Cement admixture

Abstract

To provide a cement admixture having high expansibility and heat regulating effects without causing lowering of strength.SOLUTION: A cement admixture includes an expansive material and light-burned magnesia, where the content of the light-burned magnesia having a particle diameter of 10 μm or less is 1-21 pts.mass relative to 100 pts.mass of the cement admixture. Mortar or concrete uses the cement admixture.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cement admixture for use in mortar or concrete. [Background technology]

[0002] The hardening and drying shrinkage of mortar and concrete can cause cracks. To prevent this, expansive additives have traditionally been added to concrete. Examples of such additives include lime-based expansive additives that utilize the hydration expansion of quicklime (CaO), ettringite-based expansive additives that utilize the hydration expansion of calcium sulfoaluminate, and lime-ettringite composite expansive additives that contain both. When the components of these expansive additives hydrate, heat of hydration is generated, and it is known that a large amount of heat of hydration is generated in particular during the hydration process of quicklime. Therefore, when lime-based expansive additives are used in mass concrete, there is concern that thermal cracks may occur due to the heat of hydration.

[0003] As a countermeasure, a technology has been disclosed that uses a hydration heat inhibitor such as dextrin in combination with an expansive agent (Patent Documents 1 and 2). However, although such organic hydration heat inhibitors such as dextrin are effective in suppressing the hydration heat of cement, adding an excessive amount of them can inhibit the hydration of cement, reducing strength development. In addition, the solubility of the active ingredient is easily affected by temperature, making them difficult to handle.

[0004] On the other hand, magnesium oxide is also known to react with water to become magnesium hydroxide, which exhibits expansive properties. However, because magnesium oxide causes abnormal expansion after concrete hardens, the JIS standard for expansive additives for concrete (JIS A 6202) stipulates that its content should be 5% by mass or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-165627 [Patent Document 2] Japanese Patent Application Publication No. 2020-93940 Summary of the Invention [Problem to be solved by the invention]

[0006] Provided is a cement admixture that has good expansion properties and heat-reducing effects without causing a decrease in strength. [Means for solving the problem]

[0007] The present invention has discovered a cement admixture that has good expansion performance and heat suppression effect by controlling the particle size of light-burned magnesia added to the cement admixture and using it in combination with an expansive substance, particularly a lime-based expansive substance. That is, the present invention provides the following [1] to [4]. [1] A cement admixture containing an expansive material and light-burned magnesia, characterized in that the content of particles of 10 μm or less in the light-burned magnesia is 1 to 21 parts by mass per 100 parts by mass of the cement admixture. [2] The cement admixture according to [1], wherein the light-burned magnesia has a particle content of 10 μm or less of 30 to 90 mass %. [3] The cement admixture according to [1] or [2], characterized in that the content of the light-burned magnesia is 1 to 40 parts by mass per 100 parts by mass of the cement admixture. [4] Mortar or concrete containing the cement admixture according to any one of [1] to [3]. [Effects of the Invention]

[0008] According to the present invention, a cement admixture having good expansion properties and heat suppression effect can be obtained without causing a decrease in strength. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention is a cement admixture comprising an expansive substance and light-burned magnesia, wherein the content of particles of the light-burned magnesia having a size of 10 μm or less is 1 to 21 parts by mass relative to 100 parts by mass of the cement admixture. The details will be explained below.

[0010] The expansive substance in the present invention may be any substance that exhibits expansive properties by forming crystals upon hydration. Specific examples include quicklime, expansive calcined materials containing free quicklime, calcium sulfoaluminate compounds such as 3CaO·3Al2O3·CaSO4, and gypsum. These may be used singly or in combination. In the present invention, lime-based expansive substances primarily composed of expansive calcined materials containing quicklime or free quicklime are particularly preferred. Furthermore, those containing gypsum are preferred. Anhydrous gypsum is preferred as the gypsum, and the amount of gypsum added is preferably 10 to 30 parts by mass per 100 parts by mass of the expansive substance.

[0011] Here, the expansive calcined material containing free quicklime is a calcined material obtained by calcining a calcined material containing a CaO raw material such as calcium carbonate, slaked lime, or quicklime. The calcined material may contain, in addition to the CaO raw material, an SiO2 raw material, an Al2O3 raw material, an iron oxide raw material, gypsum, or the like. The calcined material is calcined at a temperature of 1100 to 1500°C. A temperature-controllable furnace such as a rotary kiln or an electric furnace is used for calcination. The calcined material is adjusted to a predetermined particle size by pulverization and classification.

[0012] The content of free quicklime in the expansive fired product is preferably 30 to 90% by mass, more preferably 40 to 80% by mass, from the viewpoint of ensuring expansion performance. In addition to free quicklime, the expansive fired product contains hydraulic compounds such as calcium silicates such as 2CaO·SiO2 and 3CaO·SiO2, calcium aluminates such as CaO·Al2O3, 12CaO·7Al2O3 and 3CaO·Al2O3, calcium aluminoferrites such as 4CaO·Al2O3·Fe2O3 and 6CaO·2Al2O3·Fe2O3, and calcium sulfoaluminates such as 3CaO·3Al2O3·CaSO4.

[0013] The content of particles of 10 μm or less in the expansion substance in the present invention is preferably 10 to 50 mass % from the viewpoint of ensuring stable expansion performance and suppressing the heat of hydration. The maximum particle size is preferably 300 μm or less.

[0014] The magnesia (MgO) used in the present invention is light-burned magnesia. Light-burned magnesia is obtained by firing MgO raw materials such as magnesium hydroxide and magnesium carbonate at temperatures of 600 to 1100°C, preferably 700 to 1000°C, and even more preferably 800 to 900°C. Light-burned magnesia may contain small amounts of impurities derived from natural raw materials, etc., within limits that do not affect the performance of the present invention. Examples of such impurities include CaO, SiO2, Al2O3, Fe2O3, MnO, NiO, and PO3.

[0015] Next, the content of light-burned magnesia particles of 10 μm or less in the cement admixture of the present invention is 1 to 21 parts by mass relative to 100 parts by mass of the cement admixture. If the content of particles of 10 μm or less is less than 1 part by mass, the rate of heat generation during hydration may increase. On the other hand, if it exceeds 21 parts by mass, the compressive strength may decrease. It is preferably 5 to 20 parts by mass, more preferably 8 to 18 parts by mass.

[0016] The content of particles of 10 μm or less in the light-burned magnesia used in the present invention is preferably 30 to 90 mass%, more preferably 40 to 85 mass%, and even more preferably 50 to 80 mass%, and the maximum particle size is preferably 150 μm or less.

[0017] The content of light-burned magnesia in the cement admixture is preferably 1 to 40 parts by mass, more preferably 5 to 35 parts by mass, and even more preferably 10 to 30 parts by mass, per 100 parts by mass of the cement admixture.

[0018] In addition to the above-mentioned components, the cement admixture of the present invention may contain small amounts of various additives, provided that the advantages of the present invention are not impaired. Examples of such additives include air-entraining agents, water-reducing agents, foaming agents, setting regulators, hardening accelerators, waterproofing agents, water-repellents, water-retaining agents, rust inhibitors, thickeners, pigments, and anti-efflorescence agents.

[0019] The cement admixture of the present invention is used by mixing it with mortar or concrete. The amount of the cement admixture to be mixed is preferably 5 to 10 parts by mass per 100 parts by mass of cement. The amount of the cement admixture to be mixed in concrete is preferably 20 to 30 kg / m from the viewpoint of shrinkage compensation of concrete. 3 is preferred.

[0020] Examples of cement used in mortar or concrete include one or more types selected from Portland cements such as ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, low-heat Portland cement, and moderate-heat Portland cement, ecocement, and mixed cements obtained by mixing the Portland cements with blast furnace slag powder, fly ash, silica powder, silica fume, limestone powder, etc. The unit cement amount is preferably 270 to 500 kg / m 3 , more preferably 300 to 500 kg / m 3 is.

[0021] The aggregate used in the present invention is not particularly limited as long as it is an aggregate generally used for mortar or concrete. Specifically, the fine aggregate may be one or more selected from river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, lightweight fine aggregate, etc., and the coarse aggregate may be one or more selected from river gravel, mountain gravel, crushed stone, lightweight coarse aggregate, etc. Furthermore, the aggregate is not limited to natural aggregates, and artificial aggregates such as slag aggregate and recycled aggregates can also be used. Furthermore, the unit amount of the fine aggregate and coarse aggregate is preferably 500 to 1100 kg / m for both aggregates from the viewpoint of good workability. 3 , more preferably 600 to 1000 kg / m 3 is.

[0022] The water used in the present invention is not particularly limited, and any water that does not affect the strength development or fluidity of concrete, such as tap water, treated sewage water, or supernatant water from ready-mixed concrete, can be used. From the viewpoint of good workability, the unit water content is preferably 100 to 200 kg / m 3 , more preferably 120 to 180 kg / m 3 is.

[0023] Furthermore, mortar or concrete can contain commonly used admixtures such as air-entraining agents, water-reducing agents, air-entraining water-reducing agents, high-performance water-reducing agents, and high-performance air-entraining water-reducing agents. In addition to these admixtures, shrinkage-reducing agents, foaming agents, waterproofing agents, rust inhibitors, thickeners, water-retaining agents, pigments, water-repellents, efflorescence inhibitors, fibers, and re-emulsified powdered resins can also be used depending on the application of the mortar or concrete.

[0024] Mortar or concrete using the cement admixture of the present invention can be expected to have good expansion properties and heat suppression effects (specifically, reduction in maximum heat generation rate, reduction in integrated internal temperature, etc.) without causing a decrease in strength. Therefore, by using the cement admixture of the present invention, mortar or concrete with excellent resistance to thermal cracking can be obtained, and it is suitable for use in, for example, mass concrete. [Example]

[0025] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0026] <Preparation of cement admixture> (1) Manufacturing of expanding materials A mixture of silica stone, alumina shale, iron oxide, anhydrous gypsum, and industrial quicklime was fired at 1400°C in an electric furnace, and the fired product was pulverized to produce an expansive fired product containing 66% by mass of free quicklime. The main minerals other than free quicklime contained in this expansive fired product are calcium silicate (3CaO SiO2), calcium aluminoferrite (4CaO Al2O3 Fe2O3), and anhydrous gypsum (CaSO4). The produced expansive fired product was then adjusted to powder by pulverization and classification. 80 parts by mass of this adjusted expansive fired product and natural anhydrous gypsum (Blaine specific surface area 7000 cm) were mixed. 2 A lime-based expansive material was prepared by mixing 20 parts by mass of slag (10 μm or less) and 20 parts by mass of slag (10 μm or less) with slag (10 μm or less) of slag (10 μm or less). The resulting expansive material had a particle content of 58% by mass.

[0027] (2) Preparation of light-burned magnesia Commercially available light-burned magnesia (calcination temperature 800°C, purity 90%) was sieved through a 10 μm mesh sieve, and the sieved light-burned magnesia particles of 10 μm or less were mixed with the commercially available light-burned magnesia to adjust the content of particles of 10 μm or less in the light-burned magnesia (50 to 79 mass%).

[0028] (3) Preparation of cement admixture The expansive material and the light-burned magnesia were mixed in a predetermined ratio to prepare a cement admixture. The blending ratio of the cement admixtures tested and the content of light-burned magnesia particles of 10 μm or less in the cement admixtures are shown in Table 1.

[0029] [Table 1]

[0030] <Evaluation test> The prepared cement admixture was used to carry out various evaluation tests. The test methods for each evaluation test are described below.

[0031] (1) Heat generation evaluation test Heat generation evaluation of cement admixtures was carried out using a multi-microcalorimeter (Tokyo Riko Co., Ltd.). A mixture of cement and cement admixture was poured into water, and the maximum heat generation rate in the paste state was evaluated. 12 g of ordinary Portland cement (Taiheiyo Cement Corporation) was mixed with 1 g of each cement admixture shown in Table 1, and this was poured into 6.5 g of water. The measurement temperature was 20°C, and measurements were taken from immediately after pouring the water up to 72 hours later.

[0032] (2) Accumulated internal temperature test 840g of ordinary Portland cement (manufactured by Taiheiyo Cement Corporation) was mixed with 60g of cement admixture, to which 2700g of standard sand and 450g of tap water were added, and the mixture was mixed in a mixer for 2.5 minutes to prepare mortar. This mortar was used in an accumulated internal temperature test in a 20°C environment. The test method is described below. Mortar was filled into a 2 L plastic container with a body diameter of φ147 mm, height of 177 mm. A thermocouple was inserted 50 mm deep into the mortar near the center of the container's body diameter, and the opening of the plastic container was then covered with plastic wrap. The internal temperature was measured every 5 minutes, up to 2 days after the material was aged. The cumulative internal temperature was calculated using equation (1). M = Σ(θ-20)·Δt ··· Equation (1) M: Accumulated temperature θ: Mortar temperature during Δt time (℃) Δt: Internal temperature measurement interval (minutes)

[0033] (3) Compression strength test Mortar was prepared by mixing 420g of ordinary Portland cement (manufactured by Taiheiyo Cement Corporation) with 30g of cement admixture, adding 1350g of standard sand and 225g of tap water, and mixing for 2.5 minutes in a mixer. The method for preparing underwater specimens was in accordance with JSCE-G-541 "Compressive Strength Test of Filled Mortar," and the compressive strength was measured at 28 days of age. The specimen dimensions were 50mm in diameter and 100mm in height.

[0034] (4) Expansion test Mortar containing cement admixture was prepared in the same manner as in the compressive strength test. The amount of expansion at 28 days was measured in accordance with JIS A 6202:1997 "Expansive additives for concrete; Annex 1 (regulations) Expansion test method using expansive additive mortar."

[0035] <Test Results> The test results are shown in Table 2. The cement admixture containing the light-burned magnesia of the present invention had a suppressed maximum heat release rate compared to Comparative Example 1. The integrated internal temperature of the mortar was also reduced. On the other hand, in Comparative Example 2, in which the content of light-burned magnesia of 10 μm or less in the cement admixture exceeded 21 parts by mass, a decrease in compressive strength was observed.

[0036] [Table 2]

Claims

1. A cement admixture containing an expansive substance and light-burned magnesia, the cement admixture containing 70 to 90 parts by mass of the expansive substance and 10 to 30 parts by mass of the light-burned magnesia per 100 parts by mass of the cement admixture, and a content of particles of 10 μm or less in the light-burned magnesia of 1 to 21 parts by mass per 100 parts by mass of the cement admixture, and further characterized in that the expansive substance is one or a mixture of two or more selected from quicklime, an expansive calcined product containing free quicklime, a calcium sulfoaluminate compound, and gypsum.

2. 2. The cement admixture according to claim 1, wherein the light-burned magnesia has a particle content of 10 μm or less of 30 to 90 mass %.

3. 3. The cement admixture according to claim 1, wherein the content of the light-burned magnesia is 1 to 40 parts by mass per 100 parts by mass of the cement admixture.

4. A mortar or concrete containing the cement admixture according to any one of claims 1 to 3.

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