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Electro-fragmentation for the selective crushing of steel fibers reinforced concrete waste: status update

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The works previously carried out during the HISER project have showed that electro-fragmentation technology is effective for the selective liberation of the steel fibers in reinforced concrete waste. A test campaign has recently been performed on about 500 kg of fibers reinforced concrete in order to demonstrate the performances of the system and to study the quality of the recovered fractions for their use in concrete manufacturing.

 

Steel Fiber Reinforced Concrete (FRC) is a composite material made of hydraulic cement, water, fine aggregates, additives and steel fibers. Fiber reinforced concrete is usually used for the construction of special structures like bridge or hydraulic structures. This concrete has been in use since the 1970’s and has a steadily growing market. From the view point of sustainability, the treatment of FRC after the service period of concrete structures should be considered in near future.

 

The recycling of steel FRC is studied in HISER. In particular, BRGM and SELFRAG work on the selective fragmentation of this waste. The objective is to selectively liberate the steel fibers from the sand/cement paste in order to recycle both fractions in new concrete products with similar mechanical properties than the ones made using raw materials:

 

 

  • For the steel fibers: they could be used to make new FRC;
  • For the fine fraction (i.e. fraction made with the sand and cement paste): it could be used either to make new FRC or to make new normal concrete.

A demonstration campaign has recently been performed in the SELFRAG facilities (Kerzers, Switzerland) on 500 kg of steel fiber reinforced concrete using a continuous machine called “Pre-Weakening Test-Station” (PWTS). The aims of this campaign were to confirm at pilot scale and in continuous mode the performances of the system and to study the quality of the recovered fractions for their use in concrete manufacturing. In particular, it has been observed that 100% of the steel fibers are liberated when considering the size fraction below 2 mm. This demonstration campaign has been carried out successfully and valorization of the recovered fractions in the production of new concretes will be investigated in the next month by Tecnalia and Lafarge.