Clay raw materials for lightweight aggregate production
Clay raw materials for production of light-weight aggregates, exploited in Poland, may be assigned to two major types in relation to their usability: raw materials suitable for production of keramsite (light-weight bloated clay aggregates) and raw materials suitable for production of agloporit (called as glinoporyt in Poland).
Raw materials used in production of keramsite are characterized by expansion during thermal treatment. The coefficient (the quotient of clay volume in a swollen state and volume in a state output) characterizing that property, that is swelling coefficient, should be equal at least 2.5 and preferably 5.0 and more. To increase the raw material swell there are technological additives used such as: brown coal, diesel oil, alkalis. The process of production of keramsite involves roasting of appropriately prepared and granulated clay raw material in temperature of 1,050-1,300°C. In the course of roasting the granules increase their volume due to the gases emanation in a pyroclastic mass and their external layer begins to melt forming a parched shard. The obtained product is of the porous light-weight ceramic aggregate type, characterized by low soakability, high thermal insulating properties and high resistance to several agents.
Keramsite is used mainly in building industry for concretes and construction elements and as insulating and draining material. It is also used in road construction, horticulture and agriculture.
Resources of clays suitable for production of keramsite have been documented in 8 deposits. Two of them are exploited: Budy Mszczonowskie deposit located in Mazowieckie Voivodeship where Pliocene cIays are exploited and Gniew II deposit located in Pomorskie Voivodeship where Quaternary stagnant-lake clays are being produced. Till 1995 keramsite was produced also from Oligocene clays exploited in Bukowo (Szczecin-Płonia) deposit located in the Szczecin area. The remaining deposits - Gołaszyn, Nawra, Ruda, Uniejów and Wierzchocin - have not been exploited up to now.
Usually, the raw material for keramsite production can also be used for production of building ceramics wares: brick, ceramic concretes etc. In this case, the roasting process is being carried out in lower temperatures then during keramsite production – below the swelling coefficient for a particular raw material.
Raw materials used in production of agloporit are not expanding in the course during thermal treatment as their swelling coefficient is not higher than 1.0. Process of agloporit production involves roasting of granulated clay containing easily combustible particles. The combustible particles mixed with clay are burnt out during firing which makes the obtained material highly porous. The sintered granules are subsequently crushed to obtain aggregates characterized by high open porosity and relatively low density. Such aggregates were used mainly in production of light concrete, concrete blocks and hollow bricks. Production of agloporit was phased out and deposits of that raw material became abandoned.
Agloporit clay raw materials are fairly common throughout the whole country. Quality requirements which should be matched by these raw materials are generally low – lower even than those put for raw materials for making simple thick-walled ceramics for building industry. The majority of documented resources of agloporit raw materials comprise Quaternary glacial tills and loesses (loess loams) and the remaining ones – Tertiary Krakowiec clays, Poznań clays or Quaternary stagnant lake clays.
"Fired shales" represent a material close to agloporit. This material originates in the result of spontaneous fires of stockpiles of coal waste production in mining operations. The fires turn clay shales which form large part of the coal waste stockpiles, into strong ceramic material. "Fired shales" are available at the Polish market as aggregates usable in building and road construction. They are treated as reused product from waste and thus data on their resources and supplies are omitted from "The balance…".
Table 1 shows the current state of exploration and development of these deposits. Anticipated economic resources as of 31.12.2016 amounted to 168.56 million m3 (337.12 million tonnes) from which resources for keramsite were equal 40.44 million m3 (80.08 million tonnes) – 24.0% of total resources.
The resources decreased by 0.097 million m3 in comparison with the previous year due to the exploitation of the raw material for keramsite production. The output remains at the same level as in 2015.
There has not been any new documentation approved in 2016.
Deposits of clay raw materials for lightweight aggregate production (together with building ceramics raw materials) are presented on the map.
Economic resources are documented only for these parts of exploited deposits which are located within the mining areas. These resources in 2016 amounted to 2.55 million m3 (5.10 million tonnes) and decreased by 0.01 million m3 due to the exploitation.
Prepared by: Wojciech Szczygielski