JPS6152116B2 - - Google Patents

Description

[Detailed description of the invention]

This invention obtains a hardened cement molded product by molding a cement mixture made by kneading cement, aggregate, and water into a desired shape, and then subjecting the cement particles to a hydration reaction in water or air. Regarding the improvement of the method, calcium compounds were added as CaO to cement and aggregate as the main raw materials.
Calcium compound-added cement kneaded product obtained by sufficiently kneading a small amount of 5% or less in weight ratio to cement with an appropriate amount of water is pressure-molded into a desired shape, and this molding process The hydration curing process that follows is divided into a preliminary hydration curing process that is carried out earlier in terms of time, and a full-scale hydration curing process that is carried out later in terms of time, and this preliminary hydration and curing process. By incorporating a process of high-temperature firing of the intermediate product that has gone through the preliminary hydration hardening process between the final hydration hardening process and the full-scale hydration hardening process, we are able to create cement moldings with even greater mechanical strength than conventional cement molded products. The present invention relates to a method for manufacturing cement products that enables the production of cement products. When hardened cement is heated to a high temperature of 450°C or higher, its mechanical strength deteriorates significantly. For example, when a cement hardened body of Portland cement is heated at 450°C, Ca(OH) ₂ generated by hydration of lime silicate decomposes into CaO and H ₂ O, and at this time, inside the hardened cement body. It is known that the mechanical strength, especially the compressive strength, of hardened cement deteriorates significantly due to large shrinkage changes [Yu Harada and Akira Sakai, "About Heat-Resistant Concrete" (Industry and Products No. 50, p. 119) right column)]. Furthermore, it is known that the mechanical strength of alumina cement-based hardened cement deteriorates significantly when heated at high temperatures, although the chemical reasons for this are not the same as those for Portland cement. Akira Wakabayashi, “On the high-temperature properties of hardened alumina cement” (Journal of Ceramics Association 69(2), 1961, p. 28). Therefore, in the past, no one had thought of firing a hardened cement body at a high temperature in order to improve the strength of a cement molded product. Because of this technological situation, the so-called fumigation treatment, which is widely used to give beautiful color and gloss to the surface of clay molded products when manufacturing clay molded products, is not suitable for cement molded products. , was thought to be impractical because the high temperatures required for fumigation degraded the strength of cement products. Furthermore, for the same reason, various restrictions have inevitably been imposed on the glazing and finishing of the surface of cement molded products. In other words, unless the glaze is sufficiently meltable in the temperature range of 450°C or below, where no strength deterioration of the hardened cement product occurs, the glazed hardened cement product itself will significantly deteriorate in mechanical strength due to the firing performed to fuse the glaze. This is because it has no choice but to be scarce. So in 1974 (Showa 49)
) such as the invention of Japanese Patent Application Publication No. 10530,
A phosphoric acid-based frit glaze with a low melting point has been developed, but this special glaze is not only inferior in weather resistance and chemical resistance to ordinary high melting point glazes, but it is also very expensive. Moreover, the surface of glazed cement products using this method had the disadvantage that it was not very well made from an aesthetic point of view. The inventors of this invention intentionally incorporated a step of firing the hardened cement body at a high temperature into the manufacturing process of cement molded products, and performed a preliminary hydration hardening step and a full-scale hydration hardening step before and after that. proposed a method for manufacturing cement products with even greater mechanical strength than conventional cement products (Japanese Patent Application No. 1987-087196). This invention further enhances the mechanical strength of the product by adding a calcium compound as an additive to the cement and aggregate, which are the raw materials of the proposed method, at a weight ratio of 5% or less to the cement in terms of CaO. The purpose of this invention is to provide an improved method for manufacturing cement products. Another object of the present invention is to provide a method for producing a so-called smoked cement product, which has a beautiful and shiny carbon thin film formed on its surface. A third object of the present invention is to provide a method for manufacturing a beautiful glazed cement product whose surface is coated with a glaze having a high melting point. Other objects of the invention will become apparent from the following description. This invention aims to reduce the degree of deterioration in mechanical strength caused by high-temperature firing of a hardened cement body that has undergone a preliminary hydration hardening process, due to the increase in mechanical strength caused by the full-scale hydration hardening process that follows the firing process. In other words, when a preliminary hydration hardening process and a full-scale hydration hardening process are provided after the molding process, and a high-temperature firing process is incorporated between them,
Based on the inventors' research results that show that cement molded products can be obtained that have much better mechanical strength than cement molded products made using conventional methods that do not sinter the hardened cement body at high temperatures, This is an application of the new knowledge that when a small amount of calcium compound is added, the degree of mechanical strength enhancement of cement products becomes even more excellent. In other words, this invention adds a calcium compound as an additive to a mixture of cement and aggregate, calculated as CaO, at a weight ratio of 5 to cement.
A raw material kneading step in which water is added to the raw material obtained by adding % or less, further adding reinforcing material such as glass fiber as necessary, and thoroughly kneaded, and a pressure molding step in which this kneaded product is molded into a desired shape. , a preliminary hydration hardening step in which this molded body is preliminarily hydrated and hardened, a firing step in which the hardened body obtained in this preliminary step is fired at a high temperature, and a full-scale hydration hardening process in which this fired body is sufficiently hydrated and hardened. This method of manufacturing a cement product is characterized in that the steps of hydration and hardening are performed in this order. When firing the cured product that has gone through the above preliminary steps, by burning the fumigating agent in a reducing atmosphere, particulate carbon produced by thermal decomposition of the hydrocarbons contained in the fumigating agent is removed. When deposited on the surface of the pre-cured body, this special firing process yields a so-called smoked product whose surface is beautifully coated with a shiny carbon film. Furthermore, when firing the cured body that has gone through the above preliminary process, if a glaze with a high melting point is applied to the surface of the preliminary cured body in advance, this glaze will melt onto the surface of the preliminary cured body during the high temperature firing process. Because of this, beautiful and glossy glazed objects can be obtained as fired products. Although the mechanism by which the mechanical strength of cement products is increased by this invention has not yet been fully elucidated, the inventors believe that it is probably due to the following mechanism. That is, as is well known, the hardening reaction of cement due to hydration proceeds over many years. According to some research, it is said that even after more than 30 years, coarse clinker with a size of 40μ or more remains the same inside as the original clinker. Furthermore, according to research by Anderegg and Hubbel, when clinker with a particle size of 15 to 30 μm is hydrated, only a thickness of 1.5 μm reaches from the particle surface after 7 days of hydration. The sum reaction does not proceed, and 28
It is reported that the hydration reaction progressed to a thickness of 3.5μ after hydration for one day, and only 5.0μ after 90 days of hydration [Anderek and Hubel, Journal of the American Society for Testing and Materials 1929,
(Anderegg and Hubbel: Proc.ASTM,
1929, ) same concrete 1930 (Concrete,
1930)] In light of these facts, approximately 1/2 of the total hydration reaction of cement particles progresses in about 30 to 100 days, and then gradually increases in degree over a period of several years. , 30
It is estimated that more than % of the unhydrated portion remains within the hydration chamber. In contrast, according to the method of the present invention, the hardened hydrated surface layer of the cement grains, in which the hydration reaction has progressed to a thickness of several micrometers from the surface through the preliminary hydration hardening step, The cracks formed in the hardened and hydrated surface layer, which are damaged by the subsequent high-temperature firing process, function as contact passages between the unhydrated parts inside the particles and the water existing outside the particles, and at the same time, the hardening process Ca(OH) ₂ liberated in the process and calcium compounds added to the raw material in advance become CaO through the high-temperature firing process, which enters into the cement particles through the cracks in the hardened and hydrated surface layer along with water. do. As a result, during the final full-scale hydration hardening process, the particles grow deeper from the particle surface layer than if the preliminary hydration hardening process was continued without intervening the firing process. It is possible to hydrate even the innermost part of the particle, ultimately increasing the rate of progress of the hydration reaction inside the particle, and CaO that has entered the particle becomes Ca(OH) ₂ by moisture absorption. As the particles expand in volume, most of the voids that existed within the particles are filled, and the Ca(OH) ₂ that filled the voids is carbonated, resulting in a thick hardened surface layer and a dense structure. , it is thought that they are formed within a relatively short period of time. The inventors of this invention are currently working to verify the above hypothesis. It has been confirmed that the strength increases as the period of the preliminary hydration curing process increases. This fact may serve as evidence to support the validity of the above hypothesis. The present invention will be explained based on examples as follows. Example A mixture of 100 parts by weight of ordinary Portland cement, 200 parts by weight of Shinano River sand, 2 parts by weight of Adachi lime, and 60 parts of water was kneaded for 10 minutes, and the resulting cement mixture was mixed.
Pressure molded using a 500t hydraulic press at a molding pressure of 100Kgf/cm ² and a pressure holding time of 4 minutes to determine the water-solid ratio.
Obtain a cement molding of 0.1. After curing this cement molding in the air for one day to preliminarily harden it,
The temperature was raised to 850℃ over 2 hours in an electric furnace, maintained at a high temperature of 850℃ for 15 minutes, and then heated to 20℃ over 10 hours.
It was fired by lowering the temperature to . After cooling to 20℃,
A cement product was obtained by performing humid steam curing at 60°C for 7 days. The bending strength of this cement product is
When measured with Tensilon, which was set at 45 mm and a loading speed of 10 mm/min, it was 112.7 Kg/fcm ² . The bending strength of the product which was subjected to molding, preliminary hydration, firing, and full-scale hydration under the same conditions without adding any Adachi lime was 81.8 Kgf/cm ² . "Cement" which is one of the starting materials of the present invention
is a concept that encompasses not only Portland cement and alumina cement, but also mixed cements such as fly ash cement, blast furnace slag cement, and lime-slag cement. shall be understood as referring to all substances shown. In other words, the strength of the cement product according to the present invention is achieved by increasing the Juan der Waals force due to hydrates and improving the interparticle strength by applying chemical stress. It is clear that the same can also be applied. In addition, "aggregate", which is one of the starting materials of the present invention, does not undergo rapid expansion or contraction during high-temperature firing in the firing process.
It is necessary that the change in temperature = volume is small. Examples of materials that meet this requirement include heavy aggregates typified by barite, normal aggregates such as sand, gravel, crushed stone, slag, ceramic siyamots, porcelain siyamots, and artificial lightweight aggregates. Examples include lightweight aggregate. Among these, ceramic or porcelain ceramics are particularly recommended from the viewpoint of the effect of increasing mechanical strength, which is a feature of the present invention. The "calcium compound", which is an important additive in the present invention, can be of any type as long as it generates CaO through the calcination process and fills the voids. The main ones are _CaCO3 ,
There are CaO, Ca(OH) ₂ , CaCO ₃ , MgCO ₃ , etc. The relationship between the amount of calcium compound added and the bending strength of the product depends on the type of cement and the method and number of days of preliminary hydration hardening.
This will vary somewhat depending on the amount of Ca(OH) ₂ , but generally speaking, if calcium compounds are added in an amount exceeding 5% by weight of cement in terms of CaO, no additives are required. Since the bending strength of the product is lower than in the case of CaO, the amount added needs to be 5% or less based on the weight of cement in terms of CaO. (See Table 1 below). This limitation, as in the past, takes into account the risk of hygroscopic agglomeration of added CaO; however, the addition of calcium compounds to cement products does not always lead to hygroscopic agglomeration. Based on the new finding that the addition of calcium compounds below a certain amount can sufficiently improve the strength of cement products compared to the case where no calcium compounds are added, the present invention provides the following: The amount of calcium compound added was defined as described above. Next, the molding pressure of pressure molding in the present invention is 30Kgf/
cm ² or more, particularly preferably 50 Kgf/cm ² or more. A pressure holding time of 5 minutes or less is sufficient for this molding pressure. Further, the firing temperature in the firing step is preferably 650 to 950°C. The main raw materials are 100 parts by weight of Portland cement and 200 parts by weight of porcelain shamots, and several types of calcium-added raw materials are added to increase the amount by adding 0 to 30 parts by weight of CaCO ₃ (Adachi lime).
The cement mixture obtained by adding parts by weight and kneading for 10 minutes was heated to a molding pressure of 100 using a 500 ton hydraulic press.
Kgf/cm ² and a pressure holding time of 4 minutes to obtain a cement molded product with a water-solid ratio of 0.1. After curing in air for 1 day, it was fired and molded under the same conditions as in the previous example. When we actually measured the bending strength of various cement products manufactured by full-scale hydration hardening, we found that CaCO ₃
There was a relationship as shown in Table 1 between the amount of (Adachi lime) added and the bending strength of the product.

[Table] As is clear from Table 1, the bending strength of the final product is maximum when 6 parts by weight of CaCO ₃ is added to 100 parts by weight of raw material Portland cement, and when 10 parts by weight or more is added. It can be seen that the bending strength is lower than when no additive is added. Adding 8 parts by weight of CaCO ₃ to 100 parts by weight of Portland cement means that when this CaCO ₃ is converted to CaO and expressed as a weight ratio to cement, it is 4.48% by weight of CaO.
This is equivalent to adding . Therefore, it can be said that Table 1 shows that it is possible to further increase the bending strength of the product by adding calcium compounds to a weight ratio of 5% or less to cement in terms of CaO. be. The reason why the bending strength of the cement products obtained by the present invention is increased is due to the voids that exist between the cement particles, consisting of microscopic voids (26 Å or less in diameter) called gel pores and small voids (26 Å or more in diameter) called capillary pores. This is because a relatively large amount of CaO infiltrates into the voids, and the CaO that has entered the voids eventually absorbs moisture and becomes Ca(OH) ₂ , which expands in volume and fills the voids. The effects of filling such voids are, firstly, that filling shortens the distance between cement particles, which increases the Juan de Waals force and contributes to improving the strength.
By carbonating Ca(OH) ₂ , a dense structure with a thick hardened surface layer is formed in a relatively short period of time, contributing to improved strength. Thirdly, as mentioned above, Since a dense structure is formed while enduring the expansion force of the calcium compound, so-called chemical stress acts and contributes to improving the strength. In order to compare the mechanical strength of the cement product manufactured according to the present invention with that of a cement product manufactured by a conventional method that does not incorporate a firing process into the manufacturing process, the following comparative test was conducted. In other words, water is added to the raw materials mixed so that the mixing ratio of cement and aggregate is 1:2, CaCO ₃ is added at a weight ratio of 2.0% to the cement (value not converted to CaO), and the mixture is kneaded. Cement molded pieces 1 to 6 obtained by pressure molding a cement kneaded material made of
For the products obtained by baking for 10 minutes in water and curing in water for 3 weeks (group A), and for the raw materials mixed so that the mixing ratio of cement and aggregate was the same as above (1:2). , Cement molded pieces 1' to 6' obtained by press-molding a cement mixture obtained by simply adding and kneading water under the same conditions as above were molded into 4 pieces by a conventional method.
Products obtained by curing in water for a week (group B)
When the bending strength was tested, the results shown in Table 2 were obtained. In addition, cement molded pieces 1 to 6 and
The sizes of 1' to 6' are all 210 x 30 x 30 mm, and the types of aggregates used are: Test specimen 1 (1') is porcelain shamotsu with 8 mesh under and bulk specific gravity of 2.39;
(2') is a porcelain shim with 8 mesh under and a bulk specific gravity of 2.36, 3 (3') is a porcelain shim with 35 mesh under, and 4 (4') is a ceramic shim with 8 mesh under. , 5 (5') is a 35 mesh under firestone, and 6 (6') is a water slag. The test equipment used was a small material testing machine FSP-500 manufactured by Tokyo Hoshiki Co., Ltd., and the test conditions were a span interval of 90 mm and a loading rate of 12 mm/min.

[Table] As is clear from Table 2 above, no matter which aggregate is used, the products produced by the method of the present invention (Group A) in which a calcium compound is added to the raw material and a calcination step is incorporated are more effective. Its bending strength is higher than that of products produced by the conventional method (Group B) without a firing process. The effects of the present invention are not limited to simply superior mechanical strength of the product. The biggest advantage of adopting the method of the present invention is that it is possible to quickly improve mechanical strength through high-temperature firing, making it possible to smoke and glaze cement products with a high-melting-point glaze. be. In particular, when glazing cement products, it has become possible to use fritted glaze, which is inexpensive but has a high melting point, which was previously considered unusable, and it has also become possible to appropriately mix raw materials such as feldspar and viscosity into this fritted glaze. As exemplified in Tables 3 and 4, the glazed surface has excellent weather resistance, abrasion resistance, and chemical resistance, as well as impeccable color and gloss of the glazed surface.
The extremely excellent industrial advantage of the present invention is that it is now possible to use a suitable glaze for cement products, creating new and wide-ranging demand for cement products in the construction industry and other related industrial fields. Availability will be acknowledged. Table 3 M25 frit 10 parts 1121 frit 20 parts Glass powder 65 parts ZnO 5 parts Table 4 3909 frit 20 parts Glass powder 60 parts Stone 10 parts Clay 5 parts ZrO ₃ 5 parts

Claims (1)

[Claims] 1. A calcium compound as an additive is added to cement and aggregate as the main raw materials in an amount of 5% or less by weight of cement in terms of CaO, and then water is added, and if necessary, A raw material kneading step of sufficiently kneading the raw material with a reinforcing material added thereto, a molding step of molding this kneaded material into a desired shape, and a preliminary hydration hardening step of preliminarily hydrating and hardening this molded product, A glazing process in which a high-melting-point glaze is applied to the surface of this preliminary hydrated and hardened body, a firing process in which this glazed and hardened body is fired at 650 to 950°C, and a full-scale hydration process in which this fired body is sufficiently hydrated and hardened. A method for manufacturing a cement product, characterized in that a curing step is performed in this order. 2. The method for manufacturing a cement product according to claim 1, wherein glass fiber, ceramic fiber, metal fiber, or metal wire is used as the reinforcing material. 3. Claim 1, characterized in that the high melting point glaze is a raw glaze, fritted glaze, or volatile glaze made by blending or not blending fritted glaze with raw materials such as feldspar or clay. Method for producing cement products as described in Section. 4. In the firing step, the smoking agent is smoked in a reducing atmosphere to remove particulate carbon from the object to be fired due to thermal decomposition of hydrocarbons contained in the smoking agent. The method for manufacturing a cement product according to claim 1, characterized in that the method is carried out by depositing it on a surface.