JPH0366275B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of consolidating, using concrete, rubble that comes into contact with water, such as rubble for breakwater foundations, rubble for mounds, and rubble as a covering layer for seawalls. Asphalt mastic has traditionally been used to consolidate rubble underwater or near the water's edge during breakwater and revetment construction, and has been reasonably effective. However, the construction of this asphalt mastic requires heating and mixing, and the price has increased due to high oil prices. If concrete could be used as a rubble binder instead of asphalt mastic, these problems would be solved, but it is thought that it is impossible to reliably bind with conventional concrete due to the following reasons. Ta. When placing ready-mixed concrete on top of submerged rubble, it is not possible to insert the tip of a tremie pipe or concrete pump hose into the gap between the rubble.
You can't help but hope that the fresh concrete will flow into the gaps between the rubble stones due to its own weight by pouring the fresh concrete over the top of the rubble stones, but at that time, the fresh concrete will fall into the water through the gaps between the rubble stones, and the surrounding water will flow into the gaps between the rubble stones. When washed by water, the constituent particles were separated, and the particles that settled and settled did not harden into concrete or had a significant decrease in strength. In addition, since it is not always necessary to pour concrete thickly on the top surface of the rubble to solidify underwater rubble, the principle of the tremie method, which involves pouring concrete while immersing the tip of the tremie pipe into the concrete layer, may not be followed. In most cases, if this principle is not followed, water will enter the tremie pipe, or fresh concrete will fall from the tremie pipe into the water, causing the constituent particles to be washed away by water and separated.
This results in defective concrete. In addition, since the consolidation work of rubble stone is usually carried out in areas where there are waves or water currents, it is difficult to solidify reliably because the fresh concrete that has been poured is washed away by these waves and water currents. It was hot. An object of the present invention is to provide a method for consolidating rubble underwater or at the water's edge using ready-mixed concrete, which has been considered difficult in the past. It has been found that this objective is suitably achieved when the ready-mixed concrete is allowed to become viscous under predetermined conditions. In other words, when consolidating rubble in water or near the water's edge with concrete, a thickening agent is added to form ready-mixed concrete to meet certain conditions.More specifically, 400 c.c. 400 c.c. of cement paste with a water-to-cement ratio of 60% is poured down from above the water surface into a cylindrical container with a diameter of 5 cm and a height of 40 cm containing Select the type and amount of thickening agent that will make the difference in specific gravity between the two samples 0.1 or less when following the test method of taking a sample from the bottom 5 cm of the sample and measuring its specific gravity. If a thickening agent is added in the above amount to increase the viscosity of concrete mixing water and thereby form a ready-mixed concrete that is difficult to separate even when washed by surrounding water, this ready-mixed concrete can be mixed in water or It was found that sufficiently reliable concrete consolidation could be achieved even when poured onto rubble near the water's edge. Thickening agents used in the present invention include polypynyl alcohol, polyacrylamide, polyethylene oxide, sodium polyacrylate, carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and cellulose ethers represented by these. Sodium alginate, guar gum, Korean ginkgo herb, or similar thickening agents may be mentioned, and these may be added alone or in combination (two or more types) so as to satisfy the above conditions. Among these thickeners, polyacrylamide, methylcellulose, hydroxyethylcellulose and hydroxypropylmethylcellulose are preferred. Suitable polyacrylamide has a viscosity of about 4000 centipoise or more at 25°C in a 1% aqueous solution, and in the above test, such polyacrylamide has a viscosity of about 2.4% by weight or more based on cement (in the mixing water). When added in an amount of about 4.0% by weight or more), it exhibits the effect of reducing the specific gravity difference to 0.1 or less. Therefore,
For example, when such polyacrylamide is used as a thickening agent, the method of the present invention can be carried out by forming fresh concrete with an amount of addition of about 4% by weight or more relative to water. As methylcellulose, the degree of etherification is 1.7 to 2.3, and the average degree of polymerization is 900 to
1200, the viscosity of a 2% aqueous solution at 25℃ is approximately
Preferably, the hydroxyethyl cellulose has a viscosity of 20,000 to 35,000 centipoise, and a hydroxyethylcellulose having a viscosity of about 20,000 to 100,000 centipoise at 25°C in a 2% aqueous solution is preferable. In the above test, such cellulose ether can reduce the difference in specific gravity to 0.1 or less when added in an amount of about 1.0% by weight or more relative to water. Therefore, for example, when such cellulose ether is used as a thickening agent,
The method of the present invention can be carried out by forming ready-mixed concrete with an amount of addition of about 1.0% by weight or more relative to water. However, in practice, it is necessary to avoid adding an excessive amount of thickening agent. Otherwise, even if a concrete dispersant (plasticizer) is used in combination, the fluidity of fresh concrete will be significantly reduced, which will not only reduce the workability of discharging from concrete transport vehicles and pumping concrete, but also cause concrete problems. This may cause the disadvantage that the curing reaction is delayed. In order to avoid such inconveniences, the amount of thickener added is approximately 8.0% by weight of polyacrylamide relative to water.
Below, in the case of cellulose ether, the target content is approximately 2.0% by weight or less. Further, in carrying out the present invention, it is preferable to mix an antifoaming agent in fresh concrete together with a thickening agent in an amount sufficient to eliminate air bubbles caused by the thickening agent. Suitable antifoam agents include dibutyl phthalate, water-insoluble alcohols, tributyl phosphate, and silicones, which have approximately
It can be blended in a proportion of 2.0 to 10.0% by weight. Furthermore, it is preferable to mix a concrete dispersant (plasticizer) with the ready-mixed concrete of the present invention. Suitable dispersants for concrete include melamine sulfonates (sulfonated melamine condensates, highly condensed triazine compounds) and polymeric aromatic sulfonates (naphthalenesulfonic acid formalin high condensates, polyalkylaryl sulfonates). It can be blended in a proportion of about 50 to 200% by weight based on the thickening agent. Also, depending on the type of thickening agent, setting of cement may be delayed, but in such cases, adding a small amount of quick setting agent such as calcium chloride, sodium silicate, sodium aluminate, etc. good. Furthermore, depending on the type of thickening agent, if the consistency of concrete is reduced, it is also preferable to use a known water reducing agent in combination. In any case, it must be ensured that the combination of these various additives does not interfere with the adhesive effect between cement particles inherent to the thickener, and the specific gravity difference when following the above test method is 0.1. Select the type and amount of the thickener to be added to meet the following conditions, and add the various additives mentioned above according to the selected thickener to the extent that the thickening effect is not impaired. is important. The cement to be used can be conventionally known common cement, but a part of it can be replaced with fly ash, water frame slag powder, siliceous mixture, etc., and this replacement can advantageously achieve the object of the present invention. In some cases, this can be achieved. In producing the ready-mixed concrete of the present invention, there are no restrictions on the type of aggregate, including fine aggregate and coarse aggregate, and any type of aggregate can be used. The present invention is also useful in cases such as cement mortar that does not use coarse aggregate. When blending thickeners, it is important to pay attention to the mixing procedure depending on the type of thickener. In the case of a thickening agent that is difficult to dissolve in water when mixed with a normal concrete mixer, mix this thickening agent with water in advance to form an aqueous solution or suspension, and then add this to the ready-mixed concrete. It's better to.
However, it may be better to mix the other ingredients thoroughly first, and then add water and mix. The mixing procedure to be adopted can be determined depending on the type of thickening agent. According to the tests conducted by the present inventors, when a thickening agent is blended so that the difference in specific gravity of the samples collected by the above test method is 0.1 or less, the injection flow is passed through the water ( It was confirmed that almost all of the cement was placed without being washed away by water even if the concrete was dropped, and that it was possible to form a strong concrete structure by spreading it into the gaps between rubble stones. This specific gravity difference
Under conditions where the value exceeds 0.1, cement will be dispersed in water during construction and it will not be possible to form a highly reliable rubble solid. The amount of thickening agent added to make this specific gravity difference 0.1 or less varies depending on the type of thickening agent. The addition amounts of polyacrylamide and cellulose ether, which are preferred thickening agents, have been described above, but when adding other thickening agents or a combination of two or more types of thickening agents, the specific gravity difference can be determined by the above test. All you have to do is determine the amount of addition needed to make it 0.1. In carrying out the construction of the present invention, for example, as illustrated in FIG. Concrete can be poured by means of a ready-mixed concrete transport means whose discharge port is below the water surface, so that the pouring stream passes (falls) through the water. In the case of shallow water, the ready-mixed concrete may be dropped from above the water surface without submerging such a conveying means. By such a method of placing through underwater passage or falling,
Consolidation of underwater rubble into concrete, which was previously considered difficult, has become possible, and concerns such as decreased adhesion strength, unbalanced compressive strength, and the formation of defective parts have been eliminated, and the structure is reliable and can withstand the effects of waves and water currents. Concrete consolidation of the rubble stone is achieved with good workability. Representative test examples and examples are listed below. [Test Example 1] Water was added to Portland cement to make a paste with a water-to-cement ratio of 60%, and 1 was added as a thickening agent to this paste.
% aqueous solution having a viscosity of about 5500 centipores at 25° C. was added and mixed. This was poured into a cylinder with a diameter of 5 cm and a height of 40 cm containing 400 c.c. of water, and the sample was poured from above the 400 c.c. water surface and left to harden. The sample was collected and the difference in specific gravity was measured. The relationship between the weight ratio (percentage) of polyacrylamide to cement and the difference in specific gravity is shown in FIG. The amount of polyacrylamide added is 2.4% or more relative to cement (4.0% relative to water)
(above), the difference in specific gravity between the two samples was 0.1 or less. Based on the above test results, prepare ready-mixed concrete with the above-mentioned polyacrylamide added in the proportions shown in Table 1, and place it in the test tank 9 as shown in Fig.
Water was filled to a depth of 2 m, and the fresh concrete was dropped into the tank from a bucket 10 above the water surface and allowed to harden. Nine cores were taken from the resulting concrete and the compressive strength at 28 days old was examined. The results are shown in Table 2.

【table】

[Test example 2]

Test Example 1 was carried out in the same manner as in Test Example 1, except that methylcellulose having a 2% aqueous solution having a viscosity of approximately 27,500 centipoise at 25°C and hydroxyethylcellulose having a 2% aqueous solution having a viscosity of approximately 60,000 centipoise at 25°C were used as thickeners. A test was conducted to measure the difference in specific gravity by dropping the paste into water. As a result of the test, it was found that these cellulose ethers can reduce the difference in specific gravity to 0.1% at a water ratio of about 1.0% or more. Based on this test result, ready-mixed concrete was prepared with methylcellulose and hydroxyethylcellulose added as shown in Table 3.
Fill test tank 9 as shown in Figure 3 with water to a height of 2 m,
This fresh concrete was dropped into the tank from the bucket 10 above the water surface, and was allowed to harden. Six cores were taken from each of the obtained concretes, and the compressive strength at 28 days old was examined. The results are shown in Table 4.

[Table] *: Tributyl phosphate **: Highly condensed triazine compound

〔Example〕

A test to measure the difference in specific gravity by dropping cement paste into water in the same manner as in Test Example 1 was carried out to prepare ready-mixed concrete with the composition shown in Table 5.
The concrete was poured into an aquarium with a bottom area of 100cm x 100cm filled with water from 40cm below the water surface to a height of 30cm from the bottom of the aquarium, and then allowed to harden in the water. was measured. The slump and air content of each fresh concrete were also measured, and the compressive strength according to JIS A 1132 was also measured. These measured values are also listed in Table 5. Further, the type and unit amount of the antifoaming agent and/or dispersant used are also listed in Table 5. Furthermore, pouring was carried out in the same manner as described above, except that split stones with a diameter of approximately 20 cm were placed in two layers at the bottom of the water tank, using ready-mixed concrete having the composition shown in Table 5, and the hardened material obtained was Cut it vertically with a cutter and observe the cross-sectional condition. If the concrete is well filled around the broken stone, mark it with an ○.
Cases where the concrete is poor and the filling around the broken stones is poor are marked with an x mark, and those in the middle are marked with a △ mark, and are shown in the column "Evaluation of rubble consolidated concrete" in Table 5. In these examples, the viscosity of the polyacrylamide used as a 1% aqueous solution at 25°C is approximately 10,000 centipoise, and the viscosity of methylcellulose is 2.
% aqueous solution at 25°C is approximately 30,000 centipoise, and hydroxyethyl cellulose has a viscosity of 2%.
The viscosity of the aqueous solution at 25°C is approximately 35,000 centipoise.

【table】

【table】

Claims (1)

[Claims] 1. When consolidating rubble under water or near the water's edge with concrete, 5 cm in diameter containing 400 c.c. of water.
In a cylindrical container with a height of 40 cm, 400 c.c. of cement paste with a water-to-cement ratio of 60% is allowed to flow down from above the water surface, and then left to harden. Select the type and amount of the thickening agent that will make the difference in specific gravity between the two samples 0.1 or less when following the test method of taking a sample from a 5 cm area and measuring its specific gravity, and add the thickening agent to the In addition to the additive amount, an antifoaming agent is added in an amount sufficient to eliminate air bubbles caused by the thickening agent to form ready-mixed concrete. A method for solidifying rubble, which comprises pouring onto the rubble through a ready-mixed concrete conveying means having an injection port below the water surface so that the pouring flow passes through the water. 2. When consolidating rubble in the water or near the water's edge with concrete, use a 5 cm diameter container filled with 400 c.c. of water.
In a cylindrical container with a height of 40 cm, 400 c.c. of cement paste with a water-to-cement ratio of 60% is allowed to flow down from above the water surface, and then left to harden. Select the type and amount of the thickening agent that will make the difference in specific gravity between the two samples 0.1 or less when following the test method of taking a sample from a 5 cm area and measuring its specific gravity, and add the thickening agent to the In addition to the additive amount, an antifoaming agent is added in an amount sufficient to eliminate air bubbles caused by the thickening agent, and a dispersant for concrete is further added to form ready-mixed concrete. A method for solidifying rubble, which comprises pouring onto the rubble in the water or near the water's edge via a ready-mixed concrete conveying means having an injection port below the water surface so that the pouring flow passes through the water.