Discussion of the paper: ‘RILEM TC URM: Use of recycled materials in constructions’, by Ch.F. Hendricks and G.M.T. Janssen

Abstract

AustraliaThe authors on behalf of the R1LEM Technical Committee "Use of Recycled Materials" have presented an interesting and useful paper. The definition of sustainability in construction, which carries two meanings -both durable and sustainable, is correct.The authors of the discussed paper correctly point out that construction and demolition waste contain iron, wood, mastic, bitumen, chipboard, cardboard, plastics, aluminum, zinc, cooper, etc. The list is not full of course, but enough to appreciate roughly the variety of different materials presented in this waste. Further, the authors write: "During the past decades, mechanical 'reprocessing' systems have largely replaced manual processes, primarily in the metal sector both also for construction and demolition waste (CDW), so that CDW can now be used on a large scale in the construction sector".Since the mechanical "reprocessing" systems in the metal sector have been mentioned in the discussed paper, the following information could be of interest. Even the separation of steel from the slag in the basic oxygen steelmaking and electric arc furnace steelmaking is not currently perfect [1]. And this is a relatively "easy" case for the separation of the materials, since both slag and steel are in liquid forms, the specific gravity difference is threefold plus the steel is a magnetic material. The separation rubbles from the slag (as a more valuable by-product than rubbles) in steel production practically is an unresolved problem. In the construction and demolition waste, the situation is far more complicated. We are dealing with solidified (mainly non-magnetic) materials in the very wide range of specific gravity. There are materials, which after heavy handling turn into the dust, for instance, gypsum plaster. It is needless to explain potential problems associated with its presence in concrete. It is unclear how to remove