Research on Suitability of Coal Preparation Refuse in Civil Engineering in the Federal Republic of Germany )

Abstract

SUMMARY Notwithstanding the massive efforts of the West-German hardcoal industry just about 15 M t/y refuse went during the few recent years into road construction — predominantly as bulk material —, into other soil amelioration projects as well as into the construction of dams and embankments. This is roughly 20% of the total refuse yield. For this reason extensive research was done in view of further possible applications of colliery shales. Due to the more stringent regulations on thermal insulation released in the Federal Republic of Germany, energy-saving constructional designs were introduced in building construction during the past few years. At this juncture there is a scarcity of light-weight, small-size products for roughcast-and brickwork binders so that the building industry has to recur to quartz sand. It was tried therefore to produce light-weight sands from crushed small sized washery refuse and pelletized flotation tailings by means of thermal treatment in a fluidized bed furnace. The products obtained proved their usefulness for thermal insulation in different applications of the construction industry. Further to this, injection of synthetic foam into the chambers of light-weight concrete blocks substantially increased their resistance to thermal transfer. In case of hollow blocks made from lime-bound green wastes certain difficulties arose so that further tests are necessary. For checking the suitability of green refuse as a concrete aggregate a wall was erected in which were used different types of cement and reinforcing steel bars. The objective of the present investigations was firstly to find out the compressive strength of refuse-based concrete and, secondly, the carbonation and corrosive behaviour of such wastes in presence for steel reinforcing bars. Said wall which was constructed two and a half years ago has not shown so far any spallings nor other disintegrations. Afther the colouration of lime-bonded blocks from refuse by means of ferrous oxide pigments — for facade decoration — had turned up to be quite expensive, tests on colouration were run with red slurry form the aluminium industry. The results were satisfying and production cost were considerably lower. The studies on the suitability of washery refuse in underground construction were extended to include also road construction. In connection with investigations into the production of underground construction materials from cement, fluidized bed ash from flotation tailings and swept material from green refuse shot-creting test were run on a technical scale in a quarry. The outcome was, however, only a mortar of late bearing. Other tests on blends from cement, fluidized bed ash and limestone with addition of a accelerator resulted in the make-up of an early-bearing construction material for underground use. It will be tried now to increase the proportion of fluidized bed ash and replace part of the limestone by green refuse.