JP6661430B2 - Cement admixture and concrete using it - Google Patents

Description

The present invention relates to a cement admixture mainly used in the field of civil engineering and construction, particularly to an expandable cement admixture and concrete using the same.

When concrete is applied, the temperature of the concrete rises due to the heat of hydration of the cement. In particular, in mass concrete, it is known that "temperature cracks" are caused by the rise and fall of the temperature. As countermeasures, (1) use of low heat type cement, (2) use of admixture (agent), and the like can be mentioned.

Examples of the low heat-generating cement of (1) are Portland cement, which is a mixture of blast furnace slag with latent hydraulic property and fly ash of pozzolanic substance in large amounts, and low heat Portland cement, which has an increased content of belite in the cement. And the like are used, and the initial calorific value of hydration can be significantly reduced. As the admixture (agent) of (2), it has been proposed that an expanding material that imparts compressive stress to hardened concrete and a hydration heat inhibitor that affects the hydration heat generation properties of cement are effective (for example, Patent Documents 1 and 2).

JP 2001-48615 A JP 2001-122649 A

The method (1) is the most commonly used method, but low heat cement or moderate heat cement may be difficult to obtain in some regions, and unless it is a ready-mixed concrete company that has a dedicated silo. There is a current situation that ready-mixed concrete cannot be shipped. It is said that mixed cement such as fly ash cement has a large effect on fresh properties such as air volume adjustment and is difficult to handle.

On the other hand, although the hydration heat inhibitor in the method (2) is effective in suppressing the heat of hydration of cement, when added in an excessive amount, it suppresses the hydration of the cement and lowers the strength developability. It is difficult to handle because the solubility of the active ingredient is easily affected by temperature. In addition, the expansive material uses volume expansion accompanying the reaction of expansive components such as quicklime with water. However, if the reaction is too fast for hydration and hardening of cement, an effective expansion amount is obtained. Can not. When used in combination with a hydration heat inhibitor that affects the hydration of cement, it is difficult to suppress the heat generation of the concrete as a whole and to secure a stable expansion amount unless it is prepared particularly in a well-balanced manner. For this reason, when a general-purpose expander is used, it has been difficult to obtain concrete excellent in the temperature cracking effect.

The present invention has been made through various studies to solve the above-mentioned problems, and as a result, by using a specific cement admixture, and by producing concrete using the cement admixture, a finding that the above-mentioned problems can be solved. As a result, the present invention has been completed. Here, the concrete is a generic term for cement paste, mortar and concrete.

That is, the solution according to the present invention is as follows.
[1] A cement admixture containing an expansive substance and a heat-of-hydration-inhibiting component, and having a particle content of 10 μm or less of the expansive substance of 30 to 50% by mass.
[2] The cement admixture of [1], wherein the hydration heat inhibiting component is dextrin.
[3] Concrete containing the cement admixture of [1] or [2].
[4] The concrete according to [3], which has the following characteristics.
(1) The expansion coefficient is 200 ± 20 × 10 ⁻⁶ ,
(2) The ratio (T ₁ / T ₀ ) of the maximum heat generation temperature (T ₁ ) of the concrete containing the cement admixture to the maximum heat generation temperature (T ₀ ) of the concrete not containing the cement admixture is less than 1. Being,
(3) The ratio of the compressive strength (S ₁ ) of the concrete containing the cement admixture at the age of 28 to the compressive strength (S ₀ ) of the concrete containing the cement admixture at the age of 28 (S ₁ /). S ₀ ) is 0.95 or more.

By using the cement admixture of the present invention, a good expansion property without reducing strength, an effect of suppressing heat of hydration can be obtained, and concrete having a high effect of reducing temperature cracking can be obtained.

Hereinafter, the present invention will be described in detail.
The cement admixture of the present invention contains an expanding substance having a particle content of 10 μm or less in the range of 30 to 50% by mass and a heat of hydration suppressing component. By using the expanding substance and the hydration heat suppressing component in combination, the heat generation is suppressed and a cement composition having expandability can be obtained. However, in order to obtain concrete excellent in temperature cracking performance, a predetermined expansion rate (specifically, ^{Specifically,} it is necessary to stably express 200 ± 20 × 10 ⁻⁶ ). However, when using a general-purpose expanding material, it is difficult to adjust the composition, and as a result of various studies, it is found that there is a relationship between the particle size distribution of the expanding material and the effect of the heat of hydration inhibitor. I found something. In other words, by setting the content of the fine particles of the expanding substance (particle content of 10 μm or less) in a predetermined range, when used in combination with the hydration heat inhibitor, it has a stable expansion rate It has been found that heat is suppressed and strength does not decrease. Although this mechanism is not known exactly, the control of the fine particles of the expansive substance controls the timing of the heat generation and the onset of expansion by the expansive material, and as a result, the hardening and strength due to the hydration of the cement adjusted by the hydration heat suppression component. It is presumed that the expression timing matched well.

The expansive substance used in the present invention may be any substance that exhibits expansive properties by generating crystals by hydration. Specifically, expansive calcined material containing quicklime and free quicklime, 3CaO.3Al Examples thereof include calcium sulfoaluminate-based compounds represented by ₂ O ₃ .CaSO ₄ , magnesia, gypsum and the like, and one kind or a mixture of two or more kinds is used. In the present invention, it is particularly preferable to use an expanded calcined product containing quicklime or free quicklime as a main component. Further, a quick lime-gypsum type to which gypsum is added is preferable.

Here, the expansive calcined product containing free quick lime is a calcined product obtained by calcining a calcining material containing a calcium-based material such as calcium carbonate, slaked lime, and quick lime. In addition to the calcium raw material, a silica raw material, an alumina raw material, an iron oxide raw material, gypsum, etc. may be added to the calcined raw material. The firing temperature when firing the firing raw material is 1100 to 1500 ° C. A furnace whose temperature can be adjusted, such as a rotary kiln or an electric furnace, is used for firing. The fired product is adjusted to a predetermined particle size by performing pulverization and classification.

The particle content of 10 μm or less of the expanding material in the present invention needs to be in the range of 30 to 50% by mass. If the amount is less than 30% by mass, it is difficult to stably develop a predetermined expansion coefficient. On the other hand, if it exceeds 50% by mass, the effect of suppressing heat of hydration cannot be obtained, which is not preferable. Note that the maximum particle size is preferably 300 μm or less.

  Examples of the heat of hydration suppression component in the present invention include dextrins, sugars such as monosaccharides and oligosaccharides, oxycarboxylic acids and salts thereof, and may be used alone or as a mixture of two or more. Of these, dextrin is particularly preferred.

Dextrin is also commonly referred to as modified starch, and is obtained by grafting potato, sweet potato, corn, tapioca, wheat, and other raw starches by acid decomposition, oxidation, esterification, etherification, cross-linking, and copolymerization of synthetic polymers. Chemically treated to reduce the molecular weight. Those soluble in water are preferred.

  The content of the heat of hydration suppression component is preferably from 0.5 to 6 parts by mass, more preferably from 1 to 5 parts by mass, based on 100 parts by mass of the expansive substance, from the viewpoint of heat of hydration suppression and strength development.

The amount of concrete using the cement admixture of the present invention, from the viewpoint of a predetermined expansive securing and early strength development, preferably ^{10~30kg / m 3, 15~25kg / m} 3 and more preferably.

Various cements can be used in the present invention, and for example, Portland cement and mixed cement can be used. Such Portland cements include, for example, various Portland cements such as ordinary, fast, super fast, low heat and moderate heat. Examples of the mixed cement include various mixed cements in which fly ash, blast furnace slag, silica fume, limestone fine powder, and the like are mixed. Any one of these cements can be selected and used, but two or more cements may be used in combination. For mass concrete in consideration of temperature cracking, low-heat Portland cement and mixed cement are often used. However, according to the technology of the present invention, good performance can be obtained even by using general-purpose ordinary Portland cement.

The aggregate used in producing concrete in the present invention is not particularly limited, and any of fine aggregate and coarse aggregate used in ordinary production of concrete can be used. Such fine and coarse aggregates include, for example, river sand, sea sand, mountain sand, crushed sand, artificial fine aggregate, slag fine aggregate, recycled fine aggregate, silica sand, river gravel, land gravel, crushed stone, artificial coarse Aggregate, slag coarse aggregate, recycled coarse aggregate and the like can be mentioned. The amount of aggregate is preferably 800~1100kg / ^{m 3} at 700~1000kg / ^{m 3,} the coarse aggregate fine aggregate, a further fine aggregate 800~900kg / ^{m 3,} the coarse aggregate 900~1000kg / M ³ is preferred.

The water used when producing the concrete in the present invention is not particularly limited, and tap water or the like can be used. The blending amount of water (unit water amount) is preferably 150 to 180 kg / m ³ from the viewpoint of increasing material separation resistance. Further, the mixing amount of water is preferably 40 to 60 parts by mass with respect to 100 parts by mass of cement.

In the present invention, various additives (materials) may be used in combination as long as the characteristics are not impaired. Examples of such additives include water reducing agents, AE water reducing agents, high-performance water reducing agents, high-performance AE water reducing agents, dispersants such as fluidizing agents, setting retarders, strength promoters, polymers for cement, fibers, and foams. Agents, foaming agents, waterproofing agents, rust inhibitors, shrinkage reducing agents, thickeners, water retention agents, pigments, water repellents, anti-whitening agents, defoaming agents, and the like.

In the concrete of the present invention, heat generation is reduced, stable expansion performance is obtained, and sufficient strength is obtained. Specifically, the following good characteristics can be obtained.
(1) The ratio (T ₁ / T ₀ ) of the maximum temperature (T ₁ ) of the concrete containing the cement admixture to the maximum temperature (T ₀ ) of the concrete not containing the cement admixture is less than 1.
(2) The expansion rate at the age of 7 days is 200 ± 20 × 10 ⁻⁶ .
(3) The ratio of the compressive strength (S ₁ ) of the concrete containing the cement admixture at the age of 28 to the compressive strength (S ₀ ) of the concrete containing the cement admixture at the age of 28 (S ₁ /). S ₀ ) is 0.95 or more.

Therefore, by using the cement admixture of the present invention, it is possible to obtain concrete excellent in resistance to temperature cracks, and it is suitably used, for example, for mass concrete.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Table 1 shows expanding substances having different contents of 10 μm or less. The cement admixture comprising the swelling substance and the hydration heat inhibiting component was blended as shown in Table 1. Each unit dose cement 336kg / ^{m 3,} fine aggregates 815kg / ^{m 3,} the coarse aggregate 968kg / ^{m 3} and water 168 kg / ^{m 3,} based on the concrete water-reducing agent was blended 1.0 weight% on cement When concrete was used and a cement admixture was used, 20 kg / m ³ was replaced with cement. The production of concrete was performed using a 50-liter pan mixer, and the mixing time was 2 minutes.
As an evaluation test, a hydration heat suppression effect test, a compressive strength test, and a length change (expansion coefficient) test were performed.
As a result, as shown in Table 2, when the cement admixture using the dextrin in combination with the swelling substance having a content of 10 μm or less of 30 to 50% is used, the maximum temperature is suppressed, and good swelling properties and strength are obtained. It can be seen that it can be obtained.

<Material used>
(1) Swelling substance: quicklime-gypsum / swelling substance A: The content of 10 μm or less is 25%.
・ Expansion substance B: The content of 10 μm or less is 30%.
・ Expansion substance C: The content of 10 μm or less is 40%.
・ Expansion substance D: The content of 10 μm or less is 50%.
・ Expansion substance E: content of 10 μm or less is 55%
(2) Hydration heat inhibitor: dextrin (solubility: 50% type)
(3) Cement: ordinary Portland cement, manufactured by Taiheiyo Cement Co., density: 3.16 g / cm ³
(4) Coarse aggregate: crushed stone, Gmax: 20 mm
(5) Fine aggregate: mountain sand (from Kakegawa)
(6) Water reducing agent: Lignin sulfonic acid AE water reducing agent

<Test method>
(1) Hydration heat suppression effect test: The prepared ready-mixed concrete is poured into a foaming container of W28 × D18 × H14 cm (about 7 liters) to be in a simple insulated state. The central temperature of concrete in the simple heat insulation state was measured, and the effect of suppressing hydration heat was confirmed. The ratio (T ₁ / T ₀ ) of the maximum temperature (T ₁ ) of the concrete containing the cement admixture to the maximum temperature (T ₀ ) of the concrete not containing the cement admixture was evaluated. Less than 1 was regarded as good.
(2) Compressive strength test: In accordance with JIS A 1108 “Method for testing compressive strength of concrete”. The ratio (S ₁ / S ₀ ) of the compressive strength (S ₁ ) of the concrete containing the cement admixture at the age of 28 days to the compressive strength (S ₀ ) of the concrete containing the cement admixture at the age of 28 days was calculated. Was evaluated. 0.95 or more was regarded as good.
(3) Length change (expansion coefficient) test: In accordance with JIS A 6202 “Expanding material for concrete” Reference 1 “Test method for restraining expansion and shrinkage of expanded concrete” (Method A). When converted by the expansion rate at the age of 7 days, 200 ± 20 × 10 ⁻⁶ was regarded as good.

Claims (4)

An intumescent material containing an intumescent substance mainly composed of an intumescent calcined product containing quicklime or free quicklime and a heat of hydration suppressing component, and having a particle content of 10 μm or less of the intumescent material of 30 to 50 mass% . Cement admixture. The expandable cement admixture according to claim 1, wherein the hydration heat inhibiting component is dextrin. Concrete containing the expansive cement admixture according to claim 1 or 2. The concrete according to claim 3, which has the following properties.
(1) The expansion coefficient is 200 ± 20 × 10 ⁻⁶ ,
(2) said expandable to the highest heating temperature of the concrete containing no cement admixture _{(T 0),} the ratio of the maximum heating temperature of the concrete containing the expansive cement admixture _{(T 1) (T 1 /} T 0 ) Is less than 1;
(3) the ratio of the compressive strength of expandable cement Compressive strength at the age of 28 days of concrete containing no admixture for (S _0), the expandable cement admixture concrete at the age of 28, including the day (S _{1) (S} 1 / _{S 0)} is 0.95 or greater.