JPS5929549B2 - Manufacturing method of cement products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention involves forming a cement mixture obtained by kneading cement, aggregate, and water into a desired shape, and then subjecting the cement particles to a water phase reaction in water or air. Regarding the improvement of the method for obtaining hardened cement molded products, a very small amount of a calcium compound as an additive, calculated as CaO, is added to the cement and aggregate as the main raw materials, and is less than 5% by weight of cement. A preliminary hydration hardening step in which a calcium-added cement kneaded product obtained by sufficiently kneading with an appropriate amount of water is pressure-molded into a desired shape, and a hydration hardening step following this molding step is carried out first in terms of time. and the full-scale hydration-hardening process, which is carried out later in terms of time, and between this preliminary hydration-hardening process and the full-scale hydration-hardening process, there is The present invention relates to a method for manufacturing cement products, which incorporates a step of firing the product at a high temperature, thereby making it possible to obtain cement molded products with even greater mechanical strength than conventional cement molded products.

When a hardened cement body is heated to a high temperature of 450° C. or higher, its mechanical strength inevitably deteriorates significantly.

For example, 4 hours of hardened Portland cement cement
When heated at 50°C, Ca(OH)2 generated by hydration of silicate lime decomposes into CaO and H2O, and at this time, a large shrinkage change occurs inside the hardened cement body, so the machine of the hardened cement body It is known that the physical strength, especially the compressive strength, deteriorates significantly [Yu Harada and Toru Sakai, "About Heat-Resistant Concrete" (Industry and Products A50, page 119, right column)].

Furthermore, although the chemical reasons for alumina cement-based hardened cement are not the same as those for Portland cement, it is known that the mechanical strength of alumina cement-based cement deteriorates significantly when heated at high temperatures [Akira Wakabayashi] “On the high-temperature properties of hardened alumina cement” (Ceramic Industry Association Journal 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.

Due to this state of technology, the so-called smoking 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 considered to be impractical because the high temperatures required for fumigation degraded the strength of the cement product.

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, the strength of the hardened cement body does not deteriorate.450
This is because unless the glaze is sufficiently meltable in the temperature range of 0.degree.

Therefore, in 1974 (Showa 49), the first Japanese patent application announcement was made.
A phosphoric acid-based frit glaze with a low melting point, such as the invention of No. 0530, was developed, but this special glaze was not only inferior in weather resistance and chemical resistance compared to ordinary high melting point glazes. The glazed cement product itself is very expensive and has the disadvantage that the surface of the glazed cement product using it is 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 producing cement products with even better mechanical strength than conventional cement products (Japanese Patent Application No. 1987-087196).

In this invention, by further adding a calcium compound as an additive to the cement and aggregate, which are the raw materials of the proposed method, in an amount of 5% or less by weight relative to cement in terms of CaO,
The object of the present invention is to provide an improved method for manufacturing cement products that can further enhance the mechanical strength of the 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 performed after the forming process, and a high-temperature firing process is incorporated between them, the hardened cement body is not fired at a high temperature compared to the conventional method. Based on the research results of the inventors, which showed that cement molded products with far superior mechanical strength can be obtained than cement molded products produced by the method, we added a small amount of calcium compound to the cement and aggregate as the main raw materials. This is an application of the new knowledge that the degree of mechanical strength enhancement of cement products is even more excellent.

That is, this invention adds water to a raw material obtained by adding a calcium compound as a deepening material to a mixture of cement and aggregate in an amount of 5% or less by weight of cement in terms of CaO, and further adds water as necessary. A raw material kneading process in which reinforcing materials such as glass fibers are sufficiently kneaded, a pressure molding process in which this kneaded material is molded into a desired shape, and a preliminary hydration curing process in which this molded product is preliminarily hydrated and hardened. step, a firing step of firing the hardened body obtained by this preliminary step at a high temperature, and a full-scale hydration hardening step of sufficiently hydrating and hardening this fired body, which are characterized in that they are performed in this order. This is a method for manufacturing cement products.

When firing the cured product that has gone through the above preliminary steps, the fumigating agent is fired in a reducing atmosphere to preliminarily harden the fine particulate carbon produced by thermal decomposition of the hydrocarbons contained in the fumigating agent. When deposited on the surface of the body, this special firing process produces a so-called smoked product whose surface is beautifully coated with a shiny carbon film.

In addition, when firing the cured body that has gone through the above preliminary process, a high melting point glaze is applied to the surface of this preliminary cured body (
During the high-temperature firing process, this glaze fuses to the surface of the pre-hardened product, resulting in a beautiful and glossy glazed product.

The mechanism by which this invention increases the mechanical strength of cement products has not yet been fully elucidated.

The inventors believe that this is probably due to the following mechanism.

That is, (as is known, the hardening reaction of cement due to hydration proceeds over many years.

According to research conducted by
Even after more than a year has passed, it is said that the original clinker inside is still intact.

Furthermore, according to research by Anderegg and Hubbel, when clinker with a particle size of 15 to 30 μm is hydrated, only 1.5 μm is removed from the particle surface after 7 days of hydration. It has been reported that the aqueous phase reaction progressed only to a thickness of 3.5μ after 28 days of hydration, and only 5.0μ after 90 days of hydration. [Unpreque and Hübel Journal of the American Society for Testing and Materials 192]
9, U (Anderegg and Hubbel
: Proe.

A, S, T, M,, 1929, ■) Concrete 19
30 (Concrete, 1930)).

In light of these facts, approximately % of the total hydration reaction of cement particles progresses over a period of about 30 to 100 days, and then increases extremely gradually over a period of several years (but still It is estimated that 30% or more of the unhydrated portion remains inside.

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 that are damaged by the high-temperature firing process and that occur in the hardened, hydrated surface layer function as contact passages between the unhydrated parts inside the particles and the water existing outside the particles, and at the same time serve as a contact path between the unhydrated parts inside the particles and the water existing outside the particles. a (OH) 2 and a calcium compound previously added to the raw material undergo a high-temperature firing process to become CaO, which infiltrates together with water into the cement particles through cracks in the hardened and hydrated surface layer.

As a result, during the final full-scale hydration hardening process, the grains can be deep It is possible to hydrate the deep part of the particle, and as a result, the rate of progress of the hydration reaction into the particle is increased, and the CaO that has penetrated into the particle becomes Ca(OH)2 due to moisture absorption and its volume decreases. As Ca(OH)2 expands, most of the voids that existed within the particles are filled, and the Ca(OH)2 filling the voids is carbonated, resulting in a relatively dense structure with a thick hardened surface layer. It is thought that it will be formed within a short period of time.

The inventors of this invention are currently working to verify the above hypothesis, but when all other conditions are the same except for the period of the preliminary water phase curing process of this invention, the mechanical It has been confirmed that the strength increases as the period of the preliminary hydration hardening 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: 100 parts by weight of ordinary Portland cement, 2 parts by weight of Shinano river sand
00 parts by weight, 2 parts by weight of established lime, and 60 parts of water.
Knead for 0 minutes, and press-mold the obtained cement mixture using a hydraulic press under conditions of a molding pressure of 100 kgf/cd and a pressure holding time of 4 minutes to obtain a cement molded product with a water-solid ratio of 0.1. .

This cement molded product was preliminarily cured by curing it in air for 1 day, and then heated to 850°C in an electric furnace for 2 hours.
After maintaining the high temperature of 850° C. for 5 minutes, the temperature was lowered to 20° C. over 10 hours for firing.

After cooling to 20°C, wet steam curing at 60°C was performed for 7 days to obtain a cement product.

The bending strength of this cement product was measured using a Tensilon set at a span of 45 mm and a loading rate of 10 mrn/mvl, and found to be 112.7 kgf/crA.

The bending strength of a product that was formed, preliminary hydrated, fired, and fully hydrated under the same conditions without adding any standing lime was 81.
, 8 kgf/crA.

"Cement", which is the starting material of the present invention, is a concept that includes not only Portland cement and alumina cement, but also mixed cements such as fly ash cement, blast furnace slag cement, and lime-slag cement.
This term is to be understood as referring to all substances which exhibit hardening by hydration reactions of any kind.

That is, the strength development of the cement product according to the present invention is achieved by increasing van der Waalska due to hydrates and improving interparticle strength by applying chemical stress.
It is clear that the present invention can also be applied to cements other than Portland cement, which have different component compositions.

Further, the "aggregate", which is one of the starting materials of the present invention, must be a material that does not undergo rapid expansion or contraction during high-temperature firing in the firing process and has a small temperature-volume change.

Examples of materials that meet this requirement include heavy aggregates such as barite, normal aggregates such as sand, gravel, crushed stone, slag, ceramic chamotte and porcelain chamotte, and artificial lightweight aggregates. Examples include lightweight aggregate.

Among these, from the viewpoint of the effect of increasing mechanical strength, which is a feature of the present invention, ceramic or porcelain clay is particularly recommended.

"Calcium compound" which is an important additive of the present invention is
Any type of material can be used as long as it generates CaO through the firing process and fills the voids.

The main ones are CaCO3, Cao, Ca (
OH) 2, CaCO3, MgCO3, 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. (OH) 2
Although it varies somewhat depending on the amount of calcium compound, generally speaking, when calcium compounds are added in an amount exceeding 5% by weight of cement in terms of CaO, the quality of the product is lower than when no calcium compound is added. Since the bending strength decreases, this amount of Ca
It is necessary that the weight ratio of O in terms of cement weight is 5% or less (see Table 1 below).

This limitation, as in the past, takes into account the risk of hygroscopic disintegration of added CaO; however, the addition of calcium compounds to cement products does not always lead to hygroscopic disintegration; Based on the new finding that the strength of cement products can be sufficiently improved if the calcium compound is added in an amount of The amount of addition is defined as described above.

Next, the molding pressure of pressure molding in the present invention is 30 kgf/c
rA or more, especially 50kgf/crA
The above is desirable.

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.

Several types of calcium-added raw materials were used, with the main raw materials consisting of 100 parts by weight of Portland cement and 200 parts by weight of porcelain chamotte, and the amount increased by adding CaC03 (Adachi lime) to 0 to 30 parts by weight, and 60 parts by weight of water was added to these raw materials. The cement mixture obtained by kneading for 10 minutes was molded using a 500-ton hydraulic press at a molding pressure of 100 kgf/cr7.
t, a cement molded product with a water-solid ratio of 0.1 was obtained by pressure molding under the conditions of a pressure holding time of 4 minutes, and after curing it in air for 1 day, it was fired and subjected to full-scale molding under the same conditions as in the previous example. When the bending strength of various cement products manufactured by hydration hardening was actually measured, there was a relationship as shown in Table 1 between the amount of CaC03 (Adachi lime) added and the bending strength of the products.

As is clear from Table 1 (the bending strength of the final product is
It can be seen that the bending strength is maximum when 6 parts by weight of O3 is added, and when 10 parts by weight or more is added, the bending strength becomes lower than when no additive is added.

CaCO3 per 100 parts by weight of Portland cement
Adding 8 parts by weight of CaCO3 is equivalent to adding 4.48% by weight of CaO when expressed as a weight ratio to cement.

Therefore, Table 1 can be said to show that it is possible to further increase the bending strength of the product by adding a calcium compound in an amount of 5% or less based on the weight of cement in terms of CaO.

The reason why the bending strength of the cement product obtained by the present invention is increased is due to the voids that exist between the cement particles, consisting of micro voids called gel pores (diameter of 26λ or less) and small voids called capillary pores (diameter of 26λ or more). A relatively large amount of CaO infiltrated into the cavity, and CaO infiltrated into the void.
This is because Ca (OH) 2 eventually becomes Ca (OH) 2 due to moisture absorption, which expands the volume and fills the voids.

The effects of filling such voids are, firstly, that the distance between cement particles becomes shorter due to filling, and as a result, van der Waalska becomes thicker (which contributes to improved strength).
Second, by carbonating the filled C a (OH) 2 , a thick hardened surface layer and a dense structure are formed in a relatively short time, contributing to improved strength. Thirdly, since the above-mentioned 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 include a firing process in the manufacturing process, the following comparative test was conducted.

In other words, for raw materials prepared so that the mixing ratio of cement and aggregate is 1:2, the weight ratio to cement (CaO
Cement molded pieces 1 to 6 obtained by pressure molding a cement mixture obtained by adding water and kneading 2.0% CaCO3 (value not converted to A product obtained by curing in humidity for one week, baking at 800℃ for 10 minutes, and curing in water for three weeks (
Group A) and the mixture ratio of cement and aggregate is the same as above (1:
2) A cement mixture obtained by simply adding water and kneading the raw materials prepared as shown in 2) was pressure-molded under the same conditions as above, and molded cement pieces 1' to 6' were obtained by the conventional method. When the bending strength of the products obtained by curing them in water for 4 weeks (Group B) was tested, the results shown in Table 2 were obtained.

The sizes of the cement molded pieces 1 to 6 and 1' to 6' are all 210 x 30 x 30, and the type of aggregate used is test piece 1 (1 is 8 mesh under and the bulk specific gravity is 2.39).
porcelain Noyamotte, 2 (2') is 8 mesh under, magnetic chamotte with a bulk specific gravity of 2.36, 3 (3')
) is 35 mesh under porcelain chamotte, same 4 (
4') Ceramic chamotte with 8 mesh under, same 5
(5') is 35 mesh under firestone, same 6 (6')
) is 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 span spacing of 9Q.
mm, and the loading speed was 12 mm/min.

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 process is incorporated, have a higher calcination process. Its bending strength is greater than that of products produced by the conventional method (Group B).

The effects of the present invention are not limited to simply superior mechanical strength of the product.

The greatest advantage of adopting the method of the present invention is that it is possible to improve mechanical strength through high-temperature firing, making it possible to smoke and glaze cement products with a high-melting-point glaze.

In particular, when glazing cement products, it has become possible to use an inexpensive frit glaze with a high melting point, which was previously considered unusable, and the addition of appropriate raw materials such as feldspar and clay to this frit glaze. As a result, glazes suitable for cement products can be used, as illustrated in Tables 3 and 4, which have excellent weather resistance, abrasion resistance, and chemical resistance, and at the same time, have perfect color and gloss on the glazed surface. As a result, it will be recognized that the present invention has excellent industrial applicability in that it can create new and wide-ranging demand for cement products in the construction industry and other related industrial fields.

Claims (1)

[Scope of 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, The cured product obtained by this preliminary step is 650 to 95%
A method for manufacturing a cement product, characterized in that a firing step of firing at 0° C. and a full-scale hydration hardening step of sufficiently hydrating and hardening the fired body are performed in this order. 2 As the reinforcing material, glass fiber, ceramic fiber,
A method for manufacturing a cement product according to claim 1, characterized in that metal fibers or metal wires are used. 3. In the firing step, the smoking agent is smoldered in a reducing atmosphere, so that fine particulate carbon generated by thermal decomposition of the hydrocarbons contained in the smoking agent is deposited on the surface of the object to be fired. The method for producing a cement product according to claim 1 or 2, characterized in that the method is carried out by depositing the cement product.