Powders from brick rubble
The abandonment of fossil fuels for energy generation results in serious changes in the secondary raw materials economy. In concrete production, this applies most of all to coal flyash, which is used as an addition to concrete and which will then no longer be available. At the same time, new materials such as clay and/or masonry rubble from demolition of buildings are coming into focus – for which forms of reutilization must be found.
In a research project conducted by the Institute of Applied Construction Research (IAB) in Weimar, Germany, powders from brick rubble of various ages and various grades were analyzed with a view to their suitability as puzzolanic constituents of cement or as additions to concrete. The requirements placed on the chemical composition, that apply to flyash, are satisfied – both by old and new brick. Regarding reactivity as determined by the Chapelle test, there exist distinct differences, which are related to chemical composition. One-fourth of the total of 29 samples investigated involved development of strength. The fineness of the powders was identified as the most important influencing variable. A total of 15 of the 28 brick samples were again pulverized to the fineness of cement. Following a new test, 87 % showed a strength-enhancement effect.
The available quantity of graded clay rubble is rather low. Masonry rubble as a mix of brick, mortar and plaster is available in much larger quantities. In order to upgrade this mix to render it suitable for use in cements, the clay particles must be separated from the fine-grained recycling material. Initial tests with a dry process not yet introduced in construction materials recycling show promising results (Fig.).
