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 characterizing that property, that is swelling coefficient, should be equal at least 2.5 and preferably 5.0 and more. 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 and their external layer begins to melt. 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, road construction, horticulture and agriculture.
Resources of clays suitable for production of keramsite were documented in 8 deposits, two of which are exploited. Pliocene clays are exploited at Budy Mszczonowskie in the Mazowieckie Voivodeship and Quaternary stagnant-lake clays – at Gniew in the Pomorskie Voivodeship. Till 1995 keramsite was produced also from Oligocene clays exploited in Bukowo (Szczecin-Płonia) deposit in the Szczecin area. The remaining deposits - Gołaszyn, Nawra, Ruda, Uniejów, Wierzchocin - have not been exploited so far.
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 production of agloporit involves roasting of granulated clay containing easily combustible particles such as anthracite. 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 agloporite 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 and even lower than those put for raw materials for making simple thick-walled ceramics for building industry. The majority of proven resources of agloporit raw materials comprise Quaternary glacial tills and loesses (loess loams) and the remaining ones – Tertiary Krakowiec clays and Poznań clay and Quaternary stagnant lake clays.
"Fired shales” represent a material close to agloporit. This material originates in 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 31.12.2015 amounted to 168.66 million m3 (337.32 million tonnes) from which resources for keramsite were equal 40.54 million m3 (81.08 million tonnes) – 24.0% of total resources.
The resources decreased by 0.103 million m3 in comparison with the previous year – it was due to the exploitation and losses.
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 2015 amounted to 2.65 million m3 (5.30 million tonnes) and decreased by 0.01 million m3.
The output was equal 0.097 million m3 and slightly increased (by 0.003 million m3 – 3%) in comparison with the previous year (table 2).
Prepared by: Wojciech Szczygielski