JP2007169124A - Shrinkage-reducing material for cement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shrinkage-reducing material for cement capable of attaining shrinkage-reducing effect even in the curing under a normal drying condition without depending on the strength development of a hardened body. <P>SOLUTION: The shrinkage-reducing material for cement contains (A) lithium nitrite and (B) an expanding material. In a method for reducing shrinkage of a cement-based hardened body, (A) lithium nitrite and (B) the expanding material are added, kneaded, dried, and cured in the manufacturing process of the cement-based hardened body. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a shrinkage reducing material for cement that can effectively reduce shrinkage of a cement-based cured body even in curing in a dry state in air.

  Cement-based hydraulic compositions such as cement mortar and cement concrete are known to shrink the cured body due to capillary tension when pore water that cannot be consumed during curing evaporates in a dry environment. If the shrinkage rate is large, cracks may occur, and the applied mortar may cause problems such as floating and peeling.

  The first strategy to reduce drying shrinkage is to reduce the amount of water during kneading. It is known that the magnitude of drying shrinkage is proportional to the unit water volume. Therefore, if the unit cement amount is reduced, the unit water amount can be reduced, that is, drying shrinkage can be reduced, but the unit cement amount tends to increase as the demand for higher strength increases. The use of water reducing agents is increasing in order to reduce the amount of unit water without reducing the amount of unit cement.

  Also, shrinkage reducing agents that reduce the surface tension of water have been developed. That is, the action mechanism is to reduce the capillary tension derived from the surface tension of water when the pore water evaporates. Examples of these shrinkage reducing agents include lower alcohol alkylene oxide adducts, alcohols, glycol ether / amino alcohol derivatives, polyethers, low molecular weight alkylene oxide copolymers (Patent Documents 1 to 6). However, as the surface tension of the water is reduced, the evaporation of pore water is promoted. Therefore, if sufficient strength of the cured body is not exhibited at the initial curing stage after curing, there is a problem that the drying shrinkage is increased. .

In order to reduce shrinkage cracks, intumescent materials are also used. Since the expanded material has a larger volume of crystals after hydration than before hydration, it reacts after curing to reduce shrinkage of the cured body due to a gap filling effect. However, in order for the expandable material to fully perform its performance, it is necessary to supply sufficient water for the hydration of the expandable material after curing, and an effect can be obtained with concrete that is sprinkled with water. However, there is a problem that it is difficult to obtain the effect with the application mortar which is often cured as it is.
JP 59-21557 A JP 59-128250 A JP 59-152253 A JP 60-16846 A Japanese Patent Laid-Open No. 2-307849 JP-A-3-290342

The current shrinkage reduction measures are (1) there are limits to the measures to reduce the unit water volume with a water reducing agent without reducing the unit cement amount; (2) measures to reduce the surface tension of water are Depending on the strength development, the drying shrinkage is increased depending on the case. (3) The measure by adding the expansion material has a problem that the effect is weak under the condition that sufficient water cannot be supplied after curing.
Accordingly, an object of the present invention is to provide a shrinkage reducing material that is not greatly affected by the strength development of a cured product and that can reduce shrinkage even under curing to some extent.

As a result of intensive studies to solve the above problems, the inventor of the present invention, among various combinations of nitrite and an expanding material, particularly by combining lithium nitrite and an expanding material for cement, The present inventors have found that a shrinkage-reducing effect can be obtained even under curing to some extent while promoting strength development, and the present invention has been completed.
That is, the present invention provides a shrinkage reducing material for cement containing (A) lithium nitrite and (B) an expanding material.
Further, the present invention provides a method for reducing shrinkage of a cement-based cured body, characterized in that, in the manufacturing process of the cement-based cured body, (A) lithium nitrite and (B) an expansion material are added and kneaded and dried. It is to provide.

  The shrinkage-reducing material of the present invention can effectively reduce shrinkage even under curing to some extent while promoting the strength development of the cement-based cured body.

  The shrinkage reducing material for cement according to the present invention is characterized by combining lithium nitrite and an expansion material. Nitrite with other alkali metal ions such as sodium nitrite and potassium nitrite cannot be used due to the risk of alkali aggregate reaction. As shown in the examples below, a combination of an alkaline earth metal nitrite such as calcium nitrite and an expansion material cannot provide a sufficient shrinkage reduction effect, but particularly when lithium nitrite and an expansion material are combined. Excellent shrinkage reduction effect is obtained.

  The form of providing (A) lithium nitrite used in the present invention may be in the form of powder or aqueous solution. However, it should be avoided to store it in admixture with expansion material. This is because, before being provided as a shrinkage reducing material, the moisture obtained by the hygroscopic property reacts with the expansion material, and the shrinkage reduction effect is reduced. When provided as an aqueous solution, it is preferably provided at a concentration of less than 45% by weight. If it is 45% by weight or more, there is a high risk that crystals will precipitate at low temperatures. Although the compounding quantity is not specifically limited, 20-500 weight part is preferable with solid content with respect to 100 weight part of expansion | swelling materials, More preferably, 20-400 weight part is preferable. If the amount is too small, no advantage can be obtained over the use of the expandable material alone, and if the amount is too large, the effect is flat and not economical.

The (B) expansion material used in the present invention is not particularly limited as long as it is used as a cement-based expansion material. Currently commercialized products include those of quicklime, ettringite, and composites thereof. The amount added is usually the same as the amount used for cement, 15 to 25 kg per 1 m ³ of the hardened body when using quicklime, and 6 to 6 of the binder when using ettringite. 15% by weight is preferred. Here, the binder refers to (C) pozzolanes such as cement, slag, fly ash, silica fume, metakaolin, and other clay minerals, and expansion materials.

  The (C) cement used in the present invention is normal, early strength, very early strength, moderate heat, low heat, sulfate resistant and other portland cements; ecocement (ordinary type); fine cement, ultrafine cement; alumina cement; A mixed cement with blast furnace slag, fly ash, silica fume and the like; or a mixture of these various cements. Further, a cement partially substituted with limestone powder, a cement obtained by adding gypsum to a mixed cement, or the like can also be used.

  The shrinkage reducing material of the present invention can further contain a shrinkage reducing agent that reduces the surface tension of water used for cement as required. Examples thereof include lower alcohol alkylene oxide adducts, alcohols, glycol ether / amino alcohol derivatives, polyethers, and low molecular weight alkylene oxide copolymers.

  In order to produce a cement-based cured body using the cement shrinkage reducing material of the present invention, the cement shrinkage-reducing material may be added and kneaded and dried for curing during the normal cement-based cured body manufacturing process. Here, examples of the cement-based cured body include a cement mortar cured body and a cement concrete cured body. As a raw material for the cement-based cured body, in addition to cement and the above shrinkage reducing material, as required, various slag powders such as blast furnace slag, converter slag, dephosphorization slag, desulfurization slag, desulfurization slag as a hydraulic component, fly ash, Latent hydraulic substances such as silica fume, metakaolin, and other clay minerals may be added. In addition, aggregates such as coarse aggregate, fine aggregate, lightweight aggregate, slag aggregate, aggregate fine powder, water reducing agent, curing retarder / accelerator, thickener, expansion material, antifoaming agent, rust preventive agent, Organic fibers, inorganic fibers, organic polymers, pigments and the like can also be added.

For kneading, water may be added to the raw material and kneaded by a conventional method. If the drying curing is, for example, about 5 to 35 ° C. in air and about 30% or more in relative humidity, the effect of the present shrinkage reducing material can be obtained.
When the shrinkage reducing material of the present invention is used, it is not necessary to reduce the unit cement amount or the unit water amount, and a sufficient shrinkage reducing effect can be obtained even in curing in a normal dry state in air.

  EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to this at all.

Material adjustment method:
・ Knead with Hobart mixer for 3 minutes.
Test method: Measurement of length change ・ Curing conditions: Demolding after 2 days of molding, measurement of base length, and then curing at 20 ° C.-60% RH until 28 days later.
-Length change measurement method: Conforms to JIS A 1129.
Materials used ・ Cement: Ordinary Portland cement (manufactured by Taiheiyo Cement)
・ Silica sand: Silica sand from Yamagata Prefecture M.M. 1.8
(A) Lithium nitrite: manufactured by LINI 40 (Nissan Chemical) (40% aqueous solution)
→ In the table, the solid content is displayed, and the water content is expressed as the amount of water.
-(B) Expandable material:
Lime → Pacific Expan (for structure) (manufactured by Taiheiyo Materials)
Ettlingite → Taiheiyo Gypcal (Pacific Material)

  The results are shown in Tables 1 to 3.

  As apparent from Tables 1 to 3, the combination of calcium nitrite and the expansion material did not provide a sufficient shrinkage reduction effect, whereas the combination of lithium nitrite and the expansion material provided an excellent shrinkage reduction effect. It was.

Claims (2)

  A shrinkage reducing material for cement containing (A) lithium nitrite and (B) an expanding material.   (A) In the manufacturing process of a cement-type hardened | cured material, (A) lithium nitrite and (B) expansion | swelling material are added, knead | mixing and drying curing, The shrinkage reduction method of the cement-type hardened | cured material characterized by the above-mentioned.