JPS63297254A - Additive for underwater concrete - Google Patents

Abstract

PURPOSE:To obtain the titled additive giving an underwater concrete having excellent separation resistance, preventive effect to water pollution, high fluidity, self-leveling property and strength without retarding the hardening, by using a copolymer of a specific alkoxy (meth)acrylate and one or more other vinyl compounds as a component. CONSTITUTION:A copolymer having an intrinsic viscosity of >=3dl/g (measured in 1N NaOH solution at 30 deg.C) is produced by copolymerizing 1-80mol.% of an alkoxy (meth)acrylate of formula (X is 1-4C alkyl; Y is 2-4C alkoxy; n is 1-5; R is H or CH3) and other vinyl compound selected from (meth) acrylamide, (meth)acrylic acid (methyl ester), (hydroxy)ethyl (meth)acrylate, etc. The copolymer is used singly or an combination with a fluidizing agent such as cellulosic substance or salt of naphthalenesulfonic acid formalin condensation product to obtain the titled additive. Cement is mixed with 0.05-3.0wt.% of the additive.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an underwater concrete admixture for use in constructing concrete structures underwater.

Conventional technology Conventionally, when constructing concrete structures on the ocean floor or on the ocean floor, the main method used has been to dam up water with sheet piles, etc., and then pour concrete in the air. , is limited to unreinforced concrete and is only slightly used for building the foundations of structures.

This is because the quality of concrete placed directly in water is unreliable, and water pollution occurs due to dispersion of cement into water during the placing process.

In other words, the conventional underwater concrete method uses tremie pipes, concrete pumps, concrete packets, etc., and pours fresh concrete with a relatively high mix in a way that minimizes contact with water. No matter how carefully the concrete was constructed, water washed away the concrete, causing separation of the concrete materials, making it difficult to obtain a uniform product with reliable strength.

In recent years, with the progress of underwater civil engineering work, there has been a desire to develop concrete that does not separate cement and aggregate when poured underwater.

Therefore, as a measure to prevent the separation of concrete in water, for example, JP-A-57-123850, JP-A-58-115051, JP-A-58-176157,
No. 1, JP-A-59-26955, JP-A-59-
26956, JP 58-69760, JP 59-107952, JP 5'9-13
Attempts have been made to mix water-soluble polymeric materials into concrete, as disclosed in Japanese Patent Laid-open No. 1548 and Japanese Patent Application Laid-Open No. 59-54656, but satisfactory results have not always been obtained.

For example, polyacrylamide, polyvinyl alcohol,
When using nonionic thickeners such as synthetic polymers such as polyethylene oxide or cellulose ethers such as methylcellulose, it is necessary to prepare extremely viscous concrete in order to obtain concrete that does not separate in water. As a result, conventional concrete mixing and kneading equipment, concrete transportation equipment, etc. lack capacity, which not only causes problems with the equipment, but also causes insufficient entrainment of concrete into the reinforcing bars during pouring, resulting in poor adhesion of the reinforcing bars. A problem arises.

Additionally, polyhydric alcohols such as polyvinyl alcohol, cellulose, and starches tend to retard the setting of cement, and anionic thickeners such as sodium polyacrylate, sodium alginate, and carboxymethylcellulose have anionic groups. It has the drawback of bonding with calcium ions in cement, resulting in agglomeration of cement, inhibiting fluidity, and impairing operability.

Therefore, in order to improve the fluidity of underwater concrete,
Known concrete fluidizers include naphthalene sulfonic acid sodium formalin m compound, melamine sulfonic acid -
Although it is possible to use formalin condensate in combination, it is not possible to obtain good results without reducing the strength of the concrete or delaying setting, as disclosed in Japanese Patent Application Laid-Open No. 1986-1915.
Publication No. 49 proposes the combined use of an acrylamide polymer with a very high molecular weight and an acrylic acid or methacrylic acid polymer with a lower molecular weight than the former as an admixture for underwater concrete.

However, the inseparability and fluidity are still at an unsatisfactory level, resulting in poor filling properties and low compressive strength.

The problem that the invention seeks to solve.

The present invention significantly improves such non-separability and fluidity, and as a result, a concrete structure with high compressive strength, high underwater specimen strength/in-air specimen elongation ratio, and reliable strength. The object of the present invention is to provide an admixture for underwater concrete that enables construction of concrete in water without substantially delaying the setting time.

SUMMARY OF THE INVENTION The present invention achieves its objectives through the use of a special vinyl copolymer. That is, the underwater concrete admixture of the present invention has the general formula % (11 (where X represents an alkyl group having 1 to 4 carbon atoms, Y represents an alkoxyl group having 2 to 4 carbon atoms, and n represents 1 It contains a copolymer of an alkoxy acrylate or methacrylate represented by (representing an integer of ~5, R represents hydrogen or a methyl group) and one or more other vinyl compounds.

The alkoxy acrylate or methacrylate represented by formula (1) in the above copolymer is preferably contained in a proportion of 1 to 80 mol%, and if this content is less than 1 mol%, Separation resistance is poor and water pollution prevention effect is reduced. On the other hand, if it exceeds 80 mol %, the amount of air in the underwater concrete becomes too large, and the water solubility decreases, resulting in a decrease in the water pollution prevention effect, which is undesirable.

□The intrinsic viscosity [η] of the above copolymer is preferably 3 dl/g or more; if it is less than 3 dl/g, a large amount must be added in order to obtain sufficient separation resistance, making it uneconomical. becomes. However, the above-mentioned intrinsic viscosity indicates the numerical value at 30° C. in a normal caustic soda solution.

As the other vinyl compound used in the production of the above copolymer, not only ordinary water-soluble monomers but also water-insoluble monomers can be used as long as the copolymer is present as water-soluble. Commonly useful monomers include:

These include acrylamide, methacrylamide, acrylic acid, methacrylic acid, acrylamide methylpropanesulfonic acid and water-soluble salts thereof, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, hydroxyethyl acrylate, and hydroxyethyl methacrylate.

Incidentally, as a method for producing the copolymer, any ordinary polymerization method of acrylic monomers can be used.

The copolymer thus obtained may be used alone as a concrete admixture, or may be used in combination with other admixtures or additives. For example, the above copolymer can be used in combination with cellulose-based underwater concrete admixtures such as methyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, and hydroxyethyl cellulose. It can also be used in combination with a fluidizing agent such as a condensate salt or lignin sulfonate to increase the fluidity of underwater concrete.

Methods for producing underwater concrete using the admixture of the present invention include premixing the admixture with cement and aggregate in advance, adding kneading water, and mixing these components; A method of adding an admixture to the mixture may also be used, and a conventional concrete mixer or mixer can be used as the kneading machine, but it is preferable to use a forced mixing mixer.

The mixing ratio of the above-mentioned copolymer to the cement can be arbitrarily selected depending on the required water dispersion resistance, but it is preferably about 0.05 to 3.0% by weight, and more preferably about 0.05 to 3.0% by weight based on the cement. It is preferably about 2 to 1.5% by weight. If the proportion of the copolymer added to the cement is less than 0.05% by weight, the viscosity will decrease and the ability to prevent separation in water will be insufficient, while if it exceeds 3.0% by weight, the fluidity will deteriorate due to excessive viscosity. descend.

Example 1 Production of an admixture of the present invention - 0.01 g of ammonium persulfate was added as a polymerization catalyst to a mixed solution consisting of 36.6 g of acrylamide, 19.5 g of methoxyethyl acrylate, and 500 g of ion-exchanged water.
g, 0.01 g of sodium sulfite as a reducing agent was added, and aqueous solution polymerization was carried out to obtain an aqueous solution with a solid content of about 10%. After drying this aqueous solution in vacuum, the solid matter was pulverized to obtain a powder copolymer. The intrinsic viscosity [η] of this product was 11.5.

- Production of underwater concrete - 6.76 kg of cement in a forced mixing concrete mixer
, river sand 13.00 kg, coarse aggregate (maximum dimension 20 mm) 2
4.4 kg (w/c 65%) of pumped water mixed with 0.38 kg and a predetermined amount of an admixture for underwater concrete were added and kneaded for 2 qiao to obtain 20 ml of underwater concrete.

Examples 2 to 8 Example 1 except that the monomer composition was changed as shown in Table 1.
The admixture and underwater concrete of the present invention were produced in the same manner as described above.

Comparative Examples 1 to 5 Underwater concrete was produced in the same manner as in Example 1, except that an admixture having the composition shown in Table 1 was used.

Performance tests were conducted on the concrete obtained in Examples 1 to 8 and Comparative Examples 1 to 5. The results are shown in Table 1.

From this result, Examples 1 to 8 using the admixture of the present invention
In all cases, the slump flow is large at 40 to 44 cm, and the SS value and pH value, which are indicators of water pollution, are low. In Comparative Examples 3 and 4, in which the flow is extremely small and a known acrylic admixture for underwater concrete is used, relatively good fluidity and water pollution prevention properties are obtained, but compared to the product of the present invention, Its effectiveness is inferior. Note that even if the monomer composition is the same as that of the present invention, those with a low intrinsic viscosity [η] have low SS values and pH values when the addition amount is 0.8%, making it difficult to put them into practical use.

Examples 9 to 16 Copolymers were obtained in the same manner as in Example 1 except that the seven-mer composition was changed as shown in Table 2. In Example 9.11.13.15, this copolymer was used directly as an admixture of the present invention, and in Example 10.12.14.16, the copolymer was added with a melamine-fulphonic acid-based fluidizing agent ( Underwater concrete was produced in the same manner as in Example 1 by adding 35% active ingredient) and using it as an admixture of the present invention.

Comparative Example 7~1O Underwater concrete was produced in the same manner as in Example 1 except that the composition of the admixture was changed. In addition, Comparative Examples 8 and 10
In this case, the admixture contains a fluidizing agent.

Table 2 shows the results of performance tests on the concretes of Examples 9 to 16 and Comparative Examples 7 to 10.

These results show that when commercially available methylcellulose was used as an admixture (Comparative Examples 7 and 8), the setting time was significantly delayed, whereas when the admixture of the present invention was used (
In Examples 9 to 16), it can be seen that the delay in setting time is small and concrete with good performance can be obtained in a short time. In contrast, in Comparative Examples 9 and 10, in which acrylamide partial hydrolyzate was used as a mixture, the concrete had poor fluidity. However, due to the lack of filling properties, only products with poor compressive strength were obtained.

Note that the performance tests in Tables 1 and 2 were conducted according to the following method.

Air content Slump test method for slump flow concrete according to JIS A-1123 (JtS A-11
Fill the slump measuring device specified in 01) with underwater concrete in the same manner as measuring the slump of concrete,
After lifting the cone vertically, the diameter of the spread of the underwater concrete 5 minutes later was measured and used as an index of fluidity.

Amount (Underwater Mr. N La-) Pour 800 cc of water into an IQOOcc beaker with an outer diameter of 110+*m and a height of 150 mm, and gently drop 500 g of underwater concrete into 10 equal parts onto the water surface. This drop should be completed within 10 to 20 seconds, then the beaker should be allowed to stand still for 3 minutes, and the water in the beaker should be poured out using a dropper to prevent the concrete from mixing.
Take out 00cc.

This water was immediately subjected to SS (suspended solids) and pH tests.

The pH measurement was carried out three times, and the average value was taken as the pl (value).The measurement was also carried out in accordance with JISK, 0102r factory wastewater test method J14.1 suspended solids.

The compressive strength of the concrete was tested in accordance with JIS A 1108r concrete compressive strength test method. The specimens were prepared according to the procedure shown below, and were subjected to standard curing in water at a temperature of 20±1° C. until the compressive strength test was conducted after demolding. The number of specimens was three for each batch, and the average value was taken as the compressive strength of the specimens prepared in air or underwater at that age.

JI
S A 1132r How to make concrete strength test specimens”.

A cylindrical formwork for rice cultivation Arashi 1 φ 100 100 x H 200 (water depth 50 cm)
Place it in a container designed to keep it at +a,
The container was filled with water so that the water depth to the bottom of the form was 50C1l. The water temperature is 20±1℃.

A cylindrical gold 14 (Iol mesh) with a diameter of 100 au+ and a height of 300 mm is vertically placed on the upper end of the form and set so that the upper end of the wire mesh is in contact with the water surface. Mixed underwater concrete is gently dropped from the water surface through a wire mesh and filled into formwork. The amount of underwater concrete added per formwork was approximately 21 kg, and this was divided into 15 approximately equal amounts. The time required for input is 3 times per formwork.
The duration was 0 seconds or more and 1 minute or less. Make sure that the water depth does not change before and after injection. After completing the pouring of underwater concrete,
The formwork was left in water for 15 minutes, then taken out into the air and lightly tapped with a mallet from two sides of the formwork two to three times on each side in order to promote the replacement of water and concrete within the formwork. After confirming that no water came out from the interface between the inner wall of the formwork and the concrete, the top was leveled.

Subsequent curing, camping, and demolding methods are JIS A.
1132r Concrete Strength Test Specimen Preparation” was followed.

Setting time A mortar is prepared by removing coarse aggregate from the underwater concrete formulation in advance. In addition, it maintains high fluidity of underwater concrete and good self-leveling properties.Furthermore, unlike cellulose-based admixtures, there is little delay in setting of concrete due to addition, and the concrete after hardening is highly effective. There is also little decrease in strength.

Patent applicant Dai-Kogyo Seiyaku Co., Ltd. 1 person from outside the group: Ken Shin Minoru

Claims (4)

[Claims] (1) General formula: XO-(Y)_mOCC(R)=CH_2 (where, An admixture for underwater concrete, characterized in that it contains a copolymer of an alkoxy acrylate or methacrylate represented by the integer , R represents hydrogen or a methyl group, and one or more other vinyl compounds. (2) The underwater concrete admixture according to claim 1, wherein the copolymer has an intrinsic viscosity [η] of 3 dl/g or more as measured in a 1N caustic soda solution at 30°C. (3) The underwater concrete admixture according to claim 1 or 2, wherein the alkoxy acrylate or methacrylate content of the copolymer is 1 to 80 mol%. (4) The above other vinyl compounds include acrylamide, methacrylamide, acrylic acid, methacrylic acid, acrylamide methylpropanesulfonic acid and water-soluble salts thereof, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, hydroxyethyl acrylate and hydroxyethyl The underwater concrete admixture according to any one of claims 1 to 3, which is selected from the group consisting of methacrylates.