Jaw crushers, impact crushers and twin-shaft shredders are used in concrete recycling plants. Jaw crushers crush the demolition material with the pressure of their two jaws, twin-shaft crushers use the shafts as a chopper, and in the case of impact crushers, the blow bars of the rotor break the material to be crushed at an adjustable peripheral speed. With the use of a screening machine in front of the crusher, only coarse fractions are fed to the crusher. The screening leads to a reduction in the amount of material to be crushed, causes less wear of the crusher parts and increases the quality of the crushed material. In the recycled aggregates obtained through the crushing process, the proportion of sand grains below 2 mm in grain size that are not used for the preparation of concrete can vary in size depending on the type of machine used.
In the recycling process, the correct separation of the different types of material is an important step. In order to obtain a homogeneous and clean final grain, the processed material must be cleaned of contaminants in a subsequent process. In the case of dry probing methods, wind sifting is used, with which light materials such as paper and plastic can be separated. Before the wind sifting, the concrete debris crushed in the crusher is first separated into grain groups. Iron parts in the broken material, e.g. feinforced steel are removed by magnetic separators that are attached to the crusher above the main conveyor.
Utilization of recycled concrete
The recycling of concrete conserves raw material resources, saves landfill space for debris and protects the climate.The Mineral, Recycling and Utilization Association in the Federal Association of Secondary Raw Materials and Disposal (BVSE) has determined that debris, road demolition, construction site waste and soil as well as stones form the largest waste fraction in Germany. They account for around 60% of the total volume - over 200 million t of construction waste are generated annually. At the same time, the opportunities for mining sand, gravel and rocks are shrinking. Resource conservation and climate protection are also high on the social and political agenda. These arguments speak in favor of establishing a circular economy based on sustainability in the construction sector.
The core element of such a circular economy is comprehensive, quality-assured recycling. Most of the construction waste in Germany already has a high recovery rate of around 90% and the recycling companies are fully utilized according to the association. However, sales of the secondary raw materials produced prove to be problematic. While the quantities delivered to the recycling plants are increasing, the demand for the building materials produced there remain at a low level, according to bvse.
Pioneering buildings, especially from the public sector, can increase the acceptance of recycled building materials. In building construction, one of these models is the Würzburg environmental station, which was inaugurated in May 2019. It is the first building in Bavaria to consist of three quarters made from recycled concrete.
Switzerland is currently the country with the most demanding regulations for the use of resource-saving building materials. Here, the use of 70% recycled material in public contracts was defined as the goal.
Processing concrete with Rockster impact crushersRockster supplies mobile crushers and screening machinery with high and constant performance as well as versatile applications for the recycling of concrete and other building materials. Thanks to the combined use of screening system, magnetic separator and integrated air blower, Rockster impact crushers produce very good final grain qualities of the recycling material in one work flow. The various adjustment options of the impact crusher R1000S create the prerequisites for the production of final grain with a precisely definable screen mesh. The infinitely variable, fully hydraulic crushing gap adjustment with integrated measuring system, the new blow bar fixation and the automatic, load-dependent and infinitely adjustable conveying speed characterize the high technical level of development of the R1000S crusher. The hydraulically height-adjustable magnetic separator, the lowerable screen box and the swiveling platform make the operation and maintenance of the system considerably easier. Furthermore, thanks to any setting of the crusher speed and the two fully hydraulically adjustable impact arms during operation, the final grain can be optimally defined.
Efficiency increase thanks to magnetic separator and air blowerIn addition to the magnetic separator, which removes iron and metal parts, the efficiency of the construction debris recycling can also be increased by the integrated air blower, which with its variably adjustable blower can remove non-aggregate light materials such as e.g. Polystyrene, plastic, textiles, plaster, foils or wood.
In addition, the screening system - consisting of the compact circular vibrating screen RS100 in combination with the return belt RB92 - offers an excellent solution for the production of 100% defined final grain. By using an air blower, workers who would have to carry out these sorting activities in a dusty environment are no longer required. The preparation of the demolition material is handled solely by the excavator operator, who also operates the impact crusher using a wireless remote control.
Many thanks for this interesting article to Dr. Richard Sonnenberg from the German magazine "Beton"!
Images used: Rockster Austria