length was measured as shown in Table 2 based on a material age of 3 days. Was performed in the same manner as in Experimental Example 1. The results are also shown in Table 2.

[0021]

[Table 2]

As is clear from the table, the expansion strain introduced into the chemical prestress member hardly decreased over a long period of time even under dry shrinkage, which indicates that the loss of the introduced chemical prestress was extremely small. Is shown.

Experimental Example 3 An experiment was performed in the same manner as in Experimental Example 1 except that the expanding material b shown in Table 3 was mixed with 100 parts by weight of cement, and curing was performed in high-temperature water. The results are also shown in Table 3.

[0024]

[Table 3]

As is clear from the table, the expansion strain increases as the amount of the expanding material mixed increases. However, when the mixing amount of the expanding material is too large, the bending strength is reduced.

Experimental Example 4 The same procedure as in Experimental Example 1 was carried out except that the cement and the expanding material shown in Table 4 were used, and cured at the curing temperature and the curing time shown in Table 4, and the length change rate and the compressive strength were measured. went. The results are also shown in Table 4.

[0027]

[Table 4]

From the table, it is clear that by performing high-temperature water curing at a curing temperature exceeding 100 ° C., a larger expansion strain and higher compressive strength can be obtained as compared with the conventional autoclave curing at 180 ° C. and 10 atm. is there. In addition, when the holding time is constant, the curing temperature is preferably from 120 to 200 ° C, and it is clear that the largest expansion strain and compressive strength are obtained at 160 ° C. Further, when the curing temperature is constant, it is apparent that a large expansion strain and a high compressive strength can be obtained when the holding time is 2 to 5 hours.

[0029]

By producing a concrete member using the method of the present invention, the amount of introduced chemical prestress is increased and the loss of chemical prestress is increased as compared with other curing methods using the same composition. Can be obtained. Further, compared with the conventional autoclave curing, a large curing strain and a large compressive strength can be obtained with a lower curing temperature and a shorter holding time. And, since the hardening of the cement is remarkably promoted, a predetermined compressive strength can be obtained in a short period of time. Further, since a predetermined chemical pre-stress can be introduced, it is possible to suppress the amount of use of the expanding material.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 111: 34

Claims (1)

[Claims] 1. A method for producing a chemical prestressing member, comprising molding concrete kneaded with a cement composition containing cement and an expansive material and curing it in high-temperature water exceeding 100 ° C.