JP6697971B2 - Fresh concrete for salt damage - Google Patents

Description

The present invention relates to fresh concrete for salt damage control , and more particularly to fresh concrete for salt damage control that suppresses rusting of reinforcing bars.

  Corrosion (rusting) is suppressed by the alkaline component of concrete in the reinforcing bars arranged in the reinforced concrete, but for example, reinforced concrete structures constructed near the coast and snow melting agents are supplied. In reinforced concrete floors, etc., salt contained in seawater and snow-melting agents penetrates from the surface of the concrete to corrode the reinforcing bars, causing cracks in the concrete and increasing the load bearing capacity of these reinforced concrete structures. It will reduce your power.

  Therefore, as a rust preventive agent, for example, by adding nitrite to fresh concrete, after the concrete is hardened, a concrete composition capable of suppressing the progress of rusting of the reinforcing bars arranged in the reinforced concrete. Have been developed (for example, see Patent Document 1).

JP, 2005-104788, A

"SSI method (registered trademark)", a method for preventing salt damage using a salt adsorbent, issued by JR Soken Engineering Co., Ltd., October 2013

  However, according to the concrete composition of Patent Document 1, since the rust preventive agent based on nitrite has a strong hardening promoting action on cement, the concrete rapidly hardens after adding nitrite. As a result, the workable time of the fresh concrete having desired fluidity becomes short. Therefore, in Patent Document 1, it is necessary to add a special cement admixture to the concrete composition. In addition, the rust preventive agent with nitrite has a function of suppressing the corrosion of the reinforcing steel in the concrete, but the chloride ion remaining in the concrete remains, so the re-deterioration of the portion subjected to the rust preventive treatment Are likely to cause

  On the other hand, as a salt damage countermeasure method for a reinforced concrete structure, there is known a method for repairing a reinforced concrete structure by using a repair material containing a salt adsorbent based on a polymer cement system (for example, see Non-Patent Document 1). . In the salt damage countermeasure construction method using a repair material containing a salt adsorbent, for example, the deteriorated part of the reinforced concrete structure is removed to expose the corroded part of the reinforcing bar, and then the exposed part is covered to repair the deteriorated part. It is designed to repair reinforced concrete structures by applying materials. The salt adsorbent contained in the repair material is, for example, a calcium-aluminum composite oxide containing nitrite ions between layers, and sulfite ions released by adsorbing chloride ions supplied from seawater or a snow-melting agent. Improves the state in which the reinforcing bars are less likely to corrode. In addition, since the salt adsorbent can adsorb and detoxify even the salt remaining in the residual rust that could not be removed, it is possible to effectively suppress the progress of rusting and at the same time adsorb chloride ions and nitrite ions. Since it is released, it is possible to improve the area around the reinforcing bar from a state where it is easily corroded to a state where it is easy to prevent rust, and it is possible to enhance the effect of suppressing the corrosion of the reinforcing bar.

  The above-mentioned salt damage countermeasure method using a repair material mixed with a salt adsorbent is a method of repairing the rebar of the corroded part after the rebar placed in the reinforced concrete is corroded. It takes a lot of time and labor to remove concrete from the part and to clean the reinforcing bar. Therefore, there is a demand for development of a technique for improving the concrete around the reinforcing bars so that the concrete around the reinforcing bars can be easily rust-proofed immediately after placing the fresh concrete to make the reinforcing bars less likely to rust.

The present invention, for example, without the inclusion of a special cement admixture, immediately after placing fresh concrete, improve the concrete around the rebar to be in an easily rust preventive state, the rebar rusts It is an object of the present invention to provide a fresh concrete for salt damage control that can effectively suppress the above.

The present invention is a fresh concrete for salt damage prevention, which contains water, cement, fine aggregate, and coarse aggregate and is used as a fresh concrete in a fluidized state that is not yet solidified, and is a calcium-aluminum composite containing nitrite ions between layers. Oxide is added as a salt adsorbent at an addition rate of 2.5 to 3.5% by weight with respect to the weight of cement , and the slump value is within ±2.5 cm of the designed slump value. The above object was achieved by providing fresh concrete for countermeasures.

Further , in the fresh concrete for preventing salt damage according to the present invention, it is preferable that the cement is ordinary Portland cement.

The fresh concrete for salt damage prevention of the present invention preferably contains an AE water reducing agent as an admixture.

According to the fresh concrete for salt damage countermeasures of the present invention, immediately after placing the fresh concrete, the concrete around the rebar is improved so as to be easily rust-proof, and the rebar is effectively rusted. Can be suppressed.

The structures of the test pieces of Example 1 and Comparative Examples 1 to 3 will be described. (a) is a top view, (b) is a side view, and (c) is an end view of (a) as viewed from the left side. It is a chart which shows the measurement result of a natural potential. It is a chart which shows the relationship between the corrosion area ratio of a reinforcing bar, and an adsorbent addition rate.

Fresh concrete for salt damage prevention according to a preferred embodiment of the present invention, as a reinforced concrete structure, for example, in a cold region, a concrete floor slab that constitutes a road surface portion of a highway constructed near the coast, and a road surface portion Used as fresh concrete in a fluid state that has not yet solidified to form concrete wall balustrades that are placed along side edges. In the present embodiment, the highway constructed near the coast of the cold district is disposed in the reinforced concrete due to, for example, the flying salt content of seawater or the salt content of the antifreezing agent sprayed on the road surface in winter. Reinforcing bars are in an environment where corrosion (rusting) is likely to occur, but by using the fresh concrete for salt damage countermeasures of the present embodiment, even under such an environment, the reinforcing bars are generated immediately after placing the fresh concrete. By effectively suppressing rusting, it becomes possible to maintain the quality of the reinforced concrete structure for a long period of time without the need to repair the corroded part of the reinforcing bar.

Then, the salt damage countermeasure fresh concrete of the present embodiment is water, cement, fine aggregate, and coarse aggregate, is a salt damage countermeasure fresh concrete used as fresh concrete in a fluidized state not yet solidified, between the layers Calcium-aluminum composite oxide containing nitrite ion is blended as a salt adsorbent at an addition rate of 2.5 to 3.5% by weight with respect to the weight of cement , and the slump value is ± the design slump value. It is within 2.5 cm .

Further, in the present embodiment, the salt adsorbent is preferably a calcium-aluminum composite oxide containing nitrite ions between layers. Here, the calcium-aluminum composite oxide containing nitrite ions between layers, which is a salt adsorbent, has a layer structure that is positively (+) charged, and adsorbs chloride ions (Cl-) in advance. The retained nitrite ion (NO2-) is released. As a result, the salt adsorbent reduces chloride ions in the reinforcing bar and the concrete around the reinforcing bar, and makes it possible to suppress corrosion of the reinforcing bar for a long period of time. As the calcium-aluminum composite oxide containing nitrite ions between the layers which is such a salt adsorbent, the trade name "Solcut" (manufactured by Nippon Kagaku Kogyo Co., Ltd.) can be used.

In the present embodiment, as water to be mixed with the fresh concrete for salt damage countermeasure , water known as water mixed with fresh concrete such as tap water can be appropriately selected and used.

Cement that is mixed with fresh concrete for salt damage prevention is Portland cement such as normal Portland cement, early strength Portland cement, moderate heat Portland cement, mixed cement such as blast furnace cement, silica cement, fly ash cement, and special cement such as alumina cement. Known cements to be mixed with fresh concrete such as the above can be appropriately selected and used.

Fine aggregates mixed with fresh concrete for salt damage countermeasures can be appropriately selected and used from known fine aggregates mixed with fresh concrete , such as mountain sand, river sand, and blast furnace slag fine aggregate. .

As coarse aggregate to be mixed with fresh concrete for salt damage countermeasures , mountain gravel, river gravel, crushed stone, blast furnace slag coarse aggregate, and the like known as coarse aggregate to be mixed with fresh concrete are appropriately selected and used. be able to.

Further, in this embodiment, various admixtures can be added to the fresh concrete for preventing salt damage , and it is preferable that the admixture contains an AE water reducing agent. By blending the AE water reducing agent with the fresh concrete for salt damage countermeasure, it becomes possible to improve the workability of the fresh concrete and to add more salt adsorbent.

Then, in the present embodiment, the salt adsorbent is added to the fresh concrete for salt damage countermeasure at an addition rate of 2.5 to 3.5 % by weight with respect to the weight of cement.

If the amount (% by weight) of the salt adsorbent is too small with respect to the weight of the cement, there is a disadvantage that only the same rust-preventing effect can be obtained as when the salt adsorbent is not added. If the amount of the salt adsorbent blended (% by weight) with respect to the weight of the cement is too large, the slump loss becomes large and the workability of the fresh concrete is impaired, which is disadvantageous. The salt adsorbent is added at an addition rate of 2.5 to 3.5 % by weight with respect to the weight of cement, so that a sufficient rust prevention effect is obtained and the workability of the desired fresh concrete is secured. The advantage is that it can be done.

Then, according to the fresh concrete for salt damage countermeasures of the present embodiment having the above-described configuration, without containing a special cement admixture, immediately after placing the fresh concrete, it is easy to prevent the concrete around the reinforcing bars from rusting. Therefore, it is possible to effectively prevent the reinforcing bars from rusting by improving the state so that the state is improved.

That is, according to the fresh concrete for preventing salt damage of the present embodiment, as the salt adsorbent, preferably calcium-aluminum composite oxide containing nitrite ion between the layers is 2.5 to 3.5 weight with respect to the weight of the cement. % Added to fresh concrete, chloride ions are adsorbed to release sulphite ions, improving the concrete around the rebar so that it is less likely to corrode the rebar. By doing so, it becomes possible to effectively suppress the rusting of the reinforcing bar immediately after placing the fresh concrete, and without the need for construction work to repair the corroded part of the reinforcing bar, It becomes possible to maintain the quality for a long period of time.

In addition, by salt adsorbent is blended, the curing accelerating function, reduce the fluidity of fresh concrete without yet solidified, it is conceivable to impair the workability (workability), salinity of the embodiment According to the fresh concrete for countermeasures, the amount of the salt adsorbent compounded is 2.5 to 3.5 % by weight with respect to the weight of the cement, so that no special cement admixture is included. , Without excessively reducing the fluidity of fresh concrete, holding a desired stamp value, for example, by kneading concrete at the construction site and placing it in a short time after kneading, for example, the thickness of reinforced concrete It is possible to efficiently form a concrete floor slab or a concrete wall balustrade whose size is not so large, without impairing the workability.

  It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made. For example, the salt adsorbent does not necessarily have to be a calcium-aluminum composite oxide containing nitrite ions between layers, and may be a salt adsorbent containing various other nitrite ions.

Hereinafter, the fresh concrete for salt damage prevention of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the description of the Examples below.

[Specimens of Example 1 and specimens of Comparative Examples 1 to 3]
Specimens of Example 1 and specimens of Comparative Examples 1 to 3 having the shapes shown in FIGS. 1A to 1C were formed. These test pieces were 100×100×300 mm rectangular parallelepiped-shaped test pieces in which deformed reinforcing bars (D13, SD295A) having a length of 380 mm were arranged in the central portion of the exposed surface in the vicinity of the exposed surface on the upper surface side. Has become. The covering from the exposed surface of the reinforcing bar was 10 mm, and one end of the reinforcing bar was exposed with a length of 100 mm as a counter electrode for assuming a natural potential. The concrete constituting each specimen is a concrete having the composition shown in Table 1 and a water-cement ratio of 65%, and the addition rate of the salt adsorbent is 0% with respect to the weight of the cement. Specimens of 2% were designated as specimens of comparative example 2, specimens of 3% were designated as specimens of example 1, and specimens of 5% were designated as specimens of comparative example 3. After subjecting each specimen to standard curing for 28 days, five surfaces other than the exposed surface were coated with a salt-shielding epoxy resin (Epotal NB20: manufactured by Nippon Paint Co., Ltd.).

[Exposure test]
In an exposure field in an environment where the flying salt due to the splash of seawater is supplied, the test piece of Example 1 and the test pieces of Comparative Examples 1 to 3 are placed on the upper surface side on a platform having a height of 1 m. I installed it. The amount of flying salt in the exposure field measured by the dry gauze method was 1.2 to 2.0 mg/dm2/day. The spontaneous potential was measured at intervals of about 0.5 year/time. In determining the corrosion of reinforcing bars, the exposure test was terminated when the state became more base than -250 mV, which is the state where point rust occurred, and the corrosion state of reinforcing bars was visually observed.

  The measurement result of the spontaneous potential is shown in FIG. The measurement was carried out by using a copper-copper sulfate electrode after applying a compress of about 30 dispersed water on the exposed surface of the specimen. The side points of the self-potential were 5 points immediately above the reinforcing bars on the exposed surface of FIG. The spontaneous potential was determined by correcting the average value of the 5 side points with the water content of the surface layer portion measured simultaneously (natural potential correction method). The spontaneous potential at the start of the exposure test was about -180 mV for all the test pieces. At the time of 830 days (about 2.3 years) from the start of the exposure, the specimens of Example 1 and Comparative Example 3 have a self-potential of about −100 mV and are in a state without corrosion of the reinforcing bar. The test piece of Comparative Example 2 was judged to be in a state where the spontaneous potential became baser than −250 mV and point rust was generated on the surface of the reinforcing bar. From the results of measuring the self-potential, the specimens of Comparative Example 1 and Comparative Example 2 were determined to be in a state where the reinforcing bars were corroded, so the exposure test was terminated and each specimen was recovered.

  Each recovered specimen was cleaved, and the taken out reinforcing bars were visually observed. From the visual observation of the taken out reinforcing bars, no corrosion was found on the surface of the reinforcing bars of the specimens of Example 1 and Comparative Example 3, while the self-potential was in a more base state than -250 mV. In the specimens of Example 1 and Comparative Example 2, corrosion was observed on the surface of the reinforcing bar on the cover side.

In order to relatively compare the degree of corrosion of the reinforcing bars of each specimen, the ratio of the corroded portion on the surface of the reinforcing bar was obtained as the corrosion area ratio. FIG. 3 shows the relationship between the corrosion area ratio and the salt adsorbent addition ratio. From the relationship between the corrosion area ratio and the salt adsorbent addition rate shown in FIG. 3, it is found that the corrosion area ratio tends to decrease as the salt adsorbent addition rate increases. Further, the result of corrosion determination of the reinforcing bar by measuring the self-potential and the state of corrosion of the reinforcing bar by visual observation were substantially in agreement. Furthermore, the corrosion state of the reinforcing steel in the concrete differs depending on the difference in the addition rate of the salt adsorbent, and the larger the addition rate, the more effective is the corrosion inhibition effect. It has been found that, when added in an amount of 2.5 to 3.5 % by weight or more, it is possible to effectively prevent rusting of the reinforcing bar.

[Slump test]
A slump test was conducted on a plurality of types of fresh concrete containing a salt adsorbent to evaluate the workability (workability) of these fresh concretes. As the fresh concrete to be tested, the concrete having the composition shown in Table 1 and having the addition ratio of the salt adsorbent used in the sample of Comparative Example 1 of 0% by weight, the addition of the salt adsorbent used in the sample of Example 1 In addition to the concrete having a ratio of 3.0 wt% and the concrete having a salt adsorbent addition rate of 5.0 wt% used in the test piece of Comparative Example 3, the salt adsorbent addition rate is relative to the weight of the cement. Tested for the effect of salt adsorbent on the slump value using 5 types of concrete, 0.5 wt% concrete and 1.0 wt% concrete admixture with salt adsorbent did. The test results are shown in Table 1.

According to the test results shown in Table 1, the criteria for determining the slump value allowed when receiving ready-mixed concrete (fresh concrete) at the construction site is ±2.5 cm when the design slump value is 8 cm or more and 18 cm or less. If the designed slump value is, for example, 12 cm, and the allowable slump value at the elapsed time of 0 minutes is 9.5 cm to 14.5 cm, it is determined to be acceptable at the construction site. Therefore, in order to obtain the desired workability (workability), the salt adsorbent in fresh concrete should be added in an amount of 2.5 to 3.5 % by weight or less based on the weight of cement to adsorb the salt. It has been found desirable to incorporate an agent.

Claims (3)

Water, cement, fine aggregate, and coarse aggregate, which is a fresh concrete for salt damage countermeasures used as a fresh concrete in a fluidized state that does not solidify yet, wherein calcium-aluminum composite oxide containing nitrite ions between layers, Fresh concrete for salt damage countermeasure, which is mixed as a salt adsorbent at an addition rate of 2.5 to 3.5% by weight with respect to the weight of cement , and has a slump value within ±2.5 cm of the designed slump value. ..   The fresh concrete for salt damage prevention according to claim 1, wherein the cement is ordinary Portland cement.   The fresh concrete for salt damage control according to claim 1 or 2, which contains an AE water reducing agent as an admixture.