From the Armour Stone to Gravel (Basalt-Mile)
| From the Armour Stone to Gravel (Basalt-Mile) | |
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| GeoStation at the GeoRoute Tertiär - Industrie -Erlebnis Stöffel-Route | |
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| QR-Code directe: | www.qltr.de/qrka0231 |
From the Armour Stone to Gravel – A Building Material in Every Size
On the way from the basalt block to gravel, the rock has already gone through the preliminary crushing stage. The Stöffel basalt is now roughly crushed. The individual rock pieces are still of varying sizes and irregular shapes. Conveyor belts now transport the rock from the pre-crusher to the so-called secondary crushing stages. In contrast to the pre-crushing stage, where jaw crushers are used, rotary crushers are employed in the secondary stage. Their crushing tools move in slightly elliptical paths and press the rock introduced from above against the crushing chamber wall. Due to their mode of operation, rotary crushers are especially suitable for already pre-crushed rock. Larger rock pieces would get jammed and block the crushing process.
Through the gentle grinding movement of the rotary crushers, the rock pieces are uniformly crushed. Due to the arrangement of multiple grinding passes, the basalt stones achieve the desired grain shape and size. Screening systems are set up between the individual rotary crushers. Here, the pieces that have already reached the desired final size are screened out. The remaining rock is further crushed until it also meets the requirements. The end product is the so-called gravel. Since gravel is needed for various applications, it must be produced in different grain sizes, depending on its intended use. These grain sizes, combined with the gravel type, define the commercial name of the product. For example, a 2/5 premium gravel is a multi-crushed stone gravel with grain sizes from 2 to 5 mm, primarily used as a top layer in road construction due to its hardness and wear resistance.
The finished gravel is piled up and stored on the quarry grounds. Gravel is loaded and sold in the desired amount upon customer request. To do so, the customer's truck first drives onto the large truck scale at the entrance of the quarry. There, the empty weight of the truck is recorded and digitally stored. The customer’s truck then drives to the storage and loading area, where a wheel loader fills the truck with the desired amount of gravel. The wheel loader has a built-in scale, ensuring the desired amount of gravel is accurately weighed. After loading, the customer’s truck drives over the large scale again and is weighed once more. The initially recorded empty weight is then subtracted from the second measurement to determine the weight of the gravel delivered.
The loaded trucks usually drive directly to the construction site where the gravel is needed or transport the material to an asphalt mixing plant, where the crushed stone is further processed into asphalt.
A Natural Product – Not Every Stone is the Same
To meet the demands of high building material quality, a rock must fulfill specific, application-related requirements. Crushed rocks for road construction must be particularly hard and abrasion-resistant, depending on their intended use. The roughness of the basalt is also important. If it is too low, the friction from car tires would smooth the road too quickly. High-quality standards are also set for track ballast, as it must be very hard and durable. The main consumer of track ballast is Deutsche Bahn (German Railways).
The rock sand that is produced during processing is also utilized. It is mainly used in concrete production or landfill construction. Large armour stones are used for bank stabilization of water bodies. The quality of the building material and the suitability of the rock are tested both in in-house and external laboratories. For this purpose, samples are taken on-site in the quarry before basalt extraction begins.
Basalt is a natural product. The hot volcanic lava did not have the same chemical composition everywhere, so the cooled basalt rock contains varying components. For example, if the mineral analcime is present in the basalt, it becomes brittle and weathers quickly. In the past, people referred to this as basalt having a "sunburn." These occurrences are not extracted. Such abandoned quarries can be found at the geotopes Kranstein or Watzenhahner Riesen. Today, these are impressive natural attractions.
Verfasser: Carolin Geißler, Christoph Eul und Roger Lang
Stand: 4/2025