Quick-hardening admixture, quick-hardening cement composition, and method for producing quick-hardening concrete

Abstract

To provide a quick-hardening admixture that is suitable for ensuring stable concrete workability even when containing calcium aluminate and added at the construction site.SOLUTION: A quick-hardening admixture comprises calcium aluminate, a powdered water-reducing agent, and a powdered antifoaming agent. The quick-hardening admixture further may contain one or more selected from the group consisting of alkaline earth metal sulfate, alkaline metal sulfate, and alkaline metal carbonate.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rapid-hardening admixture containing calcium aluminates for use in rapid-hardening concrete. [Background technology]

[0002] Conventionally, as a method for accelerating the hardening of cement compositions such as concrete and mortar, a method has been proposed in which a fast-hardening admixture mainly composed of calcium aluminates is added to develop strength in a short time. For example, Patent Document 1 proposes a cement admixture containing a specific powdered cement dispersant in addition to an ultrafast-hardening cement mainly composed of calcium aluminates, gypsum, and inorganic salts. It is disclosed that the use of this cement admixture can impart fast hardening properties and low shrinkage to various cement compositions, and can further improve workability. However, Patent Document 1 only implements a case in which the amount of admixture is as low as 8 parts by mass relative to 92 parts by mass of cement, and the strength development is only 5 N / mm in 6 hours. 2 In recent years, there has been a demand for concrete with strength development in a shorter period of time, and concrete with strength development of at least 20N / mm at an age of 6 hours has been required. 2 The above strength development is required.

[0003] Patent Document 2 also proposes a cement admixture containing calcium aluminates, gypsum, lithium carbonate, anhydrous sodium sulfate, and a powdered dispersant. This patent discloses that by blending anhydrous sodium sulfate, which has hygroscopicity, into the cement admixture, the change in rapid hardening property and workability can be reduced even after long-term storage of the cement admixture, and as a result, a cement admixture suitable for premixing that can be stored for a long time can be obtained. In the examples of Patent Document 2, the cement admixture and ordinary Portland cement are mixed to obtain a rapid hardening cement, which is then mixed with aggregate and water to obtain a mortar sample, and the rapid hardening property, workability, and long-term storage property are evaluated. Here, the evaluation of workability is based on the J14 funnel flow time and bleeding, which is an evaluation of the so-called grout composition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-39761 A [Patent Document 2] JP 2006-335620 A Summary of the Invention [Problem to be solved by the invention]

[0005] Rapid-hardening cement admixtures containing calcium aluminates are often added to base concrete at construction sites, but the mixing equipment at construction sites is often simple and does not necessarily have sufficient mixing capacity compared to the mixing equipment used at ready-mix concrete plants. When a large amount of rapid-hardening admixtures is added and mixed using such equipment to impart strength development in a short period of time, there is a problem that it is difficult to obtain stable concrete workability, such as fluctuations in fluidity from batch to batch.

[0006] The present invention provides a rapid-hardening admixture suitable for obtaining stable workability of rapid-hardening concrete even when a rapid-hardening admixture containing calcium aluminates is added at a construction site, and also provides a rapid-hardening admixture capable of producing rapid-hardening concrete having good strength development and freeze-thaw resistance. [Means for solving the problem]

[0007] As a result of intensive research, the present inventors have found that a fast-setting admixture capable of solving the above problems can be obtained, and have completed the present invention. That is, the present invention provides the following [1] to [4]. [1] A fast-hardening admixture containing calcium aluminates, a powdered water reducer, and a powdered defoamer. [2] The rapid-hardening admixture of [1] further containing one or more selected from the group consisting of alkaline earth metal sulfates, alkali metal sulfates, and alkali metal carbonates. [3] A rapid-hardening cement composition comprising the rapid-hardening admixture of [1] or [2] and cement. [4] A method for producing rapid-hardening concrete, characterized in that the rapid-hardening admixture of [1] or [2] is added to and mixed with base concrete, which does not contain rapid-hardening admixture and which has been produced in a ready-mix concrete factory, at the construction site of the rapid-hardening concrete. Effect of the Invention

[0008] According to the present invention, even when a rapid-hardening admixture containing calcium aluminates is added at the construction site, it is possible to obtain a stable rapid-hardening concrete with workability. In addition, it is possible to obtain a rapid-hardening concrete having good strength development and freeze-thaw resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Fast hardening admixture> The fast-setting admixture of the present invention contains calcium aluminates, a powdered water reducing agent, and a powdered antifoaming agent. In particular, it is characterized by containing a powdered antifoaming agent. The following will explain in detail.

[0010] (Calcium aluminates) The fast-setting admixture in the present invention contains calcium aluminates. Here, calcium aluminates is a general term for compounds, solid solutions, glassy substances, or mixtures thereof that contain at least CaO and Al2O3 as main components. Examples of such calcium aluminates include calcium aluminates such as CaO·2Al2O3, CaO·Al2O3, 12CaO·7Al2O3, and 3CaO·Al2O3, calcium aluminoferrites such as 4CaO·Al2O3·Fe2O3 and 2CaO·Al2O3·Fe2O3, calcium fluoroaluminates such as 3CaO·3Al2O3·CaF2 and 11CaO·7Al2O3·CaF2, calcium sodium aluminates such as 8CaO·Na2O·3Al2O3, hauin (3CaO·3Al2O3·CaSO4), and alumina cement. As for the chemical components, the CaO / Al2O3 molar ratio is preferably 0.9 to 1.5 in terms of imparting rapid hardening and ensuring fluidity. The content of the vitreous substance (vitrification rate) is not particularly limited, but is preferably 5 to 70 mass%, more preferably 10 to 50 mass%.

[0011] Calcium aluminates can be produced by firing or melting raw materials such as CaO, Al2O3, and Fe2O3 using known equipment such as an electric furnace or a kiln. Raw materials such as limestone, bauxite, and recycled raw materials are used, and calcium aluminates may contain impurities derived from these raw materials. Examples of impurity components include SiO2, K2O, TiO2, MgO, SrO, and MnO. The content of impurities is preferably 10 mass% or less.

[0012] The fired or molten product is cooled and then pulverized into powder using a grinding machine such as a ball mill. The calcium aluminates used in the present invention are those having a Blaine specific surface area of ​​3000 cm2 in order to provide rapid hardening. 2 / g or more, and 4000 to 8000 cm 2The calcium aluminates are preferably contained in the rapid-hardening admixture of the present invention in an amount of 30 to 80 mass %, more preferably 40 to 70 mass %.

[0013] (Powdered water reducing agent) The rapid hardening admixture in the present invention contains a powdered water reducing agent. As the powdered water reducing agent, a melamine sulfonic acid-based water reducing agent, a naphthalene sulfonic acid-based water reducing agent, a polycarboxylic acid-based water reducing agent, etc. can be used. Among these, from the viewpoint of early strength development, a polycarboxylic acid-based water reducing agent is preferred. The content of the powdered water reducing agent is preferably 0.1 to 1.0 part by mass, more preferably 0.2 to 0.8 part by mass, and even more preferably 0.25 to 0.65 part by mass, relative to 100 parts by mass of calcium aluminates.

[0014] (Powdered defoamer) The rapid hardening admixture in the present invention contains a powdered defoaming agent. Examples of the powdered defoaming agent include polyether-based, mineral oil-based, ester-based, amine-based, amide-based, and silicone-based agents. By using the powdered defoaming agent in combination with a powdered water reducing agent, the amount of air in the rapid hardening concrete after kneading can be reduced, and stable fluidity (workability) can be ensured. In particular, polyether-based agents are preferred in terms of compatibility with calcium aluminates and foam breaking properties. The content of the powdered defoaming agent is preferably 0.01 to 0.15 parts by mass, more preferably 0.04 to 0.13 parts by mass, and even more preferably 0.05 to 0.1 parts by mass, relative to 100 parts by mass of calcium aluminates.

[0015] (Other Ingredients) The rapid hardening admixture of the present invention preferably further contains one or more selected from the group consisting of alkaline earth metal sulfates, alkali metal sulfates, and alkali metal carbonates. These metal salts can be used in combination with calcium aluminates to enhance strength development. Examples of alkaline earth metal sulfates include calcium sulfate, magnesium sulfate, and strontium sulfate. Examples of alkali metal sulfates include sodium sulfate, potassium sulfate, and lithium sulfate. Examples of alkali metal carbonates include sodium carbonate, potassium carbonate, and lithium carbonate. Of these metal salts, it is preferable to use at least calcium sulfate from the viewpoint of strength development. As calcium sulfate, natural gypsum, by-product chemical gypsum, and the like can be used. The Blaine specific surface area of ​​gypsum is 3000 to 12000 cm. 2 / g is preferred, and 4000 to 10000 cm 2 / g is more preferred.

[0016] The content of one or more metal salts selected from the group consisting of alkaline earth metal sulfates, alkali metal sulfates, and alkali metal carbonates is preferably 1 to 200 parts by mass relative to 100 parts by mass of calcium aluminates from the viewpoint of strength development. More specifically, the content of the alkaline earth metal sulfate is preferably 20 to 200 parts by mass, more preferably 50 to 150 parts by mass, relative to 100 parts by mass of calcium aluminates. The content of the alkali metal sulfate is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, relative to 100 parts by mass of calcium aluminates. The content of the alkali metal carbonate is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, relative to 100 parts by mass of calcium aluminates.

[0017] Furthermore, the rapid hardening admixture of the present invention may contain a set retarder. The set retarder acts to suppress the hydration reaction of rapid hardening concrete and ensure the working time. As the set retarder, one that is usually used in cement compositions can be used, but from the viewpoint of short-time strength development, an oxycarboxylic acid or a salt thereof is preferable. Examples of the oxycarboxylic acid and its salt include citric acid, gluconic acid, tartaric acid, heptonic acid, and their sodium salts or potassium salts. One or more of these can be used. The amount of the set retarder is preferably 0.1 to 10 parts by mass, particularly preferably 0.2 to 5 parts by mass, per 100 parts by mass of calcium aluminates.

[0018] The rapid hardening admixture of the present invention may further contain various additives used in cement and concrete, as long as the effects of the present invention are not substantially impaired. Examples of such additives include air-enhancing agents, thickeners, shrinkage reducing agents, and expansive agents.

[0019] <Fast-hardening cement composition> The rapid-setting cement composition of the present invention contains cement and the rapid-setting admixture. The content of the rapid-setting admixture is preferably 15 to 60 parts by weight, more preferably 20 to 50 parts by weight, per 100 parts by weight of cement. Here, the cement composition in the present invention is a general term for compositions containing cement, cement paste, mortar, and concrete. By using the rapid-setting admixture in the present invention, rapid-setting mortar and rapid-setting concrete having good early strength development can be produced.

[0020] The cement used in the present invention may be any of various Portland cements, such as ordinary, early strength, super early strength, moderate heat, and low heat, as well as blast furnace cement, mixed cement containing fly ash cement, and ecocement. Among these, ordinary Portland cement or early strength Portland cement is preferred from the viewpoints of strength development and economic efficiency.

[0021] <Manufacturing method of fast-hardening concrete> The method for producing fast-hardening concrete is not particularly limited, and it can be produced in the same way as in the production of general concrete by mixing Portland cement, aggregate, water, chemical admixtures, etc. in a predetermined ratio, adding fast-hardening admixtures to the mixture, and using a normal kneading device. It can also be produced by kneading all materials including the fast-hardening admixtures together, but it is preferable to produce it by first producing base concrete, adding the fast-hardening admixtures and kneading it. In particular, when a large amount of fast-hardening admixtures is mixed to develop high strength in a short time, it is preferable to add the fast-hardening admixtures and knead them at the construction site.

[0022] Specifically, after base concrete (not including rapid hardening admixtures) is produced at a ready-mix concrete plant, it is transported to the construction site by a truck agitator, where the rapid hardening admixtures are added to the base concrete and mixed. At this time, a predetermined amount of set retarder can also be added. It is recommended that the base concrete produced at the ready-mix concrete plant be JIS standard ready-mix concrete. A conventional mixer can be used for mixing at the construction site. Examples include a tilting mixer and a twin-shaft forced mixer. The rapid hardening admixture can also be added to the tank of the truck agitator and mixed.

[0023] Examples of aggregates used include fine aggregates and coarse aggregates. There are no particular limitations on the aggregates, and aggregates generally used in concrete can be used. Examples of fine aggregates that can be used include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, and mixtures thereof. Examples of coarse aggregates that can be used include river gravel, mountain gravel, land gravel, crushed stone, and mixtures thereof.

[0024] The amount of aggregate mixed is preferably 200 to 700 parts by mass, more preferably 200 to 600 parts by mass, per 100 parts by mass of the total of cement and fast-hardening admixture, from the viewpoint of preventing cracking and material separation. When fine aggregate and coarse aggregate are used in combination, the fine aggregate ratio is preferably 5 to 60%. The unit amount of aggregate in concrete is preferably 500 to 1100 kg / m for both fine aggregate and coarse aggregate. 3 , more preferably 600 to 1000 kg / m 3 It is.

[0025] The water used is not particularly limited, and may be tap water, etc. In the above cement kneaded product, the mixing ratio of water to the total of 100 parts by mass of cement and fast-hardening admixture is preferably 30 to 100 parts by mass, more preferably 40 to 70 parts by mass.

[0026] A retarder can be added to the fast-hardening concrete as necessary. Even if a retarder is mixed in the fast-hardening admixture, there may be a demand for a longer pot life depending on the temperature conditions at the construction site or the conditions at the construction site. In this case, any retarder that is normally used in cement compositions can be used, but from the viewpoint of strength development, an oxycarboxylic acid or a salt thereof is preferable. Examples of oxycarboxylic acid and its salt include citric acid, gluconic acid, tartaric acid, heptonic acid, and their sodium salts or potassium salts. One or more of these can be used. In this case, the amount of retarder added is preferably 0.1 to 2 parts by mass, more preferably 0.2 to 1 part by mass, based on 100 parts by mass of the total amount of cement and fast-hardening admixture.

[0027] In addition to the above, various admixtures (materials) used in normal concrete can be added to the rapid hardening concrete to the extent that the features of the present invention are not impaired. Examples include air entraining agents, water reducing agents, thickeners, expansive agents, shrinkage reducing agents, polymers for cement admixture, waterproofing agents, rust inhibitors, water retention agents, pigments, efflorescence prevention agents, water repellents, various fibers, fine pozzolans such as silica fume and flysh, fine blast furnace slag powder, fine limestone powder, and other stone powders. EXAMPLES

[0028] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[0029] <Preparation of calcium aluminate> The raw materials used were limestone (CaO content 56% by mass, Al2O3, MgO and SiO2 contents all less than 0.5% by mass) and bauxite (Al2O3 content 87% by mass, Fe2O3 content 1% by mass, SiO2 content 5% by mass, CaO and MgO contents all less than 0.5% by mass), and were mixed so that the molar ratio of CaO to Al2O3 was 1.2. The mixed mixture was fired in an electric furnace at a maximum temperature of 1500 (±50°C) for 3 hours. After the maximum temperature, it was removed from the furnace and immediately immersed in water, and after about 5 minutes it was removed from the water and dried in a dryer at 200°C. The obtained calcium aluminate [CA] is a compound mainly composed of CaO·Al2O3, and the vitrification rate measured by the internal standard method using powder X-ray diffraction was 15%. The fired product was pulverized in a mill to obtain a Blaine specific surface area of ​​approximately 5000 cm2. 2 / g.

[0030] <Preparation of fast-hardening admixture> The calcium aluminates prepared and the following materials (a) to (e) were mixed using a Loedige mixer to prepare a rapid hardening admixture [ADF]. The rapid hardening admixtures prepared are shown in Table 1.

[0031] <Materials used> (a) Calcium sulfate: Type II anhydrous gypsum (commercial product), Blaine specific surface area 7000 cm2 / g (b) Lithium carbonate: Reagent (Kanto Chemical Co., Ltd.) (c) Sodium sulfate: Reagent (Kanto Chemical Co., Ltd.) (d) Powdered water-reducing agent: Polycarboxylic acid-based powdered water-reducing agent (e) Powdered defoamer: Polyether-based powdered defoamer

[0032] [Table 1]

[0033] <Production of rapid hardening concrete> First, base concrete was produced using the materials (f) to (l) shown below. A rapid-hardening admixture and a retarder (prepared as an aqueous solution) were added to this base concrete, which was then mixed in a tilting mixer to produce rapid-hardening concrete. The mix proportions for the rapid-hardening concrete are shown in Table 2. An AE water-reducing agent was added to the base concrete, and it was adjusted to a target slump of 15±2 cm and air content of 4.5±1.5%. The amount of retarder added was adjusted so that the setting time would be 60 minutes or more.

[0034] (f) Cement [C]: Ordinary Portland cement (manufactured by Taiheiyo Cement Corporation), density 3.16 g / cm 3 (g) Fine aggregate [S]: mountain sand from Shizuoka Prefecture, density 2.58 g / cm 3 (h) Coarse aggregate [G]: Crushed stone from Ibaraki Prefecture, density 2.66 g / cm 3 (i) Water [W]: Tap water (j) AE water reducing agent [Ad]: AE water reducing agent standard type (Type I) (k) Coagulation regulator [R]: citric acid (reagent, manufactured by Kanto Chemical Co., Ltd.) (l) Liquid defoamers: polyalkylene glycol derivatives

[0035] [Table 2]

[0036] <Test Method> The evaluation test method is shown below. (1) Slump The test was conducted in accordance with JIS A 1101 "Concrete slump test method." (2) Measurement of air volume The test was conducted in accordance with JIS A 1128 "Pressure test method for air content in fresh concrete." (3) Compressive strength test The compressive strength was tested at 6 hours and 28 days according to JIS A 1108 "Concrete Compressive Strength Testing Method". The curing temperature was 20℃ until just before the test. (4) Freeze-thaw resistance test The test was conducted in accordance with JIS A 1148 "Concrete Freezing and Thawing Test Method." The test cycle was up to 300 cycles.

[0037] Example 1 First, the effect of adding an antifoaming agent to a rapid hardening admixture was examined. After producing base concrete, a rapid hardening admixture and a retarder (1 part by mass per 100 parts by mass of cement) were added. The slump of the base concrete was 15.5 cm, and the air content was 5.5%. Three tests were carried out for each of the following cases: 1) when a rapid hardening admixture without antifoaming agent (ADF0) was used, 2) when a rapid hardening admixture with antifoaming agent (ADF1) was used, and 3) when a rapid hardening admixture without antifoaming agent (ADF0) was used and a liquid antifoaming agent was added separately to the concrete (0.075 parts by mass per 100 parts by mass of CA), and the fresh properties of the rapid hardening concrete were evaluated. The results are shown in Table 3. The target slump of the rapid hardening concrete was 20±2.5 cm, and the air content was 2.0±1.5%.

[0038] [Table 3]

[0039] When a rapid-hardening admixture without added antifoaming agent was used (No.1-1), the air content of the rapid-hardening concrete increased significantly, and the slump also varied widely, with some cases falling outside the target slump. When a liquid antifoaming agent was added to the concrete in addition to the rapid-hardening admixture (No.1-3), the increase in the air content was suppressed, but there was variation and there were some cases where the target air content was not achieved. Furthermore, the variation in slump could not be suppressed, with some cases where the target slump was not achieved. Furthermore, the relative dynamic modulus of elasticity of the rapid-hardening concrete when a liquid antifoaming agent was used was low at 68% on average, and the freeze-thaw resistance could not be said to be good. On the other hand, when a rapid-hardening admixture containing an antifoaming agent was used (No. 1-2), the variation in air content and slump was small, and the target air content and slump were achieved all three times. From these results, it was found that by using a rapid-hardening admixture containing a powdered antifoaming agent, it is possible to reduce the variation in air content and slump, and to obtain rapid-hardening concrete with stable workability.

[0040] Example 2 Tests were conducted by varying the content of powdered water reducing agent and powdered antifoaming agent mixed into the rapid-hardening admixture. The amount of retarder added to the base concrete was 1 part by mass per 100 parts by mass of cement, as in Example 1, except for No. 2-7, where the amount was 0.8 parts by mass. The test results are shown in Table 4. By using a rapid-hardening admixture containing an appropriate amount of powdered water reducing agent and powdered antifoaming agent, rapid-hardening concrete with good workability, strength development, and relative dynamic modulus of elasticity (freeze-thaw resistance) was obtained.

[0041] [Table 4]

Claims

1. A fast-hardening admixture containing calcium aluminates, a powdered water reducer and a powdered defoamer.

2. 2. The rapid-hardening admixture according to claim 1, further comprising one or more elements selected from the group consisting of alkaline earth metal sulfates, alkali metal sulfates, and alkali metal carbonates.

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

4. A method for producing rapid-hardening concrete, comprising adding the rapid-hardening admixture according to claim 1 or 2 to base concrete not containing a rapid-hardening admixture produced in a ready-mix concrete factory and kneading the mixture at a construction site of the rapid-hardening concrete.

Images