Production method for lightweight foamed concrete

Abstract

To improve productivity of lightweight foamed concrete by shortening a "half-curing time" required for half-curing a raw material slurry in a production process of the lightweight foamed concrete.SOLUTION: Disclosed is a method for producing lightweight foamed concrete comprising: a sub-raw material slurry compounding step where a waste material comprising a calcareous raw material and a silicic raw material is wet-ground and further a calcareous raw material is added as necessary to obtain a sub-raw material slurry having a Ca / Si ratio of 0.6 or more; a high-early strength slurry compounding step where the sub-raw material slurry is added to the main raw material slurry to obtain a high-early strength slurry; a semi-curing step where the high-early strength slurry is semi-cured in a mold to obtain a lightweight foamed concrete raw cake; a cutting step where the lightweight foamed concrete raw cake is cut into predetermined dimensions with a piano wire; and a curing step where the lightweight foamed concrete raw cake cut into predetermined dimensions is steam cured at high temperature and pressure to obtain the lightweight foamed concrete.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing lightweight aerated concrete (ALC). More specifically, the present invention relates to ALC used as a building material for the walls, roofs, floors, etc. of buildings, and in particular to a method for producing lightweight aerated concrete panels (ALC panels) that can shorten the time it takes for a raw material slurry to semi-harden to the point where it can be cut with a piano wire in the process of producing the panels. [Background technology]

[0002] ALC is lighter than normal concrete and has excellent fire resistance, heat insulation, and workability, and is therefore widely used as a panel-shaped building material for the walls, roofs, floors, etc. This ALC is usually produced by a production method that sequentially includes a semi-hardening process (first curing process) in which a raw material slurry is foamed in a formwork to form a cake-like semiplastic body (referred to as "lightweight aerated concrete green cake" or "ALC green cake" in this specification), a cutting process in which the "ALC green cake" is cut to a specified size with a piano wire, and a hardening process (secondary curing process) in which the "ALC green cake" cut to a specified size is completely hardened by high-temperature, high-pressure steam curing to obtain ALC (see Patent Document 1).

[0003] At the production sites of ALC manufactured in this way, various efforts are being made to improve productivity. As one of such attempts aimed at improving productivity, various technical means have been proposed to shorten the time required to semi-harden the raw material slurry (harden it to the extent that it can be cut with a piano wire) in the semi-hardening process (first curing process) among the above-mentioned processes (in this specification, this time is referred to as the "semi-hardening time"). In the manufacture of ALC, known specific means for shortening the "semi-hardening time" of the raw material slurry include "a method of increasing the blending ratio of lime-based raw materials such as cement and quicklime, which have high hydration reactivity, in the raw material slurry" and "a method of adding calcium chloride, which is a cement hardening accelerator, to the raw material slurry".

[0004] However, in the case of the former "method of increasing the blending ratio of calcareous raw materials in the raw material slurry", the blending ratio of calcareous raw materials is increased from the normal amount, which not only leads to an increase in production costs, but also creates a risk that the ratio (molar ratio) of Ca and Si in the raw material slurry (hereinafter, this ratio will be referred to as "Ca / Si ratio") will fall outside the suitable range for the formation of tobermorite, the main crystal mineral of ALC. In addition, in the case of the latter "method of adding calcium chloride or the like to the raw material slurry", there is a risk that the strength of the ALC product will decrease due to the inclusion of a small amount of chloride inside.

[0005] On the other hand, in the field of ALC production, in an attempt to reduce costs and waste, ALC waste materials (hereinafter also referred to as "ALC waste materials") generated in construction sites and manufacturing plants are widely reused as recycled raw materials (see Patent Document 2). Patent Document 2 discloses a manufacturing method in which "ALC waste materials" are dried and finely pulverized at a heating temperature of 105°C to 300°C in order to stably maintain the compressive strength of ALC, and the crystalline tobermorite is converted into a siliceous raw material, thereby making it less susceptible to fluctuations in the amount of recycled raw materials and enabling the compressive strength to be stably maintained at the same level as that of conventional products. However, when "ALC waste materials" are used in the manner disclosed in Patent Document 2, although it is possible to improve the quality of the final product by increasing the reactivity of "ALC waste materials" in the secondary curing process (curing process), it is not possible to shorten the "semi-curing time" required to semi-cur the raw material slurry in the above-mentioned primary curing process (semi-curing process). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-199408 A [Patent Document 2] Patent Publication No. 2021-42093 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide a method for producing lightweight aerated concrete (ALC) that can improve the productivity of ALC by shortening the "semi-hardening time" required to semi-harden a raw material slurry in the ALC production process. [Means for solving the problem]

[0008] The inventors discovered that the semi-hardening time can be significantly shortened by adding a secondary raw material slurry, which is obtained by wet grinding waste materials such as "waste ALC" and has a "Ca / Si ratio" within a certain range, to the main raw material slurry of lightweight cellular concrete before the step of semi-hardening in a formwork, and thus completed the present invention. Specifically, the present invention provides the following.

[0009] (1) A method for producing lightweight aerated concrete, comprising: an auxiliary material slurry mixing step of wet-grinding waste material containing a calcareous raw material and a siliceous raw material, and further adding a calcareous raw material as necessary, to obtain an auxiliary material slurry having a Ca / Si ratio of 0.6 or more; an early-strength slurry mixing step of adding the auxiliary material slurry to a main material slurry containing a calcareous raw material, a siliceous raw material, and an aluminum powder to obtain an early-strength slurry; a semi-hardening step of semi-hardening the early-strength slurry in a formwork to obtain a lightweight aerated concrete green cake; a cutting step of cutting the lightweight aerated concrete green cake to a predetermined size with a piano wire; and a hardening step of steam-curing the lightweight aerated concrete green cake cut to the predetermined size at high temperature and high pressure to obtain lightweight aerated concrete.

[0010] According to the manufacturing method of lightweight aerated concrete (1), the "semi-hardening time" required to semi-harden the raw material slurry is shortened by a new process that effectively utilizes "waste materials containing calcareous raw materials and siliceous raw materials" such as "waste ALC" in a unique manner, thereby improving the productivity of ALC.

[0011] (2) A method for producing lightweight aerated concrete as described in (1), in which, in the auxiliary material slurry mixing process, the Ca / Si ratio of the auxiliary material slurry is set to 1.0 or more and 10.0 or less by adding the calcareous raw material.

[0012] According to the method for producing lightweight cellular concrete of (2), the above-mentioned effects achieved by the method for producing lightweight cellular concrete of (1) can be obtained in a more preferable manner and more stably.

[0013] (3) A method for producing lightweight aerated concrete described in (1) or (2), in which the solid content of the auxiliary material slurry in the early strength slurry is 0.5% by weight or more and 10.0% by weight or less relative to the solid content of the main material slurry.

[0014] According to the method for producing lightweight cellular concrete of (3), the above-mentioned effects achieved by the method for producing lightweight cellular concrete of (1) or (2) can be obtained in a more preferable manner and more stably.

[0015] (4) A method for producing lightweight cellular concrete according to (1) or (2), wherein the waste material is lightweight cellular concrete waste material.

[0016] According to the manufacturing method for lightweight aerated concrete (4), the above-mentioned effects of the manufacturing method for lightweight aerated concrete (1) or (2) can be enjoyed, thereby improving the productivity of lightweight aerated concrete, while at the same time promoting the effective reuse of lightweight aerated concrete waste generated at construction sites and manufacturing plants. Effect of the Invention

[0017] According to the present invention, the productivity of ALC can be improved by shortening the "semi-hardening time" required for semi-hardening the raw material slurry in the manufacturing process of lightweight cellular concrete. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, embodiments of the present invention will be described, however, the present invention is not limited to the following embodiments.

[0019] <Method of manufacturing lightweight cellular concrete> In the manufacturing method of the lightweight cellular concrete of the present invention, the semi-hardening step of obtaining an ALC fresh cake, the cutting step of cutting the ALC fresh cake to a predetermined size with a piano wire, and the hardening step of finally hardening the ALC fresh cake cut to a predetermined size by steam curing at high temperature and high pressure to obtain ALC can be performed in the same manner as in the manufacturing method of the conventional lightweight cellular concrete. However, in the manufacturing method of the lightweight cellular concrete of the present invention, a sub-material slurry mixing step and an early-strength slurry mixing step are performed as new and essential additional steps prior to the above steps in the conventional manufacturing method (i.e., prior to the semi-hardening step).

[0020] (Main raw material slurry) In the production of the lightweight cellular concrete of the present invention, the "main raw material slurry" used as the main material can be a slurry-like material similar to the raw material slurry used in the production of conventional lightweight cellular concrete. This slurry ("main raw material slurry") is mainly composed of siliceous raw materials such as silica stone and silica sand, and calcareous raw materials such as cement and quicklime, and also contains additives such as aluminum powder as a foaming agent and surfactants, and can be mixed by adding an appropriate amount of water to these materials and kneading them with various mixers. The Ca / Si ratio of the raw material slurry used in the production of lightweight cellular concrete is usually about 0.3 to 0.7, and the water / solid ratio is about 0.6 to 1.0. In the present invention, a raw material slurry having a Ca / Si ratio of about 0.3 to 0.7 and a water / solid ratio of about 0.6 to 1.0 can be used as the "main raw material slurry".

[0021] [Sub-raw material slurry mixing process] The auxiliary slurry preparation process is a process of wet-pulverizing waste materials containing calcareous and siliceous raw materials, such as lightweight aerated concrete waste materials (ALC waste materials), and further adding calcareous raw materials as necessary, to obtain an auxiliary slurry having a Ca / Si ratio of 0.6 or more, preferably 1.0 to 10.0. Unlike the conventional dry pulverization (the manufacturing method described in Patent Document 2) in which ALC waste materials are pulverized while drying them at high temperatures, the manufacturing method of the present invention pulverizes ALC waste materials and the like by wet pulverization with low energy costs. It is preferable to use a ball mill for wet pulverization of ALC waste materials and the like. The water / solid ratio of the auxiliary slurry is the same or approximately the same as that of the main raw material slurry.

[0022] As the "waste material containing calcareous raw materials and siliceous raw materials" that is the main material of the auxiliary raw material slurry, ALC waste materials can be preferably used, but other construction waste materials containing calcareous raw materials and siliceous raw materials, such as siding boards, calcium silicate boards, extruded cement boards, etc., can also be appropriately selected and used. In addition to these various construction waste materials, industrial waste materials such as glass waste, concrete waste, ceramic waste, and concrete fragments, which contain calcareous raw materials and siliceous raw materials like the above construction waste materials, can also be used as the main material of the auxiliary raw material slurry.

[0023] In the auxiliary material slurry preparation step, if necessary, a calcareous raw material is added separately from the calcareous raw material contained in the waste material to adjust the Ca / Si ratio of the auxiliary material slurry to the above-mentioned range, that is, 0.6 or more, preferably 1.0 to 10.0. The addition of a calcareous raw material is not essential as long as the Ca / Si ratio of the auxiliary material slurry can be maintained at 0.6 or more, but as described above, since the Ca / Si ratio of the main raw material slurry is usually about 0.7 or less, by adjusting the Ca / Si ratio of the auxiliary material slurry to a larger value of 1.0 or more, the "semi-hardening time" can be shortened more reliably.

[0024] As the calcareous raw material to be added for adjusting the Ca / Si ratio of the auxiliary raw material slurry to fall within the above range, quicklime, slaked lime, calcium carbonate, blast furnace slag, ready-mixed concrete sludge, etc. can be appropriately selected and used, and among these, quicklime or slaked lime can be preferably used.

[0025] As described above, when the ALC waste is ground by the conventional dry grinding method (the manufacturing method described in Patent Document 2) in which the ALC waste is ground while being dried at a high temperature, the "semi-hardening time" required to semi-harden the raw material slurry in the first curing step (semi-hardening step) cannot be shortened, but as demonstrated in the examples described below, according to the manufacturing method of the present invention, the "semi-hardening time" can be shortened by grinding the ALC waste in the auxiliary material slurry mixing step by wet grinding. This is thought to be because calcium silicate hydrate, which is formed by a chemical reaction between the siliceous raw material and the calcareous raw material contained in the ALC waste in the solvent (water) in which the wet grinding is performed, contributes to accelerating the hardening of the raw material slurry.

[0026] [Early-strength slurry mixing process] The early-strength slurry preparation step is a step of adding the auxiliary slurry obtained in the auxiliary slurry preparation step to the above-mentioned main raw material slurry to obtain an early-strength slurry. The amount of the auxiliary slurry added is preferably such that the solid content of the auxiliary slurry in the early-strength slurry is 0.5% by weight or more and 10.0% by weight or less (more preferably 1.0% by weight or more and 10.0% by weight or less) relative to the solid content of the main raw material slurry. If the content of the auxiliary slurry in the early-strength slurry is less than 0.5% by weight, the effect of promoting semi-hardening is difficult to fully manifest, while if the content exceeds 10% by weight, the effect of shortening the semi-hardening time reaches a plateau, and furthermore, the adverse effect of making it difficult to inject the main raw material slurry into a mold is easily generated.

[0027] The addition of the auxiliary material slurry to the main raw material slurry can be obtained by feeding the auxiliary material slurry, which has been previously slurried in the above manner, into the mixer and mixing it with the ingredients of the main raw material slurry when the main raw material slurry is kneaded and mixed with the mixer as described above. Alternatively, the auxiliary material slurry can be added to the main raw material slurry that has already been mixed in advance in the above-mentioned amount and mixed.

[0028] [Semi-curing process] The semi-hardening process is a process in which the early-hardening slurry obtained in the early-hardening slurry mixing process is semi-hardened in a formwork to obtain a semi-plastic lightweight aerated concrete green cake (ALC green cake). In this process, the early-hardening slurry is poured into a formwork such as a mold in which reinforcing steel bars are set. The injected early-hardening slurry expands in volume as hydrogen gas reacts with the aluminum powder and is stabilized as spherical bubbles by the bubble stabilizer. The early-hardening slurry then semi-hardens into a non-fluid semi-plastic body, becoming the ALC green cake, as the cement and quicklime absorb water from the raw materials and form hydrates.

[0029] [Cutting process] The cutting process is a process of cutting the ALC raw cake into pieces of a predetermined size with a piano wire. Specifically, the cutting process is performed by removing the ALC raw cake, which is a semi-hardened body, from a form and cutting the ALC raw cake into pieces of a predetermined size with a piano wire, which is an example of a wire material.

[0030] [Curing process] The hardening process is a process in which the ALC raw cake cut to a predetermined size in the cutting process is hardened by steam curing at high temperature and high pressure to obtain ALC. This steam curing at high temperature and high pressure can be performed in an autoclave at 180°C, 10 atm, and for about 6 hours, as in the conventional ALC manufacturing method.

[0031] Of the ALC obtained in the curing process, non-defective products are shipped as products, while defective products with cracks or other defects can be reused as they are within the factory as raw material for the ALC waste material used in the manufacturing method of the present invention. EXAMPLES

[0032] The method for producing the lightweight cellular concrete of the present invention will be described in detail below with reference to examples. Note that the present invention is not limited to the embodiments of the examples shown below.

[0033] <Semi-curing time measurement test> In order to verify the effect of the method for producing lightweight cellular concrete of the present invention, a test was conducted to compare the semi-hardening time in the semi-hardening process for each of the examples and comparative examples as follows.

[0034] (Main raw material slurry) In the test production of all the Examples and Comparative Examples, the main raw material slurry was prepared by mixing the materials in a mixer according to the composition shown in Table 1 below.

[0035] [Table 1]

[0036] (Sub-raw material slurry mixing process) The same ALC waste material was used as the waste material for the auxiliary raw material slurry in the test production of all the examples and comparative examples. Then, for each example and comparative example, a different auxiliary raw material slurry with a different crushing state and Ca / Si ratio was prepared as shown in Table 2 below. However, in the test production of Comparative Example 1, the semi-hardening process was performed without adding the auxiliary raw material slurry. Also, in the test production of Comparative Examples 2 and 3, the ALC waste material was not subjected to wet crushing treatment, but powder of the ALC waste material (particle size: 10 μm to 100 μm, median value 40 μm) that was subjected to only dry crushing treatment was used as the ALC waste material to be added, and water was added to this to make a slurry. Also, the amount of quicklime added was adjusted for each auxiliary raw material slurry of each example and comparative example so that the Ca / Si ratio of each auxiliary raw material slurry of each example and comparative example was as shown in Table 2. However, quicklime was not added in Example 1 and Comparative Example 2, where the Ca / Si ratio is 0.6.

[0037] (Early-strength slurry mixing process) Next, in each Example and Comparative Example, the auxiliary material slurry prepared for each Example and Comparative Example was added to the above-mentioned main raw material slurry to prepare the early strength slurry of each Example and the material slurry of each Comparative Example. The content of the auxiliary material slurry in the early strength slurry of each Example and the content of the auxiliary material slurry in the material slurries of Comparative Examples 2 and 3 were adjusted so that the solid content of the auxiliary material slurry in each slurry was 3.0% by weight in terms of the ratio to the solid content of the main raw material slurry.

[0038] (semi-curing process) Next, the early hardening slurry of each Example and the material slurry of each Comparative Example were semi-hardened in a frame at room temperature (20°C) to obtain an ALC raw cake (semi-hardening step). The size of the frame was 430 mm (length) x 130 mm (width) x 200 mm (depth).

[0039] (Measurement of half-curing time) The semi-hardening time of each Example and Comparative Example was measured. For the measurement, an iron ball with a diameter of 41 mm was dropped naturally onto the ALC raw cake from a height of 50 mm, and the semi-hardening was deemed to be completed when the diameter of the opening of the circular recess formed by the iron ball sinking into the semi-hardened body was 25 mm or less, and the time required for this completion was measured for each Example and Comparative Example. The results are shown as "semi-hardening time" in Table 2 below. It was also confirmed that the ALC raw cake that was deemed to have been semi-hardened by the above test was in a good condition for cutting with a piano wire.

[0040] [Table 2]

[0041] As can be seen from Table 2, according to the manufacturing method of lightweight aerated concrete of the present invention, it has been confirmed that the semi-hardening time can be significantly shortened by adding, to the main raw material slurry of lightweight aerated concrete before the step of semi-hardening in the formwork, a secondary raw material slurry obtained by wet grinding "waste material containing calcareous raw materials and siliceous raw materials" such as "ALC waste material" and having a Ca / Si ratio adjusted to 0.6 or more and 10.0 or less, preferably 1.0 or more.

[0042] <Curing speed measurement test> In the manufacturing method of the lightweight aerated concrete of the present invention, in order to verify the difference in the hardening speed of cement depending on whether or not wet grinding is performed, auxiliary slurries having the same Ca / Si ratio but different grinding conditions (Example 6, Comparative Example 4) were prepared, and tests were conducted to compare and verify the difference in the effect of each of these auxiliary slurries on the hardening speed of cement, as described below.

[0043] (Mixing of secondary raw material slurry) The same ALC waste material was used as the waste material for the auxiliary raw material slurry in all Examples and Comparative Examples, and auxiliary raw material slurries with different pulverization conditions were prepared for each Example and Comparative Example, as shown in Table 3 below. In both Example 6 and Comparative Example 4, a planetary ball mill was used to pulverize 200g of ALC waste material under the conditions of a rotation speed of 200 rpm, a pulverization time of 6 hours, and media of 200g of zirconia balls. Only in Example 6, 100g of pure water was added, and in Comparative Example 4, pulverization was performed without adding water, and then 100g of pure water was added to form a slurry.

[0044] (Test slurry preparation process) Next, the auxiliary raw material slurries of Example 6 and Comparative Example 4 were each added at a ratio of 5.0% by weight (solid content ratio) to 200 g of cement to prepare test slurries for each Example and Comparative Example. The same type of cement as that used for the main raw material slurry in the above-mentioned "half-hardening time measurement test" was used as the cement.

[0045] (Measurement of curing speed) Next, the test slurries of each Example and Comparative Example were subjected to a hardening test in a 300 ml disposable cup at room temperature (20°C). The hardening speed was measured by measuring the hardening state of each test slurry at predetermined time intervals from the start of curing using a push-pull gauge. The results are shown in Table 3 below.

[0046] [Table 3]

[0047] As shown in Table 3, it was confirmed that the hardening speed of cement is significantly improved by grinding the ALC waste material by wet grinding instead of dry grinding. From this result, it can be inferred that in the manufacturing method of the present invention, the specification of the grinding mode of the ALC waste material in the mixing process (specifying the grinding mode to wet grinding) also contributes significantly to the manifestation of the effect of shortening the "half-hardening time".

Claims

1. A method for producing lightweight cellular concrete, comprising: a step of wet-grinding a waste material containing a calcareous raw material and a siliceous raw material, and further adding a calcareous raw material as necessary, thereby obtaining an auxiliary material slurry having a Ca / Si ratio of 0.6 or more; a step of adding the auxiliary material slurry to a main material slurry containing a calcareous raw material, a siliceous raw material, and an aluminum powder to obtain an early strength slurry; A semi-hardening process in which the early-strength slurry is semi-hardened in a formwork to obtain a lightweight cellular concrete green cake; A cutting process of cutting the lightweight cellular concrete fresh cake into a predetermined size with a piano wire; A hardening step of obtaining lightweight cellular concrete by steam curing the lightweight cellular concrete raw cake cut to a predetermined size at high temperature and high pressure. A method for producing lightweight cellular concrete.

2. In the auxiliary raw material slurry preparation step, the calcareous raw material is added to set the Ca / Si ratio of the auxiliary raw material slurry to 1.0 or more and 10.0 or less. A method for producing the lightweight cellular concrete according to claim 1.

3. The content of the solid content of the auxiliary material slurry in the early strength slurry is 0.5% by weight or more and 10.0% by weight or less relative to the solid content of the main material slurry. A method for producing lightweight cellular concrete according to claim 1 or 2.

4. The waste material is lightweight cellular concrete waste material. A method for producing lightweight cellular concrete according to claim 1 or 2.

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