JP2020093940A - Cement admixture, and concrete using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an admixture capable of stably exhibiting a predetermined expansion coefficient while suppressing a temperature rise even under an adiabatic condition such as mass concrete, and concrete using the admixture. SOLUTION: The expansive calcined product and the heat of hydration suppressing component are contained, and the expansive calcined product has a particle content of 0 to less than 30% by mass and a particle content of 150 μm or more to 0 to 2% by mass. % Cement admixture. The heat of hydration suppressing component is preferably dextrin. [Selection diagram] None

Description

TECHNICAL FIELD The present invention relates to a cement admixture mainly used in the field of civil engineering/construction, particularly an expansive 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, mass concrete is known to cause "temperature cracks" caused by the temperature rise and fall. As measures against this, (1) low-heat type cement is used, (2) admixture (agent) is used, and the like.

The low heat generation type cement of (1) is a mixture of Portland cement with a large amount of latent hydraulic blast furnace slag and fly ash of pozzolanic material, and low heat Portland cement with an increased content of belite in the cement. Etc. are used, and the initial heat of hydration can be significantly reduced. As the admixture (agent) of (2), it is proposed that an expansive material that gives a compressive stress to the hardened concrete and a heat of hydration inhibitor that affects the heat of hydration of cement are effective (for example, Patent Documents 1 and 2).

The heat of hydration inhibitor in the method using the admixture has an effect on the heat of hydration of the cement, but when excessively added, it suppresses the hydration of the cement and the strength developability decreases, and the active ingredient Solubility is difficult to handle because it is easily affected by temperature. In addition, the expansive material utilizes the volume expansion associated with the reaction of expansive components such as quicklime with water, but if the reaction is too fast for the hydration and hardening of the cement, an effective expansion amount can be obtained. I can't. When used in combination with a heat of hydration inhibitor that affects the hydration of cement, it is difficult to secure a stable expansion amount while suppressing the heat generation of concrete as a whole unless it is prepared in a well-balanced manner. Therefore, when a general-purpose expansive material is used, it is difficult to obtain concrete having an excellent temperature cracking effect.

As a technique for solving the above, a cement admixture has been proposed which contains an expansive substance and a heat of hydration suppressing component, and has a particle content of 10 μm or less of the expansive substance of 30 to 50% by mass (Patent Document). 3). By setting the content rate of fine particles of the expansive substance (particle content rate of 10 μm or less) within a predetermined range, good expansivity and hydration heat suppressing effect can be obtained without lowering the strength, and temperature cracking can be reduced. It has been shown that highly effective concrete can be obtained.

JP 2001-48615 A JP 2001-122649 A JP, 2017-165627, A

However, in the case where the expansive substance has a large content of particles of 10 μm or less, the temperature rise becomes large under the adiabatic condition as in mass concrete, which may cause temperature cracking. If an excessive amount of heat of hydration suppressing component is added to suppress this temperature rise, the reaction of the expansive material will proceed rapidly before the hydration of the cement is suppressed and the setting of the concrete begins, and the good expansion properties May not be obtained.

The present invention provides an admixture capable of stably exhibiting a predetermined expansion coefficient while suppressing an increase in temperature even under an adiabatic condition such as in mass concrete, and concrete using the admixture.

The present invention, in order to solve the above problems, paying attention to the particle size of the expansive burned material constituting the expansive substance, as a result of various studies, a cement admixture containing an expansive burned material having a specific particle size is used. In this way, and by producing concrete using the cement admixture, the knowledge that the above problems can be solved was obtained, and the present invention was completed. Here, concrete is a general term for cement paste, mortar and concrete.
That is, the present invention is as follows.
[1] An expansive calcined product and a heat of hydration suppressing component are contained, the content of particles of 10 μm or less of the expansive calcined product is 0 to less than 30% by mass, and the content of particles of more than 150 μm is 0 to 2. Cement admixture with mass%.
[2] The cement admixture according to [1], wherein the heat of hydration suppressing 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±30×10 ⁻⁶ .
(2) In an adiabatic temperature rise test according to JCI-SQA3 “Adiabatic temperature rise test method for concrete (draft)”, the amount of adiabatic temperature rise (T _{0 of the} base admixture containing no cement admixture at 7 days of age) ), the ratio (T ₁ /T ₀ ) of the adiabatic temperature rise amount (T ₁ ) of the concrete in which the cement admixture is added by cement substitution in the base concrete mixture is less than 1.000, and the age is 14 days. The ratio (T ₁ /T ₀ ) at is less than 1.000.

By using the cement admixture of the present invention, even in mass concrete or the like, it is possible to stably develop a predetermined expansion coefficient while suppressing an increase in temperature and obtain concrete having a high effect of reducing temperature cracks.

The cement admixture in the present invention contains an expansive fired product having a predetermined particle size distribution and a heat of hydration suppressing component.

The expansive calcined product used in the present invention may be any calcined product that exhibits expansive properties by forming crystals by hydration, and specifically, free quicklime (CaO), 3CaO.3Al ₂ O ₃ An expansive calcined product containing a calcium sulfaluminate compound typified by CaSO ₄ , magnesia (MgO), calcium sulfate (CaSO ₄ ) or the like is used, and one kind or a mixture of two or more kinds is used. In the present invention, an expansive calcined product containing free quicklime as a main component is particularly preferable. The amount of free quick lime is preferably 50% by mass or more.

The expansive calcined product uses calcined raw materials such as calcium carbonate, slaked lime, and quick lime, siliceous raw material, aluminous raw material, iron oxide raw material, and gypsum as calcined raw materials, and is calcined at a temperature of 1100 to 1500°C. .. For the firing, a temperature-adjustable furnace such as a rotary kiln or an electric furnace is used. The fired product is crushed and classified to have a predetermined particle size.

The content of particles of 10 µm or less of the expandable fired product in the present invention is 0 to less than 30% by mass. Further, the content of particles of the expandable fired product in the present invention of 150 μm or more is 0 to 2% by mass. When the content of particles of 10 μm or less of the expandable fired product is 30% by mass or more, the effect of suppressing the heat of hydration cannot be obtained. Further, if the content of particles of 150 μm or more in the expandable fired product exceeds 2% by mass, it becomes difficult to stably exhibit a predetermined expansion coefficient, and the hydration heat generation suppressing effect cannot be obtained.
The content of particles of 10 µm or less of the expansive fired product is preferably 0 to 29% by mass, more preferably 1 to 28% by mass. In addition, the content of particles of 150 µm or more of the expandable fired product is preferably 0 to 1% by mass, more preferably 0 to 0.5% by mass.

Examples of the heat of hydration suppressing component in the present invention include saccharides such as dextrin, monosaccharides and oligosaccharides, oxycarboxylic acids and salts thereof, and they may be used alone or in combination of two or more. Of these, dextrin is particularly preferable.

Dextrin, which is also commonly called modified starch, is used to graft potatoes, sweet potatoes, corn, tapioca, wheat, and other raw starches by acid decomposition, oxidation, esterification, etherification, crosslinking, and copolymerization of synthetic polymers. Chemically treated to reduce the molecular weight. Those that are soluble in water are preferred.

The content of the heat of hydration suppressing component is preferably 0.5 to 6 parts by mass, and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the expansive calcined product, from the viewpoint of suppressing hydration heat and strength development. ..

Gypsum can be further added to the cement admixture in the present invention. Examples of gypsum include anhydrous gypsum, gypsum dihydrate, and gypsum hemihydrate. Anhydrous gypsum is particularly preferable. The amount of plaster compounded is preferably 0 to 50 parts by mass, and more preferably 5 to 40 parts by mass, relative to 100 parts by mass of the expandable fired product.

The content of the cement admixture in the concrete of the present invention in the concrete is preferably 10 to ³⁰ kg/m ^{3 and} more preferably 15 to 25 kg/m ³ from the viewpoints of ensuring a predetermined expandability and exhibiting initial strength.

Various cements can be used in the present invention, and for example, Portland cement or mixed cement can be used. Examples of such Portland cement include various Portland cements such as normal, early strength, ultra-early strength, low heat and moderate heat. Examples of the mixed cement include various mixed cements mixed with fly ash, blast furnace slag, silica fume, limestone fine powder, and the like. Any one of these cements may be selected and used, or two or more types of cement may be used in combination. Although low heat Portland cement and mixed cement are often used for mass concrete considering temperature cracking, the technique of the present invention can provide good performance even when general-purpose ordinary Portland cement is used.

The aggregate used in producing the concrete in the present invention is not particularly limited, and both fine aggregate and coarse aggregate used in ordinary production of concrete can be used. Examples of such fine aggregates and coarse aggregates include 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. Examples thereof include aggregate, slag coarse aggregate, recycled coarse aggregate and the like. 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 amount of water (unit amount of water) is preferably 150 to 180 kg/m ^{3 in} order to increase the resistance to material separation. Further, the blending amount of water is preferably 40 to 60 parts by mass with respect to 100 parts by mass of cement.

Various additives (materials) may be used in combination with the concrete in the present invention as long as the characteristics thereof are not impaired. Examples of this type of additive include water reducing agents, AE water reducing agents, high performance water reducing agents, high performance AE water reducing agents, dispersants such as superplasticizers, setting retarders, strength accelerators, cement polymers, fibers, and foams. Agents, foaming agents, waterproofing agents, rust preventives, shrinkage reducing agents, thickeners, water retention agents, pigments, water repellents, anti-whitening agents, antifoaming agents and the like.

The concrete of the present invention has reduced heat generation and stable expansion performance. Specifically, the following good characteristics can be obtained.
(1) The expansion coefficient at the age of 7 days is 200±30×10 ⁻⁶ .
(2) Adiabatic temperature rise amount of concrete with cement admixture added by cement substitution (amount of adiabatic temperature rise of base admixture containing no cement admixture (T ₀ ) at 7 days and 14 days of age) T ₁ ratio _(T 1 / T ₀₎ of) it is less than 1.000.
Therefore, by using the cement admixture of the present invention, it is possible to obtain concrete having excellent resistance to temperature cracks, and it is suitable for use in, for example, mass concrete.

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

<Expandable fired product>
A mixture of silica stone, shale shale, iron oxide, anhydrous gypsum and industrial quicklime was fired at 1400° C. using an electric furnace to pulverize the mixture to produce an expansive fired product containing 60% by mass of free quicklime. .. The main minerals other than free quick lime contained in the expandable fired product are calcium silicate (3CaO.SiO ₂ ) and calcium sulfate (CaSO ₄ ). The produced expansive fired product was crushed by a ball mill and then sieved (classified) by a vacuum suction type dry sieving device (air jet sieve) using sieves having openings of 10 μm, 40 μm, 70 μm, 100 μm and 150 μm. .. The classified intumescent products were adjusted to have the ratio shown in Table 1.

<Materials used>
(1) Expandable calcined product: the above particle size control product (2) Hydration heat inhibitor: Dextrin, 50% soluble type (3) Gypsum: Anhydrite (4) Cement: Ordinary Portland cement, Taiheiyo Cement Co., Density: 3.16 g/cm ³
(5) Coarse aggregate: crushed stone, Gmax: 20 mm
(6) Fine aggregate: Mountain sand (from Kakegawa)
(7) Water reducing agent: Lignin sulfonic acid type AE water reducing agent

Table 1 shows the composition of the cement admixture consisting of the particle size-adjusted product of the expansive fired product, anhydrous gypsum and dextrin. 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 Concrete (standard mix) was used. When a cement admixture was used, 20 kg/m ³ was used by replacing it with cement. The concrete was manufactured using a 50-liter pan mixer, and the mixing time was 2 minutes.

<Evaluation test>
As the evaluation test, adiabatic temperature rise test and length change (expansion rate) test were performed. Each test method is described below.
(1) Adiabatic temperature rise test: According to JCI-SQA3 "Adiabatic temperature rise test method for concrete (plan)". At 7 days of age and 14 days of age, the cement admixture was added by cement replacement in the base concrete composition to the adiabatic temperature increase amount (T ₀ ) of the base concrete not containing the cement admixture (standard composition). The ratio (T ₁ /T ₀ ) of the adiabatic temperature rise amount (T ₁ ) of the prepared concrete was evaluated. Less than 1.000 was considered good.
(2) Length change (expansion rate) test: According to JIS A 6202 “Expansion material for concrete” Reference 1 “Test method for constrained expansion and contraction of expanded concrete” (method A). It was converted into the expansion coefficient after 7 days of age, and 200±30×10 ⁻⁶ was regarded as good.

<Test results>
As a result, as shown in Table 2, when a cement admixture containing an expandable fired product having a content of 10 μm or less of less than 30 mass% and a content of more than 150 μm of 1% or less is used, It can be seen that the rise of the adiabatic temperature on the 14th and the 14th is suppressed, and good expansion performance is obtained.

Claims (4)

Contains expandable fired product and heat of hydration suppressing component,
A cement admixture having a content of particles of 10 µm or less of the expandable fired product of 0 to less than 30% by mass and a content of particles of more than 150 µm of 0 to 2% by mass. The cement admixture according to claim 1, wherein the heat of hydration suppressing component is dextrin. Concrete containing the cement admixture according to claim 1 or 2. The concrete according to claim 3, which has the following characteristics.
(1) The expansion coefficient is 200±30×10 ⁻⁶ .
(2) In an adiabatic temperature rise test according to JCI-SQA3 “Adiabatic temperature rise test method for concrete (draft)”, the amount of adiabatic temperature rise (T _{0 of the} base admixture containing no cement admixture at 7 days of age) ), the ratio (T ₁ /T ₀ ) of the adiabatic temperature rise amount (T ₁ ) of the concrete in which the cement admixture is added by cement substitution in the base concrete mixture is less than 1.000, and the age is 14 days. The ratio (T ₁ /T ₀ ) at is less than 1.000.