JP2805582B2 - Manufacturing method of prestressed concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high quality prestressed concrete with good workability.

[0002]

2. Description of the Related Art Among PC construction methods, a post-tension method in which a PC steel wire is passed through a sheath (duct) embedded beforehand after hardening of concrete has been widely used for construction of various on-site buildings.

In this case, grout is injected into the sheath for the purpose of preventing rust of the PC steel wire stretched in the sheath. This grout injection has conventionally been performed in accordance with the specifications of the Japan Society of Civil Engineers. For example, grouting of PC cables and cable stayed bridge diagonal parts, etc., according to the specification, water-cement ratio 40-50%, AE water reducing agent as admixture, aluminum powder as expanding agent (based on cement amount) 0
0.007%) grout material is used.

However, it is difficult to completely suppress the occurrence of bleeding with such a composition. For this reason, a water lens is generated in the sheath, which causes rust of the PC steel wire. In addition, when such grout material is injected into a sheath having residual water, the residual water easily mixes with the grout, so that a defective grout in which the water-cement ratio locally increases is formed. In order to prevent this, the defective portion must be pushed out from the other end of the sheath and discarded, and the amount of grout discarded increases. Further, even if there is no residual water, there is a problem in that the flow loss extruded from the other end of the sheath is generally large in the bleeding generating grout.

In recent years, it has been proposed to inject a grout material that does not cause bleeding when the required quality is high. This means that the water cement ratio is 40-45%
However, an admixture prepared by premixing a cellulose-based thickener and a high-performance water-reducing agent (for example, β-naphthalene sulfonate) is blended to form a grout material that does not cause bleeding.

[0006]

However, a grout material containing a cellulosic thickener and a high-performance water reducing agent has a problem that the viscosity becomes abnormally high and the workability deteriorates.
Further, since a large injection pressure is required, a special grouting device is required, and the grout material itself becomes expensive, so that there is a problem that the cost is greatly increased. The present invention is directed to solving such problems of the prior art.

[0007]

Means for Solving the Problems The present invention is characterized in that when grout is injected into a sheath over which a PC steel material is stretched, grout in which welan gum is blended in an amount of 0.01 to 0.2% by weight per unit water amount is injected. And

[0008] More specifically, the water cement ratio is 25-60%
A grout material comprising a cement paste or cement mortar containing 0.01 to 2.0% by weight of welan gum per unit water and 0.1 to 4.0% by weight of a high-performance water reducing agent or a high-performance AE water reducing agent per unit of cement is added to a PC. The steel material is injected into the stretched sheath. Here, as the welan gum, a dry powder composed of microbial polysaccharides produced by aerobic fermentation of ATTC 31555 cells of Alcaligenes strain is used.

[0009]

When a proper amount of welan gum is mixed with cement paste or cement mortar as a grout material, the bleeding rate can be reduced to 0% without increasing the viscosity significantly. In particular, if welan gum of 0.01 to 2.0% by weight per unit water and 0.1 to 4.0% by weight of high performance water reducing agent or high performance AE water reducing agent based on unit cement amount, the water cement ratio becomes 25 to 60%. A grout material having good fluidity and free from bleeding even when pressure is applied can be obtained.

[Detailed Description of the Invention] Welan gum used in the present invention is, for example, K.K. Clar
Mr. e is CHEMSSPEC USA'88SYMPOSI
APPLICATION OFNOVE submitted to UM
As described in the article entitled LBIOGAMS, a polysaccharide of microbial origin (BIOGAM) produced by subjecting ATCC 31555 cells of Alcaligenes strain to aerobic fermentation under carefully controlled conditions,
Its general structure is shown in Chemical Formula 1.

[0011]

Embedded image

That is, the backbone of this BIOGAM has two D
-Glucose, one D-glucuronic acid and one L
-Consisting of rhamnose, the side chains being composed of one rhamnose or one mannose.

Such welan gum is available as a dry powder product. However, when a very small amount of this welan gum powder is added to a cement grout material, it exhibits remarkable pseudoplasticity, exhibits a suspension stabilizing effect of fine particles, and has a low viscosity. The occurrence of bleeding is completely suppressed without much increase.

When welan gum is added to the grout material, the amount is preferably in the range of 0.01 to 2.0% by weight based on the amount of water. If it is less than 0.01% by weight, a sufficient bleeding preventing effect cannot be obtained. On the other hand, if it is added in excess of 2.0% by weight, the viscosity rises rapidly and the fluidity decreases, and good workability cannot be obtained. The preferred addition range of welan gum is 0.3 to 1.0% by weight based on the amount of water.

[0015] In addition to the addition of welan gum, the incorporation of a dispersant, such as a high performance water reducing agent or a high performance AE water reducing agent, which is commonly used to impart fluidity to concrete mixes, will increase the grout material flow. Properties and filling properties can be improved. Preferred are naphthalenesulfonate, melaminesulfonate, polycarboxylates and aminosulfonates.

The amount of such a high-performance water reducing agent or high-performance AE water reducing agent to be added to the grout material has a proper range depending on the type thereof. If fine powders are also present, the content may be in the range of 0.1 to 4.0% by weight based on the total unit powder amount. If it is less than 0.1% by weight, the effect of imparting fluidity is small, and the fluidity intended in the present invention cannot be secured. The other
Even if added in excess of 4.0% by weight, the effect is saturated and uneconomical.

When grout is injected into the sheath, pressure acts. Therefore, even when bleeding does not occur under non-pressure, bleeding may occur because a phenomenon occurs in which water is forcibly dehydrated during injection.
For example, in a grout material with a water-cement ratio of 30% or less, bleeding can be reduced to zero without adding a thickener, but bleeding occurs when grout is injected, causing the problems described above. . Therefore,
In evaluating the bleeding of the grout material, it is necessary to measure the water retention capacity under pressure. As such a test method, there is a pressure bleeding test method for examining a temporal change in the degree of dehydration under pressure.

Hereinafter, the effects of the grout material of the present invention will be described with reference to examples of the pressure bleeding test.

[0019]

【Example】

[Pressure bleeding test] Test equipment: 200 mm inside diameter with a drain port with a cock at the bottom,
It consists of a cylindrical container with an inner height of 240 mm and a piston with an outer diameter of 199.5 mm for pressing the grout material contained in this container from above.

Test method: Grout material is put into the container up to 3 cm from the top without any bubbles, and pressurized with a piston until the pressure on the top of the sample in the container reaches 35 kgf / cm ² .
With this pressure applied, the cock is opened and the water flowing out of the drain port is received by the measuring cylinder to measure the amount of drainage. The measurement of the drainage is performed at predetermined time intervals. However, if the amount of dewatering becomes 2 c / c or less even if the time for applying pressure in the measurement of each drainage amount exceeds 3 minutes, the pressure is reduced to 50 c / c.
Release pressure after applying to kgf / cm ² .

Test materials: The following three types of grout materials were subjected to the above pressure bleeding test.

"Sample 1" Water cement ratio: 33% Cement: ordinary Portland cement (manufactured by Nippon Cement Co., Ltd.) Water: Tokyo city water High performance water reducing agent (manufactured by Kao Corporation, trade name: Mighty 150: β)
-Naphthalene sulfonate): unit cement amount x 1.5%

"Sample 2" Water-cement ratio: 45% Cement and water: same as sample 1 Commercial admixture of "thickener + high-performance water reducing agent" (Convex, trade name, manufactured by Foseco Japan KK): Unit water volume x 2 .
5% However, the thickener in this commercial admixture is methyl
High performance water reducing agents are melamine sulfonate-based.

"Sample 3" Water cement ratio: 33% Cement and water: same as sample 1 Welan gum: unit water amount × 0.7% High performance water reducing agent (same as sample 1): unit cement amount × 2.0
%

Test Results: FIG. 1 shows the change over time in the amount of wastewater for each sample. From the results shown in FIG. 1, it can be seen that the grout material of Sample 3 has the least amount of drainage and has excellent water retention capacity under pressure.

[0026] For [fluidity test] each sample, was measured in J ₁₄ funnel flow time and bleeding amount. The grout temperature was 21 ° C. The results are as follows.

[0027]

From the above test results, the grout material of Sample 3 according to the present invention has more excellent water retention capacity under pressure and a lower tendency to decrease the fluidity than that of Sample 2 in which the thickener is also blended, and It can be seen that bleeding does not occur even when grout is injected. Therefore, PC steel
Water lens generated when injected into the sheath
And reduce the flow loss
In, it can be produced with good workability and high quality of prestressed concrete.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change over time of a drainage amount when a bleeding material of the present invention is subjected to a pressure bleeding test, in comparison with a comparative example.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C04B 111: 70 (72) Inventor Masayoshi Minami No. 1-29 Kitahama Higashi, Chuo-ku, Osaka-shi, Osaka Sansei Co., Ltd. (72) Invention Person Masato Yoshizaki 1-29 Kitahama-higashi, Chuo-ku, Osaka City, Osaka, Japan (56) References JP-A-3-290564 (JP, A) JP-A-63-315547 (JP, A) US Patent 4342866 (US, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C04B 28/00-28/36 C04B 24/38

Claims (1)

(57) [Claims] When a grout is injected into a sheath in which a PC steel material is stretched, a cement paste or cement mortar having a water / cement ratio of 0.01 to 2.0% by weight relative to a unit water amount is used. A method for producing a prestressed concrete, comprising injecting grout containing a high-performance water reducing agent or a high-performance AE water reducing agent in an amount of 0.1 to 4.0% by weight based on the amount of welan gum and unit cement.