Economically efficient processing of natural stone and recycling materials

Natural crushed stone and recycled materials in graded grain sizes are used as standard aggregate for concrete, as well as for base, binder and surface courses in road and building construction. But how are large chunks of rock converted into aggregate of defined size?

Crushers are on the move

Versatility and flexibility in application are the major trump cards that mobile crushers play in comparison to stationary crushing plants. What are mobile crushers used for? What are the differences between the various crushing techniques? What about the hardness of the rock to be processed?

Mobile crushers are used in quarries, in mining, on job sites, and in the recycling industry. The robust plants mounted on crawler tracks are capable of processing both rock and recycling material, producing mineral aggregate and recycled building materials respectively for the construction industry.

When processing natural stone or recycling material like demolition waste, concrete, asphalt, incineration ash or steel slag, an excavator or wheel loader feeds the material into the mobile crusher. Then then produced material is used for road construction or other, similar applications.

Processing of natural stone

When processing natural rock, larger rocks are broken up into defined grain sizes in a multi-stage crushing and screening process. If the rock is processed in mobile plants, excavators transfer the blasted rock to crushers which are usually located directly alongside the quarry wall.

The crushed stone is then either transferred directly to the next processing stage on conveyor belts or removed by trucks. Alternatively, the broken material can also be removed by heavy-duty trucks. Excavators or wheeled loaders load the rock onto trucks at the quarry wall for transport to the stationary processing plan.

Processing of recycling material

In addition to reinforced concrete, asphalt and bricks, rubble and mixed construction wastes are separated into their useful components by mobile crushers or stationary crushing and sorting machines.

A combined process of crushing, screening and separating metal is an efficient means of processing material to be recycled. To obtain an end-product of even higher quality, further process steps can be added, such as washing, eliminating such light materials as plastics and paper with the aid of air classification, and additional electromagnetic metal separation.

Different crushing techniques

Crushing techniques distinguish between pressure crushing and impact crushing. Jaw crushers or cone crushers use the so-called pressure crushing technique where material is reduced in size mainly by high pressure between slow-moving wear parts. Impact crushers use the so-called impact crushing technique, in which the rock is accelerated by a massive fast-moving rotor and reduced in size by impacting against breaker walls. Jaw crushers are widely used for crushing medium-hard to hard rock, and are mostly used as primary crushers. Impact crushers work as both primary and secondary crushers for processing soft to medium-hard rock, producing larger quantities of fines. Cone crushers are used predominantly as secondary crushers for hard rock.

RAP Processing

A comparison of renewal projects and newly built roads reveals that the number of renewed roads is significantly higher than the number of newly built roads.

To address environmental protection, efforts are made to reintroduce the high volume of RAP material into the materials cycle and to reuse a very high ratio. Since the 1970s, an effort has been made to recycle an increasing volume of reclaimed asphalt while continuously optimizing the energy-intensive process of asphalt production.

Granulation – the subtile difference

The highest theoretical additive volume of used asphalt mainly depends on its grading curve or, in other words, on its ingredients with regard to volume, size and composition. It therefore has to be one of the objectives to reconcile the grading curve of the crushed asphalt as much as possible with the grading curve of the final asphalt product.

The BENNINGHOVEN granulator gently separates the reclaimed asphalt into its individual components – without destroying the original grain structure. This gentle grinding technology is the perfect precondition for nearly 100% re-use of the RAP material.

Another significant benefit of this grinding technology is the substantially reduced generation of fine particles – the crucial advantage which prevents blockage of the transport paths and the parallel drum in the asphalt mixing plant as much as possible, providing ideal preconditions for feeding RAP into the asphalt mixing plant (up to 90% + x).