JPH0415183B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The present invention relates to a method for producing white cement.
More specifically, the present invention provides a cured product with high strength;
The present invention also relates to a method for producing white cement with little drying shrinkage. [Prior art and its problems] White cement is used, for example, as decoration, sign construction, or paving material. White cement is 3CaO・SiO ₂ (hereinafter sometimes simply written as “C ₃ S”), 2CaO・SiO ₂ (hereinafter sometimes simply written as “C ₂ S”),
It consists of clinker whose main components are 3CaO・Al ₂ O ₃ (hereinafter sometimes simply referred to as "C ₃ A") and gypsum, and in this respect it is no different from ordinary cement such as Portland cement. . however,
It is known that cement becomes colored when metal oxides, especially Fe ₂ O _3, are present, and in white cement, it is possible to suppress the content of Fe ₂ O ₃ , which is a coloring component, to 0.5% by weight or less. Common. For this reason, as the silica/alumina raw material for white cement, white clay or Rouseki, which have a low content of metal oxides such as Fe ₂ O ₃ , are carefully selected and used. The silica/alumina raw materials are mixed with limestone, etc., and then undergo the firing, cooling, and pulverizing steps to become white cement. In other words, when producing white cement, it is necessary to use materials with a particularly low content of metal oxides, and since these raw materials are produced only in limited areas, they have a large impact on the production cost of white cement. It is also one of the factors. Blast furnace slag, which is a by-product of steel factories, is known as a silica-alumina raw material with a relatively low Fe ₂ O ₃ content. However, blast furnace slag
In addition to Fe ₂ O ₃ , it contains oxides such as titanium, manganese, chromium, and magnesium, and it is thought that the coexistence of these oxides with Fe ₂ O ₃ will promote the coloring of cement. It was not used as a raw material. On the other hand, white cement is similar in composition to Portland cement, but because its uses are different, there has been relatively little discussion regarding its physical properties such as strength and drying shrinkage, except in special cases. That is, conventionally, white cement has been mostly used for decorative purposes, and has rarely been used particularly for applications where the cured product requires high strength or low drying shrinkage. However, recently, it has been increasingly used for the same purposes as ordinary cement such as Portland cement, and there is a demand for it to have high strength or low drying shrinkage. Methods to increase the strength of cement include increasing the C ₃ S content in cement or
A method of containing 11CaO・7Al ₂ O ₃・CaF ₂ is known. Although the strength of the obtained cured white cement increases to some extent by using these methods, there is a problem in that even if these methods are used, drying shrinkage is not reduced. [Object of the Invention] An object of the present invention is to provide a method for producing white cement that has a high strength as a cured product and exhibits less drying shrinkage. A further object of the present invention is to provide a method for producing white cement having the above-mentioned excellent properties at low cost. [Summary of the Invention] The present invention comprises () 101 to 120 parts by weight of limestone and 7 parts by weight of blast furnace slag.
By mixing ~30 parts by weight and 12 to 25 parts by weight of raw materials for silica/alumina preparation,
3CaO・SiO ₂ (C ₃ S) content ranges from 45 to 85% by weight, 2CaO・SiO ₂ (C ₂ S) content ranges from 5 to 45% by weight
range, 3CaO・Al ₂ O ₃ (C ₃ A) content is 2 to 14
Weight % range and 4CaO・Al ₂ O ₃・Fe ₂ O ₃
(C ₄ AF) Step of firing a mixture mixed so that the content is 1% by weight or less: () A step of rapidly cooling the fired product obtained in the above first step while avoiding contact with an oxidizing atmosphere: and () a step of adding gypsum to the clinker obtained in the second step and pulverizing it. In addition, in the present invention, in order to obtain white cement with high whiteness, limestone has a high iron oxide content.
Blast furnace slag has _an iron oxide content of _{0.8% by weight or less based on Fe 2 O 3} , and raw materials for preparing silica/alumina are:
It is necessary to use a material having an iron oxide content of 1.0% by weight or less based on Fe ₂ O ₃ . [Effects of the Invention] According to the method for producing white cement of the present invention, it is possible to easily produce white cement having excellent physical properties such as high strength and low drying shrinkage. In addition, it is not necessary to use special clay or rouseki as a silica-alumina raw material, and since commonly used blast furnace slag is used, manufacturing costs can be reduced. Further, as long as the production method of the present invention is followed, coloring due to coloring components such as metal oxides contained in blast furnace slag can be prevented. [Detailed Description of the Invention] The first step of the present invention is to mix raw materials for preparing silica/alumina such as limestone, blast furnace slag, and, if desired, silica stone so that the clinker forming components are in a predetermined ratio, and then mix the mixture. This is the firing process. As limestone, commonly used limestone can be used. Preferably, the iron oxide content is 0.5% by weight or less (based on Fe ₂ O ₃ ). Blast furnace slag that is commonly used as a raw material for blast furnace cement can be used, but preferably one with an iron compound content of 0.8% by weight or less (based on Fe ₂ O ₃ ) is used. Moreover, since blast furnace slag has high reactivity with lime components, the strength of mortar is increased by using blast furnace slag, and drying shrinkage is reduced. The raw material for silica/alumina preparation is used to replenish the silica and alumina components in the clinker. That is, the composition of the clinker is adjusted to be within the range of the present invention by replenishing silica and alumina, which tend to be relatively insufficient when limestone and blast furnace slag are mixed. Examples of raw materials for silica/alumina quality adjustment are:
Silica stone, Rouseki and white clay may be mentioned, and these may be used alone or in combination. In particular, it is preferable to use silica stone. When using silica stone, commonly used silica stones can be used. Preferably, the iron oxide content is 1.0% by weight or less (based on Fe ₂ O ₃ ). Further, ordinary Rouseki, Shirako, etc. can be used. In general, each of the above components is used by pulverizing and mixing each so that the residue on a 44 μm sieve is about 10 to 30%, or by mixing them at a predetermined ratio and then pulverizing the mixture to the same extent as above. . In addition, when crushing the above-mentioned limestone, blast furnace slag, silica stone, etc., stainless steel balls or ceramic balls should be used as the crushing medium to prevent components that cause coloration, such as iron, from getting mixed into the crushed material. is preferred, and use of a roll mill is preferred. The mixing ratio of the above components (ratio of clinker forming components according to the Borg formula) is such that the _C3S content in the clinker obtained by firing and rapidly cooling the mixture is 45 to 85% by weight.
range, _C2S content range from 5 to 45% by weight, _C3A
The content is in the range of 2 to 14% by weight, and the C ₄ AF content is in the range of 1% by weight or less (preferably in the range of 0.1 to 1% by weight). When the content of C ₃ S is less than 45% by weight, the strength of the cured product becomes low. On the other hand, if it exceeds 85% by weight, not only will the amount of free CaO in the clinker become extremely large, but also the content of other components such as C ₂ S will inevitably become low, resulting in cracks in the cured product. It cannot withstand normal use. If the content of C ₃ A is less than 2% by weight,
The blending ratio of blast furnace slag, which is essentially a silica-alumina raw material, becomes too small, resulting in low strength of the cured product and high drying shrinkage. On the other hand, if it exceeds 14% by weight, the blended amount of blast furnace slag will be too large, and the coloring components such as iron oxide and other metal oxides contained in the clinker will increase. Even if this is done, it becomes difficult to prevent the coloring caused by the above-mentioned coloring components, and the whiteness of the resulting cement decreases. Furthermore, when the content of C ₄ AF exceeds 1% by weight, iron oxide tends to precipitate, resulting in a decrease in the whiteness of the cement. As an example of a specific method for adjusting the ratio of clinker-forming components according to the Borg formula to be in the above range, 101 to 120 parts by weight of limestone and 7 to 30 parts by weight of blast furnace slag are added to 100 parts by weight of clinker to be obtained. , raw materials for silica/alumina quality adjustment such as silica stone.
A method of mixing 12 to 25 parts by weight can be mentioned. When producing the white cement of the present invention, it is preferable to add a CaF ₂ -containing component such as fluorite in addition to the above-mentioned limestone, blast furnace slag, and optionally added raw materials for adjusting the quality of silica and alumina.
By adding _CaF2- containing components, white cement with high strength and low drying shrinkage can be obtained. The addition rate of the CaF ₂ -containing component is generally 2% by weight or less based on CaF ₂ . The obtained mixture (or granules) is then put into a firing device and fired. For firing, a typical firing device such as a rotary kiln that is normally used for firing cement can be used. However, the firing conditions for the firing equipment are such that the theoretical oxygen excess coefficient (m) is 1.00 to 1.10.
It is desirable that the process be able to be carried out in a completely combustible atmosphere to a slightly oxidizing atmosphere. If the theoretical oxygen excess coefficient significantly deviates from the above range, the resulting white cement may be colored. Firing is generally performed at 1400-1600°C, preferably
It is carried out at a temperature within the range of 1450-1500°C. The second step is a step of rapidly cooling the fired product obtained in the first step while avoiding contact with an oxidizing atmosphere such as air. In other words, the mixture fed into a normal firing device such as a rotary kiln passes through the maximum temperature range (firing zone) of the baking device and is then fired. Avoiding contact with a harmful atmosphere, and while the temperature of the fired product is, for example, 1200°C or higher, the fired product is rapidly cooled to a temperature of 200°C or lower. The method of rapid cooling is
A method of spraying water or heavy oil onto the fired product, or a method of throwing the fired product into water can be used. In particular, it is preferable to use a method in which the fired product is poured into water. It is preferable that the water adsorbed on the clinker obtained by spraying or adding water is evaporated as much as possible by the sensible heat of the clinker, but if drying is insufficient, drying means can also be used. By performing firing under the above conditions and rapidly cooling the fired product, coloring components such as iron oxide do not precipitate and are inseparably incorporated into the cement components as, for example, C ₄ AF, resulting in a reduction in whiteness. You can get high cement. Furthermore, since there is little precipitation of iron oxide, even if components that promote coloration such as magnesium oxide, titanium dioxide, chromium oxide, and manganese dioxide are mixed, white cement with substantially less coloration can be produced. The third step is a step of adding gypsum to the clinker obtained in the second step and pulverizing it. Generally, the amount of gypsum added is in the range of 1.5 to 3.0% by weight based on _SO3 in cement. In addition, the Blaine specific surface area of the white cement obtained by pulverization is 2500 to 5000 cm ² /g.
Repeat until the range is reached. A commonly used crushing device can be used. The white cement thus obtained has high compressive strength as a hardened product due to the use of blast furnace slag that is highly reactive with lime components, and also has little drying shrinkage. That is, by manufacturing white cement according to the manufacturing conditions of the present invention using blast furnace slag that has not been conventionally used as a raw material for white cement, white cement having a whiteness normal to that of white cement can be manufactured. At the same time,
The obtained white cement has excellent properties such as higher compressive strength of the cured product and less drying shrinkage than conventional white cement. The white cement thus obtained exhibits good physical properties as described above, but inorganic white powders such as blast furnace slag, limestone, and silica powder are added to the white cement to improve its whiteness, strength, and drying shrinkage. They can be added as long as the various properties such as these are within the practical range. The inorganic white powder has a whiteness of 80% or more (preferably 84% or more) and a Blaine specific surface area of about the same level as cement, that is, 2500 to 9000 cm ² /g.
Preferably. Furthermore, when limestone is used as the inorganic white powder, the amount of limestone added is 50% by weight or less based on the white cement, and when silica stone is used, for example, the amount of limestone added is 50% by weight or less based on the white cement. For example, when blast furnace slag is used, it is 80% by weight or less based on white cement. Furthermore, the inorganic white powders can also be used in combination. Examples and comparative examples of the present invention are shown below. Table 1 shows the analytical values of limestone, blast furnace slag, silica, fluorite, and rouseki used in the Examples and Comparative Examples shown below.

[Table] Examples 1 to 7 and Comparative Examples 1 to 5 Raw materials having the chemical components shown in Table 1 are listed in Table 3 so that the composition of the resulting clinker is as shown in Table 2. They were mixed at the mixing ratio. Add water to this mixture, mold it, and heat it to 200℃.
After drying for 2 hours, the dried product was placed in a platinum crucible and fired at 1450°C for 30 minutes in a gas furnace. Firing was performed with the theoretical oxidation rate (m) set in the range of 1.00 to 1.05. The theoretical excess oxygen coefficient is
1.00 represents a complete combustion atmosphere, as it becomes higher than 1.00 it gradually becomes an oxidizing atmosphere, and as it becomes lower than 1.00 it becomes a reducing atmosphere. After 30 minutes had elapsed, the crucible was quickly taken out in the firing atmosphere with a lid on to block contact with air, and the fired product was immediately poured into water. After the water adhering to the cooled clinker was evaporated, gypsum was added to it to give a concentration of 2.0% by weight based on SO ₃ in cement, and the mixture was ground in an alumina ball mill until the Blaine specific surface area was 3500 cm ² /g. A white cement was obtained. The amount of free CaO, whiteness (W value) measured by a colorimetric tester, compressive strength of mortar according to JIS R5201 (cement: standard sand: water = 1:2:0.65, specimen size 2) for the obtained white cement. x 2 x 2 cm) and measurement of length change (drying shrinkage) after hardening and drying of mortar according to the Cement Association Standard Test Method (CAJS H-11) (cement: standard sand: water = 1:2:
0.6, specimen size 1 x 1 x 6 cm, humidity RH.50%,
6 months). In addition, drying shrinkage was calculated|required by the following formula. Drying shrinkage = (base length of specimen - length of specimen after six months) / (base length of specimen) In addition, the whiteness was determined by substituting the measured value into the following formula. Whiteness W value (%) = 100-√(100-) ² + ² + ² where a represents the degree of red to green, b represents the degree of yellow to blue, and L represents the degree of white to black. . The results are shown in Table 4. The amount of free CaO, whiteness, compressive strength of mortar, and dry strength of mortar measured in the Examples and Comparative Examples shown below were determined by the methods described above.

【table】

[Table] Blend ratios are stated in basic units for clinker.

[Table] The white cement obtained in Comparative Example 5 does not contain blast furnace slag, so it shows good values for whiteness and free CaO. However, for example, Example 2, which has a similar composition,
The compressive strength is lower and the drying shrinkage is larger than that of the cured white cement obtained in . Furthermore, when comparing the white cement of the present invention with those whose clinker compositions are not within the range of the present invention, for example, the comparison between Example 2 and Comparative Example 3, and the comparison between Example 1 and Comparative Examples 1 and 4 shows that As a result, compressive strength decreases and drying shrinkage increases. Furthermore, it can be seen that the white cement of Comparative Example 1 with a low C ₃ S content has a low degree of whiteness and is colored when compared with the white cement obtained in Example 2. Comparative Examples 6 to 8 In Example 5, instead of taking out the crucible from the firing atmosphere with the lid on and immediately putting the fired product into water, the crucible was taken out from the firing atmosphere without the lid on and placed in the air for 10 seconds. After leaving it for 30 seconds, the crucible is placed in water (Comparative Example 6), the crucible is taken out from the firing atmosphere without a lid and left in the air for 30 seconds, and then placed in water (Comparative Example 7), the crucible is placed in the firing atmosphere White cement was produced in the same manner as in Comparative Example 8, except that the cement was taken out from inside without a lid, left in the air, and cooled to room temperature (Comparative Example 8). Figure 5 shows the free CaO content and whiteness of the white cement obtained, as well as the compressive strength and drying shrinkage of the cured product. Note that the above values regarding the white cement obtained in Example 5 are also described.

[Table] It can be seen that the white cements obtained in Comparative Examples 6 to 8 have low whiteness, and furthermore, the compression illuminance and drying shrinkage of the cured products are large. Examples 8 to 10 White cement was prepared by adding 50% by weight of blast furnace slag powder (whiteness: 85%, Blaine specific surface area: 4520 cm ² /g) to the white cement obtained in Example 5. (Example 8); White cement was prepared by adding 20% by weight of fine limestone powder (whiteness: 90%, Blaine specific surface area: 3830 cm ² /g) to white cement (Example 9) A white cement was prepared by adding 50% by weight of silica fine powder (whiteness: 88%, Blaine specific surface area: 7510 cm ² /g) to white cement (Example 10). Table 6 shows the whiteness of the white cement obtained, the compressive strength of the cured product, and the drying shrinkage rate.

[Table] It is clear that even when inorganic white powders such as pulverized blast furnace slag powder, pulverized lime powder and silica stone powder are further added to the white cement of the present invention, good properties can be maintained.

Claims (1)

[Scope of Claims] 1. 101 to 120 parts by weight of limestone with an iron oxide content of 0.5% by weight or less based on Fe ₂ O ₃ and an iron oxide content of Fe ₂ O ₃
7 to 30 parts by weight of blast furnace slag with a standard content of 0.8% by weight or less, and iron oxide content of 1.0% by weight based on Fe ₂ O ₃
By mixing 12 to 25 parts by weight of the following silica/alumina preparation raw materials, the 3CaO/SiO ₂ content can be reduced.
Range of 45-85% by weight, 2CaO・_SiO2 content of 5-85% by weight
Range of 45% by weight, 3CaO・Al ₂ O ₃ content between 2 and 14
A step of firing a mixture such that the weight% range and 4CaO・Al ₂ O ₃・Fe ₂ O ₃ content is 1% by weight or less: () The fired product obtained in the above first step is oxidized. A method for producing white cement, comprising: a step of rapidly cooling the clinker while avoiding contact with the atmosphere; and () a step of adding gypsum to the clinker obtained in the second step and pulverizing it; . 2. The method for producing white cement according to claim 1, wherein fluorite is added to the mixture in the first step in an amount within 2% by weight. 3. The method for producing white cement according to claim 1, wherein the firing is performed in an atmosphere with a theoretical oxygen excess coefficient of 1.00 to 1.10. 4. The method for producing white cement according to claim 1, wherein the quenching is carried out by pouring the fired product into water or by spraying water onto the fired product. 5. Claims 1 to 5 further include adding at least one type of inorganic white powder selected from the group consisting of pulverized blast furnace slag powder, fine lime particles, and fine silica stone powder to the pulverized product obtained in the third step. The method for producing white cement according to item 4.