The cement industry causes a share of approx. 5 to 8 % of anthropogenicCO2 emissions worldwide. However, it is not only the binder cement that contributes to anthropogenic CO2 emissions in concrete. Furthermore, the mining and processing of rock for use as aggregate in concrete products is also an important environmentally relevant issue in terms of sustainability.

According to the German Federal Statistical Office, 521 million tons of mineral construction raw materials alone were used in 2013. The extraction and transport of natural construction raw materials inevitably entails considerable ecological and economic burdens due to all kinds of energy consumption, e.g. electricity, diesel and explosives. Which, in turn, exert negative effects on the environment (e.g. emission ofCO2, NOx) during production or use. Due to these huge masses, the recycling of building materials is becoming increasingly important. In 2014, a total of 210 million tons of construction and demolition waste was produced in Germany. According to the monitoring report of the construction industry, 55.1 million t of construction waste was produced in 2014 and about 73% of this was recycled into building materials. The largest share was used in road construction, earthworks and asphalt production, while the share recycled into concrete was less than 1%. Although such concrete waste is currently already partly processed into recycled sand and reused as a substitute for natural sand in the manufacture of concrete products, the substitution rate of recycled sand is only about 10% by mass of the total aggregates. The remaining material is currently disposed of in landfills at a cost.

The aim of this project is to reuse the "residual" materials arising in the production of concrete products in high-quality concrete products and thus to improve their effectiveness, especially in terms of sustainability. In this context, new types of resource-saving paving blocks are to be produced whose aggregates consist largely or even entirely of recycled and waste materials. In addition, the aim is to partially substitute the already low-energy blastfurnace cement (CEM III A or B) with calcined clays. The concrete mixes produced from recycled and waste materials are to be used both in the core concrete and in the facing layer of the pavers.

Due to the widely varying sizes and shapes of some waste products, the main need is for suitable processing or preparation for reuse as aggregates in concrete production. Depending on their material properties, attempts should be made to produce them with suitable technology in various grain fractions, if possible with uniform grain size distribution and low preparation effort, for use in both facing and core concrete.