Expandable composition and expandable admixture

Abstract

The purpose of the present invention is to provide: an expandable composition which has a satisfactory expansion rate and can improve bending strength; and an expandable admixture. This expandable composition contains free lime crystal particles having an average crystal particle diameter of 1-30 μm. The content of the free lime crystal particles is preferably 15 mass% or more. Furthermore, the expandable composition preferably comprises the free lime crystal particles and heterophases present between the free lime crystal particles. The heterophases preferably include one or more types selected from the group consisting of ternesite, gehlenite, gypsum, ye'elimite and calcium silicate. In addition, the expandable admixture contains anhydrous gypsum and the expandable composition.

Description

Expanding composition and expansive admixture

[0001] The present invention relates primarily to expansive compositions and expansive admixtures used in the civil engineering and construction industry.

[0002] Reducing cracking and improving bending strength of concrete are important from the perspectives of the reliability, durability, and aesthetics of concrete structures, and further technological advances in expansive additives, which are cement admixtures that have the effect of improving these properties, are desired.

[0003] As the expansive additive, calcium sulfoaluminate-based expansive additives, lime-based expansive additives, etc. have been known so far, and for example, expansive additives for concrete or expansive additive clinkers having excellent expansion properties have been proposed (Patent Documents 1 to 3).

[0004] JP 2002-029797 A JP 2008-201603 A JP 2008-156187 A

[0005] In recent years, further improvement in bending strength (flexural strength) has been required for cement compositions containing such expansive additives. Furthermore, when the expansion coefficient is low, the effect of introducing chemical prestress on improving bending strength is reduced. On the other hand, even when the expansion coefficient is high, excessive expansion leads to tissue destruction, resulting in a decrease in the base compressive strength, resulting in a decrease in bending strength. Therefore, it is required to set the expansion coefficient within an appropriate range.

[0006] The expanding agent (cement admixture) described in Patent Document 1 aims to provide an expanding agent that has excellent expansion performance with a small amount added, while the expanding agents (expansive compositions) described in Patent Documents 2 and 3 aim to provide an expanding composition that exhibits stable expansion. As such, the expanding agents described in Patent Documents 1 to 3 have not been studied to improve bending strength or to set an appropriate expansion rate in consideration of the improvement in bending strength.

[0007] The present invention has been made in view of the above circumstances, and aims to provide an expandable composition and an expandable admixture that can provide an appropriate expansion coefficient and improve bending strength.

[0008] The present inventors conducted extensive research to solve the above-mentioned problems, and discovered that the problem can be solved by including free lime crystal particles having a predetermined average crystal particle size, leading to the present invention. Specifically, the present invention is as follows: [1] An expanding composition containing free lime crystal particles having an average crystal particle size of 1 to 30 μm. [2] The expanding composition according to claim 1, wherein the content of the free lime crystal particles is 15% by mass or more. [3] The expanding composition according to [1] or [2], which comprises the free lime crystal particles and a heterogeneous phase present between the free lime crystal particles, the heterogeneous phase comprising one or more selected from the group consisting of ternesite, gehlenite, gypsum, eelimite, and calcium silicate. [4] The expanding composition according to [3], wherein the heterogeneous phase comprises gypsum, and the gypsum content is 3% by mass to 60% by mass. [5] The expandable composition according to any one of [1] to [4], wherein the average aspect ratio (major axis / minor axis) of the crystal particle diameter of the free lime crystal particles is 1.0 or more and 2.0 or less. [6] The expandable composition according to any one of [1] to [5], wherein the standard deviation of the maximum length of the crystal particle diameter of the free lime crystal particles is 10.0 or less. [7] The expandable composition according to any one of [3] to [6], wherein the heterophase contains at least one of ternesite and gehlenite, and the total amount of ternesite and gehlenite contained in the heterophase is 1 mass% or more. [8] An expandable admixture comprising anhydrous gypsum and the expandable composition according to any one of [1] to [7]. [9] The expandable admixture according to [8], wherein the anhydrous gypsum contains, as chemical components, 0.01 to 5.0 mass% MgO and 0.01 to 1.0 mass% SrO.

[0009] According to the present invention, it is possible to provide an expansive composition and an expansive admixture that can provide an appropriate expansion rate and improve bending strength.

[0010] 1 is an SEM image of the surface of an expanding composition.

[0011] The expandable composition and expandable admixture of the present invention will be described in detail below, but the present invention is not limited to these embodiments. In this specification, "%" and "parts" are based on mass unless otherwise specified. In addition, a numerical range specified using the symbol "to" includes the numerical values ​​at both ends (upper and lower limits) of "to".

[0012] [Expanding Composition] The expanding composition of the present invention is a composition containing free lime crystal particles having an average crystal particle size of 1 to 30 μm.

[0013] The average crystal particle size of the free lime crystal particles contained in the expanding composition is 1 to 30 μm, preferably 2 to 25 μm, and more preferably 3 to 20 μm. By including free lime in the expanding composition, expansion properties can be imparted. If the average crystal particle size of the free lime crystal particles is less than 1 μm, a sufficient expansion coefficient cannot be obtained, and it becomes difficult to obtain the effect of improving bending strength. If the average crystal particle size of the free lime crystal particles exceeds 30 μm, the expansion coefficient becomes high, and excessive expansion reduces the compressive strength and bending strength. Therefore, the average crystal particle size of the free lime crystal particles is 1 to 30 μm.

[0014] The average crystal particle size of free lime crystal particles can be measured, for example, by taking a scanning electron microscope (SEM) photograph and using appropriate image analysis software to average the sizes of 100 arbitrarily selected free lime crystal particles from the SEM photograph. The free lime crystal particles can be selected by using the results of EDS (energy dispersive X-ray spectroscopy) analysis to distinguish them from other minerals. As image analysis software, for example, "Mac View" manufactured by Mountec Co., Ltd. can be used. Specifically, in this embodiment, the analysis software is used to determine the major and minor diameters of the selected circular or elliptical free lime crystal particles. The average major and minor diameters (A) and (B) of these crystal particles are then calculated, and the average value ((A + B) / 2) is used as the "average crystal particle size." In the case of a circular shape, the diameter is the major and minor diameters, and these values ​​are the same.

[0015] The average crystal particle size of the free lime crystal particles can be adjusted by the firing temperature during production, and the average crystal particle size can be increased by increasing the firing temperature.

[0016] The content of free lime crystal particles in the expanding composition is 15% by mass or more, preferably 20% by mass to 60% by mass, and more preferably 40% by mass to 55% by mass. By setting the content of free lime crystal particles in the expanding composition within this range, an appropriate expansion coefficient and improved bending strength can be achieved.

[0017] The average aspect ratio (major axis / minor axis) of the free lime crystal particles contained in the expanding composition of the present invention is preferably 1.0 or more and 2.0 or less, more preferably 1.1 or more and 1.9 or less, and even more preferably 1.2 or more and 1.8 or less. By setting the average aspect ratio to 1.0 or more and 2.0 or less, an appropriate expansion coefficient can be obtained and bending strength can be improved. The average aspect ratio of the free lime crystal particles can be adjusted by changing the firing temperature and firing time during production.

[0018] The aspect ratio can be determined using the data used to determine the average crystal particle size described above. In the case of a circular shape, the aspect ratio is 1, and in the case of an elliptical shape, the aspect ratio can be determined by dividing the major axis by the minor axis.

[0019] Furthermore, the standard deviation of the maximum length of the crystal particle diameter of the free lime crystal particles contained in the expanding composition of the present invention is preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 6.0 or less. By setting the standard deviation of the maximum length of the crystal particle diameter to 10.0 or less, an appropriate expansion coefficient can be stably obtained and bending strength can be improved. The standard deviation of the maximum length of the crystal particle diameter of the free lime crystal particles can be adjusted by changing the firing temperature and firing time during production. Note that the "maximum length of the crystal particle diameter" refers to the longest linear distance between any two points on a single free lime crystal particle when the free lime crystal particle is observed in an SEM photograph. The maximum length can also be measured by importing the SEM image into image analysis software (e.g., Mac View).

[0020] Furthermore, the expansive composition of the present invention preferably has a heterogeneous phase between free lime crystal particles. By providing a heterogeneous phase between free lime crystal particles, the free lime crystal particles can be coated with the heterogeneous phase, appropriately delaying the reaction of the free lime crystal particles. Therefore, expansion can be appropriately induced at the time when the cement begins to harden (when the water in the cement composition evaporates and shrinkage begins), when expansion is considered to be easily induced, and bending strength can be improved by effectively introducing chemical prestress.

[0021] Figure 1 is an SEM image of the surface of an expandable composition. In the SEM image of the surface of the expandable composition, the heterogeneous phase is present between the free lime crystal particles. Alternatively, it is present along the interface between the crystal particles. In the SEM image, one or more heterogeneous phases may be present between the free lime crystal particles. In Figure 1, arrow A indicates free lime, arrow B indicates gypsum (heterogeneous phase), and arrow C indicates eelimite (heterogeneous phase).

[0022] The heterogeneous phase is ternesite (2(2CaO.SiO ２ )), gehlenite (2CaO.Al ２ O ３ SiO ２ ), gypsum, eliminite (3CaO·3Al ２ O ３ CaSO ４ It is preferable that the composite material contains one or more selected from the group consisting of calcium silicate, calcium silicate, and calcium silicate. Among these, it is preferable that the composite material contains gypsum as the heterophase component. It is also preferable that the composite material contains gypsum and ternesite, gehlenite, and eelimite (3CaO.3Al ２ O ３ CaSO ４ It is more preferable that the composition contains one or more selected from the group consisting of: (a) a mixture of the free lime crystal particles and the expanded composition; (b) a mixture of the free lime crystal particles and the expanded composition; and (c) a mixture of the free lime crystal particles and the expanded composition;

[0023] (Ternesite) The heterophase contained in the expandable composition of the present embodiment may contain ternesite. ２) CaSO ４ The inclusion of ternesite allows for the efficient introduction and accumulation of compressive stress (chemical prestress) in concrete and tensile strain (chemical prestrain) in reinforcing bars.

[0024] When the heterophase of the expansive composition contains ternesite, the amount of ternesite in the expansive composition is 0.5 to 15% by mass, preferably 1 to 12% by mass. By setting the amount of ternesite to 15% by mass or less, the reactivity of the expansive composition can be increased, thereby improving the compressive strength of the produced concrete, increasing the crack initiation load, and reducing the crack width. Furthermore, if the amount is 0.5% by mass or more, the effect of improving the crack initiation load can be fully exerted.

[0025] (Gehlenite) The heterophase contained in the expandable composition of the present embodiment may contain gehlenite. Gehlenite is a 2CaO.Al ２ O ３ SiO ２ Gehlenite has a lower hydration activity than free lime, and the inclusion of gehlenite moderately slows the reaction of free lime, expanding after the cement begins to harden, making it easier to introduce compressive stress into the concrete.

[0026] When the heterophase of the expansive composition contains gehlenite, the amount of gehlenite in the expansive composition is more preferably 0.05 to 8 mass %, and even more preferably 0.1 to 3 mass %. When the gehlenite content is within the above range, compressive stress (chemical prestress) in the concrete and tensile strain (chemical prestrain) in the reinforcing steel can be efficiently introduced and accumulated.

[0027] (Gypsum) The heterophase of the expandable composition of the present embodiment may contain gypsum. The content of gypsum in the expandable composition is preferably 3% by mass to 60% by mass, more preferably 3% by mass to 50% by mass, and even more preferably 10% by mass to 40% by mass.

[0028] (Elimite) The heterophase contained in the expandable composition of the present embodiment may contain eelimite. ２ O ３ CaSO ４ It is a mineral expressed as follows: It hydrates in the presence of gypsum and the like to form ettringite (3CaO·Al ２ O ３ 3CaSO ４ ・32H ２ O) and contributes to improving the early strength.

[0029] When the heterophase of the expandable composition contains eelimite, the amount of eelimite in the expandable composition is preferably 3% by mass to 30% by mass, more preferably 8% by mass to 25% by mass. By being 3% by mass to 30% by mass, it is possible to improve the early strength.

[0030] (Calcium silicate) The heterophase contained in the expandable composition of the present embodiment may contain calcium silicate. Calcium silicate is γ-2CaO.SiO ２ Other than dicalcium silicate and tricalcium silicate 3CaO.SiO ２ , rankinite 3CaO.2SiO ２ , wallasite CaO.SiO ２ 2CaO.SiO etc. ２ It may contain calcium silicate and the like other than the above.

[0031] The content of calcium silicate in the expandable composition is preferably 1 to 10% by mass, more preferably 2 to 8% by mass, which can improve strength.

[0032] Among the above components, the component constituting the heterophase preferably contains at least one of ternesite and gehlenite. By containing at least one of ternesite and gehlenite as the component constituting the heterophase, an appropriate expansion coefficient can be obtained and bending strength can be improved.

[0033] In this case, the total amount of turnesite and gehlenite contained in the heterophase is preferably 1% by mass or more. The total amount of turnesite and gehlenite is more preferably 2% by mass or more. By setting the total amount of turnesite and gehlenite within the above range, an appropriate expansion coefficient can be obtained and bending strength can be improved. The total amount of turnesite and gehlenite is preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 10% by mass or less.

[0034] In this embodiment, the presence of the heterogeneous phase and the content of the components constituting the heterogeneous phase can be controlled, for example, by appropriately selecting the type and amount of each component contained in the expandable composition, the method for producing the expandable composition, etc. Among these, for example, the CaO raw material, SiO ２ Raw material, Al ２ O ３ The use of a raw material mixture containing raw materials, the use of a rotary kiln lined with high-purity aluminum bricks, and / or the application of a predetermined concentration of alumina mortar to the brick surfaces inside the kiln, and appropriate adjustment of the firing temperature, dry crushing, and granulation size conditions can be cited as factors for achieving the presence of the heterogeneous phase and the desired content of the components that make up the heterogeneous phase.

[0035] The free lime content and the content of each mineral component in the expanding composition can be determined by common analytical methods. For example, the mineral composition of a pulverized sample can be determined by powder X-ray diffraction, and the data can be analyzed by the Rietveld method to quantify the mineral composition. Alternatively, the mineral composition can be calculated based on the chemical composition results.

[0036] "Method for producing the expanding composition" Next, a method for producing the expanding composition will be described. ２ Raw material, Al ２ O ３ The method includes a step of firing a raw material mixture containing the raw materials, for example, in a kiln.

[0037] The CaO raw material may be commercially available as an industrial raw material, or may contain, for example, one or more selected from the group consisting of limestone, coal ash, slaked lime, and acetylene-generated sludge (by-product slaked lime). Among these, slaked lime and by-product slaked lime may be used.

[0038] Here, coal ash (fly ash, etc.) is a general term for combustion ash obtained by burning coal, such as coal combustion ash discharged from the boiler of a thermal power plant. Examples of coal ash that can be used include ash generated in a coal-fired power plant by pulverized coal combustion and coal ash that falls and is collected from the combustion gas of the combustion boiler as it passes through an air preheater or a coal economizer, coal ash collected by an electrostatic precipitator, and coal ash that falls to the bottom of the combustion boiler furnace.

[0039] SiO ２ As the raw material, commercially available industrial raw materials may be used, such as silica stone, silica sand, quartz, diatomaceous earth, etc. These may be used alone or in combination of two or more. These may be used in combination with CaO raw materials and Al ２ O ３ SiO in the raw material ２ For example, as a CaO raw material, SiO ２ When coal ash containing the above SiO ２ No raw material needs to be added.

[0040] Al ２ O ３ The raw material may be commercially available industrial raw material, but may also contain, for example, one or more selected from the group consisting of bauxite, aluminum hydroxide, and aluminum ash. The aluminum ash may be mainly composed of aluminum hydroxide. Among these, bauxite may be used.

[0041] These raw materials are mixed and crushed to obtain a raw material mixture so that the desired mineral composition ratio is achieved after firing. The method of crushing is not particularly limited, and either dry crushing or wet crushing can be used. In the case of wet crushing, dehydration treatment is required for subsequent granulation. Furthermore, when quicklime is used as the raw material, dry crushing is preferred. Furthermore, the ratio of free lime crystal particles to heterogeneous phases in the expanded composition can be controlled by adjusting the ratio of the raw materials.

[0042] The firing temperature can be, for example, 1,200°C to 1,600°C, preferably 1,300°C to 1,550°C, and more preferably 1,400°C to 1,450°C.

[0043] For firing, a kiln such as a rotary kiln can be used. ２ O ３ A rotary kiln may be used in which the bricks in the firing zone are made of high-purity alumina bricks with a content of 99% or more by mass, and / or alumina mortar adjusted to an appropriate concentration may be applied to the inner surface of the bricks in the firing zone of the rotary kiln before firing.

[0044] The calcination produces clinker, which may be pulverized by a known method to produce a pulverized product.

[0045] The expandable composition may be a clinker obtained by burning raw material components, or may be a powder of clinker.

[0046] [Expansive admixture] The expansive admixture of the present invention contains anhydrous gypsum and the above-mentioned expansion composition. By forming a cement composition containing this expansive admixture, the formation of ettringite is promoted. By forming ettringite, it is possible to impart an appropriate expansion coefficient to the obtained hardened body and improve bending strength. In this specification, the term "cement composition" is used to include cement paste, mortar composition, and concrete composition.

[0047] The anhydrous gypsum contained in the expansive admixture preferably contains, as chemical components, 0.01 to 5.0 mass% MgO and 0.01 to 1.0 mass% SrO. The MgO content is more preferably 0.01 to 4.0 mass%, and even more preferably 0.01 to 3.0 mass%. The SrO content is more preferably 0.01 to 0.08 mass%, and even more preferably 0.01 to 0.06 mass%. By setting the amounts of MgO and SrO within the above ranges, an appropriate expansion coefficient can be imparted.

[0048] The content of anhydrous gypsum in the expansive admixture is preferably 5 to 45% by mass, more preferably 10 to 30% by mass, and even more preferably 15 to 25% by mass. By setting the content of anhydrous gypsum within the above range, an appropriate expansion coefficient can be obtained and bending strength can be improved.

[0049] [Cement Composition] The cement composition according to this embodiment contains the expansive admixture of the present invention and cement.

[0050] The amount of expansive admixture used varies depending on the purpose of use, but it is usually ３ The weight is preferably 20 to 60 kg, more preferably 30 to 50 kg per unit.

[0051] The cement is not particularly limited, and various types of Portland cement, such as normal, early-strength, ultra-early-strength, low-heat, and moderate-heat, can be used. Also usable are various blended cements obtained by mixing these Portland cements with blast furnace slag, fly ash, or silica fume; filler cements mixed with limestone powder or slowly cooled blast furnace slag powder; waste-recycled cements, so-called Ecocement®, produced from raw materials such as municipal waste incineration ash and sewage sludge incineration ash; blended cements mixed with waste-recycled cement; commercially available fine particle cements; and limestone-calcined clay cements (LC3) mixed with clay minerals such as alumina cement, sulfoaluminate cement, metakaolin, or allophane. Various cements and blended cements can also be used in a finely powdered form. Furthermore, cements prepared by increasing or decreasing the amounts of components typically used in cement can also be used, and one or more of the above can be used in combination.

[0052] The amount of water used is not particularly limited, but typically, the water / binder ratio is preferably, for example, 25 to 60%, and more preferably 30 to 55%, relative to the binder consisting of cement and an expansive admixture.

[0053] The mixing method for producing the cement composition 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, or a Nauta mixer.

[0054] The cement composition and water may be mixed at the time of application, or a part or all of the components may be mixed in advance.

[0055] The method for curing the cement composition is not particularly limited, and any of the commonly used curing methods such as room temperature and normal pressure curing, steam curing, high temperature and high pressure steam curing, and pressurized curing can be applied.

[0056] The cement composition may further contain one or more of the following admixtures in combination, within the scope that does not substantially impair the objects of the present invention: aggregates such as sand and gravel; rapid hardening agents; set adjusters; water reducing agents; high-performance water reducing agents; air entraining agents; air entraining water reducing agents; high-performance air entraining water reducing agents; thickeners; rust inhibitors; antifreeze agents; hydration heat inhibitors; polymer emulsions; clay minerals such as bentonite and montmorillonite; ion exchangers such as zeolite, hydrotalcite, and hydrocalumite; sulfates such as aluminum sulfate and sodium sulfate; phosphates; and boric acid.

[0057] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples.

[0058] (Experimental Example 1) (Preparation of Expanding Composition) The expanding composition was prepared by mixing calcium carbonate, calcium sulfate dihydrate, aluminum hydroxide, and silicon dioxide so that the contents of each component were as shown in Table 1, and then heat-treating the mixture at 1,400°C for 2 hours, allowing it to cool to room temperature, and pulverizing it using a ball mill. The Blaine value was 3,500 cm ２ / g. The average crystal particle size of the free lime crystal particles was determined by taking an SEM photograph of the surface of the prepared expanded composition and using image analysis software (Mac View). Specifically, 100 free lime crystal particles were selected from the SEM image obtained using image analysis software, and the major and minor axes of the circular or elliptical shapes were determined using image analysis software. The average major axis (A) and the average minor axis (B) of these crystal particles were determined, and the average value ((A + B) / 2) of these values ​​was defined as the "average crystal particle size". In the case of a circular shape, the diameter becomes the major axis and the minor axis, and these values ​​are the same value.

[0059] (Materials used) Calcium carbonate: 1st grade reagent, commercially available Calcium sulfate dihydrate: 1st grade reagent, commercially available Aluminum hydroxide: 1st grade reagent, commercially available Silicon dioxide: 1st grade reagent, commercially available

[0060] (Method of manufacturing concrete) Using the prepared expansive composition, concrete was mixed with 380 kg / m of cement. ３ , expanding composition 40 kg / m ３ , fine aggregate 709kg / m３ , coarse aggregate 1072kg / m ３ , and water 160 kg / m ３ A concrete composition was mixed using the above mixture to achieve a slump of 8.0±2.5 cm, air content of 2.0±1.5%, W / C of 38%, and s / a of 40%. The resulting concrete composition was pre-cured at 20°C for 10 hours, heated at a rate of 20°C / hour, and steam-cured by holding at a maximum temperature of 65°C for 2 hours. The temperature was then naturally lowered until the concrete was 1 day old, producing concrete. The expansion coefficient and flexural strength of the produced concrete were measured.

[0061] (Materials used) Cement: Ordinary Portland cement in accordance with JIS R 5210:2019, commercially available product Water: Tap water Fine aggregate: Natural sand from Himekawa, Niigata Prefecture, specific gravity 2.62 Coarse aggregate: Crushed stone from Himekawa, Niigata Prefecture, maximum dimension 25 mm, specific gravity 2.64

[0062] (Evaluation method) Expansion coefficient: The expansion coefficient on the 7th day of curing was measured based on the test method for expansive additives for concrete in JIS A 6202. Considering the improvement in bending strength, the expansion coefficient was 200 to 1000 × 10 －６ is preferably 400 to 850×10 －６ Bending strength: Uniaxially restrained expansion test specimens were prepared in accordance with JIS A 6202:2017 Appendix B, Method B, and after demolding at a material age of 1 day, the specimens were cured in water at 20°C for 7 days. A pi-type displacement gauge was attached to the test specimens, and a bending strength test was carried out in accordance with JIS A 1106:2018, and the bending strength under restrained conditions was calculated from the load at which a crack with a width of 0.05 mm or more appeared.

[0063]

[0064] The results shown in Table 1 confirm that concretes (Test Nos. 1-2 to 1-4) using an expansive composition containing free lime crystal particles whose average crystal particle size falls within the range of the present invention exhibit improved flexural strength compared to comparative examples (Test Nos. 1-1 and 1-5) whose average crystal particle size falls outside the range of the present invention. Furthermore, the concrete (Test No. 1-1) using free lime crystal particles whose crystal particle size is smaller than the range of the present invention exhibited a low expansion coefficient, while the concrete (Test No. 1-5) using free lime crystal particles whose crystal particle size is larger than the range of the present invention exhibited a high expansion coefficient and a lower flexural strength than Test Nos. 1-2 to 1-4. It can be seen that unless the average particle size of the free lime crystal particles falls within the range of the present invention, the flexural strength improvement effect is not fully exerted and the expansion coefficient does not fall within the preferred range. Furthermore, as a reference example, a concrete without the addition of an expansive additive (Test No. 1-6) was also performed. For Test No. 1-6, in which no expansive additive was added, the concrete produced had a zero expansion coefficient and low flexural strength.

[0065] (Experimental Example 2) In Experimental Example 2, the expansion coefficient and flexural strength of concrete produced by changing the components contained in the heterogeneous phase were measured. As in Experimental Example 1, an expansion composition was prepared by mixing calcium carbonate, calcium sulfate dihydrate, aluminum hydroxide, and silicon dioxide so that the contents of each component were as shown in Table 2. Concrete was also produced by the same method as in Experimental Example 1. The results are shown in Table 2.

[0066]

[0067] The results shown in Table 2 confirm that the presence of at least one heterogeneous phase can improve bending strength and keep the expansion coefficient within an appropriate range. Furthermore, it can be confirmed that the concrete (Test Nos. 2-7 and 2-8) using an expansive composition with a free lime crystal particle content of 15% by mass or more can improve bending strength and keep the expansion coefficient within an appropriate range, compared to the concrete (Test No. 2-6) using an expansive composition with a free lime crystal particle content of 14% by mass.

[0068] (Experimental Example 3) In Experimental Example 3, an expansive admixture was prepared by adding anhydrous gypsum to an expansive composition, and the expansion coefficient and flexural strength of concrete produced using the prepared expansive admixture were measured. The expansive composition was produced in the same manner as in Test Nos. 1-3. Anhydrous gypsum was added to the prepared expansive composition in the proportions shown in Table 3 per 100 parts by mass of the expansive composition to prepare an expansive admixture. Using the prepared expansive admixture, an expansive admixture was added so that the amount as the expansive composition was the same, and concrete was produced in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0069] (Materials Used) Anhydrous gypsum: Anhydrous gypsum having the composition shown in Table 4 was used.

[0070]

[0071]

[0072] The results shown in Table 3 confirm that the flexural strength can be further improved by using an expansive admixture in which anhydrous gypsum is added to the expansive composition. The flexural strength was particularly improved in concrete using an expansive admixture in which 10 to 40 parts by mass of gypsum was added per 100 parts by mass of the expansive composition.

[0073] (Experimental Example 4) In Experimental Example 4, the expansion coefficient and flexural strength of concrete produced using an auxiliary cement material as a substitute for cement were measured. The expansive composition was produced in the same manner as in Tests No. 1-3. Concrete was produced in the same manner as in Experimental Example 1, except that the cement was replaced with the auxiliary cement material shown in Table 5 in the amounts shown in Table 5 per 100 parts by mass of cement. Commercially available products were used for the ground granulated blast furnace slag, fly ash, metakaolin, and sewage sludge incineration ash. The results are shown in Table 5.

[0074]

[0075] The results shown in Table 5 show that even when an auxiliary cement material was used in place of cement, the bending strength could be improved and the expansion coefficient could be kept within a preferred range.

[0076] Experimental Example 5 In Experimental Example 5, the expansion coefficient and flexural strength of concrete were measured using expansive compositions with different average aspect ratios (major axis / minor axis) and standard deviations of maximum length of the free lime crystal particles. Similar to Experimental Example 1, the expansive compositions were prepared by mixing calcium carbonate, calcium sulfate dihydrate, aluminum hydroxide, and silicon dioxide so that the contents of each component were as shown in Table 5. By varying the firing temperature and firing time, expansive compositions containing free lime crystal particles with the average aspect ratios and standard deviations shown in Table 6 were obtained. Using the resulting expansive compositions, concrete was produced using the same method as in Experimental Example 1. The results are shown in Table 6.

[0077]

[0078] The expandable composition of the present invention has a wide range of applications in the civil engineering and construction industries.

Claims

1. An expansive composition comprising free lime crystal particles having an average crystal particle size of 1 to 30 μm.

2. The expansive composition according to claim 1, wherein the content of the free lime crystal particles is 15% by mass or more.

3. The expansive composition according to claim 1 or 2, comprising the free lime crystal particles and a heterogeneous phase existing between the free lime crystal particles, the heterogeneous phase including one or more selected from the group consisting of tricalcium aluminate, calcium ferrite, gypsum, yeelimite, and calcium silicate.

4. The expansive composition according to claim 3, wherein the heterogeneous phase contains gypsum and contains 3% by mass or more and 60% by mass or less of the gypsum.

5. The expansive composition according to claim 1 or 2, wherein the average aspect ratio (major axis / minor axis) of the crystal particle size of the free lime crystal particles is 1.0 or more and 2.0 or less.

6. The expansive composition according to claim 1 or 2, wherein the standard deviation of the maximum length of the crystal particle size of the free lime crystal particles is 10.0 or less.

7. The expansive composition according to claim 3, wherein the heterogeneous phase contains at least one of tricalcium aluminate and calcium ferrite, and the total amount of tricalcium aluminate and calcium ferrite is 1% by mass or more in the heterogeneous phase.

8. An expansive admixture comprising anhydrous gypsum and the expansive composition according to claim 1 or 2.

9. The expansive admixture according to claim 8, wherein the anhydrous gypsum contains 0.01 to 5.0% by mass of MgO and 0.01 to 1.0% by mass of SrO as chemical components.

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