Crushed sands and other finely dispersed materials from the recycling of mineral construction waste are mainly used for backfilling or deposited in landfills. Their use in construction concretes has not yet been permitted. Recycling after conversion into new materials is desirable, but does not take place in practice. The use of such materials in cement (e.g. as a main constituent of so-called R-cements) could represent an alternative recycling route. In terms of building regulations, a national technical approval (abZ) to be issued by the Deutsches Institut für Bautechnik (DIBt) is currently required.
The aim of the project was to analyse finely dispersed, mineral recycling materials of different material-granulometric compositions. It should be clarified in which way a physical or a chemical reaction with water would take place if these materials were used as cement constituents. The reaction products have a significant influence on the structural density, pore distribution, strength and durability of mortar and concrete. The relationships between the composition of R-cements and the properties of mortars were investigated when the water supply varied. Different materials and mixtures of materials from building material recycling were analysed and used in R-cements of different compositions. Materials from broken concrete, broken masonry and broken bricks were used. The experimental investigations of the material properties were carried out in laboratory tests, mainly using standard-ised analysis/testing methods for mineral materials, cements and mortars.
