Cement admixture, cement composition, cement concrete

Abstract

This cement admixture contains a calcium sulfoaluminate-based powder and an active siliceous powder, and the calcium sulfoaluminate-based powder contains 0.005–20 mass% of ternesite.

Description

[Technical Field]

[0001] The present invention relates to cement admixtures, cement compositions, and cement concrete that are primarily used in the civil engineering and construction industries. [Background technology]

[0002] Traditionally, one method for improving the waterproofing of cement concrete and other materials has been to reduce the water-to-powder ratio, and the use of water-reducing agents and high-performance water-reducing agents as specified in JIS A 6204:2011 "Chemical admixtures for concrete" has become widespread.

[0003] On the other hand, methods for improving waterproofing without reducing the water-powder ratio include, for example, using an admixture made by mixing a calcium sulfoaluminate compound with fired white clay (see Patent Document 1), mixing a water repellent and a carbonated admixture with cement (see Patent Document 2), and applying a water repellent to the surface of hardened cement concrete (see Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-219319 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-111640 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-231488 Summary of the Invention [Problem to be solved by the invention]

[0005] However, many admixtures designed to improve waterproofing have finely adjusted particle size to enhance the reactivity of the powder, but as the particle size becomes finer, the fluidity decreases, making it difficult to impart both waterproofing and fluidity retention to cement concrete.

[0006] In view of the above, an object of the present invention is to provide a cement admixture, a cement composition, and cement concrete that improve the waterproofing properties and fluidity retention properties of cement concrete. [Means for solving the problem]

[0007] As a result of intensive research conducted by the present inventors to solve the above-mentioned problems, they have arrived at the present invention, which uses a calcium sulfoaluminate powder and an active siliceous powder, and by appropriately adjusting the content of ternesite in the calcium sulfoaluminate powder, the inactive ternesite acts as a filler and has the effect of promoting the reaction of the active siliceous powder, thereby ensuring the fluidity of cement concrete while improving its waterproofing.

[0008] [1] A cement admixture comprising a calcium sulfoaluminate powder and an activated siliceous powder, wherein the calcium sulfoaluminate powder contains 0.005 to 20 mass % of ternesite. [2] Blaine specific surface area is 3,000-4,500 cm 2 / g of the cement admixture according to [1] above. [3] A cement composition comprising cement and the cement admixture described in [1] or [2] above. [4] Cement concrete containing the cement composition described in [3] above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a cement admixture, a cement composition, and cement concrete that improve waterproofing while ensuring the fluidity of cement concrete. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (the present embodiment) will be described in detail, but the present invention is not limited to this embodiment. In this specification, "%" is based on mass unless otherwise specified.

[0011] The cement admixture of the present invention contains a calcium sulfoaluminate powder and an activated siliceous powder, and the calcium sulfoaluminate powder contains 0.005 to 20 mass % of ternesite.

[0012] The calcium sulfoaluminate powder used in this invention is composed of calcium sulfoaluminates, a collective term for hydraulic substances and hydrated salts represented by the chemical formula xCaO·yAl2O3·zCaSO4·mH2O (x, y, and z are nonzero positive real numbers, and m is 0 or a positive real number). Examples include the AFt phase, represented by ettringite (3CaO·Al2O3·3CaSO4·32H2O), the AFm phase, represented by monosulfate (3CaO·Al2O3·CaSO4·12H2O), and those in which the AFt and AFm phases coexist. Calcium sulfoaluminates may be amorphous. Furthermore, a portion of the Al2O3 may be replaced with trace amounts of Fe2O3 or SiO2, and a portion of the CaSO4 may be replaced with Ca(OH)2 or CaCO3.

[0013] Calcium sulfoaluminate powder is produced by blending raw materials such as lime and other calcium raw materials, gypsum and other sulfate raw materials, and bauxite (aluminum hydroxide) and other alumina raw materials in a predetermined ratio, such as a molar ratio of CaO:CaSO4:Al2O3 of 4:3:1, firing the mixture at about 1,500°C in a kiln or the like, and pulverizing it. Silicon dioxide and other materials may also be added to the fired mixture, followed by heat treatment and pulverization, which allows the content of ternesite to be adjusted.

[0014] The calcium sulfoaluminate powder of the present invention contains ternesite. ternesite is a mineral expressed by the formula 4CaO·2SiO2·CaSO4. Because ternesite itself is virtually inactive, it acts as a filler, improving the fluidity retention of cement concrete and promoting the reaction of active siliceous powders with pozzolanic activity and / or latent hydraulic properties. This allows for fluidity retention without impairing strength development or waterproofing properties.

[0015] The content of ternesite in the calcium sulfoaluminate powder of the present invention is 0.005 to 20% by mass, preferably 0.01 to 20% by mass, and more preferably 3 to 15% by mass. If the content exceeds 20% by mass, the reactivity of the calcium sulfoaluminate powder decreases, resulting in a decrease in the compressive strength and waterproofing of cement concrete. If the content is less than 0.005% by mass, ternesite does not exert its effect, resulting in a decrease in fluidity retention. The identification and quantification of ternesite in the calcium sulfoaluminate powder can be determined by powder X-ray diffraction.

[0016] The Blaine specific surface area of ​​calcium sulfoaluminate powder is 2,500 to 4,500 cm 2 / g is preferred, and 3,000 to 4,500 cm 2 / g is more preferable, and 3,200 to 4,500 cm 2 / g. The Blaine specific surface area of ​​the calcium sulfoaluminate powder is more preferably 2,500 cm 2 / g or more, cracks due to delayed expansion can be reduced, and 2 / g or less, the slump retention can be improved. Note that the Blaine specific surface area in the present invention is measured based on the specific surface area test described in JIS R 5201:2015 "Physical Testing Methods for Cement."

[0017] The activated siliceous powder used in the present invention is a general term for powders of substances that are primarily composed of silica and have pozzolanic activity and / or latent hydraulic properties. These include fly ash, ground granulated blast furnace slag, metakaolin, silica fume, sewage sludge incineration ash, volcanic ash, and fired white clay. While the active siliceous powder is not particularly limited in the present invention, fired white clay is preferred from an economical standpoint. The activated siliceous powder reacts with the products of the hydration reaction of the cement composition, contributing to the strength development of cement concrete.

[0018] The Blaine specific surface area of ​​activated siliceous powder is 15,000 cm 2 / g or less is preferable, and 3,000 to 10,000 cm 2 / g is more preferable, and 4,000 to 8,000 cm 2 / g. The Blaine specific surface area of ​​the active siliceous powder is more preferably 15,000 cm 2 When the water-repellent viscosity is 1 / g or less, the waterproofing effect of the cement admixture can be improved.

[0019] The Blaine specific surface area of ​​the cement admixture of the present invention is 2,500 to 7,000 cm 2 / g is preferred, and 3,000 to 5,000 cm 2 / g is more preferable, and 3,500 to 4,500 cm 2 / g is more preferable. The Blaine specific surface area of ​​the cement admixture is 2.500 cm 2 / g or more, waterproofing and compressive strength can be improved, and 2 By adjusting the viscosity to 1 / g or less, the fluidity retention can be improved.

[0020] The blending ratio of the calcium sulfoaluminate powder and the active siliceous powder in the cement admixture is preferably 20 to 80 mass%, more preferably 40 to 60 mass%, of the calcium sulfoaluminate powder, and preferably 20 to 80 mass%, more preferably 40 to 60 mass%, of the active siliceous powder, based on 100 mass% of the cement admixture.

[0021] In this embodiment, the amount of the cement admixture used is preferably 0.6 to 20 parts by mass, and more preferably 1.0 to 10 parts by mass, relative to 100 parts by mass of cement. By setting the amount of the cement admixture used within the above range, the waterproofing effect of the cement admixture can be improved.

[0022] The cement composition of the present invention contains cement and the cement admixture of the present invention. The cement is not particularly limited, and any ordinary cement can be used. Specific examples include various Portland cements such as normal, early strength, very early strength, low heat, and moderate heat, various mixed cements obtained by mixing these Portland cements with blast furnace slag, fly ash, or silica, filler cements mixed with limestone powder or slowly cooled blast furnace slag powder, and waste-recycled cements, so-called ecocements. One or more of these can be used in combination.

[0023] The method for mixing the cement admixture is not particularly limited, and any existing mixing device can be used, such as a tilting mixer, a forced twin-shaft mixer, an omni mixer, a Henschel mixer, a V-type mixer, and a Nauta mixer.

[0024] The cement concrete of the present invention is obtained by kneading the cement composition and aggregate of the present invention with water. In addition to cement, the cement admixture of the present invention, and aggregates such as sand and gravel, one or more of the following may be used to the extent that the purpose of the present invention is not substantially impaired: water reducing agents, air-entraining water reducing agents, high-performance water reducing agents, high-performance air-entraining water reducing agents, admixtures such as ground granulated blast furnace slag, ground slowly cooled blast furnace slag, limestone powder, fly ash, and silica fume; hardening accelerators, antifoaming agents, thickeners, rust inhibitors, antifreeze agents, shrinkage reducing agents, polymers, setting modifiers, clay minerals such as bentonite, and anion exchangers such as hydrotalcite.

[0025] In the present invention, the method for mixing the materials is not particularly limited, and the materials may be mixed at the time of application, or some or all of the materials may be mixed in advance. [Example]

[0026] The present invention will now be further described based on experimental examples.

[0027] <Experimental Example 1> (Materials used) The materials used are listed below. The calcium sulfoaluminate powder used was prepared by mixing first-grade reagent calcium carbonate, calcium sulfate dihydrate, and aluminum hydroxide in a molar ratio of CaO:CaSO4:Al2O3 of 4:3:1, and then mixing silicon dioxide so that the calcined calcium sulfoaluminate powder contained a predetermined amount of ternesite. The powder was then heat-treated at 1,400°C for 2 hours and allowed to cool to room temperature to produce a powder with a Blaine specific surface area of ​​3,500 cm. 2 The powder was ground to a concentration of 1 / g. Water: Tap water Cement: Ordinary Portland cement, commercially available Calcium sulfoaluminate powder A: trial product, ternesite content 0% by mass Calcium sulfoaluminate powder B: trial product, ternesite content 0.05% by mass Calcium sulfoaluminate powder C: trial product, ternesite content 5% by mass Calcium sulfoaluminate powder D: trial product, ternesite content 10% by mass Calcium sulfoaluminate powder E: trial product, ternesite content 20% by mass Calcium sulfoaluminate powder F: trial product, ternesite content 30% by mass Active silica powder: fired white clay, Blaine specific surface area 5,000 cm 2 / g Fine aggregate: Natural sand from Himekawa, Niigata Prefecture, specific gravity 2.62 Coarse aggregate: Crushed stone from Himekawa, Niigata Prefecture, maximum size 25mm, specific gravity 2.64

[0028] (Cement concrete manufacturing) Cement 290kg / m 3 , fine aggregate 866kg / m 3 , coarse aggregate 946kg / m 3 and water 174 kg / m 3 Using the above, 3 parts by mass of a cement admixture consisting of calcium sulfoaluminate powder and activated silica powder in the proportions shown in Table 1 was mixed per 100 parts by mass of cement, and concrete was mixed using a concrete mix with a slump of 15.0±2.5 cm, air content of 4.5±1.5%, W / C of 60%, and S / A of 48%. The water permeability and compressive strength of the resulting concrete were measured. In addition, the change in slump over time after 90 minutes was measured, and the slump change ratio over time was calculated. The results are shown in Table 1.

[0029] (Evaluation method) Slump: The slump immediately after mixing the concrete was measured in accordance with JIS A 1101:2020 "Test method for slump of concrete." Air content: The air content was measured immediately after mixing the concrete in accordance with JIS A 1128:2019 "Pressure test method for air content of fresh concrete - Air chamber pressure method." Blaine specific surface area: Measured based on the specific surface area test described in JIS R 5201:2015 "Physical testing methods for cement." Permeability ratio: After the concrete was poured, a cylindrical specimen measuring φ100mm x 100mm was used, and cured in water at 20°C for 7 days before undergoing a permeability test. The test method was the output method, and a water pressure of 1.0MPa was applied to the outer surface of the specimen for 500 hours, and the amount of water that seeped out was measured and taken as the permeability, and the "permeability ratio" was calculated as (permeability when cement admixture is used / permeability without cement admixture). Compressive strength: Measured in accordance with JIS A 1108:2018 "Test method for compressive strength of concrete" using test specimens that had been underwater cured for 28 days. Slump change ratio over time: After the mixed concrete was discharged into a vat and allowed to stand for 90 minutes, the slump was measured according to JIS A 1101:2020 "Concrete Slump Test Method." The "slump change over time after 90 minutes" was calculated as (slump after 90 minutes of concrete mixing / slump immediately after concrete mixing). The "slump change over time ratio" was calculated as (slump change over 90 minutes with cement admixture / slump change over 90 minutes without cement admixture). From the viewpoints of concrete transportation and workability, the slump change over time ratio is preferably 1.00 to 1.60, and more preferably 1.20 to 1.60.

[0030] [Table 1]

[0031] The results shown in Table 1 demonstrate that the cement admixture of the present invention not only has excellent fluidity retention, but also improves compressive strength and waterproofing. On the other hand, as in the comparative examples shown in Table 1, when the content of ternesite in the calcium sulfoaluminate powder acting as a filler is low, fluidity retention cannot be ensured, and when the content of ternesite is high, reactivity is impaired, compressive strength and waterproofing decrease, and it was also found that the calcium sulfoaluminate powder and activated siliceous powder alone do not exhibit sufficient waterproofing.

[0032] <Experimental Example 2> 50 parts by mass of calcium sulfoaluminate powder, which had been heat-treated so that the ternesite content in the calcium sulfoaluminate powder was 10% and then pulverized to different particle sizes, was mixed with 50 parts by mass of activated siliceous powder, and the test was conducted in the same manner as in Experimental Example 1, except that the Blaine specific surface area of ​​the cement admixture was set as shown in Table 2. The results are shown in Table 2.

[0033] [Table 2]

[0034] From Table 2, the cement admixture of the present invention has a Blaine specific surface area of ​​3,000 to 4,500 cm 2 / g, it was shown that the fluidity retention and waterproofing properties were better. [Industrial Applicability]

[0035] The cement admixture of the present invention can improve the waterproofing properties while ensuring the fluidity of cement concrete, and can be suitably used for concrete that requires waterproofing of the structure, such as water supply and sewerage systems, underground pits, and coastal structures.

Claims

1. A cement admixture comprising a calcium sulfoaluminate powder and an active siliceous powder, the active siliceous powder being present in an amount of 20 to 80% by mass, and the calcium sulfoaluminate powder containing 0.005 to 20% by mass of ternesite.

2. Blaine specific surface area is 3,000 to 4,500 cm ２ The cement admixture according to claim 1, wherein the SiO 2 content is 1 / g.

3. A cement composition comprising cement and the cement admixture according to claim 1 or 2.

4. A cement concrete comprising the cement composition according to claim 3.

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