Besides pumice and tuff, lava is the third rock of volcanic origin whose extraction, preparation and further processing is a focus of ours. It consists of vulcanites, i.e., solid rocks, which solidify on the surface or in the vicinity of the molten masses that pressed together.
The highly porous lava rock is much older than tuff and pumice. The lava in the Eastern Eifel is estimated at about 300,000 years old. The pore volume is slightly lower than that of pumice. Here, too, one can assume up to 50 %. The bulk density including approx. 7 % pit moisture is approx. 900-1,000 kg/m3. The rough surface, the high grain compressive strength and the comparatively low weight make lava an ideal raw material for the production of lightweight concretes with higher compressive strength and higher bulk density. Lava is also used in road construction as a frost protection layer, as a filling material for trickling filter treatment plants, as an environmentally friendly grit in winter and increasingly as a plant substrate, especially for green roofs.
As pumice was ejected in large quantities and blown away by the wind during the eruption of the Laacher Lake volcano, the tuff poured into the valleys of the Nette and Brohlbach in huge dust avalanches, the so-called pyroclastic flows. There, the tuff was deposited in metre-thick layers. Wherever the tuff came into contact with water, it solidified into rock. Today we know of three mining horizons.
The uppermost layer solidified due to penetrating rainwater such as rain and snow. Today, we can find traces of Roman underground mining there. Underneath there is a layer of loose material – also called a tuff pocket. In the lowest layer, the groundwater brought about the solidification of the tuff.
The special characteristic of tuff rock is its high concentration of reactive silicic acid, which forms crystalline compounds with lime. Tuff rocks that have been dried and ground are referred to as trass.
The eruption of the Laacher Lake volcano about 13,000 years ago generated pumice and tuff. Pumice is a highly porous volcanic glass with up to 85 % pore volume. For this reason, the lightest pumice has a dry weight of less than 300 kg/m3. The lightweight concrete produced from this raw material has excellent thermal insulation properties combined with good strength, which makes it suitable as a building material for the construction of energy-saving residential buildings.
The Latin origin “pumex” is the eponym of the MEURIN wall building materials product range with the brand name “PUMIX” for lightweight concrete building materials based on natural pumice.