Ceramic polishing powder and AAC production
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Ceramic polishing powder and AAC production

China’s ceramic manufacturing industry has experienced a period of stable development. Output  figures of ceramic products and the number of enterprises doing their business in the ceramic industry have grown tremendously. Today, China is the largest worldwide producer and exporter of ceramics boasting a rapid development in this industry. The result is a vast amount of ceramic powder wastes on account of trimming and polishing processes during the production of ceramic walls.  According to some statistics, more than 20 million tons of ceramic waste is annually produced by  ceramic production facilities. In the past, there have not been any relevant recycling technologies;  ceramic waste was regarded by companies as “garbage” used for landfills or to fill gullies, roadbeds  and the like. Environmental problems of this nature were an extremely unpleasant phenomenon in  the Shangdong Province as well. Challenged by the Chinese government, the ceramic industry of this  province attempted to find ways in solving this environmental pollution problem especially caused by  the long-term storage of ceramic polishing powder wastes. It was therefore in 2014 that a company  located in the Shandong Province, Heyue Technology, started to cooperate with Keda Suremaker to install an AAC plant with an annual capacity of 300,000 m3. This facility has since been using ceramic  polishing powder waste as the main raw material for the production of AAC panels and blocks.

The main minerals in ceramic powder waste are  feldspar, quartz, talc, mullite, and montmorillonite.  Research has shown that ceramic powder waste  strongly reacts chemically when the content of SiO2  exceeds 65 % and the content of Al2O3 is about 16  %. Findings also seem to indicate that ceramic powder waste, owing to its advantages compared to fine  grain size and high SiO2 content, can very well be  used as a main raw material together with cement,  lime, gypsum and aluminium powder to constitute  a foaming agent for the production of autoclaved  aerated concrete blocks and panels. Based on these  findings, it can be concluded that the proportion of  ceramic powder waste can readily exceed 73 % of  total raw materials in this context. 

The Heyue project uses a special pouring mixer based  on the mixing structure of the “double cross paddle  & modular draft tube” philosophy as maintained by  Keda Suremaker. The analysis of design parameters  by means of a finite element analysis tool has proven  that this mixing structure can ensure high efficiency  mixing of ceramic powder waste and other raw materials. Compared to other pouring mixers, this mixer is  capable of reducing power consumption by as much  as 45 KW by optimizing fluid movement circuit during  the mixing process and thus addressing the demand  for energy savings and at the same time ensuring a  top-quality mixing effect. With this process, the curing time in the precuring chamber is around 2 to 3  hours at temperatures between 40 and 50° C and a  steam pressure around 1.2 to 1.4 Mpa during the constant temperature stage. 

Heyue’s AAC products show very good performance.  The thermal conductivity of Heyue blocks with a dry  density of 500 kg/m3 is only 0.09 W/(m·K), which is  lower than that of fly ash based AAC blocks of the  same dry density grade. Heyue panels with a thickness of 20 cm perform better than solid brick walls  with a thickness of 50 cm ensuring external wall heat  insulation. The compressive strength of Heyue blocks  with the above described dry density of 500 kg/m3  is at 5.3 MPa, a figure that greatly enhances seismic  performance and toughness of the material. The material is inorganic and non-combustible and does not  lose its strength even at temperature levels of 700°  C. After 15 freeze-thaw cycles at a temperature level  of -20° C / 6 h ~ +23° C / 5 h, the mass loss percentage rate of the saturated absorbent product is only  2.05 %. After 90 days of natural carbonation, the  carbonation coefficient is at 0.91. Frost resistance and carbonation tests have shown that Heyue products boast excellent durability features. In particular, the drying shrinkage of these products is only  0.29 mm/m, reducing the occurrence and severity of  shrinkage cracks caused by carbonation. 

One important type of Heyue products are thin panels with thicknesses of 5 and 7 cm. These panels exhibit extremely good thermal insulation features reducing the occurrence of cold bridges in columns in  huge demands in local markets. In order to arrive at  mass production rates for thin panels, requirements  on technologies and equipment are very demanding. Traditional horizontal cutting machines existing  in the market are equipped with 5 - 8 pairs of steel  columns for hanging steel wires and normally there  are at least three steel wires hanging on each pair  for producing panels with a thickness of 5 cm. With  this kind of arrangement, cutting gaps during simultaneous cutting operations are inevitable. Thereafter, gravity will make the cake settle, and the greater the number of cutting kerfs on the same vertical  plane, the greater the differences in height that will  occur on account of cumulatively increasing numbers  of kerfs. All this will result in quality problems, such  as the above described gravity settlement cracks. In  addition, when cutting wires discontinue their operation and leave the cake, there is a strong likelihood that cake ends will be damaged on account of  the substantial friction resulting from the numerous  steel wires pulling on the same vertical plane.

Keda Suremaker has developed a cable-stayed beam  horizontal cutting machine which is equipped with  two main cable-stayed beams and a certain number of small columns distributed evenly along the  two beams for hanging the steel wires. Each pair of  these rather small-sized columns on the two beams  is used to hang only one steel wire and hence just  one cutting kerf (0.6~0.8mm) on one vertical plane  during the cutting process, reducing the gravity  settlement crack impact. In addition, there will be a  lower degree of friction when the cutting steel wire  completes its job and leaves the cake. So this is an  innovative concept of a horizontal cutting machine  to improve the adaptability of an AAC production line  for the mass production of thin panels, a direct and  immediate benefit for clients or users.

With the advantages of low raw material cost, stable  equipment operation and strong governmental support, Heyue Technology soon accomplished a huge  return on investment. In 2018, the company set up  two new AAC plants, the second cooperation with  Keda Suremaker. This year, Heyue Technology will  be setting up yet another two AAC plants featuring  equipment supplied by Keda Suremaker as well.  By operating these five ceramic powder AAC facilities  in the Shandong province, Heyue Technology is planning to produce a total of 1.5 million square metres of  ceramic powder based, autoclaved aerated concrete  blocks or 800,000 square meters of ceramic powder based, autoclaved aerated concrete panels annually.  That is to say that more than 600,000 tons of ceramic tile polish wastes can be turned into a valuable  material each year to contribute its share to the reduction of environmental pollution problems by replacing with this material more than 500,000 tons of  fly ash or sand that would otherwise be needed.

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   2887, Tianmen Rd, Economic & Technological Development Zone, Ma’anshan, Anhui Prov., China
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