JP2003212630A - Cement composition for underwater placing and construction method of underwater mortar or concrete structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cement composition for underwater placing and a method for constructing underwater mortar or concrete structure. <P>SOLUTION: The cement composition for underwater placing is obtained by adding a chloroprene latex being a polymer having a specific gravity larger than that of water in 5-30 wt.% by the effective solid content ratio to cement during the blending of mortar or concrete. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cement composition for underwater casting and a method for constructing underwater mortar or concrete structure.

[0002]

2. Description of the Related Art Conventionally, when constructing an offshore structure or the like, an underwater casting mortar or concrete having a composition different from that of a mortar or concrete used for constructing a land structure is used. That is, the set water / cement ratio of the placed mortar or concrete does not change in land-based aerial construction, but in the underwater construction to the sea or river, the placed mortar or concrete is set. Since seawater and river water permeate into the steel to increase the water / cement ratio, the strength decreases. Also, material separation may occur. On the other hand, for example, JP 2001-2
In 53747, a styrene-butadiene rubber (SBR) resin, an acrylic resin, or the like is attached to the surface of polypropylene (PP) fiber to obtain PP fiber having a specific gravity of 1.01 or more, and the PP fiber is mixed with mortar or concrete, Proposals have been made to improve the strength by placing it in water.

[0003]

However, in the above-mentioned proposal, it is necessary to prepare PP fibers having a specific gravity of 1.01 or more in advance, and after all, fine aggregate (fiber reinforcing material) having a specific gravity larger than that of water is blended. Nothing more than. Therefore, the above-mentioned action of preventing permeation of seawater cannot be achieved. Therefore, the strength improvement of the mortar or concrete was not sufficiently improved by offsetting the strength improvement due to the blending of the fiber reinforcement and the strength decrease due to the permeation of seawater or the like. Material separation was also likely to occur. Further, the SBR resin was re-emulsified by permeation of seawater and the acrylic resin was hydrolyzed, so that the durability was low.

[0004]

The present invention has been proposed in view of the above, and during the mixing of mortar or concrete,
Chloroprene latex, which is a polymer with a higher specific gravity than water, is used in an effective solid content ratio of 5 to 30 wt% with respect to cement.
The present invention relates to a cement composition for underwater casting, which is characterized by being added. Further, although the detailed reason will be described later, it was also found that it is preferable to add 1 to 20 wt% of methyl cellulose to the effective solid content of chloroprene.

Further, the present invention also proposes a method for constructing an underwater mortar or a concrete structure in which the above cement composition is placed in water such as seawater or river water. Further, although the detailed reason will be described later, it was also found that it is preferable to use a cationic or anionic latex as the chloroprene latex and to cast it in water such as seawater in which positive and negative ions coexist.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The cement composition for underwater casting of the present invention is characterized in that a specific amount of chloroprene latex is blended as described above. The composition and raw material of the concrete are not limited in any way. Mortar blended with fine aggregate in cement, concrete blended with coarse aggregate, for example, ordinary Portland cement, early-strength Portland cement, ultra-early-strength Portland cement, etc. as the cement material, silica fume or Ultrafine powder slag, etc. can also be used in combination, various additives such as methyl cellulose, superplasticizer, water reducing agent, various aggregates,
A fiber reinforcing material or the like may be blended.

The chloroprene latex used in the present invention has a polymer specific gravity of 1.2 or more, and various products are provided on the market. Both cation latex and anion latex may be used, and a water reducing agent and a fluidizing agent may be used in combination. In this case, a water reducing agent or a fluidizing agent may be selected according to the type of chloroprene latex selected.

Further, as described above, the amount of chloroprene latex added is 5 to 3 in terms of effective solid content ratio to cement.
It is 0 wt%, and the larger the amount added, the greater the elasticity and flexibility. However, if the amount of chloroprene latex added exceeds 30 wt%, the strength will be low, and if it is less than 5 wt%, it will not be effective and will become cloudy.

When the cement composition for underwater pouring of the present invention having such a composition is put (powdered) into water such as seawater, the placed mortar or concrete is a high-viscosity body and therefore has a small specific gravity. Does not penetrate into the chloroprene latex having a large specific gravity, the increase in water / cement ratio can be suppressed, and the strength reduction can be prevented. Also, material separation can be suppressed.

After the curing, a cross-linking reaction between chloroprene and the metal oxide in the cement occurs to form a three-dimensional matrix to further increase the water resistance, and the mortar or the concrete structure which is hardly affected by the surrounding seawater or the like. Is formed. In addition, since chloroprene imparts viscoelasticity to the mortar or concrete structure after curing,
Impact resistance is improved. Therefore, a mortar or concrete structure having high durability against impact with sand, gravel, and stone is formed. Furthermore, chloroprene improves the chemical resistance of the cured mortar or concrete structure. Therefore, a mortar or concrete structure that is less affected by seawater or hot spring water is formed.

Further, by adding an appropriate amount (1 to 20% by weight, based on the effective solid content of chloroprene) of methylcellulose together with chloroprene latex during the mixing of mortar or concrete, the cohesive force and viscosity of the composition are increased. In addition, the separation of materials (cement and aggregate) can be suppressed, the water quality can be prevented from being polluted, and the strength equivalent to that when land-cast in the air can be obtained. At this time, since the fluidity decreases as the viscosity increases, it is desirable to add a water reducing agent or a fluidizing agent. This is because when the water / cement ratio is increased to improve the fluidity, the strength after hardening is reduced. Addition of a water reducing agent or superplasticizer improves the fluidity by generating micro bubbles in mortar or concrete, and it is possible to obtain a high-strength mortar or hardened concrete without increasing the water / cement ratio. .

As the chloroprene latex described above, a cement composition obtained by kneading a cationic latex having positive ions and an anionic latex having negative ions is used to prepare a cement composition such as seawater in which positive ions and negative ions coexist. When cast in water, a thin film of chloroprene is formed. That is, the cationic latex reacts with negative ions in water, and the anionic latex reacts with positive ions in water, both of which form a chloroprene thin film on the surface of mortar or concrete. This thin film has the effect of preventing the material from separating from the surface of the mortar or concrete and preventing the penetration of seawater or the like into the surface of the mortar or concrete before hardening.

Further, chloroprene latex is impregnated with PP fiber having a lower specific gravity than water to form chloroprene on the surface of the fiber to form a fiber reinforced material having a higher specific gravity. This fiber reinforced material is mixed with mortar or concrete to form chloroprene latex. It may be added together. In this case, the surface of the fiber reinforcement is chloroprene,
Since the integrity with the fiber reinforcing material is increased and the material separation is less likely to occur, a large strength improving effect can be obtained.

[0014]

[Example] 1. As a mortar for compounding experiments of cement compositions, the materials shown in Table 1 were used to conduct a test on land, underwater curing, marine exposure, and chemical resistance.

[Table 1]

2. Mortar strength (underwater casting, underwater curing) 1: 3 mortar (C / S = 1: 3) as a base, and chloroprene latex to cement in an effective solid content ratio of 5 to 30% by weight (P / C = 5 to 30). %), The mortar composition having a water-cement ratio of 40% (W / C = 40%) was measured for compressive strength and bending strength during underwater curing after casting in the sea, and the results are shown in the table. Shown in 2. In addition, for comparison, the test measurement was similarly performed for the sample to which chloroprene latex was not added (P / C = 0%).
The results are also shown in Table 2.

[Table 2]

3. Performance as mixing method (land casting) 1: 2 mortar (C / S = 1: 2) is used as a base, and various polymer admixtures for admixture with cement are used in an effective solid content ratio of 10% by weight (P / C = 10). %) For the mortar composition with a water-cement ratio of 40% (W / C = 40%), flexural strength, compressive strength, adhesive strength, water absorption after land casting according to JIS-A-6203. Water permeability,
The rate of change in length was measured, and the results are shown in Table 3. Also, for comparison, a mixture of plain and SBR type (commercial item 1), a mixture of acrylic type (commercial item 2)
Similarly, the test measurement was performed, and the results are also shown in Table 3.

[Table 3]

4. Marine exposure test 1: 2 mortar (C / S = 1: 2) was added as a base, and 10% by weight (P / C = 10%) of the polymer dispersion for admixture was added to the cement to prepare water cement. Bending strength, compressive strength, and water absorption of a specimen cast with a mortar composition with a ratio of 40% (W / C = 40%) after being exposed to a splash zone on the coast of the Sea of Japan in Yamagata Prefecture for 12 months Rate and chlorine ion penetration depth were measured, and the results are shown in Table 4. Further, for comparison, the same test results were measured for the mixture of SBR type (commercial item 1) and the mixture of acrylic type (commercial item 2), and the results are also shown in Table 4.

[Table 4]

5. Chemical resistance test 1: 3 Mortar (C / S = 1: 3) was used as a base, and the chloroprene latex to cement was changed within the range of 5 to 20% by weight (P / C = 5 to 20%) in terms of effective solid content ratio. And a 28-day specimen (4 × 4 × 1) made from a mortar composition with a water-cement ratio of 40% (W / C = 40%)
6 cm) was immersed in various evaluation chemicals for 14 days. After that, the plate was washed with water for 1 day, wiped with a compress, and allowed to stand for 7 days, and the strength was measured. The results are shown in Table 5. Also,
For comparison, chloroprene latex was not added (P
/ C = 0%) was also subjected to the test measurement, and the results are also shown in Table 5.

[Table 5]

[0019]

As described above, since the cement composition for underwater casting of the present invention contains chloroprene latex having a large specific gravity in the mixing of mortar or concrete, when it is poured into water such as seawater. In addition, it is possible to prevent the permeation of seawater and the like, suppress the increase of the water / cement ratio, prevent the strength from decreasing, and suppress the material separation. In addition, the wear resistance is improved, and the wear caused by sand and pebbles due to waves and water flow is reduced,
Increases durability. Further, after curing, water resistance and cohesive strength are increased by the cross-linking reaction between chloroprene and the metal oxide in the cement, and further the impact resistance is increased by viscoelasticity imparted to chloroprene, and chemical resistance is also improved. In addition, by suppressing the flow of alkali from the mortar or concrete by the cross-linking reaction of chloroprene and cement, the neutralization of the concrete structure is suppressed, the explosion of concrete due to the rust of the reinforcing bars is prevented, and the durability of the structure is improved. Can be improved. Furthermore, the impact on the natural environment is small by reducing alkali washout. Therefore, a mortar or concrete structure is formed which is less affected by seawater, hot spring water, etc., has high durability against water and chemical erosion, has high strength, and has high durability against physical stress such as impact.

When a proper amount of methylcellulose is added together with chloroprene latex during the mixing of mortar or concrete, the cohesive force is increased, so that the material separation is suppressed, and a water reducing agent or a fluidizing agent is added to flow the mixture. When the property is improved, a high-strength mortar or concrete hardened product can be obtained without increasing the water / cement ratio.

As a chloroprene latex, when a cement composition obtained by kneading a cationic latex or an anionic latex is poured into water such as seawater in which positive and negative ions coexist, a thin film of chloroprene is formed. It is possible to prevent the material from separating from the surface of the mortar or concrete and prevent the penetration of seawater or the like into the surface of the mortar or concrete before hardening.

Therefore, the cement composition for underwater casting and the method for constructing underwater mortar or concrete structure using the same of the present invention prevent permeation of seawater and the like at the time of placing, resulting in strength reduction and material separation. It is possible to construct an underwater structure with low pollution, high strength, chemical resistance, and impact resistance over a long period of time.

Claims (4)

[Claims] 1. During the mixing of mortar or concrete,
Chloroprene latex, which is a polymer with a higher specific gravity than water, is used in an effective solid content ratio of 5 to 30 wt% with respect to cement.
A cement composition for underwater casting, characterized by being added. 2. The effective solid content of chloroprene is 1 to
The cement composition for underwater casting according to claim 1, wherein 20 wt% of methyl cellulose is added. 3. During the mixing of mortar or concrete,
Chloroprene latex, which is a polymer with a higher specific gravity than water, is used in an effective solid content ratio of 5 to 30 wt% with respect to cement.
A method for constructing an underwater mortar or concrete structure, which comprises placing the added and kneaded cement composition in water. 4. The underwater mortar or concrete according to claim 3, wherein the chloroprene latex is a cationic or anionic latex and is cast into water such as seawater in which positive ions and negative ions coexist. Construction method for structures.