JP4905977B2 - Cement admixture and cement composition - Google Patents

Description

  The present invention mainly relates to a cement admixture and a cement composition used in the civil engineering and construction industries.

In recent years, in the field of civil engineering and architecture, there has been an increasing demand for improving the durability of concrete structures.
One of the deterioration factors of concrete structures is cracking. Cracks impair the reliability of concrete.
There are various causes for the occurrence of cracks, but among them, cracks unique to massive concrete include temperature cracks due to hydration heat generation.

  Various methods have been proposed so far to suppress temperature cracking caused by hydration exotherm. In particular, low-heat Portland cement with a low behydration heat generation and increased belite content not only significantly reduces the hydration heat generation at the time of curing, but also has excellent fluidity during construction, and exhibits medium- and long-term strength development. It has various advantages such as being good.

However, in the cement silos of ready-mix plants, ordinary portland cement, blast furnace cement, and early-strength portland cement, which have a large shipment volume, are stored. First of all, low heat Portland cement is used in a limited form for large-scale properties such as installing a live plant at the site of installation.
Thus, although low heat Portland cement has excellent properties, it is a cement type, and thus has a problem of requiring a new capital investment such as adding a silo.

Suppressing heat of hydration using a set retarder of organic acid or other cement as an admixture type that can be used by opening bags at ready-mixed concrete plants in various regions without requiring additional capital investment such as adding silos. Has been proposed (see Patent Document 1).
However, there has been a problem that strength developability is lowered or condensation is extremely delayed.

In order to improve this problem, admixtures in which quick-setting alkali metal salts such as alkali metal carbonates, silicates, aluminates, and hydroxides are added to organic acids have been proposed (patents). Reference 2).
However, this admixture has a problem that the temperature dependence of the hydration heat suppression effect is large and the hydration heat suppression effect is remarkable at low temperatures, but the hydration heat suppression effect is poor at high temperatures.

Dextrin is also known as a hydration heat inhibitor (see Patent Document 3).
However, dextrin has almost no effect of suppressing heat of hydration at low temperatures, and has a problem that hydration is extremely delayed at high temperatures.

On the other hand, an admixture mainly composed of dextrin and salicylic acid which is a kind of organic acid has been proposed (see Patent Document 4).
However, although this admixture has an effect of suppressing heat of hydration having a small temperature dependence, it has poor strength development.

As a technique for suppressing thermal cracking of massive concrete, so-called mascon, a method of applying a hydration heat inhibitor has been proposed (see Patent Documents 5 to 8).
However, in reality, sufficient performance has not yet been realized, and there is a strong demand for the development of a cement admixture that can effectively suppress temperature cracking in a wide temperature environment from room temperature to high temperature.

On the other hand, humic acid and nitrohumic acid are widely used in the agricultural field such as soil conditioners for the purpose of root activation and maintenance / improvement of geopower.
Nitrohumic acid is obtained, for example, by reacting a pulverized product of young charcoal containing a corrosive substance such as lignite and grass charcoal with nitric acid.
As a soil conditioner, this nitrohumic acid, or magnesium nitrohumate that is reacted with one or more of dolomite, magnesite, magnesia, serpentinite, magnesium silicate, magnesium hydroxide, etc. are proposed. (See Patent Document 9).
However, what effect is produced when this is used as a cement admixture is not known at all.

  The nitrohumic acid and magnesium nitrohumate are mainly composed of humic acid, but the effect of the present invention cannot be obtained simply by mixing humic acid or humic acid salt with cement.

Japanese Patent Laid-Open No. 50-080315 Japanese Patent Publication No. 07-012963 Japanese Patent Publication No.57-000261 JP 60-054955 A Japanese Patent Laid-Open No. 06-305799 JP 2002-137951 A JP 2002-241167 A JP 2003-034564 A Japanese Patent Publication No. 40-014122

  The present invention provides a cement admixture and a cement composition used in civil engineering and building applications.

The present invention, humic acid produced from lignite and nitric acid, and the reaction product obtained from light magnesia, and siliceous material, Ri name contains dextrin, chemical components of the reaction product, 45 is humic acid 58%, soluble MgO 2-13%, SiO ₂ 4-12%, Fe ₂ O ₃ 2-9%, Al ₂ O ₃ 2-8%, and moisture 0-20% Among soluble MgO, water-soluble MgO is 1 to 5%, and in 100 parts of cement admixture composed of reaction product and dextrin, reaction product is 30 to 90 parts and dextrin is 10 to 70 parts. a wood, a said cement admixture siliceous material is sandstone, particle size of the reaction product is a said cement admixture is 600μm or less, cold-water-soluble component of the dextrin is in 0-80% there the a cement admixture, Ri name contains the cement and the cement admixture, cement and cement admixture Ranaru cement composition in 100 parts of a cement admixture is from 0.1 to 5 parts, a cement composition.

  By using the cement admixture of the present invention, it is possible to impart an excellent hydration heat suppression effect in a wide range of temperature environments from room temperature to high temperature, and good mid- to long-term strength development. If it is applied to concrete, an effect is obtained such that a cement composition capable of remarkably reducing temperature cracks can be obtained.

  Unless otherwise specified, parts and% in the present invention are shown on a mass basis.

  The present invention uses a cement admixture containing a reaction product obtained from humic acid produced from lignite and nitric acid, light magnesia, and a siliceous substance, and dextrin.

In the present invention, lignite is used, but other coals such as grass charcoal, lignite, and peat from which humic acid can be obtained by reaction with nitric acid can also be used.
Further, as nitric acid, one having a concentration of 20 to 50% is usually used.
Light magnesia neutralizes the produced humic acid. In the present invention, dolomite, magnesite, magnesium hydroxide, and the like can also be used.
Examples of siliceous substances include silica and sandstone, but sandstone is usually used.

First, lignite is oxidized and decomposed with nitric acid to produce humic acid, and light magnesia and siliceous substances are added to neutralize it to produce a neutralized product.
The use ratio of lignite and nitric acid is not particularly limited, but usually 40 to 70 parts of nitric acid in terms of anhydrous matter is preferable to 100 parts of lignite in terms of dry matter.
The use ratio of light magnesia and siliceous material is not particularly limited, but when sandstone is used as siliceous material, it is usually 5-30 parts of light magnesia against 100 parts of lignite in terms of dry matter. 10 to 25 parts are preferred.
The neutralized product is granulated and then dried to form a reaction product using water or the like.

  In the present invention, the reaction product obtained from humic acid, light magnesia, and siliceous substance produced from lignite and nitric acid (hereinafter simply referred to as reaction product) is used after adjusting the particle size by classification and grinding treatment, etc. Is possible. Among these, it is preferable to use a fine particle portion of 600 μm or less. Further, it is possible to use a humic acid bitter fertilizer produced in the same manner as it is or after adjusting the particle size by sieving, classification, pulverization or the like.

Chemical components of the reaction product of the present invention is usually humic acid 45-58%, Ku-soluble MgO is 2 to 13% SiO ₂ is 4 to 12% Fe ₂ O ₃ is 2 to 9% Al ₂ O ₃ is 2 to 8% and moisture is 0 to 20%. In addition, water-soluble MgO is 1 to 5% among soluble MgO.
Here, the highly soluble MgO means MgO dissolved in a 2% aqueous citric acid solution, and the water-soluble MgO is included in the soluble MgO.

The reaction product of the present invention is mainly composed of humic acid on the chemical component, but the effect of the present invention cannot be obtained by simply using humic acid or a salt thereof.
This has been found through numerous experiments. The cause is not clear, but it is presumed that a unique composite material is formed by the interaction with light silicic substances such as light magnesia and sandstone added in the process of producing the reaction product.
It is also possible that the solubility of chemical components varies depending on the combination with these silicic substances such as light magnesia and sandstone.

  The MgO component contained in the reaction product contains a mixture that is soluble in water and a component that is sparingly soluble. This is also considered to be one factor that produces the effects of the present invention.

  The particle size of the reaction product is not particularly limited, but it is usually preferable to use a fine particle having a particle size of 600 μm or less. When coarse particles are contained, there is a possibility that a sufficient effect of suppressing heat of hydration may not be obtained, and strength development may be deteriorated.

  Dextrin is generally called a modified starch, and is usually obtained by hydrolyzing corn starch, potato, tapioca starch, wheat starch, sweet potato starch, rice starch, and the like. Above all, acid roasted dextrin obtained by adding dilute acid and decomposing to these starches is the most common, dextrin obtained by acid dipping method, maltodextrin obtained by enzymatic degradation of starch, The resulting British gum or starch-added water is heated, or the pregelatinized starch obtained by rapid dehydration of an alkali or concentrated salt solution added to alpha is used. It is possible to use a powder or the like from which most of the soluble part in the cold water is removed by dissolving in the solution and drying the residue. In addition, those obtained by chemical modification such as carboxylic acid esterification, carbonic acid esterification, and etherification can be used.

Here, the cold water soluble part of dextrin means the amount of dextrin dissolved in distilled water at a temperature of 20 ° C. Specifically, for example, 10 g of dextrin is put in a 200 ml flask and the temperature is 20 150ml distilled water at 150 ° C was added and kept at a temperature of 20 ± 1 ° C for 1 hour, then filtered, the filtrate was evaporated to dryness, and the resulting dextrin was shown as a percentage of the total amount of dextrin used. .
In the present invention, the cold water soluble content at 20 ° C. is preferably 0 to 80%, more preferably 5 to 70%, and most preferably 10 to 50%. If the cold water soluble content exceeds 80%, the effect of suppressing the heat of hydration may not be obtained. Moreover, there is a possibility that the setting delay property becomes stronger and the strength development property becomes worse.

  The mixing ratio of the reaction product and dextrin in the cement admixture is not particularly limited, but usually, in 100 parts of the cement admixture composed of the reaction product and dextrin, the reaction product is 30 to 90 parts. Preferably, 40 to 80 parts are more preferable. The dextrin is preferably 10 to 70 parts, more preferably 20 to 60 parts. When the reaction product is less than 30 parts and the dextrin exceeds 70 parts, the effect of suppressing heat of hydration in an environment of 25 ° C. or lower is not sufficient, and the effect of suppressing temperature cracking may not be sufficiently obtained. On the other hand, in a high temperature environment of 30 ° C. or higher, the setting delay is remarkably increased and the strength development may be deteriorated. If the reaction product exceeds 90 parts and the dextrin is less than 10 parts, the effect of suppressing hydration heat generation may not be sufficient in a high temperature environment exceeding 30 ° C., and the effect of suppressing temperature cracking is sufficient. There is a risk that it will not be demonstrated.

  Although the usage-amount of the cement admixture of this invention is not specifically limited, Usually, 0.1-5 parts are preferable in a cement composition which consists of a cement and a cement admixture, and 0.3-3 parts are more preferable. If the amount of the cement admixture used is small, a sufficient effect of suppressing hydration heat may not be obtained, and if used excessively, strength development may be deteriorated.

  Here, as the cement, various portland cements such as normal, early strength, super early strength, low heat, and moderate heat, various mixed cements obtained by mixing blast furnace slag, fly ash, or silica with these portland cements, limestone powder And filler cement mixed with blast furnace slow-cooled slag fine powder, etc., and environmentally friendly cement (eco-cement) manufactured using municipal waste incineration ash and sewage sludge incineration ash as raw materials. More than species can be used.

  The cement admixture and cement composition of the present invention may be mixed at the time of construction, or may be partially or wholly mixed in advance.

  In the present invention, fine aggregates such as sand, coarse aggregates such as gravel, expanded materials, quick hard materials, water reducing agents, AE water reducing agents, high performance water reducing agents, high performance AE water reducing agents, antifoaming agents, Various additives such as sticky agent, rust preventive agent, antifreeze agent, shrinkage reducing agent, polymer emulsion, setting modifier, clay mineral such as bentonite, anion exchanger such as hydrotalcite, etc., ground granulated blast furnace slag , One or more selected from the group consisting of admixed materials such as blast furnace slow-cooled slag fine powder, limestone fine powder, fly ash, and silica fume, etc. are used in a range that does not substantially impair the object of the present invention. It is possible.

  Hereinafter, the present invention will be described in more detail based on experimental examples, but the present invention is not limited thereto.

Experimental example 1
A cement admixture containing 60 parts of the reaction product shown in Table 1 and 40 parts of dextrin A was used, and the temperature cracking suppression effect of mass concrete was examined.
Use 100 parts of cement composition consisting of cement α and cement admixture, 1 part of cement admixture, unit cement composition amount 300kg / m ³ , unit water amount 170kg / m ³ , s / a = 47%, slump 18cm Then, concrete with a design strength of 21 N / mm ² was prepared, the compressive strength and the adiabatic temperature rise were measured, and the occurrence of cracks was evaluated. The results are also shown in Table 1.
For comparison, the same procedure was performed when commercially available humic acid was used as a cement admixture.

<Materials used>
Cement α: Commercially available ordinary Portland cement, specific gravity 3.15
Dextrin A: 30% cold water soluble, commercially available fine aggregate: Himekawa, Niigata Prefecture, specific gravity 2.62, maximum aggregate size 5 mm
Coarse aggregate: Himekawa, Niigata prefecture, specific gravity 2.64, maximum aggregate size 25mm
Water: Tap water Commercially available humic acid: Reagent, Humic acid

<Measurement method>
Compressive strength: Measured adiabatic temperature rise according to JIS A 1108: Adiabatic temperature rise test apparatus manufactured by Tokyo Riko Co., Ltd. was used to measure the temperature rise from concrete mixing. The concrete temperature and the ambient temperature of the kneading were set to 20 ° C. ± 2 ° C. and 35 ° C. ± 2 ° C.
Cracks: Cracking condition, concrete with 20 ° C ± 2 ° C and 35 ° C ± 2 ° C concrete temperature after completion, the formwork is kept up to 7 days old, thickness 1m, height 2.5m , Create a 10m long wall, measure the occurrence of cracks on the age of 28 days, excellent when there are no cracks that can be observed visually, the number of cracks is one, and the crack width is less than 0.05mm Good, the number of cracks is one, but the crack width is 0.1mm or more and less than 0.2mm, and two or more cracks have occurred, or the number of cracks is one, but the crack width is 0.2 The case of more than mm was made impossible.

Experimental example 2
The same reaction product as in Experiment No. 1-1 was used, and the same procedure as in Experimental Example 1 was performed except that the dextrin shown in Table 2 was used. The results are also shown in Table 2.

<Materials used>
Dextrin B: cold water soluble component 0%, commercial product dextrin C: cold water soluble component 5%, commercial product dextrin D: cold water soluble component 10%, commercial product dextrin E: cold water soluble component 50%, commercial product dextrin F : Cold water soluble 70%, commercial dextrin G: Cold water soluble 80%, commercial

Experimental example 3
The experiment was carried out in the same manner as in Experiment Example 1 except that a cement admixture consisting of 60 parts of the reaction product with the maximum particle size shown in Table 3 and 40 parts of dextrin was used. The results are also shown in Table 3.

Experimental Example 4
The same procedure as in Experimental Example 1 was conducted except that the cement admixture containing 60 parts of the same reaction product as in Experiment No. 1-1 and 40 parts of dextrin A was used in the amounts shown in Table 4. The results are also shown in Table 4.

Experimental Example 5
The same procedure as in Experimental Example 1 was conducted except that a cement admixture containing 60 parts of the same reaction product as in Experiment No. 1-1 and 40 parts of dextrin A and the cement shown in Table 5 were used. The results are also shown in Table 5.

<Materials used>
Cement β: Commercial blast furnace cement type B, specific gravity 3.06

  By using the cement admixture of the present invention, it is possible to give an excellent hydration heat suppression effect in a wide temperature environment from normal temperature to high temperature range, and it has little influence on strength development, and medium to long term strength development It has good properties, and if applied to mass concrete or prestressed concrete, it has the effect of obtaining a cement composition that can significantly reduce temperature cracking.

Claims (5)

Humic acid produced from lignite and nitric acid, and the reaction product obtained from light magnesia, and siliceous material, Ri name contains dextrin, chemical components of the reaction product, humic acid 45-58 wt%, Ku-soluble MgO is 2 to 13 wt%, SiO ₂ is from 4 to 12 wt%, Fe ₂ O ₃ is 2-9 wt%, Al ₂ O ₃ is 2-8 wt%, and water in 0-20 wt% Further, among the soluble MgO, a cement admixture containing 1 to 5% by mass of water-soluble MgO and 10 to 70 parts by mass of dextrin in 100 parts by mass of the cement admixture composed of the reaction product and dextrin .   The cement admixture according to claim 1, wherein the siliceous substance is sandstone.   The cement admixture according to claim 1 or 2, wherein the particle size of the reaction product is 600 µm or less. The cement admixture according to any one of claims 1 to 3 , wherein the dextrin has a cold water soluble content of 0 to 80% by mass . Cement, Ri name contains the cement admixture according to any one of claims 1 to 4, the cement composition 100 parts by mass consisting of cement and a cement admixture, a cement admixture is Cement composition which is 0.1-5 mass parts .