DE4021028A1 - Large vol. cellular ceramic construction elements - obtd. by foaming clay, water and chalk slurry mixt. and carbonising to produce strong calcium carbonate frame structure - Google Patents

Abstract

Method of producing large volume cellular ceramic construction elements with high dimension tolerance and density of 150-1200 kg/m3 consists of preparing an homogeneous clay slurry containing 35-50 pbw clay and 45-50 pbw H2O; heating to 50-60 deg.C; mixing in 5-15 pbw chalk (92% CaO); producing pores in the mixture by adding Al powder or a foaming agent to produce the required raw density, feeding into a mould and leaving for 2 hr. before demoulding and cutting up into parts which are then combined and dried in a tunnel furnace. Finally the parts are fired at 600-1200 deg.C to form a sintered final product. ADVANTAGE - The chalk forms calcium hydroxide which is carbonised to calcium carbonate in the tunnel furnace with a CO2 atmosphere. This crystal structure forms a mechanically stable frame for the material and prevents shrinkage and cracks forming during drying. Eventually mullite is produced which strengthens the clay material.

Description

The invention relates to a process for the preparation large-volume cell ceramic construction and construction Elements of great dimensional accuracy for construction and industry purposes, such. As blocks, plates and the like. With a void fraction of about 40 to about 95 percent of the total volume in the form of open and closed cells, wherein a bulk density of the mate Rials of 150 to 1200 kg per cbm is achieved.  

In the construction industry, gas concrete has been used for a long time However, there are a number of systemic consequences share. These disadvantages are:

• 1. After autoclaving, gas concrete has a high Residual moisture of 25-30%, which only after decreased for a long time;
• 2. Relatively high shrinkage ( 0.5 mm / m) and resulting cracking;
• 3. Low resistance to SO ₂ and CO ₂ in the atmosphere;
• 4. Low fire resistance and consequent low fire protection class.

Cell ceramic does not have and has these disadvantages compared to gas concrete additional benefits, what the old resistance, tightness, higher pressure resistance and other properties.

As for the production of cell ceramics, whether by puffing or foaming, a large amount of water is required is, in relation to the solid material between 0.7 to 0.4 moves, this results in the Her position of large-format and / or large-volume components hitherto insurmountable difficulties, because the Structure in the structure only by the burning ver consolidates.

Before this burning process can be initiated can, the water with great care from the shear must ben, without damaging it so far only in kleinmaßigen bodies with appropriate  linear deformation from the mixture to Ferti product is possible. The difficulties arise due to the drying shrinkage. During the Drying and pre-firing process is in the shard no loadable structure yet, so that it with larger bodies inevitably to cracks and Form changes come.

Object of the present invention is a method to suggest, with the help of large format and / or large-volume dimensionally stable cell ceramic body for under can be produced very different purposes.

The object is achieved in that during the drying pre-burning phase of the broken piece in this one sufficiently solid intermediate structure is formed, the is effective until the burning process by Mulliti tion has solidified the ceramic structure itself, ent speaking the characteristics of the characterizing part of Claim 1.

Advantageously, the shards during assisting the drying and pre-firing process structure in the drying and firing process as rea incorporating ingredient.

In the following the invention with reference to an example of the production of a traditional ceramic cell material, comparable to the density of 650 kg / m ³ , of gas concrete according to the standard DIN 4165/4166 (for cell ceramic is no corresponding standard) is described:
500 kg brick clay are prepared by means of a ball mill or another homogenizer and processed with 500 l of water to a sludge. This is heated to about 50-60 ° C. Subsequently, the mass is metered into a compulsory mixer finished foam and mixed for about one minute.

Then it is further added:
100 kg burned lime (95% CaO) with about one minute mixing, 0.23 kg aluminum powder and repeated mixing for about 45 seconds.

The finished mixture is then poured into molds, whereupon immediately the swelling process (expansion) and the calcium Oxyd hydration begins. The swelling process is about 25 minutes completed; the mixture starts closing due to the increased temperature due to exothermic lime-hydration process towards solidify. After 2-3 hours, this pre-cure process, the mixture for the drying and Pre-firing required strength, from closed.

The blank thus formed will now be disengaged and one Cutting machine supplied. There he will be using wires cut to the desired dimensions, z. B. 60 cm high, 25 cm wide and up to 30 cm thick.

After cutting the blanks are on waggons ver on which by means of movable bottom slats the Separation of the individual blocks takes place lengthwise,  so that they are responsible for the subsequent carbonization and the Drying freestanding surfaces have.

Subsequently, the wagons are fed to a carbonization / drying tunnel, where the carbonization and drying process begins by convection of the air gas containing CO ₂ . After its completion, the wagons come with the dried blocks in a combustion chamber, where the burning process, as usual in the Ziegelherstel development takes place.

In this way, blocks, plates or others are created Cell ceramic components with the following physical characteristics Properties:

Density: 600-620 kg / m³, Compression strength: approx. 6 N / mm², Bending strength: approx. 0.7 N / mm², after-shrinkage: around 0.03 mm / m, Dimensional change in volume from the starting mixture to the blank form-finished block: at 5'o clock%. Fire resistance: <1000 ° C (Internal temperature)

The carbonization process taking place in the production process according to the invention comes into effect after the burnt lime has been quenched by hydration (CaO + H ₂ O = Ca (OH) ₂ +15.6 kcal). By this exothermic reaction, the temperature of the mixture increases to 80-90 ° C, and the mixture automatically reaches a water content of 15-20%. It is thus ready for the subsequent carbonization process.

This is an adsorption process taking place from outside to inside over the surface, favored by the porous structure of the cullet. By growing together the crystals of calcium carbonate (CaCO ₃ ) during carbonation of calcium hydrate forms such a solid skeleton in the blank structure that the formation of cracks and the shrinkage of the initial microstructure are prevented during further drying. Since the carbonization process is also exothermic, the temperature increases in the blank, combined with a further drying of the same, so that at the end of the process, the water content lisiert to 10-14%.

For the Karbonisationsprozeß the exhaust gases of the kiln are used. Depending on the concentration of CO ₂ gas (usually 6-11%) and the thickness of the blank, the carbonization process takes 16 to 35 hours.

The carbonized blank then has a strength of 0.4 to 0.7 N / mm ² with a skeleton of calcium carbonate, which is theoretically stable up to 760 ° C, but in practice withstands temperatures up to 900 ° C.

During the subsequent firing of the blanks at the übli chen temperature by about 1000 ° C, the skeleton of the calcium carbonate remains stable for a certain time before the dissociation process CaCO _{3 is completed} to CAO + CO ₂ . During this time, the first mullite formation of the clay takes place, which now assumes the structural strength, without causing any changes in shape or cracks in the blank.

The carbonization process is a simple industrial one Operation using simple equipment, which in each ceramic factory are available (drying tunnel, exhaust fans).

The carbonization takes place with waste gases from the Kilns.

The invention has succeeded in adding a product create that verbes compared to the state of the art verbes serte properties with technologically simple means with great economic benefits.

With this method, large-sized components can be with densities between 150 to 1200 kg / cbm ago with the starting mixture next to burned Lime can also be added to cement. Because cement too contains about 50% clay-forming constituents, is the Clay content with admixture of cement then accordingly reduce to a final product with the desired To get properties.

Experiments have shown that in the production of cell ceramic bodies low volume density percentage a higher proportion of lime is required in order to ge wished to come up with a result and it is beneficial the proportion of cement compared to the lime content decrease to increase the spatial density increasingly.

Claims (3)

1. A method for producing large-volume cell ceramic construction and construction elements of large dimensional accuracy with a density of 150-1200 kg / cbm, characterized by the following process steps:

• 1) preparation of a homogeneous clay sludge of 35-50 parts by weight of ground clay and 45-50 parts by weight of water,
• 2) heating the sludge to 50-60 ° C,
• 3) admixture of 5-15 parts by weight of quick lime (95% CaO),
• 4) generation of pores in the mixture by addition of aluminum powder or a foaming agent with agitation of the mixture or by mixing of prefabricated foam according to the desired raw density,
• 5) filling the mixture into molds,
• 6) After 2-3 hours demoulding the blanks and cutting them into blanks,
• 7) separating the blanks and placing them in a carbonizing and drying tunnel, and
• 8) Final firing of the blanks between 600 ° C and 1200 ° C to the cell ceramic end product.

2. The method according to claim 1, characterized that proportions of quicklime and clay partially be replaced by cement. 3. The method according to at least one of the claims 1 to 2, characterized in that for Karbo nization of the blanks the exhaust gases of the drying and Kiln used.