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).
The 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 the technological additives used, such as: brown coal, diesel oil, alkalis. The process of the keramsite production 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 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 the lower temperatures than during the keramsite production – below the swelling coefficient for a particular raw material.
The 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).
Currently, the exploitation is being carried out only from the Quaternary dammed clays deposit – Gniew II. Previously, till 1995 the keramsite was also obtained from the Oligocene septarian clays and, since 2015, from the Pliocene clays in Budy Mszczonowskie town located in the Mazowsze area.
The raw materials used for the production of the agloporit are not expanding in the course during the thermal treatment as their swelling coefficient is not higher than 1.0. The process of the 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 a high open porosity and relatively low density. Such aggregates were used mainly in the building industry for the production of light concretes, concrete blocks and hollow bricks. Nowadays, the agloporit is not produced and deposits of that raw material are abandoned.
The agloporit clay raw materials are fairly common throughout the whole country. The quality requirements which should be matched by the raw material of this type are generally low – lower even than those put for the raw materials for making simple thick-walled ceramics for the building industry. The majority of documented deposits of the 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 the 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 a 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. The anticipated economic resources as of 31.12.2019 amounted to 167.969 million m3 (about 335.938 million tonnes) from which the resources for the keramsite production were equal 39.862 million m3 (about 79.724 million tonnes) – 23.7% of the total resources. The anticipated economic resources for the agloporite production amounted to 128.107 million m3 (about 256.214 million tonnes) – 76.3% of the total resources.
In 2019, there were not any new documentations for the clay raw materials for lightweight aggregate production approved, therefore the resources did not change.
The raw material output amounted in 2019 to 0.109 million m3 and increased by 0.009 million m3 (8.7%) in comparison with 2018.
Deposits of clay raw materials for the lightweight aggregate production (together with building ceramics raw materials) are presented on the map.
The economic resources as of the end of 2019 were equal 2.287 million m3 (about 4.574 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. The exploitation within the area of Gniew II deposit was carried out both within the economic resources and within the sub-economic resources (the resources drops amounted to 0.093 million m3 and 0.016 million m3, respectively).
The prognostic resources (category D) of the raw materials for the keramsite production within 5 areas were assessed at 38.081 million m3*. In turn, the prognostic resources for the agloporit production were assessed at 12,138 million m3 within 4 prognostic areas. There were also the prospective areas (category D2) identified.
Prepared by: Wojciech Szczygielski
* Szczygielski W., Walentek I., 2020 - Surowce ceramiki budowlanej (building ceramics raw materials), surowce do produkcji kruszyw ceramicznych i cementu (mineral raw materials for production of clay aggregates and cement clinker). In: Bilans perspektywicznych zasobów kopalin Polski wg stanu na 31.12.2018 r. (eds. Szamałek K., Szuflicki M., Mizerski W.): 239-257. PIG-PIB, Warszawa.