In the process of crushing of recycled concrete aggregate fractions for a concrete mix an overflow of fine particles is produced. As an innovative application field the fines of recycled concrete is proposed to be used as filter bed for waste water cleaning instead of natural sand. Water filtration thus become a field of application for fine fractions from the crushing process and in this way an open loop recycling can be realized for the concrete. A prestudy is going on with two filtering reactors at the RE:Concrete lab in order to assess the efficiency of the water cleaning by recycled concrete beds. The project is an interdisciplinary project with researchers from Resource Recovery and the goal is to apply for funding from Horizon 2020.