JP2008162831A - Hydraulic kneaded material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cement-based kneaded material regulating its hardening-developing age in a range from a few days to a few months where the development of hardening occurs spontaneously without an operation such as the addition of an agent and practical strength as a ground material is obtained. <P>SOLUTION: The hydraulic kneaded material is a cement-based kneaded material which has a water-cement ratio of 30-250%, contains sodium heptonate dihydrate of 0.1-2 pts.mass and carboxylic acid of 0.1-2 pts.mass vs. water of 100 pts.mass, and a bleeding rate of ≤0.5%. As a suitable carboxylic acid, citric acid is designated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cement-based hydraulic kneaded material having a property in which the strength due to curing does not develop until a certain point of several days to several months after kneading and setting, and has the property of spontaneously starting curing at that point and expressing the strength. .

  A cement-based kneaded product usually starts a hydraulic reaction as soon as it is allowed to stand after kneading, and increases its strength over time. And finally, it becomes a cured body having a certain strength. In most fields where cement-based materials are used, a material that develops strength early is desired in order to shorten the construction period. However, in the field of ground improvement or the like, there is a case where a cement-based material having a characteristic that maintains as low a strength as possible for a while (ie, having a delay effect) after kneading and placing is desired.

  For example, when the ground is improved by a mechanical stirring method, or when an underground continuous wall is constructed using a continuous excavator or an all-around turning excavator, a cement-based material having a delay effect is desired. In these construction methods, it is required to sufficiently secure adhesion and integrity at the boundary between the cement-based material applied in advance and the cement-based material applied later. If the cementitious material in the subsequent construction part is placed in a state where the cementitious material in the preceding construction part has been cured to some extent, adhesion / integration tends to be insufficient at the boundary between the two, and water shielding may not be ensured. In some cases, a cold joint is formed. In fact, many troubles that water leaks from the underground continuous wall constructed as a water-impervious wall have been reported so far. Therefore, it is desirable to take measures to delay the curing of the cementitious material in the preceding construction section.

  In addition, there is a construction method in which a core material or a structural member such as H steel is inserted (built) later into the cast cement-based material to strengthen it. In that case, in order to reduce the resistance when the core material or the like is charged, it is necessary to carry out the construction work of the core material or the like while the strength of the cementitious material is hardly expressed. Because there are problems such as traffic blockage at construction sites in urban areas, it is necessary to interrupt the construction after placing cement-based material, return the traffic, and then block the traffic again before starting the construction work. In such a case, it is necessary to take measures to delay the hardening of the cementitious material.

  As a technique for delaying the hardening of the cementitious material, it is common to add a “retarder” as an admixture. As the retarder, various carboxylic acids and carboxylic acid compounds are known (Patent Documents 1 and 2). In addition, in the ultra-fast early cement-based material, in order to ensure the handling time from kneading to placing, there is a case where a retarder as described above is also added (Patent Document 3).

  On the other hand, Patent Document 4 discloses a method of maintaining a long period until the cement material is cured and starting the curing at an arbitrary time. In the technique of Patent Document 4, a cement-type filler added with a retarder to allow the setting and hardening to be performed slowly is injected into the gap, and then a setting stimulating agent such as alkali is injected at a predetermined time. Is rapidly cured by contacting and mixing with the filler.

JP-A-61-40854 JP-A-10-310771 JP 2004-262718 A Japanese Patent Laid-Open No. 2004-244483

  In the conventional methods of adding a retarder as in Patent Documents 1 and 2, it is difficult to maintain a high strength level after curing if the curing of the cementitious material is delayed. If the retarder is added excessively, there is a risk that it will not eventually cure (causes poor curing). For this reason, in order to obtain a practical strength as a ground material, hardening can generally be delayed only for several hours to at most about 3 days.

  Urban ground work is often done only at night to minimize the impact of traffic blockage. In order to build a sound underground structure without water leakage under such conditions, it is important to expand the degree of freedom of the construction schedule, and a technique for delaying curing over a longer period than the above is required. .

  Moreover, the conventional kneaded material to which the retarder is added exhibits a slight strength after standing. For this reason, in the construction method for inserting the core material, it is necessary to perform the construction work immediately after placing the cement-based material, and it is extremely difficult to realize this construction method in the ground improvement work in the urban area. Furthermore, in recent years, the need for a method of embedding the core material while avoiding existing underground objects has increased, and in order to achieve this, the core material is moved in the horizontal direction in the cement-based material after placement. Is required. In view of these, it is desired that a cement-based material that does not exhibit strength due to a curing reaction over a long period of several days to several months after the cement-based kneaded material is kneaded and placed in place is desired.

  On the other hand, as in Patent Document 4, in the conventional technique in which curing proceeds rapidly at an arbitrary time, it is necessary to inject a coagulation stimulant such as an alkali later. The technique of Patent Document 4 is intended for a gap filler. In the ground improvement method, it is difficult to reliably contact the cement-based material and the setting stimulating agent over the entire range, and the strength varies depending on the degree of contact, so it is difficult to adopt the technique of Patent Document 4.

  In the present invention, it is possible to adjust the age at which the hardening develops in the range of several days to several months, and the onset of hardening occurs spontaneously regardless of operations such as addition of stimulants, and the practical strength as a ground material is uniform. It aims at providing the cement-type kneaded material obtained.

The above-mentioned object is that in a cement-based kneaded material having a water cement ratio of 30 to 250%, 0.1 to 2 parts by mass of sodium heptate dihydrate and 0.1 to 2 parts by mass of carboxylic acid are added to 100 parts by mass of water. It is achieved by a hydraulic kneaded material that is added in combination and has a bleeding rate of 0.5% or less. Examples of the carboxylic acid include citric acid. In other words, those in which citric acid is blended as part or all of the carboxylic acid are suitable targets. Moreover, especially in this invention, the hydraulic kneaded material by which the hardening expression age was adjusted to the range of 3 to 120 days is provided. Moreover, what has the hardening characteristic from which the uniaxial compressive strength after hardening is 0.5 N / mm < ² > or more, Preferably it is 2.0 N / mm < ² > or more is provided.

A bleeding rate is calculated | required based on the testing method (JSCE-F 522-1999) standardized by Japan Society of Civil Engineers. The uniaxial compressive strength is determined in accordance with JIS A1216. The age at which hardening occurs is the time during which the cement-based kneaded material is kneaded at the current position and placed, and the state in which the strength of uniaxial compressive strength of 0.05 N / mm ² or more is not developed is maintained.

  The hydraulic kneaded material of the present invention has a specific delay in which the start of curing is remarkably delayed in the range of several days to several months, during which time the strength remains almost zero, and then rapid curing starts spontaneously. It has such properties. In addition, with this material, the time at which curing begins can be controlled by the amount of retarder added. Moreover, the strength finally obtained is a practical level as a ground improvement material. Therefore, according to the present invention, the degree of freedom of the construction schedule is expanded, especially in the ground construction in urban areas. As a result, the influence on the traffic blockage is greatly reduced, and the water barrier of the underground continuous wall is also improved. . Furthermore, it is possible to realize a construction method for a core material that avoids existing buried objects.

  In the cement-based kneaded material of the present invention, sodium heptanoate dihydrate and carboxylic acid are added as an admixture. Sodium heptonate dihydrate is a substance that can be expected to exhibit chelating power (ion exchange) and biodegradability under high alkali. Calcium ions required for hydraulic reaction when blended in cement-based kneaded materials It is thought that it has the effect | action which couple | bonds with an aluminum ion and inhibits hardening. The effect is considered to decrease with time due to biodegradability, and eventually calcium ions and aluminum ions can be freely activated for hardening. Sodium heptonate dihydrate may be used, for example, as a retarder for very early cementitious materials.

  However, even if sodium heptonate dihydrate is added in a considerably large amount, it is difficult to delay the onset of curing for several days or more, and if it is added in a large amount, it causes a curing failure. However, the inventors have found that when sodium heptanoate dihydrate and carboxylic acid are added to a cementitious material, the delay in curing can be extended to about several months. In addition, it was confirmed that it occurred spontaneously at a certain point in time when curing started, and that the strength remained almost zero until curing began. Furthermore, as a result of detailed investigations, it was found that the time at which curing starts (curing expression material age) can be controlled by the total blending amount of sodium heptonate dihydrate and carboxylic acid. Moreover, citric acid that is easily available can be used as the carboxylic acid.

The mechanism by which such a specific delay characteristic is developed when sodium heptate dihydrate and carboxylic acid are added in combination has not been clarified at the present time.
In addition to sodium heptonate dihydrate and carboxylic acid, a conventionally known retarder may be included.

  In the present invention, various cement-based materials having a water-cement ratio of 30 to 250% can be targeted except for those using early-strong cement or ultra-early strong cement. The blending amount of sodium heptonate dihydrate and carboxylic acid (for example, citric acid) can be blended in the range of 0.1 to 2 parts by mass with respect to 100 parts by mass of water. When the water cement ratio and the blending ratio of sodium heptate dihydrate and carboxylic acid are constant, the total amount of sodium heptate dihydrate + carboxylic acid (for example, citric acid) with respect to water, It was found that there was a correlation between them (see FIG. 2 described later). Therefore, it is possible to accurately control the age at which the cured material is developed within a range of several days to several months depending on the total blending amount. For example, a material that has been cured at a certain time in the range of 3 to 120 days can be suitably used in the field of ground improvement.

  However, the age at which the hardening develops is affected also by materials other than the retarder constituting the cement-based kneaded material. For example, when the amount of the viscous soil is large, the effect of the retarder tends to be small. Correlation between the total amount of sodium heptonic acid dihydrate + carboxylic acid (for example, citric acid) with respect to water and the age of onset of curing, depending on the type and amount of materials other than the retarder constituting the kneaded product By obtaining the relationship in advance, it becomes possible to accurately control the age at which curing occurs.

The mixing ratio of sodium heptonate dihydrate and carboxylic acid (for example, citric acid) can be set in a mass ratio of approximately 1: 3 to 3: 1, and a ratio close to the equivalent (1: 1.5 to 1). 5: 1). As a blending amount per 1 m ^{3 of the} cement-based hydraulic kneaded material, the total amount of sodium heptonic acid dihydrate and carboxylic acid (for example, citric acid) may be adjusted within a range of 0.5 to 25 kg. The range of 1 to 5 kg is more preferable. As the total amount of these retarders increases, the strength level ultimately obtained tends to decrease. To be applied in soil improvement field, it is desirable that the ultimate strength is adjusted to be 0.5 N / mm ² or more in a uniaxial compressive strength, adjusted to be 2.0 N / mm ² or more It is more preferable.

Since the hydraulic kneaded material of the present invention has a hardening development material age ranging from several days to several months, it is necessary to consider that bleeding due to material sedimentation does not occur after casting. Specifically, the bleeding rate (after 24 hours) needs to be 0.5% or less, preferably 0%. Therefore, it is desirable to add a thickener as appropriate. Examples of the thickener include cellulose thickeners (for example, carboxymethylcellulose), xanthan gum, welan gum, guar gum, pectin and the like. The addition amount of the thickener may be adjusted in the range of about 3~15kg per kneaded product 1 m ^3.

  Cement-based hydraulic kneaded materials having the formulations shown in Table 1 were prepared. The cement used is blast furnace B cement. In Table 1, LP is limestone fine powder, and PLAY is clay. A cellulose-based thickener was used as the thickener.

Each kneaded product was poured into a plurality of cylindrical containers having an inner diameter of 50 mm and a height of 100 mm, and left to stand. Then, when various days passed, the uniaxial compressive strength was measured by the method based on JISA1216. The material age at the last measurement time point at which the uniaxial compressive strength was maintained at less than 0.05 N / mm ² was determined as the “cured material age” of the kneaded product. Moreover, the bleeding rate of each kneaded material was measured by the method based on the test method (JSCE-F 522-1999) standardized by Japan Society of Civil Engineers.

Table 1 shows the bleeding rate.
FIG. 1 shows the change over time in the uniaxial compressive strength. The numbers described in FIG. 1 correspond to the kneaded material No. in Table 1.
FIG. 2 shows the relationship between the total amount of retarder (the total mass part of sodium heptate dihydrate + citric acid relative to 100 parts by mass of water) in the kneaded product (Nos. 1 to 4) of the present invention example and the age at which curing occurs. Indicates.

The kneaded material of the example of the present invention in which sodium heptanoate dihydrate and carboxylic acid (citric acid) were added in combination as a retarder had a curing development material age of 7 to 90 days. It was confirmed that the strength was maintained at almost zero until the curing began, and that rapid curing occurred spontaneously after the age of curing development. Further, the final strength level was uniaxial compressive strength of ^2.5 N / mm ² or more, and it was possible to obtain 5 N / mm ² or more. In addition, bleeding is not caused by adding a thickener. In particular, as shown in FIG. 2, it is confirmed that there is a correlation between the total amount of the retarder and the age at which the hardening develops when the water-cement ratio is constant, and it is possible to control the age at which the hardening appears. It was.

  On the other hand, No. 5 as a comparative example caused bleeding because no thickener was added. No. 6 was obtained by using citric acid and sodium gluconate as a retarder and not adding sodium heptonate dihydrate. In this case, although the total amount of the retarder is as large as No. 4, the delay effect is small.

The graph which shows the time-dependent change of uniaxial compressive strength about each kneaded material. The graph which shows the relationship between the retarder total amount in the kneaded material of this invention example, and hardening expression material age.

Claims (4)

  In a cement-based kneaded material having a water cement ratio of 30 to 250%, 0.1 to 2 parts by mass of sodium heptonate dihydrate and 0.1 to 2 parts by mass of carboxylic acid are blended with 100 parts by mass of water, and bleeding. A hydraulic kneaded material having a rate of 0.5% or less.   The hydraulic kneaded material according to claim 1, wherein citric acid is blended as the carboxylic acid.   The hydraulic kneaded material according to claim 1 or 2, wherein the age at which the curing manifestation is 3 to 120 days. The hydraulic kneaded material according to claim 1 or 2, which has a curing characteristic that a uniaxial compressive strength after curing is 0.5 N / mm ² or more.

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