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 keramsite production involves a roasting of an appropriately prepared and granulated clay raw material in a temperature of 1,050-1,300oC. In the course of roasting the granules increase their volume due to the gases emanation in a soft pyroclastic mass and their external layer begins to melt forming a parched shard. The obtained porous, light-weight ceramic aggregate is 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.
There have been 8 deposits of the raw materials for keramsite production documented 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).
The exploitation is being carried out only from the Quaternary dammed clays deposit – Gniew II. Still in 2015 there were the Pliocene clays from Budy Mszczonowskie deposit in the Mazowsze area exploited, but the processes of the exploitation and production were abandoded. Till 1995 the keramsite was produced also from the Oligocene septarian clays of Bukowo (Szczecin-Płonia) deposit located in the city of Szczecin.
Raw materials used for 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 a granulated mixture of the clayey raw material and easily combustible particles. The combustible particles in the result of roasting make the obtained material highly porous. The obtained sintered granules are subsequently crushed which allows to get the 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. Nowadays, the agloporit is not produced and deposits of that raw material are abandoned.
Agloporit clay raw materials are fairly common throughout the whole country. Quality requirements which should be matched by the raw material of this type 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 are represented by the Quaternary glacial loams and loesses (loess loams) and the remaining ones – Tertiary Krakowiec clays, Poznań clays or Quaternary stagnant lake clays.
The so-called “fired shales” represent a material close to agloporit. It is also being called “shale-porite from dumps. This material originates in the result of spontaneous fires of stockpiles of the coal waste produced in hard coal 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 31.12.2018 amounted to 168.078 million m3 (about 336.156 million tonnes) from which the resources for the keramsite production were equal 39.971 million m3 (about 78.742 million tonnes) – 23.8% of total resources.
The resources decreased by 0.108 million m3 in comparison with the previous year due to the exploitation and resources losses.
The raw material output amounted in 2018 to 0.100 million m3 and decreased by 0.005 million m3 (4.8%) in comparison with 2017.
Deposits of clay raw materials for the lightweight aggregate production (together with building ceramics raw materials) are presented on the map.
Economic resources as of the end of 2018 amounted to 2.381 million m3 (about 4.762 million tonnes). The economic resources are currently documented within the mining areas for the exploited deposit Gniew II and for the abandonded Budy Mszczonowskie deposit.
Prepared by: Wojciech Szczygielski