JPH0323497B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved underwater concrete admixture composition. Conventionally, when constructing concrete structures on the seabed or riverbed, the mainstream method has been to block off water with sheet piles, etc., and pour concrete in the air. Concrete placed underwater (hereinafter referred to as underwater concrete) is limited to unreinforced concrete, and is only used to a limited extent, mainly for creating the foundations of structures. The reason for this is that the quality of the poured concrete is not reliable and that pollution occurs due to the cement leaking into the water. Conventional underwater concrete construction methods include tremie pipes,
This method uses a concrete pump and a concrete bucket to pour fresh concrete with a relatively rich mix so that it does not come into contact with water as much as possible. When washed, materials separate and cement flows out, resulting in laitance and slabs, reducing the reliability of concrete strength. In recent years, with the progress of underwater civil engineering work, there has been a desire to develop concrete that can be cast underwater without separating cement and aggregate. As a measure to prevent concrete from separating in water, attempts have been made to mix water-soluble polymer materials into concrete to produce concrete that does not separate in water.
It was not necessarily sufficient. For example, synthetic polymers such as polyacrylamide, polyvinyl alcohol, and polyethylene oxide, and nonionic thickeners such as cellulose ethers such as methylcellulose, require extremely high concentrations in order to obtain concrete that does not separate in water. It is necessary to make viscous concrete. For this reason, conventional concrete mixing equipment and concrete transportation equipment lack capacity. Furthermore, during pouring, the concrete is not sufficiently wrapped around the reinforcing bars, causing problems with the adhesion of the reinforcing bars, and polyhydric alcohols such as polyvinyl alcohol, cellulose, and starches tend to delay the setting of cement. There is. Anionic thickeners such as sodium polyacrylate, sodium alginate, and carboxymethylcellulose have anionic groups that combine with calcium ions (Ca ²⁺ ) in cement, causing the cement to coagulate, resulting in extremely poor fluidity. The thickener also produces a set-retarding effect. Cationic water-soluble resins that have secondary or tertiary amino groups or quaternary ammonium groups in their molecules have the effect of suppressing the separation of cement and aggregate and effectively suppressing the outflow of cement components into water. , alone has a strong tendency to reduce concrete strength. As a result of intensive research into cement additives that do not cause separation of underwater concrete and do not reduce its strength, the present inventors have discovered that the combination of a specific cationic water-soluble resin and a specific nonionic water-soluble resin has an excellent effect. We found that the effects of
The invention has been completed. That is, the present invention provides polyethylene oxide and/or
or polyacrylamide and one or more cationic monomers selected from acrylic esters or methacrylic esters having secondary, tertiary amino groups, or quaternary ammonium groups, vinylpyridine or its derivatives, and dialkyldiarylammonium chloride. The present invention relates to an admixture composition for underwater concrete comprising a polymer or copolymer. When concrete prepared using the admixture composition of the present invention is cast in water, there is little cement outflow even at the edge of a beach or at the bottom of a river where the flow is fast, and the concrete is stable in all parts. Concrete strength can be obtained. Therefore, even in concrete construction work that conventionally could not be cast underwater, by using concrete containing the admixture composition of the present invention, it is possible to obtain a concrete structure that satisfies the design strength. Furthermore, by using concrete containing the admixture composition of the present invention, it is possible to cast high-quality concrete with less water contamination even for underwater concrete that has been cast using tremie tubes. Next, each component of the present invention will be described. First, the specific nonionic water-soluble resin used in the admixture composition of the present invention is polyacrylamide and/or polyethylene oxide. Polyacrylamide is obtained by radical polymerization of acrylamide, and has a weight average molecular weight of
Very high molecular weight polymers of 5 million to 20 million are preferably used. As the polymerization method, any commonly used aqueous solution polymerization method, reverse layer emulsion polymerization method, etc. can be used. Polyethylene oxide is produced by ionic polymerization of ethylene oxide, and those having a weight average molecular weight of 400,000 to 4,000,000 are preferably used.
As the nonionic resin, polyacrylamide and polyethylene oxide can be used alone or in combination. The cationic water-soluble resin is produced by homopolymerization of a cationic monomer or copolymerization of a cationic monomer and a monomer copolymerizable therewith, and in the present invention, the general formula: R ₁ : Hydrogen or methyl group R ₂ : Divalent organic group R ₃ : Hydrogen, alkyl group or aralkyl group R ₄ : Hydrogen, secondary or tertiary amino group represented by an alkyl group or aralkyl group, or quaternary One or more cationic monomers selected from acrylic esters or methacrylic esters having an ammonium group (hereinafter, acrylic and methacrylic are collectively referred to as (meth)acrylic), vinylpyridine or its derivatives, and dialkyldiarylammonium chloride. Polymers or copolymers of are used. Among these, polymers or copolymers of (meth)acrylic esters having a quaternary ammonium group are preferred, and polymers or copolymers of aminoethyl (meth)acrylic esters having a benzyl group are more preferred. suitable. By using these polymers or copolymers, good water clarity can be obtained with a small amount of addition, and the influence on the reduction in compressive strength during in-air casting can be reduced. Specific examples of the aminoethyl (meth)acrylic ester having a benzyl group include acid salts of benzyldimethylaminoethyl methacrylic ester and dibenzylmethylaminoethyl methacrylic ester. As examples of monomers copolymerizable with cationic monomers, hydrophilic vinyl monomers such as acrylamide, (meth)acrylic acid esters, and vinyl acetate are preferably used, and acrylamide is particularly preferably used, and has a weight average molecular weight of Used as a copolymer of 1 million to 10 million. The copolymerization ratio of the cationic monomer is 1 to 100 mol%, preferably 20 to 80 mol%. If the proportion of the cationic monomer is small, the effect of preventing separation of underwater concrete will be insufficient. The cationic water-soluble resin can be produced by known methods such as aqueous solution polymerization, emulsion polymerization, suspension polymerization, and precipitation polymerization. In the case of aqueous solution polymerization, an aqueous solution with a monomer concentration of usually 10 to 90% by weight is prepared, and after replacing the oxygen in the system with an inert gas, a normal polymerization catalyst is added, and the polymerization is carried out at about 10 to 80°C. A copolymer can be easily obtained by polymerization. The proportion of the nonionic water-soluble resin, polyacrylamide and/or polyethylene oxide, and the cationic water-soluble resin in the composition of the present invention is based on the total amount of the nonionic water-soluble resin and the cationic water-soluble resin. 10 cationic water-soluble resins
~90% by weight is preferred, and 30-70% by weight is more preferred. When the proportion of cationic water-soluble resin is less than 10% by weight, the effect of preventing separation of cement and aggregate tends to decrease, and when it exceeds 90% by weight, concrete strength tends to decrease. The amount of the admixture composition of the present invention to be added to cement is such that the total amount of water-soluble resin is 0.05 to 0.05 to
2% by weight, preferably 0.2-0.6% by weight. If the amount added is less than 0.05% by weight, the effect of preventing separation between cement and aggregate will be insufficient, and if it exceeds 2% by weight, workability will decrease. The admixture composition of the present invention can be used by adding it to fresh concrete sequentially or simultaneously, mixing it with cement and aggregate, or dissolving it in concrete mixing water. The method of dissolving in kneading water is preferred in order to obtain uniform mixing. As the concrete in which the admixture composition of the present invention is used, concrete formulations commonly used in civil engineering and construction can be used. All conventional methods can be used to place concrete using the admixture composition of the present invention in water. Furthermore, since concrete using the admixture composition of the present invention has less bleed, it can be applied to concrete cast in the air, and is suitable for areas where less bleed is required, such as structures with a high density of reinforcing bars. used. In addition, an ordinary cement admixture can be used in combination with the underwater concrete using the admixture composition of the present invention as long as the physical properties of the concrete are not deteriorated. Examples of common cement admixtures include pozzolanic substances such as fly ash, pulverized blast furnace slag, siliceous mixtures, various water reducing agents, rapid setting agents, retarders, foaming agents, antifoaming agents, AE agents, etc. . The underwater concrete admixture composition of the present invention is
When used as underwater concrete, there is less cement runoff and sufficient concrete strength is obtained, making it possible to cast concrete even on the shoreline of a coast or at the bottom of a river with fast currents, where it was previously difficult to cast underwater. It is possible to set up a large amount of water, and there is very little water contamination. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. In addition, parts and % in each example
All represent weight parts and weight %, and the test method was in accordance with the following method. A Test method for evaluating the performance of underwater pouring (1) Water contamination One end of a transparent PVC pipe with an inner diameter of 75 mmφ and a length of 500 mm was capped and filled with water to a length of 400 mm. 400 ml of mortar paste prepared by adding the admixture composition of the present invention and kneading was added from the top, and the clarity of the water after 5 minutes was visually observed and judged. (2) Compressive strength The above specimen was left in a room at 20°C for 28 days with the water remaining on the top, and then demolded. Next, the upper 40 mm and lower 40 mm were each cut into squares of 40 x 40 x 40 mm, and the compressive strength was measured. Compressive strength was measured in accordance with JIS R-5201 (cement physical testing method). B Performance evaluation test method for aerial pouring (1) Setting test Setting time of the above mortar paste JIS R
Measured using the Vicat needle method in accordance with -5201. (2) Compressive strength The compressive strength of the concrete mixes adjusted in each example was measured in accordance with JIS A-1108. The curing conditions for the test specimen are as follows. <Concrete curing conditions> After 2 days of wet curing, the concrete was removed from the mold and cured in water at 20°C. C Weight average molecular weight (w) of water-soluble resin Calculated from the intrinsic viscosity using the following formula. However, [μ] is the intrinsic viscosity (dl/g) in 1N NaNO ₃ at 30°C. Example 1 As monomers, 20 parts of acrylamide, 80 parts of benzyldimethylaminoethyl methacrylate hydrochloride,
A cationic water-soluble resin with a nonvolatile content of 50% is produced by a conventional aqueous solution polymerization process at an initial temperature of 20°C using 100 parts of ion-exchanged water, 0.1 part of azobisisobutyronitrile, and 0.1 part of sodium bisulfite as catalysts. did.
This was dried and pulverized to obtain a cationic water-soluble resin powder with a weight average molecular weight of 2.5 million. Next, 0.25 part of the above cationic water-soluble resin and 0.25 part of polyethylene oxide having a weight average molecular weight of 1.6 million were dissolved in 99.5 parts of water to obtain a 0.5% mixed aqueous solution.
The viscosity of this aqueous solution was 690 cps (20°C). Mortar and concrete were prepared using this aqueous solution as mixing water. The formulation of the Γ mortar paste is as follows. Cement/Toyoura standard sand = 100/200 Water/cement ratio = 60%, flow value 160mm Resin/cement ratio = 0.3% The composition of Γ fresh concrete is as follows. Cement/river sand/crushed stone = 100/200/400 Water/cement ratio = 63.5%, slump = 8 cm Resin/cement ratio = 0.32% Ordinary Portland cement (trade name Asano Cement, manufactured by Nippon Cement Co., Ltd.) was used as cement. Kinokawa sand was used as the river sand, and Takarazuka crushed stone was used as the crushed stone. Various performance evaluation tests were conducted using this mortar paste and fresh concrete. The results are shown in Table 1, and the clarity of water, compressive strength,
All the coagulation tests were good. Examples 2 to 4 Various performance evaluation tests were conducted in the same manner as in Example 1 using the formulations shown in Table 1. The results are shown in Table 1, and the cleanliness, compressive strength, and coagulation test of the clean water were all good. Comparative Examples 1 to 8 Various performance evaluation tests were conducted in the same manner as in Example 1 using the formulations shown in Table 2. The results are shown in Table 2, and all were significantly inferior to the Examples. That is, Comparative Example 1,
In No. 3 and No. 4, the cement and aggregate separated when placed in water, and as a result, clean water could not be obtained, and the strength was significantly lower than in Examples. In addition, in Comparative Example 2, the strength development was slow, and the 28-day strength was significantly inferior to that of the Examples. Comparative Example 5 had poor physical properties when placed in water, and Comparative Examples 6 and 7 had a significantly increased water/cement ratio in order to obtain the same softness as the Examples, resulting in a decrease in strength. . Furthermore, with the same softness as in the examples, the physical properties during pouring in water were also insufficient. In Comparative Example 8, two types of nonionic resins were used in combination, but no improvement in performance was observed.

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Claims (1)

[Claims] 1 Selected from polyethylene oxide and/or polyacrylamide, acrylic esters or methacrylic esters having a secondary, tertiary amino group, or quaternary ammonium group, vinylpyridine or its derivatives, and dialkyldiarylammonium chloride. An admixture composition for underwater concrete comprising a polymer or copolymer of one or more cationic monomers.