Quality criteria

Impact comminution of concretes with defined properties

Summary: Building waste that can be recycled as building material is processed in various steps
and comminution has a central importance here. It is required for particle size reduction.
As regards composite building materials, comminution furthermore represents the possibility
to disintegrate ­connected components. The impact crusher has proved a success for the ­comminution of concrete or masonry building waste. On the one hand, the comminution
result depends on the stress conditions. On the other hand, it can also be expected that the concrete quality will influence the particle size reduction achieved. This question is investigated in the present article. Various types of concrete were crushed under defined conditions in a impact compressed-air cannon in order to discover the influence of the concrete on the particle size reduction and the disintegration achieved. Statements were made as regards the interdependence between the crushability and the compressive strength of the concrete to be ­comminuted. Conclusions are drawn for the processing of concretes with higher strength classes as one of the development trends in the range of concretes.

1 Types of concrete investigated

Normal concretes consisting of gravel, chippings and recycled aggregates with graded strengths – according to the designation valid at the time of manufacturing as B 25, B 35 and B 45 – were made for the investigations in the compressed-air unit. The recyclates were produced from pure concrete specimens in the laboratory. In addition, a high-strength and a lightweight concrete were also included in the investigations (Table 1). The particle size distribution of the aggregates used corresponded to the grading curve A/B with a maximum particle size of 16 mm for...

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