Clay raw materials for lightweight aggregate production
Clay raw materials exploited in Poland for the production of light-weight aggregates may be assigned to two major types in a relation to their usability:
- raw materials suitable for the production of keramsite (light-weight bloated clay aggregates),
- raw materials suitable for the production of agloporit (called as glinoporyt in Poland).
Raw materials used in the production of keramsite are characterized by an expansion during the thermal treatment. The coefficient (the quotient of clay volume in a swollen state and volume in a state output) characterizing that property, that is the 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 a roasting of an appropriately prepared and granulated clay raw material in a 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 a low soakability, high thermal insulating properties and a high resistance to several agents. Usually, the raw material for the keramsite production can also be used for the production of building ceramics wares: brick, ceramic concretes etc. In this case, the roasting process is being carried out in lower temperatures then during the keramsite production – below the swelling coefficient for a particular raw material.
Keramsite is used mainly in a building industry for the production of concretes and construction elements and as an insulating and draining material. It is also used in the road construction, horticulture and agriculture.
Resources of clays suitable for the production of keramsite have been documented in 8 deposits in Poland: Budy Mszczonowskie (located in Mazowieckie Voivodeship), Gniew II (Pomorskie Voivodeship), Gołaszyn (Lubelskie Voivodeship), Nawra (Warmińsko-Mazurskie Voivodeship), Ruda (Podkarpackie Voivodeship), Uniejów (Łódzkie Voivodeship), Wierzchocin (Wielkopolskie Voivodeship) and Bukowo (Szczecin-Płonia) (Zachodniopomorskie Voivodeship).
Raw materials used in the production of agloporit are not expanding in the course during the thermal treatment as their swelling coefficient is not higher than 1.0. The process of agloporit production involves the 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 the building industry for the production of light concrete, concrete blocks and hollow bricks. The 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 the building industry. The majority of documented deposits 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 the coal waste production in mining operations. The fires turn clay shales which form large part of the coal waste stockpiles, into a strong ceramic material. “Fired shales” are available at the Polish market as aggregates usable in the building and road construction. They are treated as a reused product from waste and thus data on their resources and supplies are omitted from “The balance…”.
Table 1 shows the current state of the exploration and development of these deposits. Anticipated economic resources as of 31.12.2017 amounted to 168.19 million m3 (about 336.38 million tonnes) from which resources for the keramsite production were equal 40.07 million m3 (about 80.14 million tonnes) – 23.8% of total resources.
The resources decreased by 0.373 million m3 in comparison with the previous year. The majority of this drop (0.267 million m3) is caused by the updating of the resources and borders of Budy Mszczonowskie deposit. These changes were included in a new documentation prepared for this deposit due to the exploitation abandonment. Remaining 0.106 million m3 is a result of the exploitation and losses from Gniew II deposit.
The raw material output amounted in 2017 to 0.105 million m3 and increased by 8.5% in comparison with 2016. It was the highest level since 2012.
Deposits of clay raw materials for the lightweight aggregate production (together with building ceramics raw materials) are presented on the map.
Economic resources in 2017 amounted to 1.16 million m3 (about 2.32 million tonnes) and accounted for only 54.6% of the level recorded in 2016.
The economic resources drop was equal 1.394 million m3. The majority of it – amounted to 1.287 million m3 – constitutes the economic resources of Budy Mszczonowskie deposit which were crossed out from the evidence due to the exploitation end. The remaining 0.106 million m3 constitute drops resulting from the exploitation and losses from Gniew II deposit.
Economic resources are currently documented only for this part of Gniew II deposit which is located within the mining area.
Prepared by: Wojciech Szczygielski
Table 1. Clay raw materials for production lightweight aggregates - million m3