METHOD FOR PRODUCING CALCINED PRODUCT COMPRISING gamma-2CaOSiO2

Abstract

By preparing a raw material mixture comprising CaO raw material, SiO.sub.2 raw material and waste material, and having a content of Al.sub.2 O.sub.3 after heating at 1000 C. of 5.0 mass % or less, and calcining at a calcination temperature of 1350 C. to 1600 C., it is possible to efficiently use waste materials as a part of raw materials, and to obtain a calcined product that comprises almost an equivalent amount of -2CaO.Math.SiO.sub.2 as conventional can be obtained.

Claims

1. A method of producing a calcined product comprising -2CaO.Math.SiO.sub.2, the method comprising preparing a raw material mixture comprising CaO raw material, SiO.sub.2 raw material and waste material, and having a content of Al.sub.2 O.sub.3 after heating at 1000 C. of 5.0 mass % or less, and calcining at a calcination temperature of 1350 C. to 1600 C.

2. The method according to claim 1, wherein the waste material is at least one waste material selected from coal ash, blast furnace slag, concrete sludge, waste concrete, incineration fly ash, and municipal waste incineration ash.

3. The method according to claim 1 or 2, wherein the raw material mixture is a raw material mixture which total content of Al.sub.2O.sub.3 and Fe.sub.2O.sub.3 after heating at 1000 C. is 5.0 mass % or more.

4. The method according to claim 1 or 2, wherein the raw material mixture is a raw material mixture which content of Al.sub.2O.sub.3 after heating at 1000 C. is over 1.7 mass %.

Description

DESCRIPTION OF EMBODIMENTS

[0017] In the production method of the present invention, as CaO raw material and SiO.sub.2 raw material for producing -2CaO.Math.SiO.sub.2, CaO raw material and SiO.sub.2 raw material known as raw material for cement clinker production can be used without limitation, and specific examples include CaO raw materials such as limestone, quicklime and lime hydrate, etc., SiO.sub.2 raw materials such as silica stone, silica fume, etc.

[0018] The most important thing in the present invention is to use waste materials in the raw material mixture in the production of calcined product comprising -2CaO.Math.SiO.sub.2, and there is an advantage of promoting efficient use of waste materials than in the past. As stated in the above, conventionally, in the production of -2CaO.Math.SiO.sub.2, it was thought that contamination of impurities was not preferable, but in the present invention, it has been found that efficient use of waste materials is possible under particular conditions.

[0019] Further, limestone (calcium carbonate) used as CaO raw material in the production of -2CaO.Math.SiO.sub.2 discharges carbon dioxide at the time of calcination. In the present invention, by using waste materials such as coal ash comprising calcium oxide that can be CaO raw material or blast furnace slag, etc. the used amount of limestone that is the cause of carbon dioxide discharge can be decreased to suppress the carbon dioxide discharge when producing -2CaO.Math.SiO.sub.2.

[0020] The waste material of the present invention means the waste material, by-product used in the production of cement, etc. The waste materials that can be used are not particularly limited, and specific examples include blast furnace slag such as granulated blast furnace slag, air-cooled blast furnace slag, etc., steel slag, non-ferrous slag, coal ash, concrete sludge (including waste fresh concrete, remaining concrete), concrete waste, sewage sludge, water treatment sludge, paper making sludge, construction soil, casting sand, fall dust, incineration fly ash, molten fly ash, chlorine bypass dust, wood waste, waste white clay, coal waste, waste tire, seashell, municipal waste, or burned ash thereof (among these, some may become thermal energy source). Among these, waste materials comprising Al.sub.2O.sub.3 which used amount is restricted by the amount of Al.sub.2O.sub.3 in the production of cement clinker are preferable from the point of further promoting the efficient use of waste materials. Examples of typical waste materials comprising Al.sub.2O.sub.3 include blast furnace slag, steel slag, non-ferrous slag, coal ash, concreate sludge, concrete waste, sewage sludge, water treatment sludge, paper making sludge, casting sand, incineration fly ash, molten fly ash, municipal waste and incineration ash thereof, etc. Among these, use of coal ash, blast furnace slag, concrete sludge, concrete waste, incineration fly ash, and municipal waste incineration ash is preferable, from the viewpoint that Al.sub.2O.sub.3 content is high as compared to normal cement clinker composition, and the main components are CaO, SiO.sub.2, Al.sub.2O.sub.3. Further, these waste materials can be used in combination.

[0021] In the production method of the present invention, as raw material mixture comprising CaO raw material, SiO.sub.2 raw material and waste material, it is necessary to use a raw material mixture having a content of Al.sub.2 O.sub.3 after heating at 1000 C. of 5.0 mass % or less. When the content of Al.sub.2O.sub.3 in the raw material mixture exceeds 5.0 mass %, -2CaO.Math.SiO.sub.2 tends to generate within the range of 1500 to 1600 C. and the content rate of -2CaO.Math.SiO.sub.2 in the calcined product obtained by calcinating would be low. Further, minerals comprising Al.sub.2O.sub.3 as its constituent element such as gehlenite tend to generate. From the viewpoint of content rate of -2CaO.Math.SiO.sub.2 in the calcined product, it is preferable that the Al.sub.2O.sub.3 content in the raw material mixture is 4.8 mass % or less, and more preferable to be 4.5 mass % or less. In this range, a calcined product having almost equivalent amount of -2CaO.Math.SiO.sub.2 content, as compared to when producing -2CaO.Math.SiO.sub.2 by using only conventional CaO raw material and SiO.sub.2 raw material can be obtained.

[0022] The lower limit of Al.sub.2O.sub.3 content in the raw material mixture after heating at 1000 C. is not particularly limited, but since Al.sub.2O.sub.3 is also comprised in the CaO raw material and SiO.sub.2 raw material that are used, it is sufficient to be more than the Al.sub.2O.sub.3 content derived from CaO raw material and SiO.sub.2 raw material, and for example, it is sufficient to be over 1.7 mass %. Naturally, larger is the Al.sub.2O.sub.3 content in the raw material mixture, the amount of waste material comprising Al.sub.2O.sub.3 used in the production of calcined product comprising -2CaO.Math.SiO.sub.2 would be large, and it is preferable from the viewpoint of promoting efficient use of waste materials, which is the most important issue in the present invention.

[0023] In the production method of the present invention, the total content of Al.sub.2O.sub.3 and Fe.sub.2O.sub.3 in the raw material mixture after heating at 1000 C. is not particularly limited. Specifically, in the production method of the present invention, as long as the content of Al.sub.2O.sub.3 in the raw material mixture after heating at 1000 C. is 5.0 mass % or less, even if the total of Al.sub.2O.sub.3 and Fe.sub.2O.sub.3 is 5.0 mass % or more, a calcined product having almost equivalent amount of -2CaO.Math.SiO.sub.2 content, as compared to when producing -2CaO.Math.SiO.sub.2 by using only conventional CaO raw material and SiO.sub.2 raw material can be obtained. Specifically, the present invention is different from the technical idea of Patent Literature 3 which essentially requires that the total of Al.sub.2O.sub.3 and Fe.sub.2O.sub.3 is less than 5.0 mass %.

[0024] The total of Al.sub.2O.sub.3 and Fe.sub.2O.sub.3 is preferably 8.0 mass % or less, and more preferably 7.0 mass % or less.

[0025] Meanwhile, the above-mentioned Al.sub.2O.sub.3 and Fe.sub.2O.sub.3 in the raw material mixture after heating at 1000 C. can be each measured by the method compliant to JIS R 5204 Chemical analysis method of cement by X-ray fluorescence.

[0026] The blending ratio of CaO raw material, SiO.sub.2 raw material and waste material can be adjusted so that the CaO/SiO.sub.2 molar ratio of the raw material mixture becomes 2.0 in stoichiometric proportion. In case it is well below 2.0, wollastonite or rankinite generates as by-product, and in case it largely exceeds 2.0, 3CaO.Math.SiO.sub.2 generates as by-product. Generally, it is preferable to adjust so that the CaO/SiO.sub.2 molar ratio becomes 1.8 to 2.2, and more preferably 1.9 to 2.1.

[0027] As a method for preparing and mixing the raw material mixture for producing a calcined product comprising -2CaO.Math.SiO.sub.2, a known method can be appropriately employed. For example, the composition of CaO raw materials such as limestone, quicklime and lime hydrate, etc., SiO.sub.2 raw materials such as silica stone, etc. and waste materials is measured in advance, the blending ratio of each raw material is calculated to be within the above-mentioned range from each component ratio of these raw materials, and the raw materials are blended with such ratio.

[0028] Smaller is the particle size of raw material mixture comprising CaO raw material, SiO.sub.2 raw material and waste material, the calcination reaction rate becomes faster, while since the electrical power consumption rate generated when each raw material and/or raw material mixture is crushed worsens, it is sufficient to prepare so that the 90 m sieve residue is 10 to 30%, preferably 20 to 26%. The method for crushing each raw material and/or raw material mixture is not particularly limited, and it can be crushed with a known method.

[0029] In the present invention, the calcination temperature of the raw material mixture after preparation and mixture is 1350 to 1600 C., and from the viewpoint of the content of -2CaO.Math.SiO.sub.2 in the calcined product, the calcination temperature is more preferably 1400 to 1600 C., and particularly preferably 1500 to 1600 C. In case the calcination temperature is less than 1350 C., the free lime (f-CaO) amount tends to be large. On the contrary, in case the calcination temperature is over 1600 C., since the raw materials melt and vitrifies, the operation becomes difficult, and it is not preferable also from the viewpoint of the thermal energy usage. The calcination time depends on the calcination temperature, while it is generally 0.5 to 10 hours, preferably 1 to 5 hours.

[0030] The calcination method is not particularly limited, and rotary kiln, shaft kiln, electrical furnace, tunnel furnace, fluidized firing type incinerator, etc. can be used. Amont these, from the viewpoint that existing Portland cement production facility can be used, apparatus with which high-temperature heating such as cement kiln represented by NSP kiln or SP kiln is possible can be suitably used. Further, it is preferable to use such cement production facility from the viewpoint of large-scale production.

[0031] In the present invention, cooling operation is performed after calcination. However, cooling conditions are not particularly limited, and for example, in the existing Portland cement production facility, after calcinating with rotary kiln, it can be immediately cooled with a cooling apparatus (air blower, sprinkler) called Clinker cooler.

[0032] The content of -2CaO.Math.SiO.sub.2 comprised in the calcined product obtained by the production method of the present invention is preferably more than the content of -2CaO.Math.SiO.sub.2, preferably 40 mass % or more of the whole calcined product, more preferably 50 mass % or more.

[0033] The calcined product obtained by the production method of the present invention can be used as admixture of cement. Concrete or mortar using cement comprising this calcined product will have a high durability since the surface part is densified by performing carbonation curing at the time of production. Further, in the production of concrete, etc., since carbon dioxide is absorbed in the concrete during carbonation curing, it is possible to reduce the carbon dioxide discharge amount when obtaining concrete products.

EXAMPLES

[0034] The constitution and effect of the present invention will be explained in the following by reference to the Examples, while the present invention is not limited to these Examples.

Examples 1 to 3, Comparative Examples 1 to 3

[0035] By using limestone as CaO raw material, silica stone as SiO.sub.2 raw material, coal ash having high Al.sub.2O.sub.3 content as waste material, raw material mixtures (90 m sieve residue 20%) having CaO/SiO.sub.2 molar ratio of 2.0 and having different composition of the total content of Al.sub.2O.sub.3 and Fe.sub.2O.sub.3 after heating at 1000 C. were prepared.

[0036] Table 1 shows the ignition loss (ig. loss) and the chemical composition of each raw material used, Table 2 shows the blending ratio of each raw material, and Table 3 shows the chemical composition of the raw material mixture after heating at 1000 C. Meanwhile, measurement of the ignition loss (ig. loss) of each raw material was performed by weighing 3.0 g of raw material in a crucible, heating at 1000 C. for 1 hour in an electrical furnace, and by calculating the decreased mass amount before and after the heating. Further, measurement of chemical composition of the raw material mixture is compliant to JIS R 5204 Chemical analysis method of cement by X-ray fluorescence, and performed by mixing 1.5 g of raw material mixture after heating for 1 hour at 1000 C. and 4.0 g of lithium tetraborate (top quality), melting for 20 min. at 1050 C., to prepare glass beads, and subjecting the same to TUBE-ABOVE SIMULTANEOUS WAVELENGTH DISPERSIVE X-RAY FLUORESCENCE SPECTROMETER (manufactured by Rigaku Corporation, Simultix 15).

[0037] These raw material mixtures after being prepared and mixed were calcined for 1 hour at a calcination temperature of 1350 C. to 1600 C. with a high-speed heating electrical furnace (manufactured by Motoyama, SUPER-BURN NH-2025D-OP), cooled slowly to 1300 C. at a rate of 10 C./min., removed from the electrical furnace, cooled down to room temperature to obtain the calcined product.

[0038] The obtained calcined product was subjected to X-ray diffraction analysis, and the content of -2CaO.Math.SiO.sub.2 was obtained by Rietveld analysis. Table 4 shows the calcination temperature and the -2CaO.Math.SiO.sub.2 amount obtained by Rietveld analysis of the calcined product obtained at each calcination temperature. Table 5 shows the chemical composition of the calcined products when calcined at 1500 C., obtained by Rietveld analysis.

TABLE-US-00001 TABLE 1 chemical composition (mass %) ig. loss(%) SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO Na.sub.2O K.sub.2O limestone 42.33 1.55 0.71 0.16 53.44 0.57 0.01 silica stone 1.52 88.19 4.8 2.62 0.21 0.63 0.38 1.06 coal ash 8.34 56.93 28.84 7.08 2.71 1.81 0.48 1.31

TABLE-US-00002 TABLE 2 raw material blending (mass %) limestone silica stone coal ash Total Reference Example 76.4 23.6 0 100.0 Example 1 75.5 21.3 3.2 100.0 Example 2 75.2 20.5 4.3 100.0 Example 3 74.6 19.1 6.3 100.0 Comparative Example 1 74.1 17.7 8.2 100.0 Comparative Example 2 73.6 16.3 10.1 100.0 Comparative Example 3 73.0 14.9 12.0 100.0

TABLE-US-00003 TABLE 3 chemical composition of raw material mixture after heating at 1000 C. (mass %) Al.sub.2O.sub.3 + SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO SO.sub.3 Na.sub.2O K.sub.2O TiO.sub.2 P.sub.2O.sub.5 MnO SrO Fe.sub.2O.sub.3 Reference Example 33.46 2.54 1.23 60.34 0.90 0.31 0.13 0.45 0.13 0.20 0.08 0.03 3.77 Example 1 32.89 3.52 1.48 59.54 0.94 0.32 0.14 0.47 0.17 0.21 0.08 0.04 5.00 Example 2 32.67 3.89 1.58 59.23 0.96 0.33 0.15 0.48 0.18 0.21 0.08 0.04 5.47 Example 3 32.04 4.50 1.72 59.03 0.99 0.34 0.15 0.49 0.21 0.22 0.07 0.04 6.22 Comparative Example 1 31.59 5.10 1.89 58.64 1.01 0.34 0.15 0.50 0.24 0.23 0.07 0.04 6.99 Comparative Example 2 31.25 5.72 2.05 58.09 1.05 0.35 0.16 0.51 0.27 0.23 0.07 0.05 7.77 Comparative Example 3 30.79 6.28 2.20 57.77 1.06 0.36 0.17 0.52 0.30 0.24 0.06 0.05 8.48

TABLE-US-00004 TABLE 4 calcination -2CaOSiO.sub.2 by Rietveld analysis (mass %) temperature ( C.) 1350 1400 1450 1500 1550 1600 Reference Example 26.66 40.90 44.32 68.25 66.46 75.56 Example 1 22.53 44.21 44.10 71.72 73.45 78.58 Example 2 26.20 46.25 44.61 71.64 63.64 78.78 Example 3 32.94 45.16 43.78 60.95 64.72 69.21 Comparative Example 1 28.75 44.77 40.92 32.22 55.17 56.19 Comparative Example 2 26.65 41.07 38.20 22.71 35.56 25.76 Comparative Example 3 25.96 44.23 44.51 8.83 13.29 9.60

TABLE-US-00005 TABLE 5 chemical composition (mass %) -C2S -C2S other Reference Example 68.25 24.17 7.58 Example 1 71.72 19.20 9.09 Example 2 71.64 20.68 8.13 Example 3 60.95 31.92 7.14 Comparative Example 1 32.22 58.49 9.29 Comparative Example 2 22.71 64.41 12.88 Comparative Example 3 8.83 78.64 12.53 -C2S: -2CaOSiO.sub.2 -C2S: -2CaOSiO.sub.2

[0039] The Reference Examples shows a case of using only the conventional CaO raw material and SiO.sub.2 raw material to calcining -2CaO.Math.SiO.sub.2, and the content of Al.sub.2 O.sub.3 after heating at 1000 C. being 2.5 mass %. The results of each Example-Comparative Example were determined to be good or bad by using the results of the Reference Example as standard.

[0040] Examples 1 to 3 are of the present invention, and the content of -2CaO.Math.SiO.sub.2 in the calcined product is almost equivalent of the Reference Examples within any range of a calcination temperature of 1350 to 1600 C.

[0041] Comparative Examples 1 to 3 have a content of Al.sub.2O.sub.3 after heating at 1000 C. of over 5.0 mass %, and it can be seen that within the range of calcination temperature of 1500 to 1600 C., the content of -2CaO.Math.SiO.sub.2 in the calcined product is significantly decreased as compared to the Reference Example. This is because -2CaO.Math.SiO.sub.2 has generated in a large amount (Table 5).

[0042] Further, in Examples 1 to 3, coal ash (including calcium oxide) used as waste material becomes the calcium source, and thus the used amount of limestone which becomes the cause of carbon dioxide emission decreases (see Table 1 and Table 2), discharge of carbon dioxide is suppressed. Converting from raw material composition, in Example 1, the amount of carbon dioxide emission was reduced by 1.2%, in Example 2 reduced by 1.6% and in Example 3 reduced by 2.4%.

Examples 4 to 5; Comparative Examples 4 to 5

[0043] Instead of coal ash as waste material, blast furnace slag (air-cooled blast furnace slag) was used, and tests were performed similarly as the above Examples 1 to 3 and Comparative Examples 1 to 3.

[0044] Table 6 shows the chemical composition of each raw material used, Table 7 shows the blending ratio of each material, and Table 8 shows the chemical composition of raw material mixture after heating at 1000 C.

[0045] Further, Table 9 shows the chemical composition of the calcined products when calcined at 1500 C., obtained by Rietveld analysis.

TABLE-US-00006 TABLE 6 chemical composition (mass %) ig. loss(%) SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO Na.sub.2O K.sub.2O limestone 42.33 1.55 0.71 0.16 53.44 0.57 0.01 silica stone 1.52 88.19 4.8 2.62 0.21 0.63 0.38 1.06 blast furnace slag 1.24 33.95 12.13 1.77 43.5 5.07 0.19 0.25

TABLE-US-00007 TABLE 7 raw material blending (mass %) silica blast furnace limestone stone slag total Reference Example 76.5 23.5 0 100.0 Example 4 71.2 20.9 7.9 100.0 Example 5 68.0 19.4 12.6 100.0 Comparative Example 4 63.0 17.0 20.0 100.0 Comparative Example 5 56.3 13.7 30.0 100.0

TABLE-US-00008 TABLE 8 chemical composition of raw material mixture after heating at 1000 C. (mass %) Al.sub.2O.sub.3 + SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO SO.sub.3 Na.sub.2O K.sub.2O TiO.sub.2 P.sub.2O.sub.5 MnO SrO Fe.sub.2O.sub.3 Reference Example 33 2.71 1.29 60.48 0.92 0.36 0.13 0.46 0.14 0.20 0.08 0.03 4.00 Example 4 32.23 3.69 1.34 59.53 1.39 0.54 0.13 0.43 0.18 0.19 0.11 0.04 5.03 Example 5 31.67 4.32 1.38 58.99 1.67 0.67 0.14 0.41 0.21 0.18 0.13 0.04 5.70 Comparative Example 4 31.18 5.17 1.41 58.00 2.07 0.84 0.14 0.38 0.25 0.17 0.15 0.04 6.58 Comparative Example 5 30.46 6.36 1.53 56.57 2.63 1.06 0.15 0.34 0.31 0.16 0.19 0.04 7.89

TABLE-US-00009 TABLE 9 chemical composition (mass %) -C2S -C2S other Reference Example 79.08 9.80 11.12 Example 4 78.55 9.60 11.86 Example 5 59.27 20.68 20.05 Comparative Example 4 21.48 50.19 28.33 Comparative Example 5 3.87 56.89 39.23 -C2S: -2CaOSiO.sub.2 -C2S: -2CaOSiO.sub.2

[0046] Examples 4 to 5 are of the present invention, and similarly as when using coal ash, the content of Al.sub.2O.sub.3 in the calcined product has a high ratio.

[0047] Further, Comparative Examples 4 to 5 have a content of Al.sub.2O.sub.3 after heating at 1000 C. of over 5 mass %, and it can be seen that the content of -2CaO.Math.SiO.sub.2 in the calcined product is significantly decreased as compared to the Reference Example similarly as when using coal ash.

[0048] Further, in Examples 4 to 5, blast furnace slag (including calcium oxide) used as waste material becomes the calcium source, and thus the used amount of limestone which becomes the cause of carbon dioxide emission decreases (see Table 6 and Table 7), discharge of carbon dioxide is suppressed. Converting from raw material composition, in Example 4, the amount of carbon dioxide emission was reduced by 8.4%, and in Example 5 reduced by 14.6%.

Example 6; Comparative Examples 6 to 7

[0049] Instead of coal ash or blast furnace slag as waste material, concrete sludge (raw concrete sludge) was used, and tests were performed similarly as the above Examples 1 to 5 and Comparative Examples 1 to 5.

[0050] Table 10 shows the chemical composition of each raw material used, Table 11 shows the blending ratio of each material, and Table 12 shows the chemical composition of raw material mixture after heating at 1000 C.

[0051] Further, Table 13 shows the chemical composition of the calcined products when calcined at 1400 C., obtained by Rietveld analysis.

TABLE-US-00010 TABLE 10 chemical composition (mass %) ig. loss(%) SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO Na.sub.2O K.sub.2O limestone 42.33 1.55 0.71 0.16 53.44 0.57 0.01 silica stone 1.52 88.19 4.8 2.62 0.21 0.63 0.38 1.06 raw concrete sludge 21.05 23.54 7.36 3.19 39.03 2.36 0.51 0.70

TABLE-US-00011 TABLE 11 raw material blending (mass %) silica raw concrete limestone stone sludge total Reference Example 76.5 23.5 0 100.0 Example 6 61.6 18.4 20.0 100.0 Comparative Example 6 46.8 13.2 40.0 100.0 Comparative Example 7 32.0 8.0 60.0 100.0

TABLE-US-00012 TABLE 12 chemical composition of raw material mixture after heating at 1000 C. (mass %) Al.sub.2O.sub.3 + SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO SO.sub.3 Na.sub.2O K.sub.2O TiO.sub.2 P.sub.2O.sub.5 MnO SrO Fe.sub.2O.sub.3 Reference Example 32.95 2.72 1.32 60.83 0.93 0.12 0.12 0.36 0.13 0.20 0.08 0.03 4.04 Example 6 31.83 4.2 1.88 59.14 1.4 0.18 0.22 0.39 0.21 0.22 0.09 0.04 6.08 Comparative Example 6 30.62 5.54 2.42 57.7 1.85 0.27 0.31 0.45 0.28 0.23 0.09 0.04 7.96 Comparative Example 7 29.51 6.80 2.95 55.89 2.28 0.64 0.41 0.59 0.35 0.25 0.09 0.04 9.75

TABLE-US-00013 TABLE 13 chemical composition (mass %) -C2S -C2S other Reference Example 67.00 18.87 14.14 Example 6 54.16 23.49 22.35 Comparative Example 6 30.66 37.61 31.73 Comparative Example 7 5.92 49.78 44.30 -C2S: -2CaOSiO.sub.2 -C2S: -2CaOSiO.sub.2

[0052] Example 6 is of the present invention, and similarly as when using coal ash or blast furnace slag, the content of -2CaO.Math.SiO.sub.2 in the calcined product has a high ratio.

[0053] Further, Comparative Examples 6 to 7 have a content of Al.sub.2O.sub.3 after heating at 1000 C. of over 5 mass %, and it can be seen that the content of -2CaO.Math.SiO.sub.2 in the calcined product is significantly decreased as compared to the Reference Example similarly as when using coal ash or blast furnace slug.

[0054] Further, in Example 6, concrete sludge (including calcium oxide) used as waste material becomes the calcium source, and thus the used amount of limestone which becomes the cause of carbon dioxide emission decreases (see Table 10 and Table 11), discharge of carbon dioxide is suppressed. Converting from raw material composition, in Example 6, the amount of carbon dioxide emission was reduced by 17.8%.