JPH0151468B2 - - Google Patents

Description

[Detailed description of the invention] The present invention creates an aqueous slurry by adding a hydraulic substance and a foaming agent to a gel-like calcium silicate hydrate in which the molar ratio of CaO and SiO ₂ is between 0.5 and 2.0. ,
The present invention relates to a method for producing lightweight cellular concrete, which is characterized by casting this into a mold, solidifying it, and then curing it with steam.

Calcium silicate hydrate-based lightweight cellular concrete is usually made from silicic acid and calcareous raw materials, namely silica, quicklime, and portland cement, to which metallic aluminum or protein-based foaming agents are added. It is manufactured by pouring the aqueous slurry into a mold, solidifying it, cutting it, and then curing it with steam.
And generally its density is 0.3 to 1.2g/
^cm3 . However, this method has three drawbacks. First, it is difficult to adjust the conditions for solidifying the slurry poured into the mold, i.e., the temperature and time, and the shape tends to collapse when cutting, or the slurry becomes too hard to cut. It's inconvenient. The second reason is that steam curing takes several hours and is uneconomical since it requires a large amount of energy because it is carried out under high temperature and pressure. Thirdly, the input raw materials are not refined during the manufacturing process and end up as products containing impurities, so when using natural products such as silica, the selection is difficult. This means that there are major restrictions.

The present inventor has completed the present invention as a result of accumulated research in order to overcome the above-mentioned deficiencies in the manufacturing technology of lightweight cellular concrete.

That is, in the present invention, a gel-like calcium silicate hydrate with a defined molar ratio range of CaO and SiO ₂ is prepared in advance, this is used as the main component of the starting material, and a calcium silicate-based water-curing solution is added to the gel-like calcium silicate hydrate. The present invention provides a new method for producing lightweight cellular concrete, which is characterized by steam-curing a slurry containing a foaming agent and a foaming agent. Further, the density of the aerated concrete in the present invention is 0.3 to 1.2 g/cm ³
is within the range of

The range of molar ratio of CaO and SiO ₂ in the present invention is
Must be between 0.5 and 2.0. If this molar ratio is less than 0.5 or more than 2.0, the coagulation time of the aqueous slurry and the steam curing time will become longer, and not only will there be no significant difference from the normal case described above, but the characteristics after steam curing, especially Compressive strength is inferior to normal case.

Gel-like calcium silicate hydrate with a molar ratio of CaO and SiO ₂ in the range of 0.5 to 2.0 is composed of quicklime and/or slaked lime as the CaO component and silica, Beppu white clay or shirasu as the SiO ₂ component. Furthermore, Portland cement, which has both components, was analyzed for CaO and SiO ₂ based on the respective chemical component analysis values.
It can be easily made by mixing the slurry so that the molar ratio is between 0.5 and 2.0, then adding water to the aqueous slurry and stirring it while heating.
In this case, it is not necessarily necessary to use a high pressure; for example, a pressure of about 90°C is also possible.

The calcium silicate-based hydraulic material in the present invention refers to a mixture of quicklime added to cement or crushed silica stone.

By the way, this gel-like calcium silicate hydrate can be produced industrially with relative ease, but even if it is steam-cured alone, it does not have sufficient strength, and it cannot be used as a lightweight foam. It will not reach the level of concrete. Therefore, using this gel-like calcium silicate hydrate as the main raw material,
A calcium silicate hydraulic substance is mixed with this,
Furthermore, in order to form bubbles, an aqueous slurry obtained by adding a foaming agent such as a protein-based or synthetic surfactant, or a foaming agent such as metal aluminum powder or a paste thereof, is placed in a molding mold. If the concrete is poured into a container and then steam-cured, a material suitable for use as a building material, ie, lightweight aerated concrete, can be obtained. In this case, if the steam curing conditions are set to 180℃ for 3 hours, for example,
The resulting lightweight cellular concrete is an aggregate of artificially synthesized mineral crystals that can be easily observed with a scanning electron microscope.
It can be seen that it is tobermorite with a peak at Å. This means that the main raw material, gel-like calcium silicate hydrate, becomes tobermorite-based crystals through steam curing, and that calcium silicate-based hydraulic substances include Portland cement or a mixture of crushed silica and quicklime. When using water, this substance initially has the effect of solidifying into a molded product conforming to the molding form due to its water-curing properties, but this also solidifies through subsequent steam curing. It can become tobermorite crystal. Therefore, the lightweight cellular concrete thus obtained is similar in appearance to that produced by conventional methods.

In a conventional method that does not involve the method of the present invention, a gel-like calcium silicate hydrate is not prepared in advance, but an aqueous slurry of silica stone, quicklime, and Portland cement with a foaming agent added is poured into a mold. After undergoing a water curing reaction, the material directly enters the steam curing process, but it generally takes 4 to 5 hours at 180°C to sufficiently grow tobermorite crystals and achieve a specified compressive strength. If the above-mentioned 3 hours are used, the tobermorite crystals will not grow sufficiently, the compressive strength will be low, and the strength will deteriorate significantly due to the absorption of carbon dioxide gas, so that lightweight cellular concrete that can be used as a building material cannot be obtained.

Further, according to the method of the present invention, even if silica stone containing 2% or more of alkali metal as an impurity in terms of oxide is used, once gel-like calcium silicate hydrate is formed, the aqueous slurry can be extracted from the aqueous slurry. If water is removed, the alkali metal can be easily removed from the system in the form of ions, and so-called low-grade silica stone can be used industrially. Furthermore, in conventional methods, when amorphous silica, such as Shirasu, is used as the SiO ₂ component, crystalline tobermorite is significantly less likely to be produced than when crystalline silica is used. If you use the method,
Since gel-like calcium silicate hydrate can be easily produced even from amorphous silica, SiO ₂
The starting material as a component is not limited to crystalline silica, but may also be amorphous silica, and when combined with the above-mentioned removal of impurities, the selection range of the SiO ₂ component becomes extremely wide. Similarly, for the CaO component,
In the conventional method, the degree of calcination of quicklime has a subtle influence on the physical properties of lightweight cellular concrete, but according to the method of the present invention, the degree of calcination of quicklime has a subtle effect on the physical properties of lightweight cellular concrete, but according to the method of the present invention, the degree of calcination of quicklime does not depend on the calcination conditions, and it is possible to Even with slaked lime, as long as the molar ratio of CaO and SiO ₂ is kept constant, it is possible to create a gel-like calcium silicate hydrate that is essentially the same, which greatly expands the range of raw materials to choose from.

As is clear from the above description, the three drawbacks of conventional methods have been significantly improved by the method of the present invention.

Furthermore, the physical properties of the lightweight cellular concrete obtained by the method of the present invention surprisingly can be such that the compressive strength, carbonation resistance, and frost damage resistance are at a level that cannot be obtained by conventional methods. I found out. In other words, lightweight cellular concrete is manufactured using an aqueous slurry of gel-like calcium silicate hydrate, which is dehydrated and fresh water is added to create a new aqueous slurry.
Compressive strength, carbonation resistance, and frost damage resistance were improved by more than 20% compared to those produced using conventional methods.

Example 1 1000 g of finely powdered silica stone (SiO ₂ min 98%) with a specific surface area of 3000 cm ² /g determined by the Blaine method by crushing Ukusu silica stone with a ball mill, and 764 g of quicklime (CaO content 99.8%) calcined at 1200°C. 10 parts of water was added to the mixture to create an aqueous slurry. This slurry
The mixture was treated at 90°C for two days and nights with stirring. Chemical analysis of the white fine powder obtained by washing the gel-like substance obtained in this way with water and drying it naturally revealed that it was CaO.
The molar ratio of SiO ₂ is 0.82, and differential thermal analysis shows that it is approximately
It turned out to be a substance that generates heat at 800°C, namely tobermorite-based gel-like calcium silicate hydrate. 100g of dry powder of this gel-like calcium silicate hydrate and 100g of Portland cement.
g, 15 g of quicklime similar to that used above, 100 g of silica stone, and plate-shaped aluminum powder with an average diameter of about 20 μm were mixed well, and 1 liter of water at 50° C. was poured into the mixture to make an aqueous slurry. Pour this into a rectangular cardboard mold with a 20 cm parallel bottom.
It was left as it was for 3 hours. Thereafter, the molded body inside was taken out from the mold and cut vertically into two blocks using a steel wire with a diameter of 0.5 mm. Place these two blocks separately in two autoclaves, one at 180 °C.
℃ for 3 hours, and the other at 180℃ for 6 hours. Both samples after this treatment are lightweight foams with an absolute dry specific gravity of 0.48, and the compressive strength of the former is 49Kg/cm ² and the latter is 48Kg/cm ² .Substantially, even though the autoclave treatment time is 3 hours, The strength was equivalent to that after 6 hours. Then, cut the sample into 5cm cubes using a rotary diamond cutter, and cut the sample into 5cm cubes with the top surface below the water surface.
When the water absorption amount was measured after 6, 12 and 24 hours, the former was 5, 10 and 19% by volume, respectively, and the latter was 6, 9 and 20% by volume, respectively. There was no significant difference between the two. On the other hand, as an example of ordinary lightweight cellular concrete, Hebel (trademark) manufactured by Asahi Kasei Industries, Ltd. was measured, and the water absorption rate was 15, 21, and 29% by volume, respectively, and the water absorption rate of the above sample was significantly lower.

In addition, finely powdered silica and quicklime were mixed so that the molar ratio of CaO and SiO ₂ in the tobermorite gel was 0.45 and 2.2, but both had a compressive strength of 30 Kg/cm ² or less and a density after 6 hours of autoclaving.
Only lightweight aerated concrete with an unsatisfactory strength of 0.52 g/cm ³ was obtained.

Example 2 As a result of a similar experiment using Beppu white clay instead of Ukusu silica in Example 1, a lightweight foam having properties similar to those of Example 1 was obtained. This 5cm
A cubic sample was subjected to a freeze-thaw test method that involves freezing in air and thawing in water, that is, freezing it in air at -20°C for 4 hours, treating it in water at +20°C for 4 hours, and repeating this process. and 120 times, the volumetric survival rates of the samples were 98 and 90%, respectively. In contrast, Hebel's case is 50, 70
and 80, 50 and 20% at 90 times, respectively;
Clearly, the freeze damage resistance of the above sample was significantly improved.

Claims (1)

[Claims] 1 Add a calcium silicate-based hydraulic substance and a foaming agent to a gel-like calcium silicate hydrate with a molar ratio of CaO to SiO ₂ between 0.5 and 2.0 to create an aqueous slurry, and use this as a molding mold. and solidify it.
A method for producing lightweight aerated concrete characterized by further steam curing.