JP2008162843A - High-strength admixture and concrete composition for centrifugal molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-strength admixture in which the fluidity suitable for construction or molding can be obtained without disturbing a setting property even if mixed with a low water-content mortar or concrete, and thus high-strength mortar or concrete can be easily obtained, and also to provide the admixture-containing concrete composition for centrifugal molding by which the generation of sludge can be controlled to be extremely low even when performing the centrifugal molding for obtaining a concrete molded material and which has high strength developability. <P>SOLUTION: The high-strength admixture comprises, by mass, 100 pts. slag, 350-6,000 pts. silica fume, 800-1,250 pts. anhydrous gypsum and 0.05-1 part water-retention agent. The concrete composition for centrifugal molding comprises portland cement and the above admixture. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a high-strength admixture for increasing strength by being used in mortar and concrete and a concrete composition for centrifugal molding using the same.

As a measure for obtaining high-strength mortar and concrete, generally, the strength increases as the blending amount of water with respect to cement is lowered. In addition, a water reducing agent is often added to compensate for a decrease in dispersibility and fluidity due to a low water content. In particular, in a molded product that requires high strength such as a concrete product, a higher-strength molded product can be obtained by performing heating curing such as steam curing in addition to such a low water content blending. However, with this method alone, there is a limit to the strength that can be improved. For this reason, the examination from the surface of a compounding component has been performed. For example, it is known to add and add a large amount of gypsum to increase the strength of a concrete molded product that has undergone steam curing treatment. (For example, refer to Patent Document 1) Furthermore, it is also known to blend and add blast furnace slag powder in addition to gypsum. (For example, refer to Patent Document 2.) In any case, long-term strength development is improved, and a molded product having higher strength can be obtained. It is also known that high strength and durability can be obtained by blending and adding a pozzolanic reactive material such as silica fume in addition to gypsum. (For example, refer to Patent Document 3.) It is also known to add and add gypsum, blast furnace slag, and pozzolanic reactive material. (For example, refer to Patent Document 4.) In order to ensure fluidity suitable for construction and molding with low water content concrete by adding such gypsum or gypsum-containing material, it is generally necessary to increase the addition amount. was there. Further, in order to make the blending water amount lower, it is necessary to use a water reducing agent in combination with such an additive and increase the water reducing agent addition amount. However, when the water reducing agent or anhydrous gypsum content increases, the setting is delayed. Since concrete containing a relatively large amount of anhydrous gypsum takes a long time to complete the hydration reaction, sludge called Noro or Toro is likely to occur during molding when it is subjected to centrifugal molding. Squeezed out and shape retention is reduced.
JP 58-45007 A Japanese Patent Laid-Open No. 3-40947 JP-A-2-289453 Japanese Patent Laid-Open No. 2005-22888

  The present invention can obtain fluidity suitable for construction and molding without affecting the cohesiveness even if mixed with mortar and concrete containing low water content, and easily obtain high strength mortar and concrete. It is an object of the present invention to provide a concrete composition for centrifugal molding which can suppress sludge generation even when centrifugal molding is performed in order to obtain a high-strength admixture and a concrete molded product that can be formed and has high strength development.

  As a result of studying the above problems to solve the above problems, the present inventors have high strength expression of mortar and concrete mixed with an admixture containing anhydrous gypsum, slag, silica fume and a water retention agent in a specific ratio, Moreover, fluidity suitable for construction and molding could be secured even with a low water content. In addition, a concrete composition in which this admixture is mixed with Portland cement exhibits good fluidity suitable for molding, and when this is centrifugally formed, the amount of sludge generated is remarkably small, and the formability such as shape retention is excellent. A concrete molded product was obtained, and the present invention was completed because it had very high strength development.

  That is, the present invention is a high-strength admixture represented by the following (1) and a concrete composition for centrifugal molding represented by (2) to (4). (1) A high-strength admixture comprising 100 parts by mass of slag, 350 to 6000 parts by mass of silica fume, 800 to 1250 parts by mass of anhydrous gypsum and 0.05 to 1 part by mass of a water retention agent. (2) A concrete composition for centrifugal molding comprising 100 parts by mass of Portland cement and 5 to 30 parts by mass of the high-strength admixture of (1). (3) The concrete composition for centrifugal molding according to (2), wherein the Portland cement is a mixture of ordinary Portland cement and early-strength Portland cement. (4) The concrete composition for centrifugal molding according to (2) or (3), further containing a water reducing agent.

  The high-strength admixture of the present invention can dramatically increase the strength development of mortar and concrete without reducing fluidity and curability. For example, when mixed with ordinary Portland cement, it is subjected to steam curing. A concrete molded article having a very high compressive strength exceeding 100 MPa can be easily obtained at the time of demolding. Moreover, in the case of centrifugal molding, not only high-speed rotation but also low-speed rotation hardly generates sludge, and a concrete molded product having excellent shape retention can be obtained.

The slag contained in the high-strength admixture of the present invention exhibits latent hydraulic properties and has an action of enhancing the binder phase. The slag to be used is not particularly limited, and examples thereof include slag generated by metal refining including iron represented by blast furnace slag, molten slag of municipal waste and sewage sludge. Preferably, the use of blast furnace slag is recommended because inexpensive and stable quality is readily available. Further, the fineness of the slag is preferably particles having a Blaine specific surface area of 2700 to 12000 cm ² / g in order to smoothly exhibit such effects.

In addition, any silica fume contained in the high-strength admixture of the present invention can be used, for example, silicon dioxide produced as a by-product during production of ferrosilicon, metal silicon, etc., and a BET specific surface area of 20000 Examples thereof include fine particles of about 200,000 cm ² / g. When silica fume is contained, dense concrete can be obtained by entering the gaps between cement hydrates due to the microfiller effect. In addition, hydrate formation by pozzolanic reaction also occurs, so that higher strength concrete can be obtained. It becomes easy. As for content of a silica fume, 500-6000 mass parts is preferable with respect to 100 mass parts of slag. A more preferable content is 1000 to 4000 parts by mass. When the silica foam content is less than 500 parts by mass with respect to 100 parts by mass of the slag, it is difficult to improve the initial strength mainly, and it is difficult to achieve high densification of the concrete. Therefore, it is not preferable, and if it exceeds 6000 parts by mass, the mixing property and fluidity of the concrete are likely to be lowered, which is not preferable.

  In addition, any anhydrous gypsum contained in the high-strength admixture of the present invention can be used, and among these, type II anhydrous gypsum is preferable. The main content of type II anhydrous gypsum is to form ettringite from a relatively early stage through a hydration reaction to form a fine structure, which contributes to high strength and also to ensure long-term strength development. The content of anhydrous gypsum is preferably 800 to 1250 parts by mass with respect to 100 parts by mass of slag. A more preferable content is 800 to 1100 parts by mass. If the content of anhydrous gypsum is less than 800 parts by mass with respect to 100 parts by mass of slag, relatively early strength development is low, and if it exceeds 1250 parts by mass, setting is delayed or expansion cracks occur in the concrete after curing. This is not preferable.

  Moreover, the water retention agent contained in the high-strength admixture of the present invention is not particularly limited as long as it can be used for mortar and concrete. Specifically, for example, polyacrylic acid, vinyl acetate / acrylic copolymer, polyvinyl alcohol, maleic anhydride copolymer, polyacrylonitrile saponified product, polyethylene oxide, starch / acrylonitrile graft polymer, starch / acrylic acid graft The thing which uses a polymer, water-soluble methylcellulose crosslinked material, etc. as an active ingredient can be mentioned. By containing a water-retaining agent, it is easy to retain moisture in mortar and concrete even with a low water content for high strength, so it is possible to suppress residual unhydrated reaction components due to early drying, Since a binder phase can be obtained and shape retention due to a water retention effect is improved, generation of noro and toro can be remarkably reduced even if centrifugal molding is performed. As for content of a water retention agent, 0.05-1 mass part is preferable in conversion of a solid part with respect to 100 mass parts of slag. A more preferable content is 0.1 to 0.5 parts by mass. If the content of the water retention agent is less than 0.05 parts by mass with respect to 100 parts by mass of the slag, the strength development is not sufficiently improved, and the shape retention at the time of molding tends to decrease, which is not preferable. This is not preferable because the fluidity is lowered.

  Further, the high-strength admixture of the present invention may contain components other than those described above as long as the effects of the present invention are not substantially lost. Examples of such components include fibers, setting modifiers, hydraulic inorganic powders, fly ash, and metakaolin, all of which can be used for mortar and concrete.

  The concrete composition for centrifugal molding of the present invention contains a high-strength admixture containing at least anhydrous gypsum, slag, silica fume, and water retention agent, and Portland cement, as described above. As an optional ingredient, other admixtures that can be used in mortar and concrete are added.

  The amount of the high-strength admixture in the centrifugal molding concrete composition of the present invention is preferably 5 to 30 parts by mass with respect to 100 parts by mass of Portland cement. If it is less than 5 parts by mass, it is not appropriate because sludge generation during centrifugal molding cannot be sufficiently suppressed. On the other hand, if the amount exceeds 30 parts by mass, the gypsum content increases excessively, and cracking due to delayed expansion or delayed expansion after curing tends to occur.

Any type of Portland cement can be used as the Portland cement contained in the concrete composition for centrifugal molding of the present invention, and examples thereof include various Portland cements such as normal, early strength, super early strength, low heat, and moderate heat. Two or more of these may be used in combination. It is preferable to use a mixture of ordinary Portland cement and early-strength Portland cement as the Portland cement. The inclusion of early-strength Portland cement generally compensates for particles of 5 to 30 μm, improves mixing when mixed with concrete, and greatly reduces the mixing time until the components are homogenized. Since the amount of alite (CaO.3SiO ₂ ) contributing to the strength development at the initial stage of hydration increases, the initial strength development can be enhanced. As for content of early strong Portland cement, 500-1000 mass parts is preferable with respect to 100 mass parts of slag. When the content of early-strength Portland cement is less than 500 parts by mass with respect to 100 parts by mass of slag, almost no inclusion effect is seen, and when it exceeds 1000 parts by mass, the viscosity after water injection with kneading water becomes too high, and workability and molding It is not appropriate because it may lead to a decrease in sex.

  Further, the aggregate used in the centrifugal molding concrete composition of the present invention is not limited. For example, natural fine aggregates such as river sand, mountain sand, sea sand, rock crushed sand, river gravel, mountain gravel, sea gravel, rock crushing Natural coarse aggregates such as products, artificial fine aggregates or coarse aggregates obtained by firing mineral powder and by-products of industrial materials, and other lightweight, normal, and heavy aggregates according to density Either is fine. The amount of aggregate used is not limited. For example, when ordinary fine aggregate and ordinary coarse aggregate are used, about 250 to 350 parts by mass is recommended with respect to 100 parts by mass of Portland cement.

  Moreover, as an arbitrary component which can be used for the concrete composition for centrifugal molding of this invention, if it is an admixture and material which can be used for mortar and concrete, it will be used in the range which does not substantially lose the effect of this invention. be able to. Examples of such admixtures / materials include swelling materials, shrinkage reducing agents, bulking agents, thickeners, water reducing agents, high performance water reducing agents, high performance AE water reducing agents, dispersants, fluidizing agents, fibers, and setting modifiers. , Pigments, antibacterial agents and the like. Preferably, water reducing agents (water reducing agent, high performance water reducing agent, high performance AE water reducing agent, dispersing agent, fluidizing agent, etc.) are contained. By including the water reducing agents, even if the concrete has a particularly low blending water amount, it becomes easy to obtain fluidity suitable for formability and homogenization of components by mixing. The blending amount in the case of containing water reducing agents is preferably 0.5 to 2.5 parts by mass in terms of solid content with respect to 100 parts by mass of Portland cement. If the amount is less than 0.5 parts by mass, the content effect may not be obtained. If the amount exceeds 2.5 parts by mass, a setting delay may occur, which is not appropriate.

  In addition, the amount of kneading water of the concrete composition for centrifugal molding of the present invention is not limited, but generally a low kneading water blending amount is recommended to obtain high strength development, for example, with respect to 100 parts by mass of the Portland cement. 0.5 to 2.5 parts by weight is recommended.

  Moreover, the concrete composition for centrifugal molding of the present invention can be obtained by centrifugally molding it, and preferably by subjecting it to steam curing treatment to obtain a hardened concrete molding with very high strength.

  EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples shown here.

  <Preparation of high-strength admixture> A material selected from the following A to E is put into a Laedige mixer so as to have the blending amount shown in Table 1, and is dry-mixed for about 1 minute. 1-7, Reference products 11-16) were produced.

A: Blast furnace slag (trade name "Fine Serament 10A", manufactured by Dai Shi Co.)
B: Silica fume (trade name “SF-SILICAFUME”, manufactured by Sakai Kogyo Co., Ltd.)
C; Type II anhydrous gypsum (commercially available)
D: Water retention agent (trade name “SEB-04T”, manufactured by Shin-Etsu Chemical Co., Ltd.)
E: High performance water reducing agent (trade name “SEB-04T”, manufactured by Shin-Etsu Chemical Co., Ltd.)

<Preparation of concrete composition>
The high-strength admixture prepared as described above, the material selected from F to J shown below, and water are put together into a biaxial mixer so that the blending amount shown in Table 2 is obtained, and the temperature is about 20 ° C. Then, kneading was performed for the time shown in Table 2 until the contained material was made uniform.
F: Fine aggregate (mountain sand)
G: Coarse aggregate (maximum particle size 20mm, crushed stone)
H: Ordinary Portland cement (manufactured by Taiheiyo Cement)
I: Early strong Portland cement (manufactured by Taiheiyo Cement)
J: High performance water reducing agent (trade name “SEB-04T”, manufactured by Shin-Etsu Chemical Co., Ltd.)

<Evaluation of fluidity of concrete composition>
The evaluation of the fluidity of the concrete composition obtained by kneading as described above was performed on the concrete composition within 1 minute after completion of the kneading by a slump test according to JIS A 1101. The results are shown in Table 3.

<Evaluation of compressive strength of concrete composition>
Using the concrete composition obtained by kneading, the compressive strength of the concrete specimen was measured by a method based on JIS A 1108. Here, the specimen used for the measurement was vibration-filled with a concrete composition in a cylindrical mold with an inner diameter of 10 cm and a height of 20 cm, and steam curing treatment (treatment condition; pre-treatment time was 4 hours while being filled, The temperature was raised to 70 ° C. at 15 ° C./HR, held at 70 ° C. for 4 hours, naturally cooled after the holding, and demolded when it reached about 30 ° C., and after demolding, at room temperature The specimen was aged 7 days old. The measurement results of the compressive strength are also shown in Table 3.

<Production of concrete molding by centrifugal molding>
In addition, the concrete composition obtained by kneading as described above was subjected to centrifugal molding under the following two conditions using a small centrifuge tube of φ20 cm × 30 cm in accordance with JIS A1136.
Normal centrifugal molding: 1 minute at 5G centrifugal force, then 2 minutes at 15G, and 8 minutes at 35G.
Low speed rotary centrifuge molding: 5 minutes at 2G centrifugal force, then 3 minutes at 4G, 3 minutes at 20G.

  After centrifugal molding, this was subjected to normal pressure steam curing. In the steam curing, the pre-treatment time was 4 hours, the temperature was raised to 70 ° C. at 15 ° C./HR, and held at 70 ° C. for 4 hours. After the holding, it was naturally cooled and demolded when it reached about 30 ° C.

<Evaluation of centrifugal molding characteristics of concrete composition>
The molding characteristics of the concrete composition subjected to the centrifugal molding were evaluated by the compaction property in the normal centrifugal molding and the shape retention property in the low-speed rotational centrifugal molding described below. These results are shown in Table 4.

  For compaction, visually check the molded product after demolding, and determine that the molded product inner surface has a smooth curved surface and that the compaction property is “good”. For example, the molded product inner surface becomes a wavy surface. Thus, all the samples that did not become smooth curved surfaces were judged to have a compaction property of “bad”. In addition, the average thickness of the fragile layer (Noro layer) remaining on the inner surface of the molded product after compaction was measured with calipers.

  The shape-retaining property is such that the molded product after demolding is visually observed, generation of sludge in a low-viscosity state is not observed, the molded product inner surface becomes a smooth curved surface, and the smooth curved surface is maintained without substantial deformation even after 30 minutes. The shape retention was judged as “good”, and the other cases were judged as “bad” in shape retention.

  From the results shown in Table 3, the concrete using the high-strength admixture of the present invention easily secures fluidity suitable for construction and molding even when blended with a low amount of water, and has high strength development after curing. Furthermore, from the results shown in Table 4, the concrete composition using an appropriate amount of the high-strength admixture has a remarkably low amount of sludge generated when centrifugal molding is performed, exhibits excellent shape retention, and very high strength development. It can be seen that a molded product having the following can be obtained.

Claims (4)

A high-strength admixture comprising 100 parts by mass of slag, 350 to 6000 parts by mass of silica fume, 800 to 1250 parts by mass of anhydrous gypsum and 0.05 to 1 part by mass of a water retention agent. A concrete composition for centrifugal molding comprising Portland cement and the high-strength admixture according to claim 1. The concrete composition for centrifugal molding according to claim 2, wherein the Portland cement is a mixture of ordinary Portland cement and early-strength Portland cement. Furthermore, the concrete composition for centrifugal molding of Claim 2 or 3 containing water reducing agents.